Impervious Surfaces
- Author:
- John Wolf
- Date Created:
- January 30, 2008
Impervious surfaces, or surfaces that do not absorb water, compose roughly 17% of all urban and suburban lands in the Bay watershed. Impervious surfaces alter the natural flow of streams because they typically carry rainfall directly into streams via gutters and storm sewers, bypassing wetlands and riparian forest buffers, both of which filter and slow down the flow of water. Impervious surfaces are sometimes built near streams and rivers, replacing existing riparian buffers, which can in turn degrade those streams. Impervious surfaces also limit the filtration of rainwater into the soil, potentially reducing the amount of water reaching shallow streams and groundwater aquifers. Finally, impervious surfaces help to carry airborne pollutants to streams. In natural landscapes, some pollutants can be retained and broken down in the soil or plants that intercept water as it flows over the land and into streams.