In a historic action designed to minimize the risk of catastrophic flooding in Baton Rouge and New Orleans, the Army Corps of Engineers has begun opening the Morganza Floodway to divert water from the rain-swollen Mississippi River into the Atchafalaya basin.
The second-ever opening of the nearly 60-year-old structure 186 miles upriver of New Orleans began at 3 p.m. sharp, when a crane lifted a gate covering one of the spillway structure's 125 bays, releasing a gusher of about 10,000 cubic feet of water per second into the floodway. A live video feed of the procedure is being streamed online by the corps.
More of the 28-foot-wide bays will be opened in the coming days to gradually increase the flow rate to about 125,000 cubic feet per second, corps officials said.
About 25,000 people and 11,000 structures are in harm's way, as up to 25 feet of flooding is expected in a 3,000 square-mile area of Cajun country stretching from Melville to Morgan City.
The water is expected to pass below Interstate 10 in a day and reach Morgan City in three days, said Col. Ed Fleming, commander of the corps' New Orleans district.
The spillway opening had been a foregone conclusion for the past week, but the corps reduced the amount of water it planed to divert into the spillway by nearly 60 percent to about 125,000 cubic feet per second.
That's less than a quarter of the control structure's capacity of 600 cubic feet per second, which could be a rare bit of good news for people with property in the spillway.
Sheriff's deputies and members of the Louisiana National Guard have been going door-to-door to alert people of the pending flooding.
The decision to open the spillway was triggered when the river's flow rate reached 1.5 million cubic feet per second and rising at Red River Landing across from the State Penetentiary at Angola. Those conditions occurred Friday afternoon, prompting corps officials to announce the spillway would be opened within 24 hours.
The Morganza control structure was completed in 1954 as part of the corps' sweeping flood-protection upgrades to prevent a repeat of the Great Flood of 1927.
The only other time the spillway opened was in 1973 to relieve pressure on the Old River Control Structure, a critical barrier 35 miles upriver that prevents the Mississippi from its natural tendency to shift course to the Atchafalaya Basin, a steeper shortcut to the Gulf of Mexico.
Such a shift would have a catastrophic economic impact on the ports in New Orleans and Baton Rouge.
Opening the Morganza Spillway and the Bonnet Carre Spillway near Norco is designed to avoid a doomsday scenario in which New Orleans could be swamped with 20 feet of water, far worse than the flooding during Hurricane Katrina in 2005.
Saturday marked the first time in history that all three floodways built by corps after 1927 flood — the Morganza Floodway, the Bonnet Carre Spillway and the Birds Point floodway in Missouri — have been in operation at the same time, according to the corps.