Thames-style flood barriers for New Orleans
A Thames-style flood barrier could be built to protect New Orleans from future storm surges, US engineers working on the city's flood defences have revealed as the anniversary of Hurricane Katrina brought the city back into the limelight.New Orleans is protected by a series of temporarily reconstructed flood gates and levees while engineers decide between three long-term flood protection plans for the city, which has still not recovered from the devastation of the August 2005 floods.
Thames barrier-style tidal gates on the two canals connecting the Gulf of Mexico with Lake Pontchartrain, on the shores of which the city lies, is one option currently on the cards.
The two flood gates capable of withstanding storm surges up to 10m high would be shut during storms, and would be accompanied by a system of pumps.
Although closing the gates may make it difficult to evacuate rainwater, that is preferable to the area getting submerged in water flowing in from the gulf via Lake Pontchartrain - the Army Corps believes.
The need for a new flood defence system became apparent when canal levees gave way under pressure from the storm surge raised by last summer's hurricane.
As Katrina hit the coast of the Gulf of Mexico, the wave that swept in from the ocean into Lake Pontchartrain and along the canals breached levees and flooded 80% of the mostly sub-sea level city with salt water.
The US Army Corps of Engineers have been investigating just why flood defences gave way since the disaster. They summarise their conclusions in the Interagency Performance Evaluation Taskforce report, a draft version of which is available at here.
So far, it is clear that it was the ground beneath the levees, and not the levees themselves, that gave way under the onslaught of water.
As New Orleans lies in the delta of the Mississippi river, the ground beneath it is naturally soft and unstable. But engineers are now looking into ways of letting the river's natural sedimentation processes help protect the city against future floods.
There are further plans to restore the natural wetlands of the gulf coast, which could also help prevent flooding.
More information on the flood defence pland for New Orleans can be found here.