Sustainable Land Development Today - March 2008 - (Page 12) Existing Wetlands: Tough to translate into a stormwater solution Trying to adapt an existing, or jurisdictional wetland to be part of a community’s stormwater control system can be a touchy issue, according to Ted Brown, water resources engineer for Biohabitats, Inc., an ecological restoration, conservation planning and regenerative design firm that has been designing wetlands for over 25 years. “Regulators are a little bit gun shy about allowing them,” he said. “It can be done so long as the runoff from the developed area is treated fully with some suite of BMPs before it discharges to any natural wetland area. One of those BMPs could actually be a constructed wetland,” he said. The discharge needs to be diffuse. Concentrated flows will create potential erosion and sediment problem in the natural wetland. “Many local governments will say that it is not consistent with the stormwater regulations for untreated stormwater to be discharged into jurisdictional wetlands,” Brown said. treatment.” May said. “Your final grading is also important. It is important to know where your drainage pathways are going to come into your wetland site.” Learn by Experience The creation of these natural, stormwater BMPs has advanced a great deal in the last 20 years as wetland restoration and treatment-wetland construction projects have become more prevalent, according to May. “There’s a whole emerging field called ecological engineering, which takes traditional engineering and combines it with a good foundation in ecosystem processes,” he said. “From a development perspective, it is extremely beneficial to retain someone who has knowledge of these systems and how they should work.” Brown said there are some key issues to consider. The size of the wetland needs to be in the range of three to five-percent of the contributing drainage area. “You want a minimum contributingdrainage area of from 10 to 20 acres and that might be dependent upon whether you are tapping into a groundwater table,” he said, to maintain water levels in the wetland. Designers should develop what is called a “water budget” which takes into account the level of evaporation and transpiration that will occur on a monthly basis to further insure adequate water to support the vegetation. “As you develop a planting plan, you also have to be fairly diligent the first couple of growing seasons to make sure the specified plants are thriving and not succumbing to invasive plants that may have come in,” Brown said. Flat slopes are critical when grading the wetland. “You don’t want to have three or four-to-one side slopes. Five to one or flatter, on your side embankments,” said Brown, who also stressed the need for a diversified design of the wetland bottom. “You have high-marsh zones, lowmarsh zones and fully inundated open water, so it is a diversity of water levels and planting zones,” he said. land. There needs to be good drainage to allow a constant, but slow, inflow and outflow of water. This prevents stagnation, which mosquitos prefer for breeding. Secondly, it is more conducive to supporting a broader range of predator species. Nature’s Aesthetic The return on investment in such designed and constructed, natural systems is far ranging and difficult to quantify in dollars and cents, according to May. “If you look at stormwater infrastructure, a dry pond doesn’t have nearly the natural capital value that a wetland system does. A dry pond is just a hole in the ground that has turf grass on it. It has no biodiversity associated with it. It has very few ecological benefits and provides much less of a water quality benefit,” he added. The payback for integrating natural systems into communities is improved water quality as well as some carbon sequestration by plant uptake of CO2. “These natural systems can do work for us as a society. They provide all these natural, free ecosystems services, but they also do an incredible amount of good for the environment and help to mitigate the ecological impacts of human development,” May said. The wetland areas also buffer the edges of manicured developments, which May contends adds a pleasant, calming psychological effect as people experience a greater connection to nature. “If incorporated properly, these places can be really wonderful areas,” said May Marketing the value of such sustainable systems is a challenge in some areas as there will be those property owners who prefer manicured, carefully mowed developments over the natural setting. “That’s an education component that has to come along with the design and how developers market their development,” Brown concluded. SLDT Photos courtesy of Biohabitats Inc. About the author: Rob Kundert is senior editor of Sustainable Land Development Today. Mosquitoes The health concerns related to mosquitoes has dogged wetland creation, especially with the heightened awareness of mosquito-borne diseases, such as West Nile, encephalitis, and eastern equine encephalomyelitis. May points out that that concern can be applied to any stormwater BMP which involves some level of open, still water. “Mosquitos are a problem anywhere. They are in planter pots and bird baths. They will always be an issue,” he said. “But with wetlands, especially those that are well-designed, fully functional, and biologically diverse, you set the stage for more complex fauna—predator species—to combat mosquito populations.” Those predators include everything from dragonflies to birds, like the Swift and Purple Martin. Bats are another species that prey on mosquitoes, but unfortunately, locating bat houses around a development may be disconcerting to some residents. “For those in the right latitudes, a population of mosquito-fish can do a very good job of suppressing the mosquito population,” May said. There are also environmentally safe and naturally occurring bacteria, such as bacillus Bt, which can be an effective measure to keep mosquito populations in check by preventing the insect larvae from emerging after they hatch in their aquatic phase. “The bacteria doesn’t harm birds, fish or people at all,” May said. Brown said another key to combating mosquitoes is in the design of the wet- 12 March 2008 Sustainable Land Development Today
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