Boingboing has some astonishing info: survivors reporting that they heard exposions coming from the 17th Street levee before they broke, and that the Army Corps of Engineers blew the levees to protect more valuable real estate

0:57 Raw transcript of comments by NOLA evacuee Clara Barthelemy: “The 17th street levee was bombed by the Army Corps of Engineers to save the more valuable real estate in the city… to keep the French Quarter protected, the ninth ward was sacrificed… people are afraid to speak out… everyone who was near there heard the bombings… they bombed seven times. That’s why they didn’t fix the levees… 20 feet of water. Gators. People dying in water. They let the parishes go, not the city center. Tourist trap was saved over human life. A six year old girl was raped in here.. 9 year old boy killed. A man in the shower beaten. No hot food. No help for elderly.”

…and…

11:22 Now I’m speaking to someone else, another woman, who says some people report having witnessed “bomb sounds,” believe 17th street levee and others were blown up to manage water flow and protect more valuable portions of real estate.

Whoa. I’m still looking for a more reputable source to pick this up, but if it’s true, wow.
Update I mentioned this on a Metafilter thread, and some people who know significantly more than I do about New Orleans weighed in. The response, to paraphrase: “Ummm…no”. :

Deliberately blowing levees is a known tactic in combating floods. There are legions of cases where someone, near a levee about to fail, would go across the river and blow the levee on the other side, causing the river to drop as it flooded over the plains on the far side, thus saving the levee on their side.

However, two factors argue against this being the case this time.

1) It wouldn’t do any good. They weren’t fighting the river. They were fighting a lake connected to the ocean. Breaching levees helps when your dealing with rivers, because there isn’t that much water. When you’re dealing with a lake connected to the ocean, you’re dealing with, for all intents, an infinite source of water. Blowing open a floodwall in the face of a storm surge on Lake Pontchartrain wouldn’t change the lake level at all.

2) When you flood 80% of the city, even if you manage to magically flood the poorest 80%, a lot of well off people are losing their homes too. They’re just not in the city right now, since they could afford to evacuate. Furthermore, look at the damage in places like the CBD and Canal St. If someone thought they’d sacrifice the poor sections to save the rich, they screwed up badly. In fact, one of the richest parts of the city, Old Metairie, was flooded out.

The reason the oldest parts survived — the oldest parts were built on the highest ground, because when they were built, there was no levee system. That’s why the French Quarter stayed mostly dry.

Finally, note that it wasn’t levees, but floodwalls, that failed. Floodwalls are fine until they’re overtopped, then they have a real problem with scour at their base, and they fail rapidly. Part and parcel of a floodwall system is the pumps to keep the backside of the wall dry to prevent this — but enough water over the wall, and you overwhelm the pumps. Given the storm surge, some parts of the wall may have been overtopped by several feet.

I’m not surprised that these walls failed. I’m also not surprised that it was the lowest floodwalls, the ones on the canals, that failed, and that the failures seem to all be on the side closest to the center of the storm. The stronger walls on the lakefront itself held, as did the river walls. But a wall is only as strong as the weakest panel, and in this case, the weakest panels were on the 17th Street and Industrial canals.
posted by eriko at 5:42 PM PST on September 7 [!]

Update 2: The Army Corps of Engineers may not have blown up the levees, but the hurricane was caused by the Yakuza (using Soviet technology) to get rich on the futures market and to get revenge for Hiroshima! Of course!