APPORTIONING DRAINAGE UTILITY IMPROVEMENTS USING GEOGRAPHIC INFORMATION SYSTEMS

A geographic information system (GIS) application has been developed to automate the process of calculating drainage utility apportionment percentages. The application applies the rational formula for estimating storm water runoff volume as the traditional method and was designed to allow for the comparison of different calculation scenarios. Consideration of additional factors such as sewer service type, retention/detention, and pollutant loadings may better reflect conditions contributing to the need for water and wastewater utility improvements and result in more equitable apportionments. The application was applied to the Twelve Towns Drainage District 2000 apportionment for improvements, known as the George W. Kuhn Drain, to their combined sewer overflow retention treatment facility located in southeastern Oakland County, Michigan. Oakland County's digital parcel data was used for calculating areas and assigning runoff coefficients to land use categories. Sewer service maps were developed and used to incorporate sewer service type into the calculation scheme. The GIS application served as an efficient and flexible tool for calculating apportionment percentages.