The Mississippi River south of New Orleans is extremely low and projected to drop lower by the end of July, posing a second year in a row of threats to local public water supplies from saltwater moving north from the Gulf of Mexico.
With the leading toe of a wedge of saltwater estimated to already have crept north to mile 44.2 above Head of Passes, or near Port Sulphur, the Army Corps of Engineers has kicked off planning efforts to block it from reaching the water intakes for the public water supplies in Belle Chasse and Chalmette.
Saltwater already has reached the intakes of Plaquemines Parish's Boothville water plant, driving up the amount of sodium and chloride, the two minerals that make up salt, in water going to homes and businesses in the southern part of the parish's west bank.
The contamination prompted the parish to issue an advisory on June 21 to residents between the Empire Bridge to Venice who may be on dialysis or low-sodium diets and subject to sodium and chloride restrictions.
At-risk residents should check with health care providers, the notice said.
The parish and the Governor's Office of Homeland Security and Emergency Preparedness are also distributing water and ice at the Boothville-Venice and Buras fire stations, with a limit of two cases of water per household per day.
Between 16 and 19 pallets of water are available daily and the parish is attempting to arrange for water "buffaloes," or tankers, to be located at the stations in the near future. Questions about the advisory should be directed to the parish's water supply contractor, Inframark, at 504.392.4177.
The water plant across the river at Pointe a la Hache has not yet been affected by the intrusion, said parish spokesperson Shannta Carter.
Carter said Inframark is attempting to locate a "reverse osmosis unit" that can remove salinity from water to be installed at the Boothville plant. The parish's engineering department also is working to repair the Port Sulphur Water Treatment Plant, which was damaged during Hurricane Ida.
"If the repairs at the Port Sulphur location can be completed without interference from the intrusion, the treatment plant would be able to produce enough water to serve the entire southern part of the parish," Carter said.
She said the parish also is looking into installing a temporary booster station near Alliance to move water from Belle Chasse to Venice. Residents from Belle Chasse to the Empire Bridge already are serviced by the Belle Chasse plant, which would expect to be protected if the Corps decides to build a sill in the river to block the advance of saltwater.
She said the parish also is working with the Corps and the state to identify additional short-term and potential long-term fixes "to what might become an annual issue."
Brown waterlines are visible on the moorings around where people board the Canal Street ferry on a low Mississippi River in New Orleans on Thursday, June 29, 2023. (Photo by Chris Granger | The Times-Picayune | NOLA.com)
Saltwater wedge
The amount of freshwater moving south in the river is not enough to stop heavier saltwater from the Gulf from moving upstream, creating a wedge of advancing saltier water.
The Corps had a survey vessel in the river on Thursday to confirm the location of the toe of saltwater, said Ricky Boyett, a spokesperson for the agency's New Orleans office.
"We will combine this real-world data with the National Weather Service's current forecast to identify the projected upriver movement/pace of the saltwater wedge," he said. "As of Tuesday, we had not reached the trigger, but conditions continue to evolve."
On Friday, the weather service's Lower Mississippi River Forecast Center measured the water level at the Carrollton Gauge in New Orleans -- at the Corps headquarters building at Riverbend -- to be 2.8 feet, and forecast it to drop to 1.9 feet by July 28.
The Corps uses that information -- and water heights at Belle Chasse -- to determine if and when the main saltwater wedge will reach river mile 80, or if the toe of the saltwater will reach mile 65 near Myrtle Grove within 10 days. If either occurs, the Corps will have a contractor build a sill -- an earthen dam -- across the deepest part of the river just above Myrtle Grove.
Last year, the Corps contracted with a dredge company to build a 1,500-foot-long underwater sill in the same location. The river at the Myrtle Grove location is around 90 feet deep.
The sill last year was not high enough to affect the largest ocean-going vessels, whose hulls can reach as much as 50 feet below the surface. It eroded when freshwater flow in the river increased in the fall and winter months.
A spokesperson for the Port of New Orleans said low water levels have not yet affected shipping in the port.
"We are actively monitoring and proactively dredging to reduce any impacts," said Kimberly Curth.
Blame this year's low river on a lack of rainfall in the Missouri, Mississippi and Ohio valleys during the past five to six weeks, according to Jeffrey Graschel, a hydrologist with the lower river forecast center.
"The lack of rainfall is attributable to more of a stagnant weather pattern, which has steered rainfall more over the Rockies and southeast U.S.," he said.
That pattern includes the present huge dome of high pressure that also is causing record-breaking heat in Texas, Louisiana, and the middle Mississippi Basin. The high pressure also blocks the creation of rain-carrying clouds.
Graschel said forecasters remain unsure when rainfall levels along the upper river will increase enough to boost river levels in the New Orleans area.
"We are getting indications over the next couple of weeks that better chances of rainfall will occur over the Midwest," Graschel said. "It is too soon to know exactly how this will impact the river, since soil moisture conditions are very dry, but any rainfall will be beneficial."
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Mississippi River is extremely low again and dropping, threatening local water supplies - NOLA.com
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