Environmental benefits of rain gardens
Rain gardens are specially designed garden areas that capture, slow, and filter rainwater runoff, offering numerous environmental benefits. They help to mitigate stormwater flooding by allowing rainwater to seep into the ground more effectively than traditional lawns, which often feature impervious surfaces. By replicating natural processes, rain gardens can filter out pollutants like oil, pesticides, and industrial residues from urban runoff, significantly improving water quality before it reaches streams and rivers. The soil in rain gardens supports the absorption of nutrients and enriches the ecosystem, contributing to healthier urban environments.
Additionally, rain gardens provide small habitats for wildlife, adding greenery and biodiversity to urban areas otherwise dominated by concrete. They help combat urban heat by cooling the surrounding environment, as vegetation absorbs and mitigates heat from hard surfaces. With careful planning and appropriate plant selection, rain gardens can be aesthetically pleasing while serving important ecological functions. Overall, rain gardens represent a sustainable approach to managing stormwater and enhancing urban landscapes.
Subject Terms
Environmental benefits of rain gardens
DEFINITION: Garden areas designed to capture, slow, and filter rainwater runoff
Rain gardens provide a number of environmental benefits, including the filtering and neutralization of water pollutants, the reduction of stormwater flooding, and the creation of small islands of natural habitat in the midst of urban areas.
The basic idea behind rain gardens is the replication, on a small scale, of the natural conditions that existed before urbanization. In forests and on farmland, rainwater soaks into the soil and percolates slowly through it. Water that is not recycled by immediate evaporation or used by plants eventually works its way through the soil to end up replenishing underground aquifers. The average suburban lawn is relatively impervious to water infiltration by this process because the grass has shallow roots, and many soils, especially clay, are not porous enough to drain well. A well-sited rain garden planted with native shrubs, perennials, and other hardy plants will allow at least 30 percent more water from rainstorms or snowmelt to seep into the ground than a lawn does.
Although the basic idea is surprisingly simple, rain gardens as a way to counter environmental damage were not widely recognized as a workable concept until the early 1990s. Larry Coffman, the environmental official in charge of creating a plan for handling stormwater in Prince George’s County, Maryland, coined the term. The use of rain gardens in some large-scale projects, such as one in Maplewood, Minnesota, in 1996, helped to popularize the practice. Maplewood officials, led by landscape architect Joan I. Nassauer, sponsored the building of rainwater-gathering garden strips along the edges of suburban streets.
Most rain-garden projects in the United States have been small in scale, created by individual home owners or by communities around schools and parks with drainage problems, rather than large initiatives by developers or municipalities. The rain garden’s acceptance as a tool to combat water has been rapid, however, and relatively conflict-free. European countries, with their traditions of centralized planning, have been more innovative in using rain gardens than have North American nations.
Environmental Benefits
As cities grow, their land area becomes almost entirely covered with the hard surfaces of buildings, streets, and sidewalk pavements. In order to move rainwater quickly out of the way, most modern cities have built gutters and storm sewers that ultimately drain rainfall into rivers and lakes. On the journey from the city, the water picks up many toxic substances from the urban landscape through which it flows. Oil products, wastes, pesticides, and other residues of industrial processes are all carried along in storm runoff. The US Environmental Protection Agency (EPA) estimates that 30 percent of pollutants in water are the result of rainwater runoff. Such water is seldom even treated before it is discharged into lakes and rivers, and any attempts at treatment are likely to be prohibitively expensive.
When stormwater is received by rain gardens, most of the pollutants are filtered out. The soil is enriched by the movement of nitrogen, phosphorus, and other compounds through the plants’ root systems and soil processes. As an added benefit, rain gardens’ comparatively slow rate helps reduce downstream from the rapid runoff that can come with heavy storms. The existence of garden spaces in urban areas also helps in a small way to combat the effect, which results when heat is absorbed by and then radiates off of the unrelieved hard surfaces of buildings and pavements.
So long as those who create rain gardens follow a few basic rules—such as not putting a rain garden so close to a house that its foundations are undermined by excess water—there is virtually no downside to this conservation concept. Rain gardens bring a touch of nature to urban and suburban residents while helping to purify water resources.
Practical Considerations
Rain gardens do not necessarily look different from purely ornamental gardens, but the creation of rain gardens requires special attention to location and soil preparation. Because water should flow into a rain garden from impermeable surfaces such as roofs and driveways as well as from lawn areas subject to flooding, the rain garden needs to be somewhat lower than the surrounding ground. Occasionally a natural depression can be used, but normally some digging—to a depth of about 20 to 25 centimeters (8 or 10 inches)—is necessary. The digging also enables the replacement of the original soil with “rain-garden soil,” an optimal mix for root establishment and permeability. A mixture of half sand and 20 to 30 percent each of topsoil and is usually suggested.
A downspout with a drainpipe or shallow troughs usually needs to be installed so that water is directed from the roof or driveway to the rain garden. At the upper or higher end of the garden, a border of grass can keep water from entering the garden too fast on stormy days. A berm or even a low wall can keep it from overflowing at the downslope border. With all this, the object is not to create a pond or small swamp. An effective rain garden will drain rain within 48 hours after a heavy rainfall.
Effective rain gardens contain a variety of plants that can thrive under both wet and dry conditions. Enough perennials and ornamental foliage fit this description that rain gardens have the potential to be pleasing landscape design elements. Once they are well established, rain gardens often become places where birds and other wildlife shelter, providing additional touches of nature in the city.
Bibliography
Dunnett, Nigel, and Andy Clayden. Rain Gardens: Managing Water Sustainably in the Garden and Designed Landscape. Portland, Oreg.: Timber Press, 2007.
Kinkade-Levario, Heather. Design for Water: Rainwater Harvesting, Stormwater Catchment, and Alternate Water Re-Use. Gabriola Island, B.C.: New Society, 2007.
"Soak Up the Rain: What's the Problem?" Environmental Protection Agency, 23 May 2024, www.epa.gov/soakuptherain/soak-rain-whats-problem. Accessed 22 July 2024.
"Stormwater Runoff: A Top Cause of Water Pollution." Sustainable Investment Group (SIG), 14 Oct. 2015, sigearth.com/stormwater-runoff-a-top-cause-of-water-pollution/. Accessed 22 July 2024.
Woelfle-Erskine, Cleo, Laura Allen, and July Oskar Cole, eds. Dam Nation: Dispatches from the Water Underground. New York: Soft Skull Press, 2007.