Upper Tana-Nairobi Water Fund Technical Report Submitted by: ETC East Africa Ltd ABC Place, Waiyaki Way, P.O. Box 76378, Nairobi, Kenya. Phone: +254 (0)20 4 445 421/2/3 Fax: 254 (0)20 4 445 424 East Africa Email: [email protected]. September 2012 Upper Tana-Nairobi Water Fund pre feasibility study was conducted by ETC East Africa Ltd in collaboration with Future Water The assignment was carried out by: Fred Muchena Davies Onduru Francis Muthuri Peter Macharia Esther Njuguna Peter Maingi Peter Droogers Johannes Hunink The contributions by TNC and Partners are highly appreciated ETC East Africa Ltd ABC Place, First Floor Unit One, Waiyaki Way, PO Box 76378-00508 Nairobi, Kenya Phone: ++ 254 (0)20 44 45 421/2/3 Fax ++254 (0)20 44 45 424 Website : www.etc-international.org Email : [email protected] Table of Contents LIST OF ABBREVIATIONS iii 1. INTRODUCTION 1 1.1 Background Information ..................................................................................................... 1 1.2 Purpose and objectives ...................................................................................................... 2 1.3 Study Approach ................................................................................................................... 2 2. LITERATURE REVIEW 3 2.1 Description of the Study Area ............................................................................................ 3 2.1.1. Location of the Upper Tana Catchment ................................................................................. 3 2.1.2 Climate and agro-ecological zones ........................................................................................ 3 2.1.3 Geology and Soils .................................................................................................................. 4 2.1.4 Water resources .................................................................................................................... 8 2.1.5 Hydrology............................................................................................................................... 9 2.2 Land Use and Land Cover of the Upper Tana Catchment ............................................. 11 2.2.1 Introduction .......................................................................................................................... 11 2.2.2 Land use patterns ................................................................................................................ 11 2.2.3 Land cover characteristics ................................................................................................... 13 2.2.4 Cost Benefit Analysis of land management practices .......................................................... 14 2.3 City Water Supply Schemes (Sasumua and Ndakaini) .................................................. 16 2.3.1. Sasumua Catchment ......................................................................................................... 16 2.3.1. Thika Dam ........................................................................................................................... 19 2.4 Socio-economic factors and livelihood systems ........................................................... 20 2.4.1. Human population ................................................................................................................ 20 2.4.2. Poverty levels ...................................................................................................................... 22 2.4.3. Access to infrastructure ....................................................................................................... 24 2.4.4. Land holdings and land tenure ............................................................................................. 24 2.4.5. Livelihoods ........................................................................................................................... 25 2.5 Ecosystem Services .......................................................................................................... 27 2.5.1 Water –related ecosystem services ..................................................................................... 27 2.5.2 Forest – related ecosystem services ................................................................................... 30 2.5.3 Agroecosystems in the Upper Tana ..................................................................................... 38 2.6 Hydrological Modelling ..................................................................................................... 38 2.6.1 Existing studies ................................................................................................................... 38 3. STAKEHOLDER OUTREACH 43 3.1 Stakeholders Reached during Phase 1 ........................................................................... 43 3.2 Overview of Stakeholder Discussions ............................................................................ 43 3.2.1 Corporates ........................................................................................................................... 43 3.2.2 Development partners ......................................................................................................... 44 3.2.3 International organisations ................................................................................................... 44 3.2.4 Local organisations .............................................................................................................. 44 3.2.5 Issues arising from the stakeholders ................................................................................... 45 4. RAPID APPRAISAL OF SELECTED SUB-CATCHMENTS 46 4.1 Introduction ........................................................................................................................ 46 4.2 Location of area visited and biophysical environment ................................................. 46 4.3 Livelihoods options for households in the upper tana catchment area ...................... 52 4.4 Summary of Ecosystem Services from the Upper Tana Catchment ............................ 58 4.5 Summary of Conservation Issues .................................................................................... 59 Upper Tana-Nairobi Water Fund-Draft Technical Report –Submitted by ETC East Africa to TNC -August 2012 Page i 4.6 Government/ Community Efforts at Addressing the Prevailing Problems .................. 60 5. MODELLING APPROACH 61 5.1 Introduction ........................................................................................................................ 61 5.2 Model Selection ................................................................................................................. 61 5.3 SWAT Model Specifications ............................................................................................. 62 5.3.1 Conceptual background ....................................................................................................... 62 5.3.2 Evapotranspiration ............................................................................................................... 63 5.3.3. Groundwater ........................................................................................................................ 64 5.3.4. Reservoirs ............................................................................................................................ 64 5.3.5. Erosion................................................................................................................................. 65 5.3.6. Sediment routing .................................................................................................................. 65 5.4 Scenario Options ............................................................................................................... 66 5.5 Water Economic Evaluation ............................................................................................. 68 6. AVAILABLE DATASETS 70 6.1 Model Input Requirements ................................................................................................ 70 6.2 Climate ................................................................................................................................ 70 6.2.1 Local station data ................................................................................................................. 71 6.2.2. Satellite rainfall estimates .................................................................................................... 72 6.3 Digital elevation model ...................................................................................................... 73 6.4 Soils .................................................................................................................................... 73 6.4.1. KENSOTER ......................................................................................................................... 73 6.4.2. Harmonized KENSOTER ..................................................................................................... 74 6.5 Land use ............................................................................................................................. 75 6.6 Calibration Datasets .......................................................................................................... 75 6.6.1. Streamflow ..........................................................................................................................