June 04, 2001
This is an image/map of the Washington,DC/Baltimore area taken with the Landsat satellite on March 27, 1998. It shows how much impervious surface (orange represents high concentrations and blue represents moderate concentrations of impervious area) exists across the DC/Baltimore region. Baltimore City (upper right) and its surrounding suburbs have at least 10% and up to 40% impervious area, and the District of Columbia (lower center) and its surrounding suburbs in Virginia and Maryland have between 10-30% impervious surfaces. The more impervious area, the greater (and faster) is the runoff into stream and river channels. Typically, once 10-15 % of an area is covered by impervious surfaces, the increase in sediment loads and pollutants can have a measurable effect on water quality. When 5-25% of a watershed is paved or impervious to drainage, the increased runoff leads to reduced oxygen levels and impaired stream life. When more then 25% of the area is impervious, many types of acquatic life will die as a result of the concentrated runoff and sediments.