Like a natural sponge, wetlands can filter pollutants in runoff approaching bodies of water, large and small. Wetlands create habitats for many different species, process a wide variety of natural gases, and create buffer zones that can lessen the effect of severe storms on shorelines by reducing wave impact and controlling flooding.
Erosion and subsidence, however, are the biggest threats to our nation’s wetlands, according to James Harris, a wildlife biologist for the United States Fish and Wildlife Service. This is as true for inland wetlands as it is for those in coastal areas. In rural as well as urban environments, development has threatened and will continue to threaten wetlands unless steps are taken to preserve and restore these areas now.
“It’s certainly an issue in Louisiana,” says Harris, who is based in Lacombe, LA. “We’re losing wetlands every day.”
In many cases, choosing to enhance nature’s power to restore itself is the best long-term decision contractors can make in terms of protecting a wetland’s future.
Dredging the Gulf Coast
Climate change is another challenge. The Gulf Coast, where coastal wetlands provide an important buffer against tropical storms and hurricanes, is the setting for a variety of wetland restoration and preservation projects.
Bayou Sauvage, a national wildlife refuge on the eastern side of New Orleans, LA, is one location where, thanks to a massive dredging project, the impact on wildlife has had a happy ending.
“Prior to Hurricane Katrina, we had access canals that ran through different parts of the refuge,” says Harris, adding that the site is used by his organization for water-control management and is also used by the public for recreational fishing. “The tidal surge picked up a lot of material-sediment and marsh grass-and basically filled in the canals. It hindered our ability to manage water levels the way we needed to, and it also prevented access by us and the public in some cases.”
When the canals were restored, the US Fish and Wildlife Service provided specifications and field oversight so the project would benefit the refuge’s wildlife and the public in the best possible way, Harris explains. The organization worked with the Tennessee Valley Authority (TVA), which provided the engineering and oversight for the project, and Wilco Industrial Services of New Roads, LA, a company that provides a wide variety of environmental services, including wetland restoration and habitat enhancement. The project was completed during the first quarter of 2009.
Wilco workers removed sediment that had begun “choking” several main drainage canals, according to Jill W. Smith, executive vice president of the company.
“The canals were silting in, and the result was that drainage was reduced. We removed the silt,” she says. That material was then used to create new wetland areas or nourish existing wetland areas in the refuge.”
The project involved 171,000 cubic yards of dredging in the 6- to 7-foot-deep canals.
“We knew we had to dig them out,” says Harris, referring to the canals. “Rather than use traditional bucket dredges or draglines that would create a big pile of dirt that ran along side the channel-a spoil mound-we elected to bring in a small suction dredge that allowed us to place that material beneficially into degraded marshes. Instead of creating a pile of dirt, we were able to create 50 or 60 acres of emergent marsh.”
The site is located within the city’s hurricane levee protection system.
“The most challenging part was just trying to get the equipment in there,” says Harris. “We couldn’t float big barges in there. This was all stuff that had to be brought in by truck.”
The project will have a huge impact on the local wildlife. “The species that will benefit from that are waterfowl-ducks-and the main species are going to be blue-winged teal, gadwall, and widgeon. We get about a dozen different species of waterfowl. Besides ducks, we also get benefits to wading birds like herons, egrets, and ibises. We’ve already seen benefits to shorebirds,” says Harris. “The shorebirds would come in on the newly created marsh while it was still the bare dirt. We also get what they call secretive marsh birds: rails and gallinules.”
The dredging will also provide benefits for alligators. “By dredging the canal itself, we’ve created some deep water habitats for aquatics,” says Harris, adding that this will also directly aid species of largemouth bass and brim in the area. “Then, of course, there’s the access issue for the public. They can now access it again.”
The Fish and Wildlife Service is replanting native marsh grasses at the site.
“This is a long-term project,” says Harris. “Barring another big storm that will move a lot of material, this should last a long time.”
Dredging also played a role in the Mackey Island wetland project completed in 2008 that will eventually result in 26 additional acres of wetland on the mouth of the Escambia River in Pensacola, FL.
“This project, designed by Corp of Engineers, utilized geotubes as erosion control to mitigate wave action deteriorating the newly created wetland. The project was challenging because it involved expanding an island and working in shallow-draft tidal zones,” says Dan McDougal, who served as contractor for the project and who is president of Dredge America, based in Kansas City, MO. “This site was designed as both a dredge containment site to receive dredge material from navigation channel and also to create new wetlands.”
Geotubes were installed by Dredge America in a large area at the site.
“We built the berm and put the geotubes on top of the berms,” explains US Army Corps of Engineers site manager Terry Jangula. An erosion control apron was also added to the site.
“The wetland plants were planted inside the geotube berm,” says McDougal of native plants that were used.
Geotubes were selected because the Army Corps of Engineers sought something temporarily hard to protect the wetland, notes Jangula. At other sites, because of their improved UV protection in recent years, he’s noticed geotubes that have remained in place for more than a decade without disintegrating.
“Even after they disintegrate,” says Jangula, “they still provide pretty good protection.”
The TVA and the Fish and Wildlife Service paired up in the same respective roles again for a wetland project in the Delta National Wildlife Refuge, located about 7 miles southeast of Venice, LA, near the mouth of the Mississippi River. The organizations worked with Great Lakes Dredge and Dock Co., which subcontracted Wilco for the project that was a response to a combination of natural processes and storm impact.
The area “is subject to a high subsidence rate,” explains Harris. Workers cut five crevasses in the refuge in early 2009.
“A crevasse mimics a natural diversion in the waterway,” says Smith. “It creates an outlet for deposit sediments from the river to create a new wetlands area.”
The length of each crevasse varies, with most being approximately 100 feet wide, depending upon the distance of the pond from the main channel, according to Harris. No additional revegetation work was necessary at the refuge. The project lasted slightly more than a month and was completed in April 2009.
“The crevasses allow us to take advantage of the natural sediment process. We’re working with nature to create wetlands,” says Harris. “It’s not an immediate thing. It takes a while for the marsh to build, but once it builds it will get used by waterfowl, wading birds, shorebirds, alligators. It creates a lot of fishery habitats around the edges.”
The Fish and Wildlife Service has employed this technique for the past two decades “with great success,” Harris explains. “We try to go with it first, because that’s usually the best: trying to work with nature.”
Protecting a Waterway From Runoff Pollutants
In South Burlington, VT, discharge from a gravel parking lot area was flowing into Potash Brook in 2007, with sediment impairing the stream. Using grant monies for the project, the city sought to protect Potash Brook by building a gravel wetland system.
“It’s an entrance into Farrell Park,” says Tom DiPietro Jr., stormwater superintendent for the South Burlington Stormwater Utility, describing the area as having walking trails and biking trails. “It sees a pretty good amount of traffic, especially during little league season.”
The need arose from the city’s desire to treat the runoff from a nearby gravel parking lot
“It’s designed to treat your normal rain events,” he says. “We’re trying to treat the water before it flows into the brook.”
A 14-foot right of way made the system installation at the site challenging.
“There were definitely constraints. We couldn’t make the access road too small,” says DiPietro, who notes that the city didn’t want to permanently sacrifice one of the two traffic lanes for the project. “We took a little piece of an access road to put the system in. It’s still two lanes.”
Department of public works employees, including a backhoe operator and two laborers, built most of the small constructed gravel wetland in the fall of 2007 and then followed up with plantings in the spring. Installation took approximately one month in total.
The water flows through a grassy swale, and then through a series of septic tanks as part of the nutrient treatment at the site, explains DiPietro.
“The water level stays below the gravel surface,” he says. “The area that it collects and treats is about an acre.”
The city used an advanced wetland stormwater filter with an air-flushing system created by EcoSolutions, based in Westford, VT.
“We’ve got tubing that’s laid on the bottom of the wetland,” explains Dave Whitney, principal engineer with EcoSolutions. “When you do a stormwater wetland, it’s made to filter out solids: you inject the water into the bottom on the inlet side, and it’s collected at the top on the outlet side. There is coarse stone-2- to 4-inch stone on the bottom, and it gets smaller all the way to the stone at the top. One hundred percent of the flow will flow through the filter media. If you were to put the water in at the top, it could just skim at the top. This way, it has to skim through the stone. It will have a preferential flow path.”
Aeration tubing was set in the base of the wetland so air could be pulsed into the system, stirring up the sediment there, explains Whitney.
“We’re pumping out sediment-laden water. We’re pumping out dirty water. You could drop a sump pump in there and pump it out to a silt bank,” he says, adding that this water needs to be pumped out at least once in the early spring and late fall. “It all depends on what’s draining into it. If it were a new subdivision without erosion control features, such as the grass, you’d have to do it more often.
“If you don’t pump that out, in seven to 10 years the system would be so clogged it wouldn’t work,” he adds. “You’d have to excavate the stone out.”
DiPietro says the system is working well. Grass and native plants, including rushes, sedges, and cardinal flowers from a local supplier, were planted at the site. Erosion control blankets and silt fence were also used at the site for stabilization, even though the site doesn’t experience serious runoff during the winter months, because the water is frozen. The system is particularly tested during the spring snowmelts.
Employing Coir for Wetland Preservation in Colorado
Fountain Creek, which winds through Colorado Springs, has had stabilization work performed on its various stretches in a variety of phases. Last spring, the water flow was particularly challenging, and Western States Reclamation Inc., based in Fredrick, CO, installed a rechannelization system on a 3-acre site.
Begun early in spring 2009, this phase of a long-term, ongoing project required workers to provide bank stabilization and drop structures. What makes the site so unusual, says Colby Reid, reclamation division manager at Western States Reclamation, is the combination of wetland preservation techniques it employs. Coir was a key material in the project because of the high velocities within Fountain Creek, he explains.
“There’s a ton of runoff after every event. It’s been raining and snowing weekly,” he says, describing conditions just after the spring installation.
The project incorporates “coir log toe protection, and coir mat with soil and seed,” which was a mix of native plant species, he says. Wetland plugs were used, fastened down with 30-inch diagonal stakes along the toe. “The banks of the creek are also covered in the coir mat and wetland-seeded up to a transition area,” he notes. Wetland plugs and willow cuttings were also used in that area. The company used a slightly longer stake this year, Reid explains, for extra stabilization.
Soil-filled riprap, with the addition of a few native cottonwood trees and 5-gallon native shrubs including sandbar willow and dogwood, were placed along the bank for erosion control, says Reid. BioSol, he says, was used for nutrient treatment on the site.
Wetlands and Water-Quality Protection
Improving water quality remains imperative when engineered wetlands are constructed to enhance existing wetlands.
Located in Shelburne, VT, on the shores of Lake Champlain, Shelburne Farms-a nonprofit organization, National Historic landmark, and 1,400-acre working farm-recently had a gravel wetland filter with an advanced flushing system constructed upslope of a Class III wetland. The installation is located near the dairy barn complex for water-quality research purposes. The project itself received no public funding. The farm has partnered with the University of Vermont, allowing students to test and monitor the stormwater runoff.
“We’re always interested in ways of improving our stewardship practices,” says Alec Webb, president of Shelburne Farms, adding that the site will allow students from the university to monitor stormwater runoff from the 26-acre dairy farm complex and observe the treatment improvements. When a storm occurs, there is the potential for the runoff to pass through the manure from the cow lanes, says Webb, as well as through some exposed yards in a typical working farm atmosphere.
The move fits with the preservation ethic that is prevalent at the farm.
“We have a grass-based dairy farm. We try to maintain productive permanent pastures as the basis for our crop production. We feel that has positive environmental benefits,” says Webb, who says the organization also works to sustainably manage its 400 acres of woodlands, which are green-certified by the Forest Stewardship Council. “When we harvest lumber, we do it very carefully with forestry plans, trying to protect wildlife habitat as well as the production of timber and firewood.”
Because of the grass-based farming system at the site, says Webb, very little soil is exposed.
“We try to maintain grass sod, which holds soil in place,” he says, adding that native plants and clover are also used for soil stabilization. “Clovers do well in that type of system.”
Foot traffic at the site can be quite high. About 130,000 people visit the farm annually to walk its trails, observe the work done there, and attend outdoor concerts and special events.
Working around an existing wetland made the project challenging. EcoSolutions and Fitzgerald Environmental Associates were contracted to develop an ecological stormwater design that would treat the runoff.
EcoSolutions has constructed the gravel wetland at the site. Fitzgerald Environmental Associates delineated a wetland there and “designed our BMPs [best management practices] to avoid impacts to the wetland,” explains Evan Fitzgerald, CPESC, principal of the Colchester, VT-based company. Fitzgerald Environmental Associates also provided “GIS analysis and mapping, including the development of topography mapping from LiDAR data, hydrologic runoff analysis and pollutant loading calculations, and incorporating the results of the runoff modeling into the design of the BMPs,” he explains.
“We used the NRCS TR-20 rainfall-runoff model for the site, and the Simple Method to predict pollutant loading from subwatersheds at the site,” says Fitzgerald. “There has been a recognition that gravel wetlands outperform other structural stormwater BMPs in our cold-climate region.”
Whitney says the system, although similar in concept to the advanced wetland stormwater filter installed at Farrell Park, will need to be flushed and pumped more frequently-perhaps once a month during the summer seasons-“because of the high nutrient load going into it.” Manure is used as a fertilizer in the pasture.
The dairy barn complex houses the farm’s herd of 125 Brown Swiss cows. Installation had to be scheduled after the first cut of hay in June 2009.
“We had natural wetlands there. We opted for this system because it had minimal disturbance. We could get in and do our construction without disturbing the natural features that were there,” says Whitney. “This should improve the health of the natural wetlands. We’re creating a transition zone from the constructed wetland into the natural wetland.”
Fitzgerald says there won’t be any direct impacts to the existing wetlands, with the gravel wetland enhancing, not replacing, wetlands on the site downstream of the designed system.
This is not the only partnership the university has had with Shelburne Farms.
“The farm supports a number of different research projects through the university,” says Webb, citing a bird-nesting project in which University of Vermont graduate students studied how farming can support wildlife bird habitats. Projects like these, he says, help the farm nonprofit group understand its own practices at the same time. The university received funding for the research, explains Webb, while “we have to raise the funds for the wetlands. We try to do that through private sources.”
Surprisingly, the recent recession has had a positive effect on wetland projects.
“I think probably the biggest change, from the perspective of wetland designers in North America, is the increase of use of engineered wetlands for industrial applications and mining applications. I think a lot of it relates to the economy, because there are site managers out there who are realizing they could trade land for mechanical complexity,” says Scott Wallace, a principal and a leading wetland specialist with Stantec in White Bear Lake, MN. “Maybe they have a mechanical treatment system that is very difficult to operate. A site manager might ask, “˜Instead of having a little tiny system, could I build a more passive treatment system? Maybe it takes about 20% of my site area, but it costs almost nothing to operate.’
“Part of it is that companies are being asked to look at their carbon footprints,” Wallace adds. “The amount of carbon-dioxide emission is linked. If you could switch from a mechanically intense system to a technology that’s a lot more passive, you’re reducing your energy costs as well as your carbon footprint.”
In addition, facility managers are recognizing that their environmental management issues will be continuing for a long time, he explains. “When you really wake up and realize that as a company that you’re in this for the long haul, you want to reduce operation and maintenance costs.”
When a company decides to install an engineered wetland for water treatment, there are three aspects it should consider, says Wallace
“Constructed wetlands are biological treatment systems. They are only capable of doing the type of treatment that plants and bacteria are capable of,” he says, noting, for example, that it’s extremely difficult to try to design a wetland system that will extract salt from water. “Have reasonable and achievable treatment goals.”
Next, do your research.
“You have to have an understanding of the water requirements of the wetland and match that to the hydraulic or civil engineering design of the wetland,” says Wallace.
Third, he says, study the effects of the size of the system and its startup.
“One thing that I see commonly as a problem is wave erosion in newly created wetland systems before you get your vegetation established. A lot of people will omit engineering controls for erosion because they are picturing in their mind the fully established system.”
While measures such as the Clean Water Act in part work to combat wetland losses, they cannot be the only line of attack. The role of wetlands in erosion control plans, as well as in shoreline biodiversity, can be vital to a project’s long-term success. And just as there is a broad spectrum of water bodies that can be considered wetlands-anything from expansive open water to a tidal marsh-the imaginative methods that can be used to protect them often pair a natural process with modern technology.
Approaching wetland preservation using manmade materials can be enhanced through applying them with an organic design.