It's called "dirt". dirtboy. They are able to haul it in big trucks and then spread it over the low spots. Kinda neat.
Good one there. ;)
It's called subsidence, Sham. The entire region is sinking because of levees. The very structures that keep out the floods also prevent sedimentation from keeping pace with subsidence. Spread five feet of dirt now to build up, and it'll just sink back down to where it was in a couple of decades. That's how NOLA came to be so far under sea level.