Stormwater Symposium

Oral

397607 - Converting Dry Detention Basins to Constructed Stormwater Wetland for Enhanced Pollutant Removal

Wednesday, June 6
2:00 PM - 3:30 PM
Location: Greenway AB
Co-Authors: William Hunt, Raleigh, NC – North Carolina State University; Sarah Waickowski, Raleigh, NC – North Carolina State University

Dry detention basins (DDB) are stormwater control measures that have been traditionally implemented for peak flow mitigation. However, water quality improvements in DDBs are minimal due to short detention times and a lack of pollutant removal mechanisms. Additionally, DDBs are often poorly maintained or consistently wet, and they begin to take on wetland characteristics. Conversely, constructed stormwater wetlands have been found to effectively remove sediment-bound pollutants and soluble nutrients. The objective of this research project is to examine the pollutant removal changes in DDBs when they are retrofitted to behave like constructed stormwater wetlands. Three DDBs in the piedmont of North Carolina were monitored from February to August of 2017 for pollutant removal. During pre-retrofit monitoring, concentration reduction efficiencies were highly variable and ranged from -268% to 74% for TSS, -186% to 59% for TP, and -93% to 38% for TN. Two of these DDBs were then retrofitted in September 2017 and the third remained unchanged as a control. The retrofits to the DDBs included (1) raising the outlet orifice to incorporate a shallow permanent pool and (2) planting wetland plants within the floor of the basin and at the bottom of the side slopes. Post-retrofit monitoring commenced in November 2018 to quantify changes in pollutant removal of the converted ponds in comparison to the non-converted basin. It is expected that there will be an increase in pollutant reduction capabilities in the retrofitted DDBs. If effective, this simple and low-cost retrofit can be adapted to the many DDBs throughout the region.

Katy E. Mazer

North Carolina State University

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