A Case Study: Bayou La Branche Wetlands Restoration
US Army Corps of Engineers
When the powerful forces of prolonged development and natural disaster strike fragile wetlands, the effect is devastating. But today in southeastern Louisiana, man is working to restore what was once lost. Through the Bayou La Branche Wetlands Restoration Project, dredged sediment has been used to restore deteriorated wetlands in a 436-acre, open-water pond in St. Charles Parish.
Located on the southwestern shore of Lake Pontchartrain, this area was once classified as a brackish marsh that served as a nursery ground for commercial and recreational fisheries. However, beginning in the 1800s, a series of events, both man-made and natural, nearly destroyed the entire marsh and converted most of the area to open water. In 1830, construction of the Illinois Central Railroad created a barrier to drainage and sheet flow across the marsh from upland areas. In the early 1900s, the area was leveed and pumped for agriculture and subsequently subsided. A hurricane broke the levee in 1915, leading to the formation of a large, open-water pond. In the 1960s, canals were dug adjacent to the area during construction of Interstate 10, further altering the distribution of water and causing brackish water to flow from Lake Pontchartrain into the interior marsh.
Finally, nature struck two more blows with Hurricane Betsy in 1965 and Hurricane Camille in 1969, flooding much of the remaining marsh with brackish water from the lake, stressing vegetation and contributing to the loss of marsh. Over the years, erosion and subsidence progressively increased the size of the pond, leaving just a narrow band of marsh along Lake Pontchartrain. Retreat of the lake's shoreline between 1955 and 1972 was estimated to be 9.5 feet per year, threatening to expose the pond to damage from lake waves through a breach in the narrow shoreline.
In recent years the pond's proximity to the lake has provided an ideal opportunity to restore the marsh using dredged sediment. The Bayou La Branche Wetlands Restoration Project was designed to create more than 300 acres of emergent land to encourage the natural establishment of wetland vegetation. The ultimate goal was to reach a ratio of 70 percent emergent marsh to 30 percent open water within five years of project completion.
Authorized by the Coastal Wetlands Planning, Protection and Restoration Act (Breaux Act), the project involved pumping nearly 2.7 million cubic yards of sediment from Lake Pontchartrain into the pond. Construction was completed April 6,1994. Three months later the dredged material was seeded with Echinochloa crusgalli, commonly known as Japanese millet, to enhance plant growth. The sediment is expected to settle to an elevation of .65 to 1.62 feet. Once the sediment is completely settled, plans call for planting brackish marsh species.
November 1993 USGS Photo
November 1997
USGS Photo
To measure the project goals, sediment elevation, soil properties, water level and vegetation are being monitored in the project area. Aerial photographs are being taken to compare land-to-water ratios in the project and reference areas. The results so far show that sediment elevation and water level variability decreased in the project area from April 1996 to December 1997. As the sediment and water levels changed, the composition of plant species improved. Dry-tolerant species decreased and wetland-specific species increased. Preliminary reports from recent monitoring show that the Bayou La Branche project has reached or surpassed its target ratio of 70 percent marsh to 30 percent open water, according to John Troutman, coastal resources scientist supervisor for the Louisiana Department of Natural Resources. Although complete results are not yet available, Troutman reports that elevation in the area has stabilized, and woody vegetation is disappearing and being replaced by wetland-specific plant species. "This is what we want," says Troutman.. "This has been a pretty successful project."