The lower Mississippi River delta is facing unprecedented threats, from hurricanes, rising seas, ground subsidence, diminishing river sediment, coastal dead zones – and decades of dredging. Because of dredging, the bed of the Mississippi River in southern Louisiana is so far below sea level and this year’s historic drought has driven water flow so low that the river can’t push back against salt water flowing in from the Gulf of Mexico.
Like many of the river’s other threats, this one is not unpredictable: it’s been on the horizon for decades, as the river’s navigation channel was increasingly dredged to accommodate larger and larger ships.
Nearly three decades ago, in 1987, environment writer John McPhee wrote about the danger this dredging posed. The U.S. Army Corps of Engineers has also long known that dredging left the river more vulnerable to saltwater intrusion. The threat was a “trade-off” for keeping the river’s ports competitive, wrote Chris Accardo, retired chief of the operations division for the New Orleans District Corps of Engineers, last week, in a letter that noted his agency’s openness about the situation.
“In fact, the Corps have said that a deepened river along with drought conditions have caused this current problem,“ Accardo wrote.
This summer, while actively planning for worst-case saltwater solutions in the lower river, the Corps’ New Orleans District announced the launch of a five-year, $25 million mega-study to examine and offer management recommendations for issues like this and “the change in river dynamics” for an area spanning from Cape Girardeau, Mo. to the Gulf.
A new consortium led by Tulane University and Louisiana State University, is also launching its own five-year study – thanks to a $22 million award announced today by the National Academies of Sciences, Engineering and Medicine – to increase the sustainability of the lower Mississippi River delta and the economy that relies on it.
The study by the new Mississippi River Delta Transition Initiative, or MissDelta, will focus on a narrower span of the lower Mississippi, stretching from New Orleans to the river’s end, the Bird’s Foot Delta at the Gulf of Mexico. (The Corps’ study includes an additional 1,000 miles of river up to Missouri.)
The initiative will forecast effects on the disappearing delta through the year 2100 – and then use models to test varying plans to reverse those effects, said Mead Allison, a consortium co-lead and chair of Tulane University’s Department of River-Coastal Science and Engineering.
“What’s really unique about this project is that it’s not just modeling water and sediment, it’s also economic and socioeconomic modeling,” Allison said. Information gleaned from the models will be used to predict the economic effects of different solutions, on jobs and industry within the region.
The team will include 38 investigators from research institutions and the National Academies’ Gulf Research Program, working in partnership with the Louisiana Coastal Protection and Restoration Authority and the U.S. Army Corps of Engineers, among others.
The consortium will include six historically Black colleges and universities in Louisiana and Mississippi—Southern University of Baton Rouge, Xavier University of Louisiana, Jackson State University, Grambling State University, Dillard University and Alcorn State University—as well as researchers from the nonprofit Water Institute of the Gulf, the Louisiana Universities Marine Consortium (LUMCON) and four other Southern schools: the University of Southern Mississippi, the University of Central Florida, the University of Louisiana at Lafayette and the College of William & Mary in Virginia.
A major portion of the funding will be directed toward creating a more diverse, technical workforce. The universities will create a mentoring network with middle and high schools to increase the number of persons from under-represented groups participating in coastal research programs.
The hope is that the five-year study and mentoring program will inspire young scientists and encourage them to stay and build careers within the delta, Allison said.
Over the next five years, said Col. Cullen A. Jones, commander of the Corps’ New Orleans District Corps of Engineers, the two studies will collectively study their sections of the river. Together, he believes, the teams of researchers can identify the best long-term management approaches for the river, so that it can continue to serve as an important commercial waterway, water supply, and ecological corridor for birds, fish, wetland plants and wildlife.
Shipborne Commerce and the Saltwater Wedge
In the time since McPhee wrote about the struggle to control the Mississippi River, the Army Corps has kept shipborne commerce booming through dredging the river’s navigation channel and ensuring that the Atchafalaya River did not overtake the Mississippi as the master stream. If nature had taken its course, the river would have spilled back towards the west, through the Atchafalaya, creating a shorter route to the Gulf of Mexico.
Each day, vessels traveling along the Lower Mississippi delta carry freight valued at approximately $300 million; the loads include 60% of the nation’s global grain exports.
River traffic began facing low-water effects as the multi-year drought in the Mississippi River Basin began three years ago, in late summer 2020.
As river levels fell and channels narrowed, barge operators had to reduce the loads and number of barges included in each tow. Record low flow along the Mississippi has led to a severe disruption in grain transported by barges for export, according to research published in farmdoc daily in 2022.
This year, as water levels moved lower and lower, the drought’s interruptions worsened, impacting both the southbound shipment of corn and soybeans from the nation’s heartland and the northbound shipment of fertilizer produced in Louisiana. Thus, for industry, it was essential that shipborne commerce was impacted as little as possible by the Corps’ efforts to prevent the intrusion of saltwater, which included a “sill” built downriver to raise the river’s floor, blocking the saltwater “wedge.” (Salt water is heavier than fresh water, so the saltwater wedge persists along the bottom of the river; the intent of the underwater dam is to block the heavier salt water without interrupting the river’s upper currents.)
To block the Gulf’s salt, the Corps has had to fight ardently against nature. The first underwater dam, built in Plaquemines Parish to stop a saltwater wedge headed upriver, was built in 1988. A second dam followed in the same location in 1999. Another sill was built in 2012. Then, again last year, the Corps constructed a sill as drought threatened Plaquemines’ drinking water.
As the drought reached full throes this summer, in July 2023, the Corps built an underwater levee on the river bottom near Myrtle Grove that was 35 feet high, or 55 feet below the surface – low enough to not obstruct ocean-going ships but high enough that it could conceivably block the heavy salt water from moving upriver.
But on September 20, salt water overtopped the 35-foot sill, sparking fears that the drinking water could be contaminated as far upriver as the French Quarter, approximately 95 miles. Within the next month, the Corps raised the earthen sill by about 25 feet. Instead of being 55 feet below the river’s surface, it is now only 30 feet down. A notch was left at the original 35-foot height in the middle to allow ships through.
In recent weeks, the Saltwater Wedge forecast has continued to ease, relieving residents as far south as the Dalcour water treatment facility at river mile 81, which is no longer in the danger zone, as of Oct. 26. In the most recent field measurement on Oct. 22, the toe of the wedge sat at river mile 65.8.
By mid-October, salt water was originally expected to reach Belle Chasse, which stands about 75 miles from the mouth of the river. That date has now been pushed back to November 30.
Many lower-river communities have been affected, however. Salt water has already reached the Boothville, Port Sulphur and Pointe a la Hache water treatment facilities. The Corps has barged fresh water to these treatment plants, where it’s blended with the seawater in an effort to bring it back within treatable levels, before it goes through the plants and is piped out to residents. The plants have also set up temporary reverse osmosis units to filter out the high levels of salt.
Water-treatment facilities use a disinfection process that isn’t safe when the water being treated is too salty. Recent state testing in lower Plaquemines Parish has shown a spike in two groups of chemicals that result from disinfecting river water mixed with seawater. Reporting by The Guardian found that in the Port Sulphur water district, toxic chemicals left behind from the disinfection process had significantly increased in tap water during the month of September.
Reverse osmosis and microfiltration machines, recently installed at the Pointe a la Hache and Port Sulphur water treatment plants, should reduce the amount of organic matter in the water and in turn reduce the toxic chemicals left behind after disinfection.
Plaquemines Parish is looking for more permanent solutions for treating increasingly salty drinking water. Parish President Keith Hinkley said improvements at the three water treatment plants could run as high as $300 million, to install permanent reverse-osmosis equipment to remove salt and replace pipes damaged by the salt water.
Yet all of these extensive modifications address only one of the threats to the lower Mississippi River: saltwater intrusion. There is much more to be addressed.
Over the next five years, the MissDelta researchers will identify the critical issues affecting people and industry within the area and then draft recommendations for decision-makers.
Within the new consortium, there is confidence that their work – identifying each issue and its possible solutions – can prevent some conditions from reaching crisis level.
“We’re moving into a brave new world of more science-based, proactive management of the river, by a more diverse and culturally anchored research community than ever before,” said Samuel Bentley, a consortium co-lead and endowed professor in Louisiana State University’s Department of Geology and Geophysics.