Over the past six months, crews have laid nearly eight miles of pipe from West Pointe à la Hache to an area of open water on the west bank of Plaquemines Parish.
The crew’s work doesn’t immediately look unusual: pipeline construction is a familiar process in this part of oil-rich Louisiana. For decades now, crews have torn into marsh to build pipelines.
But these massive pipes carry sediment, with hopes of restoring 334 acres of this brackish marsh, known as Bayou Grande Cheniere.
Bayou Grande Cheniere is part of the Barataria Basin, which has lost more than 276,000 acres of land since the 1930s, according to the National Marine Fisheries Service.
As the route of the once-meandering Mississippi River was walled into place by flood-protection levees, coastal marshes were severed from what nourished them: the freshwater, sediment and nutrients that once spilled over the river’s banks.
In recent decades, Bayou Grande Cheniere — like other wetlands within the Barataria Basin — has further eroded, because of land subsidence, storm damage, and man-made canals, mostly dug for the oil and gas industry.
Now, with hopes of keeping the bayou alive, the pipeline laid by crews from Weeks Marine is carrying dredged sediment here from the Mississippi River. Once completed, the bayou restoration will also provide added protection to residents during hurricane season, since coastal land serves as a “speed bump,” helping slow down tropical storms and storm-surge floodwaters.
According to the state Coastal Protection and Restoration Authority’s Fiscal Year 2024 Annual Plan, the hope is that marsh-restoration projects like these will provide storm-surge protection for population centers like New Orleans along with a reduction in tidal flooding in coastal communities.
The newly restored marsh in Bayou Grande Cheniere is still a work in progress. In the newly imported, nutrient-rich sediment, some cordgrass has already popped up, mostly along the “containment dike” surrounding the project, said CPRA construction manager Connor Hannan.
The dike, which surrounds the project area, looks like a thick half-wall, a raised terrace, and is built from the same sand used for the project.
As rain falls, water needs a way to flow out without taking the new sand with it. “We’re creating this big flat surface, so when it rains that water has to go somewhere,” said Hannan, noting that even the most basic parking lots include drainage designs, for when the rain comes.
In recent months, as crews built the Bayou Grande Cheniere dike, the construction team watched for low spots, where the water naturally slopes. In those low spots, the team built wooden-framed gaps in the wall of sand, to allow the water to flow out – without taking precious river sediment with it.
This area has come a long way. In 2010, Bayou Grande Cheniere and other wetlands within the Barataria Basin were heavily damaged by the Deepwater Horizon oil spill, which oiled waters, plants and creatures. Now, CPRA has implemented plans that make the Barataria Basin ground-zero for marsh-rebuilding projects.
Twelve river miles north of Bayou Grande Cheniere, officials recently broke ground for the nation’s most ambitious wetland-rebuilding project, the Mid-Barataria Sediment Diversion, which will be built with money from the 2015 Deepwater Horizon settlement. Once the diversion’s construction is completed, in five years, it will basically reconnect the river with its wetlands, by diverting some of the river’s flow into degrading marshland. Over subsequent decades, the diversion aims to rebuild 13,000 to 26,000 acres of wetlands.
The timeline is faster for Bayou Grande Cheniere. CPRA contracted engineers to transport sediment dredged from the bottom of the Mississippi, from the Point Celeste Borrow Area. And construction on the project is already complete. All of the sand needed for the project has already been dredged; the pipeline has already deposited it in Bayou Grande Cheniere. Where it’s been laid down, the newly sprouted cordgrass is a small sign of success.
Once Weeks Marine removes its equipment, nature will take over.
More Marsh-Building Projects in Barataria Basin
Upriver from Grande Cheniere, crews from Weeks Marine recently completed yet another, larger marsh-creation project. The Upper Barataria Marsh Creation Project, expected to restore 1,200 acres of wetland, is the largest restoration to date of the National Marine Fisheries Service.
From late 2021 until early last year, crews worked on the Upper Barataria project, which explicitly restored land lost from the Deepwater Horizon oil spill and was also funded by the $20 billion oil-spill settlement with BP. The Grande Cheniere Marsh Creation project was funded with grants from the Natural Resource Damage Assessment and the National Fish and Wildlife Foundation.
Soon, CPRA will ask for bids from contractors for another restoration project, located next to the completed Grande Cheniere marsh project.
The upcoming project, called the Grand Bayou Ridge and Marsh Restoration, aims to build 356 acres of marsh and restore a forested-ridge habitat using sediment from a different segment of the Mississippi River, known as the Magnolia Anchorage Borrow Area. On the ridge, the crews will eventually place plants and coastal trees, such as black willow and bald cypress trees, to strengthen the restored swampland against severe weather and to contribute to further land building, as the roots catch and trap sediment.
On a rainy day in December, Tye Fitzgerald, CPRA project manager, peered out across Bayou Grande Cheniere from a marsh buggy traveling over newly deposited sand. He was excited to see the sand accumulate, he said, and he looked forward to seeing continued marsh building in the area, as crews move to the Grand Bayou project.
Though construction did not begin until last July, Fitzgerald and Hannan began working on the Grande Cheniere project in 2020. An important first step, Hannan said, was to map the abandoned oil and gas wells in surrounding waters, to be sure that construction crews could navigate around them to the worksites, which are accessible only by water.
To locate magnetic anomalies that could be ‘orphan’ wells, experts used magnetometers to survey both bayous. Because CPRA now has a detailed map of the area, the work in Grand Bayou can proceed even faster, Hannan said.
The Impacts of Dredging
Marsh creation may seem to have little in common with saltwater traveling up the Mississippi River, a near-constant threat to southeast Louisiana this summer that seems to have finally relented — at least for now.
But marsh creation requires dredging. And recently, as the saltwater wedge moved up the river, the impacts of constant dredging came under fire.
For nearly a century, the U.S. Army Corps of Engineers has been dredging the river to allow for larger shipping vessels. Saltwater intrusion has occurred repeatedly during this time, but 2023 marked the second year in a row of major threats to municipal drinking-water systems that rely on river water.
In its 2018 environmental study, the Army Corps linked dredging with an increased threat of saltwater intrusion for drinking water in Plaquemines Parish and possibly beyond. To mitigate that risk, the Corps studied how to construct a temporary underwater barrier near Belle Chasse, to stop the heavier salt water from continuing upriver.
On Monday of last week, Jan. 22, the Army Corps estimated that the toe of the saltwater wedge had finally receded significantly, back to river mile 11, roughly 80 miles downriver from New Orleans. In its previous prediction, on Jan. 15, the Corps had estimated that the salt water reached mile 44.7.
But even mile 44.7 is more than 20 miles better than the saltwater’s farthest point this summer.
And all through those summer months, the saltwater wedge was tied to the work at Bayou Grande Cheniere, through a shared contractor: Weeks Marine.
Because of the contractor’s dredging and building expertise, Weeks was contracted to build up the underwater levee that Corps scientists had studied several years ago. The levee was at river mile 63.7, where it spanned the width of the Mississippi along its floor, acting as a barrier to help block the denser saltwater from reaching New Orleans.
As the dry summer raged, curtailing the river’s flow, Weeks Marine’s crews were subject to the ongoing demands of the saltwater wedge. In June, they first began construction on the new marsh. By July, the crew had to leave, to build the underwater levee out of sand dredged from a borrow area in an upriver section of the Mississippi.
The crew returned to work on Grande Cheniere, only to be called to the underwater levee again in September, after the salt had crossed the earthen sill at 63.7 and reached Jesuit Bend in the river, around mile 69, a mere 20 miles downriver from New Orleans. To combat the heightened fears of saltwater reaching the municipal water systems in the New Orleans area, Weeks crews left Grande Cheniere again, to raise the underwater levee, with more dredged sand.
Whenever Weeks Marine crews were able to return to Grande Cheniere, they would work with sand emerging from the big dredging pipe, which was pulling sand from a borrow spot downriver from the saltwater’s advance.
Sand for the Grande Cheniere Marsh Creation project was dredged from the Point Celeste Borrow Area, located approximately at river mile 50. For the Grand Bayou restoration, the sediment will come from a few miles downriver in a 700-foot-wide area of the river called the Magnolia Anchorage, around river mile 46.
To date, the broader criticisms of over-dredging to accommodate increasingly larger vessels don’t apply to these spot-dredging projects, say CPRA staff, who note that sediment is regularly replenished in the areas dredged for marsh-restoration projects.
“We found that the borrow area fills back in very quickly,” said Hannan. “It seems like there’s a natural elevation that the river wants to be in that area. You can dredge it deeper, but give it a couple springs and it’ll be filled back in with sand and you can start all over again.”