Project Number: 6218-13000-011-13-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Jul 1, 2011
End Date: Apr 30, 2014
To conduct a study to assess the current reservoir sedimentation status and to determine conservation practices that will minimize watershed erosion and reservoir sedimentation to ensure sufficient water resources for the growing populations under projected long-term climate change in Ruiru Reservoir watershed, Kenya.
The Ruiru reservoir watershed, located in Nairobi, Kenya, will be evaluated using standard rapid geomorphic assessment techniques to determine probable sources of sediment. A multifrequency acoustic profiling system (APS) and a vibracoring system, boat, and outboard motor and gas tank will be purchased from Specialty Devices, Inc. and transported to Kenya. Reservoir water storage capacity and long-term average annual sedimentation rates will be quantified using the bathymetric survey using the APS. One to two sediment cores will be taken from the reservoir during the wet season using the vibracore and analyzed to determine the sediment texture and bulk density. In addition, since the Ruiru reservoir was impounded prior to 1963, 137Cs analysis will be done to give early and late sedimentation rates. Dry season cores will be manually pulled using standard soil corers and analyzed to determine the soil texture and bulk density. We will obtain a digital elevation model, soils, landuse and land management, weather, and streamflow data. A Soil and Water Assessment Tool (SWAT) model project will be built, calibrated, and validated for streamflow and sediments using obtained sediment budget information and reservoir sedimentation rates. The calibrated and validated SWAT model will be used to identify "hot spots" within the watershed and to determine the impacts of climate change on reservoir/stream sedimentation rates. SWAT will be used to evaluate alternative conservation scenarios to enhance water sustainability under climate change and a growing population. Kenyan personnel will be trained in using the APS and vibracore, rapid evaluation of sediment budget methods, and SWAT modeling technologies in order to build capacity. The study findings and recommendations will be provided to policy and decision makers and local stakeholders.