Municipal Stormwater Permit Compliance in Wisconsin: Calculating Pollutant Loads and Selecting Best Management Practices across Multiple Watersheds Simultaneously

This paper documents the integration of a Geographic Information System (GIS), the Source Loading and Management Model for Windows (WinSLAMM) and database calculations into a system that calculates loadings over multiple watersheds. The presented method creates GIS files representing model input parameters, including soil classification, land use, drainage type, and existing BMPs. The batch editor module of WinSLAMM creates and analyzes required model data files. Database post-processing of WinSLAMM output determines pollutant loads and loading rates for each polygon created in GIS and the percent of TSS reduction achieved under existing conditions. Symbolizing the polygon pollutant loading rate density (lbs/acre/yr) under existing management conditions facilitates BMP site selection. Database calculations assess the loading to be removed by the potential BMPs, and this process is applied iteratively until pollutant reduction goals are met. This methodology may have widespread application as Total Maximum Daily Load (TMDL) calculations are required for other pollutants modeled by WinSLAMM.