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the levees were designed decades ago, when there were more wetlands between NOLA and the Gulf. Even then, they weren't built to spec, and the specs themselves were bad. There were three causes of levee failure in NOLA. Some along the east side of the Lake were simply topped by the massive surge. Those along the MR-GO were topped, too, as water was channeled along it, increasing the height of the surge. Those levees were just too low, and MR-GO, as it has in the past, made things worse.
Second, the Industrial Canal levee just collapsed. I'm not sure they know why, but since it is right at the end of the MR-GO, it seems likely that the water channeled into the Industrial Seaway was just too high, and maybe too fierce, for the levee to fight off. Plus, the water may have hit it from the other side, as water was topping the smaller levees up the MR-GO (Hard to explain this without a diagram or a very long post!). That's what flooded the Lower 9th Ward so catastrophically, and caused the most deaths.
Third, the levees along the 17th Street Canal and the London Avenue Canal (and I think one more, I've forgotten) failed because they were poorly designed, poorly built, and undermined by dredging over the years. Those are the canals that caused downtown NOLA to flood in the days after the hurricane, as the Lake slowly drained through the holes into the city. Those levees were hit by, essentially, a Category 1 or less hurricane, as they got the extreme west side of the storm. They could have broken after a really strong thunderstorm. This was made worse as the prehistoric pumps failed.
All of which means, it seems to me, that there has to be more than one layer of solution to the levee problem, since there was more than one type of problem. Better levees, newer pumps, state-of-the-art flood control systems involving flood gates, revitalization of the wetlands, secure storm shelters built for the purpose, an evacuation system that takes into account that not everyone can afford to drive away and stay away for days or longer, and most of all, an emergency management system that does what it was created to do, not just for NOLA, but for Iowa and other places where disasters strike, too. And other stuff thought of by smarter people than me.
Just my amateur thoughts. Probably wrong, as always.
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