Bay Raccourci Marsh Creation and Ridge Restoration (TE-156)

Post project degraded marsh and open water.

Location

The project is located in Region 3, Terrebonne Basin, Terrebonne Parish.

Problems

High saline waters from Lake Mechant have directly contributed to the loss and/or conversion of much of the historically intermediate marshes to low salinity brackish marshes north of Lake Mechant. Subsidence, canal dredging and storm damage have also contributed significantly to the loss of marsh in the area. The zone of intermediate marsh (transition zone between fresh and brackish marshes) is located just north of Lake Merchant. High salinity water entering Bay Raccourci via Bayou Raccourci/Lake Mechant flows unimpeded into low salinity marshes surrounding Bayou Raccourci, effectively short circuiting the TE-44 Project. The 1984 to 2016 USGS loss rate is -0.32%/yr for the extended boundary area.

Restoration Strategy

The primary goals of this project are; 1) restore marsh habitat in the open water and degraded marsh areas via marsh creation and 2) restore forested ridge habitat along Bayou Decade.

The project would consist of the creation of 341 acres if marsh and 103 acres of marsh nourishment with sediments dredged from Lake Mechant and confined with earthen dikes. The proposed design is to place the dredged material to a fill height of +1.17 ft NAVD88. Dewatering and compaction of dredged sediment should produce elevations conducive to the establishment of emergent marsh and within the intertidal range. Containment dikes will be gapped at the end of construction.

The northern containment dike would be built to a height of +4.0 feet NAVD88 with a 10 feet wide crown and would also serve as a ridge. Material for the ridge would be bucket dredged from both Bayou de Cade and from within the marsh creation cell. The entire 16,350 linear feet (17 acres) of ridge would be planted with saplings and bare root seedlings on the crown and smooth cordgrass along the bayou side slopes.

The project would result in approximately 342 net acres over the 20-year project life.

The project was approved for Phase I Engineering and Design in January 2020.

The project is on Priority Project List (PPL) 29.

The Federal Sponsor is US Fish & Wildlife Service.

The Local Sponsor is CPRA.

South Grand Chenier Marsh Creation – Baker Tract

Marshes within the Hog Bayou Watershed mapping unit are
stressed due to limited freshwater input and seasonal salinity
spikes exacerbated by construction of the Mermentau Ship
Channel. Other contributors to land loss in the area are
subsidence, compaction, and erosion of organic soils.
Currently, the project area is characterized as large, open
water with degraded areas of wetland vegetation and low
organic production. The dredging of the Mermentau Ship
Channel increased tidal amplitude and salt water intrusion
into the watershed.

The goal of the project is to create new wetland habitat,
restore degraded marsh, and reduce wave erosion of organic
soils. The project would promote the expansion of emergent
marsh and submerged aquatic vegetation throughout the
project area. Material dredged from the Gulf of Mexico will
be used to create and nourish approximately 420 acres of
marsh. Smooth cordgrass will be planted throughout the
area. To help facilitate estuarine fisheries access, constructed
retention levees will be degraded and approximately 11,756
linear feet of tidal creeks will be constructed.

The project is located in planning Region 4, Mermentau
Basin in Cameron Parish within the Hog Bayou Watershed
Coast 2050 Mapping Unit. The mapping unit is bordered by
Lower Mud Lake to the west, the Gulf of Mexico to the
south, Rockefeller Refuge to the east, and Louisiana
Highway 82 to the north.

This project is on Priority Project List (PPL) 23.

The South Grand Chenier Marsh Creation – Baker Tract sponsors include:

• Federal Sponsor: Natural Resources Conservation Service
• Local Sponsor: Coastal Protection and Restoration Authority

 

Plants of the Wetlands

Found at the interfaces of land formations and water, smooth cordgrass (Spartina alterniflora) is an herbaceous, native grass that densely inhabits shorelines. Compact, vegetative smooth cordgrass colonies grow along shorelines and inter-tidal flats of coastal wetlands such as canal banks, levees, marshes, barrier islands, and other regions of soil-water interface. This grass is highly adaptable to a variation of water depths and salinity levels making it a resilient species heavily used for coastal restoration. With an extensive rhizome system, smooth cordgrass is also highly effective as a soil stabilizer for loose soils, contributing to anchorage of the plants and sediment, as well as decrease of erosion effects. Smooth cordgrass acts as a natural buffer which dissipates energy of storm surge and wind impact to interior lands.

The Coastal Wetlands Planning, Protection, and Restoration Act frequently uses smooth cordgrass plugs during vegetative plantings due to the plant’s insensitivity to water and salinity levels, and its success in significant erosion protection to shorelines.