Stormwater runoff is a major pathway for transporting sediment and other nonpoint-source pollutants from watersheds to stream systems and other surface water bodies. In this study, the Soil and Water Assessment Tool (SWAT) model was used to assess sediment transport from the 17 km(2) Banha watershed located in northeast India, which is characterized by mixed land use and on-stream sediment control structures called checkdams. Calibration (1996) and validation (1997-2001) of surface runoff and sediment yield were performed with SWAT on both a daily and monthly basis by comparing model estimates versus measured data. The calibration R-2 and Nash-Sutcliffe modeling efficiency (NSE) statistics were found to range between 0.70 to 0.99 for surface runoff and 0.82 to 0.98 for sediment loss. The corresponding validation period statistics ranged from 0.60 to 0.92 for surface runoff and 0.58 to 0.89 for sediment loss. Following calibration and validation, the SWAT model was executed with and without checkdams to test its capability in visualizing the impacts of sediment control structures in the watershed. The model estimates showed that sediment loss from the watershed could be reduced more than 64% by adopting checkdams as a barrier for sediment. The results also revealed the potential for using SWAT to assess sediment transport from specific subwatersheds within a watershed, and to prioritize the siting of sediment control structures within a watershed to obtain the most effective reduction of sediment losses to surface water. Overall, the study showed that SWAT can be a useful tool for studying how checkdams can be used to manage and control sediment loss from small watersheds located in sub-humid climate conditions.
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