Army opens floodgate as cities face disaster

US ARMY engineers opened a key floodgate on the bulging Mississippi River yesterday in a move set to swamp thousands of homes and farms in rural Louisiana.

The US hopes the effort will avert a potential disaster in Baton Rouge and New Orleans further downstream.

About 25,000 people and 11,000 structures could be at risk after the gates on the Morganza "spillway" were unlocked for the first time in 38 years yesterday.

"Protecting lives is the number-one priority," said major general Michael Walsh of the Army Corps of Engineers during a flyover of the flooding, before the decision was made to open the gate.

The gate released a torrent at an estimated 10,000 cubic feet per second - capable of submerging about 3,000 square miles under as much as 25ft of water. The plan takes the pressure off the downstream levees, or manmade dams, protecting New Orleans, Baton Rouge and the numerous oil refineries and chemical plants along the lower reaches of the Mississippi.

Engineers feared that weeks of pressure on the levees could cause them to fail, swamping New Orleans under as much as 20ft of water in a disaster much worse than Hurricane Katrina in 2005.

Instead, the water will flow 20 miles south into the Atchafalaya River. From there it will roll on to the Gulf of Mexico, flooding swamps and arable land. Morgan City, an oil-and-seafood hub and a community of 12,000, shored up its flood defences as a precaution.

The army opened the gates after the river's flow rate reached a certain point. Some people living in the threatened stretch of countryside - an area known for small farms, fish camps and a drawling French dialect - have already started fleeing to higher ground.

National Guardsmen have warned people in a door-to-door sweep through the area. Shelters are ready to accept up to 4,800 evacuees.

"Now's the time to evacuate," Louisiana governor Bobby Jindal said. "Now's the time for our people to execute their plans. That water's coming."

The army employed a similar strategy this month when it blew up a levee in Missouri - inundating 200 square miles of farmland and damaging or destroying 100 homes - to take the pressure off levees protecting the town of Cairo, Illinois.