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Stormwater Runoff


What happens to a drop of rain when it falls onto the ground? It may land on a tree and evaporate; it may land on a farm field and soak into the soil; or it may land on a rooftop, driveway or road and travel down the street into a storm drain or stream.

Precipitation in an urban or suburban area that does not evaporate or soak into the ground but instead runs across the land and into the nearest waterway is considered stormwater runoff. Increased development across the watershed has made stormwater runoff (also called polluted runoff) the fastest growing source of pollution to the Chesapeake Bay.

How is stormwater runoff a pressure on the Chesapeake Bay?

As stormwater flows across streets, sidewalks, lawns and golf courses, it can pick up harmful pollutants and push them into storm drains, rivers and streams. These pollutants can include lawn and garden fertilizers, pet waste, sand and sediment, chemical contaminants and litter.

Stormwater runoff can cause a number of environmental problems:

  • Fast-moving stormwater runoff can erode stream banks, damaging hundreds of miles of aquatic habitat.
  • Stormwater runoff can push excess nutrients from fertilizers, pet waste and other sources into rivers and streams. Nutrients can fuel the growth of algae blooms that create low-oxygen “dead zones” that suffocate marine life.
  • Stormwater runoff can push excess sediment into rivers and streams. Sediment can block sunlight from reaching underwater grasses and suffocate shellfish.
  • Stormwater runoff can push pesticides, leaking fuel or motor oil and other chemical contaminants into rivers and streams. Chemical contaminants can harm the health of humans and wildlife.

Stormwater runoff can also lead to flooding in urban and suburban areas.

Forests, wetlands and other vegetated areas can trap water and pollutants, slowing the flow of stormwater runoff. But when urban and suburban development increases, builders often remove these natural buffers to make way for the impervious surfaces that encourage stormwater to flow freely into local waterways.

What are impervious surfaces and why are they a problem?

Impervious surfaces are paved or hardened surfaces that do not allow water to pass through. Roads, rooftops, sidewalks, pools, patios and parking lots are all impervious surfaces.

Impervious surfaces can cause a number of environmental problems:

  • Impervious surfaces can increase the amount and speed of stormwater runoff, which can alter natural stream flow and pollute aquatic habitats.
  • Impervious surfaces limit the amount of precipitation that is able to soak into the soil and replenish groundwater supplies, which are an important source of drinking water in some communities.
  • Impervious surfaces that replace soil and plants remove the environment’s natural ability to absorb and break down airborne pollutants.

According to the U.S. Environmental Protection Agency (EPA), the presence of roads, rooftops and other impervious surfaces in urban areas means a typical city block generates more than five times more runoff than a forested area of the same size.

Impervious surface data are used to measure the rate of development across the watershed and to identify high-growth areas and patterns of sprawling development. Between 1990 and 2007, impervious surfaces associated with growth in single-family homes are estimated to have increased about 34 percent, while the watershed’s population increased by 18 percent. This indicates that our personal footprint on the landscape is growing.

How much pollution does stormwater runoff send into the Chesapeake Bay?

Stormwater runoff is the fastest growing source of pollution to the Chesapeake Bay. According to the Chesapeake Bay Program’s Watershed Model, stormwater contributes 16 percent of nitrogen loads, 16 percent of phosphorous loads and 25 percent of sediment loads to the Bay.

Take Action

For Chesapeake Bay restoration to be a success, we all must do our part. Our everyday actions can have a big impact on the Bay. By making simple changes in our lives, each one of us can take part in restoring the Bay and its rivers for future generations to enjoy.

To lessen the impacts of stormwater runoff on the Bay, consider reducing the amount of precipitation that can run off of your property. Install a green roof, rain garden or rain barrel to capture and absorb rainfall; use porous surfaces like gravel or pavers in place of asphalt or concrete; and redirect home downspouts onto grass or gravel rather than paved driveways or sidewalks. You can also follow safe and legal disposal methods of paint, motor oil and other household chemicals to make sure they do not run into rivers and streams.



Chesapeake Bay News

In The Headlines

Reducing Nitrogen Pollution

Computer simulations of pollution controls implemented between July 2009 and June 2013, calibrated using monitoring data, indicate that nitrogen loads to the Bay would have decreased 20.28 million pounds to 262.38 million*.

Reducing Phosphorus Pollution

Computer simulations of pollution controls implemented between July 2009 and June 2013, calibrated using monitoring data, indicate that phosphorus loads to the Bay would have decreased 2.04 million pounds to 17.19 million*.

Reducing Sediment Pollution

Computer simulations of pollution controls implemented between July 2009 and June 2013, calibrated using monitoring data,  indicate that sediment loads to the Bay would have decreased 497 million pounds to 8,178 million*.

Bay 101: Stormwater Runoff

May 11, 2011

When rainfall runs across roads, lawns and golf courses, it can pick up pollutants before it enters local waterways. Mike Fritz from the Chesapeake Bay Program explains why so-called “stormwater runoff” is a major source of pollution to the Chesapeake Bay and what we can do to prevent it.

Chesapeake Unscripted: What happens to stormwater runoff after it rains? (York, Pa.)

April 12, 2012

We asked people in York, Pennsylvania what happens to stormwater runoff after it rains. Do you know the answer?

Take Action: What Flows into Storm Drains?

May 09, 2011

Chesapeake Bay Program staffer Kristin Foringer picks up trash after a rain storm in Annapolis, MD that might otherwise wash into the Chesapeake Bay.  What did she find?  Take a look and learn what you can do to help out in your neighborhood.

From the Field: Capturing stormwater naturally in Lancaster, Pennsylvania

July 07, 2012

Fritz Schroeder, Director of LIVE Green Lancaster (a program of the Lancaster County Conservancy), explains how the city is using green infrastructure to capture stormwater runoff before it makes its way to the Chesapeake Bay.
Close Captions: http://www.youtube.com/watch?v=vIMb7ldNWx4


Letter from Chesapeake Bay Leadership to Congress to Reduce Polluted Runoff from Federal Highways

Publication date: May 27, 2009 | Type of document: Policy Memorandum | Download: Electronic Version

Letter from Chesapeake Bay Leadership to Congress to Reduce Polluted Runoff from Federal Highways

Directive 01-1: Managing Storm Water on State, Federal and District-owned Lands and Facilities

Publication date: December 03, 2001 | Type of document: Directive | Download: Electronic Version

Increased population and development within the watershed have created projections regarding urban and suburban growth and the increase of imperviousness in the watershed, managing stormwater runoff is an important activity for reducing…

Storm Water Management and the Chesapeake Bay

Publication date: September 01, 2001 | Type of document: Fact Sheet | Download: Electronic Version

This backgrounder answers commonly asked questions about storm water management in the Chesapeake Bay watershed

Vegetative Filter Strips for Agricultural Runoff Treatment

Publication date: August 01, 1987 | Type of document: Report | Download: Electronic Version

This is a report on vegetative filter strips for agricultural runoff treatment

Water Quality GIT BMP Review Protocol

Publication date: | Type of document: Policy Document | Download: Electronic Version

July 14, 2014 version.

From Around the Web

Bay FAQs

  • What are impervious surfaces?
  • What is stormwater runoff?
  • What can be done to counter the effects of development that has already occurred?


Bay Terms

  • Chemical contaminants
  • Erosion
  • Impervious
  • Nutrients
  • Pollution
  • Precipitation
  • Sediment
  • Stormwater


Bay-Friendly Tips

  • Create an Infiltration Trench
  • Infiltration trenches are one of the most effective ways to keep polluted stormwater from reaching local waterways.
  • Create a Rain Garden
  • Rain gardens can add value to your home and absorb more water than a conventional lawn.
  • Create a Stormwater Pond
  • Create a stormwater pond to collect runoff and protect downstream property owners from flooding.
  • Reduce Pesticide Use
  • Instead of applying chemical pesticides to your sidewalk or garden, use boiling water to kill weeds, ant colonies and other pests.
  • Reduce Polluted Runoff
  • Spread mulch over bare ground to prevent soil erosion and stop the flow of polluted runoff from your lawn into local waterways.
  • Reduce Polluted Runoff
  • Instead of asphalt or concrete, use porous surfaces like gravel or pavers to pave your driveway or patio.
  • Use Fertilizer Properly
  • Do not apply fertilizer to dormant lawns or frozen ground, where it could easily run off your property and into storm drains.
  • Conserve Water
  • Instead of sprinklers, use soaker hoses or drip irrigation to water your lawn and garden.
  • Reduce Polluted Runoff
  • Wash your car on grass or gravel rather than pavement so soapy, grimy wash water won't run off your property.
  • Plant Trees and Shrubs
  • Plant more trees and shrubs in your yard to reduce erosion, capture runoff and provide habitat for wildlife.


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