Quantifying hydrologic impacts following dam construction along the Tana River, Kenya

Daily pre-dam and post-dam discharge data for Kenyaʹs largest river, the Tana, were analysed using flood frequency analysis and computation of various indicators of hydrologic alteration (IHA). Results from these analyses indicated statistically significant (p<00•01) augmentation of minimum river flows and reduction in peak flows. We also estimated the frequency of flooding of 71 vegetation sample plots located on various parts of the river floodplain by running a hydrologic water profile simulation program (HEC-RAS). Results from these analyses indicated that plots at elevations greater than 1•80 m above the dry season river level experienced statistically significant (p<0•01) reduction in days flooded from the pre- to the post-dam period. This documented magnitude of change in the hydrologic regime will have a negative impact on the unique riverine forest occurring along the Tana River.