USA small towns, farms, wildlife refuges flooded to try to save New Orleans and Baton Rouge
18/5/2011 New Scientist Mississippi river spillway opens to save New Orleans.Small towns, farmland and wildlife refuges have been sacrificed in an attempt to save New Orleans and Baton Rouge from the massive flood that is rolling down the Mississippi river.
Heavy rain and snowmelt are responsible for weeks of devastating floods in the southern US. The water is predicted to take another couple weeks to reach the Gulf of Mexico. In a bid to avoid massive flooding in New Orleans and Baton Rouge, on 17 May the US Army Corps of Engineers decided for the first time since 1973 to open part of the Morganza Spillway, a huge flood-control structure in Louisiana.
Eleven of the 125 spillway gates have so far been opened, releasing the water to pour across the Atchafalaya basin where up to 25,000 people are evacuating their homes. This should reduce the burden on the levees of New Orleans.
The hope is that the diversion away from the Mississippi will lower water levels flowing through New Orleans to under 42,000 cubic metres per second, and avoid overwhelming the city’s flood defenses – its now infamous levees.
Round one
Robert Criss of Washington University in St Louis believes that the Army Corps of Engineers can “probably divert enough water to prevent New Orleans flood structures from failing”.
But David Rogers at the Missouri University of Science and Technology in Rolla, warns: “This is just round one. We can’t tell exactly what’s going to happen.”
“If the river drops rapidly then comes back up again, that’s when all hell breaks loose – that’s when all the levees fail.” This was the outcome the last time the spillway was opened, in 1973. The Army Corps will have to “watch the water levels like a hawk” over the next few months to make sure they don’t drop too quickly, he says.
An overly fast drop in water levels causes a pressure change that weakens the soil in the levees, which may then fail if the water levels should quickly rise again. And when – like this year – heavy floods have already saturated the ground and filled up lakes, heavy rain could cause such rapid rises, says Rogers.
Go to: http://www.newscientist.com/article/dn20486-mississippi-river-spillway-opens-to-save-new-orleans.html