Soil and water assessment tool (swat) based evaluation of stream flow and sediment yield of golina catchment, lower awash river basin, Ethiopia

Abstract

Poor land use practices, improper management systems and lack of appropriate soil conservation measures have played a significant role in causing high soil erosion rates, sediment transport and loss of agricultural nutrients. The main objective of this study was to evaluate stream flow and sediment yield of Golina catchment. A physically based watershed model was applied based on its necessity to Golina catchment for evaluating of stream flow and sediment yield. The model was calibrated and validated for both flow and sediment concentration at Golina catchment outlet (323.4km2 ) to evaluate stream flow and sediment yield. 25 years daily metrological, flow and sediment rating curve equation for sediment data were used for model calibration and validation. The area of watershed was divided in to 8 sub basins and 29 HRUs by using soil and water assessment tool (SWAT) model. SWAT_CUP was used to calibrate the model parameters of flow and sediment with the time series of 2000 to 2009 for calibration and 2010 to 2014 for validation. Sensitivity analysis result shows that Base flow alpha factor (Alpha_Bf) and Cropping practice factor (USLE_C) were the most sensitive parameters affecting stream flow and sediment yield of the catchment respectively. The Calibrated and validated values of stream flow and sediment yields were, (R2=0.82, ENS=0.80, and (R2=0.86, ENS=0.84,) for flow. Similarly (R2=0.8, ENS=0.78, PBIAS=20.5RSR=0.46) and (R2=0.94, ENS=0.84, PBIAS=34.6, RSR=0.42) respectively for sediment yields. This result indicates that the observed values show good agreement with simulated value for both flow and sediment yield. For this study, the SWAT model yields average annual sediment of 68.82 ton/km 2 (6882 ton/ha) at Golina catchment. By applying watershed management intervention measures both land use redesign for steep slopes and terracing activities the sediment yields of Golina catchment reduced by 20.07% and 30.11% respectively. The result of the study could help different stakeholders to plan and implement appropriate soil and water conservation strategies.