Chattanooga Stormwater Sub-basins: Percent Impervious Surface

Urban green space serves as a much needed component of the modern urban environment. Green spaces are traditionally characterized by open areas bearing tree canopy or grasses. Urban green spaces provide flood control, temperature regulation, air quality controls, wildlife habitat, and recreation opportunities. The sum of green spaces within the urban environment is often referred to as the green infrastructure of a designated area. Green infrastructure, like traditional grey infrastructure such as roads, rail, and utilities, plays a necessary role in the connectivity and completeness of the Urban/Wildland environment. The ratio of impervious surfaces and open/greenspace by watershed is a useful tool in urban ecosystem assessment, essentially the ratio of green verses grey infrastructure. Consensus among researchers has indicated a significant decrease in water quality parameters and aquatic biological diversity when impervious surfaces range from 15-18% of the total area of a watershed. GIS specialist at the University of Tennessee at Chattanooga calculated the percent imperviousness for the City of Chattanooga's Stormwater division basin boundaries. The calculation was added to a polygon vector file containing a percent imperviousness field.