Rising Mississippi prompts Bonnet Carré Spillway opening

With the Mississippi River predicted to crest at Baton Rouge, La., Jan. 18 – and possibly stay at the 17’ flood stage at New Orleans into early February – the Army Corps of Engineers opened the Bonnet Carré Spillway into Lake Pontchartrain Sunday morning.

The earliest winter flood stage in living memory prompted the earliest calendar date opening for the spillway since it was built in 1931, as part of the massive federal engineering response to the flood disaster of 1927.

Engineers invited the public to witness the opening, with cautions. “If you come out please leave your drones, kayaks, jet skis, and wading boots at home,” the Corps’ New Orleans district office posted on its Facebook page.

Twenty bays were opened in the spillway structure Sunday, with 10 more to be opened Monday. The spillway is used in effect as a relief valve, to hold the river flow at 1.25 million cu. ft. per second in flood stage.

For two weeks the Corps has been preparing river interests about its planned response to historic river levels coming from weeks of rain storms, with 10” to 15” above-average rainfall, across the upper river watershed. Col. Rick Hansen, the New Orleans District commander, met last week with river communities to talk about possible impacts in floodways and the Atchafalaya River basin.

It appears the river crest on the lower Mississippi River this week can be managed without opening the Morganza Control Structure, according to new data and modeling, said Maj. Gen.Michael Wehr, commanding general, U.S. Army Corps of Engineers Mississippi Valley Division.

“The latest information indicates that theriver crest can be safely passed through South Louisiana without operation ofthe Morganza Control Structure,” Wehr said.

That means there will not be an additional diversion into the Atchafalaya Basin, but high water still will be significant there, the Corps says. Water levels for the basin are expected to reach 20’ around Jan. 17 at Butte Larose, and 8’ around Jan. 21 at Morgan City.

The Morganza Spillway in Pointe Coupee Parish Control Structure is designed to be activated when the river reaches 57’ at the structure, and when flow is forecasted at 1.5 million cu. ft. per second and rising. That 57’ river height is expected Jan. 15, but the flow is projected to be 1.44 million cu. ft. per second two days later, within the design capacity for Mississippi River levees to hold between the Morganza andthe Bonnet Carré Spillway.

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Ashley Herriman

Ashley Herriman is WorkBoat's online editor.

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