If people are going to insist on maintaining a large urban area that is largely below sea level and almost entirely below the water level of an adjoining lake and river, then they should take some lessons from the Dutch, and pour resources into self-preservation like it was going out of style. (They may not have to contend with Cat 5 hurricanes, but they do get their share of devastating storms coming in off the North Sea, and given that half of the country's elevation is under the point of 3 feet above sea level, they're understandably jumpy.) Simple dirt & dumped rock dykes (a.k.a. a large portion of the levees in the affected area) just don't cut it, even when topped by concrete sea walls. The Midwest learned that first-hand after the Mississippi flood of a few years ago. (They also learned that trying to tame and contain a major natural feature tends to make problems worse when they do happen--and they will happen.) If you're going to maintain a major metropolitan area in a zone that is that prone to problems, you need to concentrate on maintenance first and foremost.
Here's how you do it. Even if it takes fifty years to fully complete, as it took the Dutch. Or the Japanese, who are even now building giant breakwaters to block or reduce the effect of tsunamis and storm surges. This advice doesn't just go for New Orleans, but any populated coastal area at similarly high risk of storm-caused flooding. We have the engineering capability, but too much time has been spend brainstorming and pinching pennies, and not enough has been spent actually making the tough decisions, making the right decisions, and moving ahead.
Parts of New Orleans might also benefit from lessons learned in parts of Europe, particularly Venice: When your city is below sea level, stop building out and start building up. Not skyscrapers, but the entire city, streets and all. Additionally, make your ground floor out of stone & steel; that's more likely to survive most of what Mother Nature can throw your way (even if not necessarily with you inside it), and it is a lot easier to clean stone from a 10' flood than wood, drywall, and plaster.
(Of course, all this is being said by someone living close enough to one of the potential major disaster areas to be somewhat worried should the potentially most dangerous fault line in the U.S. live up to scientists' predictions of a 90% chance of a "moderate" earthquake of 6 to 7 on the Richter scale before 2040--a fault that over a 3 month period managed to generate 3 of the strongest 4 earthquakes in the lower 48 states of the last 300 years, and against which eventuality significantly less has been done than the Gulf states have done to protect against hurricanes and flooding.)
Feudalism: Serf & Turf