In the case of New Orleans, some of that high ground is within the city itself. If flooding eventually becomes frequent enough that the federal government decid

In the case of New Orleans, some of that high ground is within the city itself. If flooding eventually becomes frequent enough that the federal government decides to relocate flood insurance claimants and stop funding the Army Corps of Engineers' improvements to the levees, then the city can retreat to its pre-1930 borders. Most of those areas did not flood in Katrina and could get by with a much smaller flood protection system that might be justified by the city's economic productivity.