It is almost exactly five years since hurricane Katrina devastated New Orleans, and the city is bracing for attack.
In a revamp now nearing completion, the city鈥檚 560-kilometre perimeter has been fortified by toughened levees, concrete walls more than 9聽metres high and foreboding gates that will grind shut when the enemy 鈥� flood water 鈥� nears.
But some say that these upgraded defences, which cost the US federal government $14.45 billion, aren鈥檛 tough and comprehensive enough 鈥� in part because climate change could .
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The city is certainly safer than it was on 29聽August 2005, when Katrina made landfall. Its 8.5-metre surge went on to overpower a mishmash of poorly connected levees and flood walls.
T for tough
Now those walls have been replaced with steel-reinforced ones shaped like an inverted 鈥淭鈥�, making it harder for a storm surge to topple them, says Gregory Gunter, an officer with the .
The mud levees that Katrina washed away are now bolstered with stronger clays, while pump stations come with flood-proof safe houses so operators won鈥檛 have to evacuate like they did in 2005.
All this should protect the city from the kind of storm that historically has occurred once in 100 years. The system shouldn鈥檛 fail in a 鈥�400-year鈥� Katrina-strength storm either, although Gunter says such a surge would probably flow over the barriers. This would lead to some flooding, but nothing like the scale of Katrina, which pushed over walls and breached levees.
Go Dutch
, an engineer at the University of California, Berkeley, and long-time critic of the corps鈥檚 flood defences, says the US is still 鈥渄oing it on the cheap鈥�.
He contrasts the new defences with those that , which can withstand a 10,000-year storm. The Dutch 鈥渒now that providing adequate flood protection [costs] something in the range of $100 billion鈥�, he says.
, director of the National Audubon Society鈥檚 Louisiana Coastal Initiative in Baton Rouge, and former storm surge modeller, says the new designs presume that future storms will resemble past ones. He points out that climate change may increase hurricane strength.
Wasted wetlands
That suggestion is still a subject of hot debate. In any case, Kemp would have liked to see restoration of Louisiana鈥檚 coastal marshes, which absorb some of a storm surge鈥檚 bite. He thinks they are likely to be more resilient than artificial structures.
He adds that the destructive threat posed by hurricanes is also increasing because the buffering wetlands are constantly being destroyed.
While the corps has begun looking into as a way to protect the city, as yet no money has been set aside for this.
Kemp also calls the idea of a 100-year storm a 鈥渕ythical measure鈥�, pointing out that we only have about 100 years of reliable data to work with, which isn鈥檛 necessarily enough to reflect long-term hurricane patterns.
When this article was first posted, the first paragraph mistakenly described the new levees as made of cement.
