Sediment yield modeling in Awash Melkasa dam watershed, upper Awash River basin, Ethiopia

Soil erosion may be a main problem within the Ethiopian highlands. The Awash River basin is one among the Ethiopian highlands suffering from a high rate of surface erosion. Sediment inflow rates of reservoirs and spatial distribution of sediment yield (SY) are required at the sub-basin level to develop alternative watershed management practices. Hence, this study aimed toward estimating SY within the upper Awash River by using the soil and water assessment tool. The spatial, weather, hydrological, reservoir input, and water withdrawal data were collected and analyzed. The model had adjusted and verified for both flow and sediment. The graphical comparison and statistical indicators, coefficient of determination (R2), Nash–Sutcliffe efficiency (NSE), root-mean-square error standard deviation ratio (RSR) and percent bias (PBIAS) had used to evaluate the model's performance. Monthly streamflow and SY estimates were found to be reliable (R2 = 0.78–0.83, NSE = 0.75–0.82, RSR = 0.43–0.5 and PBIAS = 0.1–8.8) based on the model calibration and validation results. After calibration, the simulated average annual SY estimated was 22,109.5 t yr−1at the outlet, with an average spatial distribution of 6.52 t ha−1 yr−1. The model prediction outcomes showed that about 26.16% of the Awash Melkasa watershed, located in southwestern direction, is an erosion-prone area with a mean annual SY ranging from 10 to 18.54 t ha−1 yr−1execiding tolerable soil loss. These sub-basins need prior mitigation measures to reduce soil losses from the catchment.