Evaluating Four Storm-Water Performance Metrics with a North Carolina Coastal Plain Storm-Water Wetland
Publication: Journal of Environmental Engineering
Volume 137, Issue 2
Abstract
Storm-water best management practices (BMPs) are typically assessed using the performance metric of pollutant concentration removal efficiencies. However, debate exists whether this is the most appropriate metric to use. In this study, a storm-water wetland constructed and monitored in the coastal plain of North Carolina is evaluated for water quality and hydrologic performance using four different metrics: concentration reduction, load reduction, comparison to nearby ambient water quality monitoring stations, and comparison to other wetlands studied in North Carolina. The River Bend storm-water wetland was constructed in spring 2007 and was monitored from June 2007 through May 2008. Twenty-four hydrologic and 11 water quality events were captured and evaluated. The wetland reduced peak flows and runoff volumes by 80 and 54%, respectively. Reductions were significant. Concentrations for the following pollutants increased: total kjeldahl nitrogen (TKN), NH4–N, total nitrogen (TN), and total suspended solids (TSS); inflow and outflow concentrations did not change for total phosphorus (TP), while only and orthophosphorus (OP) concentrations were lower at the outlet. Using a load reduction metric, results were strikingly different, showing positive load reductions of 35, 41, 42, 36, 47, 61, and 49% for these respective pollutants: TKN, , , TN, TP, OP, and TSS. When comparing the effluent concentrations from the wetland to ambient water quality in the Trent River, all effluent nitrogen species concentration were either similar or lower. TP and TSS concentrations leaving the wetland were higher than ambient water quality data. Finally, by comparing pollutant concentrations among different North Carolina wetlands, it is apparent the River Bend wetland received relatively “clean” water and released water with pollutant concentrations comparable to all other studies examined. Major conclusions from this study include: (1) storm-water wetlands sited in sandier soils (such as those of the North Carolina coastal plain) should be considered a low impact development tool and (2) the selection of performance metric has a pronounced bearing on how a BMP’s performance is perceived. Sole reliance on a concentration reduction metric is discouraged.
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Acknowledgments
This research was funded by the NC Ecosystem Enhancement Program and the North Carolina Department of Environmental and Natural Resources-Division of Water Quality. We would like to thank the following faculty, staff, and students at North Carolina State University for their substantial help: Dr. Mike Burchell, Mr. Shawn Kennedy, Mr. Ryan Smith, Mr. Jon Hathaway, Mr. Charlie Humphrey, and Mrs. Adrienne Cizek. The willingness of the town of River Bend, and Mayor John Kirkland, to host the project is greatly appreciated.
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© 2011 ASCE.
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Received: Jan 3, 2009
Accepted: Jul 13, 2010
Published online: Jul 16, 2010
Published in print: Feb 2011
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