Watching higher Mississippi River levels

The 5th Season: Mississippi River Levels

BATON ROUGE, La. (WAFB) - High water along the Mississippi River is becoming more commonplace.

There is a question from many people:

Could a hurricane storm surge combined with the river “in flood” result in levee overtopping?

We talked with the US Army Corps of Engineers to get its perspective.

High water along the Mississippi River appears to be happening more frequently and staying around longer. This year marks an unprecedented fifth straight year with the river at Baton Rouge rising above 40′.

Last year, the “Mighty Mississippi” stayed “in flood” for a record-breaking 211 days at Baton Rouge. And, here we are, June 1 and the river has been “in flood” since January, making this year the second longest run of consecutive days in flood following last year’s record-setter. And that is back-to-back years with the Mississippi River still “in flood” as we enter the hurricane season.

Hurricane Barry in 2019 had many in New Orleans worried about levee overtopping. The fear was that Barry’s predicted storm surge on top of the already high Mississippi River would push water over the levees and produce another Katrina-like flood.

That same fear extended upriver to Baton Rouge and beyond. Storm surges from hurricanes like Katrina, Gustav, and Isaac produced rises of 4′-8′ along the river at Baton Rouge. Those kinds of rises at a time when the river was at or near 40′ would overtop the levees on both sides of the river. But those dramatic rises of the Mississippi at Baton Rouge occurred during periods when the river was relatively low. The impact of storm surge lessens as the river gets higher.

“That’s what the models show us, that the further you get upriver, the more the force, the incredible force, especially of a high river, counteracts the storm surge," said Col. Stephen Murphy, commander of the US Army Corps of Engineers in New Orleans. "It doesn’t take it away but it significantly dampens its ability to propagate upstream.”

Modeling by the Corps does show that a large storm surge could pose an overtopping threat for New Orleans, regardless of the height of the river. However, the impact of storm surge at Baton Rouge is effectively canceled when the river is running above flood stage.

Still, many wonder why the Corps doesn’t use the Bonnet Carre’ and Morganza spillways to manage the river when there is a significant storm surge threat.

“It’s really not practical,” Col. Murphy acknowledged.

When you consider the ever-changing forecasts and timelines for tropical systems in the Gulf of Mexico, the reasoning quickly becomes clear.

“It takes about three-and-a-half days to physically open Bonnet Carre',” Col. Murphy explained.

As for Morganza?

“It typically takes 10 days of preparation to open Morganza,” he added.

“It takes more time than hurricanes really allow us,” Col. Murphy noted.

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