Stormwater runoff has become one of the largest threats to water quality in the United States, and much of the problem comes from unsustainable development practices. Paved surfaces like roads, parking lots and roof tops prevent rainwater from seeping back in to the earth as it falls, meaning that water gets washed over streets, sidewalks and highways before it collects. That water – called runoff – brings with it a host of pollutants: pesticides, fertilizers, heavy metals, antifreeze, lead, oil, oxidized hydrocarbons from gasoline and diesel fuel and sediment.
Smart growth preserves the open spaces that act as natural filters for stormwater, and helps reduce stormwater runoff in the process. By building densely and reusing already-developed land, smart growth protects the quality of our streams and reservoirs.
Protect water quality by concentrating development.
One of the great environmental benefits of smart growth is that it requires less impervious, paved surfaces than dispersed development. Building housing near schools, stores and jobs has great economic benefits, but it also means less paved roads are required to get between those locations, and less pavement means more open space.
Even modest increases in development density can dramatically reduce the water quality problems associated with development. A study in the Chesapeake Bay watershed found that concentrated development required about half as much impervious surface as sparsely developed land, and as a result the concentrated development created 43% less polluting runoff.
Protect water quality with redevelopment.
Building on land that was once developed but is no longer in use is another great way to preserve open space. This strategy allows new buildings to go up without paving new land and also means no new roads have to be paved out to new development.
Mint Plaza, a project in downtown San Francisco that renovated the city’s historic U.S. Mint building, won a 2010 Smart Growth Achievement award from the Environmental Protection Agency for its innovative design. The plaza’s shifting planes direct rainwater into treatment gardens and an underground infiltration basin, reducing runoff and helping to protect San Francisco Bay.
Redevelopment also provides an opportunity to improve and retrofit existing buildings and their surroundings. New low-impact development techniques help buildings conserve water and promote water capture and reuse.
Protect water quality by protecting the air.
The benefits afforded to air quality by smart growth also help protect water quality. By reducing the carbon emissions and other air pollution, smart growth also reduces the amount of pollution that falls into our water supply via polluted rainwater.