A river gauge marks near record low water levels on the Mississippi River in New Orleans. It’s many feet lower than it would normally be and it’s creating all kinds of problems. L. Kasimu Harris for NPR hide caption
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L. Kasimu Harris for NPR
A river gauge marks near record low water levels on the Mississippi River in New Orleans. It’s many feet lower than it would normally be and it’s creating all kinds of problems.
L. Kasimu Harris for NPR
NEW ORLEANS – Ducks have perched on a strip of sand along the Mississippi River, a bank that is normally underwater.
“We have this beautiful beach here that black-bellied whistling ducks enjoy,” says Heath Jones, chief of emergency management for the New Orleans District of the U.S. Army Corps of Engineers.
The drought has dropped water levels to near-record lows in the Mississippi River. A river gauge near the corps headquarters registers only 3 feet above sea level.
“It’s getting close to some record lows that we’ve had here,” Jones said Oct. 19 as he watched from the river levee.
“As that flow in the Mississippi River goes down, it loses its ability to keep the salt water at bay,” said Heath Jones, director of emergency management for the New Orleans District of the Army Corps of Engineers. USA L. Kasimu Harris for NPR hide caption
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L. Kasimu Harris for NPR
The meandering Mississippi has a cool blue-green hue, unlike the muddy current that usually flows through.
More than a third of the rain in the United States ends up in the Mississippi River system. Jones says with little to no rain coming from the Midwest, the drought is causing problems along the river. Ships and barges are running aground and shipping is slowing up and down the busy maritime corridor.
Gulf salt is pushing upriver
Here in southern Louisiana, it is causing a unique phenomenon, changing the point where the freshwater river and the salt sea meet.
“As Mississippi River flows decrease, the Gulf of Mexico essentially moves upstream,” Jones explains.
Sand is driven from the bottom of the river to build an underwater levee on the Mississippi River in Plaquemines Parish, La. Team New Orleans; US Army Corps of Engineers hide caption
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Team New Orleans; US Army Corps of Engineers
A saltwater wedge has washed along the riverbed nearly 64 miles upstream from the mouth of the Mississippi.
“It’s almost like a triangle,” says Jones. “As that flow in the Mississippi River goes down, it loses its ability to keep saltwater at bay.”
Saltwater intrusion is threatening both municipal drinking water supplies in the New Orleans metropolitan area and commercial water users such as oil refineries that rely on freshwater from the Mississippi.
The biggest impact so far is in Plaquemines Parish with about 24,000 people and industries that depend on the water south of New Orleans.
“The Gulf is winning,” says Councilman Benny Rousselle.
The parish has declared a state of emergency and issued a drinking water advisory.
Rousselle says salt water has already compromised two of the parish’s treatment plants and is threatening a third.
“We’re bringing in some desalination units,” he says. “To be able to remove the salt and make water.”
Construction of a submerged dike to stop the salt water wedge
To save the largest plant in Plaquemines and protect the largest water system in Orleans Parish, the Corps of Engineers is trying to prevent salt water from invading further.
“We’re building, for lack of a better term, an underwater seawall,” says Jones. “We call it a saltwater sill, but it’s essentially a big pile of sand, a sand berm that stops the saltwater.”
The U.S. Army Corps of Engineers hired a contractor to build a submerged sill to prevent a saltwater wedge from invading municipal and commercial water intakes on the Mississippi River. Team New Orleans; US Army Corps of Engineers hide caption
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Team New Orleans; US Army Corps of Engineers
A contractor pumps sand from the river bed to create a submerged wall that stretches from one bank to the other across the Mississippi. The sill is built to allow 55 feet of clearance so that large ships can still pass through.
It’s hard to imagine being able to stop water from flowing over a deep dam, but Jones says the dense saltwater stays at the bottom of the water column.
“Golf doesn’t have the strength to push it over.”
Salt water comes upriver to some extent every year, but it has only threatened the water supply about every 10 years. The Corps built similar multimillion-dollar underwater seawalls in 1988, 1999 and 2012.
A taste of sea level rise
Some experts say saltwater intrusion could be a more frequent threat now that the Corps is dredging the Mississippi River even deeper for navigation, allowing saltwater to move faster. And then there is climate change.
“You’re really testing sea level rise,” says Mark Davis, director of the Tulane Institute on Water Law and Policy.
Mark Davis, director of the Tulane Institute on Water Resources Law and Policy. “You’re really testing sea level rise,” Davis says. “The more sea level rises, the more salt water comes in.” L. Kasimu Harris for NPR hide caption
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L. Kasimu Harris for NPR
Mark Davis, director of the Tulane Institute on Water Resources Law and Policy. “You’re really testing sea level rise,” Davis says. “The more sea level rises, the more salt water comes in.”
L. Kasimu Harris for NPR
“The more sea level rises, the more salt water comes in,” says Davis. “We made it easier this year because we recently dredged the mouth of the river to make it deeper, so bigger cargo ships can come in. And that just opens the door for even more salt.”
For now, the seawall will remain in place until the Mississippi River has enough flow to remove it.