Water Quality and Hydrologic Performance of a Regenerative Stormwater Conveyance in the Piedmont of North Carolina

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Abstract
Regenerative stormwater conveyance (RSC) is an open-channel, sand-filtering system composed of a series of shallow aquatic pools, riffles and weirs, native vegetation, and underlying media beds. Surface runoff entering a RSC is conveyed as nonerosive surface flow or subsurface seepage through the media, and exits the system as surface flow, seepage out, exfiltration into the parent soil, or evapotranspiration (ET). While RSCs are expected to perform similarly to other sand-media-based low-impact development (LID) stormwater control measures (SCMs), little field research on this emerging technology have been published to date in peer-reviewed literature. Hydrologic and water quality of a RSC in the Piedmont (Alamance County) ecoregion of North Carolina was monitored from July 2013–June 2014. The Alamance RSC reduced volume and peak flow by a median 78 and 76%, respectively, while mimicking both predevelopment hydrograph shape and hydrologic flow pathways. RSC outflow matches the modeled predevelopment hydrograph shape and pathway components, including both pre-event and event water, as determined by deuterium isotope concentrations. Optimal storm mitigation performance is expected when RSCs include (1) a minimum of three pool/riffle cells, (2) established vegetation, and (3) exfiltration trenches to promote exfiltration into parent soils through extended subsurface ponding. By combining seep out water with surface flow from the RSC, the practice reduced incoming total suspended solids (TSS), total phosphorus (TP), and total nitrogen (TN) loads by a median of 70, 20, and 26%, respectively, likely due to filtration. The potential exists for further nutrient reduction if vegetated, wetlandlike conditions are present. Moreover, locating the RSC over more permeable soils would likely improve hydrologic performance.

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