Detailed spatial analysis of SWAT-simulated surface runoff and sediment yield in a mountainous watershed in China

Abstract

In this study, surface runoff and sediment yields, simulated by the Soil and Water Assessment Tool (SWAT) for the Xiangxi catchment, China, are analysed at the spatial level of hydrologic response unit (HRU). This allows for a more precise targeting of best management practices than analysis at the coarser sub-basin level. It also provides the opportunity to validate simulated surface runoff and sediment yield by evaluating the plausibility of their spatial variation within the watershed. The results indicate that satisfactory model performance at a gauge does not guarantee plausible results at HRU level. Both surface runoff and sediment yields were found to vary reasonably with land use and soil types, but not with slope. The credibility of simulated surface runoff was increased by modifying selected SWAT algorithms and parameters. However, these modifications had only a marginal effect on sediment yield, which can be explained by the nonlinear relationship between sediment yield and HRU area in the modified Universal Soil Loss Equation. This study demonstrates that evaluation of model output at HRU level is highly recommended.Editor D. Koutsoyiannis; Guest editor V. Krysanova