One of the many tragic things to happen in New Orleans was that all of the hospitals lost power. Here in Houston during Tropical Storm Allison something similar happened. There were alot (though, thank God, by no means all of them) of hospitals that completely lost power due to flooding - though (thank God) by no means all of them.
Why not put the emergency generators in hospitals above the flood line? And why not have a breaker in to cut power to areas below the flood line? This way, even when the building floods, emergency power can stay on - and in a hospital this means that life-support, dialysis machines, and defibrillators will still work.
I've seen projects where chillers, boilers, and cooling towers were installed on a mezzanine 40' above street level. But the emergency generator and fuel tanks are below the flood line! WHY?
A related idea. Old fashioned cisterns on hospital roofs - during normal use they help the water pressure. During loss of power they provide a limited supply of potable water.
The idea in both cases is to keep the life-saving devices running and potable water available long enough for the building to be evacuated - not indefinitely.