VA DEQ STORMWATER DESIGN SPECIFICATION NO. 13 CONSTRUCTED WETLAND
Version 1.9, March 1, 2011 Page 22 of 30
A greater range of coastal plain tree species can tolerate periodic inundation, so designers
should consider creating forested wetlands, using species such as Atlantic White Cedar, Bald
Cypress and Swamp Tupelo.
The use of flashboard risers is recommended to control or adjust water elevations in wetlands
constructed on flat terrain.
The regenerative conveyance system is particularly suited for coastal plain situations, where
there is a significant drop in elevation from the channel to the outfall location (see
Stormwater Design Specification #11: Wet Swales).
7.3. Steep Terrain – Regenerative Conveyance Systems
Constructed wetlands are not an effective practice at development sites with steep terrain. Some
adjustment can be made by terracing wetland cells in a linear manner as with Regenerative
Conveyance Systems (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 sand channel to treat and safely detain and convey storm flow, and convert
stormwater to groundwater via infiltration at coastal plain outfalls and other areas where grades
make traditional practices difficult to implement. RSC systems combine features and treatment
benefits of swales, infiltration, filtering and wetland practices. In addition, they are designed to
convey flows associated with extreme floods (i.e., 100 year return frequency event) in a non-
erosive manner, which results in a reduction of channel erosion impacts commonly encountered
at conventional stormwater outfalls and headwater stream channels.
RCS systems are referred to as Step Pool Storm Conveyance (SPSC) channels in Ann Arundel
County, MD where systems have been installed and observed. The physical characteristics of the
SPSC channel are best characterized by the Rosgen A or B stream classification types, where
“bedform occurs as a step/pool cascading channel which often stores large amounts of sediment
in the pools associated with debris dams” (Rosgen, 1996). Due to their ability to safely convey
large flood events, RSC systems do not require flow splitters to divert smaller events for water
quality treatment, and reduce the need for storm drain infrastructure in the conveyance system.
These structures feature surface/subsurface runoff storage seams and an energy dissipation
design that is aimed at attenuating the flow to a desired level through energy and hydraulic
power equivalency principles. RSC systems have the added benefit of creating dynamic and
diverse ecosystems for a range of plants, animals, amphibians and insects. These ecosystems
enhance pollutant uptake and assimilation and provide a natural and native aesthetic at sites.
RSC systems are unique in that they can be located on the front or tail end of a treatment system
and still provide water quality and groundwater recharge benefits. Where located on the front
end of a treatment train, they provide water quality, groundwater recharge, and channel
protection, while also providing non-erosive flow conveyance that delivers flow to the
stormwater quantity practice - a constructed wetland, wet pond, ED Pond, or combination.
The Ann Arundel County design specification can be found at:
http://www.aacounty.org/DPW/Watershed/StepPoolStormConveyance.cfm