Maps
Imperviousness

All hard surfaces - roads, parking lots and rooftops - add up to prevent natural infiltration of rain water; that is, they make the land impervious. Stream health is directly correlated with the percent of hard surfaces, or imperviousness, that occurs in a catchment or watershed. As imperviousness increases, rainwater rushes directly into streams and rivers carrying sediment and other pollutants into local waters and the Chesapeake Bay. More importantly, scientists see a breakpoint at which the level of development or imperviousness in a watershed leads to marked decline in the health of the stream environment. That threshold is about 10 percent - when more than 10 percent of the watershed is hard surface, stream quality begins to suffer and sensitive species disappear. At about 15 percent imperviousness, the stream is highly stressed - only pollution tolerant species can be expected in such a stream. At 20-25 percent imperviousness, the stream is virtually devoid of complex life.

We are currently collecting data to generate maps that show imperviousness in the Washington Region. Please check this site again soon.

Washington Region in the Chesapeake Bay Watershed
| Imperviousness | Natural Resource & Agricultural Lands
Protected Lands | Protected Greenspace Inside the Capital Beltway
Urbanization

Future Growth Model