WATER RESOURCES AUTHORITY WATER RESOURCES SITUATION REPORT AUGUST 2019 July 2018 to June 2019 Water Resources Situation Report-2018/2019 Water Resources Situation Report-2018/2019 Contents List of Figures ........................................................................................................................ iv List of Tables.......................................................................................................................... vi Abbreviations and Acronyms .............................................................................................. viii Foreword ................................................................................................................................. x 1 INTRODUCTION ............................................................................................................... 12 1.1 Background Information ................................................................................................ 12 1.2 Overview ........................................................................................................................ 13 1.3 This Report ..................................................................................................................... 15 1.4 Data Availability ............................................................................................................ 16 2 CLIMATE ............................................................................................................................. 19 2.1 Description of Monitoring Network .............................................................................. 19 2.2 Improvements to the Network ....................................................................................... 22 2.2 Analysis of Rainfall, Evaporation & Climate ................................................................ 22 2.2.1 Lake Victoria North Catchment area .................................................................... 22 2.2.2 Lake Victoria South Catchment area ..................................................................... 23 2.2.3 Rift Valley Catchment area .................................................................................... 24 2.2.4 Athi Catchment area .............................................................................................. 25 2.2.5 Tana Catchment area ............................................................................................. 26 2.2.6 Ewaso Ng’iro North Catchment area .................................................................... 26 2.3 Comments on Special Events ......................................................................................... 27 3 SURFACE WATER RESOURCES .................................................................................... 29 3.1 Description of Monitoring Network .............................................................................. 29 3.2 Description of the surface water resources monitoring networks per catchment .......... 30 3.2.1 Lake Victoria North Catchment Area ................................................................... 30 3.2.2 Lake Victoria South Catchment Area.................................................................... 30 3.2.3 Rift Valley Catchment Area ................................................................................... 30 3.2.4 Athi Catchment Area ............................................................................................. 31 3.2.5 Tana Catchment Area ............................................................................................ 31 3.2.6 Ewaso Ng’iro North Catchment Area ................................................................... 31 3.3 Improvements to Network Infrastructure ...................................................................... 32 3.3.1 Rehabilitation ......................................................................................................... 32 3.3.2 Establishment of new stations ................................................................................ 34 3.3.3 Upgrading of Stations to Telemetry ....................................................................... 35 3.4 Improvements to Data Quality ...................................................................................... 35 3.5 Assessment of Surface Water Resources ....................................................................... 38 3.5.1 Lake Victoria North catchment area ..................................................................... 38 3.5.2 Lake Victoria south catchment area ...................................................................... 40 3.5.3 Rift valley catchment area...................................................................................... 42 i Water Resources Situation Report-2018/2019 3.5.4 Athi catchment area ............................................................................................... 43 3.5.5 Tana catchment area .............................................................................................. 45 3.5.6 Ewaso Ng’iro North catchment area ..................................................................... 47 3.6 Comments on Special Events ......................................................................................... 50 3.7 Special Studies ................................................................................................................ 52 4 EMERGING ISSUES .......................................................................................................... 53 4.1 Challenges ...................................................................................................................... 53 4.2 Conclusions .................................................................................................................... 53 4.3 Recommendations.......................................................................................................... 53 5 SURFACE WATER QUALITY ......................................................................................... 55 5.1 Description of Monitoring Network .............................................................................. 55 5.2 Improvements to Network Infrastructure ...................................................................... 56 5.3 Improvements to Data Quality ...................................................................................... 56 5.4 Assessment of Surface Water Quality ............................................................................ 56 5.4.1 Ewaso Ng’iro North catchment area ..................................................................... 56 5.4.2 Lake Victoria North Catchment Area ................................................................... 57 5.4.3 Results .................................................................................................................... 59 5.4.4 Athi Catchment Area ............................................................................................. 66 5.4.5 Tana Catchment Area ............................................................................................ 71 5.4.6 Lake Victoria North Catchment Area ................................................................... 76 6 GROUNDWATER RESOURCES ..................................................................................... 86 6.1 Geology and Hydrogeological settings .......................................................................... 86 6.2 The basement system ..................................................................................................... 87 6.3 The sedimentary system ................................................................................................. 87 6.4 The volcanic systems ...................................................................................................... 88 6.5 Groundwater occurrence and hydrogeology ................................................................. 88 6.5.1 Groundwater sustainable yield .............................................................................. 89 6.5.2 Groundwater Recharge and potential.................................................................... 89 6.5.3 Groundwater Allocation Balance .......................................................................... 92 6.1 Groundwater quality and major challenges ................................................................... 94 6.1.1 Dissolution of alumino-silicates ............................................................................. 94 6.1.2 Origin of F- in groundwater ................................................................................... 95 2- - 6.1.3 Dissolved Nitrate (NO3 ) and Nitrite (NO2 ) ......................................................... 97 6.1.4 Saltwater intrusion along coastal aquifers ............................................................. 98 7 THE DYNAMIC DECLINE OF GROUNDWATER LEVELS ...................................... 99 7.1 Nairobi Aquifer System water levels .............................................................................. 99 7.2 Rift Valley Basin Area Water levels ............................................................................. 100 7.3 Tana Basin Groundwater Levels ................................................................................. 101 7.4 Lake Victoria North Basin area water level trends ...................................................... 102 Water Resources Situation Report-2018/2019