Will ANY Of The Flooded Houses Or Buildings Be Salvageable?

Or will EVERYTHING have to be bulldozed and built again from scratch?

...would be nearly impossible to overcome.

Add to that the toxicity of the water itself, and I would have to say, sadly, yes. :(

In Grand Forks, North Dakota in the late 90's.... many buildings were saved - mostly the older ones made of brick, but many were bulldozed for foundation cracks and of course the buildings that were primarily made of wood. It depends on how long the water stays in them I would guess. The concrete will crack if it stays too long. I'm no professional, just that this happened up here during that horrible flood.

Here's a pic of the Grand Forks flood:

That the concrete/rebar buildings and steel girder buildings will be stripped down on the inside and rebuilt. Wood-framed houses probably won't fare so well after being weeks in water. I have known families here in the Ohio Valley who were flooded out and rebuilt with the original frame but the water came and receded within a couple of days. I had mad water damage last year when the remnants of Ivan hit and we had to rip out all the old plaster, rewire some, and put up new drywall. It's a hella lot of work. I don't ever want to do it again.

edited to add:

My Mum's house sustained major damage as well. The cinder-block foundation shifted during the rainstorms. We had to completely gut the basement/recreation area, hired a contractor to dig out and physically pull the foundation back into place and secure it with huge metal rods and plates in the ground. Then they added a rubber membrane to the outside of the foundation, install French drains around the property, and move all the dirt back. Total cost for that was $11,000, not including the cost of reframing, drywall, carpeting, etc. in the rec room. So you get an idea what these folks in N.O. are up against. It's going to cost an enormous amount of money.

then there's the rot and mold to think about. Seems like the French Quarter will be salvageable since it was higher. Hopefully they'll restore with great care as many historic buildings as possible. As for the others it would probably be cheaper to just bulldoze and rebuild.

The last time in 1993, when we had the big one. It was submerged for weeks, after the water receeded they stipped out the interior and rebuilt it, she's living there now.
So, it's possible to save buildings after a flood, some just need knocked down and a new structure erected, but, where I live we've been through many floods, and for the most part the houses and buildings were relivable afterwards.

Be assured the first priorities once the water recedes enough that power and some sort of water/sanitation system can be devised, the downtown and port areas will be priorities. It appears most of the major downtown structures needed for tourism (YES, tourism), banking and commerce could be the first back in operation, and with them the jobs that will start bringing people back to the city.

Fortunately the canals in Jefferson Parrish held and some infrastruture does remain. Unfortunately most of the affected areas are the most rundown and I suspect will be bulldozed...entire blocks and neighborhoods.

Here in Chicago, many cite the 1871 fire as being one of the greatest things to happen to this city. It wiped out a lot of substandard housing, led to a building boom, new housing standards and a bigger and better city.

New Orleans will rise again and will be as exciting and diverse as ever. Here's hoping this opportunity to re-do not only the levee and canal system but the entire eco-structure of the delta combined with some creative city planning can eventually bring a positive side to this true tragedy.

you said everything I was going to say about my hometown.

I would imagine that almost all residential housing from downtown north to the lake, and east to the Intracoastal Canal will be bulldozed.

One key thing that I am worried about is how this new residential housing is going to be insured. As much as I hate insurance companies, I wouldn't blame them if they didn't want to touch this.