ico ‘,/cca COMM ONWEALTH F UND F OR TECH NI CAL CO-OP ERATION COM M ONWEALTH SECR ETARIAT A R ECONNAISSANCE STUD Y F OR M AJ OR SURFACE WATER SCH EMES IN EASTERN BOTSWANA P H ASE I R EP OR T MAR CH 1976 SIR A LEX A N D ER GIBE & PA R TN ER S R EA D IN G and LO N D O N PJAA. om-t4---tArl COM M ONWEALTH F UND F OR TECHNI CAL k; CO-OP ER ATION COMMONWEALTH SECRETARIAT A R ECONNAISSANCE STUD Y F OR M AJ OR SUR FACE WAT ER SCHEM ES IN EASTERN BOT SWANA P H A'SE I R EP O RT M AR CH 1976 SI R AL EXA NDER GIBB & PA RT NERS REA D ING and LONDON S IR AL EX A N D ER G IBB St PA R T N ER S ST A N D A R D H O U S E CONSULTINGENGINEERS LO N D O N ST R E ET PARTNERS CONSULTANTS R EA D ING R G 1 4PS s m A N G U S P A T O N C s i n I C C HS M E E r • s c L H C. K E E F E I IC C I Is . c H : L c s o o t: u os< r fc c r i s • n t ;c.N : I . P H A I G H M • I . C 1: T ELO N I O N I. R E A D I N G S9 : 1. 1 ( I S L CN E S ) H L A N D E R O u r N A m C t: 1.1S 1I. oc • E M a d : R M A R W I C K / 1.SC TEL EG R A M S G I EID O S O W ., . .: R E A D I N G A . D . S M A N G N A L L O BE W . I4 R A N G E L E Y OM : I C E EIS TRu c TE K F. S C O T T v c. m c c N M E s E R O B E R T S US , I C E T Lu x 8 4 7 4 0 4 W T N . R E E V L F IC E *.I E IC W. W A R E) U B E M A I •C E .1 V . C O R N E Y At A I : C C F I SI E0 ,E C. S W A N I I Sc r ic L ^ N U A., G H . C O A T E S B Sc F IC E m ASC E r i s • m < y r. T . A S A M U E L S M A . I C E A . A B A C K OM . O rn . , IC C 2 4 Q U E E N A N N E S G A T 1: A. I f M U I ZR A Y (I S E F IC E C O N S U L T A N T A R C H I T E C T W E S T M I N S T E R S W : H 9 A J J H f . N N E S S y m • PAI GE m i w i s 11, L . F O R D F R I OA st R I PI 0 1110 A SSO C I A T ES L T o / El [ PH O N E 0 1 - 9 3 0 9 70 0 ASSOCIATES F? A . C R O W m E)141 R . R E A T C H L O LJS BSc F IC E S E N I O R C O N S U L T A N T S A C: . C. O W E 145 Y EE I : c c r i s Tn uc. TE I t I . F I T I C NI G US< c i C E. F AS E E E I S T A W 7 L J . W . G . P i R : t R . G . T . L A N E OSC. r I C C F I E• us • R . J . W I T C H E L L M • M C C T . .1. W O O D S EIA L L A R D 'A A F 10 E PL EAS E R C , L H 10 49c/7548 J . 14. L . K E N T B A s l i C E K . I I . N O R R I S I I C E I ASC E T . G . C A R P E R I C H OA M I C E .1 W . S JAMES O h l !.v C c st rE Au s T I IP 2nd April 1976 A .1 . W O O D F O R D BSC F I C E Fiver s The Managing Director , Commonwealth Fund for Technical Co-Operation , Commonwealth Secretariat , Marlborough House , Pall Mall , London SW1Y 5HX Dear Sir , Reconnaissance Study for Major Surface Water Schemes in Botswana In accordance with our Agreement dated 19th December 1975 , we have pleasure in submitting our Phase I report on the above study . Our Terms of Reference are reproduced in Appendix A of this report . Following our work in Botswana and discussions there and in South Africa , 73 possible dam sites were identified which are listed in Table No . 2.1. Subsequent work in the United Kingdom on hydrological and other aspects of the study lead us to believe that selection of sites for further investiga:tion in Phase II could be made from 26 most favourable sites , details of which arc given in Table 4 .1. These sites are additional to nine sites which satisfy the y ield criterion set by the Terms of Reference but have been the subject of previous reports . We look forward to receiving your instructions regarding Phase II of the study . Yours faithfully , for SIR ALEXANDER GIBE & PARTNERS (TI N 42,C uce ACKNOWLEDGEMENTS We to record our sincere appreciation of the co-operation , assistance and advice we have received from all concerned with the study . Some .of the principal organisations and individuals concerned (in Botswana unless otherwise stated) were as follows : 1 . The Reference Group . 2 . The Secretary of External Affairs. 3. The Director of Water Affairs and his staff , particularly Messrs . Wilson (also in the Reference Group ) Bjorkman , Wallander, Drake, Dewar and Wikner . The Assistant Director , Mapping, Department of Surveys and Lands and his staff. 5 . Messrs . Jones, Mosetse, Holmberg and Gale of the Geological Survey and Mines Department . 6 . The Director , Weather Bureau . 7 . Mr . David Field of the Land Utilization Division , Ministry of Agriculture . 8. Professor D . C. Midgley of the University of the Witwatersrand , Johannesburg . 9 . Mr . Du Plessis , Engineer Manager (Design) of the South African Ministry of Water Affairs , and members of his staff . CONSULTANTS ASSOCIATED WITH THE STUDY Dr . J. V. Sutcliffe of the Institute of Hydrology , Wallingford , England has been largely responsible for the hydrological aspects of the study. Mr . K. S. Jones , of Golder Hoek and Associates advised on geological aspects of the study . TABLE OF CONTENTS Page No . CHAPTER 1 - INTRODU CTION 1 .1 Ter ms of Reference 1 1 .2 Method of Study 1 CHA PTE R 2 - IDENT IFICATION OF DAM SITES 2 .1 Availab ility of aerial photographs 3 2 .2 Ava ilab ility of other data 3 2 .3 Initial study of aerial photographs 4 2 .4 Discussion w ith Reference Group 5 2 .5 Re-exam ination of aerial photographs 6 2 .6 Discussion in South Africa 6 2 .7 Con solidated list of poss ible s ites 7 2 .8 Dam Site Character istics 11 CHAPTER 3 - HYDROLOGY 3.1 Objective 18 - Meth od of analysis 19 - Reliability of results 19 3.2 Rainfall Records 20 3 .3 Evap oration 21 3 .4 Run -off Records 22 - Botswana Records 22 - Rho des ia and South Africa Record s 24 3 .5 Ca lculat ion of Mean Annual Run-off at gau ging stations 24 3 .6 Relat ionship between Rainfall and Run -off 32 3 .7 Estimation of Mea n Annual Run-off at potentia l dam sites 35 3.8 Der iva tion of dimensionless reservoir yield curve 41 References 45 CHAPTER 4 - SELECTION OF MOST FAVOURABLE DAM SITES 4 .1 Hyd ro logy 46 4 .2 Pre vious studies 46 4 .3 Effe ct of Existing dams 47 4 .4 Effect of adjacent sites 47 4 .5 Geology 48 4 .6 Most favourab le sites 49 Appendix A Term s of Reference 1 to 4 inc . Appendix B Monthly Flows at Botswana Sites 1 to 13 inc . LIST OF TABLES Tab le No . Page No . 2 .1 Consolida ted List of poss ible dam sites 8 , 9 , 10 2 .2 Dam site and reser voir characteristics 15 ,16,17 3.1 Mean monthly rainfall dur ing years in wh ich ann ual ra infa ll was lower than average 21 3 .2 Mean monthly open water evaporation 21 3 3.3 Summary of run -off (million m ) 25 ,26.27 3.4 Summary of run -off (mm ) 28 ,29,30 3 .5 Compar ison of mean ann ual rainfa ll and run-off at gauged sites 33 ,34 3.6 Estimated mean ann ua l run -off and net yield at reserv oir sites 37 ,38,39 ,40 4 .1 Details of most favourable sites 51 4 .2 Details of sites studied prev iously 52 LIST OF FIGURES Figure No .