Why is Urban Storm Water Runoff Important?
Cities contribute to the Chesapeake Bay about twice the nitrogen and phosphorus load per acre as agriculture. Urban storm water runoff is responsible for about 16% of phosphorus, 11% of nitrogen, and 9% of sediment loads to the Bay. Urban runoff loads of chemical contaminants (such as metals) rival or exceed loads from industries, federal facilities and wastewater treatment plants. Urban storm water runoff is responsible for impairments in over 1,570 miles of assessed streams in the Bay watershed and has caused flooding, streambank erosion, and habitat and living resource degradation in areas with as little as 2% impervious surfaces. Given projections regarding urban and suburban growth and the increase in impervious surfaces in the watershed, managing urban storm water runoff is one of the most important priorities the Bay Program will undertake to improve water quality and sustain progress in restoring vital habitats and living resources throughout the Bay.
Nutrient pollution is considered to be the leading threat to the Bay’s health. High levels of nitrogen and phosphorus cause algae blooms, cloud water, diminish oxygen levels, suppress bay grasses and suffocate fish and crabs. Reducing that pollution is estimated to cost $6.5 billion in Maryland alone.
What caused this problem?
Urban development has replaced forest with housing, office buildings, commercial centers and associated parking lots whose hard surfaces are impervious to the rain. Instead of infiltrating into the humus-rich forest floor and re-evaporating through the leaves of trees into the air, the rain has been captured in storm drains and emptied into the headwaters of streams with such velocity, that the flow has eroded the streams down to bedrock. Eroded soil and the rush of stormwater from buildings, parking lots and roadways is carried into rivers and the Bay. Stormwater from parking lots and roads accumulates as many as 70 potential carcinogens from brake linings, gasoline, oil, tires et al. Discarding the rain in this engineered manner reduces groundwater and base flow that sustains waterways; drinking water is reduced while erosion, flooding and habitat destruction increase exponentially.
What can we do to reduce the problem?
1. One important way to prevent stormwater pollution is to control runoff from new development and redevelopment. One of the best strategies is to minimize the amount of new impervious surfaces, an approach that saves the developer more than conventional designs. Prairie Crossing in Grayslake, IL, is a superb example by Bielinski Homes, the largest Home Builder in Illinois, who has switched to Open Space Subdivision Design. 317 residences are clustered on 132 acres of the site, which left 80% as open space. They designed the developed area around a natural drainage system consisting of vegetated swales, restored prairie, and wetlands to treat runoff, removing 85% of nutrients, metals, and suspended solids and reducing peak flows by 68%. The developer saved $2.7 million using this approach and sales are comparable or better than nearby conventional developments. (Lehner et al 1999)
2. A popular method used to restore developed areas is a Stormwater Utility. Established in more than 400 counties and municipalities across the country, Utilities charge an annual fee (average is $5 month) per unit of impervious surface for old and new development alike, to raise necessary funds for watershed restoration. The Utility is put in place by government. Fees go into a dedicated Enterprise Fund, such as Sewer and Water. A typical impervious surface runoff unit is 2400 s.f. and is multiplied by the total impervious surface in a given development. In Anne Arundel County, such fees would accumulate a $20 million fund each year. The County would prepare a priority list of restoration projects, submit the list to the County Council for public hearing, and report each year on the use of funds to the Council.
Another critically important approach is to capture the rain as close as possible to runoff points and direct it into Raingardens (bioretention areas), where it will be cleaned by plants, roots and earth. Cisterns can be used to store rain for reuse to water landscape and flush toilets. Porous paving of various types and planted swales along roadways can infiltrate the rain. Living roofs can replace asphalt ballast roofs, reducing heat by 100 degrees and absorbing up to 80% of a given rainfall. Such techniques are in use now and can be included in retrofits of urban areas. Land-owners who engage in such restoration projects will receive up to 50% credit on the Utility fee they pay.
Typical problems in Anne Arundel County
In Anne Arundel County more than 1100 stormwater ponds were installed prior to current regulations. They were designed to manage the 5-10-50-100 year storms. Pipes leaving the ponds are large in diameter and pass 90% of rainfall (small storms of 1-2inches) immediately into waterways carrying all pollution, sediment and clay particulate. Stormwater moving toward these ponds from developed areas in the watershed needs to be infiltrated using raingardens, cisterns, infiltration trenches, constructed wetlands, living roofs to reduce impacts on the waterways.
Creeks and Rivers receive an on-going load of silt from storm drains which accumulates year after year reducing depth for navigation, for boat slips, and waterfront property causing an economic burden. Dredging is increasingly costly, difficult to permit, and dredge spoils are difficult to dispose of.
Swimming and fishing in waterways becomes less inviting as summer heat causes algae blooms and fish kills. The Bay’s rich seafood business has declined to a finite percentage of its original harvest and the voluminous oysters that filtered the Bay in a day are unable to fulfill that critical function. A recent advisory warns fishermen to wear plastic gloves when handling rockfish because of a bacteria attached to the fish skin that can be harmful.
We CAN do our part to restore the Bay. By joining together, businesses, citizens, government, we can introduce policies and practices which will make a huge difference in our own daily enjoyment of the enticing creeks and rivers that draw us to this place. We can celebrate our achievements together as we see the effects of restoration practices and projects that add beauty, economic and ecological benefits to the places we call home.