Saltwater Wedge Moving Upstream On The Mississippi; 64 Miles Above The Mouth

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Already this summer, Plaquemines Parish, where the Mississippi meets the Gulf of Mexico, has been forced to provide bottled water to thousands of residents, as the area struggles with boil water notices and a constant threat of saltwater intrusion. “It’s been a trial beyond trials,” parish president Keith Hinkley told reporters at a recent news conference.

In a typical year, the flow of the Mississippi is generally sufficient to prevent salt water from intruding very far upstream. But several factors in recent months have allowed salt water to find its way at least 64 miles up the river so far.

In particular, the ongoing drought along the Mississippi means that without substantial rain further north, the river’s flow could soon reach as low as 130,000 cubic feet per second — close to its lowest recorded flow ever of 120,000 cubic feet per second in 1988. That year, the saltwater wedge stretched as far as Kenner, La., on the outskirts of New Orleans. The bottom of the river, which has been heavily dredged, is lower than sea level until it reaches Natchez, Miss. That topography also makes it easier for salt water to flow along the river bottom, underneath the less dense fresh water.

The underwater barrier that the Corps constructed in July is not unprecedented. It has undertaken similar work in 1988, 1999, 2012 and again in 2022, when a prolonged drought drove water levels on the Mississippi to historic lows. But as the current drought persists and the river’s flow weakens, Jones said, the Corps determined it had to do more to slow the influx of saltwater. Otherwise, he said, the saltwater wedge is on pace to continue upriver and expected to impact a freshwater intake facility at Belle Chase, La., in early October.

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https://www.washingtonpost.com/climate-environment/2023/09/21/saltwater-wedge-mississippi-river-drought/