Regional mapping of non-prolific sediment source catchments for small hydropower development in Tanzania

Run-of-River schemes are the main Small Hydropower (SHP) developments in sediment-laden rivers in Tanzania. Investments in this sector are not guided by non-prolific sediment source catchment map. Development of such maps requires extensive sediment load measurements on a frequent time basis, hence costly and logistically demanding. The Pacific Southwest Inter-Agency Committee (PSIAC) approach is the main framework but considered inexpensive method, after being evaluated and validated is applied in this study under ArcGIS 9.3 software environment to map suitable zones in Tanzania for SHP development. The zones of non-prolific and prolific sediment source catchments were based on Suspended Sediment Concentration (SSC) data with a recommended threshold of 3 g/l for hydropower turbine sustainability. The SSC was spatially derived as the ratio of Specific Sediment Yield (SSY) to mean annual runoff data using a computational grid of 0.02 degree. Area for non-prolific sediment source catchments zone in Tanzania covered 58.6 % with the SSC of 0 g/l to 3 g/l and the coverage area of the prolific sediment source catchments zone was 41.4 % with SSC of 3 g/l to 24.7 g/l. It should be noted that the SSC data can be used to guide the selection of the SHP development. However, the author acknowledges that more data on dam sedimentation and sediment mineralogy would improve PSIAC model prediction performance and influence the choice of SSC threshold, respectively, hence better results.