Terraces to Fix Degraded Louisiana Coastal Wetlands

Sept. 26, 2001
In a unique project designed to slow erosion of Louisiana's coastal marshes, Ducks Unlimited has partnered with public and private individuals and organizations to build duck-wing-shaped terraces that will deter wind and wave action from further stressing marsh vegetation.

South Louisiana contains the largest expanse of coastal wetlands in North America, and provided critical wintering habitat for up to two-thirds of the ducks and a third of the geese that use the Mississippi flyway. However, throughout the past seven decades the marshes have been degrading and have lost habitat and food sources necessary for waterfowl and wildlife to survive. More than 1,500 square miles of marsh have been lost as a result of subsidence, or sinking, of the marsh, as wind, weather and mankind chip away at the last remaining stretches of the Louisiana coastal marsh.

Erosion of a coastal marsh is accelerated by human activities such as building canals to access fossil fuels and support commercial barge travel. Navigation channels change the natural water-flow patterns of the landscape, and saltwater moves into areas of the marsh that have vegetation that is less salt-tolerant. As the plants are exposed to elevated salinities and tidal action they become stressed. They lose root strength, which makes them susceptible to wind-driven waves. Worsening the saltwater intrusion is coastal subsidence, a natural compaction or sinking of marsh sediments, which further stresses marsh vegetation by increasing the duration of flooding. Vegetation dies, emergent marsh converts to open water, and wind constantly creates waves that keep the open water turbid and unproductive. The result is a coastal region that is eroding at an alarming rate.

Louisiana has the highest coastal wetlands loss rate of any state in the nation. From 25 to 35 square miles of the coast's emergent wetlands are lost every year to open-water habitats.

To reduce the erosion and turbidity caused by wind-driven waves, Ducks Unlimited applied for and received a North American Wetlands Conservation Act grant for the construction of more than 20 miles of coastal terraces. Each terrace, arranged in an alternating pattern at 30-degree angles to the shoreline of the marsh ponds (which makes them look like duck wings from the air) will be 1,000 feet long, 40 feet wide at its base and about 10 feet wide at its top. The surface of each terrace will be about a foot above water level and will be planted with vegetation for stability. Implementation of the grant's objectives will be a cooperative effort among Ducks Unlimited, the Louisiana Department of Wildlife and Fisheries, the Louisiana Department of Natural Resources, the U.S. Fish and Wildlife Service, the USDA Natural Resources Conservation Service, Cameron Parish Police Jury, Miami Corporation, North American Land Co., Inc. and private landowners.

Ducks Unlimited engineers will survey and design more than 20 miles of "duck-wing" terraces. "Surveying in the open marsh is a little different from traditional surveying on agricultural lands," said Rick Parnell, engineering technician with Ducks Unlimited in Louisiana. "This is the first time I've had to use airboats, but without them we wouldn't have been able to get around in the shallow water." Actual construction of the terraces is scheduled to begin February 2002.

"The challenges of constructing terraces in an open-water marsh will be interesting," said Bobby Massey, Regional Engineering Supervisor with Ducks Unlimited. "But the benefits will be worth every bit of the effort. After they are constructed, the terraces will prevent wave action, which will reduce turbidity and allow natural aquatic vegetation to begin to grow again." Reestablishing submerged vegetation will lead to plant succession, and eventually will restore large areas of open water to a more natural interspersion of emergent marsh and open ponds.

Source: Ducks Unlimited, Inc.