Surface runoff modeling in Ketar watershed, Ethiopia

Abstract

Surface runoff is a critical input in watershed management. Runoff is a driving force for soil erosion which causes sedimentation of reservoirs located at downstream of watersheds. The present study aimed to model surface runoff using the Soil and Water Assessment Tools (SWAT) model in Ketar watershed, Ethiopia. Ketar river crosses mountainous steep slope areas. High surface runoff from the Ketar watershed flows to Lake Ziway. The Ketar watershed was delineated into 35 sub-basins and 147 Hydraulic Response Units (HRUs). In this work, surface runoff was simulated using 36 years (1980–2015) meteorological data as input. The model was calibrated and validated for streamflow using sequential uncertainty fitting-2 (SUFI_2) of the SWAT Calibration and Uncertainty Programs (SWAT_CUP). The model calibrated using 12-year measured streamflow data (1988–1997) and validated using 7-year streamflow data (1998–2004). The coefficient of determination (R2) and Nash–Sutcliffe (NSE) were used to measure the performance of the model. R2 and NSE were 0.82 and 0.7 during calibration and 0.78 and 0.71 during validation, respectively. The results show that there was an excellent relation between monthly observed and simulated streamflow during both calibration and validation. Simulated average monthly surface runoff of the watershed was 112.82 mm per month. The southwest part of the watershed, which was characterized by highest annual surface runoff, covers 27% of the total area.