Mississippi River ships and barges carry over 500 million tons of cargo through the Southwest Pass shipping channel at the river’s end to reach major ports that handle 18% of U.S. waterborne commerce. For almost 100 years, levees and other human-made flood control structures have lined the banks of the river, obstructing its land-building silt, sand and clay from naturally rebuilding land along coastal Louisiana.

That sediment is essential to rebuilding – or at this point, maintaining – the fragile coastline that has been receding for decades. Without it, the small towns that dot the lower part of the Louisiana Gulf Coast are left exposed, with no protection against storm surges and hurricane-strength winds. But to reverse coastal erosion, scientists found that they first had to understand where sediment that could be used to rebuild settles instead.

Most of the year, less than 10% of the river’s sediment reaches the critical Bird’s Foot Delta, according to scientists from the Mississippi River Delta Transition Initiative, known as MissDelta. The bird’s foot—at the southernmost reach of the river system that juts into the Gulf of Mexico—plays a vital role in coastal protection, navigation, fisheries and energy infrastructure.

In 2023, MissDelta launched a $22 million, five-year research project spearheaded by Tulane University and Louisiana State University, and funded by the National Academies of Sciences, Engineering and Medicine. The study aims to evaluate the Delta and Southwest Pass, the critical navigation channel, with hopes of finding management approaches that will benefit both the delicate ecosystem and the people who live and work in the delta region, including fisherpeople, charter-boat operators, offshore workers, shipyard builders, mechanics and petrochemical-facility operators. 

During the first year-and-a-half of the study, researchers measured discharge by plunging a 200-pound sampler into the river at various depths. By tracking sediment from the sampler, the team can measure how much settles in the wetlands upriver versus how much exits into the deepwater Gulf, said Claire Kemick, a Tulane graduate student working to collect the samples.

The study’s early findings, announced at Louisiana’s State of the Coast conference, show that the Mississippi River loses substantial amounts of water and sediment above what’s called the Head of Passes, at the mouth of the river, where the Mississippi forms its distinct bird’s foot by branching into three directions: the Southwest Pass shipping channel (west), Pass A Loutre (east) and South Pass (center). 

That means the Bird’s Foot Delta is headed toward further degradation, after losing ground for decades, said Mead Allison, co-lead of MissDelta and a professor in Tulane’s Department of River-Coastal Science and Engineering.

Above the Head of Passes, substantial amounts of sediment carried by the Mississippi River are lost through both natural and man-made channels, such as the rapidly expanding Neptune Pass near Buras, Louisiana, in lower Plaquemines Parish. But most is lost well before then.

Using data on sediment movement, the team can calibrate models to predict what will happen to the delta by 2100 under different scenarios, with varied sea-level rise, storm frequency and river-flow fluctuations. Once the researchers develop the models, they will use them to test various interventions that could save the delta, such as closing river exits and changing water-flow patterns.

In the fall, the MissDelta team will return to lower Plaquemines Parish to study the saltwater wedge that creeps up the river during low flow periods. For three years in a row, the wedge of heavy salt water has crept up the river underneath the fresh water, imperiling drinking water in the greater New Orleans area.

The goal is to find management approaches that can help build up this region, which Allison has called one of the most threatened places in the nation, if not on Earth.

But they cannot forge management solutions without an understanding of how the muddy Mississippi carries its load of sandy sediment in the lower delta. “Right now, we don’t know very much about where the sediment is in the Lower Mississippi River,” Kemick said. Further research will help determine where the coarse sand is settling in the riverbed.

Sediment loss is especially high during low or average river flow, when the water is traveling slowly enough to allow the heavy sand particles to sink to the bottom. When the river floods, the faster-moving river brings sand from throughout the drainage basin to Louisiana. But it doesn’t necessarily help to build up the Bird’s Foot area. Instead, it falls out in the channel, creating a need for more dredging to maintain the ship route.

The Mississippi River’s sediment is an important resource for coastal restoration, Allison said. “Sand is white gold for Louisiana. We need to keep it.” 

The Louisiana Coastal Master Plan was built upon this principle, with an ambitious plan for a sediment diversion, the Mid-Barataria Sediment Diversion, that would be one of the largest environmental infrastructure projects in the history of the U.S.

But the U.S. Army Corps of Engineers has suspended the permit to build the keystone project.

On Wednesday, more than 50 Louisiana business and civic leaders sent a letter to Gov. Jeff Landry urging him to resume construction of the Mid-Barataria Sediment Diversion at the size and scale that it was designed and permitted for.

“These business and civic leaders are part of the backbone of Louisiana—people who live, work, and invest in this region every day,” said Simone Maloz, campaign director for Restore the Mississippi River Delta. “Delaying or downsizing the Mid-Barataria Sediment Diversion threatens not just our coast, but our economy, our safety and our credibility as a state.”

Conversations about the Mid-Barataria Sediment Diversion were absent from this year’s State of the Coast conference, an interdisciplinary forum hosted by the Coalition to Restore Coastal Louisiana.

“In some ways, I feel like Mid-Barataria is kind of haunting this conference,” said Alisha Renfro, a coastal scientist with the National Wildlife Federation. She is hopeful that Louisiana can find a pathway to resume the project, after investing $500 million into planning. 

The state is also in danger of losing billions in federal funding if its leaders don’t commit to finishing the construction.

It may be time to look for alternative coastal restoration projects, some scientists say. For Allison, that means not only determining how the Mississippi River sediment moves now but also where dredged sand could best restore coastal wetlands like the Barataria Basin. 

Currently, dredge spoil used for coastal restoration remains relatively close to where it came from in the river. In the Barataria Basin, one project to restore approximately 302 acres of brackish marsh known as Bayou Grande Cheniere required nearly eight miles of pipes to move the sediment.

Other solutions might involve closing gaps where sediment leaks out before reaching the Bird’s Foot Delta. The Army Corps is essentially testing this theory now, Allison said, with its plan to reduce the flow at Neptune Pass, a nearby branch in the river that is creating new land in Quarantine Bay.

The plan could boost land-building in the Barataria Basin, Allison said. While the Army Corps proposes using rocks to limit the size of the channel’s entrance and minimize the risk of navigational hazards, the construction at the outflow could reinforce the crevasse’s land-building power, he said. 

In addition to building sediment retention structures, the Army Corps could pump sand out of the river and place it directly at the outflow of the channel, allowing the water to redistribute it into a more natural wetland building pattern. 

“It’s really encouraging that the Corps is thinking about these forward-looking strategies to better use dredged material,” Allison said.

This story is a product of the Mississippi River Basin Ag & Water Desk, an independent reporting network based at the University of Missouri in partnership with Report for America, with major funding from the Walton Family Foundation.