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Landscape Characterization / Impervious Surfaces / What is an Impervious Surface?
What is an Impervious Surface?
Impervious surfaces are mainly constructed surfaces - rooftops, sidewalks,
roads, and parking lots - covered by impenetrable materials such as
asphalt, concrete, brick, and stone. These materials seal surfaces,
repel water and prevent precipitation and meltwater from infiltrating
soils. Soils compacted by urban development are also highly impervious.
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Materials like cement, asphalt, roofing, and
compacted soil prevent percolation of runoff into the ground. The
amount of impervious surface grows with increasing urbanization.
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Source: Johnson, Baltimore County DEPRM.
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Impervious urban surfaces are "desert-like"
in terms of hydrology and micro-climate.
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An Overview of Impervious Surfaces
- Storm water washes over paved, sparsely vegetated surfaces in much the same
manner as it runs over a desert landscape.
- Intense storms quickly generate large volumes of runoff, followed by dry
conditions a short time later.
- Rapid runoff and the paucity of vegetation reduces evapotranspiration; therefore
insolation (incoming solar radiation) is used for heating rather than evaporation.
- Impervious surfaces have higher thermal conductivities than do vegetated,
pervious surfaces.
- Impervious surfaces cause nonpoint water pollution problems.
Impervious surfaces allow many types of pollutants, derived from a variety
of sources, to accumulate upon them. Many of these pollutants are subsequently
washed into water bodies by storm water runoff, severely degrading water
quality. This type of pollution is known as nonpoint source water pollution
and is linked to land-use activities. Water quality problems increase
with increased imperviousness and intensity of land use.
Transportation and Impervious Surfaces
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The Impervious Surface "Budget"
Derived from the city of Olympia, WA ISRS Final Report
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Most of the impervious surfaces within the
watersheds of the Chesapeake Bay and the coastal bays of Maryland
have been made impervious due to urbanization, and the majority
of these surfaces are
associated with transportation.
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Maryland Department of Natural Resources (DNR)
www.dnr.state.md.us/
Maryland Department of Planning (MDP)
http://www.mdp.state.md.us/
Maryland Department of the Environment (MDE)
www.mde.state.md.us/
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