Addressing Headwater Drainage with Regenerative Stormwater Conveyance (RSC)
Headwater streams provide many ecologic and water quality benefits. In a natural setting, these small drainage tributaries filter rainwater, recharge groundwater, and dissipate water velocity while transporting sediment from upland elevations downstream to larger water bodies. It is not surprising that people tend to populate upland areas where flooding may be mitigated by hard surface stormwater conveyance structures. As a result of this trend, headwater streams fall victim to residential and commercial development, water quality suffers, and hard surface drainage methods give stormwater runoff powerful erosive force in the urban landscape.
Maryland’s Department of Public Works surveyed their stormwater outfalls and concluded that the majority of energy dissipation devices (pipe outfalls, rip-rap, and gabions) used in the conveyance of stormwater had failed and resulted in $600 million in damage to streams, wetlands, and steep slopes in Anne Arundel County. County leaders determined that a more holistic, cost-effective, and restorative approach to stormwater management was needed, and decided to pursue the use of regenerative stormwater conveyance (RSC).
The RSC systems are open-channel, sand seepage filtering systems that utilize a series of pools, riffle weir grade controls, native vegetation, and an underlying carbon-rich sand channel to treat and safely infiltrate and convey stormwater. The RSC is thus a combination of swales, infiltration, filtering and wetland practices that provides for the combined benefits of each. Not only is RSC applicable in new development, retrofit, and restoration scenarios, but it is fully consistent with the principles of low-impact development, environmental site design, and sustainable green infrastructure.
The benefits of RSC include water quality improvements, reduced stream erosion, aquatic habitat enhancement, increased riparian vegetation, restoration of shallow groundwater, increased baseflow, and aesthetic improvements. Although the RSCs in Anne Arundel County were primarily implemented in the Coastal Plain, it is suggested, by NCSU Bio Ag for one, that implementation is viable in almost any region with minor adaptations.
In fact, RSCs have been adapted and utilized in the Washington, DC area. Within this highly urban setting of the piedmont, RSCs were used to rehabilitate Bingham Run, an ephemeral headwater tributary of Rock Creek. Rock Creek Park is a prominent recreational amenity in Washington, DC, and thus the headwaters are important drainages to the success of the aesthetic value of the park and water quality for the DC area. The RSC approach is being applied to 800 linear feet of an incised drainage channel. This involves raising the channel bed and reconnecting the stream with its floodplain and riparian wetlands to optimize the conversion of stormwater to groundwater. The approach aims to improve local hydrology by tempering the influence of stormwater runoff on the headwater drainage and larger stream system.
As regenerative stormwater conveyance continues to be implemented in tangent with swale and filter strip design, its longevity as a stormwater control measure will be dictated by continued monitoring and maintenance. Routine maintenance will allow such a system to function properly and yield the water quality benefits the design seeks to perpetuate.