Anything above a couple of feet per second is extremely difficult to wade in. To operate a boat in anything close to 10 to 15 feet per second is extremely difficult. Being in (that kind of) water is tantamount to being dead.
It looks to have been laterally pushed, not scoured in back with dirt being removed in pieces. You can see levee material, some distance pushed inside the floodwall area, like a bulldozer pushed it.
You could have done it in one year. The breach that occurred in one corner of the city basically spread throughout the whole city. Why? Why allow the water to move through the whole thing, including the French Quarter that was miles and miles away.
What you had, quite simply, is a waterfall.
But look at the alternative. You could have an entire city devastated, $20 billion dollars of damage. Or you could contain the problem, make it manageable.
The Corps knew, everybody knew, that the levees had limited capability.
