Measuring Impervious Surfaces for Non-point Source Pollution Modeling

The US EPA has reported non-point source pollution (NPS), which includes eroded sediments, toxic contaminants, nutrients, debris, and other pollutants, to be the number one threat to surface water quality nationwide. Numerous studies have established a direct relationship between the amount of impervious surface within a watershed and pollution of its surface waters. However, without detailed digital planimetric data, accurate watershed measurements of impervious surfaces are costly and time consuming to prepare. A method to determine percent impervious surface cover for different municipal zoning designations, parcel sizes and land uses (e.g. one-acre residential lots) was developed at the University of Connecticut. Large-scale digital planimetric data that included impervious surfaces from roads, parking lots, buildings, and other miscellaneous landscape features were obtained for West Hartford, Woodbridge, Marlborough, and Waterford, Connecticut. ArcInfo® 7.1.2 and ArcView® 3.1 (ESRI, Redlands, CA) GIS software were used to convert the data into a useable format (i.e. polygons) and perform overlay analyses. A relational database management system (RDBMS) was employed to analyze the data and produce summary statistics. Percent imperviousness coefficients were calculated for different zoning class and parcel size combinations. These data were analyzed with generalized land use and land cover data, previously prepared from 30 meter Landsat Thematic Mapper imagery, to produce percent imperviousness coefficients that easily can be used in watersheds without detailed planimetric data.