A Hydrological Event Model of the Tollgate Wetland∗

The Clean Water Act of 1972 as amended in 1987 requires states to control the flow of pollution from storm water into local rivers. In most cases, this requirement is carried out through installation of an expensive system of pipes and pumps. The Tollgate Drainage District, Ingham County, Michigan, examined here, uses a more economical alternate approach: water from the district flows into an artificially created and maintained wetland designed to naturally clean the district’s storm water. This report examines the mechanisms at work in the Tollgate wetland, proposes a unit hydrograph and model for water flow, describes and discusses a simulation of the system designed by the authors based on these proposals, and gives conclusions and recommendations for further study. Appendices contain reference material on the relevant hydrological phenomena and a user’s manual for the simulation model.