Bonnet Carré Spillway control structure, 28 miles upriver from New Orleans, is to open on April 11 for the first time since 1997 to relieve river-flood pressure on the levees downstream.
The Corps of Engineers will open the Bonnet Carré Spillway--a massive floodwater diversion channel upriver from New Orleans--to relieve pressure on Mississippi River levees in the city and points south. The opening is to begin April 11. It marks the first time in 11 years the spillway has been opened.
In his role as Mississippi River Commission President, Brig. Gen. Michael J. Walsh, commander of the Corps' Mississippi Valley Division in Vicksburg, Miss., signed the order April 10.
Operators open the Bonnet Carré Spillway structure when the Mississippi River flow at New Orleans is expected to exceed 1.25 million cu ft per second. With heavy rains in the Mississippi Valley swelling the river, it is expected to hit that rate on April 11.
The structure consists of a 6 mile-long, 8,000-acre floodway and a concrete, leaky weir control structure that parallels the river for a mile and a half. The structure consists of 350 gated bays, each holding 20 timber "needles," for a total of 7,000 needles. To open the structure, needles are lifted by two cranes moving along tracks atop the structure. As the needles are pulled, water spills into the floodway where it travels north between guide levees to empty into Lake Pontchartrain, and eventually exit into the Gulf of Mexico.
"We probably would start from a certain end and pull pins from strategic locations, not all at the same time," says Christopher Accardo, chief of operations for the New Orleans District. "We move to different locations to avoid scour. General Walsh will probably not give the order to fully open the Bonnet Carré."
The structure has a design capacity of 250,000 cfs, the equivalent of roughly 1, 870,000 gallons per second.
"There is no threat to the system," says Lt. Colonel Murray Starkel, deputy commander and deputy district engineer of New Orleans District. "Our number one priority is to protect the safety of the citizens of New Orleans."
Due to heavy rain throughout the Mississippi Valley, the Corps has been monitoring river levels and velocities. Since March 24, the New Orleans District has also been inspecting the 973 miles of Mississippi River levee system in Louisiana from just above the Old River Complex to Venice, on both sides of the river, as well as in the Atchafalaya Basin, from Simmesport to Morgan City, says Mike Lowe, emergency manager for the district. "We look for seepage, sand boils, settlement, slide and excessive erosion," he says.