Morganza Floodway above Baton Rouge on Saturday to allow Mississippi River floodwaters to flow into the Atchafalaya River basin, which will reduce the flow of water — and threat of flooding — along levees in New Orleans and other downstream cities.
The Friday afternoon announcement of the second-ever opening of the emergency floodway came in a three-sentence news release:
“The President of the Mississippi River Commission Maj. Gen. Michael J. Walsh has directed the New Orleans District Commander Col. Ed Fleming to be prepared to operate the Morganza Floodway within 24 hours. The operation will include the deliberate and slow opening of the structure.”
The water will spread slowly south, according to an accompanying map, reaching Melville in six hours, Krotz Springs in 12 hours and Morgan City in three days. At eight days, the floodwaters will have flowed east around Houma toward the eastern side of Timbalier Bay.
In a separate news release, corps officials said they expect to flow less water through the floodway, based on new estimates of floodwaters moving downstream. Instead of putting 300,000 cubic feet per second into the Atchafalaya Basin, as little as 125,000 cubic feet per second might need to be diverted.
That could be good news for some with property in the floodway, although hundreds are still expected to evacuate because of the water threat. The new map indicates water will not flow all the way northwest to Palmetto in St. Landry Parish, and there will be less water in areas near Melville, Krotz Springs and Butte La Rose. But much of the change would occur in sparsely populated areas that would see 10 to 16 feet of water instead of 16 to 20 feet.
In a Friday morning news conference, Gov. Bobby Jindal announced that he has instructed parish governments to begin notifying residents within the areas expected to be flooded in the Atchafalaya River basin to begin evacuations.
“Now is the time to take action. Don’t delay. Don’t hope something will change,” Jindal said.
“They’re not going to open it all at once,” Jindal said during a second news conference in Baton Rouge moments after the corps announcement. “It will be based on the modeling data, the most recent data.
“As of this morning they were telling us 15-30 cubic feet per second is what they expect to start with,” he said Friday. “They expect to start with 2-4 bays out of 125 bays. So it is going to be a gradual opening.
“You’re not going to see a foot of water immediately, there’s not going to be wall of water, but it is going to steadily increase,” he said. “And they’re going to gradually add more capacity.”
Staying under 17 feet in N.O.
The Lower Mississippi River Forecast Center, part of the National Weather Service’s Slidell office, indicated that the Mississippi River’s flow at Red River Landing, across from the Louisiana State Prison at Angola, first reached the corps trigger level of 1.5 million cubic feet per second on Friday at 7 p.m.
Opening Morganza will allow the flow to be kept at 1.5 million cubic feet or less to the south, while the Bonnet Carre Spillway, stretching between Norco and Montz, funnels 250,000 cubic feet per second into Lake Pontchartrain. That should allow the river to rise no higher than 17 feet at the Carrollton Gage in New Orleans.
Read More: http://www.nola.com/environment/index.ssf/2011/05/morganza_floodway_will_open_sa.html