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The Army Corps of Engineers pull pins to open bays of the Bonnet Carre Spillway to deal with a rapidly rising Mississippi River in Norco, La. Wednesday, Feb. 27, 2019. The spillway reroutes water from the Mississippi into Lake Pontchartrain, where it then flows into Mississippi Sound and the Gulf of Mexico. The Army Corps of Engineers opened 28 bays of the spillway.

The swollen Mississippi River may be cresting in New Orleans, but water levels likely won’t fall back to normal for weeks to come.

Officials had hoped the river would start to subside soon, but storms and snowmelt to the north now have forecasters suggesting the river will remain high for another month or longer.

“Hopefully, Mother Nature will be kind to us for the rest of the year, but certainly we have a bit more water to potentially go,” said Jeff Graschel, a hydrologist at the Lower Mississippi River Forecast Center in Slidell.

On Tuesday, the river was about 16.8 feet above sea level at the Carrollton gauge in New Orleans, just a couple inches shy of the height the U.S. Army Corps of Engineers has set as its upper acceptable limit. That was due in large part due to heavy storms in the Ohio River Valley, where some areas saw between 10 and 30 inches of precipitation over two months, and the upper Midwest.

To keep the river level 3 feet below the 20-foot-high levees that protect New Orleans, the Corps began opening bays in the Bonnet Carre Spillway in late February to divert water from the river into Lake Pontchartrain. It was the 13th time the structure has been used in its nearly 90-year history and an unprecedented third opening in four years.

Bonnet Carre Spillway to be opened Wednesday; experts say climate change fuels high water levels

About 200 bays of the spillway are open, with each of them carrying about 1,000 cubic feet of water per second away from the river.

While water levels are projected to start subsiding in a week or two, the reprieve will be brief.

Storms over the next several days are expected to dump more water across the Midwest, Graschel said. At the same time, the heavy snows of this past winter are starting to melt and flow through the Mississippi River’s massive basin toward its mouth in Louisiana.

It’s not yet clear exactly what effect that will have on the river, Graschel said, because the exact amounts of rainfall and snowmelt are still unknown. At this point, forecasters expect the crest upriver to be slightly lower than it is now, he said.

Bonnet Carre Spillway opens along Mississippi River for third time in four years

Even once that crest passes sometime in the next month or two, it won’t mean the New Orleans area will be totally out of the woods. More melting snow and storms could mean yet another rise in water levels later in the year, Graschel said.

“We’re still susceptible to having more flood events on the Mississippi River over the next few months,” he said.


Follow Jeff Adelson on Twitter, @jadelson.​