Here's one approach to "flood-proofing" New Orleans:
Raise New Orleans above sea level by filling.
Fill the low-lying parts of New Orleans with "structural" fill...i.e. something you can build on. Not
cheap but nothing is cheap when building by the water. But it seems pointless and even unethical to encourage people to move back into a city which could flood until the time we have flood-proofed it.
Suppose we figured we were inspired by the walkability of New Orleans (or at least so I am told) and wanted to re-create a fairly compact city. We don't have to fill approximately 20% of it i.e. the area which includes the French Quarter and which was not flooded. This area makes up about 20% of Old New Orleans, I have read. So let's just say we want a flood-proof New Orleans of about 3 miles by 3 miles -- you can walk across it in an hour. Now that's not a big city by any North American standard but as a pedestrian-oriented city of 9 square miles -- three miles in either direction -- it is not too shabby.
So two, immediate questions are
1. What would it cost to bring New Orleans up-to and above sea-level grade with a suitable structural fill?
2. Would/could such a fill be stable?
I'll dispense with the second question -- I simply have no remote idea -- and leave that to the geologists and engineers to tell us if such a massive fill could be stable for the next few centuries.
I have no idea what sand/gravel/aggregate costs in southern Louisiana. I suspect that the nearest
source would be hundreds and hundreds of miles away. But let's guess (based on wild extrapolation from Seattle costs for a 10 yard truckload) that structural fill could be placed/compacted etc in New Orleans (I assume it is delivered from upriver by barge) for $15/cubic yard. Assume an area to be filled of 3 miles by 3 miles (9 square miles total.) Assume a fill of 25 feet on average. Multiply it out and you get a number just shy of $4 billion. Not too bad, all things considered? And just to make sure no one misunderstands, I am talking of filling only those parts of New Orleans which are below sea level and which were destroyed by Katrina, which I understand would exclude the French Quarter etc.
Food for discussion, at any rate.
Btw, my calculation is that at a low-rise density of 40 units per acres -- quite common and by no means "high" density -- upwards of 200 thousand people could live in this nine square miles.
Thanks, Laurence, for pointing out How do they rebuild a city? I will be curious to read the (I hope inevitable) analyses. I wonder if in fact, with a commitment to finish the job from the Corps of Engineers, you couldn't create some liquidity for New Orleans property owners whose property is now practically worthless.