Restoring Ridges to Protect and Preserve Coastal Habitat

Historically, projects conducted under the Coastal Wetlands Planning, Protection and Restoration Act (CWPPRA) have focused on wetland rather than upland habitats. However, the program has long recognized the essential value of uplands in maintaining a sustainable, functional coastal ecosystem. Consequently, projects increasing the health and resiliency of marshes that protect cheniers and ridges score highly in the project selection process.

Pairing ridge and marsh to recover a bayou

In late 2007, CWPPRA approved a novel project proposing to restore both a ridge and wetlands adjoining Bayou Dupont in Jefferson Parish. “No longer meandering slowly through the marshes, Bayou Dupont is fast deteriorating,” says Cheryl Brodnax, a biologist with the National Oceanic and Atmospheric Administration. “Altered hydrology, erosion and subsidence have caused rapid land loss in the area. With water bodies coalescing, tidal surge and sheet flow move through quickly, washing away the natural ridges and eroding the bayou shoreline. Without preventative action, you soon won’t be able to tell where the bayou stops and the bay begins.”

To halt the deterioration, the Bayou Dupont Ridge Creation and Marsh Restoration project, BA-48, plans to refurbish a section of the bayou’s natural ridge and rebuild areas of highly fragmented marsh. The resulting elevation and expanse of healthy marsh will redefine the bayou, helping to return it to a slow, meandering flow, and will provide the levee adjacent to the project area protection from wave-induced erosion.

The project proposes to use material dredged from the nearby Mississippi River both to construct the ridge and to nourish the marsh. The technique has already been explored in a previous marsh creation project, but this will be the first attempt to rebuild a ridge with river sediment. Indeed, this is the first CWPPRA project to undertake rebuilding a ridge.

“The first step is to decide the target elevation,” says Brodnax, who serves as the federal project manager for BA-48. “We’ll survey the surrounding habitats and other natural ridges to learn how high we want to build our ridge, then do tests on river materials to determine their rates of compaction and settlement. Depending on the materials’ characteristics, we may have to stack materials five or six feet high initially to achieve a final ridge height of four feet.”

Stacking material along waterways is not unusual in southern Louisiana. Spoil banks, the result of maintenance dredging, line miles and miles of navigation channels and oil and gas pipeline canals. The difference between spoil banks and natural ridges, according to Brodnax, is intention.

“Spoil banks are an afterthought of maintenance,” says Brodnax. “They are built haphazardly and support whatever vegetation sprouts on them. We’re aiming to consciously re-create the topography and vegetation of a natural ridge, to construct it so that it will supply optimal ecological services. At its maturation we expect it to provide the quality habitat of native, woody plants like live oaks and hackberries.”

Building lessons from Port Fourchon

Although the ridge at Bayou Dupont is CWPPRA’s first ridge-building endeavor, some of CWPPRA’s partners are seasoned ridge builders, having participated in creating the Port Fourchon Maritime Ridge. The idea for Port Fourchon’s ridge was spawned by the inadvertent success of a spoil bank.

“Birders had discovered that a spoil bank of dredged material created during earlier port development provided terrific bird habitat,” says Davie Breaux, director of operations at Port Fourchon. “When we started to plan an expansion of the port, we decided to enhance the benefit for birds by using the dredged material to restore a maritime forest ridge.”

While the project proved that rebuilding a natural ridge is possible, it also points to the relative ease and economy of preservation compared to reconstruction. “It is costly to pump materials,” Breaux says. “We had the advantage of industrial construction in close proximity to the ridge site.”

Ridge builders underwent a learning process to make best use of those materials. “At first we tried to trap all the sediment we pumped into the site,” says Breaux, “but there was so much water in it that we lost our elevation when it dried out. In the second phase we used an open-ended containment design. The lighter sediments floated out to create an adjacent marsh and left the heavier sands to form the ridge. We learned to couple building a ridge with building an apron of marsh around its perimeter.”

Other lessons included the challenges of planting in salty soil. “The Natural Resources Conservation Service did test plantings here, as did the Louisiana Department of Natural Resources,” says Breaux, bringing up yet another lesson of the project: the importance of partnerships. Nonprofit organizations worked side-by-side with industrial heavyweights. Nature enthusiasts shared observations and insights with government scientists and engineers. Hundreds of volunteers contributed thousands of hours planting vegetation. And there’s the seemingly incongruous symbiosis between industrial activity and nature. “We’ve learned we need the natural system around us to protect us,” says Breaux, “so when we consider what we need to do to enhance our business, we look for ways to build it that can improve the environment.”

Port Fourchon has established the entire area surrounding the maritime ridge as a sanctuary. When work is finished at the 970-acre site, footpaths and boardwalks will invite visitors to view birds and other creatures benefiting from the newly created marsh and ridge habitats.