Stormwater

Do you ever think about what happens to a drop of rain that falls onto the ground? It may land on a tree and evaporate; it may land on a farm field and be absorbed into the soil; or it may land on a rooftop, driveway or road and travel down the street into a stream or storm drain.

Any precipitation in an urban or suburban area that does not evaporate or soak into the ground, but instead pools and travels downhill, is considered stormwater. Stormwater is also referred to as urban stormwater, runoff and polluted runoff. Increased development across the Bay watershed has made stormwater runoff the fastest growing source of pollution to the Bay and its rivers.

How is stormwater a pressure on the Bay?

Stormwater picks up nutrients, sediment and chemical contaminants as it flows across roads, yards, farms, golf courses, parking lots and construction sites. This polluted runoff travels into storm drains and local waterways that eventually drain into the Bay.

Development activities like clearing vegetation, mass grading, removing and compacting soil, and adding impervious surfaces have increased stormwater runoff in the Bay watershed.

• Forests, wetlands and other naturally vegetated areas slow stormwater runoff and absorb water and pollutants. When these natural buffers are removed to make way for development, stormwater and the pollution it carries are able to flow freely into local waterways.
• Impervious surfaces—roads, rooftops, parking lots and other hardened surfaces—do not allow precipitation to soak into the soil. Instead, water runs off and picks up dirt, trash, motor oil and other pollutants on its way to the nearest storm drain.
• Muddy runoff from construction of new development contributes substantial amounts of sediment to the Bay and its tributaries.
• Stormwater has eroded stream banks and damaged aquatic habitat in hundreds of miles of streams in the Bay watershed.
• Stormwater runoff can also increase flooding in urban and suburban areas.

How much Bay pollution comes from stormwater?

Stormwater from urban and suburban areas contributes a significant amount of pollutants to the Bay. Every time we drive our cars, fertilize our lawns, leave pet waste on the ground or forget to fix car leaks, we contribute to pollution in our local rivers, streams and the Bay.

• 17 percent of phosphorus, 11 percent of nitrogen and 9 percent of sediment loads to the Bay come from stormwater.
• Chemical contaminants from runoff can rival or exceed the amount reaching local waterway from industries, federal facilities and wastewater treatment plants.