Latest saltwater wedge forecast released by USACE

For Immediate Release:
Oct. 12, 2023
Public Affairs: Ricky Boyett
(504) 862-1524

Additional treatment facilities may not experience chloride levels that exceed 250 parts per

NEW ORLEANS – The U.S. Army Corps of Engineers, New Orleans District released today the
latest Saltwater Wedge Timeline forecast of when water treatment facilities may be impacted by
saltwater intrusion.
USACE uses the National Weather Service 28-day Lower Mississippi River forecast, daily river
observations and computer modeling to project the progression of the saltwater intrusion as it
relates to the multiple municipal water treatment facilities along the river.

Updates based on the latest forecast:
1. Boothville: No change
2. Port Sulphur: No change
3. Pointe A La Hache: No change
4. Belle Chasse: Oct. 27 (previously Oct. 13)
5. Dalcour: Nov. 1 (previously Oct. 17)
6. St. Bernard: Nov. 8 (previously Oct. 28)
7. New Orleans Algiers: Not anticipated to experience chloride levels exceeding 250 ppm
(previously Nov. 23)
8. Gretna: Not anticipated to experience chloride levels exceeding 250 ppm (previously Nov. 26)
9. West Jefferson: No change
10. New Orleans Carrollton: No change
11. East Jefferson: No change

The updated Saltwater Wedge Timeline is available on the New Orleans District website
The change in forecast is largely the result of augmentation of the existing underwater sill and
increased flows of the Red River, requiring less diversion at the Old River Control Structure.
Augmentation of the underwater sill, constructed in July, began in late September. As of this
week construction has brought the sill up from an elevation of -55 to -30 feet from the river
surface, while maintaining a channel at -55 for deep draft navigation on the Mississippi River.

In addition to the sill augmentation, rainfall in the Red River Basin has increased flows on the
Red River. The combined flows of the Mississippi and Red Rivers are used to calculate the
Congressionally authorized 70/30 distribution at the Old River Control Structure. With increased
flows on the Red River, less water is required to maintain the authorized distribution at Old
River Control Structure allows for greater flows down the Mississippi River.
The combination of the sill augmentation and increased river flows has led to a regression of the
saltwater wedge upriver from the sill. The toe of the saltwater wedge was measured on Oct. 9 at
river mile 63.9, the approximate location of the sill.

The new forecast shows delayed impacts at facilities upriver, but water treatment facilities in
Plaquemines Parish is still impacted by the saltwater intrusion. The impact date for the Belle
Chase treatment facility is now forecast for Oct. 27, about two weeks later than the previous
forecast. Treatment facilities in Port Sulphur and Pointe A La Hache are currently experiencing
impacts from saltwater intrusion.

USACE began barging water to the Port Sulphur and Pointe A La Hache treatment facilities to
blend with water from the intakes to bring the chloride down to treatable levels. To date, USACE
has delivered more than 9 million gallons of water. USACE has also mobilized Reverse Osmosis
Units to support processing at water treatment facilities impacted by saltwater intrusion.
The intrusion of salt water into the river is a naturally occurring phenomenon because the bottom
of the riverbed between Natchez, Miss., and the Gulf of Mexico is below sea level. Denser
saltwater moves upriver along the bottom of the river beneath the less dense freshwater flowing
downstream. Under normal conditions, the downstream flow of the river prevents significant
upriver progression of the salt water. However, in times of extremely low-volume water flow, such
as what has been occurring this year, unimpeded salt water can travel upriver and threaten
municipal drinking water and industrial water supplies. An underwater sill was constructed on
four previous occasions in 1988, 1999, 2012, and last year in 2022.

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