Watershed Management Tool for Evaluating BMPs: Case Studies in the Mackinaw and Upper Sangamon Rivers

Implementation of watershed Best Management Practices (BMPs) could serve as crucial control measures to reduce nonpoint source pollutants from agricultural watersheds, as well as restoring and protecting water quality in streams and rivers. Successful BMP implementations, however, greatly depend on the watershed management tools employed. In partnership with The Nature Conservancy, the Illinois State Water Survey developed watershed management models for evaluating the effectiveness of BMPs such as constructed wetlands, grassed waterways and filter strips for selected subwatersheds in the Mackinaw River watershed. These decision support models combined the utilization of an optimization algorithm for cost-effective selection and placement of BMPs with watershed models for simulating the hydrologic and water qual-ity impacts of applied BMPs. Building on that experience, ISWS is currently working with Agricultural Watershed Institute and Illinois Environmental Protection Agency to develop watershed management tools that will be used to prepare a Total Maximum Daily Load (TMDL) implementation plan for two tributary watersheds of Lake Decatur (Upper Sangamon River), namely Big Ditch and Big-Long Creek watershed. These tools will be calibrated with 15 years of hydrologic and nutrient data collected in the Lake Decatur watershed. The lake, which is the major source of public water supply for the City of Decatur, has been experiencing water quality problems mainly from nonpoint source pollutants from runoff. This presentation discusses the results of these watershed management tools in protecting water quality in Illinois streams and rivers.