Engineers invaded Wilson landscaping islands; battled bad weather to establish BMP beachhead |
Stormwater professionals learned lessons through trial-and-error in converting landscaping islands to stormwater treatment beds in Wilson, N.C. In 2001, engineers retrofitted eight landscape islands as bioretention areas in a Food Lion parking lot in Eagle Farms shopping center, as stormwater Best Management Practices. The BMPs store parking lot runoff, letting it pass through soil to be filtered and treated before it enters nearby streams. The data collected contributed to a statewide study on bioretention’s effectiveness as a stormwater BMP. Landscaping islands are the perfect size for bioretention beds, but since most are raised mounds, engineers designed depressions to complete the transformation. They lined the beds with plastic and fitted them with inverted pipes to hold water longer and encourage de-nitrification. This process accompanies bioretention, converting N fertilizer in water to inert N gas, which is released harmlessly to the atmosphere. “The landowner, Fred Bunn, was willing to take a risk with the project and allow the BMPs to be installed, as it was untried technology at the time,” says Bill Lord, North Carolina Cooperative Extension area environmental education agent. “When you ride through the parking lot, you can’t tell anything different is there.” But the largest benefits are embedded in the many lessons learned from the challenges that accompanied BMP installation at Eagle Farms. First, flooding. Shallow groundwater and no parking lot drainage caused the bioretention beds to flood during construction. The lots should have been divided up into mini -watersheds, says Lord, who thinks the problem could have been avoided with better communication between engineers and Cooperative Extension.
Next, mini-mudslides eroded from a neighboring field into the newly built BMPs, clogging them with sediment. “In urban areas this happens a lot,” Lord explains. “Surrounding development will ruin bioretention beds. The story here is that you must protect them after construction.” Once researchers and engineers overcame the challenges, the beds were monitored for two years, ending in May 2004. Says Bill Hunt, BAE stormwater specialist at NC State University’s College of Agriculture and Life Sciences, “The data suggested that the anaerobic configuration works better than the traditional configuration,” later proven by research completed in Greensboro. Developers benefit from the addition of this demonstration site since bioretention is “more of an innovative BMP for Wilson,” says Marc Burke, Wilson stormwater manager. “Most local engineers use retention ponds.” The BMPs were funded by an Environmental Protection Agency 319 grant awarded to the states for BMP installations. Partners in the $40,000 project included Wilson, Fred Bunn and Cooperative Extension. These islands-turned-BMPs are at the Eagle Farm shopping center, N.C. 58 North in Wilson. For information: Bill Lord at 919.496.3344 or william_lord@ncsu.edu. -- Lilly Loughner |
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