A billion-dollar coastal project begins in Louisiana. Will it work as sea levels rise?

Nearly $3 billion in settlement money from the BP Deepwater Horizon disaster that devastated the Gulf Coast and killed hundreds of thousands of marine animals is now funding a massive ecosystem restoration in southeastern Louisiana’s Plaquemines Parish.

The flat, sparsely populated land divided by the Mississippi River delta is marbled by bayous and bays. Farms, fishing camps and shrimp boats share the region with oil rig supply vessels and industrial storage. And it's about to host a vast undertaking meant to mimic Mother Nature: Enormous gates will be soon be incorporated into a flood protection levee.

The aim is to divert some of the river's sediment-laden water into a new channel and guide it into the Barataria Basin southeast of New Orleans.

If it works, the sediment will settle out in the basin and gradually restore land that has been steadily disappearing for decades. State coastal officials call it a first-of-its-kind project they are certain will work, even as climate change-induced rising sea levels threaten the disappearing coast.

Gov. John Bel Edwards called it the largest such ecosystem restoration project in the state's history. "Quite frankly I’m not aware of one on this scale any where in the country and they’re are few in the world that can match the size of this project,” he said at Thursday's groundbreaking.

Bren Haase, chair of Louisiana's Coastal Protection and Restoration Authority, estimates the project will build anywhere from 20 square miles (52 square kilometers) to 40 square miles (104 square kilometers) over the next 30 to 50 years.

The U.S. Army Corps of Engineers, which permitted the project last year, projected creating of as much as 21 square miles (54 square kilometers) by 2070. Subsidence — the natural sinking of land — and sea level rise will diminish the returns, so much so that a net loss of land remains likely. But that can be seen as a factor increasing the importance of the effort.

“As land loss accelerates due to sea-level rise and subsidence, more of the remaining wetland area would be attributed to diversion operations,” the statement’s executive summary said.

Coastal experts say south Louisiana was built by sediment deposited as the powerful river continuously altered its own crooked, meandering course over thousands of years.

Human efforts to constrain the river with flood protection levees and huge flow-control structures safeguarded cities and communities that developed along the banks as the river became a medium of navigation and commerce. But the development also stopped the millennia-old process of building land naturally.

That is a major reason Louisiana's marshy coastal wetlands have given way to growing swaths of open water, posing a myriad of environmental concerns. Those concerns include worry about the erosion of land that serves as a natural hurricane buffer for New Orleans.

“The Mississippi River built Louisiana –- and finally reconnecting it with coastal areas that are currently starved of freshwater and sediment will ensure our future,” U.S. Rep Garrett Graves, a Republican, said in a news release. Graves supported the project in Congress and served as a top coastal restoration official under former Gov. Bobby Jindal.

Channeling water from the Mississippi into the basin poses environmental and economic problems, too. Even as it granted permits for the project, the Corps noted the environmental costs of introducing non-salty river water into coastal areas where aquatic animals thrive in salty or brackish water. The changes will likely kill bottlenose dolphins and have varying effects on fish and sea turtles. Fishermen have long opposed the project because of its expected effects on shrimp and oysters as well.

Kerri Callais, a board member for the Save Louisiana Coalition, which opposes the diversion, is among opponents who favor other coast-building methods, including rebuilding barrier islands and using pipelines to pump sediment to land-depleted areas.

“These are projects that we know will build land, will not take decades, and will not take the livelihoods, culture, and heritage of our citizens away,” Callais, a member of the governing council in neighboring St. Bernard Parish, said in an email.

Opposition has remained despite state promises of efforts to mitigate harm. On Tuesday, for instance, coastal officials outlined $10 million in planned spending on a variety of projects to aid fishers and oyster harvesters who will have to change the areas where they work or make other adjustments as a result of the project. Millions more in spending is planned to help communities near the river that might see increased flood threats from the project, including elevation of roadways.

Some environmental groups see the potential benefits. Matt Rota, senior policy director for the nonprofit Healthy Gulf, said the project will use less energy than sediment pumping, and he acknowledged the need to work with the river on its natural ability to build land.

“This diversion, if it's successful, is more passive,” Rota said in a phone interview, “which means it can keep going, whether or not we have money or the fuel.”

Still, Rota said, Healthy Gulf wants to see more done to help locals who depend on fisheries and oysters for their livelihoods. He said state and federal governments must also work harder to limit pollution upriver that flows south.

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Associated Press video journalist Stephen Smith in Plaquemines Parish, Louisiana, contributed to this story.