HYDROLOGY OF THE NILE BASIN MAMDOUH SHAHIN International Institute for Hydraulic and Environmental Engineering Oude Delft 95, 2601 DA Delft, The Netherlands
ELSEVIER Amsterdam - Oxford
- New York - Tokyo
1985
E L S E V I E R SCIENCE P U B L I S H E R S B.V. Molenwerf 1 P.O. Box 21 1 , 1000 A E Amsterdam, The Netherlands
Distributors for the United States and Canada: E L S E V I E R SCIENCE P U B L I S H I N G C O M P A N Y I N C . 52, Vanderbilt Avenue N e w Y o r k , N Y 1001 7
I S B N 0-444-42433-4 (Val. 21) ISBN 0-444-41669-2 (Series)
0 Elsevier Science Publishers B.V., 1985 All rights reserved. N o p a r t o f this publication may be reproduced, stored in a retrieval system o r transmitted in any f o r m o r b y any means, electronic, mechanical, photocopying, recording o r otherwise, w i t h o u t the p r i o r w r i t t e n permission of the publisher, Elsevier Science Publishers B.V./Science & Technology Division, P.O. Box 330, 1000 A H Amsterdam, The Netherlands. Special regulations f o r readers in t h e USA - This publication has been registed w i t h the Copyright Clearance Center Inc. (CCC), Salem, Massachusetts. I n f o r m a t i o n can be obtained f r o m t h e CCC a b o u t conditions under which photocopies o f parts o f this publication m a y be made in the USA. A l l other copyright questions, including p h o t o c o p y i n g outside o f t h e USA, should be referred t o t h e publisher, Elsevier Science Publishers B.V., unless otherwise specified. Printed in The Netherlands
V
PREFACE T h i s book aims a t d e s c r i b i n g a number o f t h e h y d r o l o g i c a l a s p e c t s of t h e b a s i n o f t h e N i l e R i v e r and t h e d i f f e r e n t f a c t o r s a f f e c t i n g them. With t h i s aim i n mind i t d e a l s p r i m a r i l y w i t h t h e i n f l o w - o u t f l o w b a l a n c e of t h e N i l e s y s t e m from t h e s o u r c e up t o mouth s u b - b a s i n - w i s e . The components of t h e h y d r o l o g i c c y c l e which e n t e r i n t h e w a t e r b a l a n c e and which a r e c o n s i d e r e d h e r e a r e t h e r a i n f a l l , e v a p o r a t i o n , e v a p o t r a n s p i r a t i o n and t h e change of w a t e r i n s t o r a g e , b o t h i n volume and l e v e l . Each of t h e s e comp o n e n t s i s p r e s e n t e d a s o b s e r v e d i n n a t u r e , r e c o r d e d from e x p e r i m e n t s or found from c o m p u t a t i o n s , t o g e t h e r w i t h an e x p l a n a t i o n o f t h e p r o c e d u r e s used and t h e i n t e r p r e t a t i o n of t h e r e s u l t s o b t a i n e d . A t t e n t i o n i s p a i d t o t h e l o s s e s which t a k e p l a c e i n c e r t a i n p a r t s of t h e b a s i n . The m e t e o r o l o g i c and h y d r o l o g i c d a t a a t t h e key s t a t i o n s on t h e N i l e and i t s t r i b u t a r i e s a r e a n a l y z e d and t h e i r b a s i c s t a t i s t i c a l p r o p e r t i e s g i v e n . A s p e c i a l c h a p t e r i s d e v o t e d t o t h e geohydrology of t h e b a s i n and t o t h e groundwater s i t u a t i o n s and p o t e n t i a l i t i e s i n some of t h e c o u n t r i e s s h a r i n g t h e N i l e B a s i n . L a s t , b u t n o t l e a s t , a whole c h a p t e r h a s been l e f t t o t h e s t o r a g e , c o n t r o l and c o n s e r v a t i o n w o r k s , b o t h e x i s t i n g and p l a n n e d , and t o t h e i m p a c t s of s u c h works on t h e e n v i r o n m e n t . I n a t t e m p t i n g t o c o v e r h e r e as many of t h e h y d r o l o g i c a l a s p e c t s of t h e N i l e B a s i n a s p o s s i b l e , i t h a s n o t been i n t e n d e d t h a t t h i s book s h a l l compete w i t h e x i s t i n g l i t e r a t u r e on t h e same s u b j e c t biit r e t h e r c o m p l e t e i t . Moreover, t h i s book, when added t o t h o s e d e s c r i b i n g a s p e c t s o t h e r t h a n h y d r o l o g i c a l , s u c h a s b i o l o g i c a l and g e o l o g i c a l , s h a l l c e r t a i n l y h e l p t o p r o v i d e t h e r e a d e r w i t h a more c o m p l e t e p i c t u r e of t h i s r i v e r b a s i n . Almost t w o - t h i r d s of t h e s u r f a c e o f A f r i c a a r e d r a i n e d by s e v e n major r i v e r s , i n c l u d i n g t h e N i l e . So t h e knowledge g a i n e d o f t h e hydrology of any of them s h a l l , no d o u b t , c o n t r i b u t e t o a b e t t e r u n d e r s t a n d i n g o f t h e w a t e r r e s o u r c e s of a c o n t i n e n t w i t h an a c u t e w a t e r - s h o r t a g e problem. Such a n u n d e r s t a n d i n g i s needed by e v e r y h y d r a u l i c or w a t e r r e s o u r c e s e n g i n e e r aiming a t a more e f f i c i e n t u t i l i z a t i o n of t h e r e a d i l y a v a i l a b l e , a s w e l l a s t h e p o t e n t i a l , w a t e r r e s o u r c e s . The a u t h o r h a s depended i n some p a r t s of t h e book on h i s e x p e r i e n c e and viewp o i n t s , and on t h e e x i s t i n g l i t e r a t u r e i n t h e r e m a i n i n g p a r t s . A l i s t of t h e r e f e r e n c e s and d a t a s o u r c e s used a p p e a r s a t t h e end o f e v e r y c h a p t e r . A s e n s e of g r a t i t u d e must b e e x p r e s s e d h e r e f o r t h e many who d i r e c t l y and i n d i r e c t l y , by t h e i r c o n s t r u c t i v e c r i t i c i s m and a d v i c e , have h e l p e d i n t h e p r e p a r a t i o n of t h i s book. Most of t h e a p p r e c i a t i o n g o e s , i n f a c t , t o P r o f . i r L.J.
Mostertman, D i r e c t o r of t h e I n t e r n a t i o n a l I n s t i t u t e f o r H y d r a u l i c and
E n v i r o n m e n t a l E n g i n e e r i n g , D e l f t , The N e t h e r l a n d s , whose c o n t i n u o u s s u p p o r t and
vi
e n c o u r a g e m e n t d a t e s b a c k t o a s e a r l y a s 1962. G r a t i t u d e i s a l s o e x t e n d e d t o many o f t h e a u t h o r ' s f o r m e r c o l l e a g u e s a t t h e N i l e C o n t r o l D e p a r t m e n t ,
the
M i n i s t r y of I r r i g a t i o n , E g y p t , a n d a t t h e F a c u l t y o f E n g i n e e r i n g , C a i r o U n i v e r s i t y . S p e c i a l m e n t i o n must b e made o f M s P . E . R o e l l , L i b r a r i a n o f t h e International
I n s t i t u t e f o r H y d r a u l i c and E n v i ronment al E n g i n e e r i n g , D e l f t , f o r
p r o v i d i n g t h e a u t h o r w i t h a n enormous number o f r e f e r e n c e s a n d d o c u m e n t s , MS
P . S c h o t t - L e 6 n who u n d e r t o o k a l l t h e t y p i n g and M r W .
van N i e v e l t f o r p r e p a r -
i n g t h e g r a p h i c work i n t h i s b o o k . The a u t h o r i s g r e a t l y i n d e b t e d t o h i s f a m i l y , whose p a t i e n c e a n d t o l e r a n c e h a v e b e e n h i s s u p p o r t i n t h e many y e a r s s p e n t i n compiling t h e book.
M.M.A.
Shahin,
D e l f t , 1984
1
Chapter 1
HISTORICAL INTRODUCTION
1.1
SOURCE OF THE NILE
The known h i s t o r y o f t h e N i l e R i v e r d a t e s b a c k t o j u s t b e f o r e 5000 B . C . From t h e n t i l l r e c e n t l y v a r i o u s t h e o r i e s a b o u t t h e s o u r c e o f t h e N i l e and i t s
r i s e h a v e b e e n l a i d down. Some of t h e s e t h e o r i e s were s o c o n f l i c t i n g t h a t i t became c u s t o m a r y i n a n c i e n t Rome t o s a y : q u a e r e r e f o n t e s N i l e ( s e a r c h for t h e N i l e ) when someone t a l k e d a b o u t a m y s t e r i o u s or i m p o s s i b l e matter ( P i e r r e , 1974). The name N i l e i s s a i d t o b e d e r i v e d f r o m t h e G r e e k N e i l o s , whose o r i g i n i s unknown. B o t h N e i l o s and A i g u p t o s ( m a s c u l i n e ) w e r e u s e d i n G r e e k drama when r e f e r r i n g t o t h e N i l e , w h e r e a s A i g u p t o s ( f e m i n i n e ) a l o n e was u s e d when r e f e r r i n g t o Egypt ( E n c y c lo p a e d ia B r i t a n n i c a ,
1969).
I t i s o f t e n c l a i m e d t h a t t h e a n c i e n t E g y p t i a n s knew n o t h i n g o f t h e o r i g i n of t h e i r r i v e r . T h i s c l a i m i s s u p p o r t e d o n o n e h a n d by t h e n a i v e c o n v i c t i o n o f t h e common a n c i e n t E g y p t i a n t h a t t h e N i l e f l o w s o u t o f t h e f u l l b r e a s t s o f t h e N i l e God, H a p i . The p r i e s t s o f a n c i e n t E g y p t , o n t h e o t h e r h a n d , h a d t h e i r own t h e o r y , w h i c h t h e y f a i t h f u l l y f o u n d e d o n t h e o l o g i c a l g r o u n d s . T h o s e p r i e s t s were c o n v i n c e d t h a t somewhere t h e c o u r s e o f "The C e l e s t i a l N i l e " w a s b e s e t by m o n s t r o u s r o c k s and s t o n e s and t h a t b e l o w t h i s b a r r i e r rose E g y p t ' s N i l e or E g y p t ' s h e a v e n - d e s c e n d e d s t r e a m . A f t e r a l l , t h e N i l e p r i e s t s were one of t h e s o u r c e s t h a t provided Herodotus, t h e I o n i a n , w i t h m o s t o f t h e informat i o n t h a t a p p e a r e d i n h i s w r i t t e n a c c o u n t s on Egypt and t h e N i l e . The p h i l o s o p h e r s and s a v a n t s o f a n c i e n t Greece h a d t h e i r v i e w s o n , and o p i n i o n s o f , t h e s o u r c e o f t h e N i l e and o f i t s r h y t h m i c p a t t e r n o f f l o w . T h e s e views comprised t h e r o l e o f t h e E t e s i a n ( n o r t h e r l y ) winds i n t h e bui l d-up o f the N i l e ,
t h e o r i g i n o f t h e r i v e r from Oceanus ( t h e ocean s u r r o u n d i n g t h e
e a r t h ) , and t h e r i s e o f t h e N i l e f r o m t h e p e a k s o f t h e L y b i a n m o u n t a i n s and
i t s s u p p l y f r o m t h e m e l t e d snow t h e r e o n . H e r o d o t u s w r o t e i n h i s a c c o u n t s t h a t , d u r i n g h i s v i s i t t o Egypt i n 457 B . C . ,
one informant s a i d t h a t t h e Nile r o s e
from a p o w e r f u l s p r i n g f e e d i n g a d e e p l a k e s i t u a t e d b e t w e e n t h e h i l l s o f Mophi and C h r o p h i . T h e r e a r e two t r a i n s o f t h o u g h t :
t h e f i r s t is t h a t t h e
s a i d l a k e l i e s b e t w e e n t h e i s l a n d o f E l e p h a n t i n e and Aswan, w h i c h c o n f i n e s t h e w h o l e s t o r y t o t h e N i l e i n E g y p t , and t h e o t h e r i s t h a t t h e l a k e i s s i t u a t e d f a r more t o t h e s o u t h . I n c o m p a r i s o n w i t h r e c e n t d i s c o v e r i e s t h e l a t t e r i s s o m e t i m e s i n t e r p r e t e d as t h e l a k e s u p p l y i n g t h e S e m l i k i R i v e r which d i s c h a r g e s
i t s w a t e r i n t o Lake A l b e r t ( a l s o c a l l e d Mobutu-Sese S e k o ) . I f w e a r e prepared t o accept t h i s i n t e r p r e t a t i o n ,
i t is then f a i r t o conclude t h a t
Herodotus c a n b e complimented f o r t h r o w i n g some l i g h t on t h e w e s t e r n t r i b u t a r y o f t h e N i l e R i v e r . I n a p a p e r e n t i t l e d "The N i l e , i t s O r i g i n and R i s e "
it is
mentioned t h a t H e r o d o t u s b e l i e v e d t h a t t h e Upper N i l e flowed from w e s t t o e a s t , b u t h e c o n f u s e d t h e Niger w i t h t h e N i l e ( B i s w a s , A . , f o r q u i t e some t i m e . J u b a I 1 (20 A . D . ) ,
1966). T h i s i d e a p r e v a i l e d
t h e King o f M a u r i t a n i a , a f f i r m e d t h a t
t h e s o u r c e of t h e N i l e was i n w e s t e r n A f r i c a , t h e r e b y s u p p o r t i n g t h e c o n v i c t i o n t h a t t h e N i g e r i s a b r a n c h of t h e N i l e ( B i s w a s , A , , The Greek p h i l o s o p h e r A r i s t o t l e (384-322 B . C . )
1966, 1970).
thought t h a t t he r i v e r
descended from a mountain of s i l v e r (montagne d ' a r g e n t ) and t h a t heavy s p r i n g and summer r a i n s on t h e h i g h l a n d s of t h e catchment a r e a s (what we c a l l nowadays t h e B l u e and White N i l e s ) were r e s p o n s i b l e f o r t h e flow i n t h e N i l e . Almost two c e n t u r i e s a f t e r H e r o d o t u s , came t h e m a t h e m a t i c i a n and g e o g r a p h e r E r a t o s t h e n e s (276-194 B . C . ) who d e s c r i b e d t h e N i l e f a r b e t t e r t h a n any of h i s p r e d e c e s s o r s . H i s i d e a w a s t h a t two p r i n c i p a l streams s p r a n g o u t o f some l a k e s s i t u a t e d t o t h e e a s t and e n c i r c l e d Meroe, a c o n s i d e r a b l y l a r g e i s l a n d ( s e e map, F i g . 1 . 1 . ) . The e a s t e r n t r i b u t a r y was t h e A s t a b o r a s (now c a l l e d t h e A t b a r a ) and t h e w e s t e r n t h e A s t a s o b a s (now c a l l e d t h e B l u e N i l e ) . The Astapus
(now c a l l e d
t h e White N i l e ) was a d i f f e r e n t r i v e r e n t i r e l y , which r o s e from some l a k e s t o t h e s o u t h and c a r r i e d t h e summer r a i n s t o form t h e d i r e c t stream of t h e N i l e . P t o l e m y , t h e Roman, who l i v e d i n A l e x a n d r i a i n t h e s e c o n d c e n t u r y A . D . , t h o u g h t t h a t t h e main N i l e came from t h e Mountains of t h e Moon, which w e r e p e r m a n e n t l y c o v e r e d w i t h snow and p a s s e d t h r o u g h two l a k e s . I t i s p r o b a b l e t h a t h e meant by t h e Mountains of t h e Moon, t h e Ruwenzori r a n g e and by t h e two l a k e s , V i c t o r i a and A l b e r t Nyanza. The map of t h e N i l e a s d e v e l o p e d by Ptolemy
i s a s shown i n F i g . 1.2. From t h e s e c o n d h a l f o f t h e s e c o n d c e n t u r y o n w a r d s , f o r a t l e a s t t h i r t e e n c e n t u r i e s , t h e r e w e r e h a r d l y any d i s c o v e r i e s , w i t h t h e e x c e p t i o n of some d e s c r i p t i o n s o f t h e lower r e a c h e s o f t h e N i l e by t h e mosl m g e o g r a p h e r s i n E g y p t . Examples a r e Al-Khuwarazmi
i n 864 A . D .
and Al-Masoudy
n 957 A . D .
The t r i u m p h a n t wars of P o r t u g a l a g a i n s t t h e Moors i n n o r t h - w e s t
Africa i n
t h e f i f t e e n t h c e n t u r y h a d , no d o u b t , paved t h e r o a d t o t h e P o r t u g u e s e i n f i l t r a t i o n i n A f r i c a , b o t h e a s t and w e s t . Two P o r t u g u e s e m i s s i o n a r i e s , P e d r o Paez and Jerome Lobo, v i s i t e d E t h i o p i a i n t h e s e v e n t e e n t h c e n t u r y . F a t h e r Paez v i s i t e d Lake Tana ( 1 6 1 8 ) . H i s s u c c e s s o r , F a t h e r Lob0 w r o t e an a c c o u n t a b o u t h i s v i s i t t o T i s s i s a t F a l l s . About 150 y e a r s l a t e r , i n 1770 A . D . ,
a Scottish
e x p l o r e r named James B r u c e , a f t e r h a v i n g j o u r n i e d f i v e y e a r s i n E t h i o p i a , s u c c e e d e d i n d i s c o v e r i n g t h e s o u r c e of t h e l i t t l e Abbai ( s e e map, F i g . 1 . 1 . ) . A summary of B r u c e ' s views on Paez and Cheesman's on t h e e x p e d i t i o n of Bruce
c a n be found i n t h e Book on The B l u e N i l e (Moorehead, A , ,
1962).
3
F i g . 1.1. L o c a t i o n o f t h e o l d i s l a n d o f Mero and t r i b u t a r i e s
The j o u r n e y s made by t h e Arab t r a d e r s on t h e e a s t c o a s t o f A f r i c a t o t h e i n t e r i o r , t h e r e l i g i o u s m i s s i o n s t o E a s t A f r i c a and t h e s t e a d i l y growing conn e c t i o n s between t h e C o p t i c c h u r c h e s o f A l e x a n d r i a and E t h i o p i a have a l l l e d t o more c o n c r e t e i n f o r m a t i o n on t h e snow-capped m o u n t a i n s ( t h e Mountains of t h e Moon) d e s c r i b e d by Ptolemy i n 150 A . D . The h i s t o r y o f e x p l o r i n g t h e N i l e r i v e r s y s t e m i n t h e n i n e t e e n t h c e n t u r y b e g i n s w i t h t h e i n v a s i o n of t h e Sudan by Mohammed A l i Pasha and h i s s o n s from 1821 onwards. A s a r e s u l t of t h i s , t h e B l u e N i l e was e x p l o r e d a s f a r a s i t s
e x i t from t h e E t h i o p i a n f o o t h i l l s , and t h e White N i l e a s f a r a s t h e S o b a t mouth. The Bahr e l Ghazal w a s e x p l o r e d by P e t h e r i c k i n t h e e i g h t e e n f i f t i e s . The c o n s i d e r a b l e i n t e r e s t o f t h e Europeans came s h o r t l y a f t e r t h e r e p o r t s o f Knoblecher (1850) a b o u t t h e e x i s t e n c e of some l a r g e l a k e s i n t h e s o u t h .
4
The M o u n t a i n s of the Moon
)
Second Lake
\
F i r s t Lake
) T h e holy Sprinq
v&&Donkola "
Aswan
Upper Land
"
K?
I
t
" M i d d i e Land
"
Asiut
A l - Ashmunein
A l - Muqattam
Mediterranean
Sea
I
F i g . 1 . 2 . Map of t h e N i l e from t h e s o u r c e a t t h e Mountains of t h e Moon t o t h e mouth i n t h e M e d i t e r r a n e a n S e a , a s p r e p a r e d by Ptolemy
From a b o u t 1857 onwards for a b o u t 30 y e a r s , t h e E q u a t o r i a l Lakes P l a t e a u and s u r r o u n d i n g s w e r e t r a v e r s e d by s e v e r a l e x p l o r e r s ,
a l l s e a r c h i n g for t h e
s o u r c e of t h e r i v e r t h a t h a d p u z z l e d t h e whole w o r l d for s e v e r a l c e n t u r i e s . The p r i n c i p a l e x p l o r e r s and t h e i r e x p e d i t i o n s w e r e as f o l l o w s : i)
B u r t o n and Speke went from Bagamoyo t o Tabora t o U j i j i on Lake Tanganyika (1857-59). I n 1858 Speke a l o n e went on n o r t h w a r d s and d i s c o v e r e d Lake V i c t o r i a .
5
S p e k e and G r a n t s e t o f f on an e x p e d i t i o n (1860-63)
ii)
around Lake V i c t o r i a
and r e a c h e d Ripon F a l l s . They t h o u g h t t h a t t h e stream f l o w i n g o u t of t h i s l a k e was t h e s o u r c e o f t h e N i l e . i i i ) Samuel B a k e r , a f t e r e x p l o r i n g t h e A t b a r a , went on t o d i s c o v e r Lake A l b e r t (1862-64)
a s w e l l a s t h e A l b e r t N i l e and t h e u p p e r r e a c h of
Bahr e l J e b e l . L i v i n g s t o n e , l i k e B u r t o n and S p e k e , s e t o f f on h i s r o u t e from Tabora
iv)
to U j i j i
( 1 8 7 2 ) . H e t h o u g h t t h e Lake Nyasa m i g h t b e d r a i n i n g i n t o Lake
T a n g a n y i k a , which c o u l d t h e n b e l i n k e d w i t h t h e A l b e r t Lake and t h e N i l e . v)
S t a n l e y t r a v e l l e d up from t h e e a s t c o a s t and c i r c u m n a v i g a t e d Lake V i c t o r i a ( 1 8 7 2 ) . H i s a t t e m p t t o g e t t o Lake A l b e r t was n o t s u c c e s s f u l , though h e r e a c h e d as f a r a s t h e e s c a r p m e n t a b o u t Lake George. I n a l a t e r j o u r n e y ( 1 8 8 9 ) h e r e a c h e d t h e S e m l i k i and Lake Edward. The r o u t e s o f t h e s e l e a d i n g e x p l o r e r s a r e i n d i c a t e d o n t h e map, F i g . 1 . 3 .
(Stamp and Morgan, 1 9 7 2 ) . I n s p i t e o f a l l t h e e x p e d i t i o n s a l r e a d y m e n t i o n e d , a number of t r i b u t a r i e s o f t h e N i l e remained u n d i s c o v e r e d . E x p l o r a t i o n m i s s i o n s s t o p p e d i n t h e p e r i o d 1881 up t o 1898 a s a r e s u l t o f t h e r e b e l l i o n s o f t h e Mahdis i n t h e S u d a n . A h i s t o r i c a l a c c o u n t o f t h i s p e r i o d c a n b e found i n t h e book e n t i t l e d "The White Nile"
(Moorehead, A , ,
1 9 6 0 ) . A f t e r t h e r e o p e n i n g of t h e Sudan i n 1898 and a t
a b o u t t h e same t i m e t h e o p e n i n g up o f Kenya and T a n z a n i a ( f o r m e r l y c a l l e d T a n g a n y i k a ) and Uganda, i r r i g a t i o n s e r v i c e s and s u r v e y and g e o l o g i c a l d e p a r t ments were e s t a b l i s h e d i n t h e r e s p e c t i v e c o u n t r i e s . S i n c e t h e n t h e s e d e p a r t ments h a v e t a k e n o v e r t h e e x p l o r a t o r y work a s w e l l a s t h e c o l l e c t i o n of h y d r o l o g i c and o t h e r r e l e v a n t d a t a ( H u r s t , H . ,
1952).
A t a b o u t t h e end o f 1902 t h e I r r i g a t i o n Department o f Egypt s t a r t e d two e x p e d i t i o n s ; t h e one u n d e r M r C . E .
Dupuis t o v i s i t Lake Tana and t h e o t h e r
u n d e r S i r W . G a r s t i n t o v i s i t t h e Lakes V i c t o r i a and t h e t h e n A l b e r t and Edward. The e x p e d i t i o n s which f o l l o w e d w e r e s e n t t o c o l l e c t , or r e p o r t o n , h y d r o l o g i c a l d a t a needed f o r t h e N i l e p r o j e c t s ( H u r s t , H . E . ,
1 9 3 1 ) . Unfortun-
a t e l y , t h e M a c m i l l a n - J e s s e n e x p e d i t i o n s i n 1902 and 1905 f a i l e d i n e x p l o r i n g Lake Tana o r f i n d i n g t h e s o u r c e o f t h e B l u e N i l e . A f t e r t h i s t h e r e was a l o n g p e r i o d o f i n a c t i v i t y on t h e r i v e r u n t i l R . E .
Cheesman a r r i v e d i n 1925 i n
E t h i o p i a . F o r t h e n e x t e i g h t y e a r s Cheesman d e v o t e d h i m s e l f t o t h e e x p l o r a t i o n o f t h e g o r g e o f t h e B l u e N i l e and t o c i r c u m n a v i g a t e Lake Tana. T h i s accomplishment was t e r m i n a t e d by w r i t i n g an a c c o u n t on Lake Tana and t h e B l u e N i l e (Cheesman, R . ,
1936).
More r e c e n t e x p e d i t i o n s h a v e b e e n s e n t , e s p e c i a l l y by t h e E g y p t i a n Governm e n t , t o e x p l o r e more o f t h e t r i b u t a r i e s i n t h e c a t c h m e n t s of t h e E q u a t o r i a l L a k e s , t h e White N i l e and t h e S o b a t . However, i t was n o t u n t i l 1937 t h a t t h e
6
southernmost s o u r c e of t h e N i l e i n t h e headstreams of t h e Kagera, l a r g e s t trib u t a r y o f Lake V i c t o r i a , was l o c a t e d . F u r t h e r e x p l o r a t i o n o f t h e N i l e t r i b u t a -
r i e s i n t h e E t h i o p i a n P l a t e a u h a s b e e n f o r q u i t e some t i m e l e s s f o r t u n a t e t h a n t o o t h e r p a r t s o f t h e N i l e B a s i n . The g o r g e o f t h e B l u e N i l e ( G r e a t A b b a i ) was n o t f u l l y t r a v e r s e d u n t i l a B r i t i s h m i l i t a r y and s c i e n t i f i c e x p e d i t i o n c o n quered i t d u r i n g t h e f l o o d o f 1968 ( B l a s h f o r d - S n e l l , J . N . ,
- - -Burton - - -Speke +++++
N
8, Speke 1857-'59
1858
Speke & Grant 1860-'63
.. ....... -
----
1970).
Baker Stanley
1862-'64 1871-'72, 1874-'77 8, 1887 - '8 9 L i v i n g s t o n e 1872
b Bagamoyo Tabora r o u t e s ~ m ~ l afor r Speke & Grant a n d S t a n l e y
F i g . 1 . 3 . The r o u t e s o f some l e a d i n g e x p l o r e r s o f t h e N i l e S o u r c e ( S t a m p , L . D . and Morgan, W.T., 1 9 7 2 )
1.2 1.2.1
HISTORY O F HYDROLOGY OF THE NILE BASIN
From 3200 B . C . t o 1900 A . D .
W h e t h e r t h e a n c i e n t E g y p t i a n s knew t h e o r i g i n o f t h e i r r i v e r or n o t ,
( s e e 1.1) w h a t c a n n o t b e d e n i e d i s t h a t t h e y were d e e p l y k e e n t o o b s e r v e a l l a s t r o n o m i c a l phenomena and t e r r e s t r i a l e v e n t s a s s o c i a t e d w i t h , o r r e l a t e d t o , the N i l e floods,
7
One of t h e most a n c i e n t r e c o r d s i s a drawing of an i m p e r i a l macehead h e l d by t h e p r o t o d y n a s t i c k i n g S c o r p i o n when c e l e b r a t i n g t h e o c c a s i o n of c u t t i n g an i r r i g a t i o n d i t c h some 3200 y e a r s B . C .
(Biswas, A . ,
1 9 7 0 ) . The same r e f e r -
e n c e m e n t i o n s , among o t h e r s : damming o f f of t h e N i l e and d i v e r t i n g i t s c o u r s e by King Menes i n 3000 B . C .
A t t h e same t i m e t h e a n c i e n t E g y p t i a n s began t o u s e
t h e N i l o m e t e r s t o r e c o r d t h e f l u c t u a t i o n of
t h e const r uct i on of
( P a g a n t s dam) some 30 k i l o m e t r e s s o u t h of C a i r o and i t s f a i l u r e
Sadd e l - K a f a r a i n 2850 B . C . ,
the N i l e ,
t h e c o n n e c t i o n o f t h e N i l e and t h e Red S e a by a n a v i g a t i o n a l
c a n a l d u r i n g t h e r e i g n of S e o s t r i s I i n a b o u t 1950 B . C . ,
t h e h y d r a u l i c works
of Amenemhet I 1 1 ( i n c l u d i n g Lake M o e r i s ) i n a b o u t 1850, t h e w a t e r codes of King Hammurabi i n 1750 B . C . , d e e p ) i n a b o u t 1700, e t c .
J o s e p h ' s w e l l n e a r C a i r o (more t h a n 100 metres
(Biswas, A , ,
1 9 7 0 ) . Another r e f e r e n c e s t a t e s t h a t
" h y d r a u l i c e n g i n e e r i n g " a t t h a t t i m e r e a c h e d a h i g h d e g r e e of accomplishment; r e c l a m a t i o n schemes on t h e l e f t bank of t h e N i l e were i n i t i a t e d d u r i n g t h e f l o o d s ; dams, d i k e s and c a n a l s w e r e c o n s t r u c t e d and l a t e r w a t e r - l i f t i n g machinery was i n v e n t e d ( T e c l a f f and T e c l a f f , 1 9 7 3 ) . Probably t h e f i r s t n o n - r e l i g i o u s
t h e o r y e x p l a i n i n g t h e y e a r l y f l o o d i n g was
t h a t d e r i v e d by t h e Greek T h a l e s (600 B . C . ) ,
t h e f o u n d e r of d e d u c t i v e geo-
m e t r y . H i s t h e o r y was t h a t t h e E t e s i a n winds d r o v e t h e s e a h i g h a g a i n s t t h e mouths of t h e r i v e r and t h e r e u p o n p r e v e n t e d them from d i s c h a r g i n g t h e i r w a t e r . The r i v e r t h e r e f o r e r e t u r n e d upon i t s e l f and, whenever i t c o u l d , i t b u r s t o u t i n t o f o r b i d d e n g r o u n d . A c o u p l e of c e n t u r i e s l a t e r a n o t h e r Greek g e o m e t e r , D e m o c r i t u s , came up w i t h a somewhat d i f f e r e n t t h e o r y . H e t h o u g h t t h a t when snow i n t h e n o r t h e r n p a r t s o f t h e w o r l d was m e l t e d a t t h e t i m e of t h e s u m m e r s o l s t i c e and flowed away, c l o u d s w e r e formed by t h e v a p o u r . When t h e c l o u d s
w e r e d r i v e n towards t h e s o u t h and towards Egypt by t h e E t e s i a n w i n d s , v i o l e n t s t o r m s a r o s e and c a u s e d t h e l a k e s f e e d i n g t h e R i v e r N i l e t o be f i l l e d (Frisinger, H . ,
1959).
S i n c e t h e N i l e u s e d t o r i s e i n f l o o d a t a b o u t t h e same t i m e e v e r y y e a r , i t s b e h a v i o u r had b e e n d e s c r i b e d a s r e g u l a r . The B i b l e t e l l s u s , however,
"
....
t h e r e came s e v e n y e a r s o f g r e a t p l e n t y t h r o u g h o u t t h e l a n d of E g y p t . And t h e r e s h a l l r i s e a f t e r them s e v e n y e a r s o f f a m i n e
.."
( G e n e s i s 4 1 , 29-30).
The i n t e r -
p r e t a t i o n by J o s e p h t o t h i s dream o f t h e P h a r a o of Egypt was p r o b a b l y t h e f i r s t indication of the persistence i n the hydrologic t i m e s e r i e s . The Roman s a v a n t , P l i n y (23-79 A . D . ) ,
t h o u g h t t h e two p r o b a b l e t h e o r i e s
a b o u t t h e f l o o d i n g of t h e N i l e w e r e t h o s e o f T h a l e s and Democritus.
After a l l ,
i n b o t h t h e o r i e s t h e a c t i o n of t h e E t e s i a n winds was t h e c u l p r i t . A f t e r P l i n y , t h e E n g l i s h h i s t o r i a n and t h e o l o g i a n , Beda (674-735 A . D . ) ,
compiled and sum-
m a r i z e d t h e knowledge t h e n a v a i l a b l e a b o u t t h e N i l e f l o o d . The t h e o r y h e p r o p o s e d was v e r y s i m i l a r t o t h a t of T h a l e s . H e c l a i m e d t h a t t h e n o r t h e r l y
8
winds f o r c e d t h e s e a waves t o p i l e up s a n d a t t h e N i l e mouths, t h u s c a u s i n g t h e r i v e r t o back up upon i t s e l f and f l o o d ( F r i s i n g e r , H . ,
1 9 5 9 ) . From t h a t
t i m e onwards u n t i l t h e n i n e t e e n t h c e n t u r y t h e r e was v e r y l i t t l e done t o e x p l o r e t h e s o u r c e s o f t h e N i l e and i t s t r i b u t a r i e s , e x c e p t f o r t h e r e c o r d i n g s which
w e r e done whenever p o s s i b l e . The n i n e t e e n t h c e n t u r y was t h e c e n t u r y of d i s c o v e r i n g t h e N i l e s o u r c e and t r i b u t a r i e s r a t h e r t h a n c o l l e c t i n g a n d / o r i n t e r preting its hydrologic data. The r e c o r d of t h e N i l e l e v e l s d a t e s back t o a b o u t 3000 t o 3500 y e a r s B . C . The r i v e r gauge is. c a l l e d N i l o m e t e r ( i n A r a b i c Miqyas An-Nil).
Three t y p e s of
N i l o m e t e r s were u s e d . The f i r s t t y p e c o n s i s t e d s i m p l y o f marking t h e w a t e r l e v e l s on c l i f f s on t h e banks of t h e r i v e r , e . g . t h e s e c o n d c a t a r a c t a t Semna. The s e c o n d t y p e c o n s i s t e d e s s e n t i a l l y of a s c a l e , u s u a l l y o f m a r b l e , on which t h e w a t e r l e v e l was o b s e r v e d . The s t a n d a r d gauge c o n s i s t e d o f a s e r i e s o f s t e p s
or p i l l a r s b u i l t i n t o t h e r i v e r bank t o e a c h of which a s e c t i o n of t h e s c a l e was f i x e d . I t i s c l a i m e d t h a t t h e r e a r e 140 o f t h e s e gauges s c a t t e r e d o v e r t h e b a s i n o u t s i d e E g y p t , and many more on t h e N i l e i n E g y p t . Most o f them a r e o b s e r v e d d a i l y , and t h e r e a d i n g s o f t h e more i m p o r t a n t a r e t e l e g r a p h e d or t e l e phoned t o C a i r o ( H u r s t , H . E . ,
1 9 5 2 ) . The c a t a s t r o p h i c f l o o d s o f 1954 and 1958
were measured a t 9 3 g a u g i n g p o i n t s i n Egypt o n l y , 36 gauges i n upper Egypt and t h e r e m a i n d e r i n l o w e r Egypt (Hashem and E l - S h e r b i n i ,
1 9 6 1 ) . The t h i r d and most
a c c u r a t e N i l o m e t e r used t o b r i n g w a t e r o f t h e N i l e t o a w e l l and t h e w a t e r l e v e l was marked e i t h e r on t h e w a l l s o f t h e w e l l or on a c e n t r a l p i l l a r . The most n o t a b l e N i l o m e t e r i s s i t u a t e d a t Roda n e a r C a i r o . The r e c o r d e d w a t e r l e v e l t h e r e d a t e s back t o 6 4 1 A . D . t h e r e i n 715 A . D .
The Arab c h a l i p h s (Kings) b u i l t a new N i l o m e t e r
T h i s was r e b u i l t i n 8 6 1 A . D .
I t c o n s i s t s of a squar e w e l l
c o n n e c t e d t o t h e N i l e by means o f t h r e e c o n d u i t s . A t t h e c e n t r e o f t h e w e l l i s a g r a d e d o c t a g o n a l p i l l a r of w h i t e m a r b l e d i v i d e d i n t o 19 c u b i t s (see F i g . 1 . 4 ) . I t was r e p o r t e d t h a t a s a r e s u l t o f p o o r j o i n i n g o f t h e lower b r o k e n p a r t o f t h e p i l l a r , t h e c o r r e s p o n d i n g c u b i t now measures 31 c m o n l y i n s t e a d o f t h e o r i g i n a l 54 c m ( G h a l e b , K., 1 9 3 5 ) . T h i s example and many o t h e r s shows t h a t t h e records a v a i l a b l e s i n c e 641 A . D .
need much a d j u s t m e n t b e f o r e h a v i n g them
a n a l y z e d . The s u i t a b i l i t y o f t h e r e c o r d f o r s t a t i s t i c a l a n a l y s i s h a s b e e n a r g u e d r e c e n t l y : "Simply,
t h e r e l i a b i l i t y of f l o o d d a t a f o r t h e assessment of
w a t e r a v e r a g e s , t h e r e l i a b i l i t y o f p r e s e r v a t i o n o f a l o n g - r a n g e c o n s t a n t gauge datum i n t h e p a s t , and a c c u r a c i e s i n o b s e r v a t i o n s ( a l l k i n d s o f c h a n g e s ) , unf o r t u n a t e l y do n o t p e r m i t one t o draw d e p e n d a b l e c o n c l u s i o n s " .
(Yevjecvich, V . ,
1983). 1.2.2
From 1900 A . D .
t i l l now
The t u r n of t h e l a s t c e n t u r y and t h e b e g i n n i n g o f t h e t w e n t i e t h c e n t u r y w i t n e s s e d a number of n o t a b l e a c c o m p l i s h m e n t s . When t h e t h e n Anglo-Egyptian
9
F i g . 1 . 4 . The N i l e gauge a t Roda, C a i r o , Egypt
10
S u d a n w a s r e o c c u p i e d i n 1 8 9 8 a l l swamp r i v e r s were f o u n d b l o c k e d u p . I t w a s n o t b e f o r e 1 9 0 5 t h a t a c h a n n e l t h r o u g h t h e B a h r e l J e b e l h a d b e e n made c l e a r . The G h a z a l was n o t made n a v i g a b l e t o t h e p r i n c i p a l c a p i t a l Wau, u n t i l 1 9 0 4 . I n 1 9 0 2 t h e w o r k s i n t h e f i r s t Aswan dam and some o f t h e B a r r a g e s o n t h e N i l e i n E g y p t were c o m p l e t e d . The h i s t o r y o f s c i e n t i f i c s t u d y o f t h e h y d r o l o g y
o f t h e N i l e b e g i n s w i t h t h e i n t r o d u c t i o n o f c u r r e n t metres by S i r H . Lyons i n about 1902. Previous t o t h i s ,
f l o w m e a s u r e m e n t s h a d b e e n made by f l o a t s . The
S u r v e y D e p a r t m e n t o f E g y p t became c h a r g e d w i t h t h e s u r v e y o f a l l r i v e r g a u g e r e c o r d s s o u t h o f Aswan i n 1 9 0 2 and 1 9 0 3 . T h i s w a s t h e o r i g i n o f t h e H y d r o l o g y S e r v i c e w h i c h formed p a r t o f t h e l a t e r P h y s i c a l D e p a r t m e n t o f E g y p t ( H u r s t and P h i l i p s , 1931) . The r e s u l t s o f t h e e x p e d i t i o n s t o L a k e s T a n a , V i c t o r i a , A l b e r t and Edward c o n d u c t e d by D u p u i s and G a r s t i n i n 1901-1904
( s e e 1 . 1 ) were c o n c l u d e d i n t h e
1904 r e p o r t by S i r W. G a r s t i n . S h o r t l y a f t e r t h a t , i n 1 9 0 6 , S i r H . Lyons publ i s h e d h i s book "The P h y s i o g r a p h y o f t h e N i l e " .
T h i s book c o n t a i n e d t h e i n f o r -
m a t i o n g a t h e r e d f r o m t r a v e l l e r s and s c i e n t i f i c e x p l o r e r s a v a i l a b l e a t t h a t
time.
I n 1905 S i r M .
MacDonald i n t r o d u c e d a new method o f r i v e r m e a s u r e m e n t a t
Aswan u s i n g t h e f l o w t h r o u g h t h e s l u i c e s o f t h e dam. A l a r g e masonary t a n k w a s used t o measure t h e d i s c h a r g e of one type o f s l u i c e under a l l c o n d i t i o n s of h e a d and s l u i c e o p e n i n g . The r e s u l t s were t h e n a p p l i e d t o f l o w from o t h e r sluices. The S u d a n b r a n c h o f t h e E g y p t i a n I r r i g a t i o n S e r v i c e w a s formed i n 1 9 0 5 w i t h t h e O b j e c t o f p e r fo r m in g a l l h y d r o l o g i c and h y d r o g r a p h i c works f o r t h e d i f f e r e n t p r o j e c t s a i m i n g a t t h e i m p r o v e m e n t o f t h e w a t e r s u p p l y o f E g y p t and t h e d e v e l o p m e n t o f p e r e n n i a l i r r i g a t i o n i n t h e S u d a n . The d a t a c o l l e c t e d i n t h e p e r i o d 1906 t o 1 9 1 3 w e r e u s e f u l i n t h e d e s i g n o f t h e J e b e l A u l i a dam on t h e White N i l e ,
a b o u t 4 5 km a b o v e t h e j u n c t i o n o f t h e W h i t e a n d t h e B l u e N i l e s ,
and Makwar dam o n t h e B l u e N i l e , some 360 km a b o v e t h e same j u n c t i o n . The f o u n d a t i o n s o f t h e p r e s e n t M e t e o r o l o g i c a l S e r v i c e o f E g y p t w e r e l a i d i n 1 9 0 0 . S i n c e t h e n many s t a t i o n s w e r e e s t a b l i s h e d and more o b s e r v a t i o n s were t a k e n . I n 1 9 1 5 a l l t h e work o f a p h y s i c a l n a t u r e d o n e by t h e S u r v e y D e p a r t m e n t , and t h e h y d r o l o g i c a l work d o n e by t h e I r r i g a t i o n D e p a r t m e n t , w e r e combined t o form t h e P h y s i c a l D e p a r t m e n t o f t h e M i n i s t r y o f P u b l i c W o r k s , E g y p t . The work o n t h e N i l e p r o j e c t s s t o p p e d d u r i n g t h e F i r s t World War (1914-1918), t h o u g h r o u t i n e o b s e r v a t i o n s w e r e c a r r i e d o n . From 1 9 1 2 up t o 1 9 2 3 , e s p e c i a l l y i n t h e post-war
p e r i o d , most o f t h e p r o g r e s s w a s d i r e c t e d a t e s t a b l i s h i n g p e r -
manent d i s c h a r g e s i t e s a t a number o f i m p o r t a n t s t a t i o n s w h e r e r e g u l a r o b s e r v a t i o n s h a d b e e n t a k e n . Advances i n m e a s u r i n g d e v i c e s and t e c h n i q u e s f o l l o w e d . D a t a c o l l e c t i o n and a n a l y s i s w e n t o n and t h a t w a s a g r e a t h e l p i n t h e d e s i g n a n d c o n s t r u c t i o n o f t h e Makwar dam, w h i c h w a s f i n a l l y b u i l t i n 1 9 2 5 on t h e
11
Blue N i l e f o r t h e b e n e f i t of t h e Sudan. I n 1923 t h e M i n i s t r y o f P u b l i c Works, E g y p t , s e n t a m i s s i o n t o t h e E q u a t o r i a l L a k e s w i t h t h e aim o f p r e p a r i n g a programme f o r i n v e s t i g a t i o n s i n c o n n e c t i o n w i t h t h e p o s s i b l e Upper N i l e p r o j e c t s . T h a t m i s s i o n was f o l l o w e d by o t h e r s i n 1 9 2 4 , 1 9 2 6 , 1930 and 1931 t o i n v e s t i g a t e t h e h y d r o l o g y o f t h e Lake P l a t e a u , Bahr e l Ghazal and t h e White N i l e b a s i n s . The E a s t A f r i c a n M e t e o r o l o g i c a l S e r v i c e , l a t e r D e p a r t m e n t , EAMD, was formed i n 1 9 2 7 . T h i s d e p a r t m e n t w a s p a r t l y f i n a n c e d by t h e E g y p t i a n Government.
It
o p e r a t e s o v e r a l l o f E a s t C e n t r a l A f r i c a and t h e d a t a i t c o l l e c t s are u n d o u b t e d l y v a l u a b l e f o r t h e h y d r o l o g y of t h e N i l e B a s i n . The o r i g i n a l N i l e w a t e r s a g r e e m e n t w a s l a i d down i n 1929 and h a d , f o r some
t i m e , b e e n t h e b a s i s o f t h e w a t e r a l l o c a t i o n b e t w e e n E g y p t and t h e S u d a n . The most i m p o r t a n t i t e m i n t h e a g r e e m e n t was
". . .
no works s h o u l d b e c o n s t r u c t e d
o r m e a s u r e s t a k e n , on t h e N i l e or i t s b r a n c h e s or on t h e l a k e s from which i t flows,
i n t h e S u d a n or i n t h e t e r r i t o r i e s u n d e r B r i t i s h a d m i n i s t r a t i o n , which
w o u l d a f f e c t t h e f l o w o f t h e r i v e r i n s u c h a way as t o c a u s e p r e j u d i c e t o t h e i n t e r e s t s of Egypt". To e n s u r e t h e c o n t i n u i t y o f d i s s e m i n a t i o n o f t h e k n o w l e d g e o n t h e h y d r o l o g y o f t h e N i l e B a s i n and t o p r e s e n t t h e e v e r - i n c r e a s i n g d a t a i n a s y s t e m a t i c way, f o r b o t h s c i e n t i f i c and p r a c t i c a l p u r p o s e s ,
i t w a s d e c i d e d t o i s s u e t h e volumes
a n d s u p p l e m e n t s o f "The N i l e B a s i n " s u c c e s s i v e l y . The b a s i c d a t a a b o u t t h e s e r e f e r e n c e s are as f o l l o w s :
Volume No.
Subject matter
Author ( s)
Year of pub1 i c a t i o n
I
General d e s c r i p t i o n of t h e b a s i n ; meteorology, topography of t h e White N i l e
H . E . H u r s t and P. P h i l i p s
11
D i s c h a r g e and s t a g e m e a s u r e m e n t s o f t h e N i l e and i t s t r i b u t a r i e s (with 9 supplements: 1928-32, 33-37, 38-42, 43-47, 48-52, 53-57, 58-62, 6 3 - 6 7 and 1968-72)
H.E. Hurst, P. P h i l i p s , Y .M. Simaika, R . B l a c k and N i l e Control S t a f f
from 1932 onward
Ten-day mean and m o n t h l y mean g a u g e r e a d i n g s o f t h e N i l e and its t r i b u t a r i e s (with 9 supplements: 1928-32, 33-37, 38-42, 43-47, 48-52, 53-57, 58-62, 6 3 - 6 7 and 1968-72)
H.E. Hurst, P. P h i l i p s , Y . M . Simaika, R . P . B l a c k and N i l e Control S t a f f
from 1932 onward
I11
1931
12
Subject matter
Volume No.
Year of publication
Author ( s )
IV
Ten-day mean and monthly mean d i s c h a r g e s o f t h e N i l e and i t s t r i b u t a r i e s (with 9 supplements: 1928-32, 33-37, 38-42, 43-47, 48-52, 53-57, 58-62, 63-67, 1968-72)
H . E . Hurst, P. P h i l i p s , Y . M . Simaika, R . P . B l a c k and N i l e Control Staff
V
The h y d r o l o g y of t h e Lake P l a t e a u and Bahr e l J e b e l
H . E . H u r s t and P. Philips
VI
Monthly and a n n u a l r a i n f a l l t o t a l s and number o f r a i n y days a t s t a t i o n s i n and n e a r t h e N i l e B a s i n f o r p e r i o d s : 1938-42, 43-47, 48-52, 53-57, 58-62, 63-67 and 1968-72 ( 7 s u p p l e ments)
H.E. R.P. Y.M. Nile
VI I
The f u t u r e c o n s e r v a t i o n of t h e Nile
H.E. Hurst, R.P. Black and Y . M . Simaika
1946
VIII
The h y d r o l o g y of t h e S o b a t and White N i l e and t h e t o p o g r a p h y of t h e B l u e N i l e and A t b a r a
H.E.
Hurst
1950
IX
The h y d r o l o g y o f t h e B l u e N i l e and A t b a r a and t h e Main N i l e t o Aswan w i t h some r e f e r e n c e t o projects
H.E. Hurst, R.P.. Black and Y . M . Simaika
1959
X
The m a j o r N i l e p r o j e c t s
H.E. Hurst, R.P. B l a c k and Y . M . Simaika
1966
from 1933 onward
1938
Hurst; Black, S i m a i k a and Control S t a f f .
from 1950 onward
The d a t a and i n f o r m a t i o n c o n t a i n e d i n t h e a b o v e - l i s t e d volumes o f t h e N i l e Basin, t o g e t h e r with those appearing i n t h e o t h e r papers of t h e Physical D e p a r t m e n t , l a t e r t h e N i l e C o n t r o l D e p a r t m e n t , have b e e n employed i n t h e d e s i g n and c o n s t r u c t i o n o f t h e major h y d r a u l i c works on t h e N i l e and i t s b r a n c h e s and t r i b u t a r i e s . Examples o f t h e s e a r e : t h e h e i g h t e n i n g of t h e o r i g i n a l Aswan dam i n 1912 and i n 1 9 3 7 , t h e J e b e l A u l i a dam on t h e White N i l e i n 1934, t h e Owen F a l l s dam a t t h e e x i t o f Lake V i c t o r i a i n 1 9 5 0 ,
...
etc.
The i d e a o f c o n s t r u c t i n g a h i g h dam a t Aswan l e d t o a n o t h e r agreement between Egypt and t h e Sudan i n 1959 f o r t h e f u l l u t i l i z a t i o n of t h e N i l e w a t e r s . I t i s w o r t h w h i l e m e n t i o n i n g h e r e t h a t t h e d e s i g n o f t h i s dam was b a s e d on t h e t h e o r y o f o v e r - y e a r s t o r a g e . The e a r l i e s t t h o u g h t o f t h i s t h e o r y goes back t o b e f o r e 1946 ( H u r s t e t a l , 1 9 4 6 ) . The development o f t h e t h e o r y marked t h e b i r t h o f modern h y d r o l o g y , e s p e c i a l l y t h e s t o c h a s t i c p a r t of i t ( M a n d e l b r o t and W a l l i s , 1 9 6 8 ) . The y e a r 1959 a l s o w i t n e s s e d t h e f i r s t a t t e m p t t o p l a n f o r t h e u l t i m a t e h y d r a u l i c development of t h e N i l e V a l l e y u s i n g an e l e c t r o n i c d i g i t a l computer
13
( M o r r i c e and A l l a n , 1 9 5 9 ) . Although t h e N i l e h a s been t h e b e s t - s t u d i e d
river i n
t h e w o r l d f o r a g e n e r a t i o n , t h e need f o r many more i n v e s t i g a t i o n s and r e s e a r c h work i s t h e r e . The c o m p l e t i o n of t h e f i r s t p h a s e of t h e R o s e i r e s dam on t h e B l u e N i l e , t h e Khashm e l - G i r b a dam on t h e A t b a r a and t h e High dam on t h e Main N i l e a t Aswan a r e h y d r o l o g i c h i g h l i g h t s i n t h e n i n e t e e n hundred and s i x t i e s . A
very i m p o r t a n t s t e p which began i n 1 9 6 7 , and h a s c o n t i n u e d f o r q u i t e some y e a r s , i s t h e c o l l a b o r a t i o n between Kenya, T a n z a n i a , Uganda, t h e Sudan and Egypt i n a h y d r o m e t e o r o l o g i c a l s u r v e y of t h e c a t c h m e n t s of Lakes V i c t o r i a , Kyoga and A l b e r t . T h i s p r o j e c t i n c l u d e d t h e u p g r a d i n g of some of t h e e x i s t i n g h y d r o m e t r i c a l s t a t i o n s and t h e e s t a b l i s h m e n t of new h y d r o m e t r i c a l s t a t i o n s and r i v e r d i s c h a r g e measurement s i t e s . A l l t h e s e s t a t i o n s have been equipped w i t h modern i n s t r u m e n t s . The r a i n f a l l - r u n o f f
r e l a t i o n s h i p s were s t u d i e d i n a
number of e x p e r i m e n t a l b a s i n s and t h e r e l e v a n t p a r a m e t e r s e s t i m a t e d (WMO, 1974). The e a r l y s i x t i e s and t h e l a t e s e v e n t i e s of t h i s c e n t u r y w i t n e s s e d an unu s u a l r i s e i n t h e s u r f a c e w a t e r l e v e l s o f t h e E q u a t o r i a l Lakes and of o t h e r A f r i c a n l a k e s a s w e l l . The l e v e l o f Lake V i c t o r i a r o s e by o v e r 2 . 5 m e t r e s between 1959 and 1964 ( K i t e , G . ,
1 9 8 1 ) . For t h e same p e r i o d , t h e r i s e r e a c h e d
3 . 3 metres f o r Lake A l b e r t , 2 . 6 f o r Lake Tanganyika and 1 . 5 m e t r e s f o r Lake Malawi. The s e c o n d s u b s t a n t i a l r i s e began i n 1978 and by mid 1979 r e a c h e d about 1 . 8 metres f o r Lake V i c t o r i a , 3 . 0 f o r Lake Malawi and 1 . 0 metre f o r Lake
T a n g a n y i k a . The c o n s i d e r a b l e r i s e i n t h e Lake V i c t o r i a w a t e r l e v e l i n 1964 l e d t o an e x c e s s i v e flow i n t h e N i l e t o s u c h an e x t e n t t h a t i t f l o o d e d some p a r t s of C a i r o a t t h a t t i m e . Two p r i n c i p a l p r o j e c t s have been t a k i n g p l a c e d u r i n g t h e l a s t few y e a r s and a r e p r o b a b l y w o r t h r e c o r d i n g h e r e . One i s t h e f i r s t p h a s e of t h e d i v e r s i o n scheme ( c a l l e d J o n g l e i c a n a l ) . The c a n a l c o n n e c t s t h e B a h r e l J e b e l a t Bor s t r a i g h t t o a b o u t Malakal on t h e White N i l e and conveys 20 m i l l i o n m 3 p e r day a t maximum. The a n n u a l volume o f w a t e r s a v e d by t h i s scheme i s 3 . 8 m i l l i a r d m 3 e s t i m a t e d a t Aswan. Half o f t h i s amount w i l l b e t a k e n by t h e Sudan and t h e o t h e r h a l f by Egypt ( E x e c u t i v e Organ f o r t h e Development P r o j e c t s i n J o n g l e i Area, 1 9 7 5 ) . The s e c o n d e v e n t , s i n c e 1 9 7 8 , is t h e j o i n t work o f t h e M i n i s t r y of I r r i g a t i o n , E g y p t , r e p r e s e n t e d by i t s o r g a n s ( m a i n l y t h e Master Water P l a n and t h e R e s e a r c h I n s t i t u t e f o r Water R e s o u r c e s Development), t h e U n i v e r s i t y o f C a i r o , E g y p t , and t h e M a s s a c h u s e t t e s I n s t i t u t e of Technology, U.S.A. i n t h e a n a l y s i s of t h e h y d r o l o g i c d a t a of t h e N i l e B a s i n . The r e s u l t s s o f a r o b t a i n e d a r e a v a i l a b l e i n a s e r i e s of t e c h n i c a l r e p o r t s . A d d i t i o n a l l y , once e v e r y two y e a r s , t h e y o r g a n i z e a s o r t of c o n f e r e n c e where problems r e l a t e d t o w a t e r r e s o u r c e s p l a n n i n g , management and development a r e d i s c u s s e d , t o g e t h e r w i t h the possible solutions.
14
L a s t b u t n o t l e a s t , b o t h Egypt and t h e Sudan a r e working j o i n t l y t o e s t a b l i s h a commission o f a l l c o u n t r i e s s h a r i n g t h e N i l e w a t e r s . The r o a d t o r e a l i z i n g t h i s s t e p i s , no d o u b t , rough and f u l l of d i f f i c u l t i e s . N e v e r t h e l e s s , such a s t e p i s , i n t h e a u t h o r ' s o p i n i o n , unavoidable i f t h e s e c o u n t r i e s a r e keen on h a v i n g a more e f f i c i e n t u t i l i z a t i o n of t h e w a t e r r e s o u r c e s i n t h e N i l e Basin. REFERENCES Bixwas, A . K . , 1966. The N i l e , i t s o r i g i n and r i s e . Water and Sewage Works, 1 1 3 : 283-292 B i s w a s , A . K . , 1970. H i s t o r y of h y d r o l o g y . North-Holland, Amsterdam, 336 p p . B l a s h f o r d - S n e l l , J . N . , 1970. Conquest of t h e Blue N i l e . Geogr. J o u r n . 1 3 6 : 42-51. Cheesman, R . E . , 1 9 3 6 . Lake Tana and t h e B l u e N i l e . Macmillan, London, 400 p p . E n c y c l o p a e d i a B r i t a n n i c a , 1 9 6 9 . N i l e , Vol. 1 6 : 516-523. E x e c u t i v e Organ f o r t h e Development P r o j e c t s i n J o n g l e i A r e a , 1975. J o n g l e i P r o j e c t ( P h a s e O n e ) . Tamaddon P . P r e s s , Khartoum, 99 p p . F r i s i n g e r , H . H . , 1959. E a r l y t h e o r i e s on t h e N i l e f l o o d s . Weather, V o l . 2 0 : 206-207. G h a l e b , K . O . , 1935. D i s c u s s i o n o f : F l o o d - s t a g e r e c o r d s of t h e R i v e r N i l e , by C . S . J a r v i s . T r a n s . ASCE, P a p e r No. 1944: 1063-1067 ( d i s c u s s i o n : 1063-1067). Hashem, A . and E l - S h e r b i n i , H . , 1961. The h y d r o l o g i c f e a t u r e s of t h e 1954 and 1958 f l o o d s ( i n A r a b i c ) . The Government P r i n t e r , C a i r o , 98 p p . H u r s t , H . E . and P h i l i p s , P . , 1931. The N i l e B a s i n , Vol. I , G e n e r a l d e s c r i p t i o n o f t h e b a s i n , m e t e o r o l o g y and topography of t h e White N i l e B a s i n . P h y s i c a l Department P a p e r 2 6 , Government P r e s s , C a i r o , 128 p p . H u r s t , H . E . , B l a c k , R . P . and S i m a i k a , Y . M . , 1 9 4 6 . The N i l e B a s i n , Vol. V I I , The f u t u r e c o n s e r v a t i o n o f t h e N i l e , P h y s i c a l Department P a p e r 5 1 , E a s t e r n P r e s s , C a i r o , 159 p p . H u r s t , H . E . , 1 9 5 2 . The N i l e , a g e n e r a l a c c o u n t of t h e r i v e r and t h e u t i l i z a t i o n o f i t s w a t e r s . C o n s t a b l e , London, 326 p p . K i t e , G . W . , 1981. Recent c h a n g e s i n t h e l e v e l of Lake V i c t o r i a . B u l l e t i n o f H y d r o l o g i c a l S c i e n c e s , No. 2 6 , 3: 233-243. M a n d e l b r o t , B . B . and W a l l i s , J . R . , 1968. Noah, J o s e p h , and O p e r a t i o n a l Hydrology. Water R e s o u r c e s R e s e a r c h , V o l . 4 , N o . 5 : 909-918. Moorehead, A , , 1 9 6 0 . The White N i l e . Hamish H a m i l t o n , London. 385 pp. M o o r e h e a d , . A . , 1 9 6 2 . The B l u e N i l e . Hamish H a m i l t o n , London. 308 p p . M o r r i c e , A . W . and A l l a n , W . M . , 1 9 5 9 . P l a n n i n g f o r t h e u l t i m a t e development o f t h e N i l e V a l l e y . P r o c . I n s t . C i v i l Eng. 1 4 , P a p e r 6372: 101-155. P i e r r e , B . , 1974. Le Roman du N i l . L i b r a r i e P l o n , P a r i s , 480 p p . Stamp, D . L . and Morgan, W . T . , 1972. A f r i c a : A s t u d y i n t r o p i c a l d e v e l o p m e n t . J o h n Wiley and S o n s , I n c . , N e w York, 520 p p . T e c l a f f , L . A . and T e c l a f f , E . , 1973. A h i s t o r y of w a t e r development and w a t e r q u a l i t y . I n : Environment Q u a l i t y and Water Development ( E d i t o r s : Goldman, C . R . , McEvoy 111, J . and R i c h e r s o n , P . M . ) . W . H . Freeman and Company, San F r a n c i s c o : 26-77. World M e t e o r o l o g i c a l O r g a n i z a t i o n , 1974. H y d r o m e t e o r o l o g i c a l s u r v e y of t h e c a t c h m e n t s o f Lakes V i c t o r i a , Kyoga and A l b e r t , RAF 66-025, Tech. R e p o r t 1, Vols I , 1 1 , I 1 1 and IV. Y e v j e v i c h , V . , 1 9 8 3 . The N i l e R i v e r B a s i n : h a r d c o r e and s o f t c o r e w a t e r p r o j e c t s . Water I n t e r n a t i o n a l V o l . 8 , N o . 1: 23-34
15
Chapter 2
PHYSIOGRAPHY O F THE NILE BASIN
2.1
INTRODUCTION
The N i l e B a s i n c o v e r s a s u r f a c e o f a b o u t 2 . 9 m i l l i o n s q u a r e k i l o m e t r e s , approximately one-tenth
to
o f t h e s u r f a c e a r e a o f A f r i c a . I t e x t e n d s from 4’s
31°N l a t i t u d e and from a b o u t 21°
30’E t o 40’
30’E l o n g i t u d e . The h y d r o g r a p h i c
b o u n d a r i e s o f t h e N i l e s y s t e m a r e as shown on t h e map, F i g . 2 . 1 . The h i g h e s t and t h e l o w e s t p o i n t s i n t h e b a s i n a r e r e p r e s e n t e d by t h e t o p o f t h e Ruwenzori Range and t h e t r o u g h o f E l - Q u a t t a r a d e p r e s s i o n r e s p e c t i v e l y .
They are a t e l e v a -
t i o n s o f a b o u t 5 1 2 0 metres a b o v e mean sea l e v e l ( a . m . s . 1 . )
and a b o u t 160 metres
b e l o w mean s e a l e v e l ( b . m . s . l . ) ,
respectively.
T h e l e n g t h o f t h e R i v e r N i l e f r o m i t s most r e m o t e s o u r c e , a t t h e h e a d o f R i v e r L u v i r o n z a , n e a r L a k e T a n g a n y i k a , t o i t s mouth on t h e M e d i t e r r a n e a n S e a , i s a b o u t 6 500 k i l o m e t r e s . The r i v e r c o u r s e and i t s t r i b u t a r i e s t r a v e r s e t h e t e r r i t o r i e s o f T a n z a n i a , Uganda, Rwanda, B u r u n d i , The Congo ( Z a i r e ) , Kenya, E t h i o p i a , t h e S u d a n and t h e Arab r e p u b l i c o f E g y p t . T h i s s t a t e o f a f f a i r s h a s made an i n t e r n a t i o n a l r i v e r o f t h e N i l e , whose w a t e r i s s h a r e d by a number of c o u n t r i e s . A l t h o u g h t h e N i l e i s an a n c i e n t r i v e r ,
t h e e x i s t i n g h y d r o l o g i c p a t t e r n may b e
a s y o u n g as 10 000 y e a r s . I f w e e x c l u d e t h e d r a s t i c c h a n g e s i n t h e b a s i c n a t u r e o f t h e r i v e r , t h e u n i n t e r r u p t e d l i f e o f t h e modern N i l e c o n f i g u r a t i o n h a s b e e n a s h o r t o n e . A d d i t i o n a l l y , a wide v a r i e t y o f topographic f e a t u r e s
- climate,
l o g y , s o i l , p l a n t and v e g e t a l c o v e r and o t h e r h y d r o l o g y - a f f e c t i n g
factors
geo-
-
c a n b e f o u n d i n t h e N i l e B a s i n . The i n t e g r a t e d e f i e c t o f s u c h c a u s a t i v e f a c t o r s on t h e r u n - o f f discharge,
f r o m a r i v e r b a s i n c a n b e r e p r e s e n t e d by t h e s o - c a l l e d s p e c i f i c
i.S p e c i f i c
d i s c h a r g e v a l u e s o f some o f t h e w o r l d r i v e r s a r e l i s t e d
i n Table 2 . 1 . These values have been c a l c u l a t e d u s i n g t h e r e l a t i o n s h i p where
a
= &A,
i s t h e l o n g - t e r m mean d i s c h a r g e and A = s u r f a c e area o f t h e r i v e r c a t c h -
ment. I t i s v e r y c l e a r from T a b l e 2 . 1 t h a t o f a l l w o r l d r i v e r s w i t h d r a i n a g e b a s i n
a r e a s , e a c h l a r g e r t h a n 1 m i l l i o n km’, discharge.
I f the estimated
t h e River N i l e has t h e lowest s p e c i f i c
o f t h e Congo B a s i n , w h i c h i s g e o g r a p h i c a l l y t h e
c l o s e s t to t h e N i l e Basin, is f a i r l y c o r r e c t , t h e s p e c i f i c discharge of the
l a t t e r would t h e n b e j u s t o n e t e n t h t h e s p e c i f i c d i s c h a r g e o f t h e Congo. The two c a u s a t i v e f a c t o r s w h i c h p r o b a b l y h a v e t h e b i g g e s t e f f e c t o n t h e r u n o f f f r o m a d r a i n a g e b a s i n a r e t h e c l i m a t e and t h e t o p o g r a p h y . The f o r m e r w i l l b e d i s c u s s e d i n Chapter 3 , w h i l e t h e topography of t h e N i l e Basin i s d e a l t with i n this chapter.
16
2 5O
3 0"
3 5O
4FO
F i g . 2 . 1 . The h y d r o g r a p h i c b a s i n of t h e N i l e s y s t e m ( t h e b o u n d a r i e s of t h e d r a i n a g e b a s i n a r e i n d i c a t e d by a d a s h - d o t l i n e )
17
TABLE 2.1
S p e c i f i c d i s c h a r g e s of r i v e r s w i t h c a t c h m e n t a r e a s each l a r g e r t h a n 1 million square kilometres (Kalinin, G . ,
River
Site
Catchment a r e a , A , kmz
1971)
Long-term
-
d i s c h a r g e , 0, m3/sec ~~
Specific d i s c h a r g e , 9, l i t/sec/km2
~
Nile
Aswan
2.880 .OOO
Missouri
Hermann
1.369 .OOO
2 187
1.69
Mississippi
S t . Louis
1.817.000
4 900'
2.70 4.51
2 830
0.98
Amur
Khabarovsk
1.620.000
7 300
Ob
Salekhard
2.450.000
12 460
5.09
Volga
Kuibyshev
1.220.000
7 480
6.13
Lena
Kyusyur
2.430 .OOO
15 900
6.54
Yenisei
Ingarka
2.470.000
18 100
7.33
Congo+
R i v e r mouth
3.700.000
36 000
9.73
Yangtze
Hankow
1.490.000
23 700
15.91
+estimated
The g e n e r a l t o p o g r a p h i c map, F i g . 2.2., shows t h a t t h e b a s i n of t h e N i l e i s c h a r a c t e r i z e d by t h e e x i s t e n c e of two mountainous p l a t e a u s r i s i n g some thousands of metres above mean s e a l e v e l . The Lake P l a t e a u i n t h e s o u t h e r n p a r t of t h e N i l e B a s i n i s g e n e r a l l y a t a l e v e l of 1 0 0 0 t o 2 000 metres. The Ruwenzori mountainous r a n g e e x t e n d i n g between Lakes Edward and A l b e r t (Mobutu-Sese Seko) a t t h e w e s t o f t h e Lake P l a t e a u h a s a peak r i s i n g more t h a n 5 100 m e t r e s whereas t h e peak o f M t . Elgon n o r t h - e a s t
o f Lake V i c t o r i a is a t a l a t i t u d e of 4 300
metres. A l l t h e l a k e s i n t h i s p l a t e a u , e x c e p t Lakes V i c t o r i a and Kyoga a r e a t l e v e l s below 1 0 0 0 metres a . s . 1 . The o t h e r mountainous p l a t e a u i n t h e b a s i n a f t h e N i l e i s t h e E t h i o p i a n or A b y s s i n i a n P l a t e a u , bThich forms t h e e a s t e r n p a r t of t h e b a s i n . The p e a k s o f t h i s p l a t e a u r i s e t o more t h a n 3 500 m e t r e s a . m . s . 1 . North of t h e Lake P l a t e a u t h e b a s i n d e s c e n d s g r a d u a l l y t o t h e Sudan p l a i n s where t h e N i l e r u n s a t a l t i t u d e s lower t h a n 500 metres i n i t s n o r t h e r l y d i r e c t i o n . A t a b o u t 200 k i l o m e t r e s s o u t h of t h e s o u t h e r n f r o n t i e r o f E g y p t , t h e r i v e r c u t s i t s c h a n n e l i n a narrow t r o u g h bounded from each s i d e by t h e c o n t o u r l i n e o f 200 metres ground s u r f a c e l e v e l . I n g e n e r a l , t h e w i d t h of t h i s t r o u g h i n c r e a s e s a s t h e r i v e r p r o c e e d s n o r t h w a r d s . Almost two hundred k i l o m e t r e s b e f o r e d i s c h a r g i n g i n t o t h e s e a , t h e r i v e r b i f u r c a t e s and i t s two b r a n c h e s encompass t h e N i l e D e l t a . A f a i r l y d e t a i l e d d e s c r i p t i o n of t h e v a r i o u s p a r t s o f t h e N i l e Basin i s p r e s e n t e d i n t h e f o l l o w i n g s e c t i o n s .
18
Fig. 2.2.
Topographic map of t h e N i l e B a s i n
19
2.2 2.2.1
THE EQUATORIAL LAKES PLATEAU Lake V i c t o r i a
The G r e a t R i f t V a l l e y which r u n s w i t h some i n t e r r u p t i o n s from Zimbabwe t o t h e Jordan V a l l e y , i n c l u d i n g t h e Red S e a , i s d i v i d e d i n t o two b r a n c h e s i n t h e s o u t h -
e r n p a r t of t h e N i l e B a s i n . The e a s t e r n b r a n c h of t h e R i f t V a l l e y r u n s through Kenya and i s n o t i n c l u d e d i n t h e N i l e B a s i n . The w e s t e r n b r a n c h , however, cont a i n s Lakes T a n g a n y i k a , Kivu, Edward, George and A l b e r t .
I t continues north
along t h e Bahr e l J e b e l . The r a n g e of Mufumbiro m o u n t a i n s , w i t h peaks r e a c h i n g 4 500 m e t r e s a . m . s . l . ,
e x t e n d s between Lakes Edward, Kivu and Tanganyika and
s e p a r a t e s t h e l a t t e r two l a k e s from t h e N i l e B a s i n ( s e e map, F i g . 2.3.: Stamp and Morgan, 1 9 7 2 ) . The most u p s t r e a m t r i b u t a r y of t h e N i l e , a l s o t h e most i m p o r t a n t f e e d e r o f Lake V i c t o r i a , i s t h e R i v e r Kagera. T h i s t r i b u t a r y h a s a d r a i n a g e b a s i n of 6 3 000 km2 i n an a r e a s i t u a t e d between '1 between 29O 30'and
31° 40'E
and 4's
l a t i t u d e and
l o n g i t u d e a s shown on t h e map, F i g . 2 . 4 . P r a c t l c a l l y
t h e whole of t h e Kagera B a s i n i s mountainous c o u n t r y and t h e g r e a t e r p a r t
it
Of
i s s i t u a t e d between t h e 1 200 and 1 600 metre l e v e l s . I n t h e extrer.ie w e s t , t h e c o u n t r y l e v e l i s a t 2 500 metres n.m.s.1.
and r i s e s t o about 4 500 m e t r e s t o
form t h e peaks o f t h e Mufumbiro Range. The Kagera B a s i n i s a complex of s t r e a m s o f v a r y i n g o r d e r which a r e i n t e r c e p t e d and i n t e r c o n n e c t e d by l a k e s and swamps. T h i s complex b e g i n s w i t h t h e R i v e r L u v i r o n z a i n t h e s o u t h - w e s t of t h e Kagera Basin a b o u t 40 km from t h e e a s t e r n s h o r e of Lake T a n g a n y i k a . A f t e r f l o w i n g i n a
v e r y w i n d i n g c o u r s e for a b o u t 100 km a t l e v e l s h i g h e r t h a n l 6 0 0 m a . m . s . l . ,
it
c o n t i n u e s f o r some 180 km i n a r e l a t i v e l y s t r a i g h t c h a n n e l t r a v e r s i n g a lowerl y i n g c o u n t r y . T h e r e t h e r i v e r name changes t o Ruvuvu and i t j o i n s t h e Kagera downstream o f t h e Bugufi F a l l s . The Ruvuvu draws i t s s u p p l i e s from t h e h i g h l a n d i n B u r u n d i . Moreover, t h i s r i v e r i s j o i n e d by a number of s e a s o n a l - f l o w i n g
streams a l l coming from t h e e a s t and by t h e Nyavarongo from t h e w e s t , a few k i l o m e t r e s u p s t r e a m of t h e B u g u f i F a l l s . The R i v e r Nyavarongo f l o w s from t h e high l a n d e a s t o f Lake Kivu and r e c e i v e s w a t e r from t h e R i v e r Akanyaru i n t h e s o u t h and t h e R i v e r Nyaranda i n t h e n o r t h - e a s t
( s e e map, F i g . 2 . 4 . ) . Below t h e
j u n c t i o n of t h e s e r i v e r s t h e main stream t r a v e r s e s an a r e a s u r r o u n d e d by l a k e s and swamps up t o t h e c o n f l u e n c e w i t h t h e Ruvuvu. Downstream o f t h e Bugufi F a l l s t h e Kogera r u n s t o t h e n o r t h t h e n t o t h e n o r t h - w e s t
i n a less w i n d i n g c o u r s e f o r
a b o u t 170 km, where i t i s j o i n e d by t h e R i v e r K a l a n g a s s a from t h e south-west
and
by t h e R i v e r Kakitumba from t h e w e s t . The Kagera t h e n c o n t i n u e s i t s c o u r s e a l o n g t h e s o - c a l l e d b i g e a s t w a r d bend t o t h e v i l l a g e of B i b a t u r a where i t e n t e r s a r e l a t i v e l y l o w - l y i n g c o u n t r y . About 70 km f u r t h e r t o t h e s o u t h - e a s t
t h e Kagera
r e c e i v e s some w a t e r b r o u g h t by a s t r e a m f l o w i n g o u t of t h e Muisha swamp i n a n o r t h e r l y d i r e c t i o n . A few k i l o m e t r e s below t h e c o n f l u e n c e of t h i s s t r e a m w i t h t h e Kagera t h e l a t t e r i s j o i n e d by t h e R i v e r Ngono which r u n s w e s t o f t h e c o a s t
20
o f L a k e V i c t o r i a . The K a g e r a c o n t i n u e s i t s c o u r s e a l o n g t h e e a s t w a r d b e n d for a b o u t 20 k m b e f o r e i t f i n a l l y e n t e r s L a k e V i c t o r i a ( H u r s t , H . E .
1927).
Fig. 2 . 3 . R i f t V a l l e y s and v o l c a n i c a r e a s o f e a s t e r n A f r i c a ( S t a m p , L . D . and Morgan, W . T . , 1 4 7 2 )
21
D rainage b a s i n s : .
1. R . K a g e r a , 2 . V i c ? c r l a N W . , 3. V i c t o r i a N i l e & L . K y o g a , 4. L George & E d w a r d , 5 . L. A l b e r t & R. S e r n l i k i , 6. Victoria
7.
S.E.,
Victoria N.E. a n d 8 R. A s s u a
Fig. 2.4.
Map s h o w i n g t h e d r a i n a g e b a s i n s i n t h e E q u a t o r i a l L a k e s P l a t e a u
22
The L a k e s P l a t e a u i s s i t u a t e d between t h e two b r a n c h e s of t h e G r e a t R i f t V a l l e y . The a v e r a g e e l e v a t i o n o f t h i s p l a t e a u is a b o u t 1 300 m e t r e s a . m . s . l . T h e p l a t e a u c o n t a i n s Lakes V i c t o r i a , George, Edward and A l b e r t . Lake V i c t o r i a i s a d e p r e s s i o n whose s u r f a c e h a s an a r e a of a b o u t 69 000 km‘, w a t e r l e v e l of 1 134 m e t r e s a . m . s . 1 .
corresponding t o a
The n e t w a t e r a r e a i s a b o u t 4% less t h a n
t h e t o t a l a r e a , t h e d i f f e r e n c e is o c c u p i e d by t h e S e s e i s l a n d s i n t h e n o r t h - w e s t and t h e Ukenve i s l a n d i n t h e s o u t h - e a s t
and many o t h e r less i m p o r t a n t i s l a n d s .
The water s u r f a c e i s d i v i d e d between Kenya, a b o u t 5%, T a n z a n i a , a b o u t 51%, and Uganda, 44%. The l a k e h a s an 0-shaped Oo 30”
s u r f a c e which e x t e n d s from a b o u t 3OS t o
l a t i t u d e and from a b o u t 31° 40’E t o 34O 5 0 ’ E
l o n g i t u d e . The a v e r a g e
d e p t h of t h e l a k e i s 40 m and t h e maximum d e p t h as f a r a s i t h a s been sounded
i s 79 m . The b a t h y m e t r i c map o f t h e l a k e i s shown i n F i g . 2 . 5 .
(Talling, J . F . ,
1 9 6 9 ) . The s h a l l o w d e p t h o f t h i s l a k e i s why t h e r e i s no s t r a t i f i c a t i o n i n t h e
w a t e r t e m p e r a t u r e . I n s t e a d , c o m p l e t e m i x i n g o c c u r s and t h e water t e m p e r a t u r e v a r i e s between 2 3 . 8 O C and 2 6 . 0 ° C , d e p e n d i n g on t h e t i m e of t h e y e a r (Beauchamp, R . A .
Fig. 2.5.
,
1964)
.
B a t h y m e t r i c map of Lake V i c t o r i a ( T a l l i n g , J . F . , 1966)
23
The l a n d p o r t i o n o f t h e Lake V i c t o r i a c a t c h m e n t i s a b o u t 1 9 3 000 km2. T h i s a r e a i s d i v i d e d b e t w e e n Kenya, 44 0 0 0 , T a n z a n i a , 8 4 2 0 0 , Uganda, 3 2 100 and Rwanda-Burundi,
33 600 km2 ( Z a g h l o u l , S . S . , 1 9 8 2 ) . An i n s i g h t i n t o t h e t o p o -
g r a p h y o f t h e c a t c h m e n t s u r f a c e c a n b e s e e n from t h e c r o s s - s e c t i o n s which a r e presented i n Fig. 2 . 6 . Three s o u r c e s c o n t r i b u t e t o t h e n e t s u p p l y t o Lake V i c t o r i a . These a r e : t h e o u t f l o w o f t h e R i v e r K a g e r a , t h e d i r e c t p r e c i p i t a t i o n o n t h e l a k e s u r f a c e and t h e run-off
f r o m t h e l a n d p o r t i o n o f t h e c a t c h m e n t . The K a g e r a B a s i n h a s
a l r e a d y b e e n d e s c r i b e d . I n s p i t e o f t h e f a c t t h a t i t r e c e i v e s more r a i n f a l l t h a n t h e o t h e r two s o u r c e s and t h e s l o p e o f t h e streams d i s c h a r g i n g i n t o t h e Kagera i s , g e n e r a l l y , n o t s m a l l , t h e d i s c h a r g e o f t h e Kagera is r a t h e r low. The r e a s o n s b e h i n d i t a r e t h e swamps and l a k e s w h i c h e x i s t i n t h e b a s i n and t h e c o n s i d e r a b l e l e n g t h o f streams f l o w i n g i n i t . The d i r e c t p r e c i p i t a t i o n on t h e Lake V i c t o r i a is a l m o s t l o s t by t h e e v a p o r a t i o n from i t s s u r f a c e . A l t h o u g h t h e d i f f e r e n c e b e t w e e n t h e a v e r a g e d e p t h s o f p r e c i p i t a t i o n and e v a p o r a t i o n i n a y e a r i s t o o s m a l l , t h e c o r r e s p o n d i n g volume
i s q u i t e b i g . A y e a r l y e x c e s s o f t h e p r e c i p i t a t i o n o n t h e l a k e s u r f a c e o f 1 5 mm o v e r t h e e v a p o r a t i o n f r o m t h e l a k e s u r f a c e means a g a i n t o t h e volume o f l a k e w a t e r c o n t e n t of 1 m i l l i a r d m 3 .
This t h e r e f o r e c o n s t i t u t e s an important source
o f s u p p l y t o t h e l a k e . The t h i r d s o u r c e o f s u p p l y t o Lake V i c t o r i a i s formed by t h e p e r e n n i a l streams i n t h e e a s t e r n s i d e o f t h e l a k e . Of t h e s e may b e m e n t i o n e d t h e S i m i y u and t h e Ruwand w h i c h f l o w i n t o S p e k e G u l f , t h e Mara R i v e r which e n t e r s t h e l a k e somewhere a b o u t t h e m i d d l e p o i n t o f t h e e a s t e r n s h o r e , and t h e Nzoya, Y a l a and S i o w h i c h e n t e r t h e l a k e i n i t s n o r t h - e a s t e r n c o r n e r .
2.2.2
The Upper V i c t o r i a N i l e
The Upper V i c t o r i a N i l e is t h e o n l y o u t l e t o f Lake V i c t o r i a and i t c o n n e c t s t h e l a t t e r w i t h Lake Kyoga. The r i v e r i s a b o u t 130 km l o n g and t h e d i f f e r e n c e i n l e v e l b e t w e e n i t s h e a d and i t s t a i l i s a b o u t 1 0 5 m . T h i s d i f f e r e n c e h a s b e e n b r o u g h t by t h e Owen a n d t h e R i p o n R a l l s .
T h e s e f a l l s a r e formed by a r e e f of
r o c k c r o s s i n g t h e stream d i a g o n a l l y . S i n c e 1 9 5 2 t h e N i l e l e a v e s Lake V i c t o r i a t h r o u g h t h e t u r b i n e s o f t h e power p l a n t a n n e x e d t o t h e Owen D a m which i s b u i l t
a t t h e f o o t o f t h e Owen F a l l s . The w i d t h o f t h e w a t e r s u r f a c e i n t h e Upper V i c t o r i a N i l e v a r i e s b e t w e e n 300 and 6 0 0 m . The r e g i o n n o r t h o f L a k e V i c t o r i a h a s b e e n t i l t e d i n s u c h a way as t o r e v e r s e t h e f l o w i n t h e u p p e r p a r t o f t h e Kafu R i v e r . The v a l l e y s a t t h e h e a d o f t h e r i v e r t h e r e f o r e became f l o o d e d , t o f o r m t h e p r a c t i c a l l y c o n t i n u o u s p a i r o f L a k e s Kyoga and Kwania (Wayland, E . J . ,
1934).
24
Luera
1000 -
800
2200
-
a
-
Section
through
the
equator
-
Scales
~
Hor. : 1 / 4,000,000
2000
Ver. : 1 /
20,000
1800
-
1600
ui
g 1400 0
v1
2
1200
i
I
;1000
L
- Section
b
;2400 r--L.
through
1"s.
latitude
Kivu
.-
-;2200 1
R Nyavarongo
w
2000
1800
1600 1400 1200
F
L
Y
(1135)
loo0 800
31
30' c -
Fig. 2.6.
Victoria
Section
through
I
Is I Ukerewe
32 " 2 " S.
33"
latitude
S e c t i o n s a c r o s s Lake V i c t o r i a and a d j a c e n t c o u n t r y
34" E
25
2 . 2. 3
Lakq-K,yoga
Lake Kyoga h a s undergone some c h a n g e s i n i t s o l d p a t t e r n . The o l d e r Kyoga was a l a r g e r l a k e t h a n t h e p r e s e n t body o f w a t e r . I t i s a s h a l l o w d e p r e s s i o n c o n s i s t i n g o f a number o f a r m s , many o f which a r e f i l l e d w i t h swamp v e g e t a t i o n . The l a k e h a s a b a s i n 75 000 km2 i n a r e a i n c l u d i n g 6 270 km2 which form t h e a r e a s o c c u p i e d by t h e l a k e arms and e n c l o s i n g h i g h l a n d up t o an e l e v a t i o n o f 1 0 3 0 m e t r e s a . m . s . 1 . The d e p t h o f t h e l a k e a t i t s w e s t e r n end i s from 3 t o 5 m , t h e maximum r e c o r d e d d e p t h i s 7 m. The d r a i n a g e b a s i n o f Kyoga, w i t h t h e excepof t h e D e b a s i e n Mountain and t h e w e s t e r n h a l f o f t h e Elgon Mountain, i s c h a r a c t e r i z e d by a s e r i e s o f low h i l l s and f l a t v a l l e y s w i t h impeded d r a i n a g e ( s e e c r o s s - s e c t i o n s i n F i g . 2 . 7 ) . I n s p i t e o f t h e a l m o s t 1 300 mm y e a r l y r a i n f a l l , t h e e x c e s s i v e e v a p o t r a n s p i r a t i o n from t h e swamps c o v e r e d w i t h c y p e r u s p a p y r u s and w a t e r l i l i e s and t h e i n s i g n i f i c a n t s u p p l y b r o u g h t by many o f t h e r i v e r s d r a i n i n g i n t o t h e l a k e make Lake Kyoga a s o u r c e o f l o s s . Heavy r a i n s i n t h e l a k e b a s i n a r e l i k e l y t o s e t l o o s e l a r g e masses o f v e g e t a t i o n which b l o c k t h e o u t l e t o f t h e N i l e from t h e l a k e .
2.2.4
The Lower V i c t o r i a N i l e
The Lower V i c t o r i a N i l e l e a v e s Kyoga a t P o r t Masindi and r u n s a s a s l u g g i s h swampy r i v e r t o t h e n o r t h f o r a d i s t a n c e o f a b o u t 75 km. Here i t b e n d s w e s t wards and a f t e r a s u c c e s s i o n o f r o c k s and r a p i d s d e s c e n d s t h e Marchison F a l l s and s h o r t l y a f t e r w a r d s e n t e r s Lake A l b e r t t h r o u g h a swampy d e l t a . On t h e west o f t h e V i c t o r i a N i l e B a s i n t h e r e i s a l a r g e s y s t e m o f swamps whose d r a i n a g e e n t e r s t h e N i l e by t h e Kafu R i v e r ( s e e F i g . 2 . 4 . ) . The c o n t r i b u t i o n o f t h i s r i v e r , e x c e p t a f t e r heavy r a i n s , may b e c o n s i d e r e d n e g l i g i b l e . The d i f f e r e n c e i n t h e w a t e r l e v e l between t h e two e n d s of t h e Lower V i c t o r i a N i l e , i . e . b e t ween Lake Kyoga and A l b e r t i s a l m o s t 410 metres.
2.2.5
Lake A l b e r t (Mobutu-Sese Seko)
A s m e n t i o n e d e a r l i e r , t h e c h a i n formed by t h e l a k e s A l b e r t , Edward, and George, t o g e t h e r w i t h t h e i r r e s p e c t i v e d r a i n a g e b a s i n s , Great R i f t Valley.
forms a p a r t o f t h e
I n some p l a c e s t h e e s c a r p m e n t s o f t h e v a l l e y r i s e d i r e c t l y
from t h e w a t e r s u r f a c e o f Lake A l b e r t , which i s a t a n a l t i t u d e o f a b o u t 617 metres a . m . s . l . ,
r e a c h i n g an e l e v a t i o n of 2 000 metres or h i g h e r a s h o r t d i s -
t a n c e i n l a n d from t h e l a k e s ( s e e t h e s e c t i o n s i n F i g . 2 . 7 . ) . Lake A l b e r t h a s a s u r f a c e a r e a of 5 300 km2 c o r r e s p o n d i n g t o an e l e v a t i o n of 617 m e t r e s a . m . s . 1 . The B a t h y m e t r i c map ( F i g . 2 . 8 . ) shows t h a t t h e d e p t h o f w a t e r r e a c h e s 50 m e t r e s a t some p l a c e s i n t h e l a k e . The r u n - o f f
from t h e d r a i n a g e b a s i n o f Lake A l b e r t ,
1 7 000 km2 i n a r e a , p l u s t h e d i r e c t p r e c i p i t a t i o n on t h e l a k e i t s e l f , a r e a l l l o s t b y e v a p o r a t i o n from t h e l a k e s u r f a c e . The n e t g a i n by A l b e r t comes from
26
1800
-
1600
-
1400
-
1200
-
1000
-
800
-
600
a -
Section
through
2 O N
latitude
1600
I
1400 1200 1000
Kyoga
L
A
v
S w a m p s of the
Kafu basin
1 3000
LJ
800
2800
(620)
;600 i
2600 b -
0
Section
through
1
30' N latitude
ul
2400
L
u r
E
2200
C
2 000
.-0
I
-
1800
W
a,
1600
1400
1
1800
1
1200
yk k -
1000
- I
"
j
Scales
c
- Section I
31 Fig. 2.7.
through
l0N
latitude
Hor Ver
1 / 4,000,000 1 / 20,000
I
I
I
I
32'
33O
34O
35O
Sections across Lake Kyoga and adjacent country
27
t h e o u t f l o w of t h e R i v e r S e m l i k i , which e n t e r s t h e l a k e from t h e s o u t h - w e s t . The S e m l i k i c o n n e c t s Lake Edward t o Lake A l b e r t , a f t e r f l o w i n g a d i s t a n c e of about 250 km down t h e R i f t V a l l e y t o t h e w e s t o f t h e Ruwenzori Mountain. The d r a i n a g e b a s i n o f t h e S e m l i k i i s 8 000 km2 i n a r e a . I t c o v e r s t h e w e s t e r n s l o p e s o f t h e Ruwenzori Range and is t r a v e r s e d b y many s t r e a m s . The d i f f e r e n c e i n w a t e r l e v e l between t h e two e n d s o f t h e S e m l i k i i s 295 metres. Most o f t h e drop t a k e s p l a c e o v e r t h e r a p i d s which e x i s t i n t h e u p p e r o f t h e r i v e r ' s c o u r s e . I n t h e l o w e r p a r t , t h e r i v e r h a s a w i d t h o f 150 m i n f l o o d r e d u c e d t o 50 m a t low s t a g e . The a v e r a g e d e p t h of w a t e r i n t h e s e two s e a s o n s i s 5 m and
3 m respectively.
Fig. 2.8.
2.2.6
B a t h y m e t r i c map o f Lake A l b e r t ( f r o m Rzbska, J . , 1977)
Lakes Edward and George
Lake Edward i s c o n n e c t e d t o Lake George by t h e Kazinga C h a n n e l . Lake George
i s s i t u a t e d on t h e e q u a t o r and i t s s u r f a c e a r e a a t an e l e v a t i o n o f 915 m e t r e s a.m.s.l.,
i s 300 km2. T h i s l a k e h a s a d r a i n a g e b a s i n 8 000 km2 s u r f a c e a r e a .
28
I t i s d r a i n e d by a number of s t r e a m s f l o w i n g down from t h e Ruwenzori i n t o t h e swamps a t t h e n o r t h e r n end of t h e l a k e . The p r i n c i p a l t r i b u t a r y , t h e Mbuku, c a r r i e s a c o n s i d e r a b l e f l o w d u r i n g t h e f l o o d . The o u t f l o w from Lake George r u n s t h r o u g h t h e Kazinga C h a n n e l , which i s p r a c t i c a l l y n o t h i n g b u t a c a r r i e r . Lake Edward l i e s i n t h e w e s t e r n R i f t V a l l e y and a t an a l t i t u d e of a b o u t 915 metres a . m . s . 1 . h a s a s u r f a c e a r e a of a b o u t 2 200 km2. The c r o s s - s e c t i o n
(Fig. 2.9.)
shows how t h e e s c a r p m e n t o f t h e R i f t V a l l e y rises s t e e p l y from t h e w a t e r surf a c e l e v e l of a b o u t 915 m t o more t h a n 2 500 m on t h e w e s t e r n s i d e of Lake Edward. T h i s i s , however, n o t t h e c a s e f o r t h e o t h e r s i d e s of t h e l a k e , though a t the north-east
c o r n e r t h e o u t l y i n g h i l l s of t h e Ruwenzori Range come down
w i t h i n a few k i l o m e t r e s of t h e l a k e . The l a k e h a s a b a s i n 12 000 km2 i n a r e a , which i s t r a v e r s e d by a number of s t r e a m s o f t e n f r i n g e d by t h i c k f o r e s t a t t h e i r low e n d s . The p r i n c i p a l s t r e a m s debouching t h e i r w a t e r s i n t o Lake Edward a r e : Nyamgasani f l o w i n g down t h e Ruwenzori Range n o r t h - e a s t
of t h e l a k e , t h e
R i v e r s B e r a r a r a and I s h a s h a f l o w i n g from t h e e a s t i n a n o r t h e r l y d i r e c t i o n towards t h e l a k e , a s y s t e m of r i v e r s p o u r i n g i n t o t h e main s t r e a m , t h e Ruchuru, r u n n i n g down t h e Mufumbiro m o u n t a i n s towards t h e l a k e i n a n o r t h e r l y d i r e c t i o n and t h e R i v e r R u i n d i r e a c h i n g Lake Edward a t i t s s o u t h - w e s t
corner.
From t h e above d e s c r i p t i o n , i t i s c l e a r t h a t t h e R i v e r S e m l i k i s u p p l i e s Lake A l b e r t with t h e run-off
from a t o t a l catchment o f a b o u t 30 500 km2 i n a r e a ,
i n c l u d i n g t h e s u r f a c e s c o v e r e d by Lakes George and Edward. The N i l e f l o w s o u t of Lake A l b e r t a t t h e e x t r e m e n o r t h c o r n e r of t h e l a k e under t h e name of t h e Upper White N i l e or Bahr e l - J e b e l .
22 00
m
E 2000 ti In 1800 L
aJ
2
E
1600
c‘ 1400 ._
:1200
I
aJ -
LLJ
1000 800
Fig. 2.9. latitude
Scales H or . : 1
/ 1,000,000
Ver. i
/
1
20,000
S e c t i o n a c r o s s Lake Edward and a d j a c e n t c o u n t r y t h r o u g h Oo 3 0 ’ s
29
THE BAHR EL JEBEL BASIN
2.3
The m a j o r a f f l u e n t s o f t h e Bahr e l J e b e l or t h e Upper White N i l e and t h e swamps and l a k e s a l r e a d y d i s c u s s e d i n t h e p r e c e d i n g s e c t i o n , a r e summarized by t h e d r a w i n g p r e s e n t e d i n F i g . Z.lO.(Thompson,
K.,
1975).
From t h e o u t l e t o f Lake A l b e r t down t o Nimule, 225 km downstream, t h e r i v e r i s a r a t h e r b r o a d , s l u g g i s h , s t r e a m f r i n g e d w i t h swamps and l a g o o n s . I t meanders e a s t and w e s t t h r o u g h a narrow f l o o d p l a i n b e t w e e n h i l l y c o u n t r y on e i t h e r s i d e so t h a t t h e a r e a o f t h e swamp i s w e l l d e f i n e d . The a r e a o c c u p i e d by swamps and
open w a t e r i s e s t i m a t e d a t a b o u t 380 km2. The Bahr e l J e b e l from t h e o u t l e t o f Lake A l b e r t t o Nimule i s a p l a c i d stream w i t h a n a v e r a g e s l o p e o f o n l y a b o u t I t i s n o t a d e e p r i v e r and i t s w i d t h v a r i e s from 100
2 . 2 cm/km o r 2 . 2 x t o 300 m .
A number of s m a l l s t r e a m s j o i n t h e Bahr e l J e b e l from b o t h s i d e s i n
t h i s reach ( s e e F i g . 2 . 4 . ) .
'
B u f u m b i r a Mts.
2 50C
M t Elgon
aJ
-2 2000 0
In aJ
;
Central
C
Uganda
1500
aJ
> 0
n 0
1000 aJ c L
E
aJ
500
Murchison
Falls/
J
Upper N i l e swamps (Sudan)
0
I
6500
6000 Distance
,
i 500 from
1
5000
4500
sea. k m .
Fig. 2.10. A l t i t u d i n a l map o f m a j o r a f f l u e n t s o f t h e Upper White N i l e and t h e o c c u r r e n c e o f swamps (Thompson, K . , 1975)
30
A t Nimule t h e r i v e r c o u r s e i s t w i s t e d i n a s h a r p b e n d and i t s d i r e c t i o n c h a n g e s s u d d e n l y t o t h e w e s t t h e n t o t h e n o r t h and n o r t h - e a s t
up t o M o n g a l l a .
I n t h e r e a c h b e t w e e n Nimule and R e j a f , a d i s t a n c e o f a b o u t 1 5 6 km, t h e r i v e r
i s a n a r r o w and f a s t stream i n t e r r u p t e d by s u c h r o c k y r a p i d s as t h e F o l a and B e d a n . The r i v e r f l o w s i n t o a n a r r o w v a l l e y c u t t h r o u g h h i l l y c o u n t r y and d e s c e n d s a b o u t 150 m .
The a v e r a g e s l o p e i s n e a r l y 1 m/km or 1 x
I n t h e r e a c h from Nimule t o M o n g a l l a t h e B a h r e l J e b e l r e c e i v e s a number o f
s m a l l b u t t o r r e n t i a l streams w h i c h r u n f u l l a f t e r h e a v y r a i n s . Of t h e s e s t r e a m s t h e A s s u a , t h e Kaia and t h e K i t a r e t h e l a r g e s t . They c a r r y some f l o w e v e n i n t h e d r y s e a s o n . The R i v e r A s s u a j o i n s t h e B a h r e l J e b e l a t i t s r i g h t bank a l m o s t 20 km b e l o w N i m u l e . The f o r m e r rises i n t h e v i c i n i t y o f t h e Moroto M o u n t a i n and i s j o i n e d by some s t r e a m s d e s c e n d i n g f r o m t h e n o r t h a n d f r o m t h e e a s t n o t f a r f r o m t h e M o r o n g o l e M o u n t a i n . The A s s u a t h u s d r a i n s a v a s t a r e a e a s t o f t h e B a h r e l J e b e l , w h e r e a s t h e R i v e r Kaia d r a i n s p a r t o f t h e c o u n t r y
w e s t o f i t . The K a i a i s j o i n e d by t h e R i v e r K i j o a few k i l o m e t r e s b e f o r e i t s j u n c t i o n w i t h t h e B a h r e l J e b e l . The R i v e r K i t r i s e s from t h e h i g h l a n d b e t w e e n t h e T e r e t e i n i a and I m a t o n g M o u n t a i n s and a f t e r f l o w i n g a d i s t a n c e o f a b o u t 160 km, i t j o i n s t h e B a h r e l J e b e l a t t h e r i g h t b a n k a few k i l o m e t r e s u p s t r e a m
o f R e j a f , where i t e n t e r s t h e Sudan P l a i n s . N e v e r t h e l e s s , t h e s l o p e i n t h e 5 7 km from R e j a f t o M o n g a l l a i s r a t h e r s t e e p , o n a v e r a g e 0 . 3 m/km,
falling off
g r a d u a l l y a s t h e M o n g a l l a i s a p p r o a c h e d . From R e j a f t o some d i s t a n c e n o r t h w a r d s the valley is well-defined,
t h o u g h s h a l l o w , and t h e r i v e r w i n d s a b o u t i n t h e
p l a i n f o r m i n g t h e v a l l e y f l o o r ( H u r s t , H.E., 1 9 3 1 ) . I n t h e r e a c h from R e j a f t o M a l a k a l o n t h e W h i t e N i l e ,
t h e r i v e r i s n o t con-
f i n e d t o a s i n g l e c h a n n e l e x c e p t a t Mongalla where i t is i n one c h a n n e l a t l o w s t a g e . Between R e j a f and B o r , a d i s t a n c e o f a b o u t 180 km, t h e v a l l e y i s w i d e and f l a t and t h e r e i s u s u a l l y a c h a n n e l o n e i t h e r s i d e a l o n g t h e h i g h e r g r o u n d w h i l e o c c a s i o n a l c h a n n e l s cross t h e swampy v a l l e y f l o o r ( s e e F i g . 2 . 1 1 . ) . The d i s t r i b u t i o n o f t h e swamp v e g e t a t i o n on t h e f l o o d p l a i n i n t h e r e a c h b e t w e e n J u b a and B o r was i n v e s t i g a t e d .
I t w a s found t h a t t h i s d i s t r i b u t i o n i s
c o n t r o l l e d by s e a s o n a l f l o o d i n g and t h e f o r m o f c o n t r o l c a n b e d e d u c e d by r e l a t i n g t h e d i s t r i b u t i o n t o e l e v a t i o n and t h u s t o h y d r o l o g i c a l c o n d i t i o n s (Sutcliffe, J.V.,
1 9 7 4 ) . F u r t h e r m o r e , i t seems t h a t t h e r e s u l t s o f t h a t i n v e s -
t i g a t i o n apply to t h e r i v e r reach north of B o r . N o r t h o f Bor t h e V a l l e y w i d e n s and becomes more swampy, w h i l e t h e s i d e s a r e
less d e f i n e d . E x t e n s i v e swamps s p r e a d o u t o n e i t h e r s i d e o f t h e r i v e r and cont i n u e down t o L a k e No. T h i s r e g i o n i s known as t h e S u d d . N o r t h o f K e n i s a , a b o u t
85 km
d o w n s t r e a m o f B o r , t h e d r y l a n d c a n h a r d l y b e s e e n , e x c e p t i n a few
p l a c e s . The r i v e r f l o w s n o r t h w a r d s b e t w e e n w a l l s o f p a p y r u s and t a l l g r a s s e s r e a c h i n g 4 o r 5 m i n h e i g h t . These p l a n t s h a v e t h e i r r o o t s i n w a t e r and t h e
31
ro I
.d
m N d .
d
d
c
0
k
a,
4
c a,
m
9
a
m a,
r(
e
5
a,
4
k
c a,
m
9
R
0
+I
2
4
rl
M
N .d
h
32
r i v e r bank i s p a r t l y formed of masses of r o o t s o f f o r m e r v e g e t a t i o n . F u r t h e r more, t h e r e a r e many p a t c h e s of open w a t e r a l o n g s i d e t h e r i v e r n o r t h o f B o r , many o f which a r e c o n n e c t e d d i r e c t l y w i t h t h e r i v e r or w i t h t h e s i d e c h a n n e l s . Of t h e l a t t e r t h e Awai and A t e m R i v e r s and G a g e ' s and P e a k e ' s C h a n n e l s may b e mentioned ( s e e map, F i g . 2 . 1 1 . ) . North of Ghaba Shambe, some 140 km from B o r , t h e swamps a r e wide and t h e p l a i n i s f u l l of v e g e t a t i o n and l a g o o n s . A p l a n and c r o s s - s e c t i o n of a t y p i c a l l a g o o n i n t h i s a r e a i s shown i n F i g . 1 . 1 2 . (Hurst, H . E .
1 9 3 1 ) . Because o f t h e h i g h r a t e of loss o f w a t e r from t h e Sudd
r e g i o n and t h e v a s t a r e a from which t h i s l o s s t a k e s p l a c e ,
the t o t a l loss i n
a n a v e r a g e y e a r amounts t o a p p r o x i m a t e l y one h a l f of t h e t o t a l f l o w a t M o n g a l l a . I n a n a t t e m p t t o t r a n s p o r t t h e w a t e r i n t h i s r e g i o n w i t h less l o s s , t h e Bahr e l J e b e l was j o i n e d t o t h e Bahr e l Z a r a f by two c u t s a t d i s t a n c e s of
106 and 112 km from Shambe. U n f o r t u n a t e l y
t h e s e two c u t s and t h e c h a n n e l which
r u n s between them a r e s o h e a v i l y b l o c k e d w i t h v e g e t a t i o n t h a t t h e i r e f f i c i e n c y i n r e d u c i n g t h e t r a n s m i s s i o n l o s s e s i n t h e swamps i s q u e s t i o n a b l e . Between t h e two c u t s and Lake No i n t h e n o r t h t h e r e a r e o c c a s i o n a l i s o l a t e d s p o t s o f h i g h ground compared t o t h e s u r r o u n d i n g swamps. A t Lake No t h e Bahr e l J e b e l i s j o i n e d by t h e Bahr e l Ghazal and t h e combined s t r e a m t u r n s a b r u p t l y t o t h e e a s t , b e a r i n g t h e name "The White N i l e " . Here t h e swamps end and t h e White N i l e flows northwards i n a f a i r l y w e l l - d e f i n e d
v a l l e y of moderate w i d t h .
The Bahr e l Z a r a f s t a r t s somewhere a b o u t l a t i t u d e 7O 20"
i n t h e swamps
e a s t o f t h e mouth o f t h e R i v e r Awai. I t i s p r o b a b l e t h a t t h e r e a r e some c h a n n e l s c o n n e c t i n g t h e J e b e l , t h e Awai, t h e A t e m and t h e Z a r a f t h r o u g h which t h e l a t t e r d e r i v e s i t s s u p p l y o f w a t e r . The Bahr e l Z a r a f h a s a w i n d i n g c o u r s e o f a b o u t 280 km i n l e n g t h t o i t s mouth o n t h e White N i l e some 80 km from Lake No. Along t h i s c o u r s e t h e r e i s n o t s o much p a p y r u s a l o n g t h e J e b e l and t h e p r i n c i p a l swamp p l a n t i s um s o o f , w i t h r e e d s and b u l r u s h e s . H i g h e r ground e x i s t s n o t v e r y f a r t o t h e e a s t o f t h e Upper Z a r a f s o t h a t swamps r e a c h t h e i r d e f i n i t e l i m i t i n t h e e a s t . Some o f t h i s h i g h g r o u n d , howe v e r , becomes swampy a f t e r heavy r a i n .
I n t h e neighbourhood of t h e J e b e l - Z a r a f
c u t s and f o r a l o n g way n o r t h , t h e Z a r a f f l o w s t h r o u g h swamp, w i n d i n g a b o u t forming lagoons i n
its
bends l i k e t h e Bahr e l J e b e l .
The e d g e s o f t h e Bahr e l Z a r a f a r e swampy i n p l a c e s a s f a r n o r t h as k i l o -
metre 100 (measured from t h e mouth) and t h e r e i s always a f r i n g e of um s o o f . The banks g r a d u a l l y become h i g h a s one g o e s n o r t h w a r d s u n t i l t h e y form d e f i n i t e b o u n d a r i e s l i m i t i n g t h e Z a r a f t o a narrow c h a n n e l .
33
Hor.: Ver. :
t> 24.0 22.0
600
0 Distance
500
in m e t r e s
1000
1 / 20,000 1 / 200
1500
Fig. 2 . 1 2 . P l a n and c r o s s - s e c t i o n o f a l a g o o n i n t h e Bahr el J e b e l B a s i n ( r e p r o d u c e d from t h e N i l e B a s i n Vol. I : H u r s t , H . E . and P h i l i p s , P . , 1931)
34
THE BAHR EL GHAZAL BASIN
2.4
The Bahr e l Ghazal i s t h e name g i v e n t o t h e waterway from Meshra e l Req t o Lake N o ( s e e map, F i g . 2 . 1 1 . ) . Though t h e l e n g t h o f t h i s stream does n o t e x c e e d 160 km, t h e s i z e o f i t s b a s i n i s a p p r o x i m a t e l y 526 000 km2 which i s by f a r t h e l a r g e s t o f any o f t h e s u b - b a s i n s o f t h e t r i b u t a r i e s of t h e N i l e R i v e r . The a n n u a l r a i n f a l l on t h e b a s i n i s e s t i m a t e d a t 500 x lo9 m 3 . Of t h i s amount o n l y 0.6 x
lo9
m3/year r e a c h e s t h e b a s i n o u t l e t a t Lake No.
A l l a l o n g t h e Bahr e l G h a z a l and t o t h e s o u t h and e a s t o f i t a r e l a r g e a r e a s o f swamp which a r e f e d by a number of streams. The c o u n t r y where t h e u p p e r c o u r s e s o f t h e s e streams flow i s e n t i r e l y c o v e r e d by a s o r t o f s a v a n n a h f o r e s t . Nevertheless,
i n t h e r a v i n e s formed by t h e streams, t h e r e i s a t h i c k f o r e s t
s i m i l a r t o t h e t r o p i c a l r a i n f o r e s t o f p a r t s o f t h e Lake P l a t e a u and t h e Congo B a s i n . On t h e l o w e r c o u r s e s o f a l l t h e t r i b u t a r i e s o f t h e Bahr e l Ghazal and a l o n g t h e Ghazal i t s e l f a r e l a r g e a r e a s o f swamps. U n f o r t u n a t e l y , most o f t h e flow c a r r i e d by t h e t r i b u t a r i e s i s l o s t i n t h e swamps. Near t h e Bahr e l Arab, t h e f o r e s t i s o f t h e t h o r n y savannah t y p e and t h i s g r a d u a l l y c h a n g e s t o s h r u b s t e p p e a s one g o e s n o r t h w a r d s . On e i t h e r s i d e o f t h e Uganda-Sudan boundary t h a t c o i n c i d e s w i t h t h e d i v i d e between t h e N i l e and t h e Congo B a s i n s , numerous s t r e a m s a r i s e . Most o f them d e s c e n d t o a l a r g e swampy p l a i n i n which t h e y wind and f i n a l l y s p r e a d and c e a s e t o e x i s t as streams w i t h d e f i n i t e c o u r s e s , e x c e p t f o r t h e J u r , which p r e s e r v e s i t s c h a n n e l and j o i n s t h e Bahr e l G h a z a l . The t r i b u t a r i e s of t h e Bahr e l Ghazal from e a s t t o w e s t a r e : t h e G e l or T a p a r i , t h e Y e i or Lau, t h e Naam, t h e M e r i d i o r G e l , t h e I b b a o r T o n j , t h e J u r , t h e Lo1 and t h e Bahr e l Arab. Some o f t h e d a t a b e l o n g i n g t o t h e s e r i v e r s a r e i n c l u d e d i n T a b l e 2 . 2 . A map i l l u s t r a t i n g t h e d r a i n a g e b a s i n of t h e Bahr e l Arab and s u r r o u n d i n g s i s shown i n F i g . 2 . 1 3 . The d a t a p r e s e n t e d i n T a b l e 2 . 2 may h e l p t o show t h a t t h e J u r i s t h e most i m p o r t a n t t r i b u t a r y o f t h e G h a z a l . The f o r m e r h a s two main t r i b u t a r i e s , namely, t h e Sueh and t h e B u s s e r i . Both a r e r e l a t i v e l y l a r g e s t r e a m s . Lake Ambadi i s a b o u t 10 km l o n g by 1 km wide and m o s t l y l e s s t h a n 3 m d e e p . From t h i s l a k e down t h e Ghazal t o t h e mouth o f t h e Bahr e l Arab, t h e c o u n t r y r e m a i n s swampy and t h e r i v e r d o e s n o t h a v e a d e f i n e d b a n k . The v e g e t a t i o n b o r d e r i n g t h e r i v e r i s um s o o f w i t h l i t t l e p a p y r u s . The lower Ghazal i s f r i n g e d by p a p y r u s , though i t s growth i s s t u n t e d and l e s s l u x u r i a n t t h a n on t h e J e b e l . The many t e m p o r a r y s t r e a m s which j o i n t h e Ghazal o n b o t h s i d e s a r e u s u a l l y b l o c k e d and t h e r e f o r e c a n n o t c o n t r i b u t e much w a t e r . A s Lake No i s a p p r o a c h e d , t h e d r y l a n d n e a r s t h e r i v e r on t h e n o r t h and t h e r i v e r l o s e s i t s d e f i n e d banks. Lake No i s n o t h i n g b u t a l a r g e s h a l l o w l a g o o n . Here t h e s l u g g i s h Bahr el Ghazal
35
TABLE 2 . 2
Some d a t a o f t h e t r i b u t a r i e s o f t h e Bahr e l G h a z a l (Hurst, H . E . and P h i l i p s , P . , 1938) T r i b u t a r y of t h e Bahr e l Ghazal
I tern
River+ Tapari
River+ Yei
River Naam
River Meridi
Fiver Tonj
River
Basin a r e a , km
1 2 800
25 000
16 000
22 000
27 000
Mean r a i n f a l l , mm/yr
1 050
1 250
1 200
1 200
Trough width, m
50
100
90
Max. depth, m
4
5 400
Max. d i s charge, m 3 / s Place of observation
a
near Amadi
River Lo1
Bahr e l Arab
64 000
8 2 000
209 000++
1 220
1 200
1 100
700
-
70
130
270
35
4
-
3
6
3
5
160
-
110
600
500
near Rumbek
-
Jur
Tonj
Wau
b
C
+ ++
u s u a l l y c o n s i d e r e d as a t r i b u t a r y o f t h e B a h r e l J e b e l and n o t o f t h e Bahr e l Ghazal E x c l u d i n g t h e swamps
a A t t h e r o a d c r o s s i n g b e t w e e n Amadi and T e r r a k e k k a b I n t e r s e c t i o n w i t h r o a d from N y a m l e l l t o B a h r e l Arab ‘Safaha
due n o r t h o f Nyamlell
j o i n s t h e B a h r e l J e b e l a f t e r h a v i n g a t r e m e n d o u s volume o f w a t e r w a s t e d i n t h e v a s t swamps. A s c h e m a t i c c r o s s - s e c t i o n
t h r o u g h t h e Upper N i l e swamps from Bahr
e l Ghazal t o t h e B a h r e l J e b e l c a n b e s e e n i n F i g . 2 . 1 4 .
(Jonglei Report,
1954).
2.5
THE SOBAT BASIN The S o b a t B a s i n , a p p r o x i m a t e l y 225 000 km2 i n a r e a , i n c l u d e s most o f t h e
p l a i n e a s t o f t h e B a h r e l J e b e l and B a h r e l Z a r a f and p a r t s o f t h e A b y s s i n i a n Mountains and t h e L a k e s P l a t e a u ( s e e F i g . 2 . 1 5 . ) .
I n view of t h e l a r g e s i z e of
t h e b a s i n a r e a and t h e d i v e r s i t y i n i t s t o p o g r a p h y , t h e a n n u a l r a i n f a l l v a r i e s
from a b o u t 6 5 0 mm n e a r t h e mouth o f t h e S o b a t , t o a b o u t 2 000 mm i n t h e most e l e v a t e d p a r t s o f t h e b a s i n e a s t w a r d s . The S o b a t i s formed by t h e j u n c t i o n o f
i t s two main t r i b u t a r i e s , t h e B a r o and t h e P i b o r . T h e B a r o i s c l a i m e d t o b e t h e p r i n c i p a l f e e d e r of t h e S o b a t , though i t s b a s i n h a s a s u r f a c e a r e a o f 41 400 k m 2 , w h e r e a s t h e s u r f a c e a r e a o f t h e P i b o r i s 10 900 km2.
36
37 E&O]Tl
IT]
Ech & Ory
I
;o
1 2
1
Bahr e l Ghazal
388
I
I
E c h & Ory
3
4
I [
P
I
I
5
6
I
Echinochloa
T
1
Typhia
P
I
Papyrus
pyramidalis
&
I 7
I
Bahr e l Jebel
D i s t a n c e - km
E c h 8, O r y
P
Oryza
barthii
Fig. 2.14. S c h e m a t i c c r o s s - s e c t i o n t h r o u g h Upper N i l e swamps from Bahr e l Ghazal t o t h e Bahr e l J e b e l ( J o n g l e i R e p o r t , 1954) The Baro i s formed by a number of streams which i n some p l a c e s flow through deep g o r g e s i n t h e i r d e s c e n t from t h e p l a t e a u . A good d e a l o f t h e mountainous p a r t of t h e b a s i n l i e s above 1 5 0 0 m w i t h p o r t i o n s even h i g h e r t h a n 2 000 metres a . m . s . 1 . Soon a f t e r l e a v i n g t h e m o u n t a i n s , t h e Baro r e a c h e s Gambeila, which i s on t h e p l a i n , a l m o s t 520 metres a . m . s . 1 . H e r e t h e Baro does n o t r e c e i v e t r i b u t a r i e s , b u t r a t h e r s h a l l o w swampy khors*, a r e Khor Jokau coming from t h e n o r t h , t h e A t u r a b r a n c h ,
t h e p r i n c i p a l s o f which and t h e Mokwai.
Down of Gambeila up t o t h e j u n c t i o n o f t h e Baro w i t h t h e P i b o r , i s t h e B a r o , with an a v e r a g e w i d t h o f 100 metres, i n c r e a s i n g t o 250 metres i n some p l a c e s and an a v e r a g e d e p t h o f more t h a n 6 metres d u r i n g t h e f l o o d . U n f o r t u n a t e l y , some 40 km u p s t r e a m o f t h e j u n c t i o n some w a t e r l e a v e s t h e Baro through Khor Machar t o f e e d a l a r g e swampy a r e a n o r t h and e a s t o f E l - N a s i r .
T h i s swamp i s
f e d by o t h e r streams f l o w i n g from t h e A b y s s i n i a n P l a t e a u ( s e e map, F i g . 2 . 1 5 . ) . The p a r t f l o w i n g t o Khor Machar c o n s t i t u t e s , however, a permanent s o u r c e o f
l o s s i r o n t h e Bar0 ( H u r s t e t a l , 1 9 6 6 ) . The R i v e r P i b o r r u n s i n a n o r t h e r l y d i r e c t i o n . I t draws t h e g r e a t e r p a r t o f
i t s s u p p l y from A b y 6 s i n i a and t h e rest comes from t h e n o r t h e r n s l o p e s o f t h e l a k e p l a t e a u and from t h e Sudan p l a i n s . The b a s i n a r e a of t h e P i b o r h a s a l r e a d y been mentioned a s b e i n g l a r g e r t h a n t h a t of t h e Bar0 and t h e a n n u a l r a i n f a l l i s probably more, s i n c e t h e mountalnous p o r t i o n i n A b y s s i n i a is l a r g e r t h a n t h e c o r r e s p o n d i n g p o r t i o n o f t h e B a r 0 B a s i n . I n s p i t e o f t h e s e two f a c t o r s , t h e flow of t h e P i b o r i s q u i t e i n f e r i o r t o t h a t o f t h e B a r o . T h i s i s b e c a u s e t h e
*A khor i s a temporary stream which r u n s f u l l d u r i n g and a f t e r r a i n f a l l . I t could be o f a t o r r e n t i a l n a t u r e
38
Fig. 2.15. Map s h o w i n g t h e a p p r o x i m a t e b o u n d a r i e s o f t h e d r a i n a g e b a s i n o f t h e River Sobat
39
s l o p e of t h e P i b o r i s v e r y f l a t compared t o t h e Baro and h a s c o n s e q u e n t l y more chance of forming l a r g e swamps and e v a p o r a t i n g t h e w a t e r t h e r e o f . The P i b o r is formed by t h e j u n c t i o n o f t h e Veveno, L o t i l l a and t h e Kangen
(see map, F i g . 2 . 1 5 . ) . None of t h e s e streams c a r r i e s much w a t e r and a l l a r e reduced t o p o o l s i n t h e d r y s e a s o n . C r o s s - s e c t i o n s o f t h e s e s t r e a m s c a n be found i n Vol. V I I I of t h e N i l e B a s i n ( H u r s t e t a l , 1 9 5 0 ) . Some of t h e s e c r o s s s e c t i o n s a r e r e p r o d u c e d i n F i g . 2 . 1 6 . The P i b o r , l i k e many of i t s t r i b u t a r i e s , becomes n a r r o w e r and d e e p e r i n s e c t i o n a s i t goes down. Near i t s mouth, t h e c l e a r w i d t h o f t h e r i v e r c h a n n e l d r o p s from 150 t o 60 m , whereas t h e d e p t h i n c r e a s e s from a b o u t 4 m i n t h e upper r e a c h e s t o a b o u t 6 . 5 m . Downstream o f t h e j u n c t i o n of t h e Kangen and L o t i l l a t h e P i b o r r u n s n o r t h wards i n a w i n d i n g c o u r s e and r e c e i v e s t h e A g w e i , Akobo, G i l a and Khor Makwai on t h e e a s t b a n k . On t h e w e s t b a n k , i t r e c e i v e s t h e Khor A d e i t and s e v e r a l smaller khors.
.’ 421
E
’
5
420
-
419:
-G aJ
a
0
-
418
-
417
414-
0
3 Khor
Veveno
Lotilla
1
I
67 km. above
about
junction (scale A ) I
I
I
- 410
.
- 409
vl
E
-0
411 -
m
junction
-
407 %
- 406
Baro- Pibor ( s c a l e B ) 1
u
p LL
Veveno
0
aJ J
- 408
412-
;:
40940 8
/
I
1
\II
I
I
I
vl
405 404
Fig. 2 . 1 6 . C r o s s - s e c t i o n s of some o f t h e t r i b u t a r i e s o f t h e R i v e r P i b o r ( t a k e n from t h e N i l e B a s i n Vol. V I I I : H u r s t , H . E . , 1950)
40
From t h e Baro-Pibor
j u n c t i o n t o t h e mouth o f t h e S o b a t t h e c o u n t r y i s a f l a t
p l a i n i n t e r s e c t e d by swampy d e p r e s s i o n s o r k h o r s . The S o b a t h a s a w i n d i n g c o u r s e and i t s s u r f a c e w i d t h n e a r t h e mouth v a r i e s from 100 m o r less i n t h e low-flow p e r i o d t o more t h a n 150 m i n f l o o d t i m e .
F o r t h e s e two s e a s o n s , t h e
d e p t h of w a t e r i s a b o u t 3 . 5 and 6 . 5 m r e s p e c t i v e l y . The p r i n c i p a l k h o r s j o i n i n g t h e S o b a t i n t h i s r e a c h a r e t h e Nyanding, Wangnyait and F u l l u s . These k h o r s , i n s p i t e of t h e conveyance l o s s i n t h e S o b a t , h e l p t o i n c r e a s e t h e flow i n t h e S o b a t i n a normal y e a r from 1 2 . 4 x lo9 m 3 a t Nasir t o 1 3 . 6 x lo9 m 3 a t H i l l e t D o l e i b n e a r t h e mouth. 2.6
THE WHITE NILE
The s t r e t c h o f t h e White N i l e (An N i l E l Abiad) from Lake No down t o i t s j u n c t i o n w i t h t h e Blue N i l e i s known a s t h e White N i l e .
The r e m a r k a b l e f e a t u r e
a b o u t t h i s r i v e r i s i t s e x t r e m e l y f l a t s l o p e . I n t h e upper 120 km, i . e . from Lake No t o t h e mouth o f t h e S o b a t , t h e r e a r e s e v e r a l swamps, k h o r s and l a g o o n s . I n t h e r e m a i n i n g 800 km, i . e . from Malakal t o j u s t u p s t r e a m of Khartoum, t h e
c h a n n e l of t h e White N i l e i s a l m o s t f r e e of swamps. A s t h e a v e r a g e s l o p e of t h e r i v e r i n t h i s s t r e t c h is about 1 . 4 x
it is, for a large p a r t , sluggish.
The d r a i n a g e b a s i n o f t h e White N i l e e x t e n d s from t h e f o o t h i l l s o f t h e l a k e p l a t e a u i n t h e s o u t h t o t h e j u n c t i o n o f t h e White and B l u e N i l e s up n o r t h and from t h e f o o t h i l l s o f t h e A b y s s i n i a n P l a t e a u i n t h e e a s t t o t h e Nile-Congo d i v i d e i n t h e south-west
and Nuba Mountains i n t h e w e s t ( s e e map, F i g . 2 . 1 7 . ) .
I n t h e d i s t a n c e from Lake No t o t h e mouth o f t h e S o b a t , t h e r i v e r f l o w s i n a n u n d e f i n e d v e g e t a t e d c o u r s e i n a p l a i n w i t h a w i d t h o f 1 km a t M a l a k a l . From t h e mouth of t h e S o b a t t o n o r t h o f K o s t i t h e w i d t h o f t h e d e p r e s s i o n between t h e r i v e r banks i n c r e a s e s from 3 t o 4 k m , whereas t h e w i d t h of t h e r i v e r c h a n n e l i t s e l f i s between 300 and 400 m . North o f Malakal up t o i t s j u n c t i o n w i t h t h e B l u e N i l e , f l o w s t h e White N i l e i n a w e l l - d e f i n e d
c h a n n e l or c h a n n e l s .
From Lake No t o j u s t s o u t h of M e l u t t h e main f e e d e r s of t h e White N i l e a r e t h e Khor L o l l e , Bahr e l Z a r a f , t h e S o b a t , Khor Wol and Khor Adar. Many swampy k h o r s j o i n t h e r i v e r r e a c h between Melut and El-Renk.
Of t h e s e k h o r s , t h e Rao
o r Wadudu and t h e D o l e i b a r e t h e l a r g e s t . North o f J e b e l e i n , swampy k h o r s a r e f e w e r and t h e c o u n t r y g r a d u a l l y becomes more a r i d . THE ETHIOPIAN OR ABYSSINIAN PLATEAU
2.7 2.7.1
The B l u e N i l e
The B l u e N i l e (An N i l e l Azraq or Abbai) and i t s t r i b u t a r i e s a l l r i s e on t h e E t h i o p i a n P l a t e a u a t an e l e v a t i o n o f 2 000 t o 3 000 metres a . m . s . 1 . o f t h e N i l e Basin (Hurst, H . E . ,
Volume V I I I
1950) m e n t i o n s t h a t t h e s o u r c e of t h e B l u e Nile
i s a s m a l l s p r i n g a t a h e i g h t of 2 900 m and a t a b o u t 100 km s o u t h of Lake Tana.
41
J 4
42
m F Y
0
c, 0
a,
z
3 H
J 4
a,
w .c m a,
c.
9 4 m
.rl
.rl
c,
0,
z
m
i 0
w
9 0
.rl 0
n a, M
G .rl
a,
m 4 a
9 iJ
0
'c1
R
4
a,
9 M
F
E
.rl
R
I
l4
M
N .A
k
42
From t h i s s p r i n g t h e L i t t l e Abbai f l o w s down t o L a k e T a n a ( 1 8 2 9 m e t r e s a . m . s . l . ) . T h e r e a r e 60 a f f l u e n t s o f L a k e T a n a , o f w h i c h t h e L i t t l e Abbai i s u s u a l l y regarded as t h e m o s t i m p o r t a n t . The E t h i o p i a n P l a t e a u c o u n t r y c a n n o t b e d e s c r i b e d as f l a t . Most o f i t i s h i l l y w i t h g r a s s y downs, swamp v a l l e y s and s c a t t e r e d t r e e s . The h i g h c o u n t r y i s c u t up by d e e p r a v i n e s o r c a n y o n s i n w h i c h t h e r i v e r s f l o w , t h e g r e a t e s t o f which i s t h a t o f t h e B l u e N i l e .
I n some p l a c e s t h i s r i v e r f l o w s i n a c h a n n e l
t h a t i s a b o u t 1 200 m e t r e s b e l o w t h e l e v e l o f t h e c o u n t r y o n e i t h e r s i d e . The d r o p o f t h e p l a t e a u t o t h e S u d a n P l a i n i s , i n most p l a c e s , s t e e p . However, t h e r e a r e many o u t l y i n g h i l l s , some o f w h i c h a r e as h i g h a s t h e p l a t e a u i t s e l f . The p l a i n i s l a r g e l y c o v e r e d w i t h t h i n S a v a n n a h f o r e s t , b u t n o r t h o f l a t i t u d e 1 3 O N t h e r e i s a good d e a l o f o p e n g r a s s l a n d .
The B l u e N i l e B a s i n ,
i n c l u d i n g Lake Tana and i t s b a s i n , h a s a n area o f
324 530 km2. T h i s a r e a c o v e r s most o f E t h i o p i a w e s t o f l o n g i t u d i n a l 40°E b e t w e e n l a t i t u d e s go a n d l Z O N (see F i g . 2 . 1 8 . ) . number o f s u b - b a s i n s
and
T h i s area c a n b e d i v i d e d i n t o a
as f o l l o w s ( H u r s t e t a l , 1959) :
Lake Tana B a s i n , i n c l u d i n g t h e l a k e
1 7 500 km2
Khor D i d e s s a B a s i n
25 8 0 0
Khor B a l a s B a s i n
1 5 200
Khor Dabus or Yabus B a s i n
1 4 000
Khor Tumat B a s i n
4 370
Khor B a s h i l o B a s i n
13 900
Khor Jamma B a s i n
1 9 800
Khor Mugor B a s i n
7 270
Khor Guder B a s i n
6 390
R i v e r Rahad B a s i n
35 600
River Dinder Basin
34 700
Blue N i l e B a s i n , excluding above a r e a s Lake Tana i s a f r e s h - w a t e r
body s i t u a t e d i n n o r t h - c e n t r a l
130 000 Ethiopia. I t s
maximum l e n g t h i s 7 8 km, w i d t h 6 7 km and d e p t h 14 m . A b a t h y m e t r i c map o f t h e l a k e i s shown i n F i g . 2 . 1 9 . R e l a t i v e l y i m p o r t a n t f e e d e r s t o Lake Tana o t h e r t h a n t h e L i t t l e Abbai a r e t h e R i v e r s R e b , Gumara, M a g e t c h , G e l d a and U n f r a z . From t h i s l a k e t h e G r e a t e r Abbai f l o w s i n a l a r g e l o o p f i r s t s o u t h - e a s t ,
then
s o u t h and t h e n w e s t . About 35 km f r o m t h e e x i t o f Lake T a n a , t h e r i v e r d r o p s a p p r o x i m a t e l y f i f t y metres i n t o t h e T i s s i s a t F a l l s . F i f t y k i l o m e t r e s f u r t h e r downstream, i t b e g i n s t o c u t a d e e p g o r g e th r ough t h e p l a t e a u whi ch, a s a l r e a d y m e n t i o n e d i s , i n some p l a c e s , 1 200 m b e l o w t h e c o u n t r y l e v e l o n e i t h e r s i d e . Numerous r o c k - o u t c r o p s
o c c u r i n t h e r i v e r b e d , t h e l a s t o f w h i c h a r e a few
k i l o m e t r e s s o u t h o f R o s e i r e s , some 1 0 0 0 km from i t s s o u r c e beyond T a n a , and known as t h e Damazin r a p i d s . The B l u e N i l e e m e r g e s from t h e p l a t e a u c l o s e t o
E
1
0 0r*
-
ul0
c3 22-
CJ-
0
I: 0-
U 0-
43
z m a,
d
1
a
iJ
ld
.A iJ
3
a
iJ 0
d a, .d
a
z
rt 1
a
m
w 0
c, m
.A C
b0
a
e m
C
ld
.d
a,
M
5 3
.A C
.c
m a m
z
d W
N
b0 .3
rr
44
Fig. 2.19.
B a t h y m e t r i c map o f Lake Tana ( M o r a d i n i , G . , 1940)
t h e w e s t e r n b o r d e r o f E t h i o p i a , where i t t u r n s n o r t h - w e s t a t a n a l t i t u d e o f 490 m e t r e s a . m . s . 1 .
(seeFig. 2.20.).
acd e n t e r s t h e Sudan
Just before crossing the
f r o n t i e r , t h e r i v e r e n t e r s t h e c l a y p l a i n , t h r o u g h which i t f l o w s t o Khartoum.
A t t h i s p o i n t t h e B l u e N i l e j o i n s t h e White N i l e t o form t h e main s t e m of t h e N i l e R i v e r . The a r e a bounded by t h e s e two r i v e r s i s known a s t h e G e z i r a P l a i n ( f o r m e r l y c a l l e d Meroe I s l a n d , S e e F i g . 1 . 1 . ) . The p h y s i o g r a p h y o f t h i s a r e a c a n be s e e n i n F i g . 2 . 2 1 .
( B e r r y L . and Whiteman, A . J . ,
1968).
The D i n d e r and t h e Rahad j o i n t h e B l u e N i l e i n t h e r e a c h between S e n n a r and Wad-Medani.
The head s t r e a m s b o t h of t h e D i n d e r and t h e Rahad r i s e on t h e
E t h i o p i a n P l a t e a u a b o u t 30 km w e s t o f Lake T a n a . T h e s e two r i v e r s a r e s e a s o n a l s t r e a m s , and i n t h e d r y s e a s o n t h e y a r e r e d u c e d t o p o o l s s e p a r a t e d by s t r e t c h e s o f d r y s a n d y b e d . They a r e n e a r l y e q u a l l y l o n g , e a c h a b o u t 750 or 800 km. The e f f e c t i v e c a t c h m e n t a r e a s a r e a b o u t 1 6 000 and 8 200 km2 f o r t h e D i n d e r and t h e Rahad r e s p e c t i v e l y . The two r i v e r s a r e v e r y s i m i l a r t o e a c h o t h e r b u t t h e Rahad
45
h a s a f l o w volume i n a n o r m a l y e a r e q u a l t o 1.1 x
lo9
m 3 , w h i c h i s a b o u t one
t h i r d o f t h e a n n u a l volume o f f l o w o f t h e D i n d e r .
Distance
Fig. 2.20.
2.7.2
by
river
from
Khartoum
in k m .
Longitudinal p r o f i l e of t h e Blue N i l e
The Atbara .
The R i v e r A t b a r a , w h i c h i s t h e l a s t t r i b u t a r y o f t h e N i l e , e n t e r s t h e Main ' N i l e a t a b o u t 320 km downstream o f Khartoum.
I t i s 880 km l o n g and t h e g r e a t e r
p a r t o f i t s c a t c h m e n t i s s i t u a t e d i n E t h i o p i a . The h i g h e s t p o i n t s i n t h e c a t c h ment r e a c h more t h a n 3 500 metres a . m . s . l . , w h e r e a s t h e e a s t e r n w a t e r s h e d o f t h e A t b a r a i s , f o r t h e most p a r t , more t h a n 2 500 m h i g h . The A t b a r a d o e s n o t s p r i n g from a l a k e and r e l i e s t o t a l l y o n many s m a l l t r i b u t a r i e s , o f w h i c h t h e T a k a z z e or t h e S e t i t i s t h e p r i n c i p a l o n e . The l a t t e r h a s a c a t c h m e n t a r e a o f 68 800 km2 o u t o f 1 1 2 400 km2 ( t h e t o t a l c a t c h m e n t a r e a of t h e A t b a r a ) . Above t h e S e t i t j u n c t i o n t h e A t b a r a r e c e i v e s a number o f t r i b u t a r i e s of which t h e Bahr e l Salam is t h e p r i n c i p a l . The A t b a r a i s more s t r o n g l y s e a s o n a l i n i t s f l o w , compared t o t h e B l u e N i l e . Moreover, t h e b i g d r o p i n e l e v a t i o n b e t w e e n t h e h e a d and t h e j u n c t i o n o f t h e Salam R i v e r i s r e s p o n s i b l e f o r t h e e x c e s s i v e s e d i m e n t l o a d o f t h e A t b a r a i n p r o p o r t i o n t o i t s flow volume. I n t h i s r e a c h t h e At bara h a s a s l o p e of about
5 x
( s e e F i g . 2 . 2 1 . ) . The l o n g i t u d i n a l s e c t i o n o f t h e B l u e N i l e shows t h a t
t h i s r i v e r has a slope of only 2 x
i n t h e u p p e r 300 km.
An i m p o r t a n t p l a c e i n t h e b a s i n of t h e A t b a r a i s Khashm e l G i r b a . T h e r e t h e r i v e r was p r o v i d e d w i t h a g a u g i n g s t a t i o n a t t h e b e g i n n i n g of t h e c e n t u r y .
46
N o r t h - e a s t o f Khashm e l G i r b a l i e s K a s s a l a on t h e R i v e r Gash (see F i g . 2 . 2 2 . ) . T h i s i s , l i k e t h e A t b a r a , a t o r r e n t i a l stream, b u t much s m a l l e r and f l o w s f o r a s h o r t e r t i m e . Below K a s s a l a t h e Gash s p r e a d s o u t i n t o a D e l t a and i t s w a t e r s u l t i m a t e l y d i s a p p e a r i n t o t h e s o i l . I t i s q u i t e p o s s i b l e t h a t t h e Gash was a t r i b u t a r y of t h e Atbara i n t h e p a s t .
2 000
/ -
1500
ul
E 0 ffl
2 1000
c
; C C
500 0
>
-aJ w
0 880
Fig. 2.21.
660 Distance
440 from
head
in
380
300
16
kilornetres
L o n g i t u d i n a l p r o f i l e of t h e R i v e r Atbara
THE MAIN NILE
2.8
A d e s c r i p t i o n o f t h e p h y s i o g r a p h y and t h e t o p o g r a p h y o f t h e b a s i n of t h e
Main N i l e from Khartoum up t o t h e M e d i t e r r a n e a n S e a is g i v e n i n V o l . I X o f t h e N i l e B a s i n ( H u r s t e t a l , 1 9 5 9 ) . A summary o f t h e marked f e a t u r e s o f t h e N i l e Basin i n t h i s s t r e t c h is a s f o l l o w s :
2.8.1
From Khartoum t o Aswan
A t Khartoum t h e B l u e N i l e j o i n s t h e White N i l e and t h e combined w a t e r s flow f o r 1 8 8 5 km t o Aswan t h r o u g h a r e g i o n o f Nubian s a n d s t o n e o v e r l y i n g an o l d e r o d e d l a n d s u r f a c e of c r y s t a l l i n e r o c k s which h a s b e e n l a i d b a r e a t p l a c e s i n t h e c o u r s e of t h e s t i l l incomplete d e g r a d a t i o n o f t h e r i v e r bed. These
LEGEN9
++ +
International boundary
-..-
B o u n d a r y of river b a s i n
-----* Unsurveyed s t r e a m
Fig. 2 . 2 2 .
Map s h o w i n g t h e d r a i n a g e h a s i n of t h e A t b a r a and t h e Main N i l e below Khartoum
4 4
48
c r y s t a l l i n e r o c k s o f f e r a much g r e a t e r r e s i s t a n c e t o t h e r i v e r ' s a c t i o n t h a n does t h e s o f t e r Nubian s a n d s t o n e . Upstream, t h e r e f o r e , i n t h e p l a c e where t h e former r o c k s are e x p o s e d , d e g r a d a t i o n c e a s e s for a w h i l e , w h i l e t h e r i v e r c u t s
i t s way t h r o u g h t h e rocky o b s t a c l e . The r i v e r ' s c o u r s e t h u s c o n s i s t s o f a s e r i e s of p l a c i d r e a c h e s o f mild s l o p e s e p a r a t e d by rocky r a p i d s , c a l l e d t h e C a t a r a c t s , where t h e s l o p e i s g r e a t e r and t h e f l o w more t u r b u l e n t . The r a p i d s t h e m s e l v e s a r e c a u s e d by b a r s of h a r d r o c k c r o s s i n g t h e c o u r s e o f t h e r i v e r . These r o c k s a r e more s l o w l y e r o d e d t h a n t h e n e i g h b o u r i n g r o c k s and s o form a r e a o f t h e Main N i l e a t t h e
s i l l s o r s t e p s . The a p p r o x i m a t e c r o s s - s e c t i o n a l
l o c a t i o n s o f t h e C a t a r a c t s and i n between them i s i n c l u d e d i n T a b l e 2 . 3 . F i g . 2.23.
a l s o shows t h e l o n g i t u d i n a l p r o f i l e of t h e w a t e r s u r f a c e t o g e t h e r w i t h
t h e w a t e r s u r f a c e width a t t h e d i f f e r e n t s t r e t c h e s of t h e r i v e r . Approximate s e c t i o n a l a r e a s , i n s q u a r e metres of some s t r e t c h e s
TABLE 2 . 3
of t h e Main N i l e between A t b a r a and H a l f a S e c t i o n a l area, m2,
Location
J a n . F e b . Mar. Apr. May
f o r months o f t h e y e a r
J u n . J u l . Aug. S e p . O c t . Nov. Dec.
Atbara to 5th Cataract
2600 1900 1500 1250 1160 1800 2800 4500 6750 6100 4600 3300
5th Cataract
1800 1400 1100
900
800 1000 2000 4000 4850 4500 3500 2500
5th Cataract t o 2500 1800 1300 1100 1000 1300 2500 5700 6950 6400 5000 3600 4th Cataract 4th Cataract
1800 1400 1100
900
800 1000 2000 4000 4850 4500 3500 2500
4th Cataract t o 2300 1700 1300 1100 1000 1300 2400 5400 6550 6100 4700 3300 3rd C a t a r a c t 2600 2000 1500 1100
860
900 1900 4100 5450 5000 3900 3300
3rd C a t a r a c t t o 2600 2000 1500 1100 2nd C a t a r a c t
860
900 1900 4100 5450 5000 3900 3300
3rd C a t a r a c t
2nd C a t a r a c t
1800 1400 1100
900
860 1000 2000 4000 4850 4500 3500 2500
For t h e f i r s t 80 km n o r t h of Khartoum, t h e r i v e r f l o w s n o r t h w a r d s , t h e n c e t o B e r b e r (km 387 from Khartoum). The c o u r s e o f t h e r i v e r r u n s s u c c e s s i v e l y e a s t , north-east,
and n o r t h . North o f B e r b e r t h e r i v e r t u r n s n o r t h - w e s t
t o Abu-Hamed
(km 5781, where i t a b r u p t l y t u r n s s o u t h - w e s t t o K o r t i (km 8 7 2 ) . From K o r t i t h e c o u r s e s w i n g s around a bend back t o t h e n o r t h a t Kerma (km 1 1 4 5 ) , where i t p r o c e e d s n o r t h and n o r t h - e a s t From E l - D e r r
p a s t Wadi-Halfa
(km 1 435) t o E l - D e r r
t h e r i v e r , a f t e r a s h o r t right-hand
n o r t h e r l y d i r e c t i o n t o Aswan ( s e e F i g s . 2 . 2 2 . ,
(km 1 6 7 1 ) .
loop t o t h e s o u t h , flows i n a
2.24.,
and 2 . 2 5 . ) .
LTY~~, Khartoum
400
375
vi
i d
At baro
'""\ , Shirri
325300
Island
End of 4 t h .
-
C ._ Q,
U
225-
0
"-
5
c
200175-
a 3
-
0
-
Cataract
!
275 250-
Scales
rapids
Abu F a t m a ( Hennek, Simit and Shaban rapids ) K a i b a r rapids
I
7
Tongur
S h a b l u k a or 6 th. C a t a r a c t
I
,
rapids
Amuaol
raoids
'
I
I
I
5 th. Cataract 4 t h ~ a t a r a ct
I
I
I
I
I
I
I
i
80
41 2 I
A s w a n or lSt. C a t a r a c t
I
580 683 I
I
7
822 I
1168 I
1301 1
1438 1526 I
I
1885
50
A s d e g r a d a t i o n is s t i l l i n p r o g r e s s t h r o u g h o u t t h e r e a c h d e s c r i b e d , t h e r i v e r d e p o s i t s no f l o o d p l a i n s . C u l t i v a t i o n ,
therefore,
is c o n f i n e d t o t h o s e
few s t r e t c h e s w h e r e n a t u r a l c o n d i t i o n s p e r m i t i r r i g a t i o n . The f i r s t s t o r a g e work i n t h e N i l e Valley, t h e o l d Aswan D a m , w a s b u i l t i n
1902 a t t h e f o o t o f t h e Aswan C a t a r a c t .
2.8.2
From Aswan t o t h e M e d i t e r r a n e a n S e a
The o l d Aswan D a m h a s b e e n h e i g h t e n e d t w i c e ; o n c e i n 1912 and t h e s e c o n d
t i m e i n 1934. T h i s dam, t o g e t h e r w i t h t h e o t h e r s t o r a g e works on t h e B l u e and W h i t e N i l e s h a v e c h a n g e d t h e N i l e from Aswan t o t h e sea i n t o a p a r t i a l l y r e g u l a t e d r i v e r i n s t e a d o f a n a t u r a l l y f l o w i n g o n e . F u l l r e g u l a t i o n h a s a l m o s t been a c h i e v e d as a r e s u l t o f t h e f o r m a t i o n o f t h e Nasser L a k e u p s t r e a m o f t h e h i g h dam a t Aswan i n 1965. T h i s h u g e a r t i f i c i a l impoundment o f t h e N i l e w a t e r e x t e n d s f r o m Aswan t o a l i t t l e s o u t h o f t h e D a l C a t a r a c t b e t w e e n t h e 23O 5 8 ” and 20°
27” l a t i t u d e and 30° 35’E and 33O 1 5 ’ E l o n g i t u d e ( s e e F i g . 2 . 2 5 . ) .
T a b l e 2.4 shows t h e d e v e l o p m e n t o f t h e r e s e r v o i r l e v e l and c a p a c i t y i n t h e p e r i o d from 1964-65 t i l l 1975-76.
TABLE 2.4
The g r a d u a l f i l l i n g o f t h e r e s e r v o i r formed by t h e High Dam a t Aswan (Abu e l - A t a a ,
Highest level, m a.m.s.1.
Year
A,,
Date of occurrence
1978) Maximum storage
10’ m 3
Lowest level, m a.m.s.1.
Date Of
occurrence
Minimum storage 10’ m 3 -
9.620
111.89
1.08.1964
4.11.1966
13.590
119.02
29.07.1966
4.650
4.02.1967
24.320
113.48
26.07.1967
14.130
151.21
10.10.1967
39.640
145.27
21.07.1968
28.516
156.55
21.11.1968
39,005
150.85
22.07.1969
39.005
1964/65
127.60
18.01.1965
1965/66
132.86
1966/67
142.48
1967/68 1968/69 1969/70
161.30
25.10.1969
62,400
153.81
3.08.1970
42.280
1970/71
164.88
26.11.1970
77.468
159.65
23.08.1971
60.450
1971/72
167.64
4.12.1971
87.757
162.49
28.07.1972
68.774
1972/73
167.52
1.01.1973
87,320
158.20
8.07.1973
56.960
1973/74
166.32
9.11.1973
82.776
161.00
16.07.1974
64.500
1974/75
170.63
5.11.1974
100.309
165.60
30.07.1975
80.060
1975/76
175.71
10.12.1975
124 ,990
172.42
26.07.1976
108.370
T h i s t a b l e shows c l e a r l y t h a t t h e w a t e r l e v e l u p s t r e a m o f Aswan h a s r i s e n i n t h e l a s t t e n y e a r s by a minimum o f 40 metres compared t o t h e f l o o d l e v e l i n t h e pre-High
D a m p e r i o d ( 1 2 1 . 0 metres a . s . 1 . ) .
T h i s c o n s i d e r a b l e r i s e i n t h e water
Fig. 2.24.
M a p showing t h e Main N i l e i n t h e reach from t h e Atbara . j u n c t i o n t o Wadi-Halfa
52
l e v e l h a s r e s u l t e d i n t h e i n u n d a t i o n o f some p a r t s o f N u b i a . I n i t h n a t u r a l c o n d i t i o n , t h e l e n g t h o f t h e r i v e r from Aswan t o t h e D e l t a B a r r s g e s was 9 6 8 km i n t h e low-flow t h e s l o p e was 7 . 7 x lo-'
and 8 . 5 x
s e a s o n and 9 2 3 km i n t h e f l o o d s e a s o n and
lo-'
d u r i n g t h e f l o o d w a s a b o u t 7 500 m 2 ,
.Jelocity between 1.0 m / s
respectively.
The c r o s s - s e c t i o n a l
area
t h e mean w i d t h a b o u t 900 m and t h e mean
and 2 . 0 m / s .
From C a i r o t o a l i t t l e s o u t h o f L u x o r t h e c u l t i v a t e d l a n d i s u s u a l l y s e v e r a l k i l o m e t r e s w i d e b u t t o w a r d s Aswan i t n a r r o w s t o a b o u t o n e k i l o m e t r e , a n d i n u l a c e s t h e d e s e r t h i J l s a r e c l o s e t o t h e r i v e r . These c o n d i t i o n s p e r s i s t f o r a l o n g way s o u t h o f Wadi-Halfa. P e r e n n i a l i r r i g a t i o n i n E g y p t h a s become p o s s i b l e o n l y a f t e r t h e c o n s t r u c LioIl o f a number o f b a r r a g e s o n t h e N i l e and i t s b r a n c h e s . A b a r r a g e
time:;
-
some-
c a l l e d a n o p e n - t y p e w e i r - i s d i f f e r e n t from a dam as i t s f u n c t i o n i s n o t
t o form a s t o r a g e r e s e r v o i r , b u t m e r e l y t o r a i s e t h e l e v e l o f t h e w a t e r ups t r e a m of
i t so a s t o d i v e r t s o m e o f i t i n t o t h e c a n a l s whose e n t r a n c e s a r e
a b o v e t h e b a r r a g e . The o l d D e l t a b a r r a g e s w e r e c o m p l e t e d i n 1 8 6 1 and t h e new Ones i n 1 9 3 9 . O t h e r b a r r a g e s were b u i l t a t E s n a , Nag-Hammadi,
A s s i u t and Z i f t a .
The s u r f a c e of t h e c u l t i v a t e d a r e a i n b o t h t h e N i l e V a l l e y and t h e N i l e D e l t a amounts t o o n l y 3% o f t h e t o t a l s u r f a c e a r e a o f E g y p t . The e a s t e r n and ' w e s t e r n d e s e r t s o c c u p y 2 3 and 74'1, o f t h e s u r f a c e a r e a o f E g y p t , r e s p e c t i v e l y . The e a s t e r n d e s e r t i s r u g g e d and m o u n t a i n o u s and is much c u t up by d e e p v a l l e y s ( W a d i s ) , down w h i c h o c c a s i o n a l h e a v y r a i n s c a u s e t o r r e n t s t o f l o w . T h e r e a r e no wadi:^
i n t h e w e s t e r n d e s e r t . T h i s d e s e r t is l o w e r and more u n d u l a t i n g , b u t is
n e v e r t h e l e s s s h a r p l y d i v i d e d from t h e N i l e V a l l e y , b e c a u s e c u l t i v a t i o n c e a s e s its s o o n a s t h e g r o u n d b e g i n s t o r i s e a b o v e t h e l e v e l which c a n b e f l o o d e d by
t h e Yilo water. T h e r t ? art' a number o f o a s e s i n t h e w e s t e r n d e s e r t . T h e s e a r e s i m p l y d e p r e s -
s i o n s w h e r e t h e g r o u n d l e v e l i s n e a r t h e water l e v e l , w h i c h i s e a s i l y r e a c h e d by w e l l s .
A cross-section
e x t e n d i n g from t h e c o a s t o f t h e Red S e a i n t h e e a s t
t o t h e w e s t e r n b o u n d a r y of E g y p t p a s s i n g t h r o u g h t h e El-Khargah
O a s i s is shown
i n Fig. 2.26. The Fayum i s a d e p r e s s i o n s i t u a t e d a b o u t 70 k i l o m e t r e s s o u t h o f C a i r o and s e p a r a t e d f r o m t h e N i l e V a l l e y by a n a r r o w s t r i p o f d e s e r t . T h i s d e p r e s s i o n i s q u i t e d i f f e r e n t b o t h from t h e o a s e s i n t h e d e s e r t and t h e c u l t i v a t e d a r e a i n t h e N i l e V a l l e y o r t h e D e l t a . On one h a n d t h e Fayum g e t s i t s w a t e r v i a a c a n a l f r o m t h e N i l e , w h e r e a s t h e oases a r e s u p p l i e d by g r o u n d w a t e r . On t h e o t h e r hand t h e l a n d i n El-Fayum h a s a c o n s i d e r a b l e s l o p e compared t o t h e l a n d i n t h e Valley o r i n t h e Delta. The b o t t o m o f t h e El-Fayum
d e p r e s s i o n i s f i l l e d by L a k e Q a r u n ( i n a n c i e n t
t i m e s c a l l e d L a k e M o e r i s ) and most o f t h e r e e a i n d e r i s c u l t i v a t e d . The l a k e h a s
: t
r 4 0 E
30
,100.i
El
Farafrah
/
Oasis
El
!'
-.
i?
-,
v
L
- Dakhlah Oasis
G
Y
c
1
t t
D E S E R T
+
I I I t
I+' + + + +
I
j
+-+++++
t
I
t t
S
t
0
t
+ t Fig. 2 . 2 5 .
I
U
Scale
so 1
100 1'0 I
++++
I
200 i
++ + + + +
D km
Map showing the N i l < ? R i v e r f r o m s o u t h u f Wadi-Halfa
to a little n o r t h of A s s i u t
cn
w
54
no o u t l e t and r e c e i v e s t h e d r a i n a g e w a t e r from t h e c u l t i v a t e d l a n d . I t s l e v e l i s k e p t f a i r l y c o n s t a n t by e v a p o r a t i o n b a l a n c i n g t h e i n f l o w , s o t h a t t h e l a k e
w a t e r s t e a d i l y becomes more s a l i n e . About 50 k i l o m e t r e s s o u t h - w e s t of El-Fayum town and 80 k i l o m e t r e s w e s t of Beni-Suef
l i e s a n o t h e r d e p r e s s i o n , known a s
Wadi e l Rayyan. T h i s Wadi had o f t e n been c o n s i d e r e d a s a p o s s i b l e s o l u t i o n f o r s i d e s t o r a g e of t h e f l o o d w a t e r . The Wadi i s a d e p r e s s i o n whose maximum d e p t h
is 50 metres b . s . 1 .
a s compared w i t h t h e 45 metres o f t h e p r e s e n t Lake Qarum
level. The l a r g e s t , and a t p r e s e n t t h e d e e p e s t , d e p r e s s i o n i n t h e E g y p t i a n p a r t of t h e western d e s e r t , is t h e Qattarah depression. This depression has a s u r f a c e a r e a c o r r e s p o n d i n g t o t h e mean sea l e v e l of a b o u t 4 m i l l i o n f e d d a n s or a b o u t 50% l a r g e r t h a n t h e a r e a c o n t a i n e d between t h e two b r a n c h e s of t h e N i l e ( s e e Fig. 2.27.).
The d e e p e s t p o i n t i n t h e d e p r e s s i o n i s a t a l e v e l o f 159 m e t r e s
b . m . s . 1 . The Q a t t a r a h d e p r e s s i o n h a s , f o r t h e l a s t t h i r t y y e a r s or more, been c o n s i d e r e d a s a p o s s i b l e scheme f o r g e n e r a t i n g e l e c t r i c power. T h i s c a n b e a c h i e v e d by c o n n e c t i n g t h e d e p r e s s i o n w i t h t h e M e d i t e r r a n e a n S e a by an i n t a k e a t , or a b o u t , El-Alamein. The y e a r l y i n f l o w t o t h e d e p r e s s i o n w i l l b e b a l a n c e d by t h e y e a r l y e v a p o r a t i o n , s o t h e s u r f a c e w a t e r l e v e l i n t h e d e p r e s s i o n remains constant. The N i l e n o r t h of C a i r o b i f u r c a t e s i n t o t h e R o s e t t a and D a m i e t t a b r a n c h e s . Very c l o s e t o t h e mouth of each b r a n c h i s t h e s i t e where an e a r t h bank used t o b e c o n s t r u c t e d each y e a r . T h i s was completed when t h e flow i n t o t h e r i v e r was s h u t o f f a t t h e D e l t a B a r r a g e and a l l t h e w a t e r d i v e r t e d t o t h e c a n a l s b e c a u s e
i t w a s needed f o r c u l t i v a t i o n . The banks p r e v e n t e d s a l t w a t e r from p e n e t r a t i n g i n l a n d , and a l s o e n a b l e d s e e p a g e and d r a i n a g e back i n t o t h e r i v e r t r o u g h from t h e D e l t a B a r r a g e n o r t h w a r d s t o b e c o l l e c t e d and used for i r r i g a t i o n o f s m a l l a r e a s f u r t h e r n o r t h a l o n g t h e r i v e r . The e a r t h bank on t h e R o s e t t a b r a n c h was r e p l a c e d i n 1951 by t h e E d f i n a B a r r a g e , whereas t h e p l a n n e d b a r r a g e a t F a r a s k o u r f o r t h e D a m i e t t a b r a n c h h a s n e v e r been e x e c u t e d . A f t e r t h e c o n s t r u c t i o n of t h e High Dam a t Aswan i n 1964, t h e flow o f t h e N i l e from Aswan t o t h e M e d i t e r r a n e a n S e a h a s been under d i f f e r e n t r e g u l a t i o n . I n t h e pre-High Dam t i m e ,
i t w a s c l a i m e d t h a t t h e D a m i e t t a b r a n c h was
g r a d u a l l y s i l t i n g up and t h e r e f o r e d e c r e a s i n g i n s i z e , whereas t h e R o s e t t a b r a n c h was s c o u r i n g i n h i g h f l o o d s . The mean w i d t h of t h e R o s e t t a b r a n c h i s 500 m and t h e mean s e c t i o n a l a r e a d u r i n g t h e f l o o d was 4 000 m 2 .
The maximum,
minimum, and mean d i s c h a r g e s were a b o u t 6 500, 2 600 and 4 000 m3/sec., r e s p e c t i v e l y . The mean w i d t h o f t h e D a m i e t t a b r a n c h i s 270 m and i t s mean s e c t i o n a l a r e a d u r i n g t h e f l o o d was 2 700 m 2 .
The maximum, minimum, and mean
d i s c h a r g e s w e r e a b o u t 4 600, 1 300, and 2 300 m 3 / s e c . ,
respectively.
0 0
(
D
'
0 0
D
'
0 0
r
"
0 0
g
0 0
m
0 0
a
.
0 0
.
r
0 0
P
k
-
0 0
0
0
r 0
0
0 0 N
0 0 c?
111
c
g x cn
aJ
0
u "
0
m 0
f
55
56
The two b r a n c h e s o f t h e N i l e h a v e t h e i r mouths s i t u a t e d a t t h e c o a s t o f t h e M e d i t e r r a n e a n S e a . The c o a s t l i n e from A l e x a n d r i a t o P o r t S a i d i s an u n d u l a t i n g l i n e t h a t b e a r s t h e f e a t u r e s o f an a d v a n c i n g d e l t a ( F i g . 2 . 2 7 . ) . T h r e e s h a l l o w l a k e s occupy a g r e a t p a r t o f t h e n o r t h e r n s e c t i o n of t h e D e l t a . T h e s e a r e : Lake Idku i n t h e w e s t , L a k e B u r u l l u s i n t h e m i d d l e and Lake Manzala i n t h e east. These l a k e s r e c e i v e a c o n s i d e r a b l e amount o f t h e d r a i n a g e wager from t h e D e l t a , and a r e s e p a r a t e d from t h e s e a by narrow s t r i p s of l a n d and a l l have o u t l e t s t o the sea. The c o a s t a l l i n e of t h e N i l e D e l t a h a s , f o r some t i m e , b e e n u n d e r g o i n g a r a t h e r a c t i v e p r o c e s s of r e t r e a t . The High D a m a t Aswan h a s b r o u g h t t h e slow b u t c o n t i n u o u s p r o c e s s of b u i l d i n g t h e N i l e D e l t a t o an e n d . T h i s means t h a t t h e c o a s t a l l i n e is l e f t t o t h e e r o s i v e a c t i o n of t h e s h o r e c u r r e n t s . A d e t a i l e d d i s c u s s i o n of t h i s m a t t e r i s p r e s e n t e d i n a l a t e r c h a p t e r .
I
I
26OE
28 O
I - -
- 7
30
M E D I T E R R A N E A N
*
-+
- 28" c
Fig. 2 . 2 7 . Map showing t h e N i l e and i t s b r a n c h e s from A s s i u t Mediterranean Sea co as t
to the
57
REFERENCES Abu e l A t a a , A . , 1 9 7 8 . E g y p t and t h e N i l e a f t e r t h e High D a m ( t e x t i s i n A r a b i c ) , M i n i s t r y o f I r r i g a t i o n , C a i r o , E g y p t , 1 4 5 p p ( w i t h 18 p l a t e s ) . Beauchamp, R . S . , 1 9 6 4 . The R i f t V a l l e y L a k e s o f A f r i c a . V e r h . I n t . V e r . T h e o r . Angew. L i m n o l . 15: 9 1 - 9 9 . B e r r y , L . , and Whiteman, A . J . , 1 9 6 8 . T h e N i l e i n t h e S u d a n . G e o g r . J o u r n . 1 3 4 I : 1-37. H u r s t , H . E . , 1 9 2 7 . T h e L a k e P l a t e a u B a s i n o f t h e N i l e , 2nd p a r t , P h y s . D e p t . P a p e r 23, Government P r e s s , C a i r o , E g y p t , 6 6 p p . H u r s t , H . E . , a n d P h i l i p s , P . , 1931. The N i l e B a s i n , V o l . I : G e n e r a l d e s c r i p t i o n o f t h e B a s i n , m e t e o r o l o g y and t o p o g r a p h y o f t h e W h i t e N i l e B a s i n , P h y s . D e p t . P a p e r 2 6 , Government P r e s s , C a i r o , E g y p t , 1 2 8 p p . H u r s t , H . E . , 1 9 5 0 . The N i l e B a s i n , V o l . V I I I : T h e h y d r o l o g y o f t h e S o b a t and White N i l e and t h e t o p o g r a p h y o f t h e B l u e N i l e a n d A t b a r a , P h y s . D e p t . P a p e r 55, Government P r e s s , C a i r o , E g y p t , 1 2 5 p p . H u r s t , H . E . , B l a c k , R . P . , a n d S i m a i k a , Y . M . , 1 9 5 9 . The N i l e B a s i n , V o l . IX: The h y d r o l o g y o f t h e B l u e N i l e a n d A t b a r a a n d t h e Main N i l e T o Aswan, w i t h some r e f e r e n c e t o p r o j e c t s , N i l e C o n t r o l D e p t . P a p e r 1 2 , Government P r i n t i n g O f f i c e , C a i r o , Egypt, 207 pp. H u r s t , H . E . , B l a c k , R . P . , and S i m a i k a , Y.M., 1 9 6 6 . The Major N i l e P r o j e c t s , N i l e C o n t r o l D e p t . P a p e r 2 3 , Government P r i n t i n g O f f i c e , C a i r o , E g y p t , 1 5 9 p p . J o n g l e i I n v e s t i g a t i o n Team, 1 9 5 4 . The E q u a t o r i a l N i l e p r o j e c t and i t s e f f e c t i n t h e A n g l o - E g y p t i a n S u d a n . S u d a n G o v e r n m e n t , London. K a l i n i n , G . P . , 1 9 7 1 . G l o b a l h y d r o l o g y ( t r a n s l a t e d f r o m R u s s i a n , I s r a e l Program f o r S c i e n t i f i c T r a n s l a t i o n s L t d . ) . U . S . D e p t . o f Comm., N a t i o n a l T e c h n i c a l I n f o r m a t i o n S e r v i c e , S p r i n g f i e l d V a 22151, U.S.A. M o r a n d i n i , G . , 1 9 4 0 . R i c e r c h e L i m n o l o g i c h e . G e o g r a f i a - F i s i c a , V o l . 111, 1. M i s s i o n e d i s t u d i o a1 Lago T a n a , 319 p p . Rz6ska, J . ( e d i t o r ) , 1 9 7 6 . T h e N i l e , b i o l o g y o f a n a n c i e n t r i v e r . D r W . Junk B . V . P u b l i s h e r s , The H a g u e , T h e N e t h e r l a n d s , 4 1 7 p p . Stamp, D . L . , and Morgan, W.T., 1 9 7 2 . A f r i c a : a s t u d y i n t r o p i c a l d e v e l o p m e n t . J o h n Wiley and S o n s I n c . , N e w Y o r k , 5 2 0 p p . S u t c l i f f e , J . V . , 1 9 7 4 . A h y d r o l o g i c a l s t u d y o f t h e s o u t h e r n Sudd r e g i o n o f t h e Upper N i l e , B u l l . H y d r o . S c i . 1 9 : 237-255. T a l l i n g , J . F . , 1 9 6 6 . The a n n u a l c y c l e o f s t r a t i f i c a t i o n and p h y t o - p l a n k t o n growth i n L a k e V i c t o r i a ( E a s t A f r i c a ) , I n t . Rev. H y d r o b . 5 1 : 5 4 5 - 6 2 1 . T a l l i n g , J . F . and R z b s k a , J . , 1 9 6 7 . The d e v e l o p m e n t o f p l a n k t o n i n r e l a t i o n t o h y d r o l o g i c a l regime o f t h e Blue N i l e , J o u r n . Ecol. 55: 637-662. Thompson, K . , 1 9 7 5 . P r o d u c t i v i t y o f C y p e r u s p a p y r u s L . , I n ; P h o t o - s y n t h e s i s and p r o d u c t i v i t y i n d i f f e r e n t environments. (Ed.) J . P . Cooper; I . B . P . S y n t h e s i s S e r i e s 3 ; Cambridge U n i v e r s i t y P r e s s . Wayland, E . J . , 1 9 3 4 . R i f t s , r i v e r s , r a i n s and e a r l y man i n Uganda. J o u r n . Roy. A n t h r o p o l . I n s t . 6 4 : 333-352. 1 1 . Z a g h l o u l , S . S . , 1 9 8 2 . Water b a l a n c e o f L a k e V i c t o r i a and t h e e f f e c t o f g r a v i t y . M.Sc. T h e s i s , F a c . E n g r g . , C a i r o U n i v e r s i t y , G i z a , E g y p t , 239 p p . ( e x c l u d i n g annexes).
59
Chapter 3
CLIMATE OF THE NILE BASIN 3.1
HISTORICAL INTRODUCTION
T h e r e i s e v i d e n c e o f some c l i m a t i c c h a n g e s i n t h e N i l e B a s i n , e s p e c i a l l y i n Egypt and t h e S u d a n , i n t h e l a s t 25 000 y e a r s . I n Egypt t h e w e t p h a s e t h a t t e r m i n a t e d some 2 5 000 y e a r s BP ( b e f o r e p r e s e n t ) was f o l l o w e d by a d r y p h a s e t h a t l a s t e d a h o u t 7 000 y e a r s . The s u b s e q u e n t p e r i o d from 18 000 t o , s a y , 5 000 y e a r s BP w a s c h a r a c t e r i z e d by i t s h e a v y w i n t e r r a i n and by i n c r e a s e d f l o w i n t h e N i l e coming f r o m t h e E t h i o p i a n P l a t e a u . The g r a d u a l a r i d i t y which s w e p t o v e r E g y p t s i n c e t h e n w a s i n t e r r u p t e d by some w e t , t h o u g h s h o r t , i n t e r v a l s . T h e s e w e r e f r o m a b o u t 10 000 t o 8 000 y e a r s BP and f r o m a b o u t 6 000 t o 4 500 BP. The m o i s t i n t e r v a l s h a v e b e e n t e r m i n a t e d s i n c e a b o u t 2 500
years B.C.
(Butzer, K.W.,
1966 and 1 9 7 1 ) .
I n t h e S u d a n t h e p e r i o d f r o m 20 000 t o 1 5 000 y e a r s BP w a s v e r y a r i d . T h i s
was f o l l o w e d by a w e t p e r i o d t h a t l a s t e d f r o m 1 2 000 t o 7 000 y e a r s BP and by somewhat f l u c t u a t i n g i n t e r v a l s f r o m 7 000 t o 6 000 y e a r s BP. The c l i m a t e i n t h e i n t e r v a l from 6 000 t o 3 000 y e a r s BP c a n b e d e s c r i b e d as f a i r l y w e t . From 3 000 y e a r s a g o up t o t h e p r e s e n t ,
t h e climate i n t h e Sudan, l i k e t h a t i n Egypt, has
g r a d u a l l y b e e n becoming a r i d (Wickens, G . ,
1975).
A d e t a i l e d d e s c r i p t i o n o f t h e s e changes are beyond t h e s c o p e o f t h i s book.
Our i n t e r e s t h e r e i s f o c u s e d on t h e c l i m a t e as i t h a s b e e n i n t h e p a s t 100 y e a r s
or s o .
3.2
CLIMATIC REGIONS
A s h o r t d e s c r i p t i o n o f t h e c l i m a t e i n t h e a r e a o c c u p i e d by t h e N i l e B a s i n i s given i n V o l .
I of t h e N i l e Basin ( H u r s t , H . E .
and P h i l i p s , P . , 1 9 3 1 ) . I n t h i s
d e s c r i p t i o n t h e c l i m a t e h a s b e e n d i v i d e d i n t o t h r e e main t y p e s . T h e s e a r e : Type 1
- M e d i t e r r a n e a n c l i m a t e c o v e r i n g t h e a r e a from t h e sea coast t o a
little
s o u t h o f C a i r o . The a n n u a l r a i n f a l l d e c r e a s e s f r o m 150 t o 200 mm/yr o n t h e c o a s t t o a b o u t 2 5 t o 30 mm/yr a t C a i r o . Type 2
-
Desert or S a h a r a n c l i m a t e c o v e r i n g t h e a r e a f r o m a l i t t l e s o u t h of C a i r o t o A t h a r a . T h e r e i s p r a c t i c a l l y no r a i n f a l l i n t h i s a r e a .
Type 3
-
T r o p i c a l climate c o v e r i n g t h e a r e a s o u t h of Atbara. This type has f u r t h e r been sub-divided i n t o :
3a
- The S u d a n P l a i n s - T h e r e
is a steady increase i n r a i n f a l l south
o f t h e r a i n l e s s r e g i o n ( t y p e 2 ) . An a n n u a l d e p t h o f , s a y , 1 0 0 0 mm is reached i n t h e s o u t h .
60
3b
- The H i g h l a n d s of A b y s s i n i a - T h i s c o u l d be a r e g i o n o f r e l a t i v e l y heavy r a i n f a l l , s i n c e an a n n u a l d e p t h of 1 600 mm i s r e a c h e d i n some p l a c e s .
3c
- The H i g h l a n d s of t h e Lake P l a t e a t i - The a v e r a g e a n n u a l r a i n f a l l c o u l d b e i n t h e o r d e r o f 1 250 m m .
The c l i m a t e of t h e Sudan was d e s c r i b e d by I r e l a n d i n " A g r i c u l t u r e i n t h e Sudan" ( e d i t e d by T o t h i l l , J . D . ,
1 9 4 8 ) . The Sudan, h e m e n t i o n e d , l a y w h o l l y
w i t h i n t h e t r o p i c s between l a t i t u d e s 22'
and 3 O N .
I t i s almost e n t i r e l y lana-
l o c k e d and h a s a p r e d o m i n a n t l y c o n t i n e n t a l c l i m a t e . The e f f e c t o f t h e Red S e a i s q u i t e l i m i t e d and t h e r e a r e no l a k e s or i n l a n d w a t e r s u r f a c e s l a r g e enough t o p r o d u c e e v e n l o c a l c l i m a t i c e f f e c t s . Broadly s p e a k i n g ,
t h e r e f o r e , t h e Sudan i s
one v a s t p l a i n , i n t e r r u p t e d o n l y by t h e Marra Mountains o f D a r f u r and t h e Nuba Mountains o f s o u t h e r n K o r d o f a n . The cli.mate of t h e Sudan may be d i v i d e d i n t o 3 r e g i o n s . Kegion 1 i s s i t u a t e d n o r t h o f a b o u t l a t i t u d e 19'N.
In t h i s d e s e r t i c region the
d r y n o r t h e r l i e s p r e v a i l t h r o u g h o u t t h e y e a r and r a i n i s i n f r e q u e n t . I t e x p e r i e n c e s l a r g e d i u r n a l and a n n u a l v a r i a t i o n s i n t e m p e r a t u r e ,
c h a r a c t e r i s t i c s of a
desert climate. Region 2 i s s i t u a t e d s o u t h o f l a t i t u d e 19'N is t y p i c a l of a t r o p i c a l c o n t i n e n t ,
t o l a t i t u d e 3 O N . Here t h e c l i m a t e
though t h e n o r t h e r n p a r t is s e m i - a r i d .
Region 3 c o m p r i s e s t h e a r e a s a l o n g t h e Red S e a c o a s t and t h e e a s t e r n s l o p e s of t h e Red S e a h i l l s . L i k e r e g i o n 1, t h e n o r t h e r l i e s p r e v a i l t h r o u g h o u t t h e y e a r , e x c e p t t h a t t h e c l i m a t e i s p r o f o u n d l y a f f e c t e d by t h e m a r i t i m e i n f l u e n c e o f t h e Red S e a . The r a i n i s p a r t l y o r o g r a p h i c and p a r t l y c o n v e c t i o n a l . The c l i m a t e of A f r i c a w a s c l a s s i f i e d ( T r e w a r t h a , G . T . ,
1 9 6 2 ) , b a s e d on a
s i m p l i f i e d form o f t h e c l a s s i f i c a t i o n t h a t had o r i g i n a l l y been d e v e l o p e d by W.
Koppen. The r e s u l t s o f t h a t work have been used t o d e r i v e t h e map of t h e
c l i m a t e of A f r i c a (Stamp, D. and Morgan, W . ,
1 9 7 2 ) . The p a r t of t h e map c o v e r -
i n g t h e N i l e B a s i n i s shown i n F i g . 3 . 1 . The c a t e g o r i e s i n c l u d e d i n i t a r e : 1) The e q u a t o r i a l or t r o p i c a l r a i n f o r e s t c l i m a t e
- This
i s c h a r a c t e r i z e d by
a l m o s t c o n s t a n t h e a t , c o n s t a n t h u m i d i t y and c o n s t a n t r a i n f a l l . P l a n t growth t a k e s p l a c e throughout t h e y e a r , s o t h a t l u x u r i a n t v e g e t a t i o n i s t h e r u l e . The s u n h e a t c a u s e s e v a p o r a t i o n from l a k e s and m o i s t l a n d s u r f a c e s . The h e a t e d , s a t u r a t e d , a i r r i s e s and i s c o o l e d by c o n v e c t i o n s o t h a t r a i n f a l l s i n a l m o s t t h e same a r e a from which t h e m o i s t u r e o r i g i n a t e s ( c o n v e c t i v e rains). 2) The t r o p i c a l savannah
-
T h i s r e g i o n e x t e n d s from t h e t r o p i c a l r a i n f o r e s t on
one s i d e t o t h e d e s e r t m a r g i n s on t h e o t h e r . A c c o r d i n g l y , t h e savannah c l i m a t e v a r i e s g r e a t l y between t h e s e two l i m i t s . The v a r i a t i o n i s p r i m a r i l y i n t h e a n n u a l d e p t h of p r e c i p i t a t i o n , commonly 1 500 mm or more i n t h e
61
e q u a t o r i a l m a r g i n s t o 400 mm i n t h e s e m i - a r i d p a r t . The s e a s o n from November t o F e b r u a r y i s r e l a t i v e l y cool a n d d r y . T h i s i s f o l l o w e d by a h o t , d r y , s e a s o n w h e r e t h e h o t t e s t month i s A p r i l o r May. The coming of r a i n s from J u n e t o O c t o b e r , c a u s e s t h e l o w e r i n g o f t h e t e m p e r a t u r e . The amount o f t h e l o w e r i n g d e p e n d s on t h e amount o f r a i n f a l l . T h e s e a s o n a l d e p t h o f r a i n h a s a w i d e r e l a t i v e r a n g e b u t t h a t o f t h e m o n t h l y d e p t h i s much w i d e r . 3 , 4 ) The s e m i - a r i d
and a r i d c l i m a t e o r t h e s t e p p e and d e s e r t
l i m i t may b e t a k e n as t h e 400 mm/yr
isohyet.
-
The s a v a n n a h
I f less t h a n t h i s d e p t h , t h e
c l i m a t e may b e d e s c r i b e d as s t e p p e . I t i s r a t h e r d i f f i c u l t t o s a y where t h e s t e p p e c h a n g e s i n t o d e s e r t . On t h e p o l e w a r d m a r g i n s ,
3
low r a i n f a l l l i m i t
may b e t a k e n t o i n d i c a t e w h e r e t h e s t e p p e l a n d s f a d e i n t o t h e M e d i t e r r a n e a n Along t h e s o u t h e r n m a r g i n s , t h e r a i n y s e a s o n i s t h e h o t s e a s o n , w h e r e a s along t h e Mediterranean margins i t is t h e w i n t e r .
5 ) The H i g h l a n d s
-
T h e r e a r e two a r e a s whose c l i m a t e b e l o n g s t o t h i s c a t e g o r y ,
a r o u n d t h e E q u a t o r i a l L a k e s a n d a good p a r t o f t h e E t h i o p i a n P l a t e a u ( s e e map, F i g . 3.1.). T h e c l i m a t e h e r e i s v e r y much m o d i f i e d by t h e e l e v a t i o n . Some p a r t s r i s e t o t h e snow l i n e . The a n n u a l p r e c i p l t a t l o n e a s i l y r e a c h e s
1 500 m m . The m o i s t u r e i n d e x method h a s b e e n u s e d i n t h e h y d r o m e t e o r o l o g i c a l s u r v e y o f t h e catchments of Lakes V i c t o r i a ,
Kyoga a n d A l b e r t f o r t h e p u r p o s e o f c l a s s i f y -
i n g t h e c l i m a t e o f t h e L a k e P l a t e a u a r e a . The i n d e x h a s b e e n computed f o r s e v e r a l p o i n t s w i t h i n t h e a r e a from t h e e x p r e s s i o n I
m
100 ( S =____.__-.
-
0.6D)
(3.1)
PET
where Im
= moisture index,
S
= cumulated monthly s u r p l u s ,
(R
D
= cumulated monthly d e f i c i t ,
(PET
R
=
m
= s u b s c r i p t r e f e r r i n g t o month,
-
PET)
-
m'
R)m,
rainfall, and
PET = a n n u a l p o t e n t i a l e v a p o t r a n s p i r a t i o n The d i f f e r e n t t y p e s o f c l i m a t e c o r r e s p o n d t o t h e f o l l o w i n g I Type
Im value
__
100 and a b o v e
Perhumid Humid
Moist sub-humid
20
to
100 20
0
to
Dry sub-humid
-
20
to
0
Semi - a r i d
-
40
to
-20
Arid
-100
to
-40
values
62
Fig. 3.1.
C l i m a t o l o g i c a l r e g i o n s o f the N i l e B a s i n
63
The c o n t o u r l i n e s of e q u a l m o i s t u r e i n d e x v a l u e s i n t h e E q u a t o r i a l Lake P l a t e a u a r e as shown i n F i g . 3.2. From t h i s map one c a n e a s i l y see t h a t t h e g r e a t e r p a r t o f t h e p l a t e a u a r e a f a l l s i n t h e c l a s s of t h e d r y sub-humid c l i m a t e and o n l y a few s m a l l p a r t s f a l l i n t h e m o i s t sub-humid c l a s s . The i n f o r m a t i o n p r e s e n t e d on t h e map i n F i g . 3.2. d o e s n o t f u l l y a g r e e w i t h t h e c o r r e s p o n d i n g p a r t of t h e map i n F i g . 3 . 1 . They d i f f e r mainly i n t h a t p a r t s i t u a t e d w e s t of Lake V i c t o r i a ,
29'
E
30'
i n t h e b a s i n o f t h e Kagera and n o r t h o f i t .
31 '
32
33'
3 4'
35'
36'
F i g . 3.2. Contour l i n e s of e q u a l m o i s t u r e i n d e x v a l u e s f o r t h e E q u a t o r i a l Lake P l a t e a u a r e a (WMO, 1974)
64
3.3
NETWORK OF METEOROLOGICAL STATIONS
A d e s c r i p t i o n o f some o f t h e c l i m a t i c f e a t u r e s of t h e N i l e B a s i n a r e a i s
included i n t h e f o l l o w i n g s e c t i o n s of t h i s c h a p t e r . These f e a t u r e s i n c l u d e t h e t e m p e r a t u r e , h u m i d i t y , r a d i a t i o n , s u n s h i n e , c l o u d i n e s s , wind and g e n e r a l c i r c u l a t i o n of t h e a i r m a s s e s . T h i s d e s c r i p t i o n i s b a s e d on t h e d a t a o b s e r v e d a t some, or a l l , of t h e m e t e o r o l o g i c a l s t a t i o n s l i s t e d i n T a b l e 3.1.
TABLE 3.1
D a t a o f some o f t h e m e t e o r o l o g i c a l s t a t i o n s i n t h e N i l e B a s i n ( I r e l a n d , 1948; M i n i s t r y of War and M a r i n e , E g y p t , 1950; WMO, 1974)
Station Sidi Barrani S a 1 um ( Obs e r va t o r y )
Damietta Rosetta Mersa Matruh Edfina Port Said (Airport) Sirw Alexandria Atf Arish Sakha Mansura Damanhur Qurashiya Gemmeiza Tanta Zagazig Benha Delta Barrage C a i r o (Ezbekiya) Giza S u e z ( P o r t Tewfik) Helwan Fayum Siwa Beni Suef Minya ( A i r p o r t ) Hurghada Assiut Qena Qusseir Nag-Hammadi Luxor Dakhla Kharga Esna Deadalus KOQ Ombo Aswan
Country Egypt
Latitude N
31’ 31 31 31 31 31 31 31 31 31 31 31 31 31 30 30 30 30 30 30 30 30 29 29 29 29 29 28 27 27 26 26 26 25 25 25 25 24 24 24
38’ 33 25 24 22 18 17 14 12 11 07 07 03 02 51 48 47 35 28 11 03 02 56 52 18 12 04 05 14
11 10 08 03 39 29 26 18 55 29 02
Longitude E
25O 25 31 30 27 30 32 31 29 30 33 30 31 30 31 31 31 31 31 31 31 31 32 31 30 25 31 30 33 31 32 34 32 32 29 30 32 35 32 32
58’ 11 49 25 14 31 15 39 53 31 46 57 23 28 07 07 00 30 11 08 15 13 33 20 51 29 06 44 51 13 43 18 15 39 00 34 34 52 56 53
Altitude
metres 22 4 3 2 7 3 1 2 32 10 10 6 7 6 8 9 14 13 14 20 20 21 10 116 30 - 15 28 39 3 55 75 7 70 78 122 72 82 4 10 2 111
65
TABLE 3 . 1
(continued)
Station Wadi H a l f a P o r t Sudan Dongola Karima Tokar Atbara Khartoum Kassala J e b e l Aulia Wad-Medani El-Dueim E l Fasher Sennar Geneina E 1-0be i d S i nga Gallabat E l - Nahud El-Roseires Renk Ma1ak a 1 Addis Ababa Raga Gambe i 1a Akobo Wau Jimma Juba Tori t Loka Gulu Moroto Lira But i ab a Soroti Masindi Fort Portal Mubende Namulonge Eldoret K amp a 1a Entebbe Kitale Equator Kisumu Kericho Mbarara Kabale Bukoba Musoma Mwanza
Country
Latitude
__ Sudan
Ethiopia Sudan
Ethiopia Sudan
Uganda
Kenya Uganda Kenya Kenya Uganda Tanzania
21° 19 19 18 18 17 15 15 15 14 14 13 13 13 13 13 12 12 11 11 09 09 08 08 07 07 07 04 04 04 02 02 02 01 01 01 00 00 00 00 00 00 00 00 00 00 00 01 01 01 02
55 37 10 33 26 42 37 28 14 24 00 38 33 29 11 09 58 42 51 45 33 02 28 15 47 42 39 51 25 22 45 33 18 50 43 41 40 35 32 31 20 03 01 S 01 06 21 37 15 20 30 28
Longitude E
Altitude metres
31° 37 30 31 37 33 32 36 32 33 32 25 33 22 30 33 36 28 34 32 31 38 25 34 33 28 36 31 32 30 32 34 32 31 33 31 30 31 32 35 32 32 35
20 13 29 51 44 58 32 24 30 29 30 21 37 27 14 57 10 26 23 47 39 45 41 35 01 01 51 37 33 57 20 36 56 20 37 43 17 22 37 17 36 27 00
125 5 225 250 20 345 380 500 380 405 380 740 4 20 805 565 4 30 760 565 465 380 390 2450 460 450 400 435 1750 460 6 25 965 9 26 1524 1095 621 1127 1146 1539 1542 1148 2084 1230 1146 1896
35 34 35 30 29 31 33 32
33 35 20 39 59 49 48 55
2762 1146 2070 1443 1868 1137 1147 1140
66
The d a t a u s e d , p a r t o f which is i n c l u d e d i n t h e c l i m a t i c t a b l e s a v a i l a b l e i n t h i s book, are e x t r a c t e d from a number o f r e f e r e n c e s . Examples of t h e s e r e f e r e n c e s a r e : t h e p u b l i c a t i o n s o f t h e E a s t A f r i c a n M e t e o r o l o g i c a l Department (E.A.M.D.),
t h e C l i m a t o l o g i c a l Normals f o r E g y p t , t h e C l i m a t e s of A f r i c a and
some volumes o f t h e N i l e B a s i n . Each o f t h e c o u n t r i e s s h a r i n g t h e b a s i n o f t h e N i l e h a s i t s own n a t i o n a l network o f m e t e o r o l o g i c a l s t a t i o n s . However, t h e h y d r o m e t e o r o l o g i c a l p r o j e c t of t h e E q u a t o r i a l Lake a r e a had among i t s o b j e c t i v e s t h e s t r e n g t h e n i n g o f t h e p r e v i o u s l y e x i s t i n g networks i n Uganda, Kenya and T a n z a n i a , and l a t e r i n Rwanda and B u r u n d i . To f u l f i l l t h i s o b j e c t i v e , t w e n t y - f i v e m e t e o r o l o g i c a l s t a t i o n s have been e s t a b l i s h e d and t h i r t y e x i s t i n g s t a t i o n s have a l r e a d y been up-graded by t h e p r o v i s i o n of a d d i t i o n a l i n s t r u m e n t s . Moreover, 200 o r d i n a r y r a i n gauges have been i n s t a l l e d and 2 3 t o t a l i z e r s p l a c e d i n remote p l a c e s and i s l a n d s . F o r t h e e s t i m a t i o n of e v a p o r a t i o n from t h e E q u a t o r i a l L a k e s , a network of s i x s o l a r i m e t r e s f o r r a d i a t i o n measurement, s e v e n s t a t i o n s w i t h wind m a s t s f o r measurement of wind s p e e d , and e i g h t s t a t i o n s f o r t h e measurement of l a k e s u r f a c e water t e m p e r a t u r e , have been i n s t a l l e d . F o r t h e e s t i m a t i o n of e v a p o t r a n s p i r a t i o n ,
a network o f T h o r n t h w a i t e t a n k s
and some s p e c i a l l y s i m e t r e s have b e e n i n s t a l l e d a t a number o f l o c a t i o n s . An a u t o m a t i c w e a t h e r s t a t i o n h a d b e e n e s t a b l i s h e d on t h e Nabiyongo I s l a n d i n Lake V i c t o r i a , w i t h an a u x i l i a r y s t a t i o n a t E n t e b b e . The p r i n c i p a l s t a t i o n a t t h e l a t t e r h a s among i t s equipment t h e R u s s i a n 20 m 2 and GGI 3000 e v a p o r a t i o n pans (WMO, 1 9 7 4 ) . The m a j o r i t y o f t h e m e t e o r o l o g i c a l s t a t i o n s i n Egypt and t h e Sudan a r e s t a t i o n s of t h e s e c o n d o r d e r , where o b s e r v a t i o n s a r e t a k e n e v e r y day a t 0 8 . 0 0 , 1 4 . 0 0 and 20.00 h o u r s s t a n d a r d l o c a l t i m e . A t f i r s t - o r d e r s t a t i o n s , t h e o b s e r v a t i o n s a r e u s u a l l y t a k e n e i g h t t i m e s a day i n t h e s y n o p t i c h o u r s of o b s e r v a t i o n s , and a t t h i r d - o r d e r
s t a t i o n s , o b s e r v a t i o n s a r e taken a t 08.00 hours l o c a l t i m e
only. S c r e e n o b s e r v a t i o n s u s u a l l y c o m p r i s e t h e a i r t e m p e r a t u r e , maximum and minimum t e m p e r a t u r e s , a l l i n d e g r e e s c e n t i g r a d e , t h e b a r o m e t r i c p r e s s u r e i n m i l l i b a r s , t h e h u m i d i t y a s o b t a i n e d from t h e w e t and d r y b u l b t h e r m o m e t e r s , and t h e e v a p o r a t i v e c a p a c i t y of t h e a i r a s measured w i t h a P i c h e e v a p o r i m e t e r .
The
d u r a t i o n o f t h e b r i g h t s u n s h i n e i s measured m o s t l y by a Campbell-Stokes r e c o r d e r . The wind i s e x p r e s s e d by a number on t h e B e a u f o r t S c a l e when t h e wind f o r c e i s e s t i m a t e d , or i n k i l o m e t r e s p e r h o u r when i t s s p e e d i s measured by means o f an anemometer. The s o i l t e m p e r a t u r e i s measured a t a few l o c a t i o n s o n l y , and a t a d e p t h v a r y i n g from 0.60 m t o 2 . 1 0 m , whereas t h e g r a s s minimum t e m p e r a t u r e i s measured a t a h e i g h t o f 0 . 1 0 m above t h e ground l e v e l . The r i v e r and s e a t e m p e r a t u r e s a r e measured a t some s e l e c t e d s i t e s i n Egypt and t h e Sudan
67
The r a i n f a l l i s measured n o t o n l y a t t h e m e t e o r o l o g i c a l s t a t i o n s , b u t a l s o a t many o t h e r l o c a t i o n s . Most of t h e r a i n gauges i n s t a l l e d are c y l i n d e r i c a l i n form w i t h a c a t c h o f 200 c m 2 i n s u r f a c e a r e a and a r i m o f a b o u t 1 . 0 m h e i g h t from t h e ground s u r f a c e . The a n a l y s i s of t h e r a i n f a l l d a t a i s p r e s e n t e d i n Chapter 4 .
3.4
TEMPERATURE The mean d a i l y t e m p e r a t u r e f o r t h e months of t h e y e a r a t a number of s t a t i o n s
i n t h e N i l e B a s i n i s l i s t e d i n T a b l e 3 . 2 . These d a t a a r e b a s e d on t h e d a i l y mean t e m p e r a t u r e which is c a l c u l a t e d on t h e b a s i s of t h e number of o b s e r v a t i o n s taken e v e r y d a y . S o , f o r a l l s t a t i o n s i n Egypt and Sudan o b s e r v i n g t h r i c e d a i l y , t h e mean t e m p e r a t u r e i s o n e - f o u r t h
t h e sum o f t h e t e m p e r a t u r e s a t 0 8 . 0 0 , 1 4 . 0 0 ,
and 20.00 h o u r s p l u s t h e minimum t e m p e r a t u r e . F o r s t a t i o n s o b s e r v i n g t w i c e d a i l y , t h e t e m p e r a t u r e is t h e mean of t h e 0 8 . 0 0 h o u r and 20.00 h o u r o b s e r v a t i o n s , and for s t a t i o n s o b s e r v i n g once d a i l y t h e t e m p e r a t u r e is s i m p l y t h e mean of t h e maximum and minimum t e m p e r a t u r e s . The m e t e o r o l o g i c a l s t a t i o n s i n s t a l l e d by t h e h y d r o m e t e o r o l o g i c a l p r o j e c t i n t h e E q u a t o r i a l Lake P l a t e a u as w e l l a s t h e up-graded are spot-read
s t a t i o n s i n East Africa
v i s u a l l y d u r i n g t h e s y n o p t i c h o u r s : 06.00 Z*,
09.00 Z a n d 1 2 . 0 0 Z .
The mean d a i l y t e m p e r a t u r e shows a d i s t i n c t p a t t e r n c h a r a c t e r i s t i c of each p a r t i n t h e N i l e B a s i n . G e n e r a l l y s p e a k i n g , t h e c o o l e s t month i n Egypt i s January and t h e warmest i s J u l y , e x c e p t a l o n g t h e c o a s t s of t h e M e d i t e r r a n e a n and t h e Red S e a s , where August i s t h e warmest month. F o r t h e g r e a t e r p a r t of t h e Sudan, J a n u a r y i s t h e c o o l e s t month. The month w i t h t h e h i g h e s t mean d a i l y t e m p e r a t u r e changes r a p i d l y w i t h l a t i t u d e from J u l y i n Wadi H a l f a , s i m i l a r t o Egypt, t o May i n Wad Medani, A p r i l i n Malakal and F e b r u a r y i n J u b a down s o u t h . This main c y c l e i s f o l l o w e d , i n many p l a c e s , by a less pronounced c y c l e where t h e second minimum f a l l s i n August and t h e second maximum i n September or O c t o b e r . I n t h e E q u a t o r i a l Lake P l a t e a u t h e wave o f t h e mean d a i l y t e m p e r a t u r e
is q u i t e s i m i l a r t o t h a t i n t h e s o u t h e r n p a r t o f t h e Sudan. The primary maximum o c c u r s i n F e b r u a r y and t h e l o w e s t t e m p e r a t u r e i n J u l y . The s e c o n d a r y maximum t a k e s p l a c e i n O c t o b e r and i s f o l l o w e d by a s e c o n d a r y minimum i n November. The r a t i o of t h e mean d a i l y t e m p e r a t u r e i n t h e warmest month t o t h e mean d a i l y t e m p e r a t u r e i n t h e c o o l e s t month,
(Tmx /? mn ) ,
h a s been computed f o r a l l s t a t i o n s
given i n T a b l e 3 . 1 and p l o t t e d v e r s u s t h e l a t i t u d e ,
4.
Three curves a r e
o b t a i n e d a s shown i n F i g . 3 . 3 . I n t h e v e r y n o r t h e r n l a t i t u d e , a b o u t N 3 Z 0 ,
the
grouping of t h e s t a t i o n s i s n o t c l e a r . South of t h i s l a t i t u d e one c a n e a s i l y = Greenwich M e r i d i a n Time = mean d a i l y t e m p e r a t u r e i n t h e warmest month, and TmX= mean d a i l y t e m p e r a t u r e i n t h e c o o l e s t month mn
*Z
T
= G.M.T.
68
d i s t i n g u i s h o n e c u r v e f o r t h e s t a t i o n s l o c a t e d w e s t of t h e N i l e , a n o t h e r c u r v e
for t h e s t a t i o n s on t h e N i l e and i t s t r i b u t a r i e s and between t h e b r a n c h e s and a t h i r d c u r v e f o r t h o s e s t a t i o n s on t h e Red S e a c o a s t and e a s t o f t h e N i l e .
In
each c a s e t h e c u r v e c o n s i s t s o f a v e r y s h o r t r i s i n g limb f o l l o w e d by a l o n g f a l l i n g t a i l . The peak o c c u r s a t a p p r o x i m a t e l a t i t u d e s o f 28O, 27O and 30° n o r t h f o r t h e t h r e e c u r v e s i n t h e o r d e r d e s c r i b e d a b o v e . The c o r r e s p o n d i n g
(Tmx /? mn )
r a t i o is about 2.65,
2 . 5 and 2 . 0 5 r e s p e c t i v e l y .
The a n n u a l mean d a i l y t e m p e r a t u r e a t t h o s e s t a t i o n s l i s t e d i n T a b l e 3 . 2 have
been used f o r p l o t t i n g t h e mean a n n u a l i s o t h e r m o v e r t h e N i l e B a s i n . The map i n F i g . 3 . 4 . shows t h a t t h e mean of t h e a n n u a l mean d a i l y t e m p e r a t u r e i n c r e a s e s a l m o s t s t e a d i l y from a b o u t 19OC on t h e M e d i t e r r a n e a n S e a c o a s t i n t h e n o r t h t o a l m o s t 29OC i n A t b a r a down s o u t h . A mean t e m p e r a t u r e of 29 t o 29.5OC c o v e r s t h e b e l t from A t b a r a t o Khartoum. S o u t h o f Khartoum t h e t e m p e r a t u r e f a l l s , b u t s l o w l y , t o r e a c h 26OC a l o n g t h e s o u t h e r n f r o n t i e r of t h e Sudan. North-west
of
Lake V i c t o r i a t h e t e m p e r a t u r e d r o p s r a t h e r r a p i d l y t o r e a c h a b o u t 2l0C i n Entebbe and 20°C
i n F o r t P o r t a l . The topography of t h e h i g h l a n d s i n t h e e a s t e r n
p a r t o f t h e N i l e B a s i n c a u s e s t h e c o o l i n g of t h e mean t e m p e r a t u r e
t o about
17OC a s shown i n F i g . 3.4. The mean a n n u a l t e m p e r a t u r e h a s a s m a l l r a n g e of v a r i a t i o n . T h i s r a n g e v a r i e s from a b o u t 3OC i n t h e major p a r t o f t h e E q u a t o r i a l Lake P l a t e a u t o a maximum o f less t h a n 6 O C i n t h e c e n t r a l p l a i n s of t h e Sudan. T h i s narrow r a n g e i s produced by t h e r e l a t i v e l y s m a l l a n n u a l v a r i a t i o n o f radiation.
I n c o n t r a s t , t h e d i u r n a l r a n g e of t e m p e r a t u r e is q u i t e l a r g e . The
f i g u r e s p r e s e n t e d i n T a b l e 3 . 3 show t h e r a n g e t o b e l a r g e s t i n t h e n o r t h e r n p a r t o f t h e Sudan and t h e s o u t h e r n p a r t o f Egypt,
and s m a l l e s t i n t h e
M e d i t e r r a n e a n and Red S e a a r e a s and t h e Lake P l a t e a u a r e a .
TABLE 3 . 2
Mean d a i l y t e m p e r a t u r e a t c e r t a i n s t a t i o n s i n t h e N i l e B a s i n ( d a t a a r e from G r i f f i t h s , 1972; I r e l a n d , 1948; M i n i s t r y o f War and Marine, Egypt, 1950; WMO, 1974)
Mean d a i l y temperature i n
Station Jan.
Feb.
Mar.
Apr.
May
Jun.
Jul.
Aug.
OC
for Sep.
Oct.
Nov .
Dee.
Year
~
S i d i Barrani Salum ( O b s e r v a t o r y ) D ami e t t a Rosetta Mersa Matruh Port Said Alexandria Mansura Damanhur Tanta Zagazig D e l t a Barrage C a i r o (Ezbek i y a ) Giza S u e z ( P o r t Tewfik) Helwan Fay urn Siwa Beni Suef Minya Hurghada Assiut Qena Quss e i r Nag Hammadi Luxor Dakhla Kharga
12.3 11 3 13.2 15.2 12 4 13.7 13.7 13.4 13 6 11.6 11.5 13.0 12.3 11.2 13.8 12.3 11.6 10.7 12.4 12.2 15.8 11.7 13.2 17.8 1 2 .o 13 .O 12.3 13.1
13.2 12.3 14 . O 15.2 12.9 14 . 3 14.1 14 . O 14.2 12.3 12.6 14.0 13.5 12.5 14.6 13.5 13.2 12.6 14.1 14.1 16.2 13.3 15 .O 18.4 12.7 15.4 14.1 14.9
14.2 14.1 15.3 16 , 7 14.5 16.2 15.8 16.2 16.2 14.9 15.2 16 . O 16.3 15.4 17.1 16.4 16 1 15.8 16.9 17.1 18 . 7 17.1 19.4 20.7 16.6 19.4 18.1 19.1
16.6 16.8 18.3 19 . o 17.2 18.7 18.1 19.8 19.4 18.7 18.9 19.8 20 . 2 19.2 20.5 20.4 20.4 20.3 20.2 21.4 22.2 22.2 24.6 23.4 21.5 25 . o 23.4 23.9
19.3 19.4 22.2 22.0 19.9 21.8 2 1 .o 23.8 22.9 22.9 23.0 23.7 24.2 23.3 24.4 24.3 25.1 25.3 23.7 26.1 26.2 26.6 29.8 26.8 27.3 30.2 28.2 29 . o
22.0 22.3 24.2 24 . 5 22 9 24.6 23.6 2fi 3 25 2 25.4 25.7 26.2 26.8 26 . O 26.9 26.6 27.2 27.9 26.6 28 . O 28.5 28.8 31.7 28.9 28.5 31.4 30.4
23.8 24.3 26 . O 26.3 24 7 26.4 25.4 27 . 8 26.4 26.5 26.8 27.7 27.7 26.9 28.4 27.5 28.1 28.9 27.4 29 . O 29.5 29.4 32 .O 29.8 29.1 32.3 30.8
24.5 24.3 26.2 27.2 25.5 26.9 26.2 27 8 26.6 26.4 26.6 27.4 27.6 26.7 28.5 27.4 28.0 28.5 27.6 28.7 30 .O 29.1 32.1 30.3 29 4 32.1 30.5
23.5 23.0 24.6 26.3 24.4 25 . 8 25.3 26.1 25.2 24.4 24.5 25.2 25.3 24.3 26.3 25.4 25.6 26 . O 24.6 26.1 28.0 26.5 29.1 28.7 26.9 29.7 28.1
20.9 21.2 23.2 24.5 22.2 23.9 23.3 24 .o 23.5 22.1 22.4 23.2 22.7 22.0 24 . O 23.3 23.2 22.4 22.6 23.8 25.2 23.8 26 . O 26.7 24.6 26.8 24.9
17.4 17.8 19.8 21.2 18.7 20.4 19.9 2F. 3 19.8 18.3 18.4 19.2 18.7 18 . O 20.0 19 18.7 17.4 18.5 19.2 21.2 18.6 20.3 23.4 19.6 20.5 19.2
13.6 13.4 15.4 17.2 14.4 15.6 15,7 15.4 15.5 13.6 13.4 14.8 14 . O 13.2 15.4 14.1 13.5 12.3 13.5 14 . O 17.7 13.6 15 . O 19.6 14.6 15.1 13.8
18.4 18.4 20.2 21.3 19.1 20.7 2c.2 21.2 20.7 19 . 8 19.9 20.8 20.8 19.9 21.7 20.8 20.9 20.7 20.7 21.6 23.3 21.7 24.0 24.5 21.9 24 , 2 22.8
31.0
31.4
31.1
28.6
26 - 0
20.2
15 . O
23.6
.o
TABLE 3.2
4 0
(continued)
Mean d a i l y temperature i n OC f o r Station
Esna D e a d a l us Kom Ombo Aswan Wadi H a l f a P o r t Sudan Tokar Atbara Khar tourn Kassala W ad-Medani E l -Dueim Fasher Sennar Geneina El-Obeid Singa Gal l a b a t El-Nahud E l Roseires Renk Malakal Addis Ababa Raga Gambei l a Akobo Wau Jimma Juba Tori t
Jan.
Feb.
Mar.
Apr
May
Jun.
Jul.
Aug.
Sep.
Oct.
Nov.
Dec.
Year
13.1 21.8 14.9 15.5 15.9 23.5 24.4 22.2 23.6 25 .O 24.2 23.7 20.6 25 .O 22.4 21.0 25.7 26.0 23.4 26.2 24.7 27 .O 15.6 24.2 27.5 28.4 26.7 19.5 28.8 28.3
14.4 21.5 16.3 17.2 17.5 23.2 24.3 23.4 25 .O 26.1 25.2 25 . O 22.2 26.1 24.5 22.6 26.8 27.5 24.2 27.5 26.5 28.4 16.9 25.8 28.6 29.8 28 . O 20 .o 29.6 28.9
18.5 22.7 20.4 21.3 21.9 24.2 26 . O 26.6 28.2 28.8 28.2 27.8 25.3 29.1 25.8 25.8 29.6 29.4 25.6 29.8 28.1 30.4 18.2 27.4 29.9 30.9 29.5 20.0 29.5 28.8
23.3 24.6 25 . O 26.2 26.7 26.6 28 . O 30.4 31.4 31.6 31.0 30.9 28.4 32.0 29.1 29.3 32.0 30.6 30.4 31.6 31.9 31.0 18.0 28.8 29.4 30.2 29.8 20 .o 28.8 28.1
27.6 27.2 29.6 30.5 30.5 29.4 30.9 33.4 33.6 33.2 32.5 32.1 30.1 32.4 29.6 30.7 32.1 29.7 30.4 31.0 31.2 29.4 18.7 28.0 27.5 28 .O 28.4 19.5 27.4 26.8
29.7 28.3 31.2 32.9 32.2 32.3 33.4 34.8 33.6 32.1 31.9 31.8 30.5 31.2 29.4 30.2 30.3 26.6 30 . O 28.6 29.3 27.4 17.5 26.6 26.2 27.1 27.2 19 .o 26.5 25.9
30.1 29.7 31.4 33.2 32.2 34.5 35 . O 33.6 31.7 29.1 29.1 29.6 28.7 28.4 27.1 28.0 27.8 24.0 27.4 26.8 27.1 26.3 16.5 25.5 25.6 26.1 26.2 18 . O 25.5 24.8
30.1 30.3 31.4 33 . O 32.2 34.8 35.0 32.7 30.6 28.0 27.8 28.4 27 .O 27.4 25.4 27.0 26.8 23.8 26.6 26.4 26.3 26.2 16.1 25 , 2 25.6 26.1 26 . O 18.0 25.6 24.8
27.9 29.1 29.4 30.9 30.5 32.2 33.6 33.6 32.2 29.6 28.9 29.5 28.1 28.2 26.1 27.9 27.6 24.6 27.6 26.9 26.9 27 . O 16.3 25.8 25.9 26.9 26.6 18.5 26.4 25.8
24.2 28 .O 27.2 28.3 28.2 29.4 30.6 31.6 32.1 31.2 30.2 30.8 27.8 29.9 26.1 28.7 29.4 26 . O 28.4 28.0 28.5 27.8 16.5 26.6 26.5 27.4 27.4 18.0 27 .2 26.4
19.1 26.1 21.6 22.6 22.6 27.4 28.0 27.4 28.4 29.4 27.7 28.2 23.8 28.4 24.2 25.3 28.5 26 . O 24.8 27.8 27.3 27.6 15.1 25.3 26.8 28.2 27.5 18 . O 27.7 27 . O
14 .G 23.3 16.8 17.4 17.6 25 .O 25.6 28.2 25 .O 26.2 25.0 24.8 21.1 26 .O 23.2 22.0 26.4 25.6 23.7 26.5 26.5 27 . O 14.8 24.2 27.0 27.8 26.8 18.0 28.1 26.9
22.7 26 .O 24.6 25.8 25.7 28.6 29.6 29.5 29.6 29.2 28.5 28.6 26.1 28.7 26.1 26.6 28.6 26.6 26.9 28.1 27.9 28 . O 16.7 26.1 27.2 28.1 27.5 19 .o 27.6 26.9
TABLE 3.2
(continued)
S t a t ion
Gulu Lira Butiaba Soroti Masindi Fort Portal Entebbe Kisumu Bukoba Mwanza
Mean d a i l y t e m p e r a t u r e i n
OC
for
Jan.
Feb.
Mar.
Apr.
May
Jun.
Jul.
Aug.
Sep.
Oct.
Nov.
Dec.
Year
24.2 24.5 26.1 25.5 23.8 19.9 21.7 25.1 20.2 22.6
24.8 25.1 26.5 25.9 24.1 20.2 21.7 24.3 20.3 22.5
24.5 24.9 26.5 25.7 24.0 20.1 21.8 24.0 20.4 22.2
23.6 23.8 25.9 24.4 23.3 20.0 21.3 23.6 20.3 22.0
22.5 22.9 25.7 23.5 22.9 19.6 21.0 23.2 20.2 22.2
22.2 22.9 25.3 23.1 22.3 19.2 20.8 22.7 20.3 22.0
21.6 21.7 24.8 22.5 21.6 19.0 20.4 22.2 20.2 21.8
21.8 21.9 24.5 22.6 21.5 19.2 20.4 22.6 20.4 22.2
22.3 22.5 25.1 23.3 21.9 19.4 20.8 23.3 20.5 23.0
22.8 22.9 25.5 24.1 22.5 19.0 21.2 23.8 20.6 23.4
23.6 23.3 25.6 24.5 22.9 19.2 21.2 24.6 20.4 23.1
23.4 23.5 25.7 24.7 22.9 19.6 21.3 24.9 20.2 22.8
23.2 23.3 25.6 24.1 22.8 19.5 21.1 23.5 20.4 22.5
72 0
c
a,
.r(
1
o m
a
a,
k
5
Y
fi
;d
C
x
.d
rl
a,
a
o 0
9
9 P Y
a,
9
Y
73
Fig. 3 . 4 .
Map showing t h e mean annual isotherms i n t h e N i l e B a s i n area
4
TABLE 3.3
Mean d a i l y r a n g e of t e m p e r a t u r e a t a number of s t a t i o n s i n t h e N i l e
B a s i n ( I r e l a n d , 1948; M i n i s t r y of War
and M a r i n e , E g y p t , 1950; WMO 1974)
Station
Mean d a i l y r a n g e , i n OC, for Feb
Jan.
.
~
S i d i Barrani S a 1um ( Ob s e r va t o ry ) Damiet t a Rosetta Mersa Matruh Port Said A l e x a n d r ia Mansura Damanhur Tanta Zagazig D e l t a Barrage C a i r o (Ezbekiya) Giza S u e z ( P o r t Tewfik) Helwan Fayum Siwa Beni Suef Minya Hurghada Assiut Qena Qusseir Nag Hammadi Luxor Dakhla Kharga
10.6 9.8 9.8 5.8 9.2 8.2 7.9 12.6 12.1 13.6 14 .O 13.3 12.1 13.8 10.5 10.5 14.6 16.1 14.3 13.8 11.5 14 . O 15.8 8.8 15.0 1S.O 16.7 16.1
10.5 9.9 9.6 6.5 9.1 8.6 8.1 13.1 12.5 14.3 14.3 14.3 13.0 14.9 11 .o
11.5 14.9 16.4 15.4 14.5 12.4 15.3 17.5 8.7 16.8 19.4 17.7 17.1
Mar.
Apr.
__ 10.7 10.2 8.8 6.2 9.0 8.0 8.4 13.7 13.2 15.5 15.2 15.3 13.9 16.1 11.9 12.8 15.6 17.1 16.8 15.8 12.4 16.5 19.1 8.3 17.4 19.7 18.3 17.3
11.0 10.9 8.8 6.5 9.4 7.9 8.5 15.3 14.7 17.2 16.6 17.3 15.2 17.8 13.5 14.4 17.0 17.9 18.1 17.1 12.5 17.0 19.2 7.9 18.5 20.0 19.1 17.9
Jun .
May ~
11.6 9.8 8.8 5.7 8.8 7.9 8.2 15.7 14.8 17.4 16.8 17.6 15.7 17.9 13.9 15 .O 17 .O 18.0 18.2 17.0 12.1 16.6 18.0 7.6 17.5 19.5 18.3 16.8
Jul
.
Aug.
Sep.
Oct.
Nov.
Dec.
Year
8.5 9.7 8.7 4.5 G .6 8.0 6.8 14.0 12.4 15.2 14.8 14.6 13.3 15 .O 13.1 13.5 14.8 17.7 15.1 14.4 10.0 13.8 16.5 7.1 17.7 18.4 15.9 16.6
9.9 9.5 8.6 5.0 7.1 7.8 7.3 13.6 12.6 15.1 14.5 13.5 12.7 14.2 12.2 12.4 14.1 17.3 15.1 13.0 10 .o 12.8 16.1 6.9 14.6 17.8 15.5 15.4
10.4 10.6 8.3 5.8 8.4 7.6 8.2 12.9 13.0 14.7 14.4 13.7 13.0 14.4 11.8 11.7 14.3 17.6 14.7 12.7 11.0 12.1 16.3 7.3 15.3 18.2 16 .O 15.6
10.7 9.4 7.9 5.7 8.4 7.5 8.1 11.8 11.9 13.5 13.4 13.1 12.4 13.7 11.0 10.7 13.8 16.7 14.6 12.8 11.1 13.7 16.5 7.9 16.6 18.3 16.1 15.8
10.5 9.8 9.3 6.2 9.1 8.1 8.0 12.2 11.8 13.1 13.4 13.1 11.8 13.3 10.9 10.2 13.9 16.1 13.8 12.9 11.4 13.7 15.5 8.4 15.8 18.0 16.2 15.8
10.3 10.0 8.8 5.5 8.2 7.9 7.7 13.7 13.0 15.1 14.9 14.9 13.5 15.4 12.3 12.7 15.1 17.2 15.8 14.6 11.3 14.7 17.1 7.7 16.5 18.8 16.9 16.4
~
10.0 10.4 8.3 4.6 7.6 7.8 7.4 15.2 13.9 16.8 16.4 16.9 15.4 17.3 14 .O 14.9 16.3 18.5 17.7 16.3 11 .o 16.7 17.8 7.1 17.1 19.7 16.9 15.9
8.4 10.1 9.0 4.2 6.4 8.1 6.6 14.7 12.7 15.5 15.3 16.2 14.2 16.1 13.6 14.4 15.5 17.6 16.3 15.2 10.4 14.8 16.9 7.2 16.8 18.9 16.1 16.1
P
TABLE 3.3
(continued)
Mean d a i l y r a n g e , i n OC, f o r Station Jan.
Feb.
Mar.
Apr.
May
Jun. ~
Esna Deadalus I s l a n d K o m Ombo Aswan Wadi H a l f a P o r t Sudan Tokar Atbara Kh a r t o um Kassala Wad Medani El Dueim El Fasher Sennar Geneina El -0be i d Singa Gallabat E l -Nahud E l Roseires Renk Malakal Addis Ababa Raga Gambeila Akobo W au Juba Gulu Moro to
16.4 3.8 16.2 13.4 16.2 7.2 8.7 16.3 16.9 18.1 19.8 18.6 21.5 19.8 22.9 18.8 18.8 20 . o 16.9 20.6 19.1 17.5 17.0 22.8 18.6 16.4 18.2 17.2 15.5 15.0
17.1 3.8 17.4 14.3 17.6 8.0 9.2 17.2 17.6 19 .o 20.4 19.6 21.8 20.6 22.6 19.5 19.4 19.1 18.7 20.6 19.0 17.5 17.0 22.4 17.9 15.7 17.2 16.2 15.1 14.8
18.1 4.1 18.9 15.9 18.9 9 .o 10.2 18.1 19.0 19.1 20.8 20.3 22.2 21.2 21.2 19.9 20 .o 18.7 18.3 20 .o 19.5 17.4 16 .O 21.2 17.2 15.2 16.8 15.1 13.6 13.4
18.4 4.4 19.7 16.3 19.5 10.1 11.5 18.7 18.7 18.1 20.3 20.0 21.3 19.9 20.4 18.8 18.8 17.7 17.7 18.4 16.7 15.3 15 . O 16.9 14.8 13.7 14.7 13.6 11.6 12.2
19 .o 4.2 18.7 15.9 18.8 11.3 15.0 16.9 16.7 16 . O 17.4 17.6 18.8 17.3 19.3 16.8 16 .O 15.8 16.2 15.4 14.6 13.1 16 .O 14.4 12.2 11.9 13.2 12.1 10.5 12.1
18.0 4.5 18.7 15.9 18.2 13.2 17.4 16.1 15.0 14.6 15.2 15.4 17.2 15.6 17.3 14.6 14.6 13.7 13.5 13.1 12.3 11.3 13.0 12.9 11.1 11.4 12.1 12.0 10.5 12.3
Jul
.
Aug.
Sep.
Oct.
Nov.
Dec.
Year
16.5 5.1 17.8 14.7 16.8 11.9 13.1 14 .O 12.2 11.3
14.3 4.2 17.5 15.4 16.2 11.4 14.7 14.9 14.2 13.5 13.8 13.6 16 . O 13.7 14.8 13.4 12.9 12.5 12.5 12.6 11.5 10.7 11 .o 12.3 11.6 9.8 12.2 12.8 11.3 14.3
14.5 4.2 17.4 15.2 17.0 9.1 11.3 15.6 16.2 15.4 16.7 16.2 19.1 16.8 20.0 15.8 16.5 16.1 15.1 15.9 15.4 12.3 15 .O 14.0 13.8 11.3 13.5 14.0 12.0 13.6
16.4 4.2 16.3 14.1 16.5 7.4 10.1 15.5 16.3 16.3 18.6 17.3 21.3 18.7 20.5 17.9 18.6 19.5 16.3 17.4 18.3 16.3 18.0 19.6 15.7 13.8 16 .O 15.6 13.2 13.8
15.7 3.7 15.7 13.5 16.3 7 .O 8.9 15.9 16.7 17.3 19.3 17.9 21.8 19.3 22.1 18.8 18.5 10.2 18.2 20.4 18.8 17.7 17 .O 22.3 17.5 15.7 17.9 16.6 14.1 14 .O
16.8 4.3 17.8 15 .O 17.5 9.9 12.1 16.1 16.1 15.9 17.2 16.7 19.0 17.3 18.8 16.5 16.4 16.3 15.4 16.6 15.3 14.1 14.4 16.8 14.2 13.0 14.6 14.0 12.3 13.3
~
17.6 5.1 18.4 14.9 17.9 12.8 15.1 14.1 13.6 12.2 13.0 12.9 14.2 13.1 13 . O 12.1 11.9 11.1 10.8 11.2 10.1 10.8 9 .o 11.2 10.3 10.2 11.0 11.2 9.8 11.6
11.5 11.7 13.1 11.9 11.6 11.3 10.8 11 .o 10.4 11.1 8.9
9.7
9 .o 11.1 10.5 9.8 10 . 9 11.4 10.1 12.1
TABLE 3.3
(continued)
S t a ti o n
Lira Butiaba Mas i n d i F o r t Portal Mubende E l d o r et Entebhe Kitale Kericho Mharara I.:ab a 1e Bukoba Musoma Mwanza
Mean d a i l y r a n g e , i n 'C,
.~
tor
Jan.
Feb.
Mar.
Apr.
lay
Jun.
Jul.
Aug.
Sep.
Oct.
Nov.
Dec.
Year
17.2 7 9 14.2 14.6 10.4 16 0 9 8 10 0 15.2 12.6 14.1 10 7 8.8 8 8
16.5 7.5
14 9 7.2 12 8
12 8 7.3 11.5 11.9 9 .0 13 3 7.8 12.7 1: 8 11 . o 11.5 9 4 9.0 9.2
11.7 7.2 10.7 11.2 8.2 12.9 7.7 12 4 11 8 10.8 11.0 9.1 9.4 9.8
11.5 7.3 11.2 12.1 8.3 13.3 8.3
11.2 7.0 10.6 12.2 8.7 11.7 8.8
12.7
11 4
11.5
10.6 12.1 13.2 10.1 9.9 11.8
11.1 13.1 14.5 10.3 10.2 12.4
11.7 6.5 10.7 11.7 8.9 12.1 8.8 11.2 12.0 12.2 13.6 15.3
13.8 7 3 11.7 12.1 8 8 13 8 9 2 11 1 13 5 11 2 12.9 10.1
14.7 7.4 12.2 11.8 9.1 13.5 8.9 10 7 13 7 11.5 12.5 9.9 8.8 9.2
15.5 7.8 12.9 12.8 9.1 14.0 9 0 10.6 12.5 11.5 13.0 10.3 8.8 8.8
13.7 7.3 12.0 12.6 9.2 13.9 8.9 11 0 12.9 11.8 13.1 10.1 9.3 10 . o
14.1
14.6 10.6
16 8 9 7 10.4 15 4 12 5
13.8 10.5 9.0
9.3
1.3 5 10 0 15 9
8 8
11 5
14 6 1 : 8 13 1 10.3 9.2 9.4
9.5
11.2
7.4 11.3 12.2
a .O
14 .Q 9 4 10 . 7 i2 9 11.6 13 6 10.4 9.4 10.5
__
9.4 9.7
__
3.5
ATMOSPHERIC HUMIDITY The a t m o s p h e r i c h u m i d i t y i n t h e N i l e B a s i n area i s e x p r e s s e d m o s t l y i n terms
of
t h e r e l a t i v e h u m i d i t y . I n E g y p t and t h e S u d a n t h i s m e a s u r e m e n t i s made o n c e
or twice a day, except, of course, a t t h e f i r s t - o r d e r
s t a t i o n s . For s t a t i o n s
o b s e r v i n g t w i c e or more a d a y , t h e mean r e l a t i v e h u m i d i t y is t h e mean o f t h e r e l a t i v e h u m i d i t i e s m e a s u r e d a t 08 00 h o u r s and 20 00 h o u r s , and f o r t h o s e o b s e r v i n g o n c e d a i l y , i t i s s i m p l y t h a t m e a s u r e m e n t made a t 08 00 h o u r s . F o r t h e up-graded s t a t i o n s i n t h e c a t c h m e n t s o f t h e E q u a t o r i a l L a k e s , t h e measurements o f t h e r e l a t i v e h u m i d i t y a r e made a t 0 3 0 0 , 0 6 00 and 1 2 00 Z h o u r s , and t h e o t h e r s a r e a t 0 6 00 a n d 1 2 00 Z h o u r s o n l y . The d e v i a t i o n s from t h e mean d a i l y r e l a t i v e h u m i d i t y a v e r a g e d f o r J a n u a r y , A p r i l , J u l y and O c t o b e r f o r A l . e x a n d r i a , E g y p t , Khartoum a n d t h e S u d a n a r e shown i n F i g s . 3 . 5 ( a ) and 3 . 5 ( b ) r e s p e c t i v e l y . The g r a p h s f o r A l e x a n d r i a , and s i m i l a r l y f o r many s t a t i o n s , show t h a t t h e d a i l y mean is r e a c h e d t w i c e e v e r y d a y ; o n c e b e t w e e n 0 7 30 h o u r s and 10 30 h o u r s ( f o r e noon) and a n o t h e r t i m e b e t w e e n 17 30 h o u r s a n d 22 00 h o u r s ( a f t e r n o o n ) , dependi n g o n t h e l o c a t i o n and month o f t h e y e a r . T h i s i s n e a r l y s o e v e r y w h e r e i n t h e N i l e B a s i n , e x c l u d i n g Khartoum ( F i g . 3 . 5 ( b ) ) . G e n e r a l l y s p e a k i n g , t h e r e f o r e ,
in
t h e a b s e n c e of c o n t i n u o u s , o r f r e q u e n t , m e a s u r e m e n t s o f t h e r e l a t i v e h u m i d i t y , t h e a v e r a g e o f t h e o b s e r v a t i o n s made a t 08 00 h o u r s and 20 00 h o u r s , o r s i m p l y t h e o b s e r v a t i o n a t 08 00 h o u r s w i l l n o t b e t o o f a r f r o m t h e t r u e mean ( O l i v i e r , H.,
1 9 6 1 ) . The mean d a i l y r e l a t i v e h u m i d i t y f o r some s t a t i o n s i n E g y p t ,
the
h u m i d i t y a t 08 00 h o u r s i n t h e S u d a n a n d a t 0 6 00 h o u r s e l s e w h e r e , a r e i n c l u d e d i n Table 3 . 4 , The r e l a t i v e h u m id ity a t noon, H n ,
s e e m s t o bear a c e r t a i n relationship t o
t h e d a i l y mean h u m i d i t y , H m , o r t o t h e h u m i d i t y a t 08 00 h o u r s o r any o t h e r r e f e r e n c e hour'. thru'
T h i s r e l a t i o n s h i p i s shown g r a p h i c a l l y i n F i g s . 3 . 6 ( a ) and
( d ) f o r a number o f c o m b i n a t i o n o f s t a t i o n s f r o m some p a r t s o f t h e N i l e
Basin. Of i n t e r e s t i s F i g . 3 . 6 ( c ) , w h i c h shows two d i s t i n c t r e l a t i . o n s h i p s ; one for s t a t i o n s l o c a t e d a l o n g t h e M e d i t e r r a n e a n S e a c o a s t and t h e S u e z C a n a l , and t h e o t h e r f o r t h o s e s t a t i o n s l o c a t e d a l o n g t h e Red S e a c o a s t . F o r v a l u e s of H t h a n 80%, t h e r e l a t i v e h u m i d i t y a t n o o n , H n ,
less
i s much more f o r t h e s t a t i o n s on
t h e Red S e a t h a n f o r t h e s t a t i o n s o n t h e c o a s t o f t h e M e d i t e r r a n e a n S e a . The p l o t o f t h e HO6 h u m i d i t y v e r s u s t h e H12
r e l a t i v e humidity f o r t h e Equatorial
Lake P l a t e a u a r e a d o e s n o t e x h i b i t a s i n g l e r e l a t i o n s h i p f o r a l l t h e s t a t i o n s i n t h e a r e a . Among t h e f a c t o r s i n f l u e n c i n g t h e r e l a t i o n s h i p
are t h e geographic
l o c a t i o n o f t h e s t a t i o n , t h e a l t i t u d e , a n d t h e d i s t a n c e from t h e s t a t i o n t o t h e n e a r e s t l a k e . The g r a p h i c p l o t f o r t h e s t a t i o n s e a s t and s o u t h - e a s t o f Lake + R e l a t i v e h u m i d i t y a t 06 00 Z h o u r s
78
V i c t o r i a p r e s e n t s a much w i d e r s c a t t e r t h a n d o e s t h e p l o t f o r t h e s t a t i o n s i n and w e s t of t h e same l a k e .
t h e n o r t h , north-west
The t i m e s a r e n o t u n i f o r m a c r o s s t h e N i l e B a s i n a r e a and t h e e a r l y o b s e r v a t i o n o f h u m i d i t y i s t a k e n a t a t i m e when t h e r e l a t i v e h u m i d i t y i s c h a n g i n g r a p i d l y . I n some c a s e s t h i s i s done w i t h o u t h a v i n g a r e a d i l y a v a i l a b l e s l m u l taneous temperature t o s p e c i f y t h e c l i m a t e completely, a s i s t h e c a s e with t h e noon h u m i d i t y . I n t h i s c o n n e c t i o n , G r i f f i t h s ,
F.J.
(1972) recommends t h e u s e
Of
o t h e r p a r a m e t e r s t o d e s c r i b e t h e a t m o s p h e r i c h u m i d i t y a s t h e dew p o i n t or t h e a b s o l u t e h u m i d i t y . T h e s e two p a r a m e t e r s do n o t show t h e l a r g e d i u r n a l f l u c t u a t i o n t y p i c a l of t h e r e l a t i v e humidity c u r v e .
p
10
A
0
0
5
+
0
c
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5
0
€ - 5
-
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2
-10
ul
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-15
.5_
>
0
2
4
8
6
Local
b
n
10
14
12
standard
16
18
22
20
24
t i m e (hours )
Fig. 3.5(a) D e v i a t i o n s from mean d a i l y r e l a t i v e h u m i d i t i e s f o r A l e x a n d r i a , Egypt ( O l i v i e r , H . , 1961)
$ 20 2' 15
-<
l
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:
:
0
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10
1
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/'
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1
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1
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P e r i o d of r e c o r d :
1
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II
1908 - 1911 & 1920 -1921
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5
.-0 > - lo aJ n
- 15 - 20
0
2
4
6
8
10
Local s t a n d a r d
1 2 14 16 18 time (hours)
20
22
24
Fig, 3.5(b) D e v i a t i o n s from mean d a i l y r e l a t i v e h u m i d i t i e s f o r Khartoum, Sudan ( O l i v i e r , H . , 1961)
1
1
1
~
TABLE 3.4
The mean d a i l y r e l a t i v e h u m i d i t y a t a number o f s t a t i o n s i n t h e N i l e B a s i n ( G r i f f i t h s , 1972; I r e l a n d , 1948; M i n i s t r y of War and M a r i n e , E g y p t , 1950; W M O ,
-
Station Jan. Salum ( O b s e r v a t o r y ) Mersa Matruh Edfina Port Said Alexandria Tanta Zagazig C a i r o (Ezbekiya) Giza S u e z ( P o r t Tewfik) Helwan Fayum Siwa M i ny a Assiut Qena Qusseir Nag Hammadi Luxor Dakhla Kharga Esna Deadalus I s l a n d Aswan Wadi H a l f a Merowe Atbara Khartoum
71 76 79 76 69 81 83 74 79 68 61 68 70 64 69 63 56 69 68 51 58 61 68 45 48 31 38 29
Feb
72 73 78 75 68 78 79 68 72 66 56 63 64 58 62 56 54 59 58 47 54 54 70 40 40 26 34 24
1974)
Mean d a i l y r e l a t i v e h u m i d i t y , i n p e r c e n t , f o r
Mar.
Apr.
69 74 74 73 68 76 75 65 67 63 52 58 61 52 54 44 52 48 46 41 46 41 74 32 31 20 27 16
66 72 70 73 69 68 67 58 60 60 45 50 56 43 41 31 52 40 34 35 40 32 70 27 24 14 18 15
May
70 74 68 73 72 61 60 52 53 59 41 42 52 39 36 27 52 38 30 32 38 27 77 27 22 15 19 22
Jun.
Jul.
Aug.
Sep.
Oct.
Nov.
Dec.
Year
67 77 70 75 74 63 62 55 56 61 44 46 53 42 37 28 50 40 32 30 38 25 78 25 21 18 24 34
70 81 73 77 77 70 68 61 62 62 51 51 55 46 42 31 52 44 34 30 38 27 77 26 23 23 32 47
76 80 73 76 75 74 73 65 68 65 54 57 58 51 46 32 51 45 37 33 38 31 76 29 26 22 33 52
74 77 71 73 69 77 78 69 72 67 58 62 60 58 55 44 53 54 46 37 44 42 78 33 30 23 30 46
74 75 74 72 69 79 80 72 73 68 59 64 63 61 62 53 56 58 53 43 48 49 79 35 34 22 28 31
73 75 78 73 70 81 82 74 78 69 62 69 66 65 67 59 58 64 60 47 55 52 73 40 39 24 31 30
70 74 79 76 70 80 83 76 81 68 62 72 70 68 69 63 57 71 66 53 60 59 68 45 42 26 34 29
71 76 74 74 71 74 74 66 68 64 54 58 61 54 53 44 54 52 47 40 46 42 74 34 32 22 29 31
m
0
TABLE 3 . 4
(continued) Mean d a i l y r e l a t i v e h u m i d i t y , i n p e r c e n t , for Station
Gallabatx KassalaX P o r t SudanX E l RoseiresX Wad MedaniX E l ObeidX E l FasherX Malakal Addis AbabaX AkoboX W au Jub a ToritX Mongall a Gulu+ Moroto+ Lira+ Butiaba+ Masindi+ Fort Portal+ Mubende+ Eldoret+ Entebbe K i tale+ Kericho+ Mbarara+ Kab a l e + Bukoba+ Musoma+ Mwanza+ x =
Jan.
Feb.
Mar.
Apr.
45 62 66 41 36 37 35 30 61 43 35 43 39 50 63 57 70 68 73 87 77 62 84 70 66 85 94 85 74 77
43 56 65 34 26 28 28 24 64 43 29 41 45 52 66 55 73 67 73 87 77 58 88 76 70 84 95 86 74 78
36 48 64 27 21 23 24 36 58 45 36 50 53 55 73 62 78 70 75 89 81 62 90 73 78 85 96 86 76 79
38 40 56 31 20 26 21 46 65 63 45 63 67 68 83 72 84 73 80 90 86 73 85 80 85 87 97 88 80
r e ? a t i v e h u m i d i t y a t 0 8 h r 30
-
81
May 53 40 45 48 31 41 31 58 63 75 64 85 73 75 85 75 89 74
81
95
88
76 78 83 83 86 95 85 79 77
Jun.
Jul.
Aug.
Sep.
Oct.
Nov.
Dec.
Year
68 49 37 66 48 56 47 75 76 79 73 77 75
78 66 39 79 67 73 65 84 86 84 78 82 79 84 87 79 90 79 86 90 82 82 91 85 85 79 95 76 70 66
80 72 41 83 77 79 74 87 86 85 80 83 79 83 88 76 89 80 86 90 84 82 92 84 81 80 92 82 69 63
77 65 47 80 70 69 61 85 76 84 76 77 74 81 85 69 86 78 83 90 83 72 88 79 78 82 91 82 70 61
67 48 66 70 50 48 37 80 56 78 71 71 72 78 85 66 82 77 81 89 94 66 85 74 74 84 93 81 69 66
54 52 68 49 36 33 31 63 59 71 55 63 62 73 74 63 79 74 78
49 60 69 42 39 36 34 34 62 58 46 52 53 57 70 62 74 71 77 88 84 67 85 72 75 85 95 83 64 76
57 55 55 54 43 46 41 58 68 67 57 66 64 70 79 68 78 74 79 89 83 71 87 78 78 84 96 83 72 72
81
84 75 87 75 83 88 80 79 87 84 84 82 95 79 73 68
+ = r e l a t i v e h u m i d i t y a t 06 00 2 h o u r s
88 81
67 88 73 72 85 94 82 67 68
81
70
LEGEND
o Sakha 60
50
Qurashiya x Gemrneiza Tanta z Zagazig 3 Cairo I Giza Fayurn +
M Minya r Assiut 1 Qena Y N a g - Harnrnadi A Luxor lsna -0. A s w a n
$ 40 C
I
30
20
10
0
Fig. 3.6(a) The mean d a i l y r e l a t i v e h u m i d i t y , H , v e r s u s t h e r e l a t i v e humid i t y a t n o o n , H n , for t h e i n l a n d s t a t i o n s i n Egyp?.
70
LEGEhD
x Karirna 60
+
0 3
v 50
c
1
A
$40
Y
o
Wadi-Halfa r Atbara A Khatourn 2 Kassala I Wad Medani 3 E l Fasher 0 Geneina M El-Obeid z
Gallabat
E l - Nahud
Renk Malakal Akobo Wau Loca Juba Raga
C
I
30
20
10
0 Fig. 3.6(b) The r e l a t i v e h u m i d i t y a t 08 00 h o u r s , Hg8, v e r s u s t h e r e l a t i v e h u m i d i t y a t noon, H for t h e i n l a n d s t a t i o n s i n t h e u d a n . n'
82
0
co
0
h
0 W
0 ul
0 -3
'10 '
H
0
z
0
-
0
m
o
M
5 m
._1
fi
rl 0
X
.
L >
--..-
s
n L L
n
0 n
n >L<
> >> >< <
0 ID
n
L
0
'10
<
'(
0
0 0
0
N
n
0
OOZ1)u H
NI-
O L
0 In
N
00
L
N L
0
n
0
0
Y.
0
n
0
m
m
o m 0 .d I-'
m
E
L)
k w X
6
83
84
R A D I A T I O N , SUNSHINE AND CLOUDINESS
3.6
A l l a t m o s p h e r i c p r o c e s s e s s u c h as t e m p e r a t u r e , p a t t e r n o f b a r o m e t r i c p r e s s u r e , wind f l o w , r a i n f a l l , h u m i d i t y and e v a p o r a t i o n , a r e i n f l u e n c e d d i r e c t l y o r i n d i r e c t l y by t h e f l u x o f t h e s h o r t wave r a d i a t i o n . U n f o r t u n a t e l y , t h e d e n s i t y of t h e network o f r a d i a t i o n s t a t i o n s i n t h e N i l e B a s i n is s t i l l u n s a t i s f a c t o r y . This is t h e s t a t e of a f f a i r s
i n s p i t e o f t h e network s t r e n g t h e n i n g and t h e
u p d a t i n g o f some o f t h e p r e v i o u s l y e x i s t i n g s t a t i o n s i n t h e c a t c h m e n t s of t h e E q u a t o r i a l L a k e s . Many more s u n s h i n e m e a s u r i n g s t a t i o n s a r e , however, a v a i l a b l e than f o r r a d i a t i o n . The g l o b a l r a d i a t i o n ( s o l a r and s k y ) a t t h e t o p of t h e e a r t h ' s atmosphere depends on t h e g e o g r a p h i c l a t i t u d e and t h e t i m e o f t h e y e a r . T h i s r a d i a t i o n , e x p r e s s e d a s A n g o t ' s v a l u e , c a n b e computed from a s t r o n o m i c a l c o n s i d e r a t i o n s , and i s a v a i l a b l e i n some r e f e r e n c e s i n meteorology i n t a b u l a r or g r a p h i c a l form. The monthly Angots f o r l a t i t u d e s from 30°N up t o 10°S w i t h 10'
latitude inter-
v a l s have b e e n q u o t e d and i n c l u d e d i n T a b l e 3.5 j u s t f o r comparison w i t h t h e a c t u a l g l o b a l r a d i a t i o n a t t h e e a r t h ' s s u r f a c e measured a t some l o c a t i o n s i n t h e N i l e Basin a r e a .
TABLE 3.5
S o l a r r a d i a t i o n a t t h e t o p of t h e atmosphere e x p r e s s e d i n Langleys/day*
Latitude
Jan.
Feb.
Mar.
Apr.
May
Jun.
Jul.
Aug.
Sep.
Oct.
Nov.
Dec.
30°N
520 660 780 885 965
630 750 840 915 960
775 850 900 925 915
895 920 925 900 840
975 960 915 850 755
1000 965 900 820 710
990 960 905 830 730
925 935 915 870 795
820 875 905 905 875
685 785 865 910 935
560 685 800 890 955
490 630 760 875 960
20°N
10°N Equator 10's
The a c t u a l r a d i a t i o n r e c e i v e d on t h e e a r t h ' s s u r f a c e depends mainly on t h e t h e o r e t i c a l r a d i a t i o n , t h e c l o u d i n e s s and t h e a t m o s p h e r i c t u r b i d i t y . The e s t i mate of t h e a c t u a l r a d i a t i o n , R ,
from t h e r e l a t i v e d u r a t i o n of s u n s h i n e , n/N,
was f i r s t s u g g e s t e d by Angstrom, A .
(1924). S i n c e t h e n t h e e x p r e s s i o n i n common
use i s
R = R
A
(a + b
'
n/N)
(3.2)
where RA = t o t a l r a d i a t i o n r e c e i v e d i f t h e atmosphere were p e r f e c t l y t r a n s p a r e n t .
-.
*Langley/day
= 1 gm cal/cm2/day
85
The o v e r a l l r e g r e s s i o n e q u a t i o n d e v e l o p e d by B l a c k , J . , Bonython, C . ,
and
P r e s c o t t , J . ( 1 9 5 4 ) , f o r 3 2 s t a t i o n s s c a t t e r e d o v e r a r a n g e of l a t i t u d e s from about 7OS t o a b o u t 65ON is
R = RA ( 0 . 2 3
+ 0 . 4 8 n/N)
(3.3)
The same a u t h o r s upon g r o u p i n g t h e 32 s t a t i o n s i n t o s e v e n groups found t h a t t h e r e g r e s s i o n c o n s t a n t , a , v a r i e s from 0.19 t o 0 . 4 0 and t h e s l o p e of t h e r e g r e s s i o n l i n e , b , from 0 . 2 7 4 t o 0 . 6 1 3 . D a r l o t and L e C a r p e n t i e r found a and b a t 0 . 1 8 and 0 . 6 2 r e s p e c t i v e l y , whereas t h e d a t a a n a l y z e d by Woodhead f o r 1 5 s t a t i o n s i n E a s t A f r i c a gave 0 . 2 3 f o r a and 0 . 5 3 f o r b . The e q u a t i o n d e v e l o p e d by G l o v e r , J . , and McCulloch, J . S . t h e e f f e c t o f t h e g e o g r a p h i c a l l a t i t u d e of t h e s t a t i o n ,
R = RA ( 0 . 2 9 c o s
4 +
4,
(1958), includes
on i t . I t r e a d s
0 . 5 2 n/N)
(3.4)
For E a s t A f r i c a w e may t a k e N = 1 2 . 1 (maximum e r r o r cos $ = 1 (maximum e r r o r
-
+
-
0 . 6 ) and
c$
= 0 , so
0 . 0 1 5 ) s o t h a t e q . 3 . 4 becomes
R = R A ( 0 . 2 9 + 0 . 0 4 3 n)
For a n n u a l v a l u e s R R = 250
+ 37 n.
A
(3.5) = 850 gm cal/cm2/day
(maximum e r r o r 1 p e r c e n t ) , so t h a t
The g l o b a l r a d i a t i o n a t t h e e a r t h ' s s u r f a c e , R , i s u s u a l l y measured by t h e Gunn-Bellani
i n s t r u m e n t and t h e d u r a t i o n o f t h e s u n s h i n e i s r e c o r d e d by t h e
Campbell-Stokes
s u n s h i n e r e c o r d e r . The d a t a a v a i l a b l e f o r t h e s e two meteoro-
l o g i c p a r a m e t e r s i n t h e N i l e B a s i n a r e a a r e summarized and g i v e n i n T a b l e s 3 . 6 and 3 . 7 r e s p e c t i v e l y . From t h e d a t a i n T a b l e s 3 . 5 and 3 . 6 t h e r a t i o R / R A was computed f o r 14 s t a t i o n s s c a t t e r e d o v e r t h e r a n g e from a b o u t 2OS t o a b o u t 30°N l a t i t u d e . The r e l a t i v e d u r a t i o n o f b r i g h t s u n s h i n e was computed from T a b l e 3 . 7 f o r t h o s e s t a t i o n s h a v i n g N e q u a l t o 12 h o u r s . For t h e r e m a i n i n g s t a t i o n s , n/N was t a k e n d i r e c t l y from l i t e r a t u r e by O l i v i e r , H . The p l o t t e d p o i n t s o f n/N v e r s u s R/RA
(1961) and WMO ( 1 9 7 4 ) .
a r e shown i n F i g . 3 . 7 . I t i s c l e a r
t h a t the s c a t t e r of t h e p o i n t s is s o l a r g e t h a t a s i n g l e r e g r e s s i o n r e l a t i o n between n/N and R / R A
a p p l y i n g t o a l l t h e s t a t i o n s used h e r e w i l l not be s t a t i s -
t i c a l l y j u s t i f i e d . T h i s s c a t t e r i s p a r t l y due t o t h e d i f f e r e n c e i n t h e t i m e p e r i o d and t h e number o f y e a r s each s e t o f p o i n t s b e l o n g i n g t o a s t a t i o n r e p r e s e n t s . Another r e a s o n c o u l d b e t h a t n o t a l l t h e s u n s h i n e d a t a were measured by t h e same i n s t r u m e n t . I f t h e r e i s a n e e d , however, t o l i n k t h e two v a r i a b l e s n/N
TABLE 3.6
The monthly and annual mean s o l a r r a d i a t i o n a t t h e e a r t h ' s s u r f a c e f o r some r a d i a t i o n s t a t i o n s i n t h e N i l e Basin
Average g l o b a l r a d i a t i o n i n cal/cm2 day f o r Station
Tahrir Giza Wadi H a l f a Port Sudan Khartoum Wad-Medani El-Fasher Tozi Malakal Jub a Culu Lira Masindi Kabale Tororo Namulonge Jinja Entebbe Kericho Mbarara Kisumu Bukoba Mwanza
Jan.
Feb.
Mar.
Apr.
May
Jun.
Jul.
Aug.
Sep.
Oct.
Nov.
Dec.
Year
29 3 290 457 354 483 483 457 422 471 458 474 405 39 3 334 456 403 405 474 446 375 490 339 4 33
40 1 375 524 449 557 433 534 474 521 464 468 49 3 423 4 10 50 1 397 450 459 481 408 542 305 502
489 498 588 539 612 576 579 5 16 527 46 2 397 4 37 421 378 473 415 448 445 483 376 462 386 477
568 576 639 6 12 648 602 594 528 536 454 428 459 4 15 35 3 501 423 457 461 470 386 5 10 381 49 1
659 635 667 625 622 584 592 529 5 10 479 4 13 474 400 316 444 405 423 402 397 377 46 3 338 470
684 667 655 577 587 459 550 499 448 459 408 452 376 383 445 408 435 432 437 420 490 403 494
682 663 638 564 571 474 532 466 448 415 378 409 4 15 380 4 26 366 390 39 2 380 411 443 4 27 487
627 610 609 552 56 3 484 534 470 486 466 409 423 4 16 325 409 379 4 19 421 397 418 4 70 448 486
538 533 582 547 56 1 56 2 56 3 504 484 509 46 1 498 444 399 452 4 16 453 433 4 35 444 500 355 492
413 420 525 486 522 533 529 476 487 480 477 528 490 417 483 431 452 445 482 4 16 527 433 496
325 319 46 1 383 488 489 486 415 487 457 486 512 477 347 503 421 447 460 404 404 521 395 445
282 266 426 340 455 466 456 399 476 445 483 485 511 35 1 477 411 432 421 450 4 19 533 386 4 30
497 488 564 502 556 512 534 475 490 46 2 436 464 432 366 464 403 4 34 438 437 404 499 383 475
TABLE 3 . 7
The monthly and annual means of t h e d a i l y s u n s h i n e hours a t c e r t a i n s t a t i o n s i n t h e N i l e Basin ( G r i f f i t h s , 1972; M i n i s t r y of War and Marine, Egypt, 1950; WMO, 1974)
S t a ti o n
Jan.
Feb.
Mar.
Apr.
May
Jun.
Jul.
Aug.
Sep.
Nov
Oct.
.
~
Sallum Mersa Matruh Edfina Port Said Alexandria Tanta Cairo Giza Helwan Wadi H a l f a Karima Atbara Khartoum Kassala P o r t Sudan Wad Medani E l Obeid E l Fasher Malakal Addis Ababa Jimma W au Juba Gulu Soroti Namulonge
7.0 6.5 6.9 6.9 7 .O 7 .O 7.4 7.3 7.6 10.2 9.9 10.1 10.6 10.1 6.9 10.6 10.3 10.3 9.7 8.7 8.0 9.7 9.3 8.9 7.4 6.1
7.5 7.3 7.7 7.3 7.8 7.5 8.1 8.1 8.5 10.4 10.6 10.6 10.7 10.4 8.2 10.6 10.6 10.7 9.3 8.5 6.4 9.3 8.2 8.7 8.4 6 .O
9.0 7.8 8.7 8.6 9 .o 9.2 9.0 8.9 9.4 10.3 10.6 10.5 9.9 10.2 9.1 10.5 9.9 10 .o 9 .o 8.0 6.7 8.4 7.1 8 .O 8 .O 6.1
9.9 10 .o 10.4 9.8 10.6 10.1 10.2 10.2 10.6 10 .o 11.0 12.0 10.4 10.8 10.4 10.8 10.3 10.1 8.3 7.1 6.3 7.6 6.5 7.4 7.5 5.4
9.9 10.7 10.7 10.9 10.9 11.0 10.7 11.o 11.4 11.3 11.4 11.1 10.3 10.5 10.9 10.2 9.8 9.9 7.7 7.0 6.3 8.2 7.8 7.8 7.9 5.7
12.3 11.9 12.2 12.0 11.9 12.2 12.1 12.4 12.8 11.9 10.7 10.4 9.9 10.2 10.3 9.4 8.5 9.2 5.5 5.2 5.1 7.9 7.5 7.7 7.4 5.6
12.7 12.2 12.2 12.2 12.0 12.1 12 .o 12.1 12.6 11.0
11.1 9.9 8.6 8.4 9.9 7.7 7.3 7.7 5.3 2.2 3.4 5.7 5.9 6.2 6.2 5 .O
12.2
11.9 11.9 11.8 11.9 11.6 11.5 11.6 12.1 11.1 9.6 9.5 8.7 8.4 9.6 7.8 6.8 7.4 5.9 2.7 4 .O 6.2 6.9 6.4 6.9 4.9
10.9 10.4 11.o 11.0 11.1 10.7 10.6 10.6 11.1 10 .o 9.6 9.8 10 .o 9.7 10 .o 8.8 8.3 8.6 6 .O 4.6 5.7 7.0 7.5 8.1 7.9 5.2
9.7 8.8 9.5 10.0 9.9 9.4 9.5 9.3 9.8 10.7 10.2 10.2 10.3 10.3 9.9 10 .o 9.3 9.9 7.3 8.6 6.6 7.4 7.6 8.1 8.5 5.4
7.3 8.3 7.9 8.7 8.2 8.0 8.2 8.2 8.6 10.4 10.7 10.3 10.8 10.1 8.3 10.6 10.6 10.9 8.6 8.9 6.2 8.9 7.9 8.2 8.1 5.7
.
Year
6.8 6.6 6.7 6.6 6.7 6.6 6.8 7.2 7.6 9.8 10.5 10.1 10.6 10.0 7.6 10.5 10.5 10.5 10.1 8.6 7.3 9.8 8.1 8.6 8.3 5.7
9.6 9.4 9.7 9.6 9.8 9.6 9.7 9.7 10.2 10.6 10.5 10.4 10.1 9.9 9.3 9.8 9.3 9.6 7.7 6.4 6 .O 8.0 7.5 7.8 7.7 5.5
Dee
__
4 00
m W
TABLE 3.7
( continued)
Station Jan. Kampala Entebbe Eldoret Equator Kericho Kabale Kisumu Mwanza
7.7 7.5 8.9 8.9 8.0 4.8 8.6 7.4
Feb.
7.9 7.2 9.7 9.3 8.1 5.6 8.8 7.7
Mar.
6.6 6.6 8.6 8.6 7.6 5.0 8.5 7.5
Apr.
6.0 6.0 8.1 7.2 5.7 4.3 7.7 8.0
May
6.2 6.2 7.5 7.7 6.4 3.7 7.8 8.2
Jun.
6.3 6.2 7.6 6.7 6.8 5.7 7.5 9.4
Jul.
5.6 6.4 5.9 5.4 5.8 5.5 6.9 9.6
Aug.
5.8 6.3 5.9 5.4 5.6 4.8 6.9 9.0
Sep.
6.1 6.5 7.5 7.4 6.0 5.2 7.6 8.4
Oct. 6.3 6.5 7.8 8.0 5.7 5.1 7.7 7.8
Nov.
6.3 6.6 7.4 7.5 5.6 4.5 7.3 7.0
Dec.
Year
7.1 6.8 8.8 8.3 6.9 4.4 8.2 7.2
6.5 6.6 7.8 7.5 6.5 4.9 7.8 8.1
0.70
0
z
0
z
LEGEND
o Giza 0.65
0.60
A
z Wadi H a l f a v s Port S u d a n 1 o Khartoum y 3 Wad Medani I El- Fasher r + Malakal Juba
.
t
Gulu Namulonge Entebbe Kisumu Kericho Mwanza
-----'::
I Y
z
Y Y
h
0.55
y h'i
6
E
r
3
CK
0.50
O.LE A
0. LC
, 0.45
0.50
I
I
0.55
0.60
I
0.65
nlN
0.70
I
I
I
I
0.75
0.80
0.85
0.90
0.1
Fig. 3.7. The r e l a t i v e d u r a t i o n of b r i g h t s u n s h i n e , n/N, v e r s u s t h e r a t i o of t h e s h o r t wave r a d i a t i o n a t t h e e a r t h ' s s u r f a c e t o t h e s h o r t wave r a d i a t i o n a t t h e t o p boundary o f t h e e a r t h ' s atmosphere f o r 14 s t a t i o n s i n t h e N i l e B a s i n area
OD
W
90 and R/RA f o r t h e whole b a s i n area by a s i n g l e r e g r e s s i o n r e l a t i o n ,
the line
b e s t f i t t e d by e y e w i l l b e t h a t r e p r e s e n t e d by e q . 3.2 ( s e e F i g . 3.7). I n t h e a b s e n c e o f o b s e r v e d s u n s h i n e d a t a , one may t r y t o estimate t h e r a t i o n/N from t h e amount o f s k y c l o u d i n e s s t h a t c o u l d b e a v a i l a b l e a t t h e p l a c e i n q u e s t i o n . The monthly and a n n u a l mean c l o u d i n e s s a t a number o f s t a t i o n s s p r e a d i n t h e N i l e B a s i n a r e a a r e summarized and p r e s e n t e d i n T a b l e 3.8. The monthly v a l u e s , Sc, a r e p l o t t e d v e r s u s t h e c o r r e s p o n d i n g monthly mean r e l a t i v e d u r a t i o n o f t h e b r i g h t s u n s h i n e , n/N,
as shown i n F i g . 3.8. From t h i s f i g u r e i t i s c l e a r
t h a t t h e p o i n t s are so w i d e l y s c a t t e r e d t h a t a f a i r l y a c c u r a t e r e l a t i o n s h i p and n/N f o r a l l s t a t i o n s combined c a n h a r d l y b e d e v e l o p e d . Among t h e
between S
r e a s o n s b e h i n d t h i s w i d e s c a t t e r is t h e i n c o n s i s t e n c y o f t h e s k y c l o u d i n e s s produced by d i f f e r e n c e s i n t h e l e n g t h o f r e c o r d and f r e q u e n c y and p r e c i s i o n w i t h which measurement i s t a k e n . Doorenbos, J . , and P r u i t t , W.O. (1977), s u g g e s t e d t h e u s e o f T a b l e 3.9 as a rough g u i d e f o r c o n v e r t i n g c l o u d i n e s s i n t o e q u i v a l e n t v a l u e s o f n/N. P . (1965), upon i n v e s t i g a t i n g t h e r e l a t i o n s h i p between S
and n/N,
Palayasoot,
suggested t h e
use of t h e e q u a t i o n
n/N = 100 where S
-
1.6 S
-
0.84 Sc2
i s i n t e n t h s on t h e s c a l e 0
-
10.
From t h e d a t a i n c l u d e d i n T a b l e 3.9 and t h e r e s u l t s o b t a i n e d from e q . 3.6, two l i n e s h a v e been drawn, as shown i n F i g . 3.8. The l i n e g i v e n by Doorenbos and P r u i t t i s t h e a p p r o x i m a t e lower e n v e l o p e f o r n e a r l y a l l p l o t t e d p o i n t s , whereas t h e c u r v e d e s c r i b e d by e q . 3.6 forms t h e upper e n v e l o p e o f t h e n/N r a t i o from c l o u d i n e s s from z e r o up t o s l i g h t l y less t h a n 4 o k t a s (1 o k t a = 1 . 2 5 times 1 t e n t h ) . The t h i c k s o l i d l i n e drawn i n F i g . 3 . 8 . a n d which c a n b e d e s c r i b e d by t h e equation 2
n/N = 88
+ 0.43 S
where S
i s i n o k t a s , i s t h e c u r v e f i t t e d by t h e method of l e a s t s q u a r e s t o t h e
- 1 . 1 9 Sc
(3.7)
a n n u a l mean v a l u e s ( n o t shown i n F i g . 3.8.). T h i s c u r v e as judged by e y e seems t o f i t t h e monthly mean v a l u e s w i t h S
above 1 o k t a much b e t t e r t h a n any of t h e
e n v e l o p i n g l i n e s . I n t h e lower h a l f o f t h e g r a p h i t f a l l s i n s i d e t h e band formed by t h e boundary l i n e s , and t h e r e u p o n i t p a s s e s halfway t h r o u g h t h e p l o t t e d p o i n t s . F o r o k t a s more t h a n 4, t h e n/N r a t i o o b t a i n e d from e q . 3.6 i s c l o s e s t t o t h e measurement t h a n t h o s e e s t i m a t e d from t h e o t h e r methods. The m a j o r drawback of e q . 3.6 i s t h a t i t g i v e s f o r S
S
= 8, n/N = 15% i n s t e a d o f 0 % .
= 0 , n/N = 88% i n s t e a d of 100% and f o r
TABLE 3.8
Monthly and a n n u a l mean s k y c l o u d i n e s s a t c e r t a i n s t a t i o n s i n t h e N i l e B a s i n a r e a ( G r i f f i t h s , 1972; M i n i s t r y o f War and Marine, E g y p t , 1 9 5 0 ; WMO,
1974)
Amount of c l o u d i n e s s , i n o k t a s , f o r Station
S i d i Barrani* Sallum ( O b s e r v a t o r y ) D a m i e t taf Rosetta* Mersa Matruh Port Said Alexandria Mansura' Damanhur* Tanta Zagazig D e l t a Barrage* C a i r o (Ezbekiya) Giza S u e z ( P o r t Tewfik) Helwan Fayum Siwa Beni S u e f * Minya Hurghada* A s siut* Qena* Q u s se i r Nag-Hammadi Luxor Dakhla Kharga Esna
* = observed
Jan.
Feb.
Mar.
Apr.
May
Jun.
Jul.
3.4 3.8 3.3 4.0 3.8 3.2 4.1 2.7 3.4 3.3 2.4 2.8 3.2 3.4 2.7 3.2 2.8 1.4 1.2 1.9 1.6 1.3 1.9 1.4 1.6 2.3 1.4 1.2 1.1
3.5 3.8 2.7 3.5 3.4 2.9 3.7 2.4 2.9 3.3 2.3 2.3 2.8 3.1 2.4 2.9 2.5 1.5 1.1 1.8 1.4 1.0 1.5 1.1 0.7 1.8 1.0 0.9 0.9
2.6 3.1 2.9 3.4 2.9 2.7 3.2 2.2 2.6 2.7 1.8 2.1 2.4 2.8 2.0 2.5 2.1 1.0 0.7 1.6 1.3 0.8 1.6 0.9 1.5 1.8 0.9 0.7 0.9
2.7 2.5 2.5 2.7 2.0 2.3 2.6 1.6 2.2 2.2 1.4 1.8 1.8 2.2 1.6 2.2 1.8 0.9 0.9 1.2 0.8 0.7 1.4 0.7 0.8 1.8 0.8 0.6 0.6
2.2 3.3 2.1 2.3 2.2 1.9 2.4 1.5 1.9 2.0 1.0 1.5 1.7 2.2 1.5 1.9 1.9 1.2 0.4 1.4 0.9 0.8 1.5 0.7 0.8 1.5 0.9 0.7 0.6
1.4 1.0 1.1 1.6 1.2 1.1 1.3 1.o 0.9 0.6 0.5 0.9 0.6 0.9 0.4 0.5 0.4 0.3 0.2 0.2 0.1 0.2 0.3 0.1 0 .o 0.2 0.2 0.2 0.0
1.8 0.5 1.4 1.7 1.o 1.2 1.4 1.5 1.3 1.o 0.7 1.6 0.9 1.0 0.3 0.5 0.3 0.1 0.5 0.2 0 .o 0.1 0.2 0 .o 0 .o 0.3 0.1 0 .o 0.1
a t 0 8 00 h o u r s l o c a l t i m e
Aug.
Sep.
Oct.
Nov.
Dec.
Year
1.9
1.1 0.9 2.1 1.1 1.2 0.5 0.6 0.5 0.1 0.3 0.2 0.1 0 .o 0.2 0.1 0 .o 0.2 0 .o 0.0
1.5 1.3 1.7 2.2 1.4 1.5 1.9 0.9 1.1 1.3 0.9 1.7 1.1 1.6 0.6 0.6 0.5 0.2 0.4 0.3 0.2 0.1 0.2 0 .o 0.0 0.2 0.0 0 .o
2.2 2.4 2.1 2.3 2.1 2.0 2.4 1.4 1.6 1.8 1.2 1.8 1.7 2.0 1.3 1.5 1.3 0.6 0.6 1.1 0.7 0.4 0.9 0.6 0.4 1.o 0.3 0.3
2.4 3.8 3.0 3.4 3.4 2.6 3.4 2.4 2.7 2.8 2.0 2.3 2.5 3.0 2.0 2.4 2.3 1.2 0.6 1.7 1.1 0.8 1.4 0.8 0.8 1.2 0.6 0.6
2.8 3.5 3.4 3.7 3.5 3.2 4.1 2.7 3.2 3.4 2.3 2.6 3.0 3.4 2.6 3.1 3.0 1.7 1.2 2.3 1.9 1.3 2.0 1.1 1.6 2.1 1.1 1.0
2.4 2.4 2.3 2.7 2.3 2.2 2.7 1.8 2.1 2.1 1.4 2.0 1.9 2.2 1.5 1.8 1.6 0.8 0.7 1.2 0.8 0.6 1.1 0.6 0.7 1.2 0.6 0.5
0.2
0.1
0.4
0.5
0.9
0.5
0 .6 1.7 2.1 1.2 1.4 1.6 1.3 1.4
W
to
TABLE 3 . 8
(continued)
Station Deadalus I s l a n d Kom Ombo Aswan Wadi H a l f a + P o r t Sudan+ Dongola' Khartoum+ Kassala+ E l Roseires+ Ma1akal' Addis Ababa Wau+ Jimma++ Juba+
Gulu
Entebbe Equator Kisumu Kabale
+
Amount of c l o u d i n e s s , i n o k t a s , f o r Jan.
Feb.
Mar.
Apr.
May
Jun.
Jul.
2.3 1.2 1.2 1 3
2.0 0.8 1
1.7 0.7 0.9 1 2
1.6 0.5 0.9
1.6 0.9 0.8
0.6 0.1 0.2
1
<1
1
<1 1
<1 1
1
1 1 1
<1
1
2 3 1 3 5 4 4 5 6 6 6 6 7
2 2 2 4 5 5 5 6 6 6 7 6 7
2 2 3 5 5 5 4 6 6 6 6 5 7
3 3 4 6 6 5 5 5 6 6 6 5 6
1 1 2 3 2 3 3 5 6 6 5 7
1
3
1
1 3 4 3 3 4 5 6 5 5 7
1
= mean of 06 0 0 , 12 00 and 18 00 h o u r s l o c a l t i m e
++ = mean of 08 00 and 14 00 h o u r s l o c a l t i m e
Aug.
Sep.
Oct.
Nov.
Dec.
Year
0.8
1.0
0.1 0.2
0.1
1.1 0.1 0.2
1.6 0.3 0.4
1
1
1
<1
2.1 0.4 0.9 1
2 1 4 5 5 6 7 6 7 6 6 6 6 5 6
2 2 5 5 5 6 7 6 6 5 6 6 6 5 6
2 1 4 3 4 6 6 6 5 5 6 6 5 5 7
2.5 0.9 1.0 1 2
1.6 0.5 0.7 1 2
0.3
2
<1 2 2 3 5 4 5 3 5 6 6 6 5 7
3 <1
1 1 1 3 2 4 2
5 5 6 6
6 7
<1 1 1 1 2 2 3 2 4 5 6 6 5 7
1 2.3 2 .o 3.0 4.3 4.7 4.5 4.1 4.9 5.7 6 .O 5.9 5.2 6.8
L
\ z 0
. -
\
r s
i v A
L
9
\l"a5
1-4.
,
.,':'.
r
+
'\
LEGEND
o Sallum z Port S a i d + Alexandria x Giza 3 E l Kharga I Port S u d a n Y E l Khartoum
s I
\ x
Kassala Malakal Wau Juba Gulu Entebbe Kisumu
..
\.
045
Fig. 3 . 8 . Basin area
0.50
'.
Y Y
5 I
\.
I
I
I
I
I
I
I
0.55
0.60
0.65
0.70
0.75
0.80
0.85
nlN
'.
'.-.
L 2
0.90
0.95
The amount o f s k y c l o u d i n e s s v e r s u s t h e r e l a t i v e d u r a t i o n of b r i g h t sunshine f o r 14 s t a t i o n s i n t h e N i l e
W W
94
TABLE 3 . 9
Conversion of sky c l o u d i n e s s , Sc, i n t o r e l a t i v e d u r a t i o n of b r i g h t s u n s h i n e , n/N,
S c , o k t a s (0-8) n/N r a t i o S c , t e n t h s (0-10) n/N r a t i o 3.7
as s u g g e s t e d by Doorenbos and P r u i t t (1977)
0
1
2
3
4
5
6
7
8
.95
.85
.75
.65
.55
.45
.30
.15
-
0
1
2
3
4
5
6
7
8
9
10
.95
.85
.80
.75
.65
.55
.50
.40
.30
.15
-
WIND
I n t h i s s e c t i o n w e s h a l l t r y t o draw a s k e t c h f o r t h e s u r f a c e winds blowing i n t h e N i l e B a s i n area. Wind i s u s u a l l y measured a t a b o u t 2 metres from t h e e a r t h ’ s s u r f a c e by means o f a t m o m e t e r s . The wind c h a r a c t e r i s t i c s a t a h e i g h t o f 1 0 metres above t h e s u r f a c e a r e a u t o m a t i c a l l y r e c o r d e d a t a l i m i t e d number o f p l a c e s by means of m e c h a n i c a l r e c o r d i n g anemographs. The wind f o r c e i s g i v e n i n t e r m s of numbers on t h e B e a u f o r t S c a l e when t h e f o r c e i s e s t i m a t e d , o r i n u n i t s of v e l o c i t y as m / s e c o r km/hr,
when t h e v e l o c i t y
is measured by an anemometer. The f r e q u e n c y w i t h which t h i s v e l o c i t y i s measured v a r i e s from o n e c o u n t r y t o a n o t h e r , and f o r t h e same c o u n t r y from one g r o u p of s t a t i o n s t o a n o t h e r . I n Egypt, t h e wind f o r c e i s e s t i m a t e d o n c e a t 0 8 00 h o u r s l o c a ? t i m e , whereas t h e v e l o c i t y measurements are t a k e n a t 0 8 00, 14 00 and 20 00 h o u r s l o c a l t i m e and t h e mean g i v e n . I n t h e Sudan, t h e wind s p e e d and d i r e c t i o n are measured a t 0 7 00 and 1 3 00 h o u r s l o c a l t i m e .
I n east A f r i c a ,
wind measurements a r e t a k e n a t 06 00 Z and 1 2 00 Z ( 0 9 00 and 1 5 00 h o u r s l o c a l t i m e ) . A summary o f t h e wind s p e e d , p r e v a i l i n g d i r e c t i o n and p e r c e n t a g e f r e q u e n c y of calm c o n d i t i o n s i n E g y p t , Sudan and E t h i o p i a , Uganda and Kenya, i s g i v e n i n T a b l e s 3 . 1 0 ( a ) , ( b ) and ( c ) r e s p e c t i v e l y . I n E a s t A f r i c a , t h e v e l o c i t y measured a t a h e i g h t o f 10 metres above t h e s u r f a c e does n o t compare t o t h e f a s t b l o w i n g wind o f t e n n o t e d i n t h e t e m p e r a t e z o n e s . The monthly mean v a l u e h a r d l y r e a c h e s 10 m/sec. The maximum g u s t r e c o r d e d i s a b o u t 30 m/sec a t Kisumu, w h i l e v a l u e s above 18 m/sec are rare and seldom l a s t f o r more t h a n a m i n u t e or two ( G r i f f i t h s , J . F . ,
1971).
The s e a s o n a l v a r i a t i o n i n t h e wind s p e e d i s n o t s t r o n g e v e r y w h e r e . I n t h e h i g h l y e l e v a t e d p l a c e s s u c h as Addis Ababa, Jimma and E q u a t o r , t h e r a t i o of t h e maximum t o t h e minimum monthly mean i s between 2 . 7 t o 1 and 2.0 t o 1. Low elev a t e d s t a t i o n s s u c h a s G u l u , E n t e b b e , Kisumu and Kabale show t h e maximum t o minimum r a t i o of between 1 . 5 t o 1 and 1 . 1 5 t o 1. I n g e n e r a l , t h e wind blows f a s t e r i n t h e e a r l y s p r i n g and i n autumn t h a n i n t h e r e m a i n i n g s e a s o n s o f t h e year.
95
F o r a l l s t a t i o n s i n c l u d e d i n T a b l e 3 . 1 0 ( c ) and f o r o t h e r E a s t A f r i c a n s t a t i o n s which are n o t i n c l u d e d i n t h i s t a b l e , t h e wind v e l o c i t y measured a t
12 00 Z ( s e c o n d measurement) i s more t h a n t h a t measured a t 06 00 Z ( f i r s t measurement). The r a t i o
between t h e s e two measurements v a r i e s from 1 . 0 5 : l f o r
t h e a n n u a l mean a t t h e E q u a t o r t o 2.72 a t K a b a l e . The magnitude o f t h i s r a t i o depends, among o t h e r f a c t o r s , on t h e a l t i t u d e o f t h e p o i n t i n q u e s t i o n and i t s d i s t a n c e t o t h e n e a r e s t l a k e s h o r e . The p r e v a i l i n g wind a l o n g t h e s h o r e of Lake V i c t o r i a c h a n g e s i t s main d i r e c t i o n from s o u t h - e a s t
a t t he southern p a r t of t he
w e s t e r n s h o r e t o s o u t h a t t h e n o r t h e r n p a r t o f t h e same s h o r e , and t o s o u t h - w e s t a t t h e n o r t h e r n p a r t o f t h e e a s t e r n s h o r e . North of Lake V i c t o r i a , t h e d i r e c t i o n of t h e p r e v a i l i n g wind s w i n g s between t h e e a s t and t h e n o r t h . A more d e t a i l e d review o f t h e c h a r a c t e r i s t i c s o f t h e s u r f a c e winds i n t h e E q u a t o r i a l Lake P l a t e a u c a n b e found i n t h e r e p o r t on t h e H y d r o m e t e o r o l o g i c a l Survey o f t h e Catchments o f Lakes V i c t o r i a , Kyoga and A l b e r t ((WMO,
1974).
The wind b l o w i n g on t h e E t h i o p i a n h i g h l a n d s i s c h a r a c t e r i z e d by t h e c o n s i d e r a b l e v a r i a t i o n i n t h e p e r c e n t a g e of calm c o n d i t i o n s d u r i n g t h e y e a r w i t h t h e l o c a l c o n d i t i o n s (compare Addis Ababa t o Jimma, T a b l e 3 . 1 0 ( c ) ) . G e n e r a l l y speaki n g , however, t h e p e r c e n t a g e o f calm c o n d i t i o n i s g r e a t e s t a t t h e e a r l y morning r e a d i n g ( 0 6 00 h o u r s ) . A t Addis Ababa i t r e a c h e s t h e maximum i n May and t h e minimum i n November, b o t h a t t h e e a r l y morning r e a d i n g and i n J u l y and O c t o b e r r e s p e c t i v e l y , b o t h a t t h e midday r e a d i n g . A t Jimma i t i s autumn and w i n t e r which e n j o y t h e g r e a t e s t p e r c e n t a g e of t h e calm c o n d i t i o n . Wind d i r e c t i o n s a r e g e n e r a l l y d o m i n a n t l y e a s t t o s o u t h - e a s t e r l y d u r i n g t h e d r y s e a s o n b u t v e e r around t o w e s t e r l y o r n o r t h - w e s t e r l y
i n t h e rainy season.
The a n n u a l mean v e l o c i t y of t h e s u r f a c e wind o v e r t h e Sudan i s g e n e r a l l y n o t high.
I t i n c r e a s e s s l i g h t l y from Wadi H a l f a t o Khartoum and from t h e r e d e c r e a s e s
r a t h e r r a p i d l y i n t h e d i r e c t i o n t o t h e s o u t h . To t h e e a s t , e x c e p t on t h e Red S e a c o a s t , and t o t h e w e s t ,
t h e wind s p e e d i s , on a v e r a g e , less t h a n a t t h o s e
s t a t i o n s o n , o r n e a r , t h e N i l e and i t s main t r i b u t a r i e s . From t h e d a t a l i s t e d i n T a b l e 3 . 1 0 ( b ) i t i s c l e a r t h a t t h e maximum a v e r a g e speed o c c u r s i n t h e w i n t e r t i m e ,
e x c e p t f o r Wadi H a l f a and K a s s s a l a as i t o c c u r s
i n t h e s p r i n g and summer, r e s p e c t i v e l y . The minimum o c c u r s i n t h e summer everywhere, e x c e p t a t K a s s a l a where l a t e autumn is t h e t i m e o f o c c u r r e n c e of t h e minimum o f t h e a v e r a g e wind s p e e d . The s e a s o n a l e f f e c t i s q u i t e s m a l l , e x c e p t f o r Malakal and K a s s a l a where t h e r a t i o of t h e maximum t o t h e minimum, b o t h a t a v e r a g e s p e e d , i s a b o u t 2.7 o r 2.8 t o 1. The p r e v a i l i n g wind c h a n g e s i t s d i r e c t i o n from n o r t h a t H a l f a t o n o r t h - w e s t a t Dongola and t h e n back t o n o r t h a t Khartoum e x c e p t d u r i n g t h e summer s e a s o n where t h e d i r e c t i o n becomes m o s t l y s o u t h and s o u t h - s o u t h - w e s t . t h e "haboob"
( A r a b i c word meaning " b l o w i n g " ) ,
I n t h i s period
which r e f e r s m o s t l y t o d u s t s t o m
96
or s a n d s t o r m , o c c u r s r a t h e r f r e q u e n t l y . T h i s wind a p p l i e s t o a r a p i d l y - m o v i n g and u n s t a b l e t y p e of a i r mass a s s o c i a t e d w i t h t h u n d e r a c t i v i t y and r e l a t e d t o a d v a n c i n g or e a r l y monsoon. The a v e r a g e number o f d u s t s t o r m s r e a c h e s a maximum around Khartoum w i t h a v e r a g e s 4 , 6 , 4 f o r May, J u n e and J u l y , r e s p e c t i v e l y .
At
A t b a r a t h e maximum o f 5 o c c u r s i n August. Along t h e d i a g o n a l j o i n i n g K a s s a l a and Malakal and on b o t h s i d e s of i t s e x t e n s i o n , i . e . J u b a and Wau, t h e n o r t h - n o r t h - e a s t
wind p r e v a i l s i n t h e w i n t e r
t i m e . D u r i n g t h e s p r i n g , summer and p a r t o f t h e autumn, t h e s o u t h e r l i e s and t h e south-westerlies prevail. The u n u s u a l n a t u r e of t h e d i u r n a l wind v a r i a t i o n , i . e . t h e d e c r e a s e o f t h e wind s p e e d from morning t o midday was i n v e s t i g a t e d by F a r q u h a r s o n , J . S . H e concluded t h a t t h i s t y p e
(1939).
o f v a r i a t i o n i s a c h a r a c t e r i s t i c of t r o p i c a l A f r i c a
and n o t o n l y of C e n t r a l Sudan. I n h i s comment on t h a t work, S u t t o n p r e s e n t e d t h e two maps which a r e shown h e r e i n F i g s .
3 . 9 ( a ) and 3 . 9 ( b ) . T h e s e maps show t h a t
t h e u n u s u a l t y p e o f d i u r n a l v a r i a t i o c o c c u r s i n an e x t e n s i v e a r e a between l a t i t u d e s 20°N and S . W i t h i n t h e s e l a t i t u d e s t h e u s u a l t y p e of d i u r n a l v a r i a t i o n c o v e r s , however, l a r g e r e g i o n s ( S u t t o n , L . J . ,
1 9 3 9 ) . S u t t o n added f u r t h e r t h a t
i n some p a r t s o f t h e Sudan t h e r e are l a r g e s e a s o n a l v a r i a t i o n s . For example, i n t h e n o r t h (Merowe) t h e morning wind i s s t r o n g e r t h a n t h a t i n t h e a f t e r n o o n o n l y from August t o O c t o b e r d u r i n g t h e SW monsoon. I n t h e s o u t h ( M a l a k a l , N a s s e r ) , t h e morning wind i s s t r o n g e r t h a n t h e a f t e r n o o n wind o n l y from December t o March d u r i n g t h e p e r i o d o f NE w i n d s . But i n t h e s o u t h - w e s t ,
Bahr e l Ghazal P r o v i n c e
( A w e i l , Raga, Wau) t h e morning wind i s weaker t h a n t h e a f t e r n o o n wind a l l t h e y e a r r o u n d . The c o n t r a s t i n t h e b e h a v i o u r o f t h e wind i n t h e s e s o u t h and s o u t h -
w e s t r e g i o n s , which form a c o n t i n u o u s p l a i n i n t h e same l a t i t u d e s , d o e s n o t seem a t t r i b u t a b l e t o l o c a l v a r i a t i o n s of t o p o g r a p h y . I n t h e w i n t e r season t h e s t a t i o n s s i t u a t e d along t h e c o a s t of t h e M e d i t e r r a n e a n S e a i n Egypt and t h e s t a t i o n s i n t h e N i l e D e l t a a r e s t r o n g l y a f f e c t e d by t h e s o - c a l l e d M e d i t e r r a n e a n d e p r e s s i o n s . A t S a l l u m , which i s l o c a t e d a t t h e r e a r o f t h e t r a c k o f t h e s e d e p r e s s i o n s , t h e p r e v a i l i n g wind d i r e c t i o n i s
w e s t t o north-west.
Those p l a c e s l o c a t e d i n f r o n t of t h e d e p r e s s i o n s , . l i k e
A l e x a n d r i a and Q u r a s h i y a r e c e i v e s o u t h - w e s t e r l y winds ( s e e T a b l e 3 . 1 0 ( a ) ) . Upper Egypt and t h e n o r t h e r n Red S e a a r e a a r e p r a c t i c a l l y u n a f f e c t e d by t h e M e d i t e r r a n e a n d e p r e s s i o n s and a r e , f o r most o f t h e t i m e , u n d e r t h e e a s t e r n f l a n k o f t h e s u b - t r o p i c a l h i g h p r e s s u r e c e l l t h a t c o v e r s t h e w e s t e r n d e s e r t of Egypt (Stamp, D . L .
and Morgan, W.T.W.,
1 9 7 2 ) . The p r e v a i l i n g winds a r e , t h e r e f o r e ,
n o r t h e r l i e s (see d a t a o f Helwan, Minya and Luxor i n T a b l e 3 . 1 0 ( a ) ) . I n t h e summer s e a s o n t h e n o r t h e r l y winds p r e v a i l o v e r most o f E g y p t . The n o r t h e r n p a r t o f t h e N i l e D e l t a a r e a and w e s t o f i t up t o A l e x a n d r i a a r e an e x c e p t i o n t o t h i s r u l e . The n o r t h - w e s t
d i r e c t i o n usually p r e v a i l s .
97
The d i r e c t i o n o f t h e p r e v a i l i n g wind o v e r Lower Egypt changes i n t h e s p r i n g and autumn t o n o r t h - e a s t
b e c a u s e of t h e p a s s a g e of t h e c e n t r e of t h e Khamasin
d e p r e s s i o n s ( d u s t s t o r m s blowing from t h e w e s t e r n q u a d r a n t and l a s t i n g f i f t y days) s o u t h of t h e M e d i t e r r a n e a n c o a s t l i n e . The mean a n n u a l wind s p e e d d e c r e a s e s a l o n g t h e M e d i t e r r a n e a n c o a s t from w e s t to east.
I t a l s o d e c r e a s e s from n o r t h t o s o u t h . The n o r t h e r n p a r t of t h e Red
Sea c o a s t i s a r e l a t i v e l y windy a r e a . The wind c o n d i t i o n s i n l a n d a r e a d j u s t e d , however, by t h e l o c a l t o p o g r a p h y .
Late w i n t e r and e a r l y s p r i n g a r e t h e s e a s o n s i n which g a l e s and s t r o n g winds t a k e p l a c e i n L o w e r E g y p t . The f r e q u e n c y of t h e s e g a l e s d e c r e a s e s c o n s i d e r a b l y along t h e north-south
d i r e c t i o n . I n g e n e r a l , autumn, e s p e c i a l l y O c t o b e r , i s t h e
t i m e o f l o w e s t wind s p e e d .
TABLE 3.10(a)
Month and Year
Wind s p e e d and d i r e c t i o n a t c e r t a i n s t a t i o n s i n Egypt ( M i n i s t r y of War and Marine, E g y p t , 1950)
Avg. speed, km/hr
Prev. direction
Calm, 96
Sallum (Observatory) January February March April May June July August September October Novemh e r December Year Month and Year January February March April May June July August September October November December Year
19.9 20.4 20.3 20.0 17.1 19.8 24.9 22.6 19.3 16.1 16.6 19.6 19.7
W
Nw N
N NE N N N N N
Nw Nw N
5.5 4.8 5.4 4.6 4.2 3.2 1.3 1.7 2.4 6.7 6.1 4.6 4.2
Avg. speed, km/hr
sw NE NE NE NE N N N N NE NE NE NE
8.8 7.3 5.0 2.5 3.7 2.9 6.2 6.9 12.4 15.7 14.4 13.1 8.2
Calm, %
Avg. speed, km/hr
Port Said (Airport)
15.6 14.2 17.9 15.3 14.3 14.7 14.5 11.8 11.3 11.8 13.7 11.7 13.9
C a i r o (Almaza A i r p o r t )
12.3 11.5 14.2 13.5 13.0 11.3 7.7 8.5 8.7 9 .o 9.8 9.4 10.9
Prev. direction
W
W
N N N N N N N N N W N
8.4 7.8 1.7 2.5 3.2 2.4 1.3 3.2 4.6 5.8 5.3 10.1 4.7
9 .o
Nw Nw N N N
N Nw N
N N N N N
Calm, ~
15.8 16.4 16.3 15.5 14 .O 15.3 16.2 14.9 13.1 11.1 12.0 12.8 14.4
sw Nw NE NE NE Nw
Nw Nw N NE NE
sw Nw
13.1 14.4 17.2 19 .o 20 .o 20.2 18.1 18 .O 19 .o 18.4 15.5 12.6 17.1
N N N N N N
Prev. direction
Calm, %
Qurashiya
11.6 9.0 7.1 4.6 6.1 4.6 1.3 3.8 5.2 9.9 11.5 15.6 7.5
Helwan
26.4 22.6 16.9 14.4 15.6 10.5 11 .o 14.1 15.6 19.3 24.4 30.7 18.5
Avg. speed, km/hr
Alexandria
Giza
7.6 8.6 9.8 9.9 10.5 10.5 9.7 9.6 9.4 8.2 7.4 6.8
Prev. direction
4.9 5.7 5.5 5.9 5.4 5.6 5.4 4 .O 2.9 2.3 3.0 4.2 4.6
sw sw SE SE SE SE Nw
sw Nw
SE
sw sw sw
53.0 45.6 49.5 43.1 49.7 42.6 44.7 57.2 71 .O 76.0 71.3 59.4 55.3
Minya ( A i r p o r t )
N N N
2.5 3.5 2.3 1.2 0.3 0.2 0.2 0.5 0.7 2.7
6.4 6.8 9.4 9.6 10.7 12.7 9.5 7.7 8.3 6.9
N N N N N N N N N
N
23.9 20.8 11.0 13.7 11.1 7.1 16.8 23.2 17.1 23.6
N N N
4.6 3.7 1.9
7.1 5.6 8.4
N N N
27.3 21.5 18.1
Nw
TABLE 3.10(a)
Month
and Year
(continued)
Avg. speed, km/hr
Prev. direction
Calm, %
Avg. speed, km/hr
Qusseir January February March April May June July August September October November December Year
18.0 18 .o 18.0 18.0 18 .o 14.4 14.4 18.0 14.4 18.0 14.4 14.4 16.5
w w N N N N N N N N N/W
w
N
Prev. direction
Calm,
Avg. speed, km/hr
Luxor
4.2 5.3 6.1 9.3 9.4 7.2 10.8 13.2 8.9 7.2 2.8 2.1 7.5
6.8 7.2 7.9 7.2 7.6 7.6 7.2 7.6 6.9 5.8 6.1 6.5 7 .O
N N Nw Nw Nw Nw Nw Nw N N N N N/NW
Prev. direction
Calm, %
Avg. speed, km/hr
Dakhla
28.2 27.6 14.3 14.1 13.9 12.7 13.0 13.2 18.6 19 .o 19.3 27.5 18.5
6.3 5.9 6.8 7.2 6.8 7.2 7.7 7.7 8.1 6.8 5.4 5.9 6.8
Nw Nw Nw Nw Nw Nw
Nw Nw Nw Nw Nw
Nw Nw
Prev. direction
Calm,
%
Aswan
23.8 23 .O 15.7 12.8 10.6 9.4 6.4 6.9 5.8 11.1 16.5 19.8 13.5
7.7 7.7 8.6 8.6 8.1 8.5 7.2 7.2 8.1 7.7 6.8 7.2 7.8
N N N N N N N N N N N N N
48 . O 43.0 36.4 35.9 42.8 36.1 52.3 41.0 29.6 37.9 46 . O 45.6 41.2
W
W
TABLE 3.10(b)
Month
and Year
Wind s p e e d and d i r e c t i o n a t c e r t a i n s t a t i o n s i n t h e Sudan ( G r i f f i t h s , 1972)
Avg. speed,
Prev. direc-
km/hr
tion
Calm,
%
Avg. speed, km/hr
Prevailing direction
07 h r
Wadi H a l f a January February March April May June July August September October November December Year
14 15 16 16 16 15 14 13 14 14 13 11 14
N N N N N N N N N N N N N
13 h r
Calm, %
07 h r
13 h r
percentage frequency of avg. wind s p e e d
1-3
4-7
P o r t Sudan
5 4 3 6 5 6 10 9 4 3 4 6 5
18.5 18.5 16.7 16.7 14.8 13.0 14.7 13.0 13.0 13.0 14.9 16.7 15.3
Nw Nw Nw Nw Nw Nw
sw sw Nw Nw Nw Nw Nw
NE NE NE NE NE NE E E NE NE NE NE NE
Prev. direction
Dongola
2 3 9 15 23 33 30 23 33 6 1 4 15
0 0
0
0 0
1 1 0 0 0
0
0 0
97 96 92 93 94 95 94 94 95 96 94 96 95
2 3 8 5 4 4 4 4 5 4 6 4 5
NE NE NE NE NE NE NE NE NE NE NE NE NE
~
Calm, %
TABLE 3.10(b)
Month and Year
(continued) Avg. speed, km/hr
Prev. direction
Calm, ~
a
Avg. speed, km/hr
Khartoum January February March April May June July August September October November December Year
16 16 15 14 16 14 16 15 11 13 14 16 15
Month and Year January February March Apri 1 May June July August September October November December Year
N N
S
N N N N
1 0 0 1
S
ssw
Jub a
5 5 5 5 5 3 3 3 3 3 3 3 4
"E "E S S
S S S S S
S
S "E S
Calm, 111
b
Avg. speed, km/hr
Kassala
<1 <1 1 1 2 2 1 2 3
N N N S
Prev. direction
36 29 21 17 19 30 31 26 27 23 29 32 27
-
5 5 5 5 5 6 8 6 5 3 3 5 5
"E NNE "E N
S S S S S S
"E "E
-
Prev. direction
Calm, (I
B
Avg. speed, km/hr
Malakal
6 6 6 7 12 9 3 5 9 12 8 7 7
14 14 10 10 10 8 8 5 5 5 8 12 9
N NE
"E N S S S S S
V
V N "E
Prev. direction
Calm, 10
W au
2 5 6 8 4 8 10 13 15 14 9 5 8
5 3 5 5 5 3 3 3 3 3 3 3 4
"E "E V S
S
sw sw sw V V
NNE "E
34 29 28 23 23 28 33 35 35 38 43 34 32
TABLE 3.10(c)
Month and Year
Wind speed and d i r e c t i o n a t c e r t a i n s t a t i o n s i n E t h i o p i a , Kenya and Uganda ( G r i f f i t h s , 1972; WMO, 1974) Avg. speed, km/hr
Prev. direction
06 h r
% 12 h r
Avg. speed,
km/hr
Prev. direct ion
11.1 9.3 11.1 13.0 11.1 9.3 7.4 7.4 9.3 13.0 14.8 13.0 10.9
SSE E E E E
S S S S E
SE E
-
56 51 40 41 64 52 53 51 57 33 29 40 47
Avg. s p e e d , km/hr 09 h r 15 h r
Jimma
Addis Ababa January February March April May June July August September October November December Year
Calm, % 06 h r 12 h r
12 10 11 10 16 23 39 13 21 6 7 8 15
7.4 9.3 7.4 5.6 7.4 5.6 7.4 5.6 3.7 5.6 3.7 6.2
E
SE E E SE SSE SE E
E
SSE E
-
Prev. direction
Calm, %
Gulu
97 92 87 87 88 95 87 83 95 97 96 92
53 42 56 47 49 54 63 54 50 64 76 56
13.0 13.0 13.0 14.8 13.0 11.1 11.1 11.1 11.1 13.0 13.0 13.0 12.5
18.5 18.5 18.5 14.8 14.8 13.0 13.0 13.0 14.8 14.8 14.8 16.7 15.4
N/E N E
S
s s
N N N E E
E
-
0 0
0 0 0 0 1 0 0 0 0 0 0
TABLE 3.10(~)
Month and Year
(continued) Avg. s p e e d , km/hr 09 h r 15 h r
Prev. direction
Calm,
’
Avg. s p e e d , km/hr 09 h r 15 h r
Entebbe January February March April May June July August September October November December Year
7.4 7.4 9.3 11.1 11.1 11.1 11.1 9.3 11.1 9.3 7.4 7.4 9.4
18.5 22.2 22.2 18.5 18.5 22.2 18.5 18.5 18.5 18.5 18.5 16.7 19.3
5.6 3.7 3.7 3.7 5.6 5.6 5.6 5.6 5.6 5.6 5.6 5.6 5.1
13.0 13.0 13.0 13.0 13.0 14.8 14.8 14.8 14.8 14.8 14.8 13.0 13.9
Month and Year January February March April May June July August September October November December Year
Prev. direction
Calm,
’
Avg. s p e e d , km/hr 09 h r 15 h r
Equator
S S S S S S S S
S S S S
s
0 0 0 0 0 0 1 1 0 1 1 1 <1
Kabale NE/SE NE/SE E/SE SE SE SE SE SE SE SE E/SE E/SE
-
1 0 0 0 0 0 0 0 0 0 0 0 0
31.5 29.6 31.5 25.9 20.4 14.8 13.0 13.0 16.7 25.9 33.3 35.2 24.2
27.8 29.6 31.5 27.8 25.9 22.2 18.5 16.7 20.4 24.1 29.6 29.6 25.3
Prev. direction
Calm, %
Kisumu E E E E E E
W W
E E E E
-
0 0 0
0 1 1 4 2 1 0 0
0 1
5.6 5.6 5.6 5.6 5.6 7.4 7.4 7.4 7.4 7.4 5.6 5.6 6.4
22.2 24.1 20.4 18.5 14.8 14.8 14.8 16.7 18.5 18.5 18.5 18.5 18.4
SW SW SW SW SW SW SW SW S SW SW SW SW
1 0 1 1 1 0 1 1 0 0 1 1 1
104
al m
h
m
m
5
c 0 0
m 4J
0
0
c 0 M
c
4J
a
al
0
m 'CI
a
m m k
0
m 3
c
?
m
105
3.8.
CIRCULATION OF A I R MASSES
The g e n e r a l c i r c u l a t i o n o f t h e atmosphere i n A f r i c a i s dominated by two sub-
t r o p i c a l h i g h - p r e s s u r e b e l t s and t h e e q u a t o r i a l low-pressure b e l t between. These b e l t s move northwards i n t h e n o r t h e r n summer, l a g g i n g behind t h e overhead s u n , and southwards i n t h e s o u t h e r n summer. The c i r c u l a t i o n o f t h e a i r masses i n t h e N i l e B a s i n area i s p a r t o f t h e g e n e r a l c i r c u l a t i o n o v e r t h e c o n t i n e n t , modified
by t h e l o c a l c o n d i t i o n s . The two h e m i s p h e r i c a n t i c y c l o n e s which e x t e n d from l a t i t u d e s 30° n o r t h and s o u t h t o t h e E q u a t o r , c o n t r o l t h e wind systems i n t h e e q u a t o r i a l r e g i o n and t h e t r o p i c s . The n o r t h a n d . s o u t h a n t i c y c l o n e s a r e most i n t e n s e d u r i n g t h e n o r t h e r n w i n t e r and summer r e s p e c t i v e l y . The E q u a t o r i a l Lake P l a t e a u is covered by a p a r t of t h e e q u a t o r i a l trough which e x t e n d s o v e r C e n t r a l A f r i c a and where winds a r e g e n e r a l l y l i g h t and variable.
The e a s t e r l i e s , n o r t h - e a s t
and s o u t h - e a s t monsoons, p r e v a i l o v e r t h e
Lake P l a t e a u a r e a . The r e s u l t i n g w e a t h e r p a t t e r n , however, i s s i g n i f i c a n t l y
modified by t h e w e s t e r l i e s . The l a t t e r a r e known t o b e a r a i n - b r i n g i n g a g e n t . The n o r t h - e a s t monsoon o r i g i n a t e s from t h e n o r t h s u b - t r o p i c a l
anticyclone.
I t flows towards lower l a t i t u d e s when t h e s u n i s s o u t h of t h e E q u a t o r , from October t o March. I t i s t h a t segment which o r i g i n a t e s o v e r Saudi Arabia w h i l e t r a v e l l i n g o v e r t h e Red Sea and p a r t o f t h e I n d i a n Ocean t h a t a c q u i r e s some m o i s t u r e as i t goes down t o lower l a t i t u d e s . T h i s a i r mass p r e v a i l s o v e r t h e Lake P l a t e a u . The s o u t h - e a s t monsoon t a k e s p l a c e from A p r i l t o September and o r i g i n a t e s as a n e a s t e r l y wind from t h e s o u t h - t r o p i c a l
a n t i c y c l o n e over t h e south Indian
Ocean. By t h e t i m e t h i s a i r m a s s e n t e r s t h e e a s t e r n s e a b o a r d o f A f r i c a i t already h a s a maritime t r a j e c t o r y . T h e w e s t e r l i e s c o v e r a narrow b e l t s t r e t c h i n g from t h e e q u a t o r i a l r e g i o n s of
South America t o e q u a t o r i a l A f r i c a . They i n t r u d e i n t o t h e c i r c u l a t i o n e s t a b l i s h e d by t h e e a s t e r l i e s and p l a y a r o l e i n t h e change of t h e w e a t h e r p a t t e r n s . The n o r t h - e a s t monsoon c r o s s e s t h e Equator d u r i n g t h e w i n t e r i n t h e n o r t h e r n hemisphere and under t h e i n f l u e n c e o f t h e change i n t h e d i r e c t i o n o f t h e C r i o l i s f o r c e , t h e stream blowing s o u t h o f t h e Equator a p p e a r s a s i f coming from t h e
w e s t . The w e s t e r l y flow i s s u p p o r t e d by t h e p r e s s u r e g r a d i e n t caused by t h e Lake V i c t o r i a low. A segment o f t h e s o u t h - e a s t monsoon mentioned above and which h a s c o n t i n u e d i t s t r a j e c t o r y t o t h e w e s t s p l i t s b e f o r e l e a v i n g t h e w e s t c o a s t and i n v a d e s a narrow b e l t n o r t h o f t h e E q u a t o r . Here t h e s t r e a m moving t o t h e e a s t i s d e f l e c t e d by t h e C r i o l i s f o r c e and caused t o blow o v e r t h e Z a i r e
Basin as a w e s t e r l y wind which t h e n i n t r u d e s i n t h e e s t a b l i s h e d c i r c u l a t i o n . The zone of s e p a r a t i o n of t h e n o r t h e r n from t h e s o u t h e r n h e m i s p h e r i c a i r masses
i s known as t h e i n t e r t r o p i c a l convergence zone, I T C Z . T h i s zone m i g r a t e s i n t h e c o u r s e of t h e y e a r between t h e two t r o p i c s , i . e . between l a t i t u d e 23°30’N and
106
23O3O.S.
The winds are g e n e r a l l y s o u t h - e a s t t o s o u t h from 5's
and n o r t h t o n o r t h - e a s t
t o t h e Equator
from t h e Equator t o 5 O N . T h i s e x t e n t c o v e r s t h e Lake
P l a t e a u and t h e extreme s o u t h o f t h e Sudan. P a r t o f
t h e r a i n f a l l i n g on t h i s
area comes from t h e ITCZ a s i t f o l l o w s t h e p o l a r m i g r a t i o n o f t h e s u n and t h e thereupon l a g g e d monsoons. S i n c e t h e movement and p o s i t i o n o f ITCZ are i n f l u e n c e d by t h e s t r e n g t h o f t h e monsoons, t h e r a i n f a l l t h u s d e r i v e d is v a r i a b l e i n amount and i n t e n s i t y . A d e t a i l e d summary o f t h e work
o f T r e w a r t h a (1962) and Flohn and S t r u n i n g
(1969) c o n c e r n i n g t h e a t m o s p h e r i c c i r c u l a t i o n i n t h e Lake P l a t e a u area a p p e a r s i n t h e r e p o r t o n t h e h y d r o m e t e o r o l o g i c a l s u r v e y o f t h e catchments o f Lake V i c t o r i a , Kyoga and A l b e r t (WMO, 1 9 7 4 ) . I n t h e n o r t h e r n summer (mainly June t o August) a t r o u g h o f l o w p r e s s u r e c o v e r s t h e n o r t h e r n Sudan. An o s c i l l a t o r y b a r o m e t r i c minimum i s l o c a t e d o v e r t h e n o r t h - e a s t Sudan, w h i l e a b a r o m e t r i c maximum (of t h e I n d i a n Ocean a n t i c y c l o n e ) e x t e n d s o v e r t h e g r e a t e r p a r t o f A b y s s i n i a and s o u t h - e a s t Sudan. T h i s maximum s u f f e r s f l u c t u a t i o n s i n i t s s t r e n g t h and northward e x t e n t . The g e n e r a l wind c i r c u l a t i o n meets, t h e r e f o r e , w i t h some d i s t u r b a n c e s . Four t y p e s o f d i s t u r b a n c e s h a v e been d i s t i n g u i s h e d by El-Fandy
( 1 9 4 9 ) . These are:
Sand storms (haboobs) w i t h a m o d i f i c a t i o n o f t h e g e n e r a l c i r c u l a t i o n by t h e o n s e t o f s t r o n g s o u t h e r n l y winds. These storms a r e common o v e r t h e d e s e r t a r e a s o f t h e c e n t r a l and n o r t h e r n Sudan. Marked s t r e n g t h e n i n g and d e e p e n i n g o f t h e w e s t e r l i e s u s u a l l y accompany t h e northward e x t e n s i o n o f t h e b a r o m e t r i c maximum o f t h e s o u t h - e a s t Sudan t o g e t h e r w i t h a northward o s c i l l a t i o n o f I T C Z . The m o d i f i c a t i o n m a n i f e s t s i t s e l f by a rise o f p r e s s u r e and f a l l o f t e m p e r a t u r e i n t h e s o u t h e r n Sudan-Uganda a r e a and s p r e a d s northwards r a p i d l y . Duststorms (haboobs) w i t h "induced c o l d f r o n t s " o r l i n e s q u a l l s set up by thunderstorms. Low-level
t h u n d e r s t o r m s , which a r e formed under f a v o u r a b l e c o n d i t i o n s o f
t e m p e r a t u r e and h u m i d i t y , by d i r e c t c o n v e c t i o n w i t h i n t h e s o u t h t o s o u t h -
east monsoon. These g e n e r a l l y o c c u r when t h e ITCZ is a t i t s f a r t h e s t n o r t h , t h e m o i s t u r e c o n t e n t showing a marked i n c r e a s e w i t h i n t h e lowest layers. High-level
t h u n d e r s t o r m s f o l l o w e d by o u t b r e a k s o f r a i n c o v e r i n g a w i d e
a r e a and p o s s i b l y p e r s i s t i n g f o r about 24 h o u r s i n some p l a c e s . El-Fandy (1948) a l s o found t h a t thundery c o n d i t i o n s i n Egypt o c c u r when t h e Sudan monsoon l o w i n t e n s i f i e s towards t h e n o r t h and s u p p l i e s t h e e a s t e r n M e d i t e r r a n e a n w i t h a warm s o u t h - e a s t e r l y c u r r e n t . Q u i t e o f t e n s h a l l o w d e p r e s s i o n s form o v e r t h e s o u t h - e a s t e r n M e d i t e r r a n e a n , o r t h e a d j a c e n t l a n d a r e a s , a s a r e s u l t o f t h e m e e t i n g o f t h e above c u r r e n t w i t h t h e r e l a t i v e l y c o l d n o r t h -
107
e a s t e r l y a i r o f a n t i c y c l o n i c d i s t r i b u t i o n i n A s i a Minor. I n a few c a s e s o n l y ,
t h e y form o v e r t h e w e s t e r n d e s e r t . Once f u l l y d e v e l o p e d , t h e s e d e p r e s s i o n s move eastwards o r north-eastwards,
while t h e inflow of t h e c o l d a i r i n t h e r e a r gives
thundery showers. Such t h u n d e r s t o r m s a r e s p e c i a l l y marked o v e r t h e sea, S y r i a and I s r a e l . Over Egypt, however, h i g h - l e v e l
i n s t a b i l i t y frequently exists
between t h e w a r m c u r r e n t and t h e c o o l a i r advancing above. Owing t o t h e s t a b i l i t y of t h e s u r f a c e layers, t h i s high-level
i n s t a b i l i t y cannot pass i n t o t h e
thunderstorm s t a g e w i t h o u t s u f f i c i e n t convergence o f damp a i r . With a h i g h d e g r e e o f l a t e n t i n s t a b i l i t y , s e v e r e t h u n d e r s t o r m s are t h e n produced. The above d i s c u s s i o n o f t h e a t m o s p h e r i c c i r c u l a t i o n might h e l p us form an idea about t h e r a i n y seasons i n t h e N i l e Basin a r e a . Generally speaking, t h e r a i n f a l l o v e r t h e E q u a t o r i a l Lake P l a t e a u , t h e extreme s o u t h o f t h e Sudan up t o Juba and t h e E t h i o p i a n Highlands c a n o c c u r i n e v e r y month o f t h e y e a r . Over t h e Sudan, away from t h e Red S e a c o a s t , r a i n f a l l i s e f f e c t i v e l y c o n f i n e d t o a d e f i n i t e s e a s o n . T h i s s e a s o n l a s t s from March t o November a l o n g t h e l i n e c o n n e c t i n g Wau and M a l a k a l . F u r t h e r n o r t h , t h e s e a s o n becomes p r o g r e s s i v e l y s h o r t e r ; from May t o O c t o b e r on t h e l i n e p a s s i n g through Geneina, E l Nahoud, El-Obeid, Khartoum and Kassala, from J u n e t o September a t A t b a r a , and J u l y and August f o r p l a c e s s i t u a t e d more t o t h e n o r t h up t o Wadi H a l f a . The r a i n f a l l on Lower Egypt and t h e M e d i t e r r a n e a n c o a s t c a n o c c u r i n a l l months o f t h e y e a r e x c e p t J u n e , J u l y , and August. The peak r a i n f a l l o v e r t h e E q u a t o r i a l Lake P l a t e a u o c c u r s i n A p r i l w i t h t h e p o s s i b i l i t y o f a less pronounced second peak around November i n some p l a c e s . The r a i n f a l l o v e r t h e E t h i o p i a n P l a t e a u and t h e Sudan shows t h a t J u l y and August a r e t h e months o f peak r a i n . The month of maximum r a i n f a l l o v e r t h e Mediterranean c o a s t and Lower Egypt i s J a n u a r y , and o v e r Middle Egypt, December. Though t h e r a i n f a l l o v e r Upper Egypt i s e x t r e m e l y low, y e t i t s d i s t r i b u t i o n among t h e months of t h e y e a r c l e a r l y shows two marked maxima, one i n October and t h e o t h e r i n May. The d i u r n a l v a r i a t i o n o f t h e i n c i d e n c e of r a i n f a l l on t h e Lake P l a t e a u was i n v e s t i g a t e d and d i s c u s s e d by Thompson, B.W.
(1957). A few o f h i s many funda-
mental f i n d i n g s i s t h a t t h e maximum o f r a i n f a l l i n a day o v e r w e s t e r n Lake V i c t o r i a d u r i n g November t o May, i . e . i n t h e n o r t h - e a s t e r n monsoon, o c c u r s i n t h e e a r l y morning (00
-
06 h o u r s l o c a l time) and o v e r north-western Lake
V i c t o r i a d u r i n g May t o September, i . e . i n t h e s o u t h - e a s t monsoon, i n t h e morning (06
-
1 2 h o u r s l o c a l t i m e ) . The heavy r a i n f a l l s east o f Lake V i c t o r i a o c c u r b e t -
ween 1 2 and 18 h o u r s and o v e r n o r t h - e a s t e r n V i c t o r i a i n t h e l a t e evening (18
-
24 h o u r s ) . T h e r e i s a l a g i n t i m e between t h e i n c i d e n c e o f heavy r a i n s
i n l a n d and o n t h e l a k e . A d e t a i l e d i n v e s t i g a t i o n and d i s c u s s i o n o f t h e d i u r n a l v a r i a t i o n of t h e i n c i d e n c e of monsoon r a i n s o v e r t h e Sudan and of r a i n and
108
t h u n d e r a t A s m a r a and Addis Ababa, E t h i o p i a were g i v e n by P e d g l e y , D . E . , ( i n 1969 a and b , and 1 9 7 1 r e s p e c t i v e l y ) .
A s i m i l a r i n v e s t i g a t i o n on t h e r a i n f a l l o v e r E g y p t , w i t h emphasis on t h e d i u r n a l v a r i a t i o n o f t h e f a l l o n A l e x a n d r i a , P o r t S a i d and C a i r o (Almaza) w a s c a r r i e d o u t and r e p o r t e d by S o l i m a n , K .
(1953).
A summary o f t h e s e r e s u l t s is p r e s e n t e d i n F i g . 3.10. S i n c e J u l y and August are t h e t w o months w i t h t h e m o s t f r e q u e n t o c c u r r e n c e o f r a i n i n t h e Sudan and t h e E t h i o p i a n P l a t e a u , t h e r e s u l t s o b t a i n e d by P e d g l e y h a v e b e e n a v e r a g e d o v e r J u l y and A u g u s t . The r e s u l t s o b t a i n e d by Soliman f o r Egypt have b e e n l e f t as t h e y a r e f o r t h e whole d u r a t i o n of t h e r a i n y s e a s o n . The p a t t e r n s o f d i u r n a l v a r i a t i o n may b e grouped under f o u r t y p e s w i t h t h e following c h a r a c t e r i s t i c s : R a i n f a l l r e a s o n a b l y u n i f o r m l y d i s t r i b u t e d t h r o u g h o u t t h e d a y , w i t h a weak
(i)
maximum i n t h e a f t e r n o o n o r e a r l y e v e n i n g . T h i s is t h e case a t J u b a , M a l a k a l , E l O b e i d , Addis Ababa, e t c . (ii)
S i m i l a r t o ( i ) e x c e p t t h a t t h e weak maximum t a k e s p l a c e d u r i n g t h e e a r l y morning. T h i s p a t t e r n c a n b e found a t K o s t i and T o z i i n t h e Sudan and a t Alexandria i n Egypt.
(iii)
A w e l l - d e f i n e d peaked d i s t r i b u t i o n where t h e peak t a k e s p l a c e i n t h e l a t e a f t e r n o o n or e a r l y e v e n i n g . Examples of t h i s p a t t e r n c a n b e found a t Wadi H a l f a , Abu Hamed, P o r t Sudan, G e n e i n a , e t c .
(iv)
A w e l l - d e f i n e d peaked d i s t r i b u t i o n where t h e peak t a k e s p l a c e d u r i n g t h e l a t e e v e n i n g or e a r l y morning and w i t h i n f r e q u e n t r a i n s d u r i n g t h e m i d d l e o f t h e d a y . T h i s i s t h e case a t Wad Medani and El-Khartoum.
P e d g l e y c o n c l u d e d t h a t t h e d i s t r i b u t i o n of t h e f o u r t y p e s o f s t a t i o n s forms a d e f i n i t e p a t t e r n o v e r t h e Sudan. Type ( i i i ) i s t o b e found i n t h e m i d d l e of t h e c o u n t r y , between t h e e x t e n s i v e h i g h l a n d m a s s i f o f E t h i o p i a and t h e smaller Marra Mountains which a r e s i t u a t e d w e s t o f E l - F a s h e r .
Except f o r E l - F a s h e r
and Geneinq
t h e r e m a i n i n g s t a t i o n s o f t y p e s ( i ) and ( i v ) l i e w i t h i n 700 km o f t h e E t h i o p i a n H i g h l a n d s . On t h e d i u r n a l v a r i a t i o n o f p r e c i p i t a t i o n i n E g y p t , g e n e r a l l y speaki n g , t h e m a r i t i m e t y p e h a s i t s maximum i n t h e e a r l y morning o r d u r i n g t h e n i g h t , and t h e c o n t i n e n t a l t y p e , which h a s i t s maximum i n t h e a f t e r n o o n .
109
i
.
;
> L L
i
i N
k
r
i
:!
a
:i
W
S
a
i
d
2oBldl h ,r;
c .- 0 -; 0 # #
z
6 12 18 24
0 6
0
12 18 24
6 12 18 24
Time, hr.
E l - Fasher
30
4 0 r ~ b uH a m a d
Halfa
Port Sudan
30
20
10 0
0 6 12 18 24
O
r
0
10
10 0
10
0
6 12 18 2 4
0 6
.-c 10 L
6 12 18 24
0
6 12 18 24
20
10
10
10
0
0 6 12 18 2 4
0
-
0
Kassala
30
20
0 6 12 18 24
0
0 6
0 6 12 18 24
6 12 18 2 4
Addis Ababa
10
m
0 6 12 18 24
0
0
6 12 18 24
10
0 6 12 18 2 4
7zl 0 0 6 12 18 2 4
0
0
12 18 24
D B L2l Kosti
0
Atbara
20
i 10 0
0
Ge nei n a
30
- 'go 0
12 18 24
20b
0 6 12 18 24
0
0
Tozi
6
12 18 2 4
2Ob Malakal
2 0 b Juba
l0 o0 6
l0 o0
12 18 24
6 12 18 2 4
Time, hr
Fig. 3.10. Diurnal variation of rainfall incidence over the Sudan and Ethiopiq average of July and August, and over Egypt average for rainy season
110
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The e m p i r i c a l r e l a t i o n between s o l a r r a d i a t i o n and h o u r s o f s u n s h i n e . Q u a r t . J o u r n . Roy. Meteo. S O C . , 8 4 : 172-175. G r i f f i t h s , J . F . , 1971: E a s t A f r i c a : I t s p e o p l e s and r e s o u r c e s . C h a p t e r 9 : C l i m a t e , 107-118, e d i t e d by W.T. Morgan, Oxford U n i v e r s i t y P r e s s , N a i r o b i , London, New York. G r i f f i t h s , J . F . , 1972: C l i m a t e s o f A f r i c a , C h a p t e r 1 0 : World Survey o f C l i m a t o l o g y , e d i t e d by J . F . G r i f f i t h s , E l s e v . Pub. C o . , Amsterdam, N e w York. H u r s t , H . E . , and P h i l i p s , P . , 1 9 3 1 . The N i l e B a s i n , V o l . I , G e n e r a l d e s c r i p t i o n of t h e b a s i n , m e t e o r o l o g y and topography o f t h e White Nile B a s i n , P h y s i c a l Department P a p e r 2 6 , Government P r e s s . C a i r o , 128 p p . I r e l a n d , A . W . , 1948. 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D i u r n a l v a r i a t i o n of t h e i n c i d e n c e o f monsoon r a i n f a l l o v e r t h e Sudan, I . Q u a r t . J o u r n . Roy. Meteo. S O C . , 9 8 : 97-107. P e d g l e y , D . E . , 1969b. D i u r n a l v a r i a t i o n of t h e i n c i d e n c e o f monsoon r a i n f a l l o v e r t h e Sudan, 11. Q u a r t . J o u r n . Roy. Meteo. S O C . , 9 8 : 129-134. P e d g l e y , D . E . , 1971. D i u r n a l i n c i d e n c e o f r a i n and t h u n d e r a t Asmara and Addis Ababa, E t h i o p i a . Q u a r t . J o u r n . Roy. Meteo. S O C . , 100: 66-71. S o l i m a n , H . K . , 1953. R a i n f a l l o v e r E g y p t . Q u a r t . J o u r n . Roy. Meteo. S O C . , 79: 389-397. S o l i m a n , H . K . , 1 9 7 2 . C l i m a t e s of A f r i c a , t h e climate o f t h e U n i t e d Arab R e p u b l i c ( E g y p t ) , C h a p t e r 3: The n o r t h e r n d e s e r t , e d i t e d by J . F . G r i f f i t h s , E l s e v . Pub. C o . , Amsterdam, N e w York. Stamp, D . L . and Morgan, W.T., 1 9 7 2 . A f r i c a : A s t u d y i n t r o p i c a l d e v e l o p m e n t , 3rd e d i t i o n , John Wiley and S o n s , I n c . , New York, London, 520 p p . S u t t o n , L . J . , 1939. D i s c u s s i o n o f t h e p a p e r : The d i u r n a l v a r i a t i o n o f wind o v e r t r o p i c a l A f r i c a . Q u a r t . J o u r n . Roy. Meteo. S O C . , 6 5 : 181-182.
111
Thompson, B . W . , 1957. The d i u r n a l v a r i a t i o n o f p r e c i p i t a t i o n i n B r i t i s h East A f r i c a . Techn. M e m o r . 8 , E a s t A f r i c a n Meteo. D e p t . , N a i r o b i . T r e w a r t h a , G . T . , 1962. The e a r t h ' s problem c l i m a t e s , Univ. o f Wisconsin P r e s s , Madison, and Methuen 81 Co. L t d . , London, 334 p p . Wickens, G . , 1975. Changes i n t h e c l i m a t e and v e g e t a t i o n of t h e Sudan s i n c e 20 000 BP. P r o c e e d i n g s 8 t h P l e n a r y s e s s i o n AETFAT. Geneva, 1974, B o i s s i e r a 2 4 . WMO, 1974. H y d r o m e t e o r o l o g i c a l s u r v e y of t h e c a t c h m e n t s o f Lakes V i c t o r i a , Kyoga and A l b e r t , Vol. I : Meteorology and h y d r o l o g y of t h e b a s i n , Geneva.
113
Chapter 4 ANALYSIS OF RAINFALL ON THE NILE BASIN
4.1
NETWORK OF R A I N - G A U G I N G STATIONS AND MEASUREMENT OF RAINFALL
Measurement o f r a i n f a l l on t h e N i l e B a s i n commenced a b o u t t h e b e g i n n i n g o f t h e c e n t u r y a t a few p l a c e s o n l y . I n 1924, i t was r e p o r t e d t h a t a few r e c o r d s from E a s t A f r i c a were a v a i l a b l e f o r t h e y e a r s p r e v i o u s t o 1900 ( B r o o k s , C . E . , 1 9 2 4 ) . The t o t a l number of r a i n - g a u g i n g
s t a t i o n s i n East A f r i c a (Uganda, Kenya
and T a n z a n i a ) w a s e s t i m a t e d i n 1960 a t a b o u t 850 ( J o h n s o n , D . H . , number o f r a i n - g a u g i n g
1 9 6 2 ) . The
s t a t i o n s t h a t e x i s t e d up t o 1969, p r i o r t o t h e hydro-
m e t e o r o l o g i c a l s u r v e y o f t h e c a t c h m e n t s of Lakes V i c t o r i a , Kyoga and A l b e r t was estimated a t 721. The number of s t a t i o n s whose r e c o r d s are i n c l u d e d i n Supplements I t h r u ' V I pf t h e N i l e B a s i n Volume V I i s nuch less t h a n t h e above f i g u r e s . A s u r v e y of t h e number of t h e r a i n - g a u g i n g
s t a t i o n s o b s e r v e d i n t h e p e r i o d from 1938 up t o and
i n c l u d i n g 1967 is g i v e n i n T a b l e 4 . 1 . The g e o g r a p h i c c o - o r d i n a t e s ,
a l t i t u d e and
a n n u a l r a i n f a l l d e p t h a t e a c h s t a t i o n are t a b u l a t e d i n Apgendix A l , whereas t h e l o c a t i o n o f e a c h r a i n - g a u g i n g s t a t i o n i s shown on t h e map i n c l u d e d i n Appendix A2. I t i s u n f o r t u n a t e t h a t up t o t h e t i n e o f w r i t i n g t h i s c h a p t e r , none of t h e S u p p l e m e n t s V I I o r V I I I , which a r e supposed t o i n c l u d e t h e r a i n f a l l d a t a f o r t h e p e r i o d s 1968-72 and 1973-77 r e s p e c t i v e l y , h a s y e t a p p e a r e d , making i t i m p o s s i b l e t o i n c l u d e them i n t h e a n a l y s i s p r e s e n t e d h e r e . I t i s q u i t e s t a r t l i n g t h a t whereas t h e number of s t a t i o n s i n t h e f i r s t 5-year
s e c t i o n o f t h e s p a n o f r e c o r d was 337, i t f e l l t o 250 s t a t i o n s ( a b o u t 74%) i n t h e l a s t 5 - y e a r s e c t i o n of t h e a v a i l a b l e r e c o r d . The m i l i t a r y o p e r a t i o n s which t o o k p l a c e i n E g y p t , t h e Sudan and e a s t o f t h e M e d i t e r r a n e a n d u r i n g t h e Second World War, t h e w a r s between Egypt and I s r a e l i n 1947-48,
1956, 1967 and 1973 and
t h e r e b e l s and f i g h t s i n t h e s o u t h e r n Sudan, E t h i o p i a and Uganda, a l l have a f f e c t e d t h e o p e r a t i o n of some o f t h e r a i n - g a u g i n g s t a t i o n s h e r e and t h e r e i n one way o r a n o t h e r . The r a i n gauge i n u s e i n Egypt and t h e Sudan i s made o f s h e e t z i n c i n t h e form o f a c y l i n d e r 45 c m i n h e i g h t . I t c o n s i s t s o f an u p p e r p a r t which h a s a s h a r p r i m and f u n n e l f o r c o l l e c t i n g t h e r a i n , and a lower p a r t t o h o l d t h e v e s s e l which i s t o c o n t a i n t h e r a i n . The r i m i s made of a b r a s s r i n g o f which t h e u p p e r edge i s b e v e l l e d . The r i n g i s 1 5 . 9 c m i n d i a m e t e r . The c a t c h t h u s h a s a n a r e a o f 200 c m 2 . The z i n c gauge is s u p p o r t e d on a wooden or a n i r o n p o s t . The d e t a i l s of t h i s gauge a r e shown i n F i g . 4 . 1 .
114
TABLE 4 . 1
Number o f r a i n - g a u g i n g s t a t i o n s whose r e c o r d s are a v a i l a b l e i n t h e Supplements of V o l . V I o f t h e N i l e B a s i n ( H u r s t , H . E .
e t a l , 1950,
1955 and 1 9 5 7 ; N i l e C o n t r o l S t a f f , 1963, 1969 and 1972) Number o f s t a t i o n s r e c o r d e d i n t h e p e r i o d
Country 1938-42
1943-47
1948-52
1953-57
1958-62
1963-67
1938-67*
Egypt
62
64
59
69
67
65
65
Sudan
97
86
80
77
77
76
77
02
01
01
01
01
01
01
108
98
94
95
79
64
64
Kenya
43
42
36
31
29
25
25
Tanzania
25
25
25
25
21
18
18
337
316
295
298
274
249
250
Ethiopia Uganda
Total
*Period o f o b s e r v a t i o n t a k e n f o r t h e a n a l y s i s of r a i n f a l l d a t a One of t h e items i n c l u d e d i n t h e p r o j e c t o f t h e h y d r o m e t e o r o l o g i c a l Survey of t h e Catchments of Lakes V i c t o r i a , Kyoga and A l b e r t was t o improve t h e network d e n s i t y i n t h e s e c a t c h m e n t s . T h i s was done by i n s t a l l i n g a n a d d i t i o n a l 200 o r d i n a r y r a i n gauges i n t h e p r o j e c t l a n d area and 1 3 a u t o m a t i c Rimco-type r e c o r d i n g r a i n gauges i n Lake V i c t o r i a . Manually r e a d r a i n gauges w e r e i n s t a l l e d i n s i d e t h e Lake V i c t o r i a i n some o f t h e a c c e s s i b l e and i n h a b i t e d i s l a n d s . D e t a i l s a b o u t t h e network o f o r d i n a r y r a i n gauges b e f o r e and d u r i n g t h e p r o j e c t , i n 1971, a r e p r e s e n t e d i n Table 4 . 2 . (WMO,
I n p a r t I of V o .
I of t he p r o j e c t r epor t
1 9 7 4 ) , i t w a s c o n c l u d e d t h a t t h e a l r e a d y a c h i e v e d network d e n s i t y o f about
396 km2 p e r s t a t i o n f o r t h e l a n d a r e a c a n b e c o n s i d e r e d a s q u i t e s a t i s f a c t o r y J f o r t h e purpose of w a t e r balance s t u d i e s . R a i n f a l l observations a r e gener al l y made w i t h s t a n d a r d 5-inch
r a i n gauges, t h e s t a n d a r d exposure being with t h e r i m
o f t h e gauge a t 1 2 i n c h e s above t h e g r o u n d . The r a i n gauge i s p l a c e d i n s i d e a 5 - m e t r e s q u a r e l o t i n which g r a s s i s p e r i o d i c a l l y c u t low t o ground l e v e l . R a i n f a l l i s g e n e r a l l y measured a t 09 h o u r s E a s t A f r i c a n S t a n d a r d T i m e (06GMT) f o r t h e 24 h o u r s e n d i n g a t 09 h o u r s on t h e day of o b s e r v a t i o n and e n t e r e d agaiml t h e p r e v i o u s d a t e p r i o r t o t h e d a t e o f o b s e r v a t i o n . The Rimco r e c o r d i n g gauge works on t h e t i l t i n g - b u c k e t p r i n c i p l e and i t c a n o p e r a t e u n a t t e n d e d f o r s i x months. The a n n u a l r a i n f a l l d e p t h s i n t h e p e r i o d from 1938 up t o and i n c l u d i n g 1967 f o r 250 s t a t i o n s a r e g i v e n i n Appendix A1.As
h a s a l r e a d y been m e n t i o n e d ,
t h e s e d a t a a r e a v a i l a b l e i n V o l . V I o f t h e N i l e B a s i n , Supplements I t h r u ' VI ( H u r s t e t a l , 1950, 1955 and 1957 and t h e N i l e C o n t r o l S t a f f , 1 9 6 0 , 1969 and 1 9 7 2 ) . A l o o k a t t h e s e d a t a w i l l show t h a t n o t e v e r y s t a t i o n h a s a c o m p l e t e
115
I
Brass
N.B.
- The gauge c o n s i s t s of t h r e e main p a r t s shown s e p a r a t e d i n t h e drawing. A l l dimensions a r e i n millimetres
Fig. 4 . 1 . The normal type r a i n gauge i n u s e i n Egypt and t h e Sudan (Hurst, H . E . , and B l a c k , R . P . , 1950)
116
TABLE 4.2
Network of o r d i n a r y r a i n gauges i n t h e c a t c h m e n t s o f Lakes V i c t o r i a , Kyoga and A l b e r t (WMO, 1974)
Name
Area km2
Density E x i s t i n g No. D e n s i t y Network i n a r e a of r a i n i n area S t n s . total per stn. gauging s t n s . p e r s t n . added i n 1971 (1971) (pre-pro j e c t ) km2 km2
Lake A l b e r t Semiliki Muzizi Nkus i Kyoga N i l e from Masindi East Albert Shore
1 3 3 11 6
800 800 500 100 100
1 6 6 24 19
1 800 633 583 462 321
Lake Kyoga Kafu Mayanja Kyoga S o u t h S h o r e Victoria N i l e (Jinja) Mpologoma Malaba S a l i s b u r y Basin Kyoga North S h o r e
16 4 3 14 24 13
700 200 500 100 000 000
32 20 18 52 36 21
522 210 194 27 1 666 619
Lake V i c t o r i a Sio Nzoia Yala Ny ando Sondu Guch a-Mi g o r i Kavirondo Gulf Mara Kenya Mara T a n z a n i a Mori T a n z a n i a Suguti Ruwana-Gurumet i Mbalagati Simiyu Duma Magogo Moame Isanga V i c t o r i a South Shore Kagera T a n z a n i a Kagera Uganda R u i z i Kibale Katonga V i c t o r i a North S h o r e Mara T o t a l Kagera i n Tanz/Uganda
1 12 3 3 3 6 5 7 5 1 1 11 3 10 3 4 21 21 4 8 14 5 13 26
450 400 500 600 600 600 500 800 200 600 100 150 350 800 300 700 500 500 500 400 700 300 000 000
9 85 26 45 19 25 30 9 3 3 2 3
866 146 135 80 189 264 183 866 1 733 533 550 3 716
9 5 4 26 39 11 18 29 23 12 50
1 200 660 1 175 827 577 409 466 506 230 1083 520
V i c t . Is. S t n s . & Lake Uganda Kenya Tanzania
Total
-
-
7
70 260
-
333 610
721
5 466
2 2 2 4 8 10
-
9 3
-
1 8 8 26 23
1 800 475 437 396 265
40 30 18 52 45 24
417 200 194 27 1 544 542
2 1 3 3 1 1 4 0 3 3 4 11 10 2 2 6 3 6 12
9 85 26 45 19 27 31 12 6 4 3 7 0 12 8 8 37 49 13 20 35 26 18 62
9 2 10
16 2 15
120
841
-
-
866 146 135 80 189 244 1.77 600 867 400 366 1 010 670 900 412 470 581 425 423 442 420 203
396
117
r e c o r d c o v e r i n g t h e e n t i r e p e r i o d u s e d . A s a m a t t e r of f a c t , a b o u t o n e - t h i r d of t h e s t a t i o n s h a s a r e c o r d o f less t h a n 90% o f t h e whole p e r i o d , and a b o u t 5% of t h e s t a t i o n s h a v e r e c o r d s c o v e r i n g less t h a n 60% of t h e same p e r i o d . The f r e quency of t h e l e n g t h o f r e c o r d i n y e a r s f o r t h e d i f f e r e n t s t a t i o n s i s i l l u s t r a t e d by t h e h i s t o g r a m i n F i g . 4 . 2 .
The s e r i a l number, name, g e o g r a p h i c co-
o r d i n a t e s and a l t i t u d e o f e a c h r a i n f a l l s t a t i o n i s i n c l u d e d i n t h e t a b l e s , Appendix A l .
In o r d e r t o e n a b l e t h e a n a l y s i s of t h e a n n u a l r a i n f a l l t o c o v e r a s many of t h e l o c a t i o n s i n t h e N i l e B a s i n as p o s s i b l e , t h e m i s s i n g d a t a f o r 110 s t a t i o n s , from s e r i a l number 9 7 up t o and i n c l u d i n g s e r i a l number 206, h a v e been s u p p l e mented. The m a j o r i t y of t h e s e s t a t i o n s e n j o y s a r e a s o n a b l y l o n g r e c o r d ( s e e Fig. 4.2.),
and e a c h i s s u r r o u n d e d by s t a t i o n s w i t h more y e a r s o f o b s e r v a t i o n ,
which makes i n t e r p o l a t i o n p o s s i b l e . To supplement t h e m i s s i n g d a t a a t t h o s e s t a t i o n s i n Uganda,
t h e a d j a c e n t r a i n f a l l s t a t i o n s w i t h l o n g r e c o r d s , even t h o s e
situated outside the N i l e Basin, e . g .
i n t h e Congo, have been u s e d . The r a i n f a l l
s t a t i o n s w i t h a s e r i a l number less t h a n 9 7 are l o c a t e d i n Egypt and t h e n o r t h e r n p a r t o f t h e Sudan where t h e a n n u a l r a i n f a l l d e p t h i s s m a l l . Supplementing t h e m i s s i n g r a i n f a l l f o r t h i s g r o u p of s t a t i o n s was f e l t u n n e c e s s a r y . A comp u t e r programme f o r s u p p l e m e n t i n g t h e m i s s i n g v a l u e s by means o f i n t e r p o l a t i o n based on t h e s q u a r e d i n v e r s e o f t h e d i s t a n c e s t o nearby s t a t i o n s and a d j u s t e d f o r d i f f e r e n c e s i n a l t i t u d e h a s been d e v e l o p e d and a p p l i e d h e r e . Supplementing t h e m i s s i n g d a t a b r i n g t h e p e r c e n t a g e of r a i n - g a u g i n g
s t a t i o n s w i t h 30 y e a r s of
r e c o r d t o a b o u t 70 and of t h o s e w i t h more t h a n 27 y e a r s of r e c o r d (90% of t h e f u l l l e n g t h o f r e c o r d ) to 91 o f t h e t o t a l number of s t a t i o n s . The completed r a i n f a l l d a t a o f s t a t i o n s 9 7 t o 206 a r e i n c l u d e d i n Appendix B . These d a t a have been employed c o n j u n c t i v e l y w i t h t h e d a t a i n Supplements I t h r u ' V I o f t h e N i l e B a s i n V o l . V I f o r p r e p a r i n g t h e monthly r a i n f a l l and i t s p e r c e n t a g e t o t h e annual r a i n d e p t h f o r a l l s t a t i o n s . The r e s u l t s a r e g i v e n i n Appendix C .
180 F160 .O 140 c 0120 100 r
-
Stations f r o m
S t a t i o n s f r o m 97 t o 206
80 -
-
&60 n E, 40 z 20 0 6
-- - -1
-
10
1 to 250
I 12
14
16 Length
-~----
18 20 22 24 of record, yr.
-___-_ 26
28
30
Fig. 4 . 2 . Frequency h i s t o g r a m s f o r t h e l e n g t h o f r a i n f a l l r e c o r d a t s r a t i o n s from 1 t o 250 and from 9 7 t o 206
118
4.2
RAINFALL VARIATION
%a1
4.2.1
rainfall
The b a s i c s t a t i s t i c a l d e s c r i p t o r s o f t h e a n n u a l r a i n f a l l have b e e n computed f o r t h e 250 s t a t i o n s and t h e r e s u l t s o b t a i n e d are l i s t e d i n T a b l e 4 . 3 . These d e s c r i p t o r s a r e t h e a r i t h m e t i c mean,
2,
c i e n t s o f v a r i a t i o n , C v , skewness, Cs,
the standard deviation, s , the coeffiand k u r t o s i s , Ck,
and t h e f i r s t f i v e
s e r i a l c o r r e l a t i o n c o e f f i c i e n t s r, t h r u ' r 5 . The s e r i a l c o e f f i c i e n t s have been computed o n l y f o r t h e s t a t i o n s h a v i n g u n i n t e r r u p t e d r e c o r d s o f a minimum o f 27 years. I t may b e w o r t h w h i l e m e n t i o n i n g t h a t t h e a n a l y s i s o f t h e v a r i a t i o n of r a i n -
f a l l o n t h e c a t c h m e n t s of Lakes V i c t o r i a , Kyoga and A l b e r t (WMO, 1 9 7 4 ) , comp r i s e d 22 s t a t i o n s , 19 o f which a r e i n c l u d e d h e r e . The e a r l i e s t y e a r s o f measurement a t any o f t h e s e s t a t i o n s i s 1926 and t h e l a s t i s 1970. E a r l i e r o b s e r v a t i o n s a t some s t a t i o n s i n Uganda and T a n z a n i a were a n a l y z e d and d i s cussed (Brooks, C . E . ,
1 9 2 4 ) . Moreover, t h e r a i n f a l l d a t a up t o 1940 a t a number
o f g a u g i n g s t a t i o n s i n t h e Sudan w e r e a n a l y z e d and t h e r e s u l t s r e p o r t e d by Ireland, A.W.
( 1 9 4 8 ) . The s t a t i o n s e r i a l number and t h e p e r i o d o f o b s e r v a t i o n
a p p e a r i n g i n t h o s e works a r e summarized i n T a b l e 4 . 4 . I n t h i s s e c t i o n w e s h a l l p r e s e n t t h e methods and e q u a t i o n s which were used t o g e t t h e r e s u l t s i n c l u d e d i n Tables 4 . 3 . Denote t h e a n n u a l r a i n f a l l by X . by n . The a r i t h m e t i c mean,
?,
( i = 1, 2 ,
....,
n) and t h e y e a r s o f r e c o r d
i s t h e r e f o r e g i v e n by t h e e q u a t i o n
x- = -1 c" x j
(4.1)
i=l
t h e s t a n d a r d d e v i a t i o n , s , and t h e c o e f f i c i e n t s of v a r i a t i o n , C v ,
skew, C s ,
and
k u r t o s i s , C k , by t h e e q u a t i o n s
-
c (Xi E l 2 i=l n - 1
s =
cv
:
- _ -
X
n
cs
=
1 c n .
-
(Xi - 3 3 1=1
(4.4)
.3
(4.5) respectively.
119
The r e s u l t s o b t a i n e d from e q u a t i o n s 4 . 4 and 4 . 5 . h a v e b e e n c o r r e c t e d for t h e n2 n3 b i a s by m u l t i p l y i n g them by (n-1) (n-2) and (n-l) (n-2) (n-3) r e s p e c t i v e l y (Haan, C.T., 1977). The s e r i a l c o r r e l a t i o n c o e f f i c i e n t , r L , c o r r e s p o n d i n g t o any l a g , L ,
(L = 1, 2 ,
......,
i=n-L
z
r
L
=
4
-
(Xi
i=l
?) h a s b e e n computed u s i n g t h e f o r m u l a
-
5 (4.6)
i =n
c
(Xi
i=l
-
X)2
The 95% c o n f i d e n c e l i m i t s f o r rL c a n b e computed from t h e e q u a t i o n
-
1 5 1.96 ( n (n
-
L
-
L
- 2)'
1
(4.7)
1)
The mean a n n u a l r a i n f a l l l i s t e d i n T a b l e 4 . 3 h a s b e e n u s e d f o r c o n s t r u c t i n g t h e i s o h y e t a l map, F i g . 4 . 3 . T h i s map compares f a i r l y w e l l w i t h t h e map i n F i g . 4 . 4 . , which i s a v a i l a b l e i n Supplement V I , V o l . V I of t h e N i l e B a s i n ( N i l e C o n t r o l S t a f f , 1 9 7 2 ) . Both g i v e t h e a n n u a l p r e c i p i t a t i o n s l i g h t l y less t h a n t h a t i n t h e map g i v e n i n t h e Water R e s o u r c e s o f t h e E a r t h (UNESCO, 1 9 7 8 ) , which i s shown i n F i g . 4 . 5 . F u r t h e r m o r e , t o g e t an i d e a a b o u t t h e p o s s i b l e change i n t h e mean a n n u a l
2
r a i n f a l l w i t h t h e t i m e and number of y e a r s of r e c o r d , t h e v a l u e s of t h e mean
i n T a b l e 4 . 3 f o r t h e 3 0 - y e a r p e r i o d 1938-1967 have b e e n p l o t t e d v e r s u s t h e mean
?'
a v a i l a b l e f o r t h e s t a t i o n s l i s t e d i n Table 4 . 4 . This p l o t , t o g e t h e r with t h e
line
%
=
? I ,
i s shown g r a p h i c a l l y i n F i g . 4 . 6 . I t i s q u i t e p o s s i b l e t h a t t h e
p o s i t i o n o f t h e y e a r s o f r e c o r d on t h e t i m e s c a l e p l a y s a r o l e i n t h e v a l u e o f t h e mean a n n u a l r a i n f a l l . However, i t i s c l e a r from t h e i n f o r m a t i o n i n T a b l e 4 . 4 and t h e p l o t i n F i g . 4 . 6 . ,
t h a t t h o s e s t a t i o n s w i t h l e n g t h o f r e c o r d of 25 y e a r s
and more g i v e a l m o s t t h e same mean r e g a r d l e s s o f t h e i r p o s i t i o n s on t h e t i m e s c a l e . S t a t i o n s w i t h f e w e r y e a r s of r e c o r d s u c h a s 1 4 2 , 232, 202,
...
show a
c o n s i d e r a b l e d e v i a t i o n from t h e 1 : l l i n e . A p i c t u r e of t h e geographic d i s t r i b u t i o n of t h e c o e f f i c i e n t of v a r i a t i o n ,
cV'
of t h e a n n u a l r a i n f a l l c a n b e s e e n from F i g . 4.7., where i t c a n b e immediately noticed t h a t C
V
e x e r c i s e s a s t e e p r i s e from less t h a n 0 . 4 a l o n g t h e M e d i t e r -
ranean C o a s t t o a b o u t 4 . 0 i n s o u t h e r n Egypt and around t h e o a s e s i n t h e Western D e s e r t , T h i s i s q u i t e u n d e r s t a n d a b l e a s t h e mean r a i n f a l l t h e r e i s e x t r e m e l y low and o c c a s i o n a l l y comes a y e a r w i t h r e l a t i v e l y i n t e n s i v e r a i n f a l l , t h e r e b y p r o d u c i n g a c o n s i d e r a b l e v a r i a t i o n . The g r a d u a l improvement of t h e mean d e p t h of annual r a i n f a l l , i n a s o u t h e r l y d i r e c t i o n , r e s u l t s i n a r a p i d r e d u c t i o n i n C
V'
so t h a t a v a l u e a s low a s 0 . 4 i s r e a c h e d around Khartoum. F u r t h e r i n c r e a s e i n
120
t h e a n n u a l r a i n f a l l and i t s u n i f o r m i t y w i t h t i m e b r i n g s C
up t o 0 . 2 a l o n g t h e
f r i n g e s o f s o u t h e r n Sudan. Lower v a l u e s c a n b e found i n some p a r t s of t h e E q u a t o r i a l Lakes P l a t e a u . A g r a p h i c a l p l o t o f t h e c o e f f i c i e n t o f v a r i a t i o n v e r s u s t h e mean of t h e a n n u a l r a i n f a l l f o r t h e 250 g a u g i n g s t a t i o n s i n t h e N i l e B a s i n shows a c e r t a i n amount o f s c a t t e r . N e v e r t h e l e s s , t h e d e c l i n e i n C
with increasing
x is
defini-
t e l y u n m i s t a k a b l e . T h i s c a n b e c l e a r l y s e e n from F i g . 4 . 8 . The d i s t r i b u t i o n o f t h e skewness c o e f f i c i e n t o v e r t h e N i l e B a s i n assumes t h e p a t t e r n shown i n F i g . 4 . 9 . T h i s p a t t e r n i s n o t s i m i l a r t o t h a t o f t h e c o e f f i c i e n t o f v a r i a t i o n , a t l e a s t i n some p a r t s of t h e b a s i n . Most o f t h e s e p a r t s are c o n c e n t r a t e d i n t h e E q u a t o r i a l Lakes P l a t e a u , where t h e skewness a p p e a r s t o b e r a t h e r h i g h whereas t h e c o e f f i c i e n t o f v a r i a t i o n is q u i t e s m a l l . T h i s c o n c l u s i o r
i s c o n f i r m e d by t h e r e s u l t s a p p e a r i n g i n P a r t I , Vol. 1 o f t h e Hydrometeorologic a l S u r v e y o f t h e E q u a t o r i a l L a k e s . The skewness o f t h e a n n u a l r a i n f a l l a t most of t h e s t a t i o n s i n Uganda and T a n z a n i a which a r e l i s t e d i n T a b l e 4 . 4 seems t o be i n c l o s e agreement w i t h our r e s u l t s , which are p r e s e n t e d i n T a b l e 4 . 3 . The a n n u a l r a i n f a l l d e p t h s composing t h e series whose s e r i a l c o r r e l a t i o n coe f f i c i e n t s a r e n o t s i g n i f i c a n t l y d i f f e r e n t from z e r o a t t h e s p e c i f i e d l e v e l of c o n f i d e n c e (95%) h a v e b e e n termed as i n d e p e n d e n t , I . Those s e r i e s whose s e r i a l c o r r e l a t i o n c o e f f i c i e n t s l i e o u t s i d e t h e c o n f i d e n c e l i m i t s have b e e n termed as d e p e n d e n t , D . A number o f s t a t i s t i c a l models h a v e been t r i e d t o t h e i n d e p e n d e n t
s e r i e s , and t h e d i s t r i b u t i o n f u n c t i o n o f b e s t f i t t o t h e o b s e r v a t i o n s i n each of them h a s been u s e d f o r e s t i m a t i n g t h e a n n u a l r a i n d e p t h c o r r e s p o n d i n g t o r e t u r n p e r i o d s o f 1 . 0 1 , 2 , 5 , 10, 2 0 , 50 and 100 y e a r s . These r e s u l t s , t o g e t h e r w i t h t h e d i s t r i b u t i o n f u n c t i o n used i n e s t i m a t i n g them, are i n c l u d e d i n T a b l e 4 . 5 . O f t h e 146 i n d e p e n d e n t series a n a l y z e d h e r e , 96 s e r i e s , or 6 5 . 8 % h a v e b e e n found t o b e b e s t f i t t e d by P e a r s o n I 1 1 d i s t r i b u t i o n f u n c t i o n , 34 s e r i e s , or 2 6 . 0 % , by t h e normal d i s t r i b u t i o n and t h e r e s t , or 8.2% by t h e two-parameter lognormal d i s t r i b u t i o n f u n c t i o n . Examples o f r a i n f a l l series f i t t e d by each o f t h e s e d i s t r i b u t i o n f u n c t i o n s c a n b e s e e n i n F i g s . 4 . l O a t h r u ' c . The g e n e r a l f o r m u l a used f o r e s t i m a t i n g t h e r a i n f a l l d e p t h , XT,
t h a t c o r r e s p o n d s t o any
return period T, is
X T = ? + KT ' S The f r e q u e n c y f a c t o r , K T ,
depends on t h e d i s t r i b u t i o n f u n c t i o n used and t h e
c o e f f i c i e n t o f v a r i a t i o n , C v , or t h e s k e w n e s s , C s , b u t i o n . The t a b l e of K T ,
e x c e p t f o r t h e normal d i s t r i -
g i v e n by Chow (1964) i s s a t i s f a c t o r y f o r f i t t i n g t h e
l o g n o r m a l f u n c t i o n , whereas t h e t a b l e s p r e s e n t e d by K i t e (1977) a r e f a i r l y s a t i s f a c t o r y f o r t h e p u r p o s e o f f i t t i n g t h e normal and t h e lognormal f u n c t i o n s .
121
The frequency factors, KT, used in connection with Pearson I11 have been taken from the "Guidelines for Determining Flood Flow Frequency" by the Water Resources Council of the United States of America (1977). In the analysis of the annual rainfall which is presented in the report of the hydrometeorological survey of the catchments of Lakes Victoria, Kyoga and Albert, the two-parameter Gamma distribution is reported as the distribution function of best fit to the data of the 22 stations included in that investigation. The same function has been reported as the function best fitting the distribution of the monthly rainfall. The Pearson I11 found by us here as the distribution function of the annual rainfall at two-thirds of the stations is simply a Gamma function, but with three parameters. It may be of interest to mention that the lognormal and the Gamma functions have proven to be functions of best fit to the distribution of rainfall depths in many parts of the world (Markovic, R., 1965; Huynh Ngoc Phien et al, 1980; Kottegoda, N.T., 1980). The rain-gauging stations with complete record and not appearing in Table
4.5 have rainfall series whose elements experience some dependence. These have already been termed by the letter D in Table 4.3. In order to describe the dependent component in these series, we tried to fit an autoregressive model with lag 1, 2, 3 or 4 to the observed data. The basic equation can be written as
(4.9)
where, Xt = annual rainfall in any year t, Xt-L (L = 1, 2, 3, 4) = annual rainfall in year t-L, aL = coefficient to be found from the serial correlation Coefficients, for example in the 1st order model, X
t
- X = a1
( x ~ - X) ~
+
E ~ al , = rl,
and in the 2nd order model, x t - X = a
a
' - r l r2 = 1 and a 1 - r 2 1
' = 2
- 1'
2
I - r 2 1
.......
and so on.
Expressions for al, a Z , and a3 in a 3rd order model and for al, a 2 , a3, and a4 in a 4th order model cen be found in some of the literature on stochastic hydrology (Yevjevich, V., 1973 and Kottegoda, N.T., 1980). The computer programme developed by R. Clarke (1973) has been worked out to obtain the residuals
122
l e f t a f t e r f i t t i n g t h e l s t , 2nd, 3 r d and 4 t h o r d e r models t o e v e r y r a i n f a l l s e q u e n c e and t o o b t a i n t h e s e r i a l c o r r e l a t i o n c o e f f i c i e n t s of e a c h set of resid u a l s . The v a l u e s o f t h e s e c o e f f i c i e n t s form t h e c r i t e r i o n t o j u d g e t h e s u i t a b i l i t y o f t h e model a s a good f i t t o t h e s e q u e n c e i n q u e s t i o n . When t h e f i r s t o r d e r model i s s u i t a b l e , suitable.
t h e h i g h e r o r d e r models u s u a l l y p r o v e t o b e e q u a l l y
I n s u c h a c a s e t h e s e l e c t i o n o f t h e model o r d e r i s b a s e d on t h e
v a r i a n c e of t h e r e s i d u a l s . The o r d e r whose r e s i d u a l s gave t h e s m a l l e s t v a l u e s of t h e s e r i a l c o r r e l a t i o n c o e f f i c i e n t s and which showed t h e l e a s t v a r i a n c e h a s been s e l e c t e d . From t h e 37 s e q u e n c e s i n v e s t i g a t e d t h e a u t o r e g r e s s i v e model f a i l e d i n 4 c a s e s . For t h e r e m a i n i n g 33 s e q u e n c e s , 22 c o u l d b e f i t t e d by l a g 1 model, 9 by l a g 2 model, 0 by l a g 3 model and 2 by l a g 4 model. The b a s i c p r o p e r t i e s o f t h e s e models and t h e v a l u e s o f t h e s e r i a l c o r r e l a t i o n s of t h e r e s i d u a l s a r e g i v e n i n T a b l e 4 . 6 . Once a model i s e s t a b l i s h e d , one c a n g e n e r a t e any number of a n n u a l r a i n f a l l s which c a n b e u s e d f o r d e t e r m i n i n g t h e r a i n d e p t h c o r r e s p o n d i n g t o any g i v e n r e t u r n p e r i o d .
TABLE 4 . 3
B a s i c s t a t i s t i c a l d e s c r i p t o r s and s e r i a l c o r r e l a t i o n c o e f f i c i e n t s o f t h e a n n u a l r a i n f a l l d a t a ( S h a h i n , M . A . , 1983)
S t a ti o n No.
Basic s t a t i s t i c a l descriptors
Name
c"
cS
(2)
Serial correlation coefficients c ~ ( ~ ) r
1 2 3 4 5
Sidi Barrani Borollos L.H. Sallum Damietta L . H . D a m i e t t a (Town)
167.1 181.4 108.8 123.9 109.9
70.38 63.34 75.70 46.37 48.61
,4211 .3492 .6959 ,3740 ,4423
1.7371 - .1755 .3652
5.5214 2.7740 6.3878 2.1746 2.9334
6 7
Rosetta L.H. R o s e t t a (Town) Mersa Matruh Tolombat e l - B o s e i l i Tolombat el-Tolombat
190.7 212.7 136.2 157.1 184.7
97.40 93.23 59.43 65.47 90.41
.5108 .4382 .4360 .4167 .4895
.8184 .6060 .9754 .8627 ,3964
2.6121 2.8067 3.5703 3.5773 2.3954
Edfina
184.1 73.0 72.4 146.2 189.6
65.40 36.60 30.86 75.18 62.21
.3553 ,5014 ,4262 .5142 .3281
.2611 1.1094 ,6298 .SO9 1 .2372
2.4923 5.1014 3.4871 2.7095 2.5448
.4524 ,4929 .4544 .4185 .4616
.4635 .7069 .6722 .5187 .6 396
2.5417 3.0097 2.5902 3.4684 2.6866
.4001 ,3937 .5302 . 4 4 36 .5950
.3805 .3026 .9237 .6187 1.1690
3.1654 2.2199 3.4447 2.8923 5.5110
8 9
10 11 12 13 14 15
Sirw Kom e l - T a r f a i a Alexandria
16 17 18 19 20
Mex K a f r el-Dawar Kafr el-Sheikh Al-Arish Sakha
186.7 155.4 80.1 105.3
66.6
84.46 76.59 36.40 44.06 30.74
21 22 23 24 25
Ras el-Dabaa Mansura Fuka Damanhur Amria
135.4 57.1 113.5 89.3 141.3
54.17 22.48 60.16 39.61 84.07
Port S a i d
(1) i n mm/yr;
(2),
1.5715
- .0417
I/D(~) 1
- .0968
*2
r4
r5
.0927
- .1129
.1545
I
- ,3077 - .1742 .1309 - .0976
.0724 ,2278
.2927 -.0716
I
.0813
- .1644
,1118
.0783 .2318
I
-. 2482
.4593
-. 2212
- .0632
D I
-.Oslo
- ,0706
.2246 .2438
I I
- .2894 - . 1748
.0371
.0420
.1429
- .OX5
.3593 .1595 .1519
I I I
- .1750
.1450
- .0408
.2236
I
- . 1 2 0 3 - .5192
.2824
.2194
- .4325
D
- .0692
-.Of353
.lo63
- ,0921
I
.0857 .1708
- .2124
r3
- .0129 - ,1539 - ,050 1 - , 1 0 2 3 - .0714 ,3044 - .1534 - . 1025
- .0124
- ,0945 - .2430
-. 1168 -. 1567
-.0328 ,0616 3214 . 0 4 8 1 - .2842
.0262
.0657
-.
-. 1053
-. 2107 - ,0334 - .0258 -. 1422
( 3 ) c o r r e c t e d f o r b i a s i n e s t i m a t i o n from s a m p l e ; ( 4 ) I = i n d e p e n d e n t and D = dependent
I
I
CL N W
TABLE 4 . 3
(continued)
Station No.
Name
26 27 28 29 30
Borg el-Arab Hammam Kafr e l - Z a y y a t Tanta Faqus
31 32 33 34 35
Basic s t a t i s t i c a l d e sc r i p t o r s
%< 1)
(1)
c"
cS
(2)
Serial correlation coefficients c ~ ( ~ ) r
163.2 114 .O 36.4 50.8 39.3
74.77 61.95 24.35 22.84 18.14
.4581 .5434 .6690 .4496 ,4616
.3886 1.0013 .9544 .2651 .2650
3.2379 4.4936 2.9680 3.2317 2.7047
El-Quseima Zagazig S h e b i n el-Kom El-Has s a n a Benha
54.4 36 .O 36.3 27.5 22.6
29.09 30.87 14.96 17.77 14.63
.5346 .8575 .4125 .6470 .6473
.6022 4.1461 .1326 .1586 .I3621
3.4053 23.0186 3.3464 3.3306 2.5589
36 37 38 39 40
Wadi e l Natrun Fayed Delta Barrage Giza Kuntella
42.6 22.5 20.3 23.1 22.8
60.33 16.48 12.97 13.04 23.15
1.4161 .7308 .6391 .5645 1.0155
3.5945 1.0947 1.1863 .7487 1.4161
16.8848 4.4302 5.7927 3.5886 4.3525
41 42 43 44 45
Suez El-Nekhl Attaqua Helwan El-Themed
25.6 19 .o 14.7 25.2 18.9
19.20 18.14 12.46 20.85 19.39
.7500 .9545 .8498 .8274 1.0286
.8542 1.1977 1.9521 1.4937 1.6645
3.1395 4.5985 7.5117 4,7287 5.3242
46 47 48 49 50
Shakshuk Fayum Ras e l Negb Siwa Beni-Suef
09.3 13.1 27.4 09.3 07.0
06.97 14.16 23.18 10.14 07.29
.7495 1.0809 .8457 1.0904 1,0408
1.0465 2.0732 ,940 1 1.5194 1.8590
3.8441 8.2254 3.2016 5.2160 7.1406
(1) i n mm/yr;
I/D(~) 1
r2
r3
r4
r5
.2118
- .0341
- .0412 .0942 .0779
.0449 -.0761 .3025
-.3710 -.0726 .0637
- .1769 - .1649 -. 1720
.3406
-.0036
- .1575 .3570
- .1537
.3703
-
.1110
.0603
.0512
.1437
.3273
.0677
- .0177
- .0648
.0556
-.1254
.0206
.1379
- .2855
,2219
.1551
.3269
.lo39
.zoo2
.3238
.2423
- .1651 - .3424
.2247
.0281
-.2488
( 2 ) , (3) c o r r e c t e d for b i a s i n e s t i m a t i o n from sampl2; ( 4 ) I = independent and D = dependent
TABLE 4 . 3
(continued)
Station No.
Basic s t a t i s t i c a l d e sc r i p t o r s (1)
Name
Serial correlation coefficients
(2)
(3)
1
'S
k'
51 52 53 54 55
Baharia Tor Minya Hurghada Assiut
03.4 10.1 03.1 04.4 02.9
04.80 11.91 05.18 09.86 04.64
1.4245 1.1818 1.6716 2.2306 1.6200
1.6708 1.4658 2.2887 3.6922 1.7751
5.4642 4.6035 7,4406 17.3111 5.2604
56 57 58 59 60
Faraf r a Qena Qusseir Nag-Hammadi Luxor
01.3 04.7 03.5 01.2 00.9
02.66 11.26 08.26 04.03 01.48
1.9978 2.4197 2.3820 3.3618 1.6480
2.7785 3.9016 3.5151 4.2048 1.4795
11.6421 20.0833 16.4855 20.7059 4.1012
61 62 63 64 65
Dakhla Kharga Deadalus I s l a n d Kom Ombo Aswan
00.5 01.4 08.6 00.7 01.2
02.20 02.45 12.99 01.37 02.01
4.5850 1.7059 1.5049 2.0560 1.6205
4.9269 1.777 2.1236 1.9957 1.9584
26.8735 5.2374 6.9631 6.3826 6.7914
66 67 68 69 70
Wadi-Halfa P o r t Sudan Abu-Hamed Gebeit Sinkat
03.6 99.0 15.9 123.4 128.8
07.48 57.81 27.37 67.59 93.81
2.0970 .5839 1.7214 ,5477 .7283
2.6956 .5666 3.4710 1.1927 1.3823
10.3612 2.4869 17.1297 4.5434 5.2346
71 72 73 74 75
Kareima Tokar Tahamiyam Talguharia Atbara
39.0 92.6 79.4 79.7 65 .O
40.64 66.76 61.65 66.06 43.06
1,0421 .7210 .7768 ,8289 .6625
1.2130 .85 18 1.5774 1.9146 .7587
3.8206 3.2578 6.8951 8.4202 3.0301
(1) i n mm/yr;
(2),
cY
(3) c o r r e c t e d f o r b i a s i n e s t i m a t i o n from sample;
r3
r2
- .2050 - .2568
.0828
- ,0611 - .06 10
.1428
.1201
- .0387 - .1556
.3655
.1298 .1651
- ,1164
,1924
- .0680
-. 1359
r4
-(4) I/D' .
-
r5 .3962
I
-.0423
-. 1106
I
.0968
- .0132
- .0310
D
- .1707
-. 1081
.1488
I
.0453
- .4267
- .3828
- .0902
.0698
- .1262
-.0819
I I
- .1613
- .2365
.lo53 - .1297
I D I
- .1552 - .4202
- ,1943
- ,0523 -
.2053 .1827 .0954
- .0398
- ,1670
.3272
.0090
- .3053
I
- .2239
- .0734
.2181
- .1229
-. 1151
I
- .4458
,0121
( 4 ) I = independent and D = dependent
P CJl N
TABLE 4 . 3
(continued) Station
Basic s t a t i s t i c a l descriptors %(I)
(1)
55.4 224.7 175.1 171.5 321.4
50.99 97.29 79.61 80.81 85.88
.9198 .4330 .4547 .4712 .2672
Jebel Aulia Wadi-Turabi Kamlin Khashm e l - G i r b a Geteina
187 .O 249.5 262.9 338.1 203.3
71.31 98.14 88.97 113.49 73.52
86 87 88 89 90
Rufaa Wadi-Shair Wad Medani Managi 1 Cedaref
296.9 301.7 365.9 298.5 580.7
91 92 93 94 95
Dueim H a j Abdalla Wad-Haddad Bara E l F a s h e r A.P.
96 97 98 99 100
Mf a z a S e n n a r D.S. Geneina El-Obeid Town Kosti/Rabak
No.
Name
76 77 78 79 80
Zedi ab Abu D e l e i g Khartoum G . C Khartoum Kassala
81 82 83 84 85
(1)
ill
mm/yr;
.
Serial correlation coefficients I/D(~)
(2)
c”
I1
cS
,7291 .3946 .7576 .4881 .1322
2.9178 3.4076 3.7292 2.8969 2.7130
.3813 .3933 ,3384 .3357 .3616
.1588 ,4414 .4268 1.2700 1.3528
2.6616 3.6382 3.2821 4.3005 5.3100
89.22 82.93 107.99 102.19 99.19
.3005 .2748 .2951 .3423 .1708
.6753 .4573 .4088 .6710 .5930
4.2637 3.3238 3.6197 4.1381 4.3354
303.4 435.5 402.4 284.1 302.8
90.59 83.32 89.74 72.94 118.15
.2986 .1913 .2230 .2567 .3902
.0949 .4697 .2188 .lo31 2.1606
2.8073 4.1929 6.3673 2.1945 8 .6072
591.4 481.7 553.0 404.2 401.9
146.62 97.50 123.21 116.40 80.13
.2479 .2024 .2228 .2880 .1994
.2778
2.6046 2.6373 2.6435 3.9926 2.8227
-
-
-
- .1249
.6456 .8694 .5504
.3149
r2
r3
.2011
- . 0 9 4 1 - .0984
r4
r5
.3298
-.0123
.0135
I
.0941 .0862
.0772 .2377
.0464 .0364
I
.0854 .0285
-.2872 .lo43
I I
- .0113
- .26 18
- . 1674
-. 1228 .0525
,0244 .2779
- .0833 - . 1728
- .0869
.1708
-.2786
-.2972
I
.2431 .0331
.0392 .2043
.1177 -.2345
-.lo82 -.1463
I
.2781 -.0493
-.3380 .1317
-.1175 -.1468
I
,1020 .1489
.0391 -.0030
-.0822 -.0956
I I
.0741
-.0526
.0134
I
-.1485 .1742 -.0314 ,3030
-.5053 .2550 -.2981 -.1959
.1323
D I I
.0 160
- .2495
-. 1 2 5 3 .0580 - .2958 -. 1041 - .0800 -. 1412 - .2868 .0337 - .1179
.1990
- ,0134
-. 1728
,2899 - ,0141 -.1426
- .0726
- .0186
.2102
-
-
- .1181 -.0666 .1824
( 2 ) , ( 3 ) c o r r e c t e d f o r b i a s i n e s t i m a t i o n from s a m p l e ; ( 4 ) I = i n d e p e n d e n t and D = d e p e n d e n t
I
I I
I
TABLE 4.3
(continued)
S t a ti o n No.
Name
Basic s t a t i s t i c a l descriptors
%(I)
(1)
c"
(2) cS
-
Serial correlation coefficients
I/D(~)
c ~ ( ~ ) r1
r3
r2
r5
r4
- .1611
.2280 ,0777 - .0601 - .1570 .3092 .0922 .2310 - .2712 - ,2435 - .0758 - . 1982 - .2502 - ,1288 .1265 .1274 - .0580 - .2671 - .2101 - .0082 .0202 - .2251 - .2180 1106 - .1354
I I I
2.1020 3.4023 3.1763 3.0244 4.0764
- .0923
,0004 - .0470 .1658 - .3771 - .1112 - .0372 - .2266 ,0579 - ,1459 - .1265 .1582 .007 ,0452 .0302 - .2050 - ,0140 - . 1302 - .3542 - .4355
I I
2.8204 2.0987 2.8731 3.1320 2.6780
.4138 .2894 - .0229 - .0835 - .1324 .1318 - .0656 .0016 - .2339 - .3173 ,1801 - .1782 .1876 .0319 - .4827 - .2100 - ,2407 .4540 - .1811 - .4615 .2424 - .0487 - .0702 .3062 1635
D I D D I
101 102 103 104 105
Singa Tende 1t i Urn Rwaba Rahad E l Nahud
591.7 369.5 417.2 460.3 417.9
89.90 96.77 133.77 121.95 92.59
.1519 .2619 .3206 .2649 .2216
106 107 108 109 110
Jebelein Nyala Dilling Rashad Roseires
423.4 478.4 640.8 777.2 732.0
82.12 110 .oo 145.69 110.38 109.74
.1940 - .0374 .2293 - .1455 .2274 - .0256 ,5692 .1420 ,5775 .1499
111 112 113 114 115
Renk Abri Kadugli Talodi Kurmuk
567.0 692.2 787.6 821.2 932.1
152.52 96.76 146.56 138.58 206.18
.7772 .2690 .1398 - .0416 .5740 .1861 .0416 .1688 .2212 - .4560
116 117 118 119 120
Melut Kodok Malakal Tonga Abwong
642.1 734.7 794.5 888.8 756.7
166.17 132.61 140.98 188.23 183.81
.2588 1.7961 10.3313 4.4227 .4365 .1805 4.4517 .1774 .2079 3.3455 .2548 .2118 .2429 -1,0775 4.9807
- .0895 .1557 - .4233 - .3719 - .1797 .1484 - .3941 - .2610 .0506 ,1035 .0985 - ,0968 - .1419 - .0181 .0120 .1822 - .0851 .2688 .3979 .0225 .1878 .2165 .4598 .1535 .1373
121 122 123 124 125
Fangak Aweil Nasser Raga Meshra er-.Rek
887.7 897.5 798.2 1228.7 919.4
273.53 217.78 146.48 168.54 209.88
.1225 .3081 .2345 .1236 .1835 - .1761 .1372 .5852 ,2283 ,6294
2.6662 3.0943 4 .4046 3.8970 3.9399
,4935 .5700 .5555 .5935 .3040 .2047 - .0821 - .0925 - .0954 - .1966 - ,3231 - .1666 - .0139 .1301 .0744 - .0618 - .1259 .0115 .2992 1686 .2019 - ,1199 1887 - .0893 .0237
.2641 4.4685 .lo71 3.3796 2.6676 13.6276 1.9179 8.3518 3.2438 .2382
.1613 .3073 - .1108 .3017
-. - ,1739
-.
-.
-.
(1) i n mm/yr; (2), (3) c o r r e c t e d f o r b i a s i n e s t i m a t i o n from sample; (4) I = independent and D = dependent
I
I
I I I
D I
I D D
D I
I I I
TABLE 4.3
(continued)
Station No.
126 127 128 129 130
Name Gambei la Akobo Wau Ton j Ghabe Shambe
131 Rumbek 132 P i b o r P o s t 133 Bor 134 Amadi 135 Terakekka
Basic s t a t i s t i c a l descriptors
%(I) 1316.1 984.3 1182.3 1072.7 758.7
( 1)
287.91 194.54 159.28 206.78 185.81
(2)
c"
cS
.2188 - .4554 .1976 - ,4969 ,1347 .0969 ,1928 .7399 .2449 - ,1526
-
Serial correlation c o e f f i c i e n t s
I/D(~)
c ~ ( ~ )r 1
r2
.3175 3.8904 .2865 5.0569 .3280 - .0043 .0209 2.3407 - .3088 3.0459 - .1313 - .0793 2.4769 .1939 - .0834
r3
r4
r5
,1536 - .2162 .06 14 .lo84 .1519 - .2753 .2650 -. 1343 - .0958 .ooo 1 ,3950 - .2327 ,0935 .0728 -. 1658
962.4 209.45 909.3 242.14 892.2 153.04 1186.8 197.12 979.3 202.88
.2176 .2663 .1715 .1661 .2072
.6624 .2813 .7445 - .lo97 1.0746
3.1784 3.0006 3.6988 2.9269 4.6239
.2892 .2645 .2597 ,2438 .4272
,1854 - .0114 - . 1217 - .0952 .2788 - .1676 .3462 .2534 .2667 - .0235 -. 1918 .0565 .2953 .lo75 - ,1450 - .0033 .3382 .0550 - .0448 - .0349
.3203 .2096 -. 1431 .4648 .1936
.0292 .0586 .2159 .0997 - . 1039 - .2892 - .3982 - .1390 - ,0358 .1330 .0056 - .2692 - .0126 - .2258 - .2957 - .0587 .Of571 - .0795 - .4616 1318
136 137 138 139 140
Maridi Juba Y amb i o Loka Yei
1357.5 999.3 1472.8 1256.9 1335.4
220.43 182.54 156.64 176.99 209.92
.1624 - .0698 .1827 .2843 .lo64 .1874 .1408 - .5380 .1572 - .1908
3.1662 2.8288 3.333 3.8270 3.2537
141 142 143 144 145
Kajo Kaji Nimule Kitgum Atua Gulu
1319 .O 1275.8 1252.2 1325.3 1549.8
303.18 247.11 192.84 329.93 230.41
.2299 .5955 .1937 .8785 .1540 .0954 .2489 - .8324 .1487 - .2915
5.4390 .0640 - .4164 4 .7248 .1270 - .0458 .1748 2.4929 -.2613 .4452 .4139 3.9897 3.2422 .4105 - .1323
146 147 148 149 150
Moroto N e g e t t a Farm/Lira Aduku d i s p e n s a r y Katakawi Butiaba
910.0 218.12 1451.9 180.79 1285.9 179.63 1135.7 172.29 755.2 250.10
.2397 .1245 .1397 .1517 .3312
-.
.0018 .0261 - .0996 .4609 - .1195 - .0844 - .0200 - .2731 .1196 .0744 .1851 .0084 -. 1322 - .0749 -.1518
,2456 2.8725 - .1696 - .2104 - . 1200 - .2180 .1354 ,1309 .1881 4.3080 .3509 .0493 .0447 -. 1401 ,2752 - . 1182 - .0393 - .0743 2.9989 .2741 .2558 3.1972 - .0913 - .2879 .5121 .1181 - .0517 .0116 2.3766 10.1242 .1950 -.0433 -.1525 -.2043 -.0424
(1) i n mm/yr; ( 2 ) , (3) c o r r e c t e d f o r b i a s i n e s t i m a t i o n from s a m p l e ; (4) I = independent and D = dependent
I I I D I
I I I I
D I I I D D D D I D D
I I I I I
TABLE 4 . 3
(continued)
Station
Name
No.
Basic s t a t i s t i c a l d e s c r i p t o r s g(l)
(1)
.'"
(2) ' S
'k
Serial correlation coefficients
151 152 153 154 155
Soroti Masindi Ongino S e r e r e Agr. S t Kyere
1290.7 1254.6 1242.8 1345.1 1290.4
240.18 190.49 238.23 260.25 176.46
.1861 .1518 .1917 .1935 .1367
.3967 - .1435 - .3728 -1.0758 - .1350
3.1071 3.8712 6.2210 6.4170 2.3608
156 157 158 159 160
Bulindi Ngora Nakasangola Bukedia Kachimbal a
1301.8 1353.7 1034.1 1229.7 1196.2
197.27 176.76 174.02 194.80 218.38
.1515 .1306 .1683 .1584 .1826
.4610 .9742 .3596 ,1227 .6776
2.7500 5.0904 4.1195 2.7029 3.6600
161 162 163 164 165
Kibale Bugaya Mbale Namasagali Vukula
1385.7 1315.1 1169.0 1266.7 1363.5
242.17 228.16 245.18 214.28 255.04
.1748 .1735 .2097 .1692 ,1870
1.0664 1.1410 1.0882 1.0764 1.1595
4.9411 4.9904 3.4210 4.6595 4.6978
166 167 168 169 170
Kiboga Bulopa Nten j e r u Bukal as a Kahangi E s t a t e
1199.6 1352.9 1221.2 1298.7 1367.7
271.09 217.49 203.26 241.24 199.10
.1608 .1664 .1858 .1456
- ,0591
1.7211
.8284 1.4703 1.2295
8.5143 2.7189 3.8008 7.2773 6.1086
171 172 173 174 175
Tororo Fort Portal K a l a g a l a Agr. S t . Inganga Mubende
1426.2 1517.9 1243 .O 1279.7 1189.2
222.77 226.46 257.56 240.62 175.07
.1562 .1492 .2072 .1880 .1472
.4018 .8182 1.2027 .6356 .5325
3.1733 3.8060 5.7374 4.7638 4.2978
(1) i n mm/yr;
,2260
I/D(~)
(3)
1 .1578 ,4310 i993 .2157 .0548
. -
.2566 .0206 .0749 .2648 .4413
.0261
- . 1176 .0767
.004 1 - .1922 - .lo86 - .4277 .4008
r4
.0020
- .2533
- .2062 .1495 .0138 .0824
.0998 1811
-.
- .2046
.0485 ,0238
.0925 .0853 .0488 - . 1952 - .2806
-
.0277 .0569 - .0937 1530 .1374
.0642 -.0919 .0233 .1805 .0266
.0355 .0684 1366 .0218 - .0529
- .3792 - .0657 -
- .0130 -. .2600
r3
r2
- .4590 - .4060 - .0582
-
.0371 .3314 .1758
-
.4811 .0005 .0700
- .loo1 - ,1224
.1835
- .0852 - .0446
.1721 .0659 .0851
- ,0125
- .0824
,0152 .07 39 .ZOO4 - .0453
-
-.
.0947 - .0670 - .1762 - .0435 -
.0642 ,2379 .0156
.1745 .1325 .1150 ,0378 ,0735
D
.0285
D I I I D
- .1121 .3444
.1201 .1323
.0102
- ,1057 - .1885 .0989 - .3239 -. 1033 .Of397 - .0552 .2753 .0258 .1450 .0062
r5 .2878 .2841 .4191 .3602 ,1743
- .0680
- .1312 - .1533 .1525
- .2891 - .0845 - .2286 - .0115
I I D
I I I I I I I I
.0711
I
.3642 .0531 ,4210 .0786 .0172
D I I I I
.0 170 -
D
(2), ( 3 ) c o r r e c t e d f o r b i a s i n e s t i m a t i o n from s a m p l e ; ( 4 ) I = i n d e p e n d e n t and D = dependent
I
TABLE 4.3
(continued)
Station
Basic s t a t i s t i c a l descriptors
Serial correlation c o e f f i c i e n t s
I ” .
176 177 178 179 180
Nawanzu Dabani Nagoje Masaf u D i s p e n s a r y Lugala
1324.8 295.00 1538.8 275.11 1403.5 349.79 1539.5 326.86 1396.8 264.75
.2227 .1737 .2492 .2123 .1895
2.2355 11.5580 .6494 2.6743 .9408 3.9994 5.1022 1.3474 1.2182 4.5157
-.0403 .2294 .0135 -.0303 .3490 .4027 - . 0 8 0 2 -.0615 .0721 -.0090
.1503 -.1745 .2360 .0498 .3290 .0319 .0121 .lo97 ,1040 -.1681
I I D I
181 182 183 184 185
Moniko E s t a t e Namanve Mukono Agr. S t a t . Bwavu N s y amb a
1500.4 1345.6 1466.3 1370.4 1149.9
233.00 274.72 338.02 244.17 256.20
.1553 .2042 .2305 .1782 .2228
.7977 1.4886 .6838 1.1412 .3913
4.1457 6.2496 3.1562 4.2658 3.6206
.2662 .2340 .0091 .1521 .0332 .2433 -.lo00 -.1365 -.0679 .0887 .6001 .3714 .1404 .0305 -.2430 -.0386 .1743 -.1105 .1690 -.1744 .3099 .0286 .0996 .2682 .2089
I I D I
186 187 188 189 190
Kabas anda Bud0 K i n g ’ s S c h o o l Ngogwe C o f f e e Nursery Buvuma I s l . Kisubi
1323.5 1264.6 1540.8 1578 .O 1424.4
261.31 196.48 294.49 306.64 258.48
.1974 .1554 .1911 .1943 .1815
.6975 .6483 .6414 .1443 .1862
3.5811 2.8198 3.2720 2.2876 4.2016
.0727 -.0021 .1976 .0486 .1261
,2185 -.0798 .1392 -.0554 - .0788 - .1121 .0749 .2469 -.2967 .0312
I
191 192 193 194 195
Entebbe Nkozi Kalungu K a t i gondo Lyantonde D i s p e n s a r y
1557.7 1019 .o 1054.8 1084.5 910.7
268.05 232.93 210.60 206.18 249.56
.1721 .2286 .1997 .1901 .2740
.4874 .3978 .ZOO4 .4274 1.0695
2.8591 2.7988 3.1832 2.9364 3.7603
.2737 -.2850 -.3438 -.2210 ,0994 ,1831 .lo60 .0673 .0778 -.1258 -.0195 .0044 .1480 -.0209 -.0356 -.2628 .0171 .1786 - .1437 - .0367 .0509 -.2181 ,1746 .0945 -.lo31
I I I I I
196 197 198 199 200
Masaka Kiwala Estate K a l a n g a l a Didpensary Buunga Kyanawkaka
1076.4 1171.8
219.34 274.08
.2038 .2339
.7233 1.0211
3.2775 3.7067
.1389 -.0348 .0390 -.0468
.3062 .0116
- .0958 - .3267 - .0806 - . 1740
I I
1142.7 1155.2
248.57 218.11
.2175 .1888
.9646 1.2631
3.4779 4.3958
-.1652 -.1251 -.1606 -.0712
.0093 .3984
.lo93 -.lo04 .0216 -.1622
I D
(1) i n mm/yr;
-
-.0741 -.2642 .1899 -.1886 -.2260
-.0271 -.lo07 .2635 -.lo83 -.0384
-.0775 -.2072 -.1480 -.2205 -.2878
(2), (3) c o r r e c t e d f o r b i a s i n e s t i m a t i o n from sample; (4) I = independent and D = dependent
I
I
I I I
I
TABLE 4.3
(continued)
Station No.
Basic s t a t i s t i c a l descriptors
Name
(1)
c”
Serial correlation coefficients
I/D(~) cS
(2)
ckc3)
201 202 203 204 205
Busenyi Mbarara Bikira Lwasamaire Katera
1258.8 262.83 921.9 186 .OO 1054.4 162.41 1064.7 182.07 1165.2 176.82
.2088 .2018 .1540 .1710 .1518
206 207 208 209 210
Kabale Kapenguria Endebess (Mt. Elgon) K i t a l e Agr. S t a t . Turbo
1003.8 1264.1 1251.7 1151.3 1267.1
173.45 322.50 210.60 218.05 274.08
,1728 .2551 .1682 .1894 .2163
.9150 .2659 .5045 1.2210
211 212 213 214 215
T amb ach
Myanga Bungoma V . S . Mumais Tororo/Nangina
1206.5 1358.4 1560.9 1738.8 1396.1
276.10 483.71 260.67 317.15 205.38
.2288 .3561 ,1670 .1824 .1471
2.6351 .2147 2.2958 10.8581 2.8679 .6982 2.1907 .0118 4.5792 1.2721
216 217 218 219 220
Kakamega Kapasabe t Rangala Maseno, V.S. Equator
1982.2 1546.3 1563.8 1590.3 1552.5
284.08 290.40 245.96 269.68 286.95
.1433 .1878 .1573 .1696 .1648
.4644 .6539 .2767 .7141 .0208
2.5430 3.2129 3.0669 3.4504 3.4451
221 222 223 224 225
Miwani Kisumu P.C. Chemelil Muhoroni Fort Ternan
1122.7 1086.6 1443.5 1385.5 1249.8
184.87 228.08 398.99 302.63 207.97
.1646 .0556 ,2099 .5947 .2764 2.1485 .2184 .4448 .1664 - .1972
2.3785 2.7984 9.5738 2.9430 2.0881
(1) i n mm/yr; ( 2 ) ,
.3081 1.2704 .5790 .4334 - .1584 .6 260
2.8557 5.3994 2.6892 2.8380 3.6911 3.8610 4.5000 2.5443 3.3466 4.8852
r
1
r2
r3
r4
r5
.1746 .O 198 - .4592 - .2776 -. 1452 -. 1921 .0497 - .2075 - .0773 .0311 - .0231 - .2690 .1971 - .0966 - .3954 ,2224 - .0274 -. 1781 -. 3396 - .3965 - .2846 .0602 - .1151 .1248 -. 1532 .0459 - ,2995 - .0609 .2305 .1351 .0673 - .3649 - .0230 .0380 .0361 .0761 - .0526 .1386 - .0170 .0959 .3869
- .0018
.3475
- .0967
- .2702
.0772 - .0525
.1344 - .3544 ,3288 .2014
.3732 - .0348
D I I I I I
I I
D
,0029
I
- .0740 - .1328 -. 1452 - .0274 -. 1630 - .2435
I I
.0177 - .2055 - ,1300
- .0638
.1201
.2390 .0765
I I
- .2725
- .2582
.1285
I
.0858 - .2311 - .2736 .1719 - .0886 .1626
-.0039 .2596
.0509 .0151
I I
.2201 .1396
- .2559
.0976 - .1288
(3) c o r r e c t e d f o r b i a s i n e s t i m a t i o n from sample; (4) I = independent and D = dependent
P
w
P
TABLE 4.3
(continued)
S t a ti o n
Basic s t a t i s t i c a l descriptors
Serial correlation coefficients
c ~ ( ~ ) r1 226 227 228 229 230
Londiani Lumbwa Molo Kericho Sotik
1189.1 217.73 1108.8 176.03 1073.6 278.44 1887.0 284.73 1350.4 204.41
.1831 - .2540 .1588 - .3474 .2594 .2092 .1509 .8191 ,1514 - .4772
2.3639 3.0842 3.0331 3.8312 4.7605
231 232 233 234 235
Kisu Bukoba Tarime Musoma Kagondo
1842.4 561.75 2090.1 292.51 1442.0 323.32 825.9 152.73 1714.8 339.72
.3048 2.7433 .1399 .6911 .2242 1.7789 .1849 - ,1904 .1981 .9061
13.3440 3.0121 5.6362 2 .go22 4.4254
236 237 238 239 240
Kawalinda Rubya I gabiro Ikizu Kome
1650.4 1284.9 1078.4 967.8 1062.1
290.02 263.54 229.91 269.75 263.76
,1757 .2051 .2133 ,2787 .2483
241 242 243 244 245
Ngara Mwanza Biharamulo Ukiriguru Samvwe M i s s i o n
1017.7 1026.9 957.4 837.4 957.4
167.76 253.30 178.31 215.67 480.77
246 247 248 249 250
Geita Ngudu K i jima M i s s i o n Shanwa Addis Ababa
1007.6 794.0 755.3 769.7 1162.5
209.02 210.99 166.32 194.94 165.26
(1) i n mm/yr; ( 2 ) ,
.5554 .0248 .2966 .5966 .6855
2.8975 2.9343 3.1706 3.3395 2.6430
.1648 .2467 .1862 ,2576 .5022
.go66 .9969 1.7031 .3235 1.6237
4.1991 3.8617 8.7233 3.0355 5.9419
.2074 .2657
1.2053 .3888 1.3145 1.2028 .ti765
5.0079 3.3287 6.4833 4.8015 3.3761
.2202
.2533 .1422
-
r2
r3
r4
.1137 - ,3093 - .2416
- .1701
,1809 - .0054 -.0991 ,3645 - ,0631 -.0602 ,1299 - .4536 - .0226
- .2053
.3398
r5 .0671
I
,1017
.0383
I D D
.1777 .0259 .1884 ,3681 - .3245
.Of316 .3211 -. 1947 - .2996 ,1710 .1795 .2939 -.2571 .0742 ,1646
I I D D I
.3561 .2380 .lo56 - .2387
.1792 - .0020 .1757 - .6647
D D
,1829 .0366 - . 1106 .1655 ,6742 .3719 - .0507 - .0099 - ,0981 .0499
- .2521
-1 /.-(4) u- .
- . 1013
- .2829
.2896
.1189
- .1564
,0089
I
- .2941 -. 1091
.2635
.3133
I
- .0615
,1557
.2733
I
.1245 - .1265 - .3445 - .0146 - . O M 3 .2440 - ,0110 ,2779 - .1897 1489
I I
- .0042 - .1116 .2880
.lo73 - .1720
-.
(3) c o r r e c t e d f o r b i a s i n e s t i m a t i o n from s a m p l e ; (4) I = independent and D = dependent
133
TABLE 4 . 4
P e r i o d s of r a i n f a l l measurement a t some o f t h e g a u g i n g s t a t i o n s i n t h e Sudan, Uganda and T a n z a n i a a s r e p o r t e d i n a number of references
S t a ti o n No.
Period(a)
*
Station No.
66 67 69 71 72 75 79 80
81 82
1902-40 1905- 40 1916-40 1905-40 1913-40 1902-40 1900-40 1901-40 1920-40 1930-40
137 142 145 146 150 1 51 152 156 157 163
87 88 91 92 95 97 98 99 100 101
1929-40 1919-40 1902-40 1930-40 1918-40 1922-40 1938-40 1901-40 1938-40 1912-40
167 172 175 176 181 185
105 110 111 118 124 126 127 128 133 139
1938-40 1904-40 1938-40 1915- 40 1928-40 1909-40 1932-40 1902-40 1931-39 1929-40
20 2 206 214 222
187 191 196
229 231 232 233 234 2 38 242 24 3 249
P e r i o d(b)* 1901-13 1904-13 1911-20 1904-20 1914-20 1906-20 1909-20 1909-20 1907-20 1908-20 1901-20 1909-20 1908-20 1911-20 (1893-98, 1907-20) 1908-20 1896-1920 1902- 20 1907-20 1918-20 1896-1915 0899-1903, 1913- 1 92 0
c1893-98, 1901-11)
Period(c)x
1926-70 1933-67 1926-70
1926-70 1926-70
1934-70 1926-70
-
1926 70 1933-70 1926-70 1930-70 1926-70 1926-68 1932-69 1926-70 1932-70 1926-68 1928-69 1928-60
* ( a ) I r e l a n d , The C l i m a t e o f t h e S u d a n , e d i t e d by T o t h i l l (1948) ( b ) B r o o k s , The D i s t r i b u t i o n o f R a i n f a l l o v e r Uganda, w i t h a n o t e on Kenya Colony (1924) ( c ) UNDP & WMO, Vol. I , P a r t I , Meteorology and Hydrology of t h e B a s i n , H y d r o m e t e o r o l o g i c a l S u r v e y of t h e C a t c h m e n t s o f Lakes V i c t o r i a , Kyoga and A l b e r t (1974)
134
N
2:O
30 '
E
Sal,U>(
--
2'oofL (100)
'm&/il5; H - C
Giza Fayumo
I
Port S a i d
A I RO
41°
(SO', 3 6 O
N
30'-
.Suez
Minya Assiu t
-9 25'
F i g . 4.3.
D a k h L a> > K
(<\0
I s o h y e t a l map of t h e a n n u a l r a i n f a l l on t h e N i l e B a s i n
2 5'
135
Fig. 4 . 4 .
I s o h y e t a l map o f t h e mean annual r a i n f a l l on t h e N i l e B a s i n t i l l 1967
136
Fig. 4 . 5 . Map o f t h e mean annual r a i n f a l l on t h e N i l e B a s i n and t h e d i s t r i b u t i o n diagrams o f monthly r a i n f a l l ( t h e World Water-Balance, UNESCO, 1978)
137
21002000 -
0
100 200 300
400
500
600
19001800
-
1700 1600 ;1500
.1400 z1
E
E
-
''0
139 0 Y )
15'1
D a t a from I r e l a n d , ending 1940 D a t a from Hydrometeorological survey of the catchments of lakes Victoria, Kyoga a n d A l b e r t , e n d i n g 1970
9 00 800 700 700 800
181 0
900 1000 1100 1200 1300 1400 1500 1600 17001800 1900 2000 2100 X , mmlyr.
-
Fig. 4 . 6 . The mean annual r a i n f a l l o v e r t h e 30-year p e r i o d 1938-1967, X versus t h e mean annual r a i n f a l l o v e r o t h e r p e r i o d s o f r e c o r d , X'
138
30
_ - -- _ _ - r -
20°
- 15'
-
El oGeneina
Fasher
0,-30°10
5 O
Fig. 4.7.
C o n t o u r l i n e s o f e q u a l c o e f f i c i e n t o f v a r i a t i o n of a n n u a l r a i n f a l l
0 0
N N
0 0 N 0
0 0
“0
0 0 Lo
-
0 c
0 U
0 OD 0
0
0
Lo
0
0 U
0 0
N
139
In 0
u m
N
d
rl rl
C
w k
m
.r(
El
m
rl
m a,
9 0
w E
2 a,
c u
c u k
.rl rl
w m
d
140
N
-30'
-25'
. 20'
-15'
Fig. 4.9.
Contour lines of equal coefficient o f skewness of annual rainfall
141
TABLE 4 . 5
E s t i m a t e d a n n u a l r a i n f a l l f o r g i v e n r e t u r n p e r i o d s a t some of t h e rain-gauging
s t a t i o n s i n t h e N i l e Basin (Shahin, M . M . ,
Station Serial Number
Distribution Function
2 4 5 9 10 13 14 15 16 17 18 20 24 28 29 32 39 41 44 47 49 51 53 58 62 63 68 70 71 75 77 79 80 82 83 85 86 87 89 90 91 92 94 98 99 100 10 1 10 2 103 104 105
Normal Normal Pearson I11 Pearson I11 Pearson I11 P e a r s o n I11 Pearson I11 Normal P e a r s o n I11 Pearson I11 Pearson I11 P e a r s o n I11 P e a r s o n I11 Pearson I11 Normal Pearson I11 P e a r s o n I11 Pearson I11 Pearson I11 Pearson I11 P e a r s o n I11 P e a r s o n I11 P e a r s o n I11 P e a r s o n 111 Pearson I 1 1 P e a r s o n I11 P e a r s o n I11 P e a r s o n 111 P e a r s o n I11 Pearson I11 P e a r s o n I11 P e a r s o n 111 Normal P e a r s o n I11 Pearson I11 2 - P a r . Lognormal Pearson 1 1 1 P e a r s o n I11 P e a r s o n 111 2 - P a r . Lognormal Normal P e a r s o n I11 Normal 2 - P a r . Lognormal % - P a r . Lognormal 2 - P a r . Lognormal Normal Normal P e a r s o n 111 Pearson I11 Normal
R a i n f a l l d e p t h mm/yr,
1.01 34 16 06 47 02 15 17 45 06 18 15 10 15
-
21 00
-
00
-
00 05 00
-
27 08 122 53 83 85 134 137 112 386 93 271 115 323 200 246 38 3 144 317 338 20 3
2 181 124 107 148 179 69 136 190 180 146 76 63 85 33 51 23 22 23 20 09 07 02 01 00 01 09 05 108 31 60 218 165 321 24 2 256 19 1 288 295 287 572 30 3 4 30 284 540 388 394 592 370 367 424 4 18
5 235 163 150 206 262 97 204 242 255 216 109 91 121 55 70 42 33 41 40 22 16 06 06 06 03 21 25 19 5 69 99 304 237 394 329 334 257 368 369 379 660 380 503 346 650 493 466 667 451 482 5 36 496
1983)
f o r r e t u r n period, y r 10
20
50
100
26 3 183 174 245 304 114 247 269 29 8 258 129 107 142 69 80 66 41 51 53 32 23 10 10 13 05 25 46 254 93 123 353 278 431 378 379 294 4 16 411 434 712 4 19 546 378 719 556 507 707 494 582 6 20 537
286 200 195 278 34 3 128 285 29 2 336 29 5 146 122 16 1 82 88 95 47 61 66 41 29 13 14 20 06 35 70 310 117 144 39 5 315 463 422 4 18 340 459 448 484 757 452 583 404 775 6 18 544 740 5 29 686 704 570
311 219 2 19 320 389 146 331 317 380 340 167 140 183 98 98 137 55 72 82 55 37 17 19 30 08 47 104 38 3 146 170 445 357 498 473 465 388 511 49 2 543 809 489 627 4 34 851 690 589 776 568 8 30 812 608
329 232 2 36 349 421 158 346 334 411 37 2 182 152 199 110 104 172 60 81
95 65 43 20 22 38 10 56 131 4 36 167 189 479 388 521 509 497 432 547 521 585 850 5 14 658 454 901 748 621 80 1 59 5 940 89 5 633
142
TABLE 4 . 5
Station Serial Number
106 107 108 109
110 112 115 117 118 122 123 124 125 126 127 128 130 131 132 133 134 136 137 138 143 146 147 148 149 150 153 154 157 158 159 161 162 163 164 165 166 167 168 169 170 172 173 174 175 176 177
(continued)
Distribution Function Normal Normal Normal P e a r s o n I11 P e a r s o n I11 Normal P e a r s o n I11 P e a r s o n I11 Normal Normal Normal P e a r s o n 111 P e a r s o n I11 P e a r s o n I11 P e a r s o n I11 Normal Normal P e a r s o n I11 Normal P e a r s o n I11 Normal Normal Normal Normal Normal Normal 2-Par. Lognormal Normal 2 - P a r . Lognormal P e a r s o n I11 P e a r s o n I11 P e a r s o n I11 P e a r s o n I11 P e a r s o n 111 Normal P e a r s o n I11 P e a r s o n I11 P e a r s o n I11 P e a r s o n I11 P e a r s o n I11 P e a r s o n I11 Normal P e a r s o n I11 P e a r s o n I11 P e a r s o n I11 P e a r s o n I11 Pearson 2 - P a r . Lognormal 2 - P a r . Lognormal P e a r s o n I11 P e a r s o n I11
R a i n f a l l d e p t h mm/yr,
for r e t u r n p e r i o d , y r
1.01
2
5
10
20
50
100
232 223 30 2 567 5 24 467 385 470 466 39 1 457 9 10 5 29 553 462 812 327 377 346 621 7 28 845 575 1108 804 40 3 1077 868 795 544 625 547 1066 876 777 1013 975 794 938 987 893 847 872 99 1 1083 1131 870 820 84 3 106 1 1075
423 478 641 767 722 692 917 725 795 897 798 1212 898 1294 968 1182 759 940 909 87 3 1187 1358 999 1473 1252 9 10 1440 1286 1120 669 1258 1391 1325 1024 1230 1344 1273 1126 1229 1315 1126 1353 1194 1242 1328 1488 1193 1256 1173 1227 1555
493 57 1 76 3 866 820 774 1109 84 3 913 1082 922 1364 1087 1563 1151 1316 9 15 1142 1113 1012 1353 1543 1153 1605 1415 1094 1599 1437 1273 891 1446 1566 1488 1177 1394 1568 1483 1353 1428 1551 1377 1536 1379 1466 1513 1694 1432 1470 1329 1492 1803
5 29 6 19 8 28 9 24 878 8 16 1184 9 10 975 1177 986 1453 1198 1669 1221 1387 997 1209 1220 1096 1439 1640 1233 1674 1499 1189 1690 1516 1365 1072 1540 1635 1591 1263 1479 1710 16 19 1498 1554 1705 1558 1632 1493 1621 1635 1820 1588 1596 1420 1703 1950
559 659 881 975 928 851 1242 968 1026 1256 1039 1531 1298 1748 1274 1444 1064 1264 1308 1172 1511 1720 1300 1730 1569 1269 1766 1581 1441 1258 16 16 1681 1685 1363 1550 1843 1747 1633 1672 1847 1734 1711 1596 1768 1749 1935 1735 1710 1499 1917 2080
59 2 704 940 1037 990 89 1 1304 1037 1084 1345 1098 1625 1417 1838 1330 1509 1140 1315 1407 1264 1592 1810 1374 1794 1648 1358 1872 1655 1532 1511 1697 1722 180 1 1424 1630 2008 1909 1801 1818 2029 1965 1802 1721 1957 1893 2074 1875 1853 1597 2203 2238
615 7 34 980 1080 1033 917 1342 1085 1123 1405 1139 1691 1503 1888 1365 1553 1191 1347 1472 1330 1645 1870 1424 1837 1701 1417 19 19 1704 1601 1702 1749 1745 1886 1487 1683 2128 2013 1923 1925 2160 2136 1859 1812 2096 1999 2177 1919 1946 166 2 2422 2349
143
TABLE 4 . 5
Station Serial Number 179 180 181 182 184 185 186 187 188 189 190 191 192 193 194 195 196 197 199 20 2 20 3 204 20 5 206 20 8 209 211 213 214 219 220 2 20 224 225 226 228 231 232 235 24 2 244 246 249 250
(continued)
Distribution Function Pearson I 1 1 Pearson I 1 1 Pearson I 1 1 Pearson I 1 1 Pearson I 1 1 Pearson I 1 1 Pearson I 1 1 Pearson I 1 1 Pearson I 1 1 Normal Normal Pearson I 1 1 Pearson I 1 1 Normal Pearson I 1 1 Pearson I 1 1 2 - P a r . Lognormal Pearson I 1 1 Pearson I 1 1 Pearson I 1 1 Pearson I 1 1 Pearson I 1 1 Normal Pearson I 1 1 Pearson I 1 1 2-Par . Lognormal Normal Pearson I 1 1 Normal Pearson I 1 1 Normal 2 - P a r . Lognormal Pearson I 1 1 Normal Pearson I 1 1 Normal Pearson I 1 1 Pearson I 1 1 Pearson I 1 1 Pearson I 1 1 Pearson I 1 1 Pearson I 1 1 Pearson I 1 1 Pearson I 1 1
R a i n f a l l d e p t h mm/yr,
f o r return period, y r
1.01
2
5
10
20
50
100
1098 10 16 1097 995 10 10 6 30 852 90 1 996 865 823 841 548 56 5 671 5 26 673 740 7 39 66 1 747 700 754 680 80 1 7 20 589 1090 1030 1107 885 651 7 37 766 643 426 661 1562 1151 625 388 705 487 858
1468 1345 1470 1281 1324 1133 1293 1244 1510 1578 1424 1575 1004 1055 1070 867 1051 1126 1103 884 1039 1052 1165 986 1243 1132 1207 1531 1739 1558 1553 1064 1154 1250 1197 1074 1814 20 56 1666 985 8 26 967 732 1146
1772 1588 1682 1537 1551 1359 1529 1421 1775 1835 1642 1787 1209 1232 1252 1099 1247 1379 1332 10 54 1185 1213 1314 1142 1426 1326 1439 1767 2006 1802 1794 1267 1631 1425 1374 1308 2305 2321 1976 1219 1015 1161 913 1294
1977 1752 1812 1712 1698 1487 1671 1526 1933 1971 1756 1884 1326 1325 1356 1245 1366 1539 1476 1171 1270 1305 1392 1234 1526 1439 1560 1908 2145 1950 1920 1383 1785 1516 1461 1431 2578 2480 2170 1366 1120 1288 1031 1383
2171 1904 1929 1880 1834 1598 1798 1619 2072 2082 1850 1958 1427 1401 1447 1382 1474 1687 1608 1278 1345 1385 1456 1316 1613 1537 166 1 20 35 2260 2082 2025 1495 1920 1592 1531 1532 2812 2622 2348 1502 1211 1407 1142 1463
2417 2096 2072 2096 2008 1729 1953 1732 2241 2208 1955 2084 1546 1487 1556 1552 1601 1871 1772 14 15 1436 1481 1528 14 1 5 1712 1653 1775 2188 2390 2241 2142 1604 2078 1677 1607 1646 3084 2794 2565 1671 1316 1557 1282 1558
2599 2234 2174 2255 2133 1820 2063 1811 2366 2292 20 26 2126 1627 1545 1629 1676 1702 2002 189 1 1518 1500 1545 1577 1485 1779 1740 1824 2297 2448 2354 2220 1718 2190 1734 1655 1722 3312 29 16 2721 1793 1391 1666 1384 1628
144
800
:
LEGEND
700
+-.+
$ 600 aJ
U
= *
500
S t a t i o n NO. 2
--o
,,
V--..Y
.I
x---*
,,
2
I,
C
.-
2 -0
400
300 U
2 00 100 0
I
.01
,
I
,
I
-1 .2 .5 1 2
I
,
I
5 10 20
,
I
40
.
,
60
,
I
I
I
I
,
80 90 95 9899
P r o b a b i l i t y of non-exeedunce,
,
,
,
I
99.8 99.9
o/o
Fig. 4.10a. F i t t i n g t h e normal d i s t r i b u t i o n t o t h e annual r a i n f a l l depth a t some s t a t i o n s i n t h e N i l e B a s i n
1000 9 00 E E 800 L
c
U
-
700
2
600
-0
500
C .-
3
a
400
300 200 .01
.1 .2 .5 1 2
5 10 20 40 60 80 90 95 9899 99.8 99.95 non - exeedance, '1.
P r o b a b i l i l y of
Fig. 4.10a. F i t t i n g the normal d i s t r i b u t i o n t o t h e annual r a i n f a l l depth a t some s t a t i o n s i n t h e N i l e Basin
145
2 000 1800
5
el600
TJ
-
5 1400 + C
.-
2 1200
-0
;1000
U
800 600
400
.01
.1 .2 .5 1 2 5 10 20 40 60 80 90 95 9899 P r o b a b i l i t y of non - e x e e d a n c e , ' / .
99.8 99.5
Fig. 4.10a. F i t t i n g t h e normal distribution to t h e annual rainfall depth at some stations i n the Nile B a s i n
01
.1 . 2 .5 1 2 5 10 20 40 60 80 9 0 95 9899 R o b a b I I i t y of n on - ex ee d a n c e , '1.
99.8 99.5
Fig. 4.10b. F i t t i n g t h e lognormal distribution to the annual rainfall depth at some stations in t h e Nile B a s i n
146
800
LEGEND E E
700
0-.-.0
5a 600 U
0
C
-
0 3
.i-..-x v--v 2--.
500
Station No. 9 44 ,I
2
75 79 82 ,, 83 ,, 86 8,
(,
--.--*
3-3
'c
'p
x----x
,I
8,
I ,
I ,
400
300
C
a
200 100
0 P r o b a b i l i t y of n o n -exeedance, % F i g . 4 . 1 0 ~ . F i t t i n g t h e Pearson I 1 1 d i s t r i b u t i o n t o t h e annual r a i n f a l l depth a t some s t a t i o n s i n t h e N i l e B a s i n
2000 E 1000 E
5 1600 a
U
-- 1400 0
r
'5 1200 -
0 3 C
a
1000
800 600
400
.01
.1 .2 .5 1 2 5 10 20 40 60 80 9 0 95 98 99 99.8 99.5 P r o b a b i l i t y of non - exeedance,Oio
F i g . 4 . 1 0 ~ . F i t t i n g t h e Pearson I 1 1 d i s t r i b u t i o n t o t h e annual r a i n f a l l depth a t some s t a t i o n s i n t h e N i l e B a s i n
147
800
/;"
W'
/i
4 X y J X
F i g . 4 . 1 0 ~ . F i t t i n g t h e Pearson I 1 1 d i s t r i b u t i o n t o t h e annual depth a t some s t a t i o n s i n t h e N i l e Basin
.01
.1 .2 .5 1 2 5 10 20 40 60 80 9 0 95 98 99 99.8 99.95 Pro b a b i l i t y of non - e x e e d a n c e , '1.
F i g . 4 . 1 0 ~ . F i t t i n g t h e Pearson I 1 1 d i s t r i b u t i o n to t h e annual r a i n f a l l depth a t some s t a t i o n s i n t h e N i l e B a s i n
P
TABLE 4.6
The basic properties of the autoregressive models fitted to the rainfall sequences of the listed stations (Shahin, M.M., 1983) Model parameters
Station No.
Model al
12 22 30 69 97 111 113 114 116 119 120 121 129 135 139 140 141 142 144 145 151 152 155 156 160 171 178
Serial correlation of residuals
-0.0718 -0.1221 0.3570 -0.4458 -0.0134 0.4518 0.1864 -0.2197 -0.0895 0.3979 0.4598
-
-0.1313 0.4272 0.4648 0.1936 0,0640
-
0.4105 0.1618 0.4310 -0.0550 0.2566 0.5480 0.6260 0.3490
a2 -0.0051 -0.0147
-
-0.0347 -0.0461
-
-
-0.0255
-
-0.0030
-
-0.2418 -0.3012
-
a3
a4
l-1
r2
l-3
r4
r5
-0.039 -0.200 -0.095 -0.038 0.050 -0.074 0.017 -0.007 0.008 -0.040 -0.019
-0.114 -0.409 0.333 -0.129 -0.221 0.159 -0.224 -0.098 0.121 -0.027 -0,035
-0.173 0.180 -0.346 0.023 -0,101 -0.104 0.183 0.340 -0.399 0.254 0.062
0.352 0.194 0.347 -0.370 -0.360 -0.028 0.295 -0.149 -0.374 -0.170 0.014
-0.156 -0.250 -0.169 -0.088 0.135 -0.079 -0.432 -0.429 -0.180 0.171 0.145
-0.001 -0.087 0.070 0.001 0.033
-0.062 0.219 -0.030 0.128 -0.388
0.029 -0.068 -0.100 -0.021 0.058
0.330 -0.031 -0.274 -0.376 0.004
-0.117 -0.044 0.007 0.022 -0.066
-
-
0.074 0.045 0.070 -0.044 0.025 0.033 -0.008 -0.094
-
-
-0.258 -0.178 -0.168 -0.380 0.286 0.166 0.121 0.216
-
-
-0.016 -0.203 0.129 -0.181 0.190 -0.245 -0.047 0.043
-
-
-
-
-
-0.036 -0.151 -0.171 0.064 -0.306 0.124 0.089 0.218
-0.361 0.154 -0.127 0.100 0.072 -0.010 0.211 -0.277
2nd order 2nd order 1st order 1st order 1st order 1st order 4th order 2nd order 1st order 1st order 1st order unsuitable 1st order 1st order 1st order 1st order 1st order unsuitable unsuitable 1st order 2nd order 1st order 2nd order 1st order 2nd order 2nd order 1st order
P
03
TABLE 4.6
(continued)
No
Serial correlation of residuals
Model parameters
Stat ion
Model
.
rl
r2
r3
r4
r5
0.3490 0.6001 -0.1649 0.1801 0.3869 0.3645
-0.094 -0.001 0.061 0.107 0.042 0.070
0.216 0.107 0.187 0.196 -0.306 -0.203
0.043 0.018 0.271 -0.241 0.289 -0.029
0.218 0.120 0.047 -0.013 0.290 0.006
-0.277 -0.272 0.082 -0.210 -0.117 -0.224
0.6742 -0.0507 0.3398 -0.2705
-0.064 -0.036 0.197 -0.097
-0.207 0.338 0.085 -0.100
-0.035 0.259 0.113 0.195
0.193 -0.265 -0.020 -0.325
“1
178 183 200 20 1 210 229 230 233 234 236 237
“2
“3
“4
-
-
-
-
-
0.121 -0.053 -0.095
-0.0732
-0.0197
-0.0050
0.133
-
-
-
-
1st order 1st order 2nd order 2nd order 1st order 1st order unsuitable 1st order 1st order 1st order 4th order
c
L
W
150
4.2.2
S e a s o n a l and monthly r a i n f a l l
The d i s t r i b u t i o n of t h e r a i n f a l l among t h e months o f t h e y e a r assumes d i f f e r e n t p a t t e r n s . Those c o v e r i n g t h e 250 g a u g i n g s t a t i o n s which a r e i n v e s t i g a t e d h e r e h a v e b e e n grouped i n t o p r i n c i p a l p a t t e r n s . To make t h e comparison between one g r o u p and t h e o t h e r f e a s i b l e , t h e monthly r a i n f a l l e x p r e s s e d i n p e r c e n t o f t h e a n n u a l r a i n f a l l ( s e e Appendix C) h a s b e e n u s e d a s a b a s i s . The n i n e p r i n c i p a l p a t t e r n s which a r e shown i n F i g . 4 . 1 1 . show t h e f o l l o w i n g c h a r a c t e r i s t i c s : Group I c o m p r i s e s s t a t i o n s 1 t o 29. These are a l o n g t h e M e d i t e r r a n e a n and s o u t h wards up t o t h e c e n t r a l p a r t o f t h e N i l e Delta a r e a . The r a i n f a l l l a s t s from O c t o b e r t o A p r i l o r May and t h e maximum d e p t h f a l l s i n December o r J a n u a r y . Group I 1 c o m p r i s e s t h e s t a t i o n s i n t h e e a s t e r n p a r t o f Egypt and a l o n g t h e Red S e a c o a s t up t o P o r t S u d a n , T h i s g r o u p i s c h a r a c t e r i z e d by a h i g h peak i n November and t h e w i n t e r r a i n f a l l is r a t h e r s c a n t y . T y p i c a l s t a t i o n s i n t h i s g r o u p are N o . 45 i n Egypt and 6 7 i n t h e Sudan. Group I11 c o m p r i s e s t h o s e s t a t i o n s i n t h e n o r t h e r n and c e n t r a l p a r t s of t h e Sudan from No. 79 t o 1 0 9 . The maximum r a i n f a l l h e r e t a k e s p l a c e i n August. The t o t a l r a i n f a l l i n J u l y and August e x p r e s s e d as p e r c e n t a g e o f t h e a n n u a l r a i n f a l l v a r i e s from a b o u t 80% i n t h e n o r t h t o , s a y , 60% a t J e b e l e i n h a l f w a y between Khartoum and Malakal o n t h e White N i l e . Group I V i s s i m i l a r t o Group 111, e x c e p t t h a t t h e b a s e w i d t h i s l a r g e r and t h e peak is s h o r t e r . So t h e r a i n f a l l s on t h i s group from F e b r u a r y t o March t i l l November. The August peak i s n e a r l y 30% o f t h e a n n u a l r a i n , as a t s t a t i o n 1 1 0 , and f a l l s t o a b o u t 21% a t Meshra Er-Req,
s t a t i o n 125, i n t h e s o u t h e r n p a r t of
t h e Sudan. Group V c o m p r i s e s t h e g a u g i n g s t a t i o n s from No. 126 t o 1 3 9 . Here t h e r a i n f a l l s i n a l l months of t h e y e a r , and t h e maximum r a i n f a l l s i n August w i t h a d e p t h of 20% o r less o f t h e a n n u a l r a i n f a l l . Group V I c o m p r i s e s t h e s t a t i o n s from No. 140 t o 1 6 2 . The r a i n f a l l o v e r t h i s g r o u p of s t a t i o n s c o v e r s t h e whole y e a r e x c e p t t h a t t h e monthly r a i n a t t h e t a i l s i s more t h a n t h a t o v e r t h e s t a t i o n s i n t h e p r e v i o u s g r o u p . In o t h e r words, t h e p a t t e r n h e r e t e n d s t o b e more u n i f o r m t h a n i n t h e p r e v i o u s g r o u p , and t h i s u n i f o r m i t y improves g r a d u a l l y a s one moves t o t h e s o u t h (compare s t a t i o n N o . 140
t o s t a t i o n No. 1 6 1 , F i g . 4 . 1 1 . ) . Group V I I c o m p r i s e s t h e s t a t i o n s 1 6 3 t o 218. The m a j o r f e a t u r e o f t h i s group is t h e c o n s i d e r a b l e d e c l i n e o f t h e r a i n f a l l i n J u l y compared t o t h e p r e v i o u s groups. Another f e a t u r e i s t h e development o f t w o p e a k s ; t h e f i r s t and h i g h e r peak o c c u r s i n A p r i l o r l a y , and t h e s e c o n d and lower peak o c c u r s i n November. Group V I I I c o m p r i s e s t h e g a u g i n g s t a t i o n s 219 up t o and i n c l u d i n g 231. The main d i f f e r e n c e between t h i s group and Group V I I i s t h a t t h e r a i n f a l l i n t h e second h a l f of t h e y e a r i s more u n i f o r m l y d i s t r i b u t e d .
151
30 r
,---
---
I I--
___,
J F M A M J J A S O N O
J F M A M J J
[
0
~
;--,---;
J F M A M J J A S O N D
->r
5
2
2o
A S O N D
50
"
"
"
"
"
"
J F M A M J J A S O N D
40
30
20
10
o
I a--
I~
"
3 ~ "
"
" -- ~
'
J F M A M J J A S O N D
J F M A M J
J A S O N D
Month Fig. 4.11.
Main patterns o f monthly rainfall in percentage of annual rainfall
152 Group I X c o m p r i s e s t h e r e m a i n i n g s t a t i o n s e x c e p t N o . 250, s i t u a t e d a t Addis Ababa. The r a i n f a l l i n t h e s e c o n d h a l f o f t h e y e a r f o r t h i s group d i f f e r s from t h a t f o r Groups V I I and VIII i n t h a t i t i s d i s t r i b u t e d n e a r l y l i k e a t r i a n g l e . The monthly r a i n f a l l p a t t e r n a t s t a t i o n No. 250 i s q u i t e s i m i l a r t o t h a t o f Group 1 1 1 , e x c e p t t h a t t h e t a i l s h e r e e x t e n d t o c o v e r t h e whole y e a r . The month t o month v a r i a t i o n , sometimes r e f e r r e d t o a s s e a s o n a l v a r i a t i o n , can be formulated,
among o t h e r s , by a harmonic f u n c t i o n .
The e x p r e s s i o n u s e d i n t h e h y d r o m e t e o r o l o g i c a l s u r v e y o f t h e c a t c h m e n t s o f Lakes V i c t o r i a , Kyoga and A l b e r t , r e a d s
(4.10) where.
R t = r a i n f a l l a t any month t ( t = 1, 2 , A.
....,
= c o n s t a n t e q u a l t o t h e a n n u a l r a i n f a l l d i v i d e d by 1 2 ,
A r = a m p l i t u d e o f t h e r t h harmonic ( r = 1, 2 ,
$
12)
....,
= p h a s e a n g l e of t h e rth harmonic ( r = 1, 2 , F o r t h e above-mentioned
6 ) , and
. . . .,
6)
hydrometeorological survey, t h e parameters A
and
0
w e r e c a l c u l a t e d u s i n g t h e r a i n f a l l i n e a c h y e a r from 1931 up t o and i n c l u d i n g
1970 f o r e a c h of t h e 22 g a u g i n g s t a t i o n s i n c l u d e d i n t h a t s u r v e y . S i n c e t h e r e a r e 12 monthly v a l u e s , R t , p a r a m e t e r s c a n n o t exceed 1 2 ; 6 f o r A A
....,
and $ r ( r = 1, 2 ,
f o r each y e a r , t h e maximum number o f
and 6 f o r
0 (0,
= z e r o ) . The v a l u e s o f
6 ) a v e r a g e d o v e r t h e p e r i o d 1931-1970 a r e g i v e n i n
T a b l e 4.7. More d e t a i l e d i n f o r m a t i o n a b o u t t h e s e harmonic p a r a m e t e r s , as w e l l a s t h e i r maximum and minimum v a l u e s , d a t e s o f o c c u r r e n c e and d i s t r i b u t i o n i n s p a c e c a n b e found i n P a r t 1, V o l .
I o f t h e s u r v e y r e p o r t (WMO, 1974).
From T a b l e 4.7 i t i s a p p a r e n t t h a t t h e f i r s t two p a i r s o f t h e harmonic p a r a -
meters, i . e . A1,
+1 and A 2 , $ 2 , a r e by f a r t h e most i m p o r t a n t o f a l l s i x p a i r s
i n t h e s e r i e s . The r e l a t i v e i m p o r t a n c e o f a c e r t a i n o s c i l l a t i o n c a n b e measured by t h e s q u a r e o f t h e a m p l i t u d e of t h e c o r r e s p o n d i n g s i n e t e r m . The e x p l a i n a b l e p o r t i o n of t h e v a r i a n c e i n a series i s t h e s u m o f
4
(A ) * , whereas t h e t o t a l
variance can be expressed a s
6
Var ( R ~= ) where
E
f c
r=l
+
E
(4.11)
i s t h e r e s i d u a l l e f t a f t e r f i t t i n g t h e s i x h a r m o n i c s , which i s sometimes
r e f e r r e d t o as t h e u n e x p l a i n a b l e p o r t i o n o f t h e t o t a l v a r i a n c e .
TABLE 4 . 7
The v a l u e s of t h e harmonic p a r a m e t e r s i n t h e model d e s c r i b i n g t h e s e a s o n a l v a r i a t i o n of r a i n f a l l a t t h e l i s t e d s t a t i o n s (WMO,
1974)
Gauging s t a t i o n
No.
-
145 146 152 163 172 191 196 198 202 214 222 229 231 232 233 234 238 242 243 249
f
ff
Name El-Doret’ Bugondo** Gulu Moroto Masindi Mbale Fort P o r t a l Entebbe Masaka Kalangala Mbarara Mumias Kisumu Kericho Kisii Bukoba Tarime Musoma Igabiro Mwanza Biharamulo Shanwa
Values of harmonic parameters A1
43.9 46.9 84.5 54.4 35.3 50.9 18.5 60.4 25.9 76.7 18.2 62.3 41.0 48.6 36.9 85.8 39 . O 49.5 56.3 68.5 62.0 72.6
$1
A2
275.4 250.5 235.1 270.2 241.4 260.5 177.8 331.5 344.0 329.9 71.1 282.4 336.6 301.6 290.4 0.8 8.1 2.7 30.5 37.3 32.3 35.9
15.9 50.4 34.1 9.6 37.8 23.4 72.4 69.8 55.7 74.4 40.0 50.9 33.8 41.3 57.5 86.1 52.7 36.0 47.2 30.4 39.9 13.2
92 182.4 212.3 233.4 188.0 217.7 205.8 214.8 181.8 194.8 170.3 213.1 196.1 197.2 196.0 206.3 190.7 196.5 201.5 206.0 190.6 209.8 193.5
A3 27.3 20.0 16.5 19.8 10.8 13.9 5.8 28.4 21.9 30.2 10.2 18.2 23.1 25.1 24.4 47.2 23.1 22.1 21.0 27.9 23.3 25.3
$3 116.1 57.2 78.9 126.1 112.6 80.3 90 .o 81.9 61.9 89.7 96.7 53.5 101.2 81.6 87.6 66.5 103.3 103.1 100.1 105.6 115.8 109.6
A4
94
A5
21.2 11.1 13.9 14.0 6.3 7.2 3.2 17.0 6.8 12.4 6.1 10.6 6.6 5.7 5.9 17.5 4.3 8.0 4.4 6.7 5.4 5.4
226.9 267.8 244.8 266.5 260.8 256.1 291.0 229.3 240.7 178.5 205.9 225.9 181.4 234.1 161.5 261.5 289.8 291.1 328.1 344.9 292.0 9.7
8.0 7.7 9.5 7.4 2.9 5.0 1.2 4.7 11.3 7.4 4.1 5.5 3.1 1.7 2.9 12.8 3.3 5.9 5.2 4.3 9.7 8.0
El-Doret s t a t i o n i s s i t u a t e d a t OO36.N and 35O26’E. I t s a l t i t u d e i s 2287 m. Bugondo s t a t i o n is s i t u a t e d a t 1°37’N and 33017’E. I t s a l t i t u d e is 1067 m .
$5 164.0 117.1 358.0 88.7 20.5 74.2 241.9 79.4 88.0 83.7 221.5 106.9 177.3 23.3 230.4 115.3 153.4 203.1 171.1 241.9 208.6 189.8
3.8 5.3 15.3 5.3 5.8 0.7 6.2 8.5 4.0 4.0 3.8 2.2 3.5 3.8 5.3 5.5 2.5 5.2 0.7 0.3 1.2 7.7
154
The harmonic t e r m r = 1 means t h a t t h e p e r i o d o f t h e o s c i l l a t i o n i s 1 2 months and r = 2 means t h a t t h e c o r r e s p o n d i n g o s c i l l a t i o n h a s a p e r i o d o f 6 months. The l a t t e r i s t h e b i - a n n u a l o s c i l l a t i o n r e s p o n s i b l e f o r t h e t w o p e a k s i n A p r i l and November. T h i s i s v i s i b l e i n t h e p a t t e r n Groups V I t o I X , e s p e c i a l l y i n Groups V I I and I X ( s e e F i g . 4 . 1 1 . ) .
The h y d r o m e t e o r o l o g i c a l s u r v e y of t h e c a t c h m e n t s o f Lakes V i c t o r i a , Kyoga and A l b e r t i n c l u d e d t h e p r o b a b i l i s t i c m o d e l l i n g o f t h e monthly r a i n f a l l a t t h e chosen s t a t i o n s . I t h a s been r e p o r t e d t h a t t h e d i s t r i b u t i o n f u n c t i o n t h a t s e r v e s
as a good f i t t o t h e o b s e r v e d d a t a i s t h e two-parameter Gamma f u n c t i o n (WMO, 1 9 7 4 ) . T h i s f u n c t i o n c a n b e w r i t t e n as
/x P(X) =
xY-l
O
by
,-X/B
dx (4.12)
rw
where P(X)
r(y) y and
= cumulative p r o b a b i l i t y = gamma f u n c t i o n , and
B = parameters of t h e d i s t r i b u t i o n fu n ct i on
The monthly v a l u e s o f t h e y and $ p a r a m e t e r s f o r e a c h o f t h e 22 s t a t i o n s i n t h e c a t c h m e n t s o f t h e above-mentioned
l a k e s a r e i n c l u d e d i n T a b l e 4 . 8 . An
a c c u r a t e e s t i m a t e o f t h e s e p a r a m e t e r s is n e c e s s a r y f o r d e t e r m i n i n g t h e monthly r a i n d e p t h c o r r e s p o n d i n g t o a c e r t a i n r e t u r n p e r i o d . F o r t h i s p u r p o s e o n e needs
a t a b l e g i v i n g t h e c u m u l a t i v e gamma d i s t r i b u t i o n l i k e t h e o n e c o m p i l e d from
E.S. P e a r s o n and H.O. H a r t l e y ( ( 1 9 5 4 ) and p r e s e n t e d by C.T. Haan i n h i s books a s T a b l e E.8 (Haan, C . T . ,
1 9 7 7 ) . The p r o c e d u r e f o r d e t e r m i n i n g t h e magnitude of an
e v e n t f o r any g i v e n r e t u r n p e r i o d u s i n g t h i s t a b l e is e x p l a i n e d i n t h e same r e f e r e n c e . W e h a v e used t h i s p r o c e d u r e f o r e s t i m a t i n g t h e monthly r a i n f a l l w i t h r e t u r n p e r i o d s of 1 . 0 1 , 1.11, 2 , 5 , 10, 2 0 , 50 and 100 y e a r s a t Bukoba and t h e r e s u l t s o b t a i n e d are i n c l u d e d i n T a b l e 4 . 9 . N e e d l e s s t o s a y , t h i s same p r o c e d u r e c a n b e a p p l i e d t o any o t h e r s t a t i o n whose d a t a c a n b e w e l l f i t t e d by t h e gamma d i s t r i b u t i o n function.
TABLE 4 . 8
Values of t h e parameters of t h e Gamma d i s t r i b u t i o n f u n c t i o n f i t t e d t o t h e monthly r a i n f a l l a t 22 s t a t i o n s i n t h e catchments of Lakes V i c t o r i a , Kyoga and A l b e r t (WMO, El-Dore t
Month
Y Jan. Feb Mar. Apr May June July Aug Sep Oct.
. .
. . Nov . Dec . Month
1.094 0.844 1.684 2.485 3.012 2.175 8.586 6.102 1.623 2.146 1.443 1.079
Jan. Feb . Mar. Apr May June July Aug Sep. Oct.
. .
Nov.
Dec
.
1.314 1.819 5.897 10.518 8.360 3.208 2.306 6.778 7.686 12.869 7.314 3.493
Gulu (145)
B
Y
B
Y
B
28.60 70.99 45.16 67.35 43.56 38.16 15.55 19.82 36.60 26.72 57.67 48,23
1.152 1.428 1.438 4.310 7.492 3.241 4.866 5.458 3.815 3.473 1.109 1.196
20.30 39.13 64.66 44.67 24,24 29.37 21.65 25.93 40.20 41.23 81.96 49.41
1.017 0.913 3.386 8,440 9.228 5.751 6.256 10 .060 4.358 7.021 1.476 1.280
21.69 52.48 28.29 20.38 19.71 26.33 27.08 24.52 41.39 24.22 64.50 36.49
F . P o r t a l (172)
Y
Bugondo
Entebbe (191)
Masaka (196)
B
Y
B
Y
B
33.26 43.58 24.40 18.62 17.35 25.16 27.37 18.04 23.70 16.74 22.83 26.37
1.817 2.910 7.287 9.829 6.394 3.240 2.499 2.928 2.021 3.229 3.904 2.469
41.65 31.07 24.30 27.73 42.66 33.88 28.49 27.81 38.08 31.59 39.29 46.55
1.284 2.756 4.581 5.902 3.041 1.392 1.669 1.774 3.144 5.398 4.538 2.211
42.69 23.68 26.56 31.85 60.19 37.49 24.03 31.76 29.27 20.31 23.17 44.49
1974)
Moroto (146)
Y 0.809 0.994 1.235 1.671 2.264 1.478 2.795 1.928 1.144 1.346 0.649 0.987
B 19.43 40.35 64.58 75.25 61.62 59.23 49.74 57.84 47.67 36.46 100.78 32.49
Kalangala (198)
Y
8
Masindi (152)
Y 1.202 1.303 3.428 7.252 0.963 3.632 4.092 7.109 6.925 6.353 1.945 1.382
0 33.17 42.83 34.52 21.11 29.41 26.52 28.18 19.29 19.99 21.63 58.30 42.90
Mbarara (202)
Y 1.595 2.313 7.224 5.758 2.877 0.862 0.931 2.447 3.407 4.249 3.689 2.359
B 33.40 29.34 13.93 21.11 29.71 34.28 22.58 23.38 27.27 23.52 32.17 31.49
Mbale (163)
Y
B
0.879 1.418 2.262 5.340 7.532 5.982 8.058 4.898 4.580 4.499 1.182 1.516
40.43 37.78 44.78 29.75 22.29 18.96 15.18 25.97 22.22 19.27 55.45 33.08
Mumias (214)
Y
B
1.068 1.809 3.672 6.222 15.310 6.920 4.441 7.274 6.160 5.176 2.109 2.034
55.73 52.32 42.31 40.56 17.45 24.49 30.56 21.22 24.91 27.16 56.50 43.81
TABLE 4.8
(continued)
Month
Jan. Feb. Mar, Apr. M aY June July Aug . Sep Oct. Nov Dec
.
. .
Kisumu (222)
Kericho (229)
K i s i i (231)
Bukoba (232)
Tarime (233) ~
Y
B
1.011 2.079 4.075 5.568 4.873 2.307 2.722 2.303 3.226 1.964 1.219 2.189
52.42 40.67 34.00 33.37 29.87 32.85 19.85 31.76 18.63 27.19 75.05 43.72
1.571 50.47 1.995 47.64 2.635 62.95 5.965 41.50 11.248 19.89 9.600 14.44 4.295 26.43 8.684 16.01 4.870 24.33 4.525 24.89 2.464 47.65 2.395 45.84
1.442 41.67 1.750 53.51 2.689 68.04 6.343 40.36 12.457 17.15 6.205 22.22 3.795 26.92 6.942 21.71 3.541 45.43 4.047 35.88 2.214 65.72 1.966 59.73
4.318 3.245 9.632 12.596 7.986 2.523 1.418 2.776 3.754 5.408 6.196 4.544
Musoma (234)
Igabiro (238)
Mwanza (242)
Biharamulo (243)
Y
B
Y
B
Y
B 34.52 48.95 24.27 29.64 40.14 34.18 38.41 25.98 29.40 26.44 29.42 42.92
~~
Y
3.331 26.62 2.529 41.45 5.311 32.52 10.664 21.81 6.005 27.77 1.846 40.50 1.501 39.04 3.297 22.07 4.266 21.22 3.565 34.46 3.177 46.89 3.714 36.19 Shanwa (249)
Month
Jan. Feb. Mar. Apr May June July Aug Sep. Oct. Nov Dec
. .
. .
Y
B
1.378 1.409 2.033 6.207 3.947 1.372 0.680 1.222 1.142 1.520 2.185 1.791
46.55 51.14 62.58 29.13 27.55 18.02 40.54 17.66 25.09 26.43 38.21 38.89
Y 3.173 2.708 5.296 7.866 2.740 0.886 0.896 1.785 2.499 5.661 3.555 4.199
B 28.57 38.05 29.55 24.75 40.24 25.63 16.80 13.13 24.99 15.82 34.22 28.14
Y 4.168 1.987 2.514 7.592 2.516 0.953 0.746 0.183 1.461 1.193 2.275 2.595
8 24.27 51.64 61.17 23.97 35.03 25.39 27.08 24.86 25.90 57.09 56.89 56.56
Y 3.758 5.022 5.163 5.667 1.899 0.775 0.897 1.054 1.141 2.897 4.620 5.339
0 24.63 22.26 29.07 32.76 42.58 17.20 7.24 20.34 36.64 23 * 23 26.73 19.94
B
Y
3.438 3.039 4.593 4.027 1.319 1.298 18.848 0.848 1.545 1.037 1.759 4.046
B 32.00 36.63 27.75 37.08 35.24 4.65 0.28 12.31 8.11 28.79 50.76 33.01
157
S t a t i s t i c a l d e s c r i p t o r s o f monthly r a i n f a l l a t Bukoba i n t h e p e r i o d
TABLE 4.9
1931-1970, and t h e e s t i m a t e d monthly r a i n d e p t h f o r v a r i o u s r e t u r n periods Statistical descriptor
-
X Jan. Feb . Mar. Apr May June July Aug . Sep . Oct. Nov. Dec .
.
4.2.3
149 159 234 373 321 86 54 72 110 143 182 195
S
cV
72.11 81.82 73.37 102.74 109.11 56.24 42.97 37.97 56.81 62.18 81.89 94.96
0.4838 0.5151 0.3139 0.2752 0.3404 0.6523 0.7887 0.5264 0.5148 0.4349 0.4492 0.4869
Cs
0.83 0.15 0.07 0.21 0.17 1.88 1.08 0.26 0.71 0.58 1.49 1.40
R a i n f a l l , mm/month f o r r e t u r n p e r i o d , y r 1.01
1.11
31 25 94 172 117 09 02 09 21 38 59 40
66 59 144 245 187 28 07 24 46 69 97 79
2
5
135 142 227 359 307 74 40 63 100 134 174 161
200 225 296 451 409 125 85 103 153 190 238 237
-
10
20
50
243 279 331 507 470 158 115 129 187 225 279 284
276 328 366 557 528 190 148 155 218 258 321 327
328 387 413 619 596 232 186 186 257 294 365 381
100
366 436 4 39 656 642 258 215 208 285 320 385 4 20
Daily v a r i a t i o n
The day-to-day
e v o l u t i o n of r a i n i n E a s t A f r i c a was i n v e s t i g a t e d by D . H .
Johnson, u s i n g t h e s o - c a l l e d r e g i o n a l i n d e x o f r a i n i n e s s (1962). D a i l y r a i n f a l l s
were p l o t t e d on maps f o r e a c h day from November 1958 t o May 1960. The w e t a r e a s
were l o c a t e d and e a c h was g i v e n a n i n d e x number. T h i s number, sometimes r e f e r red t o as c o n c e n t r a t i o n , i s t h e p e r c e n t a g e , i n t e n s o f p e r c e n t , o f s t a t i o n s r e p o r t i n g r a i n t o t h e t o t a l number of s t a t i o n s c o n f i n e d t o t h e l o c a t e d a r e a . A l l d a i l y maps w e r e s o a n a l y z e d . A s a m p l e of t h e r e s u l t s o b t a i n e d is shown i n F i g . 4.12. T h i s k i n d o f a n a l y s i s i s q u i t e s u b j e c t i v e and c e r t a i n l y o f l i m i t e d v a l u e f o r d e s i g n p u r p o s e s . Moreover, t h e e x t e n t of t h e s h o r t - p e r i o d
variations i n rain-
f a l l d i s t r i b u t i o n i s s o l a r g e t h a t c o r r e s p o n d i n g months and s e a s o n s i n s u c c e s s i v e y e a r s would sometimes e x h i b i t v e r y d i f f e r e n t c h a r a c t e r s . The o r i g i n a l p a p e r by Johnson s u p p o r t s t h i s c o n c l u s i o n v e r y s t r o n g l y (1962). The h o u r - t o - h o u r ,
o r t h e d i u r n a l v a r i a t i o n o f r a i n f a l l on t h e Lake P l a t e a u ,
t h e Sudan, and Egypt h a s a l r e a d y been d i s c u s s e d i n C h a p t e r 3.
158
Fig. 4.12. Sequences of d a i l y r a i n f a l l i n d e x e s f o r t h e combined r e g i o n s A and B (Lake V i c t o r i a and Uganda), C and D (most o f K e n y a ) , and E t o I ( m a i n l y Tanganyika) . J a n u a r y t o e a r l y A p r i l 1959 ( J o h n s o n , D . H . , 1962) 4.3
EXTREME RAINFALL INTENSITY FOR DURATIONS OF ONE DAY AND SHORTER
The maximum r a i n f a l l i n a day d u r i n g t h e y e a r s o f o b s e r v a t i o n o f each r a i n f a l l s t a t i o n i n Egypt and t h e Sudan up t o 1967 i s l i s t e d i n T a b l e 4 . 1 0 . S i n c e t h e p e r i o d of o b s e r v a t i o n a t t h e s e s t a t i o n s v a r i e s i n a w i d e r a n g e , from a mini-
mum of a b o u t 20 y e a r s t o a maximum of 70 y e a r s or more, i t i s n o t p o s s i b l e t o reduce t h e observed extreme i n t e n s i t i e s t o a s i n g l e r e t u r n p e r i o d . The p r o c e d u r e used i n t h e h y d r o m e t e o r o l o g i c a l s u r v e y of t h e c a t c h m e n t s of Lakes V i c t o r i a , Kyoga and A l b e r t i s b a s e d on f i t t i n g t h e Gumbel Type I e x t r e m a l f u n c t i o n t o t h e d i s t r i b u t i o n o f t h e e s t i m a t e d c o n t i n u o u s 24-hour maximum, T h i s c a n b e o b t a i n e d from t h e r e l a t i o n (WMO, 1974)
4
R'
Rx.
(4.13)
Rx = (Rx)obs
+
where (Rx)obs
i s t h e o b s e r v e d f i x e d day maximum and R ' i s t h e h i g h e s t d a i l y
r a i n f a l l on t h e p r e c e d i n g o r f o l l o w i n g d a y . T h i s p r o c e d u r e made i t p o s s i b l e t o d e v e l o p , among o t h e r s , g e n e r a l i z e d c h a r t s of 1-day e x t r e m e r a i n f a l l of 2 and 100 y e a r s r e t u r n p e r i o d s and a nomogram f o r e s t i m a t i o n o f 1-day e x t r e m e r a i n f a l l c o r r e s p o n d i n g t o any g i v e n r e t u r n p e r i o d . A comparison between t h e t w o maps i n F i g s . 4 . 1 3 a . and 4 . 1 3 b . shows t h a t , a l l o v e r t h e a r e a c o v e r e d by t h e s u r v e y , t h e 100-year 1-day e x t r e m e r a i n f a l l i s n e a r l y t w i c e as much as t h e 2 - y e a r 1-day e x t r e m e r a i n f a l l . I f t h i s r a t i o h o l d s e v e r y w h e r e i n t h e N i l e B a s i n , o n e may u s e t h e nomogram shown i n F i g . 4 . 1 3 c . , t o g e t h e r w i t h Table 4.10, a f t e r c o r r e c t i n g t h e t abul at ed r a i n f a l l s , f o r t h e
159
e s t i m a t i o n o f t h e r a i n d e p t h c o r r e s p o n d i n g t o any r e t u r n p e r i o d . A f i x e d 24hour r a i n f a l l c a n b e c o r r e c t e d t o a c o n t i n u o u s 24-hour
r a i n f a l l s i m p l y by
i n c r e a s i n g t h e f o r m e r by a b o u t 10-13% o f i t s v a l u e . A s a n example, c o n s i d e r t h e 1-day e x t r e m e r a i n f a l l t h a t o c c u r r e d i n t h e 50-
y e a r p e r i o d 1918-67 a t s t a t i o n s 27 i n Egypt and 88 i n t h e Sudan. The o b s e r v e d d e p t h s , (Rx)obs,
R
X
w e r e 7 2 and 118 mm r e s p e c t i v e l y . T h e s e c a n b e c o r r e c t e d t o g i v e
o f 80 mm f o r s t a t i o n 27 and 130 mm f o r s t a t i o n 88. By p l o t t i n g t h e s e t w o
v a l u e s on t h e 50-year
r e t u r n p e r i o d l i n e of t h e nomogram, F i g . 4 . 1 3 c . ,
and draw-
i n g a s t r a i g h t l i n e p a s s i n g t h r o u g h each p o i n t s u c h t h a t t h e 100-year r e t u r n p e r i o d l i n e r e a d s a 1-day r a i n f a l l t w i c e as much a s t h e 1-day r a i n f a l l t o b e r e a d on t h e 2-year
Station No.
r e t u r n p e r i o d l i n e . One a r r i v e s a t t h e f o l l o w i n g r e s u l t s : R a i n f a l l , mm/day, f o r r e t u r n p e r i o d s o f 2-yr
5-yr
10-yr
20-yr
25-yr
50-yr
100-yr
27
44
55
64
71
73
80
88
88
71
88
103
114
118
130
142
I t g o e s w i t h o u t s a y i n g t h a t t h e above r e s u l t s s h o u l d b e r e g a r d e d as a p p r o x i mate o n l y . The East A f r i c a n M e t e o r o l o g i c a l D e p a r t m e n t , EAMD, h a s t h e p r a c t i c e of e x p r e s s i n g t h e extreme r a i n f a l l i n t e n s i t y f o r d u r a t i o n s s h o r t e r t h a n 1 day, ( I x ) t , by t h e r e l a t i o n (4.14) where I o , a , and n a r e p a r a m e t e r s v a r y i n g w i t h t i m e and s p a c e , and t i s t h e d u r a t i o n o f t h e r a i n s t o r m f o r which t h e maximum i n t e n s i t y ,
( I ) i s computed.
The p a r a m e t e r n h a s b e e n found t o v a r y between 0 . 5 and 1 . 0 . The s t r a n g e t h i n g i n e q . 4 . 1 4 i s t h a t i t d o e s n o t i n c l u d e any t e r m c o n n e c t e d t o t h e r e t u r n p e r i o d . On t h e o t h e r hand, t h e o b s e r v e d e x t r e m e 1-hour monthly and a n n u a l r a i n f a l l a t a few s t a t i o n s , a f t e r b e i n g c o r r e c t e d , h a v e b e e n f i t t e d by Gumbel Type-I
e x t r e m a l f u n c t i o n and e x t r e m e h o u r l y r a i n f a l l c o r r e s p o n d i n g t o any
g i v e n r e t u r n p e r i o d d e t e r m i n e d . The c o r r e c t i o n o f a f i x e d 1-hour i n t e n s i t y t o a c o n t i n u o u s 1-hour i n t e n s i t y i s d o n e , s i m i l a r t o t h e 1-day r a i n f a l l , by m u l t i p l y i n g t h e f i x e d i n t e n s i t y by a b o u t 1.13. F urther i n v e s t i g a t i o n of t h e intensity-duration-frequency-relationships
of
t h e r a i n f a l l o n t h e c a t c h m e n t s o f t h e E q u a t o r i a l Lakes is e s s e n t i a l b e f o r e s u c h i n c o n s i s t e n c y i s r e s o l v e d . Moreover, i t is c e r t a i n l y u s e f u l t o e x t e n d s u c h an i n v e s t i g a t i o n t o c o v e r o t h e r p a r t s o f t h e N i l e B a s i n area.
TABLE 4.10
Maximum r a i n f a l l i n a day a s observeh i n Egypt and t h e Sudan ( N i l e C o n t r o l S t a f f , 1972)
Station
No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
mm
No.
P e r i o d of observation
Maximum rainfall i n a day, mm
1948-67 1912-67 1946-67 1912-67 1931-67 1912-67 1931-67 1947-67 1928-67 1928-67
54 75 121 67 55 85 56 76 60 85
194 1-67 1931-67 1928-66 1942-67 1903-67 1928-67 1910-67 1936-67 1931-67 1948-67 193 1-67 1933-67 1931-67 1918-66 1921-67 1918-67 1910-67
48 41 49 65 56 58 68 59 40 49 48 51 37 59 102 72 56
48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75
1941-67 1931-67 1946-67 1931-67 1921-67 1941-67 1943-67 1946-67 1955-67 1935-67 1931-67 1942-67 1948-67 1931-67 1931-67 1931-67 1954-67 1935-67 1941-64 1906-67 1908-67 1908-67 1919-67 1917-67 1913-67 1909-67 1908-67 1907-67
20 23 17 16 37 10 25 03 11 53 34 39 06 08 08 39 04 06 19 112 53 71 101 63 82 130 77 98
P e r i o d of observation
-
Maximum rainfall i n a day,
-
S t a ti o n
Station
Maximum rainfall i n a day,
No.
P e r i o d of observation
95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111
1942-67 1910-67 1914-67 1928-67 1942-67 1943-67 1905-67 1929-67 1911-67 1908-67 1911-67 1908-67 1918-67 1915-67 1915-67 1900-67 1906-67
128 115 105 87 97 193 130 105 99 110 170 108 171 97 107 116 145
113 114 115 116 117 118 119 120 121 122
1910-67 1915-67 1913-67 1906-67 1900-67 1915-67 1906-67 1919-64 1922-67 1932-67
127 178 114 140 144 126 130 160 140 164
112
-
mm
-
TABLE 4.10
(continued) Station
No.
Period of observation
Maximrainfall in a day, mm
29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47
1931-67 1914-67 1938-64 1926-67 1946-67 1938-67 1921-67 1946-67 1941-67 1936-67 1931-67 1932-67 1931-67 1907-67 1943-67 1931-67 1921-67 1928-67 193 1-67
39 75 72 24 28 32 28 70 27 28 53 32 50 32 49 33 142 16 44
Station
No. 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94
Period of observation
Maximum rainfall in a day, mm
Station
No.
Period of observation
Naximum rainfall in a day, mm
1914-67 1905-67 1908-67 1946-67 1894-1967 1920-67 1930-67 1905-67 1903-67 1905-67 1905-67 1929-67 1918-67 1905-67 1903-67 1902-67 1920-67 1914-67 1908-67
76 120 100 84 107 102 147 87 139 126 112 89 118 143 127 130 127 125 150
123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141
1922-67 1909-67 1906-63 1905-67 1913-67 1904-67 1944-67 1903-65 1907-67 1913-67 1905-67 1924-64 1925-67 1908-67 1924-67 1921-67 1929-64 1914-67 1916-65
150 160 148 129 123 125 108 150 140 131 162 128 156 121 116 136 107 125 137
0
0'1
09
A
a
-
0 y
0
08 5' 4
3
0'11
=
oz1
0 =
001
_.
3
z 9T
163
REFERENCES Brook, C . E . P . , 1924. The d i s t r i b u t i o n o f r a i n f a l l o v e r Uganda, w i t h a n o t e on Kenya Colony. Q u a r t . J o u r n . Roy. Meteo. S O C . , 5 0 : 325-338. Chow, V . T . , 1964. Handbook o f a p p l i e d h y d r o l o g y . McGraw H i l l Book Company, N e w York, 1 4 5 3 p p . C l a r k e , R . T . , 1973. M a t h e m a t i c a l models i n h y d r o l o g y . FA0 I r r i g a t i o n and d r a i n age p a p e r 1 9 , FAO, Rome. Haan, C . T . , 1977. S t a t i s t i c a l methods i n h y d r o l o g y . The Iowa S t a t e U n i v e r s i t y P r e s s , A m e s , USA,,378 p p . H u r s t , H . E . and B l a c k , R . P . , 1950. The N i l e B a s i n , f i r s t supplement t o Vol. V I , P h y s i c a l Department P a p e r 4 9 , S . O . P . P r e s s , C a i r o , 228 p p . H u r s t , H . E . , S i m a i k a , Y . M . , and B l a c k , R . P . , 1955. The N i l e B a s i n , second supplement t o V o l . V I , N i l e C o n t r o l Department P a p e r 4 , Government P r e s s , C a i r o , 206 pp. H u r s t , H . E . , S i m a i k a , Y . M . , and B l a c k , R . P . , 1957. The N i l e B a s i n , t h i r d s u p p l e ment t o V o l . VI, N i l e C o n t r o l Department P a p e r 9 , Government P r e s s , C a i r o , 198 p p . Huynh Ngoc P h i e n e t a l , 1980. R a i n f a l l d i s t r i b u t i o n i n n o r t h - e a s t e r n T h a i l a n d . Hydro. S c i . B u l . ( e d i t e d by R . T . C l a r k e ) , 2 5 . 2 : 167-182. 1948. A g r i c u l t u r e i n t h e Sudan ( e d i t e d by J . D . T o t h i l l ) . Ireland, A.W., C h a p t e r V: The C l i m a t e o f t h e Sudan, Oxford U n i v e r s i t y P r e s s , London. 1 9 6 2 . R a i n i n E a s t A f r i c a . Q u a r t . J o u r n . Roy. Meteo. S O C . , Johnson, D . H . , 88.375 : 1-19. K i t e , G . W . , 1 9 7 7 . Frequency and r i s k a n a l y s e s i n Hydrology. Water Resources P u b l i c a t i o n s , F o r t C o l l i n s , C o l o r a d o , 224 p p . K o t t e g o d a , N . T . , 1 9 8 0 . S t o c h a s t i c w a t e r r e s o u r c e s t e c h n o l o g y . The McMillan P r e s s L t d . , London, 384 pp Markovig, R . , 1 9 6 5 . P r o b a b i l i t y f u n c t i o n s o f b e s t f i t t o d i s t r i b u t i o n s of a n n u a l p r e c i p i t a t i o n and r u n o f f . Hydrology P a p e r 8 , C o l o r a d o S t a t e U n i v e r s i t y , F o r t C o l l i n s , C o l o r a d o , 34 p p . N i l e C o n t r o l S t a f f , 1963. The N i l e B a s i n , f o u r t h supplement t o V o l . V I , N i l e C o n t r o l Department P a p e r 18, G e n e r a l O r g a n i z a t i o n f o r Government P r i n t i n g O f f i c e s , C a i r o , 192 p p . N i l e C o n t r o l S t a f f , 1 9 6 9 . The N i l e B a s i n , f i f t h supplement t o Vol. V I , N i l e C o n t r o l Department P a p e r 2 5 , G e n e r a l O r g a n i z a t i o n f o r Government P r i n t i n g O f f i c e s , C a i r o , 169 p p . Nile C o n t r o l S t a f f , 1972. The N i l e B a s i n , s i x t h supplement t o V o l . V I , N i l e C o n t r o l Department P a p e r 29, G e n e r a l O r g a n i z a t i o n f o r Government P r i n t i n g O f f i c e s , C a i r o , 160 pp. P e a r s o n , E . S . , and H a r t l e y , H . O . ( e d i t o r s ) , 1954. B i o m e t r i k a T a b l e s f o r S t a t i s t i c i a n s . V o l . 1, Cambridge U n i v e r s i t y P r e s s . Rz6ska, J . ( e d i t o r ) , 1976. The N i l e , b i o l o g y of a n a n c i e n t r i v e r . D r W . Junk B . V . P u b l i s h e r s , The Hague, 417 p p . S h a h i n , M . M . , 1983. S t a t i s t i c a l m o d e l l i n g o f r a i n f a l l d a t a on t h e N i l e B a s i n . P a p e r p r e s e n t e d t o t h e c o n f e r e n c e on water r e s o u r c e s development i n Egypt (under p u b l i c a t i o n ) , C ai ro . UNESCO, 1 9 7 8 . World w a t e r b a l a n c e and w a t e r r e s o u r c e s o f t h e e a r t h . UNESCO, Paris. United S t a t e s Water R e s o u r c e s C o u n c i l , 1 9 7 7 . G u i d e l i n e s f o r d e t e r m i n i n g f l o o d flow f r e q u e n c y . R e v i s e d e d i t i o n , Washington, D . C . Y e v j e v i c h , V . , 1972. S t o c h a s t i c p r o c e s s e s i n h y d r o l o g y . Water R e s o u r c e s P u b l i c a t i o n s , F o r t C o l l i n s , C o l o r a d o , 276 p p . W M O , 1 9 7 4 . H y d r o m e t e o r o l o g i c a l s u r v e y o f t h e c a t c h m e n t s o f Lakes V i c t o r i a , Kyoga and A l b e r t , Vol. I : Meteorology and h y d r o l o g y of t h e b a s i n , P a r t 1, Geneva.
165
Chapter 5 FREE WATER SURFACE EVAPORATION E v a p o r a t i o n i s d e f i n e d as t h e t r a n s f e r o f m o i s t u r e i n t o t h e atmosphere from an open o r f r e e w a t e r s u r f a c e , a b a r e s o i l o r i n t e r c e p t i o n on a v e g e t a l c o v e r . The w a t e r - r e s o u r c e s
e n g i n e e r u s u a l l y r e g a r d s e v a p o r a t i o n of w a t e r as a l o s s ,
whether i t o c c u r s from r e s e r v o i r s , from n a t u r a l l a k e s , from b a r e s o i l , o r from land-carrying
crops.
S i n c e t h e r a i n f a l l on many p a r t s o f t h e N i l e B a s i n i s q u i t e s c a n t y , i t i s , t h e r e f o r e , n e c e s s a r y t o h a v e r e l i a b l e i n f o r m a t i o n a b o u t e v a p o r a t i o n losses. One s h o u l d n o t f o r g e t t h a t t h e mere e x i s t e n c e of some of t h e c o u n t r i e s s h a r i n g t h e N i l e w a t e r is a l m o s t e n t i r e l y d e p e n d e n t on t h e v a r i o u s i r r i g a t i o n schemes and on
t h e s t o r a g e works on t h e r i v e r . I n t h i s c h a p t e r t h e e v a p o r a t i o n from t h e f r e e w a t e r s u r f a c e s s u c h as l a k e s and r e s e r v o i r s i n t h e b a s i n i s t r e a t e d . E v a p o t r a n s p i r a t i o n from v e g e t a t e d and cropped s u r f a c e s i s t h e s u b j e c t matter of t h e n e x t c h a p t e r . I t is known t h a t e v a p o r a t i o n c a n b e measured by atmometers and c o n t a i n e r s of v a r i o u s s h a p e s and d i m e n s i o n s . I t c a n a l s o b e e s t i m a t e d from t h e w a t e r - b a l a n c e of t h e body of water o r t h e c a t c h m e n t area i n q u e s t i o n , p r o v i d e d t h a t s u f f i c i e n t l y a c c u r a t e d a t a c o v e r i n g a l l t h e terms i n t h e b a l a n c e e q u a t i o n o t h e r t h a n e v a p o r a t i o n a r e a v a i l a b l e . I n t h e a b s e n c e of a c t u a l measurements, o r where a d e q u a t e d a t a o f t h e b a l a n c e i t e m s a r e m i s s i n g , one u s u a l l y r e s o r t s t o evaporat i o n e s t i m a t e s , u s i n g one f o r m u l a o r a n o t h e r . Our i n t e r e s t h e r e does n o t e x t e n d t o t h e h o u r l y e v a p o r a t i o n and i t s c o r r e l a t i o n w i t h t h e c l i m a t e . We are n o t even c o n c e r n e d w i t h t h e d a i l y v a l u e s , b u t w e a r e c o n c e r n e d w i t h t h e summation o f t h e d a i l y v a l u e s on a monthly a v e r a g e b a s i s , and w i t h a n n u a l v a l u e s . Measurement of e v a p o r a t i o n a t a number o f s t a t i o n s i n t h e N i l e B a s i n d a t e s back t o t h e b e g i n n i n g of t h i s c e n t u r y . I n Egypt and t h e Sudan t h e P i c h e and t h e f l o a t i n g t a n k a r e s t i l l i n u s e , whereas t h e u s e o f t h e Wild e v a p o r i m e t e r h a s s t o p p e d s i n c e 1920. The f l o a t i n g t a n k h a s a s h a p e o f a cube o f 1 m s i d e . I t i s c o n s t r u c t e d o f i r o n and f l o a t e d on a r i v e r o r a l a k e by means of a wooden r a f t . The r i m of t h e t a n k r e m a i n s a few c e n t i m e t r e s above t h e l e v e l o f t h e o u t s i d e w a t e r . The t a n k i s f i l l e d up t o t h e same l e v e l o f t h e o u t s i d e w a t e r , and t h e e v a p o r a t i o n l o s s i s measured e v e r y day by a gauge which i n d i c a t e s t h e w a t e r l e v e l i n t h e t a n k . The d i f f i c u l t y w i t h t y p e of d e v i c e i s c a u s e d m a i n l y by waves s p l a s h i n g i n t o i t , e s p e c i a l l y on windy d a y s .
166
The e a r l y e x p e r i m e n t a t i o n o f e v a p o r a t i o n measurement u s i n g d i f f e r e n t d e v i c e s
w a s described i n V o l . I of t h e N i l e Basin (Hurst, H . E . ,
and P h i l i p s , P . ,
1931).
The c o n c l u s i o n s t h a t c a n b e drawn f o r t h e i r d e s c r i p t i o n a r e : t h e e v a p o r a t i o n from a f l o a t i n g t a n k 2 m s q u a r e c a n b e c o n s i d e r e d
i)
p r a c t i c a l l y a s t h e b e s t a v a i l a b l e a p p r o x i m a t i o n t o e v a p o r a t i o n from a n extended s u r f a c e of water, t h e r a t i o between e v a p o r a t i o n from a 2 m s q u a r e f l o a t i n g t a n k and e v a p o r a -
ii)
t i o n from a 1 m s q u a r e f l o a t i n g t a n k i s 0.88, and i i i ) t h e r a t i o between e v a p o r a t i o n from a 2 m s q u a r e f l o a t i n g t a n k and evaporat i o n from a P i c h e t u b e i s c l o s e t o 0 . 5 0 . The above c o n c l u s i o n s combined w i t h t h o s e r e p o r t e d by K e e l i n g a t a n e a r l i e r
t i m e were p r e s e n t e d i n Vol. I o f t h e N i l e B a s i n w i t h t h e a i m o f t r a n s o r m i n g t h e r e a d i n g s o f a l l t h e m e a s u r i n g d e v i c e s t o f r e e water s u r f a c e e v a p o r a t i o n ( H u r s t , H.E.,
and P h i l i p s , P . ,
1 9 3 1 ) . T h i s is l i s t e d i n T a b l e 5.1. The c l i m a t o l o g i c a l
normals f o r Egypt ( M i n i s t r y o f War and M a r i n e , Egypt,
1950) show some d i f f e r e n c e
between t h e normal e v a p o r a t i o n o v e r open w a t e r and t h e o r i g i n a l v a l u e s g i v e n i n T a b l e 5 . 1 f o r a l a r g e number of m e t e o r o l o g i c a l s c r e e n s . A few y e a r s l a t e r , a d i f f e r e n t set o f v a l u e s a p p e a r e d i n "The N i l e "
(Hurst, H . E . ,
1 9 5 2 ) . A summary
of t h e d a t a a v a i l a b l e i n t h e s e t w o r e f e r e n c e s a r e a l s o i n c l u d e d i n T a b l e 5 . 1 . The d a t a i n t h i s t a b l e h a v e been u s e d i n p r e p a r i n g t h e map shown i n F i g . 5 . 1 . , so a s t o g e t an o v e r a l l p i c t u r e o f t h e a n n u a l e v a p o r a t i o n a s deduced from t h e
Piche readings. As a l r e a d y m e n t i o n e d , t h e w a t e r - b a l a n c e method c a n b e used f o r e s t i m a t i n g t h e
e v a p o r a t i o n loss from a n open w a t e r where d i r e c t measurements are n o t a v a i l a b l e . The b a l a n c e e q u a t i o n f o r a body o f w a t e r , a l a k e f o r example, c a n b e s e t up f o r a c e r t a i n p e r i o d o f t i m e as
P1 + R + I - E 1 - O = A S where P1 = d i r e c t p r e c i p i t a t i o n on t h e l a k e ,
R
= run-off
from t h e l a k e c a t c h m e n t a r e a t o t h e l a k e i t s e l f ,
I
= i n f l o w t o t h e l a k e from r i v e r t r i b u t a r i e s ,
E l = e v a p o r a t i o n from t h e l a k e ,
0
= o u t f l o w from t h e l a k e , and
AS = change i n t h e volume of water s t o r e d i n t h e l a k e .
(5.1)
TABLE 5.1
Normal e v a p o r a t i o n o v e r open w a t e r i n t h e N i l e B a s i n , i n mm/day N i l e B a s i n Vol. I (1931)
Location
Mediterranean C o a s t Mersa Matruh Alexandria Port Said N i l e Delta Qurashiya Sakha C a i r o and neighbourhood C a i r o (Ezbekiya) Giza Helwan Tor Fayum Qasr el-Gebali Minya ( C e n t r a l Egypt) Upper Egypt A s s i u t (Upper Egypt) Aswan Oases Northern Sudan (from H a l f a t o Atbara) Wadi-Half a Merowe Atbara P o r t Sudan Khartoum and neighbourhood Khartoum Kassala Gallabat Wad Medani
Period of observation
Jan.
1920-29 1920-29 1920-29
3.2 1.8 1.5
1907-29 1907-29
Climatological Normals (1950)
Year
Jul.
Oct.
Year
3.8 2.1 2.5
3.5 3.0 2.3
4.2 2.2 2.6
3.6 2.0 2.2
1.0 1.0
2.5 2.3
2.4 2.8
1.6 1.7
2.2 1.9
1909-29 1920-27 1920-29 1905-29
1.2 1.5 2.5 3.2
2.7 3.8 6.5 4.4
3.7 4.1 7.6 5.3
1.9 2.3 5.0 3.7
2.3 2.8 5.4 4.2
1920-29 1920-29
1.9 1.4
4.8 4.2
6.4 5.0
3.4 2.8
4.1 3.3
3.8
1920-29 1920-29
1.8 3.8
5.5 8.7
7.1 10.0
3.4 7.8
4.5 7.5
4.6 7.1
Apr.
The N i l e (1952) Year
3.0 2.5 2.3 2.3 2.8 2.3
3.8
4.0 4.5 6.5 7.6
1905-29 1905-29 1905-29 1905-29
4.5 5.8 6.8 3.7
9.3 9.8 10.3 4.6
9.9 9.3 9.3 7.2
8.1 8.7 8.3 3.5
7.9 8.4 8.6 4.9
1905-29 1905-29 1905-29 1905-29
6.5 4.7 6.5 6.3
10.0 7.7
6.7 4.3
7.3 5.5
7.5 5.4
8.5 9.1
2.3 4.9
3.0 5.7
5.1 6.5
7.8
TABLE 5 . 1
(continued)
N i l e B a s i n Vol. I (1931) Location
C e n t r a l Sudan (Dueim t o R o s e i r e s ) Roseires Dueim Lake Tana El-Obeid El-Fasher S o u t h e r n Sudan (Malakal and s o u t h o u t s i d e t h e swamps) Malakal W au Mong a11a Lake A l b e r t Lake Edward Lake V i c t o r i a
P e r i o d of observation
Jan.
Apr.
Jul.
-
Oct.
Year
Climatological Normals (1950) Year
The N i l e (1952)
Year
6.3 1905-29 1905-29 1921-24 1907- 29 1918-29
6.8 7.6 4.1 7.2 5.2
8.1 9.5 5.1 9.2 7.9
2.5 4.9 1.2 4.7 4.3
3.4 5.8 2.2 6.3 6.0
5.3 6.9 3.0 6.7 5.8 3.4
1915-29 1906-29 1906-29
8.5 5.9 5.5
3.5
5.4 4.5 3.0
2.9
1.4 1.8 1.4
4.4
1.8 2.3 2.2 3.7
4.5 3.7 3.0
3.6
3.9 3.9 3.8
169
N
30'
25'
20°
15O
loo
10'
5O
5'
O0
21 O Fig. 5 . 1 .
Mean annual e v a p o r a t i o n from an open water s u r f a c e i n t h e N i l e Basin
170
I t is customary among t h e h y d r o l o g i s t s t o n e g l e c t t h e change i n s t o r a g e when
t h e p e r i o d o v e r which t h e g a i n s a r e b a l a n c e d w i t h t h e l o s s e s i s s u f f i c i e n t l y l o n g , s a y 1 y e a r o r more. When t h i s i s t h e case, AS i s p u t e q u a l t o z e r o and eq. 5 . 1 can be rewritten as E 1 = P
1
+ R + I - 0
(5.2)
The e v a p o r a t i o n from t h e Great Lakes i n t h e N i l e B a s i n has been e s t i m a t e d by
e q . 5.2 u s i n g t h e y e a r as a b a l a n c e p e r i o d . A b a l a n c e e q u a t i o n q u i t e s i m i l a r t o t h a t g i v e n by e q . 5 . 2 w a s used i n p r e -
p a r i n g t h e world water b a l a n c e (Baumgartner, A . , work t h e s o - c a l l e d
and R e i c h e l , E., 1 9 7 5 ) . I n t h i s
a c t u a l evaporation over t h e s u c c e s s i v e 5 degree l a t i t u d e
zones i s i n c l u d e d . I t is n o t common t o u s e t h e t e r m a c t u a l i n c o n n e c t i o n w i t h e v a p o r a t i o n . I n s t e a d , t h i s t e r m i s used j o i n t l y w i t h e v a p o t r a n s p i r a t i o n from a v e g e t a t e d o r a cropped s u r f a c e t o d i s t i n g u i s h i t from p o t e n t i a l e v a p o t r a n s p i r a t i o n . T h e r e f o r e , t h e d i s c u s s i o n o f t h e r e s u l t s o b t a i n e d by R e i c h e l and Baumgartner c o n c e r n i n g what t h e y have c a l l e d a c t u a l e v a p o r a t i o n w i l l b e presented i n the next chapter. I n a d d i t i o n t o a l l t h a t i s mentioned above, t h e r e h a s been a number o f d e t a i l e d e x p e r i m e n t s on e v a p o r a t i o n and e v a p o t r a n s p i r a t i o n from t h e N i l e B a s i n . S i n c e t h e b u l k of t h e a v a i l a b l e i n f o r m a t i o n is b a s e d , however, on t h e r e a d i n g s o f t h e P i c h e atmometer, i t i s l o g i c a l t o b e g i n by m e n t i o n i n g some remarks about t h e k i n d of d a t a one s h o u l d e x p e c t t o o b t a i n from such a n atmometer. I t i s i m p o r t a n t t o know t h i s b e f o r e any d e t a i l e d i n v e s t i g a t i o n c a n b e a t t e m p t e d . i)
T h e P i c h e , l i k e any o t h e r atmometer,
rather than h y d ro lo g i cal purposes,
i s mainly used f o r c l i m a t o l o g i c a l
t o c h a r a c t e r i z e t h e d r y i n g a b i l i t y of
t h e a i r under a g i v e n s e t o f c o n d i t i o n s . ii)
The p r o c e s s and c i r c u m s t a n c e s o f e v a p o r a t i o n from a P i c h e t u b e ( s u r f a c e a r e a from which e v a p o r a t i o n t a k e s p l a c e , two s i d e s = 13 cm2) a r e n o t
s t r i c t l y t h e same as t h o s e from a t a n k o r from a f r e e water s u r f a c e . The e x t e n t o f t h e a r e a a f f e c t e d by h u m i d i t y c a u s e d by e v a p o r a t i o n from a nearby w a t e r s u r f a c e i s a s t r o n g f a c t o r i n f l u e n c i n g t h e r e l a t i o n s h i p b e t ween t h e e v a p o r a t i o n from a P i c h e i n s t r u m e n t and t h e e v a p o r a t i o n from an open w a t e r s u r f a c e . Another s t r o n g f a c t o r i n f l u e n c i n g t h i s r e l a t i o n s h i p i s t h e d e g r e e of e x p o s u r e of t h e atmometer t o t h e s u r r o u n d i n g c l i m a t e . I n h i s book, "The N i l e " ( 1 9 5 2 ) , H u r s t d i s c u s s e d t h e u s e o f an e v a p o r i m e t e r i n the lakes area saying
"
...
The G r e a t Lakes, however, produce a l o c a l
c l i m a t e , so t h a t a P i c h e e v a p o r i m e t e r i n a town on t h e s h o r e s of Lake V i c t o r i a w i l l n o t i n d i c a t e t w i c e t h e e v a p o r a t i o n from t h e l a k e i t s e l f , but something a p p r e c i a b l y l e s s . T h i s i s b e c a u s e t h e damp atmosphere o v e r t h e
171
l a k e e x t e n d s some d i s t a n c e i n l a n d " .
T h i s i s o b v i o u s l y n o t t h e c a s e when
t h e evaporimeter i s p l a c e d a t a s t a t i o n n e x t t o a r i v e r of comparatively much s m a l l e r w i d t h . i i i ) A s mentioned i n V o l . I o f t h e N i l e B a s i n ( H u r s t , H . E . ,
and P h i l i p s , P . ,
1 9 3 1 ) , i t i s r e a s o n a b l e t o s u p p o s e t h a t t h e e v a p o r a t i o n from a l a r g e open
w a t e r s u r f a c e i s a l i t t l e less t h a n t h a t from t h e l a r g e s t t a n k s used i n t h e e x p e r i m e n t s ( h e r e 2 m x 2 m). The r a t i o between e v a p o r a t i o n from an e v a p o r i m e t e r and e v a p o r a t i o n from a f r e e w a t e r s u r f a c e w a s reviewed by S l e i g h t ( 1 9 2 7 ) , Hickox (1946) and l a t e r by O l i v i e r ( 1 9 6 1 ) . The r e s u l t s o b t a i n e d a r e summarized i n T a b l e 5 . 2 . R e l a t i v e rates of e v a p o r a t i o n showing e f f e c t o f pan s i z e on
TABLE 5 . 2
evaporation
Diameter of p a n , i n f e e t
Description
12
Compiled by R.B. S l e i g h t
1.00
9
6
4
3.39
2.26
2
1
1 . 0 0 9 1 . 0 8 9 1 . 1 7 5 1 . 2 0 2 1 . 2 6 0 1 . 2 8 4 1.589
Compared w i t h 1 8 0 0 - a c r e 1 . 0 9 9 1 . 1 0 8 1 . 1 9 6 1 . 2 9 0 1 . 3 2 0 1.383 1 . 4 1 0 1 . 7 4 5 r e s e r v o i r as u n i t y A f t e r t h i s h i s t o r i c a l r e v i e w w e s h a l l d e a l i n t h e r e m a i n i n g s e c t i o n s of t h i s c h a p t e r w i t h e v a p o r a t i o n from open w a t e r a t a number of s t a t i o n s i n t h e d i f f e r e n t p a r t s of t h e N i l e Basin. 5.1 5.1.1
LAKE PLATEAU AREA Lake V i c t o r i a
The mean a n n u a l e v a p o r a t i o n from Lake V i c t o r i a o v e r t h e p e r i o d from 1902 up t o and i n c l u d i n g 1 9 2 3 c a n b e found from T a b l e 5 . 1 as 3 . 6 mm/day. T h i s f i g u r e was o b t a i n e d from t h e h y d r o l o g i c b a l a n c e o f t h e l a k e f o r t h e same p e r i o d . The d i s t r i b u t i o n t h r o u g h o u t t h e y e a r w a s d e v e l o p e d by comparison w i t h t h e r e a d i n g s of t h e w e t b u l b t h e r m o m e t e r . When t h e b a l a n c e p e r i o d e x t e n d s up t o 1936, t h e a v e r a g e v a l u e s o f P1,
R + I and 0 become 1 1 5 1 , 276 and 311 mm/yr r e s p e c t i v e l y ,
t h u s g i v i n g a n a n n u a l mean e v a p o r a t i o n of 3 . 0 6 mm/day o n l y ( H u r s t , H . E . , Philips, P.,
and
1 9 3 8 ) . A t h i r d e v a p o r a t i o n r a t e which w a s g i v e n l a t e r by H u r s t
(1952) i s 3.8 mm/day.
T h i s i s b a s e d o n P1,
R + I and 0 of 1463, 239 and 314
mm/yr r e s p e c t i v e l y . A f o u r t h v a l u e c a n s t i l l b e found i n V o l . X of t h e N i l e Basin ( H u r s t , H . E . ,
Black, R.P.,
and S i m a i k a , Y.M., 1 9 6 6 ) . T h i s v a l u e o f
1150 mm/yr o r 3 . 1 5 mm/day i s b a s e d o n P1 = 1260, R
+ I = 190 and 0
= 300 mm/yr
r e s p e c t i v e l y . From t h e s e f i g u r e s one c a n e a s i l y see t h a t t h e e v a p o r a t i o n r a t e
172
from Lake V i c t o r i a v a r i e s from o n e b a l a n c e p e r i o d t o a n o t h e r . Each term i n t h e b a l a n c e e q u a t i o n u n d e r g o e s v a r i a t i o n w i t h t i m e . Next t o t h i s , t h e r e a r e d e f i n i t e l y some s a m p l i n g e r r o r s . An e s t i m a t e of t h e a n n u a l r a i n f a l l on s u c h a n enormous s u r f a c e o f w a t e r a s Lake V i c t o r i a c a n h a r d l y b e a c c u r a t e . An example o f t h i s , though from o u t s i d e t h e N i l e B a s i n and t o a s m a l l e r e x t e n t a s compared t o any of t h e E q u a t o r i a l L a k e s , i s t h e Lake H e f n e r i n t h e U n i t e d S t a t e s . During t h e 1950-51 e v a p o r a t i o n s t u d y from t h i s l a k e t h e r e were 2 1 e i g h t - i n c h d i a m e t e r gauges around t h e p e r i p h e r y of t h e 2200-acre
l a k e and o n e gauge on a r a f t i n
t h e c e n t r e . D u r i n g o n e s t o r m , r a i n f a l l r a n g e d from 0 . 1 i n c h on o n e s i d e o f t h e l a k e t o n e a r l y two i n c h e s on t h e o t h e r . During summer c o n v e c t i v e s h o w e r s , t h e a r e a l v a r i a b i l i t y o f r a i n f a l l may b e s o g r e a t t h a t t h e a v e r a g e r a i n f a l l v a l u e on t h e l a k e s u r f a c e i s s u f f i c i e n t l y i n a c c u r a t e t o i n v a l i d a t e t h e computed f i g u r e o f e v a p o r a t i o n (US G e o l o g i c a l S u r v e y , 1 9 5 4 ) . The w a t e r - b a l a n c e
of Lake V i c t o r i a w a s r e c e n t l y r e v i e w e d i n c o n n e c t i o n w i t h
t h e h y d r o m e t e o r o l o g i c a l network p r o j e c t i n t h e E q u a t o r i a l Lakes a r e a (Krishnamurthy, K . V . ,
and I b r a h i m , A . M . ,
1 9 7 3 ) . Based on t h e i n f o r m a t i o n
g a t h e r e d from t h e meagre network of r a i n gauges b e f o r e t h e commencement o f t h e p r o j e c t i n 1 9 6 7 , t h e b e s t a v a i l a b l e e s t i m a t e of P1 c a n b e t a k e n as 1420 mm/yr
+ -
10%. The i n f l o w p l u s r u n - o f f
t o t h e l a k e v a r i e d , a s r e p o r t e d , from 15 t o 18
m i l l i a r d m 3 / y r . T h i s f i g u r e i s somewhat d i f f e r e n t from t h e 1 2 . 6 m i l l i a r d m3/yr a d o p t e d by H u r s t and h i s co-workers (Hurst, H . E . ,
i n p r e p a r i n g Vol. X of t h e N i l e B a s i n
B l a c k , R . P . , and S i m a i k a , Y . M . ,
1 9 6 6 ) . I n t h e b a l a n c e p r e p a r e d by
Krishnamurthy and I b r a h i m t h e y e a r l y volumes o f 18 x
m 3 2 5% were u s e d t o r e p r e s e n t t h e r u n - o f f
lo9
m 3 2 5% and 23.6 x
lo9
t o and t h e o u t f l o w from Lake V i c t o r i a
r e s p e c t i v e l y . The e v a p o r a t i o n e s t i m a t e d from t h i s b a l a n c e l i e s i n t h e r a n g e of 3 . 6 5 and 4 . 5 0 mm/day. The l o w e r l i m i t o f t h i s r a n g e d o e s n o t d e p a r t s e n s i b l y from t h e a v e r a g e of t h e e v a p o r a t i o n r a t e s o b t a i n e d f o r d i f f e r e n t b a l a n c e r a t e s by H u r s t and h i s c o - w o r k e r s .
I t i s a l s o i n r e a s o n a b l e agreement w i t h t h e a v e r a g e
of t h e r e a d i n g s of t h e P i c h e e v a p o r i m e t e r s i n s t a l l e d by t h e East A f r i c a n M e t e o r o l o g i c a l S e r v i c e a t a number of p l a c e s n e a r t h e l a k e s h o r e s . The o l d work o f K e e l i n g b a s e d on t h e wet-bulb
d e p r e s s i o n a s an estimate o f t h e d a i l y evapora-
t i o n o v e r a c e r t a i n y e a r from a s t a n d a r d Wild i n s t r u m e n t was e x t e n d e d by O l i v i e r (1961) t o g i v e t h e mean d a i l y e v a p o r a t i o n o v e r a c e r t a i n month. K e e l i n g , a s a r e s u l t o f t h e e x p e r i m e n t s made i n Egypt and t h e Sudan, recommended a f a c t o r of 1 . 4 2 t o c o n v e r t t h e r e a d i n g o f a Wild i n s t r u m e n t t o P i c h e e v a p o r a t i o n . The e v a p o r a t i o n f o r m u l a d e v e l o p e d by O l i v i e r r e a d s
173
where
M
c
P
= f r e e water s u r f a c e e v a p o r a t i o n , i n mm/day,
from a s t a n d a r d t a n k a t a
l a t i t u d e $,
= a v e r a g e d e p r e s s i o n o f w e t b u l b i n OC f o r a p a r t i c u l a r month, and
L$N = r a t i o
L
- f o r l a t i t u d e ON a s t a k e n from t a b l e s ( f o r l a t i t u d e L$S r e a d ' s i x LO
months o n ' ) . The y e a r l y v a l u e s of c a t J i n j a and Entebbe a r e 36.1°C
and 30.1°C
respect-
i v e l y . T h e s e two p a l c e s a r e l o c a t e d a l m o s t on t h e e q u a t o r . Assuming t h a t c i s u n i f o r m l y d i s t r i b u t e d o v e r t h e 1 2 months o f t h e y e a r , and u s i n g t h e monthly v a l u e s L($ =
0)
g i v e n by O l i v i e r , t h e f r e e water e v a p o r a t i o n from a s t a n d a r d
t a n k c a n b e c a l c u l a t e d from e q . 5 . 3 . The r e s u l t s o b t a i n e d from c a l c u l a t i o n t o g e t h e r w i t h t h e a v e r a g e P i c h e e v a p o r a t i o n a t t h e same p l a c e s are g i v e n i n T a b l e 5 . 3 . From t h i s t a b l e i t a p p e a r s t h a t t h e computed t a n k e v a p o r a t i o n a t b o t h J i n j a and E n t e b b e , which are s i t u a t e d c l o s e t o t h e s h o r e s o f Lake V i c t o r i a ,
i s 20 t o 30% less t h a n e v a p o r a t i o n from t h e l a k e a s o b t a i n e d from t h e waterb a l a n c e method. A d d i t i o n a l l y , t h e r a t i o P i c h e e v a p o r a t i o n t o t a n k e v a p o r a t i o n needs t o b e c h a n g e d , a t l e a s t f o r t h e p l a c e s c o n s i d e r e d , from 1 . 4 2 t o 1 . 2 1 .
E s t i m a t e o f t a n k e v a p o r a t i o n and P i c h e e v a p o r a t i o n , f o r J i n j a and
TABLE 5 . 3
Entebbe
Place Jinja
Entebbe
Method
Evaporation,
i n mm/day,
for
f
J a n . F e b . Mar. Apr. May J u n e J u l y Aug. S e p . O c t . Nov. Dec. Year
a b
2.9 4.5
3.0 4.1
3.2 3.8
3.1 3.2
2.9 2.9 3.0 3.3
2.9 3.3
3.0 3.2
3.1 3.7
3.1 4.1
3.0 4.0
2.9 3.9
3.0 3.7
a
2.5 3.2
2.5 3.5
2.6 3.1
2.6 2.3
2.5 2.4 2.3 2.6
2.4 2.6
2.5 2.6
2.6 2.9
2.6 3.0
2.5 2.8
2.4 2.7
2.5 3.0
c
*a = Eq. 5 . 3 ; b = P i c h e , 1924-27 and 1932-34; c = P i c h e , 1924-30 and 1933-34 A s e r i e s o f e v a p o r a t i o n e x p e r i m e n t s u s i n g d i f f e r e n t t y p e s o f atmometers were c a r r i e d o u t f o r a number o f y e a r s i n E a s t A f r i c a n t e r r i t o r i e s , some o f which a r e l o c a t e d w i t h i n t h e b o u n d a r i e s o f t h e catchment a r e a o f Lake V i c t o r i a . A t e l e v e n s t a t i o n s , e x p r e s s i n g t h e a n n u a l e v a p o r a t i o n i n i n c h e s , i t was found t h a t
C l a s s A pan = 0 . 8 7 P i c h e
+
24
(5.4)
w i t h a c o r r e l a t i o n c o e f f i c i e n t = 0 . 9 5 . I t was c o n c l u d e d t h a t t h e P i c h e r e a d i n g s i n a Stevenson s c r e e n g i v e a s a t i s f a c t o r y e s t i m a t e of annual e v a p o r a t i o n a s measured by a c l a s s A p a n .
174
Comparison between t h e s o - c a l l e d Kenya pan and a c l a s s A pan were c a r r i e d o u t a t D a g o r e t t i h e a d q u a r t e r s , a few k i l o m e t r e s w e s t o f N a i r o b i . Using f o u r y e a r s o f r e c o r d (1384 d a y s ) , a c o r r e l a t i o n between d a i l y v a l u e s i n i n c h e s yielded the r e s u l t C l a s s A pan ( u n s c r e e n e d ) = 1 . 3 Kenya pan ( s c r e e n e d ) + 0 . 0 2
(5.5)
with a c o r r e l a t i o n c o e f f i c i e n t = 0 . 9 5 . Comparisons of monthly means o v e r two y e a r s , assuming l i n e a r r e l a t i o n s h i p , provided t h e f o l l o w i n g r e s u l t s : C l a s s A pan ( u n s c r e e n e d )
= 100
Class A pan ( s c r e e n e d )
=
86 ( r a n g e 84-88)
C l a s s A pan ( p a i n t e d )
=
84 ( r a n g e 82-86)
Kenya pan ( u n s c r e e n e d )
=
95 ( o n l y few months)
Kenya pan ( s c r e e n e d )
=
7 1 ( r a n g e 69-74)
Kenya pan ( p a i n t e d and s c r e e n e d ) =
69 ( r a n g e 65-72)
"Screen" i s a 1 - i n c h c h i c k e n w i r e mesh. " P a i n t e d " means t h a t t h e i n s i d e is p a i n t e d d u l l b l a c k w i t h b i t u m i n o u s p a i n t and t h e o u t s i d e w i t h aluminium p a i n t . F u r t h e r d e s c r i p t i o n o f t h o s e e x p e r i m e n t s is g i v e n i n T e c h n i c a l Note No. 8 3 o f t h e World M e t e o r o l o g i c a l O r g a n i z a t i o n (WMO, 1 9 6 6 ) . The two s t a t i o n s which a r e o f d i r e c t i n t e r e s t t o us a r e Kisumu and E n t e b b e . The P i c h e ( s c r e e n e d ) and Kenya p a n ( s c r e e n e d ) e v a p o r a t i o n a t Kisumu were 96 and 106 i n / y r and a t Entebbe 36 and 89 i n / y r ,
r e s p e c t i v e l y . The y e a r l y r a t i o s o f t h e c l a s s A pan ( u n s c r e e n e a
t o Kenya pan ( s c r e e n e d ) a t Kisumu and E n t e b b e w e r e 1 . 2 8 and 1 . 1 2 r e s p e c t i v e l y . Assuming t h e r a t i o l a k e e v a p o r a t i o n t o c l a s s A pan e v a p o r a t i o n a t 0 . 7 , t h e f r e e
water s u r f a c e e v a p o r a t i o n a t Kisumu and E n t e b b e becomes 6 . 6 mm/day and 4 . 8 7 mm/day r e s p e c t i v e l y . The mean a n n u a l P i c h e e v a p o r a t i o n i s 6 . 6 7 mm/day f o r Kisumu and 2 . 5 1 mm/day f o r E n t e b b e . The l a t t e r f i g u r e e m p h a s i z e s t h e abnormal i t y i n t h e r e a d i n g s o f t h e P i c h e atmometer a t E n t e b b e .
A n o t h e r a p p r o a c h t o e s t i m a t i n g e v a p o r a t i o n from a f r e e water s u r f a c e i s t h a t o f a p p l y i n g o n e o r a n o t h e r o f t h e e v a p o r a t i o n f o r m u l a s b a s e d on t h o s e meteorol o g i c a l f a c t o r s which a r e s t r o n g l y c o r r e l a t e d w i t h e v a p o r a t i o n . R i j k s (1969) h a s e s t i a m t e d t h e e v a p o r a t i o n from t h e m e t e o r o l o g i c a l d a t a measured o v e r a swamp a t t h e n o r t h e r n boundary of t h e C o t t o n R e s e a r c h S t a t i o n a t Namulonge (0°32'N,
32O37'E and 1100 m a l t i t u d e ) , Uganda. The r e s u l t s h e o b t a i n e d from
Penman's f o r m u l a a v e r a g e d o v e r t h e 5-day p e r i o d s ; 8-12 March, 22-26 March and 7-11 A p r i l , 1965, a r e 6 . 2 , 3 . 8 and 5 . 5 mm/day r e s p e c t i v e l y . Dagg, M., on Water
R e q u i r e m e n t s o f Crops i n E a s t A f r i c a (1972) h a s mentioned t h a t d i r e c t and r e l i a b l e measurements o f open w a t e r e v a p o r a t i o n are d e c e p t i v e l y d i f f i c u l t t o o b t a i n . Using t h e estimates o f R i j k s and Owen, 1965, and o f Woodhead, 1967,
175
from t h e Penman f o r m u l a , Dagg w a s a b l e t o c o n s t r u c t a map o f t h e e v a p o r a t i v e demand f o r E a s t A f r i c a w i t h m o d e r a t e c o n f i d e n c e ( 1 9 7 2 ) . P a r t o f t h i s map h a s been i n c o r p o r a t e d i n t h e map
o f t h e e v a p o r a t i v e demand f o r t h e N i l e B a s i n p r e -
p a r e d by us u s i n g t h e Penman method. T h i s method y i e l d s a n a v e r a g e r a t e o f 4 . 6 5 mm/day f o r t h e n o r t h e r n and n o r t h - w e s t e r n p a r t s o f t h e c a t c h m e n t a r e a of Lake V i c t o r i a . The mean a n n u a l P i c h e e v a p o r a t i o n a t J i n j a , Kampala and E n t e b b e , which r e p r e s e n t t h o s e p a r t s of t h e c a t c h m e n t , is 3 . 7 , 4 . 5 and 3 . 0 mm/day respectively. The above d i s c u s s i o n of t h e e v a p o r a t i o n from Lake Victoria and i t s catchment can b e concluded w i t h t h e f o l l o w i n g remarks. i)
The w a t e r - b a l a n c e
o f t h e l a k e a v e r a g e d o v e r d i f f e r e n t p e r i o d s g i v e s a mean
a n n u a l e v a p o r a t i o n i n t h e r a n g e o f from s l i g h t l y less t h a n 3 . 1 mm/day t o
3.8 mm/day w i t h a n o v e r a l l a v e r a g e o f 3 . 4 mm/day. S u b s t i t u t i n g h i g h e r annual r a i n f a l l depths i n t h e balance eq uat i on has
led t o evaporation
r a n g i n g from 3 . 6 5 t o 4 . 5 0 mm/day. ii)
The e v a p o r a t i v e demand f o r t h e c a t c h m e n t a r e a o f t h e Lake V i c t o r i a v a r i e s from o n e p a r t o f t h e c a t c h m e n t t o t h e o t h e r . The r a n g e o f v a l u e s o b t a i n e d from t h e Penman f o r m u l a b a s e d on t h e a v a i l a b l e m e t e o r o l o g i c a l o b s e r v a t i o n s
i s from a b o u t 4 . 4 mm/day t o s l i g h t l y more t h a n 6 . 0 mm/day. i i i ) The P i c h e r e a d i n g s a t t h e s t a t i o n s n e a r t h e s h o r e s of t h e l a k e need t o b e m u l t i p l i e d by a f a c t o r r a n g i n g from less t h a n 1 . 0 t o more t h a n 1 . 5 t o b r i n g them t o t h e i r e q u i v a l e n t s o f f r e e water s u r f a c e e v a p o r a t i o n . iv)
The c o n v e r s i o n f a c t o r o f t h e Wild i n s t r u m e n t
t o t h e Piche tube reading
seems t o b e less t h a n t h e 1 . 4 2 o r i g i n a l l y proposed by K e e l i n g . L a s t b u t n o t l e a s t , i t is worthwhile t o mention t h a t t h e hydro-meteorologic a l s u r v e y p r o j e c t o f Lakes V i c t o r i a , Kyoga and A l b e r t h a s set up f i v e c l a s s A e v a p o r a t i o n pans o n f i v e i s l a n d s i n Lake V i c t o r i a a s w e l l as n i n e c l a s s A evap o r a t i o n pans o n t h e s h o r e a t some o f t h e f i r s t o r d e r m e t e o r o l o g i c a l s c r e e n s ( s e e map, F i g . 5 . 2 . ) . B e s i d e s t h e s t a n d a r d c l a s s A p a n s , a R u s s i a n e v a p o r a t i o n pan 20 m2 i n s i z e h a s a l s o b e e n s e t up t o h e l p i n t h e d e t e r m i n a t i o n of evaporat i o n by t h e pan method. F u r t h e r m o r e , i t h a s been p r o p o s e d t h a t m e t e o r o l o g i c a l d a t a b e c o l l e c t e d f o r e s t i m a t i o n o f f r e e w a t e r s u r f a c e e v a p o r a t i o n by t h e masst r a n s f e r and e n e r g y b u d g e t t e c h n i q u e s . I n t h e a u t h o r ' s o p i n i o n t h e r e s u l t s t h a t c a n b e e x p e c t e d from t h e s e methods
s t i l l need t o b e s u p p o r t e d , and p r o b a b l y a d j u s t e d , by new f i g u r e s t o b e o b t a i n e d from t h e w a t e r - b a l a n c e
method. The m e t e o r o l o g i c a l network w i l l h e l p i n
o b t a i n i n g more a c c u r a t e f i g u r e s a b o u t t h e r a i n f a l l n o t o n l y on t h e catchment b u t on t h e l a k e i t s e l f . P r i o r t o t h e p r o j e c t , 58% o f t h e t o t a l i n f l o w t o t h e l a k e was measured and t h e f l o w from t h e ungauged a r e a s was e s t i m a t e d on t h e b a s i s of r a i n f a l l , c h a r a c t e r i s t i c s o f t h e c a t c h m e n t , and s i m i l a r i t y w i t h o t h e r
176
r i v e r s . The improvement o f t h e network by t h e p r o j e c t h a s b r o u g h t t h e measured i n f l o w t o a b o u t 90% o f t h e t o t a l i n f l o w (WMO, 1 9 7 4 ) .
Map showing t h e l o c a t i o n s o f e v a p o r a t i o n p a n s s e t up by t h e hydroFig. 5.2. m e t e o r o l o g i c a l network p r o j e c t on t h e i s l a n d s and a l o n g t h e s h o r e s o f Lake Victoria. 5.1.2
V i c t o r i a N i l e Basin
The w a t e r - b a l a n c e
o f Lake Kyoga w a s drawn by H u r s t (1952) c o n s i d e r i n g t h e
i n f l o w from t h e Upper V i c t o r i a N i l e as 2 0 . 9 m l r d m3/yr, t h e o t h e r t r i b u t a r i e s a s 3 . 5 m l r d m3/yr, l a k e and t h e r u n - o f f
t h e i n f l o w b r o u g h t by
and t h e sum of p r e c i p i t a t i o n and t h e
from t h e c a t c h m e n t t o i t a s 8 m l r d m 3 / y r .
The a n n u a l o u t -
f l o w from Lake Kyoga t o t h e L o w e r V i c t o r i a N i l e w a s c o n s i d e r e d a s 1 9 . 7 mlrd m3/
y r . These f i g u r e s l e a v e 1 2 . 4 m l r d m 3 / y r
f o r e v a p o r a t i o n from t h e l a k e (1760kmg
and e v a p o t r a n s p i r a t i o n from t h e swamps (4500 km2). The a v e r a g e r a t e s of evap o r a t i o n and e v a p o t r a n s p i r a t i o n h a v e been e s t i m a t e d a t 3 . 9 mm/day and 6.1 mm/ day, r e s p e c t i v e l y .
177
The mean monthly and a n n u a l P i c h e e v a p o r a t i o n a s o b s e r v e d i n t h e V i c t o r i a N i l e B a s i n are as f o l l o w s : Evaporation,
i n mm/day,
for
Jan.
Feb.
Mar.
Apr.
May
June
July
Aug.
Sep.
Oct.
Nov.
D e c . . Year
7.4
7.7
6.0
4.3
3.5
4.1
3.9
3.7
4.2
4.5
5.0
4.9
4.9
The r e d u c t i o n f a c t o r t o b e a p p l i e d t o t h e above v a l u e s s o as t o c o n v e r t them i n t o open water e v a p o r a t i o n w a s d e s c r i b e d by H u r s t as " u n f o r t u n a t e l y v e r y uncert a i n " . A s a rough a p p r o x i m a t i o n h e a d o p t e d a f a c t o r of 0 . 6 7 t o t h e P i c h e evap o r a t i o n . T h i s f i g u r e i s t h e mean o f 0 . 8 3 , t h e f a c t o r proposed f o r Lake V i c t o r i a and 0 . 5 0 ,
t h e f a c t o r found f o r Egypt and t h e Sudan. I f t h i s f a c t o r i s a p p l i e d t o
t h e mean a n n u a l e v a p o r a t i o n , 3 . 3 mm/day e v a p o r a t i o n i s o b t a i n e d from t h e f r e e w a t e r s u r f a c e of Lake Kyoga. The method o f O l i v i e r (1961) g i v e s a mean a n n u a l e v a p o r a t i o n and a mean a n n u a l e v a p o t r a n s p i r a t i o n from t h e swamp, b o t h around S o r o t i , c l o s e t o t h e n o r t h e r n s h o r e o f Lake Kyoga, o f 7 . 0 and 4 . 7 mm/day r e s p e c t i v e l y . Assuming t h e r a t i o open water t o s t a n d a r d t a n k e v a p o r a t i o n t o b e 0 . 7 5 , t h e e v a p o r a t i o n from a f r e e water s u r f a c e i n t h e V i c t o r i a N i l e B a s i n becomes e q u a l
t o 5 . 2 5 mm/day. T h i s f i g u r e i s s l i g h t l y less t h a n t h e a v e r a g e v a l u e of 5 . 7 5 mm/ day e s t i m a t e d f o r t h e s u r r o u n d i n g s o f S o r o t i by t h e method o f Penman. Once more c o n s i d e r t h e w a t e r - b a l a n c e
drawn by H u r s t f o r Lake Kyoga and s u r -
r o u n d i n g s . I t i s n e i t h e r u n d e r s t a n d a b l e n o r j u s t i f i a b l y why t h e r a t e o f evapot r a n s p i r a t i o n from t h e swamps i s t a k e n as 1 . 6 1 t i m e s ( 6 . 1 : 3 . 9 )
t h e evaporation
r a t e from t h e l a k e i t s e l f . I f i t i s a r b i t r a r i l y assumed t h a t b o t h r a t e s are e q u a l , a g e n e r a l f i g u r e of 5 . 2 5 mm i s o b t a i n e d . From t h e f o r e g o i n g a n a l y s i s , o n e may draw t h e f o l l o w i n g c o n c l u s i o n s : i)
A mean a n n u a l e v a p o r a t i o n o f 3 . 9 mm/day seems t o b e f a i r l y s m a l l . T h i s f i g u r e n e e d s t o b e i n c r e a s e d t o a b o u t 5 . 2 5 mm/day.
ii)
The f a c t o r t o c o n v e r t P i c h e e v a p o r a t i o n t o f r e e w a t e r s u r f a c e e v a p o r a t i o n
i s n o t 0 . 6 7 a s o r i g i n a l l y s u g g e s t e d by H u r s t . T h i s f a c t o r n e e d s t o b e changed t o 1 . 0 5 or 1 . 1 0 . i i i ) The e v a p o r a t i v e demand o f t h e V i c t o r i a N i l e B a s i n r a n g e s from 5 . 5 mm/day t o 6 . 0 mm/day.
5.1.3
Lakes George and Edward, and Lake A l b e r t
I n t h e volumes o f t h e N i l e B a s i n up t o and i n c l u d i n g Vol I V t h e r e is no i n f o r m a t i o n a t a l l a b o u t e v a p o r a t i o n from Lakes George and Edward. I n V o l . V i t
i s mentioned t h a t no d i r e c t i n f o r m a t i o n a b o u t e v a p o r a t i o n from t h e s e two l a k e s
178
i s a v a i l a b l e . T h e i r s i z e and g e o g r a p h i c a l p o s i t i o n s u g g e s t , however, t h a t t h e e v a p o r a t i o n from Lakes George and Edward s h o u l d b e s i m i l a r t o t h a t from Lake Albert (Hurst, H . E . ,
and P h i l i p s , P . ,
1938).
E v a p o r a t i o n measurement a t B u t i a b a n e a r Lake A l b e r t s t a r t e d i n 1932 u s i n g t h e P i c h e atmometer. The mean monthly and y e a r l y P i c h e r e a d i n g s o v e r t h e p e r i o d 1932-1934 are as f o l l o w s : Evaporation,
i n mm/day,
for
Jan.
Feb.
Mar.
Apr.
May
June
July
Aug.
Sep.
Oct.
Nov.
Dec.
Year
6.0
6.2
5.5
5.0
4.3
4.5
3.9
3.9
4.1
4.3
4.4
4.6
4.7
H u r s t assumed a r e d u c t i o n f a c t o r o f 0 . 7 so as t o deduce open water e v a p o r a t i o n from t h e P i c h e e v a p o r a t i o n . Based o n t h i s v a l u e f o r t h e r e d u c t i o n f a c t o r , t h e e v a p o r a t i o n from Lake A l b e r t would b e 3.3 mm/day. L a t e r , i n h i s book "The N i l e "
( 1 9 5 2 ) , H u r s t g a v e t h e b a l a n c e o f t h e Lakes
George and Edward. The t o t a l i n f l o w and r u n - o f f 2 . 2 m l r d m3/yr,
t o t h e l a k e s was assumed t o b e
t h e d i r e c t p r e c i p i t a t i o n 3.4 m l r d m 3 / y r and t h e o u t f l o w from
Edward t o t h e R i v e r S e m l e e k i 2 . 0 m l r d m3/yr. These f i g u r e s l e a v e a y e a r l y volume of 3 . 6 mlrd m 3 f o r e v a p o r a t i o n . The two l a k e s h a v e b e e n c o n s i d e r e d as one l a k e 2500 k m 2 i n s i z e , though Lake George i s a t a s l i g h t l y h i g h e r l e v e l t h a n Lake Edward. The mean a n n u a l d e p t h o f e v a p o r a t i o n i s 1440 mm, or a l m o s t 3 . 9 mm/day. I n t h e same r e f e r e n c e , i . e . "The N i l e "
( 1 9 5 2 ) , t h e b a l a n c e f o r Lake A l b e r t
w a s p r e p a r e d on t h e a s s u m p t i o n t h a t t h e a n n u a l volume o f d i r e c t p r e c i p i t a t i o n on the lake is 4.6 x
lo9
m 3 , t h e a n n u a l volume b r o u g h t by t h e Lower V i c t o r i a N i l e ,
R i v e r S e m l e e k i and t h e o t h e r t r i b u t a r i e s i s 2 5 . 0 x lo9 and t h e o u t f l o w from t h e l a k e i s 2 2 . 0 x lo9 m3/yr. T h e s e f i g u r e s are b a l a n c e d by a mean a n n u a l e v a p o r a t i o n of 3 . 9 mm/day. The same v a l u e f o r t h e e v a p o r a t i o n r a t e from Lake A l b e r t appears i n Vol. X of t h e N i l e Basin ( H u r s t , H . E . , Y.M.,
B l a c k , R . P . , and S i m a i k a ,
1 9 6 6 ) . I n t h e l a t t e r , t h e b a l a n c e was drawn between t h e i n f l o w t o and t h e
o u t f l o w from, t h e l a k e and t h e change i n s t o r a g e a v e r a g e d o v e r t h e p e r i o d 19401957. A c c o r d i n g t o t h e method o f O l i v i e r , e q . 5 . 3 , t h e w e t - b u l b d e p r e s s i o n measured
a t B u t i a b a g i v e s a mean a n n u a l e v a p o r a t i o n from a s t a n d a r d t a n k of a b o u t 4 . 2 mm/day. T h i s v a l u e c o r r e s p o n d s t o p r o b a b l y a f i g u r e o f a b o u t 3 . 5 mm/day f r e e w a t e r s u r f a c e e v a p o r a t i o n . The a n n u a l e v a p o r a t i o n measured by t h e P i c h e t u b e and t h e Kenya pan a t Gulu, a l m o s t 120 km n o r t h - e a s t
of B u t i a b a , h a v e b e e n r e p o r t e d
as 76 and 9 1 i n c h e s r e s p e c t i v e l y (WMO, 1 9 6 6 ) . T h e s e f i g u r e s c o r r e s p o n d t o n e a r l y 5 . 3 mm/day
P i c h e e v a p o r a t i o n and 5 . 6 mm/day open w a t e r e v a p o r a t i o n . The a u t h o r
h a s e s t i m a t e d t h e e v a p o r a t i v e demand a t some p l a c e s between t h e Lakes A l b e r t and Edward u s i n g Penman's m e t h o d . T h e e s t i m a t e s o b t a i n e d r a n g e f r o m 3 . 5 t o 3 . 9 mm/day.
179
The above r e v i e w may l e a d u s t o t h e f o l l o w i n g c o n c l u s i o n s : i)
The w a t e r b a l a n c e of Lake A l b e r t y i e l d s a mean a n n u a l e v a p o r a t i o n o f 3.9 mm/day from t h e l a k e . The s i m i l a r i t y and t h e n e a r n e s s of t h i s l a k e t o Lakes George and Edward s u g g e s t t h a t t h e e v a p o r a t i o n from t h e s e t w o l a k e s c a n a l s o b e c o n s i d e r e d a s 3.9 mm/day.
According t o t h i s f i g u r e , t h e P i c h e r e a d -
i n g a t B u t i a b a n e e d s t o b e m u l t i p l i e d by a r e d u c t i o n f a c t o r of 0 . 8 2 t o deduce t h e open w a t e r e v a p o r a t i o n . ii)
The e v a p o r a t i v e demand o f t h e c a t c h m e n t areas of Lakes George, Edward and A l b e r t v a r i e s c o n s i d e r a b l y from o n e l o c a t i o n t o t h e o t h e r . The r a n g e Of v a l u e s i s from a b o u t 3.5 mm/day, Albert,
t o more t h a n 5.5 mm/day,
somewhere between Lake Edward and Lake i n t h e neighbourhood o f t h e n o r t h e r n edge
of Lake A l b e r t ( s e e F i g . 5.3.).
F i g . 5.3.
Map of t h e e v a p o r a t i v e demand f o r t h e E q u a t o r i a l Lakes P l a t e a u
180
i i i ) The P i c h e e v a p o r a t i o n o f 4 . 7 mm/day a t B u t i a b a and o f 5 . 3 mm/day measured
a t Gulu needs t o b e m u l t i p l i e d by a f a c t o r o f from 1.1 t o 1 . 3 t o c o n v e r t i t t o t h e e v a p o r a t i v e demand o f t h e c a t c h m e n t a t t h e s e two l o c a t i o n s . BAHR EL JEBEL BASIN
5.2 5.2.1
Bahr e l J e b e l B a s i n ( o u t s i d e t h e swamps)
I n V o l . V o f t h e N i l e B a s i n i t i s mentioned t h a t a s m a l l t a n k 0 . 3 m s q u a r e
w a s f l o a t e d i n t h e r i v e r n e a r t h e d i s c h a r g e s i t e a t Nimule. E v a p o r a t i o n from t h a t t a n k was o b s e r v e d f o r some t i m e .
The d i f f i c u l t y i n m a i n t a i n i n g t h e t a n k t o
f u n c t i o n p r o p e r l y h a s l e d t o n e g l e c t i n g a l l t h e o b s e r v a t i o n s c o l l e c t e d from i t (Hurst, H.E.,
and P h i l i p s , P . ,
1938).
Both Volumes I and V o f t h e N i l e B a s i n g i v e t h e mean a n n u a l e v a p o r a t i o n from t h e P i c h e t u b e a t a number o f s t a t i o n s as f o l l o w s : S t a tion
Period of o b s erv ati o n
P i c h e e v a p o r a t i o n , mm/day
Malakal Masindi P o r t Lira Lerua Torit Jub a Mongalla Wau
1915-1934 1934 1933- 1934 1928- 1934 1922- 1934 1925-1928 and 1931-1934 1906-1930 1906-1929
9.0 4.2 5.0 4.9 7.1 7.0 6.1 7.4
H u r s t t o o k t h e mean o f t h e s e s t a t i o n s a f t e r e x c l u d i n g Malakal and Wau and m u l t i p l i e d t h e mean v a l u e by 0 . 5 7 t o deduce t h e open w a t e r e v a p o r a t i o n from t h e s o u t h e r n p a r t o f t h e Bahr e l J e b e l B a s i n . The r e s u l t s h e g o t were
E v a p o r a t i o n , i n mm/day,
for
Jan.
Feb.
Mar.
Apr.
May
June
July
Aug.
Sep.
Oct.
Nov.
Dec.
Year
6.3
6.3
4.5
3.2
2.2
2.1
1.7
1.6
2.2
2.4
3.2
4.2
3.3
H e commented on t h e s e r e s u l t s s a y i n g " t h e whole q u e s t i o n of e v a p o r a t i o n from
open w a t e r in t h e s e s o u t h e r n d i s t r i c t s n e e d s i n v e s t i g a t i o n , b u t i s n o t e a s y on a c c o u n t o f t h e d i f f i c u l t y o f m a i n t a i n i n g f l o a t i n g t a n k s f r e e from wave a c t i o n . The d i s t r i b u t i o n t h r o u g h o u t t h e y e a r i s s i m i l a r a t a l l t h e s t a t i o n s and so t h e monthly mean v a l u e s t a k e n from a l l t h e s t a t i o n s hve b e e n r e d u c e d t o g i v e a t o t a l o f 1200 m m f o r t h e y e a r " . I n o r d e r t o e s t i m a t e t h e f r e e w a t e r s u r f a c e e v a p o r a t i o n from t h e Bahr e l J e b e l and i t s B a s i n o u t s i d e t h e swamps, t h e a u t h o r h a s worked o u t t h e f o r m u l a s of Penman and o f H a r g r e a v e s u s i n g t h e a v a i l a b l e m e t e o r o l o g i c a l d a t a a t M a l a k a l ,
181
Wau and Mongalla/Juba.
loo,
7O30' and 5'N,
These s t a t i o n s a r e s i t u a t e d c l o s e t o t h e l a t i t u d e s o f
respectively.
The f o r m u l a s u s e d r e a d as f o l l o w s : Penman's f o r m u l a H
E =
A 60
(1948)
+ y E (5.6)
A + v
where E
= f r e e water surface evaporation,
H
= n e t h e a t budget a t t h e s u r f a c e , i n cals/cm2.day,
i n mm/day,
A
= s l o p e o f t h e t a n g e n t o f t h e s a t u r a t e d vapour p r e s s u r e
y
= p s y c h r o m e t e r c o n s t a n t = 0 . 4 9 mm Hg/OC,
-
temperature curve
a t t h e mean a i r t e m p e r a t u r e , i n m m Hg/OC,
and
Ea = e v a p o r a t i o n c o r r e s p o n d i n g t o t h e h y p o t e t i c a l case of e q u a l a i r and water
temperatures. The q u a n t i t i e s H and E
c a n b e c a l c u l a t e d from t h e e q u a t i o n s
(5.7) and E
= 0.35 (e
s
-
e ) ( 1 + 0 . 0 1 u2) a
where
RA
= amount o f
e n e r g y r e a c h i n g t h e o u t e r l i m i t of t h e a t m o s p h e r e , i n c a l s / c m 2
(horizontal)
.
day,
= r e l a t i v e dura t io n of b r i g h t sunshine,
Ta = mean a i r t e m p e r a t u r e , i n d e g r e e s a b s o l u t e ,
e
= a c t u a l vapour p r e s s u r e i n t h e a i r ,
e
= s a t u r a t i o n vapour p r e s s u r e i n t h e a i r , i n mm Hg, and
i n mm Hg,
u2 = mean wind s p e e d i n m i l e s / d a y a t a h e i g h t o f 2 m above t h e w a t e r s u r f a c e . Hargreaves' E
formula (1956)
= 0 . 3 8 d (1 - hn) (T
-
32)
(5.9)
182
where Ev = monthly e v a p o r a t i o n from a class A p a n , i n i n c h e s ,
d
= monthly day-time c o e f f i c i e n t ,
hn = mean monthly r e l a t i v e h u m i d i t y a t noon, i n d e c i m a l s , and T
= mean monthly t e m p e r a t u r e , i n d e g r e e s F a h r e n h e i t
Eq. 5 . 9 i s b a s e d o n an a v e r a g e wind s p e e d o f 100 km/day.
Evaporation
i n c r e a s e s o r d e c r e a s e s a b o u t 9 % w i t h e a c h 50 km/day i n c r e a s e o r d e c r e a s e i n t h e wind s p e e d . F u r t h e r m o r e , where t h e s u n s h i n e i s m a t e r i a l l y less t h a n 90% one o u g h t t o correct t h e computed e v a p o r a t i o n as f o l l o w s : sunshine i n percent
30
correction i n percent
-34
40
50
60
70
80
90
-28
-24
- 20
-16
- 9
0
When o b s e r v a t i o n s on s u n s h i n e were n o t a v a i l a b l e , w e u s e d t h e e q u a t i o n devel o p e d by P a l a y a s o o t (1965) t o compute t h e s u n s h i n e , S , from t h e c l o u d ' c o v e r , C , scale 0
s
= 74.5
-
8 , as
+
9.5
c -
2.0
c2
(5.10)
Eq. 5 . 9 i s b a s e d on d a t a c o l l e c t e d f r o m l o c a t i o n s w i t h an a v e r a g e e l e v a t i o n o f 500 f t , s a y 150 m . S i n c e e v a p o r a t i o n i n c r e a s e s w i t h e l e v a t i o n , e q . 5 . 9 c a n b e c o r r e c t e d by i n c r e a s i n g t h e c a l c u l a t e d v a l u e s by 1%f o r e a c h 100 m i n c r e a s e i n elevation. The f i g u r e s o b t a i n e d from H a r g r e a v e s ' e q u a t i o n h a v e b e e n r e d u c e d by a f a c t o r of 0 . 7 so as t o c o n v e r t t h e c l a s s A pan e v a p o r a t i o n t o e v a p o r a t i o n from open w a t e r . The mean monthly e v a p o r a t i o n computed from e q . 5 . 6 and from e q . 5 . 9 and o b s e r v e d by t h e P i c h e i n s t r u m e n t i s l i s t e d i n T a b l e 5 . 4 . I n t h i s t a b l e , t h e s t a t i o n a t M a l a k a l i s c o n s i d e r e d a s r e p r e s e n t i n g t h e n o r t h e r n p a r t o f t h e Bahr
e l J e b e l and Mongalla/Juba as r e p r e s e n t i n g t h e s o u t h e r n p a r t , b o t h o u t s i d e t h e swamps. The s t a t i o n a t Wau c a n b e r e g a r d e d as a t r a n s i e n t p o i n t between t h e o u t s i d e and t h e i n s i d e of t h e swamps. The comparison between t h e e v a p o r a t i o n f i g u r e s p r e s e n t e d i n T a b l e 5 . 4 c a n be made somewhat e a s i e r when t h e y a r e p l o t t e d v e r s u s t h e months of t h e y e a r , as shown i n F i g . 5 . 4 . The r e m a r k a b l e f e a t u r e i n t h i s f i g u r e i s t h a t t h e t h r e e methods y i e l d , f o r a l l s t a t i o n s c o n s i d e r e d , e v a p o r a t i o n c u r v e s showing an i d e n t i c a l p a t t e r n o f v a r i a t i o n w i t h t i m e d u r i n g t h e y e a r . The e v a p o r a t i o n c u r v e , s t a r t i n g from J a n u a r y , e x h i b i t s a s l i g h t r i s e t i l l i t r e a c h e s t h e peak evaporat i o n i n February t h e n f a l l s s t e e p l y , e s p e c i a l l y i n t h e b e g i n n i n g , till t h e minimum e v a p o r a t i o n i s r e a c h e d between J u l y and August. From t h i s t i m e onwards,
183
t h e e v a p o r a t i o n i n c r e a s e s g r a d u a l l y t i l l J a n u a r y and F e b r u a r y i n t h e n e x t y e a r . TABLE 5 . 4
Mean monthly open water e v a p o r a t i o n and P i c h e e v a p o r a t i o n a t some s t a t i o n s i n t h e Bahr e l J e b e l B a s i n , o u t s i d e t h e swamps Evaporation,
Method
i n mm/day,
for
J a n . F e b . Mar. Apr. May J u n e J u l y Aug. S e p . O c t . Nov. Dec. Year 1. Malakal Penman 5.5 6.6 6 . 8 6.7 5.8 H a r g r e a v e s x 0 . 7 10.6 1 0 . 8 9 . 4 9 . 3 6 . 3 Piche 16.5 18.2 15.7 10.9 7.0
4.5 4.2 4.4
4.0 2.6 2.9
4.1 1.9 2.5
4.8 2.5 2.9
5.0 2.9 3.7
5.2 5.8 5.4 9.2 8.3 13.6
5.4 6.3 9.0
2 . Wau Penman 6 . 4 7.0 7.0 Hargreaves x 0 . 7 9 . 5 9 . 1 8 . 4 Piche 11.9 12.6 12.0
6.7 6.0 7.5 6.4 9.4 6 . 4
5.2 4.9 4.7
4.5 3.4 3.7
4.8 3.5 3.5
5.0 3.6 3.9
5.1
5.4 6 . 1 5 . 8 8.1 7.7 10.2
5.8 6.2 7.6
5.8 5.2 5.3 4.1 7.4 4.9
4.7 3.2 4.3
4.1 2.3 3.3
4.5 2.8 '3.4
4.9 3.2 4.4
5.3 4.6 7.1
5.5 5.0 7.0
3 . Mongalla/?u&
Penman 6.4 6.9 Hargreaves x 0 . 7 8 . 3 8 . 2 Piche 1 2 . 3 12.0
6.6 7.7 9.7
3.8
4.7
5.2
3.8
5.4
5.7 6.6 9.2
The f i g u r e s o b t a i n e d from t h e method o f Penman d i f f e r from t h o s e o b t a i n e d from t h e H a r g r e a v e s f o r m u l a and from t h e P i c h e e v a p o r i m e t e r i n two d i s t i n c t ways. The f i r s t i s t h a t t h e mean a n n u a l Penman e v a p o r a t i o n i n c r e a s e s from Mongalla/ J u b a t o Wau and d e c r e a s e s a t M a l a k a l , whereas t h e o t h e r two methods show i n c r e a s i n g e v a p o r a t i o n from t h e s o u t h t o t h e n o r t h . The s e c o n d is t h a t t h e v a r i a t i o n i n t h e mean monthly e v a p o r a t i o n e s t i m a t e d from t h e method of Penman i s s m a l l compared t o t h e v a r i a t i o n o f e v a p o r a t i o n e s t i m a t e d from t h e o t h e r t w o methods. The r a t i o o f t h e minimum t o t h e maximum e v a p o r a t i o n i n t h e Penman's method o f a b o u t 0 . 5 9 f o r b o t h Malakal and Mongalla/Juba and 0 . 6 4 f o r Wau. The
same r a t i o s b u t o b t a i n e d from t h e H a r g r e a v e s f o r m u l a and from t h e P i c h e t u b e a r e 0 . 1 8 and 0 . 1 4 f o r M a l a k a l , 0 . 3 7 and 0 . 2 8 f o r Wau, and 0 . 2 8 and 0 . 2 7 f o r Mongalla/Juba,
respectively.
The c l a s s A pan e v a p o r a t i o n e s t i m a t e d by t h e H a r g r e a v e s method h a s been m u l t i p l i e d by a f a c t o r of 0 . 7 to deduce t h e open w a t e r e v a p o r a t i o n . T h i s v a l u e s h o u l d b e m o d i f i e d t o 0 . 7 7 f o r M o n g a l l a / J u b a , 0.66 f o r Wau, and 0.60 f o r Malakal so a s t o y i e l d t h e same mean a n n u a l e v a p o r a t i o n as o b t a i n e d from Penman's
method. The m o d i f i e d v a l u e s l i e w i t h i n 0 . 6 0 - 0 . 8 1 , A pan f a c t o r ( L i n s l e y , R . K . ,
Kohler, M.A.,
t h e r a n g e found f o r t h e c l a s s
and P a u l h u s , J . L . ,
1958).
184
18
MALAKAL
16
14
t
/
!
;
/' /'
12
. %
0 D
10
g
8
C
.-0
6
[
L
e
Piche 9.0 - . _m.m_. l.d a y
/.-
I
x/'
>
w
2
01
12
2
10
g
8
.-E
6
E
4
. D
:
1
+,"
1
/.+-. '
1
+.
'.
I
I
I
I
1
I
I
I
\
I
>
12
MONGALLA I JUBA
>r
. E ,"
10
E
B
C
.O
6
a
4
z
c
0
+" /
/
,/'
>
w
2
Jan.
Fig. 5.4.
Feb.
Mar.
Apr.
May
Jun.
Jul.
Aug. Sep.
Oct.
Nov.
Mean monthly evaporation at Malakal, Wau and Mongalla/Juba
Dec.
185
The o l d d a t a g i v e n by K e e l i n g and t h e more r e c e n t o n e s g i v e n by O l i v i e r f o r t h e mean a n n u a l e v a p o r a t i o n from t h e s o - c a l l e d s t a n d a r d t a n k c a n b e summarized in the following: Station
K e e l i n g , mm/day
O l i v i e r , mm/day
Malakal Wau Juba
6.4 5.4 5.0
6.0 9.3 7.4
These v a l u e s , e x c e p t t h e o n e o b t a i n e d from O l i v i e r ' s f o r m u l a f o r Wau, seems t o b e i n r e a s o n a b l e agreement w i t h t h e f i g u r e s o b t a i n e d from t h e methods w e have already described. The r a t i o o f t h e P i c h e e v a p o r a t i o n t o t h e Penman e v a p o r a t i o n shows an i n c r e a s e from t h e s o u t h t o t h e n o r t h . T h i s r a t i o i s 1 . 2 7 f o r Mongalla/Juba,
1.31
f o r Wau and 1 . 6 7 f o r M a l a k a l .
5.2.2
Bahr e l J e b e l and Bahr e l Ghazal B a s i n s ( i n s i d e t h e swamps)
E v a p o r a t i o n o b s e r v a t i o n s from a 10 m s q u a r e open w a t e r t a n k f l o a t i n g i n Shambe Lagoon a r e mentioned i n V o l . X o f t h e N i l e B a s i n ( H u r s t , H . E . ,
R.P., and S i m a i k a , Y . M . ,
Black,
1 9 6 6 ) . The r e p o r t e d r e a d i n g s f o r t h e y e a r s 1948 and
1949 a r e 4 . 9 4 mm/day and 6 . 0 2 mm/day.
The d i f f i c u l t y i n m e a s u r i n g t h a t p a r t of
t h e r a i n f a l l t h a t r e a c h e d t h e t a n k i s p r o b a b l y one o f t h e f a c t o r s r e s p o n s i b l e for this difference. Unfortunately, t h e a v a i l a b l e metoeological d a t a f o r t h e a r e a i n s i d e t h e swamps ( c h a n n e l s , l a g o o n s , e t c . ) are n e i t h e r c o m p l e t e n o r q u i t e r e l i a b l e .
I t is
t h e r e f o r e n o t w o r t h w h i l e employing t h e s e d a t a f o r e s t i m a t i n g t h e e v a p o r a t i o n i n s i d e t h e swamps, a s t h i s was done f o r t h a t p a r t of t h e b a s i n o u t s i d e t h e swamps. One s h o u l d e x p e c t , however, less e v a p o r a t i o n from t h e f r e e w a t e r i n s i d e t h e swamps t h a n from o u t s i d e . T h i s argument i s s u p p o r t e d by t h e f i g u r e s g i v e n i n Vol. V o f t h e N i l e B a s i n ( H u r s t , H . E . ,
and P h i l i p s , P . , 1 9 3 8 ) . The a v e r a g e
t e m p e r a t u r e i n s i d e t h e swamps i s 2OC less t h a n o u t s i d e t h e swamps, t h e r e l a t i v e h u m i d i t y i s a b o u t 37% more, t h e c l o u d i n e s s i s 10% more and t h e wind f o r c e i s o n l y 20% of t h e wind f o r c e o u t s i d e t h e swamps. The q u e s t i o n t h a t t h e n a r i s e s i s by how much t h e e v a p o r a t i o n i n s i d e t h e swamps i s less t h a n t h e e v a p o r a t i o n o u t s i d e . I n a n a t t e m p t t o answer t h i s q u e s t i o n , O l i v i e r (1961) r e f e r r e d t o t h e o l d f i n d i n g s o f Ebermayer a b o u t t h e e v a p o r a t i o n i n s i d e and o u t s i d e t h e f o r e s t s i n Germany. Ebermayer s u g g e s t e d a r e d u c t i o n f a c t o r of 0 . 3 6 t o b e a p p l i e d t o t h e f r e e water e v a p o r a t i o n o u t s i d e t h e f o r e s t s t o deduce t h e e v a p o r a t i o n from i n s i d e the f o r e s t s .
I f t h i s r e d u c t i o n f a c t o r h o l d s i n t h e c a s e of t h e swamps, one
s h o u l d e x p e c t t h e f r e e water e v a p o r a t i o n from t h e swamps o f Bahr e l J e b e l and
186
Bahr e l Ghazal t o be about 2 . 1 mm/day. The Piche readings suggest t h e r a t i o o f 0 . 4 1 f o r t h e evaporation from t h e swamps i n p r o p o r t i o n t o t h e f r e e water surf a c e e v a p o r a t i o n . S u b s t i t u t i n g t h e d i f f e r e n c e i n t h e meteorological d a t a b e t ween t h e i n s i d e and t h e o u t s i d e of t h e swamps i n Hargreaves' formula, eq. 5 . 9 , one comes t o a r e d u c t i o n f a c t o r of about 0 . 5 . So one has t o expect a mean annual evaporation from i n s i d e t h e swamps i n t h e range of from 2 . 5 t o 3.0 mm/day. This range c o n s t i t u t e s about 50% only of t h e observed f l o a t i n g - t a n k e v a p o r a t i o n . The above d i s c u s s i o n can l e a d us t o t h e following general conclusions: i)
The open water evaporation o u t s i d e t h e swamps shows a gradual i n c r e a s e i n a n o r t h e r l y d i r e c t i o n from s l i g h t l y more than 5 mm/day a t Mongalla t o s l i g h t l y less than 6 mm/day a t Malakal.
ii)
The mean monthly evaporation a t a l l s t a t i o n s shows a well-defined p a t t e r n with time i n t h e y e a r .
iii) The range of v a r i a t i o n of t h e mean monthly evaporation estimated from t h e
Penman method is much s m a l l e r compared t o t h e same range i n t h e observed Piche readings o r t h e c l a s s A pan evaporation estimated from t h e Hargreaves formula. iv)
The r e d u c t i o n f a c t o r of t h e Piche readings t o deduce t h e f r e e water s u r f a c e evaporation i n c r e a s e s i n a n o r t h e r l y d i r e c t i o n from 1.27 a t Mongalla t o 1.67 a t Malakal.
v)
A reasonably a c c u r a t e measurement of t h e open water evaporation i n s i d e t h e
swamps is not a v a i l a b l e . I n d i r e c t e s t i m a t e s y i e l d a mean annual evaporat i o n i n t h e range of 2 . 5 t o 3.0 mm/day. 5.3
THE WHfTE NILE BASIN (from Malakal t o Khartoum)
Evaporation has been measured by means of f l o a t i n g tanks a t Malakal and Khartoum, a s w e l l a s by t h e Piche evaporimeter a t a number of s t a t i o n s . The f l o a t i n g tanks have been r e p o r t e d a s being not e n t i r e l y s a t i s f a c t o r y , though they g i v e more d i r e c t and u s e f u l information. The reason behind t h a t s t a t e of a f f a i r s was t h e d i f f i c u l t y i n p r o t e c t i n g t h e tanks completely from t h e e f f e c t s of s t r o n g winds. The evaporation from t h e White N i l e Basin has become important a f t e r t h e cons t r u c t i o n of t h e J e b e l Aulia dam, some f o r t y k i l o m e t r e s south of Khartoum. The s t o r a g e r e s e r v o i r , when f u l l , has a r e l a t i v e l y l a r g e s u r f a c e compared t o i t s volume. The mean monthly open water evaporation a t Khartoum, J e b e l A u l i a , Dueim, Rabak/Kosti, Renk and Malakal has been deduced from t h e Piche readings using a r e d u c t i o n f a c t o r of 0 . 5 . The mean annual f i g u r e s a r e presented both i n Table 5 . 1 and F i g . 5 . 1 .
H u r s t , i n Vol. VIII of t h e N i l e Basin (1950), commented on
t h e changing c l i m a t e a s one t r a v e l s south along t h e White Nile s t a r t i n g from Khartoum. The range of t h e Piche evaporation a t t h e northern end i s from 10 t o
187
20 mm/day. A t Dueim, 200 km s o u t h , t h e maximum is a b o u t t h e same b u t t h e minimum d e c r e a s e s t o 7 mm/day. A t M a l a k a l , 800 km s o u t h , t h e maximum remains a l m o s t t h e same and t h e minimum d r o p s f u r t h e r t o 3 mm/day and t h e e v a p o r a t i o n is less t h a n t h e minimum a t Khartoum f o r s e v e n months, from May up t o and i n c l u d i n g November. The mean monthly e v a p o r a t i v e demand f o r Khartoum e s t i m a t e d from t h e methods o f Penman and H a r g r e a v e s t o g e t h e r w i t h t h e P i c h e e v a p o r a t i o n i s i n c l u ded i n T a b l e 5 . 5 . TABLE 5 . 5
Mean monthly open water e v a p o r a t i o n a t Khartoum and P i c h e e v a p o r a t i o n from t h e White N i l e B a s i n Evaporation,
Method
J a n . F e b . Mar. Apr. May Penman 7.2 7.8 9.3 Hargreavesx0.7 10 . 1 11.6 13.6 Piche 12.0 1 4 . 0 17.0 Piche x 0.5+ 8 . 0 9 . 0 10.0
i n mm/day, f o r
J u n e J u l y Aug. S e p . O c t . Nov. D e c . Year
10.5 10.4 10.1 8 . 4 6 . 8 7 . 1 8 . 9 8 . 2 7 . 1 8 . 5 16.6 1 7 . 0 1 5 . 2 1 0 . 8 7 . 6 8 . 6 1 2 . 6 1 2 . 6 11.0 1 2 . 1 1 8 . 0 1 8 . 0 16.0 1 3 . 0 1 0 . 0 1 2 . 0 1 4 . 0 1 3 . 0 1 2 . 0 1 4 . 1 10.0 8 . 0 7 . 0 5 . 0 3 . 0 4 . 0 5 . 0 7 . 0 7 . 0 7 . 0
+Average o f P i c h e r e a d i n g s a t Khartoum, J e b e l A u l i a , Dueim, R a b a k / K o s t i , Renk and M a l a k a l . O t h e r d a t a b e l o n g t o Khartoum o n l y . The d a t a a b o u t Malakal i s included i n Table 5 . 4 . The mean monthly e v a p o r a t i o n g i v e n i n T a b l e 5 . 5 shows t h e same p a t t e r n f o r a l l methods u s e d . T h e r e a r e two s e a s o n s f o r t h e peak e v a p o r a t i o n , though t h e second peak h a s a n a v e r a g e v a l u e e q u a l t o a b o u t 75% o f t h e v a l u e of t h e f i r s t peak. The f i r s t peak o c c u r s i n April-May and t h e s e c o n d i n October-November. The p r o p o r t i o n o f t h e minimum monthly e v a p o r a t i o n t o t h e maximum monthly evap o r a t i o n v a r i e s from 0 . 6 5 i n t h e method o f Penman t o 0 . 4 5 i n t h e method of Hargreaves t o 0 . 5 5 f o r t h e P i c h e e v a p o r a t i o n . The r e s u l t s o b t a i n e d from t h e Hargreaves f o r m u l a when m u l t i p l i e d by 0 . 7 a r e a b o u t 434. h i g h e r t h a n t h o s e o b t a i n e d from t h e Penman method whereas t h e P i c h e r e a d i n g s need t o b e reduced by a b o u t 40% t o become e q u a l t o t h e Penman e v a p o r a t i o n . A d d i t i o n a l e s t i m a t e s o f e v a p o r a t i o n from a s t a n d a r d t a n k a r e 11.3 and 1 0 . 5 mm/day as o b t a i n e d from t h e O l i v i e r method and t h e d a t a of K e e l i n g , r e s p e c t i v e l y .
A t Khartoum o b s e r v a t o r y , c o m p a r i s o n s w e r e made among e v a p o r a t i o n d a t a from ( 1 ) a 1 2 - f t d i a m e t e r t a n k , 4 - f t d e e p ; ( 2 ) a c l a s s A p a n ; ( 3 ) a P i c h e atmometer; ( 4 ) l a k e e v a p o r a t i o n computed by Penman e q u a t i o n , and ( 5 ) l a k e e v a p o r a t i o n by K o h l e r ' s method, which i s b a s e d on c o r r e c t i n g class A pan e v a p o r a t i o n f o r h e a t t r a n s f e r t h r o u g h i t s s i d e s and b o t t o m . The r e s u l t s o b t a i n e d f o r t h e y e a r s 1961 and 1962 are g i v e n i n T a b l e 5 . 6 (WMO, 1 9 6 6 ) .
188
TABLE 5 . 6
Comparison between e v a p o r a t i o n o b t a i n e d from d i f f e r e n t methods and e v a p o r i m e t e r s a t Khartoum (WMO, 1966)
Year
1960
Month
1 2 - f t pan Piche
1 2 - f t pan Penman
1 2 - f t pan (Kohler)
Jan. Feb. Mar. Apr . May June July Aug . Sep. Oct. Nov Dec.
0.68 0.60 0.65 0.62 0.64 0.67 0.62 0.65 0.69 0.69 0.64 0.61
0.50 0.43 0.48 0.46 0.53 0.53 0.54 0.60 0.61 0.55 0.45 0.47
1.23 1.13 1.18 1.25 1.37 1.20 1.06 1.14 1.17 1.31 1.25 1.16
1.07 0.99 1.02 0.97 0.99 1.03 0.94 1.00 1.01 1.05 0.99 0.98
Annual
0.64
0.51
1.20
1.oo
Jan. Feb Mar Apr . May June July Aug . Sep. Oct. Nov . Dec
0.67 0.66 0.64 0.62 0.59 0.61 0.68 0.74 0.69 0.67 0.66 0.69
0.51 0.50 0.50 0.49 0.48 0.58 0.78 0.63 0.63 0.53 0.50 0.50
1.20 1.24 1.21 1.28 1.36 1.24 0.97 0.96 1.20 1.25 1.26 1.22
1.06 1.01 1.00 0.98 0.97 0.95 0.98 1.03 1.04 1.01 1.00 1.03
Annual
0.65
0.55
1.20
1.00
.
.
196 1
1 2 - f t pan C l a s s A pan
.
The f i g u r e s l i s t e d i n T a b l e 5 . 6 c a n b e c o n v e r t e d t o o t h e r f i g u r e s g i v i n g t h e r a t i o between e v a p o r a t i o n from a f r e e water s u r f a c e and e v a p o r a t i o n a s o b s e r v e d by an e v a p o r i m e t e r o r e s t i m a t e d from a f o r m u l a . T h i s h a s been done u s i n g t h e d a t a i n T a b l e 5 . 2 where t h e r a t i o o f 1 2 - f t pan d i a m e t e r t o an e x t e n d e d w a t e r s u r f a c e is 1 . 0 9 9 . The monthly a v e r a g e r a t i o s found f o r 1960 and 1961 o f t h e 1 2 - f t p a n : P i c h e and t h e 1 2 - f t p a n : Penman were e a c h d i v i d e d by 1 . 0 9 9 t o deduce t h e c o r r e s p o n d i n g f r e e w a t e r s u r f a c e : P i c h e and f r e e water s u r f a c e : Penman. By t h i s p r o c e d u r e two sets of mean monthly e v a p o r a t i o n v a l u e s from t h e f r e e w a t e r s u r f a c e a t Khartoum h a v e b e e n d e v e l o p e d . The new set o f d a t a o r i g i n a t i n g from P i c h e r e a d i n g s i s somewhat on t h e low s i d e , and t h a t o r i g i n a t i n g from Penman's method i s somewhat on t h e h i g h s i d e . A f a i r compromise i s t o t a k e t h e a r i t h m e t i c mean of t h e s e two s e t s . A c c o r d i n g l y , one c a n l i s t t h e f r e e w a t e r s u r f a c e e v a p o r a t i o n
a t Khartoum a s f o l l o w s :
189
Evaporation,
i n mm/day,
for
Jan.
Feb.
Mar.
Apr.
May
Jun.
Jul.
Aug.
Sep.
Oct.
Nov.
Dec.
Year
6.74
7.16
8.85
9.94
10.60
9.64
7.78
6.05
7.21
8.62
7.49
6.49
8.04
The f o r e g o i n g a n a l y s i s l e a d s u s t o t h e c o n c l u s i o n t h a t t h e f r e e w a t e r s u r f a c e e v a p o r a t i o n from t h e White N i l e B a s i n r a n g e s from s l i g h t l y less t h a n 6 mm/ day a t Malakal t o 8 mm/day a t Khartoum i n a n o r t h e r l y d i r e c t i o n o v e r a d i s t a n c e of a b o u t 800 km. The mean monthly e v a p o r a t i o n a t Khartoum h a s two p e a k s ; t h e f i r s t peak o f 10.6 mm/day o c c u r r i n g i n O c t o b e r . The minimum t a k e s p l a c e i n August and i n December where t h e mean monthly e v a p o r a t i o n f a l l s t o 6.0 and 6.5 r e s p e c t i v e l y . E v a p o r a t i o n from open w a t e r a t Malakal shows a s i n g l e peak
mm/day
o n l y . The e x p e r i m e n t s c o n d u c t e d a t Khartoum when combined w i t h o t h e r e x p e r i ments show t h a t t h e Penman e v a p o r a t i o n i s a b o u t 10% less t h a n t h e e v a p o r a t i o n from a f r e e w a t e r s u r f a c e . The r e d u c t i o n f a c t o r o f t h e P i c h e r e a d i n g s needs t o b e i n c r e a s e d t o 0.55-0.60 i n s t e a d of 0.5 t o deduce t h e open w a t e r e v a p o r a t i o n .
5.4
THE ETHIOPIAN PLATEAU
5.4.1
The S o b a t B a s i n
E s t i m a t i o n o f f r e e w a t e r e v a p o r a t i o n from t h e S o b a t B a s i n h a s been c o n f i n e d t o t h r e e s t a t i o n s , namely: Gambeila, Akobo and M a l a k a l . A s a m a t t e r of f a c t t h e s t a t i o n a t Malakal b e l o n g s t o t h e White N i l e B a s i n . However, s i n c e i t i s s i t u a t e d c l o s e t o t h e mouth of t h e S o b a t on t h e White N i l e , i t s d a t a c a n b e used t o c o m p l e t e t h e e s t i m a t e s of e v a p o r a t i o n from t h e c a t c h m e n t o f t h e S o b a t . The a v e r a g e P i c h e r e a d i n g s o v e r d i f f e r e n t p e r i o d s f o r Gambeila and Akobo a r e l i s t e d i n T a b l e 5.7 whereas t h e d a t a b e l o n g i n g t o Malakal have a l r e a d y been i n c l u d e d i n T a b l e 5.4. TABLE 5.7
P i c h e e v a p o r a t i o n a t Gambeila and Akobo i n t h e S o b a t B a s i n ( H u r s t ,
H.E., Station
1950) Evaporation,
Period
*
i n mm/day,
for
J a n . F e b . Mar. Apr. May J u n e J u l y Aug. S e p . O c t . Nov. Dec. Year
Gambeila
a b
9.0 10.0 1 1 . 0 8.0 9.8 9.6
8.0 5.0 7.5 4.0
4.0 2.5
3.0 2.2
3.0 2.1
3.0 2.6
4.0 3.3
5.0 4.3
7.0 5.9
5.9 5.1
Akobo
c
10.3 11.8 10.9
8.8 5.3
3.9
2.9
2.4
3.1
3.6
4.6
7.8
6.3
*a = 1909-34; b = 1950-57;c= 1950-57 ( i n 1950 from J a n u a r y t o March o n l y )
190
The mean a n n u a l e v a p o r a t i o n as g i v e n i n T a b l e 5 . 7 i s n o t r e a l l y c o n s i s t e n t w i t h t h e r e g r e s s i o n r e l a t i o n between t h e a n n u a l r a i n f a l l , R i n mm, and t h e P i c h e e v a p o r a t i o n , i n mm/day, which w a s d e v e l o p e d by H u r s t i n V o l . X o f t h e N i l e B a s i n ( 1 9 6 6 ) . The r e g r e s s i o n e q u a t i o n Epiche
= 10.3
-
0.0076 (R
-
714)
(5.11)
gives E f o r Gambeila and Akobo as 6 . 6 and 8 . 9 mm/day r e s p e c t i v e l y . The d i s piche c r e p a n c y between t h e s e f i g u r e s and t h e o b s e r v e d P i c h e e v a p o r a t i o n may throw some d o u b t on t h e v a l i d i t y o f e q . 5 . 1 1 , o r t h e d a t a i n T a b l e 5 . 7 , o r b o t h . The a v a i l a b l e m e t e o r o l o g i c a l d a t a of t h e S o b a t B a s i n , e x c e p t f o r M a l a k a l , are i n a d e q u a t e t o a l l o w f o r e s t i m a t i n g t h e f r e e water e v a p o r a t i o n from any f o r m u l a . W e t h e r e f o r e need t o a p p r o a c h t h e problem from a d i f f e r e n t a n g l e . The w e i g h t e d a v e r a g e P i c h e e v a p o r a t i o n ( t o t a l 32 y e a r s o f r e c o r d ) i s 5 . 7 mm/day f o r Gambeila. Assuming a l i n e a r p r o p o r t i o n between t h e e v a p o r a t i o n a t t h e two s t a t i o n s , a n a v e r a g e P i c h e e v a p o r a t i o n o f 7 . 0 4 mm/day, o v e r t h e same p e r i o d , c a n b e o b t a i n e d f o r Akobo. The t w o s t a t i o n s are s i t u a t e d o u t s i d e t h e Machar swamps and a p p a r e n t l y have s i m i l a r c o n d i t i o n s a f f e c t i n g t h e f r e e w a t e r e v a p o r a t i o n t o t h e s t a t i o n s o u t s i d e t h e swamps i n t h e Bahr e l J e b e l and Bahr e l Ghazal B a s i n s . From t h e d a t a p r e s e n t e d i n Table 5 . 4 i t is obvious t h a t t h e r e d u c t i o n f a c t o r t o t h e P i c h e r e a d i n g s a t Mongalla and Wau h a s a n a v e r a g e o f 0 . 7 5 . Applying t h i s f a c t o r t o t h e e s t i m a t e d P i c h e e v a p o r a t i o n f o r Gambeila and Akobo o n e o b t a i n s a mean a n n u a l open water e v a p o r a t i o n o f 4 . 3 and 5 . 3 mm/day r e s p e c t i v e l y . F u r t h e r m o r e , i f w e assume t h a t t h e s e f i g u r e s are d i s t r i b u t e d throughout t h e y e a r s i m i l a r t o t h e P i c h e r e a d i n g s i n Table 5 . 7 , one can o b t a i n t h e mean monthly e v a p o r a t i o n as f o l l o w s :
Station
E v a p o r a t i o n , i n mm/day,
for
J a n . Feb. Mar. Apr. May J u n e J u l y Aug. S e p . O c t . Nov. Dec. Year
Gambeila
6.6
7.7
8.0
6.0
3.5
2.5
2.1
2.1
2.2
2.8
3.6
5.0
4.3
Akobo
8.7
9.9
9.2
7.4
4.4
4.5
3.3
2.4
2.0
2.6
3.9
6.5
5.3
The S o b a t B a s i n i n c l u d e s t h e Machar swamps. The s u r f a c e a r e a o f t h e s e swamps
i s e x c e e d i n g l y v a r i a b l e . The J o n g l e i i n v e s t i g a t i o n team r e p o r t e d t h a t when t h e r a i n s were below t h e n o r m a l , t h e y became d r y , and when t h e y were above t h e n o r m a l , t h e swamps c o v e r e d a b o u t 20.000 km2. T h i s team used what t h e y r e p o r t e d
as t h e maximum s u r f a c e a r e a f o r e s t i m a t i n g t h e e v a p o r a t i o n from t h e Machar swamps. From t h e w a t e r - b a l a n c e o f t h e swamps t h e a n n u a l e v a p o r a t i o n w a s estimat e d a t 0 . 9 5 m o r a b o u t 2 . 6 mm/day. H u r s t condemned t h i s f i g u r e as b e i n g
19 1
a b s u r d l y l o w . I n s t e a d , i n V o l . X o f t h e N i l e B a s i n (1966), h e e s t i m a t e d t h e annual volume o f w a t e r d i s a p p e a r i n g by e v a p o r a t i o n from t h e Machar swamps a t 9 . 9 mlrd m 3 . H e f u r t h e r assumed t h a t t h i s volume corresponded t o 6.700 km2 s u r f a c e of t h e swamps. I f t h i s is r e a l l y so, t h e mean annual f r e e w a t e r s u r f a c e evaporat i o n becomes 4 . 1 mm/day and n o t 5.0 mm/day as computed by H u r s t . The f i g u r e of 4 . 1 mm/day seems t o b e f a i r l y c o n s i s t e n t w i t h t h o s e found by u s as 4 . 3 and 5 . 3 mm/day e v a p o r a t i o n a t Gambeila and Akobo r e s p e c t i v e l y . 5.4.2
The B l u e N i l e B a s i n
The open water e v a p o r a t i o n deduced from t h e P i c h e r e a d i n g s a t a number of places i n t h e Blue N i l e Basin is a l r e a d y included i n Table 5 . 1 .
The mean
annual e v a p o r a t i o n as g i v e n i n t h i s t a b l e v a r i e s from 3 . 0 mm/day f o r Lake Tana t o 6 . 5 mm/day a t Wad Medani and e v e n t u a l l y t o 7 . 8 mm/day a t Khartoum. Rz6ska, upon c o m p i l i n g some h y d r o l o g i c a l d a t a from H u r s t ‘ s book
,
“The N i l e “
(1976) concluded t h a t t h e mean annual l o s s e s o f open water measured i n t a n k s w e r e 1 . 0 9 (0.54-1.29)
m f o r Lake Tana and 2.30 m f o r t h e r e a c h from R o s e i r e s up
t o Wad Medani. Lake Tana h a s a s u r f a c e area o f about 3150 km2 and a catchment o f about 13400 km2. The i s o h y e t a l maps show a d i r e c t r a i n f a l l o f 1 . 2 m i n a normal y e a r o v e r t h e l a k e and about 1 . 3 m o v e r t h e catchment. The run-off
c o e f f i c i e n t f o r t h i s catchment a s o b t a i n e d from “The Water
Resources o f The E a r t h ” (1974) is 0 . 1 5 . S i n c e t h e o u t f l o w from Lake Tana i n a normal y e a r i s known t o b e a b o u t 3 . 5 mlrd m 3 , one c a n e a s i l y a r r i v e a t an annual d e p t h o f e v a p o r a t i o n o f 0 . 9 m, from t h e water b a l a n c e , e q . 5 . 2 . T h i s depth c o r r e s p o n d s t o a mean annual e v a p o r a t i o n o f 2 . 5 mm/day, which i s 20% less t h a n t h e f i g u r e p r e s e n t e d i n T a b l e 5 . 1 . The i n a c c u r a c i e s i n v o l v e d i n t h e r a i n d e p t h s , i n t h e estimate of t h e o u t f l o w from t h e l a k e , and p r o b a b l y t h e run-off c o e f f i c i e n t from t h e catchment o b v i o u s l y a f f e c t t h e a c c u r a c y of t h e estimate of evaporation. H u r s t , i n Vol. VIII of t h e N i l e B a s i n ( 1 9 5 0 ) , mentions t h a t t h e n e x t p o i n t ( n e x t t o Lake Tana) where t h e r e i s any h y d r o l o g i c a l i n f o r m a t i o n i s a t R o s e i r e s i n t h e Sudan. We h a v e t r i e d t o estimate t h e f r e e water s u r f a c e e v a p o r a t i o n from t h e a v a i l a b l e m e t e o r o l o g i c a l d a t a f o r t h r e e s t a t i o n s , namely: Addis Abbaba, R o s e i r e s and Wad Medani. The computed e v a p o r a t i o n , t o g e t h e r w i t h t h e a v a i l a b l e Piche readings a r e l i s t e d i n Table 5 . 8 . The e v a p o r a t i o n from t h e Blue N i l e B a s i n , whether computed from t h e formula o f Penman o r t h a t o f H a r g r e a v e s , or measured by t h e P i c h e i n s t r u m e n t , shows an i n c r e a s e i n a n o r t h e r l y d i r e c t i o n from Addis Abbaba t o Wad Medani and e v e n t u a l l y t o Khartoum.
192
TABLE 5.8
Computed f r e e s u r f a c e w a t e r e v a p o r a t i o n and measured P i c h e e v a p o r a t i o n a t some s t a t i o n s i n t h e B l u e N i l e B a s i n
Station and Metho'
Evaporation, J a n . Feb. Mar. Apr.
May
i n mm/day,
for
J u n e J u l y Aug. S e p . O c t . Nov. Dec. Year
Addis Abbaba
a
b
Roseires a b C
d Wad Medani a b C
d
5.2 7.3
5.3 7.5
5.4 7.7
5.7 8.5
5.6 8.3
4.9 7.0
4.2 5.6
4.1 5.3
4.7 6.5
5.0 6.9
5.1 7.1
6.3
6.5
7.8
8.3
7.6
7.4
7.9
8.1
6.6
6.4 7.2 8.4 4.2
5.0 3.9 5.0 2.5
5.1 4.0 5.1 2.6
5.3 4.6 5.8 2.9
5.5 4.8 6.8 3.4
5.7 5.8 6.3 6.3 8.4 7.9 8.8 11.4 1 0 . 6 4.4 5.7 5.3
5.8 6.3 7.8 9.2 8.9 8.3 6.4 7.8 8.7 10.2 12.9 12.5 11.3 8.1 14.3 16.5 20.4 21.5 20.4 18.7 11.3 7.1 8.2 10.2 10.8 10.2 9.4 5.6
5.3 5.7 6.6 3.3
6.3 6.5
1 0 . 0 10.7 11.9 12.3 9.2 13.6 14.7 15.8 16.2 13.2
6.8
5.2 7.3
5.0 7.1
7.5 6.6 5.6 7.0 9.5 9.2 8.1 9.2 7 . 1 11.4 14.6 13.4 14.7 3.6 5.7 7.3 6.7 7.3
*a = Penman; b = H a r g r e a v e s x 0.7; c = P i c h e ; d = P i c h e x 0.5 The f r e e w a t e r e v a p o r a t i o n computed by Penman's f o r m u l a h a s been p l o t t e d v e r s u s t h e t i m e i n months f o r t h e s t a t i o n s a t Addis Abbaba, Roseires, Wad Medani and Khartoum. The f o u r e v a p o r a t i o n c u r v e s i l l u s t r a t e d i n F i g . 5.5. p r e s e n t some marked f e a t u r e s . The r a t i o of t h e minimum e v a p o r a t i o n t o t h e maximum e v a p o r a t i o n f o r Addis a b b a b a , b e i n g 0.72, i s c e r t a i n l y h i g h compared w i t h t h e a v e r a g e o f t h e c o r r e s p o n d i n g r a t i o s f o r t h e o t h e r s t a t i o n s , which i s a b o u t 0 . 6 0
(0.57-0.64). The e v a p o r a t i o n c u r v e s f o r Addis Abbaba and R o s e i r e s are s i m i l a r t o t h o s e p l o t t e d f o r t h e s t a t i o n s i n t h e Bahr e l J e b e l B a s i n ( F i g . 5.4.) i n t h a t e a c h c u r v e h a s a s i n g l e p e a k . The o t h e r two c u r v e s f o r Wad Medani and Khartoum show two peak e v a p o r a t i o n r a t e s , t h e f i r s t o c c u r s i n April-May
and t h e s e c o n d ,
t h e s m a l l e r of t h e two, i n O c t o b e r . The f i g u r e s l i s t e d i n T a b l e s 5.6 and 5.8 i n d i c a t e t h a t t h e r a t i o o f t h e mean a n n u a l e v a p o r a t i o n computed by t h e Penman t o t h e mean a n n u a l e v a p o r a t i o n r e a d from t h e P i c h e t u b e i s n e a r l y t h e same f o r b o t h Khartoum and R o s e i r e s , 0.60 and
0.59 r e s p e c t i v e l y . The Same r a t i o c a n b e found from T a b l e 5.4 a s 0 . 6 0 f o r Malakal a l s o . I t m i g h t b e t h a t f o r t h o s e p a r t s o f t h e White N i l e and t h e B l u e N i l e B a s i n s o u t s i d e t h e swamps t h e f a c t o r 0 . 6 c a n r e a s o n a b l y b e u s e d t o c o n v e r t
t h e mean a n n u a l P i c h e e v a p o r a t i o n t o t h e c o r r e s p o n d i n g Penman e v a p o r a t i o n . Note t h a t t h i s i s s l i g h t l y d i f f e r e n t from t h e f a c t o r o f 0.5 used by H u r s t f o r c o n v e r t i n g t h e Piche readings t o f r e e water surface evaporation.
193
10
9
a x
0 D
- 7 E E C
.-
.-0
z6 n
> w
x
,..
*
.........J(‘. ......... .
5
x...........x.”
4
3
Jan.
Feb.
Mar.
Apr.
May.
Jun.
Jul.
Aug.
Sep.
Oct.
Nov.
Dec.
F i g . 5.5. Mean monthly e v a p o r a t i o n from open water a t some s t a t i o n s i n t h e Blue N i l e B a s i n e s t i m a t e d from t h e Penman method
The Penman: t h e P i c h e r a t i o f o r t h e mean monthly e v a p o r a t i o n h a s been found t o v a r y from as small a s 0 . 4 4 t o a s l a r g e a s 1 . 0 f o r R o s e i r e s and Khartoum s t a t i o n s . The r a n g e o f v a r i a t i o n f o r Malakal i s even much w i d e r s i n c e t h e mini-
m u m and t h e maximum v a l u e s f o r t h i s r a t i o a r e 0.33 and 1.66 r e s p e c t i v e l y . I n a d d i t i o n to t h e s t a t i o n s a t Addis Abbaba, R o s e i r e s , Wad Medani and Khartoum, t h e r e are t h r e e o t h e r s t a t i o n s i n t h e B l u e N i l e B a s i n f o r which t h e P i c h e r e a d i n g s o v e r t h e p e r i o d 1921-1950 a r e a v a i l a b l e . These a r e : S i n g a and S e n n a r , n e a r l y h a l f w a y between R o s e i r e s and Khartoum, and Kurmuk, t o which t h e nearest s t a t i o n is Roseires.
194
The a v e r a g e o f t h e monthly c o e f f i c i e n t s f o r Khartoum and R o s e i r e s h a v e been m u l t i p l i e d by t h e P i c h e e v a p o r a t i o n a t S i n g a and a t S e n n a r whereas t h e monthly c o e f f i c i e n t s f o r R o s e i r e s a l o n e have b e e n m u l t i p l i e d by t h e P i c h e e v a p o r a t i o n a t Kurmuk ( H u r s t , N . E . ,
B l a c k , R.P. and S i m a i k a , Y.M., 1959). The r e s u l t s
o b t a i n e d a r e l i s t e d i n T a b l e 5.9. TABLE 5.9
F r e e w a t e r s u r f a c e e v a p o r a t i o n f o r S i n g a , Sennar and Kurmuk i n t h e Blue N i l e B a s i n
Station Singa Sennar Kurmuk 5.4.3
E v a p o r a t i o n , i n mm/day, f o r J a n . Feb. Mar. Apr. May J u n e J u l y Aug. S e p . O c t . Nov. D e c . Year 7.2 7.8 7.2
8.3 9.5 7.9
8.8 9.7 8.3 11.4 12.2 9.2 8.2 6.7 4.6
8.2 9.5 3.7
5.8 6.6 3.1
3.7 4.2 2.6
3.8 5.0 2.8
5.8 7.2 2.9
8.6 9.6 4.8
7.5 7.9 6.9
7.0 7.4 5.3
The A t b a r a B a s i n
While d i s c u s s i n g t h e hydrology o f t h e A t b a r a B a s i n i n Vol.
IX o f t h e N i l e
B a s i n , H u r s t mentions t h a t t h e r e i s v e r y l i t t l e i n f o r m a t i o n a b o u t t h e evaporat i o n from t h i s b a s i n . Though Lake Tana i s j u s t o u t s i d e t h e A t b a r a B a s i n , t h e s u r r o u n d i n g c o u n t r y is s i m i l a r t o t h a t o f t h e A t b a r a c a t c h m e n t . H u r s t used t h i s c h a r a c t e r i s t i c t o g e t h e r w i t h t h e a v e r a g e o f t h e P i c h e r e a d i n g s a t Kassala and G a l l a b a t , reduced by a f a c t o r of 0.5, i n o r d e r t o s k e t c h a n approximate p i c t u r e o f t h e open w a t e r e v a p o r a t i o n i n o r n e a r t h e A t b a r a B a s i n ( H u r s t , H . E . , R.P.,
and Simaika, Y . M . ,
Black,
1959). The f i g u r e s o b t a i n e d by H u r s t and t h e f i g u r e s
w e have e s t i m a t e d by t h e Penman method d i r e c t l y f o r A t b a r a and i n d i r e c t l y as an
a v e r a g e f o r K a s s a l a and G a l l a b a t are g i v e n i n T a b l e 5.10. The f o r e g o i n g d i s c u s s i o n o f t h e f r e e water s u r f a c e e v a p o r a t i o n from t h e E t h i o p i a n P l a t e a u may l e a d t o t h e f o l l o w i n g c o n c l u s i o n s : i)
The e v a p o r a t i o n from Lake Tana i s n o t known t o a f a i r d e g r e e of a c c u r a c y . The i n e d a q u a t e i n f o r m a t i o n about t h e hydrology of t h i s l a k e p o i n t s t o a mean a n n u a l e v a p o r a t i o n o f 3.0-3.5 mm/day.
ii)
The mean a n n u a l e v a p o r a t i o n from t h e Machar swamps i n t h e S o b a t B a s i n may b e t a k e n a s a b o u t 4.1 mm/day.
i i i ) The open w a t e r e v a p o r a t i o n f o r t h e B l u e N i l e B a s i n i n c r e a s e s g r a d u a l l y i n
a n o r t h - w e s t e r l y d i r e c t i o n . The mean annual e v a p o r a t i o n a t Kurmuk i s 5.3 mm/day,
i n c r e a s i n g t o a b o u t 6.3 mm/day a t Roseires, 7.0-7.5 f o r S i n g a ,
S e n n a r and Wad Medani and becomes 8.0 mm/day a t Khartoum. The a v e r a g e f o r Kassala and G a l l a b a t i n t h e A t b a r a b a s i n i s n e a r l y 6.7 mm/day. T h i s f i g u r e i n c r e a s e s t o 8.0 mm/day a t A t b a r a .
195
iv)
The e v a p o r a t i v e demand f o r t h e White N i l e B a s i n and t h e E t h i o p i a n P l a t e a u
v)
The r e d u c t i o n c o e f f i c i e n t f o r t h e P i c h e r e a d i n g s , on an a n n u a l b a s i s ,
i s p r e s e n t e d i n F i g . 5.6. d e c r e a s e s from 0.8 f o r t h e S o b a t B a s i n t o a b o u t 0 . 6 f o r t h e b a s i n s of t h e B l u e N i l e and t h e A t b a r a . The monthly c o e f f i c i e n t v a r i e s i n a wide r a n g e w i t h an i n d i c a t i o n t o a heavy s e a s o n a l component.
TABLE 5.10
Open water e v a p o r a t i o n i n t h e A t b a r a B a s i n
Station + Method
*
P i c h e x 0.5 a b
Evaporation,
i n mm/day,
for
J a n , Feb. Mar. Apr. May J u n e J u l y Aug. S e p . O c t . Nov. Dec. Year
3.3
1.1 2.4
1.4 2.8
2.2 4.3
2.4 5.2
3.2 5.3
3.1 5.3
7.5 10.6 9.3
9.0 8.8
8.6
8.6
9.9
6.5
5.6
8.0
8.6
6.6
3.3
3.3
5.5
6.6
6.3 6.7
3.9 5.6
4.8 6.5
5.1 7.8
5.5
6.2
6.7
7.3
5.7 4.1 8.3 7.1
2.4 5.2
1.1
Penman (direct) C
(indirect) b
9.6 8.2
4.3
*a = Lake T a n a ; b = K a s s a l a and G a l l a b a t ; c = Atbara
196
1 a,
m
Y 4
n
&
a
.A .A
5
a,
w
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197
5.5 5.5.1
THE M A I N N I L E
The Main N i l e from Khartoum t o Aswan
The mean monthly a s w e l l a s t h e mean a n n u a l e v a p o r a t i o n a s o b s e r v e d by t h e P i c h e i n s t r u m e n t a t a number of l o c a t i o n s from Khartoum t o Aswan c a n b e found i n
Vol. I X of t h e N i l e B a s i n ( H u r s t , H . E . ,
Black, R.P.,
and S i m a i k a , Y . M . ,
1959). A
summary of t h e s e d a t a i s g i v e n i n T a b l e 5.11. TABLE 5.11
P i c h e e v a p o r a t i o n f o r a number of s t a t i o n s on t h e Main N i l e from Khartoum t o Aswan
Station
Khartoum* Zeidab Atbara Merowe Dongola Wadi H a l f a Aswan
Evaporation, J a n . F e b . Mar. Apr. May
13.0 16.0 1 0 . 0 12.0 13.8 16.2 11.6 13.7 8.4 10.9 8.8 1 0 . 9 7.6 9 . 1
19.0 15.0 18.9 16.8 13.5 14.4 12.9
20.0 16.0 20.8 20.0 15.6 18.1 16.8
19.0 16.0 20.8 21.2 17.9 19.4 18.5
i n mm/day,
for
J u n e J u l y Aug. S e p . O c t . Nov. Dec. Year
18.0 17.0 20.2 21.0 17.0 21.5 21.6
14.0 15.0 18.5 18.6 17.8 19.4 19.5
11.0 13.0 16.1 16.7 16.6 17.5 19.2
12.0 13.0 16.6 19.0 15.8 18.2 18.1
15.0 13.0 16.4 17.6 14.1 15.9 15.5
14.0 12.0 14.8 14.0 10.9 11.7 10.8
13.0 10.0 13.5 11.5 9.1 8.6 7.3
15.0 14.0 17.2 16.8 14.0 15.4 14.7
*Mean o f t h r e e s t a t i o n s a t Khartoum
H u r s t m e n t i o n s t h a t t h e e v a p o r a t i o n v a l u e s f o r Dongola a r e d e f i n e t l y lower t h a n woulti h a v e been e x p e c t e d from t h e o b s e r v a t i o n s a t t h e o t h e r s t a t i o n s . T h i s s t a t i o n was c l o s e d and t h e o b s e r v a t i o n s c o v e r e d 7 y e a r s o n l y . F u r t h e r m o r e , i t i s n o t p o s s i b l e now t o s a y w h e t h e r t h e d i f f e r e n c e i s r e a l o r due o n l y t o some c i r cumstance c o n n e c t e d w i t h t h e i n s t r u m e n t and i t s e x p o s u r e . The f r e e w a t e r s u r f a c e e v a p o r a t i o n a t Khartoum and A t b a r a h a s a l r e a d y been g i v e n i n t h e l a s t two s e c t i o n s . The long-term m e t e o r o l o g i c a l d a t a a v a i l a b l e f o r Merowe, Wadi H a l f a and Aswan have been worked o u t f o r e s t i m a t i n g t h e open w a t e r e v a p o r a t i o n f o r t h e s e s t a t i o n s u s i n g t h e Penman and H a r g r e a v e s methods. The r e s u l t s o b t a i n e d a r e l i s t e d i n T a b l e 5.12. I n a d d i t i o n t o t h e c o m p u t a t i o n r e s u l t s p r e s e n t e d i n T a b l e 5.12, i t may b e w o r t h w h i l e g i v i n g h e r e t h e mean a n n u a l e v a p o r a t i o n from a s t a n d a r d t a n k a s o b t a i n e d Prom t h e method of O l i v i e r . T h i s i s 1 0 . 5 f o r Khartoum, 1 1 . 0 f o r Wadi H a l f a and 10.8 mm/day f o r Aswan. The mean monthly v a l u e s f o r Aswan, a s an example, are as f o l l o w s :
Month
J a n . F e b . Mar. Apr. May
E v a p o r a t i o n , mm/day 4.9
6.4
9.5
J u n e J u l y Aug. S e p . O c t . Nov. D e c .
12.6 14.1 16.0 15.1 14.7 13.2 10.9
7.3
5.1
198 TABLE 5.12
Estimated f r e e water s u r f a c e evaporation f o r Merowe, Wadi Halfa and Aswan on t h e Main N i l e ~
Station Method
+
Evaporation, mm/day,
~
f
J a n . Feb. Mar. Apr. May
~~
for
June J u l y Aug. Sep. Oct. Nov. Dec. Year
Merowe a b
5.7 7.6
6 . 5 7 . 6 8 . 9 9.6 9 . 8 9 . 4 9 . 3 9 . 1 8 . 2 6 . 7 8 . 8 11.7 1 5 . 5 20.3 19.2 1 7 . 1 17.5 15.7 1 4 . 1 11.2
5.6 8.0 8 . 6 13.9
Wadi Halfa a b
4.5 4.3
5.8 5.8
7 . 1 8 . 7 9 . 3 9 . 8 9 . 6 9 . 3 8 . 6 7.7 8 . 3 12.0 14.6 15.8 14.7 1 4 . 3 1 2 . 8 10.4
6.1 7.7
4.0 7.5 4 . 8 10.5
Aswan a b
3.5 5.3
4.6 6.1
6 . 2 7.7 8 . 5 9 . 4 9 . 3 8 . 8 8 . 2 6 . 5 9 . 4 12.5 15.4 16.6 1 6 . 6 15.6 13.7 1 1 . 5
4.5 8.2
3.7 6 . 8 5 . 7 11.4
~
*a = Penman; b = Hargreaves x 0 . 7 The River Atbara i s t h e l a s t t r i b u t a r y of t h e Main N i l e . The annual flow downstream of t h e confluence i s t h e sum of t h e flow above i t , a t Hassanab, and t h e supply of t h e Atbara. The annual flow a t Mongalla, some 810 km downstream of t h e confluence, a t Hassanab and a t Atbara, has been averaged over a period of 30 y e a r s , 1943-72. The mean annual l o s s i n t h e reach from j u s t downstream of the confluence t o Dongola f o r t h e period considered i s about 1060 m i l l i o n m 3 . This f i g u r e i s most d e f i n i t e l y only an approximate one, a s i t v a r i e s i n a very wide range from -6236 m i l l i o n m 3 / y r
i n 1958 t o +5623 m i l l i o n m3/yr i n 1964. Our
f i g u r e is a l s o high compared t o t h a t obtained by Hurst
-
800 m i l l i o n m 3 / y r - a s
an average f o r t h e p e r i o d 1912-1952, f o r t h e reach from j u s t downstream of t h e confluence down t o Wadi H a l f a , 1210 km downstream of Atbara. Anyhow, using our f i g u r e and assuming an average width of 500 m f o r t h e r i v e r between t h e r i s i n g and t h e f a l l i n g s t a g e s , one g e t s an evaporation depth of 2.62 m / y r .
This f i g u r e
corresponds t o a mean annual evaporation of 7 . 2 mm/day, which is about 10% less than what we have obtained from Penman's method f o r Atbara and Merowe. The reach of t h e Main N i l e from Atbara t o Aswan i s c h a r a c t e r i z e d by t h e almost c o n s t a n t r a t i o between t h e Penman and t h e Piche e v a p o r a t i o n . This i s 0.465 f o r Atbara, 0.476 f o r Merowe, 0.487 f o r Wadi Halfa and 0.463 f o r Aswan, with a mean of 0.475 f o r t h e e n t i r e r e a c h . The pan evaporation f i g u r e s obtained from t h e Hargreaves method need t o be m u l t i p l i e d by a c o e f f i c i e n t of 0.44 i n s t e a d of 0 . 7 t o reduce them t o Penman's e v a p o r a t i o n . On t h e o t h e r hand, t h e evaporation from a s t a n d a r d tank computed by t h e O l i v i e r formula needs t o be c o r r e c t e d by a f a c t o r of 0.68 f o r Wadi Halfa and 0 . 6 3 f o r Aswan. One should not f o r g e t t h a t a l l t h e s e r a t i o s a r e based on mean annual e v a p o r a t i o n . For t h e comp a r i s o n between t h e mean monthly evaporation a s obtained from t h e d i f f e r e n t methods, r e f e r e n c e i s made t o F i g . 5 . 7 .
199
22.
.,
23 -
+ ,.
'.
/+ '.
18 -
c
,
''+-
'+
.\
ASWAN
+.
.'
x- --x-
m a n 6 . 8 mm.lday
I
2
I
I
I
22 30
+
/
.
I
I
I
,.-. + .'
'-
+' \.
I
'..+-.
t
I
-+.,
WADI
- HALFA
\.
21 x
b
19 17
$15 i13
.-
2 11
L
0 P
Z 9
w
7 c;
Jan.
Fig. 5 . 7 .
Feb.
Mar.
Apr.
May.
Jul.
Jun.
Aug.
Sep.
Oct.
Nov.
Dec.
Mean monthly e v a p o r a t i o n a t Atbara, Wadi H a l f a , and Aswan
200
5.5.2
The N i l e from Aswan t o G i z a , t h e O a s e s , and t h e Red S e a C o a s t
I n t h i s s t r e t c h o f t h e r i v e r , i n t h e o a s e s o f t h e Libyan d e s e r t , and a l o n g t h e c o a s t o f t h e Red S e a , t h e r e i s a r e a s o n a b l e number of m e t e o r o l o g i c a l s c r e e n s . T i l l t h e t i m e of w r i t i n g t h i s book, t h e p u b l i s h e d d a t a o f t h e s e s c r e e n s a r e up t o 1945 o n l y ( M i n i s t r y of War and Marine, screens,
1 9 5 0 ) . F o r most o f t h e
t h e d a t a up t o t h e n have t h e r e f o r e been u s e d . T h i s c o v e r s a p e r i o d o f ,
s a y , 20 t o 4 0
y e a r s f o r each s t a t i o n .
O t h e r t h a n t h e s t a t i o n a t Aswan, w e h a v e s e l e c t e d f o u r s t a t i o n s o n , o r v e r y near to,
t h e r i v e r : Q e n a , A s s i u t , Minya and G i z a ; two a l o n g t h e Red S e a C o a s t :
Q u s s e i r and Hurghada; a s e m i - d e s e r t i c
o a s i s : E l Fayum, and El-Kharga O a s i s .
S i n c e t h e c l i m a t o l o g i c a l normals f o r E l Dakhla O a s i s a r e n e a r l y t h e same as t h o s e f o r E l Kharga, t h e e s t i m a t e d e v a p o r a t i o n f o r t h e l a t t e r i s assumed t o r e p r e s e n t t h e f r e e w a t e r s u r f a c e e v a p o r a t i o n f o r t h e two o a s e s . Each o f t h e s t a t i o n s c o n s i d e r e d h e r e i s e q u i p p e d w i t h a P i c h e i n s t r u m e n t . A d d i t i o n a l l y , two c l a s s A pans h a v e b e e n i n s t a l l e d a t G i z a and E l Kharga s t a t i o n s s i n c e 1957 and 1964 r e s p e c t i v e l y . The e v a p o r a t i o n d a t a o b t a i n e d from t h e s e two pans h a v e , among o t h e r s , b e e n r e p o r t e d by t h e a u t h o r i n an e a r l i e r work ( S h a h i n , M . M . ,
1 9 7 0 ) . Some of t h e s e d a t a , t o g e t h e r w i t h t h e o b s e r v e d P i c h e
e v a p o r a t i o n and t h e f r e e water s u r f a c e e v a p o r a t i o n e s t i m a t e d by t h e methods of Penman and H a r g r e a v e s , are g i v e n i n T a b l e 5 . 1 3 . F u r t h e r m o r e ,
t h e l i n e s of equal
e v a p o r a t i v e demand f o r t h e a r e a c o n s i d e r e d are p l o t t e d on t h e map, F i g . 5 . 8 . From t h i s map, t h e g r a d u a l d e c l i n e i n t h e e v a p o r a t i v e demand from Wadi H a l f a i n
a northerly d i r e c t i o n t o Giza can e a s i l y be d et ect ed. This is a l s o t r u e f o r the c o a s t of t h e Red S e a , e x c e p t a t Hurghada, n e a r l y h a l f w a y between Q u s s e i r and S u e z , where a p o s i t i v e jump i n t h e e v a p o r a t i v e demand c a n b e s e e n . With t h e e x c e p t i o n o f t h e s t a t i o n s a t Q u s s e i r and Hurghada, which a r e s i t u a t e d a t t h e c o a s t , t h e r a t i o of t h e Hargreaves e v a p o r a t i o n t o t h e e v a p o r a t i o n e s t i m a t e d by t h e Penman method i s v e r y n e a r l y c o n s t a n t f o r a l l t h e s t a t i o n s .
In
f a c t , i t v a r i e s from 2 . 0 1 t o 2 . 2 1 w i t h an o v e r a l l a v e r a g e of 2 . 0 8 . The same r a t i o b u t f o r Q u s s e i r and Hurghada i s 1 . 5 4 and 1 . 6 6 r e s p e c t i v e l y . T h i s marked r e d u c t i o n i s o b v i o u s a s t h e h u m i d i t y a t noon, which i s a p a r a m e t e r i n t h e H a r g r e a v e s e q u a t i o n , d o e s n o t d i f f e r c o n s i d e r a b l y from t h e mean of t h e day a s i n t h e c a s e of t h e s t a t i o n s i n t h e i n t e r i o r . The pan e v a p o r a t i o n computed by H a r g r e a v e s ' e q u a t i o n i s s e e n t o b e less t h a n t h e o b s e r v e d c l a s s A pan e v a p o r a t i o n f o r El-Kharga by a b o u t 1696, and more t h a n t h e o b s e r v e d pan e v a p o r a t i o n a t G i z a by 27%. T h i s emphasizes t h e v e r y s t r o n g e f f e c t o f t h e h u m i d i t y a t noon i n H a r g r e a v e s ' method compared t o t h e mean humid i t y which i n f l u e n c e s t h e pan e v a p o r a t i o n .
201
TABLE 5.13
Observed and e s t i m a t e d e v a p o r a t i o n f o r t h e N i l e from Aswan t o G i z a , t h e Oases, and t h e Red Sea Coast
Station and Method* Qena __
a b C
Kharga (Oasis) a b C
d Assiut a b C
Qusseir (sea coast) a b C
Minya a b C
Hurghada (sea coast) a b C
Fay urn (semi-oasis) a b C
Giza __
a b C
d
Evaporation, i n mm/day, f o r Jan. Feb. Mar. Apr.
2.1 3.2 3.3
2.9 4.3 4.2
May
June July Aug. S e p . O c t . Nov. Dec. Year
5.0 6.6 8.4 9.2 8.9 8.0 7.2 5.2 7.0 10.4 13.3 14.0 13.4 13.0 10.2 7.4 6.5 9.2 10.9 12.4 11.8 11.4 8.6 6.1
3.7 5.2 4.4
2.2 5.8 3.5 8.7 3.4 7.7
2.4 3.5 5.2 6.9 8.6 9.4 9.2 8.5 7.7 5.7 3.6 2.4 6.1 3.5 4.5 6.8 9.6 11.5 13.1 13.2 12.7 10.2 8.3 5.8 4.0 8.6 9.5 11.6 16.3 20.3 24.2 25.1 24.5 23.9 22.6 19.8 13.7 9.9 18.4 6.4 8.5 12.0 16.1 20.0 23.3 21.7 19.5 18.2 14.4 9.9 6.8 14.7 1.8 2.9 3.9
3.1 3.8 5.1
4.3 6.6 8.3 8.7 8.5 8.2 6.4 6 . 1 9.2 11.8 12.9 12.6 11.5 9.3 7.6 10.8 13.7 15.6 13.9 12.8 10.6
4.9 6.6 7.1
3.1 4.2 8.0
3.9 4.6 5.6
5.1 6.2 7.3 8.2 8.5 8.0 7.3 5.5 6.2 7.6 8.9 8.4 8.3 7.3 9.6 10.0 11.3 12.9 11.5 11.9 11.2
5.4 4.4 6.0 5.0 9.4 8.8
3.2 4.5 7.9
5.9 6.4 9.8
1.9 2.5 4.2
2.6 3.2 5.7
3.8 4.7 7.1
4.1 6.4 7.3
2.0 2.9 3.7
4.8 7.0 8.8
5.3 7.0 7.7 7.7 6.9 7.4 11.0 11.7 11.5 10.5 9.8 14.2 15.2 13.7 11.8
5.6 7.9 8.7
3.4 4.7 4.9
3.3 4.6 5.5
2.0 5.5 3.1 7.9 3.7 9.1
3.7 4.4 5.6 7.0 8.3 9.5 9.6 9.0 7.7 6.2 5.2 3.8 6.7 4.8 5.2 6 . 4 8.0 10.3 10.8 11.0 10.5 8.7 7.0 5.8 5.1 7.8 10.7 11.5 13.6 15.5 17.6 21.5 19.5 19.8 17.6 13.7 11.5 10.4 15.2
1.5 2.7 3.4
2.6 3.5 4.4
3.9 5.3 6.0
1.5 2.7 3.3 2.8
2.6 3.2 4.2 3.9
3.3 5.2 6.7 7.9 7.4 4.6 7.0 9.0 10.2 9.7 5.3 7.2 9.1 9.2 8.4 5.8 8.1 10.3 11.4 10.4
5.4 7.6 8.2 8 . 2 7.3 8.2 11.8 13.5 12.3 10.8 8.6 11.8 13.3 11.8 10.1 6.2 8.5 7.0 9.5
5.5 9.1 8.0
4.0 6.6 6.5
3.0 4.6 4.5
1.6 2.8 3.2
4.9 7.6 7.6
5.0 6.9 5.5 8.1
3.5 5.7 4.8 6.1
2.3 4.1 3.5 4.1
1.5 3.0 2.9 3.0
4.4 6.2 5.9 7.0
*a = Penman; b = Hargreaves x 0.7; c = P i c h e ; d = c l a s s A pan
20 2
N
El Bahariya,
-- 6.0 m m . l d a y 25'
E
G
Y
P
T
Scale
0 50 100
Fig. 5 . 8 . Evaporative demand for t h e Main N i l e from Atbara t o G i z a , t h e c o a s t a l l i n e o f t h e Red S e a , and t h e Libyan d e s e r t o a s e s
203
Another example o f t h e r o l e p l a y e d by h u m i d i t y i n e v a p o r a t i o n e s t i m a t e s i s t h e r e s u l t s o b t a i n e d from O l i v i e r ' s method
*
Evaporation, J a n . Feb.
Mar.
Apr.
May
Jun.
i n mm/day, Jul.
Aug.
for Sep.
O c t . Nov. Dec. Year
a b
5 . 0 2 6 . 7 1 1 0 . 7 5 1 4 . 0 3 1 4 . 6 6 1 7 . 4 3 1 6 . 7 1 1 5 . 6 2 1 2 . 9 7 1 0 . 4 2 6 . 3 5 5 . 1 1 11.31 1 . 7 6 2 . 4 8 4 . 0 2 5 . 5 9 7 . 6 8 8 . 8 3 6 . 7 1 5 . 9 2 4 . 7 8 3 . 5 6 2 . 4 8 1.81 4 . 6 4
*a
= E l Kharga O a s i s s t a t i o n ; b = G i z a s t a t i o n
where t h e r a t i o o f t h e mean a n n u a l e v a p o r a t i o n f o r E l Kharga t o G i z a i s 2 . 4 4 . The r a t i o o f t h e Penman e v a p o r a t i o n a t t h e s e two s t a t i o n s i s 1 . 3 9 o n l y . F u r t h e r a n a l y s i s and d i s c u s s i o n o f t h e r e l a t i o n s h i p s between t h e e v a p o r a t i o n f i g u r e s o b t a i n e d f o r t h e d i f f e r e n t p a r t s o f t h e N i l e B a s i n c a n b e found i n section 5.6. 5.5.3
The N i l e D e l t a Area from t h e Apex t o t h e M e d i t e r r a n e a n S e a C o a s t
F o r t h e e v a p o r a t i o n s t u d y i n t h e area e x t e n d i n g from t h e apex o f t h e d e l t a t o t h e M e d i t e r r a n e a n S e a C o a s t , e l e v e n s t a t i o n s h a v e b e e n s e l e c t e d . These a r e : C a i r o , n e a r t h e a p e x o f t h e d e l t a ; S u e z , a t t h e f a r t h e s t end o f t h e Red S e a ; Z a g a z i g , El S i r w , T a n t a , E d f i n a and E l T a h r i r , i n s i d e and o u t s i d e t h e D a m i e t t a and R o s e t t a b r a n c h e s o f t h e N i l e and P o r t S a i d , A l e x a n d r i a , E l Kasr and S a l l u m , a l o n g t h e M e d i t e r r a n e a n C o a s t . The e v a p o r a t i o n f i g u r e s o b t a i n e d from Penman's method, from H a r g r e a v e s ' method, c o r r e c t e d by a f a c t o r o f 0 . 7 , and from t h e P i c h e i n s t r u m e n t , are l i s t e d i n T a b l e 5 . 1 4 . The s t a t i o n s a t E l T a h r i r and E l Kasr have each b e e n p r o v i d e d w i t h a c l a s s A pan s i n c e 1964. The a v e r a g e pan evap o r a t i o n from t h e p e r i o d 1964-1968 i s a l s o i n c l u d e d i n T a b l e 5 . 1 4 .
In this table
t h e e v a p o r a t i o n d a t a r e p r e s e n t i n g C a i r o are f o r Almaza A i r p o r t . A c t u a l l y , t h e r e a r e f o u r s t a t i o n s n e a r , or i n , C a i r o i t s e l f ; Almaza, H e l i o p o l i s , Eebekiya and Abbassiya.
No P i c h e e v a p o r a t i o n d a t a a r e a v a i l a b l e f o r t h e l a s t s t a t i o n . The
a v e r a g e o f t h e f i r s t t h r e e s t a t i o n s i s 70% of Almaza a l o n e . A c c o r d i n g l y , t h e Penman f i g u r e o f 4 . 9 mm/day o b t a i n e d f o r Almaza A i r p o r t h a s been r e d u c e d t o 4 mm/day i n o r d e r t o r e p r e s e n t t h e C a i r o a r e a . T h i s l a s t f i g u r e h a s been u s e d , among o t h e r s , f o r p r e p a r i n g t h e map of t h e e v a p o r a t i v e demand f o r t h e N i l e d e l t a a r e a shown i n F i g . 5 . 9 . F i g . 5 . 9 shows t h a t t h e e v a p o r a t i v e demand d e c r e a s e s from t h e e a s t t o t h e c e n t r e o f t h e d e l t a a r e a and t h e n i n c r e a s e s i n a w e s t e r l y d i r e c t i o n . The evap o r a t i o n i n c r e a s e s g r a d u a l l y from 4 . 4 mm/day for A l e x a n d r i a t o 4 . 9 mm/day f o r Sallum on t h e M e d i t e r r a n e a n C o a s t . The e v a p o r a t i o n d e c r e a s e s from t h e apex o f the d e l t a t o t h e c e n t r e then i n creas es i n a n or t her l y d i r e c t i o n t o t h e c o a s t .
204
TABLE 5.14
Evaporation d a t a f o r t h e N i l e d e l t a area from t h e apex t o t h e Mediterranean S e a Coast
Station and Method* Almaza (airport) a b C
Suez (Canal) a b d Zagazig a b C
Tanta _ _
a b C
Evaporation, i n mm/day, f o r J a n . Feb. Mar. Apr.
May
June J u l y Aug. S e p . O c t . Nov. Dec. Year
2.3 2.8 7.1
3.3 3.7 7.7
4.1 6 . 2 7.1 7.7 7.0 6.7 5.3 7.9 10.7 12.0 10.8 9.8 8.8 11.2 14.2 14.1 12.5 10.9
3.3 4.1 7.2
1.9 2.7 5.2
4.9 7.0 9.8
2.3 2.8 5.1
3.1 3.5 5.8
4.6 5.7 7.0 7.9 7.9 7.4 6.3 5.3 6.4 8.5 11.0 10.8 10.2 8.4 7.6 10.1 12.5 13.7 13.2 12.4 10.8
5.0 3.6 6.3 4.1 8.8 6.5
2.2 3.2 5.2
5.2 6.7 9.3
1.6 2.4 1.9
2.6 3.2 2.5
3.5 4.6 3.2
4.9 6.9 4.5
6.3 7.0 6.9 9.2 10.2 9.6 5.6 5.9 5.2
6.4 8.5 4.4
3.0 4.1 2.3
1.7 2.6 1.8
4.4 6.2 3.7
1.5 1.8 2.1
2.1 2.2 2.8
2.8 3.4 3.8
4.2 5.5 5.6
5.3 6.4 7.9 10.3 7.2 7.8
5.8 4.6 7.5 5.7 5.7 4.5
3.6 5.3 3.6
2.6 3.2 2.7
1.5 2.1 2.0
3.8 5.3 4.5
1.5 2.1 3.8
2.8 2.5 4.8
3.6 3.5 6.8
5.3 6.0 7.3 6.9 5.8 5.6 7.2 9.2 8.6 7.7 9.1 10.8 12.5 11.4 10.3
4.9 6.4 8.7
3.2 4.5 6.3
2.5 3.1 4.2
1.6 2.3 3.3
4.3 5.2 7.7
1.9 1.9 2.9
2.6 2.3 3.5
3.7 2.9 4.4
4.8 6.3 7.4 4.0 5.7 7.0 5.3 6.0 6.3
6.6 5.6 6.2 5.0 5.2 4.7
4.5 3.8 4.2
3.1 2.5 3.3
1.7 4.5 2.0 4.2 2.7 4.6
1.6 1.8 3.1
2.1 2.2 3.5
3.1 3.0 4.6
4.3 4.3 5.9
5.2 6.7 6.9 5.5 7.1 7.0 6.9 7.2 7.0
6.2 5.9 6.5
4.6 4.7 5.6
3.3 3.9 4.6
2.4 2.7 3.8
1.5 1.8 3.0
4.0 4.2 5.1
2.1 2.1 5.9
2.8 3.7 2.7 3.1 6 . 2 7.7
5.2 3.7 7.4
6.2 4.5 8.5
7.0 4.9 8.8
7.1 6.6 5.5 5.7 5.8 5.4 9 . 2 9.1 10.0
4.1 5.0 9.3
3.2 2.9 7.8
2.1 2.1 5.5
4.6 4.0 8.0
2.3 2.4 4.8
3.0 2.8 5.2
3.6 3.4 5.0
4.8 4.2 5.3
5.3 4.6 5.0
6.8 6.6 5.6 5.3 5.0 5.4 4.7 4.7 5.0
5.5 5.1 5.5
4.0 4.3 5.2
3.2 3.1 4.9
2.1 2.5 4.9
4.4 4.0 5.0
1.9 1.7 4.8
2.6 2.1 5.8
3.6 3.3 7.0
4.8 3.7 8.4
5.9 6.9 8.3 6.6 5.4 4.4 5.5 7.4 5.5 4.6 8.2 10.4 11.0 10.6 9.6
3.6 3.3 7.8
2.6 2.2 5.4
1.7 1.7 5.1
4.7 3.8 7.8
6.1 9.0 6.7
4.8 4.3 7.0 6.5 9.2 8.9
5.2 4.0 7.2 5.8 3.5 3.1
El Tahrir a b e E l Sirw
a b C
Edf i n a a b C
Port S a i d (airport) a b C
Alexandria a b C
E l Kasr a b e
7.4 7.4 6.1
*a = Penman; b = Hargreaves x 0.7; c = P i c h e ; d = P i c h e (Port T e w f i k ) ; e = C l a s s A pan
205
(continued)
TABLE 5.14
S t a tion and Method'
E v a p o r a t i o n , i n mm/day, J a n . Feb. Mar. Apr.
Sallum (Observatory) a b C
2.4 3.0 2.3 2.8 6.6 7.3
4.1 3.6 7.9
May
5.4 5.6 4.8 4.5 8.9 7.9
for
J u n e J u l y Aug. S e p . O c t . Nov. D e c . Year
7.6 7.5 9.4
8.5 8.6 9.7
7.6 5.7 6.6 5.3 8.2 7.9
3.9 4.2 7.2
3.1
3.1 6.9
2.3 2.6 7.1
4.9 4.7 7.9
*a = Penman; b = H a r g r e a v e s x 0.7; c = P i c h e I n o t h e r words, t h e e v a p o r a t i o n from t h e d e l t a h a s a bowel s h a p e w i t h d e c r e a s i n g e v a p o r a t i o n towards t h e c e n t r e .
Map of t h e e v a p o r a t i v e demand f o r t h e N i l e d e l t a a r e a and t h e c o a s t F i g . 5.9. of t h e M e d i t e r r a n e a n S e a
5.6
ANALYSIS OF THE OBSERVED AND THE COMPUTED EVAPORATION FOR THE NILE BASIN General
I n many i n s t a n c e s i n t h e p r e v i o u s s e c t i o n s , t h e o b s e r v e d P i c h e e v a p o r a t i o n a t a number of s t a t i o n s i n t h e N i l e B a s i n i s g i v e n . T h i s e v a p o r a t i o n h a s b e e n m u l t i p l i e d by t h e r e d u c t i o n f a c t o r proposed by H u r s t t o deduce t h e open w a t e r e v a p o r a t i o n for t h e whole b a s i n ( s e e F i g . 5 . 1 ) .
206
The e v a p o r a t i o n measured from t h e USWB c l a s s A pan a t f o u r l o c a t i o n s i n Egypt i s g i v e n i n s e c t i o n s 5.5.2 and 5.5.3. The supposed c l a s s A pan evaporat i o n h a s been computed f o r n e a r l y a l l t h e s t a t i o n s i n t h e b a s i n , u s i n g t h e Hargreaves formula. The r e s u l t s have been reduced by a f a c t o r 0.7 i n o r d e r t o c o n v e r t t h e pan e v a p o r a t i o n i n t o f r e e w a t e r s u r f a c e e v a p o r a t i o n . The e v a p o r a t i o n from t h e s o - c a l l e d
' s t a n d a r d t a n k ' has been computed, b u t
f o r a fewer number o f s t a t i o n s u s i n g O l i v i e r ' s method. The f r e e water s u r f a c e e v a p o r a t i o n h a s been computed d i r e c t l y u s i n g t h e Penman formula f o r most o f t h e s t a t i o n s where t h e r e l e v a n t c l i m a t o l o g i c a l s t a n d a r d s a r e a v a i l a b l e . The r e s u l t s a r e p r e s e n t e d n o t o n l y i n t a b u l a r form, b u t a l s o i n maps f o r q u i c k e r and e a s i e r u s e . The maps shown i n F i g s . 5.3.. 5.6.. 5.8., and 5.9. have been combined t o g e t h e r t o compose t h e g e n e r a l map, F i g . 5.10. 5.6.1
The f r e e w a t e r s u r f a c e e v a p o r a t i o n computed by Penman's formula
For t h e p u r p o s e o f e s t i m a t i n g t h e open w a t e r e v a p o r a t i o n f o r t h e Nile B a s i n , t h e d i r e c t method t h a t h a s been used is t h a t o f Penman. The n e c e s s a r y e q u a t i o n s have been g i v e n e a r l i e r . The new or m o d i f i e d v e r s i o n o f t h e Penman e q u a t i o n employs a wind f u n c t i o n o t h e r t h a n t h a t g i v e n i n e q . 5.8 which w e used i n o u r calculation. When combined w i t h t h e f i n d i n g s of Hickox, t h e e x p e r i m e n t s conducted a t t h e Khartoum O b s e r v a t o r y i n 1961 and 1962 showed t h a t t h e mean annual open water e v a p o r a t i o n w a s a b o u t 10% l a r g e r t h a n t h a t o b t a i n e d from Panman's method. I f w e t r u s t t h e r e s u l t s o f t h o s e e x p e r i m e n t s , t h e computed e v a p o r a t i o n from Penman's formula needs t h e n t o b e a d j u s t e d . The monthly and y e a r l y a d j u s t m e n t f a c t o r s a r e as follows: Adjustment F a c t o r January February March April May June July August September October November December Year
1.106 1.078 1.087 1.051 1.242 1.110 0.924 0.955 1.078 1.165 1.142 1.083 1.092
207
25'
20'
15'
Fig. 5.10. Mean annual free water evaporation in the Nile Basin estimated from Penman's method
20 8
T o t h e b e s t o f o u r knowledge t h e r e s u l t s o f t h e Khartoum e x p e r i m e n t s a r e p r o b a b l y t h e o n l y o n e s which may h e l p t o j u d g e t h e a c c u r a c y of Penmah's f o r m u l a f o r e s t i m a t i n g t h e f r e e water s u r f a c e e v a p o r a t i o n from t h e N i l e B a s i n .
Accor-
d i n g l y , t h e r e s u l t s presented i n t h e previous s e c t i o n e i t h e r i n t a b u l a r o r g r a p h i c a l form may b e d e s c r i b e d as f a i r l y a c c u r a t e . More a c c u r a t e e v a p o r a t i o n f i g u r e s may b e o b t a i n e d u s i n g o u r r e s u l t s t o g e t h e r w i t h t h e a p p r o p r i a t e a d j u s t ment.
5.6.2
R e l a t i o n s h i p between e s t i m a t e d e v a p o r a t i o n from a c l a s s A pan and e s t i mated f r e e water s u r f a c e e v a p o r a t i o n
I n o r d e r t o estimate e v a p o r a t i o n from a c l a s s A p a n , t h e method o f Hargreaves h a s b e e n u s e d . The e s t i m a t e d pan e v a p o r a t i o n h a s b e e n r e d u c e d by a c o n s t a n t f a c t o r , 0 . 7 , s o as t o deduce t h e open w a t e r e v a p o r a t i o n . Most o f t h e e v a p o r a t i o n f i g u r e s t h u s o b t a i n e d h a v e proved t o b e l a r g e r t h a n t h e f r e e water s u r f a c e evap o r a t i o n e s t i m a t e d d i r e c t l y from Penman's method. T h i s d i s c r e p a n c y l e a d s us t o the conclusion t h a t e i t h e r t h e reduction f a c t o r , 0.7,
i s , f o r most o f t h e s t a -
t i o n s c o n s i d e r e d , l a r g e r t h a n i t s h o u l d b e , o r t h e H a r g r e a v e s e v a p o r a t i o n i s not e q u a l t o t h e pan e v a p o r a t i o n . The s i m p l e g r a p h i c a l p l o t o f t h e H a r g r e a v e s e v a p o r a t i o n ( w i t h o u t any reduct i o n ) , Y , v e r s u s t h e Penman e v a p o r a t i o n , X , f o r 30 d i f f e r e n t s t a t i o n s , s u g g e s t s t h e p o s s i b i l i t y of h a v i n g t h e p a i r s X and Y d i v i d e d i n t o f o u r g r o u p s . The f i r s t g r o u p c o m p r i s e s 18 i n t e r i o r s t a t i o n s . The s e c o n d g r o u p i s f o r t h e t h r e e s t a t i o n s a l o n g t h e Red S e a C o a s t and t h e t h i r d i s f o r t h e s i x s t a t i o n s a t , o r n e a r t o , t h e c o a s t o f t h e M e d i t e r r a n e a n S e a . The f o u r t h g r o u p c o m p r i s e s t h e t h r e e s t a t i o n s l o c a t e d o u t s i d e t h e swamps o f t h e Bahr e l J e b e l and Bahr e l Ghazal B a s i n s . T h i s grouping h a s t h e advantage t h a t i t reduces t h e scatter of t h e p o i n t s a b o u t t h e r e s p e c t i v e r e g r e s s i o n l i n e , though does n o t e l i m i n a t e i t . F u r t h e r g r o u p i n g may s t i l l r e d u c e f u r t h e r t h e s c a t t e r . I n view o f t h e r a t h e r a p p r o x i m a t e n a t u r e of t h e c l i m a t o l o g i c a l d a t a used for e s t i m a t i n g t h e e v a p o r a t i o n , a t l e a s t f o r some of t h e s t a t i o n s , i t h a s been found u n n e c e s s a r y t o d e s c r i b e t h e r e g r e s s i o n o f Y on X by a p o l y n o m i a l o f a d e g r e e h i g h e r t h a n 2 . Under t h i s c o n d i t i o n t h e r e g r e s s i o n e q u a t i o n s of t h e f o u r groups are :
1st g r o u p
Y = 1 . 8 3 9 + 0.924 X + 0.125 X2
2nd g r o u p
Y = 1 . 2 3 9 x 1.331 X
3rd group
Y = 1.222 + 0.822 X
4 t h group
Y =-6.271
+
1.489 X
whereX andY are i n mm/day and r
+ + + XY
( I x y = 0.951)
(5.12a)
0.020 X2
( r X y = 0.950)
(5.12b)
0 . 0 4 1 X2
(rXy= 0 . 9 5 3 )
(5.12~)
0.187 X2
( r X y= 0 . 9 4 7 )
( 5 .12d)
i s t h e c o r r e l a t i o n c o e f f i c i e n t betweenX and Y .
209
The f i t of t h e r e g r e s s i o n l i n e s g i v e n by e q . 5 . 1 2 t o t h e r e s p e c t i v e group of s t a t i o n s is shown i n F i g . 5 . 1 1 a . t h r u '
c.
E s t i m a t i o n o f t h e f r e e water s u r f a c e e v a p o r a t i o n by t h e method o f Penman h a s a l r e a d y b e e n d e s c r i b e d by t h e e q u a t i o n s 5 . 6 , 5 . 7 , and 5 . 8 . I t r e q u i r e s a knowledge of t h e temperature,
t , t h e mean r e l a t i v e h u m i d i t y , h , t h e short-wave
r a d i a t i o n , R A , t h e wind s p e e d , u, and t h e r e l a t i v e d u r a t i o n o f t h e b r i g h t sun-
! shine, !
.
E s t i m a t i o n o f e v a p o r a t i o n from a c l a s s A pan u s i n g t h e H a r g r e a v e s
method, e q . 5 . 9 r e q u i r e s a knowledge o f t h e t e m p e r a t u r e , t , t h e r e l a t i v e h u m i d i t y a t noon, h n , and a c o e f f i c i e n t , d , which depends o n t h e d u r a t i o n of t h e day-time.
C o r r e c t i o n o f t h e f i g u r e s o b t a i n e d from e q . 5 . 9 r e q u i r e s , however, a
knowledge o f t h e s u n s h i n e ,
,
t h e wind s p e e d , u, and t h e e l e v a t i o n of t h e s t a -
t i o n above t h e mean l e v e l o f t h e s e a . S i n c e R A , i n t h e case o f Penman's method, and d , i n t h e c a s e o f H a r g r e a v e s ' method, a r e a v a i l a b l e f o r a g i v e n month and t h e g e o g r a p h i c a l l a t i t u d e o f any p o i n t , t h e b a s i c d i f f e r e n c e i n t h e c l i m a t o l o g i c a l p a r a m e t e r s needed f o r t h e s e two methods is c o n f i n e d t o h and h
.
Both humi-
d i t i e s a r e r e c o r d e d a t e v e r y m e t e o r o l o g i c s c r e e n , though hn a t a s l i g h t l y fewer number o f s c r e e n s .
I t i s q u i t e a p p a r e n t t h a t t h e v a l u e of h a v i n g t h e pan e v a p o r a t i o n f i r s t comp u t e d by t h e H a r g r e a v e s method t h e n c o n v e r t e d i n t o a f r e e water s u r f a c e evaporat i o n , using e i t h e r F ig . 5 . 1 1 . , o r Table 5.13, is questionable! 5.6.3
R e l a t i o n s h i p between o b s e r v e d e v a p o r a t i o n from a c l a s s A pan and estimated f r e e water surface evaporation
From t h e s t a t i o n s f o r which t h e f r e e w a t e r s u r f a c e e v a p o r a t i o n h a s been e s t i m a t e d by t h e Penman method, t h e r e a r e f i v e s t a t i o n s o n l y f o r which c l a s s A pan e v a p o r a t i o n i s a v a i l a b l e . These a r e : E l Kharga o a s i s , E l - T a h r i r ,
E l Kasr
and G i z a i n Egypt and Khartoum O b s e r v a t o r y i n t h e Sudan. The monthly and y e a r l y r a t i o s of t h e Penman e v a p o r a t i o n t o t h e pan evaporat i o n f o r t h e s e r a t i o s are l i s t e d i n T a b l e 5 . 1 5 , from which i s e v i d e n t t h a t t h e r a t i o , E penman : E pan A ( p a n c o e f f i c i e n t ) v a r i e s from o n e month t o t h e o t h e r . The l a r g e s t v a l u e o f t h e pan c o e f f i c i e n t o c c u r r s i n J u l y f o r t h e t h r e e n o r t h e r n s t a t i o n s and i n August f o r t h e two s o u t h e r n s t a t i o n s . The r a t i o of t h e maximum pan c o e f f i c i e n t t o t h e minimum pan c o e f f i c i e n t v a r i e s c o n s i d e r a b l y from one s t a t i o n t o t h e o t h e r . For t h e f i v e s t a t i o n s i n t h e i r t a b u l a t e d o r d e r , t h i s r a t i o
i s 2 . 2 7 , 1 . 5 3 , 1 . 4 2 , 1 . 1 6 and 1 . 3 7 r e s p e c t i v e l y . The mean c o e f f i c i e n t of t h e pan a l s o v a r i e s from o n e l o c a t i o n t o t h e o t h e r . The mean a n n u a l r e l a t i v e h u m i d i t y f o r t h e s t a t i o n s i n t h e i r t a b u l a t e d o r d e r i s 7 2 . 3 , 6 6 . 8 , 7 1 . 7 , 3 1 . 4 and 3 2 . 1 , respectively.
The mean a n n u a l v a l u e of t h e pan c o e f f i c i e n t and t h e a m p l i t u d e of
t h e mean monthly c o e f f i c i e n t b o t h seem t o some e x t e n t , t o b e d e p e n d e n t o n t h e mean a n n u a l h u m i d i t y .
2 10
25 24
~~~
LEGEND S X V
2:
A
0 22
a Y
21
A
20
0
3
19
C
a
L 2
18 17
J
I 3
. E A
Wad - Medani Khartoum Atbara Merowe Wadi - H a l f a Aswan Qena Asyirt E l -Kharga Oasis Minya ( A i r Port ) Fay u m Giza Almaze ( A i r Port ) A d d i s Abbaba Tanta Zagazi g El - Tahrir Rose ires
16
E 15 C
.g 1 4 2
$13 > a12 > CI
E
11
:
= 10 9
a7 -7-
6 5 4 -
1
2
3
4 5 6 7 Penman evaporation,
8
9
1 0 1 1
1 2 1 3 1 4
mm./day
Fig. 5.11a. Relationship between evaporation computed by the Hargreaves formula and evaporation computed by the Penman formula for the interior stations in the Nile Basin
16 LEGEND 15
15
s Kusseir
14 -
14 0
13
=-.12
0
E
11
-
Port S a i d
13
a t or n e a r t he coast
v Edfina
1 El Ka s r A
A
D
Sallum
?
'2
E 11
-
-
E . 10 -
E
. 1c
3
C
.0_
.-
12
2
a 9 8
a
- 9
9 -
0
9
8-
E
7 -
a 8
a >
1
d
D
2ul
:
E!6 =
D
=
5
3t
4
21 0
6-
L
54 -
1-
1
I
I
I
I
I
I
I
4 5 6 7 8 P e nma n e v a por at i on, m m . l d a y
2
3
I
9
I
10
F i g . 5.11b R e l a t i o n s h i p between e v a p o r a t i o n computed by t h e Hargreaves f o r m u l a and t h a t b y t h e Penman f o r m u l a f o r t h e s t a t i o n s a t o r n e a r t h e Red S e a C o a s t and t h e M e d i t e r r a n e a n Sea Coast
0
I
I
I
I
I
I
2 3 4 5 6 7 8 9 10 Penman e v a p o r a t i o n , m m . / d a y r i g . s . 1 1 ~ . H e l a t i o n s n i p between e v a p o r a z i o n comput e d by H a r g r e a v e s ' f o r m u l a and t h a t by Penman's f o r mula f o r s t a t i o n s j u s t o u t s i d e t h e swamps o f t h e Bahr e l J e b e l Basin 1
:: CL
212
TABLE 5.15
Monthly and y e a r l y r a t i o s of Penman e v a p o r a t i o n t o C l a s s A pan evaporation
E penman : E pan A , f o r S t i t i n n
1_.11--__
El-Kasr El-Tahrir Giza Kharga O a s i s Khartoum
J a n . F e b . Mar. Apr.
May
J u n e J u l y Aug. S e p . O c t . Nov. D e c . Year
.396 .395 .536 .375 .556
,720 .555 .650 .430 .450
.663 .584 ,693 .404 .525
.448 .583 .667 .412 .532
,414 .529 .569 .433 .540
.571 .582 .642 .429 .490
.755 .605 .712 .424 .643
.623 .563 .653 .436 .670
.563 ,563 .617 .423 .583
.462 .508 .574 .396 .532
.481 .595 .561 .364 .518
.333 .485 .500 .353 .546
.603 .558 .629 .415 .538
The o b s e r v e d pan e v a p o r a t i o n , E h a s b e e n p l o t t e d v e r s u s t h e f r e e w a t e r surP’ f a c e e v a p o r a t i o n e s t i m a t e d from t h e method o f Penman, X . The p o l y n o m i a l r e g r e s sion equations f i t t e d t o the p l o t t e d points are: El-Kasr
E
El-Tahrir
E
Giza
E
Kharga O a s i s Khartoum
where E
P
E E
P P
P P
P
= 2.082
+
1.652 X - 0.068 X 2
= 0.856
+
1.592 X
= 0.520
+
1.687 X - 0.040 X2
= 2.407
+
1.696 X
-
+
0.005 X 2
0.046 X 2
=15.613 - 2.667 X + 0.316 X 2
(r
EP I
(rEp, (rEp,
= .963) = ,993) X = .993)
(5.13)
( r E p , X = .995)
( rEp, X = .945)
and X a r e i n mm/day.
T h e s e r e g r e s s i o n r e l a t i o n s when f i t t e d t o t h e r e s p e c t i v e p a i r s o f E
and X P g i v e t h e l i n e s shown i n F i g . 5.12. Though e q s . 5.13 a r e somewhat d i f f e r e n t from t h o s e d e v e l o p e d e a r l i e r by t h e a u t h o r w h i l e a n a l y z i n g t h e e v a p o r a t i o n pan d a t a i n Egypt ( S h a h i n , M.M., 1970), b o t h s e t s of e q u a t i o n s , f o r t h e u s u a l r a n g e of X , s t i l l y i e l d a l m o s t t h e same v a l u e s o f E
5.6.4
P
.
R e l a t i o n s h i p between c l a s s A pan e v a p o r a t i o n and P i c h e e v a p o r a t i o n
The r a t i o c l a s s A pan e v a p o r a t i o n t o P i c h e e v a p o r a t i o n f o r G i z a , Kharga and Khartoum s t a t i o n s i s g i v e n i n T a b l e 5.16. The same r a t i o , a v e r a g e d o v e r t h e p e r i o d from J u n e 1954 up t o and i n c l u d i n g May 1960 for t h e Lod A i r p o r t ,
Israel
(WMO, 1966) i s a l s o i n c l u d e d i n T a b l e 5.16 f o r c o m p a r i s o n . The c o n c l u s i o n one c a n draw from t h e f i g u r e s l i s t e d i n t h i s t a b l e i s t h a t t h e mean a n n u a l r a t i o of c l a s s A pan t o P i c h e e v a p o r i m e t e r i n s c r e e n v a r i e s from a b o u t 0.8 f o r Kharga and Aswan (mean r e l a t i v e h u m i d i t y a b o u t 32%) t o 1.03 f o r G i z a (mean r e l a t i v e humid i t y a b o u t 72%). Even f o r t h e Lod, which i s s i t u a t e d o u t s i d e t h e N i l e B a s i n ,
213
23
LEGEND
22 o
21
A
20
+
z
x
Kharga Oasis Khartoum E l - Kasr E l - Tahrir Giza
19 18 17 16 1s >
. 0
u 14
E E 13
El
.- 1 2 r
2 CL 0
0 > a l
3 In 0
5
11
10
9
8 7 6 S
4
3
2
0
1
2
3 4 Penman
S 6 7 8 9 evaporation, rnm I day
1 0 1 1
12
Fig. 5.12. R e l a t i o n s h i p between observed c l a s s A pan e v a p o r a t i o n and f r e e water s u r f a c e e v a p o r a t i o n e s t i m a t e d from t h e Penman method
214
t h e r a t i o i s 1 . 0 6 . T h i s r a t i o as o b t a i n e d , b u t i n d i r e c t l y ,
from t h e 2-year e v a -
p o r a t i o n s t u d i e s i n Kenya and Uganda i s 3 . 3 f o r E n t e b b e , 1 . 6 f o r b o t h E q u a t o r and Gulu, and 1 . 4 7 f o r Kisumu. The P i c h e e v a p o r a t i o n a t E n t e b b e h a s b e e n r e p o r t e d a s b e i n g abnormal. I f w e n e g l e c t t h i s s t a t i o n , w e w i l l s t i l l b e l e f t with t h e r a t h e r high r a t i o f o r t h e o t h e r s t a t i o n s . This supports our opinion t h a t t h e P i c h e r e a d i n g s i n t h e E q u a t o r i a l Lakes a r e a are g e n e r a l l y s m a l l and much more v a r i a b l e t h a n are t a n k s .
TABLE 5 . 1 6
Monthly and a n n u a l r a t i o s o f class A pan e v a p o r a t i o n t o P i c h e evaporation
Station Giza a* b* Kharga Khartoum Lod ( A i r p o r t )
E pan A : E p i c h e , f o r J a n . F e b . Mar. Apr. .54 .92 .67 .75 .73
May
J u n e J u l y Aug. S e p . O c t . Nov. Dec. Year
.57 .60 .59 . 6 1 .67 . 7 3 .74 .69 . 9 5 1 . 0 1 . 9 8 .99 1 . 0 7 1 . 2 0 1 . 2 4 1 . 1 2 .74 .74 .79 .83 . 9 3 .89 . 8 2 .81 - 7 4 .76 .77 .82 .87 1 . 0 1 1.09 .90 .88 1 . 0 0 1 . 0 5 1.13 1 . 2 9 1 . 3 5 1 . 3 4 1 . 1 5
.62 .98 .73 .79 .94
.58 .92 .72 .73 .74
. 5 3 .64 .86 1 . 0 3 .69 .SO .75 .82 .68 1.06
*a = P i c h e u n s c r e e n e d ; b = P i c h e s c r e e n e d The r e s u l t s o b t a i n e d from t h e Namulonge C o t t e n R e s e a r c h S t a t i o n , Uganda, a r e q u i t e i m p r e s s i v e and i l l u m i n a t i n g . A g r a p h i c a l p l o t of t h e s e r e s u l t s h a s been p r e s e n t e d by O l i v i e r ( ( 1 9 6 1 ) and r e p r o d u c e d h e r e i n F i g . 5 . 1 3 .
c u
Tank
e v a p o r i m e t e r , i n c h e s per 24 h o u r s . Fiducial limits 9 : 1 .
Fig. 5.13. Comparison of r e a d i n g s o f P i c h e and t a n k e v a p o r i m e t e r s a t Namulonge C o t t o n R e s e a r c h S t a t i o n , Uganda
215
5.6.5
R e l a t i o n s h i p between P i c h e e v a p o r a t i o n and e s t i m a t e d f r e e water s u r f a c e evaporation
We have a l r e a d y mentioned a t t h e b e g i n n i n g o f t h i s c h a p t e r t h a t t h e P i c h e e v a p o r i m e t e r d o e s n o t , s t r i c t l y , p r e s e n t " f r e e water s u r f a c e " c o n d i t i o n s . The r e a s o n s b e h i n d t h i s a r e , a s g i v e n by O l i v i e r ( 1 9 6 1 ) , t h a t t h e P i c h e e v a p o r a t i o n t a k e s p l a c e from a p o r o u s b l o t t i n g p a p e r and t h e r e f o r e t h e s u r f a c e from which
water e v a p o r a t e s i s n o t as a u n i f o r m " f r e e " w a t e r s u r f a c e . F u r t h e r m o r e , r a d i a t i o n a b s o r p t i o n i s p r o b a b l y d i f f e r e n t f o r t h i s t y p e o f e v a p o r i m e t e r compared w i t h a p l a i n w a t e r s u r f a c e . A d d i t i o n a l l y , t h e area o f t h e e v a p o r a t i o n s u r f a c e
i s i n f i n i t e l y s m a l l compared w i t h any s u r f a c e a r e a o f a r e s e r v o i r or a l a k e . However, i n areas where o n l y P i c h e r e a d i n g s are a v a i l a b l e , t h e s e have t o b e used, w i t h s u i t a b l e c o r r e c t i o n s . I n o t h e r words,
the Piche evaporation has t o
be m u l t i p l i e d by a c o e f f i c i e n t i n o r d e r t o b r i n g i t t o i t s e q u i v a l e n t o f a f r e e water s u r f a c e . For t h i s purpose, Table 5 . 1 7 h a s been prepared t o g i v e t h e monthly and t h e a n n u a l P i c h e c o e f f i c i e n t s f o r 30 s t a t i o n s i n t h e N i l e B a s i n . For o t h e r s t a t i o n s , e s p e c i a l l y i n Uganda and Kenya, where t h e a v a i l a b l e d a t a allow f o r a n i n d i r e c t c o m p u t a t i o n o f t h e open w a t e r e v a p o r a t i o n , o n l y t h e annual c o e f f i c i e n t o f e a c h s t a t i o n h a s been e s t i m a t e d a s f o l l o w s :
Station
Piche Coefficient
Station
Piche C o e f f i c i e n t
Gambei 1a Akobo Gulu Eldoret Soroti Butiaba
0.78 0.84 1.07 1.10 1.12 1.17
Masindi P o r t Jinja Entebbe K amp a 1 a Kisumu Narok
1.20 1.30 1.85 1.35 1.03 1.00
The a r e a l d i s t r i b u t i o n o f t h e mean a n n u a l P i c h e c o e f f i c i e n t o v e r t h e b a s i n of t h e N i l e c a n b e s e e n from t h e map i n F i g . 5 . 1 4 . Examination o f t h i s map shows t h a t t h e mean a n n u a l v a l u e o f t h e P i c h e c o e f f i c i e n t changes i n two p r i n c i p a l d i r e c t i o n s . The f i r s t d i r e c t i o n i s s o u t h - n o r t h where t h e c o e f f i c i e n t d e c r e a s e s from a p r o b a b l e maximum o f , s a y , 1 . 3 around t h e n o r t h e r n s h o r e of Lake V i c t o r i a ( n e g l e c t i n g t h e r e a d i n g s a t E n t e b b e ) t o a minimum of about 0 . 3 5 f o r E l Kharga Oasis i n E g y p t . T h i s i s f o l l o w e d by an i n c r e a s e i n t h e P i c h e c o e f f i c i e n t up t o a b o u t 0 . 9 which i s r e a c h e d a t , or n e a r , t h e c o a s t a l l i n e of t h e M e d i t e r r a n e a n S e a between D a m i e t t a and A l e x a n d r i a . The second d i r e c t i o n i s e a s t - w e s t where t h e P i c h e c o e f f i c i e n t d e c r e a s e s from about 0 . 6 5 t o a b o u t 0 . 5 0 f o r Khartoum, Merowe, H a l f a and Aswan on t h e Main N i l e and t o 0.35 f u r t h e r t o t h e w e s t f o r E l Kharga O a s i s . T h i s p a t t e r n i s i n t e r r u p t e d by t h e r a t h e r h i g h c o e f f i c i e n t i n t h e s t r i p between Q u s s e i r on t h e Red Sea C o a s t and Qena on t h e N i l e R i v e r . T h i s i n t e r r u p t i o n i s p r o b a b l y due t o t h e s e v e r a l t o r r e n t s and Wadi's which i n t e r s e c t t h i s s t r i p . The upheaval i n t h e
TABLE 5.17
Monthly and a n n u a l P i c h e c o e f f i c i e n t s f o r t h e N i l e B a s i n E
Station
Sallum Alexandria Po rt Said Edfina Sirw Tanta Zagazig Giza Almaza ( A i r p o r t ) Suez Fayum lllinya ( A i r p o r t ) Hurghada AsyCit E l Kharga ( O a s i s ) Qena Qusseir Aswan Wadi H a l f a Merowe Atbara Khartoum Kassala/Gallabat Wad Medani Sennar Singa Roseires Kurmuk Malakal Wau Mongalla/Juba
Jan.
Feb.
Mar.
Apr.
.364 .479 .356 . 5 16 .655 .7 14 ,842 .455 ,324 .451 ,441 .452 ,346 ,462 .25 3 . 6 36 .388 .461 .511 .491 .399 . 5 18 .598 ,406 ,530 .535 .463 .459 .333 .5 38 .520
.411 .577 .452 ,600 .743 .750 1.040 .6 19 .429 ,534 .59 1 .456 .383 .608 .302 ,690 .696 .505 .532 .474 .383 .446 ,562 .382 ,573 ,494 ,442 . 4 34 ,363 .555 .575
.5 19 .720 .481 .674 .84 1 ,737 1.094 .623 .466 .605 ,650 .5 35 .412 ,566 ,319 .769 .531 ,481 .493 .452 ,397 .466 .55 1 .382 .531 .5 14 .494 .490 .4 33 .583 ,680
,607 .906 .703 .729 ,906 .750 1.089 ,722 .554 .564 .628 .54 1 ,452 ,611 .340 .7 17 .6 20 ,458 .48 1 ,445 . 5 10 .497 .578 ,428 ,595 .545 .5 13 .508 ,606 .713 ,784
May .709 1.060 .729 .754 1.050 .7 36 1.125 .7 36 .500 .560 .644 .493 .472 .606 ,355 ,771 ,646 .459 .479 ,453 .447 .558 .577 .4 36 .579 .583 .576 .573 .829 .9 37 1.061
Penman
’
Epiche’ for
June
July
Aug.
Sep.
Oct.
Nov.
Dec.
Year
.809 1.447 .795 .931 1.175 ,821 1.186 .859 .546 .577 .617 .507 .442 ,558 ,375 .742 .6 36 .435 .455 .467 .497 ,536 .6 35 .444 ,699 ,695 ,762 .77 1 1.023 1.106 1.093
.876 1.404 .772 .986 1.213 .9 10 1.327 .881 .560 .598 .695 .562 .492 . 6 12 .376 .754 .739 .477 ,495 .505 .497 .556 .651 .566 .8 32 .844 1.000 1.010 1.380 1.216 1.243
.927 1.120 .725 .954 1.270 1.018 1.455 .857 .615 .597 .723 .585 ,455 .641 .356 .702 .6 72 ,458 .531 .557 . 5 34 .550 .688 .803 . 8 19 .831 1.000 .995 1.640 1.371 1.324
.722 1.000 ,550 .821 1.191 1.022 1.486 .go9 ,522 .583 .688 .644 .4 38 .604 .347 .837 .652 .453 .473 ,479 ,5 18 .601 .590 .887 .758 .760 .9 14 .903 1.656 1.282 1.113
.542 ,769 .441 .717 1.071 1.000 1.290 .729 .483 .568 .615 .562 .453 .690 .288 .852 .574 . 4 19 .484 .466 .604 .575 .640 .658 .729 .731 .809 . 8 10 1.351 1.095 .963
.449 .653 .4 10 .6 32 .940 ,963 1.304 .657 .458 ,554 ,667 .600 .452 .694 .263 .841 .500 .417 .521 .479 ,4 39 .535 .635 .452 .640 .601 .648 .649 .627 .701 .746
.324 .429 .382 .500 .6 30 .750 ,944 ,5 17 .365 .423 .500 .541 .365 .541 .242 .647 .405 .507 .465 ,487 . 4 15 .499 .594 . 4 18 .551 .546 .509 .503 .426 .598 .6 20
.620 .880 .575 .784 .978 .844 1.189 ,746 .500 .559 .645 .600 .44 1 ,604 .332 .753 .602 .463 .487 .476 .465 .536 .632 .476 .573 .591 .594 .58 1 ,600 .763 .786
217
B
N
30'
25'
20°
15O
1 oo
5'
0'
21
'
Fig. 5.14. D i s t r i b u t i o n o f t h e mean a n n u a l c o e f f i c i e n t f o r c o n v e r t i n g t h e P i c h e e v a p o r a t i o n t o f r e e w a t e r e v a p o r a t i o n u s i n g Penman's method
218
v a l u e o f t h e P i c h e c o e f f i c i e n t a r o u n d Qena t o t h e w e s t i s c o u n t e r - b a l a n c e d by t h e d r o p around Hurghada o n t h e c o a s t of t h e Red S e a between Q u s s e i r and S u e z . T h e r e i s a r a p i d i n c r e a s e i n t h e v a l u e of t h e c o e f f i c i e n t a l o n g t h e M e d i t e r r a nean C o a s t from P o r t S a i d , i n t h e e a s t , t o A l e x a n d r i a ,
i n the w e s t . This
i n c r e a s e may b e due t o t h e h i g h r e l a t i v e h u m i d i t y b r o u g h t up l o c a l l y by t h e c o n t i n u o u s i r r i g a t i o n and t h e v e r y many c a n a l s
i n t h e N i l e D e l t a . West of
A l e x a n d r i a i n t h e d i r e c t i o n o f S a l l u m , t h e P i c h e c o e f f i c i e n t d e c r e a s e s from a b o u t 0 . 8 8 f o r t h e f o r m e r t o a b o u t 0 . 6 2 f o r t h e l a t t e r . I n g e n e r a l , t h e mean monthly c o e f f i c i e n t o f t h e P i c h e e v a p o r i m e t e r u n d e r g o e s a s e a s o n a l c y c l e . The a m p l i t u d e o f t h i s c y c l e v a r i e s from one s t a t i o n t o t h e o t h e r . Based on t h e f i g u r e s l i s t e d i n T a b l e 5 . 1 7 t h e maximum v a l u e of t h e c o e f f i c i e n t o c c u r s m o s t l y i n J u l y and A u g u s t . I n 84% of t h e s t a t i o n s i n v e s t i g a t e d t h e peak h a s been found t o t a k e p l a c e i n t h e three-month
p e r i o d July-September.
The minimum v a l u e o f t h e
monthly c o e f f i c i e n t o c c u r s f o r 90% o f t h e s t a t i o n s i n t h e three-month December-February.
period
The f r e q u e n c y h i s t o g r a m s o f t h e o c c u r r e n c e of t h e maximum
and t h e minimum v a l u e s of t h e P i c h e c o e f f i c i e n t f o r a l l s t a t i o n s a r e shown i n F i g s . 5 . 1 5 a and 5 . 1 5 b , r e s p e c t i v e l y . The r a t i o of t h e maximum t o t h e minimum, e x c l u d i n g t h e very h i g h v a l u e a t U a l a k a l , v a r i e s from 1 t o 3 . 5 . The f r e q u e n c y d i s t r i b u t i o n of t h i s r a t i o f o r t h e s t a t i o n s i n v e s t i g a t e d i s shown i n F i g . 5 . 1 5 ~ .Most o f t h e s t a t i o n s t h a t e n j o y a f a i r l y s t a b l e v a l u e f o r t h e P i c h e c o e f f i c i e n t , i . e . t h e r a t i o of t h e maximum monthly t o t h e minimum monthly c o e f f i c i e n t i s i n t h e r a n g e o f from 1 . 0 t o 1 . 5 , a r e t h o s e o n t h e N i l e R i v e r i n t h e a r i d z o n e . The l e s s s t a b l e r a t i o , from 1 . 5 t o 2 . 0 , t a k e s p l a c e i n t h o s e s t a t i o n s i n t h e N i l e D e l t a and V a l l e y a r e a s where i n t e n s i v e i r r i g a t e d a g r i c u l t u r e i s p r a c t i s e d . The l e a s t s t a b l e r a t i o , i . e . l a r g e r t h a n 2 . 0 i s a c h a r a c t e r i s t i c of t h e s t a t i o n s a t , o r c l o s e t o , t h e M e d i t e r r a n e a n C o a s t and j u s t o u t s i d e t h e swamps o f t h e Bahr e l J e b e l , Bahr e l Ghazal and t h e S o b a t B a s i n s . I n o r d e r t o i l l u s t r a t e t h e p a t t e r n of v a r i a t i o n of t h e P i c h e monthly c o e f f i c i e n t , t h e f i g u r e s l i s t e d i n T a b l e 5 . 1 7 have f i r s t been c o n v e r t e d t o modular v a l u e s . T h i s i s done by d i v i d i n g t h e c o e f f i c i e n t f o r each month by t h e mean annual c o e f f i c i e n t f o r th e s t a t i o n considered. F i g . 5 . 1 6 shows smooth c u r v e s f i t t e d t o t h e monthly c o e f f i c i e n t s v e r s u s t h e months o f t h e y e a r f o r s i x s t a t i o n s o n l y a s an example. These c u r v e s p r e s e n t o t h e r c h a r a c t e r i s t i c s i n a d d i t i o n t o t h e s e a s o n a l c y c l e , t h e months i n which t h e maximum and t h e minimum v a l u e s o c c u r , and t h e r a t i o of t h e maximum t o t h e minimum.
219
16
-
7
1412 210-
10r
8
QI
-
3
2 6 aJ 3 5 4
L:
8 -
-
LI
4 -
2
0
21
1
1
1
1
1
l
l
F i g . 5.15a. Frequency h i s t o gram of t h e month o f o c c u r r e n c e of t h e maximum v a l u e o f t h e Piche c o e f f i c i e n t
0
1.0
-
6 -
l
l
1
0
-_I
-
"
'
"
1
~
'
"
~
F i g . 5.15b. Frequency h i s t o g r a m o f t h e month o f o c c u r r e n c e o f t h e minimum v a l u e of t h e Piche c o e f f i c i e n t
1.5 2.0 2.5 3.0 3 . 5 4.0 4 . 5 5.0 M a x . coef'icient I Min. c o e f f i c i e n t
F i g . 5 . 1 5 ~ . Frequency h i s t o g r a m o f t h e r a t i o of t h e maximum monthly P i c h e c o e f f i c i e n t t o t h e minimum monthly P i c h e c o e f f i c i e n t
220
Curves s i m i l a r t o t h o s e f o r Khartoum and Minya A i r p o r t i n d i c a t e t h e p r e s e n c e o f two c y c l e s i n s t e a d o f o n e . The r i s i n g l i m b s o f t h e c u r v e s a p p r o a c h , o r e q u a l , t h e modular v a l u e 1 . 0 between t h e end of March and m i d - A p r i l .
The same modular
v a l u e i s e q u a l l e d or a p p r o a c h e d by t h e f a l l i n g l i m b s o f t h e c u r v e s i n t h e p e r i o d between mid-September and mid-November.
I’
\
0.4
0.3l
1
1
2
I
3
1
4
I
5
I
6
I
7
I
8
I
9
I
10
I
11
I
12
Month Fig. 5.16. V a r i a t i o n o f t h e modular v a l u e o f t h e P i c h e c o e f f i c i e n t w i t h t h e month o f t h e y e a r f o r some e v a p o r a t i o n s t a t i o n s i n t h e N i l e B a s i n
221
REFERENCES Baumgartner, A . , and R e i c h e l , E . , 1975. The w o r l d w a t e r b a l a n c e , R . Oldenburg V e r l a g , Munich. Dagg, M . , 1972. E a s t A f r i c a : i t s p e o p l e s and r e s o u r c e s ( e d i t e d by W.T.W. Morgan). C h a p t e r 10: Water r e q u i r e m e n t s o f c r o p s , 119-125. Oxford U n i v e r s i t y P r e s s , London, N e w York. H a r g r e a v e s , G . H . , 1956. I r r i g a t i o n r e q u i r e m e n t s b a s e d on c l i m a t i c d a t a . Paper No. 1105 J o u r n . I r . & D r . D i v . , ASCE, V o l . 8 2 , No. IR-3: 1-10. Hickox, G . H . , 1946. E v a p o r a t i o n from a f r e e w a t e r s u r f a c e . T r a n s . A m e r . S O C . C i v . E n g r s . , 111, P a p e r No. 2266, 1-33. H u r s t , H . E . , 1950. The N i l e B a s i n , V o l . V I I I : The h y d r o l o g y of t h e S o b a t and White N i l e and t h e topography o f t h e B l u e N i l e and A t b a r a . P h y s i c a l Department p a p e r No. 5 5 , The Government P r e s s , C a i r o , E g y p t , 125 p p . H u r s t , H . E . , 1952. The N i l e , a g e n e r a l a c c o u n t of t h e r i v e r and t h e u t i l i z a t i o n o f i t s w a t e r s . C o n s t a b l e , London, 326 p p . H u r s t , H . E . , B l a c k , R . P . , and S i m a i k a , Y . M . , 1959. The N i l e B a s i n , Vol. I X : The h y d r o l o g y o f t h e Blue N i l e and A t b a r a and of t h e main N i l e a t Aswan, w i t h some r e f e r e n c e t o p r o j e c t s . N i l e C o n t r o l Department P a p e r No. 1 2 , The General o r g a n i z a t i o n f o r Government P r i n t i n g O f f i c e s , C a i r o , E g y p t , 206 p p . H u r s t , H . E . , B l a c k , R . P . , and S i m a i k a , Y . M . , 1966. The N i l e B a s i n , Vol. X , The m a j o r N i l e p r o j e c t s . N i l e C o n t r o l Department P a p e r No, 2 3 , G e n e r a l Organizat i o n f o r Government P r i n t i n g O f f i c e s , C a i r o , 217 p p . H u r s t , H . E . , and P h i l i p s , P . , 1931. The N i l e B a s i n , Vol. I , G e n e r a l d e s c r i p t i o n o f t h e b a s i n , m e t e o r o l o g y and topography of t h e White N i l e B a s i n . P h y s i c a l Department P a p e r No. 2 6 , Government P r e s s . C a i r o , 128 p p . H u r s t , H . E . , and P h i l i p s , P . , 1938. The N i l e B a s i n , Vol. V, The hydrology o f t h e Lake P l a t e a u and Bahr e l J e b e l . P h y s i c a l Department P a p e r No. 3 5 , S c h n i d l e r s ' P r e s s . C a i r o , 235 p p . K r i s h n a m u r t h y , K . V . , and I b r a h i m , A . H . , 1 9 7 3 . H y d r o m e t e o r o l o g i c a l s t u d i e s o f Lakes V i c t o r i a , Kyoga and A l b e r t , G e o p h y s i c a l nomograph 1 7 : Man-Made Lakes (Ackermann, W . C . , e t a l : e d i t o r s ) , A . G . U . , Washington D . C . , 272-277. L i n s l e y , R . K . , K o h l e r , M . A . , and P a u l h u s , J . L . , 1 9 5 8 . Hydrology f o r e n g i n e e r s . M c G r a w - H i l l Book Company I n c . , N e w York, London, 340 p p . M i n i s t r y o f War and M a r i n e , E g y p t , 1950. C l i m a t o l o g i c a l normals for Egypt. M e t e o r o l o g i c a l Department of E g y p t . C , Tsoumas & Co. P r e s s , C a i r o . O l i v i e r , H . , 1961. I r r i g a t i o n and C l i m a t e , Edward Arnold ( p u b l i s h e r s ) L i m i t e d , London, 250 p p . P a l a y a s o o t , P . , 1 9 6 5 . E s t i m a t i o n o f pan e v a p o r a t i o n and p o t e n t i a l e v a p o t r a n s p i r a t i o n of r i c e i n t h e c e n t r a l p l a i n o f T h a i l a n d by u s i n g v a r i o u s f o r m u l a s b a s e d on c l i m a t o l o g i c a l d a t a . M.Sc. t h e s i s p r e s e n t e d t o t h e Utah S t a t e U n i v e r s i t y , Utah, U.S.A. Penman, H . L . , 1 9 4 8 . N a t u r a l e v a p o r a t i o n from open w a t e r , b a r e s o i l and g r a s s . P r o c e e d i n g Roy. S O C . A g r i c . , 1 9 3 : 120-145. R i j k s , D . A . , 1969. E v a p o r a t i o n from a p a p y r u s swamp. Q u a r t . J o u r n . Roy. Meteo. S O C . , 9 5 : 643-649. Rzbska, J . ( e d i t o r ) , 1 9 7 6 . The N i l e , Biology o f an a n c i e n t r i v e r . D r W . Junk B . V . P u b l i s h e r s , The Hague, The N e t h e r l a n d s , 417 p p . S h a h i n , M . M . , 1 9 7 0 . A n a l y s i s of e v a p o r a t i o n pan d a t a i n U . A . R . ( E g y p t ) . Annual B u l l e t i n o f ICID, N e w D e l h i , I n d i a , 53-69. S l e i g h t , R . B . , 1 9 2 7 . D i s c u s s i o n o f Houk's p a p e r : E v a p o r a t i o n on U n i t e d S t a t e s r e c l a m a t i o n p r o j e c t s . T r a n s . A m e r . S O C . C i v . E n g r s . , 9 0 , 303-316. US G e o l o g i c a l S u r v e y , 1 9 5 4 . Water l o s s i n v e s t i g a t i o n s : Vol. I - Lake Hefner s t u d i e s . G e o l o g i c a l Survey P r o f e s s i o n a l P a p e r No. 269. USSR N a t i o n a l Committee f o r IHD, 1 9 7 4 . World w a t e r b a l a n c e and w a t e r r e s o u r c e s o f t h e e a r t h ( t r a n s l a t e d from R u s s i a n ) , UNESCO, P a r i s .
222
WMO, 1966. Measurement and e s t i m a t i o n of e v a p o r a t i o n and e v a p o t r a n s p i r a t i o n . T e c h n i c a l n o t e N o . 83, Geneva, 1 2 1 p p . WMO, 1974. H y d r o m e t e o r o l o g i c a l s u r v e y o f t h e c a t c h m e n t s of Lakes V i c t o r i a , Kyoga and A l b e r t , V o l . I : M e t e o r o l o g y and h y d r o l o g y of t h e b a s i n , P a r t s 1 &2, Geneva.
223
Chapter 6
EVAPOTRANSPIRATION
E v a p o t r a n s p i r a t i o n i s t h e t o t a l q u a n t i t y o f w a t e r consumed by e v a p o r a t i o n and t r a n s p i r a t i o n . E v a p o r a t i o n h a s a l r e a d y b e e n d e f i n e d i n C h a p t e r 5 . T r a n s p i r a t i o n i s s i m p l y e v a p o r a t i o n f r o m t h e p l a n t . I t i s a p r o c e s s by w h i c h w a t e r v a p o u r is r e l e a s e d t o t h e atmosphere t h r o u g h s u r f a c e p o r e s i n p l a n t f o l i a g e , mainly
through stomata1 o p e n i n g s . A s m a l l p o r t i o n o f t h e e m i t t e d moisture,
generally
l e s s t h a n lo%, comes f r o m t h e y o u n g e r p l a n t s t e m s . R e l e a s e o f m o i s t u r e by t r a n s p i r a t i o n o c u r s p r i n c i p a l l y d u r i n g t h e day-time h o u r s o f t h e growing s e a s o n . P r o b a b l y n o t more t h a n 5 t o 10% o f t h e d a i l y t r a n s p i r a t i o n t a k e s p l a c e d u r i n g t h e n i g h t . The r a t e o f t r a n s p i r a t i o n u s u a l l y r e a c h e s a maximum v a l u e s h o r t l y a f t e r n o o n , a n d a minimum j u s t b e f o r e s u n r i s e . E v a p o t r a n s p i r a t i o n c a n b e d e f i n e d as t h e sum o f t h e volumes o f w a t e r u s e d p e r u n i t a r e a by t h e v e g e t a t i v e g r o w t h i n t r a n s p i r a t i o n and t h a t e v a p o r a t e d from t h e s o i l , snow or i n t e r c e p t e d p r e c i p i t a t i o n o n a g i v e n area i n any s p e c i f i e d t i m e . Evapotranspiration is usually expressed i n u n i t s of depth per u n i t o f t i m e . The t e r m c o n s u m p t i v e u s e , commonly u s e d i n i r r i g a t i o n h y d r o l o g y , i s e s s e n t i a l l y synonymous w i t h e v a p o t r a n s p i r a t i o n . The d e f i n i t i o n o f e v a p o t r a n s p i r a t i o n i m p l i e s t h a t t h e f a c t o r s a f f e c t i n g i t are e s s e n t i a l l y t h o s e a f f e c t i n g e v a p o r a t i o n and t r a n s p i r a t i o n . So t h e r a t e o f e v a p o t r a n s p i r a t i o n d e p e n d s o n t h e c l i m a t e , crop r a i s e d , s t a g e o f p l a n t development, d e n s i t y of v e g e t a t i v e cover, s o i l m o i s t u r e s u p p l y , s a l i n i t y a n d l e n g t h of g r o w i n g s e a s o n . F a c t o r s i n c l u d e d i n climate a r e : solar r a d i a t i o n , temperature,
day-time h o u r s , d u r a t i o n of sun-
s h i n e , h u m i d i t y and wind s p e e d . When e v a p o t r a n s p i r a t i o n t a k e s p l a c e f r o m a s o i l s u r f a c e c o m p l e t e l y c o v e r e d by a c t i v e l y g r o w i n g v e g e t a t i o n and t h e r e i s no l i m i t a t i o n i n s o i l m o i s t u r e , i t i s r e f e r r e d t o as p o t e n t i a l e v a p o t r a n s p i r a t i o n . I n o t h e r words, p o t e n t i a l evapot r a n s p i r a t i o n can b e c o n s i d e r e d as t h e upper l i m i t of t h e a c t u a l evapotranspirat i o n . A c c o r d i n g t o T h o r n t h w a i t e , p o t e n t i a l e v a p o t r a n s p i r a t i o n d e p e n d s o n l y on t h e amount o f s o l a r e n e r g y r e c e i v e d by t h e e a r t h ' s s u r f a c e , c o n s e q u e n t l y t h e resulting temperature,
and n o t o n t h e k i n d o f p l a n t ( T h o r n t h w a i t e , C . W . ,
1948).
The most common m e t h o d s u s e d f o r d e t e r m i n i n g t h e e v a p o t r a n s p i r a t i o n a r e t h e water-balance,
t h e t a n k and l y s i m e t e r e x p e r i m e n t s , s o i l m o i s t u r e d e p l e t i o n
s t u d i e s i n f i e l d p l o t s , c o r r e l a t i o n w i t h e v a p o r a t i o n from a pan o r from an open
water b o d y , a n d m e t h o d s b a s e d o n t h e p h y s i c s o f t h e v a p o u r t r a n s f e r a n d / o r t h e heat energy-balance.
224
A g e n e r a l i d e a a b o u t t h e a c t u a l and p o t e n t i a l e v a p o t r a n s p i r a t i o n from t h e
N i l e B a s i n c a n b e drawn from a t l e a s t t w o s o u r c e s . R e i c h e l and Baumgartner
(1975) gave t h e a c t u a l e v a p o t r a n s p i r a t i o n f o r t h e d i f f e r e n t 5 - d e g r e e l a t i t u d e zones of t h e g l o b e , which w a s b a s e d on t h e s i m p l e e q u a t i o n E T = P - R
(6.1)
where ET = a c t u a l e v a p o t r a n s p i r a t i o n , P
= p r e c i p i t a t i o n , and
R
= run-off The t h r e e v a r i a b l e s , E T , P, and R , a r e a l l e x p r e s s e d i n a d e p t h u n i t p e r
y e a r . For t h e 5 - d e g r e e l a t i t u d e zones c o v e r e d by t h e N i l e Basin t h e v a l u e s o f these variables are as follows:
Latitude, degree north
south
Precipitation, P, m/yr
Run-off,
R, m / y r
Actual evapotranspiration, ET, m / y r
-7 -5
35-30 30-25 25-20 20-15 15-10 10- 5 5- 0
151 29 31 1 51 741 1203 1329
5 55 233 34 2
158 34 30 146 686 970 987
0- 5
1488
34 3
1145
1
The s e c o n d s o u r c e o f i n f o r m a t i o n i s t h e two maps, F i g s , 6 . 1 . and 6 . 2 . ,
which
g i v e t h e a c t u a l e v a p o t r a n s p i r a t i o n and t h e p o t e n t i a l e v a p o t r a n s p i r a t i o n redrawn from t h e Water R e s o u r c e s o f t h e E a r t h (Korzun, V . ,
e t a l , 1978). Evidently
t h e s e two maps g i v e more d e t a i l e d i n f o r m a t i o n t h a n t h e v e r y g e n e r a l f i g u r e s g i v e n by R e i c h e l and Baumgartner. As an e x a m p l e , t h e 5 - d e g r e e l a t i t u d e zone e x t e n d i n g from t h e e q u a t o r up n o r t h shows an a c t u a l e v a p o t r a n s p i r a t i o n i n c r e a s i n g f r o m , s a y , 300 mm/yr
i n t h e e a s t t o a b o u t 1250 m m / y r
i n the w e s t a t the
s h o r e of Lake Edward. For t h i s z o n e , t h e above t a b u l a t e d f i g u r e s g i v e an a c t u a l e v a p o t r a n s p i r a t i o n o f 987 mm/yr. The c o u n t r i e s s h a r i n g t h e N i l e water h a v e b e e n u s i n g s e v e r a l b u t a l s o d i f f e r e n t p r a c t i c e s t o d e t e r m i n e or t o e s t i m a t e e v a p o t r a n s p i r a t i o n .
I t may, t h e r e f o r e ,
b e w i s e r t o g i v e a n a c c o u n t o f t h e p r a c t i c e s u s e d and t h e r e s u l t s o b t a i n e d t h e r e f r o m on a c o u n t r y - w i s e b a s i s i n s t e a d o f a r i v e r b a s i n - w i s e b a s i s .
225
Fig. 6 . 1 . Lines of equal a c t u a l e v a p o t r a n s p i r a t i o n , mm/yr, from t h e N i l e Basin and surroundings (redrawn from t h e World Water Balance and Water Resources o f the Earth (Korzun, V . , e t a l , 1978)
226
30'
20'
Fig. 6 . 2 . L i n e s o f equal p o t e n t i a l e v a p o t r a n s p i r a t i o n , mm/day, from t h e N i l e B a s i n and surroundings (redrawn from t h e World Water Balance and Water Resources o f t h e Earth (Korzun, V . , e t a l , 1978)
227
EVAPOTRANSPIRATION STUDIES I N THE ARAB REPUBLIC OF EGYPT
6.1 6.1.1
Tank and l y s i m e t e r e x p e r i m e n t s
The r e s u l t s o f t a n k e x p e r i m e n t s a t t h e a g r o m e t e o r o l o g i c a l s t a t i o n a t Giza have been r e p o r t e d by Omar, M . H .
(1960). D u r i n g t h e 3-year p e r i o d , 1957-1959,
p o t e n t i a l e v a p o t r a n s p i r a t i o n was measured from t h r e e e v a p o t r a n s p i r o m e t e r s of t h e t y p e known as " m o d i f i e d e v a p o t r a n s p i r o m e t e r "
d e v e l o p e d by Mather. T h i s was a
tank w i t h a n o p e n i n g a t t h e bottom where a t u b e was f i x e d i n o r d e r t o e n a b l e t h e measurement o f p e r c o l a t i o n water. Two t a n k s w e r e c y l i n d e r i c a l , a b o u t 60 cm i n d i a m e t e r e a c h , and t h e t h i r d t a n k h a d a r e c t a n g u l a r c r o s s - s e c t i o n
130 x 90 cm.
The t a n k s w e r e p l a n t e d w i t h l i b y a g r a s s and i n s t a l l e d i n t h e s t a t i o n ' s g r a s s f i e l d . Care was t a k e n t o m a i n t a i n t h e same v e g e t a t i o n l e v e l i n s i d e and o u t s i d e t h e t a n k s by c u t t i n g t h e g r a s s when n e c e s s a r y . The d i f f e r e n c e i n a r e a of t h e e v a p o r a t i n g s u r f a c e of t h e t a n k s used was r e p o r t e d t o b e o f no s i g n i f i c a n t influence. Results generally bore t h i s o u t . O t h e r measurements were made by Popoff e v a p o t r a n s p i r o m e t e r s which have a s m a l l e r a r e a (500 cm2) compared t o M a t h e r ' s e v a p o t r a n s p i r o m e t e r s
.
The former
were r e p o r t e d t o g i v e r e s u l t s a l m o s t 10% l a r g e r t h a n t h o s e o b t a i n e d from t h e b i g g e r t a n k s . A comparison between t h e e v a p o t r a n s p i r a t i o n from t h e s m a l l t a n k s and t h e b i g g e r t a n k , a l l p l a n t e d w i t h c o t t o n , c a n b e s e e n from F i g . 6.3.
-
"...',
Legend
---- Average
- Large -
,'
of s m a l l tonks. tank.
I
I
Feb.
I
I
Mar.
Apr.
May.
I
I
I
Jun.
Jul.
Aug.
Month F i g . 6.3. Comparison between p o t e n t i a l e v a p o t r a n s p i r a t i o n from s m a l l and l a r g e tanks r a i s i n g c o t t o n a t G i z a (Omar, M . H . , 1960)
228
Z e i n e l Abedin e t a1 (1967) compared t h e e v a p o t r a n s p i r a t i o n from f i e l d p l o t s t o t h a t from w e i g h a b l e l y s i m e t e r s ,
a l l r a i s i n g l a t e m a i z e , u n d e r two d i f f e r e n t
i r r i g a t i o n t r e a t m e n t s a t t h e e x p e r i m e n t a l farm o f C a i r o U n i v e r s i t y . The s o i l m o i s t u r e c h a n g e s were d e t e c t e d by a n e u t r o n m o i s t u r e metre. A summary o f some of t h e r e s u l t s o b t a i n e d from t h i s i n v e s t i g a t i o n i s p r e s e n t e d i n T a b l e 6 . 1 . From t h i s summary i t i s e v i d e n t t h a t t h e e v a p o t r a n s p i r a t i o n from t h e l y s i m e t e r s as
w e l l as t h e f i e l d p l o t s r e s p o n d s t o t h e f r e q u e n c y o f i r r i g a t i o n , c o n s e q u e n t l y t h e a v a i l a b l e s o i l m o i s t u r e . The e v a p o t r a n s p i r a t i o n from t h e l y s i m e t e r was 12.7% l a r g e r t h a n t h a t from t h e f i e l d p l o t i n t h e t r e a t m e n t t h a t r e c e i v e d more f r e q u e n t i r r i g a t i o n , and 2 2 . 9 % i n t h e o t h e r t r e a t m e n t . T h e s e d i f f e r e n c e s i n t h e amount o f e v a p o t r a n s p i r a t i o n r e s u l t e d i n an i n c r e a s e i n t h e c r o p y i e l d i n t h e
l y s i m e t e r t h a n i n t h e f i e l d p l o t by 1 0 . 5 and 5 . 2 % f o r t r e a t m e n t s 1 and 2 respectively. TABLE 6 . 1
E v a p o t r a n s p i r a t i o n from l y s i m e t e r s and f i e l d p l o t s r a i s i n g maize under two d i f f e r e n t i r r i g a t i o n t r e a t m e n t s , F a c u l t y of A g r i c u l t u r e E x p e r i m e n t a l Farm, C a i r o U n i v e r s i t y , Egypt ( 2 . e l Abedine, A . , Abdallah, M . ,
and Abdel-Samie,
1967)
Treatment 1
Year 1966
depth of r o o t zone
24.07-01.08 02.08-09.08 10.08-20.08 21.08-04.09 05.09-17.09 18.09-01.10 02.10-11.10 12.10-05.11
cm
40 60 80 100 120 140 140 140
Total Yield, ton/ha
6.1.2
Treatment 2
-
e vapo transpiration,
mm
Year 1966
Cm
lysimeter
plot
34.4 40.8 57.6 76.6 80.2 72.8 82.8 147.3
31.8 39.2 59.2 62.4 67.0 77.0 72.8 116.2
24.07-07.08 08.08-20.08 21.08-07.09 08.09-25.09 26.09-11.10 12.10-05.11
592.5
525.6
Total
4.30
depth of r o o t zone
transpiration,
m
lysimeter
plot
52.6 50.6 75.2 119.6 119.2 141.4
48.8 64.2 73.8 67.2 88.2 112.0
558.6
454.2
3.63
3.45
40 80 100 130 140\ 140
3139
S o i l moisture depletion s t u d i e s i n controlled f i e l d p l o t s
I s r a e l s e n , O.W.
( 1 9 5 6 ) mentioned t h a t t h e e a r l y measurements o f consumptive
u s e were made o n s e l e c t e d f i e l d p l o t s o f i r r i g a t e d c r o p s where t h e w a t e r t a b l e
was a t a c o n s i d e r a b l e d e p t h below t h e s u r f a c e . The p r o c e d u r e was t o measure t h e volume o f water a p p l i e d t o t h e p l o t a t each i r r i g a t i o n and t o measure any s u r f a c e run-off
t h a t might o c c u r . I n o r d e r t o a v o i d p e r c o l a t i o n of w a t e r below t h e
229
p l a n t r o o t z o n e , i t w a s n e c e s s a r y t o a p p l y t h e w a t e r i n small d e p t h s , n o t e x c e e d i n g f i v e i n c h e s i n a s i n g l e i r r i g a t i o n on o r d i n a r y s o i l s . P r e c i s e measurements o f t h e change i n s o i l m o i s t u r e w e r e n o t u n d e r t a k e n i n most o f t h e e a r l y studies. The f i e l d p l o t method was a d o p t e d f o r t h e f i r s t t i m e i n Egypt i n 1948 by t h e t h e n M i n i s t r y o f P u b l i c Works, nowadays t h e M i n i s t r y o f I r r i g a t i o n . A few y e a r s
l a t e r , El-Shal,
( 1 9 5 4 ) i n v e s t i g a t e d t h e w a t e r u s e by c o t t o n and maize a t
M.I.
S h e b i n e l Kom, El-Menufiya G o v e r n r a t e , by m e a s u r i n g t h e c h a n g e s i n s o i l m o i s t u r e u s i n g t h e s o i l t u b e . I n view o f t h e p r o x i m i t y o f t h e water t a b l e t o t h e ground s u r f a c e , t h e c r o p w a t e r u s e was p a r t l y s u p p l i e d t h r o u g h c a p i l l a r y movement o f t h e s u b s o i l t o t h e r o o t z o n e . S i n c e t h a t p a r t c o u l d n o t b e d e t e r m i n e d , i t was n o t p o s s i b l e a t t h a t t i m e t o d e t e r m i n e t h e a c t u a l w a t e r u s e by e i t h e r c r o p . Consumptive u s e o f w a t e r by v a r i o u s c r o p s h a s b e e n d e t e r m i n e d by i n t e n s i v e s o i l m o i s t u r e s t u d i e s . S o i l s a m p l e s h a v e b e e n t a k e n a t 10 c m i n t e r v a l s b e f o r e and a f t e r e a c h i r r i g a t i o n , w i t h some s a m p l e s i n between t h e s u c c e s s i v e i r r i g a t i o n c y c l e s . The d e p t h from t h e s a m p l e s t a k e n v a r i e d between 60 and 90 c m . S t a n d a r d l a b o r a t o r y p r a c t i c e s have b e e n a p p l i e d f o r d e t e r m i n i n g t h e m o i s t u r e c o n t e n t i n t h e s o i l s a m p l e s . The q u a n t i t y o f water removed from each l a y e r of s o i l was computed by t h e e q u a t i o n
d =
(Pfc
-
Pr)
’
Ps
.
D
100
where d
= d e p t h o f w a t e r removed, i n c m ,
pfc = s o i l moisture co n t en t a t f i e l d c a p a c i t y , i n per cent , pr ps
D
= remaining s o i l m o i s t u r e c o n t e n t ,
i n percent,
= a p p a r e n t s p e c i f i c g r a v i t y o f s o i l , and = d e p t h of l a y e r c o n s i d e r e d , i n c m . The t o t a l d e p t h o f w a t e r removed from t h e r o o t zone c o u l d t h u s b e o b t a i n e d
by summing up t h e m o i s t u r e e x t r a c t e d from t h e s u c c e s s i v e l a y e r s d u r i n g a cert a i n t i m e p e r i o d . T h a t d e p t h w a s c o r r e c t e d f o r t h e e x t r a c t i o n o f m o i s t u r e from t h e l a y e r s below t h e s a m p l i n g d e p t h and f o r t h e consumption o f water i n t h e i n t e r v a l o f t i m e from t h e moment o f i r r i g a t i o n a p p l i c a t i o n t i l l t h e f i e l d c a p a c i t y of t h e s o i l m o i s t u r e had b e e n r e a c h e d . The main f i n d i n g s from t h o s e e x t e n s i v e e x p e r i m e n t s which l a s t e d more t h a n t e n y e a r s c a n b e summarized as f o l l o w s : i)
The s o i l m o i s t u r e i n t h e s u r f a c e l a y e r r e a c h e s t h e s a t u r a t i o n c a p a c i t y upon t h e c o m p l e t i o n o f l a n d i r r i g a t i o n . T h i s m o i s t u r e l e v e l d r o p s r a p i d l y i n t h e f i r s t few days a f t e r i r r i g a t i o n f o l l o w e d by a less r a p i d d e c r e a s e
2 30
i n t h e s u b s e q u e n t d a y s . A s t u d y o f t h e c y c l i c change i n s o i l m o i s t u r e h a s shown t h a t t h e m o i s t u r e c o n t e n t i n t h e t o p 10 c m o f s o i l f e l l below t h e w i l t i n g p o i n t 18 d a y s a f t e r i r r i g a t i o n a p p l i c a t i o n , whereas t h e u n d e r l y i n g l a y e r s behaved d i f f e r e n t l y , e v e n w i t h e l o n g a t e d c y c l e s o f 30 days o r more. Moreover, t h e m o i s t u r e d e p l e t e d from t h e s u r f a c e 10 c m o f s o i l was negat i v e l y c o r r e l a t e d w i t h t h e a t m o s p h e r i c r e l a t i v e h u m i d i t y . The t o t a l m o i s t u r e removed from t h e u p p e r 30 c m o f s o i l was s t r o n g l y p o s i t i v e l y c o r r e l a t e d w i t h t h e a v e r a g e a i r t e m p e r a t u r e ( Z . e l Abedine, A . , M.,
ii)
and A b d a l l a h ,
1949).
F u r t h e r s t u d i e s h a v e shown t h a t t h e s i g n i f i c a n t c y c l i c c h a n g e s i n S o i l m o i s t u r e are c o n f i n e d t o t h e t o p 50 c m o f s o i l , and t h e r a t e of m o i s t u r e d e p l e t i o n d e c r e a s e s w i t h d e p t h below t h e s u r f a c e . T h i s c a n r e a d i l y b e s e e n from F i g . 6 . 4 . The amount o f m o i s t u r e d e p l e t e d from t h e r o o t zone v a r i e s from o n e i r r i g a t i o n c y c l e t o a n o t h e r , d e p e n d i n g o n t h e s t a g e of p l a n t growth a s w e l l a s t h e c l i m a t o l o g i c a l c o n d i t i o n s . F i g . 6 . 5 . i l l u s t r a t e s t h e c y c l i c v a r i a t i o n i n m o i s t u r e c o n t e n t i n t h e t o p 50 cm of s o i l , a s o b s e r v e d by El-Warith
M.,
(Khafagi, A . ,
Z . e l Abedine, A . ,
Shahin, M . ,
and E l - W a r i t h ,
1964), i n a f i e l d p l o t r a i s i n g c o t t o n a t S i d s .
50 aJ
E
al
-B 40
-5
B 4c
36
x
n
2
-. 3 2
2
aJ
c
2
c
30
c
28
C U 0
E3 2 4
?
c
.-ln
.- 20
E
I
.-
0
cn
44
3
10
0 4 8 (14-5-1958) Time f o l l o w i n g
I 12
16
20
24 28 (11-6-1958) irrigation application, days
Fig. 6.4. M o i s t u r e d e p l e t i o n from s o i l l a y e r s of a f i e l d p l o t r a i s i n g co t to n a t S i d s under an e l o n g a t e d i r r i g a t i o n t r e a t ment ( K h a f a g i , A , , Z . e l - A b e d i n e , A . , S h a h i n , M . , and E l - W a r i t h , M . , 1 9 6 4 )
E" 20
-
2 -.1 6
Mar. Apr. May. Jun. Jul. Aug. Month
Fig. 6.5. C y c l i c v a r i a t i o n of t h e moisture content i n t h e top 50 cm. o f s o i l i n a f i e l d p l o t r a i s i n g c o t t o n a t S i d s (Khafagi, A , , Z . el-Abedine, A , , Shahin, M., and E l - W a r i t h , M., 1964)
231
i i i ) The m o i s t u r e d e p l e t i o n c h a r a c t e r i s t i c c u r v e s o f t h e s o i l l a y e r s from which t h e p l a n t e x t r a c t s i t s m o i s t u r e u s e c a n b e o b t a i n e d by p l o t t i n g t h e d a i l y l o s s i n m o i s t u r e from e a c h l a y e r v e r s u s t h e t i m e s d u r i n g t h e growing s e a s o n of t h e p l a n t . Four sets o f c h a r a c t e r i s t i c c u r v e s are shown i n F i g . 6 . 6 . These s e t s r e p r e s e n t t h e d a i l y m o i s t u r e removal from t h e i n d i v i d u a l l a y e r s o f f i e l d p l o t s r a i s i n g c o t t o n , w h e a t , maize and berseem ( E g y p t i a n c l o v e r ) a t Giza and S i d s . Each c h a r a c t e r i s t i c c u r v e assumes t h e s h a p e o f a f o r c e d oscillation,
t h e a m p l i t u d e o f which damps w i t h d e p t h . The crown p o i n t o f
t h e c u r v e b e l o n g i n g t o any l a y e r l a g s b e h i n d t h e crown p o i n t o f t h e c u r v e belonging t o t h e o v erly in g l a y e r . iv)
The c o n t r i b u t i o n o f e a c h l a y e r t o t h e s e a s o n a l consumptive u s e i s s i m p l y t h e i n t e g r a t i o n o f t h e corresponding c h a r a c t e r i s t i c c u r v e , o r simply t h e t h e a r e a u n d e r i t . T h i s c o n t r i b u t i o n e v i d e n t l y d e c r e a s e s w i t h d e p t h below t h e s u r f a c e . N e v e r t h e l e s s , l a y e r s d e e p e r t h a n 5 0 cm s t i l l c o n t r i b u t e t o t h e t o t a l consumptive u s e , though by smaller amounts. The c o n t r i b u t i o n o f t h e s u c c e s s i v e l a y e r s , uz, i n p r o p o r t i o n t o t h e t o t a l e x t r a c t i o n , u, when p l o t t e d v e r s u s t h e d e p t h below s u r f a c e , z , y i e l d s t h e s e t o f c u r v e s shown i n F i g . 6 . 7 . (El-Shal,
M.I.,
1 9 6 6 ) . These c u r v e s c a n a p p r o x i m a t e l y be d e s -
c r i b e d by t h e g e n e r a l e q u a t i o n
where A and a are c o n s t a n t f o r e a c h c r o p , and a l m o s t t h e same f o r t h e f o u r c r o p s p r e s e n t e d i n F i g . 6 . 7 . F o r A = 0 . 3 5 , a = 3 . 5 , and 0 . 8 m a s d e p t h of moisture e x t r a c t i o n , t h e c o n t r i b u t i o n i n percent of t he t o t a l e x t r a c t i o n
i s 55 f o r t h e f i r s t q u a r t e r , 2 5 . 3 f o r t h e s e c o n d , 1 2 . 4 f o r t h e t h i r d and 7 . 3 f o r t h e f o u r t h q u a r t e r . These r e s u l t s a r e i n agreement w i t h t h e b a s i c f i n d i n g of Schockley, D . R . ,
t h a t most i r r i g a t e d c r o p s have s i m i l a r e x t r a c -
t i o n p a t t e r n s . H i s c o n c l u s i o n t h a t t h e f o u r s u c c e s s i v e q u a r t e r s of t h e r o o t z o n e , s t a r t i n g from t h e s u r f a c e , c o n t r i b u t e by 4 0 , 3 0 , 20 and 10% t o t h e t o t a l e x t r a c t i o n , i s n o t i n agreement w i t h ours. The f i g u r e s w e o b t a i n e d a r e more i n l i n e w i t h v a l u e s o b t a i n e d by S t a n b e r r y , C . O . Department o f A g r i c u l t u r e ,
(United S t a t e s
1955) from t h e a n a l y s i s o f t h e d a t a from 28
a l f a l f a t e s t s c o n d u c t e d i n 10 s t a t e s i n USA. Those were 4 7 , 2 6 , 17 and 10% f o r t h e f i r s t , s e c o n d , t h i r d and f o u r t h q u a r t e r o f t h e e x t r a c t i o n d e p t h , respectively.
232
2.5
I
Mar.
> n
.
1
May.
Apr.
I
I
I
1
Jun.
Jul.
Aug
Month
D
2.5
I
I
I
I
1
I
c.
0
al
.-> In In
U aJ
3
In
al
5
Nov.
Dec.
Jan. Feb. Month
Aug.
Sep.
Oct.
Mar.
Apr
Nov.
Month
2.5 2,0
I
-
I
I
I
I
I
I
I
Berseem
1.5 -
1.0
-
0.5
Oct.
Nov.
Dec.
Jan.
Feb.
Mar.
Apr.
May.
Month
Fig. 6 . 6 . M o i s t u r e d e p l e t i o n c h a r a c t e r i s t i c c u r v e s f o r t h e t o p 50 cm l a y e r s o f s o i l u n d e r f o u r d i f f e r e n t c r o p s , a v e r a g e f o r G i z a and S i d s s t a t i o n s ( E l - S h a l ,
M.I., 1966)
233
u l u , i n percent Fig. 6.7.
P a t t e r n o f s e a s o n a l m o i s t u r e e x t r a c t i o n by some c r o p s i n Egypt
A f u r t h e r s u p p o r t f o r our i d e a t h a t t h e m o i s t u r e e x t r a c t i o n p a t t e r n i s more o r l e s s e x p o n e n t i a l r a t h e r t h a n l i n e a r , a s was o r i g i n a l l y proposed by S c h o c k l e y , came from t h e a n a l y s i s o f t h e d a t a c o l l e c t e d from e x p e r i m e n t s a t S c o t t s B l u f f S t a t i o n , N e b r a s k a , USA ( U n i t e d S t a t e s Department o f Agriculture,
1 9 5 5 ) . A summary of some of t h e r e s u l t s i s a s f o l l o w s ' :
Depth,
Moisture e x t r a c t i o n i n percent of t o t a l e x t r a c t i o n f o r
I L
0-1 1-2 2-3 3-4
v)
Oats
Beets
Potatoes
Average
64 16 12
62 19 12 7
57 23
61.0 19.3 12.3 7.3
8
13 7
The c o r r e c t e d c y c l i c loss of m o i s t u r e when d i v i d e d by t h e d u r a t i o n of each
c y c l e g i v e s t h e d a i l y l o s s o r t h e c r o p w a t e r u s e p e r d a y . D a i l y , monthly and s e a s o n a l consumptive u s e o f w a t e r by a l a r g e number o f c r o p s i n Egypt
are g i v e n i n T a b l e s 6 . 2 up t o and i n c l u d i n g 6 . 8 . S p e c i f i c a t i o n s o f t h e s e tables are:
6.2 6.3 6.4 6.5 6.6 6.6 6.6 6.6 6.7 6.8
Number o f exTeriments
Number o f ex2erinent s t a t i o n s
13 7 6 1
4 4 3
1 1 1
1 2 4
1
1 1 1 1 2 2
Crop i n v e s t i g a t e d Cotton Wheat L a t e maize E a r l y maize Fenugreek Chick p e a E g y p t i a n Lupine Lentil B e r s e e m (Egyptian c l o v e r ) C i t r u s trees
Sr. No.
N
Consumptive u s e of w a t e r f o r c o t t o n i n Egypt
TABLE 6.2
Expt. S t a t . &
From
To
Investigator Sakha
22.03.1957 01.04.1957 11.04.1957 21.04.1957 01.05.1957 11.05.1957 21.05.1957 01.06.1957 11.06.1957
El-Shala
9 10 10 10 10 10 11 10 10
31.03.1957 10.04.1957 20.04.1957 30.04.1957 10.05.1957 20.05.1957 31.05.1957 10.06.1957 20.06.1957
Consumptive u s e , daily
1.19 1.19 1.63 2.29 2.29 3.68 4.27 5.38 6.12
rnm
From
monthly
10.71 51.10 106.67
21.06.1957 01.07.1957 11.07.1957 21.07.1957 01.08.1957 11.08.1957 20.08.1957 01.09.1957 11.09.1957
To
30.06.1957 10.07.1957 10.07.1957 30.07.1957 10.08.1957 20.08.1957 31.08.1957 10.09.1957 14.09.1957
Interval days
10 10 10 11 10 10 11 10 4
Sakha
18.03.1958 21.03.1958 01.04.1958 11.04.1958 21.04.1958 01.05.1958 11.05.1958 21.05.1958 01.06.1958
El-Shala
2 11 10 10 10 10 10 11 10
10.03.1958 31.03.1958 10.04.1958 20.04.1958 30.04.1958 10.05.1958 20.05.1958 31.05.1958 10.06.1958
1.34 1.34 1.34 1.72 2.60 2.60 3.69 4.42 6.36
17.42
56.60 111.52
11.06.1958 21.06.1958 01.07.1958 11.07.1958 21.07.1958 01.08.1958 11.08.1958 21.08.1958 01.09.1958
20.06.1958 30.06.1958 10.07.1958 20.07.1958 31.07.1958 10.08.1958 20.08.1958 31.08.1958 06.09.1958
10
10 10 10 11 10 10 11 6
Sakha
3 A . El-Warithb
17.03.1958 21.03.1958 01.04.1958 17.04.1958 01.05.1958 14.05.1958 01.06.1958
Season
3
20.03.1958 31.03.1958 16.04.1958 30.04.1958 13.05.1958 31.05.1958 11.06.1958
11 16
14 13 18 11
1966;
7.11 7.54 7.67 6.74 4.18 3.35 2.10 2.10 2.10
mm
monthly
186.10 226.24 98.40 29.40
6.73 7.09 7.20 7.30 4.90 4 .OO 3.00 3.00 3.00
201.80 198.90 103.00 18.00
b = Abdel-Warith,
1.60 1.60 1.60 2.10 2.10 3.50 4.30
22.40 55 .OO 90.30
12.06.1958 01.07.1958 05.07.1958 23.07.1958 01.08.1958 10.08.1958 01.09.1958
30.06.1958 04.07.1958 22.07.1958 31.07.1958 09.08.1958 31.08.1958 14.09.1958
19 4 18 9 9 22 13
5.20 5.25 7.55 5.80 5.80 3.40 3.40
146.10 209.10 127.00 44.20
694.10 mm
180 d a y s M.I.,
daily
707.24 mm
172 d a y s
Season
Consumptive u s e ,
708.62 mm
176 d a y s
Season
a = El-Shal,
Interval days
w
Y.,
1965
TABLE 6 . 2
Sr.
No.
(continued)
Expt. S t a t . &
I n v e s t i g a t or Sakha
A.
El-Warith
b
From
To
Interval days
12.03.1960 21.03.1960 01.04.1960 12.04.1960 01.05.1960 18.05.1960 01.06.1960
20.03.1960 31.03.1960 11.04.1960 30.04.1960 17.05.1960 31.05.1960 19.06.1960
9 11 11 19 17 14 19
Season
05.03.1958 11.03.1958 21.03.1958 01.04.1958 11.04.1958 21.04.1958 (‘1.05.1958 11.05.1958 2 1.05 .1958
El-Shala
Seasou
A . El-Warithb
05.03.1958 19.03.1958 01.04.1958 03.04.1958 16.04.1958 01.05.1958
Season
a = El-Shal,
1.10 1.10 1.10 2.20 2.80 4.90 5.40
monthly 22 .oo 53.90 116.20
From
To
Interval days
20.06.1960 01.07.1960 05.07.1960 20.07.1960 01.08.1960 08.08.1960 01.09.1960
30.06.1960 04.07.1960 19.07.1960 31.07.1960 07.08.1960 31.08.1960 03.09.1960
11 4 15 12 7 24 2
10.03.1958 20.03.1958 31.03.1958 10.04.1958 20.04.1958 30.04.1958 10.05.1958 20.05.1958 31.05.1958
5 10 11 10 10 10 10 10
11
1966;
daily 6.80 6.80 7.60 5.60 5.60 3.70 3.70
mm
monthly 177.40
208.40 128.00 7.40
0.85 0.92 1.59 2.14 2.42 2.48 2.97 3.35 4.65
30.94
70.40
114.35
01.06.1958 11.06.1958 21.06.1958 01.07.1958 11.07.1958 21.07.1958 01.08.1958 11.08.1958 21.08. 1958
10.06.1958 20.06.1958 30.06.1958 10.07.1958 20.07.1958 31.07.1958 10.08.1958 20.08.1958 31.08.1958
10
10 10 10 10 11 10 10 11
6.26 6.87 7.30 7.32 6.55 5.78 4.21 3.57 2.09
204.30
202.28
100.79
723.06 mm 18.03.1958 31.03.1958 02.04.1958 15.04.1958 30.04.1958 17.05.1958
14 13 2 13 15 17
b = Abdel-Warith, M . ,
1.80 2.00 2.00 2.70 3.00 3.90
51.20 84.10
18.05. 1958 01.06 1958 15.06 1958 01.07 1958 15.07 1958 0 1 . 0 8 . 1958
31.05.1958 14.06.1958 30.06.1958 14.07.1958 31.07.1958 30.08.1958
14 14 16 14 17 30
4.50 5.30 6.40 7.30 5.90 3.47
129.30 176 .80 202.50 104.10
748.00 mm
179 days
M.I.,
Consumptive u s e ,
713.30 mm
179 days
Giza
6
daily
mm
175 days
Giza
5
Consumptive u s e ,
1965
N cn W
TABLE 6 . 2
Sr. No.
(continued)
Expt. S t a t . &
Investigator Giza
7
N
w m
A.
E l Samie & Y . Barrada'
Season Sids
El-Shala
Season Sids 9
a = El-Shal, M . I . ,
From
To
Interval days
01.03.1958 23.03.1958 01.04.1958 16.04.1958 01.05.1958 03.05.1958 19.05.1958 01.06.1958 04.06.1958
23.03.1958 31.03.1958 15.04.1958 30.04.1958 02.05.1958 18.05.1958 31.05.1958 03.06.1958 22.06.1958
23 8 15 15 2 16 13 3 19
Consumptive u s e , daily 1.0 1.0 1.0 1.8 1.8 5.5 5.4 5.4 5.5
mm
monthly
31 .OO 42 .OO
161.80
From
To
23.06.1958 01.07.1958 07.07.1958 16.07.1958 28.07.1958 01.08.1958 06.08.1958 21.08.1958 30.08.1958 01.09.1958
30.06.1958 06.07.1958 15.07.1958 27.07.1958 31.07.1958 05.08.1958 20.08.1958 29.08.1958 31.08.1958 03.09.1958
Interval days 8 6 9 12 4 5 15 9 2 3
4 10 11 10
10.03.1957 20.03.1957 31.03.1957 10.04.1957 20.04.1957 30.04.1957 10.05.1957 20.05.1957 31.05.1957
10
10 10
10 11
0.74 0.74
1.11
1.75 1.99 2.35 2.78 3.42 5.33
22.57
60.90
120.63
01.06.1957 11.06.1957 21.06.1957 01.07.1957 11.07.1957 21.07.1957 01.08.1957 11.08.1957 21.08.1957
10.06.1957 20 .06.1957 30.06.1957 10.07.1957 20.07.1957 31.07.1957 10.08.1957 20.08.1957 31.08.1957
10 10 10 10 10 11 10 10 11
4.7 4.7 7.3 10.4 10.8 10.8 6.4 3.2 3.2 3.2
mm
monthly 158.30
261.90
185 .20 9.60
6.25 7.10 7.26 7.30 6.52 5.93 5.22 3.63 2.04
206.10
203.43
110.94
724.57 mm
178 days 03.03.1958 11.03.1958 21.03.1958 01.04.1958
daily
849.80 mm
187 days 06.03.1957 11.03.1957 21.03.1957 01.04.1957 11.04.1957 21.04.1957 01.05.1957 11.05.1957 21.05 .1957
Consumptive u s e ,
7 10 11
10.03.1958 20.03.1958 31.03.1958 10.04.1958
1966; c = Abd El-Samie,
10
A.G.,
0.79 0.79 1.37 1.63
28.50
and Barrada, Y., 1960
01.06.1958 11.06.1958 21.06.1958 01.07.1958
10.06.1958 20.06.1958 30.06.1958 10.07.1958
10 10 10 10
6.12 6.90 7.63 7.33
206.50
TABLE 6 . 2
Sr. NO
-
'
(continued)
Expt. S t a t . &
Investigator El-Shala
9
From
To
Interval days
11.04.1958 21.04.1958 0 1.05.1958 11.05.1958 21.05.1958
20.04.1958 30.04.1958 10 .05 .1958 20.05.1958 31.05.1958
10 10 10 10 11
Season
A.
03.03.1958 23.03.1958 01.04.1958 09.04.1958 27.04.1958 01.05.1958 17.05.1958
El-Warith
Season
11
El-Warith
59.40
122.84
To
11.07.1958 21.07.1958 01.08.1958 11.08.1958 21.08.1958
20.07.1958 31.07.1958 10.08.1958 20.08.1958 31.08.1958
Interval days 10 11 10 10 11
22.03.1958 31.03.1958 08.04.1958 26.04.1958 30.04.1958 16.05.1958 31.05.1958
b
22.02.1959 01.03.1959 17.03.1959 01.04.1959 14.04.1959 01.05.1959 17.05.1959 28.05.1959
Season
Consumptive u s e , mm daily monthly 1.76 5.62 4.88 4.14 2.46
202.70
117.26
737.20 mm 20 9 8 18 4 16 15
1.30 2 .oo 2 .oo 2.20 3.20 3.20 5 .OO
44.00
68.40 126.20
01.06.1958 16.06.1958 01.07.1958 17.07.1958 01.08.1958 03.08.1958 01.09.1958
15.06.1958 30.06.1958 16.07.1958 31.07.1958 02.08.1958 31.08.1958 02.09.1958
15 15 16 15 2 29
183 days
Sids
A.
1.98 2.33 3.16 3.69 4.94
From
181 days
Sids
10
Consumptive u s e , mm daily monthly
6.60 5.80 7.00 5.60 5.60 3.50 3.50
186.00 196 .OO 112.70 3.50
736.80 mm 28.02.1959 16.03.1959 31.03.1959 13.04.1959 30.04.1959 16.05.1959 27.05.1959 31.05.1959
7 16 15 13 17 16 11 4
183 days
0.80 0.80 1.40 1.40 2.60 3.40 5.40 6.50
5.60 33.80 62.40
139.80
01.06.1959 07.06.1959 19.06.1959 28.06.1959 01.07.1959 06.07.1959 15.07.1959 28.07.1959 01.08.1959
06.06.1959 18.06.1959 27.06.1959 30.06.1959 05.07.1959 14.07.1959 27.07.1959 31.07.1959 23.08.1959
6 12 9 3 5 9 13 4 23
6.50 7.40 8.40 8.20 8.20 8.10 6.30 4.20 4.20
228.00
212.60 92 .OO
774.20 mm
a = E l - S h a l , M . I . , 1966;
b = Abdel-Warith,
M.,
1965
N
w
-1
TABLE 6 . 2
Sr. No.
Expt. S t a t . & Investigator Sids
12
N
(continued)
El-Shala
W
From
To
09.03.1960 11.03.1960 21.03.1960 01.04.1960 11.04.1960 20.04.1960 01.05.1960 11.05.1960 21.05.1960
10.03.1960 20.03.1960 31.03.1960 10.04.1960 20.04.1960 30.04.1960 10.05.1960 20.05.1960 31.05.1960
l3
El-Shala
22.02.1960 01.03.1960 11.03.1960 21.03.1960 01.04.1960 11.04.1960 21.04.1960 01.05.1960 11.05.1960 21.05.1960
Season
a = El-Shal, M.I.,
1 10 11 10 10 10 10 10 11
Consumptive u s e , mm daily monthly
1.06 1.06 1.06 1.51 1.63 2.70 3.29 4.37 5.05
23.32
58.40
132.15
From
To
01.06.1960 11.06.1960 21.06.1960 01.07.1960 11.07.1960 21.07.1960 01.08.1960 11.08.1960 21.08.1960
10 .06.1960 20.06.1060 30.06 .1960 10 .07.1960 20.07.1960 31.07.1960 10.08.1960 20.08.1960 31.08.1960
Interval days 10 10 10 10 10 11 10 10 11
195 davs
1966
Consumptive u s e , mm daily monthly 5.61 7.36 7.92 7.62 6.10 5.75 4.02 3.29 3.29
208.90
200.45
109.29
732. 5 1 nun
175 days
Season Ma1 lawi
Interval days
29.02.1960 10.03.1960 20.03.1960 31.03.1960 10.04.1960 20.04.1960 30.04.1960 10.05.1960 20.05.1960 31.05.1960
7 10 10 11 10 10 10 10 10 11
1.20 1.20 1.38 1.66 1.82 1.97 2.96 3.51 4.57 5.03
8.40
44.06
67.50
136.13
01.06.1960 11.06.1960 21.06.1960 01.07.1960 11.07.1960 21.07.1960 01.08.1960 11.08.1960 21.08.1960 01.09.1960
10 .06.1960 20 .06 ,1960 30 .06 .1960 10.07.1960 20 .07.1960 31.07.1960 10.08.1960 20.08.1960 31.08.1960 04.09.1960
10 10
10
10 10 11 10 10 11 4
5.84 7.72 8.26 7.72 6.48 5.73 4.35 3.43 3.33 3.28
218.20
205.03
114.43 13.12
806. 87 nun
TABLE 6.3 Sr.
No
C o n s u m p t i v e u s e of w a t e r for w h e a t i n Egypt
Expt. S t a t &
Investigator Sakha
15.11.1957 21.11.1957 01.12.1957 11.12.1957 21.12.1957 01.01.1958 11.01.1958 21.01.1958 01.02.1958 11.02.1958
El-Shala
Season
To
Interval
20.11.1957 30.11.1957 10.12.1957 20.12.1957 31.12.1957 10.01.1958 20.01.1958 31.01.1958 10.02.1958 20.02.1958
days
5 10 10 10 11 10 10 11 10 10
Consumptive u s e , mm daily monthly
1.81 1.81 1.81 1.73 1.60 1.60 1.60 1.60 1.60 1.71
27.15 53.00 49.60
From
21.02.1958 01.03.1958 11.03.1958 21.03.1958 01.04.1958 11.04.1058 21.04.1958 01.05.1958 11.05.1958
To
28.02.1958 10.03.1958 20.03.1958 31.03.1958 10.04.1958 20.04.1958 30.04.1958 10.05.1958 16.05.1958
Interval days
8 10 10 11 10 10 10
10 6
22.11.1958 01.12.1958 11.12.1958 21.12.1958 01.01.1959 11.01.1959 21.01.1959 01.02.1959 11.02.1959
El-Shala
Season
30.11.1958 10.12.1958 20.12.1958 31.12.1958 10.01.1959 20.01.1959 31.01.1959 10.02.1959 20.02.1959
9 10 10 11 10 10 11 10 10
1.79 1.79 1.79 1.70 1.63 1.63 1.63 1.68 2.27
16.11 54.50 50.53
21.02.1959 01.03.1959 11.03.1959 21.03.1959 01.04.1959 11.04.1959 21.04.1959 01.05.1959 11.05.1959
28.02.1959 10.03.1959 20.03.1959 31.03.1959 10.04.1959 20.04.1959 30.04.1959 10.05.1959 12.05.1959
8 10 10 11 10 10 10 10 2
17.11.1957 01.12.1957 19.12.1957 01.01.1958 24.01.1958 01.02.1958
d
a = El-Shal,
30.11.1957 18.12.1957 31.12.1957 23.01.1958 31.01.1958 28.02.1958
169 d a y s
Season M.I.,
2.64 2.68 3.15 3.87 2.57 2.24 2.24 1.89 1.80
54.22 100.87 70.50 29.10
2.27 2.27 2.34 2.95 2.95 2.09 1.72 1.72 1.72
57.69 78.61 67.66 20.69
345.79 mm
172 d a y s
Giza
Consumptive u s e , mm daily monthly
385.04 mm
182 d a y s
Sakha
Shahin
From
1966; d = S h a h i n , M., 1959
14 18 13 23 8 28
1.56 1.56 1.92 1.92 2.10 2.10
21.84 53.04 60.76 58 .80
01.03.1958 05.03.1958 01.04.1958 04.04.1958 01.05.1958
04.03.1958 31.03.1958 03.04.1958 30.04.1958 04.05.1958
4
27 3 27 4
2.10 2 .80 2 .80 1.70 1.70
84 .OO 54.30 6 .80
339.54 mm
TABLE 6 . 3 Sr. No.
Expt. S t a t . &
Investigator Giza
4
El-Shala
Sids
El-Shala
6 El-Shala
a = El-Shal,
Interval
To
days
10.11.1958 20.11.1958 01.12.1958 11.12.1958 21.12.1958 01.01.1959 11.01.1959 21.01.1959 01.02.1959
20.11.1958 30.11.1958 10.12.1958 20.12.1958 31.12.1958 10.01.1959 20.01.1959 31.01.1959 10.02.1959
10 10
10
10 11 10
io
11 10
Consumptive use, daily 1.91 1.91 1.88 1.58 1.58 1.58 1.66 1.70 1.70
mm
month 1y 38 .20 51.98 51.10
Interval
From
To
days
11.02.1959 21.02.1959 01.03.1959 11.03.1959 21.03.1959 01.04.1959 11.04.1959 21.04.1959 01.05.1959
20.02.1959 28.02.1959 10.03.1959 20.03.1959 31.03.1959 10.04.1959 20.04.1959 30.04.1959 10.05.1959
10 8 10 10 11 10 10 10 10
09.11.1957 01.12.1957 11.12.1957 21.12.1957 01.01.1958 11.01.1958 21.01.1958 01.02.1958
10.11.1957 10.12.1957 20.12.1957 31.12.1957 10.01.1958 20 .O 1.1958 31.01.1958 10.02.1958
1 10 10 10 10 11
I0
10 11 10
1.79 1.79 1.79 1.79 1.79 1.60 1.60 1.60 1.60 1.98
37.59 53.40
11.02.1958 21.02.1958 01.03.1958 11.03.1958 21.03.1958 01.04.1958 11.04.1958 21.04.1958 01.05.1958
20.02.1958 28.02.1958 10.03.1958 20.03.1958 31.03.1958 10.04.1958 20.04.1958 30.04.1958 09.05.1958
10 8 10 10 11 10 10 10 9
M. I., 1966
daily 1.85 2.46 2.46 2.48 2.63 2.63 2.63 2.63 1.68
mm
monthly 55.18 78.33 70.90 16.80
2.36 2.36 2.49 3.01 3.01 2.83 2.56 2.30 1.90
62.28 88.11
76.90 17.10
384.98 mm
181 days
09.11.1958 11.11.1958 21.11.1958 01.12.1958 11.12.1958 21.12.1958
Consumptive u s e ,
370.49 mm
182 days
Season Sids
1
0
From
Season
5
h3
(continued)
10.11.1958 20.11.1958 30.11.1958 10.12.1958 20.12.1958 31.12.1958
1 10 10 10 10 11
2 .oo 2 .oo 2 .oo 1.68 1.61 1.62
42 .OO 50.70
11.02.1959 21.02.1959 01.03.1959 11.03.1959 21.03.1959 01.04.1959
20.02.1959 28.02.1959 10.03.1959 20.03.1959 31.03.1959 10.04.1959
10 4 10 10 11 10
2.24 2.23 2.24 2.37 3.16 3.16
57.44 80.90
TABLE 6 . 3
Sr.
No.
6
(continued)
Expt. S t a t . &
To
Interval days
01.01.1959 11.01.1959 21.01.1959 01.02.1959
10.01.1959 20.01.1959 31.01.1959 10.02.1959
10 10 11 10
Investigator El-Shala
Season Ma11awi
7
From
El-Shala
Season
a = E l - S h a l , M.I.,
Consumptive u s e , daily 1.63 1.63 1.63 1.72
mm
monthly
50.53
From
To
11.04.1959 20.04.1959 21.04.1959 30.04.1959 01.05.1959- 08.05.1959
Interval days 10 10 8
178 days
1966
daily 2.52 1.74 1.74
mm
monthly 74.20 13.92
369.69 mm
180 days 15.11.1957 21.11.1957 01.12.1957 11.12.1957 21.12.1957 01.01.1958 11.01.1958 21.01.1958 01.02.1958 11.02.1958
Consumptive u s e ,
20.11.1957 30.11.1957 10.12.1957 20.12.1957 31.12.1957 10.01.1958 20.01.1958 31.01.1958 10.02.1958 20.02.1958
5 10 10 10 11 10 10 11 10 10
1.61 1.61 1.61 1.56 1.56 1.614 1.614 1.614 1.93 2.06
24.15 48.86 50.03
20.02.1958 01.03.1958 11.03.1958 21.03.1958 01.04.1958 11.04.1958 21.04.1958 01.05.1958 11.05.1958
28.02.1958 10.03.1958 20.03.1958 31.03.1958 10.04.1958 20.04.1958 30.04.1958 10.05.1958 12.05.1958
8 10 10 11 10 10 10 10 4
2.66 3.25 3.30 3.40 2.78 2.52 2.52 1.50 1.50
61.18 102.90 78.20 18.OO
383.22 mm
Consumptive u s e of w a t e r for l a t e maize i n Egypt
TABLE 6.4 Sr.
No.
Expt. S t a t . &
Interval days
From
To
30.07.1959 01.08.1959 11.08.1959 21.08.1959 01.09.1959 11.09.1959 21.09.1959
31.07.1959 10.08.1959 20.08.1959 31.08.1959 10.09.1959 20.09.1959 30.09.1959
Investigator Sakha
El-Shala
Season Giza
El-Shala
Season Giza
E l -Gibali Season Giza
El-Gibalie Season a = hl-Shal, M . I . ,
1 10 10 11 10 10 10
N Ip N
Consumptive u s e , mm daily monthly
3.06 3.06 3.06 4.61 5.06 6.086 6.36
3.06
111.87
175 .86
Interval From
To
01.10.1959 11.10.1959 21.10.1959 01.11.1959 11.11.1959 21.11.1959 01.12.1959
10.10.1959 20.10.1959 31.10.1959 10.11.1959 20.11.1959 30.11.1959 08.12.1959
days
10 10 11 10 10 10 8
10.08.1959 20.08.1959 31.08.1959 10.09.1959 20.09.1959 30.09.1959
8 10 11 10 10 10
2.93 2.93 4.49 5.43 6.25 6.886
102.13
185.66
01.10.1959 10.10.1959 11.10.1959 20.10.1959 21.10.1959 31.10.1959 01.11.1959 10.11.1959 11.11.1959 20.11.1959 21.11.1959 30.11.1959
10 10 11 10 10 10
27.07.1962 31.07.1962 09.08.1962 23.08.1962 31.08.1962
18 4 9 14 8
3.155 5.59 5.59 5.905 6.64
79.15
01.09.1962 12.09.1962 01.10.1962 04.10.1962
11.09.1962 30.09.1962 03.10.1962 21.10.1962
11 19 3 18
122 d a v s
53.67 8.40
6.99 6.76 4.07 2.26 1.48 1.48
182.27
52.20
6.64 3.19 3.91 3.225
147.33 58.05
186.10 470.63 mm
104 d a y s 07.07.1963 01.08.1963 11.08.1963 25.08.1963 01.09.1963
167.25
522.26 mm
120 d a y s 09.07.1962 28.07.1962 01.08.1962 10.09.1962 24.08.1962
6.67 5.006 4.59 1.936 1.936 1.495 1.05
520.11 mm
131 d a y s 02.08.1959 11.08.1959 21.08.1959 01.09.1959 11.09.1959 21.09.1959
Consumptive u s e , mm daily monthly
24 10 14 7 13
31.07.1963 10.08.1963 24.08.1963 31.08.1963 13.09.1963 ~-
1966; e = E l - G i b a l i , A . ,
1966.
3.445 3.445 4.995 6.39 6.39
82.68
149.11
14.09.1963 30.09.1963 01.10.1963 04.10.1963 05.10.1963 17.10.1963 18.10.1963 31.10.1963 Oi. 11.1963 06.11.1963
17 4 13 14 6
5.20 5.20 5.04 3.315 3.315
152.30
132.73 19.89
536.72 mm
TABLE 6 . 4 Sr.
No.
(continued)
Expt. S t a t . & Investigator Sids
To
28.07.1959 01.08.1959 11.08.1959 21.08.1959 01.09.1959 11.09.1959 21.09.1959
5
E l -Shala
31-07.1959 10.08.1959 20.08.1959 31.08.1959 10.09.1959 20.09.1959 30.09.1959
Interval days 3 10 10 11 10 10 10
Consumptive u s e , daily
mm
2.95 2.95 3.12 4.68 4.68 6.25 6.45
monthly 8.85
112.18
173.80
Sids Shenouda El-Gibali Tawdros & Gamal Season
01.10.1959 11.10.1959 21.10.1959 01.11.1959 11.11.1959 21.11.1959 01.12.1959
10 10 11 10 10 10
8
Consumptive u s e ,
mm
daily 6.52 6.26 4.73 3.36 2.19 1.15 1.04
15.07.1964 27.07.1964 01.08.1964 08.08.1964 20.08.1964 01.09.1964
monthly
179.83 67 .OO 8.32
549.98 mm 26.07.1964 31.07.1964 07.08.1964 19.08.1964 31.08.1964 12.09.1964
12 5 7 12 12 12
3.62 2.66 2.66 5.74 6.21 3.75
56.74
162.02
13.09.1964 25.09.1964 01.10.1964 07.10.1964 19.10.1964
24.09.1964 30.09.1964 06.10.1964 18.10.1964 31.10.1964
12 6 6 12 19
5.56 5.31 5.31 5.52 3.31
143.58
163.99
5 2 6 . 3 3 mm
Consumptive u s e o f w a t e r for e a r l y maize i n Egypt ~
Shenouda El-Gibali Tawdros & Gamal
a = El-Shal,
10.10.1959 20.10.1959 31.10.1959 10.11.1959 20.11.1959 30.11.1959 08.12.1959
Interval days
109. days
Sids
Season
To
From
133 days
Season
TABLE 6 . 5
From
16 04.1964 01.05.1964 07.05.1964 19.05.1964 01.06.1964
30.04.1964 06.05.1964 18.05.1964 30.05.1964 31.05.1964 11.06.1964
15 6 12 12 1 11
1.85 1.85 3.06 6.25 5.93 5.93
~~
27.75
128.75
12.06.1964 24.06.1964 01.07.1964 06 .07.1964 18.07.1964 30.07.1964 01.08.1964
= Shenouda, E l - G i b a l i ,
~
12 7 5 12 12 2 8
6.91 7.47 7.47 5.44 5.60 3.20 3.20
200.44
176.23 25.60
558.77 mm
115 days
M.I., 1966; f
23.06.1964 30.06.1964 05.07.1964 17.07 .1964 29.07.1964 31.07.1964 1 8 . 0 8 .1964
Tawdros and Gamal, 1966
L N W
Month
&
No.
Investigator Assiut
Nov. Dec. Jan. Feb. Mar.
El-Gibalig
1
Fenugreek+
1965 1965 1966 1966 1966
TABLE 6.7
Nov. 10-Mar.
Chicken p e a
+
++
E g y p t i a n Lupin
Lentil
++
daily
monthly
daily
monthly
daily
monthly
daily
monthly
1.541 2.087 1.880 2.394 1.709
30.82 64.70 58.24 67.03 12.88
1.414 1.721 1.360 1.923 0.735
28.28 53.34 42.16 53.85 8.09
1.532 2.065 1.852 2.325 1.221
30.65 64.00 57.40 65.10 18.31
1.405 1.778 1.417 1.729 0.819
28.11 55.12 43.94 53.59 12.29
Season
+ = Growth s e a s o n :
L L
Consumptive u s e , i n mm, f o r t h e c r o p s
Expt. S t a t .
Sr.
Sr. No.
N
Consumptive u s e of w a t e r f o r some w i n t e r c r o p s i n Egypt
TABLE 6.6
233.67 11; ++ = Growth s e a s o n :
185 .72
235.46
193.05
Nov. 10-Mar. 15
Consumptive u s e of w a t e r f o r Berseem ( E g y p t i a n c l o v e r ) i n Egypt
Expt. S t a t . &
From
To
Interval days
10.11.1957 28.11.1957 01.12.1957 22.12.1957 01.01.1958 01.02.1958 07.02.1958 17.02.1958
27.11.1957 30.11.1957 2 1.12.1957 31.12.1957 31.0 1.1958 06.02.1958 14.02.1958 26.02.1958
17 3 21 10 31 6 8 10
Investigator Giza
Shahin
d
Season
Consumptive u s e , mm daily monthly
1.82 2.15 2.50 1.45 0.80 0.45 1.65 3.15
37.39 67 .OO 24.80
From
To
Interval days
27.02.1958 01.03.1958 28.03.1958 01.04.1958 07.04.1958 15.04.1958 01.05.1958
28.02.1958 27.03.1958 31.03.1958 06.04.1958 16.04.1958 30.04.1958 07.05.1958
2 27 4 6 10 16 7
214 days ( n o r e c o r d s w e r e a v a i l a b l e between O c t . 15 and Nov. 10)
g = E l - G i b a l i , M.H., 1969; d = S h a h i n , M . ,
1959
Consumptive u s e , daily
3.50 3.95 2.80 2.50 4.10 4.35 1.85
mm
monthly
57.70 117.85
117.40 12.95
435.09 mm
TABLE 6 . 7
Sr. No.
(continued)
Expt. S t a t . &
Investigator Sids
El-Shala
Season
TABLE 6 . 8 Sr.
No.
To
20.10.1957 01.11.1957 11.11.1957 21.11.1957 01.12.1957 11.12.1957 21.12.1957 01.01.1958 11.01.1958 21.01.1958 01.02.1958 11.02.1958
31.10.1957 10.11.1957 20.11.1957 30.11.1957 10.12.1957 20.12.1957 31.12.1957 10.01.1958 20.01.1958 31.01.1958 10.02.1958 20.02.1958
11 10 10 10 10 10 11 10 10 11 10
Consumptive u s e , daily
mm
1.564 1.564 1.530 1.526 2.047 2.068 2.261 1.659 0.757 0.757 1.229 1.700
monthly 17.204
46.200
66.021
32.487
From
To
21.02.1958 01.03.1958 11.03.1958 21.03.1958 01.04.1958 11.04.1958 21.04.1958 01.05.1958 11.05.1958 21.05.1958 01.06.1958
28.02.1958 10.03.1958 20.03.1958 31.03.1958 10.04.1958 20.04.1958 30.04.1958 10.05.1958 20.05.1958 31.05.1958 07.06.1958
Interval days 8 10 10
11
10 10 10 10 10 11 7
Consumptive u s e , daily
mm
monthly
1.821 2.671 2.671 4.953 4.433 3.859 4.337 4.165 4.091 2.940 1.558
43.858
107.903
126.290
114.900 10.906
565.769 mm
230 days
Consumptive use of w a t e r f o r c i t r u s t r e e s i n Egypt
Expt. S t a t .
From
&
Investigator Giza
1
Interval days
From
d Shahin
Interval
To
days
,
01.01.1957 01.02.1957 01.03.1957 17.03.1957 01.04.1957 29.04.1957 01.05.1957 29.05.1957 01.06.1957
31.01.1957 28.02.1957 16.03.1957 31.03.1957 28.04.1957 30.04.1957 28.05.1957 31.05.1957 12.06.1957
a = E l - S h a l , M . I . , 1966; d = S h a h i n , M . ,
1959
31 28 16 15 28 2 28 3 12
Consumptive u s e , mm daily monthly 0.72 1.47 2.25 2.35 2.81 2.87 2.87 3.43 3.53
22.32 41.16 71.25 84.42 90.65
From
To
03.07.1957 22.07.1957 01.08.1957 07.08.1957 01.09.1957 23.09.1957 01.10.1957 09.10.1957 01.11.1957
21.07.1957 31.07.1957 06.08.1957 31.08.1957 22.09.1957 30.09.1957 08.10.1957 31.10.1957 26.11.1957
Interval days 19 10 6
25 22 8 8 23 26
Consumptive u s e , daily 3.93 3.91 3.91 3.82 3.50 3.41 3.41 2.80 2.33
mm
monthly
121.25 118.96 104.28 91.68
TABLE 6 . 8
Sr. No.
N D b
(continued)
Expt. S t a t . &
Investigator d Shahin
m
From
To
13.06.1957
30.06.1957 0 2 .07.19 57
0 1.07.1957
Interval days 18 2
Consumptive u s e , daily 3.74 3.74
mm
monthly 109 .68
From
To
27.11.1957 01.12.1957
30.11.1957 31.12.1957
Interval days 4 31
01.01.1958 01.02.1958 01.03.1958 04.03.1958 01.04.1958 01.05.1958 09.05.1958 28.05.1958 01.06.1958 16.06.1958
Giza
d Shahin
31.01.1958 28.02.1958 03.03.1958 31.03.1958 30.04.1958 08.05.1958 27.05.1958 31.05.1958 15.06.1958 30.06.1958
31 28 3 28 30 8 19 4 15 15
0.91 1.38 1.38 2.17 2.40 2.72 3.48 3.50 3.58 3.62
28.21 38.64 64.90 72.00 101.88 108 .OO
01.07.1958 07.07.1958 0 1.08.1958 27.08.1958 01.09.1958 10.09.1958 0 1.10.1958 09.10.1958 01.11.1958 01.12.1958
06.07.1958 31.07.1958 26.08.1958 31.08.1958 09.09.1958 30.09.1958 08.10.1958 31.10.1958 30.11.1958 31.12.1958
6 25 26 5
9 21
8 23 30 31
2.06 1.72
mm
monthly 68.82 53.32
3.68 3.86 3.77 3.58 3.50 3.36 3.36 2.93 2.15 1.79
118.58 115.92 102.06 94.27 64.50 55.49
964.45 mm
Annual Delta Barrage
El-Nokrashy
daily
977.77 mm
Annual
2
Consumptive use,
h
01.01.1959 01.02.1959 15.02.1959 01.03.1959 07.03.1959 28.03.1959 01.04.1959 19.04.1959 01.05.1959 19.05.1959 30.05.1959 01.06.1959
31.01.1959 14.02.1959 28.02.1959 06.03.1959 27.03.1959 31.03.1959 18.04.1959 30.04.1959 18.05.1959 29.05.1959 31.05.1959 13.06.1959
31 14 14 6 21 4 18 12 18 11 2 13
1.59 1.59 2.12 2.12 2.53 2.62 2.62 5.30 3.74 6.07 4.48 4.48
49.29 51.64 76.33 110.76 143.08
11.07.1959 27.07.1959 01.08.1959 10.08.1959 23.08.1959 01.09.1959 06.09 .1959 21.09.1959 01.10.1959 06.10.1959 21.10.1959 01.11.1959
26.07.1959 31.07.1959 09.08.1959 22.08.1959 31.08.1959 05.09.1959 20.09.1959 30.09.1959 05.10.1959 20.10.1959 31.10.1959 09.11.1959
16 5 9 13 9 5 15 10 5 15 11 9
4.22 4.57 4.57 3.65 3.34 3.34 2.86 3.02 3.02 2.28. 1.53 1.53
142.35 118.59 89.80 74.83
(continued)
TABLE 6 . 8
~~
Sr. No.
Expt. S t a t .
Interval
From
&
To
Investigator E l -Nokrashy
h
14.06.1959 26.06.1959 27.06.1959 30.06.1959 01.07.1959 10.07.1959
days
13 4 10
Consumptive u s e , mm daily monthly
5.10 5.20 5.20
197.44
Interval
From
To
10.11.1959 30.11.1959 01.12.1959 24.12.1959 25.12.1959 31.12.1959
days
21 24 7
1.29 0.625 1.59
40.86 26.13
1121.10 mm
Annual Delta Barrage
E 1-Nokrashy
Consumptive u s e , mm daily monthly
h
01.01.1961 01.02.1961 07.02.1961 01.03.1961 07.03.1961 01.04.1961 22.04.1961 01.05.196 1 08.05.1961 19.05.1961 01.06.1961 13.06.1961 25.06.1961 01.07.1961 07.07.1961
Annual
h = El-Nokrashy, M . A . ,
31.01.1961 06.02.1962 28.02.1961 06.03.1961 31.03.1961 21.04.1961 30.04.1961 07 .05.1961 18.05.1961 31 .05.1961 12.06.1961 24.06.1961 30.06.1961 06.07.1961 18.07.1961
31 6 22 6 25 21 9 7 11 13 12 12 6 6 12
1.42 1.42 2.02 2.02 2.77 2.81 4.07 4.07 6.70 6.07 4.35 5.31 5.27 5.27 4.64
44.02 52.56 81.37 95.64
181.10
149.54
19.07.1961 01.08.1961 13.08.1961 25.08.196 1 01.09.1961 07.09.1961 19.09.1961 01.10.1961 21.10.1961 0 1.11.196 1 06.11.1961 26.11.1961 01.12.1961 26.12.1961
31.07.1961 12.08.1961 24.08.1961 31.08.1961 06.09.1961 18.09.1961 30.09.1961 20.10.1961 31.10.1961 05.11.1961 25.11.1961 30.11.1961 25.12.1961 31.12.1961
13 12 12 7 6 12 12 20 11 5 20 5
25 6
4.14 3.84 4.22 3.33 3.33 3.79 2.53 1.60. 1.88 1.88 1.50 0.80 0.80 1.42
141.10
120.03
95.82 52.68
43.40 28.52
1085 .80 m m
1963
P N
4
248
The c o n s u m p t i v e u s e d a t a l i s t e d i n T a b l e s 6 . 2 t h r u ' 6 . 8 , t o g e t h e r w i t h t h e Same t y p e o f d a t a f o r o t h e r c r o p s n o t i n c l u d e d i n t h i s s u r v e y , s h o u l d , no d o u b t , form t h e b a s i s o f t h e i r r i g a t i o n r e q u i r e m e n t s f o r a g r i c u l t u r e i n E g y p t . B e f o r e u n d e r t a k i n g t h i s s t e p , i t was f e l t n e c e s s a r y t o compare t h e s e d a t a w i t h t h e u s e r e q u i r e m e n t s f o r t h e same k i n d o f c r o p s r a i s e d o u t s i d e Egypt u n d e r more o r less
s i m i l a r c l i m a t i c and s o i l c o n d i t i o n s . Comparison may, however, b e e x t e n d e d t o c o n s u m p t i v e u s e r e q u i r e m e n t s f o r t h e same c r o p s i n Egypt as o b t a i n e d by o t h e r methods whenever n e e d e d . The d a t a i n T a b l e 6 . 2 h a v e b e e n u s e d f o r d e v e l o p i n g t h e consumptive u s e c u r v e s f o r c o t t o n i n Sakha, n o r t h e r n c e n t r a l p a r t o f t h e Delta, Giza, apex of t h e D e l t a , and S i d s and M a l l a w i , Middle Egypt ( S h a h i n , M . ,
and E l - S h a l ,
M.I.,
1 9 6 9 ) . T h e s e c u r v e s a r e shown i n F i g . 6 . 8 a . By n e g l e c t i n g t h e d i f f e r e n c e s i n w a t e r u s e produced m a i n l y by t h e d i f f e r e n c e s i n t e m p e r a t u r e , l e n g t h o f growing s e a s o n , d e p t h t o w a t e r t a b l e , f e r t i l i z e r s , and f r e q u e n c y and q u a n t i t y o f i r r i g a t i o n a p p l i c a t i o n s , one c a n i m m e d i a t e l y see t h a t F i g . 6 . 8 a . t o Fig. 6.8b.
i s q u i t e comparable
f o r Mesa and Tempe A r i z o n a , a s g i v e n by E r i e ( 1 9 6 3 ) , and t o
F i g . 6 . 8 ~ .f o r t h e s o u t h e r n p a r t o f B u l g a r i a ( S h a h i n , M . ,
e t a l , 1973).
O l i v i e r e s t i m a t e d t h e c o n s u m p t i v e u s e o f w a t e r f o r c o t t o n as f o l l o w s ( 1 9 6 1 ) : Growing s e a s o n Location
to
from
Station
Seasonal consumptive u s e ,
mm
Lower Egypt ( N i l e Delta and G i z a )
2 0 . 2 . -10.4
2 0 . 8 . - l o . 11
Middle Egypt ( f r o m G i z a t o Assiut)
20.2.-05.4
5.8.-20.10
Assiut
1085
Upper Egypt ( f r o m A s s i u t t o s o u t h e r n b o r d e r of Egypt)
2 0 . 2 , -05.4
5 . 8 . -15.10
Aswan
1465
Giza
7 10
T h e s e v a l u e s were o b t a i n e d from h i s f o r m u l a
cu $ = c x
LO
where C
= a v e r a g e d e p r e s s i o n o f wet-bulb
L0/L2
= cyclic (radiation/latitude) by O l i v i e r (1961)
).
i n OC f o r a p a r t i c u l a r month, and
f a c t o r f o r t h e p a r t i c u l a r month ( t a b u l a t e d
249
8 7 -
6
-
Sakha S t a t .
5 -
4 3 2 1 -
OL
Feb.
I
Apr.
Mar.
May
Jun.
Jul.
Aug.
Sep.
Jun.
Jul.
Aug.
Sep.
1
Month
, Feb.
I
I
Apr.
Mar.
May
A-
-*-
Month
9,
I
1
-X-
I
I
-v-0-
-3-
2 vy
5 4 -
3 -
"0
A
.&%@
2 1
1
I
Feb.
Apr.
Mar.
May
y +
I
I
Jun.
I
Aug.
Jul.
1957 1958 1958 1959 1959 1960
Sep
Month
0'
Feb.
I
,
I
I
Mar.
I
Apr.
I
I
I
May
I
Jun.
I
Jul.
I
I
Aug.
Sep.
Month Fig. 6.8a. Consumptive u s e o f water f o r c o t t o n a t some l o c a t i o n s i n Egypt (Shahin, M . , and E l - S h a l , M . I . , 1969)
250
h
s!
0.4
.
a!
'0
blossoms u s u a l l y matur
L
.- 0.3
.-C
$ 0.2
First
3 al
.> c
1
0.1
L1
5
+
b l ossorn
1
Seasonal
1
1
use 41.2"
g 0.0
0
Fig. 6.8b. Mean consumptive use f o r c o t t o n a t Mesa and Tempe, Arizona, 1954-1962 ( E r i e , L . J . , 1963)
80
LEGEND 1965 o 1964 3 1963 -.X 1962 _..+
70
----
.?A-
60 50 40
30 20
10
O
'
16 2 0
Apr.
& 16 20 31 lb ioo; May
Jun.
o;
Zb 31
Jul.
10 20 31 10
Aug.
o; o;
Sep.
16
2;
Oc!.
F i g . 6 . 8 ~ . Consumptive u s e for c o t t o n i n t h e southern p a r t of B u l g a r i a (Shahin, M., e t a l , 1973)
25 1
The f i g u r e o b t a i n e d by O l i v i e r f o r Lower Egypt and G i z a i s e x a c t l y l i k e t h a t g i v e n i n T a b l e 6 . 2 . The f i g u r e f o r M a l l a w i c a n b e compared t o t h e a v e r a g e of t h e consumptive use a t G i z a and A s s i u t . T h i s g i v e s a f i g u r e a l m o s t 10% l a r g e r t h a n t h e measured w a t e r u s e by c o t t o n a t M a l l a w i . The f i g u r e s o b t a i n e d from O l i v i e r ' s method f o r wheat a r e as f o l l o w s : Growing s e a s o n
Location Lower Egypt Middle Egypt Upper Egypt
From
To
25.10 10.10 5.10-30.11
15.5 20.4 10.4-10.5
Station
Seasonal consumptive u s e , mm
Giza Assiut Aswan
400 472 800
The f i g u r e s o b t a i n e d by O l i v i e r are a b o u t 8% and 10% l a r g e r t h a n t h e f i g u r e s i n T a b l e 6 . 3 f o r wheat a t G i z a and M a l l a w i r e s p e c t i v e l y . The c o n s u m p t i v e u s e f o r wheat a t D u j a i l a h e x p e r i m e n t a l s t a t i o n , I r a q , was d e t e r m i n e d by means o f t h e w a t e r - b a l a n c e method. The s e a s o n a l w a t e r u s e i s 485 mm w i t h a p r o b a b l e e r r o r o f from 10 t o 20% ( h u m a n s , J . H . ,
e t a l , 1 9 6 3 ) . The
d a i l y consumptive u s e from t h i s e x p e r i m e n t s t a t i o n i s p l o t t e d v e r s u s t h e t i m e d u r i n g g r o w t h , s o as
t o compare i t w i t h t h e c h a r a c t e r i s t i c u s e c u r v e s d e r i v e d
from t h e d a t a i n T a b l e 6 . 3 . F i g s 6 . 9 a and 6 . 9 b show t h e c h a r a c t e r i s t i c c u r v e s f o r Egypt and I r a q , r e s p e c t i v e l y . I n order t o i l l u s t r a t e the e f f e c t s of the moisture level i n the s o i l , the q u a n t i t y of f e r t i l i z e r s on t h e e v a p o t r a n s p i r a t i o n f o r wheat and t h e w a t e r u s e e f f i c i e n c y , Haise, R . ,
and V i e t s , F . , have u s e d u n p u b l i s h e d d a t a from Marvin
E . J e n s e n , A m a r i l l o e x p e r i m e n t s t a t i o n , USDA, B u s h l a n d , T e x a s , f o r t h e p e r i o d
1955-1956
( 1 9 5 7 ) . These d a t a a r e p r e s e n t e d i n T a b l e 6 . 9 . The i n t e r e s t i n g f e a t u r e
a b o u t t h e f i g u r e s i n t h i s t a b l e is t h a t e x p e r i m e n t M - 1 was r u n under i r r i g a t i o n c o n d i t i o n s v e r y s i m i l a r t o t h o s e i n Egypt b e f o r e t h e c o n s t r u c t i o n of t h e High Aswan D a m . The i r r i g a t i o n p r a c t i c e t h e n w a s t o s t o p i r r i g a t i n g t h e w i n t e r c r o p s f o r 6 weeks,
from 25 December t o 5 F e b r u a r y e a c h y e a r . T h i s p e r i o d was known as
the winter closure of canals.
I n t h e post-dam c o n d i t i o n , i . e . from 1965 and
onwards, t h e d u r a t i o n o f t h e c a n a l c l o s u r e w a s r e d u c e d t o a b o u t 3 weeks. From t h a t e x p e r i m e n t , w e see t h a t t h e a v e r a g e consumptive u s e f o r wheat under t h e t h r e e d i f f e r e n t n i t r o g e n t r e a t m e n t s i s a b o u t 500 mm f o r t h e s e a s o n . T h i s f i g u r e
i s v e r y c l o s e t o t h e one o b t a i n e d by O l i v i e r f o r A s s i u t i n t h e s o u t h e r n p a r t o f Middle E g y p t . I t a l s o a g r e e s f a i r l y w e l l w i t h t h e r e s u l t o b t a i n e d from t h e D u j a i l a h e x p e r i m e n t s t a t i o n i n I r a q . The e s t i m a t e o f t h e s e a s o n a l w a t e r u s e by t h e i n d i a n c o r n and Dura maize r a i s e d i n Lower Egypt ( f r o m 5 . 7 - 3 0 . 8
t o 15.10-
3 0 . 1 1 ) u s i n g t h e O l i v i e r method, i s 350 mm. The same method g i v e s a s e a s o n a l consumption o f 950 mm by f l o o d sorghum r a i s e d a t Aswan ( f r o m 2 0 . 8 t o 1 5 . 1 2 ) .
252
4
I
I
I
0'
I
I
I
1 1
x
. 0
E E
-0-
-x-
1957 -1958 1958 -1959
al !A
1
,
01 c
Q
5 C
0 J
I
I
I
I
1
I
I
I
_ _ _ _ _ _ ~ ~ ~
Nov
Dec
Jan
Feb
Mar
Apr
May
Month Fig. 6 . 9 a . Consumptive use o f water f o r wheat a t some l o c a t i o n s i n Egypt ( S h a h i n , M . , and E l - S h a l , M . I . , 1 9 6 9 )
.5 . 0 Q 77
I
I
I
E
4.0
measurements! o pped
al
111
3.0
al
.->
E
3
g
a
0
2.0 1.0
N o v . Dec. 1957
I
I
Jan
I
I
Feb
Mar
I
Apr.
May
1958
Fig. 6.9b. Consumptive u s e of w a t e r f o r wheat a t D u j a i l a h , I r a q (Boumans, J . H . , e t a l , 1963)
25 3
TABLE 6 . 9
Evapotranspiration (ET)
and w a t e r u s e e f f i c i e n c y (W.U.E.)
of winter
wheat f o r v a r i o u s n i t r o g e n and m o i s t u r e l e v e l s ( H a i s e , H . R . .
Viets, F.G.,
Nitrogen app 1i e d lbs/acre 0
80 120
and
1957) Moisture level*
M-1
M- 3
M-2
M-4
ET, in
W.U.E. bu/in
ET, in
W.U.E. bu/in
ET, in
W.U.E. bu/in
ET, in
W.U.E. bu/in
19.4 19.7 20.3
0.87 0.92 0.86
21.6 24.2 23.9
1.03 1.08 1.18
22.9 24.8 28.3
1.28 1.67 1.51
23.6 30.4 30.2
1.42 1.51 1.74
*M-I: NO s p r i n g a p p l i c a t i o n M-2: One 4 - i n c h a p p l i c a t i o n a t j o i n t i n g s t a g e , March 28 M-3: One 4 - i n c h a p p l i c a t i o n p r i o r t o b o o t s t a g e , A p r i l 16 and a 4 - i n c h a p p l i c a t i o n a t t h e f l o w e r i n g s t a g e , May 1 5 M-4: One 4 - i n c h a p p l i c a t i o n a t j o i n t i n g s t a g e , March, 2 8 ; one 4 - i n c h a p p l i c a t i o n a t e a r l y b o o t s t a g e , A p r i l 3 0 , and a 4 - i n c h a p p l i c a t i o n j u s t a f t e r f l o w e r i n g , May 15
The d a t a l i s t e d i n T a b l e s 6 . 4 and 6 . 5 f o r l a t e c o r n and e a r l y c o r n a r e p r e s e n t e d g r a p h i c a l l y i n F i g s . 6 . 1 0 a and 6 . 1 1 a , r e s p e c t i v e l y . F i g . 6 . 1 0 a can be compared t o F i g , 6 . 1 0 b f o r z e a maize grown i n C e n t r a l C a l i f o r n i a (FAO, 1 9 7 1 ) . The l a t t e r consumes s e a s o n a l l y 500 mm which i s a b o u t 5% l e s s t h a n t h e c o r r e s p o n d i n g f i g u r e f o r Sakha and G i z a s t a t i o n s , where t h e c l i m a t i c c o n d i t i o n s a r e a l m o s t i d e n t i c a l . Moreover, t h e c o n s u m p t i v e u s e f o r sorghum a t Mesa, A r i z o n a ( f r o m J u l y t o O c t o b e r ) a s found by H a r r i s and c o m p i l e d by Blaney (1957) i s 2 0 . 4 i n c h e s o r 520 mm f o r t h e s e a s o n . T h i s f i g u r e i s i n f u l l agreement w i t h o u r s f o r t h e s t r e t c h from Sakha t o S i d s . The r e s u l t s o b t a i n e d by H a r r o l d , L . L . ,
and
D r e i b e l b i s , F . R . , ( 1 9 5 9 ) a b o u t e v a p o t r a n s p i r a t i o n from a l y s i m e t e r 8 . 4 m 2 i n s u r f a c e a r e a n a a r C o s h o c t o n , O h i o , r a i s i n g c o r n i n t h e p e r i o d from May t o O c t o b e r a r e shown g r a p h i c a l l y i n F i g . 6 . 1 1 b . T h i s f i g u r e can b e compared t o F i g . 6 . 1 1 a showing t h e u s e f o r e a r l y c o r n a t S i d s , Middle EgyDt. The a v e r a g e e v a p o t r a n s p i r a t i o n from t h e l y s i m e t e r for t h e two y e a r s 1949 and 1953 i s 570 mm p e r s e a s o n . The c o r r e s p o n d i n g s e a s o n a l u s e a t S i d s i n 1964 was 558 m m . The cons u m p t i v e u s e f o r c o r n h a s been r e p o r t e d by B l a n e y , H . F . , and C r i d d l e , W . D . , ( 1 9 6 6 ) as 4 4 0 , 525 and 740 mm/season f o r D a v i s , C a l i f o r n i a , Manden, N . Dakota, and R e d f i e l d . S . D a k o t a .
254
$ 8
.
U
E 6
Explanation
$ 4
1
Y 2
0
1959
x
1962
+
1963
c
a E O
0'
Jul
Aug
Sep.
Oct.
Nov
Dec
I
Month
Fig. 6.10a. Consumptive u s e o f w a t e r f o r l a t e c o r n at some l o c a t i o n s i n Egypt ( S h a h i n , M . , and E l - S h a l , M.I., 1969)
0
F i g . 6.10b. (FAO, 1971)
Month
Consumptive u s e of w a t e r f o r z e a m a i z e a t C e n t r a l C a l i f o r n i a
255
Apr
V
May
Jun
Aug
Jul
Month
Fig. 6.11a. Consumptive u s e o f w a t e r f o r e a r l y c o r n a t S i d s , Egypt (Shenouda, E l - G i b a l i , Tawdros and Gamal, 1966).
e
May
Jun.
0 V
Jul. Month
Aug.
1
Sep.
Fig. 6.11b. Consumptive u s e o f w a t e r f o r c o r n from a l y s i m e t e r n e a r Coshoctcil, Ohio ( H a r r o l d , L . L . , and D r e i b e l b i s , F . R . , 1959)
The s t r a n g e s t f i g u r e s f o r water u s e by c o r n ( m a i z e ) f o r Egypt one c a n meet a r e t h o s e o b t a i n e d by Doorenbos and P r u i t t (1977). The e s t i m a t e d f i g u r e s a r e b a s e d on t h e c l i m a t o l o g i c a l d a t a o f C a i r o , which i s v e r y c l o s e t o G i z a s t a t i o n . Using t h e i r own method, t h e y came up w i t h t h e f o l l o w i n g monthly and s e a s o n a l (mid-May t o mid-September)
figures:
May
June
July
August
September
S e a s o n , mm
50 50
150 170
310 340
255 280
70 70
855 9 10
These e s t i m a t e s a r e c e r t a i n l y t o o h i g h and need t o b e r e d u c e d by a b o u t 35%. F u r t h e r m o r e , t h e y c o n t r a d i c t t h e r a n g e o f v a l u e s g i v e n i n t h e same r e f e r e n c e . The s e a s o n a l consumptive u s e r a n g e s from 400 t o 750 and f o r sorghum from 300 t o 650 mm.
The a u t h o r does n o t i n t e n d t o condemn t h e method Doorenbos and P r u i t t
have d e v e l o p e d f o r e s t i m a t i n g t h e e v a p o t r a n s p i r a t i o n , b u t t h e c r o p c o e f f i c i e n t s ,
256 a t l e a s t f o r some o f t h e c r o p s , undoubtedly need d r a s t i c c h a n g e s . The consumptive u s e c u r v e o f berseem as shown i n F i g . 6 . 1 2 a , h a s an u n d u l a t i n g s h a p e which c o n s i s t s of a number of c o n n e c t e d c u r v e s , e a c h h a v i n g a b a s e w i d t h e q u a l t o t h e t i m e i n t e r v a l between two c o n s e c u t i v e c u t t i n g s . The number o f c u t t i n g s d u r i n g t h e growing s e a s o n i s u s u a l l y t h r e e t o f o u r , a f t e r which t h e l a n d r a i s i n g berseem i s l e f t f o r s e e d d e v e l o p i n g . The marked d e c l i n e i n t h e
*
w a t e r use by t h i s c r o p d u r i n g J a n u a r y and F e b r u a r y i s c a u s e d , i n a d d i t i o n t o t h e low t e m p e r a t u r e and t h e f i r s t c u t t i n g of t h e c r o p , by t h e w i n t e r c l o s u r e a l r e a d y mentioned i n c o n n e c t i o n w i t h t h e consumptive u s e f o r w h e a t . As berseem c u l t i v a t i o n i s c o n f i n e d t o a r a t h e r l i m i t e d number o f c o u n t r i e s , one c a n h a r d l y f i n d any i n f o r m a t i o n a b o u t i t s u s e o f water i n t h e l i t e r a t u r e o f a g r i c u l t u r a l h y d r o l o g y . The r e s u l t s o b t a i n e d from e x p e r i m e n t s on berseem i r r i g a t i o n u s i n g s a l i n e w a t e r i n T u n i s i a (Combremont,
R.,
1972) a r e p r e s e n t e d i n F i g . 6 . 1 2 b . T h e r e , t h e
growing s e a s o n o f berseem is a b o u t 30 d a y s s h o r t e r t h a n t h a t i n E g y p t . The c r o p s e a s o n a l u s e o f water i s 530 nun i n T u n i s i a and 570 nun i n t h e c e n t r a l p a r t o f Middle Egypt.
7J -2.53
E E . l
5 0
I
Oct.
Nov
Dec
Jon
Feb
Mar
May
Apr
Jun
Month Fig. 6.12a. Consumptive u s e o f w a t e r f o r berseem a t two l o c a t i o n s i n Middle Egypt ( S h a h i n , M . , and E l - S h a l , M . I . , 1969)
.
E E 6
c
Oct
V
rig. 6 . 1 2 b .
1972)
Nov
Dec
Jon
Feb
Mar
I
Apr
,
May
I
Jun.
Month Consumptive u s e of water f o r berseem a t T u n i s i a (Cambremont.
R.,
25 7 The d a t a l i s t e d i n T a b l e 6 . 8 are p r e s e n t e d g r a p h i c a l l y , a s shown i n F i g . 6 . 1 3 a . Using t h e c l i m a t o l o g i c a l d a t a o f C a i r o and t a k i n g t h e c r o p c o e f f i c i e n t by Doorenbos and P r u i t t f o r c i t r u s t r e e s , which a r e c l e a n c u l t i v a t e d and p r o v i d e a l m o s t 50% ground c o v e r , one c a n o b t a i n c u r v e (1) shown i n F i g . 6 . 1 3 b . The a n n u a l consumption o f t h e s p e c i f i e d o r a n g e t r e e s u s i n g t h i s method amounts t o 1215 nun. T h i s f i g u r e i s n e a r l y 17% l a r g e r t h a n t h e a v e r a g e w a t e r u s e by t h e same c r o p r a i s e d i n t h e D e l t a b a r r a g e a r e a and G i z a s t a t i o n . The consumptive use o f w a t e r f o r o r a n g e s r a i s e d i n t h e S a l t R i v e r V a l l e y i n USA i s p r e s e n t e d by c u r v e ( 2 ) i n F i g . 6 . 1 3 b . T h i s c u r v e compares f a i r l y w e l l w i t h t h e two c u r v e s shown i n F i g . 6 . 1 3 a .
I
. GIZA
2
STAT
.a;b--o
*-0-
O0
+
I
+ '
-+o
1
Uo-+.*
+-,p4t-
5 3 -
+ . o
C
3
O----3<
1 *-;I
I
,
I
Fig. 6.13a. Consumptive u s e o f w a t e r f o r c i t r u s t r e e s a t t h e D e l t a b a r r a g e a r e a (El-Nokrashy, M . A . , 1963) and a t G i z a s t a t i o n , Egypt ( S h a h i n , M . , 1959)
.
C
0 V
Month
Fig. 6.13b. Consumptive u s e o f w a t e r f o r c i t r u s t r e e s , (1) e s t i m a t e d from t h e c l i m a t o l o g i c a l d a t a o f C a i r o , E g y p t , u s i n g t h e method o f Doorenbos and P r u i t t (1977) and ( 2 ) measured a t t h e S a l t R i v e r V a l l e y , USA ( C r i d d l e , K . D . , H a r r i s , K . , and K i l l i a r d s o n , L . S . , 1962)
258
The d a t a p r e s e n t e d i n t h i s s e c t i o n , though n o t r e p r e s e n t i n g t h e consumptive
u s e o f w a t e r f o r a l l c r o p s r a i s e d i n E g y p t , do r e p r e s e n t t h e w a t e r u s e by t h e major c r o p s which c o v e r t h e l a r g e s t a r e a s of t h e a g r i c u l t u r a l l a n d t h e r e . These c r o p s , t o g e t h e r w i t h r i c e and s u g a r c a n e , a r e c e r t a i n l y t h e l a r g e s t consumers o f the i r r i g a t i o n water. The q u e s t i o n t h a t a r i s e s h e r e i s w h e t h e r t h e d a t a l i s t e d i n T a b l e s 6 . 2 t h r u ' 6 . 8 r e p r e s e n t t h e a c t u a l e v a p o t r a n s p i r a t i o n o r whether they r e p r e s e n t t h e potent i a l o n e . B e f o r e a n s w e r i n g t h i s q u e s t i o n , one h a s t o remember t h a t t h e s e d a t a have been d e r i v e d from t h e s o i l m o i s t u r e c h a n g e s i n t h e e x t r a c t i o n zone where t h e m o i s t u r e c o n t e n t u s e d t o r e a c h t h e f i e l d c a p a c i t y 2 t o 3 days a f t e r i r r i g a t i o n a p p l i c a t i o n and n o t t o f a l l below t h e l o w e r l i m i t o f t h e r e a d i l y a v a i l a b l e moisture j u s t b e f o r e t h e next i r r i g a t i o n a p p l i c a t i o n . I n o t h e r words, two-thirds o f t h e a v a i l a b l e m o i s t u r e ( f i e l d c a p a c i t y minus permanent w i l t i n g p o i n t ) have been consumed i n e v e r y i r r i g a t i o n c y c l e . The p r o p o s e d c o n c e p t s a b o u t t h e r e l a t i o n between t h e a c t u a l e v a p o t r a n s p i r a t i o n ,
ET,,
and t h e p o t e n t i a l e v a p o t r a n s -
a g a i n s t t h e s o i l m o i s t u r e c o n t e n t have been reviewed by Tanner P' ( 1 9 6 7 ) and summarized a s shown i n F i g . 6 . 1 4 .
p i r a t i o n , ET
The a v a i l a b l e measurements o f t h e s o i l m o i s t u r e change d u r i n g an i r r i g a t i o n c y c l e u n d e r t h e d i f f e r e n t i r r i g a t i o n , c r o p and c l i m a t i c c o n d i t i o n s show s u c h a wide s c a t t e r t h a t t h e d e r i v a t i o n of a s i n g l e and c o n s i s t e n t r e l a t i o n s h i p between and t h e m o i s t u r e c o n t e n t i n t h e r a n g e o f t h e r e a d i l y a v a i l a b l e m o i s t u r e a p i s h a r d l y p o s s i b l e . N e v e r t h e l e s s t h e r e i s s t r o n g e v i d e n c e t h a t t h e r a t i o E T /ET a P i s e q u a l t o u n i t y i n t h e u p p e r t h i r d o f t h e r a n g e o f t h e a v a i l a b l e m o i s t u r e . The
ET / E T
s c a t t e r of t h e p o i n t s r e p r e s e n t i n g E T /ET versus moisture i n t h e middle-third a p c a n b e f i t t e d more or less by a s t r a i g h t l i n e . T h i s l i n e c o n n e c t s t h e upper l i m i t o f t h e m i d d l e - t h i r d a t E T /ET = 1 w i t h t h e lower l i m i t o f t h e same onea p t h i r d p o r t i o n o f t h e a v a i l a b l e m o i s t u r e a t ET / E T 2 0 . 5 . This l i n e is indicated a p within the i r r i g a t i o n a s b-c i n F i g . 6 . 1 4 . I n o t h e r w o r d s , t h e change i n E T / E T a P c y c l e c a n b e v e r y a p p r o x i m a t e l y r e p r e s e n t e d by t h e b r o k e n l i n e a b c . T h i s means
t h a t t h e c y c l i c consumptive u s e and c o n s e q u e n t l y t h e monthly and s e a s o n a l c r o p w a t e r u s e i s a b o u t 10 t o 1 2 p e r c e n t l e s s t h a n t h e p o t e n t i a l e v a p o t r a n s p i r a t i o n . 6.1.3
E m p i r i c a l methods
The l a s t t h r e e o r f o u r d e c a d e s h a v e w i t n e s s e d t h e development o f a l a r g e number o f e m p i r i c a l f o r m u l a s which r e l a t e t h e consumptive u s e o r e v a p o t r a n s p i r a t i o n t o c l i m a t o l o g i c a l measurements. These f o r m u l a s i n c l u d e one or more of t h e c l i m a t o l o g i c a l s t a n d a r d s s u c h a s mean a i r t e m p e r a t u r e , h u m i d i t y , r a d i a t i o n , wind s p e e d , day-time
l e n g t h , b r i g h t s u n s h i n e , and t a n k and pan e v a p o r a t i o n .
259
A
10
Proposed
: Veihmeyer a n d Hendr ic kson : T h o r n t h w a i t e a n d Mather : Havens : Pierce : P e n m a n , M a r l a t t et 01, Holmes a n d Robertson : S h a h i n (approximate relation )
A
0.5
B
C
a
D
F
W
E
\
0
kW
concepts
F
\
FMC: F i e l d M o i s t u r e C a p a c i t y P W P : P e r m a n e n t W i l t i n g Point O D :Oven D r y
0
-
F- M C
L-
-Readily
Avai l a b l e Moisture Available
S o i l drying
__cI
Moisture
1
4 \
\
OD
PWP
+
Fig. 6.14. P r o p o s e d r e l a t i o n s o f a c t u a l e v a p o t r a n s p i r a t i o n ET E T a s a f f e c t e d by s o i l w a t e r c o n t e n t ( T a n n e r , C . B . , 1967) P
to potential
Examples o f e x c e l l e n t r e v i e w s of t h e e m p i r i c a l methods can b e found i n t h e work o f R i j t e m a (1959) and S l a t y e r and McIlroy ( 1 9 6 1 ) . A comprehensive summary h a s b e e n g i v e n , a l s o by Tanner ( 1 9 6 7 ) .
I n t h i s s e c t i o n w e s h a l l t r y t o g i v e a b r i e f summary of some of t h e e m p i r i c a l methods. Emphasis w i l l be p l a c e d o n t h o s e methods which c a n be used f o r comp l e t i n g t h e p i c t u r e o f t h e e v a p o t r a n s p i r a t i o n from t h e N i l e B a s i n .
-
a ) T e m p e r a t u r e methods
The g e n e r a l form of t h e f o r m u l a c o v e r i n g t h e s e methods
is:
ET
P
= a
+
b
.
C d (
T - C -
O
2
r
I n )
(C3
-
C4 h )
where a , b , C o , C1, C 2 , C 4 and n a r e c o e f f i c i e n t s or c o n s t a n t s , d = measure of day l e n g t h , T = t e m p e r a t u r e i n d e g r e e s F a h r e n h e i t , and h = r e l a t i v e humidity
(6.3)
260
The Lowry-Johnson
f o r m u l a (Lowry, R . L . ,
and J o h n s o n , F . R . ,
1942) c a n b e
written as: ET = 0 . 8 P
0.156
+_ _ E 1000
(T
- 32)
(6.3.1)
where T i s t h e maximum d a i l y t e m p e r a t u r e and t h e summation i s done o v e r t h e l e n g t h of t h e growing s e a s o n . ET i s t h e s e a s o n a l consumptive u s e i n f e e t o f P w a t e r . The monthly w a t e r u s e i s ET m u l t i p l i e d by t h e r a t i o of t h e c u m u l a t i v e P day d e g r e e s ( T - 32) f o r t h e month c o n s i d e r e d , t o t h e s e a s o n a l day d e g r e e s . The Blaney-Morin f o r m u l a ( B l a n e y , H . F . , ET
P
= b
.
d
.
T (114
and Morin, K.V.,
1942) i s :
- h)
(6.3.2)
where ET b
= monthly e v a p o t r a n s p i r a t i o n i n i n c h e s ,
P
= monthly c r o p c o e f f i c i e n t ,
d
= mean monthly p e r c e n t of day-time
T
= mean monthly a i r t e m p e r a t u r e , and
hours of t h e y e a r ,
h
= mean monthly r e l a t i v e h u m i d i t y in p e r c e n t
The monthly v a l u e s o f d f o r t h e d i f f e r e n t l a t i t u d e s c a n b e found i n s e v e r a l s o u r c e s among which i s t h e o r i g i n a l p a p e r of Blaney and C r i d d l e ( 1 9 5 0 . s l i g h t l y re vised 1952). The B l a n e y - C r i d d l e method i s n o t h i n g b u t a m o d i f i e d form of e q . 6 . 3 . 2 , i n which t h e t e r m (114 ET
P
- h) i s put equal t o u n i t y . I t reads
= b . d . T
P r u i t t ' s formula ( P r u i t t , W . O . , ET
P
= -0.115
(6.3.3) 1960) c a n b e e x p r e s s e d a s
+ 1 . 6 1 8 dT
(6.3.4)
where ET T
d
P
= p o t e n t i a l e v a p o t r a n s p i r a t i o n i n inches/day, = mean d a i l y t e m p e r a t u r e i n d e g r e e s F a h r e n h e i t , and = d a i l y percentage of d ay li g h t hours,
expressed decimally.
26 1
Quackenbush and P h e l a n (1965) s u g g e s t e d t h a t t h e c o e f f i c i e n t b i n t h e B l a n e y - C r i d d l e method, e q . 6.3.3 b e s p l i t i n t o two c o e f f i c i e n t s b l and b 2 . The c o e f f i c i e n t b l i s a c r o p c o e f f i c i e n t t h a t v a r i e s d u r i n g t h e s e a s o n , whereas b2 i s a l i n e a r f u n c t i o n o f t h e mean t e m p e r a t u r e e x p r e s s e d by t h e e q u a t i o n b
2
= 0.173 T
- 0.314
Al-Barrak
(1964) c o n s i d e r e d t h a t t h e b c o e f f i c i e n t i n e q . 6.3.3 o f Blaney
(6.3.5)
and C r i d d l e was a l i n e a r f u n c t i o n of t h e mean monthly t e m p e r a t u r e . F o r i r r i g a t e d c r o p s i n c e n t r a l I r a q t h e e x p r e s s i o n h e d e v e l o p e d f o r b was b = 0.43
+ 0.0074 T
(6.3.6)
where T i s t h e mean monthly t e m p e r a t u r e i n d e g r e e s F a h r e n h e i t .
The e m p i r i c a l f o r m u l a d e v e l o p e d by T h o r n t h w a i t e (1948) i s
ETp =
Nd
30x12 .
10 T n 1.6 (-) c2
(6.3.7)
where N
= a c t u a l number o f days i n t h e month c o n s i d e r e d ,
d
= mean monthly day l e n g t h i n h o u r s f o r t h e month c o n s i d e r e d ,
C2 = s e a s o n a l o r annual h e a t index =
I: ( T / 5 ) 1’514 where t h e summation i s done
f o r t h e months of t h e s e a s o n o r of t h e y e a r , and n
= 675 x lo-’
CZ3
- 771 x
CZ2
+ 17921 x
C
2
+ 0.49239
Values of t h e h e a t i n d e x C2 and t h e power n f o r a wide r a n g e of t e m p e r a t u r e s T a r e a v a i l a b l e i n a number of r e f e r e n c e s a s t h e p a p e r of T h o r n t h w a i t e and
Mather (1955). H a r g r e a v e s d e v e l o p e d t h e f o r m u l a (1956):
ET
P
= 0.38 b
.
d (T
- 32)(1 - h )
(6.3.8)
where d = day-time measure = 0 . 1 2 t h e monthly p e r c e n t o f t h e day-time h o u r s o f t h e year, h = mean monthly r e l a t i v e h u m i d i t y a t noon, e x p r e s s e d d e c i m a l l y
26 2
Monthly v a l u e s o f d f o r t h e d i f f e r e n t l a t i t u d e s are t a b u l a t e d i n t h e o r i g i n a l p a p e r of H a r g r e a v e s . L a t e r h e p r o p o s e d s o m e c o r r e c t i o n s f o r t h e d e v i a t i o n of t h e a c t u a l s u n s h i n e p e r c e n t a g e , w i n d s p e e d , and e l e v a t i o n from t h e s t a n d a r d v a l u e s on which e q . 6 . 3 . 8 had b e e n b a s e d ( H a r g r e a v e s , G . H . ,
1966). These c o r r e c t i o n s
are given i n Chapter 5 . I n 1968 Hargreaves developed t h e consumptive u s e c o e f f i c i e n t s f o r a l a r g e number o f c r o p s c o n s i d e r i n g 10% s u c c e s s i v e i n c r e m e n t s o f t h e c r o p growing s e a s o n (1968). The f o r m u l a d e v e l o p e d r e c e n t l y by D o o r e n b o s a n d P r u i t t ( 1 9 7 7 ) s u g g e s t s t h e r e u l a c e m e n t of t h e c o e f f i c i e n t b i n t h e f o r m u l a o f B l a n e y a n d C r i d d l e , e q . 6 . 3 . 3 ,
. The s u b - c o e f f i c i e n t bl depends on t h e c r o p 2 a n d i t s r a t e o f d e v e l o p m e n t d u r i n g t h e g r o w i n g s e a s o n . The s u b - c o e f f i c i e n t b 2 i s
by t w o s u b - c o e f f i c i e n t s b l and b
a n a d j u s t m e n t f a c t o r w h i c h d e p e n d s on t h e minimum r e l a t i v e h u m i d i t y , s u n s h i n e h o u r s and d a y - t i m e w i n d e s t i m a t e s . V a l u e s o f t h e a d j u s t m e n t f a c t o r b 2 c a n b e r e a d from t h e g r a p h s p r e p a r e d by D o o r e n b o s and P r u i t t .
F o r ease o f r e f e r e n c e , t h e c o n s t a n t s a n d c o e f f i c i e n t s i n c l u d e d i n t h e a b o v e t e m p e r a t u r e f o r m u l a s h a v e b e e n summed up and l i s t e d i n T a b l e 6 . 1 0 . T e m p e r a t u r e m e t h o d s a r e o f t e n c r i t i c i z e d on t h e g r o u n d s t h a t t h e e f f e c t o f t h e c l i m a t e on t h e c r o p w a t e r u s e c a n n o t b e d e f i n e d a d e q u a t e l y by t h e t e m p e r a t u r e and a m e a s u r e of t h e l e n g t h o f d a y o n l y . I n t h e humid t r o p i c s w h e r e t e m p e r a t u r e r e m a i n s f a i r l y c o n s t a n t , t h e c r o p w a t e r u s e c h a n g e s as a c o n s e q u e n c e of c h a n g e i n o t h e r m e t e o r o l o g i c a l p a r a m e t e r s . A t h i g h a l t i t u d e s t h e h i g h l e v e l
r a d i a t i o n may c a u s e r e a s o n a b l y h i g h c o n s u m p t i o n o f w a t e r by p l a n t s , d e s p i t e t h e f a i r l y low t e m p e r a t u r e . M o r e o v e r , t h e t e m p e r a t u r e l a g c o r r e c t i o n s a r e r a r e l y i n t r o d u c e d e x p l i c i t l y i n t h e t e m p e r a t u r e f o r m u l a s . On t h e o t h e r h a n d , t h e a v a i l a b i l i t y o f t h e t e m p e r a t u r e r e c o r d s e v e r w h e r e i n q u a n t i t y and q u a l i t y compared t o o t h e r c l i m a t o l o g i c a l p a r a m e t e r s e n c o u r a g e s many p r o f e s s i o n a l s t o u s e t h e t e m p e r a t u r e m e t h o d s e x t e n s i v e l y . One s h o u l d n o t f o r g e t t h a t t h e y a r e e a s i e r t o a p p l y t h a n m o s t o f t h e r e m a i n i n g m e t h o d s . I n any c a s e , e s t i m a t e s o f c o n s u m p t i v e u s e by t h e t e m p e r a t u r e m e t h o d s h a v e , as a r u l e , t o b e c a l i b r a t e d b e f o r e b e i n g u s e d f o r any p r a c t i c a l p u r p o s e . The c u r r e n t p r a c t i c e i n E g y p t i s t o u s e t h e s o i l m o i s t u r e d e p l e t i o n s t u d i e s f o r c a l i b r a t i n g s u c h w i d e l y u s e d f o r m u l a s as B l a n e y - C r i d d l e
and T h o r n t h w a i t e ,
g i v e n by e q s . 6 . 3 . 3 a n d 6 . 3 . 7 r e s p e c t i v e l y . T h e m o n t h 1 y a n d s e a s o n a l c o n s u m p t i v e u s e c o e f f i c i e n t s f o r a l a r g e number o f c r o p s i n E g y p t o b t a i n e d from t h i s c a l i b r a t i o n a r e g i v e n i n T a b l e s 6 . 1 1 a and 6 . 1 1 b . T h e s e c o e f f i c i e n t s a r e n o t i n c r e a s e d by t h e 10 t o 12% t h a t w e p r o p o s e d i n c o n n e c t i o n w i t h t h e r e l a t i o n b e t w e e n ET
a n d ET
P
during an i r r i g a t i o n c y c l e .
0
0
m
2 E
m
d
W V
c
N V
rl 0
0
U
P
Ld
E 3 E a
c r
d m
E +a,
a
tic,
3
4
0
9 rl
, n
c
R
R
E, c
C
+ €-
ri
9 rl
2 rl
9 rl
5 0 \ .r(
R
R
c 'ri o u
E .ri \ E 0 3
R
.3 0
c w
c W
R
0
w 0
irl
c € -
rl
W 0
R
0
c w 0
9
9
0
9
9
0
0
rl
9
0
0
rl
0
9
9 rl
9 rl
00 I
W d
a,
w
w
V
w w V
a,
w
W .d
0
.r(
C
c,
.A
w w
0
.r(
a,
c
c,
a,
rl
0
N W
rl
rl
9
'
o v
c 3 w w o w 0 . R . E
oa,
c r w
0
9 9
41 a ca ,,w'
m w
u v
.ln a 0,
11
rl
rl
c,
a
9
9
rl
9
9
rl
0
0
rl
0
3
9
rl
N
0
rl
0
9
0
9
9
0
9
rl
rl
rl
9 ri
rl
0
9
0
rl
0 rl
0 0
0
9 0
9
a,
r(
0
w w
0
W * a,
w a,
c,
a,
c
.r(
V
a,
w w
a,
m
a a
0 .r( h 0 3 O h
D O
O X
a,
0
0 0
.r( .r(
.A
>
m
0
9
a,
.r(
I
0
V
9
I
s
e .r( a,
m k
c>
ale
z
r o rml m a ,
3s
M
,3 a
n
0
0
a,
I
k
a
.r(
c,
> r(
rl
rl m
0
w
.r(
w
0
.r(
c
0
w
ri
w
c,
w
m o
Ld .r( r l k
c u
m u
hrl
l a ,
.A
T I
.r(
0
0
0
a,
.r(
w
o
.r(
a,
c
0
a,
w
rl
0
rl
0
9
w
c, V
9
I .r( h.r(
m-s
4 0
m.4
ale c .r(
0
0
a,
w .r( w
.A a,
c
0
a,
w
rl
9
rl
N W
9 rl
9 d
9
x
41 W In rl
0
m
c
.r(
1 0
h m k F
0 s c0
4 3
. -
M
E
II
.A
- x.-
Lm:
e P
-
e m
W
3 w
.A h
ll
a
:
'
-
> m
.- >,
M
- m h . x
rlrl
a,o m c w a, mm k
- a R
3
@!I1
.w
m . - 3 x
c mr o
P a,*
0
Z
f
m 3
rl
2
a,
w 3
c,
h a,
B
c,
a,
9 w a,
E
m
c
.r(
P
a
a a,
rl 0
c
.r(
c, m
c
a,
.r( .r(
U
a,
w w
9
U
c, m
e
m
c,
c 0
a,
9 w h
0
m
;
vl
m
a
r(
E
0
W h
rl
w cl
m i
e
26 3
TABLE 6 . 1 1 a
Consumptive u s e c o e f f i c i e n t s f o r some c r o p s i n Egypt t o b e u s e d w i t h t h e B l a n e y - C r i d d l e
Consumptive u s e c o e f f i c i e n t f o r
Crop Jan. Cotton Wheat E a r l y Corn L a t e Corn Berseem C i t r u s Orchards Fenugreek & L u p i n Chickpea & L e n t i l S u g a r Cane F i e l d Beans P o t a t o e s (summer) Potatoes ( f a l l ) Snap Beans Cow P e a s Squash Cucumber
formula
Feb.
Mar.
-
-
.49
.59
.26 .66
-
.31 .35 .56 .42 .29 .54
-
.86
-
-
-
-
-
.42 .51 .57 .46 .72 .73 .63
.72 .55 .26 .18 .87 .67 .77
-
-
Apr.
.39 .49 .36
-
.82 .57
-
.84 .48 1.01
-
.30
May
June
July
.66 .31 .71
1.07
1.03
-
.64 .60
-
-
.90
-
.69
-
.35
-
1.06
-
.25 .64
-
-
1.00
-
.80
-
Aug.
.56
Sep.
.51
-
Oct.
-
-
-
.87 .51
-
.60 .91
-
1.13
.70
.64
.59
.80 .31 .56
1.32
1.00
-
1.36
-
.99 .44 .30
-
1.37
-
-
-
.60 1.02 .63
-
-
-
-
-
-
-
.37
.19 .80
-
1.01 .87
.79
Nov.
Dec.
.46
.37 .42 .38 .34 .79
.47
-
.62 .32 .59 .50 .41
.49 1.14
.98 .78
-
o r year
0.71 0.51 0.79 0.88 0.56 0.54 0.46 0.37 0.91 0.58 0.77 0.59 0.77 0.64 0.87 0.69
TABLE 6.11b
Consumptive use coefficients for some crops in EgyDt to be used with Thornthwaits's formula
Consumptive use coefficient for Crop Jan. Cotton Wheat Early Corn Late Corn Berseem Citrus Orchards Fenugreek & Lupin Chickpea & Lentil Sugar Cane Field Beans Potatoes (summer) Potatoes (fall) Snap Beans Cow Peas Squash Cucumber
2.15
1.49 1.47 2.86 2.13 1.22 2.44
-
3.77
Feb.
2.78
1.65 2.46 2.32 1.88 3.44 3.44 2.97
-
Mar.
Apr.
May
June
July
Aug.
Sep.
0.75 1.89
0.72 .89 .37
0.98 .42 .96
1.33
1.23
0.66
0.73
-
2.18 1.51 0.40 0.26 2.39 1.84 2.06
-
1.59 1.14
-
1.68 .96 2.02
0.55
-
.98 .88
-
1.32
-
1.01
0.52
-
-
1.28
-
.50 .82
-
1.28
-
-
-
0.99
-
-
-
-
Oct.
-
1.01 .59
.56 1.00
-
1.54
.78
.76
1.25
1.40 .28 1.00
1.63
2.80
1.79
-
-
1.52
-
-
1.18 .52 .36
-
0.71 1.21 0.75
-
0.78
-
2.14 1.85
-
0.34 1.43
-
1.41
Nov.
Dec.
.97
1.67
.82 .86 .44 .48 1.62
1.00 2.33
-
-
-
2.43 1.14 1.43 1.21 1.46
-
3.49 2.78
-
Season o r year 0.97 1.54 0.93 1.08 1.29 0.94 1.96 1.56 1.85 2.08 1.51 2.01 1.82 0.83 1.36 1.16
266
-
b) R a d i a t i o n methods
The r a d i a t i o n methods d e v e l o p e d f o r e s t i m a t i n g p o t e n t i a l
e v a p o t r a n s p i r a t i o n a r e e i t h e r b a s e d on t h e h e a t e n e r g y b u d g e t , t o g e t h e r w i t h some e m p i r i c a l a p p r o x i m a t i o n s t o u t i l i z e t h e a v a i l a b l e c l i m a t i c d a t a , or t h e y a r e c o m p l e t e l y e m p i r i c a l . I n t h e f i r s t g r o u p i s t h e f o r m u l a of Penman, which w e a l r e a d y p r e s e n t e d i n C h a p t e r 5 as a means f o r e s t i m a t i n g e v a p o r a t i o n from a f r e e water s u r f a c e , E
.
The same f o r m u l a when u s e d f o r e s t i m a t i n g t h e p o t e n t i a l eva-
potranspiration reads:
ET
= a . E
P
(6.4)
0
where a i s a c o e f f i c i e n t v e r y i n g w i t h t h e month. A l a r g e number of e m p i r i c a l f o r m u l a s , a l l b a s e d on one form
G-
a n o t h e r of
r a d i a t i o n , have been d e v e l o p e d f o r e s t i m a t i n g p o t e n t i a l e v a p o t r a n s p i r a t i o n . The g e n e r a l form of t h e e q u a t i o n embracing t h e s e f o r m u l a s can b e w r i t t e n a s
ET
P
= K .
C .
(R+a)
I n 1961, T u r c , L .
ET
P
= 0 . 4 0 (-
t
(6.5) (1961), presented h i s formula:
15)(R + 50)
+
mm/month
(6.5.1)
where
t = mean monthly t e m p e r a t u r e i n d e g r e e s c e n t i g r a d e , and R = mean incoming r a d i a t i o n i n gm c a l s / c m 2 . d a y . R c a n b e computed from t h e t h e o r e t i c a l r a d i a t i o n , R A , r e a c h i n g t h e e a r t h ' s
+
atmosphere u s i n g t h e r e l a t i o n R = R ( 0 . 1 8 A t a g e of p o s s i b l e s u n s h i n e .
0.0062 S ) , where S i s t h e p e r c e n -
The f o r m u l a d e v e l o p e d by J e n s e n and H a i s e (1963) i s :
ET
P
= (0.014 T
-
0.37) R
so
(0.35
+
0 . 6 1 S)
inches/month
(6.5.2)
where T
= mean monthly
Rso
= s o l a r r a d i a t i o n on c l o u d l e s s d a y s ,
temperature i n degrees F a h r e n h e i t ,
S
= possible sunshine expressed decimally.
Christiansen, J . E . ,
and
(1969) c o n s i d e r e d a = 0 i n e q . 6 . 5 i n o r d e r t o e s t i m a t e
e v a p o r a t i o n or e v a p o t r a n s p i r a t i o n .
H e and h i s co-workers
h a v e d e v e l o p e d an
e x t e n s i v e number of e q u a t i o n s , i n which k i s k e p t a s a d i m e n s i o n l e s s c o n s t a n t and t h e p r o d u c t kc r e p r e s e n t s t h e r a t i o o f t h e e n e r g y u t i l i z e d i n t h e e v a p o r a -
267
t i o n p r o c e s s t o t h e energy a v a i l a b l e a t t h e o u t e r s u r f a c e of t h e atmosphere. The c o e f f i c i e n t C i s t h e p r o d u c t o f a l a r g e number o f s u b - c o e f f i c i e n t s ,
each
r e l a t e d t o a c l i m a t i c or o t h e r p a r a m e t e r t h a t i s l i k e l y t o a f f e c t e v a p o r a t i o n o r e v a p o t r a n s p i r a t i o n . The f o r m u l a d e v e l o p e d by C h r i s t i a n s e n w h i c h r e l a t e s ET
t o e x t r a t e r r e s t r i a l r a d i a t i o n a s a base is
ETP = 0 . 3 2 4 R A . CTT
.
CWT
.
CHT
.
CST
.
CEl
inches/month
P
(6.5.3)
where RA = e x t r a t e r r e s t r i a l r a d i a t i o n i n e q u i v a l e n t e v a p o r a t i o n i n i n c h e s / m o n t h , CTT = 0 . 1 7 4 + 0 . 4 2 8 ( T / T ) + 0 . 3 9 8 ( T / T o ) 2
T
= t h e mean a i r t e m p e r a t u r e i n d e g r e e s F a h r e n h e i t
CWT = 0 . 6 7 2
+ 0.406
= \ k =
s T \% .
- 0 . 0 7 8 (W/W
(W/Wo) ,\\
s \ \ <
\=sx sxy
and T
0
= 68’F,
)2
0
z
Ts
xs-ye
gxa\\.
s\Y=L=%e
= m
m i l e s per b a y , CHT = 1 . 0 3 5 H
=
m
-
0 . 2 7 5 (Hm/Hmo)3
t h e mean r e l a t i v e h u m i d i t y i n d e c i m a l s a n d H
CST = 0 . 3 4 0
+
0.856 (S/So)
- 0.196 (S/SOl2
= mean s u n s h i n e p e r c e n t a g e i n d e c i m a l s and S
S C
+ 0 . 2 4 0 (Hm/Hmo)2
El
El
= 0.970
+
mo
= 0.60,
= 0.80,
and
0.030 ( E l / E l o )
= e l e v a t i o n i n f t a b o v e mean sea l e v e l and E l
The s u b - c o e f f i c i e n t s C T T , CWT, C H T , CST a n d CEl
= 300 f t
c a n b e r e a d d i r e c t l y from t h e
t a b l e s p r e p a r e d by C h r i s t i a n s e n f o r any g i v e n v a l u e f o r T, W , H m , S and E l respectively. The f o r m u l a o f O l i v i e r ( 1 9 6 1 ) h a s a l r e a d y b e e n g i v e n as e q . 6 . 2 . D o o r e n b o s recommends two r e l a t i o n s h i p s ( D o o r e n b o s , J . , and P r u i t t , W . O . , 1 9 7 7 ) . The o n e t h a t s u i t s t h e e m p i r i c a l t y p e o f r a d i a t i o n f o r m u l a s i s g i v e n by ET
P
= k . C . W . R s
,
mm/day
where k = crop c o e f f i c i e n t , C = a d j u s t m e n t f a c t o r w h i c h d e p e n d s on mean h u m i d i t y and d a y - t i m e wind
conditions. W = w e i g h t i n g f a c t o r w h i c h d e p e n d s on t e m p e r a t u r e and a l t i t u d e , and
R
= s o l a r r a d i a t i o n i n e q u i v a l e n t e v a p o r a t i o n i n mm/day.
(6.5.4)
268
is r e l a t e d t o RA a s R
R
=
R A (0.25 + 0.50
)'
N
where
i s t h e r a t i o between
N
t h e a c t u a l measured b r i g h t s u n s h i n e h o u r s and t h e maximum p o s s i b l e s u n s h i n e hours. T a b l e s and g r a p h s needed t o g i v e C and W h a v e a l r e a d y been p r e p a r e d by Doorenbos and P r u i t t . Eq. 6 . 5 . 4 i s v e r y s i m i l a r t o e q . 6 . 5 . 3 o r i g i n a l l y devel o p e d by C h r i s t i a n s e n . The s e c o n d r e l a t i o n recommended by Doorenbos and P r u i t t (1977) i s an a d j u s t ment t o Penman's f o r m u l a . They gave i t a s
ET
= k
P
.
{W.Rn + ( 1
c
-
W)
.
.
f (u)
(es - e a ) }
mm/day
(6.6)
where
k
= crop
coefficient,
C
= a d j u s t m e n t f a c t o r t o compensate f o r t h e e f f e c t of day and n i g h t
W
= temperature-related
weather co n d i ti o n s ,
= n e t r a d i a t i o n i n e q u i v a l e n t e v a p o r a t i o n i n mm/day
Rn
R n i s t h e sum of t h e n e t s h o r t wave r a d i a t i o n ,
wave r a d i a t i o n , f
weighting f a c t o r ,
(u)
Rnl'
= wind f u n c t i o n = 0 . 2 7 ( 1
+
Rns 1
and n e t l o n g
0 . 0 1 u ) , u i s t h e 24-hr wind r u n i n km/day
a t 2 m h e i g h t , and
- e
(es
) = s a t u r a t i o n vapour p r e s s u r e d e f i c i t =
e ( 1 - h) i n m i l l i b a r .
Values o f c , W , and R C.B.
(1 - W), e s , e d , R i n e q u i v a l e n t e v a p o r a t i o n u n i t s , N r R n s A a r e g i v e n i n t a b l e s i n t h e Doorenbos and P r u i t t p a p e r ( 1 9 7 7 ) . T a n n e r ,
nl (1967) m e n t i o n s t h a t b e c a u s e r a d i a t i o n methods a r e t i e d more c l o s e l y t o
e n e r g y s u p p l y , t h e y show g r e a t e s t p r o m i s e f o r s h o r t - t e r m ,
a s w e l l a s long-term,
e s t i m a t e s . Doorenbos and P r u i t t a l s o r e p o r t e d on t h i s m a t t e r s a y i n g t h a t " t h e r a d i a t i o n method s h o u l d b e more r e l i a b l e t h a n t h e B l a n e y - C r i d d l e
approach". I n
f a c t , i n e q u a t o r i a l z o n e s , on s m a l l i s l a n d s or a t h i g h a l t i t u d e s , t h e r a d i a t i o n method may b e more r e l i a b l e even i f measured s u n s h i n e or c l o u d i n e s s d a t a a r e n o t a v a i l a b l e ; i n t h i s c a s e , s o l a r r a d i a t i o n p r e p a r e d f o r most l o c a t i o n s i n t h e w o r l d s h o u l d p r o v i d e t h e n e c e s s a r y s o l a r r a d i a t i o n d a t a (Doorenbos, J . , and Pruitt, W.O.,
1977).
The a u t h o r d o e s n o t want t o a r g u e h e r e a b o u t e i t h e r t h e s u p e r i o r i t y o f one method
or one f o r m u l a t o a n o t h e r . The p o i n t which i s n e c e s s a r y t o b e a r i n mind
i s t h a t e v e r y f o r m u l a n e e d s t o b e c a l i b r a t e d . When t h e a u t h o r had t o c a l i b r a t e
a l a r g e number of f o r m u l a s , much l a r g e r t h a n t h o s e i n c l u d e d i n t h i s t e x t , u s i n g measurements from v a r i o u s c o u n t r i e s , t h e c o n c l u s i o n was t h a t each f o r m u l a needed t o b e a d j u s t e d . T h e r e i s n o t , n o r v e r y l i k e l y w i l l b e , a s i n g l e f o r m u l a of
269
u n i v e r s a l a p p l i c a b i l i t y w i t h o u t c o r r e c t i o n or a d j u s t m e n t . The i m p o r t a n c e o f l o c a l f a c t o r s , b i o l o g i c a l f a c t o r s , and t i m e f a c t o r s h a v e b e e n r e a l i z e d and r e p o r t e d by s e v e r a l i n v e s t i g a t o r s , i n c l u d i n g Penman, H . ,
i n h i s s t u d y of evapo-
r a t i o n o v e r t h e B r i t i s h I s l e s ( 1 9 5 0 ) . The s t r e s s s h o u l d t h e n b e l a i d on d e t e r m i n i n g or knowing t h e a d j u s t m e n t f a c t o r p r e c i s e l y and n o t on t h e method or t h e f o r m u l a only. The monthly and s e a s o n a l f i g u r e s o f t h e a d j u s t m e n t f a c t o r needed
for t h e f o r m u l a s o f Penman and O l i v i e r a r e g i v e n i n T a b l e s 6 . 1 2 a and 6.12b respectively. TABLE 6 . 1 2 a
Consumptive u s e c o e f f i c i e n t s f o r some m a j o r c r o p s i n Egypt t o be u s e d w i t h Penman's f o r m u l a
Crop
Cotton Wheat E a r l y Corn L a t e Corn Berseem Citrus Orchards S u g a r Cane
TABLE 6 . 1 2 b
Consumptive u s e c o e f f i c i e n t f o r J a n . F e b . Mar. Apr.
May
J u n e J u l y Aug. S e p . O c t . Nov. Dec.
-
Season
or y e a r
-
0.27 0 . 3 8 0.57 0 . 8 8 0 . 9 1 0.50 0.45 0 . 8 2 0.73 0.84 0.48 0.28 0.74 0 . 9 3 0.34 0.62 0.89 0.80 0 . 5 2 0 . 4 5 0.90 1.15 1 . 1 2 0 . 8 9 0.48 0 . 6 8 0 . 7 9 0 . 8 0 0.60 0 . 2 2 0.43 0.62 1.30
0.61 0.73 0.70 1.oo 0.72
0.54 0.56 0.60 0 . 5 5 0 . 5 6 0.57 0 . 6 2 0.62 0.60 0.77 0 . 7 1 0.67
0.62
0.45 0 . 7 9 0 . 9 5 0 . 8 1 0.84 0.89 1.20 1 . 3 3 1.34 1 . 3 7 1.33 0.86
1.03
-
Consumptive u s e c o e f f i c i e n t s f o r some m a j o r c r o p s i n Egypt t o be used w i t h O l i v i e r ' s formula
Crop
Cotton Wheat E a r l y Corn L a t e Corn Berseem Citrus Orchards S u g a r Cane
Consumptive u s e c o e f f i c i e n t f o r J a n . F e b . Mar. Apr.
May
J u n e J u l y Aug. S e p . O c t . Nov. Dec.
Season or y e a r
0.50 0.67 0.72 1.33 1.41 0.87 2.00 1.57 1.60 0 . 7 5 0 . 3 3 1.54 2.22 0 . 5 3 0.80 1.30 1 . 2 3 0.86 0.76 1.28 1.65 2.25 2.66 1.28 1 . 2 5 1.46 1.20 0.72 0 . 3 1 0 . 8 2 1 . 2 4 2.86
0.92 1.45 1.02 1.39 1.09
1 . 4 2 1 . 3 1 0.99 0.86 0 . 8 1 0 . 9 2 0 . 9 2 1.02 1 . 0 6 1 . 3 2 1.46 1.74
1.01
1.18 1 . 8 5 1 . 5 7 1 . 2 7 1 . 2 2 1 . 4 4 1 . 7 8 2 . 1 9 2 . 3 7 2 . 3 5 2 . 7 3 2 . 2 3
1.68
c ) E v a p o r a t i o n pans-
- Pan e v a p o r a t i o n and p l a n t e v a p o t r a n s p i r a t i o n a r e s i m i l a r ,
s i n c e e a c h o f them c a n b e c o n s i d e r e d a s a measure of t h e i n t e g r a t e d e f f e c t of t h e c l i m a t o l o g i c a l f a c t o r s o n t h e l o s s o f w a t e r by e v a p o r a t i o n or e v a p o t r a n s p i r a t i o n . The d i f f e r e n c e s i n b o t h r e f l e c t i o n o f t h e s o l a r r a d i a t i o n and t h e e x c h a n g e of h e a t e n e r g y from a v e g e t a t e d s u r f a c e compared t o t h o s e from w a t e r i n
270
a p a n , added t o t h e i n f l u e n c e s o f pan s i z e , c o l o u r , e x p o s u r e and placement are among t h e c a u s e s t h a t c a n make pan e v a p o r a t i o n d i f f e r c o n s i d e r a b l y from p l a n t e v a p o t r a n s p i r a t i o n . A d j u s t i n g t h e pan r e a d i n g i s , t h e r e f o r e , i n e v i t a b l e , i n o r d e r t o c o n v e r t i t t o i t s e q u i v a l e n t o f e v a p o t r a n s p i r a t i o n . The g e n e r a l form of t h e e q u a t i o n needed f o r a d j u s t i n g t h e pan e v a p o r a t i o n , E p a n , i s
)n
P = a
+
b
(6.7)
The f o r m u l a g i v e n by Penman, and by Doorenbos and P r u i t t i s ET
P
= a . E Pan
(6.7.1)
where a i s a monthly or a s e a s o n a l c o e f f i c i e n t a s g i v e n by Penman, and a p r o d u c t of two s u b - c o e f f i c i e n t s
f o r t h e pan, k
and P r u i t t ( 1 9 7 7 ) .
P’
and t h e c r o p , k c , a s g i v e n by Doorenbos
S t a n h i l l ’ s r e g r e s s i o n r e l a t i o n between t h e d a i l y e v a p o t r a n s p i r a t i o n , i n m m , from A l f a l f a and t h e d a i l y e v a p o r a t i o n , i n m m ,
ET
P
= 0.70 E
pan
+
from a c l a s s A pan (1961) i s :
0.47
(6.7.2)
B u t l e r and P r e s c o t t (1955) o b s e r v e d t h a t t h e power n i n e q . 6 . 7 i s i n t h e neighbourhood of 0 . 7 5 i n s t e a d o f 1 . 0 , s o t h e i r f o r m u l a c a n b e w r i t t e n a s
The o v e r a l l a d j u s t m e n t c o e f f i c i e n t
1,
e q . 6 . 7 . 1 w i l l j u s t be c a l l e d t h e crop
c o e f f i c i e n t . Values of a f o r t h e m a j o r c r o p s i n Egypt a r e i n c l u d e d i n T a b l e 6 . 1 3 . TABLE 6 . 1 3
Monthly and s e a s o n a l c r o p c o e f f i c i e n t s t o b e used w i t h USWB c l a s s A e v a p o r a t i o n pan f o r t h e m a j o r c r o p s i n Egypt ~~
Crop Cotton Wheat E a r l y Corn L a t e Corn Berseem Citrus Orchards S u g a r Cane
~
Consumptive u s e c o e f f i c i e n t f o r J a n . F e b . Mar. Apr.
May
J u n e J u l y Aug. S e p . O c t . Nov. Dec.
0 . 2 4 0 . 2 7 0 . 4 2 0 . 5 3 0.69 0.44 0 . 3 9 0.64 0 . 5 2 0 . 4 5 0 . 2 6 0 . 1 4 -
-
-
-
-
0.42 0 . 5 6
0.22 0.37 0 . 5 2 0 . 5 2 0.33 0 . 3 4 0.57 0 . 6 2 0 . 6 2 0.29 0.53 0.66 0.48 0.18 0.46 0 . 7 2 -
-
-
-
Season or y e a r 0.43 0.49 0.45 0.55 0.51
0.39 0 . 4 2 0 . 4 2 0 . 3 7 0 . 4 0 0 . 4 1 0 . 4 1 0 . 4 0 0 37 0 . 3 9 0 . 4 4 0 . 4 4
0.41
0 . 3 2 0 . 4 9 0 . 6 7 0 . 5 5 0 . 6 0 0.64 0.79 0 . 8 6 0 . 8 3 0 . 6 9 0 . 8 2 0 . 5 6
0.66
271
I n v e s t i g a t i o n of t h e f i g u r e s i n T a b l e 6 . 1 3 shows t h a t t h e maximum v a l u e s of t h e monthly c r o p c o e f f i c i e n t s t o b e u s e d w i t h pan e v a p o r a t i o n a r e d i s t r i b u t e d t h r o u g h o u t t h e y e a r more u n i f o r m l y t h a n w i t h any o t h e r method. The same c o n c l u s i o n w a s r e a c h e d by Tanner w h i l e u s i n g ET d a t a of i r r i g a t e d r y e g r a s s which P w e r e o b t a i n e d by P r u i t t . The d i s t r i b u t i o n of t h e monthly c o e f f i c i e n t is v e r y n e a r l y r e c t a n g u l a r , w i t h a v a l u e of a b o u t 0 . 8 ( T a n n e r , C . B . ,
6.1.4
1967).
The i n t e g r a t i o n method
W e s h o u l d have l i k e d t o u s e t h e d a t a from t h e USWB c l a s s A p a n , a f t e r conv e r t i n g them, p r e p a r i n g a map showing t h e p o t e n t i a l e v a p o t r a n s p i r a t i o n f o r Egypt. U n f o r t u n a t e l y , o n l y a few s t a t i o n s a r e e q u i p p e d w i t h c l a s s A p a n . T h i s s t a t e of a f f a i r s compels u s t o abandon t h e pan method, though i t seems p r o m i s i n g . The method t h a t s e r v e s a s a r e a s o n a b l e a l t e r n a t i v e i s t h a t o f B l a n e y - C r i d d l e s i n c e
i t h a s been c a l i b r a t e d f r e q u e n t l y u s i n g a wide v a r i e t y of i r r i g a t e d c r o p s . The o n l y m a j o r c r o p f o r which t h e B l a n e y - C r i d d l e
f o r m u l a h a s n o t y e t been c a l i b r a t e d
i s r i c e . To c o v e r t h i s d e f i c i e n c y w e s h a l l employ t h e consumptive u s e c o e f f i c i e n t s f o r r i c e grown i n t h e d r y a r e a s i n C a l i f o r n i a , U S A . These a r e a p p r o x i m a t e l y 1.1, 1 . 2 , 1 . 3 , 1 . 3 , and 1 . 0 f o r May t h r o u g h September r e s D e c t i v e l y . These
f i g u r e s , t o g e t h e r w i t h u s e c o e f f i c i e n t s o f o t h e r c r o p s which a r e g i v e n i n T a b l e 6 . 1 1 a , h a v e been p l o t t e d a g a i n s t t h e months of t h e y e a r , and t h e c u r v e envelopp i n g t h e monthly maximum v a l u e s drawn a s shown i n F i g . 6 . 1 5 . T h i s Curve r e p r e s e n t s t h e p o t e n t i a l e v a p o t r a n s p i r a t i o n r e q u i r e m e n t a v e r a g e d f o r E g y p t . The c o e f f i c i e n t a v e r a g e d o v e r t h e y e a r i s a b o u t 1.1. I t may t h e r e f o r e b e P r e a s o n a b l e t o a p p l y an a n n u a l ET c o e f f i c i e n t of 1 . 0 0 f o r t h e D e l t a a r e a , 1 . 0 5 P f o r t h e a r e a n o r t h of Minya up t o G i z a , 1 . 1 0 f o r t h e a r e a from A s s i u t up t o
ET
hIinya,
1 . 1 5 t o t h e a r e a from Q e n a up t o A s s i u t a n d 1 . 2 0 f o r t h e a r e a s o u t h o f Qena.
These f i g u r e s have been used i n p r e p a r i n g t h e map o f t h e p o t e n t i a l e v a p o t r a n s p i r a t i o n r e q u i r e m e n t f o r E g y p t , F i g . 6 . 1 6 . T h i s map shows an e v a p o t r a n s p i r a t i o n requirement s l i g h t l y d i f f e r e n t , + 5%, from t h a t f o r t h e p a r t of Egypt shown i n t h e map i n F i g . 6 . 2 . Moreover, t h e c o n t o u r i n t e r v a l i n F i g . 6 . 1 6 i s 100 mm/yr, whereas t h e c o n t o u r i n t e r v a l i n t h e o t h e r map i s 250 m m / y r . Both maps, F i g s . 6 . 2 and 6 . 1 6 g i v e t h e r e q u i r e m e n t s f o r p o t e n t i a l e v a p o t r a n s p i r a t i o n . A s u r v e y of t h e w a t e r u s e by c r o p s , even a t t h e p o t e n t i a l e v a p o t r a n s p i r a t i o n l e v e l , r e q u i r e s a knowledge of t h e c r o p p a t t e r n , a r e a and development b o t h i n t i m e and s p a c e . T h i s can b e done u s i n g t h e s o - c a l l e d (Israelsen, O.W.,
i n t e g r a t i o n method
1 9 5 6 ) . I n t h i s method t h e a g r i c u l t u r a l a r e a i s d i v i d e d i n t o a
number o f b l o c k s where t h e c r o p p a t t e r n i s f a i r l y homogeneous and t h e y e a r i s d i v i d e d i n t o a number o f i n t e r v a l s . The w a t e r u s e by a c r o p i s computed f o r each i n t e r v a l d u r i n g t h e growing s e a s o n , and t h e t o t a l w a t e r u s e f o r a g i v e n i n t e r v a l i s t h e sum o f w a t e r u s e by t h e d i f f e r e n t c r o p s i n t h a t i n t e r v a l .
272
0.8 aJ
c
0
z
a
2
u
0.7 -
8
0.6 -
0
0.5
-
0
z
L
x
x A
l
'I
0.2
-
0.1
-
0.0
-
3
" ,
3 3
x
2
-
e
-
l
-
AV
2
O
v 3
1
L
0
0
-
A V
1
+
8
1
0.3 -
-
L
1
1
A
0.4 - I
e
1
5
1
v
o
x
A
8
1
i
A
*
A
-
h
I
I
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I
I
F i g . 6.15. Monthly c o e f f i c i e n t s o f w a t e r u s e by c r o p s i n Egyut f o r t h e method o f B l a n e v - C r i d d l e . The e n v e l o p p i n g c u r v e r e p r e s e n t s t h e a v e r a g e p o t e n t i a l e v a p o t r a n s p i r a t i o n requirement f o r Egypt. W e have u s e d t h e i n t e g r a t i o n method t o d e t e r m i n e t h e w a t e r u s e of t h e c r o p p e d
a r e a i n Egvpt t w i c e . One t i m e i s f o r t h e 1 0 . 4 m i l l i o n f e d d a n s
It
cropped a r e a i n
1962, i . e . s h o r t l y b e f o r e t h e High Dam a t Aswan, and t h e o t h e r t i m e f o r t h e 1 1 . 2 m i l l i o n f e d d a n s c r o p p e d a r e a i n 1 9 7 5 , i . e . a f t e r t h e o p e r a t i o n o f t h e dam. I n each c a s e t h e month i s c h o s e n as a t i m e i n t e r v a l and t h e G o v e r n r a t e as a
f
1 f e d d a n = 4200.6 m 2
273
Fig. 6.16. Map showing l i n e s of e q u a l p o t e n t i a l e v a p o t r a n s p i r a t i o n requirement mm/vr, f o r Egyut g e o g r a p h i c u n i t . The monthly consumptive u s e i s t h e sum of t h e w a t e r u s e s by t h e d i f f e r e n t c r o p s r a i s e d i n t h e month c o n s i d e r e d f o r a l l t h e G o v e r n r a t e s of t h e c o u n t r y . The c o m p u t a t i o n r e s u l t s a r e p r e s e n t e d i n T a b l e 6.14.
274
TABLE 6 . 1 4
Q u a n t i t i e s o f w a t e r u s e d by t h e c r o p s i n 1962 and 1975 i n E g y p t ,
106 m 3
Year J a n . Feb. Mar. Apr. 1962 1047 1975 1118
May
J u n e J u l y Aug. S e p . O c t . Nov. Dec.
Year
856 1610 1833 2968 3304 3532 3174 2467 2248 1666 1904 26609 919 1740 2245 4303 5147 5065 2997 1591 1195 1414 2034 29769
The r e m a r k a b l e f e a t u r e a b o u t t h e s e r e s u l t s i s t h e d i s p r o p i r t i o n a t e i n c r e a s e i n t h e t o t a l u s e of w a t e r by c r o p s , 12%, comoared t o t h e i n c r e a s e i n t h e cropued a r e a , 7 . 7 % . T h i s i s q u i t e u n d e r s t a n d a b l e s i n c e t h e g r e a t e s t b u l k of t h e i n c r e a s e i n t h e c r o p p e d a r e a is o c c u p i e d by summer c r o p s which consume much w a t e r , e s p e c i a l l y r i c e . A l s o , most o f t h e a r e a p r e v i o u s l v i r r i g a t e d d u r i n a and f o l l o w i n g t h e f l o o d (August-November) t h e s u m m e r s e a s o n (April-August)
i n t h e pre-dam
t i m e i s now a l s o i r r i g a t e d d u r i n a
i n t h e post-dam t i m e .
L a s t but not l e a s t is t h e
s h o r t e n i n g o f t h e d u r a t i o n of t h e c a n a l s ' w i n t e r c l o s u r e from 40-45 d a y s b e f o r e b u i l d i n g t h e dam t o 18-21 d a y s a f t e r t h e dam h a s been b u i l t .
6.2
EVAPOTRANSPIRATION I N THE SUDAN A g r i c u l t u r e i n t h e Sudan does n o t depend e n t i r e l v on w a t e r s u p p l i e d by i r r i -
g a t i o n a s i n E g y o t . The Sudan c a n b e d i v i d e d i n t o t h r e e z o n e s : t h e s o u t h e r n r a i n b e l t which e x t e n d s from t h e s o u t h e r n f r o n t i e r of t h e c o u n t r y up t o an i s o h y e t a l l i n e of a b o u t 350 m m / y r ,
and t h e t h i r d zone which c o v e r s t h e r e m a i n i n g p a r t of
t h e c o u n t r y . I t i s i n t h i s l a s t zone t h a t i r r i g a t i o n i s p r a c t i s e d e x t e n s i v e l y . Supplementary i r r i g a t i o n i s u s e d t o some e x t e n t i n t h e n o r t h e r n r a i n b e l t and t o a much l e s s e x t e n t i n t h e s o u t h e r n o n e . The development of i r r i g a t i o n i n t h e Sudan i s v e r y much c o n n e c t e d w i t h t h e c o n s t r u c t i o n of
t h e S e n n a r and l a t e r t h e
R o s e i r e s Dams o n t h e B l u e N i l e and Khashm e l G i r b a D a m on t h e R i v e r A t b a r a . V a r i o u s c r o p s grow i n t h e Sudan, of which c o t t o n and c o r n (Dura) c a n b e cons i d e r e d a s t h e p r i n c i p a l o n e s . The i n t r o d u c t i o n and t h e r e a f t e r t h e e x p a n s i o n of i r r i g a t i o n i n t h e G e z i r a h a r e a ( t h e t r i a n g l e c o n f i n e d between t h e White and t h e B l u e N i l e s ) h a s r e s u l t e d i n a c o n s i d e r a b l e i n c r e a s e i n t h e a r e a growing c o t t o n from 250 f e d d a n s i n 1912 t o 194000 f e d d a n s i n 1932 and t o a b o u t 217000 f e d d a n s i n 1946. The t o t a l a r e a r a i s i n g c o t t o n i n t h e Sudan h a s expanded from a b o u t
450000 f e d d a n s i n 1946 t o a b o u t 1180000 f e d d a n s i n 1 9 7 2 . Whereas c o t t o n i s t h e c h i e f s o u r c e of t h e S u d a n ' s e a r n i n g from t h e f o r e i g n c u r r e n c y , t h e Dura ( c o r n , m i l l e t , sorghum, b u l r u s h m i l l e t ,
. . .) ,
which grows i n an a r e a of more t h a n f i v e
m i l l i o n f e d d a n s , i s t h e main e l e m e n t e n t e r i n g p e o p l e ' s food and d r i n k . The w e i g h t e d , d r a i n e d , and f l o a t i n g t y p e s o f l y s i m e t e r s have been used f o r m e a s u r i n g e v a p o t r a n s p i r a t i o n r a t e s from a number of c r o p s s u c h a s w h e a t , c o t t o n , l u c e r n e and b r o a d b e a n s . M o i s t u r e changes h a v e been s t u d i e d i n c o n t r o l l e d f i e l d
275
p l o t s and e v a p o t r a n s p i r a t i o n e s t i m a t e d for some c r o p s from O l i v i e r , Penman. and the heat-balance
6.2.1
methods.
E s t i m a t e s of e v a p o t r a n s p i r a t i o n u s i n g e m p i r i c a l methods
O l i v i e r , u s i n g h i s method, e q . 6.2, e s t i m a t e d t h e e v a p o t r a n s p i r a t i o n f o r some c r o p s a t Wad-Medani.
f o r g r a s s a t Malakal and f o r t h e marshes i n t h e Sudd r e g i o n
a t Shambe ( i n s i d e t h e swamps of t h e Bahr e l J e b e l ) . The r e s u l t s o b t a i n e d from h i s method a r e g i v e n i n T a b l e 6.14.
TABLE 6.14
E v a p o t r a n s p i r a t i o n f o r some c r o p s and v e g e t a t i o n i n t h e Sudan a s e s t i m a t e d bv O l i v i e r (1961)
E v a p o t r a n s p i r a t i o n , mm/day, Month
January February March Apri 1 May June July August September October November December Season o r y e a r
Wad-Medani
for
Malakal
swamps (Shambe)
Cotton
Wheat
Dura
Lubia
Grass
Papyrus
4.65 6.16 8.69
4.65 6.16 8.69
-
4.65
6.62 7.43 7.22
2.95 4.75 5.06 3.92
6.10 7.60 8.69 5.99 3.61 2.22 1.40 1.35 1.72 1.98 4.12 5.28
562
1517
-
10.08
-
2.23 2.95 4.75 5.06 3.92 1265
3.46 2.23 2.95 4.75
5.06 3.92 689
I t h a s been r e p o r t e d by El-Nadi
261
-
6.01 4.46 3.17 2.86 2.70 2.98 3.42
4.50 5.61 1729
(1969) t h a t wheat grown i n t h e e x p e r i m e n t a l
farm of t h e F a c u l t y o f A g r i c u l t u r e , Khartoum U n i v e r s i t y , c a n consiime w a t e r up t o 675 mm d u r i n g i t s growing s e a s o n . He a l s o r e p o r t e d t h a t i n c r e a s e d y i e l d s o f b r o a d b e a n s were o b t a i n e d from t h e s i x t h t o t h e n i n t h i r r i g a t i o n , t h e depth p e r i r r i g a t i o n b e i n g 75 mm (1970). We have e s t i m a t e d t h e consumptive u s e requirement f o r t h e same f o u r c r o p s a t Wad-Medani,
u s i n g two d i f f e r e n t e m p i r i c a l f o r m u l a s .
The f i r s t one i s t h a t g i v e n by H a r g r e a v e s . which e s t i m a t e s t h e e v a p o t r a n s p i r a t i o n a s t h e p r o d u c t of t h e measured or t h e c a l c u l a t e d pan e v a p o r a t i o n .
e q . 5.9,
t i m e s a c r o p c o e f f i c i e n t which depends on t h e p e r c e n t a g e of t h e growing s e a s o n
(1966). The s e c o n d f o r m u l a i s t h e B l a n e y - C r i d d l e o n e . The r e s u l t s o b t a i n e d from t h e c a l c u l a t i o n s a r e g i v e n i n T a b l e 6.15.
276
TABLE 6 . 1 5
E s t i m a t e s o f water u s e by some c r o p s a t Wad-Medani H a r g r e a v e s and t h e B la n e y - C r id d le
C r o p water u s e , mm/day, Month
Hargreaves formula Cotton
Wheat
Dura
9.47 9.07 7.58 6.45
6.69 10.44 10.35
-
January February March Apri 1 May June July August September October November December
1.43 3.25 7.36 10.19 10.24
2.50 4.41
Season o r y e a r
1842
885
-
-
-
-
-
3.82 5.86 7.43 7.46
using t h e
formulas
for
Blaney-Criddle formula Lubia
4.46
-
-
-
2.32 6.11 11.57 8.91
544
943
Cotton
4.71 3.75 1.93 1.27
-
-
Wheat
5.41 4.44 2.23
Dura
Lubia
-
2.65
-
-
1.00 3.45 5.40 5.75 5.32
1.88 3.61
964
480
1.83 5.14 4.80 1.34
-
347
-
-
0.86 3.43 5.36 3.92 46 1
The d i s c r e p a n c y b e t w e e n t h e r e s u l t s o b t a i n e d from t h e t h r e e m e t h o d s , i . e . O l i v i e r , H a r g r e a v e s and B la n e y - C r id d le ,
is wide i n d e e d . A l l t h e f i g u r e s o b t a i n e d
from t h e H a r g r e a v e s method a r e o n t h e h i g h s i d e , w h e r e a s t h e f i g u r e s f o u n d f r o m t h e B l a n e y - C r i d d l e m e t h o d a r e , e x c e p t f o r D u r a , o n t h e low s i d e . S i n c e t h e a v a i l a b l e e v a p o t r a n s p i r a t i o n measurements f o r t h e Sudan are r a t h e r l i m i t e d , o n e h a s t o s e a r c h f o r t h e m o s t r e a s o n a b l e estimates from t h e e m p i r i c a l a n d / o r o t h e r m e t h o d s t h a t may p r o v e r e l e v a n t . We h a v e i n v e s t i g a t e d t h e v a l i d i t y o f t h e e s t i m a t e s o f t h e c l a s s A p a n e v a p o r a t i o n from t h e H a r g r e a v e s e q u a t i o n , u s i n g t h e d i r e c t m e a s u r e m e n t s a v a i l a b l e a t Khartoum and t h e i n d i r e c t f i g u r e s f o r Wad-Medani.
The d a t a l i s t e d i n T a b l e 6 . 1 6 show t h a t t h e mean a n n u a l e s t i m a t e d
p a n e v a p o r a t i o n f o r Khartoum i s almost 10% b i g g e r t h a n t h e m e a s u r e d o n e . The l a r g e s t d i f f e r e n c e s were 20% a n d 14% f o r December and J a n u a r y r e s p e c t i v e l y . F o r t h e r e m a i n i n g m o n t h s o f t h e y e a r t h e d i f f e r e n c e s a r e a t , or b e l o w , 1 0 % . The e s t i m a t e d p a n e v a p o r a t i o n from t h e e q u a t i o n o f H a r g r e a v e s o n a n a n n u a l b a s i s a c r e e s p e r f e c t l y w i t h t h e p a n e v a p o r a t i o n f o u n d i n d i r e c t l y . The l a r a e s t d i f f e r e n c e i n a month i s i n t h e o r d e r o f 10%. T h i s s h o r t d i s c u s s i o n l e a d s u s t o t h e c o n c l u s i o n t h a t t h e w i d e d i s c r e p a n c y b e t w e e n t h e e v a p o t r a n s p i r a t i o n Computed from H a r g r e a v e s ' m e t h o d and t h e o t h e r two m e t h o d s i s n o t m a i n l y c a u s e d by t h e b a s i c e l e me n t i n t h e method, i . e .
t h e estimate of t h e class A pan e v a p o r a t i o n .
I t is q u i t e probable t h a t Hargreaves developed h i s e q u a t i o n on t h e grounds t h a t t h e e v a u o r a t i o n from a f r e e w a t e r s u r f a c e i s a b o u t 0.75 times t h e e v a p o r a t i o n from a c l a s s A p a n . T h i s i s t r u e i n many c a s e s b u t n o t i n e v e r v c a s e . The m e a s u r e d p a n e v a p o r a t i o n a t Khartoum i s 5771 mm/yr, w h e r e a s t h e f r e e w a t e r
277
TABLE 6.16
Comparison between measured and e s t i m a t e d class A pan e v a p o r a t i o n f r o m H a r g r e a v e s ' method f o r Khartoum and Wad-Medani
C l a s s A p a n e v a p o r a t i o n , mm/day, Month
for
W ad-Medani
Khartoum measured
estimated
measured"
estimated
January February March April May June July August September October November December
12.60 14.70 17.23 21.42 23.13 19.31 13.17 10.38 12.19 16.75 15.83 13.03
14.43 16.57 19.43 23.71 24.28 21.71 15.43 10.86 12.29 18.00 18.00 15.71
10.44 11.88 14.45 18.77 19.78 15.87 10.03 8.09 10.82 14.12 12.74 10.28
11.14 12.43 14.57 18.43 17.86 16.14 11.57 8.14 9.29 13.57 13.14 11.57
mean a n n u a l
15.81
17.53
13.11
13.15
~
*Penman e v a p o r a t i o n t i m e s t h e r a t i o E :E available f o r p a n Penman Khartoum
s u r f a c e e v a p o r a t i o n i s a b o u t 8 mm/day or 2920 mm/yr i n d i r e c t l y f o u n d p a n e v a p o r a t i o n a t Wad-Medani
( s e e C h a p t e r 5). The
i s 4785 mm/yr w h e r e a s t h e eva-
p o r a t i o n f r o m a f r e e s u r f a c e o f w a t e r i s 7.5 mm/day or 2738 mm/yr
( s e e Chapters.
T h e s e p a j r s o f e v a p o r a t i o n d a t a show t h a t t h e p a n c o e f f i c i e n t i s a b o u t 0.51 f o r Khartoum and a b o u t 0.56 f o r Wad-Medani.
S u c h r e l a t i v e l y s m a l l v a l u e s o f t h e pan
c o e f f i c i e n t c a n b e c a u s e d by low h u m i d i t y , s t r o n g w i n d , or d i s t a n c e t o a g r e e n c r o p p e d a r e a or d r y f a l l o w l a n d o r any c o m b i n a t i o n o f t h e t w o . T h i s s t a t e o f a f f a i r s i n c l i n e s u s t o a g r e e w i t h D o o r e n b o s and P r u i t t (1977) t h a t t h e c r o p w a t e r u s e c a n b e e x p r e s s e d as t h e p r o d u c t o f a c r o p c o e f f i c i e n t , k c , times t h e so-called
r e f e r e n c e e v a p o t r a n s p i r a t i o n , ET
.
The l a t t e r i s a l s o t h e product of
. I n o t h e r words, t h e crop Pan e v a p o t r a n s p i r a t i o n c a n b e r e l a t e d t o t h e p a n e v a p o r a t i o n by t h e e q u a t i o n t h e pan e v a p o r a t i o n t i m e s t h e pan c o e f f i c i e n t , k
ETP = k c
.
ET o -- k c . k
P
. E
Pan
(6.8)
The r e m a r k a b l e t h i n g h e r e i s t h a t t h e e s t i m a t e d s e a s o n a l e v a p o t r a n s p i r a t i o n by t h e H a r g r e a v e s method when c a l i b r a t e d by t h e c o r r e s p o n d i n g estimates f r o m t h e B l a n e y - C r i d d l e method shows t h a t k
h a s t h e v a l u e s o f 0.523, 0.542, 0.638 and P 0.489 f o r c o t t o n , w h e a t , d u r a a n d l u b i a r e s p e c t i v e l y . The a v e r a g e v a l u e , b e i n g
0.55, i s v e r y c l o s e t o t h e 0.56 f o r t h e a n n u a l e v a p o r a t i o n from o p e n w a t e r com-
278
I t i s becoming
p a r e d t o t h e a n n u a l e v a p o r a t i o n from a c l a s s A pan a t Wad-Medani.
c l e a r t h a t t h e e m p i r i c a l methods may p r o v i d e u s w i t h two p o s s i b i l i t i e s t o s o l v e t h e problem. The f i r s t i s t o o b s e r v e or c a l c u l a t e t h e e v a p o r a t i o n from a c l a s s A p a n , u s i n g H a r g r e a v e s ‘ e q u a t i o n , r e d u c e i t by t h e pan c o e f f i c i e n t and r e d u c e i t f u r t h e r by t h e H a r g r e a v e s c r o p c o e f f i c i e n t . The s e c o n d p o s s i b i l i t y , which i s f a s t e r and e a s i e r t h a n t h e f i r s t o n e , i s t o a p p l y t h e B l a n e y - C r i d d l e
formula
w i t h t h e a p p r o p r i a t e consumptive u s e c o e f f i c i e n t . These two p o s s i b i l i t i e s seem t o b e a d e q u a t e a t l e a s t f o r t h e a r i d and t h e s e m i - a r i d
zones i n t h e Sudan. How-
e v e r , b e f o r e any measure c a n b e u n d e r t a k e n t o work o u t t h i s s t a t e m e n t , one needs t o check w h e t h e r t h e f i g u r e s o b t a i n e d from t h e B l a n e y - C r i d d l e method a r e v a l i d
o r not
6.2.2
The e n e r g y - b a l a n c e method
One o f t h e methods u s e d f o r e s t i m a t i n g t h e w a t e r u s e by i r r i g a t e d c o t t o n i n t h e G e z i r a h a r e a is a c o m b i n a t i o n of m i c r o m e t e o r o l o g i c a l n i q u e s , a s d e s c r i b e d by R i j k s , D . A . ,
t e c h n i q u e s . These t e c h -
( 1 9 7 1 ) , c o n s i s t o f f o u r components: t h e
v e r t i c a l and h o r i z o n t a l f l u x e s d u r i n g t h e day and n i g h t . V e r t i c a l f l u x e s were e s t i m a t e d e i t h e r from t h e n e t r a d i a t i o n and Bouwen r a t i o s o r from t h e Thornthwaite-Holzman f o r m u l a ; h o r i z o n t a l f l u x e s from wind s p e e d s and w e t dry-bulb
and
t e m D e r a t u r e s measured a t v a r i o u s h e i g h t s above t h e c r o p and a t d i f f e r -
e n t d i s t a n c e s from t h e l e a d i n g edge of t h e e x p e r i m e n t a l f i e l d . The measurements were t a k e n on two f i e l d s a d j o i n i n g t h e G e z i r a h r e s e a r c h s t a t i o n (14O 24’N,
3 3 O 2 9 ’ E , 407 m a l t i t u d e ) . The two f i e l d s t o g e t h e r a r e 280 m
i n the north-south
d i r e c t i o n and 150 m i n t h e e a s t - w e s t d i r e c t i o n ,
the t o t a l
a r e a i s 4 . 2 h e c t a r e s . The f i e l d s were b o r d e r e d by o t h e r c o t t o n f i e l d s t o t h e e a s t and w e s t , by a f i e l d of sorghum t o t h e s o u t h and by b a r e f a l l o w t o t h e n o r t h . T h r e e m a s t s w e r e p l a c e d a t v a r i a b l e d i s t a n c e s from t h e n o r t h e r n edge of t h e f i r s t f i e l d . Each mast c a r r i e d f o u r p a i r s of w e t A s t h e c r o p grew.
and d r y - b u l t
thermometers.
t h e thermometers were g r a d u a l l y r a i s e d , s o t h a t t h e l o w e s t was
20-25 c m above t h e t o p of t h e p l a n t s . R e f e r r i n g t o t h e d e f i n i t i o n s k e t c h ( F i g . 6 . 1 7 . ) , t h e day-time
v a l u e s of E
were c a l c u l a t e d from t h e e q u a t i o n s Rn + G Ev = ___
1 + a
(6.9)
and
6
= 0.64
6T 6e
-
(6.10)
279
where
Rn
=
G
= s o i l h e a t f l u x , cal/cm2
B
= Bowen's r a t i o ,
n e t r a d i a t i o n , cal/cm2
= s l o p e of
.
unit t i m e ,
.
unit t i m e ,
and
t h e t e m p e r a t u r e , T , v e r s u s t h e vapour p r e s s u r e , e , a t e l e v a t i o n
2.
Wind direct ion ___)
Fig. 6.17. Diagram of h o r i z o n t a l and v e r t i c a l f l u x e s of w a t e r vapour and t h e symbols u s e d ; z i s t h e h e i g h t of t h e e v a p o r a t i n g s u r f a c e ; z2 t h e h e i g h t a t which t h e Bouwen r a t i o was measured (Rijks, D . A . , 1971)
The v e r t i c a l f l u x d u r i n g t h e n i g h t - t i m e
was c a l c u l a t e d from t h e formula of
of Thornthwai te-Holzman (6.11)
where L = l a t e n t h e a t of v a p o r i z a t i o n , 1)
=
cals/gm,
d e n s i t y of a i r , gm/cm3
k = Von Karman's c o n s t a n t , u = wind s p e e d , cm/sec, z = height,
cm, and
d = z e r o p l a n e d i s p l a c e m e n t , cm
Since the values obtained f o r E have been o m i t t e d .
V
f o r t h e night-time
were v e r y s m a l l , they
280
The d i v e r g e n c e o f t h e h o r i z o n t a l f l u x of t h e l a t e n t h e a t , A E h , v a t i o n s z1 and z
2
between e l e -
o v e r a g i v e n p e r i o d i s g i v e n by t h e e q u a t i o n
-
. u
6e
z
62 .6x
(6.12)
where E
= r a t i o of mole w e i g h t o f w a t e r vapour t o mole w e i g h t o f a i r ,
p = a i r p r e s s u r e , m b a r s , and
x = d i s t a n c e from l e a d i n g e d g e , cm The d a i l y e v a p o r a t i o n t o t a l s E l and E z (E b e i n g t h e more downwind of t h e two 2 e s t i m a t e s ) w e r e t a k e n t o r e f e r t o t h e r e s p e c t i v e l o c a t i o n s o f AEh. I f t h e upwind mast had been a t t h e l e a d i n g edge of t h e f i e l d , t h e y would have been t h e sum o f AE and t h e downwind e s t i m a t e of E . I f b o t h m a s t s w e r e i n s i d e t h e f i e l d , t h e h e s t i m a t e of E i s t h e sum o f AEh and t h e mean of t h e upwind and downwind v a l u e s
of E
.
The a c c u r a c y o f t h e c o m b i n a t i o n of methods employed i n t h a t work and of t h e v a r i o u s a s s u m p t i o n s made was t e s t e d by t h e e n e r g y - b a l a n c e .
The t e s t showed t h a t
t h e income and e x p e n d i t u r e o f e n e r g y f o r a g i v e n p e r i o d ( m o s t l y an i r r i q a t i o n c y c l e ) were always d i f f e r e n t , and t h e d i f f e r e n c e d e c r e a s e d w i t h i n c r e a s e i n f e t c h . When t h e whole a r e a w a s t a k e n , t h e e r r o r dropped t o 8 % . C a l c u l a t i o n s f o r p e r i o d s e a r l i e r i n t h e g r o w i n s s e a s o n have i n d i c a t e d l a r g e r d i f f e r e n c e s i n t h e e n e r g y b a l a n c e , as have c a l c u l a t i o n s f o r some i n d i v i d u a l d a v s . D e s p i t e t h o s e d i f f e r e n c e s , t h e r e s u l t s o b t a i n e d from t h a t i n v e s t i g a t i o n c a n b e viewed as t h e b e s t t h a t w e h a v e . W e s h a l l t h e r e f o r e c o n s i d e r t h e mean of
E l and E z a s a f a i r r e p r e s e n t a t i o n of t h e e v a p o t r a n s u i r a t i o n from an i r r i g a t e d c o t t o n f i e l d i n t h e G e z i r a h a r e a . The d a i l y and t h e mean monthly e v a p o t r a n s p i r a t i o n f i g u r e s a r e l i s t e d i n T a b l e 6.17. The mean d a i l y e v a p o t r a n s p i r a t i o n i n O c t o b e r . November and December g i v e n i n t h i s t a b l e d e v i a t e s from t h e c o r r e s u o n d i n g f i g u r e s e s t i m a t e d by t h e B l a n e y - C r i d d l e method by o n l y 6.7, 5.7 and 7.3% r e s p e c t i v e l y . These s m a l l d i f f e r e n c e s a r e q u i t e a c c e p t a b l e , a s t h e e n e r g y b a l a n c e s f o r O c t o b e r and December d i d n o t c o v e r t h e whole month, b u t 15 and 20 davs r e s p e c t i v e l y . Moreover, t h e r e s u l t s o b t a i n e d from t h e b a l a n c e method have been r e p o r t e d t o i n c l u d e some e r r o r as t h e e x p e n d i t u r e w a s n o t e q u a l t o t h e incoming e n e r g y ( R i j k s , D.A., 1 9 7 1 ) . I n any c a s e , t h e s a t i s f a c t o r y s i m i l a r i t y between t h e f i g u r e s o b t a i n e d from t h e two methods e n c o u r a g e s u s t o a p p l y t h e B l a n e y - C r i d d l e method. I t i s o n l y f o r t h e p u r p o s e of e s t i m a t i n g t h e a n n u a l p o t e n t i a l e v a p o t r a n s p i r a t i o n i n t h e a r i d zone i n t h e Sudan t h a t w e s h a l l i n c r e a s e t h e p r o d u c t o f t h e day-time h o u r s and t e m p e r a t u r e by a b o u t 10%.
281
TABLE 6.17
D a i l y e v a p o t r a n s p i r a t i o n from i r r i g a t e d c o t t o n i n t h e G e z i r a h a r e a e s t i m a t e d from t h e e n e r g y - b a l a n c e method Evapo t r a n s piration,
Date day'
mm
mean monthly, mm/day
18.10.1965 3.29 19.10.1965 3.77 20.10.1965 4.07 21.10.1965 3.82 22.10.1965 4.13 23.10.1965 5.56 24.10.1965 7.21 25.10.1965* 7.72 26.10.1965 7.75 27.10.1965 7.78 28.10.1965 7.79 29.10.1965 6.35 30.10.1965 31.10.1965 5.60
5.76
01.11.1965 02.11.1965 4.64 03.11.1965 5.20 04.11.1965 5.85 05.11.1965 6.91 06.11.1965* 7.80 07.11.1965 5.20 08.11.1965 6.12 09.11.1965 6.97 10.11.1965 6.49 f
Evapot r a n s piration,
Evapotranspiration,
Date
mean day' monthly, mm mm/day
11.11.1965 6.40 12.11.1965 5.66 13.11.1965 6.12 14.11.1965 15.11.1965 5.85 16.11.1965 6.35 17.11.1965 6.72 18.11.1965* 6.35 19.11.1965 6.92 20.11.1965 5.36 21.11.1965 7.08 22.11.1965 6.10 23.11.1965 6.61 24.11.1965 6.42 25.11.1965* 5.27 26.11.1965 6.31 27.11.1965 5.20 28.11.1965 4.90 29.11.1965 5.92 30.11.1965 5.52 01.12.1965 02.12.1965 03.12.1965' 04.12.1965
6.08
5.55 5.24 5.99 6.53
Date
mm
05.12.1965 06.12.1965 07.12.1965 08.12.1965 09.12.1965 10.12.1965 11.12.1965 12.12.1965 13.12.1965 14.12.1965 no records
5.85 6.70 6.02 6.36 6.08 5.02 5.16 5.93 5.58 5.26
mean monthly, mm/day
5.71
-
-
24.12.1965 25.12.1965 26.12.1965 27.12.1965 28.12.1965 29.12.1965 30.12.1965 31.12.1965'
6.29 5.57 5.11 5.53 5.47 5.31 4.89 6.21
01.01.1966 02.01.1966 03.01.1966 04.01.1966
6.95 7.42 6.78 5.65
6.70
f i e l d is i r r i g a t e d
6.2.3
Penman's method
I n t h e semi-humid
and humid areas s o u t h o f i s o h y e t of 700 mm/yr r a i n f a l l , t h e
use of t h e B l a n e y - C r i d d l e
f o r m u l a may be u n j u s t i f i e d on t h e grounds t h a t t h e
mean d a i l y t e m p e r a t u r e i s n e a r l y c o n s t a n t , whereas o t h e r f a c t o r s i n f l u e n c i n g e v a p o t r a n s p i r a t i o n could be widely v a r i a b l e Dupriez, G . L . ,
(1959) r a i s e d s e r i o u s o b j e c t i o n s t o t h e u s e of T h o r n t h w a i t e ' s
f o r m u l a , e q . 6.3.7,i n t r o p i c a l a r e a s or i n a r e a s where t h e a i r t e m p e r a t u r e v a r i e s b u t o n l y a l i t t l e d u r i n g t h e c o u r s e of t h e y e a r . The comparisons h e made between measured and c a l c u l a t e d e v a p o r a t i o n and p o t e n t i a l e v a p o t r a n s p i r a t i o n a t a number o f s t a t i o n s i n t h e Congo and i n Rwanda/Burundi
have shown t h a t t h e
Penman f o r m u l a p r o v i d e s t h e b e s t e s t i m a t e f o r t h e loss of w a t e r . The a b s e n c e o f any e x p r e s s i o n f o r t h e s a t u r a t i o n d e f i c i t i n t h e T h o r n t h w a i t e f o r m u l a i s l i k e l y
282
t o b e t h e r e a s o n why t h i s f o r m u l a o v e r e s t i m a t e s t h e ET i n t h e humid s e a s o n and P underestimates i t i n t h e dry season. The monthly p o t e n t i a l e v a p o t r a n s p i r a t i o n i s r e l a t e d t o Penman's e v a p o r a t i o n by t h e r e l a t i o n
ET
P
= 0.91 E
penman
+ 2.5
The r a t i o o f t h e a n n u a l ET measured e v a p o r a t i o n i s 0 . 9 3 .
( i n mm)
P
t o t h e annual E
(6.13)
penman
= 0.97,
and t o t h e annual
R i j k s i n v e s t i g a t e d t h e e v a p o r a t i o n from a p a p y r u s swamp a t Namulonge i n Uganda i n t h e p e r i o d from 8 March up t o and i n c l u d i n g 11 A p r i l . H e u s e d t h e Bowen's r a t i o method and t h e Penman method t o e s t i m a t e t h e e v a p o r a t i o n from a f r e e w a t e r s u r f a c e a s w e l l a s t h e e v a p o t r a n s p i r a t i o n from t h e swamp. I n t h a t p e r i o d where t h e a v e r a g e d a i l y t e m p e r a t u r e f l u c t u a t e d between 20.9°C and 24.2OC t h e a v e r a g e e v a p o r a t i o n from open w a t e r e s t i m a t e d by Penman's method was 5 . 5 mm/ d a y , p o t e n t i a l e v a p o t r a n s p i r a t i o n from t h e swamp u s i n g Penman's e v a p o r a t i o n r e d u c e d by 0 . 8 was 4 . 4 mm/day and from Bowen's r a t i o method u s i n g measured m e t e o r o l o g i c a l p a r a m e t e r s was 3.81 mm/day
(Rijks, D.A.,
1 9 5 9 ) . Those r e s u l t s
s u g g e s t t h e u s e o f a r e d u c t i o n c o e f f i c i e n t o f 0 . 6 9 t o b e m u l t i p l i e d by Penman's e v a p o r a t i o n s o a s t o deduce t h e e v a p o t r a n s p i r a t i o n from a swamp. Though t h e experiment took p l a c e d u r i n g t h e r a i n y s e a s o n , i t i s n o t c l e a r whether t h e e s t i mated e v a p o t r a n s p i r a t i o n was t h e a c t u a l or t h e p o t e n t i a l o n e . The e v a p o r a t i o n from a f r e e w a t e r s u r f a c e e s t i m a t e d from t h e method o f Penman f o r M a l a k a l , M o n g a l l a / J u b a , and Wau i s 5 . 4 , 5 . 5 and 5 . 8 mm/day f o r t h e whole y e a r . The mean monthly v a l u e s f o r t h e s e s t a t i o n s a r e g i v e n i n T a b l e 5 . 4 and i n Fig. 5.4. W e s h a l l assume t h e Penman e v a p o r a t i o n f o r Shambe i n t h e Sudd r e g i o n t o be t h e a r i t h m e t i c mean o f t h e e v a p o r a t i o n f o r t h e s a i d s t a t i o n s , i . e . 2033 mm/yr.
The p o t e n t i a l e v a p o t r a n s p i r a t i o n a t Shambe e s t i m a t e d from t h e method o f
O l i v i e r and from t h e t a n k measurements i s 1729 mm/yr
( s e e T a b l e 6 . 1 4 ) . These
f i g u r e s g i v e a r e d u c t i o n f a c t o r o f a b o u t 0 . 8 5 f o r t h e swamps and n o t 0 . 6 9 a s p r o p o s e d by R i j k s . A c c o r d i n g l y , t h e Penman open w a t e r e v a p o r a t i o n w i l l be cons i d e r e d a s t h e b a s i s f o r e s t i m a t i n g t h e p o t e n t i a l e v a p o t r a n s p i r a t i o n from t h e semi-humid and humid a r e a s i n t h e Sudan. The r e d u c t i o n f a c t o r s w e s h a l l u s e a r e from 0 . 9 5 t o 0 . 9 0 f o r t h e a r e a s o u t s i d e t h e swamps and from 0 . 8 5 t o 0 . 8 0 f o r t h o s e a r e a s i n s i d e t h e swamps o f t h e Bahr e l J e b e l and Bahr e l - G h a z a l B a s i n s , and t h e Machar swamps. T h e s e v a l u e s t o g e t h e r w i t h t h e map, F i g . 5 . 1 0 , showing t h e Penman f r e e w a t e r s u r f a c e e v a p o r a t i o n , h a v e b e e n i n c o r p o r a t e d i n p r e p a r i n g t h e p o t e n t i a l e v a p o t r a n s p i r a t i o n r e q u i r e m e n t f o r t h e S u d a n . T h i s r e q u i r e m e n t on an a n n u a l b a s i s c a n be r e a d d i r e c t l y from t h e map i n F i g . 6 . 1 8 .
283
Fig. 6.18. Map s h o w i n g l i n e s o f e q u a l p o t e n t i a l e v a p o t r a n s p i r a t i o n r e q u i r e m e n t , m m / y r , for t h e S u d a n
284
EVAPOTRANSPIRATION I N THOSE PARTS OF RWANDA-BURUNDI,
6.3
UGANDA,
TANZANIA
AND KENYA WHICH ARE SITUATED W I T H I N THE N I L E BASIN
I n t h e s e a r e a s t h e e v a p o r a t i o n from open w a t e r and t h e e v a p o t r a n s p i r a t i o n from v e g e t a t e d s u r f a c e s a r e measured from pans and l y s i m e t e r s r e s p e c t i v e l y . E s t i m a t e s are o b t a i n e d from t h e method o f Penman a n d / o r some m i c r o c l i m a t o l o g i c techniques. Dupriez, G . L . ,
(1959) c r i t i c i z e d s e v e r e l y t h e a p p l i c a t i o n of
T h o r n t h w a i t e ' s method i n e q u a t o r i a l a r e a s . H e measured t h e ET
from l y s i m e t e r s P a t t h e s t a t i o n s o f K i s o z i and Musas which are l o c a t e d w i t h i n t h e t e r r i t o r y o f
Rwanda-Burundi
!
E
v e r y c l o s e t o t h e d i v i d e o f t h e N i l e Catchment ( s e e F i g . 6 . 1 9 . )
31°
3 6O
F i g . 6.19. Map showing l i n e s of e q u a l p o t e n t i a l e v a p o t r a n s p i r a t i o n requirement, mm/yr, for some p a r t s of Rwanda-Burundi, Uganda, T a n z a n i a , and Kenya
285
The monthly ET
P
a t t h e s e two s t a t i o n s a s o b s e r v e d by D u p r i e z are t a b u l a t e d
below. The ET a t K i s o z i i s s m a l l e r t h a n t h a t a t Musas mainly b e c a u s e of i t s P h i g h a l t i t u d e and t h e r e u p o n i t s lower t e m p e r a t u r e . The most i m p o r t a n t t h i n g h e r e i n mm/day, i n t h i s a r e a i s t h a t t h e ET P) s u r f a c e e v a p o r a t i o n , a l s o i n mm/day.
Measured ET Month
Kisozi
P’
i s n e a r l y 95% of t h e Penman f r e e w a t e r
mm/month,
Musas
( S 3O33’, E 29O41’, h=2155 m )
January February March Apri 1 May June July August September October November December
76 . O 67.9 86.1 83.7 79.7 78.6 93.7 99.1 119.3 103.7 87.0 75.5
Hanna, L . W . ,
( S 3’39’,
E 3 0 ° 2 1 ’ , h=1260 m) 137.9 109.7 142.7 136.9 105.9 100.4 121.7 111.3 138.3 148.5 151.3 123.5
1 0 5 0 . 3 mm
Year
a v e r a g e of 1957-58
1 5 2 7 . 9 mm
( 1 9 7 1 ) , w h i l e s t u d y i n g t h e e f f e c t s o f w a t e r a v a i l a b i l i t y on t e a
y i e l d s i n Uganda, c o n c l u d e d t h a t ET
P
f r o & a full c o v e r of t e a i s n e a r l y 0 . 8 5
t i m e s Penman e v a p o r a t i o n . I n E a s t A f r i c a t h e b e s t e s t i m a t e of p o t e n t i a l evapot r a n s p i r a t i o n from c r o p s i s d e r i v e d from Penman‘s f o r m u l a . The network o f E n t e b b e , Kabanyolo, J i n j a and K i t u z a s t a t i o n s f o r which t h e ten-day means of Penman e v a p o r a t i o n ( s e e F i g . 6 . 2 0 . ) was r e p o r t e d by Hanna t o p e r m i t a r e a s o n a b l y a c c u r a t e e s t i m a t e o f t h e p o t e n t i a l e v a p o t r a n s p i r a t i o n w i t h i n a narrow zone a d j a c e n t t o Lake V i c t o r i a . I n t h a t z o n e , many o f t h e e s t a t e s o f s u g a r cane and t e a a r e c o n c e n t r a t e d , which makes t h e zone d e n s e l y p o p u l a t e d . A s h o r t d i s t a n c e n o r t h o f Kabanyolo i s s i t u a t e d t h e C o t t o n Research S t a t i o n a t Namulonge ( 0 ° 3 2 ’ N , 3Z037’E, and h=1100 m ) .
A t t h e n o r t h e r n boundary of t h e
s t a t i o n t h e r e i s a swamp a b o u t 500 m wide and r u n n i n g from NW t o SE. Meteorol o g i c a l measurements w e r e t a k e n i n t h e swamp and d i s c u s s e d by R i j k s ( 1 9 6 9 ) . The e v a p o r a t i o n from an o l d s t a n d o f p a p y r u s was e s t i m a t e d by t h e Bowen r a t i o method.
I t was found t h a t a b o u t 30% o f t h e n e t r a d i a t i o n r e a c h i n g t h e canopy was conv e r t e d i n t o s e n s i b l e h e a t . The l a y e r formed by t h e h e a d s o f t h e p a p y r u s seemed t o a c t a s a m a j o r r e s i s t a n c e t o t u r b u l e n t exchange o f w a t e r vapour from t h e u n d e r g r o w t h . The e v a p o t r a n s p i r a t i o n from t h e o l d s t a n d o f p a p y r u s w a s e s t i m a t e d t o be 60
15 p e r c e n t o f Penman e s t i m a t e s of e v a p o r a t i o n from open w a t e r , E
.
The mean e v a p o t r a n s p i r a t i o n from t h e swamp for t h e p e r i o d from 8 March up t o and
286
Entebbe
L
>5
. U
€ 4
E
$3 c
g 6
8
65 C
E4 G
a
Kituza/
3
'
J
F M
A
M
J J A Month
S
I
O
,
N
,
D
Fig 6 . 2 0 . Ten-day means o f Penman e v a p o r a t i o n a t f o u r s t a t i o n s i n S o u t h e r n Uganda (Hanna, L . W . , 1 9 7 1 ) . i n c l u d i n g 11 A p r i l i s 3.81 mm/day. T h i s f i g u r e i s s m a l l compared t o t h e mean a n n u a l e v a p o t r a n s p i r a t i o n from t h e Lake Kyoga swamps g i v e n a s 4 . 7 2 and 5 . 1 mm/ day by O l i v i e r and H u r s t , r e s p e c t i v e l y . I f w e t r u s t O l i v i e r ' s e s t i m a t e s ( 1 9 6 1 ) , t h e mean monthly e v a p o t r a n s p i r a t i o n f i g u r e s a r e t h e n 7 . 0 , 8 . 1 , 5 . 9 , 4 . 2 , 3 . 3 , 3 . 8 , 3 . 7 , 3 . 4 , 4 . 1 , 4 . 1 , 4 . 9 and 4 . 6 mm/day f o r t h e months from J a n u a r y t o December, r e s p e c t i v e l y . According t o Dagg, M . ,
(1972) t h e w a t e r u s e w i l l r i s e from a b o u t 0 . 4 E
when t h e p l a n t s a r e young t o 1 . 0 when f u l l c o v e r i s a c h i e v e d . The maximum ETp/Eo
=
1 . 0 f o r c o t t o n i s a t t h e b e g i n n i n g of t h e f o u r t h month a f t e r p l a n t i n g ,
Namulonge, Uganda, and 1.1 f o r s u g a r c a n e a f t e r f o u r months from p l a n t i n g , Moshi, T a n z a n i a . The e v e r g r e e n f o r e s t s have a r a t i o E T /E P
O
=
0 . 9 a s an a v e r a g e f o r t h e
whole y e a r . A t Muguga, Kenya, t h e s e a s o n a l p o t e n t i a l e v a p o t r a n s p i r a t i o n of maize
i s 560 mm, whereas t h e open w a t e r e v a p o r a t i o n f o r t h e same s e a s o n i s a b o u t 840 m m , i . e . E T /E = 0 . 6 7 . The e v a p o t r a n s p i r a t i o n from a l y s i m e t e r r a i s i n g p e r e n P O n i a l g r a s s a t t h e same l o c a t i o n was o b s e r v e d by G l o v e r , J . , and F o r s g a t e , J . , f o r a p e r i o d o f 126 days i n 1962 ( 1 9 6 4 ) . From t h i s i n v e s t i g a t i o n t h e y concluded t h a t ET = E
- 1 . 1 7 f o r 5-day p e r i o d s ( r 2 = \ 0 . 9 4 ) and
10-day p e r i o d s ( r 2 = 0 . 9 7 ) , b o t h E
ET = 1 . 0 3 E
and ET a r e e x p r e s s e d i n mm/day.
r e l a t i o n s E T = e v a p o t r a n s p i r a t i o n from t h e l y s i m e t e r and E using the r a t i o range of E
N
- 1.35 for In these
= Penman e v a p o r a t i o n
f o r t h e r e l a t i v e d u r a t i o n of t h e b r i g h t s u n s h i n e . For t h e
from 5 t o 6 mm/day t h e c o r r e s p o n d i n g r a t i o ET/E
=
0 . 7 5 . The o b s e r -
v a t i o n s from t h i s e x p e r i m e n t s u p p o r t s t h e c o n c e p t o f Veihmeyer and Hendrickson t h a t t h e a c t u a l e v a p o t r a n s p i r a t i o n remains a t t h e p o t e n t i a l l e v e l a s l o n g as t h e s o i l m o i s t u r e i n t h e t o p 4 f t i s i n t h e r a n g e from f i e l d c a p a c i t y t o w i l t i n g p o i n t .
287
L a s t b u t n o t l e a s t , we have t h e map
o f e v a p o r a t i v e demand f o r E a s t A f r i c a
p r e p a r e d by R i j k s , Owen, and Woodhead, and p r e s e n t e d by Dagg ( 1 9 7 2 ) . A s a b a s i s f o r c o n v e r t i n g t h a t map t o a n o t h e r g i v i n g t h e p o t e n t i a l e v a p o t r a n s p i r a t i o n r e q u i r e m e n t o f E a s t A f r i c a , w e c o n s i d e r e d a c o n v e r s i o n f a c t o r of 0 . 9 e x c e p t f o r t h e swamps where a f a c t o r o f 0 . 8 was u s e d . The open w a t e r e v a p o r a t i o n t h u s conv e r t e d t o p o t e n t i a l e v a p o t r a n s p i r a t i o n h a s been compared t o t h e measured ET
at P t h e l o c a t i o n s mentioned i n t h i s s e c t i o n and a t o t h e r l o c a t i o n s and t h e n e c e s s a r y c o r r e c t i o n s made. The map t h u s o b t a i n e d i s a s shown i n F i g . 6 . 1 9 . The p a r t i a l maps of t h e N i l e B a s i n shown i n F i g s . 6.16., 6.18., and 6.19., have been combined i n one map r e p r e s e n t i n g t h e p o t e n t i a l e v a p o t r a n s p i r a t i o n r e q u i r e m e n t f o r t h e whole b a s i n , a s shown i n F i g . 6 . 2 1 . Comparing t h i s f i g u r e t o Fig 1)
6 . 2 . , one c a n e a s i l y n o t i c e t h e f o l l o w i n g :
Both maps i n F i g s . 6 . 2 . , and F i g . 6 . 2 1 . , show a l m o s t t h e same p a t t e r n o f r e q u i r e m e n t from t h e M e d i t e r r a n e a n S e a c o a s t and southward up t o P M a l a k a l . The map i n F i g . 6 . 2 1 . , shows an ET r e q u i r e m e n t a l m o s t 5% s m a l l e r P t h a n t h a t g i v e n by t h e map i n F i g . 6 . 2 . The maximum d i f f e r e n c e between t h e ET
two does n o t , however, e x c e e d 10%. ii)
The map i n F i g . 6 . 2 1 . , shows two d e p r e s s i o n s : one t o t h e w e s t , i n s i d e t h e swamps o f Bahr e l Ghazal and Bahr e l J e b e l B a s i n s , and t h e s e c o n d t o t h e e a s t , i n s i d e t h e Machar swamps, i n t h e b a s i n o f t h e S o b a t . I n t h e s e two d e p r e s s i o n s t h e p o t e n t i a l e v a p o t r a n s p i r a t i o n r e q u i r e m e n t d r o p s t o less t h a n 1250 m m / y r ,
i . e . a mean a n n u a l o f 3.4 mm/day.
i i i ) S o u t h and e a s t of J u b a t h e r e i s a s h a r p r i s e i n t h e ET
warm Kenya i t may r e a c h 2300 m m / y r
mm/yr,
requirement. In P and i n n o r t h e r n Uganda i t r e a c h e s 2000
though i n a l i m i t e d a r e a o n l y . Between Lake V i c t o r i a and each o f t h e
a d j a c e n t l a k e s , Kyoga, A l b e r t , Edward and T a n g a n i y k a , t h e r e i s a share d e c l i n e or r i s e i n t h e p o t e n t i a l e v a p o t r a n s p i r a t i o n r e q u i r e m e n t . ET r e a c h 2000 mm/yr o r f a l l t o 1100 mm/yr,
may P d e p e n d i n g on t h e f a l l or t h e r i s e
i n t h e ground s u r f a c e l e v e l . iv)
The d e t a i l s i n i i ) and i i i ) do n o t a p p e a r i n F i g . 6 . 2 . A l l t h a t c a n be s e e n from i t i s t h a t t h e ET
r e q u i r e m e n t o f t h e a r e a e a s t and s o u t h - e r s t of J u b a P The a r e a w e s t , s o u t h and s o i t h - w e s t of J u b a h a s an E T P r e q u i r e m e n t o f less t h a n 1500 m m / y r , b u t s t i l l above 1250 m m / y r .
e x c e e d s 1500 m m / y r .
288
Fig. 6.21. Yap showing l i n e s o f equal p o t e n t i a l e v a p o t r a n s p i r a t i o n requirement mm/yr, f o r t h e N i l e Basin
289
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T i l e d r a i n a g e of i r r i g a t e d l a n d s i n E g y p t . T h e s i s s u b m i t t e d t o t h e F a c u l t y o f E n g i n e e r i n g , C a i r o U n i v e r s i t y i n p a r t i a l f u l f i l l m e n t of t h e r e q u i r e m e n t f o r Ph.D. d e g r e e , C a i r o , E g y p t .
29 1
S h a h i n M . M . , and E l - S h a l , M . I . , 1 9 6 9 . An i n v e s t i g a t i o n of t h e consumptive u s e o f water f o r c r o p s and t h e f r e q u e n c y of i r r i g a t i o n i n t h e United Arab R e p u b l i c . T r a n s . 7 t h Congress o f I C I D , N e w Mexico: 23.27-23.51. S h a h i n , M . M . , e t a l , 1973. I r r i g a t e d c o t t o n : A world-wide s u r v e y ( e d i t e d by F r a m j i , K . K . , and Mahajan, I . K . ) , I C I D P u b l . , N e w D e l h i , 321 p p . Shenouda, E l - G i b a l i , Tawdros and Gamal, 1 9 6 6 . I r r i g a t i o n r e q u i r e m e n t of e a r l y c o r n and t h e b e s t i r r i g a t i o n f r e q u e n c y f o r t h e c r o p w i t h a c o m p a r a t i v e s t u d y f o r t h e p l a n t r e q u i r e m e n t s o f e a r l y c o r n and l a t e c o r n i n Middle Egypt. Agr. R e s . R e v . , Vol. 4 4 , No. 1 : 159-170, C a i r o , E g y p t . S l a t y e r , R . O . , and M c I l r o y , I . C . , 1961. P r a c t i c a l m i c r o c l i m a t o l o g y . C S I R 0 , P l a n t I n d . D i v . , Canberra. S t a n h i l l , G . , 1961. A comparison o f methods of c a l c u l a t i n g p o t e n t i a l e v a p o t r a n s p i r a t i o n from c l i m a t i c d a t a . I s r . J o u . Agr. R e s . , No. 11: 1 5 9 - 1 7 1 , J e r u s a l e m . T a n n e r , C . B . , 1 9 6 7 . I r r i g a t i o n o f a g r i c u l t u r e l a n d ( e d i t e d by Hagan, R . , H a i s e , H . , E d m i n s t e r , T . , and D i n a u e r , R . ) . C h a p t e r 29: Measurement o f e v a p o r a t i o n : 534-574, ( p u b l i s h e d by t h e American S o c i e t y of Agronomy). W i s c o n s i n , USA. T h o r n t h w a i t e , C . W . , 1 9 4 8 . An a p p r o a c h toward a r a t i o n a l c l a s s i f i c a t i o n o f c l i m a t e . The Geogr. R e v . , Vol. 38, No. 1: 55-94. T h o r n t h w a i t e , C . W . , and M a t h e r , J . R . , 1 9 5 5 . The water b a l a n c e , P u b l i c a t i o n i n c l i m a t o l o g y No. 8 : 1-104. Turc, L . , 1961. E v a l u a t i o n des b e s o i n s e n e a r d ' i r r i g a t i o n , e v a p o t r a n s p i r a t i o n p o t e n t i e l l e . Ann. Agron. 1 2 ( 1 ) : 13-50. U n i t e d S t a t e s Department o f A g r i c u l t u r e , 1955. Yearbook o f a g r i c u l t u r e : W a t e r . US Government P r i n t i n g O f f i c e . Z e i n e l - A b e d i n e , A . , and A b d a l l a h , M . , 1949. C y c l i c and s e a s o n a l m o i s t u r e v a r i a t i o n s on C a i r o (Fouad I ) U n i v e r s i t y f a r m , G i z a d i s t r i c t , E g y p t . S o i l S c i e n c e , V o l . 6 8 , No. 3: 213-227. Z e i n e l - A b e d i n e , A . , A b d a l l a h , M . , and Abd e l - S a m i e , 1 9 6 7 . E v a p o t r a n s p i r a t i o n s t u d i e s on maize i n G i z a , UAR.Paper p r e s e n t e d a t t h e Symposium on t h e u s e o f r a d i o - i s o t o p e s i n e v a p o t r a n s p i r a t i o n s t u d i e s , I s t a n b u l , Turkey.
293
Chapter 7
GEOLOGY AND GEOHYDROLOGY O F THE NILE BASIN
7.1 7.1.1
GEOLOGY
The E q u a t o r i a l Lakes P l a t e a u
The o l d P r e c a m b r i a n f o r m a t i o n s o f East A f r i c a have been d a t e d between, s a y , 4 0 0 , a n d more t h a n 3000 m i l l i o n y e a r s . Of t h e s e f o r m a t i o n s t h e Nyanza S h i e l d i s t h e one l o c a t e d i n t h o s e p a r t s o f Uganda and T a n z a n i a w i t h i n t h e N i l e B a s i n . T h i s s h i e l d c o m p r i s e s r o c k s of t h e G n e i s s Complex of N o r t h e r n Uganda and of o t h e r s y s t e m s o f North-Western a n t l y east-west
Uganda and C e n t r a l T a n z a n i a and h a s a predomin-
t r e n d . The Nyanzian s y s t e m i s t h u s made up of b a s i c , i n t e r -
m e d i a t e and a c i d v o l c a n i c r o c k s w i t h i n t e r b e d d e d s e d i m e n t s of c o a r s e m a t e r i a l . The d e p t h o f t h i s s y s t e m e x t e n d s some t h o u s a n d s of metres and i s developed a r o u n d Lake V i c t o r i a ( s e e map, F i g . 7.1.) where i t s r o c k s are a s s o c i a t e d w i t h i n t r u s i v e g r a n i t e s . I n some o t h e r p a r t s of Uganda, Kenya and T a n z a n i a t h e s y s t e m c o n s i s t s m a i n l y o f b o u l d e r c o n g l o m e r a t e s , mudstones and q u a r t z i t e s . Where t h i s
i s t h e c a s e t h e s y s t e m i s c a l l e d K a v i r o n d i a n , and i n some l o c a t i o n s i t s i m p l y rests on t h e Nyanzian f o r m a t i o n s . The r o c k s of b o t h s y s t e m s , t h e Nyanzian and t h e K a v i r o n d i a n , form p a r t o f t h e Nyanza S h i e l d ( S a g g e r s o n , E . , I n Uganda t h e Buganda-Tor0
1972).
r o c k s , p r e d o m i n a n t l y a r g i l l a c e o u s , occupy a broad
a r c e x t e n d i n g from t h e n o r t h e r n s h o r e s o f Lake V i c t o r i a t o t h e Ruwenzori i n t h e w e s t e r n , a s w e l l a s t h e n o r t h e r n and e a s t e r n s h o r e s o f Lake Kyoga. The series known a s t h e Karagwe-Ankolean,
which i s t h o u g h t t o b e 1400 m i l l i o n y e a r s o l d ,
c o n s i s t s o f metamorphosed r o c k and i s a b o u t 10000 metres t h i c k . T h i s s e r i e s o c c u p i e s t h e m a j o r p a r t of t h e a r e a w e s t of Lake V i c t o r i a and t h e b o r d e r s w i t h Rwanda and B u r u n d i . The Karagwe-Ankolean
series i s s e p a r a t e d from t h e s o u t h -
w e s t e r n s h o r e o f Lake V i c t o r i a by t h e Bukoban s y s t e m , a s shown on t h e map, F i g .
7.1. The l a t t e r s y s t e m c o m p r i s e s s a n d s t o n e s , s h a l e s , q u a r t i z i t e s and conglomer a t e s o v e r l a i n by marles and l i m e s t o n e o r s a n d s t o n e . T h e r e i s h a r d l y any e v i d e n c e of P a l a e z o i c r o c k s i n t h o s e p a r t s of Uganda, T a n z a n i a and Kenya which l i e w i t h i n t h e B a s i n o f t h e N i l e R i v e r . The same remark h o l d s f o r t h e J u r a s s i c and C r e t a c e o u s p e r i o d s o f t h e Middle and Upper Mesozoic ages. The movement of t h e r i g i d b l o c k of A f r i c a l e d , among o t h e r s , t o g r e a t f r a c t u r e s on t h e e a s t e r n s i d e o f t h e c o n t i n e n t and l o c a l l y e l s e w h e r e . The g i g a n t i c t r o u g h s which e x t e n d from n o r t h t o s o u t h and c o n t a i n t h e E a s t e r n R i f t V a l l e y , a r e o c c u p i e d i n p a r t by t h e E a s t - A f r i c a n W.T.,
Lake s y s t e m (Stamp, L . D . ,
and Morgan,
1972). The E q u a t o r i a l N i l e s y s t e m s u b s e q u e n t l y d r a i n s t h e t e c t o n i c a l l y
and y e t v o l c a n i c a l l y a c t i v e Ugandan P l a t e a u a r e a where many d r a i n a g e changes
294
/ Fig. 7 . 1 .
M a j o r F a u l t s a n d Crush Zones
G e o l o g i c a l map of t h e catchments of t h e Equatorial Lakes
295
have been c a u s e d by r i f t - a s s o c i a t e d g e o p h y s i c a l a c t i v i t y . I t i s t h u s supposed t h a t t h e d e p r e s s i o n o c c u p i e d by Lake V i c t o r i a w a s formed i n t h e Miocene p e r i o d , whereas Lake Kyoga seems t o have e x i s t e d s i n c e t h e P l i o c e n e p e r i o d (Saggerson,
E., 1 9 6 2 ) . These two l a k e s have become l i n k e d t o g e t h e r a s a r e s u l t o f t h e subsidence of t h e Albert depression. This event has l e d t o t h e conclusion t h a t the Upper V i c t o r i a N i l e is p r o b a b l y a v e r y young r i v e r formed i n t h e P l e i s t o c e n e p e r i o d , as i s t h e A l b e r t N i l e (Hepworth, J . , 1964). The d e p o s i t s of t h e P l e i s t o c e n e p e r i o d o f t h e Q u a r t e r n a r y age c o v e r a g r e a t p a r t o f t h e A l b e r t a n d Edward t r o u g h s and c o u l d w e l l e x c e e d 1200 m i n t h i c k n e s s . They a r e a r g i l l a c e o u s r o c k s w i t h which mud v o l c a n o e s , s a l t and gypsum d e p o s i t s a r e a s s o c i a t e d . I n some p l a c e s t h e y a r e o v e r l a i n by t h e S e m l i k i S e r i e s d e r i v e d from t h e outwash o b t a i n e d from t h e W e s t e r n - R i f t
margin.
The T e r t i a r y t o R e c e n t p e r i o d i s s i g n i f i c a n t f o r i t s v o l c a n i c a c t i v i t y . The v o l c a n i c r o c k s a r e m i l d l y t o s t r o n g l y a l k a l i n e , c o n t a i n i n g , among o t h e r s , b a s a l t s . They h a v e g i v e n r i s e t o e x t e n s i v e l a v a p l a i n s o r are a s s o c i a t e d w i t h t h e m a j o r c e n t r a l v o l c a n o e s s u c h a s Mounts E l g o n , Kenya and K i l i m i n j a r o .
7.1.2
The N i l e i n t h e Sudan
The Basement Complex i n t h e Sudan forms o v e r t w o - t h i r d s
of t h e rock-exposures
t h e r e . I t c o n s i s t s o f i g n e o u s and s e d i m e n t a r y r o c k s o u t of which t h e p l a t f o r m was c a r v e d .
I n t h e n o r t h e r n p a r t of t h e Sudan t h e r o c k t y p e s t h a t p r e v a i l a r e
c r y s t a l l i n e s c h i s t s , gneiss, limestone, graphite-slate
and q u a r t z i t e o f v a r i o u s
d e g r e e s of metamorphism. These a r e i n t r u d e d by i g n e o u s r o c k s . I n t h e n o r t h e a s t e r n p a r t o f t h e Sudan t h e r e a r e non-metaporphic
sediments a s s o c i a t e d with
v o l c a n i c r o c k s . The Basement Complex of t h e s o u t h e r n p a r t o f t h e Sudan c o n s i s t s of g r a n o b l a s t i c - f o l i a t e d g n e i s s w i t h f e l s p a r s i n t r u d e d i n t o f o l i a t e d p a r a s c h i s t s and p a r a g n e i s s e s . The p l a t f o r m , on which t h e Nubian S e r i e s o f q u a s i - h o r i z o n t a l
s a n d s t o n e s and
mudstones was d e p o s i t e d , i s o f f o l d e d metamorphic s e d i m e n t s w i t h i n t r u d e d volc a n i c r o c k s (Andrew, G . ,
1948).
The Sudan was i n u n d a t e d by t h e s e a d u r i n g t h e Upper P a l a e o z o i c and Mesozoic a g e s , a t which t i m e t h e d e p o s i t i o n o f p a r t o f t h e Nubian S e r i e s took p l a c e . The P a l a e o z o i c s u c c e s s i o n i s r e p r e s e n t e d by s a n d s t o n e s w i t h a b l a c k s h a l e i n t e r c a l a t i o n , and i s c l o s e d by l i m e s t o n e
(Sandford, K.S.,
1935). These S e r i e s a r e
o v e r l a i n by t h e Nubian s h a l e s , mudstones and s a n d s t o n e s . The l a t t e r a r e r e g a r d e d t o h a v e o c c u r r e d d u r i n g t h e Mesozoic a g e . They c a n b e found i n t h e n o r t h - w e s t e r n a r e a o f t h e Sudan ( c o n t i n u a t i o n of t h e Libyan r e g i o n ) , t h e e a s t e r n a r e a ( c o n t i n u a t i o n o f t h e Abyssinian-Arabian-Somalian
a r e a ) and w e s t of t h e Bahr e l J e b e l i n
t h e well-known Y i r o l b e d s (see t h e g e o l o g i c a l map, F i g . 7 . 2 . ) .
96Z
297
The sea c o a s t r e t r e a t e d s t e a d i l y t h r o u g h t h e Eocene p e r i o d . T h i s w a s followed by a v e r y l o n g p e r i o d o f e r o s i o n which r e s u l t e d i n t h e removal of t h e Nubian S e r i e s from s e v e r a l p l a c e s . The Upper Eocene p e r i o d i s c h a r a c t e r i z e d by t h e r i s e o f t h e e a s t e r n p l a t e a u and t h e Red S e a h i l l s and t h e f o r m a t i o n o f t h e Red S e a . The rise of t h e p l a t e a u
was s u p p o r t e d by t h e e x t e n s i v e v o l c a n i c a c t i v i t y which t o o k p l a c e i n t h e Upper T e r t i a r y (Miocene) and which produced l a v a s capped by v o l c a n o e s ( s e e F i g . 7 . 2 . ) . The h o l l o w r u n n i n g from s o u t h t o n o r t h as a r e s u l t o f t h e e l e v a t i o n of t h e e a s t e r n p l a t e a u i s now o c c u p i e d by t h e p l a i n t h r o u g h which t h e N i l e R i v e r r u n s i n Egypt and t h e n o r t h e r n p a r t of t h e Sudan. The b o u l d e r y masses known as t h e Hudi C h e r t S e r i e s b e l o n g t o t h e L o w e r T e r t i a r y . I t i s t h o u g h t t h a t t h e C h e r t masses have t r a v e l l e d from some d i s t a n c e i n t h e u p s t r e a m t o t h e i r p r e s e n t l o c a t i o n . These masses c a n b e found east o f t h e A t b a r a mouth and n e a r Zeidab. The d e p r e s s i o n s p e n e t r a t e d by t h e White N i l e V a l l e y , t h e Sudd r e g i o n and some p a r t s o f t h e B l u e N i l e B a s i n h a v e been f i l l e d i n by d e p o s i t s s i m i l a r t o t h e f i l l of t h e p r e s e n t d e s e r t a r e a i n t h e n o r t h . T h e s e d e p o s i t s a r e r e f e r r e d t o a s t h e Umm Ruwaba S e r i e s . They c o n s i s t o f u n c o n s o l i d a t e d s a n d s w i t h o r w i t h o u t c l a y , w i t h some g r a v e l d e p o s i t s . The Bahr e l J e b e l n o r t h o f J u b a f l o w s o v e r a f o r m a t i o n of f l u v i a t i l e a n d l a c u s t r i n e s e d i m e n t s b e l o n g i n g t o t h i s series. They a r e l a i d down i n a s u c c e s s i o n of l a n d d e l t a s w i t h e x t r e m e l y low s u r f a c e g r a d i e n t s . T h i s r i v e r h a s a r e a s o n a b l y d e f i n e d v a l l e y as f a r a s t h e n o r t h of Mongalla. From J u b a t o Mongalla t h e r e a r e s e v e r a l c h a n n e l s e a c h w i t h marked l e v e e s . A s t h e p r o p o r t i o n of t h e c o a r s e m a t e r i a l c a r r i e d by t h e r i v e r d e c r e a s e s , t h e r i v e r l e v e e s become weaker and less e f f e c t i v e i n c o n f i n i n g t h e h i g h - f l o w w i t h i n t h e r i v e r s e c t i o n . I n t h e Sudd r e g i o n t h e l e v e e s a r e mainly formed o f f i n e s a n d , whereas t h e back swamp d e p o s i t s a r e composed o f s i l t and c l a y w i t h o c c a s i o n a l sandy l e n s e s . The S o b a t j o i n s t h e White N i l e n e a r M a l a k a l . I t h a s been s u g g e s t e d t h a t t h e g e o l o g i c a l h i s t o r y of i t s b a s i n must have b e e n s i m i l a r t o t h a t o f t h e Blue N i l e . I t may have o r i g i n a t e d i n p o s t - O l i g o c e n e
Traps ( B e r r y , L . ,
and Whiteman, A . ,
times on t h e s u r f a c e of t h e E t h i o p i a n
1968). The White N i l e from t h e Sobat j u n c -
t i o n down t o Khartoum h a s a v e r y s m a l l g r a d i e n t , which i s r e s p o n s i b l e f o r t h e s m a l l n e s s of f l o w v e l o c i t y i n i t . The v a l l e y i n t h i s r e a c h i s r a t h e r broad and f o r most o f t h e d i s t a n c e t h e r i v e r i t s e l f h a s a w e l l - d e f i n e d
channel.
The White N i l e i s j o i n e d by t h e B l u e N i l e a t Khartoum t o form o n e r i v e r . The g e o l o g i c a l and g e o m o r p h o l o g i c a l e v i d e n c e i n d i c a t e s t h a t t h e Blue N i l e i s an a n c i e n t r i v e r s y s t e m . I t rises on t h e g r e a t v o l c a n i c p l a t e a u o f E t h i o p i a , which
i s formed by t h e l a v a s e x t r u d e d d u r i n g t h e O l i g o c e n e p e r i o d . Lake Tana i s supposed t o have b e e n formed i n t h e P l i o c e n e and t h e Abbai canyon was e x c a v a t e d d u r i n g t h e P l i o c e n e and P l e i s t o c e n e .
I t i s p r o b a b l e t h a t an o v e r a l l t e c t o n i c
p r o c e s s t o o k p l a c e d u r i n g t h e L a t e C r e t a c e o u s - L a t e Eocene i n t e r v a l , which l e d t o
298
r o u g h l y p a r a l l e l c o u r s e s o f t h e B l u e N i l e , D i n d e r , Rahad and A t b a r a . I t i s q u i t e p o s s i b l e t h a t t h e A t b a r a a n d / o r t h e B l u e N i l e c o u l d n o t have j o i n e d t h e White N i l e o r t h e Main N i l e d u r i n g t h e P l e i s t o c e n e d r y p e r i o d s . A s a r e s u l t , t h e A t b a r a c o u l d n o t have f l u s h e d i t s s u s p e n d e d l o a d i n t o t h e Main N i l e . I n s t e a d , i t was l a i d down i n i t s own p l a i n t o form t h i c k a l l u v i a l d e p o s i t s . The geology of t h e B l u e N i l e a t t h e R o s e i r e s a r e a was i n v e s t i g a t e d i n c o n n e c t i o n w i t h t h e c o n s t r u c t i o n of t h e R o s e i r e s Dam. The bed-rock
t h e r e i s composed o f a
v a r i e d a s s e m b l a g e o f metamorphic and g r a n i t e r o c k s , f o r m i n g p a r t o f t h e Basement Complex o f t h e Sudan. Rock i s exposed f o r n e a r l y 8 km a l o n g t h e Damazin R a p i d s , b u t , f u r t h e r away from t h e r i v e r , o u t c r o p s a r e l i m i t e d t o l o c a l i n s e l b e r g or j e b e l s . The o r i g i n a l f o r m a t i o n of t h e g n e i s s e s was f o l l o w e d by t h e emplacement of e a r l y g r a n i t e s a n d p e g m a t i t e s . T h i s f o r m a t i o n was l a t e r i n t r u d e d w i t h g r a n i t e
s i l l s and p e g m a t i t e s . The e x t e n s i v e e r o s i o n which t o o k p l a c e i n a l o n g i n t e r v a l of t i m e l e d t o t h e e x p o s u r e o f t h e bed-rock
a t a number of l o c a t i o n s ( F i t t , R . L .
e t a l , 1967). The B l u e N i l e ,
from R o s e i r e s n o r t h w a r d s , f l o w s a c r o s s i t s own s e d i m e n t s .
Its
v a l l e y widens n o r t h w a r d s t o merge w i t h t h e G e z i r a P l a i n n o r t h of S e n n a r , though t h e r i v e r i s s t i l l i n c i s e d below t h e g e n e r a l c o u n t r y l e v e l . The s u r f a c e o f t h e G e z i r a i s c o v e r e d w i t h c l a y s . N e v e r t h e l e s s , t h e r e a r e some p a t c h e s o c c u p i e d by dunes and s a n d - s p r e a d s a s a r e s u l t o f overbank f l o o d s . These sandy p a t c h e s a r e a s s o c i a t e d w i t h s h a l l o w d i s c o n t i n u o u s c h a n n e l s y s t e m s . Another f e a t u r e of t h e G e z i r a P l a i n i s t h e c o m p a r a t i v e u n i f o r m i t y of t h e s u r f a c e c l a y s . The G e z i r a P l a i n h a s b e e n formed by t h e d e p o s i t s b r o u g h t mainly by t h e h e a v i l y l a d e n B l u e N i l e w a t e r . During i t s f l o o d , t h e B l u e N i l e may c a r r y i n s u s p e n s i o n up t o 3000 p a r t s p e r m i l l i o n of c l a y and f i n e s a n d , m o s t l y from E t h i o p i a n s o i l s , p l u s a s i g n i f i c a n t amount o f d i s s o l v e d l o a d . These s e d i m e n t s , t o g e t h e r w i t h t h e p r o d u c t o f a g g r e d a t i o n by r i v e r s c a r r y i n g c o a r s e m a t e r i a l s , have f i l l e d t h e t h e n - e x i s t i n g d e p r e s s i o n s and e v e n t u a l l y produced a h e t e r o g e n eous a l l u v i a l f a n . The whole s t r u c t u r e i s mounted on a t h i c k l a y e r o f Nubian s a n d s t o n e (100-150 m t h i c k ) , which was formed i n t h e L a t e o r Upper Mesozoic. I n t h e Khartoum a r e a t h e t h i c k n e s s of t h e a l l u v i u m i s v a r i a b l e , and i n some s p o t s t h e r e a r e i n f i l l e d s c o u r p o o l s where t h e t h i c k n e s s of t h e s e d i m e n t s may e x c e e d 20 m . Terraces made up of c l a y and g r a v e l f l a n k t h e r i v e r i n t h e same a r e a , however,
and t h e s e t e r r a c e s narrow r a p i d l y n o r t h w a r d s t o w a r d s t h e 6 t h
Cataract.
West o f Khartoum t h e f o r m a t i o n known a s t h e qoz i s s p r e a d o v e r t h e low ground of t h e w e s t - c e n t r a l
p a r t o f t h e Sudan ( D a r f u r and n o r t h e r n K o r d u f a n ) . T h i s f o r -
m a t i o n i s an a c c u m u l a t i o n of dune-sand c o n s i s t i n g a l m o s t e n t i r e l y o f q u a r t z g r a i n s , a n d , p o s s i b l y , d e r i v e d from t h e Nubian S e r i e s .
299
The Main N i l e n o r t h o f Khartoum f l o w s n o r t h i n t h e t e c t o n i c low b e h i n d t h e u p l i f t e d r i m of t h e c o n t i n e n t
- t h e Red S e a h i l l s . The i n t e r p l a y of long-con-
t i n u e d t e c t o n i c a c t i v i t y , r i v e r p r o c e s s e s o f e r o s i o n and d e p o s i t i o n , and t h e e f f e c t s o f c l i m a t e f l u c t u a t i o n s , o v e r t h e l a s t one m i l l i o n y e a r s o r s o , combine t o p r o d u c e a complex g e o l o g i c a l s t r u c t u r e of t h e a r e a . From Khartoum t o t h e 6 t h C a t a r a c t t h e N i l e f l o w s l a r g e l y o v e r t h e Basement Complex and Nubian f o r m a t i o n s ( s e e F i g . 7 . 2 . ) . North o f t h e 6 t h C a t a r a c t (known a s S a b a l o k a ) t h e v a l l e y widens a g a i n . I n t h e Shendi a r e a t h e s u r f a c e i s d e v e l o ped mainly on t h e Nubian f o r m a t i o n . The t e r r a c e s f l a n k i n g t h e r i v e r t h e r e c o u l d b e up t o 5 km w i d e . The r i v e r r u n s i n a n o r t h e r l y d i r e c t i o n on Nubian s a n d s t o n e a s f a r a s Ed-Darner,
where t h e Basement Complex a p p e a r s a g a i n .
I n t h e d i s t a n c e from t h e 5 t h t o t h e 4 t h C a t a r a c t t h e r i v e r r u n s a c r o s s t h e Basement Complex. Between t h e s e two c a t a r a c t s t h e r i v e r f a l l s some 90 m . The r i v e r bed t h r o u g h o u t t h e major p a r t o f t h i s d i s t a n c e i s r o c k y . The Basement con-
s i s t s o f g n e i s s e s , s l a t e s and m a r b l e . The r i v e r v a l l e y i n t h e s e c t i o n from t h e 4 t h t o t h e 3 r d C a t a r a c t h a s been c u t s i n c e t h e E a r l y P l e i s t o c e n e times. Towards Dongola t h e r e i s an e x t e n s i v e g r a v e l and s i l t t e r r a c e , w e s t o f which t h e Nubian f o r m a t i o n i s c o v e r e d w i t h c o a r s e g r a v e l f o r a d i s t a n c e of n o t less t h a n 10 km w i d e . The 3 r d C a t a r a c t i t s e l f i s composed o f g n e i s s w i t h marble v e i n s o r i e n t a t e d t o t h e west. North of t h i s c a t a r a c t t h e r i v e r p a s s e s between two mounts o r h i l l s , e a c h a b o u t 380 m h i g h . The o t h e r f e a t u r e o f t h i s a r e a i s t h a t t h e Nubian f o r m a t i o n and t h e Basement Complex a r e c u t by dykes and v o l c a n i c n e c k s a t some p l a c e s . The N i l e r u n s t h r o u g h t h e Basement Complex i n t h e s e c t i o n from t h e 3 r d t o t h e 2nd C a t a r a c t . Halfway between t h e s e two c a t a r a c t s , t e r r a c e s have been d i s t i n g u i s h e d a t 1 5 and 30 m above t h e p r e s e n t f l o o d p l a i n l e v e l . Both t e r r a c e s a r e c o v e r e d w i t h c o a r s e g r a v e l . The Semna C a t a r a c t , famous f o r i t s N i l o m e t e r (see C h a p t e r l), i s formed of h a r d g n e i s s and c r u s h e d g r a n i t e which c o n f i n e s t h e N i l e , from a b o u t 400 m w i d e , t o j u s t a 40 m wide c h a n n e l . I n g e n e r a l , v e r y l i t t l e s i l t i s d e p o s i t e d by t h e N i l e i n t h e Sudan e x c e p t d u r i n g o c c a s i o n a l overbank f l o o d s . On t h e c o n t r a r y , f l o o d s t e n d t o s c o u r r a t h e r t h a n d e p o s i t i n t h e Sudan and much of t h e s c o u r p r o d u c t i n t h e form of suspended m a t t e r u s e d t o b e d e p o s i t e d i n t h e N i l e D e l t a , a t l e a s t i n t h e pre-High Aswan Dam e r a . The r i v e r v a l l e y from t h e 2nd C a t a r a c t t o t h e s o u t h e r n f r o n t i e r of Egypt i s c u t i n Nubian s a n d s t o n e w i t h o u t c r o p p i n g of i g n e o u s and metamorphic r o c k s a t some p l a c e s , s u c h a s Aswan. 7.1.3
The N i l e i n Egypt
D u r i n g t h e A r c h e o z o i c and P r o t e r o z o i c e r a s (some 500 m i l l i o n y e a r s ago) t h e s u r f a c e of Egypt was c o v e r e d by i g n e o u s , metamorphic and c r y s t a l l i z e d r o c k s such
300
a s g r a n i t e , g n e i s s and s c h i s t . F o l l o w i n g t h a t t i m e t h e K e d i t e r r a n e a n S e a c o v e r e d a l l t h e s u r f a c e of Egypt and a c o n s i d e r a b l e area of t h e Western Desert and t h e Sudan f o r a l o n g p e r i o d e s t i m a t e d a t between 300 and 325 m i l l i o n y e a r s . I n t h a t p e r i o d , t h e P a l a e z o i c e r a , b i o l o g i c a l sea s e d i m e n t s were d e p o s i t e d . Most of thew however, were washed o u t by w e a t h e r i n g f a c t o r s , w h i l e some o t h e r d e p o s i t s were b u r i e d down under t h e s e d i m e n t a r y r o c k s which came l a t e r . The f o s s i l s of t h a t e r a , some of which a r e s t i l l p r e s e n t i n S a i n a i , b e l o n g t o t h e C a r b o n i f e r o u s p e r i o d . A t t h e e n d o f t h a t p e r i o d t h e sea r e c e d e d f o r a l o n g t i m e r a n g i n g b e t ween 50 and 75 m i l l i o n y e a r s . The r e c e s s i o n of t h e sea was f o l l o w e d by a s u b s i dence o f a c o n s i d e r a b l e a r e a o f N o r t h A f r i c a , i n c l u d i n g Egypt and t h e Sudan. Consequently,
t h e s e a w a t e r f l o o d e d t h e s u b s i d e d p a r t s f o r a p e r i o d of 5 0 t o 75
m i l l i o n y e a r s d u r i n g t h e Mesozoic e r a , t h e r e b y d e p o s i t i n g a l a y e r of a b o u t 1500
metres i n t h i c k n e s s of s a n d s and p e b b l e s , b u t f r e e from f o s s i l s . The l o w e s t onet h i r d o f t h i s l a y e r was d e p o s i t e d i n t h e J u r a s s i c p e r i o d and t h e r e m a i n i n g twot h i r d s i n t h e C r e t a c e o u s p e r i o d . The l o w e r h a l f of t h e l a t t e r i s known a s Nubian sandstone. By t h e e n d o f t h e Mesozoic e r a t h e sea r e c e d e d g r a d u a l l y and a number of changes t o o k p l a c e i n t h e C a i n o z o i c e r a (50 m i l l i o n y e a r s a g o ) . Most o f t h e s u r f a c e i n Egypt s u b s i d e d d u r i n g t h e Eocene p e r i o d , t h u s p e r m i t t i n g t h e s e a once more t o f l o o d t h e c o u n t r y and t o d e p o s i t l a y e r s o f c a l c a r e o u s s t o n e s . These d e p o s i t s have formed t h e c h a i n o f h i l l s e a s t and w e s t o f t h e N i l e V a l l e y . Again, t h e s e a r e c e d e d t o a b o u t C a i r o i n t h e Olegocene p e r i o d . A number o f minor c h a n g e s f o l l o w e d d u r i n g t h e Miocene, P l i o c e n e and P l e i s t o c e n e p e r i o d s . A s i m p l i f i e d g e o l o g i c a l map of Egypt i s shown i n F i g . 7 . 3 . The g e o l o g i c a l d i v i s i o n s shown i n t h i s map occupy t h e f o l l o w i n g a r e a s ( S a i d , R . , Geologic d i v i s i o n
1962):
A r e a , km2
P l e i s t o c e n e and R e c e n t P l e i o c e n e , Miocene and O l i g o c e n e P a l e o c e n e and Eocene Cretaceous Nubian s a n d s t o n e ( m a i n l y C r e t a c e o u s ) I g n e o u s and metamorphic r o c k s
165 000
136 204 130 290 95 Total :
000 000 000 000
000
1 020 000
The p l a t e a u s which make up t h e g r e a t e r p a r t of t h e s u r f a c e of Egypt c o n s i s t , i n t h e extreme south-west,
of metamorphic r o c k s and g r a n i t e s . These a r e c o v e r e d
i n a n o r t h e r l y d i r e c t i o n by g e n t l y i n c l i n e d s e d i m e n t s , g i v i n g r i s e a s a r e s u l t of w e a t h e r i n g , t o g r e a t f l a t - t o p p e d ,
t a b l e - l i k e h i l l s . North o f t h e s o u t h e r n
o u t c r o p s of a n c i e n t r o c k s a r e found t h e wide s t r e t c h e s of Nubian s a n d s t o n e , t h e n n o r t h w a r d , wide e x p a n s e s of l i m e s t o n e .
301
1-1
Nile Alluvium Recent a n d Pleistocene
Fig. 7.3.
1-1 . . . .... . ....
Eocene Cretaceous
...................
Nubian Sandstone Archrean (Igneous and Metamorphic)
Geological map of E g y p t (with minor approximations)
302
The p r i n c i p a l o a s e s i n t h e Western Desert a r e t h e Kharga and Dakhla Oases. Each o f them rests on Nubian s e d i m e n t s c o n s i s t i n g of a l t e r n a t i o n s of c l a y s , s h a l e s , s a n d s and s a n d s t o n e s . These s e d i m e n t s have been g r a d u a l l y exposed as a r e s u l t of e r o s i o n . The p l a t e a u b o r d e r i n g t h e Kharga O a s i s on t h e n o r t h and east
i s o f C r e t a c e o u s and Eocene r o c k s , which c o n s i s t e s s e n t i a l l y of l i m e s t o n e . E r o s i o n i s c l a i m e d t o have removed some 200 t o 300 m of t h e s e l i m e s t o n e s t o expose t h e u n d e r l y i n g Nubian f o r m a t i o n s . These are t h e f o r m a t i o n s which c o n t a i n t h e i m p o r t a n t a q u i f e r from which t h e w a t e r o f t h e o a s e s Pretorius, D.A.,
iS
drawn ( P a v e r , G . L . ,
and
1954).
The geology o f t h e c o a s t a l d e s e r t of E g y p t , t h e d e s e r t a r e a w e s t and east o f the N i l e D e l t a ,
and t h e g e o l o g y of t h e Red S e a h i l l s w a s i n v e s t i g a t e d and
r e p o r t e d i n c o n n e c t i o n w i t h water s u p p l y i n t h e Middle E a s t campaigns d u r i n g World War 1 1 . F o r i n f o r m a t i o n a b o u t t h e r e s u l t s of t h o s e i n v e s t i g a t i o n s t h e r e a d e r i s r e f e r r e d t o t h e s i x a r t i c l e s which were p u b l i s h e d by S h o t t o n , F.W., and by P a v e r , G . L . ,
1946.
The N i l e j u d g e d by i t s p r e s e n t form a p p e a r s t o b e made up of s e v e r a l d i s t i n c t s y s t e m s which became j o i n e d a t a much t o o l a t e s t a g e i n g e o l o g i c a l h i s t o r y . Each of t h e s e s y s t e m s i s r e l a t e d t o a d i f f e r e n t s t r u c t u r a l s e t t i n g a n d / o r a d i f f e r e n t g e o l o g i c a l p e r i o d . The N i l e i n Egypt began t o form i t s v a l l e y i n t h e Upper Miocene a g e . The t h e n N i l e , E o n i l e , c u t i t s g o r g e a t a much lower l e v e l t h a n t h e p r e s e n t s e a l e v e l . The bottom o f t h e canyon formed by t h e E o n i l e r e a c h e d d e p t h s from 170 m i n Aswan t o more t h a n 2500 m n o r t h of C a i r o a n d t o even g r e a t e r d e p t h s i n t h e n o r t h e r n Delta embayment ( S a i d , R . ,
1 9 8 2 ) . A s a r e s u l t of f a u l t s
and s h i f t s t h e E o n i l e changed i t s c o u r s e from n o r t h - w e s t
t o a more n o r t h e r l y
course. I n t h e Lower P l i o c e n e t i m e t h e E o n i l e V a l l e y became c o v e r e d w i t h t h e s e d i ments b r o u g h t by t h e s e a a s i t advanced a l o n g t h e v a l l e y as f a r as Aswan. L a t e r , s e d i m e n t s were b r o u g h t by t h e P a l e o n i l e , d u r i n g t h e Upper P l i o c e n e some 3.2 m i l l i o n y e a r s a g o . The s e d i m e n t a t i o n was v e r y much augmented by t h e c o n t r i b u t i o n of t h e Red S e a h i l l s v i a t h e t h e n e x i s t i n g Wadis, which c a r r i e d t h e s e d i m e n t l a d e n t o r r e n t s of w a t e r , By t h e end of t h e P a l e o n i l e s e d i m e n t a t i o n , t h e E o n i l e canyon was c o m p l e t e l y f i l l e d up and t h e D e l t a s u r f a c e became more or l e s s even w i t h a g e n t l e northward s l o p e . The i n t e r v a l from a b o u t 1 . 8 5 m i l l i o n t o 0.7 m i l l i o n y e a r s ago i s c l a i m e d t o be a p e r i o d of g r e a t c o o l i n g and d r y n e s s i n E g y p t . I t i s q u i t e p o s s i b l e t h a t t h e Paleo-Proto-Nile
( t h e t h e n N i l e i n E g y p t ) c e a s e d t o flow and Egypt i t s e l f became
a d e s e r t . The a b r a d e d m a t e r i a l was t r a n s p o r t e d by t h e blowing wind and began t o form t h e l a r g e d e p r e s s i o n s i n t h e Western Desert. D e p o s i t i o n of g r a v e l s and s a n d s w a s q u i t e a c t i v e i n t h e P r o t o n i l e p e r i o d , t h a t i s , from 0 . 7 t o 0 . 5 m i l l i o n
303
y e a r s a g o . The d e p o s i t e d m a t e r i a l took t h e form o f t e r r a c e s p a r a l l e l t o t h e modern N i l e V a l l e y . The t e c t o n i c movements which took p l a c e from t h e e n d of t h e P r o t o n i l e p e r i o d up t o a b o u t 125 000 y e a r s b e f o r e p r e s e n t h e l p e d t o form some h y d r a u l i c connect i o n between t h e N i l e i n Egypt ( t h e P r e n i l e ) and t h e E t h i o p i a n P l a t e a u . Accordi n g l y , much l a r g e r f l o o d s and s e d i m e n t s were c a r r i e d by t h e P r e n i l e t h a n by t h e P r o t o o r by t h e P a l a e o - P r o t o N i l e s . A s a r e s u l t , a l a r g e d e l t a was d e v e l o p e d , w i t h s e d i m e n t s e x t e n d i n g i n t o t h e s e a . One can t h u s c o n c l u d e t h a t t h e N i l e D e l t a o c c u p i e s a g r e a t t e c t o n i c d e p r e s s i o n , and i s bounded on b o t h s i d e s by g r a v e l l y p l a i n s which r i s e up t o 100 m above mean s e a l e v e l . On t h e e a s t e r n s i d e , t h e D e l t a r e g i o n i s bounded by a major upwarp zone which o c c u p i e s most of NorthC e n t r a l S i n a i . T h i s i s f o l l o w e d i n a n o r t h w a r d d i r e c t i o n by a downwarp zone which o c c u p i e s most of t h e D e l t a r e g i o n and t h e n o r t h - w e s t e r n p a r t of S i n a i . T h i s downwarp zone i s a f f e c t e d by a number of f a u l t s . The p l a i n s on t h e e a s t e r n and w e s t e r n s i d e s of t h e D e l t a merge i n t o t h e e l e v a t e d t a b l e l a n d s ( h i g h e r t h a n 200 m above mean s e a l e v e l ) , which a c t a s w a t e r s h e d a r e a s . The e a s t e r n t a b l e l a n d s a r e d i s s e c t e d by a number of Wadis which a c t d u r i n g r a i n y s e a s o n s a s d r a i n a g e a r t e r i e s . The s e d i m e n t a r y s e c t i o n i n t h e D e l t a h a s an e x p e c t e d t h i c k n e s s o f more t h a n 10 000 m ( S h a t a , A . ,
and El-Fayoumy,
I . , 1969).
The P r e n i l e was s o v i g o r o u s t h a t i t s h i f t e d i t s c o u r s e t o t h e e a s t of what used t o b e t h e c o u r s e of t h e P r o t o n i l e , though y e t w e s t of t h e p r e s e n t c o u r s e of t h e Nile.
The l a s t s e c t i o n o f t h e P r e n i l e p e r i o d , which t e r m i n a t e d some 125 000
y e a r s b e f o r e p r e s e n t h a d b e e n c h a r a c t e r i z e d by u p l i f t s which l e d t o reduced r i v e r f l o w i n E g y p t . T h i s was f o l l o w e d by t h e P r e - N e o n i l e , which l a s t e d from 125 000 t o 30 000 y e a r s b e f o r e p r e s e n t .
I n t h e w e t e p i s o d e s of t h i s p e r i o d heavy
r a i n f a l l s r e s u l t e d i n c o a r s e s a n d and g r a v e l d e p o s i t s . The L a t e Acheulean p l u v i a l was an i m p o r t a n t one and i t ended some 35 000 y e a r s a g o . The P r e n i l e s e d i m e n t s were l a i d down by t h e r i v e r and t h e f i n a l s h a p e of t h e p r e s e n t N i l e V a l l e y was formed ( S a i d , R . ,
1 9 8 2 ) . The N e o l i t h i c p l u v i a l l a s t e d from about
10 000 y e a r s t o , s a y , 5 000 y e a r s b e f o r e p r e s e n t . The c l i m a t e t h a t p r e v a i l e d
t h e n was s o w e t t h a t t h e s o u t h e r n p a r t of Egypt had an a n n u a l r a i n f a l l of 100 t o
300 mm ( S a i d , R . ,
1 9 8 1 ) . A t p r e s e n t t h e a n n u a l r a i n f a l l a t t h e same p l a c e i s
practically n i l . The above d i s c u s s i o n a b o u t t h e r e g r e s s i o n and t r a n s g r e s s i o n of t h e s e a d u r i n g t h e C a i n o z o i c e r a , and t h e development of t h e c o u r s e of t h e r i v e r d u r i n g t h e s u c c e s s i v e g e o l o g i c a l p e r i o d s c a n b e s e e n i n F i g s . 7.4 a t h r u '
f.
304
a. locene Period
b. Oligocene Period
c. Miocene Period
d. End of Miocene Period
e. End of Pliocene Period
f . End of Pleistocene Period
F i g . 7.4.
7.2 7.2.1
R e g r e s s i o n and t r a n s g r e s s i o n of t h e s e a d u r i n g t h e C a i n o z o i c e r a
GROUNDWATER POTENTIAL
Groundwater i n Kenya, Uganda and T a n z a n i a
I n t h e p r e v i o u s s e c t i o n i t h a s been mentioned t h a t some a r e a s i n t h o s e p a r t s of Kenya, Uganda and T a n z a n i a which are s i t u a t e d w i t h i n t h e N i l e B a s i n a r e covered w i t h Precambrian r o c k s .
I n t h e s e a r e a s it is only t h e shallow water
b e a r i n g l a y e r s c l o s e t o t h e s u r f a c e t h a t y i e l d w a t e r u n l e s s w e l l s o r h o l e s are d r i l l e d t o d e p t h s u s u a l l y of more t h a n 100 m . I n t h e v o l c a n i c a r e a s between t h e e a s t e r n and w e s t e r n R i f t V a l l e y s , h i g h e r y i e l d s of w a t e r c a n b e e x p e c t e d from t h e h i g h l y e l e v a t e d g r o u n d s . Groundwater, on t h e c o n t r a r y , i s q u i t e s c a r c e i n many o f t h e s e d i m e n t a r y a r e a s , p a r t l y due t o t h e low r a i n f a l l and p a r t l y b e c a u s e of e x c e s s i v e e v a p o r a t i o n . A c c o r d i n g l y , most
of t h e g r o u n d w a t e r
-
i f available
-
i s of r e l a t i v e l y poor q u a l i t y .
D r i l l i n g of s h a l l o w w e l l s a n d w a t e r h o l e s i s p r a c t i s e d for w a t e r s u p p l y t o v i l l a g e s a n d s m a l l c o m m u n i t i e s . P r o b a b l y 90% of t h e d r y s e a s o n demands i n t h e a r i d p a r t s o f T a n z a n i a a r e s u p p l i e d by w a t e r h o l e s and w e l l s . The w a t e r - b e a r i n g f o r m a t i o n s a r e o f t e n found on t h e s l o p e s of t h e b e d r o c k h i l l s and t h e y c o n s i s t of g r a v e l , s a n d , l a t e r i t e s , g r a n i t e ( c r e v i c e s ) and c a l c r e t e . The v a l l e y s thems e l v e s a r e c o v e r e d w i t h mbuga c l a y s a s shown i n F i g s . 7 . 5 a and 7 . 5 b . Some of t h e l e a d i n g f i g u r e s of t h e s h a l l o w w a t e r w e l l s a s p r a c t i s e d i n T a n z a n i a a r e a s f o l l o w s (D.H.V., 1976 and 1 9 7 8 ) :
305
=
Maximum d e p t h o f w e l l
10 m
S p a c i n g between w e l l s
5-10 m
I n t e r n a l diameter
1.25 m
Operation
hand pump
Duration
10 h r s / d a y
Volume of pumped water
6-10 m3/day
Number of c o n s u m e r s / w e l l
250 i n h a b i t a n t s
Bedrock h i l l
F i g . 7.5.
7.2.2
d Spring or pool +water level B M b u g a clay B w a t e r b e a r i n g layer
Shallow water-bearing
f o r m a t i o n s i n T a n z a n i a (D.H.V.,
1976)
Groundwater i n t h e Sudan
I n g e n e r a l , w a t e r i s n o t e v e n l y d i s t r i b u t e d u n d e r n e a t h t h e s u r f a c e of t h e Sudan. T h i s i s q u i t e u n d e r s t a n d a b l e s i n c e t h e g r o u n d w a t e r s u p p l i e s depend on t h e r a i n f a l l and on t h e l o c a l geology of t h e area from which water h a s t o be e x t r a c t e d . When t h e s o i l h a s a low a b s o r p t i o n c a p a c i t y a h i g h p r o p o r t i o n of t h e r a i n f a l l r e m a i n s on t h e s u r f a c e and i s l o s t by e v a p o r a t i o n . I t i s o n l y i n a few p l a c e s t h a t g r o u n d w a t e r s u p p l i e s depend on t h e r a i n f a l l a t some d i s t a n c e from t h e l o c a l underground r e s e r v o i r . I n t h e w e s t e r n p a r t of E q u a t o r i a P r o v i n c e r i v e r s may r u n d r y , b u t i f i t happens t h i s w i l l b e f o r a s h o r t t i m e .
I n s u c h a c a s e s u p p l i e s c a n be o b t a i n e d
from p o o l s o r s h a l l o w w e l l s i n s t r e a m b e d s . I n t h e e a s t e r n p a r t o f t h e same p r o v i n c e t h e h i l l s a r e t r a v e r s e d by p e r e n n i a l , though s m a l l , s t r e a m s . The p l a i n s r e m a i n , however, d r y i n t h e n o n - r a i n y s e a s o n . I n t h e p l a i n e a s t of t h e Bahr e l J e b e l , g r o u n d w a t e r c a n b e found i n some l o c a l i t i e s a t d e p t h s of 40-50 m .
I n some
306
o t h e r l o c a l i t i e s where t h e s h o r t a g e c o u l d b e a c u t e , t h e water t a b l e c a n b e found a t d e p t h s o f 100 m or more. The underground s u p p l i e s i n t h e c e n t r a l p a r t o f t h e Sudan are o f t e n q u i t e poor b e c a u s e of t h e e x t r e m e l y low p e r m e a b i l i t y of t h e c l a y c a p c o v e r i n g t h e s u r f a c e of t h e p l a i n s . The i s o l a t e d h i l l s ( i n s e l b e r g ) which p r o t r u d e t h r o u g h t h i s a q u i c l u d e a r e u s u a l l y s u r r o u n d e d by c o n e s of c o a r s e r m a t e r i a l , which are h i g h l y permeable.
I n s u c h h i l l s , l o c a l s u p p l i e s c a n be found i n p o o l s and i n w e l l s
located near the foot.
Water s u p p l y by w e l l s i s w i d e l y p r a c t i s e d f o r d o m e s t i c p u r p o s e s and f o r r a i s i n g l i v e s t o c k i n t h e Gash D e l t a i n Kassala P r o v i n c e . Water i s drawn from t h e
w e l l s t h r o u g h o u t t h e y e a r and o t h e r w e l l s f u n c t i o n o n l y s e a s o n a l l y . R e p l e n i s h ment o f groundwater is a c c o m p l i s h e d a n n u a l l y by f l o o d i n g t h r o u g h c h a n n e l s t a k i n g from t h e c a n a l s . The b a s a l t c o u n t r y of Gedaref h a s water i n j o i n t s i n t h e l a v a , b u t t h e d e e p e r l a v a s have no open j o i n t s and are d r y . The t h i c k a c c u m u l a t i o n s of c o n s o l i d a t e d s a n d s , g r a v e l s and c l a y s i n t h e d e p r e s s i o n s i n t h e Kordofan P r o v i n c e c a r r y water. Some o f t h e s e d e p r e s s i o n s , however, have t o o s a l i n e water f o r consumption. The m a r g i n a l a r e a s o f t h e s e d e p r e s s i o n s have no water t o a d e p t h of 100 m o r more, e x c e p t c l o s e t o t h e h i l l s where t h e Wadis s p i l l o u t on t o t h e outwash f a n a t t h e margin o f t h e p l a i n . The a r e a s which have been g e o l o g i c a l l y r e f e r r e d t o as q &
f r e q u e n t l y have s m a l l
s h a l l o w s u p p l i e s a t t h e f o o t o f t h e s a n d s . The d i s t r i b u t i o n of t h e s e s u p p l i e s i s mainly dependent on t h e b u r i e d t o p o g r a p h y . I n t h e s o u t h e r n h a l f of t h e u n d u l a t i n g c o u n t r y t h e number of w e l l s s u p p l y i n g good w a t e r h a s been s t e a d i l y i n c r e a s ing. The v o l c a n i c a r e a s of t h e D a r f u r P r o v i n c e are s i m i l a r t o t h e b a s a l t c o u n t r y of G e d a r e f . The s a n d s t o n e s b e l o n g i n g t o t h e Nubian S e r i e s are c o n s i d e r e d a s a s o u r c e of f a i r l y deep groundwater ( e . g . t h e a r e a between El-Nahoud and E l F a s h e r ) . The groundwater s u p p l i e s c a n b e d e s c r i b e d a s f a i r l y good. The t u b e w e l l s which a r e l o c a t e d t h r o u g h o u t t h e G e z i r a r e g i o n g i v e t h e p i e z o m e t r i c l e v e l s . These have been i n t e r p o l a t e d t o g i v e t h e c o n t o u r s of t h e p h r e a t i c s u r f a c e a s shown i n F i g . 7.6. (Salaam, A . , h a s been q u e s t i o n e d by E a g l e s o n , P . ,
1966). The c o n s i s t e n c y of t h i s map
and M i l l e r , S .
(1983).
I n t h e n o r t h e r n d e s e r t r e g i o n o f t h e Sudan t h e r e a r e two groundwater r e s o u r -
ces. One i s a permanent groundwater r e s e r v o i r i n t h e s a n d s t o n e s of t h e Nubian S e r i e s ( s e e t h e map, F i g . 7 . 2 . ) . I t u s u a l l y e x i s t s a t a f a i r l y c o n s i d e r a b l e d e p t h from t h e s u r f a c e though i t c o u l d be l o c a l l y b a r e d by e r o s i o n t o form some o a s e s r e s t i n g on a mudstone l a y e r . The o t h e r s o u r c e i s formed by l o c a l concent r a t i o n s of s u b s o i l w a t e r d e r i v e d from l o c a l r a i n s and mainly s u p p o r t e d by s e e p a g e from f l o o d s . I n t h e w e s t e r n p a r t of t h e s a n d s t o n e a r e a t h e groundwater r e s e r v e s a r e r e l i a b l e and p l e n t i f u l when compared t o t h e e x i s t i n g demand on
307
them. These r e s e r v e s r e c e i v e , however, modest amounts o f r e c h a r g e , c h a r a c t e r i z i n g such waters as mainly non-renewable.
Only i n t h e a r e a along t h e N i l e , b e t -
ween Dongola and Wadi H a l f a , due t o i n f i l t r a t i o n o f t h e N i l e and Lake Nasser i n t o t h e banks, a c o n s i d e r a b l e area o f renewable groundwater w i l l become a v a i l a b l e ( G i s c h l e r , C.E., 1979). I n t h e a r e a s c o v e r e d w i t h c r y s t a l l i n e r o c k s , which are mainly t o t h e e a s t , r e s o u r c e s are much more r e s t r i c t e d , e x c e p t a l o n g t h e
l i n e of major Wadis. As s u c h t h e y are dependent o n t h e o c c a s i o n a l f l o o d s . Thus, t h e y i e l d o f a r e s o u r c e o f t h i s t y p e i s roughly p r o p o r t i o n a l t o t h e s i z e of t h e catchment area upstream o f t h e w e l l - p o i n t
and t o t h e r a i n f a l l . Obviously, t h e
s a l i n i t y o f water i n c r e a s e s w i t h d i s t a n c e from t h e head due t o e v a p o r a t i o n .
Fig. 7.6.
P h r e a t i c s u r f a c e ; El G e z i r a , Sudan (Salaam, A . ,
1966)
308
7.2.3
Groundwater i n Egypt
7.2.3.1
Groundwater i n t h e Western Desert
The Nubian B a s i n , p a r t of which h a s a l r e a d y been d i s c u s s e d i n c o n n e c t i o n w i t h t h e groundwater i n t h e Sudan, c o v e r s a s u r f a c e a r e a o f a b o u t 1.8 m i l l i o n km2. T h i s b a s i n e x t e n d s t o Egypt w e s t o f t h e N i l e , t o t h e e x t r e m e n o r t h - e a s t
o f Chad,
and t o s o u t h and e a s t e r n L y b i a . The geology of t h e Western Desert i n Egypt h a s been e x p l a i n e d e a r l i e r . The Nubian B a s i n i s c h a r a c t e r i z e d by i t s extreme a r i d i t y . The i n h a b i t e d p a r t o f i t
i s a s e r i e s o f o a s e s . The most i m p o r t a n t o a s e s i n Egypt a r e t h e Kharga, Dakhla, F a r a f r a , B a h a r i y a and Siwa. A number of t h e o r i e s r e g a r d i n g t h e f o r m a t i o n and f l o w o f groundwater i n t h i s d e s e r t have been p u b l i s h e d . According t o B a l l , J . , (1927) t h e o r i g i n and s o u r c e of t h e a r t e s i a n w a t e r s u p p l y of t h e o a s e s i n Egypt i s a v a s t s u b t e r r a n e a n s t r e a m o r i g i n a t i n g i n t h e E r d i and Ennedi r e g i o n on t h e b o r d e r between t h e Chad B a s i n and t h e N i l e B a s i n i n t h e Sudan. T h i s underground w a t e r f l o w s i n t h e d i r e c t i o n of t h e n o r t h - w e s t , H e l l s t r o m , B.,
n o r t h and n o r t h - e a s t . (1940) d e v e l o p e d t h e f l o w n e t shown i n t h e map, F i g . 7 . 7 a .
T h i s map a l s o i n c l u d e s t h e n o r t h - w e s t e r n p a r t of t h e Sudan. The works o f B a l l and H e l l s t r o m were d i s c u s s e d i n a p a p e r which was p r e p a r e d by t h e Survey D e p a r t ment of Egypt (Murray, G.W., 1 9 5 2 ) . The f a c t t h a t was s t r e s s e d i n t h i s p a p e r i s t h a t t h e groundwater f l o w i n g f r e e l y i n t o t h e o a s e s h a s n o t h i n g t o do w i t h t h e
Nile.
I t i s merely f o s s i l w a t e r i n p r i s o n e d i n t h e Nubian r o c k s f o r s e v e r a l thou-
s a n d s o f y e a r s ; t h e l o w e s t l a y e r o f a l l groundwater may d a t e back t o t h e P l i o c e n e . The age of t h e groundwater h a s r e c e n t l y been d e t e r m i n e d a t some l o c a t i o n s u s i n g l4C and was found t o o r i g i n a t e from 40 000 t o 20 000 y e a r s BP ( b e f o r e p r e s e n t ) , i . e . from t h e l a t e Acheulean p l u v i a l . Not much g r o u n d w a t e r f o r m a t i o n took p l a c e i n t h e S a h a r a i n t h e i n t e r v a l between 20 000 and 14 000
y e a r s BP. The p e r i o d from 14 000 y e a r s BP t o p r e s e n t times i s i n t e r p r e t e d a s a p o s t p l u v i a l humid p h a s e w i t h t h e humid p e a k s a l t e r n a t i n g w i t h a r i d p h a s e s . A l l t h e younger w a t e r s o r i g i n a t e from s h a l l g r o u n d w a t e r s ( S o n n t a g , C . ,
e t a l , 1976).
Groundwater moving d o w n h i l l , r e a d i l y f l o w s i n t o C r e t a c e o u s , Eocene and Miocene s t r a t a ; d o i n g so, i t u s u a l l y becomes c o n t a m i n a t e d w i t h s a l t . The a n a l y -
s i s o f t h e w a t e r h a s shown t h a t i t i s r e l a t i v e l y h i g h l y m i n e r a l i z e d , p a r t i c u l a r l y i n i r o n , c a r b o n a t e s and sodium c h l o r i d e , w h i l e t h e g a s s e s c o n t a i n a t l e a s t some hydrogen s u l p h i d e and p o s s i b l y c a r b o n d i o x i d e . T h i s q u a l i t y of water c a l l s f o r h a v i n g t h e w e l l c a s i n g a d e q u a t e l y c o v e r e d by p r o t e c t i v e c o a t i n g s ( P a v e r ,
G.L., and P r e t o r i o u s , D . A . ,
1954). The same r e f e r e n c e estimates t h e groundwater
e x t r a c t i o n from t h e Kharga and Dakhla o a s e s o n l y a s f o l l o w s :
309
Approximate y i e l d o f s h a l l o w w e l l s , m i l l i o n m 3 / y r Approximate y i e l d o f deep w e l l s , m i l l i o n m3/yr
Dakhla
38.7
92.7
3.8
T o t a l a n n u a l w i t h d r a w a l , m i l l i o n m3 Hellstrom, B . ,
Kharga
16.8
-
-
42.5
109.5
(1940) e s t i m a t e d t h e groundwater s u p p l y t o t h e Q u a t t a r a
d e p r e s s i o n a t a b o u t 3 . 1 m i l l i o n m3/day or 1130 m i l l i o n m3/yr b i l i t y of t h e Nubian s a n d s t o n e t o l i e between 2 . 4 x
and t h e permea-
and 2 . 4 x
m/day.
The Government o f Egypt h a s u n d e r t a k e n a programme f o r e x p l o i t i n g t h e groundw a t e r r e s e r v o i r , e s p e c i a l l y i n t h e a r e a o c c u p i e d by t h e Kharga and Dakhla o a s e s . S i n c e 1959 t i l l r e c e n t l y t h e number of w e l l s d r i l l e d t h e r e h a s exceeded 350
w e l l s w i t h d e p t h s r a n g i n g between 400 and 1200 m. A s a r e s u l t of t h e e x t e n s i v e w i t h d r a w a l of t h e g r o u n d w a t e r , t h e h y d r o s t a t i c p r e s s u r e i n t h e w e l l s h’as f a l l e n by more t h a n 30 m , w i t h t h e o b v i o u s consequence t h a t many o f t h e w e l l s have c e a s e d t o f l o w f r e e l y ( a r t e s i a n ) . T h i s a l a r m i n g s i t u a t i o n h a s drawn t h e a t t e n t i o n of t h e E g y p t i a n G e n e r a l Desert Development O r g a n i z a t i o n , a s w e l l as o t h e r o r g a n s and i n d i v i d u a l s . The f u t u r e o f t h e groundwater d i s c h a r g e i n t h e Kharga and Dakhla Oases was f o r e c a s t e d t i l l t h e y e a r 2000. Using t h e f l o w n e t o r i g i n a l l y d e v e l o p e d by H e l l s t r o m and more r e c e n t d a t a , t h e s t e a d y g u a r a n t e e d r e c h a r g e w a s e s t i m a t e d a t a b o u t 204 m i l l i o n m 3 / y r , El-Dakhla.
of which 6 4 m i l l i o n t o El-Kharga and 140 m i l l i o n t o
I n s t a l l a t i o n of pumps w a s r e p o r t e d t o i n c r e a s e t h e d i s c h a r g e of wells
i n t h e s e two o a s e s by 15% and 7 % , r e s p e c t i v e l y
(Hammad, Y . H . ,
1969). Also, t h e
h y d r o l o g i c a l a s p e c t s of t h e groundwater r e s e r v o i r u n d e r l y i n g t h e Dakhla O a s i s
were e x t e n s i v e l y s t u d i e d and r e p o r t e d t o t h e M i n i s t r y of Land R e c l a m a t i o n , Egypt (Shahin, M . , 7.7b.).
e t a l , 1 9 7 0 ) . A more r e c e n t f l o w n e t h a s been p r e p a r e d ( s e e F i g .
From t h e r e c e n t d a t a i t was found t h a t t h e groundwater d i s c h a r g e s
t h r o u g h n a t u r a l s p r i n g s , d r i l l e d w e l l s and l o s s e s due t o e v a p o t r a n s p i r a t i o n from a r e a s c o v e r e d by n a t u r a l v e g e t a t i o n and due t o l e a k a g e have been e s t i m a t e d a s included i n Table 7 . 1 . I n t h e c o u r s e of t h e l a s t few y e a r s many a model s t u d y h a s been c a r r i e d o u t w i t h t h e aim of a r r i v i n g a t t h e q u a n t i t i e s of groundwater which can p o s s i b l y b e withdrawn under t h e c o n s t r a i n t o f maximum l i f t of 100 m below t h e ground s u r f a c e . I t h a s been r e p o r t e d t h a t t h e t o t a l a n n u a l e x p l o i t a b l e w a t e r i s a b o u t 1350 m i l l i o n m 3 f o r t h e n e x t 50 y e a r s . T h i s amount i s d i s t r i b u t e d as 140, 1 8 2 , 363, 509 and 156 m i l l i o n m 3 / y r Kharga O a s e s , r e s p e c t i v e l y .
f o r t h e S i w a , B a h a r i y a , F a r a f r a , Dakhla and
fl Fresh w a t e r ,
"LEDITERR ANEN
Salt water contact -2oO'Piezometric
I 7E;O
Fig. 7.7a. B., 1940)
Flow net in Sahara aquifer (Hellstrom,
level
?
/'
59 l ? O l ? O kr
30
Fig. 7.7b. Flow net in the Western Desert of Egypt (Ezzat, M., 1976)
311
TABLE 7 . 1
T o t a l d i s c h a r g e of w e l l s a n d n a t u r a l l o s s e s i n Western Desert (Ezzat, M.A.,
1976)
Area Siwa O a s i s Q u a t t a r a Depression F a r a f r a & B a h a r i y a Oases Dakhla O a s i s Kharga O a s i s South Kharga a r e a Total
7.2.3.2
Discharge of
w e l l s , m3/day 120.000 145.000 557 .OOO 225.000 1.047 .OOO
Natural l o s s e s , m3/day
Total m3/day
300.000 1.400.000 400.000 141.000 190.740 100.000
420.000 1.400.000 545.000 698.000 416.000 100.000
2.531.740
3.579.000
Groundwater i n t h e E a s t e r n Desert
T h e r e i s t o o l i t t l e known a b o u t groundwater e x t r a c t i o n from t h e a q u i f e r u n d e r l y i n g t h e E a s t e r n Desert. N e a r l y a l l o f t h e a v a i l a b l e i n f o r m a t i o n b e l o n g s t o t h e d e s e r t between t h e N i l e D e l t a and t h e Suez C a n a l , some p a r t s of t h e S a i n a i P e n i n s u l a a n d t h e s o u t h - e a s t e r n d e s e r t o f Upper E g y p t . T h e s e a r e a s used t o b e , and p r o b a b l y a r e s t i l l , o c c u p i e d by m i l i t a r y e s t a b l i s h m e n t s . The w e l l s and b o r e h o l e s e x i s t i n g between t h e D e l t a and Suez C a n a l w e r e i n v e s t i g a t e d and r e p o r t e d by S h o t t o n , F.W.,
( 1 9 4 6 ) . According t o t h i s s o u r c e t h e y
w e r e 7 3 i n t o t a l and t h e d e p t h t o w a t e r t a b l e v a r i e d between 2 m a n d 75 m , and t h e y i e l d was i n t h e r a n g e of between a few hundred t o more t h a n 40 000 g a l s / h r . Some water h o l e s w e r e d e s c r i b e d as y i e l d i n g v e r y sweet w a t e r and o t h e r s were abandoned b e c a u s e t h e water w a s b r a c k i s h o r s a l i n e . F o r t y b o r e h o l e s i n t h e s o u t h - e a s t e r n d e s e r t of Upper Egypt were a l s o i n v e s t i g a t e d . I t was c o n c l u d e d t h a t s u p p l i e s from 1000 t o 5000 g a l s / h r of good q u a l i t y
water are o b t a i n a b l e by b o r e h o l e s a l o n g t h e N i l e V a l l e y . C o n t r a r i l y , s u p p l i e s i n t h e c o n s o l i d a t e d s e d i m e n t a r y f o r m a t i o n s between t h e N i l e and t h e Red S e a a r e of low y i e l d and o f bad q u a l i t y . I n some l o c a t i o n s t h e d e p t h t o t h e w a t e r t a b l e i n t h e Nubian s a n d s t o n e c o u l d r e a c h 80 m below t h e ground s u r f a c e . S u p p l i e s of 500 t o 1000 g a l s / h r d r i n k a b l e w a t e r a r e o b t a i n a b l e by b o r e s o f a p p r o x i m a t e l y 30 m i n d e p t h i n t h e Wadis t r a v e r s i n g t h e Pre-Cambrian
a r e a , w e s t of t h e w a t e r s h e d ,
a l m o s t midway t h e l i n e between Qena, on t h e N i l e , and S a f a g a , on t h e c o a s t of t h e Red S e a . S i m i l a r s u p p l i e s a r e o b t a i n a b l e e a s t of t h e w a t e r s h e d , b u t t h e q u a l i t y o f w a t e r t e n d s t o be b a d . The sodium s u l p h a t e i n p a r t i c u l a r r e a c h e s a h i g h l e v e l . The s u p p l i e s o b t a i n e d from t h e c o a s t a l s e d i m e n t a r y s t r i p a r e e x t r e m e l y p o o r b o t h i n q u a n t i t y and q u a l i t y ( P a v e r , G.L., 1 9 4 6 ) . 7.2.3.3
Groundwater i n Upper Egypt
The c l i f f s which bound t h e c o u r s e of t h e N i l e R i v e r i n Upper Egypt a r e made up of e i t h e r l i m e s t o n e o r s a n d s t o n e . The c o n t a c t s u r f a c e between them and t h e
312
v a l l e y , i n which t h e r i v e r h a s c u t i t s c o u r s e , forms t h e boundary o f t h e a q u i f e r system. Such a n a q u i f e r h a s been formed by t h e d e p o s i t s b r o u g h t up by t h e N i l e d u r i n g t h e w e t p e r i o d s . The a q u i f e r c a n b e d i v i d e d i n t o t w o d i s t i n c t t y p e s : u n c o n f i n e d , occupying a l m o s t o n e - q u a r t e r o f t h e s u r f a c e a r e a of Upper Egypt and semi-confined,
o c c u p y i n g t h e r e s t o f t h e area. The l a t t e r i s o v e r l a i n by a r e l a -
t i v e l y t h i n l a y e r of s i l t , loam and c l a y . Both t y p e s o f a q u i f e r s a r e b u i l t u p , however, o f t h e same materials: g r a d e d s a n d s a n d g r a v e l s . L i t h o l o g i c a l s e c t i o n s a c r o s s t h e V a l l e y a t some l o c a t i o n s are shown i n F i g . ( A t t i a , F. e t a l , 1 9 8 3 ) . The s t u d y o f t h e l i t h o l o g y , and t h e a n a l y s i s o f
7.8.,
t h e pumping-test
d a t a have l e d us t o t h e r e s u l t s i n c l u d e d i n T a b l e 7 . 2 ( S h a h i n ,
M., 1 9 8 3 ) .
E .-C C
0 .-+
LEGEND
0
>
w y120 80
-
m] .
-
..
:
40+ 0 40
00
S a n d & Gravel
Limes t o n e
-
-
Fig. 7 . 8
L i t h o l o g i c a l s e c t i o n s a c r o s s t h e N i l e V a l l e y i n Upper Egypt
The w a t e r b a l a n c e of t h e r i v e r s t r e t c h between Aswan and C a i r o , t h e water b a l a n c e of t h e c u l t i v a t e d area t r a v e r s e d by t h e same s t r e t c h and t h e w e i g h t e d a v e r a g e r e c h a r g e method h a v e been worked o u t . The e s t i m a t e d r e c h a r g e t o t h e r i v e r was found t o be i n t h e r a n g e of between 1.33 mlrd m3/yr t o 2 . 6 7 mlrd m3/yr f o r t h e p e r i o d from 1972 t o 1980.
313
The downward p e r c o l a t i o n o f t h e e x c e s s o f i r r i g a t i o n w a t e r and t h e seepage from h i g h - l e v e l
c a n a l s a r e t h e two p r i n c i p a l s o u r c e s o f r e c h a r g e of t h e a q u i f e r
s y s t e m , e s p e c i a l l y i n t h e post-High
Dam p e r i o d .
G e o h y d r o l o g i c a l c o n s t a n t s of t h e a q u i f e r s y s t e m u n d e r l y i n g Upper
TABLE 7 . 2
Egypt Aquifer
Type of a q u i f e r Unconfined Semi-confined 7.2.3.4
k , m/day .
40- 80 40-120
D, m
kD, m2/day
Semi-confining l a y e r S
k ’ , mm/day d ’ , m
15- 60 1000- 5000 0 . 1 0 - 0 . 1 2 15-240 1000-20000 (5-50)
-
1-10
C, day
-
-
3-20 200-4000
Groundwater i n t h e N i l e Delta a r e a
The N i l e D e l t a a q u i f e r i s one o f t h e most i m p o r t a n t groundwater r e s e r v o i r s i n E g y p t . S y s t e m a t i c h y d r o g e o l o g i c a l i n v e s t i g a t i o n i n t h e D e l t a a r e a began i n 1954 and i s s t i l l underway. T h i s i n v e s t i g a t i o n so f a r h a s l e d t o some unders t a n d i n g of t h e groundwater p r o p e r t i e s , p a r a m e t e r s and movement i n t h e a q u i f e r system t h e r e . The a q u i f e r h a s r e c e n t l y been r e p o r t e d as c o n s i s t i n g of t h r e e d i f f e r e n t t y p e s (Shahin, M . ,
1983) and n o t o n l y of t h e u n c o n f i n e d t y p e ( S h a t a , A . ,
o r of t h e open-leaky
flow s y s t e m ( F a r i d , M.S.,
e t a l , 1969)
1 9 8 0 ) . The a p p r o x i m a t e b o u n d a r i e s
s e p a r a t i n g t h e t h r e e t y p e s o f a q u i f e r c a n b e s e e n from t h e map, F i g . 7 . 9 . An i m p r e s s i o n a b o u t t h e s t r a t i g r a p h y and l i t h o l o g y c a n b e s e e n from t h e l o n g i t u d i n a l and c r o s s - s e c t i o n s which were p r e p a r e d by S o l a i t , M.L.
(1964).
The g e o h y d r o l o g i c c o n s t a n t s of t h e t h r e e t y p e s of a q u i f e r u n d e r l y i n g t h e N i l e D e l t a a r e a t o g e t h e r with those belonging t o t h e r e s e r v o i r connecting the Delta and Upper Egypt a r e i n c l u d e d i n T a b l e 7 . 3 . Each y e a r t h e N i l e D e l t a a r e a r e c e i v e s s o m e t h i n g l i k e 35 x lo9 m 3 of s u r f a c e w a t e r from t h e N i l e f o r i r r i g a t i o n , i n d u s t r y and water s u p p l y . T h i s r e c h a r g e s t h e a q u i f e r t h r o u g h i n f i l t r a t i o n o f e x c e s s i r r i g a t i o n w a t e r and t h r o u g h seepage from an e x t e n s i v e network o f c a n a l s and d r a i n s . The water b u d g e t of t h e Nile D e l t a a r e a h a s been s t u d i e d by a number of a u t h o r i t i e s r e s u l t i n g i n a r a n g e of a q u i f e r r e c h a r g e volumes. T h i s r a n g e c o i n c i d e s w i t h t h e r a n g e of 5 t o 10% of t h e i n p u t v a l u e , i . e . from a b o u t 2 t o 4 mlrd m 3 / y r . 3 . 9 8 x lo9 m 3 / y r
Kashef, A . ,
(1983) s u g g e s t s
t o r e p r e s e n t t h e p o t e n t i a l water s u r p l u s f o r f u t u r e development,
u n l e s s u n a c c o u n t e d l o s s e s o r e r r o r s i n t h e e s t i m a t e d v a l u e s of t h e items comp r i s i n g t h e water balance appear i n t h e f u t u r e . Shahin, M . ,
(1983) h a s o b t a i n e d
a f i g u r e of 2 . 2 x lo9 m3/yr. Which f i g u r e i s more a c c u r a t e i s n o t t h e main quest i o n . What i s i m p o r t a n t i s t h a t t h e a q u i f e r u n d e r l y i n g t h e N i l e D e l t a a r e a r e c e i v e s a c e r t a i n r e c h a r g e a t t h e end of e a c h y e a r . That p a r t which does n o t e s c a p e t o t h e sea o r f l o w h e r e and t h e r e t o any of t h e e x i s t i n g d e p r e s s i o n s
314
r] .....
Phreatic Aquifer
Confined A q u i f e r
Leaky A q u i f e r
F i g . 7.9. The t h r e e t y p e s o f a q u i f e r u n d e r l y i n g t h e N i l e D e l t a a r e a and t h e r e s i s t a n c e of t h e o v e r l y i n g c a p .
TABLE 7.3
Summary of t h e g e o h y d r o l o g i c c o n s t a n t s of t h e r e s e r v o i r s u n d e r l y i n g t h e N i l e D e l t a and i t s c o n n e c t i o n w i t h Upper Egypt
Type o f aquifer Unconfined Semi-confined Confined Greater Cairo
Aquifer
k , m/day 50- 80
25-100
D, m
kD, m2/day
Semi-conf i n i n g l a y e r
S
50-150 2500-12000 0.15-0.25 100-250 2500-25000 (1-10) U N K N O W N 1000-10000 (1-28)
k', W d a y d ' , m
1-3 <1 1-5
-
C , day
-
8-20 3000-20000 20-50 20000-50000 8-10 1500-10000
produces a rise i n t h e water t a b l e l e v e l . I t i s q u i t e p o s s i b l e t o p r e v e n t t h i s
r i s e by pumping t h e g r o u n d w a t e r . Would t h e pumping w e l l s b e c o n s i d e r e d t h e n as a means of d r a i n a g e o r a s a means of e x t r a c t i n g w a t e r f o r , s a y , i r r i g a t i o n o r f o r t h e two p u r p o s e s combined? The answer t o t h e s e q u e s t i o n s depends p r i m a r i l y on t h e q u a l i t y o f t h e pumped w a t e r and i t s v a r i a b i l i t y b o t h i n t i m e and i n s p a c e .
3 15
The r e s u l t s which have b e e n o b t a i n e d from a very r e c e n t s t u d y on t h e s a l i n i t y of t h e g r o u n d w a t e r i n t h e D e l t a a q u i f e r ( K a s h e f , A . ,
1983) are r a t h e r a l a r m i n g .
They show a d e e p e r p e n e t r a t i o n o f t h e s e a w a t e r i n t o t h e a q u i f e r t h a n i t was e v e r t h o u g h t . The i n l a n d e x t e n t o f t h e zone of s a l i n e groundwater ( u n s u i t a b l e f o r most p u r p o s e s ) , i n s t e a d of b e i n g a b o u t 5 0 km, h a s been s u g g e s t e d t o b e n o t
less t h a n 120 km from t h e sea c o a s t . REFERENCES Andrew, G . , 1948. The a g r i c u l t u r e i n t h e Sudan ( e d i t e d by J . D . T o t h i l l ) . Chapt e r V I : Geology of t h e Sudan: 84-128. Oxford U n i v e r s i t y P r e s s , London. A t t i a , F . , A m e r , A . , and Hefny, K., 1983. E f f e c t of High-Aswan Dam on groundw a t e r c o n d i t i o n s i n Upper E g y p t . P r o c e e d i n g s o f t h e I n t e r n a t i o n a l Conference on w a t e r r e s o u r c e s development i n E g y p t , C a i r o : 99-119. B a l l , J . , 1927. Problems o f t h e Libyan Desert. G e o g r a p h i c a l J o u r n a l , Vol. 7 0 , N o . 1, 2 and 3 , London. B e r r y , L . , and Whiteman, A . J . , 1968. The N i l e i n t h e Sudan ( w i t h d i s c u s s i o n ) . The G e o g r a p h i c a l J o u r n a l , Vol. 1 3 4 , P a r t I : 1-38. E a g l e s o n , P . S . , and M i l l e r , S . A . , 1983. Water t a b l e d e p r e s s i o n i n t h e G e z i r a r e g i o n . P r o c e e d i n g s of t h e I n t e r n a t i o n a l C o n f e r e n c e on Water R e s o u r c e s Development i n E g y p t , C a i r o , 201-212. E z z a t , M . A . , 1 9 7 6 . R e g i o n a l g r o u n d w a t e r m o d e l s , El-Wadi El-Gadid p r o j e c t . Worki n g Document No. 2 , UNDP/FAO r e p o r t , AGON: EGY 71/561, C a i r o . F a r i d , M.S., Hefny, K . , and A m e r , A . , 1979. H y d r o l o g i c a l a s p e c t s o f t h e N i l e D e l t a r e s e r v o i r . P r o c e e d i n g s of t h e I n t e r n a t i o n a l C o n f e r e n c e on Water r e s o u r ces p l a n n i n g i n E g y p t , C a i r o : 299-320. F i t t , R . L . , Marwick, R . , and W h i t a k e r , F.W., 1967. The R o s e i r e s Dam, Sudan: p l a n n i n g and d e s i g n . P r o c e e d i n g s I n s t i t u t i o n o f C i v i l E n g i n e e r s , P a p e r 7047, Vol. 38: 21-51. G i s c h l e r , C . E . , 1979. Water r e s o u r c e s i n t h e Arab Middle E a s t and North A f r i c a . Middle E a s t and N o r t h A f r i c a n S t u d i e s P r e s s L t d . , Cambridge, E n g l a n d , 132 pp. Hammad, Y . H . , 1969. F u t u r e o f g r o u n d w a t e r i n A f r i c a n S a h a r a Desert. J o u r n a l of t h e i r r i g a t i o n and d r a i n a g e d i v i s i o n , ASCE, Vol. 9 5 No. I R 4 : 563-580. H e l l s t r o m , B . , 1940. The s u b t e r r a n e a n water i n t h e Libyan Desert. G e o g r a f i s k a A n n a l e r , Stockholm. Hepworth, J . V . , 1964. E x p l a n a t i o n of t h e geology of s h e e t s 1 9 , 2 0 , 28 and 2 9 . S o u t h e r n W e s t N i l e , G e o l o g i c a l Survey o f Uganda. K a s h e f , A . I . , 1983. S a l t w a t e r i n t r u s i o n i n t h e N i l e D e l t a . Groundwater Vol. 2 1 , N O . 2: 160-167. 1952. The a r t e s i a n water of E g y p t . Survey Department o f E g y p t . Murray, G . W . , Paper N o . 52, C a i r o . P a v e r , G . L . , 1946. Water s u p p l y i n t h e Middle East campaigns, VI - The s o u t h e a s t e r n d e s e r t o f Upper Egypt (Red S e a H i l l s ) . Water and w a t e r E n g i n e e r i n g , London, 10 p p . P a v e r , G . L . , and P r e t o r i o u s , D . A . , 1954. R e p o r t on h y d r o l o g i c a l i n v e s t i g a t i o n s i n Kharga and Dakhla Oases. P u b l i c a t i o n s of t h e Desert I n s t i t u t e o f E g y p t , No. 4 , 1 0 8 p p , C a i r o , E g y p t . S a g g e r s o n , E . P . , 1962. The p h y s i o g r a p h y and g e o l o g y o f East A f r i c a . N a t u r a l R e s o u r c e s of E a s t A f r i c a , N a i r o b i , Kenya. S a g g e r s o n , E . P . , 1972. E a s t A f r i c a : i t s p e o p l e s and r e s o u r c e s ( e d i t e d by W.T.W. Morgan). C h a p t e r 7 : Geology, 67-94. Oxford U n i v e r s i t y P r e s s , N a i r o b i , Kenya. S a i d , R . , 1962. The g e o l o g y of E g y p t . E l s e v i e r , Amsterdam and N e w York, 377 p p . S a i d , R . , 1 9 8 1 . The g e o l o g i c a l e v o l u t i o n of t h e R i v e r N i l e . S p r i n g e r - V e r l a g , N e w York, 1 5 1 pp Salaam, A . , 1966. The g r o u n d w a t e r geology of t h e G e z i r a , M.Sc. t h e s i s , Univers i t y of Khartoum.
.
316
S a n d f o r d , K.S., 1935. S o u r c e s of w a t e r i n t h e North-Western Sudan. The Geograp h i c a l J o u r n a l : l X X X V , 412-431. S h a h i n , M . A . , e t a l , 1970. H y d r o l o g i c a l a s p e c t s of t h e groundwater r e s e r v o i r u n d e r l y i n g t h e Dakhla O a s i s . P r o g r e s s Report No. 1 s u b m i t t e d t o t h e M i n i s t r y of Land R e c l a m a t i o n , E g y p t , 183 p p . S h a h i n , M . A . , 1983. R e p o r t on a TOKTEN-UNDP Assignment a t t h e Groundwater Research I n s t i t u t e . Academy of S c i e n c e and Technology and O f f i c e of UNDP, Cairo. S h a t a , A . , and El-Fayoumy, I . , 1969. Remarks on t h e hydrogeology of t h e N i l e Delta, UAR. P r o c e e d i n g s o f t h e I n t e r n a t i o n a l Symposium on t h e h y d r o l o g y of d e l t a s , B u c h a r e s t , IASH/UNESCO, Vol. 1 1 : 385-396. S h o t t o n , F.W., 1946. Water s u p p l y i n t h e Middle E a s t campaigns V . The d e s e r t between t h e N i l e D e l t a and t h e Suez C a n a l . Water and Water E n g i n e e r i n g , London, 12 pp. S o l a i t , M.L., 1964. Groundwater a t s e v e r a l p l a c e s i n t h e N i l e D e l t a and V a l l e y , The U n i t e d Arab R e p u b l i c . R e p o r t s u b m i t t e d t o t h e S e v e n t h Arab E n g i n e e r i n g C o n f e r e n c e (in A r a b i c ) , Baghdad, 79 p p . S o n n t a g , C . , K l i t z s c h , E . , and E l - S h a z l y , E . M . , 1976. l 4 C - d a t i n g o f S a h a r a g r o u n d w a t e r s and p a l a e o c l i m a t i c i n f o r m a t i o n by d e i t e r i u m and oxygen 18. Stamp, L . D . , and Morgan, W.T., 1972. A f r i c a : a s t u d y i n t r o p i c a l development, John Wiley and Sons I n c . , N e w York, 520 p p .
317
Chapter 8 THE BASIN SURFACE RUN-OFF AND THE R I V E R LEVELS AND DISCHARGES
Most o f t h e s t u d i e s of ground w a t e r i n t h e N i l e B a s i n p o i n t t o t h e r e l a t i v e
s m a l l q u a n t i t i e s o f ground water d i s c h a r g e , r e c h a r g e and i n s t o r a g e . T h i s s t a t e -
ment s h o u l d n e i t h e r b e u n d e r s t o o d n o r i n t e r p r e t e d a s an a t t e m p t t o b e l i t t l e t h e i m p o r t a n c e o f ground water i n v e s t i g a t i o n a n d / o r e x p l o i t a t i o n . Both a r e c e r t a i n l y i m p o r t a n t i n some s p e c i a l s i t u a t i o n s . The c o n c l u s i o n a s g i v e n h e r e i s b a s e d , however, on t h e p r o p o r t i o n o f t h e q u a n t i t y of ground w a t e r t o t h e q u a n t i t y of s u r f a c e water. F o r example, t h e volume o f t h e ground water c o n t a i n e d w i t h i n t h e f i s s u r e s y s t e m i n t h e E q u a t o r i a l Lakes P l a t e a u r e p r e s e n t s o n l y a b o u t one h a l f of t h e mean a n n u a l p r e c i p i t a t i o n on t h e c a t c h m e n t s o f t h e s e l a k e s . The ground water d i s c h a r g e t o t h e l a k e s i s p r o b a b l y less t h a n 0 . 2 % of t h e t o t a l mean a n n u a l runo f f t o them. F o r t h i s r e a s o n o u r d i s c u s s i o n on t h e b a s i n r u n - o f f f i n e d t o t h e s u r f a c e run-off
8.1 8.1.1
s h a l l b e con-
only.
CATCHMENT OF LAKE V I C T O R I A
Run-off
coefficient
The c a t c h m e n t a r e a o f Lake V i c t o r i a h a s been g i v e n i n C h a p t e r E a s 193 000 km2, and t h e a r e a c o v e r e d by t h e l a k e water a s 6 7 600 km2. The s u r f a c e a r e a o f t h e gauged b a s i n s i s 153 640 km2, o r a b o u t 78.5% o f t h e t o t a l catchment a r e a . The r e s t , which c o m p r i s e s 21.5% o f t h e catchment a r e a , i s ungauged. I t seems t h a t t h e c o n t r i b u t i o n o f t h e ungauged s t r e a m s t o t h e t o t a l r u n - o f f
t o Lake
V i c t o r i a i s q u i t e i n f e r i o r compared t o t h e c o n t r i b u t i o n o f t h e gauged b a s i n s . T h i s c a n b e a t t r i b u t e d t o t h e f a c t t h a t much o f t h e ungauged s u r f a c e i s c o v e r e d by swamps and r e l a t i v e l y l o w - l y i n g a r e a s . C o n s e q u e n t l y , any e r r o r i n t h e e s t i m a t i o n of t h e c o n t r i b u t i o n o f t h e ungauged p a r t w i l l n o t a f f e c t t h e t o t a l i n f l o w t o t h e l a k e t o any c o n s i d e r a b l e e x t e n t . The r a i n f a l l and r u n - o f f
data for the
p e r i o d 1906-1932 w e r e r e p o r t e d by H u r s t i n V o l . V o f tile N i l e B a s i n ( H u r s t , H.E.,
and P h i l i p s ,
P.,
1 9 3 8 ) . A summary of t h e r e s u l t s a r e g i v e n i n T a b l e 8 . 1 .
A d d i t i o n a l l y , t h e 1969 and 1970 r a i n f a l l and r u n - o f f
d a t a c o l l e c t e d by t h e
h y d r o m e t e o r o l o g i c a l p r o j e c t of t h e E q u a t o r i a l Lakes (WMO, 1974) have heen worked o u t so as t o e v a l u a t e t h e monthly and t h e a n n u a l run-off
coefficients.
T h i s c o e f f i c i e n t i s t h e p e r c e n t a g e o f t h e r a i n f a l l on t h e catchment t h a t r e a c h e s t h e l a k e . The r e s u l t s o b t a i n e d a r e p r e s e n t e d i n T a b l e s 8 . 2 and 8 . 3 . The r u n - o f f
c o e f f i c i e n t s f o r t h e ungauged s u b - b a s i n s have been t a k e n a r b i -
t r a r i l y a t 2% f o r t h e n o r t h e r n and t h e s o u t h e r n s h o r e s of t h e l a k e , and a t 3% f o r t h e e a s t e r n and t h e w e s t e r n s h o r e s , s i m i l a r t o t h e h y d r o m e t e o r o l o g i c a l
318
s u r v e y p r o j e c t o f t h e l a k e s . These v a l u e s o f t h e r u n - o f f
c o e f f i c i e n t are some-
what d i f f e r e n t from t h o s e assumed by H u r s t . From T a b l e 8 . 3 i t i s c l e a r t h a t t h e r u n - o f f
c o e f f i c i e n t s f o r t h e y e a r 1969
a r e much c l o s e r t o t h o s e a v e r a g e d o v e r t h e p e r i o d 1946-1970 t h a n t h e 1970 c o e f f i c i e n t s . I t is q u i t e n a t u r a l t h a t t h e run-off
coefficient increases with the
p r e c i p i t a t i o n d e p t h . I n 1969 t h e r a i n f a l l w a s 1054 mm and i n 1970, 1 2 1 3 mm. T h i s i n c r e a s e i n r a i n f a l l r e s u l t e d i n t h e r i s e of t h e c o e f f i c i e n t from 8.95% i n 1969 t o 10.09% i n 1 9 7 0 . I t i s t h e r e f o r e q u i t e r e a s o n a b l e t o t a k e 9% as t h e y e a r l y c o e f f i c i e n t , a v e r a g e d o v e r a l o n g s e q u e n c e o f y e a r s . F o r t h e 27-year p e r i o d , from 1906 up t o and i n c l u d i n g 1 9 3 2 , t h e v a l u e of t h e y e a r l y c o e f f i c i e n t s u g g e s t e d by H u r s t w a s 8% ( T a b l e 8 . 1 ) . The Kagera R i v e r h a s always been d e s c r i b e d a s t h e p r i n c i p a l f e e d e r t o Lake V i c t o r i a . The b a s i n o f t h e Kagera h a s a t o t a l s u r f a c e o f 58370 km3 and i t comp r i s e s s i x s u b - b a s i n s . The a r e a , mean a n n u a l r a i n f a l l and a n n u a l r u n - o f f f i c i e n t o f each o f t h e s e s u b - b a s i n s
coef-
o v e r t h e p e r i o d 1958 up t o 1962, e x c e p t f o r
t h e l a s t two s u b - b a s i n s where t h e d a t a a p p l y t o 1970 o n l y , a r e a s f o l l o w s : River sub-basin
Area, km2
Mean a n n u a l r a i n f a l l , mm
Akyanaru Nyvarongo Ruvuvu Middle Kagera Mwisa Ngono
5285 13315 12300 22835 20 35 2600
1180 1182 1158 1100 1000 1200
T o t a l and means
58370
1139
TABLE 8 . 1
The run-off
Run-off
coefficient,
% 11.8 16.7 14.6 2.3 2.5 18.0 1
10.0
o f Lake V i c t o r i a f o r t h e p e r i o d 1906-1932 ( H u r s t , H . E . ,
and P h i l i p s ,
P.,
1938)
M e an
District
aLA1laLL,
i n mm
Area, i n km2
Estimated percentage
of rainfall
reaching L. Victoria
T o t a l water r e a c h i n g Lake Victoria, i n 1 0 6 m'/yr 7.900
Kagera B a s i n
1.242
60.000
North-western and northern portion
1.302
30 000
1
400
North-eas t e r n
1.248
50.000
10
6.200
995
50.000
7
3.500
Islands i n L. Victoria
1.150
3.000
10
300
Means & T o t a l s
1.190
193.000
8
18.300
S o u t h - e a s t e r n and southern portion
10.6
TABLE 8.2
The run-off coefficients of the sub-basins contained in the catchment of Lake Victoria for 1969 and 1970, computed from the data collected by the Hydrometeorological Survey Project (WMO, 1974)
Catchment area Name
Sio
Nsioa
Yala
Kibos
Nyando
Cheronoit
Sondu
Area, km2
Monthly and yearly values of the run-off coefficient Jan.
Feb.
Mar.
Apr.
May
June
July
Aug.
Sep.
Oct.
Nov.
Dec.
Year
29.38 67.91 21.17 17.96 36.62 98.21 31.48 24.74 33.00 83.06 26.33 21.35
1080
8.57 10.23 9.40
4.48 4.80 4.64
8.72 11.54 10.13
7.89 10.14 9.01
21.74 27.53 24.64
53.32 18.73 67.10 23.84 60.21 21.29
14.82 22.27 18.87 19.48 16.85 20.88
11980
8.19 9.25 8.72
26.47 23.28 24.88
6.71 8.16 7.44
4.37 10.95 7.66
15.20 19.63 17.42
15.71 11.48 27.02 23.44 21.36 17.46
8.35 17.36 19.22 9.42 14.61 25.23 30 .80 34.89 42.60 21.70 18.32 22.71 21.62 29.98 20.46
2650
11.59 8.37 9.98
25.64 11.85 17.50 5.01 21.57 8.43
20.86 12.77 16.82
32.40 23.23 27.81
33.08 23.05 28.06
32.48 23.71 28.10
38.70 42.99 45.69 48.67 66.44 30.01 26.04 31.24 32.70 45.58 33.04 20.61 32.37 37.12 39.20 47.12 49.74 25.31
490
3.88 5.07 4.47
8.96 7.33 8.14
4.14 4.71 4.42
7.97 10.05 9.01
18.90 16.07 17.48
20.90 16.30 18.60
26.84 19.26 23.05
10.80 5.74 8.27
13.06 9.72 11.39
11.95 10.20 11.07
9.60 8.70 9.15
5.49 6.44 5.97
10.20 9.11 9.65
2650
3.54 5.05 4.30
39.14 17.47 28.30
8.74 8.26 8.50
4.43 12.23 15.57 25.65 10.00 19.94
7.09 15.51 11.30
7.68 11.62 9.65
6.50 19.75 13.12
8.58 10.09 24.18 16.24 17.13 12.41
9.81 11.41 10.61
7.94 10.76 9.35
8.44 14.83 11.64
560
2.95 3.82 3.38
14.49 5.98 10.24
4.05 5.10 4.58
2.70 8.11 5.40
7.87 8.54 6.20
0.56 12.32 6.44
9.53 12.93 11.23
1.70 4.67 3.18
2.55 6.87 4.71
1.09 3.57 2.33
0.00 2.56 1.28
3.73 6.36 5.04
3230
13.50 6.02 9.76
72.64 25.52 49.08
21.67 24.44 23.06
15.76 40.84 28.30
28.29 55.88 42.09
10.53 34.13 25.60 30.96 52.58 58.40 20.74 43.36 42.00
15.48 28.38 21.93
7.83 21.57 14.70
21.09 34.48 27.78
24.55 16.85 53.99 32.88 39.27 24.86
2.42 8.00 5.21
11.24 20.81 16.03
For each catchment area, the top line gives the run-off coefficient for 1969, the middle line for 1970, and the bottom line gives the average run-off coefficient for 1969 and 1970
w
(D w
TABLE 8.2
(continued)
Catchment area Name
Monthly and y e a r l y v a l u e s o f t h e run-off
Area, km2
Jan.
Feb.
AwachKaboun
610
23.68 10.93 17.30
GuchaMigoei
6840
Mori
Mara (Mines )
Suguti
Ruana Gruneti
Mbalageti
Mar.
Apr.
May
June
124.50 22.72 73.61
33.02 10.87 21.95
15.19 19.45 17.32
15.46 47.44 31.45
3.62 5.00 4.31
11.70 18.77 15.23
11.15 14.79 12.97
11.32 17.22 14.27
23.00 34.48 28.74
16.39 44.12 30.25
590
2.71 15.09 8.90
3.99 10.97 7.48
3.08 13.86 8.47
23.87 74.94 49.40
10830
2.13 3.14 2.63
4.62 8.54 6.58
1.80 5.29 3.55
1020
1.84 0 .oo 0.92
2.97 1.79 2.38
11430
3.44 4.59 4.02
3730
0.16 3.33 1.75
coefficient
Aug.
Sep.
Oct.
Nov.
Dec.
Year
48.92 56.28 67.95 95.63 58.43 75.95
14.20 30.17 22.18
16.68 74.47 45.57
10.02 47.90 28.96
14.01 29.25 21.63
9.36 20.42 14.88
29.51 31.65 30.58
11.30 15.78 18.54
3.13 8.75 5.94
5.95 14.34 10.15
2.99 8.96 5.98
5.98 9.39 7.69
4.90 6.32 5.61
9.40 16.05 12.72
34.90 85.95 60.43
38.52 16.95 88.14 33.15 63.33 20.05
6.16 10.80 8.48
4.35 4.25 4.30
6.05 4.60 5.32
1.71 2.13 1.92
4.89 4.49 4.69
10.17 28.74 19.45
6.25 11.17 8.71
16.24 18.05 17.15
17.82 23.14 20.48
18.06 14.82 16.44
18.76 11.40 15.08
21.06 14.44 17.75
12.93 12.41 12.67
9.79 9.04 9.42
6.10 4.58 5.34
9.78 10.22 10 .oo
1.74 4.07 2.91
9.80 21.19 15.50
18.59 0 .oo 9.30
39.22 201.96 120.59
21.01 0.00 10.50
56.02 0.00 28.01
14.71 0.00 7.36
6.54 0.00 3.27
4.67 0.00 2.33
2.13 0.34 1.24
7.06 7.33 7.20
5.47 7.08 6.28
1.21 1.62 1.42
7.29 9.77 8.53
1.75 2.40 2.07
7.88 6.79 7.34
2.63 5.15 3.89
5.26 45.50 25.38
2.69 4.06 3.38
1.62 2.45 2.03
0.66 0.88 0.77
0.93 1.33 1.13
2.98 4.44 3.71
3.38 3.41 3.40
0.72 6.79 3.76
1.56 9.14 5.35
3.30 2.92 3.11
22.34 29.10 25.72
22.12 24.78 23.45
53.62 131.64 92.63
0.00 13.38 6.69
0.00 6.22 3.11
10.23 3.46 6.85
1.37 6.72 4.05
2.38 6.33 4.36
July
F o r each catchment a r e a , t h e top l i n e g i v e s t h e run-off c o e f f i c i e n t f o r 1969, t h e middle l i n e f o r 1970, and t h e bottom l i n e g i v e s t h e average run-off c o e f f i c i e n t f o r 1969 and 1970
TABLE 8 . 2
(continued)
Catchment a r e a Name
Area, km2
Monthly and y e a r l y v a l u e s of t h e run-off Jan.
Feb.
Mar.
Apr.
May
June
coefficient
July
Aug.
Sep.
Oct.
Nov.
Dec.
Year
10790
5.40 3.34 4.37
20.93 5.64 13.28
2.49 8.14 5.31
13.73 10.10 11.91
14.80 10.84 12.82
103.20 153.94 128.57
47.27 39.10 43.18
44.49 91.11 67.80
14.30 21.62 17.96
1.08 2.89 1.98
2.22 11.09 6.60
2.17 9.90 6.04
5.51 7.71 6.61
Ngogo
1200
1.64 2.00 1.82
2.60 2.21 2.40
4.50 5.18 4.84
1.67 1.71 1.69
4.10 2.65 3.38
0.00 0.00 0.00
0.00 0.00 0.00
0.00 0.00 0.00
0.00 0.00 0.00
0 .oo 0.00 0.00
10.51 0.00 5.26
5.28 0 .oo 2.64
3.85 4.58 4.22
Mo ame
2090
0.81 0.75 0.78
1.28 0.84 1.06
1.11 1 3 . 3 3 5.61 1.83 9.47 1.47
18.40 1.06 9.73
39.88 0.00 19.94
95.70 0.00 47.85
47.85 0.00 23.92
20.51 0.00 10.26
5.04 0.00 2.52
1.14 0 .oo 0.57
0 .oo 0 .oo 0 .oo
4.37 2.86 3.62
Isanga
4780
2.62 5.93 4.28
0.77 1.17 0.97
1.29 3.97 2.63
3.04 7.78 5.41
44.83 8.37 26.60
83.68 0.00 41.84
62.76 0.00 31.38
31.38 0.00 15.69
16.74 0.00 8.37
0.44 0 .oo 0.22
0.64 0.00 0.32
0.38 0 .oo 0.19
2.62 2.86 2.74
Kagera
58370
13.58 10.04 11.81
16.05 10.85 13.45
9.19 5.97 7.58
7..36 5.36 6.36
17.52 14.38 15.95
179.04 196.65 187.85
61.56 88.92 75.24
32.40 34.20 33.30
18.01 21.18 19.60
11.89 12.97 12.43
8.61 8.50 8.55
8.52 8.87 8.70
14.73 13.56 14.15
5670
1.42 2.13 1.78
1.21 2.05 1.63
0.81 1.18 1.oo
0.85 1.18 1.02
1.64 3.28 4.61
10.88 21.71 16.30
3.85 5.67 4.61
1.76 2.29 2.02
0.57 1.70 1.13
0.52 0.74 0.63
0.48 0.68 0.58
1.01 1.73 1.37
1.35 1.18 1.26
13020
0.47 0.68 0.58
2.28 3.07 2.68
0.50 0.75 0.63
0.34 0.68 0.51
1.28 2.14 1.71
9.45 17.92 13.69
1.26 0.30 0.78
0.58 0.94
0.51 0.79 0.65
0.29 0.33 0.31
0.34 0.61 0.48
0.91 1.66 1.29
0.70 0.79 0.75
SiniyuDuma
Ruizi
Katonga
0.76
For each catchment a r e a , t h e t o p l i n e gives t h e run-off c o e f f i c i e n t f o r 1969, t h e middle l i n e for 1970, and t h e bottom l i n e g i v e s t h e average run-off c o e f f i c i e n t f o r 1969 and 1970
W h) P
W N N
(continued)
TABLE 8 . 2
Catchment a r e a Name _____
A r e a , km2
Monthly and y e a r l y v a l u e s of t h e r u n - o f f Jan.
Feb.
Mar.
Apr.
Yay
June
July
Aug.
coefficient Sep.
Oct.
~
Nov.
Dec.
Year
~~
Northern shores
5060
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
Southern shores
16 140
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
Eastern shores
12100
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
Western shores
6990
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
For e a c h catchment a r e a , t h e t o p l i n e g i v e s t h e r u n - o f f c o e f f i c i e n t f o r 1969, t h e middle l i n e f o r 1970, and t h e bottom l i n e g i v e s t h e average run-off
c o e f f i c i e n t f o r 1969 and 1970
323
TABLE 8.3
Average o v e r a l l monthly and y e a r l y r u n - o f f
coefficients f o r the
y e a r s 1969 and 1970, and f o r t h e p e r i o d 1946-70
Run-off
c o e f f i c i e n t , i n percent f o r
Month and Year
1969
1970
1969 and 1970
January February March Apri 1 May June July August September October November December Year
6 .OO 11.15 5.91 5.47 12.69 30.16 17.46 12.11 12.96 7.51 6.26 5.82 8.95
5.33 7.62 5.50 6.88 13,44 37,lO 24.91 16.49 17.07 10.49 7.56 6.31 10.09
5.67 9.38 5.71 6.18 13.06 33.63 21.18 14.30 15.01 9 .oo 6.91 6.06 9.52
Average of
The f i g u r e s g i v e n by H u r s t f o r t h e r u n - o f f
(see T a b l e 8.1) and 11%( H u r s t , H . E . ,
Average of
1946-1970 5.0 10.0 7.0 7.0 8.5 25.0 17 . O 12.0 10.0 7.5 6.5 6.5 8.94
from t h e Kagera B a s i n a r e 10.6%
and P h i l i p s ,
P . , 1938). Any o f t h e s e two
v a l u e s i s , i n view o f t h e r a i n f a l l c a u s i n g t h e r u n - o f f , more r e c e n t f i n d i n g s . F o r e s t i m a t i n g t h e run-off
s m a l l compared t o t h e
c o e f f i c i e n t from a g i v e n r a i n -
f a l l on t h e Kagera B a s i n w e recommend t h e e x p r e s s i o n
r = 6
+
0.05 ( P
-
lOOO), i n p e r c e n t
where r i s t h e r u n - o f f
(8.1)
c o e f f i c i e n t and P i s t h e a n n u a l p r e c i p i t a t i o n i n m m .
The graph p r e s e n t e d i n Vol. I V o f t h e r e p o r t on t h e h y d r o m e t e o r o l o g i c a l p r o j e c t
of t h e E q u a t o r i a l Lakes can b e t r a n s l a t e d t o t h e e x p r e s s i o n
r = 4.6 + 0.17 (P - 1100), i n p e r c e n t
(8.2)
The r a n g e o f P i s from 1000 t o 1200 m m f o r e q . 8.1 and from 1100 t O 1200 mm f o r e q . 8.2. These two e x p r e s s i o n s g i v e f o r P = 1200 mm/yr an a n n u a l c o e f f i c i e n t of 16% and 21.6%, r e s p e c t i v e l y , i n s t e a d o f t h e 10.6 o r 11.0% proposed by H u r s t . The monthly and t h e a n n u a l d i s c h a r g e s of t h e Kagera a t Kyaka F e r r y f o r t h e p e r i o d from 1940 up t o and i n c l u d i n g 1971 are l i s t e d i n T a b l e 1, Appendix U. The mean hydrograph of t h e r i v e r f o r t h e same p e r i o d i s shown i n F i g . 8.1., whereas t h e b a s i c s t a t i s t i c a l d e s c r i p t o r s of t h e s e d a t a a r e i n c l u d e d i n T a b l e
8.4.
324
640 r
600
E 580 .
m
560.
W
540,
& 520, L
500. tJl
0
480' 460. 440, 420,
Fig. 8.1. The a v e r a g e hydrograph of t h e R i v e r Kagera a t Kayaka F e r r y f o r t h e p e r i o d 1940-71 The r e s u l t s p r e s e n t e d i n T a b l e 8 . 4 show c l e a r l y t h a t t h e mean monthly and a n n u a l d i s c h a r g e s are a l l s e r i a l l y c o r r e l a t e d . S i n c e t h e t w e l v e monthly and t h e a n n u a l series have a l m o s t t h e same p a t t e r n of s e r i a l c o r r e l a t i o n , t h e model t h a t can b e used t o d e s c r i b e any of t h e series i s t h e same f o r a l l t h e 13 series. A first-order
a u t o r e g r e s s i v e scheme h a s proved t o b e a d e q u a t e f o r t h i s
p u r p o s e . T h i s model c a n b e w r i t t e n a s
(Xt
-
X)
=
a(xt-l
-
x,
(8.3)
+ Et
i s t h e v a r i a t e v a l u e a t any t i m e t , X t - l
where X t
-
i s t h e v a l u e a t t i m e t-1, X
i s t h e mean, a i s t h e f i r s t s e r i a l c o r r e l a t i o n c o e f f i c i e n t , r l , and s t i s t h e residual a t t i m e t.
8.1.2
Water l e v e l and s t o r a g e t o Lake V i c t o r i a i n a normal y e a r is e s t i m a t e d a t
The t o t a l s u r f a c e r u n - o f f (1.050 x 0.895 x 193 x l o 9 )
+
( 1 . 2 5 x 0 . 1 0 x 1400 x l o 6 ) = 1 8 . 3 x
a h i g h y e a r a t ( 1 . 2 5 x 0 . 1 0 x 193 x 10')
+
lo9
m3,
and i n
1 . 7 x 0 . 1 2 x 1400 x l o 6 ) = 2 4 . 4 x
109 m 3 . The r u n - o f f f a c e , P1,
t o t h e l a k e , R , p l u s t h e d i r e c t p r e c i p i t a t i o n on t h e l a k e s u r -
less t h e e v a p o r a t i o n from i t , E l , p l u s t h e change i n t h e s t o r a g e
c o n t e n t , AS, e q u a l s t h e o u t f l o w from t h e l a k e .
TABLE 8 . 4
The b a s i c s t a t i s t i c a l d e s c r i p t o r s of t h e Kagera monthly and annual d i s c h a r g e s a t Kyaka F e r r y f o r t h e p e r i o d 1940-1971
Month and Year January February March April May June July August Septernber October November December Year
Basic s t a t i s t i c a l descriptors
i ,m 3106
s , 106
436.1 408.3 472.3 505.4 601.0 612.0 634.1 589.5 518.0 485.9 441.4 450.8 6154.7
120.9 133.2 174.5 203.2 270.4 286.1 289.2 246.4 187.8 145.6 117.4 116.1 2168.6
m3
‘v 0.2772 0.3262 0.3694 0.4020 0.4498 0.4674 0.4561 0.4180 0.3625 0.2997 0.2660 0.2575 0.3523
cS
1.3597 1.5377 0.3170 1.1882 1.1135 1.0813 1.1078 1.3136 1.3541 0.9973 0.7227 0.7421 1.0744
Serial correlation coefficients ‘k
5.4370 5.7681 4.1510 3.6699 3.3572 3.3385 3.7140 4.8183 5.5765 4.5614 3.5304 3.5192 3.5682
rl
r2
r3
r4
r5
‘6
r7
r8
0.7023 0.7055 0.6735 0.6911 0.6766 0.5911 0.5712 0.5793 0.5612 0.5816 0.6821 0.7190 0,7270
0.4174 0.4953 0.3690 0.5769 0.5576 0.5864 0.5171 0.3592 0.2966 0.3055 0.4234 0.4593 0.5122
0.3005 0.3294 0.1672 0.3497 0.3494 0.3390 0.3236 0.2239 0.2274 0.2594 0.3651 0.3938 0.3413
0.3714 0.3787 0.2828 0.4513 0.4713 0.4680 0.3824 0.2458 0.2021 0.2414 0.3372 0.4199 0.3949
0.4760 0.4609 0.4386 0.4365 0.5074 0.4514 0.4423 0.4755 0.5004 0.5303 0.5553 0.5265 0.5193
0.4357 0.3568 0.3815 0.4116 0.5020 0.5198 0.4450 0.4130 0.4104 0.4328 0.4622 0.4788 0.4829
0.1460 0..1309 0.1690 0.1327 0.1546 0.1652 0.1565 0.1628 0.1557 0,1767 0,2270 0.2300 0.2036
.0832 0.0695 6.0878 6.0085 0 .0590 0.1161 0.0781 0.0627 0.0615 0.0662 0.1179 0.0681 0.0580
N w GI
326
The w a t e r b a l a n c e o f Lake V i c t o r i a h a s a l r e a d y b e e n d i s c u s s e d i n c o n n e c t i o n w i t h e v a p o r a t i o n from t h e l a k e s u r f a c e . A l s o , t h e b a l a n c e f o r e a c h o f t h e y e a r s 1969 and 1970, and f o r t h e s o - c a l l e d
normal y e a r , i s g i v e n i n P a r t 1 1 , Vol. I o f
t h e r e p o r t on t h e h y d r o m e t e o r o l o g i c a l s u r v e y o f t h e c a t c h m e n t s o f Lakes V i c t o r i q Kyoga and A l b e r t (WMO, 1 9 7 4 ) . The b a l a n c e g i v e n f o r t h e s o - c a l l e d normal y e a r h a s been b a s e d on t h e a v e r a g e o f t h e d a t a f o r t h e p e r i o d 1946-1970.
This period
can b e s p l i t i n t o two s e c t i o n s , t h e f i r s t s e c t i o n l a s t i n g f o r 16 y e a r s , from 1946 up
t o 1961, and t h e s e c o n d f o r 9 y e a r s , from 1962 t o 1970. The f a c t t h a t
t h e l a t t e r was e x c e s s i v e l y w e t h a s c a u s e d t h e a v e r a g e o v e r t h e whole p e r i o d t o b e r a t h e r h i g h . The mean a n n u a l o u t f l o w from t h e l a k e f o r t h e 1946-61 p e r i o d i s 20.12 x
lo9
m3,
p e r i o d , 28.61 x
f o r t h e 1962-70 p e r i o d , 4 3 . 9 2 x lo9 m 3 and f o r t h e 1946-1970
lo9
m3/yr,
70-year p e r i o d , 1900-1970,
a l l measured a t J i n j a . The a v e r a g e o u t f l o w f o r t h e
lo9
i s about 2 3 . 5 x
m3/yr.
F o r t h e same p e r i o d , t h e
change i n s t o r a g e , AS, showed an a v e r a g e v a l u e of 2 3 mm/yr.
E x p r e s s i n g a l l terms
i n t h e b a l a n c e e q u a t i o n i n millimeters o v e r t h e s u r f a c e of t h e l a k e : R = 270 mn)
0 = 347 mm, AS = 2 3 m ; t h e d i f f e r e n c e P
-
E l = 100 mm.
A summary o f some o f t h e w a t e r b a l a n c e s f o r Lake V i c t o r i a i s as f o l l o w s :
pl' m/yr
R,
0
AS 9
mm/yr
mm/yr
m/yr
mm/yr
mm/day
1969 1970 1906-1932
1765 1827 1151
269 352 276
680 654 311
-248 +128
1602 1399 1116
4 . 37a 3.83' 3. 06b
1946-1970 1900-1970
1691 1560
278 270
4 26 347
1473 1460
4 .03a 4 .OO
Year
a = WMO, 1974;
b = Hurst, H . E . ,
+
-
70
+ 23
and P h i l l i p s , P., 1938
The c o n t i n u o u s v a r i a t i o n o f t h e i n f l o w t o , and t h e o u t f l o w from, t h e l a k e h a s r e s u l t e d i n t h e change i n t h e volume o f water s t o r a g e i n t h e l a k e . T h i s is r e f l e c t e d i n t h e c o n t i n u o u s v a r i a t i o n of t h e l a k e water s u r f a c e l e v e l . The change i n b o t h l a k e w a t e r l e v e l and s t o r a g e v e r s u s t i m e , from 1900 up t o and i n c l u d i n g 1970 i s shown i n F i g . 8 . 2 . The f i r s t t h i r t y years o f r e c o r d show a d i s t i n c t maximum l a k e s u r f a c e l e v e l and a d i s t i n c t minimum l a k e l e v e l o n c e e v e r y 10 t o 11 y e a r s . The n e x t t h i r t y y e a r s show i n s t e a d a c y c l e o f a b o u t 5 y e a r s l e n g t h , and i n t h e l a s t t e n y e a r s no r y t h m i c c y c l i c i t y i n t h e water l e v e l c a n b e seen.
I n V o l . V o f t h e N i l e B a s i n ( 1 9 3 8 ) , H u r s t w r o t e : "Some y e a r s a g o , D r C . E . P . Brooks p u b l i s h e d a p a p e r on ' V a r i a t i o n s i n t h e L e v e l s o f t h e C e n t r a l A f r i c a n L a k e s ' i n which h e p o i n t e d o u t a c o n n e c t i o n between t h e l e v e l s o f Lakes V i c t o r i a and A l b e r t and t h e f r e q u e n c y of s u n s p o t s " .
r
-
I
7
I
'W3
I
,
- +
' J6DJO)S
, 1
U!
, ,
J6UDc(3
,
,
,
,
,
328
I n h i s d i s c u s s i o n on t h e p a p e r on "Flood-Stage p u b l i s h e d by C . S . J a r v i s i n 1 9 3 5 , J . W .
Records o f t h e R i v e r N i l e "
Shuman mentioned t h e d i f f e r e n t c y c l e s
and showed w i t h some g r a p h i c a l t e c h n i q u e s and d a t a smoothening p r o c e d u r e s t h a t b o t h a n n u a l r a i n f a l l on t h e catchment o f Lake Victoria and t h e l e v e l of w a t e r s u r f a c e i n t h e l a k e f o l l o w t h e s o l a r c y c l e ( 1 1 y e a r s ) and t h a t t h e l a k e l e v e l s l a g one y e a r w i t h t h e a n n u a l r a i n f a l l c u r v e . I n h i s d i s c u s s i o n on t h e same paper, H u r s t mentioned t h e p e r i o d i c a n a l y s e s made by T u r n e r , C r a i g and B r o o k s . Headded t h a t p e r i o d s v a r y i n g from 2 t o 240 y e a r s h a v e been found ( J a r v i s , C . S . ,
1935).
Again, H u r s t , i n Vol. V o f t h e N i l e B a s i n , c o n c l u d e s t h a t t h e h i g h c o r r e l a t i o n which e x i s t e d between l a k e l e v e l and s u n s p o t numbers o f t h e y e a r s 1696-1922 which w e r e u s e d by B r o o k s , h a s p r a c t i c a l l y d i s a p p e a r e d f o r t h e s u b s e q u e n t y e a r s 1923-1934.
N e i t h e r i s t h e r e any c o r r e l a t i o n between s u n s p o t numbers and change
of l a k e l e v e l o r r a i n f a l l . H e a d d s : " I n f a c t t h e o n l y c o r r e l a t i o n which remains
i s t h e s t r a i g h t f o r w a r d o n e between r a i n f a l l and change of l a k e l e v e l " ( H u r s t ,
H.E., and P h i l i p s ,
P . , 1938).
The r e l a t i o n s h i p between t h e h y d r o l o g i c s e r i e s of monthly p r e c i p i t a t i o n , a n n u a l p r e c i p i t a t i o n and a n n u a l r u n - o f f
t o s u n s p o t numbers was i n v e s t i g a t e d by
I . Rodriguez and V . Y e v j e v i c h u s i n g c r o s s - c o r r e l a t i o n
analysis f o r various t i m e
l a g s . No s i g n i f i c a n t c o r r e l a t i o n w a s found between t h e s e h y d r o l o g i c series and s u n s p o t numbers (1967)
.
The r e l a t i o n s h i p between t h e c y c l i c i t y i n t h e c l i m a t i c and t h e h y d r o l o g i c
t i m e series and t h e 1 1 . 1 - y e a r s u n s p o t c y c l e o r t h e 2 2 . 2 - y e a r Briickner c y c l e h a s been s t r o n g l y emphasized by K i n g , J . W .
( 1 9 7 5 ) , and e q u a l l y d e n i e d by Ghani and
o t h e r s . The whole q u e s t i o n o f t h e c y c l i c i t y i n t h e h y d r o l o g i c t i m e series would t h e r e f o r e seem f a r from b e i n g s e t t l e d . The l e v e l o f t h e water s u r f a c e i n Lake V i c t o r i a u n d e r g o e s a s e a s o n a l v a r i a t i o n . The maximum o c c u r s between A p r i l and May and t h e minimum o c c u r s o n c e i n J a n u a r y - F e b r u a r y and a n o t h e r t i m e between J u l y and O c t o b e r . The p a t t e r n i s s o r e g u l a r t h a t t h e mean s e a s o n a l v a r i a t i o n i n t h e l e v e l o f V i c t o r i a h a s been r e p r e s e n t e d a s t h e sum of s i x harmonic components. T h i s c a n b e w r i t t e n as
X, = X
+
6 C
A. sin (
2 " ; '
l J L -i1 2 +
e .J )
(8.4)
where A . and 8 . are t h e a m p l i t u d e and p h a s e a n g l e of t h e j t h h a r m o n i c , X i s J J t h e mean l e v e l and t is t h e number of t h e month. I t h a s been found t h a t t h e 12-monthly
and t h e 6-monthly cycles a r e r e s p o n s i b l e f o r a b o u t 96% o f t h e t o t a l
s e a s o n a l v a r i a t i o n , and t h e 4-monthly o s c i l l a t i o n i s r e s p o n s i b l e f o r j u s t 3% of the total variation.
329
The c u r v e r e p r e s e n t i n g e q . 8.4 i s shown i n F i g . 8.3. The means o f t h e o b s e r v e d monthly d e p a r t u r e s from t h e annual mean l a k e l e v e l a r e supposed t o coincide with t h i s curve.
f
-
25 20
Computed change level
of
al
A
15
0
al
Observed a n d computed change of level 1900 - 1970
E 10
-0 z
5
El+
w
o
€
5
f -
-: -5 2
I
Ian. Feb.' Ma;.
10
15
Apr.
Actual change 1896 - 1934
May
I
.- . L-j
;,I
\
of l e v e l
\
.
a
20 F i g . 8.3.
S e a s o n a l o s c i l l a t i o n o f w a t e r l e v e l i n Lake V i c t o r i a
H u r s t r e p o r t s t h a t t h e l e v e l of Lake V i c t o r i a h a s a y e a r l y o s c i l l a t i o n and t h e normal r a n g e of t h e l a k e i s o n l y 30 cm. The extreme r a n g e i n t h e p e r i o d 1896-1934 was 1.74 m ( H u r s t , H . E . ,
and P h i l i p s ,
P . , 1938). The o b s e r v e d v a r i a -
t i o n i n l a k e l e v e l and t h e computed one from t h e l a k e b a l a n c e f o r t h a t p e r i o d a r e a l s o shown i n F i g . 8.3. T h e i n c r e a s e i n t h e a m p l i t u d e o f o s c i l l a t i o n seems t o b e r a t h e r s m a l l , b u t t h e l o c a t i o n o f t h e maximum and minimum l e v e l s seems t o have undergone a one-month r e t a r d a t i o n . The s e a s o n a l r a n g e of v a r i a t i o n i n t h e l a k e s t o r a g e based on t h e mean monthly d e p t h s f o r t h e p e r i o d from 1900 up t o and i n c l u d i n g 1970 h a s been a n a l y z e d s t a t i s t i c a l l y and t h e v a l u e s of t h e b a s i c d e s c r i p t o r s a r e : mean = 44 cm/yr, s t a n -
d a r d d e v i a t i o n = 13.15 c m / y r and skewness = 0.296. The d a t a have a l s o shown t o be s e r i a l l y u n c o r r e l a t e d ( s e e F i g . 8.4.). The P e a r s o n t y p e I 1 1 h a s proven t o be t h e d i s t r i b u t i o n f u n c t i o n o f b e s t f i t t o t h e d a t a . The g r a p h i c a l p l o t of t h e o b s e r v e d d a t a and o f t h e d i s t r i b u t i o n f u n c t i o n i s shown i n F i g . 8.5. The t h e o r e t i c a l l y o b t a i n e d r a n g e s o f v a r i a t i o n f o r a number of non-exceedance p r o b a b i l i t i e s are g i v e n i n t h e same f i g u r e .
330
S e r i a l c o r r e l o g r a m of t h e s e a s o n a l v a r i a t i o n o f t h e s t o r a g e d e p t h Fig. 8 . 4 . i n Lake V i c t o r i a
8.1.3
Lake o u t f l o w
The o u t f l o w l e a v e s Lake V i c t o r i a o v e r Ripon F a l l s and f l o w s i n a r a v i n e o b s t r u c t e d by r o c k s and r a p i d s f o r a d i s t a n c e o f a b o u t 6 5 km.From j u s t u p s t r e a m of Namasagali down t o Lake Kyoga, a d i s t a n c e o f a b o u t 50 km, t h e V i c t o r i a N i l e h a s a m i l d s l o p i n g c h a n n e l . The t o t a l l e n g t h of t h e r i v e r from t h e e x i t o f Lake V i c t o r i a a t J i n j a t o i t s e s c a p e i n t o Lake Kyoga i s 125 k m . The s i t e a t Namasagali had been used f o r m e a s u r i n g t h e d i s c h a r g e of t h e V i c t o r i a N i l e . A d e t a i l e d a n a l y s i s of t h e d i s c h a r g e measurement a t t h i s s i t e was g i v e n by C . L . Berg ( 1 9 5 3 ) . The c o n c l u s i o n drawn from t h i s a n a l y s i s i s t h a t t h e measurement p r a c t i c e b a s e d on c o n s i d e r i n g t h e mean v e l o c i t y f o r a v e r t i c a l a s 0 . 9 6 t i m e s t h e v e l o c i t y a t h a l f t h e d e p t h of t h e v e r t i c a l g i v e s a d i s c h a r g e 5 . 3 % i n e x c e s s of t h e a c t u a l d i s c h a r g e . H e p r o p o s e d t h a t t h e c o n s t a n t 0 . 9 6
s h o u l d b e r e d u c e d t o 0 . 9 1 . A f t e r t h e c o n s t r u c t i o n and t h e p u t t i n g i n t o o p e r a t i o n of t h e Owen F a l l s Dam a s from 1 9 5 4 , t h e r e l e a s e t h r o u g h t h e d a m c o n s t i t u t e s t h e most r e l i a b l e e s t i m a t e of t h e d i s c h a r g e of t h e V i c t o r i a N i l e . The r e l a t i o n s h i p between t h e measured d i s c h a r g e s a t Namasagali and t h e gauge r e a d i n g a t J i n j a was set u p , and used t o b e termed " t h e a g r e e d r a t i n g c u r v e " . T h i s c u r v e was l a t e r e x t e n d e d by means o f h y d r a u l i c model t e s t s t o g i v e d i s c h a r g e s c o r r e s p o n d i n g t o l e v e l s above 1 2 . 0 m J i n j a l o c a l gauge r e a d i n g . Unfort u n a t e l y , t h e m o d i f i e d c u r v e gave d i s c h a r g e s which w e r e , on a v e r a g e , 15% l e s s t h a n t h e measured o n e s . The gauging s i t e a t Mbulamuti s i t u a t e d some 50 km downstream of J i n j a was r e c e n t l y chosen f o r d i s c h a r g e measurement and f o r c o n s t r u c t i n g t h e r a t i n g c u r v e t h a t r e p r e s e n t s t h e n a t u r a l regime o f t h e V i c t o r i a N i l e between Lakes V i c t o r i a and Kyoga. The a g r e e d c u r v e and i t s e x t e n s i o n , t h e blbulamuti r a t i n g c u r v e and t h e d i s c h a r g e s r e p o r t e d by H u r s t a r e summarized and p r e s e n t e d i n F i g . 1, Appendix E .
331
90
Probability of non - exceedance
80
Range (cm.)
( "lo )
5 10 20 50 80 90 95 98 99
70
60
u C
.-0
.-G 50
0
A'
/
17.4 23.7 27.7 32.8 43.5 54.9 61.3
1
/"
P
66.8 7 3.9
78.5
L
? v
40
aJ
m
C
0
(L
30
20
in
001
01 0 2 0 5 1
10 20 30 40 50 60 7 0 80 90 95 Non - e x c e e d a n c e p r o b a b i l i t y , ' l o
5
2
98 99
99 9
Fig. 8.5. F i t o f P e a r s o n Type I 1 1 f u n c t i o n t o t h e d i s t r i b u t i o n o f t h e s e a s o n a l r a n g e of v a r i a t i o n of t h e s t o r a g e d e p t h i n Lake V i c t o r i a The monthly and a n n u a l d i s c h a r g e s o f t h e V i c t o r i a N i l e a t J i n j a i n t h e 25-yr p e r i o d 1946-1970 a r e g i v e n i n T a b l e 2 , Appendix D . The a v e r a g e d i s c h a r g e hydrograph f o r t h i s p e r i o d i s shown i n F i g . 8.6., whereas T a b l e 8.5 g i v e s t h e b a s i c s t a t i s t i c a l d e s c r i p t o r s and s e r i a l c o r r e l a t i o n s f o r t h e monthly and annual d a t a .
.
0
E 2.6 -
0
2.5 -
.2.4
ai
y2.3
r .-
2.2
a 2.1
J
Fig.
8.6. 1946-70
F
M
A
M
J
Month
J
A
S
O
N
D
The a v e r a g e h y d r o g r a p h of t h e V i c t o r i a N i l e a t J i n j a for t h e p e r i o d
w w TABLE 8 . 5
The b a s i c s t a t i s t i c a l d e s c r i p t o r s o f t h e o u t f l o w s from L a k e V i c t o r i a a t J i n j a f o r t h e p e r i o d 1946-1970
Month and Year
January February March April May June July August September October November December Year
Basic s t a t i s t i c a l descriptors
2,
109 m3
2.2964 2.1376 2.3548 2.3872 2.6772 2.6160 2.5404 2.4240 2.2808 2 . 3024 2.2676 2.4040 28.6152
Serial correlation coefficients
109 m3
c"
cS
ck
rl
r2
r3
r4
r5
'6
1.0298 0.9375 1.0774 1.0482 1.1203 1.1135 1.0738 1.0167 0.9532 0.9607 0.9228 1.0135 12.1148
0.4484 0.4386 0.4575 0.4391 0.4185 0.4256 0,4227 0.4194 0.4179 0.4173 0.4070 0.4216 0.4234
0.8070 0.7498 0.7820 0.7184 0.6142 0.5993 0.6352 0.6024 0.6200 0.6250 0.4244 0.5188 0.6301
2.5252 2.4221 2.3322 2.1296 1.9226 1.8727 2.0348 1.9469 1.9993 2.0063 1.6900 1.7861 1.9134
0.8803 0.8541 0.8730 0.8653 0.8457 0.8421 0.8267 0.8273 0.8164 0.8116 0.7787 0.9093 0.8755
0.7080 0.6761 0.6891 0.7071 0.7252 0.7185 0.6716 0.6668 0.6802 0.6999 0.6872 0.7542 0.7257
0.5412 0.5295 0.5763 0.5816 0.5829 0.5735 0.4907 0.4866 0.4836 0.5021 0.5347 0.6185 0.5739
0.4242 0.4159 0.4985 0.5158 0.5220 0.4988 0.4668 0.4584 0.4637 0.4679 0.4609 0.5230 0.4994
0.2627 0.2796 0.3965 0.4156 0.3927 0.3793 0.4167 0.4136 0.3943 0.3751 0.3929 0.4364 0.3974
0.0509 0.1213 0.2098 0.2429 0.2356 0.2371 0.3057 0.2970 0.2936 0.2756 0.2213 0.3039 0.2435
s ,
N
333
The mean a n n u a l o u t f l o w from Lake V i c t o r i a v a r i e s a g r e a t d e a l from one p e r i o d of t i m e t o a n o t h e r and from one d u r a t i o n o f t h e p e r i o d t o a n o t h e r . T h i s c a n be s e e n from t h e f o l l o w i n g f i g u r e s : Period
Duration
Mean
from
to
years
109 m 3 / y r
1896 1906 1946 1962 1946
1945 1932 1961 1970 1970
50 27 16 9 25
21.4 20.6 20.1 43.9 28.6
max = 3 3 . 1 i n 1917 and min = 1 2 . 3 i n 1922
The p e r i o d from 1896 up t o and i n c l u d i n g 1970 h a s a mean o f 2 3 . 8 x and a s t a n d a r d d e v i a t i o n o f 7 . 9 4 x
lo9
f i g u r e s , t h e 75-yr p e r i o d , 1896-1970,
m3/yr.
lo9
m3/yr
A s one might n o t i c e from t h e above
c a n b e d i v i d e d i n t o two s u b - s a m p l e s ; t h e
f i r s t from 1896 t o 1945 and t h e s e c o n d from 1946 up t o and i n c l u d i n g 1970. The mean a n n u a l volumes o f o u t f l o w a r e a s g i v e n above and t h e s t a n d a r d d e v i a t i o n s a r e 4 . 7 x 10’ m 3 / s e c . , and 1 2 . 1 1 x
lo9
m3;sec.
f o r t h e two sub-samples
in their
r e s p e c t i v e o r d e r . The f i r s t p e r i o d i s c h a r a c t e r i z e d by t h e s m a l l v a r i a t i o n of t h e a n n u a l volumes o f f l o w i n comparison t o t h e s e c o n d o n e , from 1946 t o 1961 w i t h a mean of 2 0 . 1 x
lo9
m3/yr and an e x c e s s i v e l y w e t p e r i o d from 1962 up t o
and i n c l u d i n g 1 9 7 0 . Applying t h e F i s h e r F - t e s t
t o t h e v a r i a n c e s of t h e flow i n
t h e p e r i o d s 1896-1945 and 1946-1970 l e a d s u s t o t h e c o n c l u s i o n t h a t t h e two v a r i a n c e s a r e non-homogeneous
( s i g n i f i c a n c e l e v e l = 5 % ) . The means of t h e s e two
s a m p l e s , however, when t e s t e d by t h e d - t e s t do n o t a p p e a r t o b e s i g n i f i c a n t l y d i f f e r e n t one from t h e o t h e r ( a t 5% s i g n i f i c a n c e l e v e l ) . The r e s u l t s i n T a b l e 8 . 5 show t h a t t h e monthly and a n n u a l volumes of l a k e o u t f l o w a r e s e r i a l l y c o r r e l a t e d . The s e r i a l c o r r e l o g r a m s o f t h e 12 months and of t h e y e a r a r e a l l q u i t e s i m i l a r . The model p r o p o s e d f o r d e s c r i b i n g and f o r gener a t i n g the data is the f i r s t - o r d e r
a u t o - r e g r e s s i v e o n e , a s e x p r e s s e d by e q . 8 . 3 .
The model p a r a m e t e r f o r t h e y e a r l y volumes of flow a t J i n j a i s t h e f i r s t c o r r e l a t i o n c o e f f i c i e n t , 0.8755, 8.2
THE BASIN O F THE VICTORIA NILE
8.2.1
Run-off
t o Lake Kyoga
The V i c t o r i a N i l e B a s i n c o m p r i s e s t h e Upper V i c t o r i a N i l e , from Lake V i c t o r i a t o Lake Kyoga, t h e Lower V i c t o r i a N i l e , from Lake Kyoga t o Lake A l b e r t , t h e b a s i n of t h e R i v e r Kafu and t h e complex o f Lakes S a l i s b u r y , Kyoga and Kwania. The t o t a l s u r f a c e a r e a o f t h e V i c t o r i a N i l e B a s i n , which is 74713 k m 2 , can b e s u b - d i v i d e d i n t o t h e f o l l o w i n g component a r e a s :
334
Gauged a r e a s i n c l u d i n g t h e c a t c h m e n t s o f Lake S a l i s b u r y and R i v e r Kafu
46255.8 km2
Ungauged a r e a s
12406.6
Areas n o t c o n t r i b u t i n g t o t h e i n f l o w of Lake Kyoga
11315.6 4735 .o
Open w a t e r l a k e s and swamps The monthly r u n - o f f
from t h e V i c t o r i a N i l e Basin t o Lake Kyoga was e s t i m a t e d
by H u r s t i n Vol. V o f t h e N i l e B a s i n a t 3% ( H u r s t , H . E . ,
and P h i l i p s , P . ,
1938).
The r e p o r t o f t h e H y d r o m e t e o r l o g i c a l s u r v e y of t h e c a t c h m e n t s o f Lakes V i c t o r i a , Kyoga and A l b e r t g i v e s e s t i m a t e s of t h e r u n - o f f
f o r t h e y e a r s 1969 and 1970, and
f o r t h e s o - c a l l e d normal y e a r (hM0, 1974). The d a t a p r e s e n t e d i n t h e s e two r e f e r e n c e s a r e summarized i n T a b l e 8.6.
TABLE 8.6
Run-off
from t h e catchment of t h e V i c t o r i a N i l e t o Lake Kyoga Run-off
t o Lake Kyoga, m i l l i o n m 3
Month
1932
1969
1970
year
Jan. Feb. Mar. Apr. May Jun.
110
299 185 208 169 368 252
128 56 272 398 495 284
156 86 111 30 1 284 269
110 190 310 350 260
Month year
Jul. Aug.
Sep. Oct. Nov. Dec. Year
'
1932
1969
1970
year
190 220 270 270 250 180 2700
161 130 175 230 251 100 2527
178 356 419 528 341 180 3638
193 2 35 249 297 326 270 2906
Hydrologic i n v e s t i g a t i o n o f t h e b a s i n o f t h e R i v e r Kafu, which o c c u p i e s
16700 km2, o r a b o u t 22.5% of t h e t o t a l c a t c h m e n t a r e a o f t h e V i c t o r i a N i l e , h a s shown t h a t t h e r u n - o f f
c o e f f i c i e n t v a r i e s from 1.1%i n t h e d r y y e a r s t o 5% i n
t h e w e t y e a r s . I n t h e s e two g r o u p s o f y e a r s , 1953-60 and 1961-70, t h e mean a n n u a l r a i n f a l l was 1150 mm and 1240 nun, r e s p e c t i v e l y . The a v e r a g e up t o 1932 was g i v e n by H u r s t a t 1295 mm/yr
f o r t h e whole catchment a r e a of t h e V i c t o r i a
Nile. Owing t o t h e s c a r c i t y o f t h e r u n - o f f v a l u e s of t h e monthly and a n n u a l r u n - o f f
d a t a , i t is not p o s s i b l e t o g i v e t h e c o e f f i c i e n t s with a f a i r degree of
a c c u r a c y . The q u a n t i t i e s l i s t e d i n T a b l e 8.6 s u g g e s t , however, a v a l u e of a b o u t
3% i n a normal y e a r i n c r e a s i n g t o 4% i n a w e t y e a r f o r t h e a n n u a l c o e f f i c i e n t . The i n f l o w and o u t f l o w components of t h e water b a l a n c e o f Lake Kyoga f o r t h e y e a r s 1969, 1970 and t h e s o - c a l l e d normal y e a r , have b e e n i n c l u d e d i n P a r t 2 of
V o l . I of t h e r e p o r t o f t h e h y d r o m e t e o r o l o g i c a l s u r v e y . These components, t o g e t h e r w i t h t h o s e o b t a i n e d by u s f o r t h e p e r i o d 1948-1970 a r e as f o l l o w s :
335
Year 1969 19 70 normal 1948-70
p1 mm/yr
I
R
0
mm/yr
m/yr
mm/yr
mm/yr
1160 1238 1220 1220
9032 8732 5622 6222
558 798 639 639
9475 9281 5897 6331
-150 +110 + 67 + 50
Balance
El,
mm/yr
Penman Kohler
1420 1377 1516 1700
1867 1751 1623 1916
1591 1594
-
The above r e s u l t s show t h a t t h e a n n u a l e v a p o r a t i o n from t h e l a k e v a r i e s from 1700 m m ,
a s found from t h e w a t e r b a l a n c e f o r t h e p e r i o d 1948-70,
t o 1916 mm a s
found from Penman's method. The v a r i a t i o n o f E l from one p e r i o d t o a n o t h e r and from one method t o a n o t h e r i s much less compared t o t h e v a r i a t i o n o f I or 0 . The v a l u e s g i v e n by H u r s t a v e r a g e d f o r t h e p e r i o d 1917-1932 were P mm/yr,
I = 4351 m m / y r ,
R = 428 m m / y r ,
g i v e a w e i g h t e d a v e r a g e o f 1995 m m / y r
0 = 4076 mm/yr
= 1292 1 and AS = 0 . These v a l u e s
f o r e v a p o r a t i o n from open w a t e r (1205 mm/
y r ) and p o t e n t i a l e v a p o t r a n s p i r a t i o n from t h e swamps (2228 mm/yr?. N o t i c e t h a t
t h e c a l c u l a t i o n s made by H u r s t are b a s e d on an open w a t e r s u r f a c e o f 1760 km2 and on swamps o f 4510 km2 ( H u r s t , H . E . ,
B l a c k , R . P . , and S i m a i k a , Y . M . ,
I n Vol. V I I o f t h e N i l e B a s i n , H u r s t and h i s co-workers
1966).
s t a t e t h a t t h e gauging
s i t e a t Masindi P o r t where t h e o u t f l o w from Kyoga u s e d t o b e measured, h a s proved t o b e an u n r e l i a b l e s i t e . The a v e r a g e d i s c h a r g e s f o r t h e p e r i o d 1940-1945 above and below Lake Kyoga were 2 1 . 0 and 1 9 . 3 m i l l i a r d m 3 / y r f o r Namasagali and P o r t Masindi r e s p e c t i v e l y . H u r s t c o n c l u d e s t h a t t h e i n f o r m a t i o n a v a i l a b l e was f a r t o o l i t t l e t o g i v e any c e r t a i n t y a b o u t t h e Kyoga B a s i n e r e g i m e , e x c e p t t h a t
o n t h e w h o l e , Lake Kyoga i s p r o b a b l y a s o u r c e of l o s s i n t h e o r d e r of 1 or 2 milliards a year. Comparison hetween t h e o l d measurements a n d / o r e s t i m a t e s of t h e components of t h e w a t e r b a l a n c e and t h e more r e c e n t ones shows t h a t Lake Kyoga, i n s t e a d of b e i n g a s o u r c e of l o s s w i t h 0 = 0 . 9 3 7 I , i s a s o u r c e o f s m a l l g a i n where 0
=
1.045 I .
8.2.2
Water l e v e l and s t o r a g e
The d i f f e r e n c e between t h e n e t i n f l o w t o t h e l a k e and t h e o u t f l o w from i t c a u s e s t h e change of i t s s u r f a c e w a t e r l e v e l and t h e r e u p o n t h e volume o f c o n t e n t i n s t o r a g e . The w a t e r l e v e l a t Bugondo P i e r f o r t h e p e r i o d s 1928-1938 and 19421970 i s shown i n F i g . 8 . 7 .
I n t h e same f i g u r e t h e a n n u a l v a r i a t i o n o f t h e
s t o r a g e d e p t h f o r t h e same p e r i o d s i s shown. Lake l e v e l o b s e r v a t i o n s were s t a r t e d i n 1916 a t L a l e P o r t . I n 1927 a n o t h e r gauge w a s e r e c t e d a t Bugondo. From t h e n t i l l 1938 i t worked p r o p e r l y , and from 1939 up t o and i n c l u d i n g 1 9 4 1 no l e v e l measurements were t a k e n a t any of t h e g a u g i n g s i t e s . From 1942 up t o and i n c l u d i n g 1968 measurements of l a k e w a t e r l e v e l w e r e t a k e n a g a i n a t Bugondo. Four a d d i t i o n a l gauging s i t e s were e r e c t e d i n
336
t h e p e r i o d 1965-1967. I n 1968 t h e l e v e l gauges a t Bugondo and a t a n o t h e r s i t e
were r e p l a c e d by a u t o m a t i c r e c o r d e r s . The y e a r 1961 w i t n e s s e d t h e maximum g a i n i n t h e m o n t h l y , as w e l l as t h e a n n u a l , s t o r a g e . These w e r e 710 and 1815 mm r e s p e c t i v e l y . C o n t r a r i l y , t h e y e a r
1918 w i t n e s s e d t h e maximum l o s s i n t h e m o n t h l y , a s w e l l a s t h e a n n u a l , s t o r a g e . These w e r e 340 and 1505 mm r e s p e c t i v e l y . The t o t a l change i n s t o r a g e o v e r t h e p e r i o d 1928-1970 ( n o t i n c l u d i n g 1939-1941) w a s 805 mm, showing a r i s i n g t r e n d o f
20 mm/year
. 180
160 140 120 100 80 E
U
60 80
’
10.01 1928’30
I
35
I
40
I
45 Year
I
50
I
55
I
60
I
65
I
70
F i g . 8.7. Lake Kyoga l e v e l a t Bugondo deduced from 10-day means from gauge r e a d i n g s 1928-39 and 1942-70. The dashed l i n e r e p r e s e n t s t h e a n n u a l change i n lake storage The s e a s o n a l o s c i l l a t i o n of t h e w a t e r l e v e l i n Lake Kyoga i s i l l u s t r a t e d i n F i g . 8.8. by two c u r v e s : one r e p r e s e n t i n g t h e l e v e l a t Bugondo P i e r f o r t h e y e a r s 1928-38 and 1942-70, and t h e s e c o n d r e p r e s e n t i n g t h e l e v e l a t L a l e p i e r f o r t h e y e a r s 1917-32.
337
c
Measured a t Bugondo gauge m e a n of 1 9 2 8 - ' 3 8 a n d '70
x,
---- -
*__
~
-
0
2
0
0
-
Jan
Feb
Mar
Apr
I'
M a y Jun
a35
Jul
A u g Sep.
Oct
Nov
M e a s u r e d at L a l i pier gauge e a n of 1917- ' 3 2
5
Fig. 8.8.
m
I
Dec
Y\
S e a s o n a l o s c i l l a t i o n o f w a t e r l e v e l i n Lake Kyoga
I n s p i t e of t h e d i f f e r e n c e i n a m p l i t u d e t h e two c u r v e s a g r e e c o m p l e t e l y on t h e t i m e s o f o c c u r r e n c e o f t h e maximum and minimum w a t e r l e v e l s . S i m i l a r t o Lake V i c t o r i a , t h e w a t e r l e v e l o s c i l l a t i o n i n Lake Kyoga c a n be d e s c r i b e d by t h e equation
Xt
= X
O
+
6
X
j = 1
2 n j t ( A . cos ___ 2 n j t + ~ . s i n - 12 J 12 J
(8.4')
which i s a d i f f e r e n t form of t h e e q u a t i o n 8 . 4 used i n c o n n e c t i o n w i t h Lake V i c t o r i a . The harmonic c o e f f i c i e n t s A . and B . are 1 . 1 6 1 3 and -16.8934, 3.7917 J J and 2 . 3 2 0 5 , -1.3833 and 0 . 2 8 3 4 , 0 . 2 2 5 0 and -0.4790, 0 . 1 2 2 1 and -0.0732 and 0 . 2 8 3 3 and z e r o , r e s p e c t i v e l y , f o r j = 1, 2 , 3 , 4 , 5 and 6 . The 12-monthly c y c l e e x p l a i n s 9 1 . 2 % o f t h e t o t a l v a r i a t i o n i n t h e l a k e l e v e l ; t h e 6-monthly c y c l e e x p l a i n s 6.3% and t h e 4-monthly t h e 3-monthly,
2.4-monthly
c y c l e , 0 . 6 % . The r e m a i n i n g c y c l e s combined, i . e .
and 2-monthly
c y c l e s , a r e r e s p o n s i b l e f o r 1 . 9 % of t h e
t o t a l variation only. The s e a s o n a l r a n g e o f v a r i a t i o n i n t h e l a k e s t o r s g e b a s e d on t h e mean monthly d e p t h s f o r t h e p e r i o d from 1942 up t o and i n c l u d i n g 1970 h a s been a n a l y z e d s t a t i s t i c a l l y . The v a l u e s of t h e b a s i c d e s c r i p t o r s a r e : mean = 54 cm/yr;
standard
d e v i a t i o n 2 7 . 9 5 cm/yr; skewness = 2 . 2 0 9 and k u r t o s i s = 1 1 . 1 5 4 .
A s i n t h e c a s e o f Lake V i c t o r i a , t h e d a t a of Lake Kyoga have shown t h e y are s e r i a l l y u n c o r r e l a t e d ( s e e F i g . 8 . 9 . ) . The P e a r s o n Type I 1 1 h e r e h a s a l s o proved t o be t h e d i s t r i b u t i o n f u n c t i o n o f b e s t f i t t o t h e o b s e r v e d d a t a . The g r a p h i c a l
338
p l o t s of t h e o b s e r v e d d a t a and of t h e d i s t r i b u t i o n f u n c t i o n are shown i n F i g . 8 . 1 0 . The t h e o r e t i c a l v a l u e s of t h e r a n g e o f v a r i a t i o n of t h e s t o r a g e d e p t h f o r a number o f non-exceedance
0.5
p r o b a b i l i t i e s a r e g i v e n i n t h e same f i g u r e .
95°/0 Upper c o n f i d e n c e l i m i t
0.4 C
2 0.3 .-
+
.& 0.2 0
" 0.1
-0 K
0
+
0.0
-?!
0.1
-
0.3
&
0.4
5 0.2
.-
ul
05
--
b 5 ° / 0 Lower
confidence l i m i t
Fig. 8.9. S e r i a l c o r r e l o g r a m o f t h e s e a s o n a l v a r i a t i o n of t h e s t o r a g e d e p t h i n Lake Kyoga
8.2.3
Lake o u t f l o w
The flow i n t h e lower r e a c h of t h e V i c t o r i a N i l e , known a s Kyoga N i l e , had been measured f o r m e r l y a t , or n e a r , Masindi P o r t . The normal monthly mean d i s c h a r g e s o b t a i n e d from t h e measurements i n 1913 and 1915-32 were r e p o r t e d by H u r s t i n Vol. V o f t h e N i l e B a s i n a s 1 . 4 5 , 1 . 2 4 , 1 . 3 4 , 1 . 3 2 , 1 . 4 8 , 1 . 5 2 , 1 . 6 2 ,
1.64, 1 . 6 0 , 1 . 6 6 , 1 . 6 0 and 1 . 5 8 m i l l i a r d m3/month from J a n u a r y t o December. The annual mean flow was t h u s g i v e n a s 18 m i l l i a r d m 3 ( H u r s t , H . E . , P.,
and P h i l i p s ,
1 9 3 8 ) . L a t e r , t h e d i s c h a r g e measurements were t a k e n a t F a j a o . From 1962 and
onwards, t h e m e a s u r i n g s i t e was moved t o P a r a a , which i s s i t u a t e d a few k i l o m e t r e s downstream o f F a j a o . The r a t i n g c u r v e s o f t h e Kyoga N i l e a t P a r a a a r e shown i n F i g . 2 , Appendix E , whereas t h e d i s c h a r g e s from 1948 up t o and i n c l u d i n g 1970 measured a t P a r a a or c o r r e c t e d f o r t h e change o f l o c a t i o n a r e l i s t e d i n T a b l e 3, Appendix D The a v e r a g e hydrograph for t h e p e r i o d 1948-70 ( F i g . 8 . 1 1 . ) a g r e e s w e l l w i t h t h e s e a s o n a l o s c i l l a t i o n o f t h e w a t e r l e v e l i n Lake Kyoga, shown i n F i g . 8 . 8 . , e x c e p t for t h e s t e e p f a l l o f t h e d i s c h a r g e i n O c t o b e r f o l l o w e d by t h e r i s e i n November. From t h e p r e v i o u s s e c t i o n w e have a l r e a d y s e e n t h a t t h e 1 8 . 0 x 19.3 x
lo9
lo9
or t h e
m 3 g i v e n by H u r s t for t h e mean of t h e a n n u a l flow i n t h e Kyoga N i l e
is quite small.
339
160
I
I
?
I
,
P r o b a b i l i t y of non - exceedance ( "1. ) 1
1 40
123
100
E
,
C
,
,
,
,
I
I
Range (cm.)
i
28.7 29.4 30.4 33.0 44.8 70.0 89.9 110.1 137.0 158.0
5 10 20 50 80 90 95 98 99
J
.g 80 I
.0 L
0
>
-60 PI
cn
' 40
C
[I
20
0
0.01
0.1 0 . 2 0 . 5 1
2
5
10
90
20 30 40 50 60 70 80
Non -exceedance
95
98 99
99.9
p r o b a b i l i t y , "1.
Fig. 8.10. F i t o f Pearson Type I 1 1 f u n c t i o n t o t h e d i s t r i b u t i o n o f the s e a s o n a l range o f v a r i a t i o n o f t h e s t o r a g e depth i n Lake Kyoga
2.7
C
2.6
1000
5 0
m
.9 8 0 U
L
c
1020
E
m
m
m
2.5 2
E 960
0,
940
P
2 . 4 ,"
0
'I, 9 2 0
U
m
.n
6 900
2.3
880
Month Fig. 8.11. 1948-1970
The average hydrograph o f t h e Kyoga N i l e a t Paraa f o r t h e p e r i o d
340
The s t a t i s t i c s p r e s e n t e d i n T a b l e 8 . 7 g i v e a mean o f 950 m3/sec. or 2 9 . 9 milliard m3/yr.
T h i s i s much g r e a t e r t h a n t h e f i g u r e s r e p o r t e d by H u r s t . I t i s
t r u e t h a t t h e w e t s p e l l from 1961 t o 1970 had a s i g n i f i c a n t e f f e c t on t h e g e n e r a l mean f o r t h e p e r i o d 1948-1970, y e t n e i t h e r 1 8 . 0 n o r 1 9 . 3 m i l l i a r d m 3 can b e r e g a r d e d a s a long-term mean. I n s e c t i o n 8 . 2 . 2 ,
the r a t i o I t o 0 for
Lake Kyoga w a s found a s 1 . 0 4 5 . I f t h i s r a t i o i s m u l t i p l i e d by t h e mean flow i n t h e V i c t o r i a N i l e above Lake Kyoga which i s 2 3 . 8 x 1900-1970,
lo9
m3/yr f o r t h e p e r i o d
one g e t s an a n n u a l flow i n t h e Kyoga N i l e below t h e l a k e o f 2 4 . 9
milliard m3/yr.
W e s h a l l c o n s i d e r t h i s f i g u r e as t h e a n n u a l flow volume b r o u g h t
by t h e Kyoga N i l e t o Lake A l b e r t i n a normal y e a r . The monthly and a n n u a l d i s c h a r g e s of t h e Kyoga N i l e f o r t h e p e r i o d 1948-1970 a p p e a r t o b e s t r o n g l y s e r i a l l y c o r r e l a t e d . The c o e f f i c i e n t o f s e r i a l c o r r e l a t i o n d r o p s a l m o s t l i n e a r l y w i t h t h e l a g , from 1 t o a b o u t 0 . 4 , c o r r e s p o n d i n g t o l a g s o f 0 a n d 5 r e s p e c t i v e l y . T h i s i s t h e c a s e w i t h t h e t w e l v e months and t h e y e a r . W e t r i e d t o f i t t o t h e s e d a t a t h e f i r s t - o r d e r Markov model l i k e t h e one w e u s e d i n c o n n e c t i o n w i t h t h e d i s c h a r g e s o f t h e Kagera and t h e V i c t o r i a N i l e . The f i t t e d model i s t h a t d e s c r i b e d by e q . 8 . 3 w i t h p a r a m e t e r a = 0 . 9 3 2 1 . The r e s i d u a l series gave s e r i a l c o r r e l a t i o n s o f 0 . 2 5 2 8 , 0.1263, - 0 , 2 1 6 5 , -0.2109
and 0 . 0 5 3 4 f o r l a g s 1, 2 , 3 , 4
and 5 , r e s p e c t i v e l y . The c o e f f i c i e n t s o f t h e o r i g i n a l series f o r t h e f i v e l a g s i n t h e i r o r d e r a r e 0 . 9 3 2 1 , 0 . 8 0 7 4 , 0 . 6 4 8 8 , 0 . 5 3 3 2 and 0.4230 ( s e e T a b l e 8 . 7 ) . The s e r i a l c o r r e l a t i o n s o f t h e r e s i d u a l s f a l l w e l l i n s i d e t h e 95% c o n f i d e n c e band p o i n t i n g t o t h e i n d e p e n d e n c e of t h e r e s i d u a l s a t t h i s l e v e l of c o n f i d e n c e . THE BASIN OF LAKES GEORGE AND EDWARD AND RIVER SEMLEEKI
8.3 8.3.1
H y d r o l o g i c regime of t h e b a s i n
The t o t a l s u r f a c e a r e a o f t h i s b a s i n i s 30500 km2 o f which 2500 km2 a r e open w a t e r ; 300 km2 a r e o c c u p i e d by Lake George and 2200 km2 by Lake Edward. The catchment a r e a s of t h e s e two l a k e s a r e 8000 km2 and 12000 km2, r e s p e c t i v e l y . The r e m a i n i n g 8000 km2 are t h e catchment a r e a o f t h e R i v e r S e m l i k i . The two l a k e s a r e c o n n e c t e d t o e a c h o t h e r by Kazinga C h a n n e l , which i s a f a i r l y wide and deep c a r r i e r . The s i t u a t i o n produced by h a v i n g Lake Edward j o i n e d t o Lake George by t h i s c h a n n e l from one s i d e and t o Lake A l b e r t by t h e S e m l i k i R i v e r
from a n o t h e r s i d e q u a l i f i e s t h e whole a r e a t o be c o n s i d e r e d a s a o n e - h y d r o l o g i c u n i t . The o l d regime r e p o r t e d by H u r s t and h i s co-workers b a s e d upon d i r e c t p r e c i p i t a t i o n on t h e l a k e s o f 1 . 3 6 5 m / y r 1.30 m/yr. t h e run-off
i n t h e N i l e B a s i n was and e v a p o r a t i o n of
The r a i n f a l l on t h e whole c a t c h m e n t was t a k e n e q u a l t o 1 . 3 6 5 m / y r , c o e f f i c i e n t was c o n s i d e r e d t o b e 12% and t h e change i n t h e l a k e s '
s t o r a g e , AS = 0 . These f i g u r e s g i v e an o u t f l o w from L a k e Edward o f 3 . 6 5 x m3/yr.
I n a d d i t i o n t o t h i s volume, t h e S e m l i k i R i v e r r e c e i v e s a volume of
2.05 x
lo9
m 3 each y e a r a s run-off
lo9
from i t s c a t c h m e n t . Our e s t i m a t e f o r t h e
TABLE 8.7
The b a s i c s t a t i s t i c a l d e s c r i p t o r s o f t h e o u t f l o w s from Lake Kyoga a t Paraa f o r t h e p e r i o d 1948-1970
Month and Year
January February March April May June July August Sep t embe r October November December Year
Basic s t a t i s t i c a l descriptors
X,
m3/s
912.6 868.7 870.7 876.9 921.9 961.9 981.5 994.7 1015.7 968.6 1003.6 984.0 949.9
s ,
m3/s
438.2 417.1 444.7 462.1 488.7 487.3 481.4 474.9 461.7 410.6 471.0 475 .o 456.2
cV
0.4801 0.4800 0.5107 0.5269 0.5301 0.5065 0.4905 0.4775 0.4546 0.4240 0.4693 0.4828 0.4802
C
S
0.4585 0.4723 0.5545 0.6474 0.5927 0.5638 0.5197 0.5529 0.5622 0.5388 0.4800 0.3411 0.5013
Serial correlation coefficients ‘k
1.7528 1.7656 1.9137 2.0946 1.8903 1.8277 1.7744 1.8597 1.9540 1.8225 1.9122 1.6393 1.7251
rl
r2
=3
r4
r5
0.8947 0.8849 0.8819 0.9183 0.9172 0.8987 0.8884 0.9013 0.8851 0.8314 0.8930 0.9141 0.9321
0.7865 0.7722 0.7595 0.7694 0.7585 0.7535 0.7561 0.7592 0.7683 0.7469 0.8236 0.8132 0.8074
0.6852 0.6823 0.6068 0.6255 0.6161 0.6239 0.6308 0.6008 0.5871 0.6735 0.6493 0.6735 0.6488
0.5173 0.5159 0.4920 0.5027 0.5023 0.4967 0.5039 0.5015 0.5144 0.5455 0.5411 0.5316 0.5332
0.3898 0.3919 0.3882 0.3923 0.4222 0.4303 0.4374 0.4263 0.4035 0.4325 0.4046 0.4184 0.4230
w CL L
342
p e r i o d 1948-1970 i s b a s e d on somewhat d i f f e r e n t v a l u e s f o r t h e h y d r o l o g i c v a r i a b l e s i n t h e r e g i m e . The mean a n n u a l r a i n f a l l on t h e l a k e s w a s 1400 mm and t h e e v a p o r a t i o n from t h e l a k e s u r f a c e was 1800. These f i g u r e s show a d e f i c i t o f 1 . 0 m i l l i a r d m 3 a y e a r . The r u n - o f f
c o e f f i c i e n t i s t a k e n as 13% and t h i s b r i n g s
t h e a n n u a l o u t f l o w from Lake Edward t o : 0 . 1 3 x 1 . 4 x 20 x 2.64 x
lo9
lo9 -
1.0 x
lo9
=
m3/yr. The r a i n f a l l on t h e S e m l i k i Catchment was a b o u t 1600 mm/yr i n
t h e p e r i o d 1948-70 and t h e r u n - o f f of about 2 . 0 5 x
lo9,
a b o u t 16%. These f i g u r e s produced a run-off
which means a t o t a l flow i n t h e S e m l i k i
of 4 . 6 9 x
lo9
m3
p e r y e a r . T h i s f i g u r e a g r e e s q u i t e w e l l w i t h t h e mean of t h e a n n u a l d i s c h a r g e g i v e n i n T a b l e 4 , Appendix D.
8.3.2
S e a s o n a l o s c i l l a t i o n o f l a k e l&
The s e a s o n a l o s c i l l a t i o n o f t h e w a t e r l e v e l i n Lake Edward i s shown i n F i g . 8 . 1 2 . T h i s o s c i l l a t i o n t o o c a n be d e s c r i b e d by t h e same r e l a t i o n g i v e n a s e q . 8 . 4 ' . The A and B c o e f f i c i e n t s o f t h e harmonics 1 t h r u 6 a r e : 7.7292 and 0 . 8 4 5 3 , 1 0 . 0 1 2 and 2 . 3 0 9 5 , - 0 , 1 7 8 7 and - 0 . 1 5 4 7 , 0 . 5 0 0 0 and 0 . 2 6 8 0 , 0 . 4 9 9 5 and z e r o , and - 0 . 0 1 2 and z e r o r e s p e c t i v e l y . A s w i t h Lakes V i c t o r i a and Kyoga, t h e f i r s t and s e c o n d harmonics combined, i . e . t h e sum o f t h e 12-monthly and 6-monthly c y c l e s e x p l a i n a l m o s t 94% of t h e t o t a l v a r i a t i o n . I n s p i t e of t h i s s i m i l a r i t y , one f i n d s t h a t t h e 12-monthly c y c l e i n Lake Edward e x p l a i n s 34% o f t h e t o t a l v a r i a t i o n and n o t 9 1 % , as i n Lakes V i c t o r i a and Kyoga, whereas t h e 6-monthly c y c l e i n Lake Edward's l e v e l i s r e s p o n s i b l e f o r 60% o f t h e t o t a l v a r i a t i o n and n o t o f 6% o n l y a s i s t h e c a s e w i t h Lake V i c t o r i a or Kyoga
Jan. Feb. Mar Apr
Fig. 8.19.
May Jun Jul Month
Aug. Sep. O c t .
Nov. Dec.
S e a s o n a l o s c i l l a t i o n o f w a t e r l e v e l i n Lake Edward
343
D liki River _ - i_ s c h a r g e s o f t h-.e S e m~.
8.3.3
~~
~
The m o n t h l y a n d a n n u a l d i s c h a r g e s o f t h e S e m l i k i i n t h e p e r i o d 1948-1970
are g i v e n i n T a b l e 4 , Appendix D . From t h e s c a n t y d a t a t h a t p r e v a i l e d up t o 1 9 3 2 , t h e a v e r a g e m o n t h l y d i s c h a r g e s o f t h e S e m l e e k i g i v e n by H u r s t w e r e : 130, 1 0 2 , 103, 106, 1 1 2 , 116, 1 1 2 , 1 1 6 , 1 1 2 , 1 0 3 , 106, 1 2 1 , 1 3 5 and 140 m 3 / s e c .
f o r t h e months f r o m J a n u a r y t o
December, r e s p e c t i v e l y . The S e m l i k i h a s b e e n g a u g e d r e g u l a r l y s i n c e 1 9 4 0 . The r a t i n g c u r v e s m e a s u r e d a t Bweramul a r e shown i n F i g . 3 , A p p e n d i x E . The a v e r a g e d i s c h a r g e h y d r o g r a p h
f o r t h e p e r i o d 1948-1970 i s shown i n F i g . 8.13., whereas T a b l e 8 . 8 g i v e s t h e b a s i c s t a t i s t i c a l d e s c r i p t o r s o f t h e monthly and a n n u a l d i s c h a r g e d a t a f o r t h e same p e r i o d .
170 r
1
160 . E " 150
Average for the perlod
&140
F
0 L
"
130
,? 120
1948 - ' 7 0
-
I-
.",'
/
'\
0
110 loor
(tail ).
Average f o r t h e p e r i o d u p t o / ' ',,1932 ( h e a d );**.-., ?,' \
J
I
',
.'
I__
F
F i g . 8.13.
----2 M
'
A
',/*
'
M
'
J ' J Month
A
I
5
'
0
'
N
'D
The a v e r a g e h y d r o g r a p h o f t h e R i v e r S e m l i k i
The c o m p a r i s o n b e t w e e n t h e a n n u a l d i s c h a r g e o f t h e S e m l i k i , T a b l e 4 , Append i x D,
a n d t h e a n n u a l d i s c h a r g e o f t h e V i c t o r i a N i l e , T a b l e 2 , o r t h e Kyoga
N i l e , T a b l e 3, b o t h A p p e n d i x D,
shows t h a t t h e r e s p o n s e o f t h e S e m l i k i B a s i n t o
t h e w e t s p e l l 1961-1970 i s le s s t h a n t h a t shown by e i t h e r t h e V i c t o r i a o r t h e Kyoga B a s i n s .
I n f a c t t h e s t r o n g l y n o t i c e a b l e rise i n t h e Semliki discharge
t o o k p l a c e d u r i n g t h e 3 - y e a r p e r i o d 1962-64 o n l y . T h i s p r o b a b l y l e d t o a r i s e
o f n o t more t h a n 10% i n t h e g e n e r a l mean o v e r t h e p e r i o d 1 9 4 8 - 7 0 . The d i s c h a r g e s e r i e s o f t h e S e m l i k i R i v e r d o e s n o t b e h a v e d i f f e r e n t l y from t h e o t h e r r i v e r s d e a l t w i t h u n t i l now, a s f a r as t h e i r s e r i a l c o r r e l a t i o n i s c o n c e r n e d . F u r t h e r m o r e , t h e h i s t o r i c a l d a t a of t h e S e m l i k i c a n b e d e s c r i b e d by
a f i r s t - o r d e r a u t o - r e g r e s s i v e model l i k e t h e o n e g i v e n by e q . 8 . 3 , w i t h a p a r a meter cx = 0 . 6 2 0 6 , The r e s i d u a l s e r i e s l e f t f r o m f i t t i n g t h i s model t o t h e h i s t o r i c a l d a t a a p p e a r s t o b e u n c o r r e l a t e d w i t h 95% c o n f i d e n c e .
TABLE 8.8
The b a s i c s t a t i s t i c a l d e s c r i p t o r s of t h e d i s c h a r g e of t h e Semliki River i n t h e p e r i o d 1948-1970 ~~~~
Month and Year
Basic s t a t i s t i c a l descriptors
2,
m3/s
s , m3/s -~
c"
cS
~
~
~~~~~~~~~~
Serial correlation coefficient ck
rl
r2
r3
r4
r5
0.5485 0.5990 0.5689 0.4725 0.4756 0.4603 0.3900 0.5737 0.4635 0.4481 0.5751 0.4370 0.6206
0.0557 0.1143 0.0864 0.0937 0.0924 0.1133 0.0631 0.0619 0.1424 0.0608 0.1421 6.0268 0.1261
p .0874 0.0710 p ,0684
6.2181
6.1604 6,1688 6.1699 6.1634 6.1632 6.2674 6.2393 0.3093 0.3380 0.4278 5.2060 0.1980 6.2456
0.0444 0.0589 0 ,0885 0.0826 0.0196 0.0798 0 .0653 0.1528 0.4123 0.3885 0.2021 0.0468 0,1021
~
January February March April May June July August September October November December Year
138.3 125.5 124.5 144.3 163.8 148 $ 6 148.6 159.5 157.5 155.9 160.9 155.3 150.6
58.96 50.01 50.28 58.26 86.56 64.51 54.77 55.37 52.13 42.77 51.65 56.70 51.13
0.4263 0.3984 0.4038 0.4037 0.5286 0.4340 0.3686 0.3472 0.3309 0.2743 0.3209 0.3651 0.3395
1.2368 1.6881 1.6870 1.4727 2.9423 2.4654 2.3550 1.6507 I.4275 1.6791 1.3237 1.4672 2.0387
3.9216 5.7768 6.7057 5.4226 13.3763 11.2517 11.1160 5.7890 4.5335 6.3812 4.0309 4.3285 14.0376
0.1928 6.2552 2559 0.4122 0.3420 0.2115 0751 0.2542 6.1865
p.
5.
345
8.4 8.4.1
LAKE ALBERT CATCHMENT Run-off
t o Lake A l b e r t
The c a t c h m e n t area o f Lake A l b e r t , n o t i n c l u d i n g t h e d r a i n a g e b a s i n o f t h e Semliki, is
17000
km2. The s u r f a c e a r e a of t h e l a k e i t s e l f i s 5300 km2. The
Kyoga N i l e f l o w s i n t o t h e n o r t h - e a s t e r n
end of t h e l a k e and t h e Semleeki i n t o
i t s s o u t h e r n e n d . These two r i v e r s s u p p l i e d Lake A l b e r t w i t h 2 9 . 9 1 and 4 . 6 4 m i l l i a r d m 3 r e s p e c t i v e l y , a s means f o r t h e p e r i o d 1948-1970. H u r s t gave t h e f i g u r e s of 1 8 - 1 9 . 3 x
lo9
f o r t h e Kyoga and 5 . 7 x
lo9
on a y e a r l y r a i n f a l l o f 1256 mm and a r u n - o f f
m 3 a y e a r f o r t h e S e m l i k i . Based c o e f f i c i e n t o f a b o u t 128, h e gave
t h e annual run-off
from t h e l a k e c a t c h m e n t a s 2 . 5 6 x
added t o t h e 5 . 7 x
lo9
lo9
m3/yr.
This f i g u r e ,
m 3 s u p p l i e d by t h e S e m l i k i , b r i n g s t h e a n n u a l i n f l o w
i n t o Lake A l b e r t t o 8 . 2 6 m i l l i a r d m3/yr or 1 . 5 5 m s p r e a d o v e r t h e l a k e s u r f a c e . The r a m a i n i n g f i g u r e s u s e d by H u r s t t o draw t h e regime of t h e Lake A l b e r t mean f o r t h e y e a r s 1913 a n d 1915-1932, w e r e 0 . 8 1 m r a i n f a l l a t B u t i a h a and 1 . 2 m / y r e v a p o r a t i o n from t h e l a k e s u r f a c e . The i n f l o w t o t h e l a k e from t h e Lower V i c t o r i a N i l e t a k e n as 3 . 4 m b r o u g h t t h e sum o f t h e g a i n s t o t h e l a k e t o 5 . 7 6 m . S i n c e t h e sum of t h e l o s s e s w a s c l a i m e d t o have been 5 . 7 4 m and t h e a v e r a g e r i s e of t h e l a k e l e v e l d u r i n g t h a t p e r i o d , AS, was 0 . 0 6 m ,
t h e t o t a l l o s s was e s t i -
mated a t 5 . 8 0 m . The d i f f e r e n c e between t h e g a i n s and l o s s e s ( 4 cm s p r e a d o v e r t h e l a k e s u r f a c e ) was r e g a r d e d as t h e e r r o r i n t h e b a l a n c e s h e e t of Lake A l b e r t (Hurst, H.E.,
and P h i l i p s ,
' P . , 1938).
The h y d r o m e t e o r o l o g i c a l s u r v e y o f t h e c a t c h m e n t s of Lakes V i c t o r i a , Kyoga and A l b e r t used t h e r e l a t i o n between t h e s l o p e of t h e main d r a i n a g e c h a n n e l i n a b a s i n and t h e a n n u a l r u n - o f f
c o e f f i c i e n t , o b t a i n e d from t h e gauged s u b - b a s i n s
( o n l y 301 o f t h e l a k e c a t c h m e n t ) ,
f o r e s t i m a t i n g t h e t o t a l catchment r u n - o f f .
Remarkable enough i s t h a t t h e a n n u a l r u n - o f f
c o e f f i c i e n t , e s t i m a t e d by t h i s
method a t 1 2 . 3 7 1 , i s v e r y c l o s e t o t h e 12% assumed by H u r s t more t h a n 40 y e a r s a g o . The mean a n n u a l p r e c i p i t a t i o n f o r t h e p e r i o d 1948-1970 was 1285 m m . T h i s r a i n f a l l produced a n a n n u a l r u n - o f f
of 17 x
lo9
x 0.1237 x 1.285 = 2.702 m i l -
l i a r d m 3 , which i s e q u i v a l e n t t o a 5 0 3 m i l l i m e t r e d e p t h d i s t r i b u t e d uniformly o v e r t h e s u r f a c e of Lake A l b e r t . T h i s d e p t h i s d i s t r i b u t e d i n t o 2 8 , 2 1 , 2 4 , 3 6 , 5 6 , 3 1 , 2 2 , 2 6 , 3 9 , 6 4 , 80 and 75 mm f o r t h e 1 2 months from J a n u a r y t o December, r e s p e c t i v e l y (WMO,
1974).
The b a l a n c e s h e e t s f o r t h e y e a r s 1969 and 1970 and f o r t h e s o - c a l l e d normal y e a r , as r e p o r t e d by t h e h y d r o m e t e o r o l o g i c a l s u r v e y and for t h e p e r i o d 1948-1970 b a s e d on our estimates are a s f o l l o w s :
546
mm/yr
1969 1970 Normal 1948-70 8.4.2
0,
as
Kyoga
mm/yr
m/yr
m/yr
m/yr
8990 8799 5602 5642
540 578 50 3 5 10
9490 9081 6282 6364
-260 120 42 42
1913 2223 1546 1431
I, mm/v
p1
Year
Semliki
766 102 1 709 800
849 1026 864 885
R,
*
9
Lake water l e v e l and s t o r a g e
Records of w a t e r l e v e l a t t h e gauge of B u t i a b a are a v a i l a b l e s i n c e 1912. These l e v e l s p l o t t e d a g a i n s t t i m e i n y e a r s up t o and i n c l u d i n g 1970 are shown i n Fig. 8.14.
I n t h i s f i g u r e t h e a n n u a l change i n t h e s t o r a g e d e p t h of t h e l a k e i s
a l s o shown. I t i s c l e a r t h a t t h e change i n t h e l e v e l o f Lake A l b e r t and i n i t s s t o r a g e d e p t h i s p r i n c i p a l l y produced by t h e change i n t h e regime o f Lakes V i c t o r i a and Kyoga and t o a much less e x t e n t by t h e r e g i m e s o f Lakes George and Edward. The w a t e r l e v e l a t t h e b e g i n n i n g of e a c h month for t h e p e r i o d 1912-1970 i s i n c l u d e d i n t h e r e p o r t o f t h e h y d r o m e t e o r o l o g i c a l s u r v e y o f t h e c a t c h m e n t s of
Lakes V i c t o r i a , Kyoga and A l b e r t (WMO,
1 9 7 4 ) . The d i f f e r e n c e between t h e maxi-
mum and t h e minimum l e v e l f o r e a c h y e a r , i . e . t h e r a n g e of o s c i l l a t i o n h a s been computed and t e s t e d s t a t i s t i c a l l y . T h i s r a n g e r e a c h e d a minimum o f 18 cm i n 1969 and a maximum of 1 9 7 . 5 cm i n 1917 w i t h a mean of 6 7 . 3 cm/yr, s t a n d a r d d e v i a t i o n of 38.26 c m / y r ,
skewness o f 1 . 5 3 5 and k u r t o s i s o f 5 . 3 7 1 . The s e r i a l c o r r e l o g r a m
of t h e s e r i e s o f r a n g e i s shown i n F i g . 8 . 1 5 . The e m p i r i c a l f r e q u e n c y d i s t r i b u t i o n o f t h i s s e t of d a t a and t h e f i t o f t h e P e a r s o n Type I 1 1 f u n c t i o n t o i t a r e shown i n F i g . 8 . 1 6 . The v a l u e s of t h e r a n g e o f v a r i a t i o n e s t i m a t e d from t h e d i s t r i b u t i o n f u n c t i o n f o r some o f t h e none x c e e d a n c e p r o b a b i l i t i e s a r e a l s o g i v e n i n t h e same f i g u r e . The mean w a t e r l e v e l i n Lake A l b e r t f o r t h e p e r i o d 1912-1970 h a s been computed,
a s w e l l a s t h e mean l e v e l a t t h e b e g i n n i n g o f e a c h month. The p l o t o f t h e
monthly d e p a r t u r e from t h e g e n e r a l mean v e r s u s t i m e i n month i s r e p r e s e n t e d by c u r v e ( 4 ) i n F i g . 8 . 1 7 . W e have t r i e d t o f i t t o t h i s c u r v e t h e b a s i c model desc r i b e d by e q . 8 . 4 ' and t h e r e s u l t i s shown a s c u r v e ( 3 ) i n t h e same f i g u r e . The A-coefficients
a r e 1 6 . 6 1 , 4 . 4 1 , 0 . 3 4 , 2 . 0 3 , z e r o , and - 0 . 2 3 and t h e B-coef-
f i c i e n t s are -4.97,
-0.42,
-0.23,
-1.13, 0 . 0 3 a n d z e r o f o r t h e 1, 2 , 3 , 4 , 5 and
6 harmonics r e s p e c t i v e l y . F o r Lake A l b e r t , one f i n d s t h a t t h e 12-monthly c y c l e i s r e s p o n s i b l e f o r 88% o f t h e t o t a l v a r i a t i o n i n t h e l a k e l e v e l , and t h e 12- and
6-monthly c y c l e s combined e x p l a i n 94% o f t h e t o t a l v a r i a t i o n The s o - c a l l e d a c t u a l and c a l c u l a t e d w a t e r l e v e l s which were r e p o r t e d by H u r s t f o r t h e p e r i o d 1913 and 1915-32 i n V o l . V o f t h e N i l e B a s i n have been p l o t t e d i n F i g . 8 . 1 7 a s c u r v e s ( 1 ) and ( 2 ) r e s p e c t i v e l y . The d i s a g r e e m e n t between t h e two
s e t s of c u r v e s ( ( 1 ) and ( 2 ) , and ( 3 ) and ( 4 ) ) i s c e r t a i n l y t o o b i g . T h i s s i t u a t i o n i s s i m i l a r t o t h a t of t h e w a t e r l e v e l i n Lake V i c t o r i a ( s e e F i g . 8 . 3 ) .
347
1
14.2 14.c
13.f 13.t 13.1 13.2
200 180 160
I'i
13.C
12.8
140 120
100
12.6
80
12.L
E 60 u
2.2
40
2.c E
1.8
+
IJI c
1.6
-
20
&
g
-
o .-c
2o
Q
m
6 60 6
40
80
0
100 106
I20
_J
10.4
140
10 2
160
10.0
180
98
200
9.6 94
92 90
I
1912 '15
'20
'25
I
I
I
I
I
I
I
I
I
'30
'35
'40
'45
'30
'55
'60
'65
'70
Year
Fig. 8.14. Lake A l b e r t l e v e l a t Butiaba deduced from 10-day means from gauge r e a d i n g s 1912-70. The dashed l i n e r e p r e s e n t s t h e annual change i n l a k e s t o r a g e
348
0.4 L
.-
0.3
U
; ; 0.2 r
3 0.1 t
=
0.0
-0
0.1
$
0.2
-
.F! (1,
-
U
-
0.3
.-0
& 0.4
J,
v
10
i
11
12
13 14
95"10 Lower c o n f i d e n c e l i m i t
Fig. 8.15. S e r i a l correlogram o f t h e s e a s o n a l o s c i l l a t i o n of t h e water l e v e l i n Lake Albert
2 00
175
150
i
u
125
C
0
.-
5 10 20
24.6 28.7 35.8 57.9 93 5 1 1 8.3 142 1 172.7 I95 6
50 80 90 95 98 99
0100
.-
-? O
75
(51
C
0
LI
50
25 0
0
0.01
01 0.2 0 5 1
2
5
10
20 30 40 50 60 70 80
Non exceedance p r o b a b i l i t y ,
90
95
98 99
o/o
Fig. 8.16. F i t of Pearson Type I 1 1 f u n c t i o n t o t h e d i s t r i b u t i o n of t h e s e a s o n a l range of v a r i a t i o n of t h e water l e v e l i n Lake Albert
99 9
349
0,
.. . . . . . . ..
30 C
0
2 20
-
,
-
-
5
}
G i v e n by H u r s t for 1913 a n d 1 9 1 5 - 1 9 3 2
Observed
1912
- 1970.
I
Jan. Feb.
10
Calculated
r ----_ A c t u a l Calcu'a'ed } For
Ma?.'Apr.
May Jun. Jul.
"
A u g . Sep.
Oct.
Nov\Dec.
\:..
%, -..C'
\
L
20
Fig. 8.17.
S e a s o n a l o s c i l l a t i o n o f w a t e r l e v e l i n Lake A l b e r t
The a n n u a l v a r i a t i o n i n t h e s t o r a g e d e p t h f o r t h e p e r i o d c o n s i d e r e d has been s t a t i s t i c a l l y t e s t e d , and t h e s u c c e s s i v e terms found t o b e s e r i a l l y u n c o r r e l a t e d a t t h e 95% l e v e l of c o n f i d e n c e . The series h a s a mean of 5 4 . 7 5 m m / y r s t a n d a r d d e v i a t i o n of 652 m m / y r .
and
The skewness 'of t h e series i s q u i t e s m a l l ,
0 . 0 7 1 5 , j u s t i f y i n g t h e p o s s i b i l i t y o f f i t t i n g t h e normal f u n c t i o n t o t h e empiric a l d i s t r i b u t i o n o f t h e d a t a . I n F i g . 8 . 1 8 . , t h e d a t a a r e p l o t t e d and s o a r e t h e t h e o r e t i c a l d i s t r i b u t i o n s , a s g i v e n by t h e normal and t h e P e a r s o n I 1 1 f u n c t i o n s .
8.4.3
Lake o u t f l o w
The d i s c h a r g e of t h e A l b e r t N i l e used t o b e measured f o r some t i m e a t Pakwach, a s h o r t d i s t a n c e downstream o f t h e c o n f l u e n c e of t h e Kyoga N i l e w i t h t h e e x i t f l o w from t h e l a k e . U n f o r t u n a t e l y , none o f t h e r a t i n g c u r v e s developed a t Pakwach h a s shown s t a b i l i t y f o r a s u f f i c i e n t l y l o n g t i m e . T h e r e f o r e , a n o t h e r s i t e c a l l e d Panyanpo, f u r t h e r downstream of Pakwach, h a s been used f o r gauging t h e l a k e o u t f l o w i n t o t h e A l b e r t N i l e . F i g u r e 4 , Appendix E , shows t h e r a t i n g c u r v e a t Panyango and i t s r e l a t i o n w i t h Pakwach. The monthly and annual d i s c h a r g e s f o r t h e p e r i o d 1948-70 a r e g i v e n i n T a b l e 5 , Appendix D . The t a b u l a t e d d i s c h a r g e s have been a n a l y z e d s t a t i s t i c a l l y and t h e i r b a s i c d e s c r i p t o r s a r e g i v e n i n T a b l e 8 . 9 . From t h e s e r i a l c o r r e l a t i o n s g i v e n i n t h i s t a b l e , i t i s c l e a r t h a t a l l t h e monthly and t h e a n n u a l s e r i e s undergo a s t r o n g dependence among t h e i r i n d i v i d u a l s . F u r t h e r m o r e , e a c h of t h e s e series behaves more or l e s s s i m i l a r l y from t h e o t h e r s . I t h a s a c c o r d i n g l y been found s u f f i c i e n t t o t r y t o f i t the first-order
a u t o - r e g r e s s i v e model, e q . 8 . 3 , t o t h e a n n u a l series o n l y .
For t h i s d i s c h a r g e s e r i e s t h e model p a r a m e t e r h a s a v a l u e o f 0 . 9 0 6 5 . The
35 0
2000
E
Pr obab ility o f non exceedance ( "lo ) 1 5 10
1500
m
a
&
20 50 80 90 95 98 99
1000
P c
In
.-
500
C
.-0
-
.-
AS,
Normal distribution -1462 1 -101 7.5 - 780.9 - 494.5 54.7 603.5 890.3 11 27.5 1393.8 1571.5
0
$
a
mm.lyr. Pearson 111 distribution -1427.6 -1 0 0 4 . 2 - 775.6 - 496.1
0
-500
3 C
C
6
- 1000
- 1500 I
- 2000
0.01
0.10.2 0.5 1
2
5
I0
Non
1
20 30 LO 50 60 70 80
exceedance
pr obabi l i t y,
I
1
90
95
1
1
98 99
99-8
'10
F i g . 8.18. F i t o f normal and P e a r s o n Type I 1 1 f u n c t i o n s t o t h e d i s t r i b u t i o n of t h e annual v a r i a t i o n i n t h e s t o r a g e d e p t h i n Lake A l b e r t d u r i n g t h e p e r i o d 1912- 1970
r e s i d u a l terms i n t h i s model a p p e a r t o b e u n c o r r e l a t e d s e r i a l l y a t t h e 95% l e v e l of c o n f i d e n c e . With t h i s s i m p l e model, one c a n g e n e r a t e any number o f a n n u a l d i s c h a r g e s a s may b e needed. The mean hydrograph o f t h e o u t f l o w o f Lake A l b e r t f o r t h e p e r i o d 1948-1970
i s shown i n F i g . 8 . 1 9 . From 1904 up t o 1955 t h e l a k e o u t f l o w used t o b e found from a r a t i n g c u r v e e s t a b l i s h e d between t h e d i s c h a r g e o f t h e Bahr e l J e b e l a t Mongalla and t h e l a k e l e v e l a t B u t i a b a . The d i s c h a r g e a t Mongalla was r e d u c e d by 5% t o a c c o u n t f o r t h e l o s s e s between t h e l a k e e x i t and Mongalla (440 km). The mean o f t h e o u t f l o w found by t h i s method f o r t h e p e r i o d 1904-1947 was a b o u t 24.6 x
lo9
m3/yr.
The p e r i o d from 1948 up t o and i n c l u d i n g 1970 c a n b e d i v i d e d
i n t o two s e c t i o n s . I n t h e f i r s t , from 1948 t o 1 9 5 5 , d i s c h a r g e s were found s i m i l a r t o t h e d i s c h a r g e s from 1904 up t o 1947. From 1956 and onward, t h e d i s c h a r g e s w e r e o b t a i n e d from t h e Panyango-Pakwach
r a t i n g r e l a t i o n s h i p . The mean f o r t h e
p e r i o d 1948-1970 was a b o u t 33.7 m i l l i a r d m 3 / y r ,
which i s a b o u t 30% l a r g e r t h a n
t h a t f o r t h e p e r i o d 1904-1947. A l m o s t t h e same d i f f e r e n c e e x i s t s between t h e
TABLE 8 . 9
The b a s i c s t a t i s t i c a l d e s c r i p t o r s of t h e outflows from Lake A l b e r t a t Panyango f o r t h e p e r i o d 1948-1970
Month and
Basic s t a t i s t i c a l descriptors
Serial correlation coefficients
Year
x, m 3 / s
s , m3/s
c"
cS
ck
rl
r2
r3
r4
r5
January February March Apri 1 May June July August September October November December Year
1090.9 1046.9 1014.1 1004.3 1034.5 1033.8 1040.9 1062.2 1099.9 1118.6 1157.0 1163.5 1071.9
576.05 583.10 586.65 589.65 587.57 596.19 591.40 586.29 574.93 569.40 574.40 589.16 577.24
0.5281 0.5570 0.5785 0.5877 0.5680 0.5767 0.5682 0.5519 0.5227 0.5090 0.4965 0.5064 0.5395
0.5398 0.5637 0.6080 0.6109 0.6207 0.6046 0.6087 0.5969 0.5907 0.5704 0.4433 0.3701 0,5902
1.9144 1.9350 2.0092 2.0221 2.0545 2.0189 2.0111 1.9656 1.9785 1.9928 1.8601 1.7179 1.9514
0.9192 0.9055 0.8895 0.8818 0.8590 0.8562 0.8566 0.8721 0.8736 0.8931 0.9328 0.9372 0.9065
0.7330 0.7087 0.6835 0.6739 0.6356 0.6375 0.6409 0.6712 0.6987 0.7402 0.7945 0.7865 0.7204
0.5627 0.5335 0.5023 0.4862 0.4634 0.4620 0.4753 0.5006 0.5124 0.5450 0.5947 0.6009 0.5384
0.3973 0.3591 0.3222 0.3018 0.2951 0.3107 0.3446 0.3839 0.3949 0.4263 0.4504 0.4513 0.3865
0.2344 0.1929 0.1561 0.1414 0.1318 0.1759 0.2074 0.2562 0.2720 0.2746 0.2892 0.2996 0.2356
-
352
c o r r e s p o n d i n g monthly v a l u e s o f t h e t w o p e r i o d s ( s e e F i g . 8 . 1 9 . ) .
The two
methods combined g i v e an o v e r a l l mean of a b o u t 2 7 . 7 m i l l i o n m3/yr for t h e o u t flow of Lake A l b e r t d u r i n g t h e p e r i o d 1904-1970.
T h i s f i g u r e i s s t r o n g l y sup-
p o r t e d by t h e estimate o f t h e mean o u t f l o w u s i n g t h e long-term lake.
balance of t h e
age for t h e period 1
1100
' O 5OI
v 1000
6,
0 -
9501
t
. 900-
,
6501, J
F
, M
M
,
,
, A
J J Month
A
,
, S
O
{
, N
D
Fig. 8.19. The a v e r a g e h y d r o g r a p h s of t h e A l b e r t N i l e a t t h e e x i t of Lake A l b e r t f o r two d i f f e r e n t p e r i o d s The i n f l o w t o t h e l a k e s u p p l i e d by t h e Semleeki i s 4 . 6 4 x t h e Kyoga N i l e , 2 4 . 9 x
lo9
lo9
m3/yr ( s e c t i o n 8 . 2 . 3 ) . The long-term
c o e f f i c i e n t is 12.4%.
l a k e catchment i s a b o u t 1250 mm/yr and t h e a n n u a l r u n - o f f These f i g u r e s p r o d u c e an a n n u a l r u n - o f f
m3/yr and by
r a i n f a l l on t h e
t o t h e l a k e equal t o 2.63 x
lo9
m3.
The
d i r e c t p r e c i p i t a t i o n on t h e l a k e i s a b o u t 800 mm/yr and t h e a n n u a l e v a p o r a t i o n
i s i n t h e o r d e r of 1700 mm ( s e e C h a p t e r 5 ) . T h i s means a l o s s o f 4 . 7 7 x
lo9
m3/
y r . From s e c t i o n 8 . 4 . 2 , w e have a l r e a d y s e e n t h a t t h e y e a r l y change i n t h e s t o r a g e d e p t h i n t h e l a k e is close to 5.5 c m . T h i s i s e q u i v a l e n t t o a l o s s of 0 . 2 9 m i l l i a r d m3/yr. The a n n u a l o u t f l o w t h e n e q u a l s 4 . 6 4
-
0 . 2 9 = 2 7 . 1 1 m i l l i a r d m3/yr.
+
24.90
+
2.63
- 4.77
The d i s t r i b u t i o n of t h i s volume between t h e
months of t h e y e a r f o l l o w s t h a t shown i n F i g . 8 . 1 9 .
35 3
8.5
THE BAHR EL J E B E L BASIN
8.5.1
The Bahr :=be1
8.5.1.1
from t h e e x i t of Lake A l b e r t t o hiongalla
The t o r r e n t s between Lake A l b e r t a n d Mongalla
The l e n g t h o f t h e Bahr e l J e b e l from t h e e x i t of Lake A l b e r t t o Mongalla i s a b o u t 440 km
and t h e s u r f a c e a r e a of i t s b a s i n i s 79000 km2. From Lake A l b e r t
t o Nimule, a d i s t a n c e o f a b o u t 225 km, t h e r i v e r i s a b r o a d s l u g g i s h stream f r i n g e d w i t h swamps and l a g o o n s . The d i s t a n c e between Nimule and R e j a f i s a b o u t 155 km. The r i v e r i n t h i s r e a c h i s a f a s t - f l o w i n g stream whose c o u r s e i s o b s t r u c t e d by some r a p i d s , I n t h e n e x t s t r e t c h , which e x t e n d s from Rejaf t o Mongalla, a d i s t a n c e o f a b o u t 6 0 km, t h e bed s l o p e d e c r e a s e s c o n s i d e r a b l y . A number of s m a l l streams j o i n t h e Bahr e l J e b e l between Lake A l b e r t and Nimule. D i s c h a r g e measurements a t Nimule began i n 1913 and t h e r a t i n g c u r v e i s shown i n F i g 5 , Appendix E . T h e r e a r e , however, many b r e a k s i n t h e a v a i l a b l e r e c o r d s . One may t h e r e f o r e t a k e 1 . 5 m i l l i a r d m3/yr a s a lump sum c o n t r i b u t i o n o f t h e s e s t r e a m s t o t h e f l o w i n t h e Bahr e l J e b e l above Nimule. C o u n t e r b a l a n c i n g t h i s g a i n t h e r e is a c e r t a i n conveyance l o s s between Lake A l b e r t and Nimule. T h i s l o s s c a n b e e s t i m a t e d a t a b o u t 4% o f t h e a n n u a l volume
of t h e l a k e ' s o u t f l o w . A c e r t a i n p o r t i o n o f t h i s loss i s i n f a c t t h e r e s u l t a n t of t h e e v a p o r a t i o n from t h e open w a t e r (260 km2 and e v a p o r a t i o n d e p t h a b o u t 1800 mm/yr)
,
t h e e v a p o t r a n s p i r a t i o n from t h e swamps (120 km2 and e v a p o t r a n s p i -
r a t i o n r a t e o f a b o u t 2000 mm/yr),
and t h e a n n u a l p r e c i p i t a t i o n , which i s a b o u t
1300 mm/yr. Based upon o u r estimate o f t h e Lake A l b e r t o u t f l o w , 2 7 . 1 mlrd m3/yr, t h e long-term mean f l o w a t Nimule must t h e n b e a b o u t ( 2 7 . 1 x 0 . 9 6 )
+ 1 . 5 = 2 7 . 5 mlrd
m3/yr. T h i s amount f l o w s a d i s t a n c e of 155 km b e f o r e i t r e a c h e s Mongalla. The Assua R i v e r j o i n s t h e Bahr e l J e b e l a t a s h o r t d i s t a n c e below Nimule. I t s u p p l i e s t h e main r i v e r by a b o u t 1 . 5 x
lo9
m3 i n an average y e a r . Fig. 6 ,
Appendix E , shows t h e r a t i n g c u r v e of t h e Assua R i v e r . H u r s t u s e d t h e r a i n f a l l and run-off
d a t a of t h e Assua B a s i n f o r t h e p e r i o d 1924-1935 t o d e v e l o p e x p r e s -
s i o n s g i v i n g t h e monthly and t h e a n n u a l d i s c h a r g e f o r any g i v e n r a i n f a l l . The a n n u a l run-off
c o e f f i c i e n t t h a t c o r r e s p o n d s t o r a i n f a l l o f a b o u t 1300 mm
i s c l o s e t o 3%. S i n c e t h e s u r f a c e area o f t h e Assua B a s i n i s 39000 km2, t h e annual run-off
becomes 1 . 3 x 0 . 0 3 x 39 x
t h e Bahr e l - J e b e l 2.4.,
lo9
= 1.52 x
lo9
m 3 . Other streams j o i n
i n t h e r e a c h between Nimule and Mongalla ( s e e t h e maps, F i g s .
and 2 . 1 1 . ) . These streams a r e known t o f e e d t h e main r i v e r by some 1 . 2
mlrd m3/yr. The a v e r a g e h y d r o g r a p h s o f t h e t o r r e n t s between t h e e x i t of Lake A l b e r t and Mongalla and between Nimule and Mongalla, R i v e r Assua b e i n g i n c l u d e d ,
are shown i n F i g . 8 . 2 0 .
354
.
*E 25
*s! 20 -15 m
vgen Nimule a n d J
F
M
A
M
J J Month
A
S
O
\ \ N
D
Fig. 8.20. The average hydrographs of t h e t o r r e n t i a l s t r e a m s between Lake A l b e r t and Mongalla and between Nimule and Mongalla f o r t h e p e r i o d 1923-1932 The annual r a i n f a l l on t h e Bahr e l J e b e l Basin i n t h e reach between Nimule and Mongalla can be taken a s 1250 mm. T h i s i s t h e a v e r a g e of t h e r a i n f a l l a t
N i m u l e , S t a t . 142, and Kajo K a j i , S t a t . 141 ( s e e Appendix C ) . The e v a p o r a t i o n r a t e f o r t h e same s t r e t c h of r i v e r o u t s i d e t h e swamps i s on average 5 mm/day, o r about 1800 mm/yr.
The d e t a i l s about t h i s f i g u r e can be found i n Chapter 5 .
To account f o r t h e o t h e r t r a n s i t l o s s e s such a s seepage and s p i l l i n g w e s h a l l c o n s i d e r t h e flow a t Mongalla a s b e i n g 4% l e s s t h a n t h a t a t Nimule. The long-
t e r m mean of t h e annual d i s c h a r g e a t Mongalla t h e n becomes 0 . 9 6 x 27.5 p l u s t h e 2 . 7 mlrd m3 s u p p l i e d by t h e t o r r e n t s between Nimule and Mongalla. The r e s u l t a n t outflow a t Mongalla can t h u s be e s t i m a t e d a t 2 9 . 1 mlrd m 3 / y r .
8.5.1.2
Discharges a t Mongalla
The monthly and annual d i s c h a r g e s measured a t Mongalla f o r t h e p e r i o d 19121973 a r e given i n Table 6 , Appendix D . The gauge-discharge p o i n t s used f o r e s t a b l i s h i n g t h e r a t i n g c u r v e i n t h e p e r i o d 1911-27 a r e shown i n F i g . 7 , Appendix E The annual volume of flow a t Mongalla i n t h e p e r i o d c o n s i d e r e d showed a maximum of 5 5 . 8 x
lo9
m 3 i n 1917 and a n o t h e r maximum of 6 0 . 5 x lo9 m3 i n 1963.
The l a t t e r was, however, much b r o a d e r t h a n t h e former. The minimum flow was observed i n 1922 and has a v a l u e of about 1 5 . 3 x
lo9
m3.
I t goes w i t h o u t s a y i n g
t h a t t h e occurrence of t h e maximum and minimum flows t o g e t h e r w i t h a l l o t h e r flows a t Mongalla i s p r i m a r i l y i n f l u e n c e d by t h e h y d r o l o g i c s i t u a t i o n i n t h e complex of t h e E q u a t o r i a l Lakes. The g r a p h i c a l p l o t of t h e annual d i s c h a r g e s e r i e s of Mongalla i s shown i n F i g . 8 . 2 1 . The p a r t spanning t h e p e r i o d from, s a y , 1925 up t o , s a y , 1955, f l u c t u a t e s i n t h e range between 20 and 30 mlrd m3/yr. p a r t occur r a t h e r r e g u l a r l y
The ups and downs i n t h i s
- once every 5 y e a r s , on a v e r a g e .
35 5
L
>
2
70
-
E60 -
m
050
i & O
230
S
U
!. 2 0 n
-
-
1912 ' 1 5
' 2 0 ' 2 5 '30 ' 3 5 ' 4 0 ' L 5 ' 5 0 Year
'55
'60 ' 6 5
'70'73
Fig. 8.21. G r a p h i c a l p l o t o f t h e annual d i s c h a r g e series o f Mongalla i n t h e p e r i o d 1912-1973
W e h a v e e x a m i n e d t h e s t a t i s t i c a l p r o p e r t i e s o f t h e 12 months and o f t h e
-
a n n u a l s e r i e s . The v a l u e s of t h e mean, X , s t a n d a r d d e v i a t i o n , s , t h e v a r i a t i o n coefficient, C
t h e skewness, C
V'
and t h e k u r t o s i s , have b e en computed from
e q s . 4 . 1 t o 4 . 5 , r e s p e c t i v e l y . The skew a n d t h e k u r t o s i s h a v e b e e n c o r r e c t e d f o r t h e b i a s i n t h e i r e s t i m a t e . E q . 4 . 6 h a s b e e n used t o c o m p u t e t h e s e r i a l c o r r e l a t i o n c o e f f i c i e n t , r,,, c o r r e s p o n d i n g t o l a g L . S i n c e t h e s i z e o f t h e s a m p l e N i s 6 2 y e a r s , w e h a v e t o s t o p w i t h o u r c a l c u l a t i o n of rL a t L
=
N
4 The r e s u l t s o b t a i n e d f r o m t h e s e c a l c u l a t i o n s are p r e s e n t e d i n T a b l e 8.10. ~
or 15.
The s e r i a l c o r r e l a t i o n c o e f f i c i e n t s show t h a t a l l t h e e x a m i n e d s e r i e s h a v e more o r l e s s t h e same p a t t e r n o f c o r r e l a t i o n . E a c h s e r i e s i s s e r i a l l y c o r r e l a ted up t o l a g L
=
6 o r 7 . T h i s can b e s e e n from t h e e x a m p l e c o r r e l o g r a m o f t h e
J a n u a r y d i s c h a r g e s shown i n Fig, 8 . 2 2 . The a u t o g r e g r e s s i v e model h a s b e e n f i t t e d t o t h e m o n t h l y s e r i e s , a n d t h e y a l l showed t h a t t h e f i r s t - o r d e r m o d e l , e q . 8 . 3 , gives the best f i t . A much b e t t e r f i t t o t h e s e r i e s o f
a n n u a l d i s c h a r g e s was o b t a i n e d f r o m t h e
s e c o n d - o r d e r a u t o r e g r e s s i v e model. T h i s o r d e r h a s been d e s c r i b e d and used i n c o n n e c t i o n w i t h t h e a n a l y s i s o f t h e r a i n f a l l d a t a ( s e e C h a p t e r 4 ) . The model p a r a m e t e r s al and a
a r e c c m p u t e d f r o m r l ( l - r ) / ( l - r l z ) and ( r 2 - r 1 2 ) / ( l - r 1 2 ) , 2 2 r e s p e c t i v e l y . The model p a r a m e t e r o f e a c h o f t h e m o n t h l y s e r i e s i s i t s f i r s t
s e r i a l c o r r e l a t i o n c o e f f i c i e n t , a: = r
a1 = 1 . 2 7 4 3 a n d a 2 =
-
( s e e T a b l e 8 . 1 0 ) . For t h e annual s e r i e s , 1 0 . 4 3 5 9 , The s e r i a l c o r r e l a t i o n c o e f f i c i e n t s of t h e r e s i -
d u a l s l e f t from t h e f i t o f t h e f i r s t - o r d e r
model t o t h e m o n t h l y d a t a and f r o m
t h e f i t o f t h e s e c o n d - o r d e r model t o t h e a n n u a l d a t a a r e l i s t e d i n T a b l e 8 . 1 1 . The p r o b a b i l i t y d i s t r i b u t i o n f u n c t i o n s o f good f i t t o t h e m o n t h l y a n d a n n u a l d i s c h a r g e series a t Mongalla a r e t h e two-parameter
lognormal and t h e P e a r s o n
Type 1 1 1 f u n c t i o n s . T h e s e t w o f u n c t i o n s g i v e a l m o s t t h e same v a r i a t e v a l u e f o r
a 100-year r e c u r r e n c e i n t e r v a l . N e v e r t h e l e s s , t h e two-parameter
lognormal has
proven t o b e s l i g h t l y s u p e r i o r t o t h e Pearson 1 1 1 and t o p r o v i d e , i n g e n e r a l ,
TABLE 8.10
The b a s i c s t a t i s t i c a l d e s c r i p t o r s and s e r i a l c o r r e l a t i o n c o e f f i c i e n t s of t h e monthly and annual d i s c h a r g e s of t h e Bahr e l - J e b e l a t Mongalla for t h e p e r i o d 1912-1973
Item
Basic s t a t i s t i c a l descriDtOr
X,
106 m 3 s , 106 m 3 C
CV
c:
Month of t h e y e a r Jan.
Feb.
Mar.
Apr.
2328 1065 0.4574 1.2190 3.4060
2030 972 0.4790 1.2000 3.2276
2137 1002 0.4687 1.2174 3.3746
2187 978 0.4470 1.2620 3.6285
0.8342 0.6569 0.4982 0.9974 0.3260 0.3077 0.2531 0.1763 0.1336 0.0644 0.0585 0.1376 0.1176 6.0616 0.0446
0.8439 0.6666 0.5163 0.4254 0.3644 0.3548 0.3095 0.2306 0.1720 0.0915 0.0445 0.1369 1190 9.0692 0.0511
0.8356 0.6540 0.5211 0.4253 0.3505 0.3252 0.2730 0.1851 0.1377 0.0562 0.0647 0.1450 2.1235 0.0682 0.0575
0.8483 0 .6590 0.4984 0.3938 0.3465 0.3278 0.2865 0.2112 0.1566 0.0683 0.0490 0.1314 0.1086 0.0779 6.0577
June
July
Aug.
Sep.
Oct.
Nov.
Dec.
Year
2629 1082 0.4116 1.2484 3.9149
2521 1044 0.4141 1.1701 3.6491
2728 1005 0.3684 1.0805 3.5332
3178 1143 0.3597 0.9634 3.2432
3119 1280 0.4105 1.2189 4.0455
3101 1347 0.4344 1.3824 4.7638
2777 1195 0.4305 1.0611 2.8798
2584 1162 0.4498 1.0529 2.7898
31381 12610 0.4018 1.1497 3.1595
0.7865 0.5681 0,4002 0.3305 0.2869 0.2619 0.2120 0.1375 0.1161 0.1103 0.0096 0.1570 1681 0.1173 6.0861
0.8052 0.5735 0.4015 0.3170 0.2971 0.2749 0.2216 0.1312 0.0917 0.0773 0.0071 0.1639 1748 0.1031 0 .0673
0.7591 0.6067 0.4275 0.3876 0.3315 0.3084 0.1610 0.1812 0.0552 0.0084 .0724 0.1830 0.2157 0.1248 0.0301
0.7379 0.5586 0.4428 0.3704 0.3601 0.3710 0.1812 0.1161 0.0782 0 .0244 0.0558 0.1039 1916 0.0116 0.0740
0.6996 0.4953 0.2978 0.2532 0.2370 0.2992 0.2175 0.1437 0.0645 0.0399 0.1077 0.1060 0.1584 0.0340 0.1058
0.7165 0.5235 0.3994 0.2518 0.2293 0.3112 0.2029 0.1507 0 . I702 0.0581 0.0389 0.0341 0,0729 0.0469 0.1034
0.8421 0.7030 0.6234 0.4674 0.4087 0.3966 0.2859 0.2119 0.2033 0,0847 -0.0122 0.0707 0.0799 0.0627 0.0454
0.8509 0.6910 0.5992 0.4851 0.4333 0.3932 0.3037 0.2309 0.2174 0.1331 0.0135 0.0728 0.1286 0 . 0874 0.0645
0.8875 0.6951 0.5290 0.4222 0.3715 0.3441 0.2760 0.2011 0.1456 0.0716 .0351 0.1214 0.1298 0.0642 6.0207
May
S e r ia1 corre l a tion coefficient
c.
c.
c.
C
g.
w 01
357 c
Correlogram
discharge series
of
/'
- 0.2
-
95'10 Correlogrom
Lower
confidence
limit
of r e s i d u a l s
Fig. 8.22. S e r i a l correlogram of t h e January d i s c h a r g e series a t Mongalla and of t h e r e s i d u a l s l e f t from t h e f i t of t h e f i r s t - o r d e r a u t o r e g r e s s i v e model t o i t
is an example of t h e f i t of t h e
a b e t t e r f i t t o t h e observed d a t a . F i g . 8.23.
lognormal f u n c t i o n t o t h e e m p i r i c a l d i s t r i b u t i o n of t h e annual d i s c h a r g e s e r i e s from 1912 up to and i n c l u d i n g 1973. For t h i s series and a l s o f o r t h e 12-month s e r i e s , t h e 100 and 200-year
d i s c h a r g e s computed by t h i s d i s t r i b u t i o n f u n c t i o n
are : Discharge, 106 ,3 J a n . Feb. Mar. Apr. May 100-yr 200-yr
200
~,lOO
-
$50
-
June J u l y Aug. Sep. Oct. Nov. Dec.
Year
5693 5092 5303 5307 6059 5789 5823 6615 7164 7479 6434 6140 70724 6290 5626 5865 5864 6687 6352 6326 7133 7881 8273 7031 6709 77408
I
,
I
I
I
,
I
I
I
I
I
I
I
I
1
1
1
1
,
I
I
1
I
I
1
I
l
l
l
l
1
I
I
1
I
1
90 -Q) 80 9 70 . 60 -
;
40
a
30 -
5
20 -
In
C
Q
10
-
Fig. 8.23. F i t of t h e lognormal f u n c t i o n t o t h e d i s t r i b u t i o n of t h e annual d i s c h a r g e s a t Mongalla i n t h e p e r i o d 1912-1973
TABLE 8 . 1 1
Serial correlation coefficients of the residuals left from fitting autoregressive models to the discharge series at Mongalla
Month
Serial correlation coefficients
&
Year January February March April May June July August September October November December Year
r
-
r 1
r 2
-
r
r 3
4
.058 .030 .lo7 .189 .156 .200 -.048 .001 -. 0 0 3 -.038 .009 .188
,052 ,105 -.115 ,107 .lo6 T135 -, 0 9 1 .053 :044 -.016 ,070 .084
,192 ,011 ,027 ,099 ,126 ,138 ,181 ,035 ,169 ,079 .209 .043
-.005 ,119 ,046 -.139 ,018 .077 .lo7 .008 -.067 -.065 ,159 .063
.115
,151
TO63
.048
-
5
.014 ,043
.ZOO
.048 .126 .150 .032 -.063 -.028 ,042 .047 .040
,138 .161 .162 .120 .lo9 .257 .346 .225 ,255 .225 .176
.098
.275
.002
.
r 6
r
r 7
:048 .lo6
-
r 8
-
r 9
r 10
-. 0 1 7
.005 .003 ,036 .094 :121 ,036 _046 .073 ,015
,019 ,144 -, 1 3 2 1075 .097 I098 -,080 .021 -. 0 4 1 ,065 ,157 .198
.059 TO95 .096 TO07 .091 .138 .235 .177
.136 .091 .199 -.033 .021 ,158
,005 ,158 ,122 .057 .038
TO07
T114
.011
.244
.044
.028
.114 .125
,082
.137 .088 .069 .063 .159
r 11
.121
.037
-.028
-.069
.018 .236 .227
.010
r
r
r
12
13
14
15
,094 ,111 ,135 ,109 ,127 ,183 .058 .090
YO84 T127 ,080 ,040 ,140 ,167 .185 T301 -.277 .173 .006
.128 .lo4 .112 .144 .159 .125 .153 .114 .043
.012
TO24 .071 .086 .034 .018 .051 .002 .124 .140 .lo7 .021 .082
T291
.139
,226
-
.lo1
,070 ,127 .035
Tl2l
.066
.088 .085
359
The Bahr e l J e b e l from Mongalla t o Lake No
8.5.2 8.5.2.1
General d e s c r i p t i o n of t h e r i v e r v a l l e y
This s t r e t c h of t h e Bahr e l J e b e l B a s i n i s c h a r a c t e r i z e d by t h e e x i s t e n c e o f
v a s t swamps, l a g o o n s and s i d e c h a n n e l s e a s t a n d w e s t o f t h e main r i v e r . The l e n g t h o f t h e c o u r s e o f t h e main stream between Mongalla and Lake N o i s a b o u t 770 km and t h e area o f t h e permanent swamps i s c l a i m e d t o b e a b o u t 8500 km2. T h i s is o b v i o u s l y an area where s e v e r e l o s s o f w a t e r t a k e s p l a c e . Some of t h e g e o g r a p h i c , p h y s i o g r a p h i c a n d h y d r o l o g i c f e a t u r e s of t h e a r e a have been d e s c r i b e d i n some o f t h e volumes o f t h e N i l e B a s i n , e s p e c i a l l y Vol. V ( H u r s t , H.E.,and P h i l i p s ,
P.,
1 9 3 8 ) . The p e r t i n e n t f e a t u r e s o f t h e r i v e r v a l l e y
c a n , however, b e summarized i n t h e f o l l o w i n g p o i n t s : The w i d t h o f t h e swamps i n c r e a s e s from a b o u t 3 km a t Mongalla t o a b o u t 7 km
i)
a t T e r r a k e k a some 30 km n o r t h o f Mongalla. ii)
The h e a d o f t h e A l i a b R i v e r a p p e a r s some 90 km n o r t h of Mongalla and j o i n s t h e main r i v e r n o t f a r from Bor.
iii) A t B o r , a b o u t 140 km n o r t h o f M o n g a l l a , t h e w i d t h o f t h e v a l l e y becomes 9 km. North of Bor are many l a g o o n s and open c h a n n e l s . On t h e e a s t e r n s i d e
a p p e a r s t h e Atem-Awai s y s t e m o f r i v e r s . T h i s f l o w s i n a w i n d i n g c o u r s e t o j o i n and r e j o i n t h e Bahr e l J e b e l a t a n d n e a r Ghabe Shambe ( s e e t h e maps F i g s . 2.9., and 2 . 1 2 . ) . iv)
T h e r e t h e swamps a r e r o u g h l y 15 km w i d e .
The e a s t e r n c h a n n e l s u l t i m a t e l y j o i n t o form t h e Upper Z e r a f . Here a t a l a t i t u d e of 7O30’ t h e swamp o c c u p i e s a w i d t h o f , s a y , 30 km, i n c r e a s i n g t o
a maximum o f 35 km a t a l a t i t u d e of 7O40’. v)
A t a l a t i t u d e o f 7O35’, t h e l a g o o n s b e g i n on t h e w e s t o f t h e main r i v e r t o form P e a k e ’ s Channel l a t e r , which r e j o i n s Bahr e l J e b e l a t a s h o r t d i s t a n c e north of t h e Jebel-Zeraf
c u t s . These c u t s a r e meant t o m a i n t a i n t h e flow i n
t h e Bahr e l Z e r a f . The s o u t h e r n c u t i s u s u a l l y r e f e r r e d t o a s No. 1 and t h e n o r t h e r n as N o .
2.
The u p p e r p a r t o f t h e Z e r a f s o u t h o f t h e h e a d s i s u s u a l l y b l o c k e d , b u t from t h e c u t f i n o r t h w a r d , t h c Lover Z e r a f h a s a more o r less d e f i n e d c h a n n e l . I n
i t s l o w e r c o u r s e from a b o u t l a t i t u d e 8O30’, t h e Z e r a f i s a s t r e a m w i t h f i r m b a n k s , r i s i n g a b o u t . t h e normal w a t e r l e v e l and s e p a r a t e d from t h e J e b e l by a wide s t r i p of d r y l a n d . vi)
From H i l l e t Nuer (Adok) on t h e J e b e l n o r t h w a r d s ,
t h e permanent swamp i s a
few k i l o m e t r e s w i d e . The J e b e l ends i t s c o u r s e downstream Lake No. E i g h t y k i l o m e t r e s f u r t h e r downstream, t h e L o w e r Z e r a f j o i n s t h e White N i l e t h r o u g h t h e Abu Tong c u t . F i g . 8 . 2 4 is a s o r t o f l o n g i t u d i n a l p r o f i l e of t h e Bahr e l J e b e l from Mongalla t o Lake N o , on which t h e l o c a t i o n s of t h e p r i n c i p a l c h a n n e l s l e a v i n g or j o i n i n g t h e main stream are shown. A v e r y g e n e r a l p i c t u r e of t h e d i s c h a r g e
360
1100 1000
900
800 . * 700 E
6 600
P 5
500
0 400 300 200 100
0
700
600
500
Distance
from
400 Lake
300
2 00
100
No a l o n g r i v e r , km.
Fig. 8.24. The t o t a l d i s c h a r g e p a s s i n g any c r o s s - s e c t i o n o f t h e v a l l e y o f t h e Bahr e l J e b e l between Mongalla and Lake N o ( H u r s t , H . E . , and P h i l i p s , P . , 1938) p a s s i n g any c r o s s - s e c t i o n of t h e Bahr e l J e b e l v a l l e y i n t h e r e a c h c o n s i d e r e d can b e o b t a i n e d from c u r v e s (1) and ( 2 ) . These l i n e s show c l e a r l y t h a t , i n g e n e r a l , a heavy l o s s t a k e s p l a c e from one s e c t i o n t o a n o t h e r . The loss p e r k i l o m e t r e l e n g t h o f t h e main stream i s , however, h e a v i e r from Gemmeiza/Gigging t o t h e Z e r a f c u t s (300 km from Lake No) t h a n i n t h e lowermost 300 km. I n t h e upper 400 km r e a c h t h e h i g h water l o o s e s i t s d i s c h a r g e a t t h e r a t e o f a b o u t 1 . 2 2 5 m3/km'
compared t o a b o u t 0 . 9 2 5 m3/km'
f o r t h e a v e r a g e water. F o r t h e s e two
w a t e r s t h e l o s s i n t h e l a s t 300 km i s 0 . 4 m3/km and 0 . 1 m3/km, r e s p e c t i v e l y . The 1100 m3/sec.
d i s c h a r g e a t Gemmeiza r e a c h e s t h e o u t l e t a t Lake N o a t 470 m3/sec.,
a f t e r l o o s i n g a b o u t 5 7 . 3 % , and from t h e i n i t i a l 900 m3 a t Gemmeiza, 44.4% is
lost i n i t s way t o t h e e s c a p e . I n v e r y g e n e r a l t e r m s , a f i g u r e of 50% f o r t h e l o s s of water i n t h e Bahr e l J e b e l B a s i n downstream o f Mongalla i s n o t unreason-
c
able.
The s t a g e - d i s c h a r g e measurements u s e d f o r m e r l y f o r p r e p a r i n g t h e r a t i n g c u r v e s o f t h e main r i v e r and some of i t s p r i n c i p a l c h a n n e l s a r e p l o t t e d g r a p h i c a l l y i n a s e t o f f i g u r e s . These f i g u r e s , which a r e i n c l u d e d i n Appendix E , a r e : Fig.
8
Fig.
9
-
Khor Unyam K o j i e , 2 . 5 km s o u t h o f B o r , R i v e r A l i a b , T a i l 1, 16 km n o r t h o f B o r ,
F i g . 10
- Bahr e l J e b e l a t B o r ,
F i g . 11
-
El J e b e l - Z e r a f
c u t 1 a t t a i l and a t h e a d ,
0
361
Fig. 12
- E l Jebel-Zeraf c u t 2 a t t a i l and a t head,
F i g . 13
- Bahr e l J e b e l downstream o f t h e J e b e l - Z e r a f c u t 2 ,
F i g . 14
- Bahr e l J e b e l a t a d i s t a n c e o f 281 km from L a k e No, downstream o f t h e
F i g . 15
-
t a i l of Peake's F i g . 16 Fig. 17
The White N i l e i n t h e neighbourhood o f Lake No, Bahr e l Z e r a f , 3 km from t h e mouth, and The White N i l e a t Abu Tong i n t h e neighbourhood o f t h e Zeraf mouth.
The J o n g l e i c a n a l p l a n n e d t o convey p a r t o f t h e Bahr e l J e b e l w a t e r from n e a r J o n g l e i t o t h e mouth o f t h e Z e r a f w i t h t h e a i m o f s a v i n g some of t h e w a t e r l o s t i n t h e swamps w a s o r i g i n a l l y t h o u g h t o f by A . D .
Butcher. W e s h a l l d e s c r i b e t h i s
d i v e r s i o n c a n a l i n some d e t a i l i n c o n n e c t i o n w i t h t h e s t o r a g e and c o n s e r v a t i o n works o f t h e N i l e Water.
8.5.2.2
The l o s s o f water i n t h e Bahr e l - J e b e l
swamps
The B a h r e l J e b e l swamps c o m p r i s e t h e swamps i n t h e b a s i n s o f t h e Bahr e l J e b e l i t s e l f and i t s o f f - s h o o t t h e Bahr e l Z e r a f . The a r e a o f t h e permanent swamps h a s b e e n f r e q u e n t l y g i v e n as 8300 km2. I t i s n o t p o s s i b l e t o g i v e any f i g u r e f o r t h e temporary swamps, as t h e i r area v a r i e s from one s e a s o n t o a n o t h e r and from one y e a r t o a n o t h e r . The e s s e n t i a l p a r t i c u l a r s a b o u t t h e l o s s of water i n t h e swamps c a n b e found i n t h e N i l e B a s i n Volumes V , V I I and X. A few a d d i t i o n a l f i g u r e s c a n b e found i n t h e J o n g l e i c a n a l r e p o r t . The a v a i l a b l e d a t a show t h a t t h e h i g h e s t c o r r e l a t i o n between t h e d i s c h a r g e s above and below t h e swamps c a n b e o b t a i n e d w i t h a l a g of t h r e e months. From 1912 t o 1922 t h e below swamps d i s c h a r g e w a s t a k e n as t h e d i f f e r e n c e between t h e d i s c h a r g e s of t h e White N i l e
a t Malakal and o f t h e S o b a t , b o t h b a s e d on t h e d i s c h a r g e c u r v e s c o n s t r u c t e d from t h e d i s c h a r g e s measured d u r i n g t h e same y e a r . From 1923 onwards, t h e swamp d i s c h a r g e was t h e sum o f t h e d i s c h a r g e s o f t h e Z e r a f and of t h e White N i l e a t Abu Tong, o b t a i n e d by l i n e a r i n t e r p o l a t i o n between measured d i s c h a r g e s . The r e l a t i o n between t h e q u a r t e r l y mean d i s c h a r g e s a t Mongalla and below t h e swamps from t h e d a t a i n t h e p e r i o d 1912-1945 i s shown g r a p h i c a l l y i n F i g . 8 . 2 5 . From t h e a n n u a l f l o w volumes a t Mongalla and t h e a n n u a l f l o w volumes below t h e swamps, t h e c u r v e i n F i g . 8 . 2 6 . .
h a s been c o n s t r u c t e d so as t o r e a d t h e p e r c e n -
F
t a g e w a t e r l o s t g i v e n t h e f l o w a t Mongalla. T h i s c u r v e c a n b e d e s c r i b e d by t h e equation
L = 2.25 V
M
- 0.0175
V
M
(8.5)
where L is t h e l o s s i n p e r c e n t a n d Vy i s t h e a n n u a l f l o w volume a t Mongalla, i n m i l l i a r d m3.
0
u a r t r r l y m e a n s 1912- 1945 v a r i a b l e and d i s t r i b u t e d lag Quarter at M o n g a l l a previous t o swamps q u a r t e r , 106 m 3 / d a y below 7 0 f r o m 7 0 to 119 t r o m 120 t o 159 160 a n d above
I
I
I
I
p' I
"0
I
20
60
40
80 Mongalla
F i g . 8.25.
270
r
!lo
-
-0
a
0
10
~
~
15
M o n g a l l a discharge u s e d tor d r a w i n g t h e curve Previous q u a r t e r Mean of 2 previous quarters Mean of 3 previous quarters Meanof 4 previous quarters
180
100 120 140 160 discharge, 106 m 3 / d a y
200
The r e l a t i o n between t h e d i s c h a r g e a t Mongalla and below t h e swamps
~
~
20
'
25
~
Annual
"
30
~
flow
~
35 at
~
40
~
~
45
Mongalla,
"
50
"
~
55
~
~
60
~
~
~
~
~
~
m l r d m?
F i g . 8.26. The r e l a t i o n between t h e a n n u a l flow volume a t Mongalla and t h e P p e r c e n t a g e water l o s t i n t h e swamps The long-term mean of VM h a s been e s t i m a t e d a t 29.1 x lo9 m 3 / y r
(see section
8.5.1). Eq. 8.5 g i v e s a l o s s of 49.1% f o r t h i s v a l u e , o r a b o u t 14.3 x lo9 m3/yr. I n o t h e r w o r d s , from an a n n u a l volume of 29.1 m i l l i a r d m3 a t Mongalla, o n l y 14.8 m i l l i a r d m 3 r e a c h t h e White N i l e and t h e rest i s l o s t . These d i s c h a r g e v a l u e s a r e i n p e r f e c t agreement w i t h t h e 29 and t h e 1 4 . 7 m3/yr a t Mongalla and Malakal respectively,
for t h e p e r i o d 1905-66, as g i v e n i n t h e P h a s e I - J o n g l e i P r o j e c t
Report ( J o n g l e i Area E x e c u t i v e Organ f o r Development P r o j e c t s , 1975).
~
'
~
36 3
One c a n t h e r e f o r e p r o c e e d w i t h t h e c a l c u l a t i o n u s i n g t h e s e f i g u r e s c o n f i d e n t l y . The a n n u a l loss e x p r e s s e d as d e p t h o v e r t h e swamp area i s 1 7 2 3 mm/yr. The a n n u a l r a i n f a l l s t i l l h a s t o b e added, so as t o o b t a i n t h e t o t a l loss.
The t h i r t y - y e a r
mean r a i n f a l l i s 868 mm a t Tonga, s t a t i o n 1 1 9 ; 1076 mm a t
Fangak, s t a t i o n 1 2 1 ; 795 mm a t Ghabet Shambe, s t a t i o n 1 3 0 ; 9 0 3 mm a t B o r , stat i o n 133 and 905 mm a t T e r r a k e k k a , s t a t i o n 135 ( s e e Appendix C ) . The mean o f t h e s e f i v e s t a t i o n s , which i s 909 mm/yr, b r i n g s t h e t o t a l d e p t h o f water l o s t i n t h e swamps up t o 2632 mm/yr or 7 . 2 mm/day.
The d e p t h s g i v e n by H u r s t i n Vol. V
of t h e N i l e B a s i n are 2300, 2360 a n d 2400 mm/yr f o r t h e p e r i o d s 1927-31, 1927-37 and 1932-37 r e s p e c t i v e l y ( H u r s t , H . E . ,
P . , 1 9 3 8 ) . The a v e r a g e of
and
t h e s e t h r e e f i g u r e s i s 2353 mm/yr or 6 . 5 mm, which is 10% less t h a n o u r e s t i m a t e . Both 7 . 2 mm/day o r 6 . 5 mm/day as l o s s o f w a t e r from t h e Bahr e l - J e b e l
swamp a r e
s i g n i f i c a n t l y l a r g e r t h a n t h e l o s s e s t i m a t e d from any o f t h e O l i v i e r , T h o r n t h w a i t e , Penman o r t h e e n e r g y - b a l a n c e methods ( s e e C h a p t e r 5). I f w e keep t h e 5 mm l o s s p e r day and t h e 8300 km2 area o f t h e swamp, t h e a n n u a l loss s h o u l d t h e r e f o r e h e (365 x 5
- 910) x
m l r d m 3 less t h a n t h e 1 4 . 3 x
x 8300 x
lo9
lo6
= 7.6 x
lo9
m 3 , which i s 6 . 7
m3 a l r e a d y g i v e n . T h i s d i f f e r e n c e c a n b e a t t r i -
b u t e d t o t h e i n a c c u r a c y i n t h e d i s c h a r g e measurement, some c h a n n e l s w i t h o u t h a v i n g i t measured,
t h e e s c a p e of w a t e r i n t o
and most i m p o r t a n t o f a l l , t h e inunda-
t i o n o f t h e temporary swamps. The d j v i s i o n of t h e f l o w between t h e Bahr el J e b e l a n d t h e Bahr e l Z e r a f c a n b e s e e n from t h e f o l l o w i n g example: P e r i o d : from 1927 t o 1931 Bahr e l - J e b e l
u p s t r e a m t h e c u t s = 11140 x
C u t 1 a t head = 2490 x
lo6
lo6
m3/yr
m3/yr r e d u c e d t o 2370 x
Upper Z e r a f j u s t above t a i l o f c u t 1 = 1050 x
lo6
Cut 2 a t head = 805 x lo6 m 3 / y r r e d u c e d t o 797 x Z e r a f below c u t 2 = 4490 x J e b e l below c u t 2 = 7440 x
lo6 lo6
m3/yr ( g a i n = 2 7 3 m3/yr ( l o s s = 405
lo6
m3/yr a t t a i l
m3/yr
lo6 m3/yr a t x lo6 m3/vr) x lo6 m3/yr)
tail
T h i s d i v i s i o n o f t h e flow c a n b e s e e n from t h e map i n F i g . 8 . 2 7 . The proport i o n of t h e f l o w i n t o t h e Bahr e l Z e r a f t o t h a t i n t h e Bahr e l J e b e l i s v a r i a b l e , d e p e n d i n g m o s t l y on t h e l e v e l o f water i n t h e swamp. On a v e r a g e , t h e flow i s divided such t h a t two-thirds
o f i t f i n d s i t s way i n t o t h e Bahr e l J e b e l and t h e
r e m a i n i n g o n e - t h i r d i n t o t h e Bahr e l Z e r a f .
36 4
Fig. 8.27. Map showing t h e d i v i s i o n o f t h e flow between t h e Bahr e l J e b e l and t h e Bahr e l - Z e r a f
8.6
THE BAHR EL-GHAZAL BASIN The Bahr e l - G h a z a l B a s i n i s s i t u a t e d w e s t o f t h e Bahr e l J e b e l B a s i n and
e x t e n d s t o t h e d i v i d e Congo-Nile.
The s u r f a c e a r e a above t h e swamps and i n c l u d -
i n g t h e s u b - b a s i n s of t h e w e s t e r n t r i b u t a r i e s of t h e Bahr e l J e b e l below Mongalla i s 528 000 km2. The b a s i c p a r t i c u l a r s p o i n t t o an a n n u a l r u n - o f f t h i s a r e a o f 1 8 . 4 mlrd m 3 ( 1 . 1 m/yr r a i n f a l l and 3.2% r u n - o f f
from
coefficient).
N e g l e c t i n g t h o s e t r i b u t a r i e s which d i s c h a r g e t h e i r water i n t o t h e Bahr e l J e b e l , t h e a n n u a l flow e n t e r i n g t h e swamps h a s been e s t i m a t e d a t 1 6 . 0 mlrd m3. Ahmed gave t h e f o l l o w i n g d i s c h a r g e v a l u e s (Ahmed, A . A . , R i v e r Lo1 ( a t Nyamlel) R i v e r Punjo ( a t Aluk)
4000 x 500
lo6
m3/yr
x lo6 m3/yr
R i v e r Jur ( a t Wau)
5000 x
lo6 lo6 x lo6
m3/yr
River Tonj ( a t Tonj)
1500 x
m3/yr
lo6
m3/yr
R i v e r G e l ( a t Chui B e t )
550
R i v e r N a a m ( a t Mvolo)
520 x
R i v e r Y e i ( a t Monderi)
m3/yr
2000 x 106 m3/yr 14070 x
lo6
m3/yr
1960):
365
H u r s t and h i s co-workers
h a v e shown t h a t t h e a v e r a g e flow a t Wau on t h e R i v e r Of t h i s amount, 1117 x 106m3
J u r f o r t h e p e r i o d 1928-1935 was 5929 x lo6 m3/yr. p e r y e a r r e a c h e d Ghabat el-Arab t h e Bahr e l - G h a z a l
lo6
a n d f i n a l l y 656 x
m3/yr r e a c h e d t h e mouthof
a t Lake N o . F i g . 8.28. i s a map showing t h e r i v e r s and t h e
l o c a t i o n of t h e g a u g i n g p o i n t s mentioned h e r e .
28'
E
I
F i g . 8.28.
30 ' I
32' I
The swamps o f t h e Bahr e l - G h a z a l B a s i n
The 14.07 m i l l i a r d m 3 / y r f l o w i n t o t h e swamps and o n l y 0.6 m i l l i a r d m3/yr r e a c h t h e mouth a t L a k e P o . The 80 k i l o m e t r e r e a c h from Meshra e r Req t o Ghabat el-Arab
h a s a s l o p e o f 1 cm/km.
r e a c h from Ghabat el-Arab
T h i s s l o p e i n c r e a s e s t o 2.2 cm/km f o r t h e 54 km
t o Yondi. But from Yondi t o Lake No, a d i s t a n c e of
76 km, t h e swamp h a s no s l o p e a t a l l . T h i s t o o - l i t t l e s l o p e does n o t produce any r u n - o f f ,
so w a t e r s p r e a d s on t h e swamps and i s l e f t t o b e e v a p o t r a n s p i r e d .
The t o t a l loss i n t h e swamps of t h e Bahr e l - G h a z a l is (14.1
-
0.6) x
lo9 +
(0.95 x 14.5) x lo9 = 26.8 x lo9 m3/yr. The a n n u a l r a i n f a l l on t h e swamps i s t a k e n a s 950 mm/yr
( s e e F i g s . 4.3.-4.5.). The t o t a l l o s s when d i v i d e d by 14 500
km2 g i v e s a d e p t h of water of a b o u t 1880 mm/yr, or 5.15 mm/day. T h i s f i g u r e
366
r e p r e s e n t s t h e r a t e of e v a p o t r a n s p i r a t i o n from a swamp, as a l r e a d y d i s c u s s e d i n C h a p t e r 6 and i n t h e p r e v i o u s s e c t i o n , i n c o n n e c t i o n w i t h t h e Bahr e l J e b e l swamps. The d i s c h a r g e o f t h e Bahr e l Ghazal a t i t s mouth a t Lake No h a s b e e n m e a s u r e d r e g u l a r l y s i n c e 1923. The g a u g e - d i s c h a r g e measurements of t h e Bahr e l Ghazal and t r i b u t a r i e s n e a r Lake No a r e shown g r a p h i c a l l y i n F i g . 18, Appendix E . The mean a n n u a l volume of f l o w is c l o s e t o 650 m i l l i o n m 3 .
T h i s volume is
d i s t r i b u t e d o v e r t h e months o f t h e y e a r , as shown i n F i g . 8 . 2 9 .
I n t h e same
f i g u r e t h e water l e v e l i n Lake No i s shown. T h i s w a t e r l e v e l , l i k e t h e o t h e r l a k e s d i s c u s s e d i n t h e p r e v i o u s s e c t i o n s , undergoes a s e a s o n a l f l u c t u a t i o n and c a n b e d e s c r i b e d by e q . 8 . 4 ' . The mean l e v e l c a n b e t a k e n a t 1 3 . 6 8 metres o n t h e gauge. The harmonic c o e f f i c i e n t s A1 t h r u ' 6 are 2 1 . 8 7 , - 0 . 2 5 ,
0 . 3 3 , -0.58,
and 0 . 2 5 , r e s p e c t i v e l y and t h e c o e f f i c i e n t s B1 t h r u ' 6 are - 1 6 . 9 5 ,
-0.17,
0.40 -0.42,
0 . 2 2 , 0 . 1 2 a n d z e r o , r e s p e c t i v e l y . The c o e f f i c i e n t s A1 and B1 d e s c r i b i n g t h e f i r s t harmonic (12-month c y c l e ) e x p l a i n a l m o s t 99% of t h e t o t a l v a r i a n c e o f t h e monthly l e v e l s a b o u t t h e mean.
E
I " " ' " " '
14.00
/
$
3.80
Mean 13.68
3.60 m
3.40
€ 4
,'
Lo
0 3
.---._ --____--_ -./
B a h r e l G h a z a l a t mouth
2
(51
0
0*0*
4'
J
F
M
A
M
J J Month
A
S
O
N
D
Fig. 8.29. The d i s c h a r g e hydrograph o f t h e Bahr e l - G h a z a l a t mouth a n d t h e w a t e r l e v e l i n Lake No THE WHITE N I L E BASIN
8.7 8.7.1
6
The White N i l e from Lake No t o t h e mouth of t h e S o b a t
I n t h e r e a c h from Lake No t o t h e mouth o f t h e S o b a t t h e White N i l e h a s a
small s l o p e and i t s c o u r s e i s f r i n g e d w i t h swamps. A number of t r i b u t a r i e s p o u r t h e i r w a t e r i n t o t h e White N i l e i n t h e s a i d r e a c h . These t r i b u t a r i e s are shown s c h e m a t i c a l l y i n F i g . 8 . 3 0 . The g a i n s and l o s s e s i n t h e s t r e t c h from Lake N o t o t h e Abu-Tong c u t have been c a l c u l a t e d f o r a number of y e a r s and t h e n e t l o s s was found a t 0 . 4 m i l l i o n m3/day.
36 7
-
Khor Lolle
123 k r n . b E ,
- - - - t--
L a k e No Bahr el G h a z a l n 14 km.
0
N
I
0, L
.c m
F J. 8 . 3 0 . t h e Sobat
The t r b u t a r i e s of t h e Whi
B Ni
?tween L; .e No and 1 e mouth of
The a v e r a g e l o s s i n m i l l i o n m3/day for t h e months from J a n u a r y t o December
is: -1.2,
-0.4,
0.3, 0.3, 0.7,
1.3, 2 . 0 ,
1.3, 0 . 5 , -0.4,
0.6 and - 0 . 1 ,
respec-
t i v e l y . H u r s t r e p o r t e d t h a t t h e l o s s i n t h i s s t r e t c h of t h e r i v e r s h o u l d be i n c r e a s e d by a minimum amount o f 0 . 5 m i l l i o n m3/day t o a l l o w f o r t h e c o n t r i b u t i o n s o f t h e Khors ( H u r s t , H.E., and P h i l i p s ,
P . , 1 9 3 8 ) . The l o s s i n t h e 5 0 km
s t r e t c h from Abu-Tong c u t t o t h e mouth of t h e S o b a t was e s t i m a t e d a t 1.5 million m3/day. The t o t a l n e t l o s s from t h e r e a c h e x t e n d i n g from Lake No t o t h e mouth of t h e Sobat is 2.4 x
lo6
m3/day o r 875 x lo6 m3/yr or a b o u t 35% more t h a n t h e
i n f l o w o f t h e Ghazal i n t o Lake No. The a n n u a l r a i n f a l l h e r e c a n be t a k e n a s t h e mean o f t h e r a i n f a l l a t M a l a k a l , S t a t i o n 118, Tonga, S t a t i o n 1 1 9 , and a t M e s h r a ' e r Req, S t a t i o n 125. The l o n g - t e r m means a t t h e s e s t a t i o n s a r e 819, 868 and 830 mm/yr,
r e s p e c t i v e l y , and t h e o v e r a l l mean i s 840 mm/yr.
t r a n s p i r a t i o n i n t h i s s t r e t c h is 1650 mm/yr or 4 . 5 mm/day,
Since theevapo-
t h e n e t l o s s must b e
810 mm/yr or 2 . 2 2 mm/day. From t h e s e f i g u r e s t h e s i z e o f t h e w e t a r e a fromwhich t h e n e t loss t a k e s p l a c e must b e a b o u t 875 t 0 . 8 1 o r 1080 km2. T h i s l o s s b r i n g s t h e 1 4 . 7 mlrd m3 f l o w i n g i n t h e Bahr e l J e b e l and e l - Z e r a f
i n a normal y e a r t o
1 4 . 4 5 mlrd m 3 j u s t above t h e mouth o f t h e S o b a t . The r e p o r t on P h a s e I of t h e J o n g l e i P r o j e c t g i v e s t h e sum o f t h e d i s c h a r g e s of t h e J e b s l and Zeraf a s 14.74 mlrd m3/yr a t Malakal f o r t h e p e r i o d 1905-1965.
w a s 33.0 x
lo9
The maximum d u r i n g t h i s p e r i o d
m3/yr and i t t o o k p l a c e i n 1964. The minimum was 1 0 . 3 x
i n 1922. The s t a t i s t i c $
lo9 m3Ar
t e s t i n g of t h i s s e t o f d a t a shows t h a t t h e s t a n d a r d
d e v i a t i o n i s 3.356 mlrd m 3 / y r
and t h e skewness i s 3 . 3 2 4 . F u r t h e r m o r e , t h e s e d a t a
a p p e a r t o b e s t r o n g l y c o r r e l a t e d . The r e s i d u a l s o f t h e f i r s t - o r d e r
autoregres-
s i v e model, A R I , do n o t , however, a p p e a r t o b e s i g n i f i c a n t l y d e p e n d e n t a t t h e 95% l e v e l of c o n f i d e n c e .
The s e r i a l c o r r e l a t i o n c o e f f i c i e n t s of t h e o r i g i n a l and
of t h e r e s i d u a l s e r i e s f o r t h e f i r s t 15 l a g s a r e a s f o l l o w s :
36 8
Lag No.
8.7.2
S e r i a l c o r r e l a t i o n of original series
residual series
0.7303 0.3512 0,0997 -0.0237 -0.0394 -0.0282 -0.0034 0.0223
0.1985 0.1165 -0.0902 -0.0808 -0.0261 -0.0442 -0.0037 0.0282
S e r i a l c o r r e l a t i o n of
Lag. No.
original
residual
0.0301 0.0088 -0.0365 -0.0463 -0.0335 0.0570 0.1291
0.0574 0.0501 -0.0337 -0.0184 -0.1290 0.0525 0.1342
series
9 10
11 12
13 14 15
series
The White Nile A t Malakal
The flow a t El-Malakal
on t h e White N i l e i s produced by t h e flows i n t h e B a h r
e l J e b e l , e l - Z e r a f , el-Ghazal and by t h e Sobat and its t r i b u t a r i e s . The hydrology of a l l t h e s e s t r e a d l s , except t h e Sobat and i t s t r i b u t a r i e s , h a s been p r e s e n t e d i n t h e p r e v i o u s s e c t i o n s . One needs, however, t o i n v e s t i g a t e t h e hydrology of t h e Sobat b e f o r e drawing any complete p i c t u r e of t h e flow a t Malakal. 8.7.2.1
The hydrology of t h e Sobat and i t s t r i b u t a r i e s
T h i s was d e s c r i b e d i n Vol. VIII of t h e N i l e B a s i n . I n Vol. X of t h e N i l e Basin one a l s o f i n d s a d d i t i o n a l i n f o r m a t i o n about t h e Machar swamps. The Sobat
is formed by two s t r e a m s : t h e Bar0 and t h e P i b o r . 8.7.2.1.1
The hydrology of t h e Baro
The Baro s p r i n g s from t h e E t h i o p i a n P l a t e a u and flows from e a s t t o w e s t . The s u r f a c e a r e a of i t s b a s i n i s 41400 k m 2 ,
of which 23500 k m 2 a r e c o n s i d e r e d moun-
t a i n o u s and t h e r e s t is a low-elevated c o u n t r y . A good d e a l of t h i s b a s i n l i e s above 1500 m and p o r t i o n s a r e above 2000 m .
In t h e mountainous p a r t , t h e annual
r a i n f a l l is a t , or more t h a n , 1500 mm, a t Gambeila (between 500 m and 1000 m a.m.s.1.)
t h e r a i n f a l l i s about 1290 m m / y r
and i n t h e p l a i n ( S t a t i o n 123 a t
Nasser, S t a t i o n 127 a t Akobo Post and S t a t i o n 132 a t P i b o r P o s t ) i t drops t o 880 mm/yr.
The e v a p o r a t i o n v a r i e s from s l i g h t l y less than 4 . 0 mm/day t o more
than 5 mm/day, depending on t h e l o c a t i o n .
r"
In t h e p l a i n t h e Baro i s j o i n e d by a few streams coming from t h e P l a t e a u . The
m o s t important of t h e s e s t r e a m s a r e t h e Khor Jokau, t h e River Adura, t h e Khor Mokwai "2" and t h e Khor Machar. These streams a r e shown on t h e map, F i g . 2 . 1 5 . , and t h e i r l o c a t i o n s measured from t h e Baro-Pibor
j u n c t i o n can be s e e n from t h e
schematic drawing, F i g . 8 . 3 1 . T h i s f i g u r e a l s o shows t h e inflow-outflow c y c l e of t h e main r i v e r and i t s t r i b u t a r i e s , a s e s t i m a t e d f o r a normal y e a r (June November).
-
1.3
0
11 1.1
m
A l l discharges given here a r e m e a n s for the period 1942 - 1956, they are in mlrd m3/yr.
Fig. 8.31.
The inflow-outflow c h a r t of t h e River Bar0 and i t s t r i b u t a r i e s
The d a t a p u b l i s h e d i n t h e N i l e B a s i n , Vol. X, g i v e a mean flow volume of 11.6 x
lo9
m3/yr
f o r t h e p e r i o d 1928-56 and of 11.5 x
1942-56 ( H u r s t , H . E . , t o an annual run-off
Black, R . P . ,
lo9
m3/yr f o r t h e p e r i o d
and Simaika, Y.M., 1966). E i t h e r f i g u r e l e a d s
c o e f f i c i e n t f o r t h e mountainous p a r t of t h e b a s i n of about
35% ( a r e a = 23500 km2, annual p r e c i p i t a t i o n of 1400 mm). The s u r f a c e a r e a of t h e Bar0 Basin down Gambeila i s about 18000 km2. I t r e c e i v e s an annual r a i n depth o f , s a y , 1 . 0 5 m , on a v e r a g e . Consider an annual run-off
c o e f f i c i e n t of 14%. a a f i g u r e t h a t was found f o r some p a r t s of t h e
b a s i n . The B a r 0 s h o u l d t h e n r e c e i v e an a d d i t i o n a l flow of 2 . 6 x
lo9
m3/yr a t i t s
mouth. Accordingly, one s h o u l d e x p e c t an annual flow volume of about 14 m l r d m3/yr a t t h e mouth of t h e Baro. I n s t e a d , a volume of 7.6 mlrd m3/yr was found a s a long-term mean. The l o s s from Gambeila t o t h e Baro-Pibor t a k i n g account of a l l t h e run-off 11.5
-
7.6 = 3.9 mlrd m 3 / y r ,
j u n c t i o n , without
t h a t should be d i s c h a r g e d i n t o t h e Baro, was
4 . 0 mlrd m 3 / y r and 4 . 1 m3/yr f o r t h e p e r i o d s 1942-
56, 1929-62 and 1929-57, r e s p e c t i v e l y . The 4 mlrd m3/yr
r e p r e s e n t i n g t h e aver-
age l o s s between Gambeila and t h e Baro-Pibor j u n c t i o n a r e d i s t r i b u t e d such t h a t
1.5 mlrd m3 i s l o s t be-een
Gambeila and t h e head of t h e Adura, 1 . 5 mlrd m3
between t h e head and t h e t a i l of t h e Adura and almost 1 . 0 mlrd m 3 between t h e t a i l of t h e Adura and t h e mouth of t h e Baro. The d r a i n a g e b a s i n of t h e River Bar0 i s c h a r a c t e r i z e d by t h e l o s s of n o t l e s s t h a n 35% of i t s annual y i e l d , due t o s p i l l a g e o v e r t h e p l a i n and a l s o t h e feedi n g of t h e Khors, which flow through t h e Machar swamps. The a r e a of t h e s e swamps has been e s t i m a t e d a t 6700 km2 ( H u r s t , H . E . , 1966).
Black, R.P.,
and Simaika, Y.M.,
370
The average outflow through t h e Khor Machar, which i s 0 . 9 mlrd m3/year, flows through t h e swamps and i s l o s t t h e r e . Other l o s s e s on t h e B a r 0 a r e mainly due t o s p i l l a g e o v e r its banks. I n a d d i t i o n t o t h e s e f a c t s , one h a s t o mention t h a t t h e Machar swamps do n o t c o n t a i n any l a k e s o r lagoons t o s t o r e t h e s p i l l e d w a t e r and thereupon t o l e t p a r t of i t r e t u r n t o t h e main stream i n t h e dry s e a s o n , a s i n t h e c a s e of t h e J e b e l swamps. T h i s s t a t e of a f f a i r s has r e s u l t e d i n an almost uniform s t a g e hydrograph which r e p e a t s i t s e l f r e g u l a r l y each y e a r , whether t h e f l o o d i s moderate o r r i c h . The s t a g e hydrograph of t h e Baro a t Gambeila f o r t h e p e r i o d 1929-1933 i s shown i n F i g . 8 . 3 2 ( H u r s t , H.E., 8 . 4 ' w i t h a mean l e v e l X ficients A
1
1950). To t h e s e hydrographs one may f i t t h e e q u a t i o n
= 11.034 metres on t h e l o c a l gauge. The harmonic coef-
t h r u ' A6 a r e : -0.5720,
and t h e c o e f f i c i e n t s B1 t h r u ' B
-0.4125,
-0.1567,
a r e : -1.946,
0.1733, 0.0508 and 0.0217
0.2007, 0.2500, 0.1913, -0.0710
and z e r o , r e s p e c t i v e l y . The f i t t e d hydrographs a r e a l s o shown i n F i g . 8.32.
8.7.2.1.2
The Machar Swamps
The i n f l o w t o t h e Machar swamps i s s u p p l i e d from t h r e e s o u r c e s . The f i r s t s o u r c e i s t h e d i r e c t r a i n f a l l , which, on a v e r a g e , amounts t o 0 . 9 m/yr.
Consider-
i n g t h e a r e a covered by t h e swamps a s 6700 km2, t h e t o t a l volume of r a i n comes
to 6 . 0 3 mlrd m3/yr. The second s o u r c e i s t h e run-off
from t h e e a s t e r n t r i b u t a r i e s
coming from t h e E t h i o p i a n f o o t h i l l s . These t r i b u t a r i e s a r e t h e Khor Ahmar, Tombak, Yabus, Daga and Lau and t h e a r e a s of t h e i r b a s i n s a r e 600, 900, 4300, 2900 and 1600 km2, r e s p e c t i v e l y . C o n s i d e r i n g an annual run-off 14% and an annual r a i n f a l l depth of 1 . 0 m, t h e annual run-off
m3/yr
(Hurst, H . E . ,
B l a c k , R.P.,
and Simaika, Y . M . ,
c o e f f i c i e n t of r e a c h e s 1 . 4 4 mlrd
1966). The t h i r d s o u r c e of
inflow t o t h e swamps is t h e s p i l l i n g of t h e Baro. T h i s h a s a l r e a d y been mentioned i n t h e p r e v i o u s s e c t i o n and found t o b e , on a v e r a g e , 4 mlrd m 3 / y r . two-thirds
+
1.44
+
Assuming t h a t
of t h i s volume r e a c h e s t h e swamps, t h e t o t a l i n f l o w amounts t o ( 6 . 0 3
2.67) x 1 0 9 ' 0 r 10.14mlrd
m3/yr.
T h i s amount d i s a p p e a r s t o t a l l y by eva-
p o t r a n s p i r a t i o n i n t h e swamps. Assuming t h i s i s a l l c o r r e c t , t h e e v a p o t r a n s p i r a t i o n from t h e Machar swamps should be i n t h e o r d e r of 1515 mm/yr,
o r 4.15 mm/day.
f-
The same f i g u r e has been given w h i l e d i s c u s s i n g t h e e v a p o r a t i o n from t h e Sobat Basin (Chapter 5 ) . P r e v e n t i n g o r minimizing t h e b s s of water from t h e b a s i n of t h e Bar0 was d i s cussed i n some of t h e N i l e Basin volumes, e s p e c i a l l y Vol. X. An account of t h e water c o n s e r v a t i o n schemes i n t h i s r i v e r b a s i n s h a l l be p r e s e n t e d i n t h e next chapter.
n
z
0 m
Q
I: LL 7
n Z
0 m Q
m
7c-4
-E I:
Q
I LL 7
0
z
0
m Q
m
7.-
7 m
m
I
m
m N
m
c,
W
c,
c 0
w rn
a
c
k
M k
a
cR
I-
M
a
c, rn
W
Q
7
I
LL
Z 0
w .rl
m
n
Q
5
0
2 -
-.a
8
m
2
E
c
0)
f2
rn
W
$
P
4
a
W
c, c,
7 0 7
a
I LL
7
n Z 0 m
Q
-
7s ' I
Q
I: LL
7
371
372
8.7.2.1.3
The h y d r o l o g y o f t h e P i b o r
The main stream o f t h e P i b o r f l o w s from s o u t h t o n o r t h , whereas s e v e r a l o f
i t s t r i b u t a r i e s rise i n t h e mountains o f E t h i o p i a . The b a s i n of t h e P i b o r and i t s t r i b u t a r i e s h a s an a r e a of 109 000 km2, i . e . , a b o u t 24 t i m e s t h e a r e a o f t h e B a r 0 Basin. N e v e r t h e l e s s , t h e c o n t r i b u t i o n of t h e P i b o r t o t h e flow i n t h e Sobat
i s much less t h a n t h a t o f t h e S o b a t . F i g . 8.33. i s t h e i n f l o w - o u t f l o w
c h a r t of t h e P i b o r a n d i t s t r i b u t a r i e s . The
d i s c h a r g e v a l u e s w r i t t e n on t h i s c h a r t a r e a b o u t t h e a v e r a g e f o r t h e 1929-1933 p e r i o d , a r a t h e r low-flow p e r i o d . According t o H u r s t and h i s co-workers,
the
2.84 m l r d m3/yr s h o u l d b e i n c r e a s e d up t o , s a y , 3 . 1 m l r d m3/yr due t o t h e uncert a i n t i e s i n some o f t h e measurements ( H u r s t , H . E . ,
1 9 5 0 ) . The a n n u a l r a i n f a l l a t
Akobo P o s t , s t a t i o n 1 2 7 , was 940 mm and a t P i b o r P o s t , s t a t i o n 1 3 2 , 909 mm, b o t h means o f t h e p e r i o d 1938-1967
( s e e Chapter 4 ) . I f w e c o n s i d e r 0.925 m a s t h e
average r a i n f a l l , t h e annual run-off
c o e f f i c i e n t must t h e n b e i n t h e o r d e r O f % ,
a very low f i g u r e i n d e e d .
.-c
0
n
&
-Y
Q PI
2
0
5 0
Q
L
L
18km.
a8
53km. 0.14 0
7km.
C
PI
>
U
0
I
aJ
>
0
L
z
b
0
c r
.c
I:
Y
i
Y
All d i s c h a r g e s g i v e n h e r e o r e m e a n s for t h e p e r i o d 1929 - 1933, they a r e in mlrd m3/yr.
i
H u r s t a l s o gave an e s t i m a t e o f t h e g r o s s volume of flow from P i b o r Port to t h e mouth on t h e S o b a t , a d i s t a n c e of 312 km, a t 3 . 6 mlrd m 3 / y r
and t h e n e t a t
3.1, a s a l r e a d y m e n t i o n e d . T h i s means t h a t t h e loss i s a b o u t 0 . 5 mlrd m 3 / y r ,
or
a b o u t 14% o f t h e g r o s s f l o w .
8.7.2.1.4
The S o b a t below t h e Pibor-Baro
Below t h e Pibor-Baro
Junction
j u n c t i o n , t h e main stream i s known a s t h e S o b a t . I t
f l o w s a d i s t a n c e o f a b o u t 350 km i n a n o r t h - w e s t e r l y
direction before it joins
373
t h e White N i l e . The S o b a t below t h e j u n c t i o n h a s a s u b - b a s i n of a b o u t 36 800 km2 i n a r e a , which b r i n g s t h e t o t a l d r a i n a g e b a s i n area t o 187 200 km2. The S o b a t h a s a n a v e r a g e s l o p e of 3 cm/km i n t h e low-flow i n t h e high-flow
s e a s o n and 4 cm/km
s e a s o n . The main t r i b u t a r i e s a r e t h e Khor F u l l u s , Nyading,
Twalor a n d Wakau. They j o i n t h e main r i v e r a t d i s t a n c e s o f 1 6 , 239, 290 and 307 km from t h e mouth, r e s p e c t i v e l y . I n a normal y e a r t h e S o b a t a t a head c a r r i e s 1 2 . 4 mlrd m3/yr.
Of t h i s amount, 3 . 1 m l r d m3 are s u p p l i e d by t h e P i b o r and t h e
rest by t h e Bar0 ( s e e s e c t i o n 8 . 7 . 2 . 1 . 3 ) .
The a v e r a g e r a i n f a l l on t h e S o b a t sub-
b a s i n c a n b e t a k e n a s 780 mm/yr. T h i s f i g u r e is t h e a v e r a g e of t h e a n n u a l r a i n d e p t h s a t Kodok, s t a t i o n 1 1 7 , M a l a k a l , s t a t i o n 118, Abwong, s t a t i o n 1 2 0 , and
Nasser, s t a t i o n 123. F o r t h e s e s t a t i o n s i n t h e i r o r d e r , t h e mean r a i n f a l l f o r t h e p e r i o d 1938-1967 w a s 738, 8 1 9 , 7 6 3 and 894 mm/yr. c o e f f i c i e n t a t 4%, t h e run-off
Assuming t h e a n n u a l r u n - o f f
s h o u l d t h e n b e 0 . 0 4 x 0 . 7 8 x 36.8 o r 1 . 1 5 mlrd m3
p e r y e a r . T h i s f i g u r e i s s l i g h t l y h i g h e r t h a n t h e 1.08 m l r d m3/yr r e p o r t e d i n Vol. V I I I of t h e N i l e B a s i n a s a mean f o r t h e p e r i o d 1934-1947 ( H u r s t , H . E . , 1 9 5 0 ) . The sum o f t h e f l o w a t t h e S o b a t h e a d and t h e r u n - o f f
i s 1 3 . 5 5 mlrd m3/yr.
Reducing t h i s amount by a b o u t 5% f o r t h e n e t conveyance l o s s , t h e amount t h a t f i n a l l y r e a c h e s t h e mouth on t h e White N i l e i s 1 2 . 9 mlrd m3/yr. The d i s c h a r g e s o f t h e S o b a t a t H i l l e t D o l e i b , 9 km above t h e mouth, have been measured s i n c e 1911. The d i s c h a r g e - g a u g e measurements f o r t h e r a t i n g c u r v e can b e s e e n from F i g . 1 9 , Appendix E. The a v e r a g e hydrograph a t H i l l e t D o l e i b c o r r e s ponding t o an a n n u a l volume o f 1 2 . 9 mlrd m3/yr i s shown i n F i g . 8 . 3 4 .
5
F
; m
20
0"
J
Fig. 8.34.
F
M
A
M
'
"
J J Month
A
I
S
"
O
'
N
D
'
The d i s c h a r g e hydrograph of t h e S o b a t a t H i l l e t D o l e i b , n e a r mouth
The r e l a t i o n between t h e d i s c h a r g e s measured a t t h e S o b a t mouth, i n f a c t a t
H i l l e t D o l e i b , Y, and t h e d i f f e r e n c e between t h e d i s c h a r g e a t Malakal less t h e d i s c h a r g e s of t h e Bahr e l G h a z a l , J e b e l and Zeraf as a t M a l a k a l , X, h a s been
374
examined f o r t h e p u r p o s e o f c h e c k i n g t h e c o n s i s t e n c y o f t h e r e s u l t s . The l i n e a r r e g r e s s i o n r e l a t i o n found i s
Y =
-
0.4255
-+ 0 . 9 8 2 7 X
(8.6)
w i t h a c o r r e l a t i o n c o e f f i c i e n t o f 0 . 9 6 1 9 . S i n c e t h e mean f l o w a t Malakal f o r t h e p e r i o d 1905-1966 was 2 8 . 8 2 mlrd m3/yr and t h e sum o f t h e J e b e l and Z e r a f w a s 14.74 mlrd m3/yr,
t h e mean of Y must b e 1408 m l r d m3/yr.
same p e r i o d , as o b t a i n e d from e q . 8 . 6 , h a s t o b e 14.76
The mean o f X o v e r t h e 1 . 8 4 o r i n t h e r a n g e of
between 1 6 . 6 0 a n d 1 2 . 9 2 mlrd m3/yr ( c o n f i d e n c e l e v e l = 9 5 % ) . T h i s r e s u l t shows t h a t t h e f i g u r e 2 9 . 2 m l r d m3/yr,
though on t h e low s i d e , y e t n e e d s n o t b e
rejected.
8.7.2.2
The d i s c h a r g e s a t Malakal
The monthly and a n n u a l d i s c h a r g e s o f t h e White N i l e a t Malakal f o r t h e p e r i o d 1912-73 are g i v e n i n T a b l e 7 , Appendix D ( C a i r o U n i v e r s i t y I n s t i t u t e of Technology,
-
Massachusetts
1 9 7 7 ) . The g a u g e - d i s c h a r g e measurements u s e d f o r p r e -
p a r i n g t h e r a t i n g c u r v e o f t h e White N i l e a t Malakal are shown i n F i g . 2 0 , Appendix E . The a n n u a l f l o w volume a t Malakal i n t h e p e r i o d i n v e s t i g a t e d showed two maxima; t h e e a r l i e r one took p l a c e i n 1918 and w a s s h a r p , and t h e s e c o n d i n 1964 and w a s b r o a d e r . The two f l o w volumes i n t h e i r o r d e r o f o c c u r r e n c e were 44.35 and 4 8 . 6 4 mlrd m 3 / y r
respectively.
Each o f them i s a l m o s t 80% of t h e r e c o r d e d
maximum a t Mongalla on t h e Bahr e l - d e b e l
(see section 8.5.1.2).
The l o w e s t mini-
mum o b s e r v e d a t Malakal w a s 23.32 m l r d m3/yr a n d i t t o o k p l a c e i n 1940. T h i s i s s l i g h t l y less t h a n t h e minima which w e r e o b s e r v e d i n 1 9 1 3 , 1922 and 1950 and t h e i r v a l u e s w e r e 2 3 . 8 3 , 23.59 and 2 3 . 7 5 mlrd m3/yr.
The a v e r a g e of t h e s e f o u r
minima i s s l i g h t l y more t h a n 1 . 5 t i m e s t h e minimum a t Mongalla on t h e Bahr e l J e b e l . The mean f l o w volume a t M a l a k a l , b e i n g 2 9 . 4 4 mlrd m3/yr,
is a b o u t 6% less
t h a n t h e mean f l o w volume a t N o n g a l l a f o r t h e same p e r i o d 1912-1973.
These f i g -
u r e s show t h e i n t e r a c t i o n between t h e c o n t r i b u t i o n s o f t h e B a h r e l - G h a z a l ,
Jebel
and Zeraf on one hand and t h e c o n t r i b u t i o n s of t h e B a r o , P i b o r and t h e S o b a t on r t h e o t h e r . Of s p e c i a l i n t e r e s t is t h a t t h e mean a n n u a l f l o w a t Malakal is s l i g h t l y less t h a n t h e mean a n n u a l f l o w a t Mongalla. T h i s r e s u l t means t h a t t h e g a i n from t h e 750 000 km2, which c o m p r i s e t h e s u b - b a s i n s o f t h e G h a z a l , J e b e l , Z e r a f , B a r o , P i b o r and t h e S o b a t , a l l downstream o f Mongalla, a r e a few p e r c e n t
less t h a n t h e l o s s which t a k e s p l a c e i n t h e swamps and t h e l o w - l y i n g a r e a s . An i m p o r t a n t f e a t u r e i n t h e a n n u a l f l o w series a t Malakal is t h a t t h e r a t i o o f t h e maximum t o t h e minimum is a b o u t 2 : l ( s e e F i g . 8 . 3 5 ) , whereas t h i s r a t i o , e x c e p t f o r Mongalla, i s a b o u t 4 : l ( s e e F i g . 8 . 2 1 ) .
375
Fig. 8.35. G r a p h i c a l p l o t o f t h e a n n u a l d i s c h a r g e s e r i e s of Malakal i n t h e p e r i o d 1912-1973
The s t a t i s t i c a l p r o p e r t i e s of t h e 12-monthly series and o f t h e a n n u a l s e r i e s have been examined and t h e r e s u l t s p r e s e n t e d i n T a b l e 8 . 1 2 . These r e s u l t s show t h a t t h e monthly d i s c h a r g e s e r i e s , e x c e p t t h a t o f March, c o n t a i n a r a t h e r s t r o n g s e r i a l c o r r e l a t i o n between t h e i r e l e m e n t s ; t h e s e r i a l c o r r e l a t i o n i n t h e a n n u a l
series i s even s t r o n g e r . The c o r r e l a t i o n c o e f f i c i e n t which i s s i g n i f i c a n t l y d i f f e r e n t from t h e z e r o , a t a c o n f i d e n c e l e v e l of 95%, i s l i m i t e d h e r e t o l a g 2 o r 3. I t h a s been f o u n d , however, t h a t one c a n remove a good d e a l of t h e dependence from any of t h e s e r i e s by f i t t i n g a l i n e a r a u t o r e g r e s s i v e model t o i t . The r e s i d u a l s l e f t a f t e r f i t t i n g t h e model have shown t h e y a r e u n c o r r e l a t e d a t t h e same l e v e l o f s i g n i f i c a n c e . T h i s c a n b e s e e n from T a b l e 8.13. The o r d e r o f t h e model w e l l f i t t i n g t h e monthly series i s t h e f i r s t + , whereas t h e s e c o n d o r d e r
++
is a b e t t e r f i t t o t h e a n n u a l s e r i e s . I n t h i s r e s p e c t t h e d i s c h a r g e series of Malakal r e s e m b l e t h o s e o f Mongalla. The p r o b a b i l i t y d i s t r i b u t i o n f u n c t i o n of good f i t t o t h e monthly and a n n u a l
series of Malakal i s t h e P e a r s o n Type I11 o n l y . F i g . 8 . 3 6 . shows t h e f i t of t h i s d i s t r i b u t i o n f u n c t i o n t o t h e a n n u a l d i s c h a r g e s e r i e s . F o r t h i s s e r i e s and f o r t h e 12-monthly
o n e s , t h e 100 a n d t h e 200- y e a r d i s c h a r g e s computed by t h i s func-
tion are: Discharge, lo,j ,3 Jan. Feb. Mar. Apr. May 100-yr 200-yr
J u n e J u l y Aug. Sep. O c t . Nov. D e c .
Year
5563 4465 4914 2940 2723 2949 3514 4125 4763 5 5 3 3 5574 5699 49060 6094 5014 5652 3221 2910 3094 3684 4268 5082 2928 6009 6125 52660
+ Model p a r a m e t e r i s t h e f i r s t s e r i a l c o r r e l a t i o n c o e f f i c i e n t r l ( s e e T a b l e 8.12)
++ Model p a r a m e t e r s awe a
1
= 1 . 0 5 1 3 and a2 = -0.3499
The b a s i c s t a t i s t i c a l d e s c r i p t o r s and s e r i a l c o r r e l a t i o n c o e f f i c i e n t s of t h e monthly and annual d i s c h a r g e s of
TABLE 8 . 1 2
t h e White N i l e a t Malakal f o r t h e p e r i o d 1912-1973
Month of t h e y e a r
I tern
B a s i c s t a t i s t i ca 1 descriptor
i,
106 m 3
s, 106 m 3 C
CV
Jan.
Feb.
Mar.
Apr.
May
June
July
Aug.
Sep.
Oct.
Nov.
Dec.
Year
2446 9 39 0.3839 1.4868 5.7$71
1735 1704 732 786 0.4219 0.4614 2.2417 3.0920 8.6520 13.7243
1484 404 0.2723 2.0042 7.9193
1650 350 0.2120 1.1324 4.3800
2015 309 0.1525 1.0071 3.7999
2505 312 0.1246 1.3408 4.4741
2871 370 0.1287 1.5958 5.9292
3080 470 0.1525 1.9511 8.9434
3402 609 0.1789 1.7958 8.3041
3310 628 0.1898 2.0020 9.5429
3158 789 0.2500 1.3147 6.9154
29438 5671 0.1926 1.7325 5.9970
0.4934 0.2832 0.2296 v.0390 0.0285 0.1015 0.0720 0.1442 0.1305 0.0046 0.1468 0.0174 0.0642 0.0230 0.2570
0.6058 0.3385 0,2464 0.0321 0.0348 0.1166 0.1201 0.0989 0 .0794 0.0342 0.0861 0.0861 0.0708 0.0310 0.0980
0.2808 0.0966 0.0540 0 .0064 0.0058 0.0214 0.0459 0.0202 q.0186 0.0593 0.1119 9.1119 0.0856 6.0500 6.0851
0.6661 0.3905 0.2622 0.1548 0.2050 0.2133 0.2212 0.2071 0.1226 0.0445 .0600 0.0600 0.0987 0.0259 0.0725
0.6498 0.4005 0.2977 0.1755 0.1894 0.2395 0.2442 0.2261 0.1808 0 . 1317 0.0234 0.1392 0.1347 0.1629 0.0257
0.6193 0.3590 0.2877 0.0453 0.0215 0.1474 0.1696 0.1309 0.1534 0.1054 c.0536 0.1214 6.1616 6.1879 6.0702
0.7472 0.4872 0.3361 0.1710 0.1435 0.2142 0.2016 0.1338 0.0930 0.0398 4.0782 0.1368 0.1681 6.1571 6.0788
0.7649 0.5115 0.3029 0.2172 0.1778 0.1595 0.1470 0.1023 0.1014 0.0402 .0829 0.1822 0.2101 .1128 0.0145
0.6785 0.4623 0.2718 0.1660 0.1009 0.0773 0.0718 0.0473 6.0157 0.0440 .lo56 0.1655 0.1689 6.0399 0.0490
0.6987 0.5010 0.3794 0.2955 0.1624 0.0563 0.0237 0.0644 .0803 0.0763 1283 0.1330 0.1076 0.0233 0.0604
0.6708 0.4449 0.2809 0.0901 0.0620 0.0399 0.0271 0.0320 q.0441 0.0660 4.1279 1156 0.1237 6.0009 0.0721
0.5145 0.2916 0.2321 0.0450 0.0592 0.0986 0.0422 0 .OQ74 0.0378 0.0871 1721 0.0200 0.0494 0.0424 0.1849
0.8010 0.5162 0.3218 0.1675 0.1035 0.1257 0.1347 0.0997 0 .0268 0.0397 G.0957 0.1482 0.1324 6.0146 0.0826
Serial correlation coefficient rl r2
r3 r4 r5 r6 r7 r8 r9 r10 rll r12 '13 r14
r.
-
p
p
p
p
p q.
0.
G.
W
9
TABLE 8 . 1 3
S e r i a l c o r r e l a t i o n c o e f f i c i e n t s of t h e r e s i d u a l s l e f t from f i t t i n g a u t o r e g r e s s i v e models t o t h e d i s c h a r g e
series a t Malakal
Month 8 Year January February March April May June July August qeptember October November December Year
Serial correlation coefficients
-
2
rl
-
.018 -.025 .090 -.020 .011 .bo6
r3
,053 ,065 .009 .096 -.013 ,008 -.030 0 16 .016
-. l o 6 -.ill -.124 -.134
.006
,189 .153 .026 .015 .062 .238 -.071 -.140 .053 .009 .076 .162
.019
.152
.152
-.
.061 -.039 0 18 .004
.
-
r4
rs
-.196 -.0 38 -.192 -.0 35 .010 .009 -.151 .lo3 -. l o 1 -.027 -.217 -.059 -.189 .110 :005 -.ooo .024 -.033 -. l o 9 .011 -.149 .0 19 .096 .027 .032
.043
r6 -128 .lo8 0 39 .093 .143 .225 -.192 -.029 -0 15 -.080 .013 .079
.
.
.086
r7
r8
.076 .018
.lo9 .035 0 10 .099 .073 .037
-
.028
.022 .053 .041
.088
.052 .037 .064 .051 .008 .022
rg .026
r 10
-.029 -.075
. -.051
-.050 -.018
-
.021 .116
,034 .002 .040 .091 -.071 .025 .034 .052 -.065 .054
.060
.046
.lo6 -.052 -.097 .054 .068 .079
.010 .024 .081
-.116 -.0 39 -.0 39 .002
-
-
-
11
-.210 .096 -.070
.090 .005 -0 35
-.
.om
-.066 -.023 -.066 -.067 .213 .064
'12 .055 .001 -.063 .011 .152 .069 .082 .042 -.077 .054
c
-
.ooo
-.112 .121
13
14
-.076
-.071
-.ill -.0 17 -.048 -.063 -.225 -.149 -.120 -.131 .lo2 -
-.026
'15 .182
-.053 -.070 -.134 .041 .008 .048
.210
-
.133 -.139 .lo7 .001 .035 .096 -.049 .010 .031
.150 .124 .037 .028
.lo8 .lo3 .088
,056 .154
.239
378
55
50
45
-E 40 01
2 -35
Q
m 0
L
U
.%'
D
-0 3
2
30
25
Q
20 15 1 0.01
I
1
I
1
1
0.1 0.2 0.5 1
I
2
5
1
I
1
1
1
1
1
I
I
1
10 20 30 4 0 50 60 70 80 90 95 Non exceedance probability, '10
1
8
98 99
99.9
Fig. 8.36. F i t o f t h e P e a r s o n Type I 1 1 f u n c t i o n t o t h e d i s t r i b u t i o n of t h e annual d i s c h a r g e s a t Malakal i n t h e p e r i o d 1912-1973 8.7.3
The White N i l e from Malakal t o j u s t above t h e j u n c t i o n w i t h t h e Blue Nile -
B e l o w t h e c o n f l u e n c e of t h e S o b a t , t h e White N i l e f l o w s a d i s t a n c e o f , s a y ,
840 km, w i t h o u t b e i n g j o i n e d by any i m p o r t a n t t r i b u t a r y e x c e p t by t h e Blue N i l e
a t t h e downstream end o f t h i s r e a c h . The d i s c h a r g e s have f o r some t i m e been measured a t Mogren upstream o f t h e j u n c t i o n of t h e Blue N i l e and n e a r Khartoum. The gauge-discharge measurements f o r t h e p e r i o d 1912-27 a r e shown i n F i g . 21, Appendix E. The gauging s i t e a t Mogren w a s d e s c r i b e d as b e i n g good enough a t low d
s t a g e , b u t n o t good i n a f l o o d . T h i s might e x p l a i n t h e t e r r i b l e s c a t t e r of t h e p o i n t s i n t h e s t a g e - d i s c h a r g e diagram. F o r t h e f i r s t 358 km, t h e r i v e r h a s a waterway o f from 300 t o 500 metres i n w i d t h w i t h numerous i s l a n d s . The mean w i d t h may b e t a k e n a s 425 metres i n low supply when t h e r i v e r i s w i t h i n t h e banks. F o r t h e n e x t 490 km t o t h e t a i l a t Khartoum, t h e mean w i d t h o f t h e water s u r f a c e i s 850 metres i n low s u p p l y . The g e n e r a l d e p t h o f t h e w a t e r a t l o w s t a g e i s 4 metres, and 7 metres i n f l o o d . On e i t h e r s i d e o f t h e waterway o f t h e upper r e a c h i s a low r i d g e swamped i n f l o o d
379
and beyond t h a t i s a deep d e p r e s s i o n , deep i n t h e c e n t r e and r i s i n g t o t h e r i d g e on one s i d e and t o t h e h i g h l a n d and f o r e s t on t h e o t h e r . Each d e p r e s s i o n may be
3 km i n w i d t h where i t i s wide and a few hundred metres where i t i s narrow, so t h a t t h e f l o o d e d v a l l e y may have a w i d t h o f 6 km i n some p l a c e s . The r i d g e s are broken by openings through which t h e water p a s s e s i n and o u t o f t h e marshy d e p r e s s i o n s . These d e p r e s s i o n s are o c v e r e d by a d e n s e growth o f needs. A t B e g e l e i n t h e s i d e d e p r e s s i o n s c o n t r a c t and t h e f o r e s t s approach t h e r i v e r . F i f t y k i l o m e t r e s f u r t h e r t o t h e n o r t h , t h e e x t e n t o f t h e swamps decreases and t h e r i v e r w i d t h v a r i e s from 700 t o 900 metres. Some 30 k m f u r t h e r t o t h e n o r t h t h e sudd g r a s s e s d i s a p p e a r , and though t h e r e i s f l o o d i n g , t h e r e are no swamps. The summer c h a n n e l i n t h e 490 km upstream o f Khartoum i s 850 metres i n w i d t h and t h e f l o o d channel i s 4 . 3 km. The summer d e p t h o f water i s about 4 m. The r a i n f a l l i n t h e 850 km r e a c h o f t h e White N i l e d i e s o u t almost l i n e a r l y w i t h d i s t a n c e from Malakal t o Khartoum. F o r t h e 30-year p e r i o d 1938-1967,
t h e mean r a i n f a l l over
the different stations was: Station No.
Location
Rainfall mm/y r
Station No,
Location
Rainfall m/yr
118
Malakal Kodok Melut Renk Gebelein
8 19
100 91 85 81 79
Kosti/Rebeck Dueim Geteina Jebel A w l i a Khar t oum
403 315 20 2 199 156
117 116 111 106
738 644 541 431
F o r t h e same r i v e r r e a c h , t h e open water e v a p o r a t i o n h a s been e s t i m a t e d a t about 1900 mm/yr a t Malakal t o about 2920 mm/yr a t Khartoum (see C h a p t e r 5 : Evap o r a t i o n ) . From t h e s e f i g u r e s i t i s c l e a r t h a t t h e l o s s p e r y e a r v a r i e s from a b o u t 1080 mm a t Malakal t o 2760 mm a t Khartoum; i f w e take 1 . 9 m as an a v e r a g e l o s s f o r t h e whole r e a c h and t h e a v e r a g e width of t h e water s u r f a c e a t , s a y , lkm,
i t i s t h e r e f o r e n o t d i f f i c u l t t o r e a l i z e t h a t t h e White N i l e from below t h e c o n f l u e n c e o f t h e S o b a t t o j u s t above t h e White N i l e j u n c t i o n looses, on average, 1 . 6 mlrd m3/yr. T h i s f i g u r e d e p a r t s s l i g h t l y from t h e a v e r a g e l o s s f o r t h e p e r i o d 1914-1937, which was 1 . 9 mlrd m3/yr w i t h a s t a n d a r d d e v i a t i o n o f 1 . 2 mlrd m3/yr.
H u r s t r e p o r t e d t h a B m o s t of t h e v a r i a t i o n i n t h e l o s s w a s due t o t h e f a c t
t h a t t h e l o s s w a s t h e d i f f e r e n c e between two much l a r g e r q u a n t i t i e s , t h e r e b y c o n t a i n i n g t h e e r r o r s of b o t h . Not much weight can be a t t a c h e d t o t h e l o s s i n any p a r t i c u l a r y e a r , b u t t h e mean l o s s i s p r o b a b l y c o r r e c t a t h a l f a m i l l i a r d . The J e b e l e l - A u l i a r e s e r v o i r w a s p u t i n t o u s e f o r t h e f i r s t t i m e i n 1937.The e s t i m a t e d l o s s i n t h e p o s t - r e s e r v o i r p e r i o d , 1937-1948, w a s 2.9 mlrd m3/yr. The
a i m and f u n c t i o n o f t h i s s t o r a g e work s h a l l be d i s c u s s e d , however, i n C h a p t e r 9 . I f w e now a d h e r e t o a mean annual flow o f 29.44 mlrd m % r
a t Malakal, t h e n a t u r a l
r i v e r d i s c h a r g e above t h e Blue N i l e j u n c t i o n c a n be t a k e n as 27 t o 28 mlrd m 3 / y r .
380
8.8 8.8.1
THE BLUE NILE BASIN Lake Tana
The Lake Tana a n d i t s c a t c h m e n t have been d e s c r i b e d i n C h a p t e r 2. The c a t c h ment a r e a e x c l u d i n g t h e l a k e , which i n i t s e l f i s 3000 km2, i s 13750 km'.
The
h y d r o l o g i c v a r i a b l e s a r e s o t h a t t h e a v e r a g e r a i n f a l l and e v a p o r a t i o n b a l a n c e e a c h o t h e r a t a b o u t 1300 mm/yr;
t h e run-off
from t h e catchment t o t h e l a k e ,
assuming no change i n s t o r a g e , must t h e n e q u a l t h e l a k e o u t f l o w . T a k i n g t h e annual run-off m3/yr.
c o e f f i c i e n t a s 22%, t h e a n n u a l l a k e o u t f l o w i s a b o u t 3.93 mlrd
T h i s f i g u r e i s n e a r l y t h e same as t h e mean o f t h e o u t f l o w s i n t h e p e r i o d
1920-1933, which w a s 3.85 mlrd m3/yr.
These o u t f l o w s are g i v e n i n T a b l e 8,
Appendix D . For a g i v e n l a k e l e v e l t h e d i s c h a r g e c a n b e r e a d from t h e r a t i n g c u r v e , F i g . 22, Appendix E . T a b l e 8, Appendix D , h a s b e e n u s e d f o r p r e p a r i n g t h e a v e r a g e hydrograph o f Lake Tana o u t f l o w , which is shown i n F i g . 8.37.
c?
ro
300
9
;200 CI
2 z
U
i i 100
Month F i g . 8.37.
The a v e r a g e hydrograph o f t h e B l u e N i l e a t t h e e x i t o f Lake Tana,
Roseires, a n d S e n n a r
6
8.8.2
The B l u e N i l e from Lake Tana t o R o s e i r e s
The B l u e N i l e r e c e i v e s t r i b u t a r i e s a s h o r t d i s t a n c e away from i t s e x i t from Lake Tana. The f i r s t t r i b u t a r y i s c a l l e d C h i m b i l and i s s a i d t o b r i n g as much as 10 m3/sec.
i n f l o o d . Below t h e j u n c t i o n of C h i m b i l i w i t h t h e B l u e N i l e t h e t r i -
b u t a r i e s i n c r e a s e i n s i z e and i m p o r t a n c e as t h e r i v e r e n t e r s t h e canyon i n which
i t r e m a i n s u n t i l w i t h i n a few k i l o m e t r e s from t h e Sudan b o u n d a r y . The B l u e N i l e i n i t s u p p e r r e a c h i s j o i n e d by t h e R i v e r B a s h i l e and R i v e r
Jamma ( s e e t h e map, F i g . 2.18.). The i m p o r t a n t t r i b u t a r i e s o f t h e l o w e r r e a c h e s
381
a r e t h e D i d e s s a , Dabus and Balas. H u r s t a n d h i s co-workers e s t i m a t e d t h e f l o w a t about 2.2 x
lo6
m3/day i n low-flow s e a s o n and a t a b o u t 220 x
lo6
m3/day i n f l o o d
s e a s o n . T h i s means t h a t a f t e r f l o w i n g f o r a b o u t 330 km, t h e d i s c h a r g e becomes a b o u t 10 times as much a s i t s i n i t i a l v a l u e a t t h e e x i t o f t h e l a k e . The Blue
N i l e d i s c h a r g e a t R o s e i r e s , 935 km below t h e e x i t o f Lake Tana, i s a b o u t 7 m i l l i o n m3/day,
e m p h a s i z i n g t h a t t h e c o n t r i b u t i o n of t h e r e a c h below Kutai ( K i l o
330) i s more t h a n t h e c o n t r i b u t i o n of t h e upper r e a c h . I t seems, however, t h a t t h e d i s c h a r g e from Lake Tana up t o R o s e i r e s i n c r e a s e s w i t h d i s t a n c e from t h e lake. The r a t i n g c u r v e of t h e B l u e N i l e a t R o s e i r e s i s shown i n F i g . 2 3 , AppendixE, and t h e monthly and a n n u a l d i s c h a r g e s i n t h e p e r i o d 1912-1973 a r e g i v e n i n T a b l e 9 , Appendix D. The s t a t i s t i c a l d e s c r i p t o r s and t h e s e r i a l c o r r e l a t i o n c o e f f i c i e n t s o f t h e s e d a t a have b e e n c a l c u l a t e d and g i v e n i n T a b l e 8 . 1 4 . From t h i s t a b l e o n e c a n n o t i c e t h a t t h e monthly and t h e a n n u a l d i s c h a r g e s a t R o s e i r e s are v e r y much l e s s d e p e n d e n t t h a n t h e monthly and t h e a n n u a l d i s c h a r g e s a t e i t h e r Mongalla o r M a l a k a l . I t i s o n l y t h e months o f low f l o w , J a n u a r y t h r u ' May, and O c t o b e r t h a t show s i g n i f i c a n t c o r r e l a t i o n a t t h e 95% l e v e l of c o n f i d e n c e . The d i s c h a r g e s of J a n u a r y , F e b r u a r y and March a r e s e e n t o b e s e r i a l l y c o r r e l a t e d up t o l a g 3 , w h e r e a s A p r i l i s s e r i a l l y c o r r e l a t e d a t l a g 1 o n l y and t h e f i r s t
s e r i a l c o e f f i c i e n t is j u s t s i g n i f i c a n t l y d i f f e r e n t from z e r o a t t h e 95% c o n f i d e n c e l e v e l . The May and O c t o b e r series show s e r i a l c o r r e l a t i o n a t l a g 3 and a t l a g 1 or 2 . The months J u n e t h r u ' December, w i t h t h e e x c e p t i o n o f May, and t h e y e a r , are n o t s e r i a l l y c o r r e l a t e d . One c a n g e t some rough i m p r e s s i o n a b o u t t h e l a c k o f d e p e n d e n c e i n t h e s e series by comparing t h e g r a p h i c a l p l o t o f , f o r example, t h e a n n u a l series a t R o s e i r e s ( F i g . 8 . 3 8 . ) t o t h e a n n u a l series a t Malakal o r Mongalla. The dependentcomponent i n t h e series o f J a n u a r y t h r u ' A p r i l c a n b e d e s c r i b e d , however, by a f i r s t - o r d e r a u t o r e g r e s s i v e r e l a t i o n h a v i n g t h e f i r s t c o r r e l a t i o n c o e f f i c i e n t as a p a r a m e t e r ( s e e T a b l e 8 . 1 4 ) . The r e s i d u a l s l e f t a f t e r removing t h e d e p e n d e n t component a p p e a r t o b e u n c o r r e l a t e d a t 95% c o n f i d e n c e l e v e l . The s e r i a l c o r r e l a t i o n c o e f f i c i e n t s of t h e r e s i d u a l s o f t h e s e series are p r e s e n t e d i n T a b l e 8 . 1 5 . The p r o b a b i l i t y d i s t r i b u t i o n f u n c t i o n s t h a t may s e r v e as good f i t t o t h e monthly and a n n u a l d a t a are t h e h e a r s o n Type I11 and
t h e normal f u n c t i o n s . The
f i t o f t h e l a t t e r t o t h e a n n u a l d i s c h a r g e d a t a i s as shown i n F i g . 8 . 3 9 . For a l l t h e d i s c h a r g e series t h e 100 and 200-year d i s c h a r g e s computed from t h e d i s t r i b u t i o n f u n c t i o n b e s t f i t t i n g e a c h series are a s f o l l o w s : Discharge, 106 m 3 J a n . Feb. Mar. Apr. May 100-yr 200-yr
June J u l y
Aug.
Sep.
Oct.
Nov. Dee. Year
1642 1414 1385 1116 1851 3426 10902 22918 19941 13088 4639 2495 73091 1752 1586 1577 1267 2096 3780 11300 23595 20619 13876 4886 2588 75270
w
TABLE 8.14
The b a s i c s t a t i s t i c a l d e s c r i p t o r s and t h e s e r i a l c o r r e l a t i o n c o e f f i c i e n t s o f t h e monthly and annual d i s c h a r g e s o f t h e Blue N i l e a t R o s e i r e s for t h e p e r i o d 1912-1973
I tern
Basic s t a t i s t i c a l descriptor
X,
106 m 3 s , 106 ln3 C
CV
Month of t h e y e a r Jan.
Feb.
Mar.
Apr.
878 268 0.3050 0.7348 4.0851
543 2 35 0.4335 2.1822 8.6791
445 369 246 199 0.5520 0.5378 2.4359 2.2961 9.7202 10.5525
0.5b59 0.4093 0.3560 0.1784 0.3179 0.1772 0.2330 0.2221 0.1424 0.2617 0.0815 0.1939 0.1665 0.0153 0.0572
0.7513 0.5161 0.3503 0.1801 0.1226 0.1404 0,1080 0.1086 0.1483 0.1309 0.1146 0.1227 0.1230 0 .0410 0.0219
0.5126 0.4183 0.3555 0.1091 0.0646 0.0574 0.0394 0.0463 0.1040 0.0960 0.0879 0.2886 0.0445 0.0880 0.1392
May
June
601 1632 34 1 533 0.5679 0.3265 2.1238 1.6445 8.3400 10.0111
July
Aug.
6548 15499 1691 2881 0.2582 0.1859 0.3363 0.2392 3.4673 5.6194
Sep.
Oct.
Nov.
Dec.
Year
12515 2884 0.2305 0.1443 4.1538
6813 2386 0.3502 0.4263 3.4400
2672 748 0.2799 0.4241 3.5667
1470 398 0.2709 0.0479 3.4878
49216 9272 0.1884 0.1747 3.9756
0.1891 0.0527 0.0991 0.1384 0.0237 0.0259 0.0597 0.1337 0.0238 0.1651 0.1826 0.2214 0.0178 6 . 0284 6.1043
c.0237 0.0690 I!.3098 0.1597 0.0514 0.2608 0.0409 0.0815 0.0739 0.0971 0.1670 6.0225 0.0429 6 .OM3 6.1357
q.0613 0.0563 0.0882 0.2219 0.0201 0.0369 0.0206 0 .Of506 0.0126 0.1538 I!.1889 0.1009 0.0307 0.0958 0.0238
0.2171 0.1383 0 . 1 6 0 3 0.0166 0.1329 0.1574 0.1290 0.1441 0.1724 0.0448 0.0616 0.0963 0.1086 0.0237 0.0749 0.0232 0.0140 0.0778 0.1764 0 .0466 6.1365 0.2977 1467 0.1970 0.0065 0.0573 6.1136 0.1566 0.1581 0.0275
Serial correlation coefficient rl
r2 r3 r4 r5 r6 l-7 r8 r9 r10
rll
r12 r13 r14 r, r
,
0.2489 0.0902 0.1394 0.1305 0.0301 0.0989 0.1533 0.1586 0.0659 0.2179 0.2505 0.3045 0.0059 0.0277 0 .0055
0.0269 0.0381 0.3173 0.0754 0.0528 0 . 2903 0.0249 0.0338 0.1250 0.0337 0.0483 6.0710 0. 0094 0.2652 0.0161
0.1702 0.1173 0.0468 0.0898 ,0312 0 .0059 0.1119 0.1735 0.1254 0.2370 0.2221 0.1646 0.0445 0.1590 0.0017 0.1283 0.1117 0.0147 0.0500 0.0876 0.1069 6.0782 0.0515 0 . 1616 6.1430 0.1510 .2122 3026 0 . 1 9 9 1 0.1783
p
c.
c
6.0705
0 .0381
0.0248 0.0987 0.0248 0.1481 0.0557 0.0057 0.0846 0.1179 0.0035 0.3042 0.2180 6.0826 6.0007
0.
01
383
1012'15
0
'20
'25 '30 '35 '40 '45 '50 '55 '60 '65 '70'73 Year
F i g , 8.38. G r a p h i c a l p l o t of t h e annual d i s c h a r g e s e r i e s of R o s e i r e s i n t h e p e r i o d 1912-1973 TABLE 8.15
S e r i a l c o r r e l a t i o n c o e f f i c i e n t s of t h e r e s i d u a l s l e f t from f i t t i n g a u t o r e g r e s s i v e models t o some o f t h e d i s c h a r g e series a t R o s e i r e s Serial correlation coefficients
Month
Jan. Feb. Mar. Apr.
,082 :073 .079 TO16
.067 TO47 _076 .005
.167 .041 .166 .091
T183 T163 TO73 .087
.231 ,111 1085 .017
TO74 _077 .026 .073
.042 . l o 8 TO94 .216 ,031 TO39 .095 .013 TO42 TO20 .054 .029 .081 .131 T156 .160
,127 TO19 ,082 .131
.097 .021 .299 .231
.136 .121 ,131 ,081
T152 ,024 .007 .026
.042
TOO8 .192 .017
80 70 0
E 60
m
0 F
50
0
r U ?!'.U 40
-
s 30
U
0
20
10 0.01
,
I
0.1 0.2 0.5 1
2
I
,
I
I
5
10
,
1
1
1
1
1
I
20 30 40 50 60 70 80
Non exceedance
,
I
90 95
probability, '10
,
I
98 99
99.9
Fig. 8.39. F i t of t h e normal f u n c t i o n to t h e d i s t r i b u t i o n o f t h e annual d i s c h a r g e s a t R o s e i r e s i n t h e p e r i o d 1912-1973
384
The f i r s t phase of t h e c o n s t r u c t i o n of a c o n c r e t e dam on t h e Blue N i l e a t Roseires was completed i n 1966. The primary purpose of t h i s dam i s t o s t o r e water and r e l e a s e i t downstream i n t h e s h o r t a g e season t o supply t h e Gezinah Managil Extension and t h e r i v e r bank pump schemes with water a s may be needed.
We s h a l l d e s c r i b e t h i s s t o r a g e work i n more d e t a i l i n t h e next c h a p t e r . 8.8.3
The Blue N i l e from Roseires t o Sennar
The Blue Nile below Roseires i s a mild stream w i t h a s l o p e of about 0.12 x which is about one-tenth t h e s l o p e of t h e t o r r e n t i a l stream which p r e v a i l s a l l t h e way from t h e e x i t of Lake Tana t o R o s e i r e s . There is a gauging s t a t i o n a t Wadi el-Aies,
n e a r Singa, about 180 km downstream of R o s e i r e s , and another a t
Makwar, n e a r Sennar, s o m e 270 km below Roseires. The r a t i n g curves of t h e s e two s t a t i o n s i n t h e given o r d e r a r e shown g r a p h i c a l l y i n F i g s . 24 and 25, AppendixE, respectively. The mean annual r a i n f a l l of t h e 30-yr p e r i o d 1938-67 a t R o s e i r e s , s t a t i o n
llq
i s 785 mm; a t Singa, s t a t i o n 101, 580 mm and a t Sennar, s t a t i o n 97, 463 mm.These d a t a suggest t h e f i g u r e of 600 mm a s an average depth of r a i n i n t h e reach from Roseires t o Sennar. For t h e same reach of t h e Blue N i l e t h e average annual evap o r a t i o n i s about 2450 mm. The n e t l o s s can t h e r e f o r e be e s t i m a t e d a t 1.85 m / y r . I f w e take 1 km a s an average value f o r t h e r i v e r width, t h e evaporation minus p r e c i p i t a t i o n l o s s comes t o 0 . 5 mlrd m3/yr. Hurst and h i s co-workers gave t h e average volume of flow a t Roseires f o r t h e p e r i o d 1912-1950 a s 49.6 x,109 m3/yr and t h a t a t Sennar f o r t h e s a m e p e r i o d as 48.7 x
loy
m3/yr with 0.9 mlrd m 3 / y r
a s t h e t o t a l transmission l o s s e s . They considered t h e l o s s i n a normal y e a r a s 2% and i n a high y e a r a s 4%, both of t h e flow volume a t t h e upstream s t a t i o n , i . e . R o s e i r e s . T h e r e s u l t s of o u r c a l c u l a t i o n f o r t h e mean flow a t t h e two s t a -
t i o n s i n t h e p e r i o d from 1912 up t o and i n c l u d i n g 1973 show t h a t whereas t h e mean a t Roseires was 49216 x
lo6
m3/ yr,
t h a t a t Sennar was 47185 x
These f i g u r e s b r i n g t h e t o t a l l o s s t o 2 mlrd m 3 / y r ,
lo6
m3/yr.
which i s somewhat b i g g e r
than t h e previous r e s u l t s , p o i n t i n g t o t h e p o s s i b i l i t y of i n c r e a s i n g withdrawal of water from t h e r i v e r between Roseires and Sennar. The s t a t i s t i c a l d e s c r i p t o r s and _the s e r i a l c o r r e l a t i o n s of t h e monthly and
annual d a t a a t Sennar a r e given i n Table 8.16. Although t h e mean monthly flows a t Roseires and Sennar are very n e a r l y equal (see F i g . 8 . 3 7 . ) ,
t h e p a i r of
s e r i e s f o r each month a t t h e s e two s t a t i o n s do not always behave s i m i l a r l y . Of t h e Sennar s e r i e s , which show dependence a t l a g 1 w i t h 95% confidence, a r e those of February, September and December; a t l a g 2 , November; l a g 3 , October and l a g 4 , March. For a l l t h e s e s e r i e s , except t h a t of March, one can d e s c r i b e t h e dependence i n t h e s e r i e s by t h e f i r s t - o r d e r l i n e a r Markov model. The c o e f f i c i e n t s of s e r i a l c o r r e l a t i o n of t h e r e s i d u a l series have been computed and
TABLE 8.16
The b a s i c s t a t i s t i c a l d e s c r i p t o r s and t h e s e r i a l c o r r e l a t i o n c o e f f i c i e n t s of t h e monthly and annual d i s c h a r g e s of t h e Blue N i l e a t Sennar f o r t h e p e r i o d 1912-1973
Item Basic s t a t i s t i c a l descriptor
X,
106 m 3 s , 106 m 3
C CV
Month of t h e y e a r Jan.
Feb.
Mar.
Apr.
May
June
July
Aug.
Sep.
Oct.
Nov.
Dec.
Year
682 260 0.3&+7 1.1508 5.4273
449 160 0.3565 1.0651 4.4911
404 170 0.4204 1.1641 5,6132
373 153 0.4094 0.6165 2.9148
573 304 0.5313 1.9219 8.2095
1402 573 0.4083 1.4886 8.6921
5892 1852 0.3143 6.1255 3.9041
15222 2771 0.1820 0.0882 5.1156
12383 3159 0.2551 0.5352 6.4598
6437 2632 0.4089 0.6046 3.8337
2202 1003 0.4554 1.2769 5.8684
1186 476 0.4016 0.9890 5.7073
47185 10012 0.2122 0.5123 5.0149
0.1811 0.0996 0. 1784 0.0421 0.2182 0.0753 0.1118 0.1109 0 .0212 0.1525 6.1070 0.1571 0.0595 0.1780 6.0560
0.3267 0.0450 0.0561 0.2558 6.1209 0.0251 0.0638 0.0303 0.0773 0.0718 0.0516 0.2162 .0719 0.0523 0.0523
0.1574 0.0108 0.0538 0.3774 2031 0.1041 0.1558 0.0492 0.1523 0.0612 0.0366 0.3133 0.0118 .0806 0.0463
0.1699 0.0327 0_.0012 0.2155 .0765 0.0142 0.0669 0.1085 0.1633 0.0398 0.1117 0.0715 0.0559 .2350 0.3877
0.0846 0 . 2 3 3 3 0.0326 0.0599 0 . 1991 0. 0771 0.0713 0.0902 6.0424 6.0880 0.1976 0.1817 0.0517 0.1005 0.0553 6.0205 0.0474 0.1754 0.0160 0.0678 0.0547 0.1207 6.0565 0.1078 0.0155 6.1611 0.2107 6.1245 0.0137 6.2046
0.0274 0.1135 0.1331 0.0552 0.0815 0.1002 0.1756 0.1384 0.0120 0.0276 6.1403 0.1298 0.0776 1453 0.0846
p.0845 0.0529 6.0951 6.1391 6.0497 0.1225 0.0580 0.0652 0.0440 0.0269 0.0153 0.2387 2285 0.1220 0.0294
0.2805 0.0655 0,0979
0.1353 0.0640 0 ,2551 0.0728 0.0250 0,1917 .0240 $. 1433 .OM9 0.0879 2224 0.0716 0.0186 1617 0.0904
0.1973 0,2722 0.2628 0.0144 0.0915 0.1574 0.0790 0.1010 0.0049 0.0910 6.1724 0.0475 0.0237 6.1117 0.0101
0.3017 0.2635 1619 0.0717 0.0793 0.0648 0.0253 0.0916 0.0128 0.0924 6.1445 0.0425 0.0558 1096 0.0244
0.1872 0.0301 0.1176 6.0110 0.0110 0.1281 2.0630 0.0150 0.0374 0.0059 6.1759 0.1837 0,0054 0.1207 0.0368
Serial correlation coefficient rl r2 r3 r4 r5 r6 r7 r8 r9 r10 '11 '12 r13 r14
r15
0
c.
p
p
c.
p.
6.1118
0.0480 0.0425 0.0513 0.1631 0.0179 0.0783
6.1638 0.1748 0.0585 0.0298 0 .0819
0
0
p.
p.
0.
p.
386
l i s t e d i n Table 8.17. The t a b u l a t e d values do n o t j u s t i f y r e j e c t i n g t h e n u l l hypothesis t h a t t h e s e r i a l c o r r e l a t i o n c o e f f i c i e n t s a r e n o t s i g n i f i c a n t l y d i f f e r e n t from zero a t t h e 95% l e v e l of confidence. TABLE 8.17
S e r i a l c o r r e l a t i o n c o e f f i c i e n t s of t h e r e s i d u a l s l e f t from f i t t i n g a u t o r e g r e s s i v e models t o some of t h e discharge s e r i e s a t Sennar Serial correlation coefficient
Month
Feb. Sep. Oct. Nov. Dec.
r1
r2
r3
r4
r5
:075 :021 ,047 ,032 .024
,009 .014 .096 .203 .179
.036 .122 .078 -210 .131
I275 I131 :084 ,048 .120
Tl68 .120 .033 .076 .lo0
r6
r7
I054 T O 3 1 . O O ~,089 .057 .053 -140 .026 .075 TO23
r8
r9
r10
rll
r12
lo07 :178 .063 .098 .074
.076 :054 :llO :020 .053
.057 I033 .lo6 .099 .121
.001 I179 .146 1147 .173
.179 .223 _014 ,008 .096
'13
r14
r16
_040 I064 Llll,022 .029 ,132 .031 :088 .019 .086
I034 :041 .039 .026 .008
The Sennar Dam (Makwar) was b u i l t a c r o s s t h e Blue Nile i n 1925 a few k i l o metres above Sennar. This dam w a s b u i l t e x c l u s i v e l y i n t h e i n t e r e s t of theSudan. I t s e r v e i t w o purposes: i t raises t h e l e v e l s u f f i c i e n t l y high f o r t h e w a t e r t o
flow i n t o t h e main Gezirah c a n a l , and i t s t o r e s water from t h e f l o o d t o be used during t h e p e r i o d January t o A p r i l when t h e r e i s no s u r p l u s water i n t h e Blue Nile over Egypt's requirements. More d e t a i l e d d e s c r i p t i o n of t h i s s t o r a g e w i l l appear i n Chapter 9 . 8.8.4
The Blue N i l e below Sennar t o Khartoum
Below Sennar, t h e Blue Nile flows north-west
f o r a d i s t a n c e of 350 km b e f o r e
i t j o i n s t h e White N i l e a t Khartoum. Between Sennar and Wad Medani t h e Blue N i l e r e c e i v e s t h e Rahad. This t r i b u t a r y rises on t h e E t h i o p i a n P l a t e a u a few k i l o metres w e s t of Lake Tana under t h e name of t h e Sidd. I n i t s course of 750 km t h e r i v e r flows i n t h e Ethiopian P l a i n s a s t h e A i m a and changes i t s name i n t h e Sudan t o t h e Dinder. The drainage b a s i n of t h e Dinder has an a r e a of 160 000 km2. The average a r e a l r a i n f a l l is about 0.80 t o 0.85 m/yr and t h e annual run-off c o e f f i c i e n t reaches 22%. These f i g u r e s suggest a t o t a l run-off
of about 3 mlrd
m3 i n a normal y e a r . Vol. I X of thecNile Basin g i v e s 2.97 mlrd m3 a s an average volume of flow p e r y e a r i n t h e period 1912-1950 and 3.83 mlrd m3 a s t h e flow volume i n a high year (1946). The gauge-discharge measurements f o r e s t a b l i s h i n g t h e r a t i n g curve of t h e Dinder a r e taken a t H i l l e t I d r i s . The d a t a for t h e p e r i o d 1924-1927 a r e shown i n F i g . 26, Appendix E . The Blue Nile below Wad Medani r e c e i v e s t h e Rahad, which SprinRs n e a r l y from t h e same p l a c e a s t h e Dinder. This t r i b u t a r y has a l e n g t h of 800 km and a drainage b a s i n of about 8000 km2. For t h e same r a i n f a l l a s on t h e catchment of t h e
387
Dinder, i . e . 0.80-0.85
m/yr,
and an annual run-off
c o e f f i c i e n t o f , s a y , 161, t h e
t o t a l flow reaching t h e mouth of t h e Rahad comes t o about 1.1 mlrd m3/yr. Vol.
I X of t h e N i l e Basin g i v e s 1.08 mlrd m3 a s t h e y e a r l y average f o r t h e p e r i o d 1912-1950. The r a t i n g curve of t h e Rahad f o r t h e p e r i o d 1922-1927 a t Abu-Haraz, n e a r t h e mouth, i s shown i n F i g . 27, Appendix E. The Dinder and t h e Rahad hardly c a r r y any water i n t h e p e r i o d from January t o May. The hydrograph of each of t h e s e two t r i b u t a r i e s has a more o r l e s s triangul a r shape w i t h a base width of about 200 days. The peak d i s c h a r g e s have been found t o be about 480 and 160 m3/sec.
f o r t h e Dinder and t h e Rahad, respectively.
The mean annual r a i n f a l l v a r i e s from 463 mm a t Sennar, s t a t i o n 97, t o 340 mm a t Managil, s t a t i o n 89 t o 385 a t Wad Medani, s t a t i o n 88, t o 312 a t Ruffa, s t a t i o n 86 t o 254 mm a t Kamlin, s t a t i o n 83, t o 160 mm a t Khartoum s t a t i o n s 78/79.In t h i s reach of 350 km, average depths of 320 mm and 2740 mm/yr can be used f o r r a i n f a l l and evaporation, r e s p e c t i v e l y . Assuming an average width of t h e r i v e r of 800 m, t h e l o s s becomes (2.74
-
0.32) x 350 x
lo6
x 0 . 8 = 0 . 6 8 mlrd m3/yr t o
be rounded t o , s a y , 0.85 mlrd m3/yr t o account f o r some seepage loss. The b a l ance a t t h e mouth of t h e Blue N i l e n e a r Khartoum i s 47.185 0.850 = 50.385 mlrd m 3 / y r .
+ 2.970 + 1.080
-
This f i g u r e i s about 2% less t h a n t h a t given by Hurst
i n Vol. I X of t h e N i l e Basin ( H u r s t , H . E . ,
Black, R.P.,
and Simaika, Y.M.,1959).
The monthly and annual d i s c h a r g e series of t h e Blue N i l e a t Khartoum a r e presented i n Table 11, Appendix D. The d a t a used f o r p r e p a r i n g t h e r a t i n g curve a r e shown i n F i g . 28, Appendix E. The change of t h e gauge s i t e a l t e r n a t i v e l y between B u r i , Soba and Khartoum could be one of t h e reasons r e s p o n s i b l e f o r t h e heavy s c a t t e r of t h e p l o t t e d p o i n t s . The a l r e a d y d e r i v e d annual flow volume a t Khartoum i s n e a r l y i n p e r f e c t agreement with t h e mean annual flow f o r t h e p e r i o d 1912-1973, which was 50.369 mlrd m 3 / y r ( s e e Table 8 . 1 8 ) . E i t h e r f i g u r e , derived o r computed, shows t h a t t h e flow a t Khartoum i s about 6.8% l a r g e r than t h a t a t Sennar. One should not forg e t , however, t h a t t h i s i s an average percentage f o r 62 y e a r s , around which i n d i v i d u a l years f l u c t u a t e p o s i t i v e l y and n e g a t i v e l y . The g r a p h i c a l p l o t of t h e annual series a t Sennar and Khartoum, F i g . 8.40. shows t h a t t h e flow volume i n some y e a r s a t Sennar was equal t o , o r even l a r g e r t h a n , t h a t a t Khartoum. 6
Some of t h e monthly series and t h e annual discharge series a t t h e mouth of t h e Blue N i l e appear t o be s l i g h t l y s i g n i f i c a n t l y d i f f e r e n t from z e r o a t t h e 95% l e v e l of confidence. The remaining series, which a r e t h e May, J u l y , August, September and October s e r i e s , a r e not s i g n i f i c a n t l y d i f f e r e n t from t h e zero a t t h e same l e v e l of confidence. The s e r i e s showing s i g n i f i c a n t dependence a t l a g 1 a r e t h o s e of February, A p r i l , June, December and t h e y e a r . Those a t l a g s 3, 4 , 5 and 6 a r e t h e series of November, March, January and June, r e s p e c t i v e l y . The dependence i n a l l t h e s e series can be adequately d e s c r i b e d by a f i r s t - o r d e r
TABLE 8 . 1 8
w
The b a s i c s t a t i s t i c a l d e s c r i p t o r s and t h e s e r i a l c o r r e l a t i o n c o e f f i c i e n t s of t h e monthly and annual d i s -
W W
charges of t h e Blue N i l e a t Khartoum f o r t h e p e r i o d 1912-1973
Month of t h e y e a r
Item Basic s t a t i s t i c a l descriptor
6,
106 In3
s, 106 El3 C
cz
CV
Jan.
Feb.
Mar.
Apr.
May
740 26 3 0.3551 1.0112 5.5867
455 159 0.3491 1.0912 4.8671
408 157 0.3847 1.3087 6.6164
386 180 0.4657 1.7888 7.8484
0.1420 0.0902 0.1664 0.0247 0.2745 0.0672 0.0450 0.0796 4.0269 0.1097 0.1097 0.1336 0.0280 0.2083 0.0379
0.2836 0.0295 0.0427 0.2222 0.0090 0. 1 2 1 1 0.0100 0.0100 2.0567 0.0066 0.0058 0.1659 0.1313 0.0363 6.0754
0.2268 6.0426 g.1317 0.3582 6.1651 1057 0.1141 6.0155 0.1768 0.0200 0.1111 0.2714 0.0500 0.0710 6.0331
0.2848 0.1060 0.1544 0.0865 0.0540 0.1790 .2050 6.0574 0.1528 6.2076 1588 0.0940 0.1233 6.0238 0.0043 6.2028 0.0458 .0848 0.2177 0 . 1029 0.0896 0.0512 0.2490 0.0508 0.1506 0.0325 0.0117 0.2270 0.0258 0.0420
June
July
Aug.
Sep.
Oct.
Nov.
Dec.
Year
480 1137 225 500 0.4685 0.4394 1.7085 2.2234 7.3397 11.8552
5371 1730 0.3221 0.3456 3.1507
15853 2835 (1.1788 0.5503 4.2886
13945 3243 0.2326 0.1190 4.5216
7657 2932 0.3829 0.5897 4.0881
2487 1061 0.4267 0.1503 5.2131
1264 486 0.3843 0.8370 5.0576
50369 10258 0.2037 0.1919 3.9845
0.2403 0.0230 0.1538 0.0580 6.0206 0.3831 0.0188 6.0390 0.1915 0.1051 0.1125 0.2121 1338 0.2470 0.1809
0.1562 0.0039 .0680 0.1442 0.1104 0.1682 0.1670 0.1587 0.1043 0.0908 0.0584 0.1279 6.0797 6.1616 6.1759
6.1054 0.0913 0.1318 0.0479 0.1228 0.0627 0.0317 0.1298 0.0258 0.0096 0,0254 0.1158 0.2944 0.1556 0.0787
0.1593 0.1411 0.1638 0.1046 0.1783 0.0342 0.1139 1811 0 . 1033 0.0663 0.1801 0.1679 0.0902 0.0071 0.0152
0.1458 0.0216 0.1908 0.1095 0.0287 0 .2068 0.0271 6.1240 0 .0015 0.1174 4.1772 0.0182 0.0033 0.1239 0.1162
0.1345 0.1660 0.2458 0.0630 0.0724 0.0721 0.0171 2.0970 0.0010 0.1105 0.1609 0.0818 0.0037 0.1255 0.0154
0.3182 0.2251 0.1552 6.0411 0.0570 0.0687 0.0226 0.0850 0.0384 0.0725 0.1999 0.0412 0.0238 0.1113 6.0367
0.2521 0.1146 0.0675 0.0950 0.0089 0.1187 0.0746 0.0439 0.0760 .0671 0.1999 0.0913 0 .OX2 0.1343 0.1344
Serial correlation coefficient r1 r2 '3 r4 r5 r6 r7 r8 r9 r10 rll 12 r13 r14 r15
g.
4 g.
g
i.
p
g.
389
80
70
.+0
60
-5
50
2%.- 40
-CI 2 3-30
$2 20
'20 '25 '30 '35 '40 ' 4 5 '50 '55
1912 '15
'60 '65
'70 '73
Year F i g . 8.40. The g r a p h i c a l p l o t of t h e annual series a t Sennar and Khartoum on t h e Blue N i l e i n t h e p e r i o d 1912-1973 a u t o r e g r e s s i v e model f o r which t h e f i r s t s e r i a l c o r r e l a t i o n c o e f f i c i e n t i s a parameter. The r e s i d u a l s l e f t from f i t t i n g t h i s model t o each of t h e dependent s e r i e s when t e s t e d appear not t o be s e r i a l l y c o r r e l a t e d a t t h e chosen l e v e l of confidence. The only exception can be found a t l a g 6 f o r t h e month of June, which i s s i g n i f i c a n t l y d i f f e r e n t from zero. The s e r i a l c o r r e l a t i o n c o e f f i c i e n t s of t h e r e s i d u a l series a r e given i n Table 8.19.
TABLE 8.19
S e r i a l c o r r e l a t i o n c o e f f i c i e n t s of t h e r e s i d u a l s l e f t from f i t t i n g a u t o r e g r e s s i v e models t o some of t h e d i s c h a r g e s e r i e s a t Khartoum -
Month
Serial correlation coefficient
&
Year
rl
r2
r3
r4
r5
r
r7
6
r8
r9
r10
rll
=12
r13 ~~~
Jan. Feb Mar. Apr June Nov Dec . Year
.
.
.
-057 .lo7 .053 TO14 -.020 .016 TO42 .033
.095 .030 TO31 ,045 .089 .155 .154 .087
,071 lo81 :037 .238 .066 1278 .077 :183 .171 :113 .229 .080 .135 1091 .062 .079
-162 1158 1202 ,087 .084 .095
I058 .031 TO89 1108 .396 .067 .080 .066 .013 . l l O
TO40 TOO9 TO46 I090 .067 .005 YO33 .058
The monthly series of t h e low-flow
.116 .051 TO04 _029 .063 .lo6 _062 .031
TO91 .058 ,191 .073 :199 .018 ,003 .031
.120 I 0 9 1 .003 :042 .046 ,123 -.209 L054 .137 .087 .099 ,123 -.115 _222 .017 .183
.064 .116 .251 .183 .228 TO35 .117 .133
.061 .077 .012 :053 .110 ,016 .002 .003
r14
r15
1194 .063 1080 .082 T133 1091 1080 .098
.033 .003 .022 -.088 .062 0 16 -0 15 .049
~~
~~
. .
season a r e d i s t r i b u t e d l i k e a lognormal,
whereas t h e monthly series of t h e high-flow season are d i s t r i b u t e d more o r less l i k e a Pearson Type I 1 1 d i s t r i b u t i o n . The s e r i e s of annual discharges is n e a r l y normally d i s t r i b u t e d (see F i g . 8.41.).
390
Non exceedance
probability
Fig. 8.41. F i t of t h e normal f u n c t i o n t o t h e d i s t r i b u t i o n of t h e annual d i s charges a t Khartoum on t h e Blue Nile i n t h e p e r i o d 1912-1973
For a l l d i s c h a r g e s e r i e s a t Khartoum, t h e 100 and 200-year d i s c h a r g e s computed from t h e d i s t r i b u t i o n f u n c t i o n b e s t f i t t i n g each s e r i e s a r e a s f o l l o w s : Discharge 106
,3
100-yr 200-yr
J a n . Feb. Mar. Apr. May 1537 946 912 1670 1041 998
June J u l y
Aug.
Sep.
Oct.
Nov. Dec. Year
1016 1255 2995 9835 21268 21482 15720 5797 2686 74424 1133 1396 3367 10388 21693 22658 16834 6328 2895 77194
THE MAIN NILE BELOW KHARTOUM TO JUST ABOVE THE JUNCTION OF THE ATBARA
8.9 8.9.1
Tamaniat d i s c h a r g e s
Regular d i s c h a r g e measurement of t h e MaixPNile began a t Tamaniat i n 1912. This s t a t i o n i s s i t u a t e d 41 km below t h e confluence of t h e Blue and White N i l e s a t Khartoum. Since 1934 t h e f l o o d measurements have been taken a t Shambat, which
is 6 km f u r t h e r below. The gauge-discharge measurements f o r t h e p e r i o d 1912-1973 a r e p l o t t e d i n F i g . 29, Appendix E. The monthly and annual discharges f o r t h e same p e r i o d a r e given i n Table 12, Appendix D. These d i s c h a r g e d a t a have been s t a t i s t i c a l l y analyzed and t h e r e s u l t s presented i n Table 8.20.
TABLE 8 . 2 0
The b a s i c s t a t i s t i c a l d e s c r i p t o r s and t h e s e r i a l c o r r e l a t i o n c o e f f i c i e n t s of t h e monthly and annual d i s c h a r g e s of t h e Main N i l e a t Tamaniat f o r t h e p e r i o d 1912-1973
I tem
B a s i c s t a t ist i c a l des c r i D t o r
i,106 8 ,
In3 106 m 3
C CV
Month of t h e y e a r Jan.
Feb.
Mar.
Apr.
3219 832 0.2585 0.6503 3.8837
2387 639 0.2678 1.3988 6.1783
2397 6 50 0.2710 0.3981 3.2296
2352 903 0.3840 0.6738 2.7410
0.2789 0.1997 1381 0.0930 0.0624 0,0287 0.0683 0.0225 0.0129 0.0401 0.1861 0.0024 0.0498 0.0432 0.1759
0.3731 0.1855 0.2437 p.0707 0.0560 0.1120 0.0351 0.0119 0.0617 0.0181 0.0932 0.0178 .0820 0.0626 0.1269
0.6303 0.4002 0.4779 0.3513 0.2665 0.3933 0.4059 0.3795 0.4047 0.3090 0.2545 0.2720 0.169 1 0.1381 0.2128
0.7757 0.6804 0.6463 0.5397 0.5138 0.5044 0.5175 0.4840 0.4621 0.3999 0.3479 0.3387 0.2713 0.2433 0.2760.
June
July
Aug.
Sep.
Oct.
Nov.
Dec.
Year
2328 893 0.3838 0.9868 3.2408
2889 724 0.2506 1.2860 5.1900
6645 1586 0.2388 0.5751 3.8961
16585 3103 0.1871 0.8162 4.9800
16339 3379 0.2068 0.0114 3.6400
10906 3136 0.2075 0.8752 4.8392
5406 1366 0.2527 1.2665 5.7600
4031 822 0.2040 0.5521 4.1110
75575 11341 0.1506 0.4132 4.3247
0.6064 0.4715 0.4051 0.2572 0.3301 0.2965 0.3474 0.3770 0.2576 0.2468 0.1141 0.0379 0.0158 0.0130 0.0820
0.3581 0.1138 0.0609 6.2451 6.1449 0.0493 0.0265 0.0586 0.1402 0.0570 0.0340 0.0437 .2559 0.2786 6.1287
0.2470 0.0055 6.1191 6.1707 6.1613 0.0942 0.0651 0.1061 6.0450 0.0629 6.0068 0688 0.1081 0.1969 6.2367
6.0886 0,1776 0.0279 0.0265 0.0229 0.0898 0.0081 0.0645 0.0182 0.0757 0.0801 0.0810 0.2072 0.1799 0.1238
0.2839 0.1672 0 . 1653 0.1067 0.0629 6.0372 0.0642 0.0469 0.0724 0.0561 0.1577 0.1733 6.0084 0.0222 0.0803
0.1636 0.0327 0.1862
0.1431 0.1943 0.1992 0.0858 0.0175 0.0775 0.0417 0.0627 0.0030 0.1366 0.0918 0.0260 0.0523 0.0822 0.1304
0.3896 0.2659 0.1655 0.0791 6.0690 q.0987 0.1471 0.0874 0.0576 0 .0174 0.1027 0.0981 0 .0638 0.0462 0.0631
0.2998 0.0869 0.0043 4.2272 0.1608 .0685 0.1356 0.1054 0.0829 0.0312 6.1376 0.0995 0.0982 0.1396 0.0412
May
Serial correlation coefficient rl
r2
r3
r4 r5 6 ' r7
r8
r9 r10
rll
I12 r13 r14 r15
0.
p
q
c.
6.1114
6.0526 0. 1676 0.0410 0.1441 6.0074 6.0900 6.1566 0.0419 0.0822 0.0755 0.0353
q
392
The discharge of t h e Main N i l e a t Tamaniat is equal t o t h e sum of t h e d i s charges of t h e Blue N i l e and t h e White N i l e , both a t Khartoum. Since t h e l a t t e r has been e s t i m a t e d from t h e Malakal d i s c h a r g e s , one can say t h a t t h e d i s c h a r g e
a t Tamaniat i s e q u a l t o t h e d i s c h a r g e of t h e Blue N i l e a t Khartoum p l u s t h a t of t h e White N i l e a t Malakal minus t h e l o s s e s from Malakal t o Khartoum. Because of t h e s m a l l d i s t a n c e between Khartoum and Tamaniat, 40 km, t h e conveyance l o s s
between t h e s e two s t a t i o n s can be ignored without any marked e f f e c t on t h e f i n a l r e s u l t . Since t h e outflow of t h e Blue N i l e a t mouth is n e a r l y twice a s much a s t h e flow o f t h e White N i l e a t Khartoum, i t i s then n o t s t r a n g e t h a t t h e d i s charge s e r i e s a t Tamaniat, e s p e c i a l l y t h e annual series, a r e more a f f e c t e d by t h e Blue N i l e d i s c h a r g e s than by t h e White N i l e ones. T h i s can be made e v i d e n t by comparing t h e p l o t i n Fig. 8.42. with t h o s e i n Figs. 8.40. and 8.35.
I0
5 60
m
E 50
m
s! 40 al
01
b
30
5 20 ul
i 10 l
L ~ ~ l - ~a 1 n o *l S t 8
1912'15
'20
'25
i
n I s I 1 1
l l l l a
n n I I .a* l l l l
I I 1 l a l l l l l
'
'30 '35 '40 '45 '50 '55 '60 '65 ' 7 0 ' 1 3 Year
Fig. 8.42. Graphical p l o t of t h e annual discharge s e r i e s a t Tamaniat on t h e Main N i l e i n t h e p e r i o d 1912-1973 I n t h e above discussion; no account has been taken f o r t h e e f f e c t of t h e t i m e l a g between one s t a t i o n and t h e o t h e r , t h e e f f e c t of t h e backwater produced by t h e j u n c t i o n of t h e two N i l e s and of t h e s t o r a g e i n r e s e r v o i r s , t h e e f f e c t of r e s e r v o i r r e g u l a t i o n and t h e s t o r a g e losses and inaccuracy i n measuring t h e water s t a g e and d i s c h a r g e . The o v e r a l l e f f e c t of these items can be seen from t h e r e s u l t s of t h e r e g r e s 6
s i o n and c o r r e l a t i o n a n a l y s i s of t h e d i f f e r e n c e i n t h e flow between Tamaniat on t h e Main N i l e and Khartoum on t h e Blue N i l e ,
Y, and t h e flow a t Malakal on t h e
White N i l e , X. The a n a l y s i s was performed on t h e monthly and t h e annual series. The X ' s a r e r e a d i l y a v a i l a b l e i n Table 7 , Appendix D, whereas t h e Y's a r e t h e d i f f e r e n c e s between Tables 12 and 11, Appendix D.
39 3
Let Y = a + b X
(8.7)
where a and b a r e t h e r e g r e s s i o n c o n s t a n t and c o e f f i c i e n t , r e s p e c t i v e l y . The c o r r e l a t i o n c o e f f i c i e n t rxy can be computed from t h e formula
r
XY
=
-
{ n EX'
n CXY
(CX)'
-
ZXCY n EYz
-
(8.8)
(EY)~ }3
The values of a , b , and rXYf o r t h e 13 Series have been c a l c u l a t e d and put i n Table 8.21. The c o e f f i c i e n t of l i n e a r c o r r e l a t i o n is a t a f a i r l y high value i n January and February then f l u c t u a t e s between moderate t o f a i r l y s t o n g t i l l J u l y . The high f l o o d discharges of t h e Blue N i l e are probably t h e reason behind t h e almost z e r o t o poor c o r r e l a t i o n during August, and September and October, res1
p e c t i v e l y . From November onwards t i l l t h e end of t h e y e a r , t h e c o r r e l a t i o n b e t ween X and Y improves considerably.
TABLE 8 . 2 1
Regression of t h e flow d i f f e r e n c e between Tamaniat and Khartoum on t h e flow a t Malakal
Month Year January February March April may June July August September October November December Year
a, 106 m 3
b
969.375 756.845 -1214.280 -275.977 -1551.564 1190.822 1419.763 -1449.095 257.030 1658.424 903.017 1113.904 792.214
0 . 6 18756 0.675871 0.454712 1.512053 2.06 1950 1.45989 1 1.75955 6 , Z O 1233 0.855047 0.467589 0.608749 0.524 161 0.834794
Regression Equation
&
Y Y Y Y Y Y Y Y Y Y Y Y Y
= =
=
=
= = = =
=
= = = =
969.375 756.845 1214.280 - 275.977 -1551.564 -1190.822 -1419.763 1449.095 - 257.030 1658.424 903.017 1113.904 792.214
+ 0.618756 X + 0.675871 X
+
0.454712 1.512053 + 2.061950 + 1.459891 + 1.075955 - 0.201233 + 0.855047 + 0.467589 + 0.608749 + 0.524161 + 0.834794
+
X X X X
X
X
X X
X X X
-
rXY 0.84493 0.84838 0.57058 0.73911 0.84765 0.79768 0.60137 0.06804 0.33322 0.38881 0.71579 0.82904 0.91140
X and Y a r e expressed i n m i l i i o n m3
The s t r o n g e s t c o r r e l a t i o n between X and Y can be found, a s can be expected, i n t h e annual series. The r e g r e s s i o n l i n e for t h e s e d a t a i s shown i n F i g . 8.43. The e s t i m a t e of t h e mean d i f f e r e n c e of flow between Tamaniat and Khartoum is 25367
2
4310 or from 21057 t o 29677 m i l l i o n m3/yr (95% confidence l e v e l ) . As o u r
e s t i m a t e of t h e annual flow a t Khartoum on t h e White N i l e j u s t above t h e conf l u e n c e of t h e Blue Nile i s a t 27 t o 28 mlrd m3 ( s e e s e c t i o n 8 . 7 . 3 ) , one is not
394
44 m’
E 42
cn
2 40
>. 38
5 36
0
c
;34
L
Y I
32
c
_0 30 C
28
5 26
t-
-2 2 4 -+ 2 2 I?
C
20 18 16 16 18 20 22 24 26 28 30 3 2 34 36 38 40 42 44 46 48 50 52 Annual
f l o w at
Moloka, X ,
lo9
rn3.
Fig. 8.43. Simple l i n e a r r e g r e s s i o n of t h e d i f f e r e n c e i n a n n u a l f l o w between Tamaniat a n d Khartoum, Y, and t h e a n n u a l f l o w a t M a l a k a l , X, f o r t h e p e r i o d 1912-1973 j u s t i f i e d i n r e j e c t i n g t h e h y p o t h e s i s t h a t t h e two estimates are n o t s i g n i f i c a n t l y d i f f e r e n t one from t h e o t h e r a t t h e g i v e n l e v e l of c o n f i d e n c e . The r e s u l t s p r e s e n t e d i n T a b l e 8 . 2 0 i n d i c a t e t h a t a l l t h e d i s c h a r g e series a t T a m a n i a t , e x c e p t t h o s e o f August, O c t o b e r and November, are s e r i a l l y c o r r e l a t e d . The dependent component i n t h e series w i t h c o r r e l a t i o n c a n b e d e s c r i b e d by an a u t o r e g r e s s i v e model o f t h e f i r s t or s e c o n d o r d e r . The series of t h e r e s i d u a l s have been t e s t e d a n d f o u n d n o t s e r i a l l y c o r r e l a t e d . T h i s c a n b e s e e n from t h e r e s u l t s included i n Table 8.22. The p r o b a b i l i t y d i s t r i b u t i o n f u n c t i o n s t h a t h a v e been found a s good f i t t o t h e d i s c h a r g e s a t Tamaniat a r e t h e P e a r s o n T y p e y I I I and t h e 2-parameter
lognormal.
F i g . 8.44.shows t h e f i t o f t h e l a t t e r t o t h e a n n u a l volumes o f f l o w d u r i n g 19121973. The 100- and 200-yr d i s c h a r g e s o b t a i n e d from t h e t h e o r e t i c a l f u n c t i o n s f o r a l l t h e 1 2 mont,hs a n d t h e y e a r are as f o l l o w s : Discharge 106 ,3 J a n . Feb. Mar. Apr. 100-yr 200-yr
May
June J u l y
Aug.
Sep.
Oct.
Nov. D e c .
Year
5540 4477 4097 4902 5027 5213 10983 21953 24212 20110 9757 6267105402 5863 4833 4314 5262 5443 5600 11577 22263 25043 21506 10474 6572109144
395
TABLE 8.22
S e r i a l c o r r e l a t i o n c o e f f i c i e n t s of t h e r e s i d u a l s l e f t from f i t t i n g a u t o r e g r e s s i v e models t o some of t h e d i s c h a r g e series a t Tamaniat
Month
Serial correlation coefficient
83
Year
rl
r2
r3
r4
r5
r6
*7
r8
r9
'10
rll
r12
'13
'14
r15
~~
.011 :084
Jan. Feb Mar. Apr
. .013 .014 . --168
-.089 ,003 .034 . -.060 . -.055 .037
May June July Sep Dec Year
:028 .254 TO55 :027 :058 .004 .098 .137 .061
.120 .213 .294 .204 .185 .121 TO94 .150 .129 .032
--
1218 .153 .025 .098 Tl60 T287 1070
:lo3 :060
.016 .099 .111 .163 .055 .121 .201 .087 .096 .181 1128 :lo9 ,121 .163 :073 T123 :004 .026 T151 .047 .039
1133 .030 .098 .036 :052 .085 .030 2113 2114 .lo6
,044 .003 .064 .014 .173 .041
.lo3
TO76 TO28 .093 .112
.OOO
-.128 .058
TO29 I065 .037 -.038 .040 .050
1036 1163 .026 TO12 :067 ,129 .056 TO62 .038 :015 .117 TO52 Toll , 0 3 1 .126 TO57 .156 ,010 .008 1039 .015 ,069 .044 _171 .036 :057 .lo8 .094 .006 1176 .219 TO98 :047 :167 .129 .027 .006 .156 . l l O .068
TO59 .137 TO62 .141 TO78 .143 TO61 .138 1028 ,062 _151 :056 .098 .083 _021 .025 :074 _049 .132 .005
2 00
-300
E rn 80
SI
60
& 50 L
," 40
: U
-
30
:20 20 C C
4
i. n "
.01
.05.1 .2 .5 1
2
10
5
Non
20 30 40 50 60 70 80
exceedance
probability
9 0 95
98 9999.5
F i g . 8.44. F i t of t h e 2-parameter lognormal f u n c t i o n to t h e d i s t r i b u t i o n of t h e annual d i s c h a r g e s of t h e Main N i l e a t Tamaniat i n t h e p e r i o d 1912-1973 6
8.9.2
Hassanab d i s c h a r g e s
The Main N i l e flows a d i s t a n c e of 277 km below Tamaniat b e f o r e i t r e a c h e s Hassanab s t a t i o n , which i s l o c a t e d about 5 km above t h e j u n c t i o n of t h e Atbara w i t h t h e N i l e . I n t h i s r e a c h of t h e Main N i l e t h e r e i s no g a i n a t a l l . The annual r a i n f a l l d e c r e a s e s from about 160 mm/yr a t Khartoum t o about 65 mm/yr a t Atbara and Zeidab. The p o t e n t i a l e v a p o r a t i o n i n a l l t h i s r e a c h h a s an average of 8 =/day
o r 2920 mm/yr.
The n e t loss can be taken a s 2800 mm/yr.
Assuming t h e
396 average width of t h e a r e a from which t h e l o s s e s t a k e p l a c e a s 1 . 5 km, t h e annual
lo6
l o s s should then be i n t h e o r d e r of 277 x 1.5 x 2.8 x a y e a r . T h i s i s about t h e same a s 1 . 2 mlrd m3/yr Vol. I X of t h e N i l e Basin ( H u r s t , H . E . ,
or about 1.16 mlrd m3
given f o r t h e p e r i o d 1912-52 i n and Simaika, Y . M . ,
Black, R . P . ,
1959).
The gauge-discharge measurements f o r t h e p e r i o d 1924-1927 a t Hassanab a r e shown g r a p h i c a l l y i n F i g . 30, Appendix E . The monthly and annual d i s c h a r g e s i n t h e p e r i o d 1912-1973 a r e given i n Table 1 3 , Appendix D , and t h e r e s u l t s of t h e i r s t a t i s t i c a l a n a l y s i s a r e i n Table 8 . 2 3 . From t h i s t a b l e and from Table 8 . 2 0 , one can compute t h e monthly and y e a r l y volumes r e p r e s e n t i n g t h e change i n t h e c o n t e n t s of t h e r i v e r trough p l u s t h e l o s s e s o r g a i n s averaged o v e r t h e same p e r i o d , i . e . 1912-1973. The r e s u l t s of computation a r e given below t o g e t h e r w i t h t h e f i g u r e s averaged f o r t h e p e r i o d 1912-1952,
f o r comparison.
Change of c o n t e n t s p l u s g a i n s o r l o s s e s , Period
lo6
m3,
averages f o r
J a n . Feb. Mar. Apr. May June J u l y Aug. Sep. O c t . Nov. Dec. Year
1912-52 -50* 0 1912-73 -51 -23
40 32
70 69
150 280 125 295
650 698
600 603
100 93
-400 -260 -30 -331 -192 -58
1200 1299
These r e s u l t s show c l e a r l y t h a t t h e sum of g a i n s i s s m a l l e r t h a n t h e sum of l o s s e s . The n e t y e a r l y loss is about 1 . 2 t o 1 . 3 mlrd m 3 / y r .
The g a i n between
Tamaniat and Hassanab t a k e s p l a c e i n t h e p e r i o d from October t o February, whereas t h e l o s s t a k e s p l a c e i n t h e remaining months. The change i n t h e flow from Tamaniat t o Hassanab caused by t h e g a i n s , l o s s e s and change i n r i v e r trough c o n t e n t s h a s a f f e c t e d t h e s t r u c t u r e o f some of t h e d i s c h a r g e s e r i e s . Compared t o Tamaniat, t h e J u l y , September and t h e y e a r l y s e r i e s of Hassanab a r e s e r i a l l y u n c o r r e l a t e d . The low-flow
s e r i e s , i . e . January
t h r u ' June and December remain, as do t h o s e of Tamaniat, s e r i a l l y c o r r e l a t e d . Like t h e s e r i e s of t h e upstream s t a t i o n s , t h e dependence i n t h e c o r r e l a t e d d i s charge s e r i e s of Hassanab can be d e s c r i b e d by an a u t o r e g r e s s i v e model. The resid u a l s e r i e s have been t e s t e d and found n o t t o be c o r r e l a t e d ( c o n f i d e n c e l e v e l = 957,). Table 8 . 2 4 g i v e s t h e v a l u e s of t h e s e r i a l c o e f f i c i e n t s of t h e r e s i d u a l s e r i e s . The m a j o r i t y of t h e d i s c h a r g e series a t Hassanab can be w e l l f i t t e d by t h e Pearson Type I 1 1 f u n c t i o n and t h e rest by t h e normal and lognormal f u n c t i o n s 6
The 100-yr and t h e 200-yr d i s c h a r g e s o b t a i n e d from t h e t h e o r e t i c a l d i s t r i b u t i o n s of a l l t h e s e r i e s a r e a s f o l l o w s : Discharge 106 ,3 J a n . Feb. Mar. Apr. May 100-yr 200-yr
f
June J u l y
Aug.
Sep.
Oct.
Nov. Dec.
Year
5320 4386 4024 4511 4587 4351 10132 20522 22890 18523 9400 5913 98210 5581 4700 4236 4799 4916 4606 10692 20803 23498 19417 9947 6121 100931
a l l t h e minus s i g n s h e r e mean g a i n
TABLE 8.23
The b a s i c s t a t i s t i c a l d e s c r i p t o r s and t h e s e r i a l c o r r e l a t i o n c o e f f i c i e n t s of t h e monthly and annual d i s charges o f t h e Main N i l e a t Hassanab for t h e p e r i o d 1912-1973
Item
Month o f t h e y e a r
Basic s t a t i s t i c a l descriDtor
X,
Jan.
Feb. ~~
~~~
Mar. ~
Apr. ~~
May ~
June ~~
July ~
~
C CV Serial correlation coefficient
r--
Sep.
0.2873 0.0539 0.1465 0.1117 0.0354 0.0152 0.0901 0.0367 0.0860 0500 . 0.1967 0.0888 0.0625 0.0731 0.0971
5.
0.3053 0.1360 0.2461 6.0916 0.1068 0.2651 0.0670 0.2068 0.2060 5.0066 0.0689 0 .0308 0.0897 0.0823 0.1244
0.5758 0.3374 0.4184 0.3218 0.3637 0.4761 0.4200 0.4044 0.3867 0.2597 0.2527 0.2850 0.1510 0.1189 0.1701
0.7643 0.6791 0.6500 0.5617 46114 0.6035 0.5762 0.5329 0.4821 0.4157 0,3772 0.3661 0.3019 0.2869 0.3064
0.6911 0.5679 0.4898 0.3491 0.4237 0.4329 0.4501 0.4135 0.3026 0.2592 0.1445 0.0960 0.0921 0.1035 0.1404
0.3636 0.3156 0 .0960 0.2080 0.0035 0.0428 0.2141 0.2329 0.2518 0.0612 6.0823 0.0887 4.1614 0.1369 0.1285
0.1626 5.0495 0.1053 0.1198 0.1018 0.1686 0.1506 0.1119 6.1292 0.0737 0.0151 0.1835 0.0638 0.1422 0.2713
Oct.
Nov.
Dec.
Year
~~
16432 5947 15982 2203 2594 2365 2283 3270 2410 3039 1533 2602 840 621 632 847 784 638 0.2399 0.2648 0.2674 0.3709 0.3814 0.2393 0,2578 0.1628 0.1849 0.3969 1.1142 0.4132 0.4204 0.7249 0.7058 0.5622 0.7796 0.2655 3.5739 5.8476 4.0487 2.4931 2.6125 3.1923 4.1176 4.0537 3.7169
lo6 m 3
s , 106 m 3
1' 2' 3' r4 r5 r6 r7 r8 r9 r10 '11 r12 r13 r14
Aug.
z. 0772
0.0206 0.0752 0 .0356 0.0385 0.1348 0.0465 0.0553 6.0467 6.0145 6.0609 0.1280 6.0750 0.0216 0.0099
0.1237 0.1007 0.1229 0.1156 0.0694 6.0984 0.0332 0.1550 0.1062 6.0396 6.1459 0.2487 0.0161 0.1102 0.1608
74276 5598 4089 11237 1320 757 9931 2864 0.2548 0.2358 0.1851 0.1337 0.2945 0.7769 0.1384 0.1379 3.5484 4.4776 3.6457 4.1719
0.1608 0.0179 0.2022 0.1083 0.0384 0.1996 0.0365 0.1493 0.0253 6.0730 6.2051 0.0987 0.1107 0.0288 0.0324
0.1173 0.0632 0.1232 0.0942 0.1448 0.0012 0.0316 0.1315 0.0085 0.1245 6.0811 0.0329 0.1170 0.0214 0.1623
0.2747 0.1578 0.0630 2.0960 0.0378 1935 0.1105 6.0034 0.0088 0.0280 6.1206 0.0955 0.0670 0.0483 0.0029
5.
0.2194 0.0144 0.0220 2.2246 0.1460 .0098 1094 0.1353 0.1150 6.0711 6.0961 0.1633 0.0008 0.0228 0.0048
p
0.
TABLE 8.24
S e r i a l c o r r e l a t i o n c o e f f i c i e n t s of t h e r e s i d u a l s l e f t from f i t t i n g a u t o r e g r e s s i v e models t o some of t h e discharge s e r i e s a t Hassanab Serial correlation coefficient
Month rl
Jan. Feb. Mar. Apr. May June Dec.
.052 :020 ,012 .171 l125 .088 .037
8.10
2 '
'3
1035 ,060 ,171 .028 .022 .191 .092
.115 .212 .240 .169 .165 .073 .052
r4
6 '
r5
1151 1018 TO39
.161 TO32 1165 ,215
.025 .033 .158 .152 .071 .159 .035
1z
.128 .237 .130 _096 ,020 .175
=7
r8
1109 .044 .071 .052 .lo5 :131 .073
1019 .015 .086 .057 .138 _095 .007
r9
r10
rll
r12
r13
'14
r15
.006 ,068 1199 . l o 3 1034 1059 .076
.002 j075 .116 .080 _045 .079 ,140
.183 ,060 .033 ,154 .024
,020 .029 .011 ,001 _ l o 7 ,042 .018 _070 .041 .178
.278 .lo2 1026 .035 .lo2
:035 .047 1010 .087 .026
1029 .020 1004 ,107 .053
.112 .127 .048 .128 .027
-
THE ATBARA R I V E R
The t o t a l s u r f a c e a r e a of t h e drainage b a s i n of t h e Atbara i s about 100 000 km2, of which about 68000 km2 comprise t h e b a s i n of t h e S e t i t , which i s t h e major t r i b u t a r y of t h e Atbara. The rest of t h e a r e a belongs t o t h e lower Atbara below t h e j u n c t i o n of t h e S e t i t . I t i s t h e r a i n f a l l on t h e catchment a r e a of t h e S e t i t t h a t is r e s p o n s i b l e f o r t h e major p a r t of t h e flow i n Atbara. The annual mean r a i n f a l l on t h e catchments of t h e S e t i t and Lower Atbara can be taken a s 800 mm/yr and 300 mm/yr r e s p e c t i v e l y . The annual run-off two catchments
i n t h e i r o r d e r can be taken a s 0.20 and 0.10 r e s p e c t i v e l y . These
f i g u r e s produce an annual run-off 11.84 x
lo9
coefficients for these
of 68 x
lo9
x 0.8 x 0.2
+
32 x lo9 :0 . 3 x 0 . 1 =
m3/yr.
The gauge-discharge measurements of t h e Atbara a t mouth a r e shown g r a p h i c a l l y i n F i g . 31, Appendix E . The monthly and annual d i s c h a r g e s i n t h e p e r i o d 1912-73 a r e given i n Table 14, Appendix D , and t h e r e s u l t s of t h e s t a t i s t i c a l a n a l y s i s of t h e s e discharge d a t a a r e included i n Table 8.25. The mean flow a t Atbara, near t h e mouth of t h e r i v e r , f o r t h e p e r i o d considered was 11.88 mlrd m3/yr. This volume of flow d i s t r i b u t e s i t s e l f o v e r t h e months, i n a normal y e a r , a s shown i n Fig. 8.45. The f i r s t f i v e months of t h e y e a r a r e p r a c t i c a l l y d r y . The e f f e c t i v e base width of t h e hydrograph i s from June up t o and i n c l u d i n g December. The flood season covers August and September and t h e remaining months r e p r e s e n t t h e low-flow season. The Atbara, i n t h i s r e s p & t ,
resembles t h e Blue N i l e ; both
a r e t o r r e n t i a l streams. This f e a t u r e l e a d s us t o review t h e r e s u l t s i n Table 8.25 c a r e f u l l y . The p e r i o d from January up t o and i n c l u d i n g May i s p r a c t i c a l l y dry. There a r e a few y e a r s i n which t h e r i v e r can b r i n g some l i t t l e water i n t h i s period. This does n o t , however, improve t h e long-term mean s e n s i b l y . I n s t e a d i t produces a considerable s c a t t e r l e a d i n g t o a high c o e f f i c i e n t of v a r i a t i o n and r a t h e r meaningless c o e f f i c i e n t s of skew and k u r t o s i s .
TABLE 8.25
The b a s i c s t a t i s t i c a l d e s c r i p t o r s and t h e s e r i a l c o r r e l a t i o n c o e f f i c i e n t s of t h e monthly and annual d i s charges of t h e River Atbara a t A t b a r a , n e a r mouth, f o r t h e p e r i o d 1912-1973
I tem
Basic s t a t i s t i c a l descriptor
X, S ,
106 m 3 106 m3
c
CV
f:onth of t h e y e a r Jan.
Feb.
Mar.
Apr.
May
7.7 1.1 3.6 31.8 4.1 18.8 1 . 5 19 2.7352 I g e 7 3.6348 5.2828 4.1288 2.2993 5.0538 5.7714 5.7813 4.6593 10.1766 32.8253 40.6174 36.8470 24.6862 20.3
Y
7.2
June
July
Aug.
Sep.
Oct.
Nov.
73.2 1616 812 101 1.3748 0.5026 1.5918 1.9888 4.9233 9.7805
5582 1842 0.3299 1.4805 7.1945
3496 1421 0.4065 0.4947 3.6017
812 415 0.5115 0.8970 4.6077
176 112 0.6332 1.1367 5.7258
6.2172 1892 0.1145 0.1876 0.0185 0.1052 0.1247 0.0462 0.0659 0.1261 0.0823 0.2258 0.0834 .0059 0.1900
0.2240 0 .0149 0.1476 0.0483 0.0479 0.1144 0.1125 0.2373 0.1087 0.0488 0.1270 0.0459 .0521 0.1179 0.0508
0.2212 0.0159 0.0318 0 .0637 0.2231 0.0124 0.0920 0.0740 0.1521 0.1084 1111 0.0197 0.0700 .1699 0.1220
0 .4174 0.2319 0.1443 0.0701 0.1295 0.1486 0.0979 0.0196 0.0256 0.1576 4.1224 0.1538 0.1043 0.3209 0.3084
0.2469 0.3424 0.2688 0.1054 0,2966 0.0774 0.0165 0.1580 4.1589 0.0237 c.2330 0.2523 0.1108 6.2930 6.1448
Dec. 57.6 47.2
0.8186 0.6843 2.9403
Year 11885 3913 0.3292 1.0933 5.6846
Serial correlation coefficient rl r2 r3 r4 l-5
r7 '8
r9 l-10 rll r12 r13 r14
r- -
0.3363 0.3139 0.3972 0.1523 0.3116 0.1995 0.1824 0.3030 0.0171 0.0152 0.1243 0.0051 0.0919 0.0372 0.0204
0.1957 0,1248 0.1756 0.0069 0.1404 0.0640 0.0740 0.3010 6.0327 0.0074 0.0759 0.0728 0.0434 0.0470 0.0523
0.0886 0.0784 0.1637 0.0072 0.1384 0.0435 0.1557 0.0752 0.0816 0 .0621 0905 .0892 0. 0812 0916 0.0843
4. 0
0.
c.
0.4284 0388 0.0401 0.0414 6.0428 .0442 0.0311 0.0084 0.1007 0.0593 .0111 0 .0120 0 .0130 0.0140 0.0151
p
4
0,3328 .0122 0 .0358 0.0186 0.0701 .0700 0.0477 0.0304 6.0125 0.0130 4.0338 0.0134 .0376 0.0396 0.0417
p
p
p
p.
p
6.2936 0.0429 0.0944 0 . 0504 0.0793 0.0079 0.0311 0.2671 0.2832 0.1466
4 .om1 0.1616 0.0231 0.0985 6.0406
p.
0.4918 0.3979 0.3274 0.2067 0.2861 0.1414 0.1690 0.1940 0.0322 0.1379 0 . 2048
0.1300
0.0515 0.2120 0.1217
0.0342 0 . 0400 0.0062 0.0427 0.0956 0 . 0772 0 .0590 0 . 1909 0.1857 0.0571 0.1697 0695
0.
2.0464
0.1643 6.0702
400
Month Fig. 8.45. The average hydrograph of t h e Atbara f o r t h e p e r i o d 1912-1973 a t Atbara, n e a r mouth
W e s h a l l , t h e r e f o r e , consider t h e monthly series from June t o December only and t h e annual series. Of t h e s e series t h o s e belonging t o June, October, November and December a r e t h e ones whose i n d i v i d u a l s appear t o be s e r i a l l y c o r r e l a t e d . F i r s t - o r d e r a u t o r e g r e s s i v e models have been f i t t e d t o t h e h i s t o r i c d a t a of t h e s e s e r i e s and t h e r e s i d u a l s examined s t a t i s t i c a l l y . The s e r i a l c o r r e l a t i o n s of t h e r e s i d u a l s e r i e s a r e given i n Table 8.26. They show t h a t they a r e not s i g n i f i c a n t l y d i f f e r e n t from zero with 95% confidence, except f o r November a t l a g s 2 and 4, and f o r December a t l a g 8 .
TABLE 8.26
S e r i a l c o r r e l a t i o n c o e f f i c i e n t s of t h e r e s i d u a l s l e f t from f i t t i n g a u t o r e g r e s s i v e models t o some of t h e d i s c h a r g e s e r i e s a t Atbara
~
Serial correlation coefficient
Month rl
July Oct. Nov. Dec.
r2
:136 :058 :188 .003 :067 .121 .166
r3 .023 TO97 .189 .232
r4
r5
r6
:217 .121 I 0 3 1 .019 .097 .154 .OOO .021 .153 .250 .010
.fi
r7
r8
r9
'10
'11
TO97 .165&1023 .162 T201 TO76 .010 :132 .078 :058 1031 .204 _158 :060 :150 .042 .115 .029 .049
.=
r12 .049 :069 :154 .161
r13
r14
r15
1170 1016 I087 :021 :134 :228 .005 :193 .039 .091 .124 .063
The p r o b a b i l i t y d i s t r i b u t i o n f u n c t i o n s t h a t s e r v e a s Rood f i t t o t h e d i s charge d a t a of t h e Atbara a r e t h e 2-parameter lognormal and t h e Pearson I 1 1 f u n c t i o n s . The f i t of t h e former t o t h e annual flow volumes i n t h e p e r i o d 19121973 i s shown i n F i g . 8.46.
40 1
40
-
30 m
I
,
I
,
I
,
I
0
.20 -
E
m
0
-
10
c
$ 8 ;
5 6 -
sul 5 -
-0
4 -
$ 3 U
2 -
1
I
,
,
I
,
I
1
1
I
l
l
,
,
I
,
1
s
The computed 100-yr and 200-yr discharges f o r t h e months from June up t o and i n c l u d i n g December and f o r t h e y e a r a r e a s f o l l o w s : Discharge 106 m3 100-yr 200-yr 8.11
8.11.1
June
July
Aug.
Sep.
Oct.
Nov.
Dec.
Year
415 476
4543 5106
11697 12747
7311 7817
2039 2223
524 571
191 210
23961 25874
THE MAIN NILE BELOW THE MOUTH OF THE ATBARA
The discharge of t h e Main N i l e a t Dongola
The monthly and annual discharges of t h e Main N i l e a t Dongola f o r t h e period 1912-1973 is given i n Table 15, Appendix D. The Main N i l e flows a d i s t a n c e of about 760 km below t h e c o d l u e n c e of t h e Atbara b e f o r e i t reaches Dongola. A p i c t u r e of t h e average width of t h i s reach of t h e r i v e r during t h e high-flow season can be seen from F i g . 2.23. The o v e r a l l average width between high and low flow seasons can be taken a s 400 m . This r i v e r reach runs i n a r e a l a r i d zone with about 8 mm/day f r e e water evaporation. This f i g u r e l e a d s us t o t h e conclusion t h a t t h e annual flow reaching Dongola i s about 0 . 8 8 mlrd m3/yr
less
than t h a t flowing j u s t below t h e Atbara j u n c t i o n . From Table 8.27, which cont a i n s t h e v a l u e s of t h e b a s i c s t a t i s t i c a l d e s c r i p t o r s and t h e s e r i a l c o r r e l a t i o n c o e f f i c i e n t s of t h e monthly and annual discharges a t Mongalla, one can f i n d t h e
40 3
annual flow volume averaged over t h e p e r i o d 1912-1973 a t 85.57 mlrd m3. This f i g u r e i s 0 . 5 8 mlrd m3/yr
less t h a n t h e sum of t h e mean flows a t Hassanab and
Atbara f o r t h e same p e r i o d . F i g . 8.47. shows a g r a p h i c a l p l o t of t h e annual flow volumes a t t h e mouth of t h e Atbara, a t Hassanab and a t Dongola. Because of t h e l a r g e n e s s of t h e flow a t Hassanab i n p r o p o r t i o n t o t h e flow a t t h e Atbara mouth, almost 6 t o 1, i t i s q u i t e u n d e r s t a n d a b l e t h a t t h e p l o t of t h e flow series a t Dongola i s very much p a r a l l e l t o t h a t of Hassanab and n o t of t h e Atbara.
1912'15 '20 '25 '30 '35 '40 '45 '50 '55
'60 '65 '70'73
Year F i g . 8.47. Graphical p l o t of t h e annual flow volume series a t A t b a r a , Hassanab and Dongola i n t h e p e r i o d 1912-1973
The s c a t t e r diagram of t h e sum of t h e flows a t Hassanab and a t t h e mouth of t h e Atbara, Y, a g a i n s t t h e flow a t Dongola, X , can b e seen from F i g . 8 . 4 8 . The r e g r e s s i o n of Y on X can be r e p r e s e n t e d by t h e e q u a t i o n
Y = 3.4125 + 0.96703 X
i n which Y and X a r e given i n mlrd m3/yr.
(8.9) The c o r r e l a t i o n c o e f f i c i e n t , r
b e i n g equal t o 0.96632, i s c e r t a i n l y s t r o n g .
XY'
From t h e v a l u e s of t h e s p i a l c o r r e l a t i o n c o e f f i c i e n t s l i s t e d i n Table 8 . 2 7 , one can observe t h a t a l l t h e s e r i e s , except t h o s e of t h e h i g h f l o o d d i s c h a r g e s , August and September, a r e s i g n i f i c a n t l y c o r r e l a t e d , a t l e a s t w i t h l a g 1. The f i r s t c o r r e l a t i o n c o e f f i c i e n t shows, i n g e n e r a l , a c o n s i d e r a b l e rise with d e c r e a s i n g mean d i s c h a r g e . The d e t e r m i n i s t i c component i n t h e s e r i a l l y c o r r e l a t e d d i s c h a r g e series can be f i t t e d each by a f i r s t - o r d e r a u t o r e g r e s s i v e scheme with t h e f i r s t s e r i a l c o e f f i c i e n t a s a parameter. The s t o c h a s t i c o r t h e r e s i d u a l component, which was l e f t from t h e f i t , was t e s t e d and t h e n u l l h y p o t h e s i s t h a t
404
Annual
flow
at
Dongola,
lo9
m3
Fig. 8.48. Simple l i n e a r r e g r e s s i o n between t h e sum of t h e f l o w s a t Hassanab and A t b a r a mouth, Y, and t h e f l o w a t Dongola, X, f o r t h e p e r i o d 1912-1973 that its s e r i a l
c o r r e l a t i o n c o e f f i c i e n t s a r e n o t s i g n i f i c a n t l y d i f f e r e n t from
z e r o (95% c o n f i d e n c e i e v e l ) c o u l d n o t b e r e j e c t e d . The o n l y e x c e p t i o n w a s t h e r e s i d u a l s e r i e s o f J u n e where t h e c o e f f i c i e n t a t l a g s 3 a n d 4 d i f f e r s s l i g h t l y from z e r o a t 95% l e v e l of c o n f i d e n c e . The s e r i a l c o r r e l a t i o n s of t h e r e s i d u a l
series are l i s t e d i n T a b l e 8 . 2 8 . The p r o b a b i l i t y d i s t r i b u t i o n f u n c t i o n s which a r e good f i t t o t h e monthly and a n n u a l d i s c h a r g e series a r e t h e P e a r s o n 111, t h e 2 - p a r a m e t e r l o g n o r m a l and t h e normal f u n c t i o n s . The f i t o f t h e P e a r s o n Type I 1 1 f u n c t i o n t o t h e d i s t r i b u t i o n o f t h e a n n u a l flow volumes a t Dongola i s shown g r a p h i c a l l y i n F i g . 8 . 4 9 . The t h e o r e t i c a l l y computed 100-yr and 200-yr d i s c h a r g e s are as f o l l o w s : P
Discharge 106 ,3 J a n . Feb. Mar. Apr. May 100-yr 200-yr
J u n e J u l y Aug.
Sep.
Oct.
Nov.
Dec.
Year
5517 4708 4685 4389 4622 4486 9524 27322 30690 22923 12103 6814 117755 5788 5079 4806 4688 5005 4846 9 8 1 1 28053 31600 24027 12845 7114 121617
405
TABLE 8 . 2 8
S e r i a l c o r r e l a t i o n c o e f f i c i e n t s of t h e r e s i d u a l s l e f t from f i t t i n g a u t o r e g r e s s i v e models t o some of t h e d i s c h a r g e series of t h e N i l e a t Dongola
Serial correlation coefficient
Jan. Feb. Mar. Apr. May June July Oct. Nov. Dec.
.050 .067 .067 1052 :119 :044 .024 ,037 ,004 .018
.083 .086 1208 ,037 TO38 1137 1012 TO62 1092 I120 .045 1066 .003 .079 .135 ,220 ,070 .061 .053 .006 .001 ,062 ,208 .046 ,042 7112 .161
TO69 Tl6l T155 TO36 .019 .040 .033 .169 .212
.154 .148 .154 ,250 .222 .232 .243 .154
,081 .042 1109 .326 .003 :077
.065 .050 .118 .155 .081 ,082 .173 .d87 .033 .026 .239 .080 .159 .076 TO79 .070 TO20 .008
.087 TO16 .047 ,096 .056 .039 ,076 .092 .015 TO50 ,051 .154 .038 .077 T O 4 8 .060 .162 :061 .111 _005 TO26 .128 .153 .lo1 .095 ,009 .063 . l o 5 .068 ,107 . 0 1 1 .082 TO36 . l o 4 . l o 8 TO90 .026 TO53 .113 T122
.lo4 .118 .027 .041 .138 .098 .021 .115
,045 .027 ,012 ,127 .166
,076
1050 .174 TO98 .022 :096 .063 .094 .094 T l l l
120
110
100 0
rn
90
0
&
80
L
0
II
s1
0
-0
70
C
2
60
50
0
40 Non
- exceedance
.114
.039 .094
p r o b a b i l i t y , '10
Fig. 8.49. F i t o f t h e Pearson Type I 1 1 f u n c t i o n t o t h e d i s t r i b u t i o n of t h e annual d i s c h a r g e s i n t h e Main N i l e a t Dongola f o r t h e p e r i o d 1912-1973
.077 .093 T147
.006
.096 .135
406
8.11.2
The d i s c h a r g e of t h e Main N i l e a t Aswan
Downstream of Dongola t h e Main N i l e flows t o t h e n o r t h then bends t o t h e e a s t and t o t h e w e s t and once more t o t h e e a s t t h e n n o r t h - e a s t t o Wadi H a l f a . T h i s reach i s about 450 km i n l e n g t h . Discharge measurement a t Wadi H a l f a began i n 1911, and w i t h a gap d u r i n g t h e F i r s t World War, c o n t i n u e d
u n t i l 1931. The
gauge-discharge measurements, 1911-1927, which were used f o r c o n s t r u c t i n g t h e r a t i n g curve f o r t h i s s t a t i o n a r e shown i n F i g . 32, Appendix E . The measuring s i t e a t Wadi H a l f a was inundated by t h e backwater caused by t h e second heighteni n g of t h e Aswan Dam about 1934. The s i t e was moved t o K a j i n a r t i , which i s about 50 km s o u t h of H a l f a . The l o s s i n t h e reach below t h e j u n c t i o n of t h e Atbara w i t h t h e Main N i l e and Wadi H a l f a i s about 1210 km x 0 . 4 km x 2.7 m , or about 1 . 3 mlrd m 3 / y r .
Vol. I X
of t h e N i l e Basin g i v e s 8 6 . 1 mlrd m 3 / y r as t h e sum of t h e flows a t Hassanab and t h e Atbara mouth. The flow i n t h e Main N i l e a t K a j i n a r i t y or H a l f a was 85.3 mlrd
m3/yr.
These two f i g u r e s a r e t h e averages f o r t h e p e r i o d 1912-1952. T h i s means
t h a t t h e l o s s averaged over t h e same p e r i o d i s 0 . 8 mlrd m 3 / y r . T h i s i s r e l a t i v e l y much l e s s t h a n t h e 1 . 3 mlrd m3/yr
a l r e a d y given by u s . One s h o u l d n o t f o r g e t ,
however, t h a t t h e a b s o l u t e f i g u r e i s i n i t s e l f q u i t e s m a l l , and having i t e s t i mated as t h e d i f f e r e n c e between two much l a r g e r q u a n t i t i e s s t r o n g l y i n f l u e n c e s
i t s accuracy. The Main N i l e flows about 345 km i n a r e a l a r i d zone, w i t h r a i n f a l l of less than 10 m m / y r ,
b e f o r e r e a c h i n g Aswan. The r a t i n g c u r v e p o i n t s measured i n t h e
p e r i o d 1918-1927 a t Khannaq s t a t i o n a r e shown i n F i g . 33, Appendix E.The monthly and annual d i s c h a r g e s a r e l i s t e d i n Table 1 6 , Appendix D . These d a t a d i f f e r from t h e corresponding ones a t Dongola by t h e conveyance l o s s b e t w e e n t h e two s t a t i o n s and t h e s t o r a g e l o s s e s a t Aswan. The t o t a l loss i n a y e a r averaged over t h e p e r i o d 1912-1973 was 3.368 mlrd m 3 , or about 3.94% of t h e annual flow a t D o n g o l a . The c l o s e resemblance between t h e d i s c h a r g e s a t Aswan and Dongola can be s e e n , f o r example, from a comparison between F i g . 8.50.and F i g . 8 - 4 7 . , both showing t h e p l o t of t h e annual flow volumes. The monthly and annual d i s c h a r g e series a t Aswan, l i k e a l l main s t a t i o n s on t h e N i l e , have been analyzed s t a t i s t i c a l l y and t h e r e s u l t s o b t a i n e d a r e presen5
t e d i n Table 8 . 2 9 . Examination of t h e s e r e s u l t s shows t h a t a l l d i s c h a r g e series a t Aswan, monthly and y e a r l y , undergo some s i g n i f i c a n t dependence i n t h e i r s t r u c t u r e . The dependent component i n each s e r i e s can be d e s c r i b e d by a f i r s t - o r d e r a u t o r e g r e s s i v e e q u a t i o n i n which t h e f i r s t s e r i a l c o r r e l a t i o n c o e f f i c i e n t i s a parameter. The r e s i d u a l s l e f t a f t e r removing t h e dependent component from each d i s c h a r g e s e r i e s have been examined and t h e h y p o t h e s i s t h a t t h e s e r i a l c o r r e l a t i o n between t h e i t e m s of t h e r e s i d u a l series i s n o t s i g n i f i c a n t ( a t 95% c o n f i dence l e v e l ) could n o t be r e j e c t e d f o r most of t h e d i s c h a r g e series. I t i s
407
120
3
0
110
..- 19000 -2 80 :rn' 70 O
3
3
E 60
3
< z 50 1912'15
'20 '25
'30 '35 '40 '45 '50 '55 '60 '65 '70'73 Year
F i g . 8.50. G r a p h i c a l p l o t o f t h e a n n u a l f l o w volume series a t Aswan on t h e Main N i l e i n t h e p e r i o d 1912-1973 p o s s i b l e t h a t t h e dependence i n some o f t h e r e m a i n i n g series n e e d s t o b e d e s c r i b e d by h i g h e r - o r d e r a u t o r e g r e s s i v e e q u a t i o n s so as t o r e n d e r t h e r e s i d u a l components t o b e u n c o r r e l a t e d . The s e r i a l c o r r e l a t i o n c o e f f i c i e n t s of t h e resid u a l series c a n b e f o u n d i n T a b l e 8.30. The a v e r a g e h y d r o g r a p h a t Aswan f o r t h e p e r i o d 1912-1973 i s shown i n F i g . 8 . 5 1 T h i s h y d r o g r a p h does n o t r e p r e s e n t , i n t h e f i r s t p l a c e , t h e n a t u r a l c o n d i t i o n . The low-flow s u p p l y o f t h e r i v e r i n t h e p e r i o d from November up t o and i n c l u d i n g J u n e i s somewhat m o d i f i e d by t h e e x i s t i n g s t o r a g e works on t h e N i l e . The s t o r a g e r e s e r v o i r a t Aswan a l o n e h a s r e s u l t e d i n t h e i n c r e a s e i n t h e a v e r a g e volume of f l o w d u r i n g t h e mentioned s e a s o n from 26.12 m l r d m3 a t Dongola t o 27.69 mlrd m 3
a t Aswan, i . e . a n e t g a i n of 1 . 5 7 m l r d m 3 . A d e t a i l e d d i s c u s s i o n of t h e s t o r a g e on t h e N i l e s h a l l b e p r e s e n t e d , hwoever, i n t h e n e x t c h a p t e r . The p r o b a b i l i t y f u n c t i o n s t h a t s e r v e a s good f i t t o t h e monthly d i s c h a r g e d a t a a r e t h e P e a r s o n Type I 1 1 and t h e % p a r a m e t e r l o g n o r m a l . The normal f u n c t i o n
is a v e r y good f i t to t h e d i s t r i b u t i o n o f t h e a n n u a l d i s c h a r g e series. T h i s c a n b e s e e n from F i g .
8 . 5 2 . The monthly and a n n u a l f l o w s w i t h 100 and 200 y e a r s
r e t u r n p e r i o d have been computed from t h e s e d i s t r i b u t i o n f u n c t i o n s and a r e as g i v e n below:
Discharge 106 ,3 J a n . Feb. Mar. Apr. May 100-yr 200-yr
J u n e J u l y Aug.
Sep.
Oct.
Nov.
Dec.
Year
5546 4898 5162 4659 6337 8018 8355 26416 28792 21265 13145 7624 117618 5809 5208 5587 5025 7 0 3 1 9056 8816 27114 29144 21696 13640 8001 121416
The above a n a l y s i s o f t h e d i s c h a r g e s a t Aswan i s b a s e d on t h e a s s u m p t i o n t h a t t h e y a r e homogeneous. The v a l i d i t y o f t h i s a s s u m p t i o n seems q u e s t i o n a b l e .
9.
TABLE 8 . 2 9
0 0
The b a s i c s t a t i s t i c a l descriptors and the s e r i a l correlation c o e f f i c i e n t s of the monthly and annual discharges of the N i l e a t Aswan, for the period 1912-1973
~
I tem
Basic s t a t i s t i c a l descriptor
?, 106 m3
s , 106 m3 C
CV
Month of the year June
July
Aug.
Sep.
Oct.
NOV.
Dec.
Year
2399 1610 0.6713 0.7765 5.1028
4670 1420 0.3040 0,3694 3.0563
16623 5168 0.3109 0.5681 2.9880
19466 6388 0.3282 0.1680 4.1945
13742 4311 0.3137 0.7856 4.0836
7376 2241 0.3038 0.3376 3.2447
4788 1020 0.2131 0.6138 4.1724
82202 15224 0.1852 0.1610 3.1683
0.4750 0.2813 0 $0503 0.0802 0.0975 0.2759 0.1627 0.1331 0 ,0604 I,.0417 0.0129 0.0877 0.1041 0.2234 0.2515
0.4028 0.6773 0.4415 0.5779 0.3200 0.4575 0.2886 0.3050 0.1232 0.2561 2.1201 2.0435 0.0411 0.0300 .1222 0.0605 0 . 1825 0.1917 0.1010 0.1563 0.1659 0.1708 0.0629 0.1021 0.2363 0.1945 0.1882 0.1713 0.1817 0.0873
0.5825 0.2422 0.3128 0.4198 0 -2059 0.2150 0.3146 0.2193 0.1412 0.1217 5.0769 6.1717 0.1336 0.0817 0.0609 0.0754 0.0023 0.1121 0.0169 0.1147 0.1706 2.0695 0.0579 0.0423 0 , 0969 6.0967 0.0354 0.1163 0.0451 0.0575 0,1198 0.1707 0.1302 2.0512 0.1166 0.0295 0.0742 0.0208 2 -0927 0.1647 0.1612 0.0592 0.1277 0.0213 0.1157
0.4838 0.2979 0.1679 0.0033 0 .0239 0.0362 0,. 1360 0.0973 0 , 1543 0.0974 0 . 1478 0.0282 0.1212 0,2148 0,1268
Jan.
Feb.
Mar.
APr.
3578 740 0.2069 0.4676 4.3987
2704 777 0.2874 0.6999 3.8095
2480 868 0.3501 1.0892 3.7018
2153 861 0.3998 0.8272 2.9905
2214 1261 0.5695 1.3802 4.0417
0.2623 0.0012 0.0265 2332 0.1661 0.y 8 8 0.1844 0.0753 0.1196 0.0425 6.2115 0.0185 0.0043 0.0589 0.1374
0.4792 0.3085 0.3268 0.0584 0.1387 0.1851 0.1207 0.1917 0.1302 0.0568 0.2149 0.0536 0.0352 0.0422 0.1113
0.6342 0.5246 0.4820 0.3157 0.3027 0.3187 0.2627 0.2659 0.1591 0.0497 0.0226 0.0232 6.0005 8.0104 0.0873
0.7779 0.6737 0.6242 0,5071 0.4893 0.4737 0.4597 0.4613 0.3885 0.3437 0,3166 0.2938 0 .a389 0.2256 0.2340
0.8389 0.7964 0.7537 0.7179 0.6772 0.6410 0.5665 0.4976 0.5169 0.4611 0.4455 0.3325 0.4047 0.2246 0.3662 0.2296 0.2990 0.1062 0.2463 0.0775 0.2038 0.0079 0.1759 0.0198 0.1637 0 -0268 0.1439 0.0524 0.1496 0.0045
May
S e r i a l correlation coefficient rl
r2 r3 r4 r5 '6 r7 r8 r9 r10 rll r12 r13 r14 1. c
!.
p
409 TABLE 8 . 3 0
S e r i a l c o r r e l a t i o n c o e f f i c i e n t s of t h e r e s i d u a l s l e f t from f i t t i n g f i r s t - o r d e r a u t o r e g r e s s i v e models t o t h e d i s c h a r g e a e r i e s of t h e Main N i l e a t Aswan
Month
Serial correlation coefficient
0
Year Jan * Feb. Mar. Apr May June July Aug Sep. Oct. Nov.
.
.
DeC
.
Year
I1
.*
r2
448 .%
;126 1117 .221 .114 T255 TO40 -. 1 4 3 .046 -.229 .083 -.049 - 1 2 3 -.074 .% -.110 .197 -. 0 4 3 . 1 3 4 -.026 .185 -.051 -154 .041 .114 4
'3
r4
IS
'6
.=1067
-
r8
.=.=.=.=1040
-076 1176 -004 .009 .349 .268 .063 .135 .239 .150 .042 .178 -195 .138 .278 .209 :339 .087 .118 -080 .024 -254 .141 .203 .029 :175 .173 1007 .086 .202 ,060 .161 . 1 4 1 .231 ,083 .151 ,031 .163 :170 .059 .036 .096 .015 .034 .082
-_
'7
.=
'9
,247 ,057 :OS7 .OS8 .006 .069 ,066 .061 .141 .003 :043 ,021 ,023 .079 :143 ,032 ,038 . O W ,029 .095 ,090 .037 :lo2 .044 :137 -032 ,049 :070 . l o 2 OS9 .093 .040 1070
.382 .240 -106 .097 .1S8 .002 .161 .130 ,018 .165 ,160 .094 ,033 -.188 ,141 -.034 .058
'10
.
'11
'12
:252 ,203 :208 .030
.a21 .071 .lo4 .061
:008
-050
'13
'14
,189 ,178 ,007 ,001 ,027 ,080 .010 ,129 :004 ,056 ,010 :138 ,054 ,112 ,194 ,044 ,227 ,015 -031 -103 .043 I124
_045 .086 :059 - 1 7 3 ,151 .113 :115 .182 :041 ,054 ,129 .061 ,159 .055 ,068 :086 .134 . l o 6 .096 .117
'15 .189
.OW
.147 .136 .lo7 ,155 _134 :053 :041 .069
~~
The u n d e r l i n e d v a l u e s are t h o s e s e r i a l c o e f f i c i e n t s which are s i g n i f i c a n t l y d i f f e r e n t from z e r o a t 95% c o n f i d e n c e l e v e l
F i g . 8.51. 1912-1973
The a v e r a g e hydrograph o f t h e Main N i l e a t ASWM
.OX
,092 .024
f o r t h e period
4 10
120
110
100 m
m
90
0 $ 80 L
0
r d U
< 70
-
0 3
Q
60
50
.01
.05 .1 .2 .5 1
2
5
10
Non
20 30 40 50 60 70 80
- cxceedancc
probability, -1.
90 95
98 99 99.5
F i g . 8.52. F i t of t h e normal f u n c t i o n t o t h e d i s t r i b u t i o n of t h e annual d i s charges i n t h e Main N i l e a t Aswan f o r t h e p e r i o d 1912-1973 A mathematical model of t h e River N i l e from i t s e x i t a t Lake Albert t o i t s
e n t r a n c e i n t o Lake Nasser upstream Aswan has very r e c e n t l y been designed and c a l i b r a t e d (Fahmy, A . ,
Panattoni, L.,
and Todini, E., 1982).
The d i f f e r e n t components of t h e N i l e system w e r e a l l modelled using t h e soc a l l e d Constrained Linear Systems model (CLS). This type w a s chosen as a consequence of an a n a l y s i s of t h e purposes of t h e model and t h e amount and n a t u r e of t h e a v a i l a b l e d a t a . The f i r s t component covers t h e reach from Pakwach ( e x i t of t h e N i l e a t Lake A l b e r t ) t o Mongalla; t h d s e c o n d covers t h e reach from Mongalla t o Malakal and H i l l e t Doleib on t h e White Nile and t h e t h i r d , which is divided i n t o two p a r t s , covers t h e River Sobat. The f o u r t h component o r submodel covers t h e reach from Malakal (downstream t h e mouth of t h e Sobat) t o Mogren; t h e f i f t h d e a l s with t h e Blue N i l e , and t h e s i x t h covers t h e reach from Mogren t o Wadi Halfa. A f t e r t h e i n d i v i d u a l submodels w e r e i d e n t i f i e d , they w e r e assembled t o g i v e a model of t h e e n t i r e system from Lake A l b e r t t o Lake Nasser. A f o r t r a n programme was used t o s i m u l a t e t h e behaviour o f a l l t h e system and t h e d i f f e r e n t reaches.
411 The model has been used by i t s d e s i g n e r s f o r computing t h e discharges a t Wadi Halfa a f t e r feeding i t with t h e discharges a t Pakwach i n t h e period from 1953 t o 1972. The comparison between t h e observed and computed hydrographs a t Wadi Halfa show t h a t t h e r e s i d u a l s have a mean and a s t a n d a r d e r r o r o f 2.55 and 28.6 m i l l i o n m3/day, r e s p e c t i v e l y . The l a t t e r f i g u r e corresponds t o 12.2% of t h e d a i l y discharge a t Wadi Halfa. 8.11.3
From Aswan t o t h e Mediterranean Sea
The water t h a t had been l e a v i n g t h e o l d Aswan Dam every y e a r used t o flow i n t h e Nile and i t s branches on i t s way t o t h e Mediterranean Sea. A c e r t a i n p a r t of t h i s flow had been used f o r l a n d i r r i g a t i o n and f o r domestic purposes and t h e
rest had been discharged i n t o t h e s e a . The annual q u a n t i t y passing downstream of Aswan Dam i n such a normal y e a r a s 1947 was 8 4 . 3 mlrd m3. Of t h i s amount, 6 . 6 mlrd m 3 were used f o r b a s i n i r r i g a t i o n , 38.1 mlrd m 3 f o r p e r e n n i a l i r r i g a t i o n and less than 1 mlrd m 3 f o r domestic and i n d u s t r i a l purposes. The rest, almost 39 mlrd m 3 was thrown i n t o t h e s e a . The consumption of water i n Egypt t h a t y e a r , which reached 45.7 mlrd m3, was very n e a r t o t h e f u l l s h a r e of Egypt i n t h e N i l e water a t t h a t t i m e . This was l i m i t e d t o 48 mlrd m3/yr.
I r r i g a t i o n was, and s t i l l
i s , accomplished v i a an i n t r i c a t e c a n a l system. The g e n e r a l l a y o u t of t h e main
c a n a l s i s shown i n F i g . 8.53. From Aswan t o C a i r o t h e r e i s hardly any r a i n f a l l worth mentioning and t h e discharge downstream of Aswan is p r a c t i c a l l y t h e only s o u r c e of water. I n t h i s r e a c h , gauge d i s c h a r g e measurements a r e taken more o r less r e g u l a r l y a t a number of p l a c e s . Examples of t h e s e a r e given f o r Hawatka s t a t i o n n e a r Assiut i n 19261927, F i g . 34, Appendix E , and f o r Beleida s t a t i o n n e a r Koraimat i n 1920-1922, F i g . 35, Appendix E. Before t h e c o n s t r u c t i o n and o p e r a t i o n of t h e s t o r a g e works on t h e N i l e , a g r i c u l t u r e i n Egypt depended almost e n t i r e l y on t h e n a t u r a l supply of t h e r i v e r . The annual inundation of t h e N i l e Valley i n t h e l a t e summer g e n e r a l l y supplied enough moisture t o t h e s o i l t o e n s u r e f a i r crops i n t h e f a l l and w i n t e r . No wonder, t h e n , t h a t t h e most important annual event i n Egypt was t h e Nile flood and, t h e r e f o r e , r e c o r d s were engraved on t h e c l i f f w a l l s i n v a r i o u s p l a c e s , 9
notably a t Semna, a s e c t i o n of . t h e second c a t a r a c t ( s e e map, F i g . 2.25.). Several s e c t i o n s of n i l o m e t e r s , a t v a r i o u s p o i n t s along t h e stream channel, have been discovered, and t h e i r i n s c r i p t i o n s have been deciphered and c o r r e l a t e d . C.S.
J a r v i s combined t h e d i s c o v e r i e s and memoires of S i r H . Lyons, M . LeGrain,
P r i n c e O m a r Toussoun, Aboul Mehasin and many o t h e r s who kept themselves busy with t h e N i l e w a t e r l e v e l s . This l e d J a r v i s t o p u b l i s h h i s marvellous paper on t h e flood-stage records of t h e River N i l e i n Egypt ( J a r v i s , C . S . ,
1935). From
4 12
t h i s paper we have copied t h e maximum and minimum annual l e v e l s of t h e r i v e r a t t h e Roda n i l o m e t e r , Cairo, i n t h e p e r i o d from 622 up t o 1933 and p r e s e n t e d i t
h e r e as Fig. 8.54.
MEDITERANEAN
SEA
lsmailia Canal
Western N a g Hammadi Canal
Kallabiya
Canal
u
1 1, Y--
Assiut
Barrage
Eastern N a g H a m m a d i Canal
Asfoun C a n a l
Esna
Barrage
Old Aswan D a m H i g h Dam
i'
Fig. 8.53. The d i s c u s s i o n s on t h i s paper by Hurst and K.O. Ghaleb, both w e l l equipped w i t h o u t s t a n d i n g information gained from a c t u a l experience w i t h t h e r i v e r , have pointed t o a number of sources of error i n t h e s e d a t a . With f u l l r e c o g n i t i o n of t h e s e e r r o r s and o t h e r p o s s i b l e d i s c r e p a n c i e s i n t h e d a t a , one cannot deny t h e value of t h e l e n g t h of t h i s series and i t s f a i r completeness, e s p e c i a l l y from about 622 t o about 1450 A.D.
413
From t h e s e d a t a J a r v i s found t h e rise i n t h e N i l e f l o o d l e v e l a s c r i b a b l e t o sedimentation t o range from 0.10 t o 0.15 m p e r c e n t u r y . J . C .
Stevens repeated
t h i s c a l c u l a t i o n u s i n g t h e simple 10-yr averages and t h e p r o g r e s s i v e 50-yr averages ( J a r v i s , C.S.,
1935). H e concluded t h a t t h e average r i s e was p r a c t i -
c a l l y 4 inches (0.10 m) p e r century f o r both t h e maximum and minimum s t a g e s . He f u r t h e r concluded t h a t no p e r i o d i c c y c l e w a s i n evidence, but high c y c l e s a l t e r n a t e d w i t h low c y c l e s of i r r e g u l a r d u r a t i o n . From t h a t n e a r l y continuous record and from t h e s p o r a d i c records of i s o l a t e d p e r i o d s running back over 5000 y e a r s , t h e r e appears t o have been l i t t l e o r no c l i m a t i c changes t h a t can be d e t e c t e d . The conclusions drawn by T . H . Means from h i s d i s c u s s i o n on t h e same paper were almost i d e n t i c a l t o t h o s e given by Stevens which have a l r e a d y been presented ( J a r v i s , C.S.,
1935).
We s h a l l p r e s e n t t h e change i n t h e r i v e r bed a s a r e s u l t of t h e c o n s t r u c t i o n of t h e High Aswan Dam i n Chapter 9 . The evaporation l o s s between Aswan and C a i r o i n t h e pre-High Dam p e r i o d could be f i g u r e d o u t approximately a s t h e l e n g t h of t h e reach, 900 km, times t h e average weighted width, 500 m , t i m e s t h e annual evaporation depth, 2 m . This gives 0 . 9 mlrd m3/yr t o be rounded o f f t o 1 . 5 mlrd m 3 / y r t o account f o r t h e l o s s e s from t h e network of i r r i g a t i o n c a n a l s . Whether t h e r e s u l t a n t of t h e seepage from t h e r i v e r and t h e r e t u r n flow t o i t could be considered as a n e t gain
or n e t l o s s i s n o t p r e c i s e l y known. The r e l a t i o n s h i p between both t h e l o s s or g a i n and t h e f a c t o r s a f f e c t i n g i t i n t h e post-High Dam p e r i o d , w a s s t u d i e d by Saleeb, S.I. (1977). To implement t h i s study, t h e r i v e r reach from downstream of Aswan t o C a i r o w a s divided i n t o four reaches ( s e e map, F i g . 8 . 5 3 . ) . The outflow from an upstream reach i s cons i d e r e d a s inflow t o t h e next downstream r e a c h , and so on. Taking t h e town of Assiut a s t h e c e n t r e of g r a v i t y of t h e reach from Aswan t o C a i r o , t h e l o s s or g a i n w a s found t o be a f f e c t e d by t h e d i s c h a r g e j u s t downstream of Aswan, themean a i r temperature and humidity a t Assiut 5 days lagging behind Aswan and t h e groundwater l e v e l a t A s s i u t . The r e g r e s s i o n models f o r t h e d a i l y and monthlyloss or g a i n have been developed and t h e optimum monthly discharges found. These d i s -
charges are included i n Table 8.31. The monthly means of t h e 6-yr p e r i o d 1968-73 and of t h e 56-yr p e r i o d 19f2-67 a r e a l s o included i n t h i s t a b l e f o r t h e purpose of comparison. The optimum d i s c h a r g e s have been found on t h e grounds t h a t they correspond t o t o t a l l o s s o r g a i n equal t o z e r o . A s h o r t d i s t a n c e below C a i r o , t h e r i v e r b i f u r c a t e s i n t o i t s t w o branches:
D a m i e t t a and R o s e t t a . These branches are t h e main source of w a t e r feeding t h e i r r i g a t i o n c a n a l s i n Lower Egypt. They were a l s o used i n t h e pre-High Dam period t o convey t h e excess f l o o d water t o t h e Mediterranean Sea. This i s no longer t h e
case a f t e r e x e r c i s i n g f u l l c o n t r o l on t h e N i l e water by means of theHighAswanDam
4 14
415 In F i g . 8 . 5 4 . , t h e v a r i o u s p l o t t e d p o i n t s may be i d e n t i f i e d a s follows: Applying t o a l l t h e records:
= f i v e - y e a r average f o r t h e d a t a shown by d o t s , sup-
V
X
*
plemented by - o r (-) when t h e l o c a t i o n of t h e dot i s n o t given; = ten-year average f o r d a t a shown by d o t s , suppleo r (-) when t h e l o c a t i o n of t h e dot i s mented by n o t given; and, = one hundred-year average
-
Applying t o t h e Roda Gauge a t Cairo: r e c o r d s compiled by Omar Toussoun+ covering t h e 1300-yr p e r i o d from 622 t o 1921 A.D.; confirmation from t e x t u a l n o t e s f o r t h e r e c o r d s compiled by Omar Toussoun: when - i s l a c k i n g , an agreemept is i n d i c a t e d between a l l t h r e e s o u r c e s ; r e c o r d s compiled by Aboul Mehasin++, covering t h e p e r i o d , 20 t o 855 of t h e Hegira, o r 641 t o 1451 A.D., a t o t a l of 811 y e a r s . A small + i n d i c a t e s e x t r a d a t a , r e p r e s e n t i n g 25 s u r p l u s y e a r s of Mohammedan reckoning; r e c o r d s from n o t e s compiled by Ibn Iyas and others+++, f o r t h e period 769 t o 1878 A.D. r e c o r d s by Lyons'; and r e c o r d s i n d i c a t i n g "wafa", or t h e s t a g e t h a t a s s u r e s p l e n t y , a t which t h e c a n a l s w e r e opened t o supply t h e b a s i n s ; t h e maximum f l o o d s t a g e , o r d i n a r i l y , w a s somewhat h i g h e r . Applying t o t h e gauge downstream from Aswan Dam:
A = maximum annual r i v e r s t a g e s a t t h e Aswan gauge above t h e assumed datum, 71.0 m, or 232.9 f t , above mean Mediterranean Sea l e v e l ;
w = maximum ten-day average gauge h e i g h t s , and, t h e r e f o r e , somewhat below t h e a c t u a l maximum.
Applying t o t h e E l - L e i s i
* =
gauge, 37 miles upstream from Cairo:
maximum ten-day average gauge h e i g h t s and, t h e r e f o r e , somewhat below t h e a c t u a l minimum.
The gauge h e i g h t s p l o t t e d a s o r d i n a t e s i n F i g . 8 . 5 4 . a r e readings from t h e Roda gauge on t h e N i l e River a t Cairo. The e x c e p t i o n s , marked A o r J , r e f e r t o r e a d i n g s of t h e Aswan gauge and t h o s e marked 0 r e f e r t o readings of t h e E l - L e i s i gauge, 37 m i l e s above C a i r o . I n a l l c a s e s t h e r e a d i n g s a r e t h e mean Mediterranean Sea l e v e l e l e v a t i o n s a t Alexandria,.
Scale of Meters 0
10
20
I . ~ . ' . 25 ' . I ' " . 'I ~.50l ' ' . , ! - ' 75, ' * : - ' " I Scale of Feet Scale of Cubits (Egyptian) 10 0 I . . ... . . ! . .'!. :. * * :. . .'.. 30 20 0 10 Scale of Feet
30
0
.I..
1 Cubit
=
-
6'.
9
I
23.9417 Digits, 10 Digits
++
100
- - - :, 20
I
50
40
: . ' . ' -125: ~ " * . 150 '"''*.I 154 T.'...'.
40
- . ...
30 I
.-I
5051 L
8.5875 Inches
++
LOC. C i t . , 1923, Vol. 4 . ; loc. cit., +Memoirs, I n s t . of Egypt, 1925 Vol. 9 . ; 1923 and 1925, Vol. 4 and 9 . ; *"The Nile Flood i n 1905", by Capt. H.G. Lyons
4 16
TABLE 8 . 3 1
Comparison between t h e a c t u a l and t h e proposed optimum discharges downstream of Aswan Dam
Month &
Average f o r t h e p e r i o d s , mlrd m 3
Year
1912-67 (56 y r s )
1968-73 (6 y r s )
January February March April May June July August September October November December Year
36 25 25 79 2335 1968 1894 1959 4448 17743 21095 14808 7777 4948 85149
3142 3870 3836 3877 5200 6507 6 742 6167 4265 3788 3634 3296 54324
Optimum d i s c h a r g e from m u l t i p l e r e g r e s s i o n model mlrd m3 2713 3646 3900 3588 5 180 6552 6699 5943 389 1 3419 3069 2880 51480
REFERENCES Ahmed, A . A . , 1960. Recent developments i n N i l e c o n t r o l . Proceedings I n s t i t u t i o n of C i v i l Engineers, London, Vol. 17, Paper No. 6102: 137-180. Berg, C . L . , 1953. D e t a i l e d a n a l y s i s of a discharge measurement on t h e V i c t o r i a N i l e . Proceedings I n s t i t u t i o n of C i v i l Engineers, London, P a r t 111, Vol. 2, Paper No. 5935: 609-613. C a i r o University/MIT, 1977. The River N i l e p r o j e c t ; s t o c h a s t i c modelling of t h e N i l e inflows t o Lake Nasser. Cairo University/MIT t e c h n o l o g i c a l planning programme, C a i r o , Egypt. Fahmy, A . , P a n a t t o n i , L . , and Todini, E . , 1982. A mathematical model of t h e River N i l e . Engineering a p p l i c a t i o n s of computational h y d r a u l i c s (Abbott, M.B., and Cunge, A . J . : e d i t o r s ) , Pitman, London: 111-130. H u r s t , H . E . , and P h i l i p s , P . , 1932. The N i l e Basin, Vol. 11, measured discharges of t h e N i l e and i t s t r i b u t a r i e s , P h y s i c a l Department Paper N o . 28, Government P r e s s , C a i r o , Egypt. Hurst, H . E . , and P h i l i p s , P . , 1933. The N i l e Basin, Vol. I V , ten-day mean and monthly mean discharges of t h e N i l e and i t s t r i b u t a r i e s . Physical Department Paper No. 30, Government P r e s s , Cairo, Egypt. Hurst, H.E., and P h i l i p s , P . , 1938. The N i l e Basin, Vol. V , t h e hydrology of t h e Lake P l a t e a u and t h e Bahr e l - J e b e l . P h y s i c a l Department Paper No. 35, S c h n i d l e r ' s P r e s s , C a i r o , 235 pp. Hurst, H . E . , Black, R.P., and Simaika, Y . M . , 1951. The N i l e Basin, Vol. V I I , t h e f u t u r e c o n s e r v a t i o n of t h e N i l e . PhysiSal Department Paper No. 51, Eastern P r e s s ( r e p r i n t e d ) , C a i r o , 157 pp (with appendices). Hurst, H . E . , 1950. The Nile Basin, Vol. V I I I , t h e hydrology of t h e Sobat and White Nile and t h e topography of t h e Blue Nile and Atbara, Physical Dapartment, Paper No. 55, Government P r e s s , C a i r o , 125 pp. Hurst, H . E . , Black, R.P., and Simaika, Y . M . , 1959. The N i l e Basin, Vol. I X , t h e hydrology of t h e Blue Nile and Atbara and of t h e Main N i l e t o Aswan with Some r e f e r e n c e t o p r o j e c t s . N i l e Control Department, Paper No. 12, General Organiz a t i o n f o r Government P r i n t i n g O f f i c e s , Cairo, 206 pp. Hurst, H . B . , Black, R.P., and Simaika, Y . M . , 1966. The N i l e Basin, Vol. X , t h e major N i l e p r o j e c t s . Nile Control Department, Paper No. 23, General Organizat i o n f o r Government P r i n t i n g O f f i c e s , C a i r o , 217 pp.
4 17
J a r v i s , C . S . , 1935. Flood-stage records of t h e River N i l e , Transactions ASCE, Paper No. 1944 (with d i s c u s s i o n s by H.P. G i l l e t e , R . W . Davenport, H . E . Hurst, T . H . Means, J . W . Breadsley, J . C . Stevens, J . W . Shuman, K.O. Ghaleb and C . S . J a r v i s ) : 1012-1071. J o n g l e i Area Executive Organ for Development P r o j e c t s , 1975. J o n g l e i P r o j e c t , r e p o r t on phase I , Tamaddun P r e s s , Khartoum, 100 pp. King, J . W . , 1975. S o l a r phenomena, weather m d c l i m a t e . European Space Agency, ESA B u l l e t i n No. 3, Neuilly-sQr-Seine, France: 24, 49-51. K i t e , G.W., 19Sl. Recent changes i n l e v e l of Lake V i c t o r i a , B u l l e t i n of hydrol o g i c a l s c i e n c e s , V o l . 26, No. 3: 233-243. Rodriguez, I . and Yevjevich, V . , 1967. Sunspots and hydrologic t i r e a e r i e s . Proceedings of t h e I n t e r n a t i o n a l Hydrology Symposium, F t . C o l l i n s , Colorado, V o l . I : 397-405. Saleeb, I . S . , 1977. River N i l e r a t e r s y s t e m a n a l y s i s u s i n g d i g i t a l computers. Proceedings of t h e I n t e r n a t i o n a l Conference on Computer A p p l i c a t i o n s i n Developing C o u n t r i e s . AIT, Bangkok, Vol. 11: 777-791. Shahin, Y . , 1983. E f f e c t of s t o r a g e works i n t h e N i l e River system on t h e hog e n e i t y i n t h e annual flow series. Proceedings of t h e Symposium on K a t e r Resources, Varna, Bulgaria: 11-23. W,1974. Hydrometeorological survey o f t h e catchments of Lakes V i c t o r i a , Kyoga and A l b e r t , Vol. I , P a r t s I 0 11: meteorology and hydrology of t h e b a s i n , WHO, Geneva. WHO, 1974. Hydrometeorological survey of t h e Catchments of Lake8 V i c t o r i a . Kyoga and A l b e r t , V o l . 111: p r e l i m i n a r y r e p o r t s on t h e index catchments, .yy). Geneva. WMO, 1974. Hydrometeorological survey of t h e catchments of Lakes V i c t o r i a , Kyoga and A l b e r t , Vol. I V : h y d r o l o g i c a l s t u d i e s of s e l e c t e d r i v e r b a s i n s , WMO, Geneva.
4 19
Chapter 9 WATER STORAGE AND CONSERVATION INTRODUCTION
While analyzing and d i s c u s s i n g t h e stream flow i n t h e River N i l e system, Chapter 8, a b r i e f mention was made t o water s t o r a g e and conservation works. This c h a p t e r w i l l d e a l with a somewhat d e t a i l e d d e s c r i p t i o n of such works; those completed and f u n c t i o n i n g and those which a r e underway. The f i r s t s t o r a g e work b u i l t , a t l e a s t i n contemporary h i s t o r y , i s t h e o l d dam a t Aswan, Egypt (1898-1902).
The o p e r a t i o n of t h i s work was based on s t o r i n g
a s m a l l volume of f l o o d water and r e l e a s i n g i t i n t h e next low-flow season t o t h e downstream reach of t h e r i v e r t o improve t h e n a t u r a l discharge. Both s t o r a g e and r e l e a s e were accomplished i n t h e same water y e a r . One may thus d e s c r i b e t h e r e s e r v o i r s formed by t h e o l d Aswan Dam and i t s heightenings a s annual s t o r a g e works. Subsequent s t o r a g e works have been designed and operated on t h e same b a s i s . The only exception is t h e High Dam a t Aswan, Egypt (1956-1964) which was designed according t o t h e theorem of long-term o r century s t o r a g e . The p r i n c i p a l l i n e s of t h e annual and long-term s t o r a g e theorems a r e b r i e f l y reviewed and d i s cussed i n t h e next s e c t i o n s . 9.1
WATER STORAGE I N THE NILE BASIN
9.1.1
Annual s t o r a g e
The method used t o determine t h e l i v e - s t o r a g e c a p a c i t y of a r e s e r v o i r was developed i n 1882 by Rippl. Since t h i s method can, p r e f e r a b l y , be worked o u t g r a p h i c a l l y , i t i s commonly r e f e r r e d t o a s t h e Rippl-diagram o r mass curve method. 9.1.1.1
Simple c a s e of seasonal s t o r a g e where demand and supply a r e equal and t h e r e a r e no s t o r a g e l o s s e s
Suppose t h a t t h e d a t a i n cobumns 2 and 4 of Table 9 . 1 r e p r e s e n t t h e monthly n a t u r a l flow reaching a r e s e r v o i r and t h e demand downstream of i t , r e s p e c t i v e l y . The graphic p l o t of t h e s e data v e r s u s t h e t i m e i n months shows c l e a r l y t h a t t h e r e a r e months of excess ( n a t u r a l supply > demand) and months of d e f i c i t ( n a t u r a l supply < demand). Fig. 9 . l a . shows t h a t t h e season from August t o January i s a p e r i o d of excess whereas t h e r e s t of t h e y e a r , except February, i s one of d e f i c i t . February is t h e only p e r i o d without excess or d e f i c i t . This case i m p l i e s t h a t t h e r e s e r v o i r must be f i l l e d i n t h e p e r i o d of e x c e s s , n e i t h e r f i l l e d nor emptied i n February, and emptied from March t o J u l y t o compensate f o r
420
the d e f i c i t of t h e n a t u r a l supply i n t h i s p e r i o d . The Rippl-diagram method o f f e r s a simple tool f o r determining t h e r e q u i r e d r e s e r v o i r c a p a c i t y . The mass curves of t h e supply and demand can be o b t a i n e d by p l o t t i n g t h e f i g u r e s i n columns 3 and 5 , Table 9 . 1 , v e r s u s t i m e . The d i f f e r e n c e between t h e o r d i n a t e s of t h e two mass curves a t any i n s t a n t equals t h e volume of r e s e r v o i r c o n t e n t s a t t h a t p a r t i c u l a r i n s t a n t . I n t h e p r e s e n t example t h e maxi-
mum s t o r a g e i s a t t a i n e d a t t h e end of January and remains c o n s t a n t t i l l t h e end of February, a f t e r which t h e r e s e r v o i r i s emptied t i l l t h e end of t h e y e a r . The same r e s u l t can be seen i n t h e l a s t column i n Table 9 . 1 . TABLE 9 . 1
Monthly and cumulative supply and demand (Shahin, M., 1971)
Month August September October November December January February March April May June July
Monthly supply, 106 m 3
Cumulative supply, 106 m 3
Monthly demand, 106 m 3
Cumulative demand,
Cumulative supply-demand, 106 m 3
80 70 35 25
80 150 185 2 10 230 245 255 265 275 2 85 290 300
30 15 15 10 05 05 10 20 30 40 50
30 45
50 105 125 140 155 165 165
20
15 10 10 10 10 05 10
106 m 3
60
70 75 80 90 110 140 180 2 30 300
70
155 135 105 60 0
Sometimes i t could be m o r e convenient to draw t h e s o - c a l l e d " d i f f e r e n t i a l mass curve", which i s simply a g r a p h i c a l p l o t of t h e o r d i n a t e d i f f e r e n c e between t h e two mass curves versus t i m e , using a h o r i z o n t a l datum. This curve f a c i l i -
t a t e s t h e reading of t h e r e s e r v o i r c o n t e n t s a t any t i m e during t h e year ( s e e Fig. 9 . l b . ) .
In t h i s example, t h e maximum c a p a c i t y of t h e r e s e r v o i r a s read from
t h e l a s t column of Table 9 . 1 i s 165 x
lo6
m3.
The same f i g u r e can be o b t a i n e d
e i t h e r from t h e maximum o r d i n a t e d i f f e r e n c e between t h e two curves or simply a s t h e maximum o r d i n a t e of t h e d i f f e r e n t i a l mass curve. b
9.1.1.2
C a s e of supply g r e a t e r than demand
I f , i n t h i s c a s e , w e use t h e same mode of computation as i n s e c t i o n 9.1.1.1, a c e r t a i n amount of water w i l l remain u n u t i l i z e d up t o t h e end of t h e y e a r (see Fig. 9 . 2 a . ) . This amount is simply t h e excess of t h e y e a r l y supply over t h e y e a r l y demand. Were i t assumed t h a t t h e r e s e r v o i r must be empty by t h e end of t h e y e a r , t h e l a s t o r d i n a t e s of t h e supply and demand m a s s curves must then be e q u a l , The method of computation can be modified a s follows: w i t h r e f e r e n c e t o
42 1
Fig. 9.2a.,
i n s t e a d of s t a r t i n g t h e computation o f t h e m a s s demand from t h e
b e g i n n i n g of t h e y e a r a t 0 , t h e order of t h e p r o c e d u r e is r e v e r s e d , and t h e comp u t a t i o n s t a r t s from p o i n t B c o r r e s p o n d i n g t o t h e end o f t h e y e a r . The mass demand i s now drawn from r i g h t t o l e f t u n t i l i t i n t e r s e c t s t h e mass s u p p l y a t C . From C down t o 0 t h e mass demand s h o u l d c o i n c i d e w i t h t h e mass s u p p l y . I n o t h e r words, t h e r e s e r v o i r h a s t o b e k e p t empty i n t h e p e r i o d OC and f i l l i n g s t a r t s o n l y on t h e d a t e c o r r e s p o n d i n g t o C . T h i s method r e s u l t s i n a maximum r e s e r v o i r c a p a c i t y R2 smaller t h a n R1 ( t h e d i f f e r e n c e b e i n g e q u a l t o t h a t between t h e mass s u p p l y and t h e mass demand). A s t h e d i s c h a r g e o f a r i v e r c a n h a r d l y be f o r e c a s t a c c u r a t e l y , one may, i n s t e a d o f waiting till t h e t i m e r e p r e s e n t e d by p o i n t C , b e g i n t h e f i l l i n g a t 0 apd c o n t i n u e till t h e r e q u i r e d amount i s s t o r e d . A f t e r t h a t , t h e r e s e r v o i r h a s t o b e m a i n t a i n e d f u l l , u n t i l demand e x c e e d s t h e n a t u r a l supply. Another way t o accomplish t h e same p u r p o s e i s shown i n F i g . 9.2b. The diagram shown c a n b e c o n s t r u c t e d by f i r s t p l o t t i n g t h e mass s u p p l y c u r v e . The o r d i n a t e s of t h e mass demand a r e computed and t h e r e s e r v o i r s i z e , R2, found. The mass demand i s t h e n drawn s t a r t i n g from t h e o r i g i n . On t h i s diagram t h e o r d i n a t e DE, e q u a l t o R2, c a n b e found. From E a c u r v e p a r a l l e l t o t h e mass s u p p l y c u r v e i s drawn, as i s a c u r v e p a r a l l e l t o t h e m a s s demand c u r v e s t a r t i n g from p o i n t B. The t w o m a s s c u r v e s i n t e r s e c t a t p o i n t G and t h e l i n e OEGB s h o u l d r e p r e s e n t t h e
m a s s curve o f t h e outflow. This curve can be divided i n t o t h r e e d i s t i n c t p a r t s : i n which t h e o u t f l o w e q u a l s t h e demand and t h e f i l l i n g o f t h e r e s e r v o i r
0-E,
t a k e s p l a c e ; E-G,
i n which t h e o u t f l o w exceeds t h e demand t h e t h e r e s e r v o i r con-
t e n t s are k e p t c o n s t a n t , and G-B, i n which t h e o u t f l o w e q u a l s t h e demand t h e and t h e r e s e r v o i r emptying t a k e s p l a c e .
. 90
5 c
W
80
; .70
6 100
5 200
m
“0E
m, E
60
U
50
C
.,
--
!!j40
Mass suppl
7-
‘izoo Q
0
5 30
1
ln
--
.-Y 100
0 20 10
0
300
0
0 3
8 9101112 1 2 3 4 5 6 7 Month
Fig. 9 . l a . Hydrographs of n a t u r a l s u p p l y and demand
s V
I
I
/#S.
./
-e--
o
Mass demand
I
8 9101112 1 2 3 4 5 6 7 Month
Mass c u r v e s o f supply Fig, 9.lb. and demand. D i f f e r e n t i a l mass c u r v e and r e s e r v o i r c a p a c i t y , a l l f o r e q u a l c u m u l a t i v e s u p p l y and demand
42 2
400
B
300
B'
'cl
2
x
/ \ Mass oYg'9;o'11'1;1
demand
'2'3'&'7' Month
8 9 1011 12 1 2 3 4 5 6 7 Month
Fig. 9 . 2 a . Mass curves of supply. demand and outflow and minimum r e s e r v o i r s i z e f o r t h e c a s e of cumu l a t i v e supply g r e a t e r than cumulat i v e demand
9.1.1.3
Fig. 9.2b. A possible solution f o r t h e minimum r e s e r v o i r c a p a c i t y i n t h e c a s e of cumulative supply g r e a t e r t h a n cumulative demand ( n o t i c e t h e change i n mass outflow than i n 9 . 2 a . )
Case of supply equal t o , o r g r e a t e r t h a n , demand, i n i t i a l s t o r a g e required
In t h e above cases supply and demand have been arranged so t h a t t h e o r d i n a t e of t h e mass supply a t any t i m e i s equal t o , o r g r e a t e r t h a n , t h e o r d i n a t e of t h e
mass demand. This i s , however, n o t always t h e case and t h e two mass curves o f t e n i n t e r s e c t a t least once. The s t o r a g e c a l c u l a t i o n h e r e can b e t t e r be e x p l a i n e d using t h e d a t a i n Table 9 . 2 (Shahin, Y . ,
TABLE 9 . 2
1971).
Monthly and cumulative supply and demand and d i f f e r e n c e between mass supply and demand w i t h and without i n i t i a l s t o r a g e
Month
August September October November December January February March April May June July
Cumulative supply minus Monthly Cumulative Monthly Cumulative cumulative demand, lo6 m3 supply, supply, demand, demand, lo6 m 3 lo6 m 3 lo6 m3 lo6 m 3 without i n i t i a l with i n i t i a l storage storage 10 15
30 60
80 50
20 10 10 05 05 05
10 25 55 115 195 245 265 2 75 2 85 290 295 300
45 35
30
15 10 05 10 15 25
30
35 45
45 80 110 125 135 140 150 165 190 220 255 300
-35
-55 -55 10 60 105 115 110 95 70 40 0
-
20 0
0 45 115 160 170 165 150 125 95 55
413
W e s t a r t by p l o t t i n g t h e supply and demand hydrographe a8 shown in Fig. 9.3..
This p l o t shows one p e r i o d o f e x c e s s , whereas t h e d e f i c i t is s p l i t i n t o two s h o r t e r p e r i o d s ; one a t t h e beginning o f t h e y e a r and t h e o t h e r from March t i l l t h e end of t h e year. Since the y e a r l y demand and supply are e q u a l , t h e volumes of e x c e s s and d e f i c i t m u 6 be equal too. As b e f o r e , w e s t a r t by drawing t h e m p s s supply and demand curves. F r o m Fig.
9.3b. and Table 9 . 2 one can see t h a t t h e r e q u i r e d demand cannot be f u l f i l l e d ,
u n l e s s a c e r t a i n i n i t i a l s t o r a g e is provided. Furthermore, t h e m a x i m u m negative cumulative d i f f e r e n c e which Table 9 . 2 g i v e s a s 55 x lo6 m3 should be considered a s t h e minimum volume needed f o r t h e i n i t i a l s t o r a g e . To a d j u e t t h e mass supply curve t o t h i s s i t u a t i o n one need8 t o add an amount of 55 x lo6 m3 t o i t s o r d i n a t e s . F i g . 9.3b.,
a s w e l l a s Table 9 . 2 , show t h a t t h e m a x i m u m d i f f e r e n c e bet-
ween t h e a d j u s t e d mass supply and t h e a d j u s t e d mass demand is 170 x lo6 m 3 . This r e p r e s e n t s t h e f u l l c a p a c i t y r e q u i r e d f o r t h e r e s e r v o i r . The same volume can be fouad from t h e d i f f e r e n t i a l mass curve and from t h e last column in Table 9 . 2 . The mass diagram can b e s p l i t i n t o f o u r p a r t s . The p a r t i a l l y f u l l r e s e r v o i r (55 x
lo6
m3) in Augu6t i s d e p l e t e d g r a d u a l l y and becomes e r p t y a t t h o end of
September. The demand is e q u a l t o t h e n a t u r a l supply in October and so t h e r e s e r v o i r r e m a i n s empty. In November t h e supply exceeds t h e demand and t h e storage continues t i l l t h e r e s e r v o i r becomes completely f u l l a t t h e end of February (volume of c o n t e n t s = 170 m i l l i o n m 3 ) .
From t h e beginning of March t i l l t h e end
of t h e y e a r t h e r e s e r v o i r is p a r t l y emptied till t h e volume o f c o n t e n t s reaches t h e i n i t i a l s t o r a g e ( 5 5 x lo6 m3) by t h e end of J u l y .
1 100 - 1
5
6 E
E
90 80
:100
70
0
0
s. 6500
(D
400
I
.....,..,.
Adjusted mass supply
u
P 40 0
5ul
30
20 10
0"
' " '
I
'
" '
'
J
8 91011 12 1 2 3 4 5 6 7 Month
Fig. 9.311. Hydrographs or n a t u r a l supply and demand
8 91011121 2 3 4 5 6 7 Month Fie. 9 . a . Mass curves and d i f f e r e n t i a l mass curves. I n i t i a l s t o r a g e is needed
424
9.1.1.4
C a s e of a sequence of y e a r s , t h e cumulative supply i n each y e a r being
e q u a l t o , or g r e a t e r t h a n , t h e cumulative demand I t i s common i n r e s e r v o i r o p e r a t i o n t o c o n s i d e r a sequence of y e a r s r a t h e r than a s i n g l e year. The demand i s f i x e d according t o t h e purpose f o r which w a t e r
i s used: i r r i g a t i o n , h y d r o - e l e c t r i c power development, f l o o d c o n t r o l , e t c . , and f o r a t l e a s t some t i m e , i t remains t h e same, o r n e a r l y t h e same, each y e a r . The quota f o r Egypt i n t h e pre-High Aswan Dam c o n d i t i o n was l i m i t e d t o 48 mlrd m3/yr (1929-1964).
This quota has been i n c r e a s e d t o 55.5 mlrd m3/yr i n t h e post-dam
c o n d i t i o n which began i n 1965. From 1869-1870 up t o 1979-1980 t h e annual supply a t Aswan always exceeded e i t h e r f i g u r e , except in t h e water year 1913-1914 when the supply f e l l t o about 42 mlrd m3.
A number of methods f o r determining t h e " s a f e y i e l d " given a r e s e r v o i r was reviewed by B e r n i e r J .
(1966).He defined t h e s a f e y i e l d a s t h a t y i e l d correspon-
ding t o a c e r t a i n p r o b a b i l i t y of f a i l u r e i n f i l l i n g t h e r e s e r v o i r . The method he developed f o r computing t h e s a i d p r o b a b i l i t y is based on t h e theory of t h e Markov processes which allow t a k i n g i n t o account t h e dependence between t h e i n p u t s t o t h e r e s e r v o i r . For a more e x t e n s i v e p r e s e n t a t i o n of t h e a v a i l a b l e techniques and methods r e l a t e d t o r e s e r v o i r c a p a c i t y and y i e l d , t h e r e a d e r is r e f e r r e d t o t h e work of McMahon, T . ,
and Mein, R. (1978). F i g . 9.4.
shows a s h o r t
sequence composed of t h r e e y e a r s . In t h e f i r s t y e a r supply e q u a l s demand and t h e r e s e r v o i r c a p a c i t y needed t o guarantee t h e f i x e d demand i s 165 x f i g u r e can be obtained a s d e s c r i b e d i n s e c t i o n 9 . 1 . 1 . 1 . same r e s e r v o i r c a p a c i t y , i . e . 165 x t h e n e t supply i n t h i s year (380 x
(300 x
lo6
lo6 m3 is necessary lo6 m3) is, however,
lo6
m3.
This
In t h e second y e a r t h e t o s a t i s f y demand. Since i n excess of t h e demand
m3), t h e r e s e r v o i r a t t h e end of t h e water year i s not t o t a l l y empty.
I n s t e a d , t h e r e remains a volume of c o n t e n t s of 80 x
lo6
m 3 . I f the reservoir
should be empty by t h e end of t h e y e a r , t h e procedure described i n s e c t i o n 9 . 1 . 1 . 2 ( s e e Fig. 9.2b.) has t o be used. A s a r e s u l t of t h e excess of t h e n e t supply over t h e demand, t h e outflow curve does n o t c o i n c i d e i n its f u l l l e n g t h with t h a t of t h e demand. The outflow curve h e r e c o n s i s t s of t w o e x t e r n a l arms each similar t o t h e corresponding p a r t s of t h e demand curve, and of a c e n t r a l p a r t which is p a r a l l e l t o t h e supply curve apd i n which t h e volume of t h e reserv o i r c o n t e n t s is maintained c o n s t a n t . The t h i r d y e a r has a cumulative supply of 420 x
lo6
m 3 a t i t s end which is g r e a t e r t h a n t h e f i x e d demand (300 x lo6 m 3 ) .
Moreover, t h e monthly values of t h e supply and t h e demand a r e so t h a t a new r e s e r v o i r c a p a c i t y R2 s m a l l e r than R
1
would be adequate t o guarantee t h e
r e q u i r e d demand. I f t h e supply could be p r e c i s e l y f o r e c a s t e d one needs t o f i l l (115 x lo6 m 3 ) . The r e s e r v o i r c o n t e n t s should then 2 be kept c o n s t a n t a t t h i s volume t i l l t h e n a t u r a l supply begins t o f a i l t o the r e s e r v o i r p a r t l y up t o R
s a t i a f y t h e demand. From t h i s moment onwards t h e r e s e r v o i r c o n t e n t s a r e depleted
425
gradually t i l l t h e end of t h e y e a r . The above-described case is n o t r e a l l y t o o d i f f e r e n t from t h a t of t h e annual s t o r a g e on t h e Main N i l e or its t r i b u t a r i e s . The annual supply is, i n g e n e r a l , much g r e a t e r than t h e annual demand. Nevertheless t h e d a i l y supply is, i n some months, less than t h e d a i l y demand and i n o t h e r months, more. The s t o r a g e capac i t i e s a r e f a i r l y s m a l l , so most of t h e f l o o d water i s r e l e a s e d downstream without being used, and a s m a l l amount only is s t o r e d t o h e l p improve t h e n a t u r a l supply d u r i n g t h e low-flow season to meet with t h e demand.
' 8
1012 2 4 6 8 1 0 1 2 2 4 6 8 1 0 1 2 2 4 6
+Year
nP 1 -+-Year
Month n-0 2
+Year nS! 3 -4
Fig. 9.4. Reservoir c a p a c i t y and o p e r a t i o n f o r a sequence of y e a r s i n which t h e y e a r l y n e t supply e q u a l s or exceeds t h e y e a r l y demand 9.1.2 9.1.2.1
Annual s t o r a g e works on t h e N i l e and i t s t r i b u t a r i e s The o l d Aswan Dam
Up t o t h e beginning of t h e beginning of t h e t w e n t i e t h century t h e amount of water t h a t could be used f o r i r r i g a t i n g t h e summer crops i n Egypt was almost l i m i t e d t o t h e n a t u r a l supply of t h e r i v e r . Such an amount i n a low-flow y e a r was hardly s u f f i c i e n t f o r i r p i g a t i n g 1 . 5 m i l l i o n a c r e s . Under t h e t h r u s t of i n c r e a s i n g population i t was decided t o extend p e r e n n i a l i r r i g a t i o n to a v a s t area. To f u l f i l l t h e necessary i r r i g a t i o n requirement t h e Aswan Dam was f i r s t b u i l t i n 1898-1902 t o s t o r e j u s t 1 mlrd m 3 of t h e f l o o d water and t o use i t t o g e t h e r w i t h t h e n a t u r a l supply of t h e r i v e r i n t h e followi n g low-flow season.
The dam was f i r s t heightened i n 1912 and thereupon t h e
s t o r a g e c a p a c i t y of t h e r e s e r v o i r i n c r e a s e d t o about 2 . 3 mlrd m 3 . The second heightening of t h e dam took p l a c e i n 1934, which brought t h e c a p a c i t y t o a
426
f i g u r e between 5 . 0 and 5 . 1 mlrd m 3 ( n o t i c e t h a t i n t h e p e r i o d 1902-1964 t h e mean annual s u p p l y w a s a b o u t 84 mlrd m3 and t h e a n n u a l demand 48 mlrd m3). I n 1944 t h e i d e a o f a t h i r d h e i g h t e n i n g o f t h e dam by a b o u t 11 metres, which would have i n c r e a s e d t h e r e s e r v o i r c a p a c i t y up t o 10 mlrd m 3 , w a s proposed. The i d e a w a s g i v e n up owing t o t h e danger of s i l t d e p o s i t i o n i n t h e r e s e r v o i r when used f o r f l o o d p r o t e c t i o n and t o t h e d i f f i c u l t y of f i l l i n g t h e e n l a r g e d reserv o i r w i t h n o n - s i l t y water, and a l s o t o r e l u c t a n c e t o c o m p l i c a t e t h e s t r u c t u r e any f u r t h e r ( H u r s t , H.E., B l a c k , R.P., and Simaika, Y.M., 1959). The c r o s s - s e c t i o n o f t h e dam and i t s two h e i g h t e n i n g s i s shown i n F i g . 1, Appendix F. Some o f t h e t e c h n i c a l d a t a r e l e v a n t t o t h e dam and t h e s t o r a g e r e s e r v o i r are i n c l u d e d i n t h e same Appendix. The r u l e c u r v e i l l u s t r a t i n g t h e u s u a l o p e r a t i o n o f t h e r e s e r v o i r is shown i n F i g . 9.5. f o r 1953. Towards t h e e n d
of J u l y the r e s e r v o i r w a s r a t h e r empty and i t s l e v e l had f a l l e n t o a b o u t 98 where i t remained f o r a s h o r t t i m e u n t i l t h e f l o o d wave r a i s e d t h e l e v e l t o something between 1 0 1 and 103 ( n o t i c e t h a t t h e water l e v e l i n t h e N i l e down-
stream t h e dam had i n c r e a s e d by a b o u t 6 m). The r e s e r v o i r l e v e l f e l l t o about 99
a t t h e end o f September and by t h e t e n t h o f October t h e normal f i l l i n g u s u a l l y began and was complete a t l e v e l 121 sometime i n December. I t remained a p p r o x i mately a t t h a t l e v e l u n t i l t h e s u p p l y r e a c h i n g t h e r e s e r v o i r f a i l e d t o cope w i t h t h e r e q u i r e m e n t s f o r i r r i g a t i n g t h e summer c r o p s . T h i s u s u a l l y happened a t t h e b e g i n n i n g o f F e b r u a r y . Water from t h e r e s e r v o i r w a s t h e n used t o supplement t h e s u p p l y and t h e l e v e l f e l l u n t i l t h e r e s e r v o i r was a l m o s t empty towards t h e e n d o f J u l y . I t w a s customary t o b e g i n the f i l l i n g p h a s e when t h e r i v e r s t a g e downstream Aswan w a s 90.5 m above sea l e v e l o r when t h e f a l l i n g limb of t h e s u p p l y hydrograph r e a c h e d 530 m i l l i o n m3/day.
T h i s always took p l a c e between t h e t e n t h and
t h e 2 0 t h o f October e v e r y y e a r . These f i g u r e s were t h e outcome of e x p e r i m e n t s which showed t h a t a t l e v e l 90.50 t h e suspended matter i n t h e N i l e w a t e r had p r a c t i c a l l y no i n f l u e n c e on t h e s t o r a g e c a p a c i t y o f t h e r e s e r v o i r . The r e s u l t o f t h e e x p e r i m e n t s f o r t h e p e r i o d 1914-1927 i s shown i n F i g . 9 . 6 . The f i n a l programme of t h e f i l l i n g phase had t o be planned as soon as t h e r e a d i n g of t h e l o c a l gauge a t Atbara r e a c h e d 1 4 . 0 0 , which meant t h a t t h e l e v e l chosen a t Aswan would be r e a c h e d t h e r e a b o u t 8 days l a t e r ( d i s t a n c e = 1555 k m P
and v e l o c i t y of p r o p a g a t i o n o f f l o o d = 2 . 2 5 m/sec.). The r e s e r v o i r was used a number o f times as an emergency f l o o d e s c a p e t o r e d u c e t h e danger o f b r e a c h i n g t h e r i v e r banks i n Middle and Lower Egypt. T h e volume of s i l t y water impounded i n t h e r e s e r v o i r d u r i n g t h e d i s a s t r o u s f l o o d of 1954 was a b o u t 3 mlrd m 3 w i t h a s i l t c o n t e n t of a b o u t 9 m i l l i o n m 3 .
42 7
. 95
d
94 93 VI t 92 F 91 €. 9 0 lJi
lJ
-
ASWAN
(D.S. Dam)
-
Jan. Feb.Mar. Apr. May Jun. Jul. Aug. Sep. Oct. Nov.Dec. Month Fig. 9 . 5 . The s t a g e hydrograph of t h e N i l e downstream of Aswan and t h e r u l e curve of t h e r e s e r v o i r , both f o r 1953 (Hurst, H.E., Black, R.P., and Simaika, Y.M., 1959) Some of t h e r e s u l t s obtained from i n v e s t i g a t i n g t h e s i l t regime i n t h e N i l e , e s p e c i a l l y a t K a j n a r t i , Wadi Halfa and Gaafra ( c l o s e s t t o Aswan), have been publ i s h e d , among o t h e r s , by Hurst and co-workers i n Vol. IX of t h e Nile Basin (Hurst, H . E . ,
Black, R.P., and Simaika, Y.M., 1959), by Simaika and El-Sherbini
(1957) and by Simaika alone (1961). The main r e s u l t obtained from t h a t l a s t i n v e s t i g a t i o n i s t h a t t h e s i l t c o n c e n t r a t i o n , expressed i n p a r t s p e r mi1lio.n p e r weight, was approximately 400, P O O , 2 5 0 0 , 1000 and 300 f o r J u l y , August, September, October and November, a l l measured a t Wadi Halfa. The measurements a t Gaafra seemed t o be i n f l u e n c e d by t h e o p e r a t i o n of t h e Aswan r e s e r v o i r . Longterm averages a t Gaafra were, however, 300, 3000, 2 0 0 0 , 700 and 170 p a r t s per m i l l i o n by weight f o r t h e months J u l y up t o and i n c l u d i n g November s u c c e s s i v e l y . I t was f u r t h e r r e p o r t e d t h a t t h e amount of t h e suspended sediment i n t h e r i s i n g s t a g e of t h e f l o o d was much h i g h e r than i n t h e f a l l i n g s t a g e . With t h e advancement of t h e f l o o d wave i n time from t h e end of J u l y towards t h e end of October a s i g n i f i c a n t i n c r e a s e i n t h e percentage of t h e c o a r s e f r a c t i o n (sand) and a
428
c o r r e s p o n d i n g d e c r e a s e i n t h e f i n e f r a c t i o n ( s i l t and c l a y ) had b e e n n o t i c e d . The d e t a i l e d r e s u l t s o b t a i n e d from i n v e s t i g a t i n g t h e s i l t i n t h e N i l e have been employed i n t h e e s t i m a t i o n of t h e c a p a c i t y t o b e a l l o t t e d t o dead storage ( s t o r age of s e d i m e n t s ) i n t h e r e s e r v o i r c r e a t e d by t h e Aswan High Dam.
93.5
r
I
I
I
I
I
6.0 2.5 5.0 7.5 10.0 12.5 15.0 17.5 20.0 22.5 Silt load,
m3
Water l e v e l a t Aswan and t h e s i l t l o a d i n t h e r i v e r w a t e r
F i g . 9.6. 9.1.2.2
lo6
The Sennar (Makwar) Dam
The dam c o n s t r u c t i o n w a s completed i n 1925. I t i s b u i l t on t h e Blue N i l e some 350 k i l o m e t r e s s o u t h - e a s t of Khartoum f o r t h e b e n e f i t of t h e Sudan. I t s purpose i s t o s t o r e p a r t o f t h e Blue N i l e w a t e r f o r i r r i g a t i n g t h e c o t t o n r a i s e d i n t h e
Gezirah a r e a and t o r a i s e t h e water i n t a k e d p s t r e a m o f t h e G e z i r a h c a n a l up t o t h e r e q u i r e d l e v e l . The r e s e r v o i r c a p a c i t y c r e a t e d by t h e Sennar Dam i s a b o u t 0 . 8 m l r d m3.
The c r o s s - s e c t i o n of t h e dam and some of t h e r e l a t e d t e c h n i c a l d a t a
are p r e s e n t e d i n F i g . 2 , Appendix F . The Sennar r e s e r v o i r h a s been d e s i g n e d t o o p e r a t e i n such a manner t h a t duri n g t h e low s t a g e s of t h e r i v e r , i . e . from J a n u a r y t o J u l y , t h e d i s c h a r g e downs t r e a m o f t h e dam remains t h e same as i t would have been had t h e r e been no dam
a t a l l . T h i s means t h a t t h e d i s c h a r g e p a s s i n g through t h e s l u i c e s i n t h i s p e r i o d i s about e q u a l t o t h a t which e n t e r s t h e r e s e r v o i r from t h e upstream; b u t a s t h e
429
G e z i r a h c a n a l s t i l l c o n t i n u e s t o draw i t s f u l l y s u p p l y , t h e amount o f water l e a v i n g t h e r e s e r v o i r d u r i n g i t s emptying p e r i o d must b e g r e a t e r t h a n t h e amount t h a t e n t e r s i t . Therefore, t h e r e s e r v o i r l e v e l during t h e s a i d period drops g r a d u a l l y w i t h t i m e ( s e e F i g . 9 . 7 . , El-Zein Sagheyroon, S . S . ,
425
420 d
v; 415 0
410
aJ
2
-J
405
I
:ents
it‘n
400 I
R.L.LZ1.70
1965).
1
u -----_____-----
sluices River level downstream of the reservoir I
I
I
Jan. Feb. Mar, Apr. May Jun. Jul. Aug. Sep. O c t . Nov. Dec. Month
Fig. 9.7.
O p e r a t i o n o f t h e S e n n a r r e s e r v o i r and t h e downstream w a t e r l e v e l
B e a r i n g i n mind t h a t i r r i g a t i o n o f the G e z i r a h l a n d m u s t b e g i n a t t h e e n d o f J u l y , t h e f i r s t f i l l i n g i s a c c o m p l i s h e d i n t h e s e c o n d h a l f o f J u l y so t h a t on t h e t h e f i r s t o f August t h e l e v e l u p s t r e a m o f t h e dam i s r a i s e d t o 417.20 t o e n a b l e t h e c a n a l t o draw i t s f u l l s h a r e from t h e r i v e r . The c r i t e r i o n t o s t a r t f i l l i n g t h e r e s e r v o i r i s t h a t t h e d a i l y n a t u r a l f l o w of t h e B l u e N i l e e q u a l s o r e x c e e d s 160 m i l l i o n m3/day. On t h e f i r s t of August t h e river flow becomes b i g enough t o p e r m i t f u r t h e r r a i s i n g of w a t e r t o l e v e l s h i g h e r t h a n 4 1 7 . 2 0 . However, t h i s cann o t be done u n t i l t h e N i l e w a t e r i s s u f f i c i e n t l y c l e a r o f s i l t , t o e n s u r e t h a t s o l i d s a r e n o t d e p o s i t e d i n t h e r e s e r v o i r . Sediment d e p o s i t i o n below t h e l e v e l o f 417.20 is n o t , however, too h a r m f u l as t h e c o r r e s p o n d i n g r e s e r v o i r c o n t e n t s m e r e l y act as a water c u s h i o n a n d have n o t h i n g t o do w i t h l i v e s t o r a g e . To a v o i d accumulation of silt d e p o s i t s a t h i g h e r l e v e l s t h e r e s e r v o i r l e v e l s h o u l d remain
a t 417.20 t i l l t h e B l u e N i l e water i s s u f f i c i e n t l y f r e e of s i l t , u s u a l l y a r o u n d mid-October,
A t t h i s t i m e t h e se’cond f i l l i n g of t h e S e n n a r r e s e r v o i r s t a r t s and
i s c o n s i d e r e d c o m p l e t e when t h e l e v e l i s 4 2 1 . 7 0 , a t t h e end of November. The r e s e r v o i r l e v e l i s k e p t a t , o r h i g h e r t h a n , 417.20 a s l o n g a s t h e G e z i r a h l a n d h a s t o b e i r r i g a t e d and t h e G e z i r a h c a n a l h a s t o draw i t s f u l l s h a r e . T h i s c o n t i n u e s t i l l t h e f i r s t of A p r i l , a f t e r which t h e l e v e l i s a l l o w e d t o f a l l below 4 1 7 . 2 0 , The c a n a l t h e n s e r v e s i n s u p p l y i n g water f o r d o m e s t i c p u r p o s e s . The f a l l goes on u n t i l t h e r e s e r v o i r a t t a i n s i t s minimum l e v e l between t h e end o f May a n d mid-July
(see Fig. 9.7.),
and t h i s d a t e can t h e r e f o r e be taken as t h e
430
end of t h e emptying phase of t h e o p e r a t i o n c y c l e . 9.1.2.3
The J e b e l el-Aulia Dam
This dam was c o n s t r u c t e d i n 1937 on t h e White N i l e some 44 k i l o m e t r e s s o u t h of Khartoum t o s t o r e water f o r t h e b e n e f i t of Egypt. The s t o r a g e c a p a c i t y of t h e r e s e r v o i r a t t h e t i m e t h e dam was completed was 3 . 5 mlrd m 3 . Due t o t h e continuous s i l t i n g up of t h e r e s e r v o i r b a s i n t h e l i v e c a p a c i t y has shrunk g r a d u a l l y t o 2.2 mlrd m3 a t Aswan by 1960. The c r o s s - s e c t i o n of t h e J e b e l el-Aulia Dam and some t e c h n i c a l l y - r e l a t e d d a t a a r e given i n Fig. 3, Appendix F. The o p e r a t i o n of t h e J e b e l el-Aulia r e s e r v o i r depended t o a l a r g e e x t e n t on conditions a t Aswan. A t t h e beginning of February both r e s e r v o i r s used t o be f u l l . Since demand f o r i r r i g a t i o n i n Egypt a t t h a t t i m e exceeded n a t u r a l supply, t h e emptying of t h e Aswan r e s e r v o i r used t o begin i n February; when i t reached a c e r t a i n l e v e l , t h e emptying of t h e J e b e l el-Aulia r e s e r v o i r s t a r t e d . By t h e t i m e t h e r e l e a s e d w a t e r a r r i v e d a t Aswan, t h e volume of t h e r e s e r v o i r c o n t e n t s
had f u r t h e r decreased, so t h a t enough room was a v a i l a b l e f o r r e c e i v i n g t h e r e l e a s e d w a t e r as w e l l as t h e n a t u r a l r i v e r supply. The volume of r e s e r v o i r c o n t e n t s is t h a t volume of water o v e r l y i n g t h e surf a c e l e v e l of t h e n a t u r a l r i v e r . For a c e r t a i n l e v e l i n a r e s e r v o i r , t h e cont e n t s drop a s t h e l e v e l of t h e n a t u r a l r i v e r rises, and vice-versa.
The estimate
of t h e r e s e r v o i r c o n t e n t s t h e r e f o r e depended on t h e upstream gauge l e v e l (Wadi Halfa i n t h e case of the Aswan Dam). curves i n t e r m s of t h e r e s e r v o i r
F i g . 9.8. shows t h e r e s e r v o i r content
l e v e l and t h e gauge reading a t Halfa.
The emptying phase of o p e r a t i o n of t h e J e b e l el-Aulia r e s e r v o i r s t a r t e d b e t ween t h e f i r s t of February and t h e f i r s t of March according t o t h e n a t u r a l i n come o f t h e r i v e r . This phase used t o l a s t about two-and-a-half
months, while
t h a t of t h e Aswan r e s e r v o i r continued u n t i l t h e end of J u l y , when t h e n a t u r a l income began t o s u r p a s s t h e q u a n t i t y of water r e q u i r e d . S i m i l a r t o t h e Sennar r e s e r v o i r , t h e J e b e l el-Aulia was f i l l e d i n two s t a g e s ; t h e f i r s t from t h e end of J u l y t i l l t h e t w e n t i e t h of August, when t h e r e s e r v o i r l e v e l reached 376.50 m above mean s e a l e v e l and t h e second s t a g e from t h e f i r s t of September and continued t i l l t h e l e v e l reached 377.20. The d i f f e r e n c e between t h e two l e v e l s , i . e . 376.50 and 377.20, l e f t during t h e break between t h e two f i l l i n g s t a g e s corresponds t o 1 mlrd m 3 .
I t was meant t o a c t as a s a f e t y valve when t h e Blue
Nile showed an extremely high f l o o d . I f t h i s occurred, a l l t h e s l u i c e s of t h e dam were f u l l y opened and p a r t of t h e f l o o d water flowed backwards i n t o t h e White N i l e .
431
0
1
2 3 4 5 Reservoir contents, log,?
6
7
F i g . 9.8. A s w a n ' r e s e r v o i r c o n t e n t s and t h e i r r e l a t i o n t o H a l f a gauge r e a d i n g and t h e r e s e r v o i r l e v e l ( H u r s t , H.E., B l a c k , R.P., and Simaika, Y.M., 1959) I n t h e pre-High Aswan Dam p e r i o d , t h e o l d Aswan and t h e J e b e l e l - A u l i a reserv o i r s used t o c o n t r i b u t e about 7 . 8 m l r d m3/yr a t Aswan t o t h e s u p p l y i n t h e lowflow s e a s o n , February t o J u l y .
9.1.2.4
Khashm e l - G i r b a Dam
The main o b j e c t i v e o f t h e r e s e r v o i r c r e a t e d by t h i s dam is t o r e g u l a t e some o f t h e A t b a r a water i n o r d e r t o s u p p l y t h e i r r i g a t i o n canals o f t h e A t b a r a scheme w i t h t h e n e c e s s a r y flow. I n t h e t e c h n i c a l d a t a i n F i g . 4, Appendix F, i t
is mentioned t h a t t h e i n i t i a l
s t o r a g e c a p a c i t y was 1 . 3 mlrd reduced t o about
0.95 m l r d m 3 by 1971, w i t h &he p o s s i b i l i t y o f a f u r t h e r r e d u c t i o n by 40 m i l l i o n
m3 e a c h y e a r . The f l o o d o f t h e A t b a r a b e g i n s i n t h e l a t t e r h a l f of J u n e , depending on t h e
d a t e of f a l l of t h e t o r r e n t i a l r a i n s . The f i r s t f i l l i n g of t h e r e s e r v o i r up t o l e v e l 462.00 m above mean sea l e v e l b e g i n s i n t h e p e r i o d from t h e f i r s t o f J u l y
t o t h e t e n t h o f J u l y e v e r y y e a r i n o r d e r t o o p e r a t e t h e t u r b i n e pumps t o l i f t
water t o t h e main c a n a l . T h i s c a n a l b r a n c h e s a t k i l o 26 o f f t o t h r e e branch c a n a l s and a t k i l o 14 t h e r e i s a pumping s t a t i o n f o r d i r e c t i r r i g a t i o n of some
4 32
land. I t may b e of i n t e r e s t t o mention t h a t a l l t h e land i r r i g a t e d by t h e s e c a n a l s i s d e s t i n e d f o r t h e people of Wadi Halfa and d i s t r i c t who were d i s p l a c e d by t h e High Aswan Dam p r o j e c t i n Egypt. During t h e f i r s t p a r t of t h e f i l l i n g phase t h e main s l u i c e s of t h e dam a r e l e f t open t o l e t t h e s i l t - l a d e n water flow t o downstream. This goes on t i l l t h e end of August o r when t h e r i v e r d i s c h a r g e n e a r t h e dam s i t e f a l l s t o 110 x
lo6
m3/day. The second p a r t of t h e f i l l i n g phase then begins and continues t i l l t h e beginning of October when t h e r e s e r v o i r l e v e l reaches 473.20. During and a f t e r t h i s p e r i o d a l l t h e e x c e s s w a t e r is allowed t o flow downstream u n t i l t h e f l o o d c e a s e s . In t h e second p a r t of t h e f i l l i n g phase t h e main s l u i c e s of t h e dam a r e shut o f f . The s t o r e d w a t e r s e r v e s t o supply t h e main c a n a l from t h e beginning of November t i l l t h e end of May. 9.1.2.5
The Roseires Dam
The s t o r a g e r e s e r v o i r formed by t h i s dam w a s designed t o r e t a i n water up t o l e v e l 480 m above mean s e a l e v e l i n i t s f i r s t phase and up t o 490 m above mean s e a l e v e l i n i t s second phase. These two l e v e l s correspond to volumes of 3 mlrd
m3 and 6 . 8 mlrd m3, r e s p e c t i v e l y . The primary purpose of t h e Roseires Dam i s t o s t o r e water and t o p a s s i t downstream when r e q u i r e d by t h e Cezirah, Managil e x t e n s i o n and t h e r i v e r bank pump schemes (see F i g . 2 . 2 2 . ) ,
a l l f o r t h e b e n e f i t of t h e Sudan.
The Roseires r e s e r v o i r i s operated i n conjunction w i t h Sennar w i t h t h e purpose of s a t i s f y i n g t h e i r r i g a t i o n requirements upstream and downstream of t h e dam, and g e n e r a t i n g t h e maximum p o s s i b l e power. The f i l l i n g of t h e r e s e r v o i r during t h e r i s i n g f l o o d i n c l u d i n g t h e peak, when t h e s i l t c o n t e n t i s a t its max-
i m u m , i s avoided and f i l l i n g i s delayed t o t h e l a t e s t p o s s i b l e t i m e during t h e f a l l i n g f l o o d . Therefore t h e f i l l i n g d a t e i s enforced by e i t h e r t h e f i r s t of September, i f t h e flow h a s never r i s e n above 325 m i l l i o n m3/day,
or by t h e day
l a t e r than t h e f i r s t of September when t h e d i s c h a r g e has f a l l e n t o 325 m i l l i o n m3/day. Cross-sections
and some of t h e t e c h n i c a l d e t a i l s of t h e dam are given i n Fig..
5 , Appendix F .
9.1.3
Over-Annual s t o r a g e
Consider t h e s u c c e s s i o n of mass inflow curves shown i n F i g . 9.9. Assume t h a t l i n e AB has a s l o p e Q t h a t should n o t be exceeded t o avoid t h e flooding of t h e
area downstream of t h e s t o r a g e r e s e r v o i r . For t h i s purpose t h e maximum s i z e R2 needs t o be empty before t h e a r r i v a l of t h e f l o o d i n t h e second y e a r t o s t o r e
a l l inflow discharge i n excess of Q. From t h e same f i g u r e i t is c l e a r t h a t i n
433
y e a r number 3 one needs a n empty s p a c e R3 < R2 f o r r e g u l a t i n g t h e flow from t h e r e s e r v o i r t o t h e downstream. The assumed Q, however, i m p l i e s t h a t t h e r e s e r v o i r cannot be emptied completely b e f o r e t h e f l o o d i n t h e f o u r t h y e a r comes. A reserv o i r as s u c h is s a i d t o h a v e an o v e r - y e a r or over-annual s t o r a g e . T h i s t y p e of s t o r a g e work does n o t e x i s t i n t h e N i l e B a s i n . A l l t h e s t o r a g e works t h e r e b e l o n g t o e i t h e r t h e annual s t o r a g e , o r t h e long-term s t o r a g e t y p e s .
C Long term storage
2
1
Fig. 9.9. 9.1.4
3 Year No.
4
5
Over-annual and long-term r e s e r v o i r o p e r a t i o n
Long-term s t o r a g e
A s s u m e t h a t t h e i n f l o w and demand mass c u r v e s i n F i g . 9 . 9 . ,
i n s t e a d of b e i n g
f o r f i v e y e a r s o n l y , r e p r e s e n t a much l o n g e r s e q u e n c e . L e t t h e l i n e c o n n e c t i n g
OC have a s l o p e e q u a l t o t h e mean n e t i n f l o w of t h e s e q u e n c e , ;e
r e q u i r e d t o p r o v i d e t h e downstream w i t h demand
6
4.
The s t o r a g e
is R i . T h i s i s known as long-
t e r m s t o r a g e and sometimes a s c e n t u r y s t o r a g e . 9.1.4.1
Design o f r e s e r v o i r c a p a c i t y
The Rippl-diagram
method c a n also b e used f o r d e t e r m i n i n g t h e c a p a c i t y of a
long-term s t o r a g e r e s e r v o i r . L e t t h e a n n u a l volumes of i n f l o w t o such a reserv o i r b e X 1, X2, r a t e ) and
.....
X
and t h e a n n u a l demand b e a i , where 0 < 1 (a = d r a f t
% i s t h e long-term mean i n f l o w .
4 34
According t o Kottegoda, N. (1980), one needs t o determine t h e e a r l i e s t y e a r , j , which s a t i s f i e s t h e c o n d i t i o n
X. 2 a J
X
,
> X.
J+1
j = l , 2
,..., n
- 1
(9.1)
Suppose t h i s corresponds t o year j = K1,
i t i s suggested t h a t two computa-
t i o n s have t o be made: i)
The l e n g t h 1 of t h e p e r i o d i n which t h e r e s e r v o i r l e v e l l i e s below t h e l e v e l a t t i m e K1.
From a l l such d e p l e t i o n p e r i o d s s e l e c t t h e maximum l1 f o r which
t h e following c o n s t r a i n t is s a t i s f i e d
ii) The d e f i c i t d given by t h e e q u a t i o n
d =
-
max (aXm l<_mil 1
-
m
Z XK +i) i=l 1
(9.3)
L e t t h e maximum value of d be c a l l e d d
t o dl be m
1'
1
In order t o f i n d t h e next value j = K 2 ,
and t h e value of m which maximizes d
a f t e r t i m e 1 + K1, equation 9 . 1 has 1 1, K + l1 + 2 , ...., n - 1, u n t i l t h e
t o be a p p l i e d f o r t h e years j = K1 + 1 + 1 1 c o n s t r a i n t i t r e p r e s e n t s is s a t i s f i e d . Equations 9 . 2 and 9 . 3 a r e used t o d e t e r mine l 2 and d2 and m2.
This procedure is r e p e a t e d f o r t h e whole sequence and t h e
following s t a t i s t i c s evaluated: the maximum d e f i c i t t h e maximum d u r a t i o n
:
t h e longest d e p l e t i o n p e r i o d :
m = m., max J max
and
= 1 . = max ( l i ) , J
i = 1, 2 , 3,
...,
a l l f o r a withdrawal r a t e ax. ap
is t h e minimum r e s e r v o i r c a p a c i t y The maximum d e f i c i t f o r any given a , d") max' r e q u i r e d t o supply ax every y e a r . This c a p a c i t y depends on t h e h i s t o r i c a l
sequence of length n , which does not r e c u r over a f u t u r e design period of l e n g t h n. To avoid t h i s shortcoming i n t h e Rippl-diagram method, Hurst, H . E . approached t h e problem using t h e a d j u s t e d range R ( i = 1, 2,
...., n)
can be expressed a s
(1951),
of a sequence of X . values
obtained from t h e cumulative d e p a r t u r e from t h e mean
%.This
4 35
i
max t Exi l < i < n i=l
R~ =
-
if)
-
min 1Sjln
t
j
EX.
j=lJ
-
jji}
To proceed w i t h t h e q u e s t i o n of long-term
(9.4)
s t o r a g e , Hurst developed t h e varia-
b l e known a s t h e a d j u s t e d r e s c a l e d range R /s, where s is t h e e s t i m a t e of t h e s t a n d a r d d e v i a t i o n from t h e sample d a t a . This v a r i a b l e was computed f o r 720 phenomena and t h e values obtained l e d t o t h e conclusion t h a t R / s v a r i e s with t h e s i z e of t h e d a t a sample n according t o t h e r e l a t i o n
(9.5) where K i s a v a r i a b l e index, o f t e n r e f e r r e d t o a s Hurst c o e f f i c i e n t . The o v e r a l l mean and s t a n d a r d d e v i a t i o n of K are 0.72 and 0.092, r e s p e c t i v e l y . Moreover, t h e frequency d i s t r i b u t i o n of t h e K values is claimed t o be t h e normal one, a s shown i n F i g . 9.10.
m
( H u r s t , H.E., 1951).
100
'T)
C
51 0
5 &Q >r
; . 50 c al -0
i7 aI
3
U
pc
LI
0
0.5
0.6
0.7
0.8
0.9
1.(
K Fig. 9.10.
Frequency d e n s i t y graph of index
Equation 9 . 5 can be r e w r i t t e n a s
Rn _ -
0 . 6 1 (n)
0.72
(9.6)
I t should be noted, however, t h a t f o r a purely random t i m e s e r i e s process tends towards 0 . 5 0 ( F e l l e r , W. 1951). The f a c t t h a t n a t u r a l time series y i e l d an average K g r e a t e r than 0.50 i s known a s t h e H u r s t phenomenon.
436
F o r a d e t a i l e d r e v i e w , d i s c u s s i o n and i n t e r p r e t a t i o n o f t h e work o f H u r s t and h i s co-workers,
t h e r e a d e r may b e r e f e r r e d t o H u r s t ( 1 9 5 1 a n d 1 9 5 6 ) , F a t h y and
Shukry ( 1 9 5 6 ) , K l e m e s ( 1 9 7 4 ) , Boes and S a l a s ( 1 9 7 8 ) , and H i p e l and McLoed (1978). P r a c t i c a l c o n s i d e r a t i o n s may sometimes make i t i m p o s s i b l e t o p r o v i d e a s t o r a g e c a p a c i t y a s l a r g e as R
.
C o n s e q u e n t l y , a d i f f e r e n t problem a r i s e s when i t i s
r e q u i r e d t o g u a r a n t e e a d r a f t less t h a n t h e mean. H u r s t a n d h i s co-workers i n v e s t i g a t e d t h i s problem and d e v e l o p e d a number o f f o r m u l a s t o be used f o r comp u t i n g t h e new c a p a c i t y S g i v e n a new d r a f t B , which i s less t h a n t h e long-term mean i n f l o w i n t h e r e s e r v o i r . These f o r m u l a s are
loglo
(K' S
S
loglo
2-B
=
-
0.08
-
1 . 0 0 (-)
(9.7)
=
-
0.11
-
2-B 0.88 (--)
(9.8)
0.91
-
%-B 0.89 (-)
and =
4
(9.9)
F o r t h e 5 1 - y e a r s e q u e n c e (1906-1956) N i g e r a t K o u l i k o r o , Mali, i f t h e mean
a = 0.85. R
2
of t h e a n n u a l f l o w volumes of t h e R i v e r
i s t a k e n a t u n i t y , s = 0 . 2 3 9 8 , B = ai,
w i l l be a p p r o x i m a t e l y 2 . 8 ( t h i s c o r r e s p o n d s t o K = 0 . 7 5 ) . E q u a t i o n s
9 . 7 , 9 . 8 and 9 . 9 y i e l d v a l u e s of S o f a b o u t 0 . 5 5 , 0 . 6 1 and 0 . 5 8 , r e s p e c t i v e l y . = 0 . 6 7 o b t a i n e d from t h e mass max c u r v e a n a l y s i s , y e t t h e y are of a b o u t t h e same o r d e r o f magnitude ( K o t t e g o d a ,
Though t h e s e v a l u e s do n o t compare e x a c t l y t o N.T.,
1980). The i m p o r t a n t c o n c l u s i o n i s t h a t by t a k i n g a = 85%, i . e . assuming,
t h e new d r a f t t o b e 15% less t h a n t h e o r i g i n a l mean i n f l o w and s u b s e q u e n t l y t h e r e d u c t i o n i n d r a f t i n p r o p o r t i o n of t h e s t a n d a r d d e v i a t i o n t o b e a t 6 2 . 5 % , t h e new s t o r a g e c a p a c i t y i s o n l y 20 t o 24% of t h e o r i g i n a l c a p a c i t y R
.
The r e d u c t i o n i n t h e s t o r a g e c a p a c i t y o b t a i n e d from t h e d i f f e r e n t f o r m u l a s a s a r e s u l t of r e d u c i n g t h e d r a f t below t h e long-term mean i s r e p r e s e n t e d by t h e curve i n F i g . 9.11. S.1.4.2
R e g u l a t i o n of long-term s t o r a g e r e s e r v o i r s a
H u r s t i n v e s t i g a t e d a number of r e g u l a t i o n schemes f o r long-term e r v o i r s (1956). I n t h e f i r s t r e g u l a t i o n , t i n g c o n t e n t of r e s e r v o i r w a s
&
RIOO
s t o r a g e res-
32 phenomena were c o n s i d e r e d , t h e s t a r -
(where Rloo = 1 6 . 7 s ) a n d t h e d r a f t w a s
t a k e n e q u a l t o t h e mean o f t h e h i s t o r i c a l d a t a X. The r e s e r v o i r showed t o b e f i l l e d i n 66% o f t h e cases and e m p t i e d i n 59% o f them. I n t h e s e c o n d r e g u l a t i o n t h e s t a r t i n g c o n t e n t was RIOO
and t h e r e s e r v o i r e m p t i e d i n 41% of t h e cases. The
n e x t s e v e n r e g u l a t i o n s were d i v i d e d by H u r s t i n t o 4 main t y p e s : ( a ) h a s a
437
0
Fig. 9.11.
I
I
10
20
30
40
50
60
70
I
I
80
90
I
100
R e l a t i o n s h i p between r e d u c e d d r a f t B and maximum d e f i c i t S
c onstant d r a f t , (b) h as a d r a f t t h a t v a r i e s w it h inflow t o r e s e r v o i r ,
( c ) has a
d r a f t t h a t v a r i e s w i t h volume o f r e s e r v o i r c o n t e n t s and ( d ) h a s a d r a f t t h a t v a r i e s b o t h w i t h i n f l o w and volume o f r e s e r v o i r c o n t e n t s . The r e s u l t s o f r e g u l a t i o n s b a s e d on i n i t i a l d a t a of 30 y e a r s are g i v e n i n T a b l e 9 . 3 . The s u b s c r i p t d e n o t e s t h e l e n g t h of p e r i o d , s ' = 1.1 s30 and t h e capacity
€tioo= 1 6 . 7
From t h e s e r e s u l t s i t i s c l e a r t h a t r e g u l a t i o n 7 is
s'.
s u p e r i o r t o 4 a s t h e s t a r t i n g c o n t e n t i n t h e two r e g u l a t i o n s i s e q u a l , 500' and a r e d u c t i o n of d r a f t of 0 . 1 s ' would have p r e v e n t e d t h e r e s e r v o i r emptying
a
i n 94% of cases (14 o u t of 1 5 ) . I f i t were p e r m i s s i b l e t o s t a r t w i t h t h e reserv o i r f u l l , as i n r e g u l a t i o n 6 , a d r a f t of
xlo
c h a n g i n g e v e r y y e a r would have m e t
a l l c a s e s e x c e p t 1, i . e . a l l b u t 2%. TABLE 9 . 3
R e s u l t s o f r e s e r v o i r r e g u l a t i o n t y p e s ( a ) and ( b )
Regulation
Number Starting of content TvDe Number uhenomena
Draft
4
(a) (b)
3 4
5 6
7
51 51
4
51 51 51
4
"ioo
-
Xl0
'30 changing every 5 y e a r s
changing Rioo -%,, Xl0 c h a n g i n g Rioo Rio0 xl0 c h a n g i n g Rio0
% o f cases r e s e r v o i r f i l l s empties 44
38
23
19
every 5 y e a r s
56
5
every 5 y e a r s
-
1
every y e a r
12
15
438
Regulation 8 , type ( c ) was t r i e d i n one c a s e o n l y , i . e . t h e N i l e discharge a t Aswan, and a d r a s t i c s c a l e of r e d u c t i o n of d r a f t with d e c r e a s i n g content was needed t o prevent emptying. Furthermore, i t was r e p o r t e d t h a t t h e scheme was not considered good enough, compared with o t h e r s , t o warrant examination (Hurst, H.E.,
1956).
The l a s t r e g u l a t i o n , number 9 , belongs t o type ( d ) . I n t h i s r e g u l a t i o n t h e
?lo
r e s e r v o i r s t a r t e d h a l f - f u l l , and t h e d r a f t began with
then changed every
y e a r a s i n r e g u l a t i o n 7. The d r a f t was f u r t h e r reduced or i n c r e a s e d by a s l i d i n g s c a l e i n which t h e r e s e r v o i r content was divided i n t o n i n e p a r t s . When t h e cont e n t was i n t h e middle n i n t h , t h e d r a f t was maintained a t f o u r t h one-ninth
(%
-
-
(from t h e bottom) i t w a s reduced t o (X
-
%
' when i n t h e 10' g ) , and so on down t o
4g), where g i s t h e s t e p of t h e s c a l e . As a measure of s a f e t y a g a i n s t
floods t h e s c a l e could be a p p l i e d t o t h e r e s e r v o i r c o n t e n t s i n t h e upper fourn i n t h s of t h e r e s e r v o i r t o i n c r e a s e t h e d r a f t . I t was concluded t h a t r e g u l a t i o n 9 looked a s i f i t w e r e t h e type which would be most g e n e r a l l y u s e f u l . The rest of t h i s s e c t i o n s h a l l be devoted t o a numerical example i n which r e g u l a t i o n number 7 i s a p p l i e d t o t h e annual flow volume of one of t h e C e n t r a l European r i v e r s included i n Table 9 . 4 a . TABLE 9.4a
Year 185 1 1852 1953 1854 1855 1856 1857 1858 1859 1860
H i s t o r i c a l flow d a t a used i n connection with r e g u l a t i o n 7
Serial NO.
Flow, 109 m3/yr
Year
10.88 9.27 10.38 12.24 13.18 8.76 6.94 6.09 8.20 10.91
186 1 1862 186 3 1864 1865 1866 1867 1868 1869 1870
- 29 - 28 -27
- 26 - 25 - 24 -23 -22 -21 -20
Serial NO.
Flow, 109 m3/yr
- 19 - 18 - 17
7.88 :
7.00
5.39 5.82 7.73 5.46 14.19 10.50 7.41 8.86
- 16 - 15
- 14 -13 - 12 -11 - 10
Serial
Year
Flow, 109 m3/yr
NO.
-9 -8 -7 -6 -5 -4 -3 -2 -1
1871 1872 1873 1874 1875 1876 1877 1878 1879 1880
10.28 5.85 5.17 4.92 7.16 11.95 8.77 8.45 9.05 12.30
0
Consider the 30-year sequence from 1851 up t o and i n c l u d i n g 1880. The y e a r 1851 s h a l l be r e f e r r e d t o a s y e a r -29,
year 1852 a s y e a r -28,
year 0 , 1881 a s year 1, 1882 a s year 2,
x30
...
....,
1880 a s
e t c . This set of d a t a has a mean
= 2.55 x lo9 m 3 / y r , skewness = 30 0 . 3 7 , k u r t o s i s = 2.55, K = 0.758 and t h e s e r i a l c o e f f i c i e n t s from l a g 1 t o l a g 7 = 8.70 x
lo9
m3/yr,
as 0.3322, -0.0380,
standard deviation S
-0.1134,
-0.0734,
-0.1202,
-0.1936
and -0.1632,
The r e s e r v o i r content a t t h e beginning of r e g u l a t i o n 7 is 1.1 x s30 = 23.67 x
lo9
m3.
f
Rio0
=
respectively.
f
x 16.7 x
The annual flow volumes i n t h e p e r i o d from 1881 up
4 39
t o and i n c l u d i n g 1964 a r e i n c l u d e d i n T a b l e 9 . 4 b . Using t h e s e d a t a i n r e g u l a t i o n number 7 t h e f o l l o w i n g r e s u l t s c a n b e o b t a i n e d : r e s e r v o i r c o n t e n t s a t t h e end o f y e a r 1 = f Rio0 8.39) 109
lo9
= 25.37 x
+
lo9
+ I~ - o2 = 25.37
27.56 x 1, 2 ,
-
lo9
. . . .,
X (-8-tl)
m3.
-
I1
-
O1 =
4
R;oo
+
I1
- xc-M,
= (23.67
-
+ 10.09
m 3 , r e s e r v o i r c o n t e n t s a t t h e end of y e a r 2 = 25.37 x
-
109 +
Notice t h a t I 1, 12,
....
= (25.37
+ 10.56 - 8 . 3 7 )
x
lo9
=
are t h e i n p u t s t o r e s e r v o i r i n y e a r s
i s t h e mean i n f l o w f o r t h e t e n - y e a r p e r i o d 1871-1880,
X(-+@)
i s t h e mean f o r t h e t e n - y e a r p e r i o d 1872-1881,
.... e t c .
The p r o c e d u r e
h a s been r e p e a t e d t o d e t e r m i n e t h e y e a r l y d r a f t and t h e volume o f r e s e r v o i r cont e n t s a t t h e end of e a c h p e r i o d (see T a b l e 9 . 4 b ) . U n f o r t u n a t e l y ,
w e have t o s t o p
t h e r e g u l a t i o n a f t e r y e a r number 6 1 b e c a u s e t h e r e s e r v o i r i s f i l l e d . T o resume t h e r e g u l a t i o n t h e d r a f t i n t h a t y e a r s h o u l d h a v e b e e n i n c r e a s e d by a t l e a s t 1 . 7 8 7 mlrd m 3 ,
9.1.5
or a b o u t 0 . 6 4 s :
Long-term s t o r a g e works i n t h e N i l e B a s i n
9.1.5.1
Owen-Falls
Dam
T h i s dam may b e r e g a r d e d a s t h e f i r s t long-term s t o r a g e work c o n s t r u c t e d on the N i l e .
The s t o r a g e r e s e r v o i r was d e s i g n e d w i t h t h e i d e a of r a i s i n g t h e l e v e l
o f Lake V i c t o r i a t o 1134.75 m
above s e a l e v e l , i . e . r a i s i n g i t by a b o u t 3.0 m ,
t h e r e b y i n c r e a s i n g t h e l a k e s t o r a g e by 200 mlrd m 3 . Because of t h e l a r g e n e s s o f t h e s u r f a c e a r e a o f t h e r e s e r v o i r ( a b o u t 6 7 x
m2)
lo9
i t n e e d s t o o l o n g a t i m e b e f o r e i t a t t a i n s t h e d e s i g n l e v e l . From C h a p t e r 8
w e have a l r e a d y l e a r n t t h a t t h e l o s s e s i n t h e Sudd r e g i o n and i n t h e Bahr e l J e b e l B a s i n i n c r e a s e c o n s i d e r a b l y w i t h t h e flow l e a v i n g Lake V i c t o r i a . Moreover, s u c h an o u t f l o w h a s t o t r a v e l s u c h a l o n g d i s t a n c e b e f o r e r e a c h i n g Y a l a k a l o r Aswan t h a t t h e u s e f u l n e s s of any improvement i n t h e l a k e o u t f l o w t o t h e Sudan or Egypt becomes q u e s t i o n a b l e u n l e s s t h e conveyance c o n d i t i o n s of t h e r i v e r c h a n n e l a r e e q u a l l y improved. A cross-section
of t h i s dam and some o f i t s l e a d i n g t e c h n i c a l p a r t i c u l a r e s
are g i v e n i n F i g . 6 , Appendix F. Since its construction,
t h e dam h a s been used f o r h y d r o - e l e c t r i c power deve-
lopment f o r t h e b e n e f i t o f Uganda o n l y .
9.1.5.2
The High Dam a t Aswan
The p o p u l a t i o n of Egypt was e s t i m a t e d by t h e French m i s s i o n of Napoleon B o n a p a r t e a t less t h a n 2 . 5 m i l l i o n . f i g u r e : 2.536.000.
I n 1821 Mohammed A l i found a somewhat h i g h e r
I n 1846 t h e p o p u l a t i o n had r e a c h e d 4 . 5 m i l l i o n ; i n 1882
n e a r l y 7 m i l l i o n ; by 1927 t h i s had doubled t o 1 4 . 2 m i l l i o n . S i n c e t h e n t h e popul a t i o n h a s a l m o s t t r i p p l e d . By 1970 i t was 3 3 m i l l i o n and i n 1980 i t w a s e s t i mated a t 4 0 m i l l i o n . These f i g u r e s d e m o n s t r a t e t h e r e m a r k a b l e i n c r e a s e i n t h e
440
TABLE 9 . 4 b
Volume of water i n s t o r a g e and annual d r a f t
S e r i a l Inflow, 109 m3,yr Year No. 1881 1882 1883 1884 1885 1886 1887 1888 1889 1890 1891 1892 1893 1894 1895 1896 1897 1898 1899 1900 1901 1902 190 3 1904 1905 1906 1907 1908 1909 1910 1911 1912 1913 19 14 1915 19 16 1917 1918 19 19 1920 1921 1922
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42
10.09 10.56 9.71 8.79 6.47 9.15 6.37 12.40 9.52 13.69 9.40 9.30 7.41 8.92 11.29 11.89 13.62 8.64 9.02 14.29 9.65 8.10 8.14 7.05 9.24 9.27 10.31 7.08 9.84 14.29 8.14 10.81 8.42 9.24 15.04 11.70 10.38 5.58 10.28 12.24 5.93 10.72
Draft 109 m3,9r 8.39 8.37 8.84 9.30 8.79 9.62 9.33 9.09 9.49 8.96 9.10 9.03 8.91 9.25 9.26 9.74 10.02 10.77 10.37 10.32 10.38 10.40 10.29 10.36 10.17 9.97 9.70 9.37 9.22 9.30 9.30 9.15 9.42 9.45 9.66 10.24 10.49 10.49 10.34 10.39 10.18 9.96
Initial S t o r a g e , Year 109 m 3 23.67 25.37 27.56 28.43 27.92 25.60 25.13 22.16 25.47 25.50 30.22 30.52 30.79 29.29 28.97 31.00 33.14 36.75 34.61 33.26 37.24 36.51 34.21 32.06 28.76 27.83 27.13 27.74 25.45 26.08 31.07 29.90 31.57 30.58 30.37 35.75 37.20 37.09 32.18 32.11 33.96 29.71
1923 1924 1925 1926 1927 1928 1929 1930 1931 1932 1933 1934 1935 1936 1937 1938 1939 1940 194 1 1942 1943 1944 1945 1946 1947 1948 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 196 1 1962 1963 1964
S e r i a l Inflow, Draft 109 m 9 y r 109 m3,9r NO, 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66
67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84
10.88 10.78 9.05 16.97 11.23 8.51 6.62 8.42 10.53 8.89 5.39 4.79 7.85 8.70 9.87 11.04 14.98 15.12 21.98 9.97 4.89 12.21 9.84 9.84 8.07 10.66 7.13 5.87 6.62 7.62 6.78 7.03 11.48 10.85 10.41 12.84 6.94 8.85 8.96 8.45 5.68 6.29
9.95 10.20 10.35 9.75 10.28 10.37 10.65 10.29 9.91 10.37 10.19 9.64 9.04 8.92 8.09 7.96 8.21 9.05 9.72 filled
Initial
s
~ 30.47 31.40 31.98 30.68 37.89 38.84 36.98 32.94 31.07 31.69 30.21 25.41 20.57 19.38 19.15 20.93 24.01 30.78 36.85
0 0
a
a a
d
al
0
d
c,
4
II)
W
E
h
0
4
..-I
0
c,
>
d d
7 M
al
e:
h 0)
m 0)
e:
~
~
a
~
441
p o p u l a t i o n of Egypt i n t h e l a s t c e n t u r y - a n d - a - h a l f . Such a s t a t e o f a f f a i r s had t o b e m e t w i t h , a t l e a s t i n p a r t , by i n c r e a s i n g t h e s h a r e of Egypt i n t h e N i l e ' s w a t e r a n d , more i m p o r t a n t , r e d u c i n g t h e immense v a r i a b i l i t y of t h e flow a t Aswan between t h e f l o o d and t h e low-flow s e a s o n . The f u t u r e c o n s e r v a t i o n o f t h e N i l e a s p o r t r a y e d by H u r s t , Black and Simaika i n Vol. V I I o f t h e N i l e B a s i n , c o n s i s t e d of long-term
r e s e r v o i r s i n Lakes
V i c t o r i a and A l b e r t , a r e g u l a t o r below Kyoga t o a v o i d t h e d e l a y i n t h e p a s s a g e o f w a t e r below t h e Upper V i c t o r i a N i l e ,
t h e J o n g l e i d i v e r s i o n c a n a l t o reduce
t h e l o s s e s i n t h e Bahr e l J e b e l B a s i n , an o v e r - y e a r s t o r a g e r e s e r v o i r i n Lake T a n a , and a n c t h e r r e s e r v o i r a t t h e 4 t h C a t a r a c t on t h e Main N i l e n e a r Merowe f o r a n n u a l s t o r a g e and r e g h a t i o n o f t h e d i s c h a r g e coming from t h e Upper N i l e reservoirs (Hurst, H.E.,
B l a c k , R.P., and S i m a i k a , Y.M.,
1946).
By 1950, o f a l l t h e above-mentioned w o r k s , o n l y t h e Owen F a l l s Dam had been
b u i l t . From t h e p r e v i o u s s e c t i o n w e have s e e n t h a t t h e b e n e f i t o f t h i s s t o r a g e work t o e i t h e r Egypt o r t h e Sudan is l i m i t e d . I n 1952 H u r s t and h i s co-workers s u g g e s t e d a c o m b i n a t i o n of t h e Upper N i l e p r o j e c t s and a h i g h dam t o b e b u i l t a t Aswan f o r t h e f u l l u t i l i z a t i o n o f t h e N i l e water. The h y d r o l o g i c d e s i g n of t h e l i v e s t o r a g e i n t h e High Aswan r e s e r v o i r was b a s e d on e q u a t i o n s 9 . 6 and 9 . 7 w i t h
x = 92 mlrd
m3/yr,
B = 84 mlrd m 3 / y r
and
s = 18 mlrd m 3 / y r .
These v a l u e s g i v e a maximum d e f i c i t S = 8 5 . 9 mlrd m 3 ,
o f f t o 90 mlrd m 3 .
I n o t h e r words a r e s e r v o i r w i t h a l i v e s t o r a g e volume of 90
mlrd m 3 can g u a r a n t e e a gross d r a f t of 84 mlrd m3/yr r e s e r v o i r l o s s e s were e s t i m a t e d a t 10 mlrd m 3 / y r ,
rounded
a t Aswan. The maximum
t h u s b r i n g i n g t h e annual n e t
d r a f t t o 74 mlrd m 3 . The a n n u a l r a t e of s e d i m e n t a t i o n a t Aswan h a s been e s t i m a t e d a t a b o u t 60 t o 6 2 m i l l i o n m 3/ yr
and t h e l i f e a g e of t h e r e s e r v o i r a t 500 y e a r s . The volume
a l l o c a t e d t o dead s t o r a g e is t h u s 31 mlrd m 3 . An a d d i t i o n a l room of 4 1 mlrd m 3 h a s been l e f t a s a s a f e t y measure f o r prot e c t i o n a g a i n s t h i g h f l o o d s when t h e r e s e r v o i r i s f u l l . The t o t a l s i z e of t h e r e s e r v o i r formed by t h e High Dam i s t h u s 162 x The n e t d r a f t , which i s 74 mlrd m 3 / y r ,
lo5
m3.
i s g r e a t e r t h a n t h e sum of t h e s h a r e s
of Egypt, 48 m l r d , and t h e Sudan, 4 . 5 m l r d , i . e . 5 2 . 5 mlrd m 3 / y r , dam c o n d i t i o n . The g a i n o f 2 1 . 5 mlrd m 3 / y r
i n t h e pre-
i s d i v i d e d i n s u c h a way t h a t Egypt
g e t s 7 . 5 m l r d , b r i n g i n g i t s new s h a r e t o 55.5 mlrd m3/yr and t h e Sudan g e t s 1 4 . 0 m l r d , b r i n g i n g i t s new s h a r e t o 1 8 . 5 mlrd m3/yr.
The r a t i o between 5 5 . 5 and 1 8 . 5
i s e q u a l t o t h e r a t i o between t h e E g y p t i a n and t h e Sudanese p o p u l a t i o n s a t t h e
t i m e of amending t h e N i l e Water T r e a t y i n 1959. The d i s c h a r g e s p a s s i n g down-
stream o f t h e dam w e r e 5 3 . 1 2 , 5 4 . 8 5 , 55.36, 5 5 . 9 6 , 5 5 . 2 9 , 5 6 . 2 9 , 5 6 . 2 5 , 5 4 . 4 0 , 5 4 . 7 1 , 5 7 . 6 6 , 6 2 . 1 8 , 5 8 . 0 3 and 5 6 . 7 , 5 6 . 7 2 mlrd m 3 f o r t h e y e a r s 1968-69, 19697 0 , 1970-71,
.....,
1979-80 and 1980-81, r e s p e c t i v e l y ,
w i t h an a v e r a g e of
442
5 6 . 2 mlrd m 3 ( A b u l - A t t a ,
A.,
1975).
The s u r f a c e a r e a of t h e r e s e r v o i r and t h e volume of i t s c o n t e n t s c o r r e s p o n d i n g t o t h e d i f f e r e n t w a t e r l e v e l s a r e g i v e n i n T a b l e 9 . 5 . When t h e s t o r a g e i n r e s e r v o i r i s a t f u l l l e v e l , i . e . 175 m above mean sea l e v e l t h e s u r f a c e a r e a r e a c h e s 5168 km2 and t h e c o r r e s p o n d i n g e v a p o r a t i o n l o s s amounts t o a b o u t 14 mlrd
m 3 i n a normal y e a r . T h i s f i g u r e i s n e a r l y 40% g r e a t e r t h a n t h a t assumed by t h e M i n i s t r y of I r r i g a t i o n i n E g y p t .
TABLE 9 . 5
Area of w a t e r s u r f a c e and volume of r e s e r v o i r c o n t e n t s ( A b u l - A t t a , A.,
Water level, m.a.s.l. 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141
1978)
S u r f a c e Volume of Water area, content level, kin2 lo9 m 3 m . a . s . 1 . 450 480 5 10 540 5 70 600 6 34 668 70 2 736 749 796 844 89 2 940 988 1038 1089 1140 1191 1242 1311
5.2 5.7 6.2 6.8 7.3 7.8 8.5 9.2 9.9 10.6 11.3 12.1 12.9 13.7 14.6 15.6 16.6 17.6 18.7 19.9 21.2 22.5
S u r f a c e Volume o f Water area, content level, km2 lo9 m 3 m . a . s . 1 .
142 143 144 145 146 147 148 149 150 151 152 15 3 154 155 156 157 158 159 160 16 1 16 2 16 3
1380 1449 1511 1589 166 3 1737 1812 1887 1962 205 2 2142 2232 2323 24 14 2521 26 28 2735 2842 2950 3076 3202 3328
23.8 25.2 26.7 28.3 29.9 31.6 33.4 35.3 37.2 39.2 41.3 43.5 45.7 48.1 50.5 53.1 55.7 58.5 61.5 64.5 67.6 70.9
164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185
S u r f a c e Volume of area, content lo9 m 3 km2 3454 3581 3726 3871 40 16 4162 4308 4480 4652 4824 4996 5168 5 358 5548 5738 5928 6118 6 329 6540 6751 6962 7174
74.3 77.9 81.5 85.3 89.2 93.3 97.6 101.9 106.4 111.1 116.1 121.3 126.5 131.9 137.5 143.4 149.5 155.8 162.3 168.9 175.7' 182.7
The r e s e r v o i r h a s been i n o p e r a t i o n s i n c e mid 1964. S i n c e t h e n , up t o and i n c l u d i n g 1976, t h e change i n t h e volume of i t s c o n t e n t s i s shown i n F i g . 9 . 1 2 . The o p e r a t i o n r u l e a d o p t e d by t h e M i n i s t r y of I r r i g a t i o n , E g y p t , i s t o release t h e q u o t a a s s i g n e d t o Egypt e a c h a v e r a g e y e a r , and t o release more w a t e r t o t h e downstream i n y e a r s w i t h h i g h f l o o d s . A t any r a t e t h e r e s e r v o i r l e v e l on t h e f i r s t of August e a c h y e a r s h o u l d n o t exceed 175 m above mean s e a l e v e l t o b e a b l e t o accommodate t h e coming f l o o d . The w a t e r b a l a n c e of t h e r e s e r v o i r i s drawn e a c h y e a r , and t h e a c t u a l losses and t h e n a t u r a l r i v e r s u p p l y are computed. T a b l e 9 . 6 g i v e s t h e r e s u l t s o b t a i n e d from s u c h a b a l a n c e f o r t h e p e r i o d 1964-76.
The p e r i o d i c f i g u r e s of t h e mean
443
s u p p l y and s t o r a g e l o s s e s c a n b e u s e d i n t h e f u t u r e t o amend t h e N i l e Water T r e a t y between Egypt and t h e Sudan whenever t h i s p r o v e s n e c e s s a r y . The n a t u r a l s u p p l y a t Aswan i n 1973 was q u i t e s m a l l and t h e r e s e r v o i r had t o be e m p t i e d by 30.36 x lo9 to3 i n t h e p e r i o d from f i r s t o f J a n u a r y t o e i g h t h of J u l y t o cope w i t h t h e demand. T h i s happened i n a s i n g l e y e a r , i . e . 1973. However, t h e r e i s a l w a y s t h e c h a n c e of h a v i n g a s u c c e s s i o n of low-flow y e a r s , which w i l l e v e n t u a l l y l e a d t o t h e f a i l u r e o f s u p p l y i n g t h e f u l l demands of Egypt and t h e Sudan. The a p p l i c a t i o n of a r e d u c e d d r a f t i s t h e n n e c e s s a r y t o c o v e r p a r t o f t h e
water r e q u i r e m e n t s of e a c h c o u n t r y . T h i s h a s t o b e s t r i c t l y a p p l i e d w i t h t h e i r c o n s e n t t o a v o i d c o m p l e t e d e p l e t i o n o f t h e l i v e s t o r a g e i n t h e r e s e r v o i r . These o p e r a t i o n r u l e s a p p e a r i n d e t a i l i n t h e items i n c l u d e d i n t h e N i l e Water T r e a t y o f 1959.
o.140E 130-
b,
0
Reservoir f u l l
-120-
F1100
;loo-
.c 8
9070-
Year F i g . 9.12.
F i l l i n g of t h e r e s e r v o i r formed by t h e High Aswan Dam
I n s p i t e of t h e f a c t t h a t o n l y a v e r y s m a l l p o r t i o n of t h e room a l l o c a t e d for t h e dead s t o r a g e h a s been o c c u p i e d by t h e s e d i m e n t s d e p o s i t e d i n t h e l a s t 15 y e a r s , t h e t o t a l volume d e s i g n e d f o r b o t h dead and l i v e s t o r a g e s h a s been n e a r l y f u l l w i t h water o n l y s i n c e 1975-76.
The r e s e r v o i r s u r f a c e and volume o f c o n t e n t s
a r e , t h e r e f o r e , a t t h e i r maxima ( s e e F i g . 9 . 1 2 .
and T a b l e 9 . 6 )
444
Water b a l a n c e of t h e r e s e r v o i r formed by t h e High Dam a t Aswan, Lake
TABLE 9 . 6
Nasser (Abul-Atta,
Year
1964 1965 1966 1967 1969 1969 19 70 1971 1972 1973 1974 19 75 19 76
A.,
1978)
Water b a l a n c e method, mlrd m 3 Maximum. E s t i m a t e d l o s s e s , mlrd m 3 storage Loss by level Seepage Evapo- T o t a l I n f l o w O u t f l o w Total and m . a . s .la. r a t i o n l o s s e s t o l a k e change in lossess e e p a g e + absorption storage absorption
,
126 .OO 133.61 140.74 142.40 156.50 161.23 164.87 167.62 165.26 166.24 170.61 175.70 176.51
+
0.279 1.022 0.448 6.836 4.363 4.251 3.994
-
4.878 10.468 1.929
1.872 2.308 4.003 5.466 6.782 7.823 9.158 9.587 8.763 9.694 11.167 12.443
2.151 3.330 4.451 12.302 11.145 12.074 13.152 9.587 8.763 14.572 21.635 14.372
88.411 71.422 90.185 73.768 74.047 77.258 77.152 58.050 79.527 84.934 97.988 68.964
87.611 69.662 86.535 66.598 65.977 68.324 66.517 45.145 60.502 70.465 81.629 54.820
0.800 1.760 3.650 7.170 8.070 8.934 10.635 12.905 9.025 14.469 16.359 14.144
1.704 1.288 1.111 1.477 3.318 0.262 4.775 5.192 1.701
For a b e t t e r i n s i g h t i n t o t h e i n p u t t o t h e r e s e r v o i r , w i t h t h e a i m of e s t a b l i s h i n g a b e t t e r o p e r a t i n g p o l i c y and h e l p i n g t o e v a l u a t e f u t u r e p r o j e c t s , synt h e t i c stream flow d a t a h a v e been g e n e r a t e d by means of s t o c h a s t i c models. These a r e t h e m u l t i v a r i a t e a u t o r e g r e s s i v e Markovian model, t h e d i s a g g r e g a t i o n model and t h e Broken l i n e model. The t h r e e t y p e s of models have been a p p l i e d t o f o u r s t a t i o n s : Malakill, Khartoum, A t b a r a and Aswan and t h e r e s u l t s t e s t e d . I t h a s been c o n c l u d e d t h a t i f t h e Broken l i n e method i s f i r s t i n v o k e d f o r g e n e r a t i n g a n n u a l stream f l o w , and t h e o b t a i n e d d a t a a r e d i s a g g r e g a t e d t o monthly l e v e l s u s i n g t h e d i s a g g r e g a t i o n model, t h e c o m b i n a t i o n w i l l r e p r e s e n t a more h i g h l y p o w e r f u l t o o l t h a n t h e i m p l e m e n t a t i o n of t h e Markovian model by i t s e l f ( C a i r o University
-
M a s s a c h u s s e t s I n s t i t u t e o f Technology T e c h n o l o g i c a l P l a n n i n g Pro-
gram, 1 9 7 7 ) . I t i s n o t known y e t how t h e High Dam A u t h o r i t y o r t h e M i n i s t r y of I r r i g a t i o n , Egypt, w i l l b e a b l e t o i n c o r p o r a t e t h e g e n e r a t e d stream f l o w s i n t h e o p e r a t i o n of t h e r e s e r v o i r
(Lake N a s s e r ) .
I n a d d i t i o n t o t h e s i x t u n n e l s w i t h t h e i r t w e l v e o p e n i n g s which f e e d t w e l v e t u r b i n e s of t h e power s t a t i o n ( s e e F i g . 7 , Appendix F ) , t h e r e is a number of s p i l l w a y s . The main s p i l l w a y h a s t w e l v e s l u i c e s ; t h e a u x i l i a r y s p i l l w a y s i t u a t e d u n d e r n e a t h t h e main one h a s t w e l v e s l u i c e s a l s o , and t h e emergency s p i l l w a y h a s t h i r t y s l u i c e s . The l a t t e r i s d e s i g n e d t o o p e r a t e when t h e r e s e r v o i r l e v e l r e a c h e s 178 m above mean s e a l e v e l . A l l t h e s e s l u i c e s combined c a n d i s c h a r g e 11000 m 3 / s e c . , o r a b o u t 950 m i l l i o n m3/day,
t o t h e downstream. N e e d l e s s t o s a y ,
445
t h e High Aswan Dam A u t h o r i t y h a s l a i d down t h e r u l e s t o o p e r a t e t h e d i f f e r e n t s p i l l w a y s and d e v e l o p e d t h e r a t i n g r e l a t i o n s ( s t a g e - d i s c h a r g e ) of t h e i r s l u i c e s (Abul-Atta, A . ,
1978).
I n o r d e r t o l i m i t t h e r e l e a s e t o t h e downstream of L a k e Nasser i n t h e highflow y e a r s t o t h e f i x e d demands of Egypt o n l y , t h e M i n i s t r y of I r r i g a t i o n t h e r e h a s t h o u g h t o f r e l e a s i n g t h e e x c e s s w a t e r t o Toshka d e p r e s s i o n . T h i s d e p r e s s i o n
i s l o c a t e d s o u t h - w e s t of t h e High Dam and i t s l e v e l v a r i e s from 121 t o 180 above mean sea l e v e l . A t t h e l e v e l of 180 m t h e d e p r e s s i o n h a s a s u r f a c e a r e a of
6000 km2 and a s t o r a g e volume of 120 mlrd m 3 . The r e s e r v o i r i s connected t o t h e d e p r e s s i o n by an o l d c h a n n e l (Khor) 72 km i n l e n g t h (see F i g . 9 . 1 3 . ) .
With some
improvement t h e c h a n n e l can s e r v e a s a d i v e r s i o n c a n a l from Lake N a s s e r t o t h e escape depression. I t h a s been e s t i m a t e d t h a t i f t h e r e i s an abnormally h i g h y e a r , s i m i l a r t o 1878-1879,
w i t h an a n n u a l volume o f flow i n t h e o r d e r o f 150 mlrd m 3 ,
the
release t o t h e d e p r e s s i o n may r e a c h 54 mlrd m3. A s e q u e n c e of h i g h - f l o w y e a r s s i m i l a r t o t h a t i n t h e p e r i o d from 1870 t o 1902 w i l l need a b o u t 25 y e a r s t o f i l l t h e d e p r e s s i o n a f t e r s a t i s f y i n g t h e l o s s by e v a p o r a t i o n and a l l o t h e r l o s s e s . On t h e o t h e r h a n d , i n a s e q u e n c e o f normal y e a r s , as t h a t which happened from 1940 t o 1970, t h e r e i s no need t o release water t o t h e e s c a p e d e p r e s s i o n f o r p e r i o d s a s l o n g a s 20 y e a r s or more.
30'
E
31
32O
N
2L0
24O
23O
x i s of connecting
30
F i g . 9.13
'
31 32 P l a n of Toshka d e p r e s s i o n
23'
33O
446
CONTROL WORKS ON THE MAIN NILE BETWEEN ASWAN AND THE MEDITERRANEAN SEA
9.2 9.2.1
Introduction
The i d e a of h a v i n g a c o n t r o l on t h e N i l e w a t e r l e v e l s and t h e amounts d i v e r t e d t o t h e c a n a l s t a k i n g from t h e r i v e r i n t h e r e a c h between Aswan and t h e M e d i t e r r a n e a n d a t e s back t o t h e t i m e Mohammed A l i was r u l i n g E g y p t . The d i f f i c u l t i e s e n c o u n t e r e d w i t h t h e c o n s t r u c t i o n of t h e f i r s t b a r r a g e s a t t h e a p e x o f t h e D e l t a c a u s e d a d e l a y i n t h e c o m p l e t i o n o f t h a t work u n t i l 1861. The o r i g i n a l d e s i g n was t o r a i s e t h e w a t e r l e v e l by 3 . 5 m . When i n 1863 t h e head was r a i s e d from 1 t o 1 . 5 m,
c r a c k s a p p e a r e d i n t h e b a r r a g e and f u r t h e r d e t e r i o r a t i o n took
p l a c e l a t e r . R e p a i r s were u n d e r t a k e n and o n l y upon t h e i r c o m p l e t i o n i n 1890 w a s t h e b a r r a g e a b l e t o h o l d i t s d e s i g n e d head f o r t h e f i r s t t i m e . The b a r r a g e s a r e , i n f a c t , open t y p e weirs or dams where t h e w a t e r f l o w s t h r o u g h t h e v e n t s and does n o t s p i l l o v e r a c r e s t . The p r i n c i p a l r e a s o n b e h i n d t h e c h o i c e o f s u c h a t y p e o f c o n s t r u c t i o n was t o r e d u c e t h e c h a n c e of s e d i m e n t a t i o n upstream o f t h e b a r r a g e and t h e s c o u r downstream of i t , common f e a t u r e s a s s o c i a t e d w i t h t h e c o n s t r u c t i o n o f weirs on a l l u v i a l s t r e a m s . The f l o w t h r o u g h t h e v e n t s a s w e l l a s t h e water l e v e l s u p s t r e a m and downstream of t h e s t r u c t u r e a r e r e g u l a t e d by means of v e r t i c a l s t e e l g a t e s r e s t i n g e i t h e r d i r e c t l y on t h e c o n c r e t e f l o o r or on a w e i r c r e s t b u i l t m o n o l i t h i c a l l y w i t h t h e b a r r a g e f l o o r . The l a t t e r d e s i g n h e l p s i n r e d u c i n g t h e h e i g h t o f t h e g a t e s , t h e i r own w e i g h t and t h e c a p a c i t y of t h e l i f t i n g o r g a n s . Moreover, i t was found more e c o n o m i c a l t o u s e two o v e r l a p p i n g s h o r t p r i n c i p a l g a t e s i n s t e a d o f a t a l l p r i n c i p a l o n e . Emergency g a t e s a r e p l a c e d u p s t r e a m and downstream of t h e p r i n c i p a l o n e . The former a r e u s u a l l y made of t i m b e r . The u p s t r e a m emergency g a t e s a c t as a f i r s t l i n e o f d e f e n c e t o t h e b a r r a g e i n case of c o m p l e t e c l o s u r e f o r any sort o f r e p a i r . The downstream emergency g a t e s when set i n p o s i t i o n i s o l a t e t h e b a r r a g e from t h e downstream w a t e r and i t t h u s becomes p o s s i b l e t o e v a c u a t e t h e b a r r a g e from t h e volume of w a t e r impounded i n i t . T h i s c o n d i t i o n h a s always been t a k e n i n t o c o n s i d e r a t i o n w h i l e d e s i g n i n g t h e f l o o r as i t i s t h e n s u b j e c t e d t o t h e maximum d i f f e r e n c e i n h e a d . To r e d u c e t h e f l o o r t h i c k n e s s w i t h o u t e n d a n g e r i n g it, r e p a i r work r e q u i r i n g c o m p l e t e c l o s u r e of t h e b a r r a g e s h o u l d b e c a r r i e d o u t duri n g the lowest p o s s i b l e r i v e r l e v e l s . The p r o t e c t i o n o f t h e downstream r e a c h a g a i n s t s c o u r i s u s u a l l y a c c o m p l i s h e d by e x t e n d i n g t h e f l o o r h o r i z o n t a l l y and by p l a c i n g v e r t i c a l c u t - o f f w a l l s and i n
some i n s t a n c e s by end s i l l s . I n a d d i t i o n t o a l l t h e s e m e a s u r e s , f u r t h e r downs t r e a m p r o t e c t i o n o f t h e r i v e r bed and s i d e s a g a i n s t s c o u r i s a c h i e v e d by s t o n e p i t c h i n g f o r a d i s t a n c e between 10 and 20 m .
447
9.2.2 9.2.2.1
The b a r r a g e s on t h e N i l e from Aswan t o t h e M e d i t e r r a n e a n S e a
Esna barrage
The c o n s t r u c t i o n o f t h e o r i g i n a l b a r r a g e a t Esna was completed i n 1908. I t h e l p e d i n r a i s i n g t h e u p s t r e a m water l e v e l by 2 . 5 m t o g u a r a n t e e t h e r e q u i r e ments f o r b a s i n i r r i g a t i o n i n t h e P r o v i n c e of Qena (see F i g . 9 . 1 4 . ) .
The b a r r a g e
c o n s i s t s of 120 v e n t s e a c h 5 m w i d e . Every t w o a d j a c e n t v e n t s a r e s e p a r a t e d by a 2 m t h i c k p i e r , and e v e r y t e n v e n t s form a u n i t s e p a r a t e d from t h e a d j a c e n t u n i t s by a 4 m t h i c k p i e r . The b a r r a g e i s combined w i t h a l o c k 80 m l o n g and 16m w i d e . The Esna b a r r a g e was r e m o d e l l e d i n t h e p e r i o d between 1945 and 1947 t o w i t h s t a n d a head d i f f e r e n c e of 4 . 5 m .
9.2.2.2
Nag-Hammadi b a r r a g e
T h i s b a r r a g e was c o n s t r u c t e d i n t h e p e r i o d 1927-1930 t o h e l p i r r i g a t e t h e b a s i n s s i t u a t e d between Nag-Hammadi and Dayrut ( a b o u t 210 000 h e c t a r e s ) . The d e s i g n e d maximum d i f f e r e n c e i n head is 4 . 5 m . The b a r r a g e c o n s i s t s of 100 v e n t s e a c h 6 m wide s e p a r a t e d by p i e r s each 2 m t h i c k . Every t e n v e n t s form a u n i t s e p a r a t e d from t h e a d j a c e n t u n i t s by a 4 m t h i c k p i e r . S i m i l a r t o t h e Esna b a r r a g e , t h i s one i s a l s o combined w i t h a l o c k , t h e b a s i n of which i s 80
9.2.2.3
x 16 m .
Assiut barrage
T h i s b a r r a g e was c o n s t r u c t e d i n 1902 t o h e l p i n t h e summer i r r i g a t i o n of an
area o f a b o u t 400 000 h e c t a r e s s i t u a t e d i n Middle Egypt and E l Fayum P r o v i n c e (see Fig. 9.14.)
t h r o u g h t h e I b r a h i m i a c a n a l . I n 1938 t h e b a r r a g e was r e m o d e l l e d
t o w i t h s t a n d a d i f f e r e n c e of head o f 4 . 3 m . T h i s b a r r a g e c o n s i s t s of 110 v e n t s each 5 m wide. The p i e r i s , as u s u a l , 2 . 0 m t h i c k , b u t h e r e e v e r y n i n e v e n t s form a u n i t s e p a r a t e d from t h e a d j a c e n t u n i t s by a 4 m t h i c k p i e r . 9.2.2.4
The D e l t a b a r r a g e s
I n 1935 i t became o b v i o u s t h a t t h e o l d Mohammed A l i b a r r a g e s had r e a c h e d a p o o r s t a t e and c o u l d n o t s t a n d any f u r t h e r r e m o d e l l i n g . The new Delta b a r r a g e s
were t h u s c o n s t r u c t e d i n 1937 and completed i n 1939 t o w i t h s t a n d a maximum head d i f f e r e n c e of 3 . 8 m d u r i n g t h e summer s e a s o n . The new b a r r a g e s a r e s i t u a t e d a' s h o r t d i s t a n c e downstream of t h e o l d o n e s and u p s t r e a m o f t h e submerged s i l l s . The b a r r a g e o n t h e D a m i e t t a b r a n c h c o n s i s t s o f 34 v e n t s whereas t h a t on t h e R o s e t t a b r a n c h c o n s i s t s of 46 v e n t s . The w i d t h o f e a c h v e n t is 8 m and t h e p i e r s e p a r a t i n g one v e n t from t h e o t h e r i s 2 . 5 m t h i c k . Each b a r r a g e i s combined w i t h a l o c k o f 80 x 12 m .
448
Bahariya Oasis
Farafra Oasis
Kharga Oasis
E
G
Y
P
T
i i I
!
I--.__
20O
Scale
100
Fig. 9.14.
200 k m .
Map showing the location of the Nile control works in Egypt
20 a
449
9.2.2.5
Z i f t a barrage
T h i s b a r r a g e is s i t u a t e d on t h e D a m i e t t a branch some 87 km downstream o f i t s mouth. The b a r r a g e was f i r s t c o n s t r u c t e d i n 1903 t h e n r e m o d e l l e d between 1949 and 1953. I t c o n s i s t s o f 50 v e n t s e a c h 5 . 0 m wide. The p i e r t h i c k n e s s i s 2 . 0 m and e v e r y 10 v e n t s form a s e p a r a t e u n i t h a v i n g a p i e r 3 m t h i c k . The d e s i g n d i f f e r e n c e o f head i s 4 . 0 m and t h e summer u p s t r e a m w a t e r l e v e l i s enough for t h e c a n a l s f e e d i n g t h e e a s t e r n p a r t o f t h e N i l e D e l t a . Combined w i t h t h e b a r r a g e i s a l o c k whose chamber i s 55 x 12 m .
9.2.2.6
Edfina barrage
T h i s b a r r a g e was c o n s t r u c t e d on t h e R o s e t t a b r a n c h i n t h e p e r i o d 1948-1951. The b a r r a g e was d e s i g n e d w i t h t h e aim of a v o i d i n g t h e d i s c h a r g e of e x c e s s i v e amounts of f r e s h - w a t e r
i n t o t h e s e a d u r i n g t h e summer s e a s o n . T h i s was done t o
p r e v e n t t h e i n t r u s i o n of t h e s a l t w a t e r from t h e sea i n t o t h e r i v e r b r a n c h . T h i s c o n t r o l work h a s no d o u b t h e l p e d t o improve i r r i g a t i o n c o n d i t i o n s i n a v a s t a r e a i n t h e n o r t h - w e s t e r n p a r t o f t h e N i l e D e l t a . The summer d e s i g n head on t h e E d f i n a b a r r a g e was 2 . 8 m . The number of v e n t s i s 46, e a c h 8 m w i d e ; e v e r y two v e n t s a r e s e p a r a t e d by a 2 . 5 m t h i c k p i e r . The l o c k combined w i t h t h e b a r r a g e h a s a chamber of 8Q x 12 m. F i g . 8 , Appendix F, shows some c r o s s - s e c t i o n s of t h e a b o v e - d e s c r i b e d b a r r a g e s .
WATER CONSERVATION SCHEMES
9.3 9.3.1
C o n s e r v a t i o n schemes o f Bahr e l J e b e l and Bahr e l Z e r a f w a t e r
Next t o s t o r a g e and c o n t r o l o f N i l e w a t e r , c o n s e r v a t i o n schemes aiming a t s a v i n g t h e tremendous amounts which a r e l o s t i n c e r t a i n s u b - b a s i n s o f t h e r i v e r have been p l a n n e d and t h e e x e c u t i o n of one o f them i s a l r e a d y under way. I n many p a r t s o f t h e book, e s p e c i a l l y i n C h a p t e r 8 , w e have emphasized t h a t t h e l o s s i n t h e Bahr e l J e b e l and Bahr e l Z e r a f s u b - b a s i n s amounts t o n o t less t h a n 14 mlrd m 3 / y r .
I n o r d e r t o s a v e a l l , or some, o f t h i s w a t e r , two b a s i c
schemes have been t h o u g h t o f : t h e d i v e r s i o n c a n a l scheme or t h e J o n g l e i c a n a l and t h e embankment scheme. The l a y o u t s of t h e d i f f e r e n t schemes have been comb i n e d i n one map ( F i g . 9 . 1 5 . ) and a n a l y z e d by S a l i h , A . M . A .
(1981).
The d i v e r s i o n c a n a l h a s always been c o n s i d e r e d s u p e r i o r t o t h e embankment scheme a n d i t s e x c a v a t i o n and t h e c o n s t r u c t i o n o f t h e r e l a t e d r e g u l a t i o n works a r e u n d e r way. The f i r s t p h a s e , which i s a b o u t t o b e c o m p l e t e d , c o m p r i s e s t h e e x c a v a t i o n of o n e c a n a l a l o n g t h e d i r e c t l i n e ( F i g . 9 . 1 5 . ) , t h a t a l l o w s t h e flow o f 20 m i l l i o n m3/day,
with a cross-section
and t h e c o n s t r u c t i o n of t h r e e r e g u l a -
t o r s : one a t t h e o u t l e t and one on t h e R i v e r A t e m a t J o n g l e i l a t i t u d e . In t h i s p h a s e , o u t o f t h e a v e r a g e d i s c h a r g e of 75 m i l l i o n m3/day a t Mongalla, 66 m i l l i o n m3/day r e a c h J o n g l e i ; 20 flow t h r o u g h t h e c a n a l and t h e rest t h r o u g h Bahr e l
450
J e b e l and Bahr e l Z e r a f . The J o n g l e i c a n a l w i l l d e l i v e r 19 m i l l i o n every day a t t h e o u t l e t , a n d t h e n a t u r a l r i v e r s ( J e b e l and Z e r a f ) , 32. The t o t a l volume of flow d e l i v e r e d i n an average day a t t h e o u t l e t i s 5 1 m i l l i o n m 3 . The amount of water r e a c h i n g Malakal without having a d i v e r s i o n c a n a l i s about 39 m i l l i o n m3/ day ( s e e F i g . 8 . 2 5 . ) .
So t h e f i r s t phase of t h e J o n g l e i c a n a l s a v e s about 4.4
mlrd m3/yr a t Malakal o r 3.6 mlrd m3/yr e s t i m a t e d a t Aswan, Egypt. T h i s g a i n s h a l l be d i v i d e d e q u a l l y between Egypt and t h e Sudan. The d e t a i l e d c a l c u l a t i o n of t h e g a i n t o b e expected i n such a low-flow
year a s 1912 and i n a n o t h e r y e a r
such a s 1960 a r e i n c l u d e d i n Table 9 . 7 (Executive Organ f o r Development P r o j e c t s i n J o n g l e i Area, 1975).
F i g . 9.15.
P l a n of t h e proposed schemes
The second phase i s planned on t h e b a s i s of having a long-term s t o r a g e i n t h e E q u a t o r i a l Lakes t o e q u a l i z e t h e i r n a t u r a l outflows and improve t h e c a r r y i n g c a p a c i t i e s of t h e channels of Bahr e l J e b e l n o r t h of Mongalla a s w e l l a s of Bahr e l Zeraf t o e n a b l e them t o t r a n s m i t t h e normal flow of 75 m i l l i o n m3/day. I f t h i s improvement can be r e a l i z e d , t h e n 7 1 m i l l i o n w i l l reach J o n g l e i , of which 5 1 w i l l be c a r r i e d by t h e J e b e l and t h e Zeraf and 20 by t h e c a n a l . These w i l l d e l i v e r 45 and 19 m i l l i o n m3/day a t t h e o u t l e t , r e s p e c t i v e l y . The d a i l y flow reaching Malakal on an average day a f t e r implementing phase two i s expected t o
TABLE 9.7
Expected s a v i n g of Nile water produced by phase 1 of J o n g l e i scheme
D e s c r i p t i o n of i t e m Monthly mean d i s c h a r g e a t Mongalla
Discharge i n m i l l i o n m'/day Jan. 52.6
Feb.
Mar.
51.3
54.3
Apr. 61.1
May 67.3
f o r t h e months of t h e y e a r 1912
June 61.9
July
Aug.
71.2
80.7
Sep.
Oct.
Nov.
Dec.
89.6
78.3
65.9
71.0
76.2
77.2
69.2
88.1
Monthly mean d i s c h a r g e a t J o n g l e i
53.4
47.8
46.8
49.4
55.5
60.7
56.2
64.0
Canal d i s c h a r g e r e a c h i n g Malakal
19.0
19.0
19.0
19.0
19.0
19.0
19.0
19.0
19.0
19.0
19.0
19.0
D i s c h a r g e s of J e b e l and Zeraf r e a c h i n g Malakal
32.0
27.6
23.0
22.0
24.4
28.9
31.8
29.2
33.1
35.2
36.4
36.6
51.0 37.5
46.6 35.8
42.0 34.4
41.0 34.1
43.3 34.9
47.9 36.3
50.8 37.5
48.2 36.4
52.1 38.1
54.2 39.6
55.4 40.6
55.6 40.7
13.5 418.0
10.8 304.0
7.6 236.0
6.9 207.0
8.4 260.0
11.8 11.6 13.3 14.0 14.6 348.0 412.0 366.0 420.0 453.0
14.8 444.0
14.9 462.0
T o t a l d i s c h a r g e a t Malakal - a f t e r having t h e c a n a l -beforehaving the canal N e t g a i n a t Malakal N e t g a i n , lo6 m3/month N e t g a i n , lo9 m3/yr a t Malakal N e t g a i n , lo9 m3/yr a t Aswan
D e s c r i p t i o n of i t e m
4.33 3.50 Discharge i n m i l l i o n m3/day f o r t h e months of t h e y e a r 1960 Jan.
Feb.
Mar.
Apr.
May
June
July
Aug.
Sep.
Oct.
Nov.
Dec.
Monthly mean d i s c h a r g e a t Mongalla
53.9
47.7
44.7
47.7
51.8
45.5
74.1
94.1
100.0
70.9
68.1
63.5
Monthly mean d i s c h a r g e a t J o n g l e i
63.8
49.0
43.4
41.6
43.3
47.1
47.0
66.0
79.9
83.5
69.8
61.4
Canal d i s c h a r g e r e a c h i n g Malakal
19.0
19.0
19.0
19.0
19.0
19.0
19.0
19.0
19.0
19.0
19.0
19.0
Discharges o f J e b e l and Zeraf r e a c h i n g Malakal
32.1
29.8
24.1
19.5
18.0
19.4
22.4
22.3
33.8
37.3
38.0
35.0
51.1 41.1
48.8 31.7
43.1 25.4
38.5 34.5
37.0 33.5
38.4 32.7
41.4 34.4
41.3 36.8
52.8 38.6
56.3 37.0
57.0 34.6
54.0 44.0
10.0 310.0
17.1 493.0
17.7 548.0
4.0 120.0
3.5 108.0
5.7 170.0
7.0 217.0
4.5 140.0
14.2 436.0
19.3 598.0
22.4 672.0
10.0 310.0
T o t a l d i s c h a r g e a t Malakal - a f t e r having t h e c a n a l - b e f o r e having t h e c a n a l N e t g a i n a t Malakal N e t g a i n , lo6 m3/month
N e t g a i n , lo9 m3/yr a t Malakal N e t g a i n , lo9 m3/yr a t Aswan
4.32 3.50
Ln ~
452
be 64 m i l l i o n m 3 , whereas w i t h o u t p h a s e s one and two i t i s l i m i t e d t o 40 m i l l i o n
m3. The s a v i n g a t Malakal w i l l t h e n b e 8.8 m l r d m3/yr e s t i m a t e d a t 7.8 mlrd m 3 / y r a t Aswan. The a l t e r n a t i v e s o l u t i o n i s t o d o u b l e t h e c a r r y i n g c a p a c i t y of t h e d i v e r s i o n c a n a l e i t h e r by w i d e n i n g phase-one
c a n a l or e x c a v a t i n g a n o t h e r l i n e .
Of t h e 40 m i l l i o n m3/day c a r r i e d by t h e s e c a n a l s , 38 m i l l i o n are e x p e c t e d t o r e a c h Malakal and from t h e 31 m i l l i o n m 3 c a r r i e d by e l Jebel and e l Z e r a f , 25 m i l l i o n m3 a r e expected t o r e a c h Malakal. The s a v i n g of 8.8 mlrd m3/yr a t Malakal or of 7.8 mlrd m3/yr a t Aswan w i l l b e e q u a l l y d i v i d e d between t h e Sudan and Egypt. A c c o r d i n g l y , t h e s h a r e s of t h e two c o u n t r i e s i n t h e N i l e w a t e r w i l l i n c r e a s e t o a b o u t 23 and 59 mlrd m3/yr,
respec-
tively. I n h i s r e v i e w of t h e J o n g l e i development p r o j e c t , I b r a h i m , A . M . ,
mentioned
t h a t t h e t o t a l loss i n t h e Bahr e l J e b e l and Bahr e l Z e r a f B a s i n s amounts i n a normal y e a r t o more t h a n 20 mlrd m 3 , Of t h i s amount, around 7 mlrd m 3 a r e l o s t by d i r e c t e v a p o r a t i o n from t h e r a i n f a l l (1977). H e added t h a t i f t h i s amount i s p r o p e r l y u s e d i n i r r i g a t e d a g r i c u l t u r e t h e a n n u a l r e v e n u e w i l l b e n o t less t h a n
200 m i l l i o n pounds ( b a s e d on 1977 p r i c e s ) . 9.3.2
C o n s e r v a t i o n scheme of Bahr e l Ghazal water
The o n l y c o n s e r v a t i o n schemes l a i d down f o r t h e r e c l a m a t i o n of t h e Bahr e l Ghazal swamps w e r e t h o s e p l a n n e d by Ahmed, A.
e l A z i z (1960). A c c o r d i n g t o him
t h e t o t a l known loss from t h e complex o f t h e s u b - b a s i n s Zeraf and e l Ghazal i s i n t h e o r d e r o f 28 mlrd m3/yr.
o f t h e Bahr e l J e b e l , e l
From C h a p t e r 8, t h e d i s -
c h a r g e s of t h e streams i n t h e Bahr e l Ghazal B a s i n a t t h e s i t e s i n d i c a t e d on F i g . 8.28. a r e a b o u t 14.07 mlrd m 3 i n a normal y e a r . Of t h i s amount o n l y 0.6 mlrd m 3 r e a c h e s t h e White N i l e a t Lake N o and t h e r e s t , i . e .
13.47 mlrd are l o s t
i n t h e swamps. Obviously t h e d i f f e r e n c e between t h e l a s t f i g u r e and t h e 28 mlrd
m 3 i s l o s t i n t h e swamps of t h e Bahr e l J e b e l and Bahr e l Z e r a f B a s i n s . The i d e a o f e x c a v a t i n g a main c o l l e c t o r r u n n i n g around t h e marshy l a n d l e a d i n g d i r e c t l y t o t h e White N i l e ( s e e F i g . 9.16) w a s c o n s i d e r e d . T h i s p r o p o s a l , however, w a s n o t a p p r e c i a t e d .
I t w a s t h o u g h t i m p r a c t i c a b l e b e c a u s e of t h e
extreme f l a t n e s s of t h e c o u n t r y ; even i f i t were p r a c t i c a b l e , t h e d i f f i c u l t i e s i n h e r e n t i n t h e m a i n t e n a n c e of t h e c h a n n e l and banks o f t h e c o l l e c t o r d r a i n i n s u c h a t e r r i t o r y would b e bound t o e n t a i l enormous r u n n i n g e x p e n s e s . Ahmed, A . e l Aziz (1960) p r o p o s e d a h y d r o - e l e c t r i c
scheme which h e c l a i m e d
c o u l d d e a l w i t h a l l t h e l o s s e s i n c u r r e d i n t h e swamps o f b o t h t h e Bahr e l J e b e l and t h e Bahr e l G h a z a l . The scheme i n v o l v e d t h e g e n e r a t i o n of power from a
series o f w a t e r f a l l s i n t h e Bahr e l J e b e l between Nimule and R e j a f , of which F o l a r a p i d s ( a d r o p of a b o u t 16 m) a r e t h e b e s t known. The power would b e t r a n s m i t t e d s e v e r a l hundred k i l o m e t r e s t o two p o i n t s on t h e White N i l e , where
45 3
e l e c t r i c a l l y d r i v e n pumping s t a t i o n s would b e i n s t a l l e d a t t h e o u t l e t s of t h e Bahr e l J e b e l and Bahr e l Z e r a f r e s p e c t i v e l y fo,r l i f t i n g water from t h e swamps i n t o t h e White N i l e . The o b j e c t o f t h e pumping scheme i s t o c r e a t e an a r t i f i c i a l s l o p e i n a r e a l l y f l a t l a n d , whose f l a t n e s s i s t h e r e a s o n f o r t h e f o r m a t i o n of t h e swamps. The d r o p c r e a t e d by t h e pumps, however s m a l l , would g r e a t l y enhance t h e f l o w i n t o t h e d e p r e s s i o n t h u s formed. I n h i s d i s c u s s i o n o f t h e p a p e r o f Ahmed, A . ,
H u r s t c r i t i c i z e d t h e conserva-
t i o n scheme on t h e g r o u n d s t h a t of t h e c o m p l i c a t e d and c o s t l y scheme, o n l y t h e embanking o f t h e lower p a r t s o f t h e Bahr e l J e b e l and Bahr e l Ghazal made a s m a l l r e d u c t i o n o f t h e l o s s e s i n t h e Sudd r e g i o n . The dam and power s t a t i o n a t Bedden ( s e e F i g . 9 . 1 6 . ) ,
t h e t r a n s m i s s i o n l i n e and t h e two pumping s t a t i o n s con-
t r i b u t e d n o t h i n g (Ahmed A . p a p e r , S n e l s o n , K.E.
e l A z i z e t a l , 1 9 6 1 ) . I n h i s d i s c u s s i o n of t h e same
p r o p o s e d t o b u i l d r e s e r v o i r s i n t h e r i v e r s above t h e swamps,
and t o l e a d t o t h e White N i l e t h e s h a r e o f t h e i r w a t e r which u s e d t o flow n o r t h ward by a g r a v i t y c h a n n e l w i t h an a c c e p t a b l e s l o p e . The p r o p o s e d a l i g n m e n t
Of
t h i s c o l l e c t o r d r a i n i s shown by t h e d a s h - d o t l i n e i n F i g . 9 . 1 6 . A s t h e hydrol o g y of t h e Bahr e l Ghazal swamp w a s n o t a c c u r a t e l y known, t h e t h o u g h t t h a t t h e c o n s e r v a t i o n scheme p r o p o s e d by Ahmed would l e a d t o a s a v i n g of 1 2 mlrd m3/yr
454
on t h e b a s i s of 1 m l r d m3/month, from b e i n g l o s t i n t h a t swamp was n o t w i d e l y a c c e p t e d (Ahmed, A.
e l Aziz e t a l , 1961).
I t i s remarkable t h a t s i n c e t h a t t i m e ,
1960-61, n o t h i n g h a s been p l a n n e d o r
u n d e r t a k e n t o c o n s e r v e t h e water l o s t i n t h e Bahr e l Ghazal swamps. I t seems t h a t S n e l s o n , K . w a s r i g h t when he s a i d t h a t t h i s would b e t h e l a s t a n d almost c e r t a i n l y t h e most e x p e n s i v e s t a g e of N i l e development and would p r e s e n t a n e n g i n e e r i n g c h a l l e n g e of magnitude t o t h e e n g i n e e r s o f t h e f u t u r e who would u n d e r t a k e i t (Ahmed, A .
e l Aziz e t a l , 1961).
Any of t h e s e schemes, however, i s e x p e c t e d t o y i e l d a s a v i n g of 12 mlrd m3/yr a t Malakal o r r o u g h l y 10 mlrd m3/yr a t Aswan.
I f t h i s net gain is divided
e q u a l l y between Egypt and t h e Sudan t h e i r s h a r e s i n t h e N i l e water a t Aswan w i l l
rise t o a b o u t 6 4 and 28 m l r d m3/yr r e s p e c t i v e l y .
9.3.3 9.3.3.1
C o n s e r v a t i o n schemes i n t h e b a s i n of t h e S o b a t a n d t r i b u t a r i e s C o n s e r v a t i o n of t h e Baro
U n t i l now t h e r e are no d e f i n i t e p l a n s l a i d down f o r c o n s e r v i n g t h e water l o s t i n t h e b a s i n o f t h e S o b a t a n d t r i b u t a r i e s , s i m i l a r t o t h o s e o f t h e Bahr e l Jebel,
e l Zeraf and e l Ghazal. The r e a d e r w i l l o n l y f i n d a number of g u i d e l i n e s d i s c u s s e d h e r e and t h e r e , e s p e c i a l l y i n Volumes V I I t h r u ’ X o f t h e N i l e B a s i n (1946, 1950, 1959, 1 9 6 6 ) . The B a r o d i s c h a r g e undergoes l o s s e s from J u n e t o November e a c h y e a r . I n t h i s p e r i o d , n o t w i t h s t a n d i n g t h e i n f l o w t o t h e s e c o n d a r y streams, t h e r i v e r s t r e t c h from Gambeila dcwn t o t h e P i b o r - B a r 0 j u n c t i o n l o o s e s a b o u t 4 mlrd m 3 i n a normal y e a r . I f t h e i n f l o w t o t h e s e streams i s c o n s i d e r e d , t h e l o s s s i m p l y r e a c h e s 5 mlrd m 3 e a c h y e a r . The d e t a i l s of t h e s e f i g u r e s have a l r e a d y been p r e s e n t e d i n
Fig. 8 . 3 1 , Chapter 8 . The c o n s e r v a t i o n scheme c o n s i s t s of two components; a s t o r a g e r e s e r v o i r and r i v e r embankment w h e r e v e r n e c e s s a r y . The e s t i m a t e d r e s e r v o i r c a p a c i t y s h o u l d b e between 5 and 7 mlrd m3.
S i n c e t h e p r e c i p i t a t i o n up t h e v a l l e y o f t h e Baro
e x c e e d s e v a p o r a t i o n , any s i t e s u i t a b l e from c o n s t r u c t i o n a l and g e o t e c h n i c a l cond i t i o n s would be s u i t a b l e a s f a r as h y d r o l o g y i s c o n c e r n e d . Two major d i f f i c u l t i e s a r i s e i n r e l a t i o n t o t h e s t o r a g e scheme. F i r s t l y , t h e p o s s i b i l i t y of heavy s i l t a t i o n i n t h e r e s e r v o i r and s e c o n d l y , t h e dam s i t e , i f one e x i s t s , i s bound t o b e deep i n E t h i o p i a and t h e r e u p o n i t s c o n s t r u c t i o n , m a i n t e n a n c e and o p e r a t i o n s h a l l need a l l t h e s u p p o r t a n d c o - o p e r a t i o n (Hurst, H . E . ,
Black, R.P.,
and Simaika, Y . M . ,
from t h e E t h i o p i a n a u t h o r i t i e s 1 9 6 6 ) . The embankment of some
s t r e t c h e s of t h e B a r 0 and i t s t r i b u t a r i e s l i k e Khor Mokwai and Khor Adura have
t o b e p l a n n e d and d e s i g n e d i n c o n j u n c t i o n w i t h t h e s t o r a g e r e s e r v o i r .
455
C o n s e r v a t i o n o f water l o s t i n t h e Machar swamps
9.3.3.2
The water b a l a n c e o f t h e Machar swamps h a s a l r e a d y been d i s c u s s e d i n s e c t i o n 8.7.2.1.2,
C h a p t e r 8. The i n f l o w c o n s i s t s o f a b o u t 6 . 0 3 mlrd m3/yr r a i n f a l l ,
1 . 4 4 mlrd m3 run-off and El-Ahmar,
from t h e e a s t e r n t r i b u t a r i e s ; Khor Lau, Daga, Yabus, Tombak
and 2 . 6 7 mlrd m3 from t h e B a r 0 s p i l l . The t o t a l sum of 10.14 mlrd
m3/yr i s l o s t a l t o g e t h e r by e v a p o t r a n s p i r a t i o n from t h e swamp. The c o n s e r v a t i o n scheme so f a r c o n s i d e r e d is t h a t b a s e d on t h e d i v e r s i o n o f t h e Baro. T h i s r e q u i r e s t h e c o n s t r u c t i o n o f a b a r r a g e a t t h e h e a d of Khor Machar, enlarging t h e cross-section
of Khor Machar, e x c a v a t i n g a c a n a l t h r o u g h t h e
marshes t o c o n n e c t Khor Machar t o Khor Adar and improving t h e c a r r y i n g c a p a c i t y of t h e Adar up
t o i t s mouth on t h e S o b a t ( s e e F i g . 2 . 1 5 . ) .
This conservation
scheme i s e x p e c t e d t o y i e l d a n e t g a i n o f 3 m l r d m3/yr. Another l i n e of t h o u g h t i s t o combine t h e d i v e r s i o n of t h e B a r 0 w i t h t h e r e c l a m a t i o n of t h e Machar swamps. T h i s i n c l u d e s t h e c a n a l i z a t i o n o f t h e e a s t e r n t r i b u t a r i e s which f e e d t h e marshes and t h e Khor Machar and Khor Wol. The r e m a i n i n g p a r t of t h e scheme i s as a l r e a d y mentioned a b o v e , i . e .
enlarging the
Khor Machar and e x c a v a t i n g t h e c a n a l c o n n e c t i n g t h e same Khor t o Khor Adar. T h i s scheme, known as t h e combined scheme, is e x p e c t e d t o y i e l d an a v e r a g e g a i n o f 4 . 4 mlrd m3/yr
a t t h e White N i l e , o r a b o u t 4 mlrd m3/yr a t Aswan. An e q u a l d i v i -
s i o n o f t h i s g a i n w i l l b r i n g t h e s h a r e of Egypt and t h e Sudan i n t h e N i l e w a t e r up t o , s a y , 66 and 30 mlrd m3/yr r e s p e c t i v e l y The sum of t h e s e two f i g u r e s , 96 mlrd m 3 / y r ,
c o i n c i d e s w i t h t h e grand t o t a l
of 9 6 . 5 7 mlrd m3/yr o b t a i n e d by Dekker, G. (1972) from t h e d a t a p u b l i s h e d by H u r s t f o r t h e p e r i o d 1912-1947.
The d e t a i l s of t h e l a t t e r are q u i t e d i f f e r e n t
from o u r s . Dekker a s s i g n s 6 2 a n d 2 3 . 8 mlrd m3/yr f o r t h e r e q u i r e m e n t s i n Egypt and t h e Sudan r e s p e c t i v e l y .
Of t h e rest, which i s a b o u t 1 0 . 8 mlrd m3/yr,
7.31
mlrd m3 are f o r E t h i o p i a ; 2 . 4 6 mlrd m 3 f o r Kenya, Uganda and T a n z a n i a ; 1 . 0 mlrd
m 3 f o r Rwanda and B u r u n d i . O b v i o u s l y , t h e l a r g e s t d i f f e r e n c e between t h e two estimates l i e s i n t h e 7 . 3 mlrd m 3 a s s i g n e d by Dekker t o E t h i o p i a and n o t t o Egypt and t h e Sudan a s i t s h o u l d b e .
SOME ENVIRONMENTAL IMPACTS OF THE NILE STORAGE, CONSERVATION AND CONTROL WORKS
9.4 9.4.1
Introduction
The c o n s t r u c t i o n of water s t o r a g e , c o n s e r v a t i o n and c o n t r o l works f o r stream f l o w and water l e v e l r e g u l a t i o n is m o s t l y u n a v o i d a b l e t o s a t i s f y t h e i n t e r e s t s o f l a n d i r r i g a t i o n and d r a i n a g e , hydro-power
development, i n l a n d n a v i g a t i o n and
o t h e r p u r p o s e s . Such w o r k s , which are o f t e n r e f e r r e d t o as man-made works, event u a l l y l e a d t o e n v i r o n m e n t a l c h a n g e s . These changes need t o b e c a r e f u l l y i n v e s t i g a t e d and c e r t a i n measures implemented b e f o r e any d e t r i m e n t a l e f f e c t arises.
456
I n t h i s s e c t i o n w e s h a l l m e n t i o n o n l y some o f t h e e n v i r o n m e n t a l c h a n g e s o b v i o u s l y c a u s e d b y man-made w o r k s , m o s t l y i n E g y p t . Of t h e s e w o r k s t h e HighAswan Dam is o n e t h a t p l a y e d , and p r o b a b l y s t i l l p l a y s , a major r o l e . 9.4.2
Environmental changes
9.4.2.1
Water q u a l i t y
The Main N i l e i n E g y p t r e c e i v e s i t s water, as w e a l r e a d y know,
from t w o p r i n -
c i p a l s o u r c e s : t h e E q u a t o r i a l L a k e s P l a t e a u a n d t h e A b b y s i n i a n P l a t e a u . The cont r i b u t i o n s o f t h e s e two s o u r c e s a re a b o u t t w o - s e v e n t h s
and f i v e - s e v e n t h s ,
res-
pectively. The water l e a v i n g L a k e V i c t o r i a h a s as much l o w c o n c e n t r a t i o n o f d i s s o l v e d compounds as t h e w a t e r o f t h e l a k e . The a l k a l i n i t y i s a s o d i u m b a l a n c e d a l k a l i n i t y , with r a t h e r l o w Ca
++
c o n c e n t r a t i o n s . The c o n t r i b u t i o n f r o m Lake
A l b e r t h a s a p r o n o u n c e d e f f e c t . The h i g h c o n c e n t r a t i o n o f t o t a l s a l t s , a l k a l i n i t y , pH, p h o s p h a t e , s u l p h a t e and c h l o r i d e i n t h e l a k e l e a d t o s t r o n g i n c r e a s e s i n t h e s e q u a n t i t i e s d o w n s t r e a m i n t h e A l b e r t N i l e . The i n f l u e n c e o f p a p y r u s swamp i n t h e Sudd r e g i o n i s r e m a r k a b l e ,
f o r h e r e s u l p h a t e d e c r e a s e s and i r o n
i n c r e a s e s s h a r p l y due t o t h e l o w oxygen c o n c e n t r a t i o n s . The a c c u m u l a t i o n o f d i s s o l v e d s a l t s i n t h e Lake N o swamp i s r e m a r k a b l y h i g h , b u t t h e w a t e r w h i c h f l o w s from i t is a p p a r e n t l y i n s u f f i c i e n t t o a l t e r t h e c o n d u c t i v i t y o f water i n t h e main stream. The R i v e r S o b a t h a s a d i l u t i n g e f f e c t . I t r e s e m b l e s t h e B l u e N i l e i n h a v i n g a g r e a t e r calcium t h a n s o d i u m c o n t e n t , h i g h n i t r a t e a n d l o w c h l o r i d e c o n t e n t s d u r i n g f l o o d , f o r t h e y b o t h s p r i n g from one p l a t e a u .
In t h e Blue N i l e
a l k a l i n i t y i s m a i n l y b a l a n c e d by c a l c i u m , w h i l e i n t h e W h i t e N i l e N a + p r e d o m i nates over Ca
++
b e c a u s e t h e White N i l e d e r i v e s i t s water from t h e E q u a t o r i a l
L a k e s P l a t e a u , w h e r e t h i s i s a common phenomenon. The a l g a l g r o w t h , w h i c h i n A f r i c a n waters i s more l i m i t e d by t h e a v a i l a b i l i t y o f n i t r o g e n t h a n by p h o s p h a t q d i c t a t e s t h e l e v e l s o f PO -P a n d NO - N ( G o l t e r m a n , H . , 1 9 7 5 ) . 4 3 The s a l t c o n c e n t r a t i o n i n t h e N i l e w a t e r , i n p a r t s p e r m i l l i o n ,
as o b t a i n e d
from o l d a n a l y s e s o f s a m p l e s c o l l e c t e d f r o m d i f f e r e n t l o c a t i o n s , is as f o l l o w s : Bahr
Bahr e l Zeraf
River Sobat
Lake Victoria
Lake Albert
1884 1902-06
120 134
540
270
360
-
-
-
-
164
220
70
Year
White Nile
Lake Tana
Blue Nile
River Atbara
Main N i l e (Cairo)
1884 1902-06
170 140-200
170
120 103- 106
170
-
-
Lake George
Lake Edward
Year
-
-
el Jebel
-
124-260
45 7
The l o w e s t and h i g h e s t c o n c e n t r a t i o n s of t h e Main N i l e a t C a i r o i n t h e p e r i o d 1919-1927 were 128 ppm ( a v e r a g e f o r September: f o r A p r i l : n e a r t h e e n d of t h e low-flow
f l o o d s e a s o n ) and 232 ( a v e r a g e
s e a s o n ) . The c o r r e s p o n d i n g f i g u r e s f o r
1963 were 167 ppm for O c t o b e r and 200 ppm f o r March. The M i n i s t r y of I r r i g a t i o n , E g y p t , h a s r e p o r t e d t h a t t h e c o n c e n t r a t i o n s of t h e N i l e w a t e r n e a r C a i r o i n 1972 and 1975, i . e . 8 and 11 y e a r s a f t e r t h e cons t r u c t i o n o f t h e High Dam, were 198 and 170 ppm, r e s p e c t i v e l y .
The main r e s u l t s
o b t a i n e d from t h e 1972 a n a l y s i s a r e a s g i v e n i n T a b l e 9 . 8 .
R e s u l t s of a n a l y s i s of N i l e water n e a r C a i r o i n 1972 ( A b u l - A t t a , A . ,
TABLE 9 . 8
1978)
--
Month
Total dissolved s o l i d s , ppm
Ca 0
tdg 0
SO4
c1-
January February March April May June July August September October November December
211 198 190 20 7 207 181 16 8 177 181 237 20 7 221
12 16 18 10 10 18 12 12 14 16 16 16
58.0 53.0 55.0 53.0 63.0 52.5 4 6 .O 42.0 47.0 61.0 62.0 61.0
18.0 22.5 22.0 26 .O 15 .O 11.2 14.5 18 .o 17.5 17.0 17.5 20.0
26 .O 21.5 20.0 18.0 20.0 18.0 16 . O 15.5 19.0
15 . O 27.5 28.0
In a d d i t i o n t o t h e q u a l i t y o f t h e N i l e w a t e r n e a r C a i r o , t h e d i s s o l v e d s o l i d s i n t h e w a t e r o f Lake N a s s e r was measured i n May ( b e f o r e t h e a r r i v a l of t h e f l o o d ) and found t o b e 1 7 5 , 1 5 1 and 146 ppm f o r t h e s u r f a c e l a y e r i n t h e y e a r s 1975, 1976 and 1977, r e s p e c t i v e l y . Moreover, t h e c o n c e n t r a t i o n d i d n o t show any c o n s i d e r a b l e v a r i a t i o n w i t h d e p t h up t o 6 0 m below t h e s u r f a c e . Between Aswan and C a i r o t h e c o n c e n t r a t i o n of t h e s a l t s i n w a t e r can be s e e n from t h e l o n g i t u d i n a l s e c t i o n , F i g . 9 . 1 7 . The N i l e water c h a r a c t e r i z a t i o n p r i o r t o and a f t e r t h e c o n s t r u c t i o n of t h e High Aswan Dam, e s p e c i a l l y a t t h e C a i r o a r e a , h a s been under o b s e r v a t i o n by t h e Water P o l l u t i o n Department o f t h e E g y p t i a n N a t i o n a l R e s e a r c h e s C e n t r e s i n c e 1963.
S t u d i e s have i n d i c a t e d t h a t a f t e r c o m p l e t e impoundment, 1970-1973,
a
d r o p i n b a c t e r i a l c o u n t s o c c u r r e d below t h e dam, a l t h o u g h a rise i n COlifOrm d e n s i t i e s were r e c o r d e d i n t h e impounded water. Moreover, t h e f a e c a l s t r e p t o c o c c u s g r o u p i n numbers g e n e r a l l y e x c e e d i n g
lo2
100 m l - l
were o b s e r v e d i n t h e
s a m p l e s c o l l e c t e d i n t h e C a i r o d i s t r i c t . The u s u a l f a e c a l s t r e p t o c o c c i Counts f a l l between
lo1
100 ml-l
to
lo2
100 ml-l
f o r w a t e r samples c o l l e c t e d b o t h
upstream and downstream o f C a i r o . The r i s e in t h e C a i r o area c o u l d p o s s i b l y be
4 VI
W
Distance tram G a a f r a Fig. 9.17.
in k i l o m e t e r s
S a l i n i t y c o n c e n t r a t i o n , ppm, of t h e N i l e w a t e r between Aswan and C a i r o
459
due t o human i n t e r f e r e n c e on a l a r g e scale and t o a p o s s i b l e r i s e i n t h e p o l l u t a n t load r e a c h i n g t h i s p a r t o f t h e r i v e r ( S a l e h , F . , 1980). One may f a i r l y c o n c l u d e t h a t some b i o l o g i c a l , as w e l l as chemical, changes i n t h e q u a l i t y of t h e N i l e water have been, and s h a l l b e , caused by t h e l o n g impoundment o f water i n t h e r e s e r v o i r . One o f t h e n o t i c e a b l e e f f e c t s of t h e s e changes i s t h e thermal s t r a t i f i c a t i o n of water i n Lake N a s s e r , e s p e c i a l l y d u r i n g t h e summer s e a s o n . The s t a g n a n t w a t e r l a y e r a t and n e a r t h e l a k e bottom h a s l e d t o t h e s i t u a t i o n where b i o l o g i c a l decomposition o f o r g a n i c m a t t e r completely removes d i s s o l v e d oxygen, which c a n n o t b e r e p l e n i s h e d . The absence of oxygen might w e l l t h r e a t e n t h e lake as a f u t u r e p o t e n t i a l f i s h e r y . 9.4.2.2
Sedimentation
The s e d i m e n t s t r a n s p o r t e d by t h e N i l e a r e made up o f bed and suspended l o a d s . The i n v e s t i g a t i o n s c a r r i e d o u t i n t h e pre-High Darn p e r i o d have shown t h a t t h e bed-load t r a n s p o r t was o n l y 1 t o 2% o f t h e t o t a l t r a n s p o r t o f t h e r i v e r . I t a c c o r d i n g l y became customary t o c o n s i d e r t h e t o t a l sediment l o a d e q u a l t o t h e suspended l o a d . The l a t t e r w a s r e g u l a r l y measured (1928, 29, 30, 31, 38,
...,
63,
... )
e s p e c i a l l y d u r i n g t h e f l o o d (August-November)
Gaafra (35 km downstream of Aswan), El-Hanady,
El-Samata,
. . . , 55,
a t Wadi H a l f a ,
S a l l a m and El-Ekhsas.
The main c o n c l u s i o n s drawn from t h o s e i n v e s t i g a t i o n s were as f o l l o w s : i)
98% o f t h e annual s e d i m e n t s a r e b r o u g h t by t h e N i l e d u r i n g t h e f l o o d s e a s o n
(August-November).
The o b s e r v e d sediment v a r i e s from 100 t o 5800 ppm c o r -
r e s p o n d i n g t o d i s c h a r g e s of 200 t o 1000 m i l l i o n m3/day ( s e e F i g . 9 . 1 8 . ) . The annual volume o f s e d i m e n t s r e a c h i n g Aswan amounts t o a b o u t 60 m i l l i o n
m 3 , weighing a b o u t 125 m i l l i o n metric t o n s . ii)
The p e r c e n t a g e s of c l a y , s i l t and s a n d f r a c t i o n s i n t h e suspended l o a d change w i t h t i m e d u r i n g t h e f l o o d s e a s o n . The a v e r a g e p e r c e n t a g e s are as follows: Month
Clay < .002 mm
August September October November
35 30 30 35
S i l t .002 45 45 45 35
-
.02 mm
Sand .02
-
. 2 mm
20 25 25 30
iii) The g r a p h i c p l o t o f t h e d i s c h a r g e Q r e a c h i n g Aswan a g a i n s t t h e c o n c e n t r a -
t i o n C looks l i k e a h y s t e r i s i s l o o p , i n d i c a t i n g t h a t t h e sediment concent r a t i o n f o r a given discharge is b i g g e r during t h e r i s i n g flood than during the f a l l i n g flood. The r e l a t i o n s h i p between t h e sediment c o n c e n t r a t i o n i n ppm and t h e d i s c h a r g e i n m i l l i o n m3/day was found t o b e of t h e t y p e (Qublennec, R . , and Kruk, C . B . ,
1974):
460
(9.10) where a = 1.525 x 10-1 and b = 2.59 f o r t h e r i s i n g f l o o d and
12 00
,
and b = 2.79 f o r t h e f a l l i n g f l o o d
a = 1.823 x
1
1
1
1
1
1
( a ) Wadi
1
.
1
I
.
- Halfa
.
I
.
.
I
’
.
,
( b ) Gaafra
I, I t 1 , I 1 I I\ I
-
>r
$1000
6000
5000
0
m
E
Q
.--s 800 .-
4000
u- 600
3000
E
a 8
Q VI
P
6 0 C .-c
0
5
2000
.a K! 400
3
I
0
1000
2 00
0
y
0
V
1
1
1
1
1
1
1
1
1
1
1 10 20 31 10 20 3 0 10 20 31 10 Aug. Sep. Oct. Nov 1931
I
,
I
I
I
I
I
,
I
I
1 10 20 31 10 20 30 10 20 31 Aug. Sep. Oct. Nov.
0
1955
F i g . 9.18. D i s c h a r g e and c o n c e n t r a t i o n of s u s p e n d e d m a t t e r i n t h e N i l e w a t e r d u r i n g t h e f l o o d s e a s o n s o f 1931 and 1955
The High Aswan Dam h a s been i n o p e r a t i o n s i n c e 1964. When t h e f l o o d r e a c h e s Lake N a s s e r t h e v e l o c i t y of water d r o p s from more t h a n 1 . 0 m / s e c . m/sec.
t o a b o u t 0.02
T h i s c o n s i d e r a b l e f a l l i n v e l o c i t y l e a d s t o t h e d e p o s i t i o n o f a b o u t 98%
of t h e suspended m a t t e r i n t h e l a k e formed by t h e High D a m . The s e d i m e n t l o a d which p a s s e d t h r o u g h t h e dam t o t h e downstream was e s t i m a t e d a t 26.3, 5.7, 3.8,
3.2, 2.3, 1.9, 2.8, 2.4, 27. and 2.7 m i l l i o n metric t o n s f o r t h e years 1964, 65, 66, 67, 68, 69, 1970, 71, 72 and 73, r e s p e c t i v e l y . I n o t h e r w o r d s , t h e a v e r a g e weight of s e d i m e n t s p a s s i n g downstream of Aswan i n t h e post-dam
condition is
a b o u t 2.5 m i l l i o n m e t r i c t o n s compared w i t h 125 m i l l i o n metric t o n s i n t h e p r e dam c o n d i t i o n ( S h a l a s h , S., 1974). G e n e r a l l y , t h e tendency i s g r e a t e r f o r d e p o s i t i o n o f s i l t i n t h e upper r e a c h e s o f t h e r e s e r v o i r r a t h e r t h a n i n t h e v i c i n i t y of t h e dam. O b s e r v a t i o n on c o n c e n t r a t i o n o f s o l i d m a t e r i a l s on s e c t i o n s of t h e r e s e r v o i r showed t h a t i t d e c r e a s e s from y e a r t o y e a r a t t h e s e c t i o n s n e a r t h e dam. During t h e f l o o d o f
46 1
1971 t h e c o n c e n t r a t i o n of s i l t became n e g l i g i b l e a t t h e s e c t i o n s i t u a t e d 250 km u p s t r e a m of t h e dam. I n t h e f i r s t y e a r s of t h e i n i t i a l f i l l i n g of t h e dam (1965-
1967) s i l t w a s d e p o s i t e d j u s t u p s t r e a m o f i t (Abu Z e i d , M . ,
1979).
The N i l e i s a s i l t - b e a r i n g r i v e r and t h e d e l t a and v a l l e y i n Egypt a r e made up o f i t s s e d i m e n t s ( C h a p t e r 7). The r a t e o f s e d i m e n t a t i o n i n t h e p r e - s t o r a g e p e r i o d w a s e s t i m a t e d a t 6 t o 15 c m / c e n t u r y , w i t h an a v e r a g e of 0.8 mm/yr,
used
t o c o v e r t h e s u r f a c e o f a g r i c u l t u r a l s o i l i n Egypt. S i n c e 1964 t h i s amount ceased t o reach t h e s o i l , w i t h t h e f o l l o w i n g consequences: i)
l o s s of a u n i q u e s o u r c e of n a t u r a l n o u r i s h m e n t t o t h e s o i l , and
ii)
l o s s o f s u p p l y of f r e s h s o i l , t h e r e b y e l i m i n a t i n g any chance of n a t u r a l improvement o f d e p t h t o water t a b l e . The losses d e s c r i b e d by i ) and i i ) may b e overcome by a r t i f i c i a l f e r t i l i z e r s
and s o i l amendments. Both seem t o b e energy-consuming
9.4.2.3
and e x p e n s i v e .
D e g q d a t i o n of r i v e r c h a n n e l
The d e g r a d a t i o n of t h e r i v e r c h a n n e l from Aswan t o t h e M e d i t e r r a n e a n c o a s t
was o b s e r v e d l o n g b e f o r e t h e c o n s t r u c t i o n of t h e High Aswan Dam. The d e p t h o f t h e s c o u r h o l e downstream o f t h e Nag-Hammadi b a r r a g e r e a c h e d a l m o s t 70 c m s h o r t l y a f t e r i t w a s p u t i n t o o p e r a t i o n . The c h a n n e l s c o u r i s r e g a r d e d as a phenomenon a s s o c i a t e d w i t h s u c h c o n s t r u c t i o n o f s t o r a g e and cont r o l works as t h e o l d Aswan D a m ,
t h e Esna and t h e Nag-Hammadi b a r r a g e s , e t c . ,
s i n c e t h e y are c h i e f l y r e s p o n s i b l e for d i s t u r b i n g t h e f l o w and s i l t regime i n t h e r i v e r . F u r t h e r d e g r a d a t i o n o f t h e N i l e a s a r e s u l t o f t h e High Dam was a n t i c i p a t e d p r i o r t o i t s c o n s t r u c t i o n . Many s c i e n t i f i c and t e c h n i c a l a u t h o r i t i e s have b e e n , and p r o b a b l y s t i l l a r e , i n v o l v e d i n e s t i m a t i n g t h e r a t e and u l t i m a t e d e p t h o f d e g r a d a t i o n a t d i f f e r e n t p o i n t s on t h e N i l e between Aswan and t h e sea. The bed d e g r a d a t i o n from 1964 up t o 1971 r e a c h e d 0.22, 0 . 4 1 , 0.24 and 0.27 m downstream Aswan Dam, Esna b a r r a g e , Nag-Hammadi b a r r a g e and A s s i u t b a r r a g e , resp e c t i v e l y ( S h a l a s h , S., 1974). F o r t h e same s i t e s t h e maximum d r o p i n t h e w a t e r l e v e l of t h e N i l e w a s 0 . 4 0 , 0.80, 0.58 and 0.50, r e s p e c t i v e l y (Kenawy,
I . , et
a l , 1973). A more c o m p l e t e p r e s e n t a t i o n o f t h e d r o p i n w a t e r l e v e l i n t h e p e r i o d from 1963 up
t o and i n c l u d i n g 1977 a t t h e s a i d f o u r s t a t i o n s plus t h e s t a t i o n
o f El-Ekhsas i s shown i n F i g . 9.19 ( H a r t u n g , F . ,
1978). T h i s f i g u r e shows
c l e a r l y t h a t d e g r a d a t i o n downstream of t h e dam and f a r t h e r t o t h e downstream of Esna b a r r a g e h a s been r e c o v e r i n g s i n c e 1973 a t a r a t e o f 3 t o 4 cm/yr. C o n t r a r y
t o t h i s o b s e r v a t i o n , t h e c h a n n e l below t h e Nag-Hammadi b a r r a g e h a s been e r o d i n g a t a b o u t t h e same r a t e , and a s h o r t d i s t a n c e below t h e A s s i u t b a r r a g e a t a b o u t 1 . 5 cm/yr.
The g r a p h of El-Ekhsas shows a r i s e i n t h e w a t e r l e v e i o f 43 cm i n 14 y e a r s o r 3 cm/yr p o i n t i n g to bed a g r a d a t i o n i n t h i s r e a c h of t h e r i v e r . T h i s means
46 2
82.18
7 \
Gaatra 35 km. D.S. Aswan dam
0.67 m.
-aJ
&
73.09
E l - Hamadi 12 km. D.S. Esna barrage
aJ C
0.79 m.
0
E m
>
0
n
73.30
0 ul
Somata 24 km. D.S. Nag-Hammadi barrage
c
c
4
r
1
-
6
0
.
2
4 Sallam 10 km. D.S.Assiut barrage
0.60 m. .oa
.60
0.W m. 1963 ‘65
‘67
‘69 ‘71 Year
’73
‘75
E l - Ekhsas 68 km. U.S. Delta barrage
’77
F i g . 9.1Y. Change o f N i l e water l e v e l s i n c e 1963 a t f i v e d i f f e r e n t s i t e s c o r r e s p o n d i n g t o d i s c h a r g e of 100 m i l l i o n m3/day) t h a t bed d e g r a d a t i o n h a s n o t t a k e n p l a c e f o r some d i s t a n c e u p s t r e a m of t h e D e l t a b a r r a g e s and f o r t h e whole r e a c h from t h e s e b a r r a g e s down t o t h e sea. A number of theorems and a p p r o a c h e s have been d e v e l o p e d and worked o u t f o r p r e d i c t i n g t h e u l t i m a t e bed d e g r a d a t i o n and t h e t i m e t h e r i v e r n e e d s b e f o r e i t s e q u i l i b r i u m i s r e a c h e d . The wide d i s c r e p a n c y between t h e r e s u l t s so f a r o b t a i n e d h a s b e e n a r g u e d on t h e f o l l o w i n g g r o u n d s : i)
t h e a s s u m p t i o n s u s e d i n d e v e l o p i n g t h e theorems d e s c r i b e n e i t h e r t h e a c t u a l c h a r a c t e r i s t i c s of t h e r i v e r channel n o r t h e flow c o n d i t i o n s a d e q u a t e l y ;
ii)
t h e measures a d o p t e d by t h e M i n i s t r y o f I r r i g a t i o n , Egypt, seem t o b e e f f e c t i v e , a t l e a s t l o c a l l y , i n d e c c e l e r a t i n g t h e d e g r a d a t i o n , and
i i i ) t h e number o f y e a r s o f o b s e r v a t i o n i s so f a r t o o s h o r t t o b e a b l e t o draw
463
any d e f i n i t e c o n c l u s i o n a b o u t t h e e x t e n t of agreement between t h e o r y and observation.
I t d o e s n o t seem p o s s i b l e , however, t o p r e d i c t f u t u r e d e g r a d a t i o n w i t h a h i g h d e g r e e o f a c c u r a c y . N e v e r t h e l e s s , t h e d a t a c o l l e c t e d p o i n t c l e a r l y t o t h e need f o r s t r e n g t h e n i n g or r e c o n s t r u c t i n g t h e b a r r a g e s on t h e N i l e from Aswan t o t h e
sea and f o r p r o v i d i n g a b e t t e r p r o t e c t i o n t o t h e bed and s l o p e s o f t h e r i v e r i n t h i s reach.
9.4.2.4
Beach e r o s i o n
Since ancient t i m e s ,
t h e s e a c o a s t d e f e n d e d i t s e l f a g a i n s t wave a t t a c k ,
s t o r m s , and sea and c o a s t a l c u r r e n t s . A quasidynamic e q u i l i b r i u m was a c h i e v e d and t h e b a l a n c e between t h e sea f o r c e s , t h e s e d i m e n t s c a r r i e d away from t h e s h o r e s and t h e s e d i m e n t s s u p p l i e d by t h e N i l e seemed t o swing i n f a v o u r o f a c c r e t i o n o n t h e c o a s t . A l l h y d r a u l i c s t r u c t u r e s on t h e N i l e between Aswan and t h e s e a and which l e d t o i n s t a b i l i t y i n t h e amount, rate and t e m p o r a l d i s t r i b u t i o n of t h e silt t r a n s p o r t to t h e sea, r e s u l t e d i n d i s t u r b a n c e t o t h e s a i d equil i b r i u m . Beach e r o s i o n n e a r t h e r i v e r mouths a t D a m i e t t a and R o s e t t a w a s o b s e r v e d as e a r l y a s 1902. S i n c e t h e n , t h e s h o r e l i n e h a s been f r e q u e n t l y mapped b o t h b e f o r e and a f t e r t h e c o n s t r u c t i o n o f t h e High Aswan D a m . According t o Wassing, F . ( 1 9 6 4 ) , t h e r a t e of r e t r e a t o f t h e p r o m o n t o r i e s a t Damietta and R o s e t t a had an a v e r a g e o f 29 m / y r
i n t h e p e r i o d from 1898 t o 1960. The g r a d u a l
development of t h e c o n t o u r l i n e of t h e s h o r e a t t h e mouths o f t h e r i v e r b r a n c h e s
i s as shown i n F i g . 9 . 2 0 .
MEDITERRANEAN: SEA N
N
rr
'v
F i g . 9.20. Retreat of t h e s h o r e l i n e n e a r t h e mouth of e a c h o f t h e D a m i e t t a and R o s e t t a b r a n c h e s from 1898 t o 1960
464
B e f o r e t h e c o n s t r u c t i o n o f t h e High Dam, an a n n u a l mean of a b o u t 35 mlrd m 3 of N i l e w a t e r w a s d i s c h a r g e d t o t h e M e d i t e r r a n e a n t h r o u g h o u t t h e f l o o d p e r i o d from August t o November. T h i s volume o f w a t e r u s e d t o c a r r y n o t less t h a n 90 m i l l i o n metric t o n s of s e d i m e n t s a l o n g t o t h e s e a . I n t h e pre-dam c o n d i t i o n , t h e s u r f a c e c u r r e n t v e l o c i t y a t t h e mouths o f t h e b r a n c h e s w a s 4 k n o t s and less t h a n
0.5 knot a t t h e bottom, both d u r i n g t h e f l o o d season. A f t e r t h e c o n s t r u c t i o n o f t h e dam t h e s e v e l o c i t i e s dropped c o n s i d e r a b l y . The f a c t t h a t t h e N i l e h a s no l o n g e r d i s c h a r g e d i t s s e d i m e n t s t o t h e s e a s i n c e 1964 i s p r o d u c i n g a n i m b a l a n c e i n t h e near-coast
s e d i m e n t b u d g e t , t h e r e b y making t h e coast v u l n e r a b l e t o con-
siderable erosion. The E g y p t i a n a u t h o r i t i e s h a v e , f o r q u i t e some t i m e , been i n v e s t i g a t i n g t h e beach e r o s i o n phenomenon, b o t h t h e o r e t i c a l l y a n d i n t h e f i e l d , w i t h t h e h e l p o f some o f t h e i n t e r n a t i o n a l o r g a n i z a t i o n s . Some measures a i m i n g a t b o t h e r o s i o n p r e v e n t i o n and a c c r e t i o n on t h e coast a r e under way. The High Dam i s n o t o n l y r e s p o n s i b l e f o r t h e a c c e l e r a t e d i n s t a b i l i t y o f t h e s h o r e l i n e , b u t a l s o f o r t h e change i n t h e e s t u a r i a n e c i r c u l a t i o n p a t t e r n from two-layered
t o o n e - l a y e r e d f l o w . Such a change i n t h e c i r c u l a t i o n p a t t e r n h a s
l e d t o i n c r e a s e d s u r f a c e s a l i n i t y i n t h e post-dam p e r i o d . T h i s c a n e a s i l y b e s e e n from F i g s . 9 . 2 1 a .
and 9 . 2 1 b . The s a l i n i t y o f t h e deep w a t e r o b s e r v e d d u r i n g
September and O c t o b e r i n t h e post-dam
years is similar t o t h a t during the flood
s e a s o n i n t h e pre-dam y e a r s ( S h a r a f e l - D i n ,
S.,
1976).
1 36'
33'
32'
31'
29'
30'
31'
32'
33'
3 4'
35'
36'
Fig. 9.21a. Map showing t h e s u r f a c e s a l i n i t y d i s t r i b u t i o n d u r i n g t h e f l o o d s e a s o n (August-October) b e f o r e t h e c o n s t r u c t i o n o f t h e High Dam
46 5
33'
29' E
30'
32 '
31'
33O
34O
35 O
36'
330
N
32'
32'
31'
31'
29'
30°
32 '
31'
33'
34O
35O
36'
F i g . 9.21b. Map showing t h e s u r f a c e s a l i n i t y d i s t r i b u t i o n d u r i n g t h e p e r i o d (August-September) a f t e r t h e c o n s t r u c t i o n o f t h e High Dam 9.4.2.5
Groundwater l e v e l
As a r u l e , when l a n d i s p u t u n d e r i r r i g a t i o n , t h e w a t e r t a b l e rises, and i f
no p r o p e r d r a i n a g e i s a p p l i e d t h e r i s e c o n t i n u e s t i l l t h e s o i l mass becomes w a t e r - l o g g e d and p r a c t i c a l l y p r o d u c e s no y i e l d . The s i t u a t i o n i n Egypt i s no d i f f e r e n t t h a n e l s e w h e r e . B a l l s , W.L.
( 1 9 5 3 ) , l i s t e d t h e minimum l e v e l s o f t h e
water t a b l e i n t h e neighbourhood o f C a i r o i n t h e p e r i o d from 1894-1951. The l e v e l s i n w e l l s a n d / o r p i t s s i t u a t e d a t 1 km, 2 km and between 1 and 2 km from t h e N i l e o n t h e G i z a f a r m are g i v e n i n T a b l e 9 . 9 . B a l l s commented o n t h e s e measurements s a y i n g ,
"...
i t i s e v i d e n t t h a t t h e minimum l e v e l o f t h e w a t e r
t a b l e i s c o n d i t i o n e d by s e e p a g e w a t e r from c a n a l s , and by d r a i n a g e w a t e r from s u r f a c e i r r i g a t i o n , s u p e r p o s e d on a f o u n d a t i o n o f mass i n f l i t r a t i o n from t h e b a r r a g e ( D e l t a ) pond". TABLE 9 . 9
Minimum l e v e l s o f t h e w a t e r t a b l e i n t h e neighbourhood o f C a i r o (Balls, L.,
Year
1953)
Water l e v e l 1 km
2 km
14.29 14.84 14.73 14.75 14.50 14.85 14.24 14.70 14.74 14.90 15.41 15.39 15.43
14.67 14.95 14.81 14.81 14.55 15.03 14.40 14.74 14.89 15.03 15.55 15.48 15.47
Year
Water l e v e l 1 km
2 km
15.39 15.43
15.48 15.47
Year
Water l e v e l
~
1894 1895 1896 1897 1898 1899 1900 190 1 1902 190 3 1904 1905 1906
190 7 1908 1909 19 10 1911 19 12 1913 19 14- 22 1923 1924 1925 1926 1927
-
16.00 16.44 No d a t a 116.70 16 .30 16.25 16.20 16.20
-
1928 1929 1930 1931 1932 1933 1934 1935 1936 1937 1938 1939 1950 1951 -
~
16.40 16,45 16.30 16.30 16.30 16.80 16.35 16.35 16.65 16.80 16.5C 16.90 16.80 16.75
466 I n t h e pre-High Dam p e r i o d t h e hydrograph o f t h e N i l e a t Aswan c o n s i s t e d of f o l l o w e d by a f l o o d s e a s o n (August-
a l o n g low-flow s e a s o n (December-July) November).
A s a r e s u l t of t h e h y d r a u l i c c o n n e c t i o n between t h e N i l e and t h e
g r o u n d w a t e r , t h e r i v e r f l o o d was t r a n s m i t t e d t o t h e groundwater r e s e r v o i r i n t h e form of a r e d u c e d wave. The r e v e r s e happened d u r i n g t h e low-flow s e a s o n , i . e . t h e wave w a s t r a n s m i t t e d from t h e groundwater r e s e r v o i r t o t h e r i v e r and t h e b a s e f l o w used t o s u s t a i n t h e low-flow i n t h e r i v e r . I n t h e l o c a t i o n s where t h e semi-confining
l a y e r has a l i m i t e d r e s i s t a n c e t o v e r t i c a l flow, i t w a s possi bl e
t o o b s e r v e t h e e f f e c t s o f c a n a l r o t a t i o n s and i r r i g a t i o n a p p l i c a t i o n s on t h e groundwater l e v e l (ShaQin, M . ,
1955).
S i n c e t h e c o n s t r u c t i o n o f t h e High D a m , t h e d i s c h a r g e s p a s s i n g downstream of Aswan are r e g u l a t e d i n s u c h a way a s t o s a t i s f y t h e demand. A s a r e s u l t , t h e d i s c h a r g e i n what u s e d t o b e a low-flow s e a s o n h a s been improved and t h e f l o o d s e a s o n does n o t e x i s t any l o n g e r . These c o n d i t i o n s h a v e c a u s e d t h e water i n t h e semi-confcining l a y e r t o r e a c h a l e v e l a l m o s t h i g h e r t h a n t h a t o f t h e p i e z o m e t r i c head o f t h e g r o u n d w a t e r . The l a t t e r , i n t u r n , i s h i g h e r t h a n t h e c o r r e s p o n d i n g w a t e r l e v e l i n t h e N i l e . T h i s c a n be a t t r i b u t e d t o t h e a p p l i c a t i o n of i r r i g a t i o n w a t e r i n amounts f a r i n e x c e s s o f t h e a c t u a l need of t h e s o i l and t h e s e e p a g e from t h e c a n a l s r u n n i n g a t h i g h l e v e l s f o r a l o n g t i m e . The h y d r o g r a p h s of t h e groundwater l e v e l s a t some l o c a t i o n s i n Upper and Middle Egypt b e f o r e and a f t e r t h e c o n s t r u c t i o n o f t h e High Dam a r e shown i n F i g . 9 . 2 2 . ( A t t i a , F . , e t a l , 1983). From t h i s f i g u r e i t is c l e a r t h a t a l l t h e h y d r o g r a p h s show much more u n i f o r m i t y w i t h t i m e a f t e r t h e c o n s t r u c t i o n of t h e dam t h a n b e f o r e i t , S e c o n d l y , most of t h e h y d r o g r a p h s show a r i s e i n t h e w a t e r l e v e l i n what u s e d t o b e t h e low-flow s e a s o n d u r i n g t h e pre-dam c o n d i t i o n . T h i s
i s m o s t l y c o u p l e d w i t h a f a l l i n t h e l e v e l i n what u s e d t o b e t h e f l o o d s e a s o n b e f o r e t h e dam c o n s t r u c t i o n . T h i r d l y , t h e p i e z o m e t r i c h e a d s a t many p l a c e s seem t o have approached a s t a b l e l e v e l d u r i n g t h e l a s t few y e a r s .
.................. I
I
E 21
-->
19
-------.a-
- - -=-
0
35
C
e
I
I
,---_-___ -L-
3 33'3 ...................
-0
29
......
z-=. -
4--- - -.-.- . ~ . ~ .......... ~ ~ ~ . ~ ~ ~ ~ ~ - ~ .~.--:-.-~--..~-.,,-;-:~.'.~.,. .,_, I
1
2
....... ...............
....
I
I
....
__--
................
I
I
I
I
........... ....
........
__-_-__---.
-.---.-- -. -. _. .............:.- ..........~s,y-:.-.i---~=d'
I
46 7
-L
-
_------_ _-
8 5
-
-- ----_
L
aJ
0
5 6 :.......
3
^. -.-a................................................ .-.-,-. I ~
-;,,
.--,,,F 'h
__-----__ ,...... .......... -- -.
__*r
,
.-...... ...........
........
......... ,__-_.L . - - - . - - -
-.-._
:.-:-.:-..
Mon t h
I
LEGEND
.................. 1964 1970
----_- 1976 1978
Fig. 9.22.
9.5
(continued)
REFERENCES
A b u l - A t t a , A . , 1975. The w a t e r p o l i c y o f E g y p t . M i n i s t r y o f I r r i g a t i o n , C a i r o , E g y p t , 1 5 pp ( w i t h d r a w i n g s ) . Abul-Atta, A , , 1978. Egypt and t h e N i l e i n t h e post-dam e p o c . M i n i s t r y of I r r i g a t i o n and Land R e c l a m a t i o n , C a i r o , Egypt, 145 pp ( i n A r a b i c , w i t h drawings). Abu Z e i d , M . , 1 9 7 9 , S h o r t and l o n g - t e r m i m p a c t s o f t h e R i v e r N i l e p r o j e c t s . Water Supply and Management, V o l . 3: 275-283, U K . Ahmed, A . e l - A z i z , 1960. Recent developments i n t h e N i l e c o n t r o l . P r o c e e d i n g s of t h e I n s t i t u t e of C i v i l E n g i n e e r s , V o l . 1 7 , P a p e r no. 6102: 137-180, London, U K . Ahmed, A . e l - A z i z , 1961. D i s c u s s i o n of ' R e c e n t developments i n t h e N i l e cont r o l ' , P a p e r n o . 6102, and of 'An a n a l y t i c a l s t u d y o f t h e s t o r a g e l o s s e s i n t h e N i l e B a s i n w i t h s p e c i a l r e f e r e n c e t o Aswan D a m R e s e r v o i r and t h e High Dam R e s e r v o i r ' P a p e r n o . 6370. P r o c e e d i n g s of t h e I n s t i t u t e of C i v i l Engin e e r s . V o l . 19 ( s p e c i a l e x c e r p t ) : 337-415, London, UK.
46 8
A t t i a , F . , A m e r , A . , a n d H e f n y , K . , 1 9 8 3 . E f f e c t of High Aswan D a m o n g r o u n d w a t e r c o n d i t i o n s i n Upper E g y p t . P r o c e e d i n g s o f t h e I n t e r n a t i o n a l C o n f e r e n c e o n Water R e s o u r c e s Development i n E g y p t , C a i r o , E g y p t : 99-119. B a l l s , L.W., 1 9 5 3 . The y i e l d s o f a c r o p , E . & F.N. Spon L i m i t e d . London, U K , 144 p p . B e r n i e r , J . , 1 9 6 6 . Sur l a g a r a n t i e a s s u r e e p a r un r e s e r v o i r d e r e g u l a t i o n s a i s o n n i h r e . I n t . Assoc. S c i . H y d r o . , Symposium o f G a r d a . Pub. n o . 7 1 , V o l . 2 : 575-589. B e r t l i n , D . P . , and O l i v i e r , H . , 1 9 5 4 . Owen F a l l s , c o n s t r u c t i o n a l p r o b l e m s . P r o c e e d i n g s o f t h e I n s t i t u t e o f C i v i l E n g i n e e r s , 3, P a r t I , P a p e r n o . 6 0 0 8 : 6 7 0 - 6 9 9 , London, UK . B o e s , D . , and S a l a s , J . , 1 9 7 8 . N o n s t a t i o n a r i t y o f t h e mean a n d t h e H u r s t phonomenon. Water R e s o u r c e s R e s e a r c h , V o l . 1 4 : 135-143. C a i r o University/Massachussets I n s t i t u t e o f T e c h n o l o g y , 1 9 7 7 . S t o c h a s t i c modell i n g of N i l e i n f l o w s t o L a k e Nasser. P u b l i s h e d by C a i r o U n i v e r s i t y , G i z a , Egypt. 1966. The c o n s t r u c t i o n o f Roseires D a m . The S u d a n E n g i n e e r i n g Corney, J . V . , S o c i e t y J o u r n a l , n o . 11: 7-13, Khartoum, t h e S u d a n . D e k k e r , G . , 1 9 7 2 . A n o t e on t h e N i l e . W a t e r R e s o u r c e s R e s e a r c h , V o l . 8 n o . 4 : 818-828. E x e c u t i v e Organ f o r Development P r o j e c t s i n J o n g l e i Area, 1 9 7 5 . J o n g l e i p r o j e c t , p h a s e o n e . Tamaddon P r e s s , Khartoum, t h e S u d a n . F a t h y , A . , a n d S h u k r y , A . S . , 1 9 5 6 . The p r o b l e m o f r e s e r v o i r c a p a c i t y f o r l o n g term s t o r a g e . P r o c e e d i n g s o f t h e American S o c i e t y of C i v i l E n g i n e e r s , P a p e r n o . 8 2 , Hy 5 : 1-27. F e l l e r , W . , 1 9 5 1 . The a s y m p t o t i c d i s t r i b u t i o n o f t h e r a n g e of sums o f i n d e p e n d e n t random v a r i a b l e s . A n n a l e s o f M a t h e m a t i c a l S t a t i s t i c s , 2 2 : 427-432. F i t t , R., Manvick, R., and W h i t a k e r , F . , 1 9 6 7 . The Roseires Dam, S u d a n : p l a n n i n g and d e s i g n . P r o c e e d i n g s of t h e I n s t i t u t e f o r C i v i l E n g i n e e r s , V o l . 38, P a p e r n o . 7 0 4 7 : 2 1 - 5 1 , London, U K . G o l t e r m a n , H . L . , 1 9 7 5 . R i v e r e c o l o g y ( e d i t e d by B . A . W i t t o n ) . C h a p t e r 2 : Chemist r y , 39-80. The U n i v e r s i t y o f C a l i f o r n i a P r e s s , 7 2 5 p p . H a r t u n g , F . , 1 9 7 8 . 75 J a h r e N i l s t a u b e i A s s u a n , E n t w i c k l u n g und F e h l e n t w i c k l u n g . B e r i c h t no. 4 0 , V e r s u c h a n s t a l t f u r Wasserbau < d e r T e c h i n s c h e n U n i v e r s i t a t Munchen-Oskar v . Miller I n s t i t u t , Munich, W . 'Germany. H i p e l , K . , and McLoed, A . I . , 1 9 7 8 . P r e s e r v a t i o n o f t h e r e - s c a l e d a d j u s t e d r a n g e , P a r t o n e - a r e a s s e s s m e n t o f t h e H u r s t phenomenon, W a t e r R e s o u r c e s R e s e a r c h , V o l . 1 4 : 491-508. H u r s t , H . E . , B l a c k , R . P . , and S i m a i k a , Y . M . , 1 9 4 6 . The N i l e B a s i n , V o l . V I I , t h e f u t u r e c o n s e r v a t i o n o f t h e N i l e . P h y s i c a l Department P a p e r n o . 5 1 , E a s t e r n P r e s s , C a i r o , E g y p t . 159 pp ( w i t h d r a w i n g s ) . H u r s t , H . E . , 1 9 5 0 . The N i l e B a s i n , V o l . V I I I , t h e h y d r o l o g y o f t h e S o b a t a n d t h e W h i t e N i l e and t h e t o p o g r a p h y o f t h e B l u e Nile and A t b a r a . P h y s i c a l D e p a r t ment P a p e r n o . 5 5 , Government P r e s s , C a i r o , E g y p t , 1 2 5 p p . H u r s t , H . E . , 1 9 5 1 . Long-term s t o r a g e c a p a c i t y o f r e s e r v o i r s ( w i t h d i s c u s s i o n ) . T r a n s a c t i o n s o f t h e American S o c i e t y o f C i v i l E n g i n e e r s , V o l . 1 1 6 , P a p e r n o . 2 4 4 7 : 770-808. H u r s t , H . E . , 1 9 5 6 . Methods o f u s i n g l o n g - t e r m s t o r a g e i n r e s e r v o i r s ( w i t h d i s c u s s i o n ) . P r o c e e d i n g s o f t h e I n s t i t u t i o n of C i v i l E n g i n e e r s , P a r t I , P a p e r n o . 6 0 5 9 : 519-590. London, U K . H u r s t , H . E . , B l a c k , R . P . , and S i m a i k a , Y . M . , 1 9 5 9 . The N i l e B a s i n , V o l . IX, t h e h y d r o l o g y o f t h e B l u e N i l e a n d A t b a r a and t h e Main N i l e t o Aswan, w i t h some r e f e r e n c e t o p r o j e c t s , N i l e C o n t r o l D e p a r t m e n t P a p e r n o . 1 2 , Government P r i n t i n g O f f i c e s , C a i r o , E g y p t , 206 p p . H u r s t , H . E . , B l a c k , R . P . , and S i m a i k a , Y . M . , 1 9 6 6 . T h e N i l e B a s i n , V o l . X , t h e major N i l e p r o j e c t s , N i l e C o n t r o l D e p a r t m e n t P a p e r n o . 2 3 , Government P r i n t i n g O f f i c e s , Cairo, Egypt, 247 pp. I b r a h i m , A . M . , 1 9 7 7 . J o n g l e i d e v e l o p m e n t p r o j e c t . ICID B u l l e t i n , V o l . 2 6 , n o . 2 : 70-72 a n d 81, N e w D e l h i , I n d i a .
469
Kinawi, I . Z . , and El-Ghamry, O . , 1971. Some e f f e c t s o f t h e High D a m on t h e Environment. 1 1 t h C o n g r e s s on Dams and Grand B a r r a g e s , Madrid, S p a i n , 440, R59 : 959-973. a p u z z l e ? Water R e s o u r c e s R e s e a r c h , Klemgs, V . , 1974. The H u r s t phenomenon Vol. 10: 675-688. Kottegoda, N . T . , 1980. S t o c h a s t i c w a t e r r e s o u r c e s t e c h n o l o g y . The MacMillan P r e s s L i m i t e d , London, U K , 384 p p . Kruk, C . B . , and Quklennec, R . , 1975. Suspended s e d i m e n t t r a n s p o r t o f t h e N i l e . P a p e r s u b m i t t e d t o a s e m i n a r on N i l e s e d i m e n t o l o g y , A l e x a n d r i a , E g y p t , 7 pp (with drawings). McMahon, T . A . , and Mein, R . G . , 1978. R e s e r v o i r c a p a c i t y and y i e l d . E l s e v i e r S c i e n t i f i c P u b l i s h i n g Company, Amsterdam, 213 p p . S a l e h , F.A., 1980. I s o l a t i o n and e n u m e r a t i o n o f F a e c a l S t r e p t o c o c c i from N i l e w a t e r (1975-1976). Water R e s e a r c h , Vol. 1 4 : 1669-1678. S a l i h , A . M . , 1981. R e c l a m a t i o n o f water from e l - J e b e l Swamps. Water I n t e r n a t i o n a l , Vol. 6 n o . 2: 71-74. S h a h i n , M . , 1955. E f f e c t o f N i l e and c a n a l w a t e r l e v e l s on s u b s o i l w a t e r movement i n i r r i g a t e d f a r m s . T h e s i s s u b m i t t e d t o t h e F a c u l t y of E n g i n e e r i n g , C a i r o U n i v e r s i t y f o r M.Sc d e g r e e , Egypt. S h a h i n , M., 1971. Hydrology of t h e N i l e B a s i n , L e c t u r e n o t e s , 2nd e d i t i o n , I n t e r n a t i o n a l C o u r s e s i n H y d r a u l i c and S a n i t a r y E n g i n e e r i n g , D e l f t , The N e t h e r l a n d s , 140 pp. S h a l a s h , S . , 1974. F a c t s a b o u t d e g r a d a t i o n . P r o g r e s s r e p o r t o f t h e H y d r a u l i c R e s e a r c h S t a t i o n of t h e M i n i s t r y of I r r i g a t i o n , E g y p t , 32 pp ( w i t h drawings). S h a r a f e l - D i n , S . , 1976. E f f e c t o f t h e N i l e f l o o d on t h e e s t u a r i n e and c o a s t a l c i r c u l a t i o n p a t t e r n along t h e Mediterranean Egyptian c o a s t . Hydrological S c i e n c e s B u l l e t i n XXI, 3 : 451-461. S i m a i k a , Y . M . , and E l - S h e r b i n i , H . , 1957. Some a s p e c t s o f e r o s i o n i n E g y p t . P r o c e e d i n g s of t h e I n t e r n a t i o n a l A s s o c i a t i o n o f S c i e n t i f i c Hydrology, T o r o n t o , Canada, Vol. I : 381-386. S i m a i k a , Y . M . , 1961. D e g r a d a t i o n of t h e N i l e due t o i n t e r c e p t i o n of t h e s i l t i n t h e High Aswan R e s e r v o i r . P r o c e e d i n g s o f t h e 7 t h Congress on Dams and Grand B a r r a g e s , Rome, I t a l y , C - 7 : 639-656. Wassing, F . , 1964. C o a s t a l e n g i n e e r i n g problems i n t h e D e l t a r e g i o n o f UAR ( E g y p t ) . Memoranda Wl-W6, R e p o r t s of U N e x p e r t t o t h e Department of P o r t s and L i g h t h o u s e s , A l e x a n d r i a , Egypt. W e s t l a k e , C . , Mountain, R . , and P a t o n , T . , 1954. Owen F a l l s , Uganda, hydroe l e c t r i c d e v e l o p m e n t . P r o c e e d i n g s o f t h e I n s t i t u t i o n of C i v i l E n g i n e e r s 3 , P a r t I , P a p e r no. 6007 ( w i t h d i s c u s s i o n ) : 630-669, London, U K . L1-Zein Sagheyroon, S . , 1965. Proposed p r o j e c t s f o r t h e u t i l i z a t i o n of t h e Sudan s h a r e of N i l e w a t e r . The Sudan E n g i n e e r i n g S o c i e t y J o u r n a l , no. 10: 5-12, Khartoum, t h e Sudan.
-
470
APPENDIX A
- Annual
1
Station No.
Name
depth of r a i n f a l l , in mm
Latitude, N
Longitude, E
Altitude,
M
1938 1939 1940 1941 1942 1943 1944 1945 1946 1947
ECY PT __ 1 2 3 4 5
-
-
-
-
-
170
143 (
49)
260
263
187
113
120 38
114 79
97 74
170 158
184 108
133 79
256 50 71 49
-
-
153 167
89 194 266
121 151 320
248 66 171 114
46 93
277 80 95 185 194
216 122 123 130 218
223 88 61 117 198
170 113 45 46 ( 30) 95 54 144 113
78 53 67 98 75
171 261 116 121 136
270 242 90 210 89
225 200 130
92 69 56
83
62
81
43
81
61
151
76
160
-
-
-
-
83 98 50
45 36 54
92 95 56
24 17 86 ( 08) 25 36
75 37
112 38 38 64 13
28 21 32 06 13
102 33 11 16 05
57
06
-
-
S i d i Barrani Borollos (L.H.) Sallum Damictta ( L . H . ) Damietta
31° 31 31 31 31
38' 36 33 31 25
25O 31 25 31 31
58' 05 11 51 49
27 10 07 02 03
178 200 85 180 93
127 84 84 91 60
6 7 8 9 10
Rosetta ( L . H . ) Rosetta Mersa Matruh Tolombat E l - B o s e i l i Tolombat El-Tolombat
31 31 31 31 31
24 24 22 20 18
30 30 27 30 30
25 25 14 24 04
02 02 07 02 01
132
-
191 126 172 ( 56) 215 57
143 155
116 88
53 58
11 12 13 14 15
Edfina Port S a i d (A.P.) Sirw Kom e l T a r f a i a Alexandria
31 31 31 31 31
18 17 14 14 12
30 32 31 30 29
31 15 39 09 53
03 01 02 02 32
252 64 54 204 228
93 57 42 97 75
132 25 26 144 199
153 68 63 101 155
96 67
-60
16 17 18 1, 20
Mex Kafr El-Dawar Kafr El-Sheikh El-Arish Sakha
31 31 31 31 31
09 08 07 07 07
29 30 30 33 30
50 08 57 46 57
05 03 07 10 06
160 167 77 (126) 88
77 61 46 104 35
184 142 62 94 66
124 137 58 108 74
21 22 23 24 25
Ras E l Dabaa Mansura Fuka Damanhur Amria
31 31 31 31 31
06 03 02 02 01
28 31 27 30 29
28 23 56 28 48
15 07 26 06 11
161 47) 153 64 110
101 34
72 30
-
_
-
56
73
22 26
47 92
99
58
26 27 28 29 30
Borg El-Arab Hammam Kafr El-Zayyat Tanta Faqus
30 30 30 30 30
55 50 49 47 44
29 29 30 31 31
32 25 49 00 48
10 15 10 14 10
180 80 17 ( 51)( 41
20 46 37 23 29
108 73 14 51 50
-
-
31 35 33 34 35
El-Quaeima Zagazig Shebin El-Kom El-Hassana Benha
30 30 30 30 30
40 35 33 28 28
34 31 31 33 31
22 30 00 48 11
330 11 11 250 14
29
-
07 16
54 38
06
00 03
45 10
36 37 38 39 40
Wadi El-Natrun Fayed Delta Barrage Giza Kuntella
30 30 30 30 30
23 20 11 02 00
30 32 31 31 34
21 17 08 13 41
01 13 20 21 540
41 42 43 44 45
Suez El-Nekhel Attaqa Helwan El-Themed
29 29 29 29 29
56 55 54 52 40
32 33 32 31 34
33 45 28 20 22
08 406 03 112 6 16
-
(
-
-
-
-
-
-
_
-
_
70 ( 49) 69 65
-
-
-
_
38 37
-
-
-
-
47 36
62 08
-
-
-
29 18
43 25
29 43
43 39
-
-
-
-
-
-
-
-
-
-
-
-
307
48 43
116 188 149 110 100
71 87 41 37 29
-
27
-
-
74
-
-
48
-
-
15 ( 02) 19 29 17 38
-
5 1 ( 52) 33 ( 17) 36 30 76
28 16 12 30 07
16 16
30 37
38 13 18 64 13
14 ( 07) 10 06 42 12 17 13 06 07
11 09 57
-
24 15
18
58
27
21 56
25 06
21 06
35 07
-
-
60 48
20 18 22
-
-
17 16
-
-
26 08 ( 10) 31 44 47 18
-
-
68 25 81 72
12 01 37 08
471
Annual depth of r a i n f a l l , i n mm 1948 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967
133 144 240 224 324 ( 54) 182 169 228 168
98 116 33 89 116
189 157 173 133
161
174 216 112 121 287
128 140 41 39 45
204
130
104
342
-
121
162 99 85 114 255
92 260 274
129 120 298
186 150 213
273 220 281
123 81 72 79 139
1 7 5 96 75 146 70 128 142 164 241
-
-
96 166 44) 118
106 137 34 77 109) 94
052) 268 102 189 124
241 166 221 170 123 ( 144) ( 191 159 137 126 f
363 379 274 27 2 379
311 307 163 287 329
82 146 153 125 126
119 95 82 132 170
29 1 66 76 298 284
274 101 120 283 294
178 75 95 92 150
179 61 79 128 130
299 306 163 87 122
278 244 122 80 111
107 86 50 127 53
114 84 45 64
108 70 49 64 42
126 48
153 64
132 98 90 127 235
117 30 86 53 148
119 38 88 92 146
197 66 130 42 84
225 139 27 51 73
133 81 26 44 47
136 113 28 47 62
118 99 09 39 25
34 31
35 29
27 51
26 38
113 321 17 32 32
( 26)
35
16
-
-
100
-
131
-
83 88
-
-
-
43
17
31
12
15
11
48
20
92 99
197 52 123 67
104 86 30 39 42
207 142 29 68 47
179 (163) 295 183 284 203 30 49 50 47 48 76 74 34 40
31 36 42 11 29
41 21 28 26 13
18 40 29 03
27 30 24 30 31)
101
41 39 14 23 07 (
-
19
03
06
33
57
04 14
07 76
08 ( 06) 15 62
-
-
-
-
61 55
-
-
16 11
100 87 267 307
132 59 83 60
-
29 ( 22) 24 12
-
-
5 3 ( 33) 66 48 75 115 185 250
120 62 81 67 104
ti4
-
-
-
-
179 261 43 130 36
-
-
-
246 216 61 113 65
281 29 29 16 54 09 - ( 14)(
17 17 25
-
46 11 16 07
-
-
-
11
24 17 16 13
14 02 18 18 14)
220 301 175 189 105 78 ( 64) 57 50 168 66 221 104
-
-
(
25)
-
43 34
-
-
55
43
03 18
11 33
-
-
115 116 103 86 46
-
39
95 25 23 05 05
59 59 11 68 07 - ( 3 3 ) 52 07
18
-
13
-
-
36 35 28
-
-
-
-
143 149 95 75 59
-
-
-
110 76 53 45 40
92 146 39 90 108
155 71 165 130
-
-
-
34 1 182 313 2 30 139 98 16 1 149 115 169
143 20 3 128 127 129
171 138 105 133 124
343 373 215 321 318
169 212 215 173 103
239 233 145 182 266
104 166 101 132 57
81 73
66 74
154 310 102 138 120 226 111 214
46 47 243 203
26 39 167 55 ( 67) 19 9 3 277 112 178 127 169
60 73 61 124
88 133 254 290
173 99 159 165
269
175
275 166 54 108 59
144 97 59 46 33
344 167 141 150 112
225 122 31 55 32
151 79 36 155 30
373 34 1 142 128 107
189 176 122 193 108
237 149 107 63 29
164 114 102
80) 155 45 87 75 184 116 128
24 2 95 158 183
133 36
90 86
-
87 31 37 74
169 66
-
73 23 50 55
138
93
65
183 a3 16 47 26
256 124 58 80
230 183 85 65 23
100
31
87 100 40 70 17 12 23 34 11 38
81 35
170 13 40 17
53 13 63 26
-
50
100 13 27
33 43 31
30 43 33 30
42 58
13
55 55 31 44
20 19
21 65 20 19 ti1
39 13 19 19 16
18 21
73 37 55 15 27
08 36 08 17 37
-
188 113 24 45 17
-
(
50 ( 51) 31 31 26 34
-
52
-
12
00 03 12
37 31 12 17 13 07 11 24 17 ( 0 3
03 02 07 01 03
19 12 04 25 09
00
229 245 160 180 171
126 77 106 214
244 ( 36) 36 95 44 59 67 244 63 98 142 - (324) (144)
44 54
-
138 93 144
132 163 84 82 106
14 01 12 09 14
-
184 -
50 17
-
34
-
22 06
-
38
-
-
-
06
19
-
-
78 103 98
-
-
-
00 01 08 08 00
07 10
17 27 07 10 18
03 00 00 08 08
12 24 27 13 18
11 33 16 16 02
-
-
118
66
64
28
22
13 14
-
472
APPENDIX A1
S t a tion
Name
No.
(continued)
Latitude, N
Longitude, E
Altitude, M 1938 1939 1940 1941 1942 1943 1944 1945 1946 1947
EGYPT 46 47 48 49 50
Shakshuk Fayoum Ras E l Negb Siwa Beni Suef
29O 29 29 29 29
28' 30' 18 30 36 34 12 25 04 31
42' 51 52 19 06
43 28 760 17 28
51 52 53 54 55
Bahariya Tor Minya Hurghada Assiut
28 28 28 27 27
20 14 05 17 11
28 33 30 33 31
54 37 44 46 06
128 03 39 01 71
56 57 58 59 60
Farafra Qena Qusseir Nag Hammadi Luxor
27 26 26 26 25
03 10 08 03 40
27 32 34 32 32
58 43 18 15 42
90 73 06 69 95
61 62 63 64 65
Dakhla Kharga Deadalus I s l . Kom Ombo Aswan
25 25 24 24 24
29 26 55 29 02
29 30 35 32 32
00 34 52 56 53
110 70 03 100 108
02 09
20 05
02 27
17 24
-
11
07
_
00
_
00
06 30 19 ( 01) 15
01 15 02 43 03
14 10 00 00 03
00 43 00 09 03
_
-
_
_
_
-
-
_
_
04 20 26 21
05 27 09 ( 64) 09 28 08 04
07 45 35 41
16 06 15 04
11 11 08 02
00 11 02 00 06
13 07 04 ( 04) 00 00 11 01 13 06
02 01 06 15
00 00 00 00 00
00 02 00
_ -
__
_
_
_
-
_
00
-
03 00
01 02
13 03
00 01
03 00
00
04
04
02
00
01 00 00 01
00 01 02
00 00 00
00 00 03
00 00 04
11 00 06
-
_
-
08 09
01 13
08 08
05 06
00 43
01
00
05
03
00
01
05
08
00
00
01 01 72 57 00 04 93 213 10) 167
00 74 00 36 25
09 104 14 201 277
09 41 04 153 116
00
00
04 122 133
01 93 20
-
11
15 171 85 74 45
32 35 69 72 61
56 100 31 37 75
07 50 00 77 55
-
-
-
_
_
_
-
_
_
_
_
-
18 10 20 ( 11) 18 02 00 00
_
_
13 00 01 00
00 00 00 00
-
SUDAN
~
66 Wadi Halfa
-
_
-
138 00
63 57 233 169
136 08 82 118 (
67 68 69 70
P o r t Sudan Abu-Hamed Gebeit Sinkat
21 19 19 18 18
55 37 32 57 50
31 37 33 36 36
20 13 20 51 50
125 06 312 797 859
71 72 73 74 75
Kareima (Merowe) Tokar Tahamiyam Talguharai Atbara
18 18 18 18 17
33 25 20 17 42
31 37 36 35 33
51 45 34 55 58
253 18 647 539 348
22 ( 2O)( 04) 8 3 ( 73) 232 45 168 62 107 319 98 31 42 74
12 166 00 07 15
41 52 133
41 42 27
76 77 78 79 80
Zediab Abu Deleig Khartoum G.C. Khartoum (A.P.) Kassala
17 15 15 15 15
23 55 37 36 28
33 33 32 32 36
55 49 33 33 24
365 400 385 380 501
26 240 382 364 310
00 180 119 96 358
00 149 149 73
-
00 143 165 91 (340)
00 318 213 275 452
211 175 204 215
64 225 118 152 212
72 196 106 203 350
82 196 222 248 386
26 2 10 69 67 334
81 82 83 84 85
J e b e l Aulia Wadi Turabi Kamlin Khashm E l Girba Geteina
15 15 15 14 14
14 08 04 59 52
32 33 33 35 32
30 08 11 55 22
380 39 3 387 468 379
336 357 484
119 185 285
76 218 253
159 197 278
241 300 384
142 70 259
151 234 328
244 316 427
154 431 328
185 204 281
294
289
183
199
205
113 20 2
192
144
169
86 87 88 89 90
Rufaa Wadi-Shair Wad l e d a n i Managil Gedaref
14 14 14 14 14
45 42 24 15 02
33 33 33 33 35
22 17 30 00 24
403 400 407 390 610
342 ( 106) 309 248 355 548 335 260 394 704
326 323 300 379 563
265 232 79 378 611
366 354
20 1 336
252 427
254 570
257 246 251 182 554
363 238 334 221 426 25 1 311 236 86 1 497
68
78
-
-
-
-
60
-
-
295 310 477 336 495
-
473
Annual depth of r a i n f a l l , i n mm 1948 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967
08 08
17 28
01 06
12 26
13 18
23
06
02
07
22
18 00 14
00 00
02
00 04
01
00 01 03
06
00
00
00
00
00
00
00 00
57 06 03
00 00 00
00 00 00
00 00 09
00 00 10
00 00 06
00
02
00 76 00 42 90
_
_
_
_ _
-
_
-
_ _
_
_
_
_
_ -
- -
01
-
_ -
_
(
10 08 37 03 03
25 17 54 03 27
06 03 16 08 01
06 06) 01
05 29 10
00 02 34 0 2 ( 02)
06
00
04
00
03
11
10
00 00 00
00 00 01
00 01 00
-
-
03 02 12 00 00 0 0 -
40
29
17 10
-
-
-
-
-
00 18
-
03 73 00 08
00 10 10 02
00 04 01 01 00
00 08 02 00 00
00 00 02 02 00
02 15 02 02 00
00 00
00 00 00 00 00
00 00 04 00
00 00 01
02 00 00 00 00
00 00
00
_
_
00 01 13 00
01 03 01 00 00
00 05 02
03
00 06 49 00 01
01
00 00 00 00 00
01 67 15 189 358
00 28 48 106 213
00 15 04 103 80
00 46 00 85 43
00 46 34 168 150
00 146 01 53 51
00 85 18 89 146
01 145
119 26
106 17
07 01
08 51
65
131 115
100 107
-
47 27
51 85 79 155 104
43 166 66 25 41
38 58 112 45 110 129 45 100 149 85
15 194 126 117 337
77 123 236 ( 389)( 340) 240 - 165 132 117 224 176 179 285 401 359 265
72 316 249 239 429
47 334 190 178 317
348 146 149 451
135 470 246 229 336
292 392 321 585 419
165 184 185 245 173
190 270 177 297 204
292 496 188 495 193
232 214 260 599 185
149 317 183 296 119
281 283 335 369 154
209 213 235 343 148
235 169 195. 397 189
342 369 430 225 713
228 204 237 247 469
269 223 382 165 575
212 474 276 455 571
265 407 463 295 557
194 243 318 197 588
459 500 442 477 698
249 343 327 161 474
317
00 00 04
00 00 00
00 00 00
04
00
00
02 179 23 77 114
30 213 139 231 216
00 209 02 65 80
03 28 20 26 11
86 42 39 99 39
137 83 252 157 166
09 36 92 76 206
17 102 45 47 388
136 261 196 178 442
126 167 200 (262) 196
206 210 151 360 164
265 398 445 384 518
236 174 247 108 615
-
_
-
68
-
_
-
_
_
58
-
-
-
-
-
03 00 01 05 01
_
_
_
-
-
07 12
_
_
-
_
_
10 12
-
-
439 270 590
00
08 00 00
68
19 327 405
00 00
09 11
-
08 17
00 00 00 04 00
00 00 00
20 133 03 66 44
02 08 09 01 00
06 01 14 24 04
05 00 06
00 07
01 06 52 02 07
09 05 73 01 04
01
06
00 00
21 02 00 00
00 05 00 00 00
02 10 00 02 00
09 06 01 02 02
00 04 02
00 00 00 00 00
00 01 01 00 00
02 00 00 00 01
00 00 00 00 04
03 00 02 00 02
00 00 12 00 00
00
00 01 25 00 01
00 00 37 00 00
-
-
00
00
00
00
00 01 00 01
02 00 00 00
02 00 03 00
00 00 01 00
02 117 09 171 82
0 7 197 20 113 138
0 0 165 00 77 58
47 27 129 195
144 16 69 54
77 00 107
00 200 88 15 16
47 75 102 180 51
29
117 101 30 87
02 69 104
-
22 57 87 75 53
-
88
06 01
-
10 07 00
-
30 08 142 146
16
133 102 35 07 56
19 138 72 70 293
176 293 278 242 267
112 202 209 209 286
21 108 274 133 277 143 294 207 465
87 179 138 135 234
04 75 171 155 131
67 140 331 316 265
71 375 357 126 250 300 248 -228
-
253 276 327 360 227
252 273 230 385
50 250 184 222 108
151 294 341 232 108
100 239 263 241 298
106 112 99 231 157
139 168 223 340 207
283 323 556 291 589
348 309 367 306 599
425 336 435 585 574
245 241 319 352 743
543 334 421 378 555
416 338 312 373 600
272 236 269 310 616
359 229 504 246 661
-
00 48 11 250 31 169 15 75 8 134
220 156 270 207 439
-
-
-
474
APPENDIX A1
(continued)
__.__________
Station
Latitude. N
Name
KO.
-
Longitude,
E
Altitude.
M
1938 1939 1940 1941 1942 1943 1944 1945 1946 1947
___
~
SUDAN 91 92 93 94 95
Dueim Haj Abdalla Wad Haddad 8ara El-Fasher (A.P.)
13' 13 13 13 13
59' 58 49 42 38
33O 33 33 30 25
20' 35 33 22 20
379 415 417 490 790
___
480 422 487 363 310
446 479 442 422 409
439 415 461 304 201
138 360 432 267 232
326 511 343 372 167
403 466 451 251 273
319 473 346 334 252
230 438 427 329 393
318 565 652 270
-
_
-
-
-
-
-
-
-
-
-
159 340 299 207
-
96 97 98 99 100
Mafaza Sennar ( D . S . ) Geneina El-Obeid (A.P.) Kosti
13 13 13 13 13
37 33 29 10 10
34 34 22 30 32
32 37 27 14 40
435 4 19 779 570 378
403 520 388 388
504 504 419 383
514 375 312 334
496 419 274 484
580 477 351 374
516 496 451 359
393 504 313 353
471 490 599 384
399 814 716 416
449 677 394 309
101 102 103 104 105
Singa Tendelti Um Rawaba A 1 Rahad 61-Nahud
13 13 12 12 12
09 02 53 43 42
33 31 31 30 28
57 55 13 39 26
433 413 446 498 540
626 430 436 514 537
704 611 373 610 490
531 483 358 389 482
599 371 348 473 251
771 358 439 301 352
625 375 416 364 353
686 339 351 352 412
658 443 419 383 506
549 505 983 539 514
561 289 309 414 414
106 107 108 109 110
Jebelein Nyala Dilling Rashad El-Roaeires
12 12 12 11 11
37 04 02 52 51
32 24 29 31 34
50 53 38 03 23
386 634 699 885 467
515 606 925 728 1034
542 498 899 844 824
497 295 600 613 723
419 244 808 750 697
379 504 649 656 744
369 478 488 745 666
465 477 691 798 706
428 497 664 704 657
318 611 867 978 728
311
111 112 113 114 115
Renk Abri Kadugli Talodt Kurmuk
11 45 11 38 11 00 10 37 10 33
32 30 29 30 34
47 55 43 21 17
382 746 513 503 702
439 466 793 705 1074 960 856 825 1022 1039
392 838 758 664
552 673 855 916
451 642 678 627
413 730 735 718
508 499 712 940 906
904 869 848 633 833 664 669 805 797 589 832 1059 904 1175 950
116 117 118 119 120
Melut Kodok Malakal Tonga Abwong
10 09 09 09 09
27 53 32 28 07
32 32 31 31 32
12 07 39 03 12
383 384 389 390 389
387 473 725 683 695
542 746 825 823 836
648 793 710 831 695
580 886 568 864 795
684 791 792 841 756 664 733 900 944 833 1079 1167 835 923 702
121 122 123 124 125
Fangak Aweil Nasir Raga Meshra E l Rek
09 08 08 08 08
04 46 37 28 25
30 27 33 25 29
53 24 04 16
388 400 39 7 460 427
1163 1033 1033 1305 1245 1162 1138 1178 1461 1047 1164 1053 798 1035 592 808 974 945 1265 836 970 870 532 753 881 690 711 788 932 740 1398 1709 1261 1005 1332 1305 1104 1010 1343 1065 871 942 710 652 663 973 1124 921 859 756
126 127 128 129 130
Gambeila Akobo Post Wau Tonj Ghaba Shambe
08 07 07 07 07
15 48 42 16 07
34 33 28 28 30
35 03 01 45 46
450 403 433 430 405
- 1162 - 943 1174 1057 1292 1414 1726 1592 1010 974 419 923 1080 814 724 1221 1432 1217 1318 1156 1081 1165 944 892 1389 957 1189 1352 _ _ - - 1139 1024 953 1187 642 774 764 816 754 582 859 847 764 847
131 132 133 134 135
Rumbek P i b o r Post Bor Amadi Terrakekka
06
48 48 12 31 27
29 33 31 30 31
42 08 33 20 45
4 20 4 10 422 500 437
1070 1001 631 929 1009 890 692 655 699 987 932 822 755 872 823 1351 1607 1195 1289 1150 891 815 740 911 1117
OG 06
05 05
41
681 708 684 701 751
710 595 900 591 472
-
-
-
-
966 705 670 797 875
-
701 774 899
747 811 775 856 826
1173 1103 979 1292 986 516 682 456 1074 804 1068 797 1359 1140 1260 1140 1256 886 922 990
475
__
.-
-.
Annual depth of rainfall, in mm 1948 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967
-
271 416 421 375 294
407 249 430 207 417
284 442 276 310 718
287 340 467 168 245
312 656 442 308 311
196 340 400 339 232
331 413 353 241 228
366 575 423 353 326
154 414 351 255 285
349 377 356 353 250
323 399 442 412 324
262 450 366 169 279
261 481 509 304 297
456 443 433 193 332
185 411 141 192 247
217 560
239 586
325 390 330 207 228
630 412 387 256 256
495 548 567 324 431
629 441 483 513 347
736 396 623 433 306
345 609 514 353 533
870 286 789 487 557
760 349 716 402 390
728 576 651 665 521
453 572 516 307 464
406 685 495 396 464
465 548 441 375 548
528 397 554 317 308
612 385 731 466 547
509 419 586 512 395
710 521 715 315 344
814 580 737 544 371
450 567 435 359 368
561 302 502 216 319
535 600 396 267 409
605 410 388 627 306
336 206 205 351 361
768 217 342 489 462
524 367 572 454 440
610 545 276 343 502 381 433 509 403 659
629 431 396 389 346
666 478 369 391 334
705 456 546 485 486
491 388 344 491 487
810 477 388 470 431
490 373 494 513 404
498 210 322 342 486
532 374 383 423 307
534 361 524 660 442
526 209 496 909 299
635 603 568 374 317 246 389 441 291 388 408 389 500 483 312
566 367 312 349 279
516 296 634 782 589
285 320 542 735 673
414 543 573 812 778
315 456 573 696 749
442 522 (406) 371 520 524 647 634 666 664 (972) 825 765 828 924
435 570 478 781 601
556 567 752 739 665
294. 485 751 855 610
478 486 800 703 515
378 469 799 697 588
332 429 396 595 728
524 458 509 884 812
469 448 502 644 803
548 621 697 898 829
347 620 587 796 75:
353 335 562 687 575
391 472 471 421 303 526 940 1029 741 658
765 583 543 723 805
731 456 618 616 738 1040 800 1075 - 913
476 618 826 784 853
592 702 683 526 647 579 751 773 800 719 690 1019 1046 554 724 702 1054 821 772 869 945 1083 1205 1066 1196
439 534 765 573 733 650 853 519 809 1042
617 554 642 836 872
358 590 438 752 418 606 812 633 728 625 835 788 1046 827 1042 837 860 999 943 965 1135 1073 1090
419
540
403 683 774 859 917
534 813 792 871 874
734 554 495 698 725
660 734 626 726 874 821 861 1008 622 767
548
769
519
875 1032
299 432 359 333 237
289 472 428 212 172
533 476 521 454
-
605 568 683 642 1032 1176 1031 919 856 879
270 335
664 1290 428 676(388) 804 776 602 801 811 948 887 808 676 736 963 1333 1222 1052 930 966 749 1068 849 -
652 601 726 721 805 725 1097 920 1031 602
-
575 903 705 686
-
596 882 778 756 430
631 554 771 776 203
-
494
-
868 760 741 788 775 673 627 1296 1077
-
-
806 689 1267 578 792 742 981 798 918 848 808 811 812 749 435 621 744 356 703 976 1195 660 990 1179 1071 944 970 947 895 558 948 671 755 544 757 727 619 1167 756 681 987 728 949 789 919 654 875 698 847 806 877 420 1035 1125 1144 1354 1132 1218 1116 1308 1150 1381 1280 1257 973 1331 1200 1441 1042 1396 - 957 1420 1031 542 720 856 808 919 799 1135 634 716
-
-
-
-
235 234
-
-
646 1120 873
-
-
576
535
842
873
-
-
-
-
-
1270 1495 1261 1447 1170 1240 1756 1430 1427 916 1214 1374 1179 1784 1460 1581 1790 1092 1494 1339 1163 1238 1111 989 899 997 945 870 1096 944 919 918 1037 1162 1113 786 975 665 957 957 1068 1159 1487 985 1094 1181 1117 1328 1031 1210 1366 1211 1197 1100 1387 1275 1365 1004 1429 1033 - 921 822 754 1456 1040 878 829 1491 1067 937 973 1173 895 1458 1147 1413 1101 1033 960 947 638 554 684 533 655 746 595 947 661 371 990 708 463 485 987 833 1156 1163 687 869 712 835 848 1098 1112 1277 918 904 840
885 1197 845 1164 1070 1172 530 526 638 591 989 1004 606 1083 981 1064 941 1197 1174 799 855 836 a3931445 830 961 751 787 777 1008 962 787 825 632 1101 965 964 1085 (850) 859 1005 1256 927 1356 1317 1084 1205 1016 - 1312 806 1152 1259 1592 670 901 704 826
-
957 877 1091 996 800 1142 1310 1085 1278 1358 1196 -
-
-
-
-
882 1174 953 881
-
-
856
846
476
APPENDIX A1 S t a t ion
No.
Name ~
136 137' 138 139 140
(continued) Latitude, N/S
Longitude,
E
Alti-
tude, M 1938 1939 1940 1941 1942 1943 1944 1945 1946 1947
SUDAN
Maridi Juba Yambio Loka Yei
04' 04 04 04 04
55' 51 34 16 05
29O 31 28 31 30
28' 37 34 01 40
748 462 724 965 830
03 03
53 36
31 32
40 03
1030 620
1645 1250 1167 1253 1476 1107 1198 1369 1657 1244 1320 1180 1174 1376 1270 931 1099 1337 1333 1235
143 Kitgum 144 Arua 145 Gulu
03 03 02
17 01 45
32 30 32
53 55 20
937 1280 1106
1188 1094 1212 1248 1138 994 1457 1164 1651 1306 1474 1259 1327 1866 1509 1241 1376 1176 1432 1121 1200 1657 1768 1463 1002 1483 1522 1457 1809
146 147 148 149 150
Moroto Ngetta farm Aduku d i s p e n s a r y Katakawi d i s p e n s a r y Butiaba
02 02 01 01 01
33 17 59 54 50
34 32 32 33 31
36 56 43 59 20
1524 1095 1036 1158 621
- 697 1024 967 1397 1035 1452 1449 1271 1029 1323 1392 1360 971 1227 1427 666 649 863 883
1111 1331 1118 1055 804
600 542 855 1270 1240 1360 1408 1543 1020 1190 1525 1578 1066 1173 1093 1077 492 587 774 768
1080 1793 1389 1096 770
151 152 153 154 155
Soroti Masindi Ongino S e r e r e Agr..Sta Kyere
01 01 01 01 01
43 41 34 31 29
33 31 34 33 33
37 43 01 27 37
1127 1146 1219 1139 1067
1224 920 1045 1114 - 1088 1205 938 1088 1209
1096 1396 1260 1457 1394
1868 1429 1430 1496 1431
1642 983 1170 1125 1390 1252 1098 1331 1371 1192 1305 (488) 1146 1047 1194 1458 997 1481 1449 1485 1298 1041 1359 1324 1554
1411 1190 1261 1156 1511
156 157 158 159 160
Bulindi Ngora C.M.S. Nakasangola Bukedia Kachumbala R . S .
01 01 01 01 01
28 27 19 19 15
31 33 32 34 34
28 46 28 03 06
1036 1128 1274 1113 1146
1066 1389 710 1144 1079
1349 1277 1110 865 1152
1136 1247 980 1457 1325
1520 1354 1177 1548 1206 1514 1539,1396 1128 1505 1351 1421 1161 948 707-1295 1126 1099 1283 1492 1018 1196 1228 1350 1242 1037 981 1004 1299
1382 1592 1168 1361
161 Kibale V . T . C . 162 Bugaya 163 Mbale 164 Namasagali 165 Vukula
01 01 01 01 00
12N 06 06 01 57
33 33 34 32 33
47 1097 15 1067 11 1220 57 1036 36 1097
1323 1145 1006 1231 1126
1088 1263 1340 1064 1045
1584 1499 1133 1261 1555
1612 1679 1029 1315 1403
1272 1433 1481 1392 1355
166 167 168 169 170
Kiboga Bulopa Ntenjeru Bukalasa Agr. S t . Kahangi E a t .
00 00 00 00 00
55 51 44 43 42
81 33 32 32 30
46 15 53 31 28
1219 1097 1158 1128 1524
- 1359 1249 1105 1096 940 935 1494 1474 1216 1009 984 1378 1361 1342 1119 1283 1385 1326 1336 - 1355 1323 1491 1166
171 172 173 174 175
Tororo Fort Portal Kalagala Agr. S t . Iganga Mubende
00 00 00 00
00
42 40 37 36 35
34 30 32 33 31
10 17 37 28 22
1226 1539 1037 1161 1553
1137 1164 1294 1056 1051
1079 1393 968 1076 1163
1421 1429 1572 1345 1272
1527 1624 1273 1501 1178
1470 1214 1331 1228 1653 1384 1360 1456 1162 1426 1335 997 1348 853 1181 1431 900 1321 1096 1329 1271 1248 974 981
1468 1642 1468 1376 1283
176 177 178 179 180
Nawanza Dabani Nagoje E s t a t e Masafu Dispensary Lugala E s t a t e
00 00 00 00 00
33 28 27 24 24
33 34 32 34 33
30 05 53 02 02
1189 1219 1152 1219 1280
1371 1398 1140 1344 1183
1316 1370 1191 1339 1155
1406 2001 1310 1297 1606
1532 1427 1312 1190 1364
1305 946 1377 1023 1712 1123 1324 1315 1120 893 - 1215 1417 1021 1380 1519 1424 1115 1629 1390
1459 1868 1363 1331 1378
141 Ka joka j i 142 Nimule
1153 1366 1650 999 1703
1363 1078 1359 1062 1424
1249 832 1438 1408 1245
1394 975 1642 1368 1613
1110 742 1328 1264 1276
1076 693 1351 1089 1143
1056 1194 1424 1273 1476
1338 1317 1723 1311 1207
1265 1200 1381 1382 1488
1316 1044 1321 1355 1291
UGANDA _ _
1432 938 1217 956 1400 972 1106 916 1382 1040 1274 1220 1247 834 1164
1558 1440 963 1066 1336
1322 1180 1309 1194 1162
1316 1276 1101 1161 1375
-
1296 870 970 1045 1752 1438 1264 1509 - 1382 1443 1156 1244 1206 1136 1329 1310 - 1327 1392
-
1284 1407 992 1627 1191
4 77
Annual d e p t h of rainfall, in m m 1948 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967
1550 968 1499 1240 1503
1680 768 1485 1015 1133
1401 841 1309 1368 980 784 946 695 1455 1351 1657 1168 1161 1293 1326 1294 1178 1500 1225 1250
-
1340 1054 1041 1019 1505 1322 1457 1243 1409 1383 1415 0294)1507
1767 1164 1399 1181 1267
-
1504 1440 1385 933 923 968 931 1460 1508 1713 1830 1347 13980249) 1138 1463 1291 1733
1665 1300 1403 1473 1566
1396 1444 1724 1435 1694 1006 961 820 983 1294 1646 1554 1152 1502 1502 1456 - 1111 1552 1276
-
1183 1203 1065 1269 1577 658 1487 2252 (l51l)1201 1151 1344 1392 1606 1174 1555 1669 1342 1290 1005 1397 1573 1216 1238 - 1685 1035 - (1019)1333 1033
-
-
-
-
-
-
1067 1508 914 1262 1007 953 - 1021 1400 1034 - 1150 1421 1408 1352 1358 1293 1237 1252 - 1481 - 1316 - 1453 1513 1513 1334 1491 1367 1393 1632 1879 1756 1594 1417 1949 1726 1379 1519 1544 1377 1518 1629 1563 1505 1650 1368 1772 1894 1897 1874 1622 1484 1389 1452
-
902 903 685 1023 610 733 1259 870 917 730 975 820 816 1560 1654 1256 1533 1326 1229 1300 1583 1427 1217 1484 1509 1520 1326 1154 1318 1289 981 1116 1030 1247 1438 1167 1086 1274 1337 979 1072 1464 1063 806 1058 1157 1268 936 1006 636 584 493 685 400 730 610 746 608 630 592 714 636
-
1011 1336 1200 1147 1135
1570 1459 1449 1507 1588
1266 1261 - 1263 1133 1106 1437 1165 1035 1288
1249 1265 1048 1343 1141 1222 - 903 998 1081 865 1175 1064 799 997
1331 1910 1008 1388 1507
1067 1411 1013 1126 1349
1347 1118 1136 1480 1253
1010 1030 1195 1235 969
1222 1426 1123 1223 1237
1312 1141 1474 1306 1281
-
-
1437 1211 1362 1720 1278 1082 1243 1150 1096 2012 995 1219 1022 890 1365 1775 1207 923 1299 958 1194 1828 1048 1102 1384 1367 1305 1932 1470 1133
1306 1158 1144 1353 1282
1104 803 1367 2198 1380 1341 1206 1504 1230 926 986 1361 1121 995 1250 1630 1284 1344 1353 2025
1238 845 1289 1193 979 1334 1556 1292 1211 1187 1100 966 1117 1279 1111 1276 1289 1106 1456 1246 1396 1409 1233 1110 1350
930 1048 1043 1051 1321
1115 1303 1080 1180 1236
1247 1125 887 1362 1115
1245 1208 921 1212 1041
1243 1317 1455 1013 1023
1247 1115 1330 1637 1539 1604 1564 1385 1896 1306 1010 945 1305 1662 988 1264 - 1395 1495 922 1233 1336 1581 -
1054 1283 1385 1419 1664 2116 1452 1225 1080 1096 1037 980 1260 1110 1220 -
1226 1199 1056 1693 1411 1329 1621 2152 1338 1026 1383 1946 - 1493 2444 - 1061 1104 1585
951 1019 1430 1061 1292 1320 1583 1625 1430 1615 1191 930 1072 1180 1342 1368 1399 1542 1159 1201 1608
-
-
1017 1304 1159 1264 1087
-
-
-
1426 1458 1284 1079 1427
-
1310 1103 976 1258 1113
1267 1328 1193 1072 1135
-
-
-
-
-
-
1487 1146 1257 1131
1352 1042 1423 1476
1363 1488 1083 1807 1288
1336 1684 1235 1185 - 1169 1671 1334 1407 1258
1427 1960 1347 1382 1474 1346 1149 1632 1377 1111 1432 2075 1503
1250 1180 951 1081 1351
1596 1516 1360 1532 1040 1256
-
-
1074 1093 1072 1780 1370
1033 1544 1279 1383 1044
1256 1684 1417 1332 1582
1387 1457 1071 1548 1410
-
1578 1163 1297 1054 1296 1431 1509 1041 967 - 1057 1336 1115 1282 1485 1245
-
-
-
1327 1692 1627 1255 1654
1345 1637 1981 1753 1795 1564 1398 1957 1620 1805 1402 1495 1194 848'2004 1335 1661 1133 969 1647 1228 1312
-
-
1145 1316 1284 1225 1114
2073 1746 1687 1806 1876
-
-
1044 1445 1330 1474 1386
1495 1589 - 1359 1056 1333 1483 1561 1469
1175 1435 1248 2518 1345 1569 1644 2109 1168 1384 1478 1171 1941 - 1427 -
-
1498 1634 1550 1509 1074
1774 1605 1495 1616 1778
1315 984 1399 1095 1691 1151 1095 1782 1134 2125 1563 1395 1692
-
-
1408 716 1067 923 574 974 1698 1438 1930 1528 1374 1447 1537 1561 1437 1306 1395 1197 1304 1709 1531 989 1251 1086 878 1127 1023 - 570 695 549 939 904 1076
1440 873 1405 1643 - 1153 1262 - 1629 1080 - 1803 1663 1556 968 1422 1306 1273 1387 1501 1822 - 1554 1450 1425 999
1137 1069 1342 1234 1072 1109 1178 1268 1154 1104 949 856 1159 1057 913 1073 1051 1239 1023 1097 1070 881 1071 - 1073 1163 1196 946 1235 1321
-
-
1329 1608 1622 1563 1307
1612 2005 2406 1923 2169
1313 1328 1447 1293 1465
-
-
1249 1569
1635 1304 1528 1580 1553 1400 1795 1408 1188 1101 1071 1403
-
-
-
-
1182 1185 1117 1229 1398 1281 1327 1410 1569 1945 1985 1897 1689
-
-
-
-
-
1689 1337 1250 1352
478
APPENDIX A1
(continued)
~~
Station No.
Name
Latitude, N/S
Longitude, E
Altitude,
P
1938 1939 1940 1941 1942 1943 1944 1945 1946 1947
UGANDA OOo 23' 32O 55' 1250
181 182 183 184 185
Monika E s t a t e Namanve Mukono Agr. S t . Bwavu E s t a t e Nasmbya
00 00 00 00
21 21 21 18
32 32 33 32
41 45 01 35
1135 1184 1280 1134
1571 1525 1646 1420 1366 1103 1513 1170 1138 1393 1445 1293 1082 1433 1274 1302 1628 1509 1287 1066 1626 - 1099 1452 - 1006 1000 1311 1285 884 1170
1288 1346 1370 1544 942
1387 1301 1401 1158 1092
1542 1127 1317 1415 970
186 187 188 189 190
Kabasanda Bud0 K i n g ' s Coll. e g e Ngogwe C.N. Buyuma I s l a n d K i s u b i S t . M.C.
00 00 00 00 00
17 16 14 11 07
32 32 32 33 32
13 29 59 18 32
1158 1311 1158 1158 1173
882 1028 1373 1175 974 1299 1703 1306 1110 1413 1954 1586 - 1484 1463 944 1026 1498 1416
1041 1204 1279 1077 1614
1569 1123 1420 1574 1150
1947 1143 1509 1710 1561
191 192 193 194 195
Entebbe Obs. Nkozi Kalangu Katigondo Lyantonde
00 00 00 00 00
04 01s 10 13 20
32 32 31 31 31
29 01 45 44 09
1182 1189 1219 1311 1219
1079 881 785 738 745
999 1600 1698 1828 1521 1837 1446 1534 705 1136 1003 1116 817 1503 982 1002 654 985 908 1235 763 1338 1185 1044 846 1134 1111 1317 851 1522 1104 1073 806 915 1495 875 689 1236 1287 1000
1722 1209 1280 1473 918
196 197 198 199 200
Masaka Kiwala E s t . K a l a n g a l a Zaza Buwunga Kyanamukaka
00 00 00 00 00
20 20 20 23 30
31 31 32 31 31
44 48 19 47 41
939 790 1069 993 1200 1028 1313 1298 - 792 1265 942 1238 927 1158 (2653 1515 2355 2550 3355 1729 1250 1049 954 1273 986 1271 870 1219 1231 954 1206 1032 1181 1005
201 202 203 204 205
Bushenyi Mbarara Bikira Lawasamaire Katara Songo
00 00 00 00 00
335 37 37 50 55
30 30 31 30 31
12 39 34 08 38
01
15
29
1 4 N 35
206 Kabale
_
_
-
-
-
1287 1209 1743 1836 1955
1025 1516 1325 1249 1610 1260 1758 1439 -
-
1535 1196 946 1523 1087 1098 - 1371 1403 1108 995 1335 1186 996
1310 1720 2720 1733 1576
1631 1443 1219 1646 1189
786 1377 1440 1578 1430 1109 1104 1103 1157 689 946 852 1128 855 708 823 938 1053 1063 1006 1050 1090 1165 849 1111 931 975 928 1061 1069 1450 1321 1029 901 1040 709 1206 994 1307 727 1304 983 1306 1064 1178
1185 731 1321 977 1524
59
1871
1166
09 30 10 03
2134 2225 1890 1809
914 630 1229 1327 1221 1018 923 1215 1341 1322 1165 756 963 1271 957 1225 1012 1096 1558 1085
979
966 1486 1217
777
947 1059
951
916
KENYA __
207 208 209 210
Kapenguria Endabess I t . E l g o n K i t a l e Agr. Dep. Turbo
01 01 01 00
01 38
34 35 35
211 212 213 214 215
Tambach Mayanga S t a t . Bungoma V . S . Numias Tororo
00 00 00 00 00
36 33 31 19 18
35 34 34 34 34
32 27 30 30 09
1829 1248 1372 1340 1219
1066 1128 1391 1883 1372
679 1210 1274 1511 1401
1434 1299 1782 2069 1444
216 217 218 219 220
Kakamega Kapsabet Rangala Maseno V.S. Equator
00 00 00
00 00
14 12 10 00 01s
34 35 34 34 35
51 07 21 37 24
1676 1998 1384 146 3 2012
1843 1395 1375 1602 1461
1565 1131 1223 1260 1098
2246 2049 1808 1744 1802 1498 - 1385 1563 1658 1740 1572 1855 1816 1502
221 222 223 224 225
Miwani S t a t . Kisumu P . C . Chemelil S t a t . luhoroni S t a t . F o r t Ternan
00 00 00 00 00
05 06 06 09 10
34 34 35 35 35
59 45 07 12 23
1219 1146 1230 1300 1768
10
1542 1308 2035 1938 1938
1077 1029 1161 1465 1414 1186 1088 1178 1288 1607 1009 993 1166 1344 1253 1273 1240 1205 1399 1500
1129 983 1257 1321 1199 1315 1393 1163 1645 - 1294 1925 1380 1176 1420
984 1275 1385 1333 1100
1203 1441 1445 1973 1486
1893 1781 1577
-
1795 1443 1390 1368 1673
1962 1607 1744 1859 1757
2398 1757 1632 1899 1975
1411 1163 1364 1437 1127 1001 1146 1046 1132 1155 878 1310 1335 1018 935 1229 862 1421 1038 - 1430 1472 1303 1081 1658 1341 1474 1418 1646 1604 1103 1494 1116 1336 1357 877 1393 1478 1270 935 1259 1133 1242
1234 1100 2821 1981 1548
1196 1199 1227 1308
1801 1383 1559 1420 1505
1522
-
4 79 Annual depth of rainfall, in mm 1948 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967
-
1177 1231 1429 1797 1217 1008 1307 2010 1219 1031 1439 1852 - 1189 1012 1981 1030 743 1036 1556
1180 1291 1331 1176 1040
1418 1226 1298 1242 943
1352 944 1160 1087 588
1802 1489 1534 1348 953
1493 1236 1397 1237
1310 1086 2059 1287
1347 1516 2142 1119 1132 1589 2226 1829 1980 2260 2097 1147 1458 1395 1847 1078 - 1765
1692 1972 1751 1558 1466 1603 1658 1535 1458 1972 1616 1192 -
1464 1531 1085 1371
1628 1413 1066 1343
1402 1148 1305 1356 1357
1121 1050 1500 1512 1374
1243 1091 1609 1536 1330
1021 1146 1288 1253 969
1301 1452 1670 1328
1329 1134 1471 1844
1575 1500 1584 1990
1333 1055 1514 1222
1320 1628 1283 1011 1199 1332 1381 1579 - 1099 1767 - 1781 1163 1665 2002 1886 1461 1957 - 1525 1577 -
1261 1338 1179 1783
1108 1189 1940 1048 1444 1656 - 2074 1099 1680 2219 957 1438 2087
-
1411 1128 1783 821 767 1136 1387 969 907 975 904 1087 1259 742 715 i 3 4 lb.32
-
-
-
-
-
-
-
1422 1238 1628 1244
-
1557 1266 1727 1326
-
-
1620 1543 2276 1967 1289
-
-
-
-
801 1156
-
-
-
1446 1253 1217 1854 1015 910 858 742 1520 697 995 824 1118 1378 969 1037 910 1041 1401 897 1057 872 1127 1531 1041 914
-
1567 1374 1046 1519 1754 1705 1722 1444 1834 1641 1944 1938 1458 1368 1569 797 709 689 656 840 925 1122 965 1063 1371 1166 1490 919 1049 1161 1183 1154 1020 919 1056 1114 1566 - 692 1105 944 - 759 834 962 949 1329 938 1153 1104 1056 1151 1199 980 1471 1082 915 707 - 763 - 774 599 909 811 600 632 660 823 885
851 818 1061 1252 826 845 1029 890 811 1281 954 929 1248 1213 - 1296 1006 996 1132 1537 978 947 671 1126 1217 1783 1825 1689 1390 1890 3509 2040 1526 - 2330-2095 2144 2192 2057 1998 821 934 1111 1727 865 894 927 1057 1042 1066 1101 956 1519 1489 1065 878 1070 1421 923 1087 983 975 978 979 1182 1395 1295
704
-
1480 1188 922 1239 1150
1341 1633 1125 853 1280 1046 1099 1242 1066 857 1226 1111 1986 2497 2070 1638 2198 - 1203 1291 1063 1595 1146 975 1774 1139
-
-
1281 1127 1637 1318 1556 1036 1149 1159 1365 1606 1678 1137 969 936 1101 849 1141 897 798 846 1151 1040 1228 946 781 780 - 1280 992 1599 1015 806 1070 1078 964 943 1013 1252 993 1204 1165 1315 1100 871 924 1199 li71 1106 1173 - 924 887 - 1197 1315 - 1037 1253 1175 1150 1056 1048 1251 1272 1341
-
794 1034 1082 922 1076 1095 1233
-
872
-
800 1000 1016 1281
-
975
934 743 934 860 935
897 1032 1148
- 1127 1151 1316 2026 1195 1500 1030 864 1396 1096 1143 1183 1354 940 1072 1532 1096 959 1129 1310 1345 1473 1485 1264 1013 1563 1081 1136 1254 1070 1462 1019 887 1210 877 1076 1043 1461 862 1050 1712 1375 1092 1231 1596 2056 1544 1167 1598 1851 1161 1191 1341 871 906 1126 1010
1747 1384 1444 1014
1514 949 1359 2069 1378 1003 1299 1705 1213 1019 - 1340 1163
941 865 903 1496 1384 943 - 1821 1326 1412 1364 2073 1511 1546 1621 2203 1194 1222 1229 1834
1457 1034 1070 1800 1135 1078 946 1743 3201 1504 1447 1184 1650 2118 1752 1531 1759 1887 2278 2164 - 1303 1297 1821 1352
1634 1597 1867 2245 1602
808 - 1977 1537 1476 2059 1642 1391 1319
1881 1743 - 1277 1479 1821 1411 1510 1650 1560
2389 2308 - 1340 1911 1736 2267 1882 1963 1475
1813 1579 1111 1310 1413
1612 1250 1409 1170 1376
1829 2111 1954 1289 1840 1818 1544 1602 1239 2037 1463 1249 1831 1474
-
-
1079 1469 1474 1179 1231 1403 788 1560 832 881 1002 1917 1350 1540 1594 1310 1475 1989 1284 1585 1244 1219 1559 - 1354 1251 1247 1210
1258 1261 1514 1025
1551 1445 1620 1445 1551
889 1000 891 1422 1201 947 1086 871 952 764 1562 1126 974 979 - 1158 993 1307 1216 1689 1238 1147 1101 1306 1941 1272 955 1241 963 974 1084 1405 1044 978 1160
2027 1621 1445 1483 1454
1831 1529 1602 1503 1374
1715 1301 1942 1613 1394
2440 1727 1552 1405 1501
2385 2241 2103 2128 2220
2333 1911 1922 1754 1795
1309 1218 1172 1182 862 880 805 1006 944 916 709 963 1498 1517 - 1180 1405 1754 1619 1178 1643 1482 1128 1029 1315 1457 1953 1924 1281 1113 1393 1329 1098 1384 1560 1496
-
1273 1476 1421 1499
-
1035
-
1705 1153 1529 1584 935
-
1373 1062 1503 1525 1504 1887 1421 1353 2007 2601 1605 2154
-
-
1714 1671 1571 1814
975 1291 1172 874 1156 1012 1886 1412 1467 999 1472 851 1492 -
-
-
480
APPENDIX A1 ( c o n t i n u e d )
S t a ti o n No.
Latitude, N/S
Longitude, E
Altitude, M 1938 1939 1940 1941 1942 1943 1944 1945 1946 1947
KENYA -
226 227 228 229 230
Londiani Lumbwa S t a t . Molo S t a t i o n Kericho S o t i k , Monieri
231 K i s s i
00’ 00 00 00 00
10’ 12 15 23 40
35O 35 35 35 35
35’ 28 44 17 05
2316 1931 2458 1981 1813
1217 878 1347 1056 774 1100 997 679 1295 1856 1475 1843 1209 750 1373
00
41
34
47
1768
1501 1344 1567 2062 1710 1202 1687 1473 1471 1913
1486 1177 1646 2230 1495
1158 963 966 1238 977 838 1050 1227 1604 1196 1164 888 1814 1387 1608 1714 1313 1142 1340 1362
1197 1148 1228 1671 1254
1495 1444
-
1242 1621
TANZANIA
232 233 234 235
Bukoba Tarime Musoma Kagondo
01 01 01 01
20 22 30 33
31 34 33 31
49 23 48 42
1144 1524 1147 1296
2192 1991 2237 2046 2051 1640 2346 1998 1813 2676 1209 1332 1405 1420 1294 1193 1334 1138 1263 1354 624 637 774 713 852 710 852 710 998 759 1867 1435 1876 1415 1677 1424 1634 1960 1315 1900
236 237 238 239 240
Kwalinda Rubya Mission Igabiro Estate I k i z u Mission Kome Mission
01 01 01 01 02
34 43 48 56 21
31 31 31 34 32
43 37 33 03 29
1295 1433 1524 1524 1134
1624 1388 1716 1354 1684 1433 1478 1639 1269 2062 1651 986 1579 1153 1070 1095 1578 1429 936 1554 1307 836 1261 1062 815 968 1252 1055 830 1428 - 788 - 1153 942 865 927 796 989 921 1183 1476 1541 774 776 985 1176 1087 1348
241 242 243 244 245
Ngara Mwanza Biharamulo Ukiriguru Sumuvwe
0 2 28s 02 31 02 38 02 42 02 46
30 32 31 33 33
38 54 19 01 13
1798 1131 1478 1199 1219
805 1032 949 1322 855 735 985 1482 970 1054 1113 1020 704 536 977 1025 305 647 1037 1149
246 247 248 249
G e i t a Gold mine Ngudu Kijma Mission Shanwa D . O .
02 02 03 03
52 57 04 10
32 33 33 33
10 21 07 46
1292 1219 1143 1341
837 853 443 526
09
02
38
44
2440
907 730 686 719
972 1016 963 1073 725 886 669 1072
936 1080 913 775 935 785 761
-
860
888 1014 846 1080 1154 737 1235 1006 932 1197 714 948 818 972 850 438 714 843 888 1013 598 812 892 735 978 769 1041 1071 629 846 792 584 - 729 692 703 620
940 1108 692 933 639 818 524 793
ETHIOPIA
250 Addis Ababa
1011 1104
938 1107 1154 1054 1083 1006 1137 1261
481 -.-
Annual d e p t h o f r a i n f a l l , i n mm 1948 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967
1108 956 1151 1914 1365
1056 794 1335 987 745 1219 1077 864 1523 1906 1941 2454 1087 1304 1788
1121 799 1189 1130 947 1018 799 557 757 1755 1563 1764 1373 1058 1215
1392 1126 971 1780 1369
1384 1283 1173 1763 1270
1352 1261 1058 1682 1518
1271 914 1010 1568 1344 1422 1430 863 1217 1322 1139 1350 1181 1078 1005 1411 940 1138 1379 608 1804 1850 2125 1632 2272 2090 2003 1645 1553 1267 1245 1645 1517 1581 1320 1232
-
-
-
1161 1215 1229 983 783 1742 1985 1410 1536
1591 1556 1296 2105 1610 1561 1832 2013 1837 1837 1913 1800 1759 1992 2517 1963 1998 2728 4202 1231
1883 1901 2038 2428 1910 2445 1770 1959 1806 1708 1713 1953 2410 2735 1981 2638 1970 2105 2272 2087 1226 1348 1246 1539 1218 1365 1365 1129 1248 1421 1367 1202 1189 2267 2322 2222 1803 1519 1584 1737 650 932 849 468 955 948 781 613 1014 895 772 1039 896 869 1136 949 968 706 976 732 1512 1394 1853 1805 1298 1562 1930 2301 1455 1337 1262 1947 1976 2736 1343 2128 1847 2010 1540 1704 1504 1390 1789 1863 1356 1566 1491 1680 1303 1355 1185 1577 1782 1217 1737 1979 2196 2104 1955 1736 - 1568 1398 1119 700 1225 1235 1236 1250 1590 1104 1421 1225 1367 1005 1533 895 1245 1269 1845 1008 712 1067 1429 978 975 1037 1112 851 1169 671 - 1603 1092 1217 1225 1472 1451 564 1060 - 565 759 736 944 1422 979 1009 1311 849 789 1591 987 932 836 914 - 1015 843 - 743 - 1283 -
-
842 720 964 763 839 1051 735 728 659
923 1198 1006 762 933 1488 662 774 1599 496 693 1355 478 866 1735
923 1180 941 864 808 909 744 585 744 795
897 1080 960 923 777 967 871 958 856 927 961 889 1008 1205 1019 634 791 754 831 777 633 795 812 1053 492
790 582 696 663
900 515 673 880
922 461 756 688
1361 1204
786 648 715 770
1302 1280 1229 1169
934 1059 1027
874 399 830 673
778 1273 1347 800 760 716 746 1077 676 547 784 925
766 856 688 603
-
-
-
-
-
988 941 638
1138 651 1700 1190 1019 830 1145 1109 696 1666 -
916 637
954 1647 1144 1213 1121 1184 1079 883
847
526
-
-
-
-
-
-
1490 1163 1264 1462 1135 868 1119 979
-
-
802 1344
-
-
891
-
-
-
812 1143 998 938 1059 1025 815 902 793 1124 1048 - 1816 2428
-
983
-
782 675
898 1163 1573 1126 1102 1384 1051 1213 1461 CL195) 1398 1320 1227
-
651
-
-
980
686 1012
-
-
APPENDIX B Mean annual precipitation, in millimeters, after supplementing the missing data Station number Year
1 2 3 4 5 6 7 8
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
97
98
99
100
101
102
103
104
105
106
107
108
403 504 5 14 496 580 5 16 393 47 1 399 449 533 412 548 44 1 396 609 286 349 576 57 2 685 548 397 385 4 19 521 580 567 302 600
520 504 375 4 19 477 496 504 490 814 677 476 387 567 483 623 514 789 7 16 651 516 49 5 441 554 731 586 715 737 4 35 502 396
388 4 19 312 274 351 451 313 499 7 16 394 521 256 324 513 433 353 487 402 665 307 396 375 317 446 5 18 315 544 359 216 267
388 383 334 484 374 359 353 384 416 309 454 256 431 347 306 533 557 390 521 404 464 548 308 547 395 344 371 368 319 409
6 26 704 531 599 77 1 625 686 658 549 56 1 605 336 768 524 610 545 629 666 705 49 1 610 490 498 532 534 526 635 603 568 566
4 30 611 483 371 358 375 339 443 505 289 4 10 206 217 367 276 34 3 431 478 456 388 477 373 210 374 36 1 209 374 317 246 367
4 36 373 358 348 439 4 16 351 4 19 988 309 388 205 342 c72 502 381 396 369 546 344 388 494 322 383 524 496 389 44 1 29 1 312
514 610 389 473 301 364 352 383 539 4 14 627 351 489 454 433 509 389 39 1 485 491 470 513 342 4 23 660 909 388 408 389 349
537 490 482 25 1 352 353 412 506 5 14 4 14 306 36 1 462 440 403 659 346 834 486 487 431 404 486 307 442 299 500 483 312 279
515 54 1 479 4 19 379 369 465 428 318 311 5 16 285 4 14 315 442 522 406 435 556 294 478 378 332 5 24 489 548 347 353 39 1 473
606 498 295 244 504 478 477 497 611 732 296 320 54 3 456 373 520 524 570 567 485 486 469 429 458 448 621 620 335 471 421
925 899
600 808 649 488 691 664 867 701 634 542 573 57 3 647 634 666 478 752 751
800 799 396 509 502 697 587 562 303 526
109
110
7 28 1034 824 844 723 6 13 697 750 744 656 666 745 706 789 657 706 7 28 978 774 899 782 589, 673 7 35 778 812 749 696 765 664 828 972 9 24 825 69 1 781 665 739 610 855 525 703 588 697 728 595 812 884 803 644 898 829 751 796 575 687 74 1 940 658 1029
111
112
113
4 39 466 392 552 451 413 508 904 869 848 765 731 456 476 592 702 683 526 647 439 534 617 358 590 438 752 4 18 4 19 532 494
793 1074 705 960 838 758 673 855 642 678 730 735 712 499 633 669 805 833 797 664 583 543 618 738 616 1040 826 618 690 579 751 1019 773 1046 554 800 724 7 19 733 765 650 573 642 554 728 606 615 812 835 633 788 823 7 17 1046 868 621 760 771 74 1 824
114
115
856 1022 825 1039 664 508 916 610 627 627 718 591 940 906 589 904 832 1175 1059 950 723 805 800 637 1075 913 784 853 702 945 1054 1083 821 1205 772 1066 869 1196 853 809 519 1042 836 872 827 943 1042 965 837 1135 860 1073 999 1090 788 627 775 1296 673 1077
9
0,
w
APPENDIX B (continued) Mean annual precipitation, in millimeters, after supplementing the missing data Station number Year 116
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
681 7 10 387 542 648 580 684 791 792 747 605 568 40 3 534 734 664 1290 428 676 388 652 601 660 734 575 594 631 548 769 646
117
118
119
708 684 701 595 900 591 473 725 683 746 825 823 793 710 831 886 568 864 841 733 833 900 1079 756 944 1167 664 811 775 856 683 1032 1031 642 1176 919 683 774 859 813 792 871 495 698 554 804 948 963 887 1333 776 602 808 1222 801 676 1052 811 736 930 805 1097 728 721 725 920 626 874 861 726 821 1008 903 705 686 882 778 756 554 771 776 541 519 491 801 875 1032 1120 873 732
120 751 472 695 8 36 695 795 835 923 702 826 856 879 9 17 874 725 966 749 1068 849 846 1031 602 622 767 699 430 203 474 808 806
121
122
123
1163 1164 1033 1053 1033 798 1305 1035 1245 59 2 1162 808 1138 974 1178 945 1481 1265 1047 836 806 703 689 976 1287 1195 660 578 990 79 2 742 1179 981 1071 944 798 970 9 18 947 848 895 808 811 558 948 812 671 749 435 755 544 621 757 744 356 1128 576 1450 535 1048
970 870 532 753 881 690 711 788 932 740 727 619 1187 756 681 987 728 940 789 919 654 875 698 847 865 806 877 420 842 873
124
125
126
127
128
1398 871 1709 942 1261 710 1005 652 1332 663 1305 973 1104 1124 1010 921 1343 859 1065 756 1035 9 19 1125 799 1144 1135 1354 634 716 1132 980 1218 856 1116 808 1308 1150 1027 926 1381 1280 1026 957 1257 973 1420 1331 1031 1200 542 720 1441 1042 1157 979 1398 1418 1439 1027 1040
964 1162 521 943 1174 1057 1292 1414 1726 159% 1270 1495 1241 1447 1170 1240 1756 1430 1427 916 1214 1374 1179 1784 1460 1581 1790 1032 1494 1339
1010 974 4 19 923 1080 814 724 1221 1432 1217 1163 1238 1111 989 899 997 945 870 1096 944 919 918 1037 1162 1113 786 975 665 9 57 957
1318 1156 1081 1165 944 892 1389 957 1189 1352 1068 1159 1487 985 1094 1181 1117 1328 1031 1210 1366 1211 1197 1100 1387 1275 1365 1004 1429 1033
129
130
642 1091 1066 774 8 10 764 8 16 967 9 34 754 975 582 1139 859 1024 847 953 964 1187 847 822 1033 754 960 1456 947 1040 638 878 554 829 684 1491 533 1067 655 9 37 746 973 595 1173 947 89 5 661 1458 371 1147 990 1413 708 1101 46 3 485 1110 921 1096 1453 955 1118 890
131
132
133
134
890 932 1070 822 692 1001 655 755 631 872 929 699 823 1009 987 705 670 966 1173 986 1074 1103 516 804 682 1068 979 456 797 129% 712 987 1163 687 835 833 869 848 1156 606 830 885 96 1 1197 1083 981 751 845 1164 1046 787 941 777 1070 1172 1197 1006 962 530 1174 787 799 526 638 825 855 632 591 836 989 1395 1101 1004 1445 965 957 1081 1142 877 996 1310 971 800 1085 1297 953 882 1031 1174 881
1351 1607 1195 1289 1150 797 1359 1140 1260 1140 1098 1112 1277 964 1085 850 859 1005 1256 927 1356 1317 1084 1205 1016 1278 1356 1502 1306 1463
APPENDIX B (continued) Mean annual precipitation, in millimeters, after supplementing the missing data Station number Year
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
135
136
89 1 815 740 911 1117 875 1256 886 922 990 9 18 904 840 670 901 704 826 1056 1048 1110 1312 806 1152 1259 1592 1196 1080 899 856 846
1153 1363 1249 1394 1110 1078 1056 1338 1265 1316 1550 1680 1401 84 1 1309 1368 1073 1118 1340 1767 1504 1272 1440 1385 1665 1396 1444 1724 1435 1894
137
138
139
140
141
142
1366 1650 1078 1359 832 1438 975 1642 742 1328 693 1351 1194 1424 1317 1723 1200 1381 1044 1321 968 1499 768 1485 980 1455 784 1351 946 1657 695 1168 1054 1505 1041 1322 1019 1457 1164 1399 933 1460 923 1508 968 17 13 931 1830 1300 1403 1006 1646 961 1554 820 1152 983 1502 1294 1502
999 1062 1408 1368 1264 1089 1273 1311 1382 1355 1240 1015 1161 1293 1326 1294 1243 1409 1383 1181 1347 1398 1249 1642 1473 1456 1243 798 957 1089
1703 1424 1243 1613 1276 1143 1476 1207 1488 1291 1503 1133 1178 1500 1225 1250 1415 1294 1507 1267 1138 1463 1291 1733 1566 1552 1276 819 977 1111
1645 1250 1167 1253 1476 1107 1198 1369 1657 1244 1183 1203 1065 1269 1577 668 1487 2252 1511 1201 1151 1344 1392 1606 1174 1555 1669 781 935 1191
1320 1180 1174 1376 1270 931 1099 1337 1333 1235 1342 1290 1005 1397 1573 1216 1238 2009 1522 1255 1685 1035 1386 1648 1019 1333 1033 824 986 1222
143
144
1188 1474 1094 1259 1218 1327 1248 1866 1138 1509 994 1241 1457 1376 1164 1176 1651 1432 1306 1160 1067 1513 1509 1513 914 1334 1262 149 1 1007 1367 953 1393 1458 1632 1576 1879 1021 1756 1400 1594 1034 1417 9 55 1442 1150 1481 1421 1057 1408 1316 1352 1005 1358 1453 57 1 1293 669 1237 544 1257
145
146
147
1121 1165 1397 1200 697 1035 1657 1024 1452 1768 967 1449 1463 1111 1331 1002 600 1240 542 1360 1483 1522 855 1408 1457 1270 1543 1809 1080 1793 902 1560 1949 1726 903 1654 685 1256 1279 15 19 1023 1533 1544 6 10 1326 733 1229 1377 1518 1259 1300 1629 870 1583 917 1427 1563 7 30 1217 1505 1650 975 1484 1368 820 1509 1772 816 1520 1894 1408 1698 1897 7 16 1438 1874 1067 1930 1622 923 1528 1484 574 1374 1389 974 1447 1452 1084 1537
148
149
150
151
152
153
1271 1029 1323 1392 1118 1020 1190 1525 1578 1389 1326 1154 1318 1289 981 1116 1030 1247 1439 1167 1086 1393 1288 1561 1437 1306 1395 1197 1304 1709
1360 971 1227 1427 1055 1066 1173 1093 1077 1096 1337 979 1072 1464 1063 806 1058 1157 1268 936 1006 1220 1274 1531 989 1251 1086 878 1127 1023
666 649 863 883 804 492 587 774 768 770 636 584 493 685 1287 730 610 746 608 630 592 714 636 939 904 1076 1717 570 695 549
1224 920 1096 1868 1642 983 1170 1125 1390 1411 1347 1010 1011 1570 1266 1261 1222 1312 1440 873 1196 1267 1405 1643 1498 1363 1044 1145 1336 1684
1045 1114 1396 1429 1252 1098 1331 1371 1192 1190 1118 1030 1336 1459 1047 1263 1426 1141 1080 747 1153 1262 1225 1629 1634 1488 1445 1316 1235 1185
1194 1088 1260 1430 1305 488 1146 1047 1194 1261 1136 1195 1200 1449 1133 1106 1123 1474 1663 1556 968 1175 1227 1808 1550 1083 1330 1284 1246 1169
IP 0, W
APPENDIX B (continued) Mean annual precipitation, in millimeters, after supplementing the missing data Station number Year
1 2 3 4 5 .6
7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 a5 26 27 28 29 30,
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
1205 9 38 1457 1496 1458 997 481 1449 1485 1156 1480 1235 1147 1507 1437 1165 1223 1306 1422 1306 1273 1387 1500 1822 1509 1807 1474 1225 1671 1334
1088 1209 1394 1431 1298 1041 1359 1324 1554 1511 1253 969 1135 1588 1035 1288 1237 1281 1450 1425 999 1245 15 17 1554 1074 1288 1386 1114 1407 1258
1006 1349 1136 1520 1354 1177 1548 1206 1514 1382 1249 1265 1048 1331 1067 1137 1069 1342 1234 1072 1243 1317 1538 1774 1495 1589 1578 1163 1297 1054
1389 1277 1247 1539 1396 1128 1505 1351 1421 1592 1343 1141 1222 1910 1411 1109 1178 1268 1154 1104 1455 1231 1443 1605 125 1 1359 1345 1296 1431 1509
7 10 1110 980 1161 948 707 1295 1126 1099 1168 997 903 998 1008 1013 949 856 1159 1057 913 1013 740 932 1495 1056 1333 1041 967 1234 1054
1144 865 1457 1283 1492 1018 1196 1228 1340 1361 1113 865 1175 1388 1126 1073 1051 1239 1023 1097 1023 1208 1249 16 16 1483 1561 1336 1115 1282 1485
1079 1152 1325 1242 1037 981 1004 1299 1262 1384 1064 799 997 1507 1349 1070 881 1071 1008 1073 1026 1195 1212 1778 1469 1587 1245 109 1 1253 1445
1323 1088 1584 1612 1432 9 38 1558 1322 1316 1272 1437 1211 1362 1720 1278 1082 1306 1163 1247 1245 1310 1217 1379 2073 1427 1960 1347 1250 1596 1516
1145 1263 1499 1679 1217 956 1440 1180 1276 1433 1243 1150 1096 2012 995 1219 1148 1196 1125 1208 1103 1487 1352 1746 1382 1474 1346 1180 1380 1532
1006 1340 1133 1029 1400 972 963 1309 1101 1481 1022 890 1365 1775 1207 923 1144 946 887 921 976 1146 1042 1687 1149 1632 1377 951 1040 1256
1231 1064 1261 1315 1166 9 16 1066 1194 1161 1392 1299 9 58 1194 1828 1048 1102 1353 1235 1362 1212 1258 1257 1423 1806 1231 1642 1111 1081 1477 1359
1126 1045 1555 1403 1382 1040 1336 1162 1375 1355 1384 1367 1305 1932 1470 1133 1282 1321 1115 1041 1113 1131 1476 1876 1432 2075 1503 1351 1249 1569
1249 1105 1096 1390 1359 1274 1296 870 970 1045 1104 803 1367 2198 930 1115 1238 845 1289 1193 979 1215 984 1684 1074 1327 1313 1033 1256 1387
940 935 1494 1474 1216 1220 1752 1438 1264 1509 1380 1341 1206 1504 1048 1303 1334 1556 1292 1211 1187 1399 1095 1691 1093 1692 1328 1544 1684 1457
1009 984 1378 1361 1342 1247 1443 1156 1195 1382 1230 926 986 1361 1043 1080 1100 966 1117 1279 1111 1151 1095 1782 1072 1627 1447 1279 1417 1071
1119 1283 1385 1326 1336 834 1244 1206 1136 1329 1121 995 1250 1630 1051 1180 1276 1289 1106 1456 1246 1315 1134 2125 1780 1255 1293 1383 1331 1548
1129 1355 1323 1491 1166 1164 1310 1138 1327 1392 1284 1344 1353 2025 1321 1236 1396 1409 1233 1110 1350 1563 1395 1692 1370 1654 1465 1044 1582 1410
1137 1079 1421 1527 1470 1214 1331 1228 1653 1468 1247 1114 1330 1637 1539 1054 1283 1385 1419 1426 1267 1345 1637 1981 1753 1795 1635 1304 1528 1580
1164 1393 1429 1624 1384 1360 1456 1162 1426 1642 1604 1564 1385 1896 1306 1664 2116 1452 1225 1458 1328 1564 1398 1957 1620 1805 1553 1400 1795 1408
APPENDIX B (continued) Mean annual precipitation, in millimeters, after supplementing the missing data Station number Year 173 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
174
175
176
177
178
1294 1056 1051 968 1076 1163 1572 1345 1272 1273 1501 1178 1335 1431 974 995 900 981 1348 1321 1223 853 1096 1271 1181 1329 1248 1468 1376 1283 10 10 1264 1233 945 1231 1336 1305 1395 1146 1662 1495 1581 988 922 922 1080 1260 983 1096 1057 1220 1037 1453 85 1 980 1110 1196 1284 1079 1427 1193 1072 1135 1340 1194 1133 1335 969 848 2087 2004 1647 1402 1335 1228 1495 1661 1312 1188 1424 1182 1101 1314 1185 107 1 1356 1117 1403 1487 1229
1371 1316 1406 1532 1305 946 1377 1023 1284 1459 1226 1199 1056 1693 1017 951 10 19 1430 106 1 1292 1175 1435 1248 25 18 1328 1612 1398 1281 1327 1457
1398 1370 200 1 1426 1712 1123 1314 1315 1407 1868 1411 1329 1621 2152 1304 1320 1583 1625 1430 1615 1345 1569 1644 2109 1608 2005 1410 1569 1945 1985
1140 1191 1310 1312 1120 89 3 1282 1215 992 1363 1338 1026 1383 1946 1159 1191 930 1672 1180 1794 1168 1384 1478 1777 1622 2406 1897 1689 1882 1365
179
180
181
182
1344 1183 1339 1155 2397 1606 1190 1384 1417 1424 1021 1115 1380 1629 1519 1390 1627 1191 1331 1378 1389 1181 1292 106 1 1493 1104 2444 1585 1264 1887 1342 1159 1530 1201 1368 1608 1399 1281 1542 1306 1171 1195 1540 146 1 1637 1427 1941 1909 1563 1307 1923 2169 1438 1689 1533 1337 1884 1250 1927 1352
1571 1525 1646 1420 1366 1103 1513 1288 1387 1542 1177 1281 1429 1797 1180 1418 1352 1802 1493 1310 1347 1470 1516 2142 1692 1972 1751 1480 1464 1628
1170 1138 1393 1445 1293 1082 1433 1346 1301 1127 1217 1008 1307 20 10 1291 1226 944 1489 1236 1086 1119 1132 1589 2226 1558 1466 1603 1188 1531 1413
183
184
1274 1216 1302 1234 1628 1629 1509 1383 1287 1433 1066 1099 1626 1452 1370 1544 1401 1158 1317 1415 1219 1181 1031 1189 1439 1012 1852 1981 1331 1176 1298 1242 1160 1087 1534 1348 1397 1237 2059 1287 1829 1147 1980 1458 2260 1395 2097 1847 1658 1420 1535 1972 1458 1616 922 1239 1085 1371 1066 1343
185
186
187
1047 882 974 1006 1028 1299 1000 1373 1703 1311 1175 1306 1285 1287 1209 884 1025 1014 1170 1516 1325 942 1041 1204 1092 1569 1123 970 1947 1143 1030 1402 1148 743 1108 1048 1036 1189 1444 1556 1940 1656 1040 1121 1050 943 1243 1091 588 1021 1146 953 1301 1452 1169 1329 1134 1493 1575 1500 1102 1333 1055 1078 1422 1238 1359 1557 1266 1765 1620 1543 1192 1320 1332 1444 1628 1381 1607 1283 1579 1150 1011 1137 1187 1199 1099 1355 126 1 1338
188
189
190
191
1110 1236 1413 1484 1954 1719 1586 1463 1743 1836 1249 1260 1610 1758 1279 1077 1420 1574 1509 1710 1305 1356 1185 1099 1191 1680 2074 2219 1500 1512 1609 1536 1288 1253 1670 1328 1471 1844 1584 1990 1514 1222 1628 1244 1727 1326 2276 1967 1767 1665 2046 2002 1781 1886 1163 1461 1394 1951 1179 1783
944 1026 1498 1416 1955 1439 1661 1614 1150 1561 1357 957 1438 2087 1374 1330 969 1432 1571 1655 1524 1365 1291 1289 1536 1523 1577 1373 1307 1512
1079 999 1600 1698 1828 1521 1837 1446 1534 1722 1411 1128 1783 1978 1567 1374 1046 1519 1754 1705 1722 1444 1285 1834 1641 1944 1938 1458 1368 1569
P
APPENDIX B (continued)
00
m
Mean annual precipitation, in millimeters, after supplementing the missing data Station number Year 192 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
193
194
195
738 785 881 705 846 654 1136 985 1134 1003 908 1111 1116 1235 1317 817 85 1 763 1503 1338 1522 982 1185 1104 1002 1044 1073 1209 1280 1473 821 975 969 907 767 904 1136 1130 1087 1387 1349 1259 834 877 797 962 692 709 689 1105 949 944 1329 656 989 840 938 925 1250 1153 1122 1187 1104 965 1056 1056 1063 1114 1151 1371 1566 1199 980 1166 1055 1490 1154 1471 919 1020 1082 1049 9 19 915 1161 1320 1259 1183 86 3 759
745 806 915 1495 875 689 1236 1287 1000 9 18 742 7 15 794 1532 823 885 999 999 707 1194 959 763 1259 774 599 909 811 600 632 660
196
197
963 9 39 762 790 1069 1265 942 993 1200 1238 927 1028 1535 1523 1196 1087 946 1098 1310 1720 85 1 1006 818 996 106 1 1132 1252 1537 978 826 947 845 87 1 1029 890 1126 811 1217 1281 1783 954 1825 929 9 50 1248 1363 1213 1296 1341 1099 1633 1242 1125 1066 853 857 1280 1226 1046 1111
198
199
200
1049 954 1273 986 1271 870 1403 1108 995 1733 821 934 1111 1727 865 894 927 1057 1042 1066 1101 956 1519 1489 1196 1435 1118 888 1203 1291
1231 954 1206 1032 1181 1005 1335 1186 996 1576 1065 878 1070 1421 923 1087 983 975 1032 978 979 1182 1395 1295 1063 1595 1146 975 1774 1139
201
202
203
204
205
206
786 689 1377 946 852 1440 1578 1128 1430 855 1109 708 1104 823 1103 938 1157 1053 1185 731 1446 910 858 1253 742 1217 1854 1520 697 1015 969 1281 936 1127 1637 1101 849 1318 1556 1141 897 1036 798 1149 846 1159 1365 1151 1606 1040 1678 1228 946 1137 781 845 780 883 743 9 34
1063 1006 1050 1090 1165 849 1111 931 975 1321 995 824 1118 1378 869 1078 964 943 1013 1252 924 887 1388 1204 1165 1315 1100 871 924 860
928 1061 1069 1450 1321 1029 901 1040 709 977 1037 910 1041 1401 897 1199 1171 1106 1173 1362 924 887 9 10 1204 1165 1315 1100 871 924 860
1206 994 1307 727 1304 983 1306 1064 1178 1524 fO 57 872 1127 1531 1041 1253 1175 1150 1056 1048 1251 1272 1341 1302 1197 1315 1146 1037 1257 935
1166 979 966 1486 1217 777 947 1059 951 9 16 704 914 801 1156 794 1034 1082 922 1076 109 5 1233 872 800 1000 1016 1281 975 897 1032 1148
APPENDIX C - Monthly r a i n f a l l , i n mm and i n p e r c e n t a g e of t h e a n n u a l r a i n f a l l S t a tion No.
Name
Month of t h e y e a r Jan.
Feb.
Mar.
Apr.
May
June
July
Year Aug.
Sep.
I
Oct.
Nov.
Dec.
S i d i Barrani
35.0 22.3
26.0 16.6
14.5 09.2
03.0 01.9
02.5 01.6
0 0
0 0
0 0
0 0
14.5 09.2
24.0 15.3
37.5 23.9
Borollos L i g h t House
47.0 24.8
35.0 18.5
16.0 08.5
05.0 02.6
02.0 01.1
0 0
0 0
0 0
0 0
07 .O 03.7
33.0 17.5
44.0 23.3
Sallum
22.0 20 .o
17 .O 15.3
10 .o 09 .o
02.0 01.8
03.0 02.7
0
0
01.0 00.9
09 .o 0 8 .O
25.0 22.5
21.0 18.9
Damietta L i g h t House
30 .O 24.3
22.0 17.7
14 .O 11.3
03.0 02.4
02.0 01.6
0
0
0
0
0 0
07.0 05.6
18.0 14.5
28.0 22.6
124
Damietta
27.0 25.8
20 .o 19.0
10.0 09.5
03.0 02.8
02 .o 01.9
0 0
0 0
0 0
00.5 00.5
06.0 05.7
15.5 14.8
21.0 20.0
105
Rosetta L i g h t House
46 .O 26.4
31.5 18.2
12.5 07.2
03.0 01.7
00.8 00.5
0 0
0 0
0 0
00.3 00.2
07.5
23.0 13.2
49.0 28.3
174
04.3
Rosetta
6 1 .O 30.2
35.0 17.3
12 .o 05.9
06.5 03.2
04 .O 02.0
0 0
0 0
0 0
00.5 00.2
10 .o 05.0
24 .O 11.9
49.0 24.3
202
Mersa Matruh
38.0 25.0
22.0 14.5
12.5 08.2
03.0 02.0
02.0 01.3
0 0
0 0
0 1 .o 00.7
14 . O 09.2
26.0 17.1
33.0 21.7
152
Tolombat el Boseili
42.0 28.4
24.5 16.6
06.5 04.4
02.5 01.7
01.5 0 1 .o
0 0
0 0
0
0
0
06.5 04.4
23.0 15.5
41.5 28.0
148
lo
To lomba t e l Tolombat
49.5 27.6
34.5 19.3
0 8 .O 04.5
01.0 00.6
0 0
0 0
0 0
0 0
07.0 03.9
23.5 13.1
54.5 30.4
179
11
Edfina
35.5 22.9
36.0 23.2
12 .o 07.7
03.5 02.3
03 .O 01.9
0
0 0
0 0
0 0
09 .o 05.8
19.0 12.3
37.0 23.9
155
12
P o r t Said
15.0 19.6
13.5 17.5
08.5 11.o
03.5 04.5
02.0 02.6
0
0
0
0 0
06.0 07.8
10.5 13.6
17.5 22.8
77
0
13
Sinv
16.5 25.0
11.5 17.5
06 .O 09.1
03.0 04.5
03.0 04.5
0 0
03.0 04.5
07.5 11.4
22.7
1
3
5
7
0
0
0
00.5 00.3 0
0
00.5 00.6 0 0
0
0
0
00.5 00.8
01.0 00.9 0
0
15.0
157
111
66
APPENDIX C ( c o n t i n u e d ) Station No.
Name
4 iil
f!onth o f t h e y e a r Jan.
Feb.
Mar.
Apr.
May
June
July
Aug.
14
Kom e l Tarf a i a
47.5 29.7
33.5 20.9
08.0 05.0
02.0 01.3
00.5 00.3
0 0
0 0
0 0
15
Alexandria (Kom e l Nadura)
49.5 26.4
25 .O 13.4
11.0 05.9
03.0 01.6
02.0 01.1
0 0
0 0
0 0
16
Mex
44.0 25.9
26 .O 15.3
08.5
03.0 01.8
0 1 .o
05.0
00.6
0 0
0 0
0 0
17
Kafr e l Dawar
42.5 26.9
29 .O 18.4
10.0 06.3
03.5 02.2
0 1 .o 00.6
0 0
0 0
0
Kafr e l Sheikh
17.0 22.7
15 .O 20.0
08.2 10.7
02.0 02.7
02.0 02.7
0
0 0
01.0 01.3
19
E l Arish
17.5 18.5
18 .O
18.9
13.0 13.7
06.0 06.3
02.5 02.6
0 0
0
20
Sakha
19.5 24.1
16.5 20.4
09.0 11.1
03.5 04.3
02.5 03.1
0
0 0
21
Ras e l Dabaa
30.5 22.9
19.5 14.7
12.5 09.4
02.5 01.9
01.5 01.1
0
0
0 0
0
22
Mansura
12.0 21.8
10.0 18.2
07.0 12.7
03.5 06.4
03.5 06.4
00.5 00.9
0 0
0 0
23
Fuka
19 .o 19.3
16.0 16.2
09.5 09.7
02.0 02.0
03.0 0 3 .O
0 0
0 0
0 0
24
Damanhur
23.0 24.5
19.5 20.7
10.0 10.6
03.5 03.7
02.5 02.7
0
0
0
0
0 0
25
Amria
40.5 28.4
29.5 20.6
07.0 04.9
02.0 01.4
0 1 .o 00.7
0 0
0 0
0
26
Borg el-Arab
40.5 26.8
23.0 15.2
06.0 04.0
02.0 01.3
01 .o 00.7
0
0 0
0
0
0
0
0
0
0 0 0 1 .o 01.2 0
0
0
Sep. 0 0
Oct.
Nov.
Dec.
Year
04.5 02.8
18.0 11.3
46.0 28.7
160
06.5 03.5
32.5 17.4
56.5 30.2
187
0 0
06.5 03.8
29.0 17.0
52.0 30.6
170
0 0
06.5 04.1
21.0 13.3
44.5 28.2
01.5 02.0
04.5 06.0
08.5 11.3
15.5 20.6
75
0
04.5 04.7
14.5 15.3
19.0 20.0
95
0 1 .o 01.2
05.0 06.2
09.0 11.1
14.0 17.3
81
00.5 00.4
05.5 04.1
24.0 18.0
36.5 27.5
133
07.3
.O
06.5 11.8
08.0 14.5
55
09.0 09.2
17.0 17.3
22.5 22.8
93.5
0 0
04 .O 04.3
10.0 10.6
21.5 22.9
94
0 0
02.5 01.7
18.0 12.6
42.5 29.7
143
0 0
09 .o 06 .O
31.5 20.8
38.0 25.2
15,
0 1 .o 00.5
0
0 0 00.5 00.5
04
158
0
APPENDIX C ( c o n t i n u e d ) Month of t h e y e a r
Station Name
No.
Jan.
Feb.
Mar.
Apr.
27
Hammam
28.0 25.4
15.5 14.2
05.5 05.0
02.0 01.8
28
Kafr e l Zayyat
12.5 21.2
11.0 18.6
07.0 11.9
02.0 03.4
29
Tanta
10.0 20.8
09.0 18.8
04.0 08.3
30
Faqus
11.5 21.7
07.0 13.2
31
E l Qusseima
08.5 18.0
32
Zaeazig
33
May
June
July
Aug.
Sep.
Oct.
Nov.
Dec.
Year
0 0
0 0
0
02.0 01.8
07.0 06.4
22.0 20.0
28.0 25.4
01.5 02.5
0 0
0
0 0
0 0
03.5 05.9
09.5 16.1
12.0 20.4
59
0
03.5 07.3
04.0 08.3
0
0 0
0 0
0
04.5 09.4
05.0 10.4
08.0 16.7
48
0
06.5 12.3
02.5 04.7
02.0 03.8
0 0
0 0
0 0
06.0 11.3
08.5 16.0
08.5 16.0
53
05.0 10.6
11.0 23.4
04.5 09.6
02.5 05.3
0
0
0
0
0 0
02.0 04.3
06.0 12.8
07.5 16.0
47
05.5 17.8
06.5 21.0
04.0 12.9
02.0 06.4
02.0 06.4
0
0
0
0
02.0 06.4
04.0 12.9
05.0 16.2
Shebin e l Kom
07.0 20.6
07.5 22.1
02.5 07.4
02.0
05.8
04.0 11.8
0 0
0 0
0
0
02.0 05.8
02.5 07.4
06.5 19.1
34
34
El-Hassana
04.0 14.7
03.0
11.1
05.5 20.4
02.0 07.4
01.5 05.6
0
0
0 0
0 0
0 0
01.5 05.6
06.5 24.1
03.0 11.1
2,
35
Benha
04.0 18.2
03.0 13.6
0 3 . 0 . - 01.0 13.6 04.6
01.0 04.6
0 0
0 0
0
0 0
01.5 06.8
03.5 15.9
05.0 22.7
22
36
Wadi e l Natrun
04.5 11.8
04.5 11.8
02.5 06.6
01.0 02.6
05.0 13.3
0 0
0 0
0 0
00.5 01.3
10.0 26.3
09.5 25.0
38
37
Fayed
02.0 09.1
02.0 09.1
04.5 20.4
01.0 04.5
02.5 11.4
0 0
0
0 0
0 0
00.5 02.3
02.0 09.1
07.5 34.1
22
0
38
Delta Barrage
03.0 16.7
04.0 22.2
03.0 16.7
00.5 02.8
01.0 05.5
0 0
0 0
0 0
0 0
02.0 11.1
00.5 02.8
04.0 22.2
39
Giza
04.5 17.6
04.0 15.7
03.5 13.7
02.0 07.8
01.5 05.9
0 0
0 0
0
0 0
02.5 09.8
02.5 09.8
05.0 19.7
0
0
0
00.5 01.0 0 0
0
0
0
0
0
0
0
0
0
00.5 01.3
llo
31
25.5 4 W Y
APPENDIX C (continued) Stat ion No.
Name
Month of the year Year Jan.
Feb.
Mar.
Apr.
May
June
July
Aug.
Sep.
Oct.
Nov.
Dec.
40
Kuntella
06.0 27.3
02.5 11.4
02.0 09.1
01.5 06.7
02.0 09.1
0 0
0 0
0 0
0 0
02.0 09.1
02.0 09.1
04.0 18.2
22
41
Suez
02.0 09.5
03.0 14.3
03.0 14.3
01.0 04.8
01.0 04.8
0 0
0 0
0 0
0 0
02.5 11.9
04.5 21.4
04.0 19.0
21
42
El-Nekhl
05.0 22.7
05.0 22.7
04.0 18.3
02.0 09.1
01.5 06.8
0 0
0 0
0 0
0 0
00.5 02.3
01.0 04.5
03.0 13.6
22
43
Attaqua
01.0 06.1
02.0 12.1
01.5 09.1
00.5 03.0
05.5 33.3
0 0
0 0
0 0
0 0
01.5 09.1
01.5 09.1
03.0 18.2
16.5
44
Helwan
05.5 19.3
04.0 14.0
04.0 14.0
02.5 08.8
02.5 08.8
0 0
0 0
0 0
0 0
01.0 03.5
03.5 12.3
05.5 19.3
45
El-Themed
03.0 09.1
06.0 18.2
04.5 13.6
01.5 04.5
02.0 06.1
0 0
0 0
0 0
0 0
03.0 09.1
10.0 30.3
03.0 09.1
46
Shakshuk
01.5 15.0
01.5 15.0
01.0 10.0
01.0 10.0
01.0 10.0
0 0
0 0
0 0
0
0
00.5 05.0
01.0 10.0
02.5 25.0
47
Fayoum
01.0 07.1
02.0 14.4
02.0 14.4
01.0 07.1
01.0 07.1
0 0
0 0
0 0
0 0
01.0 07.1
01.0 07.1
05.0 35.7
14
48
Ras el Nagb
04.0 08.7
04.0 08.7
04.5 19.6
02.0 08.7
02.0 08.7
0 0
0 0
0 0
0 0
01.0 04.3
02.0 08.7
03.5 15.2
23
49
Siwa
01.0 10.0
01.5 15.0
01.0 10.0
01.0 10.0
01.5 15.0
0 0
0 0
0 0
0 0
0 0
01.0 10.0
03.0 30.0
50
Beni-Suef
01.0 12.5
02.0 25.0
01.0 12.5
00.5 06.3
00.5 06.3
0 0
0 0
0 0
0 0
0 0
51
Baharia
0 0
0 0
0 0
0 0
0 0
0 0
52
Tor
0 0
0 0
0 0
0 0
0 0
0 0
01.5 12.5
01.7 33.3 02.0 16.7
0 0
02.0 16.7
00.5 10.0 0 0
01.0 08.3
28'5 33
10
10
03.0 37.4
o8
01.3 26.7
01.5 30.0
o5
02.0 16.7
03.5 29.1
12
0 0
h
m h
s
h
m s
:
V
n >
0
z
0
Y
0
a s
vl
M
4
h
d
2
a
R
Z
m
0)
c,
E'
L4
n
m
h
--.
4
h
a
c 3
s
s c ,
5 u
o c c, C
2
E
o
L)
d
m
Y
vl
0
z
m 0
0
r w
0 0 O N
0
n l
0
o m l m r
0 0
0 0
rlm
O N
Y 9 Y ? 9'9
o w orl
4 m
m
0
~
0
0
~
l
m
o
o
0
0 0
o
o
0 0
0 0
n
0N O2 0 0
0
wln o w
0 0
o
N O
?? ?? ?? o m
o n
?? ??
4 0
N O 0 -
r
m 0
n
. .
rom w w
O N
ION
99 o m
0
0 0
0
l
0 0
0 0
r
0 0
O N
? ? 9'9 N O
o m
0 0
0 0
o m rl
0 0
??
0
Y?
0 0
?? ??
1'9
Y? 02
Y? 4 0
0 0
0 0
0 0
o w
410
O N
rl
40
0 0
d o
0 0
0 0
0 0
0 0
o m
0 0
0 0
0 0
0 0
0
0 0
0 0
0 0
0 0
0 0
0 0
0 0
0 0 0 0
0 0
0
0 0
0 0
0 0
l n. m.
0 0
O2
4 0
93
0
0 0
0 0
N. w. 0 0
0 0
0 0
0 0
0 0
"9 o w
0 0
0 0
0 0
0 0
0 0
0 0
0 0
0 0
0 0
0
0 0
0 0
0 0
0 0
0 0
0 0
0
0 0
0 0
0 0
0 0
0 0
0 0
0
0
0 0
0 0
0 0
0 0
0 0
0 0
0 0
0 0
0 0
0 0
0 0
0 0
0 0
0 0
0 0
0 0
0 0
0 0
0 0
0 0
0 0
0 0
0 0
0
0 0
0 0
0
0 0
0 0
0 0
0 0
0 0
Y? 0 0 02
0 0
00
0 0
0 0
o
0 0
?? do
O N
?Y
0 0 0
0 0
0 0
a a
-40 0"
0 0
m
n
rl
0 0
0 0
d
Z T
w g m m
U
0 0
0 0
0 0
0 0
0 0
??
0 0
o m
o w
0 0
0 0
0 04
m. N.
O N
9'9 rlm
0 0
h 1
r
0 0
d m
o m o. m.
rlm
o m
m h
49 3
r
l
P
10
Station
P
Month of t h e y e a r Year
No.
Name
Jan.
0 0
Feb.
0 0
66
Wadi H a l f a
67
Port Sudan
68
Abu Hamed
69
Gebeit
70
Sinkat
0 0
0 0
71
Kareima
0 0
0 0
72
Tokar
73
Taharniyam
0 0
0 0
74
Talguharia
0 0
0 0
75
Atbara
0 0
76
Zediab
77
78
06.5 05.3 0 0 01.5 01.2
21 .o 23.2
01 .o 00.8
0 0 01 .o 00.8
Mar.
0 0
00.5 00.4 0 0
Apr.
0 0
00.5 00.4 0 0
May
01 .o 40 . O 01 .o 00.8 01 .o 07.4
June
0 0 00.5 00.4 0 0
July
01 .o 40 .O
Aug.
0 0
Sep.
Oct.
0 0
00.5 20 .o
0 0
10 .o 08.2
08.0 06.6
03.5 02.7
02.0 14.8
09.5 70.4
01 .o 07.4
0 0
Nov.
0 0
62.0 50.9 0 0
03.5 02.8
09 .o 07.3
07.5 06.1
27.0 22.0
47 . O 38.2
13.0 10.6
08.0 06.5
02.5 02.1
0 0
02.5 02.0
09.5 07.6
08 .o 06.4
24.5 19.6
54 .o 43.2
17.5 14 .O
07.0 05.6
02 .o 01.6
0 0
0 0
01 .o 03.2
0 0
09 .o 29 . O
17 . O 54.9
03 . O 09.7
01.0 03.2
02.0 01.6
0 0
Dec.
0
28.5 23.5 0
01 . o 08 .o 0 0
0 1 .o 01.1
01.5 01.7
02.5 02.7
01 .o 01.1
05.0 05.5
03 . O 03.3
01 .o 01.1
08.5 09.4
24 .O 26.5
01.0 01.1
02.0 02.1
07.0 07.4
04.5 04.7
26 . O 27.3
34.5 36.3
12.5 13.2
06.5 06.8
01 .o 01.1
0 0
01.0 01.2
03.5 04.3
02.0 02.4
22 .o 26.8
34.5 42.1
14.5 17.7
04 . O 04.9
00.5 00.6
0 0
0 0
01.0 01.5
02.5 03.5
02 .o 02.9
19.5 28.5
36.5 53.3
06 .O 08.8
01.0 01.5
0 0
0
0 0
0 0
0 0
0 0
03 .O 04.6
02.5 03.8
21.5 33.1
31.5 48.5
06 . O 09.2
00.5 00.8
0 0
0
Abu-Deleig
0 0
0 0
0 0
01 .o 00.5
09 .o 04.1
09.5 04.3
66 . O 30 . O
96.5 43.9
31.5 14.3
06 . O 02.7
00.5 00.2
Khartoum G.C.
0 0
0 0
0 0
01 .o 00.6
04 . O 02.5
08.5 05.2
53.5 32.6
72.0 43.9
20.5 12.5
04.5 02.7
0 0
04 .O 04.4
18 .O 19.9
02.5 122 13.5 123 125 31 90.5
;
95
O
82
0
O
0 0
68.5 65 220 164
APPENDIX C (continued) Month of the year
Station
Year No.
Name
Jan.
Feb.
Mar.
Apr.
May
June
July
Aug.
Sep.
Oct.
156
0 0
327
0 0
199
0 0
259
0 0
254
01.5 00.3
0 0
431
04.5 02.2
0 0
0 0
202
47 . O 15.1
07.5 02.4
0 0
0 0
312
103.0 36.0
43.0 15.0
07 .O 02.4
0 0
0 0
286
128.0 33.2
137.0 35.5
57 .o 14.8
13.0 03.4
0 0
385
28.0 09.2
107.0 31.5
125.0 36.8
56.5 16.6
09.5 02.8
0 0
0 0
340
28.5 04.4
97.0 14.9
178.0 27.4
202.0 31.2
103.5 15.9
26.5 04.2
06 . O 00.9
0 0
649
14 . O 04.4
24.5 07.8
93.5 29.7
119.0 37.8
49 . O 15.6
12.5 03.9
0 0
0 0
315
05.0 03.2
05.5 03.5
48.5 31.1
68.5 43.9
25.0 16.1
03.0 01.9
03.5 01.1
13.0 04 .O
28.5 09.7
94.0 28.7
123.0 37.6
56.0 17.1
08.0 02.4
0 0
00.5 00.3
04 . O 0 2 .o
16.0 08.0
59.0 29.6
85.5 43.0
27.0 13.6
07 . O 03.5
0
0 0
02 .o 00.8
13.0 05 . O
26.5 10.2
80.0 30.9
93.0 35.9
35.5 13.7
08.5 03.3
0 0
0 0
0 0
11.0 04.3
16.5 06.5
79.5 31.3
98.0 38.6
42.5 16.7
06.5 02.6
Khashm el-G i rba
0 0
0 0
0 0
01.0 00.3
15 .O 03.5
39.0 09.0
146.0 33.9
152.0 35.3
67 . O 15.5
09.5 02.2
85
Geteina
0 0
0 0
0 0
01 .o 00.5
05.5 02.7
09.5 04.7
60.5 30.0
95.0 47.0
26 . O 12.9
86
Rufaa
0 0
0 0
0 0
03.0 01 .o
09.5 03.0
25.5 08.2
101.0 32.3
118.5 38.0
87
Wadi-Shair
0 0
0 0
0 0
01.5 00.5
10 .o 03.5
28.0 09.8
93.5 32.8
88
Wad-Medani
0 0
0 0
0 0
03.0 00.8
13 .O 03.4
33.0 08.6
89
Managil
0 0
0 0
0 1 .o 00.3
01.5 00.4
11.5 03.4
90
Cedaref
0 0
0 0
01.5 00.2
06 .O 00.9
91
Dueim
0 0
0 0
00.5 00.2
02.0 00.6
Khartoum
0 0
0 0
80
Kassala
0 0
0 0
81
J e b e l Aulia
0 0
0 0
82
Wadi Turabi
0 0
0
83
Kamlin
84
0 0
01.0 00.2
0 0
Dec. 0 0
00.5 00.3
79
Nov. 0 0
01.0 00.2
0 0 00.5 00.2
0 0
01 .o 00.3
P W
APPENDIX C ( c o n t i n u e d ) S t a tion No.
Name
Jan.
Feb.
Mar.
Apr.
~
~~
92
0)
Month of t h e y e a r May ~
0 0
0 0
0 0
June
Year
July
Aug.
Sep.
Oct.
Nov.
Dec.
~~
04 .O 00.9
22.5 05.2
40.5 09.3
120.0 27.6
165.0 37.8
65.5 15 . O
17.5 04 . O
01 .o 00.2
0 0
436
93
Wadi Haddad
0 0
0 0
01.0 00.2
04.5 01.1
13.5 03.3
42 . O 10.5
118 . O 29.3
140 . O 34.8
65.0 16.1
19 .o 04.7
0 0
0 0
403
94
Bara
0 0
0 0
0 0
00.5 00.2
10.5 03.5
20.5 06.9
91.0 30.6
116 . O 39.1
47.5 16.0
1 1 .o 03.7
0 0
0 0
297
95
El-Fasher
0 0
0 0
0 0
01 .o 00.3
10.5 03.5
15.5 05.2
95.0 32.0
133 . O 44.8
36.5 12.4
05.5 11.8
0 0
0 0
29 7
96
Mafaza
0 0
0 0
0 0
0 0
26.0 04.5
88 . O 15.3
167.0 29.1
183.0 31.9
86.0 15 . O
21 .o 03.7
03.0 00.5
0 0
574
0 0
0
0
00.5 00.1
03.5 00.8
25 .O 05.4
55.5 12 .o
127 .O 27.5
163.0 35.0
66.5 14.4
21 .o 04.6
01 .o 00.2
0 0
463
97
Sennar
D.S.
98
Geneina
0 0
0 0
01.0 00.2
04.5 00.8
27 . O 04.9
39 .o 07.1
164.5 29.9
233.0 42.4
72.5 13.2
08.5 01.5
0 0
0 0
550
99
El-Obeid
0 0
0 0
00.5 00.1
02.5 00.6
20.5 05.0
33.0 08 . O
115.5 28 . O
140 .O 34 . O
79.0 19.2
21 .o 05.1
0 0
0 0
412
100
Kos ti/Rabak
0 0
0 0
00.5 00.1
03.0 00.8
18.5 04.6
41.5 10.3
109.5 27.2
141.5 35.1
59 .O 14.6
29 . O 07.2
00.5 00.1
0
101
Singa
0 0
0 0
0 0
04.5 00.8
31 .O 05.3
73.5 12.7
163.0 28.1
191.5 33 .O
89 . O 15.3
26.5 04.6
01.0 00.2
0 0
580
102
Tendel t i
0 0
0 0
0 0
02.5 00.6
16 . O 04.1
32 . O 08.1
110.5 28.0
147 . O 37.3
65 . O 16.5
21 .o 05.4
0 0
0 0
394
103
Om Rwaba
0 0
0 0
0 0
00.5 00.1
14.5 03.8
29.5 07.7
129 .O 33.5
142.5 37.0
56.5 14.7
12.5 03.2
0 0
0 0
385
104
Rahad
0 0
0 0
0 0
02.0 00.5
21.5 05.3
40.5 123.0 10.0 30.3
131.5 32.4
65.5 16.1
22 .o 05.4
0
0 0
406
0
0
403
APPENDIX C ( c o n t i n u e d ) Station No.
Name
Month of t h e y e a r Jan.
Feb.
Mar.
Apr.
May
June
July
Aug.
Sep.
Oct.
Nov.
105
El-Nahud
0 0
0 0
0 0
04.0 0 1 .o
24.5 06.1
42.0 10.4
102.0 25.3
129 . O 31.9
8 2 .o 20.3
19.5 04.8
01.0 00.2
106
Jebelein
0 0
0 0
0 0
0 3 .O 00.7
21.5 05 . O
48.0 122 .o 11.1 28.3
124 .O 28.8
81.5 18.9
27.0 06.3
04.0 00.9
107
Nyala
0 0
0
0 1 .o 00.2
04 . O 00.8
32.0 06.4
60 . O 12.0
132.0 26.3
168.5 33.6
85.5 17 . O
19.0 03.7
0 0
108
Dilling
0 0
0
02.0 00.3
10.5 01.6
53.5 08.0
89.5 13.4
168.5 25.2
170.5 25.5
124 . O 18.5
49.5 07.4
01.0 00.1
109
Rashad
0 0
00.5 00.1
0 1 .o 00.1
14.5 01.9
70 . O 09.3
98.5 13.1
116 .O 15.4
191.5 25.4
162.5 21.5
93.5 12.4
06.0 00.8
110
Roseires
0 0
00.5 00.1
02 .o 00.3
14 . O 01.8
58.5 07.4
129.5 16.4
178 .O 22.7
216.5 27.6
147.5 18.8
33.5 04.3
05.0 00.6
06.5 01.2
33.5 06.2
81.5 15.1
133.0 144 .O 24.6 26.6
92.5 17.1
46.0 08.5
04.0 00.7
0 0
0 0
0
Dec. 0 0 0
0
O 00
8
0 0
112
Abri
0 0
02.0 00.3
00.5 00.1
10.0 01.4
63.0 08.7
100 .o 14 . O
163 .O 22.7
172.0 24.0
134.5 18.8
67.0 09.4
04.0 00.6
113
Kadugli
0 0
01.5 00.2
01.5 00.2
17 . O 02.2
83.0 10.9
120 .o 15.7
151.5 19.9
158.5 20.8
140.5 18.4
83.5 11.0
00.7
0
114
Talodi
0 0
0 0
05.0 00.6
21 .o 02.6
85.5 10.5
119 .o 14.6
169 . O 20.7
173 .O 21.2
151.O
18.5
86.0 10.4
07.5 00.9
0
115
Kurmuk
0 0
0 1 .o 00.1
05.5 00.6
26 . O 02.8
1 1 2 .o 11.9
140.5 14.9
166 .O 17.7
203.5 21.6
164 .O 17.5
105.0 11.2
15.5 01.6
116
Melut
0 0
0 0
02.5 00.4
14 . O 02.2
55 . O 08.5
94.5 14.7
134 .O 20.8
154 . O 23.9
117.5 18.2
69.5 10.8
00.5
117
Kodok
0 0
0
02.5 00.4
19 .o 02.6
65 . O 08.8
126.5 17 . O
152.0 20.6
174.0 23.6
123.0 16.7
71.5 09.7
04.5 00.6
0
404 431 502 669
111 Renk
0
Year
754 785 541 716
05.0
0 1 .o 00.1
03.0
762 817 940 644
O 0
738
A
APPENDIX C ( c o n t i n u e d )
ID
00
Month of t h e y e a r
Station
Year
No.
Name
Jan.
118
Malakal
0 0
119
Tonga
0 0
120
Abwong
0 0
121
Fangak
122
Feb. 0 0 01.0 00.1 0 0
Mar.
Apr.
May
June
July
Aug.
Sep.
Oct.
Nov.
Dec.
06.0 00.7
28.0 03.4
90.5 11.1
123.5 15.1
167.5 20.5
181.5 22.2
138.0 16.8
74 . O 0 9 .o
09 .o 01.1
05.5 00.6
26.0 03.0
86.5 10 .o
135.0 15.6
166.5 19.1
206 . O 23.7
152.5 17.6
84 . O 09.7
05.0 00.6
0
06 . O 00.8
26 . O 03.4
74 . O 09.7
112.0 14.7
166 . O 21.8
175.0 22.9
121.5 15.9
73.0 09.6
09.5 01.2
0
01'0 00.1
819 868 763
0
0 1 .o 00.1
07.5 00.7
38.5 03.6
115.0 10.7
147.5 13.7
229.5 21.4
242.5 22.6
176 . O 16.5
106.5 09.9
09 .o 00.8
0
Aweil
0 0
02.5 00.3
10.0 01.1
35.5 03.7
133 . O 14 . O
156.5 16.4
206 . O 21.6
203.5 21.4
149 .O 15.7
51.5 05.4
03.5 00.4
0
123
Nasser
0 0
01.0 00.1
11 .o 01.3
37.5 04.7
119.0 14.8
127.5 15.8
145.5 18.1
177.5 22.1
126 . O 15.7
50.5 06.3
08 .O 01.0
00.5 00.1
804
124
Raga
0 0
03.0 00.3
16 . O 01.3
54.5 04.6
144 . O 12.1
173.5 14.6
223.5 18.8
264 . O 22.2
202 .o 17.0
96 . O 08.1
11.o 00.9
01'5 00.1
1189
125
Meshra e r Rek
0 0
0 1 .o 00.1
05.0 00.6
26.5 03.2
75.0 09 .o
135.5 16.4
169.0 20.4
168.0 20.2
154.5 18.6
86.5 10.4
09 .o 01.1
0
0
1076 951
830
126
Cambeila
06.5 00.5
1 1 .o 00.9
35.0 02.7
77 .O 06 . O
163.0 12.7
171.5 13.3
223.0 17.3
258 . O 20 .o
182.5 14.2
99.5 07.7
48.5 03.7
12.5 0 1 .o
1288
127
Akobo
01 .o 00.1
03 .O 00.3
20.0 02.1
76.5 08.1
130.5 13.9
119.0 12.7
159.5 17.0
194 . O 20.6
144 . O 15.3
72.0 07.7
18.0 01.9
02.5 00.3
940
128
Wau
0 1 .o 00.1
05.0 00.4
23.5 02.1
64 . O 05.7
135.5 12.1
167.5 15.0
193.5 17.3
216.5 19.4
171 . O 15.3
126.5 11.3
14 . O 01.3
0
129
Tonj
0 1 .o 00.1
01.5 00.1
21.5 0 2 .o
69.5 06.6
129 . O 12.1
171.5 16.1
204 . O 19.3
205 . O 19.3
171.5 16.1
73.0 06.9
15.5 01.4
0
130
Chabe-Shambe
04 . O 00.5
17 . O 01.1
47.5
87.5 11.0
125.5 15.U
149.5
163.0 20.5
121.5 15.3
68.0
06.0
0U.6
10 .o 01.3
0
0
lU.U
O1.O 00.1
1118 1063 794.5
APPENDIX C (continued) Stat ion
Month of the year Year
No.
Name
Jan.
Feb.
Mar.
Apr.
May
June
July
Aug.
Sep.
Oct.
Nov.
Dec.
06.5 00.6
26.0 02.6
86.5 08.5
145 . O 14.2
155.5 15.3
174 . O 17.1
199.5 19.6
138.0 13.5
71.5 07 . O
15.5 01.5
O1.O 00.1
1019
06.5 00.7
10.5 01.2
34.5 03.8
80 . O
08.8
123.5 13.5
117 . O 12.9
141.5 15.6
146 . O 16.1
115.5 12.7
78.5 08.6
40 . O 04.4
15.5 01.7
909
Bor
02.0 00.2
08 .O 00.9
29.0 03.2
83.5 09.3
124 . O 13.7
118.5 13.1
139.0 15.4
136.0 15.1
129.0 14.3
101.5 11.2
26 .O 02.9
06'5 00.7
903
134
Amadi
03.0 00.3
18.5 01.5
49.0 04.1
130 . O 10.9
175.5 14.6
146.5 12.2
190.0 15.9
170.0 14.2
147.0 12.2
128.0 10.7
35 .O 02.9
05'5 00.5
1198
135
Terakekka
00.3 00.3
12.5 01.4
33.5 03.7
92.5 10.2
159.5 17.6
117 . O 12.9
136.0 15.0
128.0 14.1
105.0 11.6
81.0 09 .o
29 .o 03.3
09.0 00.9
905
136
Maridi
10.0
00.7
27.5 02.0
68 .O 05 . O
162.0 11.8
194.0 14.1
172.5 12.5
183.0 13.3
188.0 13.7
159 . O 11.5
135 . O 09.8
62.0 04.5
15 . O 01.1
1375
137
Juba
04.0 00.4
11.0 01.1
40.5 04.2
108.5 11.2
153.0 15.7
127.5 13.1
135 . O 13.9
136.5 14 . O
109 .o 11.2
99 .o 10.2
36.0 03.7
13*0 01.3
973
138
Yambio
14.5 01 .o
29 .o 02 .o
93.5 06.5
151.5 10.6
179 . O 12.5
161.5 11.2
171 .O 11.9
189.5 13.2
176.0 12.3
177 . O 12.3
74.5 05.2
19'0 01.3
1436
139
Loka
10.0 00.8
24 .O 01.8
64 .O 04.8
135 .O 10.3
160 . O 12.2
164.5 12.5
178.5 13.5
198 .O 15 . O
144.5 10.9
151 . O 11.4
62.5 04.7
02.1
140
Yei
10.0 00.7
30 .O 02.1
70.5 05 .O
154.5 10.9
183.5 12.8
159.5 11.2
179.5 12.7
195 . O 13.8
172.0 12.1
167 . O 11.8
76 .O 05.4
20'5 01.5
1418
141
Kajo Kaji
06.5 00.5
24.5 01.8
68.0 05.1
159 .O 12 .o
168.0 12.6
161.0 12.1
166.0 12.7
180.5 13.6
151.5 11.4
148 .O 11.1
72.0 05.4
01.7
23'0
1328
142
Nimule
07.0 00.6
24 . O 03.1
57.5 05 . O
122.5 10.6
152 .O 13.1
121.5 10.5
150 . O 12.9
156.5 13.5
137.5 11.8
129.5 11.1
79 . O 06.7
24'0 02.1
1161
143
Kitgum
06.5 00.5
28.5 02.3
77.5 06.1
133.5 10.5
179 . O 14.2
136 . O 10.8
176 . O 13.9
174.5 14.1
128.5 10.2
112.0 09.9
70.5 05.5
37'5 03 .O
1265
131
Rumbek
132
Pibor Post
133
0 0
1320
e
W
W
ul
APPENDIX C (continued)
0 0
Month of the year
Station
Year No,
Name
Jan.
Feb.
Mar.
Apr.
May
June
July
Aug.
Sep.
Oct.
Nov.
Dec.
144
Atua
22.5 01.6
49.5 03.5
85.0 06.1
143.0 10.2
141.0 10.1
121.5 08.7
149.0 10.6
192.0 13.7
169.0 12.1
180.0 12.8
102.5 07.3
145
Culu
11.5 00.8
46.5 03.0
88.5 05.8
173.5 11.3
203.0 13.3
146.0 09.6
162.5 10.6
224.0 14.6
172.0 11.2
61 . O 10.5
98.5 06.4
45’0 02.9
1532
146
Lloroto
09 .o 01.0
35 . O 04 . O
71.5 08.1
126.0 14.3
144.5 16.3
83.5 09.4
143.5 16.2
98.5 11.1
55.5 06.3
45 .O 05.1
47 .o 05.4
25’0 02.8
884
25.0 01.8
37 .O 02.6
89.0 06.3
175.0 12.4
190.0 13.5
129.5 09.2
126.0 08.9
216.5 15.4
158.5 11.3
37.5 09.8
82.0 05.8
42 .O 03.0
1408
147 Negetta Farm/Lira
46’0 1401 03.3
148
Aduku dispensary
41.0 03.2
50.0 03.9
87.5 06.8
139 . O 10.7
164.0 12.7
103.5 08 .O
108 .O 08.3
168.5 13 .O
139 . O 10.7
133 .O 10.3
98.0 07.6
62.5 04.8
1294
149
Katakawi
18.0 01.6
39 .O 03.3
77 . O 150.0 12.9 06.6
170.5 14.6
122.0 10.6
136.5 11.7
157.5 13.5
115.5 09.9
86.5 07.4
61 .O 05.2
31.5 02.7
1165
150
Butiaba
13.5 01.7
31.5 04.1
59 . O 07.6
99.5 12.8
97.5 12.6
57.5 07.4
67.5 08.7
87 .O 11.2
78 .O 10.1
86.0 11.2
70 .O 09 .o
28.0 03.6
775
151
Soroti
19 .o 01.4
52.5 04 .O
79 . O 06 .O
183.5 13.9
194 .O 14.6
128.0 09.7
117 .O 08.9
180 .O 13.6
140 .O 10.6
115 .O 08.7
83 .O 06.3
31‘0 02.3
1322
152
Masindi
28.5 02.2
57 .o 04.4
100.5 07.8
159.5 12.4
147.5 11.5
102 .o 07.9
110 .o 08.5
136.5 10.7
139.5 10.8
143.0 11.1
118 . O 09.2
45 .O 03.5
1287
153 Ongino
20.5 01.7
58 . O 04.8
101 .o 08.3
190.5 15.6
197.5 16.2
113 .O 09.3
122 .o 10 .o
130 .O 10.7
88.5 07.3
74.5 06.1
79.5 06.5
43’0 1218 03.5
154 Serere Agr. Stat.
22.0 01.6
57.5 04.2
95 .O 06.9
207.5 15.2
187 .O 13.7
107 .O 07.8
117.5 08.6
165 .O 12.1
146 .O 10.7
113.5 08.3
96 . O 07 . O
53’0 03.9
1367
155
Kyere
21 .o 01.6
45.5 03.5
91.0 07.0
218.0 16.9
192.0 14.9
114 .O 06.8
130 . O 10.2
151.0 11.7
115.5 08.9
87 . O 06.7
81.0 06.3
45.0 03.5
1291
156
Bulindi
33.5 02.6
06.5 05.0
110.5 08.4
176 . O 13.4
132.5 10.1
89 .O 06.8
87.5 06.7
152.0 11.6
163.0 12.5
138 . O 10.5
107.0 08.2
55.0 04.2
1309
b
-
Month o f t h e year
Station
Year No.
Name
Jan.
Feb.
Mar.
Apr.
May
June
July
Aug.
Sep.
Oct.
Nov.
Dec.
157
Ngora
24.0 01.8
54.0 04 . O
106.5 07.9
185.5 13.8
205.5 15.3
125.5 09.3
121.5 09.1
121.5 09.1
174 . O 12.9
122.0 09.1
83.0 06.2
41*5 03.1
1344
158
Nakasangola
18.5 01.8
39.5 03.9
85.5 08.5
162.0 16.1
137 .O 13.6
65 . O 06.5
77 . O 07.7
109.5 10.9
86.5 08.6
89 .O 08.9
95 .O 09.4
41'5 04.1
1006
159
Bukedia
22.0 01.8
40.5 03.3
109.5 09.0
199 .o 16.2
173.5 14.2
119 .o 09.7
132.0 10.8
151.0 12.4
87.5 07.2
74 -0 06.1
77 . O 06.3
37.0 03.0
1222
160
Kachimbala
23.5 02.0
50.5 04.3
103.5 08.9
170 . O 14.6
166 . O 14.3
128.5 11 .o
112.0 09.6
138.0 11.9
99.0 08.5
66.5 05.7
60.5 05.2
46'0 04 . O
1164
161
bibale
35.5 02.6
58.5 04.3
104 . O 07.6
213.5 15.6
201 .o 14.7
121.5 08.9
111.5 08.2
157.5 11.5
113.5 08.2
99 .o 07.2
84.5 06.2
68'o
1368
162
Bugaya
34.0 02.6
40.5 03.0
103.5 07.8
217 .O 16.3
173.5 13.1
9 1 .o 06.8
103.0 07.8
137 .O 10.3
113.5 08.5
117 .O 08.8
129.0 09.7
70.0 05.3
1329
163
male
28.5 02.4
55 . O 04.7
94 . O 08.0
162.0 13.7
167.5 14.2
125.5 10.6
113.5 09.6
134 .O 11.3
111 .o 09.3
85 . O 07.2
64.5 05.5
41'5 03.5
1182
164
Namasagali
31.5 02.6
50.5 04.2
124 . O 10.3
175'.0 14.6
145 . O 12.1
74.5 06.2
65 . O 05.4
120.5 10 .o
119 .o 09.9
124 . O 10.3
100.5 08.4
71.5 06 . O
1201
165
Vukula
39.5 03.0
59.5 04.5
116.5 08.7
197 . O 14.7
190.5 14.3
88.5 06.6
101 .o 07.6
132.5 09.9
113.0 08.4
111.0 08.3
124.0 09.3
63'0 04.7
1336
166
Kiboga
34.5 02.9
52.0 04.3
93.5 07.8
176.0 14.7
133.5 11.1
54.5 04.5
78 . O 06.5
135.5 11.4
121.5 10.1
149 . O 12.4
104 . O 08.7
67.0 05.6
1199
167
Bulopa
42.5 03.1
74.5 05.5
95.0 07 .O
194 . O 14.4
165.5 12.3
78 . O 05.8
107.0 07.9
143.0 10.6
121 .o 09 .o
128.5 09.5
138.5 10.3
62'5 04.6
1350
168
Ntenjeru
49 .O 04.1
73.5 06.2
101.5 08.5
193 .O 16.2
122.0 10.2
55 . O 04.6
67.5 05.6
103.0 08.6
111.0 09.3
118.5 09.9
126 .O 10.5
75*0 06.3
1195
169
Bukalasa
47.0 03.7
66.0 05.2
129 .O 10.3
141.5 11.2
130 .O 10.3
80.5 06.4
76.0 06.0
114.5 09.1
128.5 10.2
148 .O 11.9
114.0 09.1
84'0 06.7
1259
05 . O
01
APPENDIX C ( c o n t i n u e d )
0 PJ
Month of t h e y e a r
Station No.
Name
170
Kahangi E s t a t e
Jan.
Feb.
Mar.
Apr.
May
June
July
Aug.
Sep.
Oct.
Nov.
Dec.
Year
44 . O 03.2
75.0 05.5
122.5 08.9
175.5 12.8
130 . O 09.5
75.5 05.5
59.5 04.3
112.0 08.1
159.5 11.6
180 . O 13.1
160.5 11.7
81.0 05.8
17 1 Tororo
44 . O 03.3
67.5 05.2
127.0 09.5
197.5 14.8
207 .O 15.6
115.0 08.7
102.5 07.7
105.5 07.9
92.0 06.9
113.0 08.5
97.5 07.3
61.5 04.6
172
Fort Portal
32.5 02.2
74.5 05.0
138.0 09.3
188 . O 12.7
143.5 09.7
80.5 05.4
62.0 04.2
116.0 07.8
188.0 12.7
216.0 14.6
167.0 11.3
75.0 05.1
1481
173
Kalagala Agr. S t a t .
50.5 04.2
82.5 06.8
117.5 09.7
151.5 12.5
128.5 10.6
86.5 07.1
62.0 05.1
103.0 08.5
125.0 10.3
119.5 09.9
118.0 09.7
68.5 05.6
1213
174
Iganga
48.5 03.7
64.5 04.9
143.0 10.9
185.0 14.0
157.5 1 2 .o
81.0 06.2
65.5 05.0
122.5 09.3
123.0 09.4
121.5 09.2
120.0 09.1
83.0 06.3
1315
175
Mubende
37.5 03.1
65.5 05.4
103.0 08.5
152.0 12.5
104.5 08.6
60.5 05 .O
58.5 04.8
121.0 10.0
143.5 11.8
157.0 13.0
138.0 11.4
71.0 05.9
176
Nawanzu
48.0 03.6
56.5 04.3
145.0 10.9
194 .O 14.7
150.5 11.4
80.0 06 .O
89 . O 06.7
116.5 08.8
122.5 09.2
127 . O 09.6
120.5 09.1
75.5 05.7
1325
177
Dabani
64 . O 04.1
77.0 04.9
131.0 08.4
232.0 14.9
212.0 13.6
106 . O 06.8
99 .o 06.3
124.0 07.9
148.0 09.5
139.5 08.9
148.0 09.5
80.5 05.2
1561
178
Nago j e
62.5 04.8
72.5 05.6
120.5 09.3
196.5 15.1
164.0 12.6
102.0 07.9
55.0 04.2
90.5 07.0
99.5 07.7
121 .o 09.3
120.0 09.3
92.0 07.2
1297
179
Masafu Dispensary
57 . O 03.7
66.0
04.3
161.0 10.5
224.5 14.7
219 . O 14.3
98 . O 06.4
107 . O 07 . O
117.0 07.6
143.5 09.4
133 .O 08.7
128.5 08.4
75.5 04.9
180
Lugala
6 1 .O 04.4
86.5 06.3
142.5 10.4
190 .o 13.9
159.5 11.7
102.5 07.5
70 .O 05.1
105.0 07.7
99.0 07.2
134.5 09 .a
116.5 08.5
102.0 07.5
1369
181
Monika Estate
60.5 04.3
100.5 07.1
134.0 09.5
189 .O 13.4
171.5 12.3
102.0 07.2
76 . O 05.4
104.0 07.4
119.5 08.4
131.5 09.3
119.0 08.6
100.5 07.1
1408
182
Namanve
57.5 04.3
77.5 05.8
126.5 09.6
196.0 14.8
154.0 11.6
78.0 05.9
58.0 04.4
93.5 07.1
110.5 08.3
123.0 09.3
148.5 11.2
102.0 07.7
1325
1375
1330
1212
1530
APPENDIX C ( c o n t i n u e d ) Month of t h e y e a r
Station
Year
Name
No.
Jan.
Feb.
Mar.
Apr.
Nay
June
July
Aug.
Sep.
Oct.
Nov.
Dec.
183
Mukono Agr. S t a t .
83.5 05.8
97.5 06.8
148.5 10.3
211 .o 14.7
168.5 11.7
94.5 06.5
58 . O 04 .O
106.5 07.4
106 .O 07.3
130.5 09 .o
135.0 09.3
104.5 07.2
1444
184
Bwavu
68 . O 05.0
93.5 06.9
136.5 10.1
178.5 13.3
159 .O 11.8
91 .o 06.7
76.5 05.7
99 .o 07.3
116 . O 08.6
111.5 08.3
117.5 08.7
103.0 07.6
1350
185
Nsayamba
58.5 05.1
74 . O 06.5
103.5 09 .o
167.0 14.5
149.5 13.1
70.5 06.2
47.5 04.2
86 . O 07.5
90.5 07.9
101.5 08.9
123.5 10.8
72.0 06.3
1144
186
Kabasanda
71 . O 05.6
75 . O 05.9
112.5 08.9
176.5 13.6
107.5 08.5
69.5 05.5
54 . O 04.3
96.5 07.6
119 .o 09.4
127 .O 10 .o
147.0 11.7
113.5 09.0
1264
College
53.0 04.4
62.5 05.2
115.0 09.5
175 .O 14.6
145.0 12.0
76 . O 06.3
49 . O 04.1
96.0 08 . O
110 .o 09.1
115 . O 09.5
123.5 10.2
85.0 07.1
1205
Ngogwe C o f f e e Nursery
88 . O 05.7
102.5 06.6
154.5 10.0
220.5 205.5 14.2 13.3
130 .O 08.4
89.5 05.8
95.0 06.1
98.5 06.4
102.0 06.5
147.0 09.5
117.0 07.5
1550
189
Buvuma I s 1
91.0 05.7
113.5 07.1
184.5 11.5
250 .o 15.6
272.0 17 . O
116 . O 07.3
60.5 03.8
71.5 04.5
80.5 05.0
91.5 05.7
128.0 08.0
141.0 08.8
1600
190
Kisubi
54.5 03.8
92.5 06.6
153.0 10.9
243 .O 17.3
227.5 16.2
97.5 06.9
63.0 04.5
78 . O 05.5
73.0 05.2
97.0 06.9
126.0 09.0
101.0 07.2
1406
191
Entebbe
69.0 04.5
88.5 05.8
164.5 10.8
262.0 17.1
250.5 16.4
119 .o 07.8
77 . O 05.0
76.5 05.0
76.0 04.9
94 . O 06.2
131.0 08.6
120.0 07.9
1528
192
Nkosi
49 . O 04.7
48.5 04.6
110.5 10.6
165.5 15.9
142.5 13.7
61 .O 05.9
31.0 03 .O
60.0 05.8
78.5 07.5
86.5 08.3
122.0 11.7
86.0 08.3
1041
193
Kalungu
44.5 04.5
63.0 06.4
96 . O 09.7
159.5 16.0
125.5- 41.5 04.2 12.7
26 . O 02.6
73.0 07.4
88 . O 08.9
91.5 09.2
107.0 10.8
75.5 07.6
991
194
Katigondo
50.5 04.7
73.0 06.8
111.5 10.4
160.0 14.9
156.5 14.6
42.5 04 .O
26.5 02.5
61.0 05.7
87.5 08.2
108.5 10.2
108.5 10.2
83.0 07.8
1069
195
Lyantonde D i a pens a rg
53.0 05.8
66 . O 07.3
95.5 10.5
121.5 13.3
77 . O 08.5
27 . O 03 .O
17.5 01.9
55.5 06.1
102.0 11.2
115.5 12.7
104.5 11.5
75.0 08.2
910
187 Budo K i n g ’ s
VI
0
w
01
APPENDIX C ( c o n t i n u e d )
0 ID
S t a tion No. 196
Name Masaka Kiwala
lg7 E s t a t e
Month of t h e y e a r Jan.
Feb.
Mar.
Apr.
May
June
July
Aug.
Sep.
Oct.
Nov.
Dec.
Year
51.5 04.7
66.5 06.1
115.0 10.5
179.5 16.4
168.0 15.4
46 . O 04.1
36.5 03.3
54.5 05 . O
86 . O 07.9
102.5 09.4
99 .o 09.1
88.0 08.1
1093
54.5 04.8
65.5 05.8
115 . O 10.2
178.0 15.8
214 . O 18.9
67.0 05.9
33.5 02.9
51.5 04.6
70 . O 06.2
80 .O 07.1
100 .o 08.9
100 .o .08.9
1129
121.5 05.4
149 . O 06.7
244.5 10.9
354 . O 15.8
352.5 15.7
208.0 09.3
117 . O 05.2
108.5 04.8
105.0 04.7
117 .O 05.2
179.5 08.0
186.5 08.3
2243
198
Kalangala Dispensary
199
Buunga
51.0 04.4
61.5 05.2
138.5 11.7
205.0 17.3
212.0 17.9
65.5 05.5
36 . O 03.0
45.5 03.8
89.5 07.6
86.5 07.3
100 .o 08.4
94 . O 07.9
1185
2oo
Kyananwkaka
58.5 05.1
67.5 05.8
139 . O 12.0
197.5 17.1
206.5 17.9
57 . O 04.9
30 . O 02.6
42.0 03.6
81.5 07.1
81.5 07.1
101.o 08.7
93.0 08.1
1155
201
Busenyi
76 . O 06.0
105.0 08.3
124 . O 09.8
166 .O 13.2
100 .o 07.9
40 . O 03.2
42.0 03.3
86 . O 06.8
118 . O 09.3
148.5 11.7
151.0 11.9
109.5 08.6
1266
202
Mbarara
43.5 04.8
66.5 07.4
97 . O 10.7
119 .o 13.2
79 . O 08.8
27 . O 03.0
22.5 02.5
59 . O 06.5
102.0 11.3
104 . O 11.5
110.5 12.2
73.0 08.1
903
203
Bikira
58.5 05.3
66 . O
06.0
155 . O 14 . O
171.5 15.5
185.5 16.7
32 .O 02.9
23.0 02.1
37 . O 03.3
9 1 .o 08.2
95.5 08.6
109 .o 09.8
84.0 07.6
1108
204
Lwasamaire
61.5 06.0
87.0 08.5
108.5 10.6
118,5 11.5
81.0 07.9
27 . O 02.6
26.5 02.6
72.0 07.0
104.0 10.1
109 .o 10.6
128 . O 12.4
105.0 10.2
1028
205
Katera
77.0 06.5
82.0 06.9
154.5 220.5 13.1 18.7
213.5 18.0
36 . O 03 . O
01. I
20.5
41.5 03.5
57.5 04.9
79.5 06.7
95.5 08.1
105.0 08.9
1183
206
Kabale
56.0 05.3
86.5 08.3
118 .O 11.3
145,5 13.9
112.5 10.7
42 .O 04 . O
37.5 03.6
74.0 07.1
97.5 09.3
96.5 09.2
100 .o 09.5
82.0 07.8
1048
207
Kapenguria
12 .o 01.0
31.5 02.6
80.5 06.6
149 .O 12.4
201 .o 16.6
132.5 10.9
188.0 15.5
170.5 14.1
97.5 08.1
70.0 05.8
52.5 04.3
26.0 02.2
1211
208
Endebess
22.5 01.9
39.5 03.3
79.5 06.6
152.5 12.6
152.5 12.7
123.5 10.2
177 . O 14.7
174.0 14.4
98.0 08.1
84.0 07.0
68.0 05.6
35.0 02.9
1206
APPENDIX C (continued) Month of t h e y e a r
Station
Year No.
Name
Jan.
Feb.
Mar.
Apr.
May
June
Oct.
July
Aug.
Sep.
Nov.
Dec.
161 .O 13.8
171 .O 14.7
103.0 08.9
64.5 05.5
54 . O 04.6
37.0 03.2
1164
43.0 03.4
49 .O 03.8
25.5 02.0
1282
74 .O 102.5 06.2 08.5
63.0 05.2
1200
209
Kitale Agr. S t a t .
18.0 01.6
39.5 03.4
67 .O 05.8
154 .O 13.2
210
Turbo
26 . O 02.0
43.0 03.4
75 . O 05.9
164.5 166.5 13 .O 12.8
147.5 11.5
183 .O 248 .O 111.0 14.2 19.3 08.7
211
Tambach
34.5 02.9
36.5 03.0
91.0 202.5 07.6 16.9
180.0 15.0
104 . O 08.7
133.0 11.1
121 .o 10.1
58.0 04.8
212 Myanga
37.5 02.7
47.5 03.5
122.5 08.9
223.5 233.5 16.3 17.1
120.5 08.8
94.5 06.9
112.5 08.2
100.5 07.3
119 .o 08.7
93.5 06.8
66.0 04.8
1371
213 Bugoma V .S.
47 . O 03.0
68 .O 04.4
119 .o 07.6
222.0 243 .O 149 . O 15.6 09.6 14.2
129.5 08.3
138.0 08.8
139 . O 08.9
116.0 07.4
106.5 06.8
84 . O 05.4
1561
214
Mumais
43.0 02.4
95.0 05.3
142.5 07.9
247 .O 13.7
279.5 15.5
172 .O 09.5
146.0 08.1
165.0 09.2
162.5 09 .o
140.5 07.8
114 . O 06.3
96 . O 05.3
1803
215
Tororo/Naninga
49.5 03.6
69.5 05.1
122.0 200.5 14.7 09.8
192 .O 14 .O
85 .O 06.2
82 .O 06 .O
103.5 07.6
115 .O 08.4
137 .O 10 .o
140.0 10.2
73.0 05.3
1369
216
Kakarnega
79.5 04.1
101.0 05.3
147 . O 07.7
255.5 13.3
283.5 200.0 166.5 10.4 08.7 14.7
208.5 10.9
178 .O 122.0 09.3 06.3
99 .o 05.1
80.5 04.2
1921
217
Kapas abe t
47.5 03.1
74.0 04.8
117.5 07.6
194 . O 12.6
210.5 13.7
158.0 10.3
173.0 11.2
201.0 13.1
144.5 09.4
87.0 05.6
77 . O 05 .O
56 .O 03.6
1540
218
Rangala
55 .O 03.6
77.5 05 . O
138.5 230.0 15 .O 09 .o
214.0 13.9
108.5 07.1
96.0 06.2
116 .O 07.6
144 .O 09.4
122.5 08 .O
140.0 09.1
94 . O 06.1
1536
219
Maseno V S
61.5 04 .O
86.5 05.6
151 .O 09.8
230 .O 14.9
208.5 13.5
118.5 07.7
92.0 06.0
127.5 08.3
126.5 08.2
114.5 07.4
131.0 08.5
93.5 06.1
1541
220
Equator
34 . O 02.2
59.0 03.8
94 .O 06.1
206.5 13.4
221 .o 14.4
156.5 10.1
185 .O 12 .o
221 .o 14.4
139.5 09.1
80.5 05.2
81.0 05.3
62.0 04 .O
1540
221
Yiwani
48.0 03.9
76.5 06.3
134.5 217.0 159 .O 11.0 13 .O 17.7
87.5 07.1
69 .O 05.6
92.0 07.5
75 . O 06.1
88 .O 07.2
100 .o 08.2
77.5 06.4
1224
. .
167.0 128 .O 14.3 11 .o
u
0
u
VI
APPENDIX C ( c o n t i n u e d )
0
Q,
Month of t h e y e a r
Station Name
No.
Jan.
Feb.
Mar.
Apr.
May
June
July
Aug.
Sep.
Oct.
Nov.
Dec.
Year
222
Kisumu P.C.
48.5 04.3
80.5 07.1
134.5 11.9
188 .o 16.7
150 . O 13.3
83.0 07.3
58 . O 05.1
76 .O 06.7
66.0 05.8
56 . O 05.0
90.0
99.5
08.0
08.8
223
Chemelil
54 . O 04.1
83.0 06.3
126.0 09.6
232 .O 17.7
191 .o 14.6
94.5 07.2
82.5 06.3
104 . O
76.5 05.8
74.5 05.7
106.5 08.2
84.5 06.5
1309
08.0
224
Muhoroni
60.5 03.9
118.0 07.6
160.0 10.3
249.5 16.0
194 . O 12.5
119.5 07.7
109 .o 07.0
134 .O 08.6
103.0 06.6
80 .o 05.1
122.5 07.9
106.0 06.8
1556
38.5 03.1
79.5 06.4
119.0 09.6
177 .O 14.3
155 . O 12.4
124.5 10 .o
134 . O 10.8
135 . O 10.9
86 . O 06.9
63.0 05.1
74.0 06.0
55.5 04.5
1241
1130
226
Londiani
30.0 02.7
46.0 04.1
82.0 07.3
156 .O 14 .O
141.O 12.6
122 .o 10.9
135.5 12.1
165 . O 14.8
95.0 08.5
50.5 04.5
55.5 05.0
39.5 03.5
1118
227
Lumbwa
35 .O 03.0
63.5 05.4
94.0 08.1
173.5 14.9
162.5 14 . O
128.5 125.0 11.1 1 0 . 8
134 . O 11.5
90 .o 07.8
59 .o 05.1
53.5 04.6
42.5 03.7
1161
228
Yo10
34.5 02.7
52.5 04.1
100.0 07.8
181.5 14 :2
149 . O 11.7
122.5 09.6
142.5 11.2
175 .O 13.7
99.5 07.8
64.5 05.1
89.0 07.0
64.5 05.1
1275
229
Kericho
65.5 03.6
95.5 05.2
157.0 08.6
264.0 14.4
246.5 13.4
164.5 09 .o
152.5 08.3
188.0 10.3
150.0 08.2
136.5 07.4
124.0 06.8
89.0 04.8
1833
230
Sotik
68 . O 05 .O
103.0 07.6
137.0 10.2
183.5 13.6
145.0 10.7
120.5 08.9
92.0 06.8
127.5 09.5
114.0 08.5
86.5 06.4
93.0 06.9
79.0 05.9
1349
231
Kisii
63.0 03.7
99.5 05.8
164.5 09.5
252.5 14.7
211 .o 12.2
146.5 08.6
105.0 06.1
150.5 08.7
154 . O 08.9
131.5 07.6
143.5 08.3
102.5 05.9
1724
232
Bukoba
152.5 07.7
158.0
243.0 12.2
337.0 17 .O
308.5 15.6
87 . O 04.4
45 .O 02.3
79 .O 04 .O
102.5 05.2
124 .O 06.3
161.5 08.1
183.0 09.2
1981
08.0
233
Tarime
82 .O 05.9
99.5 07.2
157.5 11.4
231.5 16.7
159.5 11.5
79.5 05.7
46 . O 03.3
78.0 05.6
82.5 05.9
120.5 08.7
129.0 09.3
121.5
1387
234
Musoma
58.0 07.6
67.0 08.7
117.5 15.3
164.5 21.5
106.5 13.9
23 .O 03.0
18.0 02.3
20.5 02.7
23.0 03.0
34.5 04.5
74.0 09.7
59.5 07.8
766
08.8
APPENDIX C (continued) Month of t h e year
Station Name
NO.
Jan.
Feb.
Mar.
Apr.
May
June
July
Aug.
Sep.
Oct.
Nov.
Dec.
Year
235
Kagondo
115.5 07.2
133.0 08.2
217.0 13.4
301.0 18.7
237.0 14.7
38.5 02.4
27.5 01.7
53.5 03.3
76 .O 04.7
108 .o 06.7
157 .O 09.7
150 .O 09.3
236
Kawalinda
113.5 07.0
135.5 08.4
194 .O 12.0
294.0 237.0 14.6 18.1
41.5 02.6
21.5 01.3
60.0 03.7
76.5 04.7
123.5 07.6
161.5 10 .o
162.5 1621 10.0
237
Rubya
115.5 08.8
133.0 10.1
172.0 13.1
216.5 16.4
156.5 11.9
27.5 02.1
11.0 00.8
39.0 02.9
73.0 05.5
109 .o 08.3
138 .O 10.5
127 .O 09.6
238
Igabiro
95.5 08.5
103.5 09.3
167.5 15.0
195.5 17.5
123.5 11.0
23.0 02.1
09.0 00.8
24.5 02.2
53.0 04.7
90.5 08.1
239
Ikizu
86.5 08.3
83.0 08.0
142.5 13.7
154.0 14.8
99 .o 09.5
35.5 03.4
09 .o 00.9
35.0 03.4
47.5 04.6
106.5 10.3
127.5 112.0 10.8 12.3
1038
240
Kome
95.0 08.7
99.0 09.1
147.5 13.5
157 .O 14.3
75.5 06.9
20.5 01.9
16 .O 11.5
48.0 04.4
75.0 06.9
125.5 11.5
129 . O 11.8
104 . O 09.5
1092
241
Ngara
100 .o 09.7
110.5 10.6
120.5 11.6
184.0 18.1
102.0 09.8
14.5 01.4
04 . O 00.4
21.0 02.0
62.0 06.0
75.5 07.3
129.0 12.5
110 .o 10.6
1033
242
Mwanza
95.5 108.0 09.2 10.4
149.5 14.5
185.5 18 .o
93.0 09 .o
18 .o 01.7
12.5 01.2
21.0 02.0
39.5 03.8
54.5 05.3
120.5 11.6
137.5 13.3
1035
243
Biharamulo
97.0 10 .o
111.0 11.5
150.5 15.6
190.5 19.7
76 . O 07.9
12.5 01.3
03.5 00.4
20 .o 02.1
33.0 03.4
62.0 06.4
99 .o 111.0 10.2 11.5
966
244
Ukiriguru
95.0 11.4
82.0 09.8
132.5 15.9
139.5 16.7
72.5 08.7
09.5 01.1
01 .o 00.1
13.5 01.6
23.0 02.8
41.5 05 .O
119 .o 106.0 14.2 12.7
835
245
Sumvwe Mission
82.0 10.6
80.5 10.4
120 .o 15.5
123.5 15.9
77.5 10 .o
16.5 02.1
06.0 00.8
07 .O 00.9
16.0 02.1
36.0 04.7
103.0 106.0 13.7 13.3
774
246
Geita
94.5 09.7
106 .O 10.9
138.5 14.2
162.5 16.6
80.5 08.3
09.5 01.0
03.0 00.3
20 .o 02.1
35.5 03.6
64.5 06.6
130 .O 13.3
130.5 13.4
975
247
Ngudu
90.0 10.9
96 .O 11.6
135.5 16.4
154 .O 18.6
69 .O 08.3
10 .o 01.2
03.5 00.4
04 .O 00.5
11.0 01.3
26.5 100.5 128.0 03.2 12.1 15.5
828
1614
1318
106.0 126.5 1118 09.5 11.3
APPENDIX C (continued) Station
Month of the year Year
No.
Name
Jan.
Feb.
Mar.
Apr.
May
June
248
Kijima Mission
105.5 13.9
86.0 11.4
134.5 17.8
118.0 15.6
64.0 08.5
09.0 01.2
249
Shanwa
116.0 14.7
97.0 12.3
117.0 14.9
147.0 18.7
51.5 06.5
04.0 00.5
250
Addis Ababa
14.0 01.2
39.5 03.3
65.5 05.4
83.0 06.9
84.0 07.0
130.5 10.8
July
Aug.
Sep.
Oct.
Nov.
Dec.
06.0 00.8
14.5 01.9
30.5 04.0
72.5 09.6
115.5 15.2
757
0 0
04.0 00.5
08.5 01.1
26.0 03.3
87.0 11.0
130.0 16.5
788
275.5 22.8
286.5 23.7
188.0 15.6
19.5 01.6
14.0 01.2
06.0 00.5
1206
01.0 00.1
509 APPENDIX D
-
Monthly and annual d i s c h a r g e s of t h e N i l e and i t s t r i b u t a r i e s a t a number of key s t a t i o n s
TABLE 1
Monthly and annual d i s c h a r g e s of t h e Kagera R i v e r a t Kyaka F e r r y , m i l l i o n m 3 (WMO, 1974)
Year J a n . Feb. Mar. Apr. May 1940 418 1941 385 1942 431 1943 412 1944 322 1945 319 1946 341 1947 298 1948 404 1949 322 1950 287 1951 293 1952 518 1953 410 1954 368 1955 339 1956 335 1957 403 1958 445 1959 391 1960 410 1961 397 1962 434 1963 6 4 1 1964 826 1965 617 1966 506 1967 497 1968 496 1969 656 1970 530 1971 505
Source:
370 333 39 8 36 7 304 288 300 281 360 29 1 260 266 482 369 325 318 298 343 392 337 379 365 5 36 6 36 844 555 496 448 508 6 86 480 450
June J u l y Aug. Sep. Oct. Nov. Dec. T o t a l
434 411 459 486 549 542 385 390 422 396 418 437 505 540 6 5 1 672 676 648 39 7 399 412 390 384 375 326 336 384 333 350 360 319 312 263 351 338 332 332 312 356 318 328 335 304 330 487 504 657 620 390 388 433 409 398 382 331 345 325 326 306 325 292 319 351 319 325 322 326 360 460 606 550 30 1 592 596 647 604 604 635 418 451 420 421 403 4 16 382 385 503 544 547 512 372 388 362 391 397 36 9 316 432 479 520 485 299 410 556 670 680 660 40 3 450 457 527 506 515 491 377 379 436 388 406 419 433 530 6 3 1 701 694 586 400 398 436 424 449 450 824 924 928 960 927 778 873 1148 1136 1339 1328 810 9 5 1 1052 1204 1243 1245 1048 644 746 808 819 715 626 4 10 699 885 901 913 6 7 1 499 496 570 544 566 564 693 847 1204 1300 1300 1115 838 882 1082 963 8 6 1 730 562 660 900 1080 1010 850 5 15 540 640 620 695 690
Date from 1940-1966 Date from 1967-1971
-
477 466 429 428 591 542 354 347 354 360 315 325 312 305 537 515 349 344 280 275 310 304 465 450 591 552 398 388 419 409 368 350 465 452 605 566 432 425 400 419 509 476 397 396 795 724 1133 931 771 665 600 555 584 536 522 513 873 725 612 565 700 630 630 610
W.D.D. Uganda Hydromet. P r o j e c t
411 420 471 3 15 339 306 285 441 324 272 2 74 405 484 36 5 378 34 3 400 504 383 386 4 37 420 654 756 601 502 473 499 6 36 5 27 545 5 70
385 5.420 437 4.890 443 6.570 322 4.490 338 4.100 338 3.900 30 1 3.800 431 5.420 324 4.510 282 3.680 3.650 290 4.980 496 454 6.760 4.860 400 36 4 5.140 4.350 355 42 3 4.900 6.290 4 86 402 5.430 396 4.740 6.210 425 5.000 494 9.120 6 34 757 11.490 6 2 3 11.070 5 32 7.720 46 4 7.410 6.250 5 34 6 78 10.370 8.920 521 8.480 5 30 7.030 565
5 10
TABLE 2
Monthly and annual d i s c h a r g e s of t h e V i c t o r i a N i l e a t J i n j a , m l r d m 3
(WMO,
1974)
Year J a n . Feb. Mar. Apr. May
June J u l y Aug. Sep. Oct. Nov. Dec.
1946 1 . 3 0 1947 1 . 4 5 1948 1 . 9 2 1949 1.76 1950 1.36 1951 1 . 3 2 1952 1.96 1953 2.05 1954 1 . 7 2 1955 1 . 5 3 1956 1.56 1957 1 . 5 8 1958 1 . 6 9 1959 1.16 1960 1.54 1961 1 . 5 2 1962 3 . 0 1 1963 3.48 1964 4.25 1965 4 . 4 7 1966 3.52 1967 3.30 1968 3.27 1969 3.79 1970 2.90
1.36 2.25 2.02 1.61 1.50 1.65 2.50 1.96 1.91 1.56 1.78 2.07 1.86 1.64 1.94 1.71 3.45 4.10 4.40 4.31 4.25 3.28 4.07 4.14 4.08
TABLE 3
1.08 1.35 1.78 1.55 1.20 1.99 1.81 1.74 1.47 1.44 1.52 1.44 1.54 1.14 1.46 1.36 2.69 3.16 3.79 4.12 3.17 2.89 3.01 3.54 3.20
1.16 1 . 1 2 1 . 5 7 1.74 1 . 9 2 1.86 1 . 6 1 1.56 1.33 1.42 1.32 1.47 1.98 2.07 1.88 1.86 1.62 1 . 7 4 1.56 1 . 5 8 1.56 1 . 6 3 1 . 6 3 1.75 1 . 7 1 1.66 1.59 1 . 5 7 1 . 6 9 1.88 1.52 1.62 2.99 3.06 3 . 6 3 3.56 4.14 4 . 2 3 4.60 4 . 2 8 3.62 3.66 3.10 3.04 3.46 3 . 5 7 4.03 4.01 3 . 6 5 3.84
1.32 2.23 2.08 1.68 1.58 1.69 2.52 2.12 1.89 1.73 1.86 2.02 1.91 1.72 2.06 1.80 3.52 3.89 4.55 4.40 4.23 3.42 4.11 4.35 4.25
1.33 2.21 2.01 1.57 1.51 1.59 2.41 1.92 1.84 1.50 1.71 2.04 1.86 1.61 1.84 1.65 3.46 4.15 4.61 3.70 3.65 3.30 4.00 4.03 4.01
1.33 2.18 1.99 1.53 1.44 1.48 2.32 1.79 1.78 1.42 1.63 1.92 1.79 1.50 1.67 1.59 3.35 4.01 4.28 3.55 3.46 3.16 3.80 3.79 3.84
1.30 2.05 1.88 1.43 1.37 1.34 2.21 1.67 1.66 1.36 1.56 1.77 1.67 1.40 1.58 1.55 3.22 3.67 4.12 3.29 3.33 2.92 3.49 3.51 3.67
1.30 2.10 1.86 1.41 1.38 1.35 2.23 1.67 1.66 1.48 1.60 1.67 1.66 1.44 1.61 1.61 3.36 3.63 4.20 3.31 3.37 3.01 3.46 3.47 3.72
Total
1.26 1 . 4 2 1 5 . 2 8 2.94 1 . 9 9 23.06 1.81 1.82 22.95 1.30 1.32 1 8 . 3 3 1 . 3 2 1 . 3 3 16.74 1.40 1 . 7 1 1 7 . 5 1 2.12 2 . 1 1 26.24 1.61 1 . 7 5 22.02 1 . 5 2 1.56 20.27 1 . 3 9 1.46 1 8 . 0 1 1 . 5 3 1 . 5 8 19.52 1 . 6 1 1 . 6 9 21.16 1.52 1 . 5 8 20.45 1 . 4 4 1 . 5 5 17.76 1 . 5 7 1 . 5 8 20.42 1.95 2.69 20.57 3.20 3.38 38.69 3.53 3.99 44.80 3.88 4 . 0 1 50.46 3 . 3 1 3.52 46.86 3.30 3 . 3 8 42.94 2.99 3.35 37.76 3.36 3 . 7 1 43.31 3 . 3 2 4 . 0 2 46.00 3 . 5 1 3.60 44.27
Monthly and annual mean d i s c h a r g e s of t h e Kyoga N i l e a t P a r a a , m3/sec (WMO, 1974)
Year Jan.
Feb. Mar. Apr. May
June J u l y Aug. Sep. O c t . Nov. Dec.
Year
1948 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970
682 615 420 398 705 538 437 558 492 588 524 508 631 620 1340 1352 1345 1618 1347 1228 1287 1447 1300
687 552 450 515 693 551 584 530 541 694 541 536 820 640 1210 1757 1688 1668 1468 1262 1607 1623 1508
699 560 46 1 509 687 5 28 56 1 577 571 65 3 557 558 7 39 769 1326 1544 1728 1596 1441 1287 1483 1527 1492
718 656 450 417 719 581 428 579 524 613 550 528 640 700 1442 1405 1457 1700 1403 1322 1327 1458 1373
667 572 404 390 715 503 448 543 471 573 506 498 631 574 1320 1322 1675 1557 1363 1165 1312 1538 1280
655 539 417 417 671 522 434 540 464 569 496 492 644 580 1123 1357 1683 1742 1408 1217 1330 1530 1338
671 549 429 465 674 551 435 523 483 622 528 520 695 610 1177 1627 1707 1742 1435 1235 1463 1600 1462
708 545 465 544 718 545 624 534 569 768 581 546 870 654 1237 1740 1691 1630 1510 1285 1640 1625 1545
635 549 484 571 667 537 660 601 595 788 620 560 820 732 1273 1735 1815 1558 1473 1305 1635 1586 1578
737 569 525 575 718 534 676 720 664 706 640 604 890 816 1350 1694 1882 1482 1490 1293 1585 1550 1662
725 571 532 581 720 516 708 650 692 666 626 640 772 884 1408 1537 1040 1472 1485 1360 1547 1482 1664
714 524 505 590 671 498 669 595 698 643 555 636 756 1100 1500 1487 1927 1498 1498 1368 1543 1450 1657
685 475 456 642 627 458 627 556 657 608 508 630 604 1318 1527 1515 1830 1490 1412 1402 1530 1443 1532
511 TABLE 4
Monthly*and annual d i s c h a r g e s
Of
t h e River S e m l i k i f o r t h e p e r i o d
1948-1970 (WMO, 1974) Year Jan. Feb. Mar. Apr. May
1948 104 1949 68 1950 90 1951 102 1952 223 1953 114 1954 89 1955 100 1956 110 1957 126 1958 122 1959 160 1960 103 1961 72 1962 207 1963 278 1964 268 1965 210 1966 128 1967 119 1968 117 1969 153 1970 119 TABLE 5
100 95 78 100 182 93 81 100 103 107 106 103 101 74 171 273 229 179 135 104 116 146 111
109 107 82 94 86 97 102 163 163 185 99 99 77 105 97 104 96 122 123 143 96 104 84 92 102 112 63 83 162 165 284 317 213 247 170 170 138 210 98 106 146 147 151 138 124 210
June J u l y Aug. S e p . O c t . Nov. Dec.
125 135 118 126 100 96 155 158 216 176 118 110 112 126 89 102 132 104 158 179 134 126 118 99 91 105 87 84 222 200 500 388 284 231 166 15 1 166 145 147 132 151 15 7 171 150 184 172
162 124 124 140 173 95 127 107 118 141 169 79 103 95 183 351 210 158 143 138 145 145 187
169 184 156 153 130 127 141 150 113 109 136 153 156 125 123 193 133 157 148 276 192 189 165 153 129 133 113 101 123 112 116 133 130 112 121 111 126 164 122 120 136 143 171 146 131 15 1 136 121 130 156 138 131 131 112 115 103 100 114 127 113 91 100 107 115 118 127 140 168 - 280 275 265 239 324 286 271 278 286 243 280 271 231 2 32 138 131 158 194 155 149 172 160 165 144 131 110 125 143 145 147 126 131 151 179 132 136 123 136 123 207 215 194 183 153
Total
mlrd m 3 4.29 3.53 3.60 5.08 5.65 3.44 3.50 3.53 3.97 4.38 3.91 3.37 3.28
-
6.78 10.09 7.73 5.20 4.89 3.94 4.51 4.48 5.42
Monthly and annual d i s c h a r g e s of t h e A l b e r t N i l e a t Panyango f o r t h e p e r i o d 1948-1970 (WMO, 1974)
Year Jan. Feb. Mar. Apr. May
1948 918 878 844 1949 874 818 769 1950 638 587 552 1951 526 488 467 1952 728 703 661 1953 780 719 661 1954 590 558 541 1955 642 624 594 1956 540 580 630 1957 550 492 480 1958 620 537 482 1959 625 541 480 1960 435 390 370 1961 754 623 547 1962 1765 1790 1829 1963 2071 2049 2046 1964 2069 2027 2997 1965 1903 1874 1845 1966 1766 1728 1702 1967 1630 1550 1460 1968 1490 1450 1385 1969 1645 1635 1625 1970 1522 1437 1357
794 752 551 486 733 644 540 600 575 494 412 417 387 530 1845 2050 2981 1831 1704 1360 1395 1613 1406
June J u l y . A u g . S e p . O c t . Nov. Dec.
821 841 862 911 743 736 724 724 556 541 560 571 492 501 500 519 780 799 792 816 683 664 657 661 568 575 571 612 640 520 475 505 685 645 645 510 514 580 577 592 480 462 530 582 485 460 540 580 427 439 437 510 489 482 510 620 1886 1916 1932 1933 2123 2146 2141 2142 1980 1964 1964 1983 1821 1799 1778 1768 1728 1720 1726 1729 1380 1360 1380 1390 1390 1480 1500 1550 1621 1628 1608 1626 1501 1523 1532 1597
*monthly d i s c h a r g e s g i v e n i n m i l l i o n m3/month
972 997 1010 963 736 750 729 694 601 624 625 568 540 564 617 717 845 870 868 840 660 653 664 646 648 680 683 650 630 545 525 500 476 525 600 590 662 622 655 655 620 625 590 575 600 650 610 590 627 697 815 825 760 932 1373 1694 1982 2018 2073 2097 2143 2111 2096 2100 2019 2068 2081 2033 1750 1740 1770 1780 1743 1759 1782 1763 1400 1430 1515 1560 1610 1600 1660 1680 1610 1590 1597 1597 1664 1678 1673 1644
Total mlrd m 3
28.41 23.78 18.32 16.87 24.79 21.25 18.95 17.88 17.91 18.05 17.10 17.30 16.70 24.44 60.54 66.20 63.43 56.50 54.20 45.30 48.40 50.96 48.70
5 12
TABLE 6
Monthly and annual d i s c h a r g e s of t h e Bahr e l J e b e l a t Mongalla f o r t h e p e r i o d 1912-1973 ( C a i r o U n i v e r s i t y
-
Massachusetts I n s t i t u t e of
Technology, 1977)
Year
Measured flows i n m i l l i o n m 3 J a n . Feb. Mar. Apr. May
June J u l y Aug. Sep. Oct. Nov. Dec. Year
1912 1670 1380 1380 1430 1610 1550 2300 2920 3000 2200 2040 1950 23430 1913 1480 1370 1470 1660 2340 2320 2480 2440 1880 1810 1930 1820 23000 1914 1680 1400 1530 1480 1860 1700 2040 2810 2590 2660 3270 2500 25520 1915 2010 1710 1870 1900 2330 2340 2260 2620 2820 2970 2790 2270 27890 1916 1990 1730 1780 1910 2490 2920 3300 4080 5250 4810 4040 3590 37890 1917 3200 2850 3060 3060 4380 4910 4990 5420 6430 7350 5300 4850 55800 1918 4850 4080 4410 4110 4320 3970 3950 4010 3610 3650 3180 2990 47130 1919 2770 2330 2390 2360 2660 2380 3010 2780 2860 2700 2570 2380 31190 1920 2320 1760 1660 1860 2200 2310 2340 2560 2190 2480 2140 1990 25910 1921 1530 1220 1200 1120 1190 1200 1630 1830 1580 1650 1290 1180 16620 1922 1070 8 9 1 999 1050 1250 1160 1240 1560 1950 1550 1460 1080 15260 1923 9 8 3 8 0 1 853 9 1 3 1430 1330 2090 2850 1930 2200 2170 1780 19330 1924 1640 1440 1420 1650 1910 1550 1600 1720 1930 2020 1920 1660 20460 1925 1540 1300 1430 1450 1670 1520 1560 1860 1610 1520 1750 1650 18860 1926 1390 1180 1300 1470 1880 1660 2320 3130 2750 3020 2400 2350 24850 1927 2230 1940 2090 2150 2240 2230 2260 2340 2220 2260 2090 1990 26040 1928 1850 1620 1640 1960 3830 2620 2520 2330 2060 2380 2000 1830 26640 1929 1700 1440 1480 1510 2240 1760 1780 1950 1930 2000 1880 1660 21330 1930 1540 1320 1500 1750 1940 1800 1820 2040 2120 2300 2440 2060 22630 1931 1960 1680 1880 1940 2300 2180 2760 3300 3130 3020 2470 2410 29030 1932 2250 1940 2180 2060 2680 2380 2980 3720 3570 3480 2760 2650 32650 1933 2480 2180 2350 2260 2500 2280 2570 2680 3410 3040 2470 2350 30570 1934 2180 1810 1910 1980 2420 2130 2480 3080 2460 1990 1960 1890 26290 1935 1760 1500 1590 1670 2340 2170 2280 2130 2260 2240 1820 1720 23480 1936 1600 1420 1560 1600 1860 2040 2210 2490 2450 2310 1940 1900 23380 1937 1810 1630 1730 1890 2500 2250 2910 3170 2350 2650 2730 2510 28130 1938 2310 2000 2100 2060 2430 2550 2570 3470 3110 2810 2470 2270 30150 1939 2140 1830 1940 2120 2190 2020 2220 2300 2140 2010 2120 1900 24930 1940 1720 1530 1610 1710 2230 1730 2050 2500 2100 1760 1630 1680 22250 1941 1580 1320 1560 1520 2150 2760 2100 1980 1970 1970 1920 2040 22870 1942 1890 1650 1940 1960 2600 2650 3100 3780 3990 3150 2720 2730 32160 1943 2610 2210 2270 2170 2460 2530 2760 2750 2640 2270 1950 1840 28460 1944 1710 1450 1510 1540 2140 1610 1950 1850 1970 1950 1600 1450 20730 1945 1320 1070 1070 986 1510 1550 1790 2300 2200 1920 1520 1500 18736 1946 1280 1100 1120 1190 1600 2100 1870 3260 2890 2280 1900 1620 22210 1947 1510 1340 1500 1850 2210 2000 2590 3300 3350 3310 2440 2510 27910 1948 2340 2090 2150 2060 2350 2540 2770 3130 3430 3620 2940 2480 31900 1949 2220 1890 1960 1860 2160 2050 2600 2890 2890 2480 1910 1770 26680 1950 1630 1350 1410 1530 1660 1560 1880 2720 2580 2880 1710 1450 22360 1951 1350 1130 1190 1310 1510 1560 1510 1890 1450 1870 2120 2100 19990 1952 1870 1640 1680 1910 2400 2180 2420 3530 3180 3150 2400 2250 28610 1953 1990 1660 1690 1610 1910 1950 2130 2340 1880 1920 1900 1650 22630 1954 1510 1280 1380 1520 1910 1800 2020 2890 3010 2230 1870 1700 22920 1955 1640 1440 1510 1500 1740 1530 1690 2200 2860 3060 2370 1780 23320 1956 1620 1430 1490 1640 1950 1850 1940 2500 3060 3010 2100 1860 24450 1957 1780 1570 1780 1940 2380 2690 2170 2480 2090 2080 1960 1910 24830 1958 1810 1570 1700 1730 2080 2100 2770 2870 2520 2470 1940 1880 25440 1959 1760 1490 1580 1550 2120 1910 1900 2440 2390 2220 2030 1820 23210 1960 1630 1490 1680 1830 2090 2860 2210 2500 2640 2780 2350 2040 25100
513 TABLE 6
Year
(continued)
Measured flows i n m i l l i o n m 3 J a n . Feb. Mar. Apr. May
1961 1900 1962 3450 1963 4420 1964 4390 1965 5260 1966 4290 1967 3990 1968 3720 1969 4309 1970 4061 1971 4402 1972 3596 1973 3844
TABLE 7
1620 3040 3890 3740 4530 3780 3410 3190 3944 3813 4185 3565 3658
1770 3560 4280 3860 4780 4130 3620 3503 4309 3720 4030 3286 3193
1790 3660 4790 4510 4570 4130 3370 3480 4020 3810 3900 3060 3240
2010 4330 6050 5290 4740 4360 3780 4030 4650 4185 4185 3317 3937
June J u l y Aug. Sep. O c t . Nov. Dec. Year 2040 4090 5640 4940 4430 4060 3710 4140 4320 4200 3960 3390 3630
2590 4700 3500 5720 4580 4250 4070 4557 4495 4557 4216 3503 3689
3550 4890 5540 6320 4810 4510 5084 5115 5363 5766 4557 3534 4278
2730 5000 5310 6860 4440 4690 4790 4620 5040 6600 4920 3570 4140
4250 5040 4970 7340 5040 4750 5000 4774 4526 6200 4898 3968 4050
4730 4520 5010 5760 4900 4750 5120 4620 4410 5250 4140 4320 3960
4080 4370 5070 5270 4840 4310 4560 4650 4340 4557 3844 4247 4844
34060 50650 60470 64000 56920 51980 50504 50399 53726 56719 51237 43356 45443
Monthly and annual d i s c h a r g e s of t h e White N i l e a t Malakal f o r t h e p e r i o d 1912-1973 ( C a i r o U n i v e r s i t y
-
Massachusetts I n s t i t u t e of
Technology, 1977)
Year 1912 1913 1914 1915 1916 1917 1918 1919 1920 1921 1922 1923 1924 1925 1926 1927 1928 1929 1930 1931 1932 1933 1934 1935 1936 1937 1938
Measured flows i n m i l l i o n m 3 J a n . Feb. Mar. Apr. May
June J u l y Aug. Sep. Oct. Nov. Dec. Year
1880 1810 1450 2600 1950 4280 4970 2190 1870 1750 1500 1710 1830 1860 1650 2500 1400 1920 2180 1550 1680 3420 2300 2420 1980 1640 1800
1580 1720 1630 1850 1840 2390 2910 2260 1990 1720 1560 2010 1680 1830 1970 1700 2070 2300 1830 1690 2000 1960 1970 2230 2030 1980 1900
1460 1390 1230 1460 1410 3240 4620 1810 1490 1240 1040 1040 1320 1270 1180 1400 1170 1410 1430 1190 1360 1820 1510 1520 1570 1320 1350
1370 1460 1310 1390 1360 2220 4840 1800 1420 1230 963 1060 1270 1290 1340 1390 1200 1410 1400 1250 1360 1670 1540 1520 1470 1340 1430
1220 1330 1260 1300 1300 1860 2880 1580 1240 1130 860 1300 1310 1210 1240 1310 1320 1360 1340 1200 1310 1600 1460 1510 1310 1240 1380
1190 1710 1310 1510 1460 2010 2450 1760 1450 1430 1040 1410 1540 1470 1590 1340 1820 1960 1530 1270 1510 1670 1680 1720 1570 1540 1530
2310 2250 2170 2440 2500 2880 3330 2810 2380 2210 2110 2460 2180 2360 2310 2250 2490 2680 2340 2310 2470 2420 2590 2700 2390 2320 2430
2920 2620 2730 2820 2910 3230 3800 3160 2630 2500 2440 2940 2490 2660 2680 2560 2850 2870 2630 2640 2840 3130 2940 2930 2620 2820 2710
3160 2730 3230 2980 3400 3520 4010 3220 2740 2580 2540 3160 2620 2750 2880 2650 2980 2990 2670 2870 3120 3450 3150 2970 2750 2960 2860
3310 2960 3590 3270 3990 4140 4000 3500 3040 2870 2860 3360 2940 2990 2330 2850 3300 3310 2830 3180 3690 3730 3420 3180 2980 3320 3300
3070 2220 3380 3270 4080 4400 3610 3460 2960 2710 2860 3070 2840 2880 3150 2710 3240 3150 2670 3160 3720 3660 3380 3120 2880 3080 3290
2710 1630 3340 3050 4280 4810 2930 2880 2760 1600 2820 2960 2810 2590 3090 1810 3080 3080 2040 2810 3870 3420 3410 3070 2400 2750 3400
26180 23830 26630 27940 30480 38980 44350 30430 25970 26840 23593 26480 24830 25160 26410 24470 26920 28440 24890 25120 28930 31950 29350 28890 25950 26310 27380
514
TABLE 7
(continued) Measured flows in million m 3
Year Jan. Feb. Mar. Apr. May
June July Aug. S e p . Oct. Nov. Dec. Year ~~
~
1939 3170 1780 1600 1480 1750 2160 2540 2710 2790 3030 3000 2530 28540 1940 1650 1350 1370 1280 1370 1730 2190 2490 2590 2790 2630 1900 23320 1941 1460 1190 1240 1160 1340 1940 2360 2620 2710 2880 2840 2910 24650 1942 2050 1330 1440 1210 1480 1940 2380 2690 2960 3140 3000 2730 26350 1943 1640 1259 5340 1310 1510 1730 2210 2590 2740 2950 2900 2510 28689 1944 1600 1320 1320 1320 1600 2040 2420 2670 2810 3080 2860 2400 25440 1945 1670 1270 1270 1070 1230 1810 2260 2570 2810 3240 3150 3110 25460 1946 2290 1310 1220 1060 1220 1700 2260 2950 3510 3780 3740 3880 28920 1947 3780 2340 1460 1420 1560 1930 2410 2720 2920 3270 3210 3350 30370 1948 2700 1510 1440 1320 1480 2000 2450 2720 2890 3140 3150 3340 28140 1949 2940 1730 1520 1450 1450 1920 2370 2720 3010 3440 3280 3340 29170 1950 3080 1710 1480 1420 1710 1960 2430 2820 3090 3420 3300 3180 29600 1951 2210 1350 1350 1160 1190 1630 2110 2330 2460 2690 2650 2620 23750 1952 1780 1270 1220 1180 1420 1740 2190 2470 2570 2780 2750 2560 23930 1953 1670 1260 1280 1250 1430 1750 2200 2600 2770 3040 2970 2450 24670 1954 1710 1250 1290 1290 1360 1780 2320 2770 3130 3490 3360 3220 26970 1955 2610 1550 1400 1400 1500 1930 2350 2590 2790 3080 3040 3090 27330 1956 2840 1970 1580 1540 1820 2080 2480 2750 3000 3320 3180 3240 29800 1957 3040 1780 1650 1790 1600 2060 2450 2740 2790 2960 2800 2340 28000 1958 1600 1280 1290 1180 1380 1750 2340 2670 2840 3110 2960 3010 25410 1959 2220 1360 1380 1240 1560 1910 2300 2530 2680 2920 2860 2940 25900 1960 2320 1430 1500 1320 1610 1950 2390 2640 2680 2840 2780 2730 26090 1961 1820 1320 1380 1380 1380 1730 2310 2850 3220 3730 3430 3400 27950 1962 3300 2700 2420 1810 1900 2260 2720 3060 3240 3530 3500 3730 34170 1963 3760 2950 2270 1880 2350 2610 3020 3450 3880 4630 4680 4760 40240 1964 3930 3100 2890 2480 2440 2560 3170 4150 5200 6090 6210 6420 48640 1965 6060 4460 3800 3070 2800 2800 3500 4050 4200 4560 4400 4130 47830 1966 3200 2320 2190 1990 2320 2780 3250 3610 3920 4410 4520 4400 38920 196'1 3560 2390 2140 1900 1870 2170 2740 3250 3560 4210 4090 4060 35940 1968 3720 2674 2266 1848 1888 2214 2706 3097 3330 4689 3720 3255 35407 1969 2592 2158 2189 2040 2130 2508 3063 3286 3420 3813 3870 3813 34882 1970 2806 2216 2167 1929 1975 2373 2861 3255 3570 3968 3990 4154 35264 1971 3472 2500 2372 2067 1993 2181 2775 3255 3570 3968 3960 4092 36205 1972 3255 2248 2068 1836 2306 2451 3013 3255 3210 3317 3030 2492 32481 1973 2043 1682 1693 1581 1916 2283 2691 2979 3150 3379 3360 3286 30043
5 15
rABLh 8
The monthly and annual o u t f l o w s from Lake Tana i n t h e p e r i o d 1920-33 (Hurst, H . E . ,
Year 1920 1921 1922 1923 1924 1925 1926 1927 1928 1929 1930 1931 1932 1933
and P h i l i p s , P . , 1933)
Monthly mean d i s c h a r g e s i n m i l l i o n m3/day J a n . Feb. Mar. Apr. May
-
-
-
-
7.3 6.7 7.8 8.6 9.2 5.3
4.8 4.3 5.0 5.5 5.9
3.1 2.4 3.1 3.3 3.7
-
-
-
6.6
4.0 3.5 5.2 3.4 3.7 4.1
1.6 2.0 3.5 1.8 2.0 2.7
1.0 1.0 1.8 0.9 1.0 1.4
-
4.8 7.1 4.7 5.4 6.9
TABLE 9
3.1
-
1.5 1.1 1.7 2.2 2.0
-
June J u l y Aug. Sep. Oct. Nov. Dec.
-
0.7 0.7 1.1 1.0 1.1
-
0.3 0.4 1.1 0.9 0.7
-
-
0.8 0.7 1.1 2 . 1 1.0 1.5 0.6 0.5 0.7 0.6 0.7 0.6
1.2 2.3 3.2 4.1 1.4
12.4 11.8 15.8 19.1 21.9 11.4
3.5 8.6 4.7 1.3 2.9 1.5
14.8 33.6 16.0 10.1 18.1 10.1
-
-
25.0 25.7 36.2 38.4 48.4 21.3
26.3 25.8 31.8 31.5 34.1 18.7
25.9 55.0 30.3 25.2 39.4 28.7
18.0 16.7 20.0 20.1 23.8 12.3
19.4 38.7 19.3 23.1 29.3 24.5
-
11.4 10.6 12.1 13.4 15.2 7.9
Total mlrd m 3
-
3.34 4.08 4.44 5.16 2.94
-
-
14.3 8.5 20.6 1 3 . 2 1 2 . 5 7.7 13.8 8 . 3 16.8 12.6 1 7 . 3 11.6
3.08 5.63 3.36 2.85 4.04 3.35
Monthly and annual d i s c h a r g e s of t h e Blue N i l e a t R o s e i r e s f o r t h e p e r i o d 1912-1973 ( C a i r o U n i v e r s i t y - Massachusetts I n s t i t u t e of Technology, 1977)
Year 1912 1913 1914 1915 1916 1917 1918 1919 1920 1921 1922 1923 1924 1925 1926 1927 1928 1929 1930 1931 1932 1933 1934 1935 1936
Measured flows i n m i l l i o n m3 J a n . Feb. Mar. Apr. May
June J u l y
856 573 358 576 352 272 190 143 146 873 468 337 726 410 240 1190 670 500 1160 753 649 700 464 318 625 393 396 778 468 306 640 384 268 707 428 412 804 535 385 922 524 399 722 427 398 797 436 400 573 315 254 752 467 334 1070 622 459 630 344 257 675 383 259 707 419 327 805 452 317 878 485 360 999 746 471
1450 5930 14200 8690 396 2320 6620 6090 975 5660 16900 11400 1250 3640 8190 11100 1390 7450 19400 16800 1760 8210 18400 21100 1980 5850 12600 8670 1600 7200 15100 13100 2210 7230 12700 9910 1290 4330 15000 12300 1460 5510 14200 12200 1930 6890 18000 13100 1830 6960 15100 13900 2030 4890 12900 9900 1990 7320 17300 14000 1850 6130 12500 9080 2250 8900 17600 11900 4130 11000 19300 16600 1610 7090 14300 11300 1450 4890 15300 12700 1520 6260 16000 15500. 1210 4510 13300 13400 1700 7620 17900 12700 2590 10900 18900 16700 1510 8410 16400 14700
238 260 232 227 219 372 540 162 227 204 184 478 530 291 354 242 413 373 526 192 203 248 280 380 445
248 604 187 560 490 632 949 500 882 428 371 1080 564 701 1850 266 1540 1880 608 221 747 512 452 1100 535
Aug.
Sep.
Oct.
Nov. D e c . Year
3440 2140 8850 6940 10900 10900 3860 4280 7350 5690 6850 5160 5930 5280 7060 5220 5760 9890 4280 7520 7140 7130 7390 8100 5760
1620 743 4610 2960 4500 3910 1720 1800 2860 2190 2330 2380 3540 2380 2670 1840 2560 3230 2020 2570 2240 2900 2750 2830 2330
871 319 1740 1350 2210 2030 883 942 1320 1100 1220 1530 1630 1160 1550 990 1330 1890 1080 1200 1210 1510 1590 1590 1360
38474 20692 51033 37895 64735 69674 39614 46164 46103 44084 45617 52095 51708 41377 55691 39751 53395 69846 44965 47274 52137 46173 53936 45813 53606
5 16
TABLE 9
(continued) ~-
Year
Measured flows i n m i l l i o n n3 Jan. Feb. Mar. Apr. May
1937 824 478 371 1938 696 383 384 1939 932 541 405 1940 792 470 334 1941 475 291 208 1942 661 370 715 1943 734 500 438 1944 684 400 281 1945 616 344 225 1946 945 502 326 1947 906 517 461 1948 734 500 438 1949 893 500 419 1950 937 474 359 1951 718 405 350 1952 763 425 321 1953 616 336 280 1954 768 431 320 1955 1100 599 379 1956 911 514 382 1957 1090 605 1100 1958 590 398 256 1959 1050 642 456 1960 1190 714 536 1961 794 509 366 1962 1150 602 489 1963 881 483 400 1964 944 565 340 1965 1150 666 448 1966 880 563 467 1967 1600 512 725 1968 1321 1122 1057 1969 1293 1299 1528 1970 1575 1491 741 1971 1448 1183 1085 1972 1494 966 970 1973 899 707 415
236 217 364 243 126 288 222 246 180 292 688 219 358 508 243 245 245 252 459 467 1290 319 283 405 502 289 416 396 483 376 489 771 978 327 537 654 447
June J u l y
598 1370 370 1660 650 1630 345 1090 733 2350 556 1420 419 864 765 1580 756 1390 335 1820 415 1040 348 2580 439 2070 802 1780 382 1170 361 1150 569 912 304 1630 669 1500 440 2330 706 1780 382 1870 610 1100 547 1310 361 1410 558 1700 1250 1520 443 1670 277 1200 608 2190 487 1420 353 1647 753 1944 302 1095 412 1290 409 1404 638 1926
Aug.
Sep.
7360 17000 13100 9120 19000 16500 5620 11800 10800 3950 15100 10200 6170 12200 10100 8070 16600 12900 5070 14800 13800 6370 14400 11000 5660 12700 13700 9480 25200 15200 4920 17100 14900 7730 14500 14000 7740 16000 13900 5940 15100 13900 4340 15500 9670 6020 15300 11500 6850 17700 11200 8690 18100 15000 7500 16800 15300 7160 15000 12000 5660 17200 10500 7780 19000 13800 5380 16200 16100 7040 16300 13600 8990 17300 16800 5350 15100 14200 6140 16900 12500 8870 16900 14600 4760 13400 9420 5170 12300 11300 5920 14200 14200 7440 12990 5460 6479 18200 10470 4650 16957 11190 6851 15314 10680 5084 9021 4800 5532 15655 10800
Qct.
Nov. Dec. Year
4810 2280 1270 49697 10000 3230 1610 63170 6500 2910 1390 43542 3870 1580 816 38790 7040 3070 1350 44123 6870 2210 1210 51314 5940 2410 1230 46427 4190 1900 1940 43756 8490 3530 1690 49281 7227 3030 1580 65937 6580 2250 1380 51162 10200 3530 1590 56369 6600 2490 1680 52985 5570 2090 1190 48650 7440 3160 1540 45118 6510 2170 1110 45875 5840 2330 1290 48071 8570 3040 1620 58725 8750 3050 1640 57746 14100 4320 1950 59574 3720 1720 1000 46371 9670 3410 1700 59175 9290 3850 1980 56941 6980 2450 1400 52472 11100 3550 2330 63912 8940 2560 1460 52608 4860 2620 2300 50270 10600 3720 1950 60998 7200 3070 1750 43824 2260 2230 2410 40754 9052 3120 2020 53745 7409 2166 1485 31530 3100 1929 1804 33397 6200 2541 1262 48331 4526 2646 1500 47472 3441 1674 927 30844 6138 2346 1274 46577
517
TABLE 10
Monthly and annual discharges of the Blue Nile at Sennar for the period 1912-1973 (Cairo University
-
Massachusetts Institute of
Technology, 1977) ~
~~~
Measured flows in million m 3 Year Jan. Feb. Mar. Apr. May
--~ ~~
19 12 1913 1914 19 15 1916 1917 1918 1919 1920 1921 1922 1923 1924 1925 1926 1927 1928 1929 1930 1931 1932 1933 1934 1935 1936 1937 1938 1939 1940 1941 1942 1943 1944 1945 1946 1947 1948 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960
1100 765 254 1240 862 1600 1450 654 606 788 702 731 783 953 619 706 426 669 952 440 473 537 630 719 843 573 506 749 621 267 501 434 471 369 782 671 490 648 712 410 648 471 649 852 720 862 486 939 939
~
677 450 148 705 476 9 15 947 429 416 439 389 445 511 527 405 455 318 505 658 289 36 1 387 362 440 639 400 354 486 417 235 310 360 4 15 304 439 465 388 42 3 411 347 476 302 408 554 434 479 400 590 56 3
463 326 142 472 262 727 719 276 370 295 265 403 369 393 580 465 393 483 594 307 331 374 424 420 540 426 421 489 371 233 687 348 289 244 430 5 16 544 413 333 368 429 309 36 3 404 380 866 252 492 427
~~~
29 3 201 189 334 186 505 584 146 233 164 173 463 489 26 1 510 480 627 572 539 395 222 335 360 529 542 353 294 424 300 152 363 242 280 216 362 701 260 446 498 342 324 230 284 660 398 770 330 294 486
June July
Aug.
Sep.
Oct.
Nov. Dec. Year
~~
199 1280 697 472 158 689 607 1350 384 935 668 1630 982 2010 343 1450 497 1860 307 1050 245 1020 811 1920 518 1280 460 1730 1240 1810 331 1700 1470 2240 1860 3960 722 1520 226 1140 779 1390 573 1170 496 1540 1020 2600 603 1330 560 1320 421 1460 687 1530 388 1050 626 2420 660 1330 498 614 820 1410 776 1380 391 1800 502 922 357 2310 417 1870 852 1570 368 1000 438 939 554 1010 343 120 688 1310 510 1540 719 1580 398 1780 673 1030 607 1180
6590 14100 9940 4340 2290 1260 42532 2090 6750 6750 2140 752 374 21767 5620 18000 12400 10300 5540 2260 55700 3650 9390 11300 7520 3160 1640 41368 7160 20500 19400 13700 5600 2850 72315 8390 19900 24500 13700 4620 2620 79575 180 14100 10600 4720 2150 1130 39572 6850 14500 13000 3970 1790 966 44374 7130 13300 10800 8330 3030 1490 48032 3730 14100 12300 6250 2360 1230 43013 5090 15600 13700 7840 2680 1300 49006 6800 14500 13200 6030 2800 1540 49643 6490 15100 13300 6010 3450 1650 53950 4350 12900 9670 5120 1810 1100 39274 6630 17200 14000 7030 2250 1370 53644 6240 14300 10700 5240 1310 804 42731 8440 16700 11400 5140 2040 1180 50374 10500 18700 16600 10000 2920 1660 68429 6580 14000 11100 3940 1480 844 42929 4360 15100 13000 7520 2010 1010 45797 5920 15800 14900 6770 1810 1020 49776 3890 13000 13800 7320 2540 1340 45266 7150 18000 13100 7050 2200 1340 52652 10100 17900 15500 8010 2340 1460 61038 7940 16300 14400 5640 1820 1040 51637 7170 17200 12800 4460 1710 1050 48022 8560 18700 16400 9910 2750 1430 61206 4980 11400 10700 6140 2490 1180 41245 3490 14900 9900 3440 984 572 36433 5610 11700 9520 6420 2540 1100 40823 7450 16400 12100 6340 1610 875 48626 4910 15100 13300 5560 1880 998 44324 5180 13700 10500 4210 1280 801 39356 5398 12900 13900 8140 3210 1570 48407 9060 24000 15000 7060 2730 1380 63434 4230 15990 13200 5320 1670 1150 45337 7150 13600 13100 9310 3140 1340 51989 6650 15600 13900 6400 1910 1240 49917 5970 15000 13800 5190 1490 859 44685 4000 14400 9150 7180 2760 1370 41695 5530 14500 11000 5890 1560 805 42469 6290 16400 10400 5070 1700 998 44034 7950 18900 16200 8690 2330 1200 57347 6930 16500 15500 8280 2190 1250 53918 6660 14700 11600 12500 3510 1530 54482 5400 16200 10400 3200 1090 740 42306 7320 18200 13200 9020 2680 1340 53426 4830 14700 15100 8040 3150 1530 51268 6160 15300 13000 6350 1760 862 47634
5 18
TABLE 10
Year
(continued)
Measured flows i n m i l l i o n m 3 dan. Feb. Mar. Apr. May
196 1 4 34 1962 869 196 3 376 1964 5 3 3 1965 687 1966 411 1967 1128 1968 796 1969 458 1970 657 1971 709 1972 725 1973 254
TABLE 11
331 266 344 360 213 166 281 84 330 117 257 210 310 254 777 675 713 1023 658 322 727 520 429 362 220 232
-
437 477 1200 365 360 433 589 254 635 280 381 282 381
45 7 338 318 155 40 1 200 357 5 37 726 246 399 420 240
June J u l y
Aug.
Sep.
951 1700 1420 1350 973 1960 1062 1050 1296 822 735 843 1239
14900 13400 16000 18200 12400 11300 14198 14477 17515 16771 14415 8742 15717
15900 12800 11300 15600 8570 10900 12540 5550 8940 10320 9450 3360 9480
6800 4350 5090 8090 3880 4320 4681 6727 5332 3720 5890 3999 3689
Technology,
1912 1913 1914 1915 1916 1917 1918 1919 1920 1921 1922 1923 1924 1925 1926 1927 1928 1929 1930 1931 1932 1933 1934 1935 1936
9710 6180 4220 9430 5870 1230 6417 4247 1754 3875 3162 2046 4216
Nov. Dec. Year 2980 1740 1320 2580 1780 887 2103 1074 723 1362 1539 510 1056
1980 818 1050 1290 1020 1380 1345 644 709 313 647 272 403
55146 44376 43269 57958 36388 33488 44984 36808 39248 39346 38574 21990 37127
Monthly and annual d i s c h a r g e s of t h e Blue N i l e a t Khartoum f o r t h e p e r i o d 1912-1973 ( C a i r o U n i v e r s i t y
Year
Oct.
- Massachusetts I n s t i t u t e of
1977)
Measured flows i n m i l l i o n m 3 J a n . Feb. Mar. Apr. May
June J u l y
1340 824 576 324 870 473 351 217 340 203 166 158 1250 680 478 318 942 537 358 250 1730 1020 835 551 1290 780 625 537 726 438 321 175 646 368 358 308 888 433 347 202 727 388 297 171 782 507 375 454 848 572 420 414 860 493 436 304 644 454 507 535 813 456 464 416 500 299 301 420 632 386 348 355 1020 622 535 374 460 273 282 350 577 345 316 235 649 349 384 251 721 361 395 351 891 483 440 464 914 6 2 1 583 513
484 5910 15900 11400 466 1880 7520 8620 734 5250 19000 14300 971 3320 8060 11300 828 6760 20200 21500 1410 7300 17700 22900 1170 5370 18900 11300 1120 6200 16800 17300 1650 6170 13200 11400 865 3410 14600 14500 8 0 1 4570 16000 16100 2000 5890 16500 13900 1000 5890 15000 15600 1260 3840 13300 10700 1710 5590 18900 15100 1290 5450 16200 12900 1720 8100 17100 12800 3610 10300 18600 18400 1370 6330 14700 12200 868 3570 14800 15100 1240 4890 15600 15900 1030 3220 13200 15100 1260 7020 18200 14900 2190 9450 20300 18400 913 7170 17400 16700
207 566 246 461 368 645 400 241 313 259 175 569 497 417 1090 391 1110 1380 578 215 516 495 142 756 547
Aug.
Sep.
Oct.
Nov. Dec. Year
4390 3000 11300 8430 16100 15800 5000 5180 8750 7350 8990 7290 7200 6010 7950 6900 6090 11300 4750 8630 8070 8400 8530 9140 7580
2210 1140 5720 3510 6050 4820 2000 2220 3170 2310 2560 2850 3800 2070 2440 1660 2170 3240 1680 2440 2090 2940 2620 2760 2200
1230 390 2260 1840 2960 2500 1150 1230 1870 1180 1350 1700 1830 1110 1480 860 1180 1700 859 1100 1040 1470 1470 1540 1050
44805 25693 59677 40618 76853 77211 48522 51951 48203 46344 52129 52817 53071 40800 56400 47800 51790 70231 52749 48088 45319 47489 55966 66814 56191
5 19
TABLE 11
(continued)
Measured flows i n m i l l i o n m 3 Year Jan. Feb. Mar. Apr. May
June J u l y
Aug.
Sep.
Oct.
Nov. Dec. Year ~
19 37 19 38 19 39 1940 1941 1942 1943 1944 1945 1946 1947 1948 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 196 1 1962 196 3 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973
611 588 771 655 383 557 477 509 398 656 788 597 777 824 518 738 533 710 925 896 997 450 887 950 450 883 450 658 748 486 1110 850 388 704 69 1 896 198
387 464 39 7 426 496 489 39 3 40 1 26 1 302 330 537 352 327 377 280 266 276 387 329 507 533 424 59 1 483 453 446 36 8 348 394 461 428 321 338 440 389 635 425 467 401 587 797 389 215 482 475 56 3 462 324 354 480 392 280 168 284 136 433 205 285 207 384 170 740 536 722 1020 5 80 487 693 446 447 347 168 229
365 316 397 302 16 3 409 25 7 239 2 10 338 747 343 438 436 356 29 3 233 310 457 365 1140 275 297 438 402 383 300 168 204 272 443 495 921 711 606 641 444
433 1050 373 995 550 1170 353 851 359 1940 511 1010 422 439 542 778 392 841 380 1250 570 799 332 1760 268 1750 781 1330 289 889 410 770 486 1100 278 1090 613 1160 541 1230 759 1500 344 1330 540 810 498 807 460 850 427 1280 870 1120 453 984 466 637 265 1400 472 825 450 1038 651 1071 419 582 391 591 239 462 384 1041
6470 17500 14800 7380 18800 18200 4680 12100 11800 2940 16000 12700 4830 11400 10900 6560 18000 14200 4050 15800 15200 4880 13800 11400 3810 13400 14800 7750 23000 13000 3630 16400 16300 7520 14600 14400 6190 15900 15200 5390 16500 16300 3570 14400 11000 4860 15400 13500 6230 18000 12600 7800 20000 18200 5980 17600 16200 6500 15700 13100 4270 16400 11800 6600 19000 14400 3970 14200 17800 5190 17000 14300 7340 17400 18300 3870 15300 14500 5180 16700 12900 7460 19300 17300 3120 12400 9690 3580 12300 12200 4320 15000 14500 5766 14167 6420 4743 17887 10230 2142 15407 12360 5084 14260 11310 3286 9641 3780 3224 14539 10710
5600 1950 11700 3290 7160 2920 4070 1120 7110 2900 8210 1860 6750 2290 4910 1310 9600 3490 7970 2950 7280 1990 10800 3670 7910 2310 8270 1880 8180 3170 7050 1810 6260 1930 10500 2600 10200 2570 14500 4490 3570 1270 9370 2960 9210 3890 7930 1940 11000 2920 8850 1830 4780 1320 11200 3380 6980 2020 2050 1070 8210 2270 5952 1386 2037 906 4619 1773 3968 2106 2858 549 6014 1425
1100 50730 1460 63925 1280 43813 697 40482 1100 41648 912 53096 974 47338 634 39659 1380 48863 1500 59510 1270 56814 1440 56477 1430 53109 916 53664 1450 44558 860 46560 1070 48301 1300 63617 1450 58215 1690 59880 758 43848 1410 56743 1740 54301 966 61044 1990 61890 978 49153 1040 45108 1340 62663 1100 38003 1410 35525 1500 49204 1063 38869 626 41202 527 40311 725 40871 242 23388 564 38940
520
TABLE 12
Monthly and annual d i s c h a r g e s of t h e Main N i l e a t Tamaniat f o r t h e p e r i o d 1912-1973 (Cairo U n i v e r s i t y
-
Massachusetts I n s t i t u t e of
Technology, 1977)
Year
Measured flows i n m i l l i o n m 3 Jan. Feb. Mar. Apr. May
June J u l y
1912 3320 2280 1830 1450 1380 2010 1913 2960 1810 1650 1410 1870 2050 1914 1710 1280 1310 1230 1420 1820 1915 4240 2830 2100 1470 1820 2650 1916 3360 2140 1690 1510 1630 2460 1917 4940 4090 3380 2140 2100 2910 1918 5050 3920 4110 4390 4480 4490 1919 3220 2270 2100 1700 1710 3020 1920 2690 1890 1720 1410 1440 3150 1921 3410 2010 1860 1540 1500 2440 1922 2930 1750 1340 950 1050 2060 1923 3360 1670 1420 1330 1700 3440 1924 3320 1980 1530 1560 1810 2360 1925 3370 1980 1600 1280 1680 2840 1926 2800 1720 1700 1630 2230 3320 1927 3600 2340 1900 1680 1660 2490 1928 2070 1510 1520 1670 2660 3380 1929 3050 1890 1700 1590 2980 5510 1930 3670 2330 2020 1750 2090 2830 1931 2130 1460 1410 1350 1300 2150 1932 2780 1710 1610 1390 1740 2880 1933 4070 3150 2300 1860 2060 2660 1934 3730 2180 1890 1720 1980 2830 1935 3790 2420 1980 1840 2170 3760 1936 3350 2300 2160 1740 1840 2440 1937 2640 1720 1770 1520 1710 2580 1938 2780 2080 2070 1600 1610 2200 1939 3460 2630 2170 2380 2300 2840 1940 2580 2410 2500 1620 1620 2150 1941 1960 2110 2180 1370 1420 3160 1942 2730 2120 2620 2430 1710 2580 1943 2310 2340 2590 2120 1720 1860 1944 2010 2610 2800 2380 1930 2710 1945 2000 2270 2580 2140 1550 2670 1946 3180 2120 2930 2520 1860 2570 1947 3860 3040 3030 2950 3090 3030 1948 3310 2570 2950 2660 2170 3170 1949 3200 2110 2830 2840 2450 3030 1950 3460 2620 2840 2850 2980 2750 1951 3060 1880 2940 2790 1660 2120 1952 2530 2650 2640 2080 1590 2160 1953 2270 1980 2830 2160 1740 2400 1954 2150 2350 2760 2420 1510 2460 1955 3400 2360 2650 2920 3120 2740 1956 3310 2480 2810 2710 2950 3290 1957 3620 2660 2850 3090 3350 3970 1958 2140 2060 2380 2380 1620 2700 1959 3160 2100 2730 2690 2230 2410 1960 2960 2240 2820 2820 2520 2370
Aug.
Sep.
Oct.
6500 16800 11800 7820 3270 8740 10800 5710 5970 20100 17500 14900 4960 10000 12800 11000 8430 21800 23800 20500 8280 18100 25400 21000 7780 14800 16500 9690 7620 17900 19700 9780 7890 15900 15200 13100 5100 15800 16400 11500 5920 15100 18800 13400 7320 18300 18100 10900 6990 16600 18900 10300 5820 14500 13300 9310 6410 18700 17500 11300 6440 16300 14400 9700 9460 18200 17000 9690 11800 20200 21200 15300 7630 18900 17100 8210 5580 16500 18300 11600 6260 17300 18000 11700 4960 14600 17800 12400 8180 18800 18500 12100 10200 20000 20000 13800 7960 18000 20100 11400 7460 18300 18000 9050 7740 19600 21300 15200 5230 13100 14600 9630 4110 15900 14300 7090 5310 12900 12100 10000 7120 18200 14800 11200 4950 15100 16500 8970 6190 14800 12800 7590 5250 13800 15700 12300 8840 24100 20400 11100 4660 16900 17600 10100 7890 16600 15900 13700 7120 16600 16300 10800 6160 17100 17000 10700 4460 14600 12200 10200 5780 15400 14100 8910 7040 17800 13900 8810 8450 20700 20600 13500 7190 18100 18000 12900 6900 18000 15900 17000 5790 17100 13700 5800 7560 20200 16100 12000 5510 15800 19900 11400 6240 16300 15600 10600
Nov.
Dec.
5030 3900 3470 2370 9170 5520 6270 4600 10300 6440 8980 6200 5820 4390 5110 3750 6490 4580 5500 4140 5980 4330 5410 4410 6450 4410 4860 3790 5810 4510 4350 3300 5110 4120 6620 4630 4110 3190 5500 3890 5530 4400 6600 4940 5840 4620 5940 4350 5200 3770 4650 3810 5990 4320 5430 3900 3380 2580 5880 3370 4360 3510 4450 3140 3860 2810 6370 4220 6130 4200 4580 3900 6460 4020 5290 4070 4660 3600 5240 3680 3940 3070 4280 3320 5430 4160 5070 3920 7510 4370 3510 2720 5470 3720 5990 3910 4090 3050
Year
64120 46110 81930 64740 104060 107520 85420 77880 75460 71200 76610 77360 76210 64330 77630 68160 76390 96470 73830 71170 75500 77400 82370 90250 80260 73210 86490 67690 60180 61760 73380 66050 62490 70850 89950 76140 81400 76640 76720 74830 62690 66530 86490 82370 87230 68160 78330 77830 72470
,521
TABLE 12
Year 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1975 1973
(continued) Measured flows i n m i l l i o n m 3
J a n . Feb. Mar. Apr. May
June J u l y
2400 3700 3220 4150 5800 3710 4670 3844 2635 5022 3565 3844 2136
2110 4080 3660 4490 4570 3820 3270 3360 2934 2451 2544 2568 3360
TABLE 13
2000 2770 2720 3360 4830 2900 2900 3538 2436 2477 3190 2807 1668
2890 3060 2640 3100 4270 2650 1990 3193 3224 2691 2883 2920 2027
2800 3310 3050 3370 3660 3870 3490 3630 4740 3870 4080 3840 3060
1840 3440 3830 4240 4910 3510 3450 3689 3968 3072 3379 3056 3224
8160 5560 8010 9330 5860 6200 5850 7192 5797 4061 6572 5177 4557
Aug.
Sep.
Oct.
18900 16000 19000 21200 13600 13300 16400 6262 17949 15531 15097 9455 13702
20200 16500 15300 20800 12300 15400 16800 9270 13020 14070 13410 6900 12840
14100 11200 8590 15000 10900 5750 11800 9145 5394 8122 7223 6200 8122
Nov. 5770 4700 4140 8050 5640 4610 5580 4230 3620 5220 4770 3120 4110
Dec.
Year
4590 85760 3920 78240 4460 78620 5910 103000 4680 81020 5200 70900 5090 81290 4061 71434 3503 69320 3255 69842 3751 70646 2508 51395 3091 61897
Monthly and annual d i s c h a r g e s of t h e Main N i l e a t Hassanab f o r t h e p e r i o d 1912-1973 ( C a i r o U n i v e r s i t y
-
Massachusetts I n s t i t u t e of
Technology, 1977)
Year
Measured flows i n m i l l i o n m 3 J a n . Feb. Mar. Apr. May
1912 4350 2970 2440 1913 3710 2370 2090 1914 1710 1070 1050 1915 4100 2810 2010 1916 3300 2000 1520 1917 4710 3620 3150 1918 4790 3790 4070 1919 2800 1930 1740 1920 2580 1630 1460 1921 3260 2120 1530 1922 2970 1800 1270 1923 3200 1840 1520 1924 3610 2290 1750 1925 3420 2030 1690 1926 2950 1810 1680 1927 3520 2390 1860 1928 2060 1520 1460 1929 3240 2050 1850 1930 3800 2490 2000 1931 2260 1490 1420 1932 2940 1770 1580 1933 3940 3050 2240 1934 3840 2350 2000 1935 3860 2410 1960 1936 3610 2350 2160
June J u l y
1980 1820 2250 1830 1830 1860 949 1110 1460 1520 1690 2250 1130 1240 2020 1890 1680 2560 4000 3560 3450 1420 1270 2090 1170 1130 2720 1030 1070 1890 857 862 1700 1470 1620 3230 1560 1780 2260 1380 1640 2440 1560 2040 3390 1620 1620 2160 1600 2560 3120 1640 2440 1800 1650 2010 2520 1340 1330 1880 1400 1630 2460 1690 1800 2350 1600 1830 2560 1860 2040 3480 1810 1820 2320
6780 2670 4610 4470 7150 7670 7230 6520 7320 4570 5220 6780 6660 5390 5970 5300 8550 10900 6410 4530 6040 4340 8300 9610 7850
Aug.
Sep.
1.8500 16700 8030 10500 17100 16300 11200 14100 19000 21500 18200 23100 13800 14600 16100 18800 16300 14300 15200 18100 17400 18100 19000 18400 16400 18300 14400 12900 18900 18400 15500 14100 16600 16200 20100 21400 16800 15200 15200 17200 17800 18600 14200 17100 18400 19100 20000 20600 17600 19700
Oct.
Nov.
Dec.
Year
9890 5650 14700 12200 18800 18900 8900 9250 12500 12000 13200 12600 11900 9260 11900 9770 9820 16200 8930 12700 12800 12700 13200 14700 11800
6260 3360 7290 6670 10100 8390 5210 5020 6700 5630 6130 5910 7016 5120 6010 4390 5540 7240 4450 5950 5860 7120 6310 6310 5490
4810 78750 2370 46270 5110 72459 4470 67490 6190 93950 6000 100470 3970 77370 3860 70800 4330 72140 4030 70430 4160 73669 4520 80090 4660 77286 4060 63730 4350 78960 3260 65490 4250 73280 4720 86340 3340 69600 3920 69220 4320 77200 4860 75390 4550 84040 4450 91280 3780 80290
TABLE 13
(continued)
Measured f l o w s i n m i l l i o n m 3
Year Jan. Feb. Mar. Apr. May
June J u l y
1937 2730 1770 1750 1430 1580 2370 1938 2920 2080 2080 1600 1580 2060 1939 3689 2880 2210 2370 2300 2690 1940 2620 2300 2500 1620 1510 1940 1941 1850 2090 2180 1460 1300 2950 1942 2880 2200 2690 2580 1700 2550 1943 2580 2340 2560 2180 1650 1710 1944 2130 2380 2650 2410 1880 2560 1945 2090 2150 2590 2030 1300 2430 1946 3210 2020 2840 2390 1810 2310 1947 3930 3070 3060 2900 2970 2960 1948 3300 2550 2920 2690 2200 2840 1949 3390 2490 2720 2750 2550 2660 1950 3560 2590 2750 2770 2960 2770 1951 3010 1860 2810 2650 1740 1950 1952 2680 2670 2750 2250 1610 2040 1953 2460 2060 2810 2300 1750 2390 1954 2360 2330 2840 2590 1670 2260 1955 3620 2510 2560 2820 2910 2660 1956 3490 2570 2800 2740 2980 3060 1957 3630 2760 2800 3030 3250 3840 1958 2350 2060 2380 2560 1840 2560 1959 3090 2210 2760 2630 2190 2250 1960 2960 2260 2540 2630 2390 2120 1961 2300 1820 2600 2690 1890 1840 1962 3630 2740 2950 3200 3300 3740 1963 3180 2700 2630 3140 3800 3660 1964 4380 3460 3150 3300 4050 4280 1965 5710 4880 4380 3640 4180 4060 1966 3920 2950 2580 3650 3550 3610 1967 4690 3030 2110 3480 3510 3170 1968 4120 3570 3010 3300 3320 3210 1969 2800 2330 2970 4380 3910 2870 1970 3130 2290 2290 3450 2950 2260 1971 3780 3330 2590 3960 3440 2480 1972 3840 2820 2660 3360 3010 2960 1973 2210 3330 2590 2630 2610 2550
Aug.
Sep.
6620 18200 18100 6640 19800 20600 5030 13100 15100 3780 15400 14400 5050 12000 12200 6570 18300 15800 4560 13600 16400 5480 14500 13400 4393 13800 15900 7340 20800 21300 4120 15900 18200 7130 16000 16100 6630 17000 17300 5430 16300 16800 4440 14100 12600 4460 11500 14700 6290 16600 14400 7440 18500 18500 5530 15600 16500 6750 16200 14900 5440 14100 13400 6510 16900 15000 4920 16100 20900 5470 16300 15800 7140 18000 21300 5540 15000 16900 2710 17300 15800 8540 19400 20600 5340 12400 13400 5480 11900 15200 5540 15700 17800 6570 15250 10020 5740 17580 14280 3970 16710 15480 5920 16180 15060 5050 8770 7050 4280 14380 14370
Oct.
Nov.
Dec.
9740 16100 10300 7390 10200 11500 10000 8820 12900 12100 11100 13600 11300 10100 10500 9670 9990 14000 12800 14400 6100 12400 11900 10900 14400 11700 9150 15000 10400 6300 12200 9610 5450 8150 7500 6450 8340
4860 3920 6500 4590 5890 3890 3610 2700 6010 3480 4560 3560 4920 3210 3960 2810 6050 4340 6920 4840 4750 3970 6760 4200 5600 4160 4890 3670 5750 3750 4440 3160 4760 3560 5860 4390 5300 3980 7740 4880 3640 2920 3650 3900 6390 3950 4110 3010 6050 4580 4940 3960 4680 4780 7980 5310 5800 4800 4650 5050 5790 4900 4290 4000 3810 3600 5340 3840 5040 3910 3390 2550 4320 3130
Year
73070 866 10 69450 59770 60770 74890 65710 62780 69973 87860 76930 80290 78550 74590 65160 6 19 30 69370 82710 76 790 82510 64030 72 110 79190 704 80 84 7 30 78600 73530 99450 79110 68840 8 1920 706 70 69720 69860 73190 5 19 10 62070
523
TABLE 14
Monthly and annual d i s c h a r g e s of t h e River Atbara a t Atbara, near mouth, f o r t h e p e r i o d 1912-1973 (Cairo U n i v e r s i t y
-
Massachusetts
I n s t i t u t e of Technology, 1977) Measured i n f l o w i n million m 3 Year Jan. Feb. Mar. Apr. May June J u l y Aug.
1912 1913 19 14 1915 19 16 1917 19 18 19 19 1920 1921 1922 1923 1924 1925 1926 1927 1928 1929 19 30 1931 19 32 1933 1934 1935 1936 1937 19 38 1939 1940 1941 1942 1943 1944 1945 1946 1947 1948 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960
30 34 0 25 5 68 35 0 0 0 0 0 12 0 0 0 0 0 0 0 0 0 8 0 0 0 0 0 0 0 0 0 25 17 16 37 39 50 59 54 46 18 62 0 0 112 57 43 59
5 3 0 3 0 10 9 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 8 0 0 17 13 13 0 2 0 1 19 0 0 61 37 14 23
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 9
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 2 0 0 29 5 2 5
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 16 0 0 0
0 126 0 0 0 1 0 0136 0 7 9 0 221 3 2 2 0 100 0 219 0 5 0 0 4 3 0 7 2 0 6 4 0 4 8 0 0 0 5 5 0 173 0236 0 4 1 0 2 2 0 7 0 0 0 333 6 232 0 0 0 9 0 0 0 1 3 0 0 0 3 7 0 0 0 0 0 0 123 295 0 316 0 34 0 231 0 92 0 0 0 3 1 0 0 0 212 0 171 0 0 0 0 9 72 0 97 0 0 0 8
1990 593 1570 858 5160 1240 1050 1790 1860 1150 1990 1280 2480 1120 2020 1610 1300 2580 2370 1060 1930 874 2830 1460 1740 1560 1590 1270 1070 789 1600 1270 2360 1210 2440 893 1650 1090 2180 1080 1120 2060 2310 1030 1940 774 1540 1740 1510
Sep. O c t . Nov. D e c . Year
6990 3330 407 136 2350 1690 210 32 7180 3280 1030 331 3060 2750 684 146 13200 6440 1540 454 1430 7410 1210 270 3620 1200 390 67 4650 2910 457 79 6040 2600 922 200 5520 3430 776 147 7900 7470 1000 169 6100 3680 725 139 6080 4460 774 259 3950 2020 466 74 4580 3340 624 142 4350 2750 615 75 4670 2350 476 105 7240 3760 974 165 4170 2510 449 110 5520 3550 931 186 6330 4360 813 145 3640 4190 994 290 7420 3300 1040 171 5040 4850 1130 192 5580 4750 810 176 6400 3780 780 154 7360 4820 1380 260 3970 2580 820 190 4700 2230 390 78 3090 1710 562 274 5420 3220 807 150 6010 5640 998 234 5390 2720 593 123 4510 3810 1390 290 10680 3750 901 294 4940 3350 826 145 4580 2990 990 191 4110 3180 834 183 6550 4930 832 182 4570 2860 856 314 4950 3260 637 137 7350 3710 950 216 9020 6880 2140 384 5250 5010 1860 298 6020 3790 1940 607 5270 3140 410 108 7360 4020 1110 207 8240 5560 1100 337 4200 3330 805 170
46 5 82 35 173 95 8 2 43 12 17 45 58 0 0 0 0 36 19 54 49 119 66 66 64 47 93 39 28 60 59 69 50 82 102 70 89 81 92 115 44 112 163 76 158 71 81 129 55
13060 4717 13453 7697 27051 14954 6404 9988 11884 11085 18389 12041 14187 7678 10706 9455 7074 14991 9669 11332 13634 10107 15168 12976 13100 12730 15503 8882 8496 6522 11256 14221 11269 11727 18499 10313 10763 9633 14825 9882 10238 14629 21049 13524 14455 10072 14514 17165 10165
524
TABLE 14
Year
(continued) Measured flow
million m3
Jan. Feb. Mar. Apr. May June J u l y Aug.
1961 22 1962 67 1963 44 1964 37 1965 165 1966 6 1967 8 1968 0 1969 0 1970 0 1971 0 1972 0 1973 0
TABLE 15
in
4 25 18 23 135 0 3
0
0 0 0 0 0
0 6
0 7 0 0 3 0 0 0 0 0 0
0 0
0 0 0 126 78 0 0 0 0 0 0
0 4 7
0
15 0 15 117 190 0
0 0 0 0 0
4440 1180 17 1450 0 2040 40 1120 692 415 111 1580 0 1670 0 1250 0 1070 0 1180 0 25 10 0 0
6130 6050 5050 7230 3960 3490 5960 3880 5210 6320 3690 3500 6080
0
Sep. Oct. Nov. Dec. Year 4830 1200 253 4490 1000 230 3350 812 149 4760 917 191 2260 324 35 1820 217 42 4000 934 90 680 370 10 1440 80 10 2990 310 70 2370 280 30 590 150 0 1540 400 42
155 158 103 18 0 31
14 3 4 31 0 0 0
17081 13206 11008 15223 8054 6956 12971 6613 7994 1079 1 7550 6750 8062
Monthly a1.d annual discharges of t h e Main N i l e a t Dongola f o r t h e period 1912-1973 (Cairo University
-
Massachusetts I n s t i t u t e of
Technology, 1977)
Year
Measured flows i n m i l l i o n m 3 Jan. Feb. Mar. Apr. May
1912 3880 1913 3650 1914 2100 1915 4190 1916 3510 1917 5340 1918 5350 1919 3700 1920 3430 1921 3800 1922 3420 1923 3650 1924 3730 1925 3760 1926 3390 1927 3850 1928 2590 1929 3480 1930 4210 1931 2720 1932 3440 1933 4200 1934 4190 1935 4200 1936 3950
2540 2310 1420 2930 2170 4130 4350 2390 2050 2180 1960 1970 2400 2470 2230 2740 1690 2230 2870 1640 2010 3380 2710 2850 2640
1920 1870 1290 2050 1500 3790 4810 2070 1590 1680 1380 1260 1650 1820 1820 1960 1460 1810 2210 1470 1679 2730 2010 2140 2230
1450 1480 1100 1380 1180 2410 4540 1620 1310 1300 1050 1130 1240 1370 1690 1590 1330 1480 1730 1260 1360 1670 1670 1700 1770
1230 1360 1180 1290 1130 1760 4340 1470 1220 1120 880 1520 1400 1290 1760 1570 1720 1790 1740 1340 1390 1760 1660 1840 1730
June July
Aug.
Sep.
Qct.
Nov.
Dec.
Year
1080 1700 1140 1600 1320 2080 3460 1680 1970 1380 1000 2370 1550 1630 2700 1500 2710 3770 1910 1200 1980 1930 1820 2680 1800
20800 7680 22900 12300 27100 19600 15600 19200 20700 17900 19300 22500 19600 15700 21600 18300 19900 25400 19700 16900 20200 14400 22100 22900 20000
19600 13400 22300 16400 31700 31500 18800 22400 19100 21500 25500 23100 23300 17900 23100 20300 21000 25800 18500 21600 23100 22800 24400 24200 25500
11100 7860 18000 15000 23200 24200 11900 13000 15800 15200 17000 16700 14500 12800 14900 13700 12200 18700 11500 14800 15900 15100 16500 17200 15600
6100 4140 10500 7840 12200 11600 6670 6260 8710 7140 8130 6970 7900 5940 7500 5510 6610 9320 5230 7920 7300 8690 7400 7520 6890
4580 3020 6260 4910 7060 6880 5010 4500 5180 4580 5060 4790 5290 4080 4810 3670 4350 5210 3660 4420 4680 5660 5020 4950 4200
77980 50800 91090 72970 118170 119120 91130 83360 87290 81080 88500 90960 88290 73210 90580 79440 83080 108990 78850 78640 88109 86130 97080 100180 92640
3700 2230 2900 3080 6100 5830 6300 5070 6230 3300 3820 5000 5730 4440 4960 4750 7520 10000 5590 3370 5070 3810 7600 8000 6230
525
TABLE 15
Year
(continued) Measured flows i n m i l l i o n m 3
Jan. Feb. Mar. Apr. May
1937 3170 1938 3350 1939 4120 1940 3160 1941 4040 1942 2990 1943 3030 1944 2670 1945 2610 1946 3700 1947 3990 1948 3410 1949 3490 1950 3750 1951 3110 1952 3040 1953 2490 1954 2560 1955 3520 1956 3410 1957 3750 1958 2320 1959 3220 1960 3120 1961 2550 1962 3670 1963 3350 1964 4300 1965 5750 1966 3930 1967 4650 1968 4092 1969 2954 1970 3255 1971 3472 1972 3472 1973 2192
1900 2090 3160 2080 1820 2080 1850 1700 1880 2299 3080 2680 2590 2720 1890 2320 1830 1790 2580 2730 3020 1880 2310 2220 2780 2760 2820 3240 5080 3020 3306 3422 2294 2575 3422 3103 1494
1650 2210 2340 2500 2150 2540 2500 2570 2750 2510 3060 2500 2410 2540 2320 2760 2320 2550 2150 2470 2480 2170 2280 2230 2310 2590 2560 2860 4390 2540 2108 2883 2635 2145 2297 2378 1559
1450 1670 2140 1830 1670 2520 2220 2450 2280 2470 2600 2560 2520 2510 2420 2250 2420 2350 2480 2590 2920 2400 2540 2500 2600 2990 2820 2700 3580 3210 2985 3150 3840 3480 3660 3660 2568
1400 1470 2220 1350 1150 1810 1610 1800 1500 2130 2860 2200 2550 2720 1990 1590 1510 1650 2530 2720 3070 1770 2270 2500 2030 2980 3250 3630 4170 3550 3317 3255 3782 3193 3503 3348 2858
June J u l y 1800 1600 2170 1550 1930 1920 1560 2130 2010 1610 2920 1830 2010 2270 1300 1490 1740 1440 2390 2630 3390 1610 1860 1800 1510 3220 3590 4100 4520 3110 3030 2988 2571 2199 2352 2490 2769
4840 4520 4230 3430 4430 5450 3280 5190 3890 7370 3480 5860 4630 5430 3400 3930 5200 6870 5030 6660 4770 5920 3970 4480 6550 5000 6990 7920 5820 5570 5890 7006 5890 3441 5487 5084 4092
Aug.
Sep.
Oct.
Nov.
Dec.
Year
21600 23800 14000 16200 13300 22400 12000 18300 16000 26900 16400 17500 18500 22400 16500 15790 23000 25200 19900 20100 18600 25200 19500 17400 23200 17400 22100 24900 14800 12800 19902 17825 19778 19499 19096 11129 17174
23800 27000 18400 18200 15100 21000 24300 18500 19600 27700 22900 19200 20200 23300 18200 20450 20400 27600 22900 20800 19500 22700 27800 20400 26800 22600 19700 25700 15600 17500 22050 11400 17400 20760 20160 8820 16560
13500 19800 12400 9760 11100 14500 12900 12100 15900 14600 13900 15500 13200 14100 11900 11400 12700 19000 17200 17900 8530 15200 14800 13500 17400 15500 10600 16400 11000 7290 13919 9951 6262 9114 9300 7378 10199
5790 8850 7580 4280 7430 5520 6090 5040 8000 8230 5760 8690 6960 5910 7610 5300 5430 7370 6400 11100 4360 7150 8470 5370 7560 5830 4880 9450 6600 4470 6240 4590 3960 4860 5550 3630 4860
4310 5260 4360 2990 3990 3810 5300 3640 4890 5200 4060 4560 4380 3780 4420 3280 3620 4490 4090 5260 3020 4540 4350 3140 4920 4020 4560 5850 4910 4530 5270 3689 3348 3751 4185 2558 3131
85210 101620 77120 67350 66110 86540 76640 76090 81310 104719 85010 86490 83440 91430 75060 73600 82660 102870 91170 98370 77410 92860 93370 78660 99210 88560 87220 111050 86220 71520 92667 74251 74714 78272 82484 57050 69456
526
TABLE 16
Monthly and annual discharges of t h e Main Nile a t Aswan f o r t h e period 1912-1973 (Cairo University - Massachusetts I n s t i t u t e of Technology, 1977)
Year
Measured flows i n m i l l i o n m 3 Jan. Feb. Mar. Apr. May
June J u l y Aug.
Sep.
Oct.
Nov.
Dec.
Year
1912 3380 2470 1890 1410 1180 984 3170 18500 18200 11100 5690 4170 72140 1913 3260 2040 1480 1280 1170 1470 1740 6500 12200 7540 4120 2830 45630 1914 1720 1150 1070 947 998 975 2010 19400 20000 16500 10700 6930 82480 1915 4510 3090 2130 1360 1170 1460 2850 10700 14900 14700 8090 5270 70230 1916 3850 2400 1610 1180 1090 1340 5010 25000 26600 22400 13300 7880 111660 1917 5370 3910 3580 2320 1680 1860 4830 17500 27800 22800 11600 7460 110710 1918 5270 3990 4330 4090 3960 3230 5190 13600 17700 11100 6210 4580 83250 1919 3440 2180 1910 1520 1350 1520 3680 16600 20800 12600 6140 4410 76350 1920 3320 2090 1600 1370 1220 1710 5370 18200 17800 15000 8960 5570 82410 1921 3820 2370 1760 1330 1180 1300 2980 15400 19600 14800 7590 4700 76830 1922 3530 2090 1460 996 801 900 3280 18800 23600 15900 8240 4880 84480 1923 3030 2350 1540 1200 1380 2050 4440 20100 21400 16200 7250 5170 86110 1924 4000 2650 1850 1320 1470 1630 5050 18000 22300 14300 7990 5590 86150 1925 3840 2540 1830 1370 1260 1580 3910 13400 16600 12500 6450 4480 69760 1926 3440 2150 1640 1340 1330 2390 4360 19200 20600 14500 8330 5230 84510 1927 3940 2910 2030 1440 1300 1290 4180 15600 18300 13300 6090 4010 74390 1928 2600 1630 1310 1160 1320 2560 6290 18200 20000 12400 7300 4820 79590 1929 3670 2400 1770 1340 1390 3250 8770 23200 24500 18000 9910 5580 103780 1930 4250 2950 2120 1540 1530 1660 4400 18300 17600 11800 5640 4020 75810 1931 2350 1790 1500 1220 1090 1140 2850 15900 21300 15000 8620 4840 77600 1932 3580 2260 1680 1320 1270 1700 4280 18900 22900 13800 7720 5050 84460 1933 4170 3470 2850 1680 1600 1800 3280 13100 22100 15300 9150 5940 84440 1934 4340 2960 2110 1550 1440 1700 6050 20500 23700 16400 8370 5250 94370 1935 4170 2990 2170 1530 1520 2330 7100 21300 24100 17700 8220 5200 98330 1936 4000 2800 2180 1560 1450 1530 5490 19000 23900 15800 7420 4550 89680 1937 3340 2100 1740 1360 1130 1500 3950 19800'22300 14300 6050 4590 82160 1938 3540 2160 2160 1560 1280 1450 3710 23200 27800 19500 9520 5520 101400 1939 4120 3240 2430 1960 2220 1960 3920 13100 18400 13000 7980 4770 77100 1940 3420 2130 2430 1810 1310 1330 3050 15300 18000 10900 4630 3370 67080 1941 2260 1830 2070 1630 1100 1550 4320 12000 14400 11100 8040 4540 64840 1942 3200 2330 2460 2310 1930 1710 4530 20300 20300 14900 6360 4240 84570 1943 3230 1910 2570 2080 1670 1480 2670 15600 24700 14200 6840 4270 81220 1944 3070 2000 2660 2270 1890 1810 4180 16700 18100 12600 5240 3850 74370 1945 2590 1340 2550 2150 1580 1610 3580 14900 18900 16400 8410 5360 79370 1946 3840 2550 2360 2310 2120 1340 6130 25100 27800 15800 9100 5980 104430 1947 4420 3480 3180 2520 2770 2850 3170 14900 22500 15000 6550 4640 85980 1948 3710 2950 2510 2370 2330 1530 5430 16600 19300 15700 9790 5190 87410 1949 3610 2830 2440 2400 2510 1900 4080 18100 20400 14300 7490 4840 84900 1950 3860 2900 2500 2390 2530 2280 4610 20800 22500 14800 6610 4460 90240 1951 3390 2240 2270 2340 2150 1180 2850 15400 17800 12000 7790 4940 74250 1952 3280 2380 2680 2100 1610 1690 3210 14900 21100 12500 6240 3710 75400 1953 2790 1890 2180 2410 1600 1460 3860 22000 20800 13900 6330 4120 83340 1954 2870 1830 2550 2270 1820 1180 5630 24800 28300 20500 8550 5050 105350 1955 3820 2710 2080 2280 2490 2180 4320 19200 22700 18000 7410 4580 91770 1956 3580 2800 2350 2310 2250 2370 5780 19700 20700 18400 12400 5760 98700 1957 3990 3110 2380 2630 3010 2960 4450 17600 21400 9920 4890 3380 79720 1958 2560 1850 2080 2150 1700 1300 5000 24600 24500 15700 8410 4870 94720 1959 3430 2420 2250 2420 2340 1620 3370 18700 29600 16600 9670 5090 97510 1960 3650 2420 2220 2460 2370 1730 3790 17100 20900 14500 6610 3740 81490
527
TABLE 16
(continued) Measured flows i n million m 3
Year
1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973
Jan. Feb. Mar. Apr. May
June July Aug.
Sep.
Oct.
2940 4140 3710 4770 5880 4380 2745 3281 2900 3060 3554 3450 2610
1310 3140 3310 3840 4540 2330 5869 6350 6570 6520 6490 6535 6580
27000 22500 21800 27000 17300 16900 7096 4180 4200 4285 4445 4245 4235
18600 9410 5680 101890 26700 7260 4730 90560 13200 6 150 5110 90080 18300 12300 6980 116570 12400 9770 5750 92150 11400 5020 4870 74480 126 10 5598 4670 69540 3795 3590 3240 53800 3810 3640 3390 53510 3750 3395 3245 54700 3775 3670 3295 55890 3745 3590 3025 55470 3855 3920 3580 55430
1980 3080 2960 3570 5250 3140 3390 4228 3700 3980 3785 4020 3505
2210 2780 2700 3040 4940 2510 3888 4063 3970 4090 4275 4240 4380
2540 2900 2550 2550 3660 2580 3557 3700 3660 3920 3940 4040 4000
2220 2840 2880 3480 3660 3570 4480 4785 4870 5420 5475 5290 5360
5400 4690 5310 5840 5600 5480 6618 6065 6710 6720 6965 6990 7005
22600 15800 20400 24900 13400 12300 8921 6105 5890 6110 6225 6290 6380
Nov.
Dec.
Year
528
13.:
APPENDIX E
Extension of the agreed curve u s i n g h y d r a u l i c model t e s t s .
13.C
c
'
E
___----
12.5
m C
0
12.c
0
"
The agreed curve
"
L
e
m 3 0
*
11.5
,i/
/-
1 1 .o
10.5
/
J
Measurements reported b y Hurst.
,
I
1
1
aJ m
3
* 13.0 0
,
1
1
1
1
1
4
1
1
529
APPENDIX E
9.0I
25
150
200 Discharge,
2 50
300
3 50
m 3 /sec.
' \
L
100
Rating c u r v e s of t h e River Semliki measured a t Bweramul
Fig. 3
'
I
I
50
\
! I
1
1
!
1
I
I
I
, I
I
I
I
I
I
11.0 10.6 10.2 9.8 9.4 9.0 1000 1200 1400 1600 1800 2000 2200 2400 Pakwach gauge r e a d i n g , rn. Panyango discharge, m 3 l s e c . Fig. 4
Rating curve of t h e Albert N i l e a t Panyango
4 00
5 30
APPENDIX E
531
APPENDIX E
3.0
-
2.8
2.6 -2.2 -
0.4
0
Fig. 6
1
20 20 6 0 80 100 120 140 160 180 2 0 0 2 2 0 2 4 0 260 280 300 Discharge,
m3/sec
R a t i n g c u r v e of t h e R i v e r A s s u a (1923-1927)
5 32
.
APPENDIX E
X
X
al
d
al
c Y
al
0
w
> a M
m
c,
.rl
m
APPENDIX E
I " " ." ." "
...
. .. . ..
..
.. . .
-
1
r
-
1 7
P rl d
4
h
O
h
c o x m
0 0
w w
¶
O
O cC, S h J
o m
533
I
534
1
APPENDIX E
1 N c
.-.
I
9 c
XX
I
1
I
z-
'U
x
I
x
X
I
.
I
x
I
G
I
..
. ,
I
G a6no9
I
. . . .:: .. x,,
' 6UlpDJJ
I
.x
X
I
.
I
. . ..
. . x :?;
I
G
I
.. .
I
X
I
x
I
I
0 0 LD
2 In
N 0 In
0 W U
0 JU
sai
5 35
APPENDIX E
2 8.2
28.0 -
..
27.8 27.6 G27.4 -
.-C D 0
*
-
g26.8-
1
11.91
,11.8 g1i.j
.
C
0 1 1 .6
:
E11.5.
t
g11.4.
. ..
-
3
z11.3'
26.4 -
11.2'
26.2 26.0'
( b ) Head
0
27.0-
0 0 26.6
'&.
. .
:
27.2 -
12.0-
!-4. !-4.
'*
. ..
E
:.. . .....r\;
*'. y
( a ) Tail
11.1 I
'
I
II
II
1 1 -0
I
,
,
0 10 20 30 40 50 60 70 80 90 Discharge, m3/sec.
F i g . 11 1927)
Rating curve o f t h e Jebel-Zaraf Cut 1 a t ( a ) t a i l and ( b ) head (1926-
26.7 26.6 26.5 26.4 E 26.3
G26.2 C
0 26.1 CI
2 26.0 &25.9 3
25.8 25.7 25.6 25.5 0
F i g . 12 1927)
5 10 15 20 25 30 35 40 4 5 Discharge,
m 3 I sec.
Rating curve o f t h e Jebel-Zaraf
Discharge,
m3 / sec.
Cut 2 a t ( a ) t a i l and (b) head (1926-
536
APPENDIX E
ID
0
.. . .
U
m
. ..
N
537
APPENDIX E
--
13.9
E 13.8
-
m c 13.7
.-
U
13.6
6
13.5 -
m
x.
x
X
xx
-
0
E
Rising stage Falling s t a g e
x
14.0
13.4
-
13.3
.r
0 X '
13.8 13'6 13.4 13.2
1
.
x
-
-
X
XX
..
x .
-
I
.
x x x.*
13.0 12.8
.
Rising stage Falling stage
X&
>
X X X-
SX X F
J
$(
x
'X
..
P
'
10.8 10.6 40
.. . . : .
:. .;a..-.. x. *.,
1
80
120
160
.
I
200
I
I
240
.
I
280
I
320
13.0
-
12.8
-
12.6
Rising stage Falling stage
X
.-
1
3.9
x
0
.-
-
Q
0
X
t1
f
-
X
cn X
..;. .
X f
I
X
*
I
. x . .. . .. ..
0
*
10.8 180 200 220 240 I
'
*
I
.x+ ..:. ..x . t' .. x x x., . ... . ...
3.4 x :x 3.5 . x
.
.*
I x
.:
x
11.0
t
al
X X
11.4
X
C
0
0
m
.1
X
;11.8 011.6
t
E
-
D
9,
R i s i n g stage F a l l i n g stage
1
X
12.4 -
p12.0
X
*
g
-
x
1 4.0
X*
X
. x. ..
-
E 12.2
x x
3.3L
.
X
'
I
1
x
x . I
I
I
I
I
1
1
260 280 300 320 340 360 380 m 3 /sec.
Discharge,
F i g . 17 Rating curve of t h e White N i l e and some of t h e Khors measured a t Abu Tong i n t h e neighbourhood of t h e Zeraf mouth (Tonga S t a t i o n 1922-26)
3.2
I
0
10
1
20
40 50 D i s c h a r g e , m 3 / sec. 30
I
1
60
70
I
80
F i g . 18 Rating curve of t h e Bahr e l Ghazal and i t s t r i b u t a r i e s measured near L a k e No (1921-27)
5 39
APPENDIX E
15
14
E 13
11
10
0
200
400
600 Discharge,
800
1000
1200
1400
m31sec.
F i g . 19 Average r a t i n g curves o f t h e Sobat a t Millet D o l e i b 9 km above t h e r i v e r mouth (1911-27)
540
APPENDIX E
0 0 m c
..-
0 .0 r
-
0 0 m
c
0
:: U
m
c
.
m
o E
0 -
a
.m _
0 .c u
L
m
- a J
0 m 0
0
e
0
s
0
::
a,
Y
d
.d
z
a,
5
a,
YI
h 0
a, M
c
h
< N 0 M .d
c
w
I
.
I
X
x
. -. . .
X
. . . .' . .. .
x
xx
x
x
.* . . .
. . ..
APPENDIX E
X
X
6 X
5 Y
x
x
..
x
I
0 0
z 0 0 LD 7
0
8
IS , 2 LJ a2
owl
0 .
Om E 0 G-
0
a p
c)
0 L
o w 7
86
0
s
0 0 N
0
8 r 4
8 9
541
542
APPENDIX E 81.2
81.2 81.1
81.0 80.9
80.8 80.7 E
m
.E v
80.6 80.5
0
c m
80.4
$ 80.3
0
809 80.1
80.0 79.9 79.8 79.1 79.6
79.5
0
100
300 , 400 D i s c h a r g e , m 3 /se c. 2 00
500
F i g . 22 Average r a t i n g curve o f t h e Blue N i l e measured a t i t s e x i t from Lake Tana ( B u r i f a s a s S t a t i o n 1920-24) ,1
APPENDIX E X
1
I
0
0 N U
ci
0 N
N
0 0
0 N
8
c
a3
0 0
2
2'
0 0
U
4J
0 -
K
0
.-
al
: g: 0
0 Q,
8 a
8 0
s
0
543
1
1
1
1
E m .-
W
0
!?
0
m 3
0
0
111
0
'
I
2000
4000
Discharge,
6000
m 3 i sec.
I
8000
F i g . 24 Average r a t i n g curve of the Blue N i l e measured a t Singa (Wad e l Ales S t a t i o n 1922-26)
0
1000
2000
3000
&OOO
5000
6000
Discharge, rn / sec.
7000
8000
9OOO
F i g . 25 Average r a t i n g curve of the Blue N i l e a t Sennar S t a t i o n (Makwar Gauge 1923-27)
APPENDIX E
0
aD
n
*LO N
545
546
APPENDIX E
17
x
16
.
Rising stage Falling stage
15 14 € 613 c .D 0
F 12 *m
*The measuring s i t e was changed a l t e r n a t e l y between B u r l , Soba and Khartoum
3
Sll 10
9
0
Fig. 28
1000
2000
3000
4OOO Moo 6000 7000 Discharge, m 3 1 s e c .
8OOO
goo0
R a t i n g c u r v e of t h e B l u e N i l e a t Khartoum* (1902-27)
1OOOO
11000
APPENDIX E
4 I 4
4 Y
0
w
m
N
547
540
APPENDIX E 17 X
R i s i n g stage Fall,ing stage
16
15 14 m
.-C
D
0 13
E
aJ m
:12
X
0
11
1c
1000
2000
3000 4OOO 5000 6000 Discharge, m3lsec.
7000
8000
9O00
F i g . 30 Rating curve of t h e Main N i l e a t Hassanab 5 km upstream t h e mouth of t h e Atbara (1924-27)
15 X
14
E
,lC .-C
D
0
E
11
al
m 2
0 0 11
1(
F i g . 31
400
800
1200 1600 2000 Discharge, m 3 lsec
Rating curve of
2400
2800
3200
t h e Atbara measured 3 k m from i t s mouth (1926-27)
APPENDIX E
d
r(
T
r(
U
E
al
>
1 0
549
550
APPENDIX E
' W
' 6 u ! p o J ~ a6no9
0
M
k al
4
m m
In
N
APPENDIX E
I N
u
N
'UJ
P) N
N
N
N
I
0
I v
N
' 6 U!p O a ~ a h 0 9
w ' 6 u ! p o a ~ a61709
-
m
6
c,
h
4
X
s
U
m
I
h
PI N
I W
N
m
w m G e4.l X
w -X
2 %
551
552
APPENDIX F ASWAN DAM
~
Full
-
Res. R . L . 21.10
1930
- 1933
ORIGINAL
DAM
.20 All dimensions
.in m e t e r s .
ROCK
Fig. 1
BED
‘W
Cross-section of the pierced part set 2 of the Aswan Dam
Some Technical Data Locat i on
: at Aswan on the Main Nile, Egypt
Period of construction: 1898-1902 Fi rs t heightening
: 1912
Second heightening
: 1934
I tern
Original dam
1st heightening
2nd heightening
Storage capacity, rnlrd m 3 Total length of dam, m Height above bed, m Height above foundation, m Maximum storage level
1.06 1950.00 21.50 38.80 106.00
2.30 1982.00 26.50 43.80 113.00
5.10 2129.00 35.50 52.80 121.00
5 53 APPENDIX F Aswan Dam ( c o n t i n u e d )
T o t a l number of v e n t s : 180 h a v i n g l e v e l s and d i m e n s i o n s as f o l l o w s :
No. o f v e n t s
sill level
height, m
width, m
65 75 18 22
87.65 92.00 9 6 .OO 100.00
7.0 7.0 3.5 3.5
2.0 2.0 2.0 2 .o
Number of l o c k chambers: 5 , e a c h 8 0 . 0 m l o n g x 9 . 5 m w i d e . The h y d r o - e l e c t r i c g e n e r a t i n g p l a n t c o m p r i s e s s e v e n 47-WY a n d two 11.5-MW v e r t i c a l Kaplan t u r b i n e s and a l t e r n a t o r s o p e r a t i n g o v e r a r a n g e o f 10-33 m. The o u t p u t o f t h e main t u r b i n e s v a r i e s from 6500 HP a t 6 m head t o 65000 HP a t a head of 27-31 m .
554
APPENDIX F SENNAR ( M A W A R ) DAM
All
Fig. 2
d i m e n s i o n s in m e t e r s
Cross-section
Some T e c h n i c a l
o f S e n n a r (Pakwar) D a m , The Sudan
Data
Location
: on t h e Blue N i l e a b o u t 350 km s o u t h e a s t
of
Khartoum
Year of c o n s t r u c t i o n
: 1925
S t o r a g e c a p a c i t y of r e s e r v o i r
: 0.8 mlrd m3 (between t h e l e v e l s
417.2) Length of p i e r c e d s e c t i o n of dam: 600 m Number of s l u i c e s
:80
S l u i c e dimensions
: 2.0
m i n width x 8 . 4 m i n hei ght
Number of s p i l l w a y s
: 112
Width of s p i l l w a y
: v a r i a b l e , from 3 t o 5
T o t a l l e n g t h of dam
: 3000
m
m
of 4 2 0 . 7 and
555
APPENDIX F
JEBEL EL-AULIA DAM
Fig. 3
C r o s s - s e c t i o n of t h e J e b e l e l - A u l i a Dam a t k i l o , 1004
Some T e c h n i c a l Data Location
: on t h e White N i l e a b o u t 40 km u p s t r e a m of
P e r i o d of c o n s t r u c t i o n
: 1934-1937
R e s e r v o i r dimensions
: 314 km i n l e n g t h x 4 . 2 km i n w i d t h
I n i t i a l storage capacity
: 3 . 5 mlrd
its
junction with the Blue N i l e
m3
Length of s o l i d p a r t of dam: 1126 m 454 m
Length of p i e r c e d s e c t i o n
:
Number of s l u i c e s
: t o t a l = 6 0 , o p e r a t i n g = 5 0 , b l i n d ( r e s e r v e ) = 10
m i n width x 4 . 5 m i n h e i g h t
S 1u i c e d i m e n s i o n s
: 3.0
Maximum head d i f f e r e n c e
: 6.45
Lock s e c t i o n
: 60
m
m
Length of e a r t h e r n s e c t i o n : 3360 m T o t a l l e n g t h of dam
: 5000
m
556 APPENDIX F KHASHM EL-GIRBA DAM
Fig. 4 Some T e c h n i c a l Data Location
: on t h e A t b a r a R i v e r a t Khashm e l - G i r b a
some
400 k m s o u t h - e a s t t h e r i v e r mouth a t A t b a r a P e r i o d of c o n s t r u c t i o n
: 1960-1964
Length of c o n c r e t e s e c t i o n
: 466 m
Length of e a r t h e r n s e c t i o n
: 3380
m
T o t a l l e n g t h of dam
: 3846
m
T o t a l number of s l u i c e s
: 12
Lower s 1u i ces
: 5, e a c h w i t h a c a p a c i t y of 200 m3/sec.
Upper s l u i ces
: 7 (for p a s s i n g f l o o d ) ,
Maximum r e l e a s e c a p a c i t y
: 8700
e a c h w i t h a c a p a c i t y of
1100 m3/sec.
m3/sec., or 750 x lo6 m3/day
Dimensions of s t o r a g e r e s e r v o i r : 80 km i n l e n g t h x 1.5 km i n w i d t h I n i t i a l s t o r a g e c a p a c i t y (1964): 1 . 3 0 mlrd m 3 A c t u a l s t o r a g e c a p a c i t y (1971) : 0 . 9 7 mlrd m 3 E s t i m a t e d r a t e of s e d i m e n t a t i o n : 40 m i l l i o n m3/yr
557
APPENDIX F EL-ROSEIRES DAM
CAxis
of
reference A l l dimensions
3 -
Downstream
in meters
___
-L%5
MaX.T.W.C.
7
T. \N . L .
Grout Curtain
Fig. 5a
4Drainage galleries
T y p i c a l s e c t i o n deep s l u i c e s
Some T e c h n i c a l Data Location
: on t h e B l u e N i l e a t Damazin r a p i d s , a p p r o x i m a t e l y
P e r i o d of c o n s t r u c t i o n
: 1961-66
T o t a l l e n g t h of dam
: 16 km
120 km from t h e E t h i o p i a n b o r d e r s
Length of c o n c r e t e s e c t i o n : 1 km Number of b u t t r e s s e s
: 69
S p a c i n g of b u t t r e s s e s
: 14 m i n c r e a s e d t o 18 m a t t h e i n t a k e of power h o u s e
The s t a n d a r d b u t t r e s s e s a r e m o d i f i e d i n v a r i o u s p a r t s of t h e c o n c r e t e s e c t i o n t o accommodate t h e i n t a k e s f o r i r r i g a t i o n c a n a l s on t h e two r i v e r banks Number of s l u i c e s
: 5 low-level
s l u i c e s , 7 h i g h - l e v e l s p i l l w a y s and t h e
i n t a k e s f o r 7 t u r b i n e s i n t h e h y d r o - e l e c t r i c power s t a tion Length of e a r t h embankments: 15 km
550
APPENDIX F E l - R o s e i r e s Dam ( c o n t i n u e d ) Maximum s t o r a g e l e v e l i n the f i r s t stage
: 480 m above mean s e a l e v e l
Maximum s t o r a g e c a p a c i t y i n the f i r s t stage (gross) : 3 mlrd m 3 Maximum s t o r a g e l e v e l i n t h e second s t a g e
: 490 m above mean
sea l e v e l
Maximum s t o r a g e c a p a c i t y i n the second s t a g e ( g r o s s ) : 7 . 6 mlrd m 3 Minimum r e s e r v o i r l e v e l t o command i r r i g a t i o n by gravity : 467 m above mean sea l e v e l Mean n e t head f o r hydroe l e c t r i c power development i n the f i r s t stage : 27.8 m Mean n e t head f o r hydroe l e c t r i c power development i n t h e second s t a g e : 30.6 m Type of t u r b i n e s
: v e r t i c a l Kaplan t u r b i n e s of 41500
HP under a head
of 29 m
Axis
-
2
0
HIGH
of reference
SECTION - WEST BANK ( 1.3 k m . )
10 m.
Scale
10m.
0
1
Gravel
4 Jiginol
Clay core
INTERMEDIATE
F i g . 5b
SECTION ( 2.7 k m . )
LOW SECTIONS (6.3 k m . )
T y p i c a l c r o s s - s e c t i o n s of e a r t h embankments
559
APPENDIX F
OWEN FALLS DAM
Chamber for l i f t i n g apparatus
!C.L. o f road
hll I nII
M a x . Reserv. 113L.75 Level ~
-
-
L A K E VICTORIA
II
sluice w a y s
,111.76
Fig. 6
-Some -
o f t h e Owen F a l l s D a m
Cross-section
T e c h n.i-ca l. .Da.tfi .
Locat ion
: on V i c t o r i a N i l e a b o u t 3 k m d o w n s t r e a m o f
the exit at
t h e f o o t o f Owen F a l l s below t h e Rippon F a l l s P e r i o d of c o n s t r u c t i o n : 1948-1950 Type o f dam
: mass c o n c r e t e g r a v i t y
t y p e w i t h some s t e e l r e i n f o r c e m e n t
around t h e sluices Dimensions
: a b o u t 30 m i n h e i g h t and 760
Sluices
: 6 i n number,
Outflow
: average
m i n length
each 5 m i n h e i g h t and 3 i n width
i s a b o u t 620 m 3 / s e c . r e d u c e d t o a b o u t 500 m 3 /
s e c . The d i f f e r e n c e i s u s e d t o b u i l d up s t o r a g e i n t h e l a k e u n t i l r e q u i r e d by E g y p t A v a i l a b l e head
: b e t w e e n 18 a n d 22 m ,
Turbines
:
w i t h a n a v e r a g e o f 20 m
10 K a p l a n t u r b i n e s e a c h c o u p l e d t o a 1 5 000 KW a l t e r -
n a t o r . The p l a n t commenced g e n e r a t i n g e l e c t r i c i t y i n 1954 w i t h o n e u n i t a n d s i n c e t h e n t h e o t h e r u n i t s h a v e been i n s t a l l e d p r o g r e s s i v e l y
560
APPENDIX F
THE H I G H DAM AT ASWAN
A x i s of
Fig. 7 Some _ _
U.S.
Cross-section
Technisa-1
cofferdam
A X I S of d a m
o f t h e High D a m a t Aswan
Data
Loca t i on
on t h e Main N i l e n e a r Aswan, E g y p t , 6 . 5 km u p s t r e a m o f t h e o l d dam
Periods of c o n s t r u c t i o n : F i r s t phase
1960-64
S e c o n d p h a s e 1965-68 Hydro-electric Type o f dam, m a t e r i a l and d i m e n s i o n s
rock-fill
power p l a n t 1967-72
111 m i n h e i g h t ,
40 m t o p w i d t h a n d 9 8 0 m
b a s e w i d t h . The dam h a s a t o t a l l e n g t h o f 3600 m o f which 520 m s p a n t h e N i l e .
Depth o f g r o u t c u r t a i n is
213 m ( s e e t h e cross-section) Diversion canal
l o c a t e d on t h e e a s t e r n bank o f t h e r i v e r . D e s i g n e d f o r
a maximum d i s c h a r g e o f 11000 m3/sec. I t c o n s i s t s o f o p e n r e a c h e s i n t h e u p s t r e a m a n d t h e downstream p a r t s j o i n e d i n t h e m i d d l e by t h e main c o n t r o l t u n n e l s u n d e r t h e dam. The u p s t r e a m t a i l o f t h e c a n a l i s 1150 m i n l e n g t h , t h e d o w n s t r e a m t a i l i s 485 m a n d t h e t u n n e l s and p o w e r h o u s e 315 m , i . e . t o t a l l e n g t h = 1950 m . The u p s t r e a m c a n a l w i d t h = 250 metres n a r r o w i n g down t o
50 m i n a d i s t a n c e o f 630 m. The n a r r o w e s t w i d t h i s k e p t c o n s t a n t t h e n i n c r e a s e s g r a d u a l l y 230 m a t t h e
56 1 APPENDIX F The High Dam a t Aswan ( c o n t i n u e d )
i n l e t o f t h e t u n n e l . The downstream r e a c h b e g i n s w i t h a w i d t h of 2 7 8 . 5 m which narrows g r a d u a l l y t o 40 m i n a d i s t a n c e of 330 m from t h e powerhouse. Tunnels
: s i x t u n n e l s e a c h 282
m i n length s e r v e i n connecting
t h e upstream r e a c h of t h e d i v e r s i o n c a n a l w i t h i t s downstream t a i l a c r o s s t h e powerhouse. The t u n n e l i s c i r c u l a r i n t h e major p a r t of i t s l e n g t h , t h e diameter b e i n g a b o u t 15 m and t h e maximum v e l o c i t y i s n e a r l y
10 m/sec. To resist t h i s h i g h v e l o c i t y t h e t u n n e l s have a r e i n f o r c e d c o n c r e t e l i n i n g more t h a n 1
thick.
B e f o r e j o i n i n g t h e powerhouse, e a c h t u n n e l b r a n c h e s o f f i n t o two r e c t a n g u l a r c o n d u i t s , e a c h 7 . 5 x 2 . 2 m; one d e l i v e r s water t o t h e g e n e r a t i n g u n i t and t h e o t h e r c a r r i e s t h e e x c e s s w a t e r needed f o r i r r i g a t i o n d i r e c t l y t o t h e downstream c a n a l w i t h o u t p a s s i n g t h r o u g h t h e turbine. Power s t a t i o n
: The s t a t i o n i s l o c a t e d a t t h e downstream e n d o f t h e
spillway tunnels.
I t c o n s i s t s of 12 g e n e r a t i n g u n i t s
e a c h f e d from one of t h e 12 b r a n c h e s . The g e n e r a t i n g u n i t is a F r a n c i s t y p e t u r b i n e d i r e c t l y connected t o a g e n e r a t o r . Range of head = 35-77 m , c a p a c i t y a t d e s i g n head = 180 00 KW and d i s c h a r g e = 346 m3/sec. A t r a n s former s t a t i o n h e l p s i n r a i s i n g t h e v o l t a g e from 15 700 t o 500 000 v o l t s ,
56 2
I - E d f i n a barrage (1948 -1951)
I IT-17.30'
I
'
11 -
fta
11
barrage
1901 -1903 a n
1953 - 1955 )
I
I
111 - New Rosetta barrage (1937 -1939) I
I
+ 10 00 +li+
12.30
Fig. 8 Sections of large barrages on the Nile between Aswan and the Mediterranean Sea
56 3
IV
- Assiut barrage
(
1898 - 1902 and 1934 - 1938 )
I
N.F.L.v45.30 .-
E
V
-
Naq - Hammadi
barraqe ( 1927
- 1930 )
H .F.L.v68.50 -
L.F.L., 63.50
V I - Esno barrage ( 1945 - 1947 )
I
I 8:
Fig. 8
continued
II
564
INDEX Abbai ( G r e a t Abbai o r Blue N i l e ) : R i v e r , 6 , 40, 297 A b r i : R.G.S.,+ 1 2 7 , 474, 497 Abu D e l e i g : R.G.S., 1 2 6 , 472, 494 Abu named: R.C.S., 48, 1 0 8 , 1 2 5 , 472, 494 Abu Tong: G . S . , + + 361, 367 Abwong: R.G.S., 127, 373, 474, 498 A b y s s i n i a n P l a t e a u , 1 7 , 3 5 , 37, 40 65, 70, 75, 80, Addis Ababa: M.S. 87, 92, 9 4 , 9 5 , 101, 108, 132, 1 5 2 , 1 9 1 , 1 9 2 , 480, 508 Adj u s tment f a c t o r e v a p o r a t i o n , 206 Aduku D i s p e n s a r y : R.G.S., 1 2 8 , 476, 500 Agnot: r a d i a t i o n , 85 Agwei: R i v e r , 39 Akanyaru: R i v e r , 1 9 , 318 Akobo (Akobo P o s t ) : M.S., 6 5 , 70, 7 5 , 8 0 , 1 2 8 , 1 2 9 , 1 9 0 , 215, 368, 372, 474, 498 Akobo: R i v e r , 39 Albert d r a i n a g e b a s i n , 2 5 , 345 Lake and s h o r e s , 1, 10, 13, 1 7 , 22, 25, 27, 29, 116, 168, 178, 287, 326, 333, 345, 346, 349, 351, 352, 410, 441 N i l e , 5 , 349, 352 Alexandria M.S., 6 4 , 6 9 , 7 4 , 79, 8 7 , 9 1 , 9 8 , 1 2 3 , 1 6 7 , 470, 490 Town, 7 7 , 108, 203, 204, 215 A l f a l f a : 270 A l i a b : R i v e r : 359, 533 Alluvium: 298 Amadi: R . G . S . , 3 5 , 1 2 8 , 474, 499 Amarillo: A . S . Amria: R . G . S . , 1 2 3 , 470, 490 Amplitude: harmonic, 1 5 2 , 328, 329 Anemograph: 94 Anemometer: wind s p e e d m e a s u r i n g d e v i c e , 6 4 , 94 Annual o s c i l l a t i o n : h y d r o l o g i c v a r i a b l e , 1 5 3 , 328 A n t i c y c l o n e : 105, 107 A r c h e o z o i c : g e o l o g i c e r a , 299 Arid: climate, 61 A r i s h : M.S., 6 4 , 1 2 3 , 470, 490 Arua: R.G.S., 476 A s s i u t (AsyOt) A.S., M.S., 6 4 , 6 9 , 7 4 , 7 9 , 9 1 , 1 2 5 , 1 6 8 , 2 0 0 , 2 1 6 , 244, 248, 271, 472, 493, 551
,*
**
++
Assua: R i v e r , B a s i n , 30, 353, 531 Astaboras (Atbara): River, 2 Astapus (White N i l e ) : R i v e r , 2 Astasobas (Blue N i l e ) : R i v e r , 2 Aswan Dam, R e s e r v o i r , 1 0 , 5 0 , 407, 411, 413, 419, 425, 426, 526, 550, 552 G . S . , 13, 4 6 , 5 0 , 1 9 7 , 312, 406-410 M.S., 6 4 , 7 0 , 7 5 , 7 9 , 9 2 , 9 9 , 1 2 5 , 1 6 7 , 216, 248, 472, 493 Atbara G.S., M.S., 6 5 , 6 8 , 70, 75, 79, 8 7 , 125, 167, 216, 399, 472, 494, 5 2 3 , 548 R i v e r , B a s i n , 1 2 , 13, 4 5 , 194, 1 9 5 , 1 9 7 , 1 9 8 , 298, 398, 400-403, 431 A t e m : R i v e r , 3 2 , 359, 390 A t f : M.S., 64 Atmometer: 1 6 5 , 170 A t t a q u a : R.G.S., 124, 470, 492 Atua: R.G.S., 1 2 8 , 500 A u t o r e g r e s s i v e models: h y d r o l o g i c s e r i e s , 1 2 1 , 1 2 2 , 1 4 8 , 1 4 9 , 324, 340, 343, 349, 355, 367, 375, 377, 383, 3 9 5 , 3 9 8 , 400, 403, 406, 409 A v a i l a b l e s o i l m o i s t u r e , 258 Awach-Kaboun: r i v e r b a s i n , 320 Awai: R i v e r , 32, 359 Aweil: M.S., 9 6 , 1 2 7 , 474, 498 B a h a r i a : O a s i s , M.S., 1 2 5 , 308, 309, 311, 472, 492 Bahr e l Arab: R i v e r , 34 Bahr e l G h a z a l : R i v e r , B a s i n , 3 , 11, 3 4 , 3 5 , 9 6 , 185, 186, 218, 2 8 2 , 2 8 7 , 364, 365, 374, 452, 454, 538 Bahr e l J e b e l d r a i n a g e b a s i n , 1 8 0 , 185, 192, 218, 282, 287, 305, 353, 354, 359, 360, 441, 452 R i v e r , 1 2 , 1 3 , 2 8 , 2 9 , 3 5 , 297, 353, 367, 368, 374, 449, 450, 5 3 4 , 536 Bahr e l Salam: R i v e r , 45 Bahr e l Z a r a f : R i v e r , B a s i n , 3 2 , 359, 360, 361, 367, 368, 374, 450, 5 35-5 36 B a r a : R.G.S., 1 2 6 , 474, 496 Baro: R i v e r , 3 5 , 3 7 , 39, 368, 369, 372, 374, 454 B a r o m e t r i c p r e s s u r e , 6 5 , 66 B a r r a g e s , 52, 446, 462 A s s i u t , 5 2 , 413, 447, 461, 5 6 3 D e l t a , 5 2 , 447, 462, 491, 562 E d f i n a , 5 4 , 449, 562 E s n a , 5 2 , 447, 461, 5 6 3
+R.G.s. = r a i n gauging s t a t i o n , G . S . = r i v e r g a u g i n g s t a t i o n , *Y.s. = meteorol o g i c a l s t a t i o n , **A.s. = a g r i c u l t u r a l s t a t i o n
565
Nag-Hammadi, 5 2 , 447, 461, 5 6 3 Z i f t a , 5 2 , 449, 562 A l - B a r r a k ' s f o r m u l a , 261, 263 Basement Complex, 294, 299 Beach e r o s i o n : 463 B e a u f o r t : s c a l e of wind f o r c e , 6 6 , 94 Benha: M.S.,* 6 4 , 1 2 4 , 470, 4 9 1 Beni-Suef: M.S., 6 4 , 6 9 , 7 4 , 9 1 , 1 2 4 , 472, 492 B e r a r a r a : R i v e r , 28 B e r b e r : 48 Bi-annual o s c i l l a t i o n : h y d r o l o g i c v a r i a b l e , 328, 336, 342 Biharamulo: R . G . S . , + 132, 1 5 3 , 1 5 5 , 480, 507 B i k i r a : R.G.S., 131, 4 7 8 , 504 B l a n e y - C r i d d l e ' s method, 260, 262, 263, 268, 275-277, 280 Blaney-Morin's f o r m u l a , 2 6 0 , 263 Blue N i l e d r a i n a g e b a s i n , 191, 192, 194, 297, 298 R i v e r , 3 , 5 , 1 0 , 1 2 , 40, 44-46, 274, 378-381, 384, 385, 388-392, . 410 Bor: G . S . , + + 30, 1 2 8 , 359, 360, 363, 474, 499 Borg e l Arab: R.G.S., 1 2 4 , 470, 490 B o r o l l o s : R.G.S., 1 2 3 , 470, 489 Bouwen's r a t i o , 278, 279, 285 Budu, K i n g ' s S c h o o l : R.G.S., 1 3 0 , 478, 5 0 3 Buganda-Toro: g e o l o g i c a l f o r m a t i o n , 29 3 Bugaya: R.G.S., 476, 5 0 1 Bugoma: R.G.S., 505 B u k a l a s a : A . S . , f * R.G.S., 1 2 9 , 476, 50 1 Bukedia: R . G . S . , 1 2 9 , 476, 5 0 1 Bukoba: M.S., 6 5 , 7 1 , 7 6 , 8 0 , 8 6 , 1 3 2 , 153-155, 506 Bukoban s y s t e m : g e o l o g i c a l f o r m a t i o n , 293 B u l i n d i : R.G.S., 1 2 9 , 476, 500 Bulopa: R.G.S., 1 2 9 , 476, 500 Bungoma V e t e r i n a r y S t a t i o n , 131, 476 B u r u n d i , 1 5 , 1 9 , 2 3 , 6 6 , 281, 293 B u s e n y i : R.G.S., 131, 476, 504 B u s s e r i : R i v e r , 34 B u t i a b a : M.S., G.S., 6 5 , 7 1 , 7 6 , 1 2 8 , 1 7 8 , 1 8 0 , 1 8 5 , 2 1 5 , 350, 476, 500 Buunga: R.G.S., 130, 478, 5 0 3 Buvuma: R.G.S., 1 3 0 , 478, 5 0 3
++
Bwavu: R.G.S., 130, 478, 5 0 3 Bweramul: G . S . , on S e m l i k i , 529 C a i n o z o i c : g e o l o g i c a l e r a , 300, 303 Cairo Almaza: a i r p o r t , 9 8 , 1 6 7 , 203, 204, 2 16 E z b e k i y a : M . S . , 6 4 , 6 9 , 7 4 , 79, 8 7 , 9 1 , 167, 203, 312 Town: 5 2 , 5 4 , 411, 416, 457 Campbell-Stokes: s u n s h i n e r e c o r d e r , 6 6 , 85 Cataract f i r s t (Aswan). 50 s e c o n d , 4 8 , 299 t h i r d , 4 8 , 299 f o u r t h , 4 8 , 299, 4 4 1 f i f t h , 48 s i x t h ( S h a b l o k a ) I 298 Catchment a r e a , 17 Chad, 308 C h e m e l i l : R.G.S., 131, 478, 506 C h i m b i l i : R i v e r , 380 C h r i s t i a n s e n ' s f o r m u l a , 267, 268 C i r c u l a t i o n : a i r masses, 105 C l i m a t i c r e g i o n s , 59 C l i m a t o l o g i c a l normals f o r Egypt, 6 6 , 166 Cloud c o v e r , 182 C l o u d i n e s s , 6 4 , 8 5 , 9 0 , 9 4 , 185 C o e f f i c i e n t o f v a r i a t i o n , 118, 355 Confidence: l i m i t , l e v e l , 119, 120, 350, 367, 375, 386, 3 8 7 , 393 C o n g l o m e r a t e s , 293 . Congo, 1 1 7 , 281 Congo ( Z a i r e ) : R i v e r , B a s i n , 1 5 , 34 C o n s e r v a t i o n : w o r k s , 419, 455 Consumptive u s e of c r o p s b e a n s , 263, 265 berseem: E g y p t i a n c l o v e r , 233, 244, 256, 264, 265, 269, 270 c h i c k p e a , 233, 244, 264, 265 c i t r u s t r e e s ( o r c h a r d s ) , 233, 264, 265, 269, 270 c o t t o n : 233-238, 264, 265, 2 6 9 , 270, 276, 277 cucumber, 264, 265 d u r a , 276, 277 e a r l y maize ( c o r n ) , 233, 243, 264, 265, 269, 270 f e n u g r e e k , 233, 244, 2 6 4 , 265 l a t e maize ( c o r n ) , 233, 242, 243, 264, 265, 269, 270 l e n t i l e , 233, 244, 264, 265 l u b i a , 276, 277 l u c e r n , 274
G.S. = r i v e r gauging s t a t i o n , = r a i n gau i n g s t a t i o n , = agricultural station l o g i c a l s t a t i o n , *f,.s.
+R.G.s.
f
M.S. = meteoro-
566
l u p i n s , 233, 244, 264, 265 p e a s , 264, 265 p o t a t o e s , 264, 265 sorghum, 251, 278 s q u a s h , 264, 265 s u g a r c a n e , 264, 2 6 5 , 269 C o n t i n e n t a l climate, 60 C o n t r o l works, 446, 455 C o n v e c t i o n a l r a i n , 60 C r e t a c e o u s : g e o l o g i c a l e r a , 293, 300, 302, 308 C o r r e l a t i o n c o e f f i c i e n t , 208, 333, 39 3 C o r r e l o g r a m , 333, 338, 357 Crop c o e f f i c i e n t , 257, 262, 270, 275, 277 Cumulative p r o b a b i l i t y , 154 Cyclicity: hydrological variables, 326, 337 Cyperus p a p y r u s , 25 Dabani: R . G . S . , + 1 3 0 , 476, 502 6 4 , 69, El-Dakhla: Oasis, M.S. 7 4 , 7 9 , 9 1 , 9 9 , 1 2 5 , 308, 309, 311, 472, 493 Damanhur: M.S., 6 4 , 6 9 , 74, 9 1 , 1 2 3 , 470, 490 Damie t t a b r a n c h , 5 4 , 447 M.S., 6 4 , 6 9 , 74, 9 1 , 1 2 3 , 203, 215, 470, 489 D a r f u r : Town, P r o v i n c e , 6 0 , 306 Day l e n g t h , 259 Deadalus I s l a n d : M . S . , 6 4 , 7 0 , 7 5 , 7 9 , 9 2 , 1 2 5 , 472, 4 9 3 Debasien: mountain, 25 D e f i c i t : a v a i l a b l e moisture o r water, 61, 434, 437 Degradation: r i v e r channel, 461 D e l t a b a r r a g e s : A.S.,** M.S., 6 9 , 74, 9 1 , 1 2 4 , 2 4 6 , 2 4 7 , 257, 470 Demand, 419, 420, 422, 430 E l - D e r r , 48 D e s e r t i c r e g i o n , 60 D i l l i n g : R.G.S., 1 2 7 , 474, 497 Dinder: R i v e r , B a s i n , 4 2 , 4 4 , 45, 298, 386, 387 D i s c h a r g e : measurement, s e r i e s , 324, 330, 331, 338, 353, 354, 361, 374-377, 380, 389, 390, 392, 394, 395, 401, 406, 411 D i u r n a l v a r i a t i o n : r a i n f a l l , 108 M.S., 6 5 , 9 2 , 9 5 , Dongola: C.S.,++ 100, 1 9 7 , 299, 307, 401-406, 524
,*
+
++
D o o r e n b o s - P r u i t t ' s method, 2 6 1 , 263, 267, 268, 270, 277 D r a f t : r e s e r v o i r ' s o u t f l o w , 437, 440, 44 1 Dry-bulb t e m p e r a t u r e , 278 Dry sub-humid: climate, 6 1 , 6 3 El-Dueim: M.S., 6 5 , 7 0 , 7 5 , 1 2 7 , 1 6 8 , 1 8 6 , 379, 474, 495 D u j a i l a h : experiment s t a t i o n , 251 D u s t s t o r m s : 106 Early Pleistocene: geological t i m e , 299 E a s t A f r i c a , 113, 1 5 7 , 174, 285, 287 E a s t African Meteorological Service (EAMD), 11, 6 6 , 172 E a s t e r n Desert, 311 Ed-Darner, 299 6 4 , 7 9 , 8 6 , 1 2 3 , 204, Edfina: M.S., 216, 470, 489 Edward: Lake and s h o r e s , 5 , 1 0 , 1 7 , 1 9 , 2 2 , 2 7 , 2 8 , 1 6 8 , 1 7 7 , 1 7 8 , 224, 287, 340, 342, 346 E g y p t , 8 , 12-14, 1 7 , 5 9 , 6 6 , 68, 77, 9 4 , 113, 1 3 3 , 1 5 7 , 1 5 8 , 209, 262, 271, 274, 302, 303, 411, 441, 4 4 3 E l d o r e t : M.S., 76, 80, 88, 1 5 3 , 1 5 5 , 2 15 Elephantine I s l a n d , 1 Elgon: m o u n t a i n , 2 5 , 295 E m p i r i c a l methods, 258, 259, 275 Endebess: R.G.S., 131, 478, 504 Energy-balance method, 278, 280, 363 E n n e d i , 308 E n t e b b e : M.S., 6 5 , 6 6 , 6 8 , 7 1 , 7 6 , 8 0 , 8 6 , 88, 1 0 1 , 1 5 3 , 1 5 5 , 1 7 4 , 2 1 5 , 285, 478, 503 Eocene: g e o l o g i c a l t i m e , 2 9 7 , 300, 302, 308 E o n i l e , 302 E q u a t o r : M .S ., 6 5 , 88, 9 4 , 9 5 , 1 0 1 , 131, 478, 505 E q u t o r i a P r o v i n c e , 305 E q u a t o r i a l L a k e s , 13, 354 E q u a t o r i a l Lake P l a t e a u , 4 , 1 7 , 2 2 , 6 7 , 6 8 , 77, 101, 1 0 7 , 1 2 0 , 1 5 7 , 456 E r d i , 308 Esna: M.S., 6 4 , 70, 75, 79, 9 1 E t h i o p i a , 3 , 1 5 , 4 4 , 5 9 , 9 4 , 1 1 3 , 454 E t h i o p i a n P l a t e a u , 6 , 4 0 , 4 2 , 44, 5 9 , 6 1 , 1 0 7 , 1 8 9 , 1 9 5 , 2 9 7 , 3 0 3 , 386, 456 E v a p o r a t i o n : f r e e water s u r f a c e , 1 6 5 , 170, 175, 205, 208, 401
R . G . S . = r a i n gau i n g s t a t i o n , G . S . = r i v e r gauging s t a t i o n , logical station, ~ 5 A . s . = agricultural station
4.s.
= meteoro-
56 7 E v a p o r a t i o n p a n , 269, 335, 352 Evaporimeter, 171 Evapotranspiration a c t u a l , 170, 224, 258, 286 p o t e n t i a l , 61, 66, 1 6 5 , 1 7 0 , 1 7 6 , 223, 258, 260, 271, 280, 287, 335, 366 E v a p o t r a n s p i r o m e t e r : m o d i f i e d , 227 Experimental b a s i n s C h e r o n o i t , 319 Gucha-Migori , 1 1 6 , 320 I s n a g a , 116, 321 Kafu-Manyanja, 1 1 6 , 334 Katonga, 1 1 6 , 3 2 1 K i b o s , 319 Mara, 116, 320 M b a l a g a t i , 1 1 6 , 320 Moame, 1 1 6 , 321 Mpologoma Malaba, 116 M u z i z i , 116 M w i s a , 318 Ngogo, 3 2 1 Nyando, 1 1 6 , 319 Nzoia (Nzoya), 1 1 6 , 319 R u i z i - K i b a l e , 1 1 6 , 321 Ruwana-Gurumeti, 1 1 6 , 320 S i m i y u , 2 3 , 1 1 6 , 321 S i o , 2 3 , 1 1 6 , 319 Sondu, 1 1 6 , 319 S u g u t i , 1 1 6 , 320 Y a l a , 1 1 6 , 319 Extreme r a i n f a l l , 1 5 8 , 159 F a j a o : G.S.,++ 338 Falls Bedan, 30 Bugugi, 19 Murchison, 25 Owen, 2 3 Ripon, 5 , 2 3 , 330 Tissisat, 2 Fangak: R.G.S. ,+ 1 2 7 , 363, 474, 498 Faqus: R.G.S., 1 2 4 , 470, 4 9 1 F a r a f r a : O a s i s , R . G . S . , 1 2 5 , 308, 309, 311, 472, 493 Faraskour, 54 E l - F a s h e r : M.S. 65, 7 0 , 80, 8 6 , 8 7 , 1 0 8 , 1 2 6 , 1 6 9 , 474, 496 Fayed: R.G.S., 1 2 4 , 470, 4 9 1 E 1-Fay um d e p r e s s i o n , 5 2 , 1 6 7 , 200, 201, 216 M.S., 6 4 , 6 9 , 7 4 , 7 9 , 9 1 , 1 2 4 , 472, 492 F i e l d c a p a c i t y : s o i l m o i s t u r e , 229, 286 F l o a t i n g t a n k , 166
,*
++
F o r t P o r t a l : M.S., 65, 6 8 , 7 1 , 7 6 , 8 0 , 1 2 9 , 1 5 3 , 1 5 5 , 476, 502 F o r t Ternan: R.G.S., 131, 478, 506 Frequency d i s t r i b u t i o n , h i s t o g r a m , 218 f a c t o r , 120 Fuka: R.G.S., 1 2 3 , 470, 490 G a a f r a : G.S., 427 G a l l a b a t : M.S., 6 5 , 7 0 , 7 5 , 8 0 , 1 6 8 , 1 9 4 , 1 9 5 , 216 Gambeila: G . S . , M.S., 3 7 , 6 5 , 7 0 , 7 5 , 1 2 8 , 1 8 9 , 1 9 0 , 215, 369, 369, 454, 474, 498 Gash D e l t a , 306 G e b e i t : R.G.S., 1 2 5 , 4 7 2 , 494 G e b e l e i n : R.G.S., 379 G e d a r e f : R.G.S., 1 2 6 , 495 G e i t a : R.G.S., 1 3 2 , 480, 507 G e l : R i v e r , 3 4 , 364 Gelda: R i v e r , 42 Gemmeiza: A.S. 64 Geneina: M.S., 6 5 , 7 0 , 7 5 , 1 0 8 , 474, 496 George Lake: s u r f a c e , b a s i n , 5 , 1 9 , 2 2 , 2 7 , 2 8 , 1 7 7 , 1 7 8 , 340, 346 G e t e i n a : R.G.S., 1 2 6 , 379, 472, 495 Gezirah p l a i n , c a n a l , 44, 274, 281, 2 9 8 , 384, 386, 428, 429 r e s e a r c h s t a t i o n , 278 Ghaba Shambe, 32, 1 2 8 , 363, 474, 498 Ghabat e l - A r a b , 365 G i l a : R i v e r : 39 G i z a : A . S . , M.S., 6 4 , 6 9 , 74, 79, 8 6 , 8 7 , 9 1 , 9 8 , 124, 1 6 7 , 200, 201, 203, 209, 212, 2 1 6 , 2 3 5 , 236, 239, 240, 242, 244-246, 2 4 8 , 251, 255, 257, 271, 470, 491 G n e i s s : r o c k , 295, 298, 299 G r a n i t e : r o c k , 2 9 3 , 298-300, 304 Great L a k e s , 170 Great r i f t , 1 9 , 22 Groundwater a q u i f e r , 312 l e v e l , 466 p o t e n t i a l , 304, 306 Gulu: M.S., 6 5 , 7 1 , 7 5 , 80, 8 6 , 9 2 , 9 4 , 1 0 1 , 1 2 8 , 1 5 3 , 1 7 8 , 180, 476, 500 Gumara: R i v e r , 42
,**
Haboob: blowing wind, 95 Haj-Abdalla: R.G.S., 1 2 6 , 474, 496 Hammam: R.G.S., 1 2 4 , 470, 491
= r a i n gauging s t a t i o n , G.S. = r i v e r g a u g i n g s t a t i o n , l o g i c a l s t a t i o n , **A.s. = a g r i c u l t u r a l s t a t i o n
+R.G.s.
*M.s. =
meteoro-
568 H a r g r e a v e ’ s f o r m u l a , 181-183, 187, 191, 198, 200, 205, 208, 263, 274, 276, 277, 279 Harmonic: p a r a m e t e r , c o e f f i c i e n t . 152, 342, 346, 366, 370 El-Hassana: R.G.S. ,+ 124, 470, 491, 548 Hassanab: G . S . ,++198, 395-398, 403, 406, 521 H e l i o p o l i s , 203 Helwan: M . S . , * 64, 69, 74, 79, 87, 91, 96, 98, 124, 167, 470, 492 H e a t i n d e x , 261 High-Aswan D a m , 12, 13, 50, 54, 251, 272, 413, 419, 428, 432, 439, 441, 443, 460, 466, 560 H i l l e t D o l e i b : G . S . , on S o b a t , 373, 410, 539 H i l l e t I d r i s : G . S . , on D i n d e r , 386, 545 H i l l e t Nuer (Adok), 359 Humid: climate, 61 Humidity: a b s o l u t e , r e l a t i v e , 64, 77, 78, 182, 200, 203, 209, 212, 218, 259, 267, 277 Hurghada: M.S., 64, 69, 74, 91, 124, 200, 201, 216, 472, 493 Hydrograph, 338, 343, 351, 353, 366, 373, 387, 400, 407, 409, 411 H y d r o m e t e o r o l o g i c a l Survey o f t h e Catchments of Lakes V i c t o r i a , Kyoga and A l b e r t , 13, 61, 95, 113, 120, 121, 133, 152, 157, 172, 317, 345 I g a b i r o : R.G.S., 132, 153, 155, 480, 507 Igneous r o c k s , 299, 300 I k i z u : R.G.S., 132, 480, 507 Imatong: m o u n t a i n , 30 I n d e x of r a i n i n e s s , 157 Inganga: R.G.S., 129, 476, 502 I n s e l b e r g : 306 I n t e g r a t i o n method: 271 I n t e r t r o p i c a l Convergence Zone (ITCZ), 105 I r r i g a t i o n c y c l e , 229 I s h a s h a : R i v e r , 28 I s o h y e t : 61, 274 I s o t h e r m : 68 Jebel Aulia dam, r e s e r v o i r , G . S . , 10, 12, 186, 379, 430, 555 M.S., 65, 472, 495 J e b e l e i n : R.G.S., 127, 150, 474, 497
++
J e n s e n and Haise’s f o r m u l a , 266 Jimma: M.S., 65, 70, 87, 92, 94, 95, 101 J i n j a : M.S., G . S . , on V i c t o r i a N i l e , 86, 215, 285, 326, 330, 331, 510, 528 J o n g l e i C a n a l , 13, 362, 451 J o r d a n V a l l e y , 19 Juba on Bahr e l J e b e l , 30, 67, 96, 107, 181, 182, 216, 287 M.S., 65, 70, 75, 80, 87, 92, 101, 128, 476, 499 J u r : R i v e r , 34, 364 J u r a s s i c : g e o l o g i c t i m e , 293 Kabale: M.S., 65, 76, 86, 88, 92, 94, 95, 101, 103, 478, 504 Kabanyolo: M.S., 285 Kabasande: R.G.S., 130, 478, 503 Kachimbala: R.G.S., 129, 476, 501 K a d u g l i : R.G.S., 127, 474, 497 K a f r e l - D a w a r : R.G.S., 123, 470, 490 e l - S h e i k h : R.G.S., 123, 470, 490 e l - Z a y y a t : R.G.S., 124, 470, 491 Kafu: R i v e r , 23, 25 Kagera B a s i n , 63, 116, 318, 321 R i v e r , 9 , 19, 20, 23, 318, 340 Kagondo: R.G.S., 480, 507 Kahangi E s t a t e : R.G.S., 129, 476, 502 Kaja: R i v e r , 30 K a j i n a r t y : G.S. on Main N i l e , 427 Kajo-Kaji: R.G.S., 128, 354, 476, 499 Kakamega: R.G.S., 131, 478, 505 Kakitumba: R i v e r , 19 K a l a g a l a : A.S.,** 129, 153, 155, 476, 502 K a l a n g a l a : M.S., 504 K a l a n g a s s a : R i v e r , 19 Kalungu: R.G.S., 130, 478, 503 Kamlin: R.G.S., 126, 387, 472, 495 Kampala: M.S., 65, 88, 215 Kangen: R i v e r , 39 K a p a s a b e t : R.G.S., 131, 478, 505 Kapenguria: R.G.S., 131, 478, 504 Karagwe-Ankolean: g e o l o g i c a l format i o n , 293 Karima (Kareima): M.S., 65, 87, 125, 472, 494 E l - K a s r : M.S., 204, 209, 212 Kassala M.S., 65, 70, 75, 79, 87, 92, 95, 101, 167, 194, 195, 216, 472, 495 P r o v i n c e , 306 Katakawi: R.G.S., 128, 476, 500
+R.G.s. = r a i n gauging s t a t i o n , G . S . = r i v e r gauging s t a t i o n , l o g i c a l s t a t i o n , **A.s. = a g r i c u l t u r a l s t a t i o n
*M.s.
= meteoro-
569
Katera: R.G.S.,+ 131, 478, 504 K a t i g o n d o : R.G.S., 1 3 0 , 4 7 8 , 5 0 3 Kavirondian: g e o l o g i c a l formation, 29 3 Kawalinda: R.G.S., 1 3 2 , 507 Kazinga C h a n n e l , 2 7 , 2 8 , 340 K e n i s a , 30 Kenya: 5 , 13, 1 5 , 1 9 , 2 2 , 2 3 , 6 6 , 9 4 , 133, 215, 286, 293, 295, 304 K e r i c h o : M.S. 6 5 , 7 6 , 8 0 , 8 6 , 88, 1 3 2 , 1 5 3 , 1 5 5 , 4 8 0 , 506 Kerma, 48 Khamasin: d u s t s t o r m l a s t i n g 50 d a y s , 97 Khannaq: G . S . , + + on Main N i l e , 406 El-Kharga ( h ) : O a s i s , M.S., 5 2 , 6 4 , 6 9 , 7 4 , 7 9 , 9 1 , 200, 201, 203, 2 0 9 , 212, 215, 216, 302, 3 0 8 , 309, 311, 472, 493 Khartoum G . S . , M.S., 6 5 , 7 5 , 7 9 , 8 6 , 8 7 , 9 2 , 9 5 , 101, 1 6 7 , 206, 276, 378, 379, 387-390, 472, 494, 5 1 8 , 546 Town, 4 0 , 4 5 , 6 8 , 7 7 , 1 1 9 , 1 2 6 , 1 5 0 , 1 6 7 , 1 8 6 , 1 9 2 , 1 9 7 , 2 1 2 , 293 Khashm e l - G i r b a D a m , r e s e r v o i r , 13, 45, 274, 431, 556 R.G.S., 1 2 6 , 4 7 2 , 495 Khor: old, i n t e r m i t t e n t stream A d e i l , 39 Adura, 3 6 8 , 369, 455 Ahmar, 370, 455 B a l l a s , 4 2 , 381 B a s h i l o , 4 2 , 380 Dabus, 4 2 , 381 Daga, 4 2 , 455 D i d e s s a , 42, 3 8 1 D o l e i b , 40 F a l l u s , 4 0 , 373 Guder, 42 Jamma, 4 0 , 380 J o k a u , 3 7 , 368 Lau, 370, 455 Machar, 3 7 , 368, 455 Makawi, 39, 368 Mugor, 42 Nyanding, 40, 3 7 3 Rao, 40 Tombak, 370, 445 Toshka, 445 Tumat, 42 T w a l o r , 373 Unyam-Kojie, 360, 5 3 3 Wangnyai t , 40 Wol, 4 0 , 455 Yabus. 369. 455
,*
++
K i b a l e : R.G.S., 1 2 9 , 476, 5 0 1 Kiboga: R.G.S., 1 2 9 , 476, 5 0 1 K i j i m a M i s s i o n , R.G.S., 1 3 2 , 480, 508 K i j o : R i v e r , 13 K i l i m i n j a r o : m o u n t a i n , 294 K i s i i : R.G.S., 1 3 2 , 1 5 3 , 1 5 5 , 480, 506 K i s o z i : l y s i m e t r y s t a t i o n , 284, 285 K i s u b i : R.G.S., 130, 478, 5 0 3 Kisumu: M.S., 6 5 , 7 1 , 8 6 , 88, 9 2 , 9 4 , 1 0 1 , 131, 1 5 3 , 1 5 5 , 1 7 4 , 215, 478, 506 K i t : R i v e r , 30 K i t a l e : M.S., 6 5 , 76, 8 0 , 131, 478, 505 Kitgum: R.G.S., 1 2 8 , 476, 499 K i t u z a : M.S., 285 Kivu Lake, 19 Kiwala E s t a t e : R.G.S., 1 3 0 , 478, 504 Kodok: R.G.S., 1 2 7 , 373, 379, 474, 49 8 Kom e l - T a r f a i a : R.G.S., 1 2 3 , 470, 490 K o m Ombo: M.S., 6 4 , 7 0 , 7 5 , 9 2 , 1 2 5 , 472, 493 Kome: R.G.S., 1 3 2 , 480, 5 0 7 Kordof an P r o v i n c e , 306 Town, 60 K o r t i , 48 K o s t i , 4 0 , 108, 474 Kosti/Rabak: R.G.S., 1 2 6 , 1 8 6 , 379, 496 K u n t e l l a : R.G.S., 1 2 4 , 470, 492 Kurmuk: R.G.S., 127, 193, 194, 216, 474, 497 K u r t o s i s : c o e f f i c i e n t , 118, 329, 337, 346, 355, 398, 438 Kwalinda: R.G.S., 480 Kwania Lake, 2 3 , 333 Kyanawkaka: R.G.S., 130, 478, 504 Kyaka F e r r y : G . S . on K a g e r a , 3 2 3 , 509 Kyere: R.G.S.: 129, 476, 500 Kyoga d r a i n a g e b a s i n , 2 5 , 335, 338, 343 Lake, s h o r e s , 13, 1 7 , 2 3 , 2 5 , 1 1 6 , 1 7 6 , 1 7 7 , 2 8 7 , 330, 333, 335, 337, 340, 3 4 1 , 342, 345, 346 N i l e , 1 1 6 , 352 Lag: t i m e , 355, 403, 438 L a l e P o r t : G . S . , 335 L a t e Acheulean: g e o l o g i c a l t i m e , 303, 308 L a t e C r e t a c e o u s : g e o l o g i c a l t i m e , 297 Lau: R i v e r , 34 L a t e r i t e : r o c k , 304 E l - L e i s i : G.S. on N i l e n e a r C a i r o , 415 L e r a u , 180
+R.G.s. = r a i n gauging s t a t i o n , G . S . = r i v e r gauging s t a t i o n , l o g i c a l s t a t i o n , **A.S. = a g r i c u l t u r a l s t a t i o n
'M.s.
= meteoro-
570
Limestone, 293, 295, 311 L i r a ( N e g e t t a f a r m ) : M.S.
,* 65, 71,
76, 80, 86, 180, 476, 500
L i t h o l o g y , 312 Loka: M.S., 65, 128, 499 L o l : R i v e r , 364 L o n d i a n i : R.G.S.,+ 132, 480, 506 Long-term S t o r a g e : 419, 433, 435,
436, 439, 450
L o t i l l a : R i v e r , 39 Lower E g y p t , 8, 97, 248, 251 Lower P l i o c e n e : g e o l o g i c a l t i m e ,
302
Lower T e r t i a r y : g e o l o g i c a l t i m e , 297 Lower V i c t o r i a N i l e : R i v e r , 24, 176 Lowry-Johnson's method, 260 L u g a l a : R.G.S., 130, 476, 502 Lumbwa: R.G.S., 132, 480, 506 L u v i r o n z o : R i v e r , 15, 19 Luxor M . S . , 64, 69, 74, 79, 91, 98,
125, 472, 493 Town, 52, 96 Lwasamaire: R.G.S., 131, 478, 504 Lyantonde D i s p e n s a r y : R.G.S., 130,
478, 503 L y b i a , 308 L y s i m e t e r , 223, 227, 228, 253,
274, 286 Machar: swamp, 190, 191, 194, 282,
287, 369, 370
Magetch: R i v e r , 42 Main N i l e , 12, 13, 46, 197, 215,
299, 390, 392, 395, 401, 406, 407, 409, 410, 457
Malakal
G . S . + + on White N i l e , 13, 30, 40, 67, 96, 186, 189, 282, 297, 362, 367, 368, 373-379, 381, 410, 450, 513, 540 M.S., 65, 70, 75, 80, 86, 87, 91, 95, 101, 150, 168, 180, 216, 474, 498 M a l a w i Lake, 13 Mallawi: A . S . * * 238, 241, 248 Managil: R.G.S., 126, 387, 472, 495 Managil E x t e n s i o n , 384, 432 Mansura: M.S., 64, 69, 74, 91, 470, 490 Mara: R i v e r , 23 M a r i d i : R.G.S., 128, 476, 499 Marle: r o c k , 293 Marra: mountain, 60, 108 Masafu D i s p e n s a r y : R.G.S., 130, 476, 502
+R.G.s.
++
Masaka: R.G.S.,
130, 153, 155, 478,
504 Maseno: R.G.S., 131, 478, 505 M a s i n d i : M.S., 65, 71, 76, 80, 129,
153, 476, 500 Masindi P o r t , 25, 180, 215, 335 Mass c u r v e method, 420-423 Mbale: R.G.S., 129, 153, 155, 476, 501 Mbarara: M.S., 65, 76, 80, 86, 131,
153, 155, 478, 504 Mbuku: R i v e r , 28 Mbulamuti: G . S . , 330 Mean, a r i t h m e t i c , 118, 329, 337, 346, 367 M e d i t e r r a n e a n S e a : c o a s t , 15, 46, 54, 77, 96, 203, 205, 218, 300, 411, 416 Melut, 40, 379, 474, 497 El-Menufiya G o v e r n r a t e , 229 M e r i d i : R i v e r , 34 Merowe: M.S., 79, 167, 197, 215, 216 Mersa-Matruh: M.S., 64, 69, 74, 79, 87, 91, 123, 167, 470, 789 Meshra er-Req: M.S., 127, 150, 365, 367, 474, 498 Mesozoic: g e o l o g i c e r a , 300 Metamorphic s e d i m e n t s , 295, 299, 300 M e t e o r o l o g i c a l s c r e e n s , 1 6 6 , 175 M e t e o r o l o g i c a l S e r v i c e of E g y p t , 10 Mex: R.G.S., 123, 470, 490 Mfaza: R.G.S., 126, 474, 496 Middle E a s t , 302 . Middle Egypt: 248, 251, 253, 256 Middle Mesozoic: g e o l o g i c a l t i m e , 293 M i n i s t r y of I r r i g a t i o n ( P u b l i c Works) o f E g y p t , 10, 229, 442, 462 Minya: M.S., 64, 69, 74, 79, 91, 96,
98, 125, 167, 220, 271, 472, 493 Miocene: g e o l o g i c e r a , 300, 308 M i s s i n g r a i n f a l l d a t a , 117, 483-488 Miwani: R.G.S., 131, 478, 505 Mobutu-Sese Seko ( A l b e r t ) L a k e , 117 Model: s t a t i s t i c a l - s t o c h a s t i c , o r d e r , p a r a m e t e r s , 120-122, 324, 346, 349,
375, 403-410 Moeris: a n c i e n t l a k e , 7, 52 Mogren: G.S., 378 Moist sub-humid: climate, 61, 63 Moisture d e p l e t i o n , 231 e x t r a c t i o n p a t t e r n , 233 i n d e x , 61, 63 Molo: R.G.S., 132, 480 Mongalla G . S . on Bahr e l J e b e l , 30, 32, 198,
216, 282, 297, 350, 353, 354, 358,
= r a i n gauging s t a t i o n , G . S . = r i v e r gauging s t a t i o n , l o g i c a l s t a t i o n , **A.s. = a g r i c u l t u r a l s t a t i o n
*M.s. =
meteoro-
571 361, 374, 381, 401, 410, 512, 532 M . S . , * 80, 168, 180, 183 130, 478, Moniko E s t a t e : R.G.S. 502 Monsoon: r a i n storms, 96, 105 Morongole: mountain, 30 Moroto: M.S., 65, 75, 80, 128, 153, 155, 476, 500 Mubende: M.S., 65, 76, 80, 129, 476, 502 Mufumbiro: mountain, 19, 28 Muguga: A . S . , = * 286 Muhoroni: R.G.S., 131, 478, 506 Puisha: swamp, 19 Mukono: A.S., 130, 478, 503 Mumais: R.G.S., 131, 153, 155, 505 Musas: Lysimetry s t a t i o n , 284, 285 Musoma: P . S . , 6 5 , 76, 80, 132, 153, 155, 480, 506 Mwanza: M.S. 6 5 , 71, 76, 80, 8 6 , 88, 132, 153, 155, 480, 507 Myanga: R.G.S., 131, 478, 505
,+
,
Naam: River, 34, 364 Nabiyongo I s l a n d : automatic weather s t a t i o n , 66 Nag-Hammadi: M . S . , 64, 69, 74, 80, 91, 125, 472, 493 El-Nahud: M.S., 65, 70, 75, 107, 127, 474, 497 Nakasangola: R.G.S. 129, 476, 501 Namanve: R.G.S., 130, 478, 502 Namasagali: G.S.++ on V i c t o r i a N i l e , 129, 330, 335, 476, 501 Namulonge: A.S., 65, 86, 174, 285, 286 Narok, 215 E l - N a s i r : G.S. on Sobat, 37, 40 Nasser: Lake, 50, 307, 410, 444, 457, 459, 460 Nasser (El-Nasir): R.G.S., 127, 368, 474, 498 Nawanzu: R.G.S., 130, 476, 502 El-Nekhl: R.G.S., 124, 470, 492 Neonile, 303 Ngara: R.G.S., 132, 480, 507 Ngogwe: c o f f e e n u r s e r y , 130, 476,
,
503
Ngono: R i v e r , 1 9 , 318 Ngora: R.G.S., 129, 476, 501 Ngudu: R.G.S., 132, 480, 507 Nile Basin, 15, 19, 78, 85, 107, 113, 117, 158, 172, 205, 259, 287, 304, 433
++
D e l t a , 17, 96, 167, 203, 205, 218, 299, 311, 312 level, 8 River, 1, 15, 218, 294, 301, 303, 311 v a l l e y , 52, 218, 312 Nilometer: l e v e l gauge, 8, 412 Nimule: M.S., G . S . , 29, 128, 180, 353, 354, 452, 476, 499, 530 Nkozi: R.G.S., 130, 503 No: Lake, 34, 40, 359, 365, 366, 537 Nsyamba: R.G.S., 503 Ntenjeru: R.G.S., 129, 476, 501 Nuba: d e s e r t , 40 Nubian sandstone, 46, 48, 298, 299, 302, 309, 311 S e r i e s , g e o l o g i c a l formation, 295, 298, 306 Nyala: R.G.S., 127, 474, 498 Nyamgasani: River, 28 Nyambell, 35 Nyanza S h i e l d , 293 Nyanzian Formation, 293 Nyaranda: River, 116 Nyasa: Lake, 5 Nyavarongo: River, 19, 318 Nzoya: River, 23 El-Obeid: M . S . , 65, 70, 75, 80, 87, 126, 168, 474, 496 Oligocene: g e o l o g i c a l time, 297, 300 O l i v i e r ' s method, 248, 251, 267, 269, 276, 286, 363 Ongino: R.G.S., 129, 476, 500 Orographic: r a i n , 60 Outflow, 324, 326, 338, 349, 352, 353 Over-annual s t o r a g e , 432 Owen F a l l s Dam, 1 2 , 23, 330, 439, 559 Packwach/Panyango: G.S. on Albert N i l e , 349, 351, 411, 511, 529 Paleocene: g e o l o g i c a l time, 300 P a l e o n i l e 302 Pan, C l a s s A: evaporation pan, 173, 175, 183, 187, 203, 206, 209, 212, 270, 276 Pan, Kenya: evaporation pan, 174, 178 Pan f a c t o r : c o e f f i c i e n t , 183, 206, 209, 277 Papyrus: swamp, 34, 382 Paraa: G.S. on Kyoga N i l e , 338, 341, 510, 528 Peake's Channel, 359 Pegmatites: rocks, 298 Penman's method, 175, 177, 181, 183,
,
+R.G.s. = r a i n gauging s t a t i o n , G.S. = r i v e r gauging s t a t i o n , l o g i c a l s t a t i o n , **A.S. = a g r i c u l t u r a l s t a t i o n
f
M . S . = meteoro-
5 72
Rainfall g a u g e s , 6 6 , 6 7 , 113, 1 1 4 , 1 1 7 , 1 2 1 , 133, 172 maximum i n a day, 1 6 0 measurement, 113, 1 1 7 , 395 v a r i a t i o n , 118 Rangala: R.G.S., 131, 478, 505 Rapids Damazin, 42 Fola, R a s el-Dabba: R.G.S., 1 2 3 , 470, 490 R a s el-Negb: R.G.S., 1 2 4 , 472, 492 Rashed: R.G.S., 127, 474, 497 R a t i n g c u r v e , 330, 338, 3 4 3 , 373, 374, 381, 386, 406 Reb: R i v e r , 4 2 R e c e n t : g e o l o g i c a l t i m e , 300 Red S e a , coast: 1 9 , 5 2 , 7 7 , 9 6 , 200, 215, 311 R e g r e s s i o n : s t a t i s t i c s , 393, 394, 464 R e j a f , 3 0 , 452 Renk: M.S., 6 5 , 7 0 , 75, 1 2 7 , 1 8 6 , 379, 474, 497 R e s e r v o i r c a p a c i t y : s i z e , 423, 424, 426, 433 R e t u r n p e r i o d , 1 2 0 , 1 2 2 , 1 5 4 , 1 5 9 , 355 R i f t V a l l e y ( G r e a t ) , 1 9 , 27 Roda gauge: N i l o m e t e r , 413, 415 Root z o n e , 228-230 Roseires D a m , R e s e r v o i r , G.S.++ on Blue N i l e , 13, 42, 2 7 4 , 298, 380, 384, 432, 515, 543, 557 M.S., 6 5 , 7 0 , 7 5 , 8 0 , 9 2 , 1 2 7 , 1 6 8 , 191-194, 216, 2 9 8 , 497 Rosetta b r a n c h , 5 4 , 447 M.S., 6 4 , 7 9 , 9 1 , 1 2 3 , 470, 489 Rubya: R.G.S., 132, 480, 507 Ruchuru: R i v e r , 2 8 R u f f a : R.G.S., 387, 472, 495 Rumbek: R.G.S., 1 2 8 , 474, 499 Run-off volume, 317, 323, 3 3 4 , 340, 345, 352, 364 c o e f f i c i e n t , 1 9 1 , 317-323, 353, 369, 370, 398 Ruvuvu: R i v e r , 1 9 , 318 Ruwand: R i v e r , 2 3 Ruwenzori r a n g e : m o u n t a i n , 2 , 1 5 , 1 7 , 27, 28 Rwanda, 1 5 , 2 3 , 6 6 , 2 8 1 , 293
185-187, 191-195, 1 9 7 , 1 9 8 , 205, 206, 208, 209, 212, 268, 269, 281, 282, 284, 285, 335 Perhumid: c l i m a t e , 6 1 P i b o r : R i v e r , 35, 37, 368, 372, 374 P i b o r P o s t : R.G.S.,+ 1 2 8 , 474, 499 Piche: evaporimeter, 6 6 , 165, 166, 1 7 0 , 1 7 4 , 1 7 8 , 183, 187, 189-192, 1 9 5 , 1 9 7 , 198, 205, 212, 215, 218 P l e i o c e n e : g e o l o g i c a l t i m e , 297, 300 P l e i s t o c e n e : g e o l o g i c a l t i m e , 297, 300 P l o t , f i e l d e x p e r i m e n t , 228 6 4 , 6 9 , 7 4 , 79, P o r t S a i d : M.S. 8 7 , 9 1 , 9 8 , 1 0 8 , 1 2 3 , 1 6 7 , 203, 204, 216, 218, 470, 489 P o r t Sudan: M.S., 6 5 , 7 0 , 7 5 , 8 0 , 8 6 , 8 7 , 9 1 , 1 0 0 , 1 2 5 , 472, 494 P r e c a m b e r i a n : g e o l o g i c e r a , 304, 311 P r e n i l e , 303 Probability distribution function gamma, 2 - p a r a m e t e r , 1 2 1 , 154 Gumbel, t y p e I , 159 lognormal, 2-parameters, 120, 141-143, 355, 357, 394-396, 400, 401, 404, 407 n o r m a l , 141-143, 383, 389, 390, 396, 410 P e a r s o n 1 1 1 , 1 2 0 , 141-143, 329, 337, 346, 355, 375, 381, 389, 394, 396, 400, 404, 405, 407 P r o t e r o z o i c : g e o l o g i c e r a , 299 P r o t o n i l e , 203 P r u i t t ' s f o r m u l a , 2 6 0 , 263 P u n j o : R i v e r , 364
,*
Qasr e l - G e b a l i , 1 6 7 Qena: M . S . , 6 4 , 6 9 , 7 4 , 79, 91, 1 2 5 , - 201, 215, 216, 271, 311. 472, 4 9 3 Qoz: g e o l o g i c f o r m a t i o n , 298, 306 Quackenbush-Phelan's f o r m u l a , 2 6 1 , 26 3 Q u a r t i z i t e s : r o c k , 293 Quarun: Lake, 52 Q u a r s h i y a : M.S., 6 4 , 9 6 , 98, 1 6 7 El-Quseima: R.G.S., 1 2 4 , 470, 4 9 1 Q u s s e i r : M.S., 6 4 , 6 9 , 74, 7 9 , 9 1 , 9 9 , 1 2 5 , 200, 2 0 1 , 215, 216, 472, 49 3 E l - Q u t t a r a , d e p r e s s i o n , 1 5 , 5 4 , 311 R a d i a t i o n : measurement, methods, 6 4 , 8 5 , 2 6 6 , 267, 279, 285 Raga: M.S., 6 5 , 7 0 , 7 5 , 498 Rahad: R i v e r , 4 2 , 44, 3 8 6 , 474, 497, 545
++
-
Sadd e l - K a f a r a : Dam, 7 S a f a g a , 311 M.S., 2 3 4 , 235, 239, Sakha: A . S .
,**
+R.G.s. = r a i n gauging s t a t i o n , G . S . = r i v e r gauging s t a t i o n , = agricultural station l o g i c a l s t a t i o n , "A.s.
*M.s.=
meteoro-
573
242, 248, 253, 470, 489 S a l i s b u r y : Lake, B a s i n , 116, 333, 334 Sallum: M . S . 6 4 , 69, 7 4 , 9 1 , 98, 1 2 3 , 205, 470, 489 Samvwe M i s s i o n : R.G.S.,+ 1 3 2 , 480, 507 S a t u r a t i o n c a p a c i t y : s o i l , 229 Savannah f o r e s t , 34 S c h i s t : r o c k , 295 Seasonal c y c l e : hydrologic v a r i a b l e , 218, 342, 349 Sediment c o n c e n t r a t i o n , 459 Semi-arid: c l i m a t e , 6 1 Semliki: R i v e r , Basin, 5 , 27, 116, 342-346, 352, 5 1 1 Semna: c a t a r a c t , 299, 4 1 1 S e n n a r (Makwar) Dam, R e s e r v o i r , G . S . + + on B l u e N i l e , 1 0 , 380, 384, 3 8 5 , 428, 429, 432, 5 1 7 , 544, 554 M.S., 6 5 , 7 0 , 1 2 6 , 1 9 2 , 1 9 4 , 216, 298, 384, 474, 496 S e r e r e : A . S . , * * 1 2 9 , 476, 500 Serial correlation, coefficient, 1 1 9 , 1 2 1 , 1 2 2 , 1 4 8 , 1 4 9 , 324, 325, 332, 341, 344, 3 5 1 , 355, 356, 358, 367, 375-377, 382, 383, 385, 386, 388, 389, 391, 395, 397-405, 408, 409 S e t i t ( T a k a z z e ) : R i v e r , 45, 398 S e s e I s l a n d , 22 S h a b l o k a : 6 t h c a t a r a c t , 49 Shakshuk: R.G.S., 1 2 4 , 472, 492 S h a l e s : r o c k , 293, 302 Shambat: R.G.S., 390 Shanwa: R.G.S., 1 3 2 , 1 5 3 , 1 5 5 , 480, 50 8 S h e b i n e l - K o m : R.G.S., 1 2 4 , 470, 49 1 S i d i - B a r r a n i : M.S., 6 4 , 6 9 , 7 4 , 9 1 , 470, 489 S i d s : A . S . , 236-240, 243, 244, 248, 253 S i n g a : M.S., G.S on Blue N i l e , 6 5 , 7 0 , 127, 1 9 3 , 1 9 4 , 216, 384, 474, 496, 544 S i n k a t : R.G.S., 1 2 5 , 472, 494 Sirw: R.G.S., 1 2 3 , 203, 2 0 4 , 470, 489 Siwa: O a s i s , M.S., 6 4 , 6 9 , 7 4 , 79, 9 1 , 1 2 4 , 308, 309, 311, 472, 492 Skewness: c o e f f i c i e n t , 118, 1 2 0 , 329, 337, 346, 349, 355, 367, 398, 438 S l a d e s : r o c k , 299
,*
+R.G.s.
++
Sobat B a s i n , 1 8 9 , 1 9 0 , 194, 1 9 5 , 218, 285 R i v e r , 3, 5 , 1 2 , 35, 4 0 , 297, 366, 368, 372, 378, 379 S o i l h e a t f l u x , 279 S o i l moisture, 223, 228, 262 S o l a r r a d i a t i o n , 223, 266 S o r o t i : M.S., 6 5 , 71, 8 7 , 1 2 9 , 1 7 7 , 215, 476, 500 S o t i k : R.G.S., 1 3 2 , 4 8 0 , 506 S p e c i f i c d i s c h a r g e , 15 S t a n d a r d d e v i a t i o n , 118, 329, 337, 346, 349, 355, 367, 379 S t a t i s t i c a l d e s c r i p t o r s , 1 5 7 , 324, 325, 329, 331, 332, 341, 343, 351, 356, 376, 382, 385, 388, 391, 397, 399, 401, 402, 408 Steppe, 6 1 Storage phenomena, volume, 324, 329, 335, 346, 349, 386, 392, 419, 440 w o r k s , 411, 433, 455 Sudan, 3, 12-14, 1 7 , 3 7 , 44, 5 9 , 6 6 , 6 8 , 9 4 , 9 6 , 1 0 6 , 1 0 7 , 113, 1 1 7 , 1 3 3 , 1 5 0 , 157, 1 5 8 , 1 6 8 , 1 9 1 , 209, 274, 280, 294, 305, 306, 441, 443 Sudd r e g i o n , 297, 439, 453 Such: R i v e r , 34 Suez: M.S.., 6 4 , 6 9 , 7 4 , 79, 9 1 , 1 2 4 , 470, 492 Suez C a n a l , 7 7 , 204, 311 S u n s h i n e : i n t e n s i t y , d u r a t i o n , 6 4 , 85, 9 0 , 9 4 , 181, 182, 266, 267, 286 S u p p l y , 419, 420, 422, 4 3 1 S u r p l u s : w a t e r , 6 1 , 312 Suspended s e d i m e n t , 427 Tahamiyam: R.G.S., 1 2 5 , 472, 494 E l - T a h r i r : M.S., 8 6 , 203, 204, 2 0 9 , 212 T a l g u h a r i a : R.G.S., 125, 472, 494 T a l o d i : R.G.S., 1 2 7 , 497 Tamaniat: G.S. on Main N i l e , 390, 392, 396, 520, 547 Tambach: R.G.S., 131, 4 7 8 , 505 Tana, Lake, B a s i n , 2 , 5 , 1 0 , 4 2 , 44, 1 6 8 , 1 9 1 , 1 9 4 , 1 9 5 , 380, 386, 515, 542 T e n d e l e t i : R.G.S., 474, 496 Tanganyika Lake, 5 , 13, 1 5 , 287 Tank: e v a p o r a t i o n , e v a p o t r a n s p i r a t i o n , 1 7 3 , 1 8 5 , 1 8 7 , 227 T a n t a : M.S., 6 4 , 6 9 , 7 4 , 7 9 , 9 1 , 124, 203, 204, 216, 470, 491 T a n z a n i a , 5 , 1 5 , 2 2 , 2 3 , 6 6 , 120, 293, 30 4
= r a i n gauging s t a t i o n , G.S. = r i v e r g a u g i n g s t a t i o n , l o g i c a l s t a t i o n , **A.s. = a g r i c u l t u r a l s t a t i o n
s
M . S . = meteoro-
5 74
T a p a r i : R i v e r , 34 Tarime: R.G.S. ,+ 1 3 2 , 1 5 3 , 1 5 5 , 480, 506 Temperature: a i r , 6 4 , 6 7 , 85, 259, 266, 267, 281 T e r e t e i n i a : mountain, 30 T e r r a k e k k a , 35, 1 2 8 , 359, 363, 474, 499 El-Themed: R.G.S., 124, 470, 492 T h o r n t h w a i t e ' s f o r m u l a , 26 1-26 3, 278, 279, 281, 3 6 3 Thunderstorms, 106, 1 0 7 Tokar: M.S. 6 5 , 7 0 , 7 5 , 472, 494 Tolombat e l - B o s e i l i : R.G.S., 123, 470, 489 Tolombat el-Tolombat: R.G.S., 1 2 3 , 470, 489 Tonga: R.G.S., 127, 363, 367, 474, 498 T o n j : R.G.S., 128, 474, 498 Tonj ( I b b a ) : R i v e r , 34, 364 T o r i t : M.S., 6 5 , 7 0 , 8 0 , 180 Tororo: M.S., 8 6 , 1 2 9 , 478, 502 Tororo/Naninga: R.G.S., 505 T o r r e n t , 353, 354 Toshka D e p r e s s i o n , 445 T o t a l i z e r : r a i n g a u g e , 66 T o z i : M.S., 8 6 , 108 T r a n s p i r a t i o n , 223 T r o p i c a l r a i n f o r e s t , 60 T r o p i c a l savannah, 60 T u n i s i a , 256 Turbo: R.G.S., 131, 478, 505 T u r c ' s method. 266
V i c t o r i a Lake, 5 , 6 , 1 2 , 13, 1 7 , 1 9 , 2 0 , 2 2 , 2 3 , 9 5 , 1 0 7 , 168, 1 7 0 , 287, 293, 326, 333, 337, 340, 342, 346, 439, 4 4 1 catchment a r e a , 1 7 3 , 175 s h o r e s , 1 1 6 , 1 7 0 , 215, 285, 317, 322, 330 V i c t o r i a N i l e : R i v e r , Basin, 116, 176, 1 7 7 , 317, 330, 331, 333, 338, 340 Vukula: R.G.S., 1 2 9 , 476, 5 0 1
Uganda, 5 , 13, 1 5 , 2 2 , 2 3 , 6 6 , 9 4 , 1 1 7 , 1 2 0 , 133, 1 7 4 , 215, 285, 287, 293, 309, 439 U k i r i g u r u : R.G.S., 1 3 2 , 480, 507 Urn Ruwaba R.G.S., 474, 496 s o i l series, 297 Unfraz: R i v e r , 42 Upper Egypt, 8, 9 6 , 248, 311, 312 Upper ( l a t e ) Mesozoic: g e o l o g i c a l e r a , 293, 298 Upper P l i o c e n e : g e o l o g i c a l t i m e , 30 2 Upper V i c t o r i a N i l e : R i v e r , 2 3 , 176 Upper White N i l e (Bahr e l J e b e l ) , 2 8 , 29
Wad-Haddad: R.G.S., 1 2 6 , 474, 496 W a d-Me dan i G . S . + + on B l u e N i l e , 44, 6 7 , 275, 277, 386 M.S., 6 5 , 70, 8 0 , 8 6 , 1 0 8 , 1 2 6 , 1 6 7 , 1 9 1 , 1 9 2 , 1 9 3 , 216, 387, 472, 495 Wadi el-Rayyan: d e p r e s s i o n , 5 4 Wadi H a l f a G.S. on Main N i l e , 48, 5 2 , 6 7 , 7 5 , 125, 1 9 7 , 307, 406, 427, 549 M.S., 6 5 , 7 0 , 7 5 , 7 9 , 9 2 , 9 5 , 1 0 0 , 1 6 7 , 494 Wadi e l - N a t r u n : R.G.S., 1 2 4 , 470, 4 9 1 Wadi-Shair: R.G.S., 1 2 6 , 472, 495 Wadi-Turabi: R.G.S., 1 2 6 , 495 Water-balance, 166, 172, 177, 1 9 0 , 312, 326, 442, 444 Wau: M.S., 6 5 , 70, 75, 8 0 , 8 7 , 9 2 , 9 6 , 1 0 1 , 1 6 8 , 1 8 0 , 1 8 2 , 183, 2 1 6 , 474, 498 Water l e v e l , 324, 326, 335, 336, 337, 346, 349, 350, 411 Water q u a l i t y , 456 Western Desert, 300, 308 Wet-bulb d e p r e s s i o n , 1 7 8 , 248 Wet-bulb t e m p e r a t u r e , 178 Wheat: consumptive u s e , 233, 239-241, 251, 264, 265, 269, 2 7 0 , 276, 277 White N i l e B a s i n , 1 8 6 , 1 8 9 , 1 9 2 , 195 R i v e r , 3 , 5 , 1 0 , 1 2 , 13, 4 0 , 4 6 , 150, 274, 361, 376, 379, 392, 430, 455, 538 Wild: e v a p o r i m e t e r , 1 6 5 , 172 W i l t i n g p o i n t : s o i l m o i s t u r e , 230, 258, 286 Wind: d i r e c t i o n , f o r c e , s p e e d , 6 4 , 9 4 , 9 6 , 9 7 , 181, 267, 268, 277, 279 Withdrawal r a t e : g r o u n d w a t e r , 434
Vapour p r e s s u r e a c t u a l , 181 s a t u r a t e d , 181, 268 Veveno: R i v e r , 39
Yala: R i v e r , 23 Yambio: R.G.S., 1 2 8 , 476, 499 Y e i : R.G.S., 1 2 8 , 476, 499 Y e i : R i v e r , 364
,*
+R.G.s. = r a i n gauging s t a t i o n , logical station
++
G.S.
= r i v e r gauging s t a t i o n ,
*M.s.
= meteoro-
575
Zeidab: R . G . S . 494 Zimbabwe, 19
Y i r o l b e d s : rock b e d s , 295 Yondi, 365
,*
,+1 2 6 ,
6 4 , 74, 79, 91, 124, Z a g a z i g : M.S. 203, 204, 470, 491
+R.G.s. = r a i n g a u g i n g s t a t i o n ,
'M.s. =
meteorological s t a t i o n
197, 297, 472,
