Polluted Runoff

The Gray Funnel of the Chesapeake

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Polluted runoff is one of the most harmful sources of pollution to the Bay and its waters, and it's increasing.

Nitrogen and phosphorus are good for plant growth, but the Chesapeake and many bodies of water nationwide have too many nutrients. They are enriched by waste from sewage plant discharges, fertilizers from farms and lawns, even nitrogen oxides from air pollution and poultry operations.

As rain water runs off our streets, parking lots, lawns and other surfaces, it picks up pet waste, pesticides, fertilizer, oil, and other contaminants. People are sometimes surprised this polluted runoff typically is not treated, say at a sewage plant. It flushes straight into local creeks, rivers, and the Chesapeake Bay. Untreated runoff adversely affects water quality and aquatic life. The speed and volume of the runoff also gouges stream banks, and carries sediment downstream. Polluted runoff is a major problem for the Bay, and the main source of dirty water in many urban and suburban areas. Scientists say climate change will increase the intensity of storms and rainfall in the Bay region, thereby increasing flooding and polluted runoff. Sprawl development also will add to the problem.

Urban and suburban polluted runoff is one of the few major sources of pollution still increasing in the Chesapeake area. None of the six states in the Bay watershed, or the District of Columbia, is meeting its Chesapeake Clean Water Blueprint goals to reduce polluted runoff. Though responsible for greater percentages of pollution, sewage plants and agriculture have been making greater progress.

In urban and suburban areas with lots of pavement, lawns, and other surfaces that collect pollutants, runoff often is the main source of nutrient pollution. For example, about 86 percent of the nitrogen entering Virginia's Elizabeth River is from urban and suburban polluted runoff from the Portsmouth area.

Nutrients aren’t the only problem associated with runoff. As hard 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. This sediment keeps sunlight from reaching underwater grasses. As these plants die, the animals that rely on them are imperiled.

Not only wildlife is endangered by stormwater pollution. Polluted runoff carrying bacteria has resulted in serious illnesses in humans. The state of Maryland cautions people not to swim in waterways for 48 hours after a heavy rain. Also, in urban and suburban areas where ground surfaces have been hardened and the polluted water has no place to go, local streets and basements often flood, causing repeated and costly damage to homes and businesses.

These problems are expected to get worse with climate change. Already, the northeastern United States has seen dramatically more rainfall during heavy storms in recent decades. That trend is expected to continue. The summer of 2018 saw record-setting rainfall in many parts of the Bay region. With those downpours came severe flooding, and property damage. Polluted runoff will increase from these more intense storms. Computer modeling by the Chesapeake Bay Program suggests nine million more pounds of nitrogen will wash into the Bay due to climate change and 500,000 pounds of phosphorus. States and localities are failing already to deal adequately with polluted runoff; climate change will add to their burdens.

Development will, too. Sprawl is insufficiently managed growth that gobbles up farms, forests and other natural areas, that typically would soak up the runoff. Unfortunately, many local governments encourage sprawl. Invariably, increased polluted runoff is one of the problems that results.

Developers and local governments in years past often simply piped or channeled runoff to drain a landscape as quickly as possible. No attempt was made to slow down or treat the runoff. We call this the "gray funnel" approach to managing runoff. Now we know that’s a problem. Better management of the runoff is an increasingly necessary but admittedly expensive proposition for local governments.

One promising solution is greening the landscape strategically, a tool called "green infrastructure." The idea is simple: slow down and soak up runoff. Build "rain gardens" and other natural areas in key drainage areas. Where possible, replace old pavement with pervious pavement. Plant gardens on rooftops. These and other green solutions not only are cost effective; they provide secondary social benefits: shade, wildlife habitat, a more pleasant neighborhood, to name a few. We call this the green filter approach to managing runoff.

CBF is introducing local Bay jurisdictions to a new way of financing these green filters. It's called "impact investment." It helps slow down and soak up runoff, and also creates local sustainable jobs and more healthy, vibrant communities.

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

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