MODELING RUNOFF AND SEDIMENT YIELD OF KESEM DAM WATERSHED, AWASH BASIN, ETHIOPIA

Abstract

Soil erosion, transport and deposition are a cause for reservoir sedimentation. Modelling runoff and sediment yield of watershed are the most important steps to alleviate reservoir sedimentation. This study mainly focused on modeling runoff and sediment yield of Kesem dam watershed using SWAT model. The drainage area of Kesem dam watershed to its outlet Kesem dam site is 2660km 2 which contributing sediment to the reservoir. The method adapted to address this study based on the model sequential applicability. The model input data were metrological daily data, hydrological and spatial data based on HRUs process by overlapping mechanism and model run. After model run, the manual calibrations were applied using the time series data of the study from 1994 to 2010. The model performance was checked by statistical model performance indicators such as coefficient of determination (R 2 ), Nash-Sutcliffe model efficiency (NSE), and observations standard deviation ratio (RSR) and Percent bias (PBIAS) and the value was in acceptable range. The model calibrated mean annual flow at Kesem dam site was 35.14m 3 /s. The mean annual runoff and sediment yield of the Kesem dam watershed were 543.67mm and 11.43t/ha/yr respectively. From the Sediment yield mapping, sub basin 12 and 13 were high sediment yielding sub basins among those 41 sub basins. For these critical sub basins, Watershed management scenarios were applied. From the existing baseline condition, the mean annual sediment yield reduced to 8.39t/ha/yr due to 5m filter strip width, 5.61t/ha/yr due to 10m filter strip width, 8.76t/ha/yr due to grass waterway and 7.55t/ha/yr due to terracing. Generally, filter strip 10m significant ly reduce sediment yield.