Many of the people in New Orleans found "higher ground" in the form of multi-story buildings. Many people in New Orleans found other forms of shelter, such as the Superdome or ahem... their attics. Many people in New Orleans are dead because they were cornered in their "shelters" and "higher grounds" with little to no sustenance by infectious waters that in many places were too high to walk through. This is exactly the reason that it was imperative to get these people out of the city as soon as possible, but due to economic conditions and criminal negligence on the part of the government, this didn’t happen. So these people have died a horrific, senseless death.