CAMPAIGN: Ethical and Sustainable Living
Natural landscapes naturally slow the movement of stormwater, and capture and filter some of it as it percolates back into the groundwater supply. But the built environment is dominated by impervious surfaces. Paved surfaces, roofs and building façades change the movement of water over the landscape and increase the volume, speed and temperature of the runoff. Rushing stormwater picks up pollutants, fertilizers and pesticides and can also cause flooding and erosion.
The EPA offers a "Stormwater Calculator," available to urban planners, architects, designers and homeowners, which helps the user identify strategies from reducing stormwater impacts from the site. Whether designing a new home or a remodel, Low Impact Development (LID) strategies can mitigate many of these negative stormwater impacts by slowing and/or capturing stormwater flows onsite.
Rain Gardens and Swales
Rain gardens are shallow, landscaped depressions, which retain and filter stormwater. These gardens ideally include a variety of native trees, shrubs and herbaceous plants. During storms, runoff ponds above the mulch and soil, then filters through the soil matrix, where plant roots take up water and filter nutrients and other pollutants.
Plants at the bottom of the depression must be able to tolerate both wet and dry conditions; upland species will thrive at the edges. Sometimes rain gardens are designed with an underdrain system—a perforated pipe encased in a gravel bed—that collects filtered runoff at the bottom of the bed and directs it to the storm drain system.
A bioswale, sometimes called a grassed channel or biofilter, is a vegetated, open channel designed to treat and weaken stormwater runoff. Vegetation slows down stormwater as it flows along such a channel, encouraging sedimentation, filtering through the subsoil, and/or infiltration into underlying soils.