Constructed Wetlands

More than 15 years ago, Tom Schueler published Design of Stormwater Wetlands, which became the foundation for most of the constructed wetland design specifications in the Bay states, and elsewhere in the nation, for that matter. The basic design of constructed wetlands has hardly changed since then, despite the fact that we have learned an enormous amount about what makes them work (or not work). We now have hundreds of good and bad wetland examples in the ground, and have a much better idea of the long-term trajectory of their wetland plant community.

So, after consulting our colleagues at CWP and NCSU, CSN has taken a long, hard look at the ancient design, and has come up with a real wetland makeover. In addition to the Constructed Wetland Design Specification, some of the new wetland design concepts are illustrated in a slideshow.

Constructed Wetland

Constructed wetlands should appear as naturally occurring ecosystems.

So, here is the ten minute summary on the major changes proposed for constructed wetland design:

  • The Demise of the Low Marsh Zone. The new design emphasizes deeper pools for nutrient removal, and vigorous wetland growth within the high marsh zone set at – 6 to + 6 inches, relative to the normal pool.
  • Constructed wetland on gold course

    Variety of plants and terrain features allow for a more successful wetland.

    Emergent vs. Mixed/Wooded Plant Community. The new design approach emphasizes the creation of a more mixed wetland community that includes a combination of deep pools, emergent plants, and water-loving trees and shrubs.

  • The End of Extended Detention (ED)? The old ED wetland design option has been dropped, and major limits on the vertical depth of ED are proposed.
  • The Pocket Wetland Sent Packing. This one-cell “micro” wetland was created to treat runoff from small drainage areas, but truth be told, it was not one of my better ideas. Most of the ones I have seen in the field are little McWetlands that are either overgrown “chia pets”, a public nuisance, or both. Submerged gravel or small upflow wetlands appear to show some promise, but need more testing.
  • Mosquito Bites. Perceptions about mosquito breeding, often unfounded, sharply reduced the number of constructed wetlands built over the last decade. The new design has numerous design features to reduce the potential for mosquito breeding, and increase habitat for their predators.
  • Mandating micro topography. The new spec mandates that at least two forms of microtopography structure be included in every design. Low cost forms of micro-topography include snags, inverted rootwads, tree peninsulas, coir fiber island, internal pools and cobble sand weirs, to name a few.
  • Natural Geometry. One of the best new designs to come on the scene is the Regenerative Stormwater Conveyance (RSC) system. The RSC is used in ravines and zero-order streams, and employs an alternating sequence of weirs and pools. Design specs and calculation methods for the RCS (also known as coastal plain outfalls) first developed by Underwood and Associates are included in the new spec, and can be accessed here.
  • Water Balance: The new spec argues that many of the rules from the original design are no longer needed, and replaces them with an alternative water balance equation. The simple equation seeks to maintain some water in the deepest pools after a one month rain-free period. Wetlands are pretty tough; it’s OK to dry them out once in a while.
  • Seeing the Forest Through the Wetland: The new spec guides the wetland community to evolve into a natural forest.

Constructed Wetlands & Regenerative Stormwater Conveyance Systems

Design, Installation & Maintenance of Constructed Wetlands & Regenerative Stormwater Conveyance Systems

Size (18 MB) | File type (.pps) | Download

Design Choices for Stormwater Wetlands

Slideshow demonstrating design choices for stormwater wetlands.

Size (2 MB) | File type (.pdf) | Download

Design Specification No 13: Constructed Wetlands

VA Stormwater Design Specification No 13: Constructed Wetland.

Version 2.0, january 2013 | Size (1 MB) | File type (.pdf) | Download

Design of Constructed Wetlands Presentation

Presentation on Design of the Next Generation of Constructed Wetlands

Size (4 MB) | File type (.pdf) | Download

Other Resources

Download All Files Above

Download all the files in Constructed Wetlands section as a compressed .zip file.

Size (43.22 MB) | File type (.zip) | Download