I I I irVERAFRICAN COMMITTEE FOR HYDRAULIC STUDIES I OUAGADOUGOU I UPPER VOLTA 1 I SAVANNA REGIONAL WATER RESOURCES AND LAND USE I SAVANNA RESOURCES 1 VOLUME 1 I REPORT I 1 I I I I I CIEH-USAID 1 Grant Agreements 345 Park Ave. 625-11-120-712 New York I and 698-0415 dlQ I 1 I INTERAFRICAN COMMITTEE FOR HYDRAULIC STUDIES I I OUAGADOUGOU I UPPER VOLTA 1 SAVANNA REGIONAL WATER 1 RESOURCES AND LAND USE I SAVANNA RESOURCES VOLUME 1 1 REPORT I 1 I 1 I 1 LIBRARY. INTE" '•^ATîOr-'AL REFERENCE CEMTFúT. F':.'•! ; v.-,:' -ITY WAVER SUPPLY AND i-.'.,-':- • 1 P.O. ['.: ' .... 09 AD 7"-e Hague Te!. (0/ü, o. •;-, i i ext. 141/142 RN: O'TobU TAM: 1 CIEH-USAID L0: Grant Agreements 82M/flF^« Gol í) 345 Park Ave. 625-11-120-712 1 New York 10022 I and 698-0415 I I I I This SAVANNA RESOURCES Study consists of 4 Volumes: I I VOLUME 1. REPORT — VOLUME 2. MAPFOLIO I' I VOLUME 3. APPENDICES -, VOLUME 4. STUDY PROPOSALS • I I I I I I 1 I TABLE OF CONTENTS 1 VOLUME 1. SAVANNA RESOURCES - REPORT Page 1 INTRODUCTION 1 CHAPTER 1. SAVANNA REGION 1 1.1 INTRODUCTION 1-1 I 1.2 DEFINITION OF REGION 1-1 1 1. 3 AREAL EXTENT AND SUBDIVISION OF REGION 1-4 1.4 MAPPING 1-4 CHAPTER 2. CLIMATIC RESOURCES 2.1 INTRODUCTION 2-1 I 2.2 DEFINITIONS AND MATERIALS STUDIED 2-1 2.2.1 Definitions 2-1 I 2.2.2 Materials Studied 2-4 2.3 RESULTS 2-5 I 2.3.1 Climatic Elements 2-5 2.3.1.1 Mean Annual Rainfall 2-6 I 2.3.1.2 Onset of Rains 2-8 2.3.1.3 Termination of Rains and the End of the I Growing Season 2-9 2.3.1.4 Radiation and Thermal Regimes 2-11 I 2.3.1.5 Evapotranspiration 2-14 2.3.2 Climate and Rainfed Agriculture 2-15 I 2.3.2.1 Physical Factors 2-15 2.3.2.2 Biological Factors 2-16 I 2.3.3 Bioclimatic Regions 2-21 I 2.3.3.1 Sahel Bioclimate 2-22 2.3.3.2 The Sudan Bioclimate 2-32 I 2.3.3.3 The Northern Guinea Bioclimate 2-33 2.3.3.4 The Southern Guinea Bioclimate 2-33 1 2.3.4 Net Biomas s Production and Yield of Crops 2-35 I I 1 I Page CHAPTER 3. WATER BALANCE I 3. 1 INTRODUCTION 3-1 3.2 PROGRAM FOR THE EVALUATION AND FREQUENTIAL 1 ANALYSIS OF THE ORBVCR SYSTEM WATER BALANCE 1 ELEMENTS 3-4 1 3.2.1 Characteristics of the System 3-6 I 3.2.1.1 Increasing Usable Soil Moisture 3-6 1 3.2.1.2 System Inputs 3-7 1 3.2.1.3 System Outputs 3-13 3.2.2 Statistical Analysis of the Information 3-16 1 3.2.3 Basic Information 3-17 3.2.3.1 Rainfall 3-17 1 3.2.3.2 Potential E vapotranspirátion 3-18 3.3 ORBVCR SYSTEM RESULTS 3-19 • 3.3.1 Model Control and Validity 3-19 3.3.2 Runoff/Drainage Period Expected for One Year 1 Out of Two 3-20 3.3.3 Rainwater Supply for Grasslands 3-21 1 i 3.4 ORBVCR SYSTEM APPLICATIONS 3-22 3.4.1 Agronomy 3-23 3.4.2 Phytoecology 3-25 3.4.3 Hydrology and Hydrogeology 3-25 1 CHAPTER 4. SURFACE WATER RESOURCES 4. 1 DESCRIPTION OF AREA 4-1 1 4.1.1 Chad Basin 4-2 4.1.1.1 Lake Chad 4-3 \ 4.1.2 Niger Basin 4-5 4.1.3 Volta Basin 4-8 i 4.1.3.1 Black Volta 4-9 4.1.3.2 White Volta 4-9 I 1 \ 4.1.3.3 Oti 4-10 4.1.3.4 Volta 4-10 ii I I Page CHAPTER 4. SURFACE WATER RESOURCES (Cont'd) I 4.1.4 Senegal Basin 4-11 I 4.1.5 Gambia Basin 4-11 4.1.6 Lesser Basins 4-12 1 4.2 MATERIAL STUDIED 4-13 4.3 METHODS AND RESULTS 4-17 1 403.1 Annual Stream Flow 4-17 4.3.1.1 Reference Period 4-17 I 4.3.1.2 Variability 4-18 4. 3.1. 3 Equivalent Depth of Runoff 4-18 I 4.3.1.4 Water Balance 4-18 4.3.2 Monthly Streamflow 4-24 I 4.3.3 Flood Flows 4-26 4.3.3.1 Evaluation of Flood Flows 4-27 I 4.3.3.2 Ten-Year Floods 4-28 4.3.3.3 100-Year Floods 4-35 I 4.3.3.4 Conclusions Concerning Flood Flows 4-37 4.3.4 Low Flows and Drought 4-37 I 4. 3. 4.1 Sequences of High and Low Flows 4-41 4.3.5 Small Watershed Runoff 4-42 1 4.3.6 Sediment Transport 4-43 4.3.7 Water Quality 4-48 I 4.4 SUMMARY 4-52 CHAPTER 5. GROUNDWATER RESOURCES I 5.1 INTRODUCTION 5-1 5.2 GEOLOGY 5-2 I 5.2.1 Geologic and Structural Setting 5-2 5.2.1.1 The Basement Complex 5-2 I 5.2.1.2 The Sedimentary Basins 5-3 5.2.1.3 Historical Geology 5-3 I I iii ;"•"• ;•'• •'••"' ;"'--i I ÏOÎ Mijf.'/l'1;.-'';-/ T.ll.l: •.•..J:.\J I Page r' CHAPTER 5. GROUNDWATER RESOURCES (Cont'd) 5.2.2 Lithostratigraphy 5-4 I 5.2.2.1 The Basement Complex 5-5 • 5.2.2.2 The Sedimentary Basins 5-5 , i 5.3 THE AQUIFERS 5-6 • 5.3.1 Classification 5-9 5.3.2 The Basement Complex 5-11 • 5.3.2.1 Groundwater Occurrence 5-11 5.3.2.2 Well Yields and Depths 5-12 • 5.3.3 The Sedimentary Basins 5-13 5.3.3.1 Paleozoic Cover 5-14 M 5.3.3.2 Continental Intercalaire 5-14 5.3.3.3 Cretaceous 5-15 I 5.3.3.4 Maestrichtian 5-15 5.3.3.5 Paleocene (and Eocene) 5-16 I 5.3.3.6 Continental Terminal 5-16 5.3.3.7 Plio-Quaternary and Quaternary 5-17 fl; 5.3.3.8 Summary 5-17 5.3.4 Conclusion 5-18 I 5.4 GEOHYDROLOGY 5-19 5.4.1 Groundwater Depth 5-20 I 5.4.2 Groundwater Movement 5-21 5.4.3 Safe Yield 5-22 I 5.4.4 Gtoundwater Storage ' 5-27 5.4.5 Groundwater Quality 5-32 m 5.4.6 Conclusion 5-34 5.5 CONCLUSIONS 5-37 I GLOSSARY 5-41 CHAPTER 6. LAND RESOURCES I 6.1 INTRODUCTION 6-1 ! 6.2 METHODS USED AND MATERIAL STUDIED 6-2 I 6.2.1 The Basic Soils Data 6-2 iv I I I Page 1 CHAPTER 6. LAND RESOURCES (Cont'd) I 6.2.2 Method of Interpretation 6-11 6.2.3 Case Studies 6-15 I 6.3 RESULTS 6-16 6.3.1 Map Legend 6-16 I 6.3.2 Limiting Factors 6-20 6.3.3 The Mapping of Major Soils and Associated Soils 6-21 I 6. 4 INTERPRETATION AND USE OF THE LAND CAPABILITY MAP 6-22 6.5 CONCLUSIONS 6-24 I 6. 5.1 Extent of Land Capability Classes 6-24 6. 5. 2 Area and Distribution of Soils in Each Capability I Class 6-27 CHAPTER 7. HUMAN RESOURCES I 7. 1 INTRODUCTION 7-1 7O 2 METHODS AND MATERIALS STUDIED 7-2 I 7.2. 1 Selection of Data Sources 7-2 7.2.2 Demographic Indicators 7-5 I 7.3 RESULTS 7-6 7.3.1 General Social Profile of the Savanna 7-6 I 7.3.2 Demographic Profile 7-9 7.3.3 Migration 7-12 I 7.4 CONCLUSIONS 7-14 I REFERENCES Part I Books, periodicals, maps, reports and studies (Listed alphabetically) R-l 1 Part II Hydrological Yearbooks (Listed by country and year) R-29 1 1 I I I LIST OF TABLES I Table 1-1 Political Subdivisions of the Savanna Region 1-5 • 1-2 Topographic Maps of the Savanna Region 1-6 ' 2-1 Adaptability Groups of Crops according to Similarities in Assimilation Pathway and Equal Photosynthesis Ability 2-18 2-2 Southern Sahel Bioclimate and Crop Adaptability 2-23 m 2-3 Sudan Bioclimate and Crop Adaptability 2-25 _ 2-4 Northern Guinea Bioclimate and Crop Adaptability 2-27 I 2-5 Southern Guinea Bioclimate and Crop Adaptability 2-29 IÄ 2-6 Climatic Characteristics of the Bioclimatic Regions 2-31 • 2-7 Total Net Biomass Production for the Growing Season and _ Average Rate of Net Biomass Production per Day for five I Locations in West Africa 2-36 2-8 Total Net Biomass Production and Yield of Selected Crops 2-37 • 3-1 List of Rainfall Stations Used 3-2 4-1 Hydrologie Yearbooks Available at CIEH 4-15 ™ 4-2 Annual Streamflow - Chari Basin 4-19 £ 4-3 Annual Streamflow - Logone Basin 4-20 '• 4-4 Annual Streamflow - Volta Basin 4-21 » 4-5 Annual Streamflow - Niger Basin 4-22 • 4-6 Annual Streamflow - Senegal Basin 4-23 4-7 Annual Streamflow - Gambia Basin 4-23 I 4-8 Mean Monthly Discharges at Selected Stations 4-25 4-9 Ten-Year Flood Flows in Chari Basin 4-29 I 4-10 Ten-Year Flood Flows in Logone Basin 4-29 4-11 Ten-Year Flood Flows in Niger Basin 4-30 1 4-12 Ten-Year Flood Flows in Volta Basin 4-32 m 4-13 Ten-Year Flood Flows in Senegal Basin 4-34 • 4-14 Ten-Year Flood Flows in Gambia Basin 4-34 • 4-15 Average Relation Between the Ten-Year Flood Flows and '* the Watershed Area 4-34 4-16 Maximum Observed and Estimated 100-Year Floods 4-36 | VI I I I LIST OF TABLES (Cont'd.) Page Table 4-17 Comparison of 100-Year Flood Estimates (m S-l) 4-35 I 4-18 Low Flows - Return Period 4-38 4-19 Annual Quantities of Suspended Sediment 4-45 1 4-20 Annual Quantities of Suspended Sediment Transported to Lake Chad as Measured near N'Djamena 4-47 1 4-21 Analyses of Water from West African Rivers 4-49 5-1 Lithostratigraphy of Western/Central Africa 5-7 1 5-2 Aquifer Outcrop Areas in the Project Area 5-10 5-3 Well Yields and Depths in the Basement 5-13 I 5-4 Well Yields and Depths in Paleozoic Rocks 5-14 5-5 Estimated Natural Recharge Versus Rock or Aquifer Types 5-23 I 5-6 Estimated Safe Yield per Aquifer, Country and Basin 5-25 5-7 Estimated Groundwater Storage Versus Rock or Aquifer Types 5-2 8 1 5-8 Estimated Groundwater Storage per Aquifer, Country and Basin 5-29 I 5-9 Groundwater Quality in the Basement 5-33 5-10 Groundwater Quality in Sedimentary Aquifers 5-35 I 6-1 Synopsis of the French Classification of West African Soils 6-4 6-2 Synopsis of the FAO 1:5 million Mapping Units Used in the I West African Savanna Region 6-9 6-3 Cross Key Showing the Correlation Between the French Soil Orders and the Major FAO Soil Mapping Units in the West 1 Africa Savanna Region 6-14 6-4 Synopsis of the CIEH Soil Capability Classification of the I 72 Soil Units of the Soil Map of the West African Atlas (OAU, 1971) 6-18 6-5 Percentages of the Total Savanna Area Occupied by Each I Map Unit, and the Percentages Occupied in Total by Each of the Soil Capability Classes 1,2,3,4 and 5 6-25 I 6-6 Relative Areas of Map Units Dominated by Soils of Each of the Five Capability Classes 6-26 1 6-7 Extent of Capability Classes 6-27 I 7-1 Selected Demographic Indicators of the Savanna Countries 7-10 I vu LIST OF FIGURES I Page Figure 1-1 The West and Central African Savanna Region in Africa 1-1 I After Page ^ 2-1 Relationship Between the Average Annual Precipitation I and the Average Length of the Growing Period 2-8 • 2-2 Relationship Between the Average Annual Precipitation, M the Onset of the Rains and the Termination of the Growing Period 2-10 ^ 2-3 Relationship Between the Growing Period and the Average • Daily Values of Incoming Short Wave Radiation 2-12 2-4 Relationship Between the Growing Period and the Amount m of Incoming Radiation Received During the Season 2-12 2-5 Relationship Between the Growing Period and the Maximum I) and the Minimum Screen Temperatures, Day Time Tempera- ™ ture and Night Time Temperature 2-12 2-6 Relationship Between the Excess of Precipitation Over g Evapotranspiration Demands During the Growing Season and the Length of the Growing Period 2-14 m 2-7 Average Relationship Between Maximum Photosynthesis ™ Rate and Temperature 2-16 '.