ESTIMATION OF RUNOFF AND SEDIMENT YIELD USING SWAT MODEL AT YAHYA SHERKA WATERSHED OF BABILE EAST HARARGHE, ETHIOPIA

Abstract

Knowledge of the internal renewable water resources of a country is strategic information which is needed for long-term planning of a nation’s water and food security, among many other needs. New modeling tools allow this quantification with high spatial and temporal resolution. In this study, Soil and Water Assessment Tool (SWAT) was used to calibrate and validate flow and sediment yield at Erer river gauging station and predict the water and sediment yield of Yahya Sherka watershed. Sensitivity analysis, model calibration and validation were also performed to assess the model performance. Ten highly sensitive parameters were identified of which curve number was the most sensitive one. The coefficient of determination (R2) and Nash-Sutcliffe (ENS) was used to evaluate model calibration and validation. The R2 values were 0.855 and 0.87, respectively, for the flow during the calibration and validation periods. The respective R2 values for the monthly sediment yield were 0.864 and 0.900. A good agreement between the measured and simulated average monthly flows was also demonstrated by ENS values of 0.853 and 0.868, respectively, during the calibration and validation periods. The corresponding ENS values for sediment yields were 0.80 and 0.90. In most instances, the simulated average monthly flows and sediment yields were close to the average monthly measured values during both the calibration and validation periods at Erer gauged station. The water and sediment yield of Yahya Sherka watershed was quantified. After calibration and validation of the model the mean annual simulated water and sediment yield of Yahya Sherka watershed were estimated as 0.97Mm3 and 0.145 tons/ ha respectively. The SWAT model could be effectively used to predict runoff and sediment yield in order to effectively design water resource related development in absence of gauged information. In both case, for runoff and sediment yield simulation, SWAT model has showed a strong predictive capacity from the watershed. Therefore, the model can be used for simulating runoff and sediment from ungauged watershed that having similar physiographic and climatic condition with Erer watershed.