Saltwater creeping up the Mississippi River from the Gulf of Mexico threatens drinking water supplies in southeast Louisiana, including New Orleans, and has set off a scramble by officials to avert a crisis.
Freshwater in the Mississippi River, which courses through 10 states, is a source of drinking water for many Louisiana communities.
The U.S. Army Corps of Engineers built an underwater barrier called a sill to slow the movement of saltwater upriver in July. But saltwater spilled over the top of that barrier on Sept. 20.
The Corps is now making the sill 25 feet taller to give local officials another 10 to 15 days to prepare for saltwater to arrive.
“It is a means of buying additional time,” said Ricky Boyett, public affairs chief for the U.S. Army Corps of Engineers’ New Orleans district. “It’s not going to stop it.”
The saltwater is forecast to reach Belle Chasse, slightly downriver of New Orleans, in mid-October. The new saltwater barrier will reach a height of 30 feet below the river’s surface.
A navigation channel will remain deeper to allow ocean-bound vessels to keep moving. Ship traffic in that area will be reduced to one lane, which will impede the flow of goods from the Heartland to ports during harvest season, Boyett said.
Saltwater has moved up the Mississippi River before. The Corps previously constructed saltwater barriers in 1988, 1999, 2012 and 2022, when low-water conditions grounded barges along the Mississippi.
Big storms such as hurricanes can help alleviate the saltwater intrusion. But Joshua Lewis, a professor of river and coastal studies at Tulane University’s ByWater Institute, said this year’s incident could last longer than the one in 1988, given that there is little rain in the forecast.
The flow of freshwater down the Mississippi typically stops the saltwater from flowing upstream. But a second year of dry conditions has reduced the Mississippi’s flow to about half the rate needed to keep saltwater in the Gulf.
As soon as this week, the Corps will be able to move about 15 million gallons of freshwater downriver a day by barge, and eventually wants to move 36 million gallons a day. It used barges to move water in 1988 and 2012, Boyett said.
The water will be mixed with river water at the intake points of water treatment plants to reduce overall salinity, said Mike Steele, a spokesman for the Louisiana Governor’s Office of Homeland Security and Emergency Preparedness.
If salinity levels exceed the Environmental Protection Agency’s maximum standard of 250 milligrams per liter, it would risk corroding water distribution systems, machinery and appliances, state officials said.