Stormwater runoff is becoming increasingly discussed as a pollution problem, but not everyone knows about it, and or why it’s a problem. During any precipitation event, some of the precipitation falls onto pervious surfaces, like forests, fields, and some lawns, and some of it falls onto impervious surfaces, like roads, parking lots, rooftops, sidewalks, driveways, and more. In a natural or highly rural area, where pervious surfaces are dominant, when precipitation falls, it mostly is absorbed into the soil, intercepted by canopy and evaporated, or evapotranspired by plants, and only a small amount actually runs off the surface into the local waterways.
In urban and suburban areas, impervious surfaces can cover upwards of 70-85% of the land surface, with pervious surfaces like yards making up small amount of the land. This means that precipitation, whether it be rain or snow, that would normally fall on a pervious surface, is now mostly collecting on impervious surfaces and running straight off. But where does that runoff go?
Contrary to popular assumption, stormwater is not usually treated and cleaned like wastewater. Typically, stormwater runoff goes straight from the source into a pipe, and eventually, is dumped out into the closest waterway. Newer developments from the past 20 years or so have been required to include “detention basins.” These were intended to help capture the stormwater runoff from parking lots and rooftops, and hold it for a short time and then release it slowly into the closest waterway. Unfortunately, these basins do very little to remove pollutants from stormwater runoff, and it’s also been shown that they do not replicate natural hydrologic functions.
According to EPA estimates, as much as 40 percent of all U.S. waterways that do not meet water quality standards are at least partially impaired from polluted stormwater runoff. Pollutants commonly found in stormwater runoff include sediments, nutrients from fertilizers, bacteria and other pathogens, debris (plastic everything, cigarette butts!), and household hazardous wastes, like paints, motor oil, and more.
KWA works to try and encourage policies, projects, and practices that help reduce the impacts of stormwater runoff. More and more, “green infrastructure” (GI) and “low-impact development” (LID) methods are being utilized to capture stormwater on-site, reduce the amount of runoff, and to also remove pollutants from the runoff. These practices include rain gardens, green roofs, bioswales, pervious paving, rainwater harvesting, and more. The fundamental goal of these practices is to better mimic natural hydrologic functions, and try to reduce the overall amount of stormwater runoff and increase the overall quality of stormwater runoff.
Recently, one of our state partners, Watershed Watch of Kentucky, released a draft “Kentucky Green Infrastructure Action Plan” that will hopefully guide the state towards more widespread use of GI/LID practices. Other states and cities are doing it, like Portland, OR, Seattle, WA, Philadelphia, PA, Washington, D.C., and more. Check out some of these GI practices from around the country!