Urban areas contain substantial expanses of hardscape in the form of buildings, paved roads, parking lots and concrete sidewalks. The impervious nature of these surfaces leads to runoff during periods of heavy precipitation. Up to 55 percent of precipitation in urban areas may be in the form of stormwater runoff. In addition, compacted soils with poor drainage will also contribute to runoff. Environmental drawbacks of stormwater runoff include erosion of slopes and other surfaces, overloading municipal wastewater treatment systems and introduction of pollutants (chemicals, oils, fertilizers) into natural bodies of water.
Source: Living Architecture Monitor