SWAT-based runoff and sediment simulation in a small watershed, the loessial hilly-gullied region of China: capabilities and challenges

Model calibration and validation are necessary before applying it for scenario assessment and watershed management. This study presented the methodology of evaluating Soil and Water Assessment Tool (SWAT) and tested the feasibility of SWAT on runoff and sediment load simulation in the Zhifanggou watershed located in hilly-gullied region of China. Daily runoff and sediment event data from 1998-2008 were used in this study; data from 1998-2003 were used for calibration and 2004-2008 for validation. The evaluation statistics for the daily runoff simulation showed that the model results were acceptable, but the model underestimated the runoff for high-flow events. For sediment load simulation, the SWAT performed well in capturing the trend of sediment load, while the model tended to underestimate sediment load during both the calibration and validation periods. The disparity between observed and simulated data most likely resulted from limitations of the existing SCS-CN and MUSLE methods in the model. This study indicated that the modification of SWAT components is needed to take rainfall intensity and its duration into account to enhance the model performance on peak flow and sediment load simulation during heavy rainfall season.