Performance Evaluation of SWAT-CN and SWAT-WB Hydrological Models for Estimation of Runoff in the Didessa Watershed, Abbay Basin, Ethiopia

Abstract

Watershed models are powerful tools for simulating the effect of watershed processes and management on soil and water resources. The Soil Water Assessment Tool is a watershed model widely used to predict water quantity and quality under varying land use and water use regimes. The objectives of this research were to test the performance evaluation of the SWAT-CN and SWAT-WB models for prediction of Runoff in the Didessa watershed. To determine the respective amounts of infiltration and surface runoff, SWAT uses the popular Curve Number method. Water balance models generally take the runoff generation processes in the assumption of saturation excess and in curve number method runoff generation processes in the assumption of infiltration excess. In order to use SWAT in monsoonal climates, the CN routine to predict runoff was substitute with a simple water balance routine in the code base. The calibrated and validated, SWAT-CN and SWAT-WB models performed well for simulation of monthly stream flow. Statistical model performance measures, coefficient of determination of 0.71 & 0.77 , the Nash–Sutcliffe simulation efficiency of 0.66 & 0.68, Index of volumetric fit of 0.96 & 0.88 and Percent bias -3.79 & -13.46, for calibration and 0.70 & 0.77, 0.68 & 0.69, 1.06 & 0.88 and 6.32 & 13.58 respectively for validation, both model indicated good performance of the model simulation on monthly time step. These results suggest that both SWAT can successful model saturation-excess and infiltration excess technique for runoff generation processes in the Didessa watershed. The calibrated model can be used for further analysis of the effect of climate and land use change as well as other different management scenarios on stream flow and soil erosion.

Keywords: Runoff; SWAT-CN; SWAT-WB; Didessa watershed