US military opens Mississippi floodgates

Monday 16th May 2011 by theWeather Club

US army engineers have opened floodgates in Louisiana that will inundate over 5,000 sq km of land in an attempt to protect large cities along the Mississippi River. It is hoped the move will ease pressure on Baton Rouge and New Orleans. This is the first time in four decades that the level of the Mississippi has forced the floodgates to be opened, with about 25,000 people and 11,000 buildings being adversely affected. Heavy rains combined with the spring thaw further up the Mississippi and its tributaries have caused massive flooding, and officials have said the flooding in Louisiana is the worst since 1927.

The Morganza Spillway, 72km north-west of Baton Rouge, was last opened in 1973, but the US Army Corps of Engineers warned that if the spillway was not opened, New Orleans could be flooded by about 6m of water. The spillway stands above the Mississippi's normal water level, and comes into play only when the Mississippi is already swollen and endangering the surrounding areas. By opening its floodgates engineers are able to control the flow of the floodwaters, diverting them around Baton Rouge into the Atchafalaya river basin, a low-lying area of central Louisiana. Built in 1954 the spillway is 32.2km long and its 125 gates release up to17,000 cubic metres per second.

Once through the gates, water will flow south, flooding the land under an expected 4-6m of water, inundating homes and farmland as it goes. Over several days, the water will eventually enter the Gulf of Mexico. Col Fleming explained that the opening would be slow to ensure people understood that water was coming their way and that they had to leave in accordance with local evacuation plans. Wildlife in the area also needed time to get to higher ground, he added.

Col Fleming said the main water crest was not expected at the spillway until 24th May and would last for 10-14 days, so the spillway has the potential to be open for the better part of three weeks. Maj Gen Michael Walsh added: “The crest is still up in Arkansas. It's a marathon, not a sprint - there is huge pressure on the system as we work the water through. The protection of lives is the number one thing we're looking for.”

The current flooding is approaching records set 84 years ago, when hundreds of people in the region died. The trigger for the spillway opening came when 42,500 cubic metres of water per second flowed down the Mississippi River at Red River Landing, just north of the spillway. While some local residents are angry that their region has been effectively sacrificed to save Baton Rouge and New Orleans, others say they have lived for years with the knowledge that when the next flood came, it would come their way.

New Orleans Mayor Mitch Landrieu said although he believed his city would be safe, this was a tragic situation for those in the Atchafalaya basin. “Our hearts go out to them. It doesn't make us feel any good that [by] protecting New Orleans, other folks are going to get hurt.”