The Mississippi River's rapid rise in the coming days is expected to lead to precautions undertaken by the Army Corps of Engineers and local officials, including preparations for a possible , though projections so far indicate it won't be necessary.
Storms in parts of the South and Midwest have caused the river to swell, and those waters are making their way to Louisiana. Projections are showing the river cresting in New Orleans around April 25, lasting around five days.
A river flow rate of 1.25 million cubic feet per second triggers a Bonnet Carre opening, and that tends to correlate to 17 feet on the Carrolton gauge in New Orleans, or roughly 17 feet above sea level. Current projections are showing it top out just below that, at around 16.5 feet, though the margin of error includes levels above.
Corps spokesman Ricky Boyett said National Weather Service forecasts do "not indicate operation of the Bonnet Carre’ Spillway at this time, though I will note that forecasts change daily as better information becomes available. A recommendation to operate the Bonnet Carre is based on actual river flow measurements."
Louisiana state climatologist Jay Grymes had earlier Friday indicated the Corps was evaluating the possibility of a possible partial spillway opening "for upwards of nine days" later this month. But Boyett said the Corps prepares for it in case needed when the river rises as it is now to ensure it is ready to act if necessary.
Any spillway opening, if it would occur, may be relatively short-lived since the river is expected to gradually fall soon after its crest. Bonnet Carre has not been opened since 2020.
"Fortunately, the forecasted crests along the lower Mississippi are expected to give way to slow-but-steady falls during the final week of April," Grymes said in an email update on river levels. "That will limit the duration of openings at Bonnet Carre."
The Corps has already projected that it will enter what is known as a phase I flood flight on Monday, which means inspections of the levee system twice per week for potential seepage or other concerns. Unauthorized subsurface work within 1,500 feet of levees is banned during phase I, which is triggered when the Carrolton gauge reaches 11 feet.
Aerial of Interstate 10 looking west as it crosses Lake Pontchartrain at the Bonnet Carré Spillway, seen Friday, September 13, 2024, in Kenner, La.
Bonnet Carre, located in St. Charles Parish, connects the river to Lake Pontchartrain through a floodway and bays that are opened when needed. It was built as part of the levee system along the river following the great flood of 1927, which severely inundated Louisiana communities.
It has been opened 15 times, including twice in 2019 due to heavy rains that year in the Ohio and Mississippi river valleys. The river rises in the late winter and spring due to seasonal rains and snow melt flowing down from the Midwest.
Opening the spillway relieves pressure on the levees, a key flood-protection measure in south Louisiana. But the influx of fresh water into Lake Pontchartrain, through the Rigolets and out to the Gulf can damage commercial shrimp and oyster fisheries, which has in the past led to declarations of emergency as a result.
The Mississippi drains more than 40 percent of the contiguous United States.
