How many cubic feet of water do you think ended up in NOLA? Some math: If the flooded area is the size of Washington DC it is 1/8th the size of Lake Ponchartrain.
So 8 ft of water pumped out is only a rise of 1 foot in the Lake. I think there is less water than that in the city. I think that emergency repair will hold.
The rise in Lake P isn't the issue. The issue is the head. How high inside versus how high outside.
The counter to that is sheet piling under the repair. If it's there, the fill will hold, if not, it won't.
Keep in mind that dry ground isn't related to the head. The water table exists underground as if the land wasn't even there.
On a related note, how to you clean a water supply system that has been compromised as New Orleans' has?
Treatment can clear the major supply lines, then you need residents to run the water under a Biol Order foir a few days to clean out the "last mile".
All well and good, but that's the procedure for bioligical contamination. This system hs been compromised with chemical contamination as well.
Big job, but as posted earlier, New Orleans recovered from 5 to 7' flooding during Betsy in the 60's.