Water is always on the move.
Under natural conditions, rainwater and snowmelt – also called stormwater - disperse in a number of ways: soaking into the soil, evaporating, nourishing plants and eventually making their way to groundwater, streams and lakes. Natural landscapes lush with trees, shrubs and plants play an important role in slowing the water's flow and filtering out pollutants. When we alter natural landscapes, we alter these services, frequently causing problems with water quality and quantity.
Streets, roofs, parking lots and other hard, non-porous surfaces repel water instead of absorb it. Water repelled by these surfaces, and pollutants whisked away by that water, rush into roadside ditches, storm drains and culverts that dump it directly into our streams and lakes. The Environmental Protection Agency estimates that a typical city block generates over five times more stormwater runoff than a woodland area of the same size.
As stormwater increases in volume and speed, it can erode stream banks, degrade aquatic habitat and threaten streamside property. As stormwater moves across the land's surface, it also picks up soil, excess nutrients like phosphorous and nitrogen, animal waste, pathogens, toxic chemicals, motor fluids and trash. The vast majority of stormwater flows untreated into streams, lakes or groundwater.
Stormwater runoff and the pollutants it carries can cause problems in the following areas:
Polluted storm water runoff is a concern for water quality across the United States. To address this concern, a federal regulation, commonly known as "Stormwater Phase II," went into effect in 1999. In New York, the Department of Environmental Conservation is responsible for administering this law.
Last updated October 20, 2020