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Stormwater and Drainage

Rainwater and snowmelt that runs off impervious surfaces rather than infiltrate into the soil. Through a drainage system of underground pipes, stormwater carries nutrients, fine soils, plant debris, drippings from vehicles, and other substances from the drainage basin. Technically, all runoff is stormwater. However the term "stormwater" is generally used in reference to urban runoff in constructed stormwater drainage systems.

Most lakes, ponds, and wetlands are connected to the stormwater system. A form of nonpoint source pollution, stormwater runoff can carry many suspended or dissolved contaminants-including oils, greases, and other petroleum products; fecal matter; organic debris; fertilizers and pesticides; trash; and silt and sand-from the air and land into the water.

It is usually expressed in inches of water uniformly distributed over the area that contributes the water. The first inch of stormwater runoff, called the first flush, contains the highest levels of pollution.

Sanicon: Stormwater Management and Urban Drainage in Developing Countries (Thematic page)
In the cities of the developing world, it is the urban poor who are affected the most by problems related to poor drainage. Poor communities often inhabit low value marginal land which is prone to flooding or on steep-sided hillsides and therefore unattractive for development.
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