There’s a new plan to plug a leak in the Mississippi River. Could it also build land?

The power of the Mississippi River comes clearly into focus far south of New Orleans, at a spot where the mighty waterway forces its way through a widening gap in its banks – prompting what could become an innovative solution to the problem that poses.

The gap known as Neptune Pass, capturing nearly a fifth of the river’s flow, is helping form what one scientist calls “probably the largest new delta in North America.” But it has also become a flashpoint in a debate between shipping interests and coastal advocacy groups over the river’s best use.

The Army Corps of Engineers has sought a compromise, and a new plan being presented to the public aims to achieve one, incorporating features previously used in coastal restoration projects.

If it works as intended, the plan would greatly reduce the flow of the river pouring into the pass and limit its effects on shipping. But it would continue to allow some sediment through. That could provide a model as the state faces worsening land loss along Louisiana’s coast.

So far, the response has been mixed. While the Corps has shown a willingness to think more creatively to balance the competing interests, the current proposal does not provide publicly available modeling and data that scientists believe should be used to determine the solution’s potential effectiveness.

Alex Kolker, a coastal scientist with the Louisiana Universities Marine Consortium who has closely studied the pass and spoke of it creating the continent’s largest new delta, highlighted that concern as well as the need to take multiple factors into consideration.

“I think most of us would like to see Louisiana with more land than less land, but at the same time, no one wants to see a boat laden with chemicals run aground,” Kolker said.

“So that might be a way of thinking about the management and the need to get the science right. Right now, I have more questions than answers.”

The Corps says it is working on a report on the modeling and will make it available when complete. It was not clear if that would occur before the public-comment period on the plan’s draft environmental assessment ends on Aug. 31.

For the Coalition to Restore Coastal Louisiana, which has worked on land-loss issues since 1988, the new plan is reason for cautious optimism since the pass would not be totally closed and devices to help with land building would be installed. James Karst, the nonprofit’s communications director, called certain aspects of it “innovative.”

“We wanted this land-building tool to be left on,” he said. “And it is still on, and would be still on under this plan.”

Where the river runs wilder

The reason why the seemingly simple task of plugging a hole in the river’s bank has generated such controversy is because it was never as simple as it seems.

The debate surrounding it is tied to numerous strands of Louisiana’s past, present and future. When it ran free and meandered thousands of years ago, the river deposited the sediment that eventually formed the land that became south Louisiana.

A catastrophic 1927 flood and the need for a reliable shipping channel led the Corps to embark upon a massive levee-building project along the river’s banks, forever altering geological forces. That project, along with factors such as oil and gas operations, set in motion the devastating land loss now afflicting Louisiana’s coast.

Since then, the state has found itself in a paradox. It needs the river’s sediment to replenish disappearing wetlands, but the levees protect nearby communities from flooding and help ensure steady shipments along one of the world’s most important transportation lanes.

Neptune Pass exists slightly outside those circumstances. The levee system ends more than 15 miles upriver, and the Mississippi runs wilder down there, breaking through its banks in several spots.

The pass had existed for years as a much smaller crevasse, but the high rivers of 2019 turned it into a full-scale blowout. It went from capturing around 6% of the river’s flow to roughly 16%, the Corps says.

So much of the Mississippi was being diverted that it slowed the current in the main channel, causing sediment there to drop to the bottom and build up. That forced the Corps to dredge in areas it hadn’t before to keep the channel deep enough for vessels.

The current sweeping into the pass also became strong enough that it posed a navigational hazard.

Earlier suggestions that it could be closed drew concern from coastal advocates. The pass was building land the way the river used to, amounting to several thousand acres so far, says Kolker.

Some of the new land has emerged above the surface, its muddy striations extending atop the water line, while other areas remain below, slowing accumulating.

‘Wear your loafers’

An earlier attempt at a compromise seemed to please few. Coastal advocates said it cut off too much of the sediment flow, while the positioning chosen for the sill meant the water could have eroded paths around it.

The Corps went back to the drawing board, but in the meantime twice put down blankets of rock to stabilize the bank and keep it from eroding further, amounting to nearly 150,000 tons at a cost of $6.7 million.

The new plan would involve a rock sill at the entrance of the pass with a notch in the middle to allow recreational boats, water and sediment to pass through. The notch would be 100 feet wide and 26 feet deep, sloping up on either end, eventually reaching five feet above sea level at the banks of the pass. A total of 168,000 tons of stone would be used.

An intriguing aspect of the new plan is what are known in engineer-speak as sediment retention enhancement devices, or SREDs, made with mud, fabric and stone. They would resemble terraces, forming giant Vs and stretching 300 feet long. They would be built in Quarantine Bay, where Neptune Pass leads, helping slow the flow of water and deposit sediment for land building.

A total cost or construction timeframe is not yet known.

The aim for the Corps is to return the flow of the pass to what it was prior to the 2019 blowout to address the threat to navigation, but the addition of the terraces adds a unique layer to the project.

“This kind of approach has been used to build land in coastal restoration projects,” Corps spokesperson Ricky Boyett said of the terraces. “We’re applying it to a navigation project, essentially.”

For coastal advocates, Neptune Pass is acting as a cost-free river diversion, similar to the nearly $3 billion artificial one, the Mid-Barataria Sediment Diversion , the state has planned on the opposite side of the river. They point to Neptune Pass as proof that such diversions work.

“You can walk on pieces of land where you would have been swimming five years ago,” said Karst. “So if you don’t believe the river can build land, go see it for yourself, and feel free to wear your loafers.”