The Bonnet Carre Spillway opened Wednesday as the U.S. Army Corps of Engineers looks to head off potential flooding caused by a fast rising Mississippi River.
It marks just the 13th occasion the Spillway had opened over its 91-year existence. But it is also the second straight year it has opened and the third time in the past four years.
Want to see Wednesday’s spillway opening? Click here.
Chris Brantley, the spillway’s project manager for the U.S. Army Corps of Engineers, said the decision to open comes when the river is flowing past the spillway toward New Orleans at a rate of 1.25 million cubic feet per second. With the river water steadily rising, the flow was projected to surpass that rate on Wednesday.
While the New Orleans area has seen ample rain over recent weeks, the projected change comes from a high volume of rain that has fallen in the Tennessee and Ohio river valleys in past weeks. More rain is expected to fall over those areas.
“They’ve been getting a series of fronts … we’ve gotten rainfall, but not like they’ve had,” Brantley said. “There’s a larger drainage area up there, basically from the Rockies to the Appalachians … everything in between drains into the Mississippi River.”
When the river flows at the trigger point of 1.25 million cubic feet per second, the Spillway’s job is to maintain that consistent flow, take the excess and divert it into Lake Pontchartrain. The operation of the structure relieves pressure on main line levees, maintains river stages and regulates river flow.
It is the fifth time since the year 2008 the Spillway has opened. The most recent occasion came on March 8 of last year, and prior to that there were openings in 2016, 2011 and 2008. Last year’s opening saw roughly half of the spillway’s 350 bays opened. The last time all bays were opened came in 1983.