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Model Evaluation of the Effectiveness of BMPs in Small Watersheds in Indiana
This research applies the distributed model Soil Water Assessment Tool (SWAT) to evaluate the effectiveness and design of Best Management Practices (BMPs) to manage sediment and nutrients yields in two small agricultural watersheds, the Smith Fry and Dreisbach, situated within the Black Creek watershed. The Black Creek watershed (50 km2) is located in Allen County northeast of Indiana, and is part of the Maumee River basin. This watershed was identified as perhaps one of the very few watersheds with both daily measured water quality data and with detailed information on various implemented BMPs. Four different types of agricultural BMPs were installed in the Dreisbach and Smith Fry watersheds in the early 1970s, including field borders, parallel terraces, grassed waterways, and grade stabilization structures. In the first phase of the project, a SWAT model was calibrated and validated for flow, sediment and nutrients transport and fate in the two watersheds. The model was used to identify sediment sources in the upper lands, investigate the effect of spatial resolution (watershed discretization) on model performance, and simulate the effectiveness of BMPs at the local farm and watershed scales. Simulations showed that field borders and parallel terraces that were installed on the upland areas reduced sediment and nutrient loads from the fields where they have been installed by nearly 50%. However, since they have been installed to influence less than 2% of the total area of the Dreisbach and Smith Fry watersheds, their impact at the watershed scale would not be effective. On the other hand, model simulations showed that grassed waterways and grade stabilization structures would be more effective BMPs in reducing sediment and nutrient yields at the watershed scale.
In the second phase of this project, uncertainty analysis will be conducted with the calibrated SWAT model to establish numerical margins of safety for TMDLs in the Black Creek watershed. The model will be used through optimization to explore cost-effective placement and design of BMPs that would reduce sediment and nutrients loads in this watershed.
Contact: Mohamed M. Hantush, USEPA, (EIMS#131911)