Introduction Land and water planners frequently wrestle with the problems of uncontrolled growth and sprawl and their deleterious impacts on water quality. Our research at the University of Delaware, Institute for Public Administration outlines an approach to control sprawl in the First State through land use planning based on natural boundaries - the watersheds. Impervious cover controls can be used to focus growth into watershed planning districts where development would have the least impact on stream water quality. However, too many buildings and roads in a particular watershed can have a deleterious effect on stream water quality. Impervious surfaces alter the natural hydrology and prevent the infiltration of water into the ground.
Impervious surfaces change the flow of stormwater over the landscape.
In undeveloped areas, vegetation holds down soil, slows the flow of stormwater over land, and filters out some pollutants, by both the slowing the flow of the water and trapping some pollutants in the root system. In addition, some of the stormwater filters down through the soil, replenishing groundwater sources. As land is converted to other uses such as commercial developments, many of these natural processes are altered when vegetation is cleared and soil paved over. As more impervious surface coverage is added to the landscape, more stormwater flows faster off the land. The greater volume of stormwater increases the possibility of flooding, and the fast speed that the stormwater moves at does not allow for pollutants to settle out, meaning that more pollution gets concentrated in the stormwater runoff.