Stormwater Runoff

Residential runoff flows into a storm drain during a heavy rainfall. Photo © Krista Schlyer/iLCP

The Gray Funnel of the Chesapeake

When it rains, water accumulates on man-made surfaces such as roads, roofs and parking lots. These hard (impervious) surfaces prevent the rain from soaking in to the soil, nature's "green filter." As more houses, roads, and shopping centers are built, more water runs off the impervious surfaces, usually untreated, through gutters and storm drains to the nearest stream. This water is called stormwater or urban/suburban runoff, and it eventually finds its way into the Chesapeake Bay.

Stormwater carries a host of contaminants from the land into the water: sediment, phosphorus, nitrogen, toxic metals, herbicides and pesticides, organic material, oil compounds, and bacteria. Roadways, for example, release oil and grease, tailpipe emissions, and other toxics from motor vehicles. Lawns contribute fertilizer and animal waste. Construction sites release quantities of mud, sediment, and debris.

As impervious surfaces channel large quantities of rainwater into streams at high velocity, the runoff wreaks havoc. The flow scours stream banks, destabilizes stream contours and alters depths. It muddies drinking water sources and also carries bacteria, making the treatment and use of such water more expensive.

In the Bay's tributaries, eroded material and dirt from the land become suspended in the water, blanketing aquatic habitat. Sediment keeps sunlight from reaching underwater grasses. As these plants die, the animals that rely on them are imperiled.

According to the Environmental Protection Agency (EPA), stormwater is the source of about 14 percent of the total nitrogen entering the Bay, and is the only source that is still increasing. In some rivers it makes up an even higher percentage of the problem. It is one of the major reasons that the Bay remains on EPA's "dirty waters" list and is now subject to the Chesapeake Clean Water Blueprint.

Solutions for Addressing Stormwater Pollution

The Chesapeake Bay Foundation (CBF) advocates strong construction and post-construction stormwater regulations at the state level.  CBF also advocates for strong, progressive municipal stormwater permits. We believe that the best strategy for reducing stormwater pollution combines the following four elements. This overview represents the standards CBF advocates; these may be higher than those currently in place in any particular location.

1. Prevention: Planning and Zoning—Through comprehensive plans and zoning ordinances, local jurisdictions decide where development should occur, how much development is allowed, and the amount of open space or working land in a community must be conserved or protected from such development. Steering development away from sensitive areas where stormwater runoff does the most harm and protecting wooded and other open spaces that can naturally filter rainwater are both critical strategies for reducing stormwater pollution levels in the Bay.
2. Design, Construction, and Post-Construction—Once development is approved and goes forward an important consideration is the design and construction of the specific sites. These elements are often controlled by local subdivision, stormwater, and sediment and erosion control ordinances. A site under construction is a potential hot-spot for stormwater pollution. Unless effective erosion and sediment control measures are designed well and adequately implemented, a rainstorm can wash large amounts of sediment and debris into the nearest stream, impairing local water quality. It's crucial to minimize both the amount of soil and the amount of land exposed and the amount of time time soil is exposed to the elements.
   
   Once construction is complete, redevelopment projects should manage their sites and buildings for the full "water quality volume" of stormwater—about an inch of runoff, more or less, across the Chesapeake Bay watershed. New development projects should manage for full "channel protection volume," a much greater amount of water; this prevents runoff from adversely affecting nearby streams. New development sites should also use "low impact" and "environmental design" techniques (also called "green infrastructure") that mimic the natural flow and filtration of water, if at all possible.
3. Enforcement—Ordinances, construction management practices, and environmental side design standards are meaningless unless people follow them. When construction sites are not adequately monitored and requirements are not strictly enforce, development can cause enormous damage to nearby streams. If stormwater management practices are not regularly inspected and maintained long after construction is complete their ability to function properly cannot be guaranteed. 
4. Retrofits—The final piece of the puzzle pertains to fixing stormwater systems in existing urban and suburban communities. In many of these areas the stormwater system is simply comprised of curbs and gutters, sewer pipes or concrete channels, all funneling directly into streams without treatment of any kind. In other instances, while the community may have required the installation of stormwater management devices 10 or 20 years ago, they don't meet modern standards or they simply haven't been maintained. Such situations present a legacy of on-going pollution that requires resolution.
   
   In communities that have poorly performing practices in place the most cost-effective solution is to bring the existing ponds and other practices up to current standards. In places where there has been no stormwater management at all solutions can be more expensive and often the best solution may be the development or improvement of a local stormwater utility to finance new practices that can be "inserted" by the municipality. However, many options are available, such as:

• Large parking lots and street-sides can be altered with "green infrastructure" such as planted, filtering trenches;
• Concrete channels can be converted to more natural swales with a series of rock weirs;
• Sewer inlets can be upgraded;
• Outfalls to streams can, in some cases, be improved with the addition of rocks, filtering surfaces, wetlands, and plants;
• Streams themselves can sometimes be helped with careful design and channel and bed improvements.

How to Improve Existing Stormwater Regulations and Permits

The federal Clean Water Act (CWA) requires the largest municipalities to obtain and hold permits for their stormwater discharges (called "Municipal Separate Storm Sewer System Permits," or MS4s). Many of these important permits are being changed in 2012 and 2013, and need to be strengthened in the process. (Contact your local CBF office for ways to help.) At the local level, stormwater issues are being raised by groups of concerned citizens.

CBF has increased its outreach efforts in Maryland, Pennsylvania, and Virginia to join with more watershed groups and assist them in stormwater abatement advocacy. This effort emphasizes education about stormwater, its causes, and ways to prevent or reduce its effects. CBF helps watershed groups create advocacy strategies to address stormwater pollution in their local streams and waterways, which in turn will reduce pollution of the Chesapeake Bay.

How You Can Help

Join the Get The Dirt Out Program of Waterkeepers Chesapeake.

At Home:

• Detach your downspouts to prevent them from flowing into municipal storm drain systems. Install rain barrels to collect the flow instead. 
• Create "pervious" walkways and driveways (of crushed stone, mulch, or other materials) that return rainwater to the ground. 
• Reconfigure your yard to create rain gardens in low-lying areas, and replace grass turf with native plants.

Additional information about stormwater management can be found at the following websites:
The Center for Watershed Protection
Low Impact Development Center
Low Impact Development Urban Design Tools