Corps of Engineers planning further steps to slow saltwater wedge progression up Mississippi River

Published Sept. 15, 2023

The U.S. Army Corps of Engineers, New Orleans District, held a press conference Sept. 15, 2023, at their headquarters in New Orleans, La., to discuss planned efforts to address continued low-water conditions on the Mississippi River.

Col. Cullen Jones, USACE New Orleans District commander, briefed media on current steps the Corps plans to take to augment the existing underwater sill while working with the U.S. Coast Guard and navigation industry to maintain navigation along the Mississippi River. In addition, Plaquemines Parish President Keith Hinkley and Governor’s Office of Homeland Security and Emergency Preparedness director, Casey Tingle, spoke to media at the conference about steps to ensure safe and sufficient water supplies for parish residents.

“The current National Weather Service Mississippi River forecasts the river’s volume to fall to historic lows over the next several weeks,” said Jones. “If these conditions occur, the USACE-constructed saltwater barrier sill is expected to be overtopped by saltwater intruding upriver from the Gulf of Mexico, leading to unsafe salinity conditions at municipal water intakes located north of the sill location.”

Efforts under consideration include barging water downriver to municipal treatment facilities and placement of Reverse Osmosis Water Purification Units to allow for treatment of river water with high chloride levels. USACE has already issued a contract to place a reverse osmosis water purification unit at the East Pointe a la Hache Water Treatment Plant.

To mitigate for the Deep Draft Shipping Channel’s influence on the rate of upriver saltwater progression, USACE constructed an underwater barrier sill in July 2023 to create an artificial basin that delays the ingress of saltwater beyond river mile 64 above Head of Passes. An underwater sill was constructed on four previous occasions in 1988, 1999, 2012 and last year in 2022. During previous low-water events, such as 1988 and 2012, barging was used to transport fresh water to treatment facilities downriver of the saltwater wedge.

USACE continues to closely monitor, survey and model the impacts these conditions may have on the river with regards to both navigation and saltwater intrusion from the Gulf of Mexico. Saltwater intrusion is a naturally occurring phenomenon when the river flows fall below 300,000 cubic feet per second because the mass of fresh water is no longer capable of preventing saltwater from moving into the below-sea-level river channel. The current National Weather Service forecast projects river levels falling to approximately 130,000 cubic feet per second in the New Orleans area. These levels represent the lowest river volume in this area since the recorded low of 120,000 cubic feet per second in 1988.

“This low-water event marks the first time underwater sills were required in back-to-back years as a result of saltwater intrusion from the Gulf of Mexico,” Jones added. “However, the New Orleans District is ready to meet this challenge with the best science, engineering data, and technology available.”

Ryan Labadens