From the Society of Wetland Scientists
The impact of the hurricane would have been reduced if Louisiana had not lost so many of its coastal wetlands. A map summarizing wetland loss in Louisiana from 1932-2000 is posted on the web site of the National Wetlands Research Center (NWRC) (http://www.nwrc.usgs.gov/). Note the particularly heavy loss south, southwest, and southeast of New Orleans.
The ocean is strong, but natural coastal systems are good at cushioning the impact of massive amounts of rushing water.
Marshes and dunes are not preferred for permanent human habitation, however, so we destroy them and build walls to prevent flooding. It works well, by and large, but Mother Nature can do wonders.
Arguing that New Orleans would have been spared if the Corps of Engineers got the money to bolster dikes misses the point: Living in flood zones is risky. Choosing to take that risk means accepting the consequences. Low-probability events are not no-probability events.
(Earthquakes, tsunamis, unprecedented cold snaps and dry spells, tornados, et cetera... You could say Living is risky.)