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Rain Gardens Help Recharge Groundwater MADISON, Wisconsin, April 29, 2002 (ENS) - A growing number of Wisconsin gardeners are putting their green thumbs to work creating rain gardens to protect the health of nearby streams and rivers, state water quality officials say. Rain gardens on urban, suburban and waterfront properties capture runoff from roofs, lawns and driveways while beautifying yards and providing habitat for butterflies and songbirds. Roger Bannerman, a Wisconsin Department of Natural Resources runoff researcher who has created four rain gardens at his Madison home, says, "Rain gardens are something you can do to reduce runoff and replenish groundwater - they not only help solve the environmental problems but they improve the aesthetics of your yard, they can attract wildlife, and they're fun."
Constructed to lie a few inches below ground, rain gardens consist of two layers: a top, soil layer for growing plants, and a lower, permeable layer of sand and gravel. When it rains, water first pools in the garden's plant zone, percolating quickly from there into the permeable layer underneath. The permeable zone then stores the water until it seeps into the subsoil. These shallow depressions are planted with flowers and other deep rooted vegetation that can soak up rain water and at the same time filter out pollutants the water may pick up. Rain gardens can soak up nearly all of the water that would otherwise run off into the gutters and sewers of city streets and then, carrying pesticides, fertilizer, pet waste, oil and other contaminants with it, wind up polluting Wisconsin lakes and rivers. Polluted runoff from urban areas, combined with runoff from construction sites, farms and roads, is considered the biggest threat to water quality in Wisconsin lakes and streams. Such runoff is one of the major reasons that 44 percent of Wisconsin's river miles and 61 percent of its lake acreage do not fully support the fish and other aquatic life they should, according to the U.S. Environmental Protection Agency's latest assessment of Wisconsin's waters. Two engineers at the University of Wisconsin have big ideas for rain gardens. Kenneth Potter, a civil and environmental engineering professor, and doctoral student Alejandro Dussaillant hope to convince city planners and commercial developers that rain gardens represent a cost effective way to mitigate the polluted storm water runoff and ground water loss that often accompany urban development. "What we've been able to do is some modeling analysis to show how effective rain gardens can be," Potter says. "And the most exciting thing we've come up with is that a rain garden can be relatively small and have maximum impact on ground water recharge."
"The way we calibrate the size of a rain garden is how big it is compared to the impervious surface," Potter says. "If you're mainly interested in ground water recharge, a rain garden does best if it's only about a tenth of the impervious surface." Potter's rain garden work stems from his concern about the effects of urban development on natural systems. As development proceeds, an increasing number of impervious surfaces such as rooftops, driveways and parking lots are preventing water from soaking into the ground and replenishing groundwater aquifers. This, in turn, contributes to dropping water tables in some areas, decreasing water available for the streams that count on ground water during dry months, and declines in the abundance and diversity of fish and other aquatic life in streams in urban and urbanizing areas. Cities and suburbs deplete ground water by tapping it as a water supply. Dane County pumps ground water at twice its recharge rate, Potter says. Although plenty of ground water is available in the county for human use, lower ground water tables spell trouble for streams, lakes and wetlands, which dry up or are supplied instead by dirtier and warmer surface water. Constructing rain gardens, Potter says, is one way to help counter these effects.
"Interest is exploding right now in rain gardens because they empower people to do something about a problem they've become aware of," says Bannerman. He is increasingly being contacted by developers interested in rain gardens. In fact, Bannerman says, four developments planned or underway in Dane County and Sauk County will feature individual rain gardens and deed restrictions requiring homeowners to maintain the gardens. Bannerman says rain gardens also can provide habitat for butterflies and songbirds, and, depending on the homeowner's desire, can be planted to encourage other wildlife. "It's really exciting," Bannerman says. "For most of the 30 years I've worked on storm water issues, the audience could fit inside a telephone booth. Now it's hundreds of people in the audience. People are really embracing the idea and taking some responsibility for helping sustain the health of their ecosystems." Bannerman worked with Applied Ecological Services of Brodhead and the University of Wisconsin Extension to develop a how-to brochure, "Rain Gardens: A Household Way to Improve Water Quality in Your Community." The brochure is available online at: http://clean-water.uwex.edu/pubs/raingarden/index.html The brochure is also available from Wisconsin Department of Natural Resources service centers, and from UW-Extension Publications, 45 N. Charter St., Madison, 53715. Tel: 608-262-3346 or toll-free 877-947-7827. Copyright Environment News Service (ENS) 2002. All rights reserved. |
Rain garden in Madison, Wisconsin (Photo courtesy 
A rain garden under construction at the Dane
County Heritage Center will help capture rainfall to recharge ground water in the area. (Photo by Alejandro Dussailant)
Parking lot rain garden in St. Paul, Minnesota provides on-site treatment of polluted parking lot runoff. (Photo courtesy 