Surface runoff modeling using SWAT analysis in Dabus watershed, Ethiopia

The highlands of Ethiopia are highly threatened by soil erosion. Surface runoff is essential input to manage the watershed. Runoff causes soil erosion which makes sedimentation of reservoirs. The study aimed to simulate surface runoff using the Soil and Water Assessment Tools (SWAT) model in Dabus watershed, Ethiopia. The Dabus River is one of the major tributaries of the Blue Nile River which starts from southeastern highland and flows toward north. Since the topography of the watershed is mountainous steep slope areas, surface runoff is high. The Dabus watershed was delineated into 33 sub-basins and 82 hydraulic response units (HRUs). In this study, surface runoff was simulated using 30 years (1987-2016) meteorological data as an input. The model was calibrated and validated for stream flow using sequential uncertainty ftting-2 (SUFI_2) of the SWAT Calibration and Uncertainty Programs (SWAT_CUP). The model was calibrated using 9-year measured streamflow data (1994-2003) and validated using 8-year streamflow data (2004-2011). The coefficient of determination (R-2) and Nash-Sutclife (NSE) were used to measure the performance of the model. R-2 and NSE were 0.82 and 0.70 during calibration and 0.78 and 0.71 during validation, respectively. The results show that there was very good relation between monthly observed and simulated streamflow during both calibration and validation. Simulated average annual surface runoff of the watershed was 690.84 mm. The southeast part of the watershed was characterized by the highest annual surface runoff. Thus, this study shows that SWAT hydrological model can be used to model Dabus watershed for better assessment and simulation of the hydrological responses. The study recommends more researches which incorporate the land use change of the watershed in the model.