Hydrologic Performance of Regenerative Stormwater Conveyance in the North Carolina Coastal Plain

Abstract

Regenerative stormwater conveyance (RSC) is an open channel, sand-filtering system composed of a series of shallow aquatic pools, riffle weirs, native vegetation, and underlying media beds. Surface runoff entering an RSC is conveyed as nonerosive surface flow or subsurface seep through the media, and exits the system as surface flow, seep out, exfiltration into parent soil, or evapotranspiration (ET). Regenerative stormwater conveyances are expected to perform similar to other sand-media-based low-impact development (LID) stormwater control measures (SCMs), but the hydrological and water quality efficiencies of RSC have not been sufficiently validated in a variety of hydrogeological conditions to date. A RSC was installed in the coastal plain of North Carolina, receiving runoff from 5.2 ha. Surface flow was reduced substantially through the RSC, with 84% of inflow converted to a shallow interflow-like seep, referred to in this paper as seep out. High groundwater levels resulted in small overall exfiltration rates, but increased evaporation rates due to extended ponding. The conversion of surface runoff to seep out has significant implications for stormwater mitigation, releasing filtered water at slower rates than conventional conveyance channels, similar to undeveloped watersheds. The Brunswick RSC released similar fraction of seep out to that of shallow interflow observed in undeveloped watersheds.