Spatially distributed assessment of short- and long-term impacts of multiple best management practices in agricultural watersheds

Best management practices (BMPs) are a critical tool for preventing or mitigating the degradation of water quality caused by soil erosion. However, currently available assessment models are primarily designed for use over and, therefore, are only valid over these particular spatial and temporal scales. This study investigates the feasibility of combining three models that were designed for use at different spatial scale into a single assessment tool that allows for more detailed, spatially-explicit assessment of BMPs over both short (four to eight years) and longer (100 year) time scale. The three models evaluated were: 1) the Water Erosion Prediction Project (WEPP) model for hillslope and small watershed up to 260 ha (642 ac); 2) the Geospatial interface for WEPP (GeoWEPP), which utilizes geographic information system (GIS) or precision farming datasets of topography, soils, and landuse to automatically derive WEPP model input; and 3) a linked GeoWEPP-SWAT model, which injected WEPP model output as point sources into the Soil and Water Assessment Tool (SWAT). The linked GeoWEPP-SWAT model provides a mechanism for applying the WEPP model to larger watershed scales beyond the validity of its channel routing algorithms. This paper summarizes the challenges, validity, and opportunities of this modeling approach for BMP assessment in large watersheds.