Sediment inflow estimation and mapping its spatial distribution at sub-basin scale: the case of Tendaho Dam, Afar Regional State, Ethiopia

Abstract

Sedimentation is a major problem of reservoir operation in Ethiopia. Deforestation, overgrazing and poor land management practices are some that accelerate the rate of erosion. The topography of Ethiopia in general and TDW in particular is undulating and local farmers commonly cultivate on the hilly sides causing easy topsoil wash away. This study aims to determine the sediment yield at Tendaho dam reservoir, identify the high sediment source sub-basins and check the applicability of SWAT model in the area. To achieve these goals, the hydro-meteorological, sediment, topographic, land use and soil map data were used as inputs for the model. The model was successfully calibrated and validated for measured stream flow and sediment yield of AR at Wonji, Melka Werer and Tendaho stations. It was thus found applicable in this watershed with acceptable performance evaluation statistics values. From the model simulated output, sub-basins 27, 34, 29 and 50 were found to be the top four severely eroded sub-basins with average annual sediment yield of 26.66t/ha, 24.22t/ha, 23.79t/ha and 19.13t/ha, respectively. While, sub-basins 31, 18 and 21 were found to be the least sediment sources with annual averaged sediment yield of 0.02t/ha, 0.04t/ha and 0.04t/ha, respectively. In general, the results found in this study are very important inputs in selecting appropriate watershed management strategies and the methodologies used can also be valuable guides for the researchers in similar studies.

Keywords: SWAT Model; Sediment yield modeling; Sub-basins; Tendaho reservoir