Sustainable Land Development Today - March 2008 - (Page 10) STORMWATER Nature’s Stormwater Treatment Solution In the right locations, stormwater wetlands offer advantages over traditional, hard-engineered systems. By Rob Kundert C Part of the reason they are often not the go-to solution is because the upfront cost is higher than the cost of constructed wet or dry detention basins to store stormwater. “However, wetlands are much more efficient at pollution control and filtration of sediments, metals, nutrients and nutrient processing,” May said. “They also provide ecosystem services for wildlife and other benefits for communities that incorporate them into their development.” Planned for low areas in the landscape, these systems are designed to treat stormwater runoff through natural means before it is allowed to move into a stream or other body of water. Wetland plants slow down the water flow, allowing some pollutants to settle out of suspension while breaking down and taking up nutrients into plant tissues. By slowing the water, these systems also reduce the potential for flooding and allow better infiltration into sub soils to recharge groundwater. 10 March 2008 Sustainable Land Development Today onsidered a stormwater Best Management Practice (BMP) for years, constructed wetlands are far from a mainstream solution, yet proponents say they offer much more to a development than simply a place to send stormwater. Constructed wetlands are a more beneficial alternative compared to the predominantly used wet or dry basins as a method to handle excess stormwater, according to Dr. Peter May, an environmental scientist with Biohabitats, Inc., an ecological restoration, conservation planning and regenerative design firm headquartered in Baltimore, Md. How They Work The most-often used stormwater BMPs, detention or retention basins, serve a basic purpose, according to May. “They just provide storage and some sediment settling capabilities. But studies have found that they don’t treat the stormwater runoff nearly as well as wetlands,” he said. Wetlands filter and trap sediment. Natural biological processes within them involving plants, bacteria and algae further trap and convert pollutants that would otherwise be passed along to downstream natural water bodies. Wetlands take in the runoff containing concentrations of pollutants such as heavy metals, organics and nutrients, and bind them to particles in the still or slow moving water or in organic matter. A portion of these pollutants are taken up by the wetland plants and are trapped in their tissues. The wetland has the ability to become a sink for those pollutants. Though not perfect for every location or climate, these natural treatment systems, when incorporated into a development-wide design, can be an economical, long-term solution that combines the form of an appealing amenity with the function of a stormwater BMP. “One important benefit of these systems is they are very low cost relative to harder, engineered systems,” May pointed out. “You don’t have the kind of piping involved, and their long-term maintenance costs are less.” Further, May pointed out that wetlands soften the landscape of modern developments, providing people with a connection to nature and a sense of place, which can have a positive psychological effect. “People generally appreciate natural areas and often prefer them to hardscapes,” he said. “When people feel better about where they live or work, this can also translate into better quality of life, improved productivity and even higher resale value.”
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