I could, and I probably will, chase links for hours, learning what I can about the history of plans to mitigate flooding in New Orleans, L. Ponchartrain, etc... (I do have some background in stormwater management already).

One point stands out already, without digging too deeply -- and these posts in this thread are not my only source:

No matter what happened during construction -- and for my purposes that's irrelevant -- the design was for a Category 3 storm.

Katrina was a 5 until just before landfall, when she weakened to a 4. And please remember: the categories are based solely on wind velocity, not barometric pressure at the center, or the amount of rain carried by the storm overall.

As our good friend Nick Hoffman has pointed out elsewhere, the "100-year flood" is a satistical convenience. I can tell you from profesional experience that stormwater systems are designed around a similar statistical convenience. To the best of my knowledge, the 100-year average is not a running average. The rainfall rates (given in inches per hour over a certain duration) around which systems are designed remain identical from year to year, from one edition of the "model" code to the next.

They are not designed with the capacity to handle catastrophic storms.

I have seen a large portion of a suburban county of Philadelphia submerged for long enough to ruin hundreds of homes, because the storm drains backed up (and the homes in question had no basements). The sewers were designed to a parameter of 5"/hr for a duration of 15 minutes. It took me an hour and a half to get home, needing multiple backtracks to miss flooded intersections and overtopped bridges (the trip took 40 minutes in dry weather). The storm that did it dropped nearly 8"/hr over an hour and a half, for a total of 11".

And that was for a region safely above sea level.

What's my point? Learn from experience. Compared to what actually occurred, the design for New Orleans was a compromise to start with. It was underdesigned from the beginning, regardless of whether it was built or not.

There is plenty of blame to go around, and I (for one) hope every bit of it lands where it should. However, blame does not forestall the same thing happening again. Soon, I hope, the responsible parties -- by which I mean, the people actually doing the work, not their patronage or elected bosses -- will get past the ass-covering, throw out the model codes, and design to a realistic expectation of maximum capacity.

Realistic? That's also an open question. Given warming (with or without a concomitant rise in sea level), how long d'you suppose it'll be before the first Category 6?