Regenerative Stormwater Conveyance: An Innovative Approach to Meet a Range of Stormwater Management and Ecological Goals

Abstract

Drainage infrastructure, whether it be simply conveyance based or intended for other stormwater management criteria (e.g., detention, channel protection), typically results in the concentration of flows at discrete outfall points. Standard energy dissipation (e.g., flared end sections with rip rap or engineered stilling basins) together with overcontrol of discharge, frequently prove to be inadequate to protect against outfall erosion and related receiving stream degradation. The result seen throughout urbanizing watersheds is impaired habitat, excessive erosion and transport of sediment and nutrients to downstream sinks (e.g., ponds, lakes, estuaries, etc.), and compromised infrastructure. Based on an inventory of stormwater outfalls, Anne Arundel County, Maryland has concluded that the majority of pipe outfalls, rip-rap and gabion level spreaders and energy dissipation devices used to convey stormwater have failed and resulted in more than $600 million in damage to streams, adjacent wetlands, and steep slopes. A more thoughtful, cost-effective, and restorative approach to handling urban stormwater flows was clearly needed, and leaders in the County Department of Public Works decided to pursue design solutions that provide a full range of benefits including improved water quality, stable conveyance, increased groundwater recharge, floodplain reconnection, and wetland creation. The new preferred approach is often referred to as regenerative stormwater conveyance (RSC). Regenerative stormwater conveyance (RSC) systems are open-channel, sand seepage filtering systems that utilize a series of shallow aquatic pools, riffle weir grade controls, native vegetation, and underlying carbon-rich sand channel to treat and safely detain and convey storm flow, and convert stormwater to groundwater through infiltration. RSC systems combine features and treatment benefits of swales, infiltration, filtering, and wetland practices. RSC is applicable in new development, retrofit, and restoration scenarios and is fully consistent with and even expands upon the principles of low impact development, environmental site design and sustainable green infrastructure.