New Orleans can't and maybe shouldn't ever be what it once was without very serious engineering work on the levee system. Use the most heavily flooded areas for warehouses, not for high density housing.
Back in the 1970's the Corps of Engineers proposed a system of flood gates similar to the dikes that protect the Netherlands from floods. It was killed by a federal judge after environmental groups filed suit. Do you want to guess the political affiliation of the president who appointed that judge?