Corps Revises Lower Mississippi River Salt Water Intrusion Forecasts Again
Although the Mississippi River remains extremely low, flows below Baton Rouge, along with mitigation efforts by the New Orleans Engineer District, continue to hold at bay salt water intruding up the river from the Gulf of Mexico.
For the past week, the leading edge of the salt water wedge has been at Mile 63.9 on the Mississippi River, just below a sill the New Orleans District has built to a depth of -30 feet, with a notch in the middle to -55 feet.
Each day the salt water is held back is a day closer to traditional high water on the river, and with it flows necessary for pushing salt water below communities in South Louisiana that use the Mississippi River as their source for fresh water. According to the Corps, a flow rate of about 300,000 cubic feet per second (cfs.) is needed to flush the river of the salt water.
Based on the National Weather Service’s 28-day Lower Mississippi River forecast, St. Bernard Parish is no longer expected to experience chloride levels above 250 parts per million, the upper boundary for safe drinking water. Municipal intakes at Algiers, Gretna, West Jefferson, New Orleans and East Jefferson are also expected to avoid unsafe chloride levels.
The Corps has pushed back estimates for communities below St. Bernard Parish by about two weeks. The Dalcour community is expected to see unsafe chloride levels around November 18 (previously November 1), and Belle Chasse is expected to cross that threshold on about November 13 (previously October 27).
The communities of Pointe à la Hache, Port Sulphur and Boothville, all in Plaquemines Parish, are already dealing with unsafe chloride levels—and have been since early summer. To mitigate elevated chloride levels in the river, the state has been providing bottled water, while the Corps has assisted in delivering water by barge and in securing reserve osmosis systems.
According to the district, the Corps has delivered more than 23 million gallons of water to those communities thus far.
As of October 19, the Mississippi River gage at Carrollton Avenue in New Orleans was at just above 2 feet, with a three-tenths of a foot rise over the previous 24 hours. The latest flow rate at Belle Chasse was about 189,000 cfs.
