Louisiana is one of the few places in the world where the mix of freshwater and saltwater means that alligators swim beside dolphins. Bass swim next to redfish and speckled trout. It’s a delicate balance though. Add to that equation the fact that humans have a way of creating problems in these estuaries–but then we also come up with amazing ways to solve them.
Over eons, the Mississippi River twisted and turned and shifted, spitting out sediment downstream by overtopping its natural banks, and building up Louisiana’s coast, creating land in every direction. Since then, humans have, for economic and cultural purposes, artificially trapped the river in place with levees and such, and in the process keep it from building more land the way it otherwise naturally would—which is one reason why Louisiana has lost over 1.2 million acres in the past century.
Every six years since 2007, Louisiana’s Coastal Protection and Restoration Authority (CPRA), updates its Coastal Master Plan. The Coastal Master plan outlines priority projects meant to restore and protect Louisiana’s coast.
“We’ve completed around 140 projects included in variations of the Master Plans,” said Bren Haase of Louisiana’s Coastal Protection and Restoration Authority (CPRA). “These projects are spread out across our coast and include things like large-scale marsh restoration and structural risk reduction measures that are designed to decrease impacts from hurricanes and tropical storms.”
One of the more ambitious projects being executed right now is the Mid-Barataria Sediment Diversion on the West Bank of the Mississippi River, south of New Orleans and east of Lafitte. “One of the most important projects in the history of coastal Louisiana,” explained Haase, “the Mid-Barataria Sediment Diversion has the ability to restore the Barataria Basin back to a living and growing estuary for our children and grandchildren.”
New coastal land is usually created, replaced and repaired using two restoration tactics: dredging or sediment diversions. In Louisiana, sediment diversions are projects designed to restore the natural land building processes of the Mississippi River and redistribute sediment into areas that have been disconnected from the river by levees.
A slice of the levee is cut out along the Mississippi River, and a manmade channel allows river water and sediment, silt, and nutrients to naturally flow in and strategically build land into the various deteriorating coastal areas. A multi-billion-dollar project, the Mid-Barataria Sediment Diversion is now being undertaken by CPRA in coordination with the U.S. Army Corps of Engineers, and other south Louisiana coastal partners.
Dredging, on the other hand, means digging up sediment from the bottom of the Mississippi River or another borrow source and pumping it elsewhere to create and repair damaged marshes. Because sediment diversions inevitably bring freshwater into areas with higher salinity–building land, but sometimes drastically changing the ecosystem—Louisiana fishermen often prefer dredging projects to diversion projects.
The state is using both methods.
“We’ve dredged and built around 10,000 acres in the Barataria Basin, building and restoring barrier islands and marshlands,” Hasse said, “but we are not in a position to argue over one method versus the other when it comes to restoring our coast. We have to use every tool in our toolbox to effectively address our land loss problem. We’ve created about 60,000 acres over the last 10 to 15 years through dredging. That’s 42 to 45 Superdomes worth of sediment.”
Yes, that’s right, we in Louisiana do often measure land in Superdome-sized chunks.
Haase admitted, “The Mid-Barataria Sediment Diversion will pump freshwater into the Basin at certain times of the year, meaning some places that are salty and ripe for oyster growth will change. But then, other new places will be,” Haase said. “The project will simply move some resources around—same with shrimp and crabs and other fish.”
Brad Barth, CPRA’s program manager for the Mid-Basin Sediment Diversion program added, “When dredging, we’re just using what’s sitting on the bottom of the river, but with the sediment diversion we’re capturing what is continually going out into the Gulf of Mexico.” The Mid-Barataria Sediment Diversion alone is expected to build and sustain up to 26,000 acres of wetlands. These wetlands will increase storm surge protection and reduce flood risk to communities, businesses, and residents in southeast Louisiana.”
Dredging, however, doesn’t do as much to address the problems that caused our coastal land loss in the first place; as soon as a dredging project is complete it begins to deteriorate. A sediment diversion, on the other hand, builds and sustains land continuously, offering a more sustainable solution to coastal land loss. The Mid-Barataria Sediment Diversion will also help sustain the land created through other coastal restoration projects, including dredging projects such as the Upper Barataria Marsh Creation Project.
Haase went on to say, “Dredging is also more expensive overall, takes a lot of manpower and a lot of fuel, and while a sediment diversion is expensive as well, it’s the gift that keeps on giving. A dredging project tends to last 20 years, but land created with a sediment diversion will last and benefit the coast for about 50 years.”
The Mid-Barataria Sediment Diversion will not only protect communities south of New Orleans on the Westbank, but, said Haase, “The investment of project funds will be an economic boost to that region; the multi-billion-dollar project will inject a significant amount of capital into the local economy.”
The Mid-Barataria Sediment Diversion, already underway, is expected to create around 340 new jobs annually over the life of the project. “Taking into consideration hurricanes and flood seasons, I’m expecting this one project to take about five years to complete,” Barth said. “That means five years of spending billions on construction, which includes hundreds of millions toward mitigation. Plus, it will generate tens of millions in local and state tax revenue and grow household earnings.”
It’s fair to ask how the recent much touted “salt wedge” coming down the river this Fall fits into this plan. Pumping saltwater instead of freshwater into the marshes wouldn’t benefit the wetlands in the same ways, and could even potentially cause harm; it’s a delicate balance. “The salinity gets high on the Mississippi whenever we have a low river in the late summer and early fall,” said Haase. “It’s happened a few times over the last few decades. The salt is always somewhere in the river, but these are the months where it starts marching its way up to New Orleans, especially during extended drought periods like we’re seeing this year.”
Haase explained that the Mid-Barataria Sediment Diversion is actually opened and closed using a gate system, where each gate is about 66 feet wide. “The salt wedge usually happens in the opposite season of when we would run the project,” he said. “This year has been a drought year so there are more saltwater issues. It’s all about flood seasons upriver, meaning torrential rains and snow melt. But in general, we will mostly operate the project when there are no saltwater intrusion issues. As a controlled gated structure, when it needs to be closed it will be closed.”
Though a monumental and costly effort, the project’s gates, once open, will build land, so that the alligators and dolphins and redfish and bass can continue to coexist in one of the world’s most diverse, beautiful ecosystems.
