Corps says if Morganza Floodway is opened, flow may only be a fourth of its capacity

The Army Corps of Engineers announced today that if it opens the Morganza Floodway north of Baton Rouge to reduce the height of Mississippi River floodwaters flowing south, the flow into the Atchafalaya River basin may be limited to only a fourth of the floodway's capacity.

Until today, corps officials have said 300,000 cubic feet per second of water, half the floodway's capacity, would flow down the Atchafalaya.

In its statement, the corps said the flow at Red River Landing had reached 1.45 million cubic feet per second at 7 a.m. today, and is projected to reach 1.5 million cubic feet per second this weekend.

"Given the current flow rate predictions, which are subject to change, the corps is anticipating opening the floodway to allow for up to 150,000 cfs of water to pass through the structure at peak flow," said the brief staement.

Corps officials said Thursday they were preparing computer analyses to determine what kind of flooding would occur in both the Atchafalaya basin and along the Mississippi, if the flow were limited to 150,000 cubic feet per second. It's expected the reduction could reduce flooding in some populated areas within the basin.

The key will be whether that's enough to keep water flow levels above the Bonnet Carre Spillway to 1.5 million cubic feet per second. That spillway, when all 350 bays are opened, diverts 250,000 cubic feet per second of water into Lake Pontchartrain, which would allow only 1.25 million cubic feet per second to pass the Carrollton Gage in New Orleans.

At that flow rate, the river height would stay close to 17 feet, which is the official flood level.

Hydrologists with the Lower Mississippi River Forecast Center in Slidell have predicted that without opening the Morganza Floodway, the river would crest at 19.5 feet in New Orleans on May 23. That would drop to 17 feet, they have said, if the floodway is opened, but their estimate has been based on a 300,000 cubic feet per second opening.

The U.S. Coast Guard has said it will ratchet up restrictions on deep draft vessels at 17.5 feet in New Orleans and could ban movement of deep draft vessels between Baton Rouge and Boothville if the river reaches between 18 and 19 feet.

Such a closure could result in an economic loss of $295 million a day, said Gary LaGrange, executive director of the Port of New Orleans, during a news conference Thursday.