Corps Precaution At Weirs Built To Keep Mississippi In Place
NEW ORLEANS (AP) — Although the Mississippi River is no higher than normal for this time of year, the Army Corps of Engineers is getting ready just in case water keeps rising at the complex built to keep the river flowing past New Orleans.
Crews at the Old River Control Structure opened gates Thursday at the "Overbank Structure" — the larger and higher of two huge weirs built in 1959 to make sure that no more than 30 percent of the Big Muddy's water escapes into the lower Atchafalaya River, corps spokesman Rene Poche said.
It's a precaution taken because higher water would make it impossible to open the structure's 73 bays, each 44 feet wide, said Mike Stack, emergency management director for the corps' New Orleans Division. The bays are designed to be opened when the river is 52 feet deep — 1.5 feet above flood stage — at the complex near Simmesport. Pressure from higher water can hold them shut, Stack said.
A third weir, 442 feet long, was built in the 1980s after the flood of 1973 partly undermined the "Low Sill Structure," a 566-foot-long construction with 11 gates through which water always flows into the Atchafalaya.
After that third weir was built, Stack said, officials decided the 3,356-foot-long Overbank Structure could stay closed. The record flood of 2011 convinced them otherwise.
"We saw we were really maxing out the capacity of the Low Sill Structure," though the structure wasn't damaged, he said.
Opening the Overbank Structure allows more flexibility in distributing the Mississippi's water if it gets higher, he said.
The river is at about an average level for early spring, said Jeff Graschel, a hydrologist with the National Weather Service in Slidell.
"We didn't really have a whole lot of snow in the Upper Mississippi," he said. "We had a tremendous amount in the Northeast, but all that snowfall goes into the Atlantic and not into the Mississippi or Ohio" rivers.
Three to 5 inches of rain earlier in March and about 1½ feet of snow in Kentucky have created a "rise" that is working its way down the Ohio and Mississippi rivers, he said.
Graschel said that rise should reach southeast Louisiana by the end of the month and the river could reach flood stage at Baton Rouge. "That's typical this time of year," he said.
– by AP Reporter Janet McConnaughey