The Bonnet Carre Spillway needs to be opened — possibly as soon as Saturday — to divert the slug of floodwater coming down the Mississippi River after heavy December rainfall up north, the head of the U.S. Army Corps of Engineers’ New Orleans office said Tuesday.
Col. Rick Hansen, commander of the Corps’ New Orleans District, said that he is recommending to the commander of the Corps’ Mississippi Valley Division that the spillway be opened.
Once that is approved, it’s just a matter of waiting until the river gets to the trigger point of 1.25 million cubic feet per second through New Orleans. National Weather Service forecasts indicated that level of water flow could occur by Saturday.
“We won’t open the spillway until we have to,” Hansen said.
If it moves forward, this will be the 11th time the spillway has been opened, channeling water into Lake Pontchartrain and relieving pressure on the levees down river.
The spillway structure, built after the deadly 1927 flood and most recently utilized in 2011, is made up of 350 bays that are closed off by 7,000 wooden pins. Ricky Boyett, public affairs chief at the Corps district, said about 20 bays a day can be removed, and it’s expected that all of the bays will need to be opened to accommodate the floodwaters.
The purpose of diverting water into the lake is to keep a relatively steady 1.25 million cfs of river flow through New Orleans, which roughly works out to keeping the water at 17 feet. The levees in downtown New Orleans protect up to 20 feet.
Although designed to be able to pass 250,000 cfs of water, the spillway and receiving area can handle more, said Boyett.
“In 2011, we put 300,000 cfs through to keep the water where we wanted,” he said.
When the spillway opens, it becomes a popular sight-seeing outing, especially because it doesn’t happen very often, Hansen said. However, he cautioned that people need to stay out of the water, noting that in years past, kayakers have tried to navigate through the spillway.
The high water in the Mississippi River is the result of recent heavy rainfall in the Arkansas, Mississippi and Ohio river valleys, which has already caused major flooding in the Midwest. River waters overtopped levees in Illinois and Missouri, flooding many communities. Authorities in those two states reported about two dozen deaths related to the floods.
A decision on whether to open the Morganza Spillway, which sends floodwater into the Atchafalaya River Basin, is still being discussed. Hansen said the Corps is holding meetings with stakeholders — including fishermen, environmental groups and elected officials — during the next several days.
The trigger to open the Morganza Spillway occurs when river levels reach 57 feet at the structure and there is a 10-day forecast river flow to reach 1.5 million cubic feet per second. Hansen said the National Weather Service forecasts are indicating that 1.5 million cfs level might be reached.
Editor’s note: This article was changed on Wednesday, Jan. 6, to note that 20 bays a day can be removed from the Bonnet Carre spillway structure.
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