With water rising and forecasters predicting more rain, the U.S. Army Corps of Engineers said Thursday it expects to begin opening one of its emergency relief valves on the lower Mississippi River next week.
The Corps could open flood gates at the Bonnet Carre' Spillway as early as next Wednesday. It would be the 13th time to flood the spillway and mark the first time since the concrete diversion structure was built in 1931 that it was used two years in a row. The Bonnet Carre' also was opened in 2016 — meaning it will have been opened three times in four years.
"Unless something significant changes, operation of the spillway will be recommended," said Ricky Boyett, a spokesman for the Corps' New Orleans district. "We're trying to pin down when."
The spillway is opened when the water flow in the Mississippi reaches 1.25 million cubic feet per second in front of the structure 23 miles west of New Orleans. Boyett said the levee system downstream of the Bonnet Carre' and past New Orleans isn't designed to handle water flow of more than 1.25 million cubic feet per second.
Boyett said continued rain in the Mississippi and Ohio river valleys has made water levels higher than normal for February.
More typically, the spillway has been opened during the traditional spring time high water between late March and May. But in recent years, the spillway has been opened early, including in March last year and in January 2016.
"It's becoming more and more frequent to have higher water earlier," Boyett said.
He added that, at this time, there are no plans to open the Morganza Control Structure north of Baton Rouge. Located in Pointe Coupee Parish, that spillway on the west bank of the Mississippi was last opened in 2011 and, ultimately, diverts water into the Atchafalaya River and its swamp basin.
Located in St. Charles Parish near Norco, the concrete Bonnet Carre' control structure has 350 bays with 7,000 wooden needles that largely hold back river water until removed.
Once opened, the bays allow river water to flow across a 7-mile stretch of land into Lake Pontchartrain and away from the lower river's channel. The overland section of the spillway has guide levees that run between the diversion structure on the river and the lake. They contain and route the river water.
Boyett said the wooden needles at the diversion structure are removed gradually, ensuring river flow downstream of the spillway remains below 1.25 million cubic feet per second. Fully opened, the spillway can divert 250,000 cubic feet per second from the Mississippi.
He said the current river level at the Carrollton gauge in New Orleans is 14.9 feet. At 15 feet, the Corps would restrict activity on or around levees.