The Mississippi River Mouth is distributing debris into the gulf and slowing the flowing river. The build up is exacerbated by the fertilizers and run off from up river cities and rural areas; these nutrients are helping the growth, which is limiting the water flow. The water is thus rising; while the silt builds up in the river mouth. The City of New Orleans is also sinking and the cities sea wall is getting older each year. No one knows which year will be the demise of the City from a Hurricane, only that the city is doomed.
The New York Times, Scientific America, USA Today have all done stories on this problematic situation. Billions have been spent building, maintaining and upgrading the sea wall there. In most of New Orleans the water table is above ground and you cannot hardly dig a hole anywhere without ground water filling it up. Floods come often to the city, from rains and when severe storms cause breaches in the sea wall. Up until now nothing too overwhelming has occurred, but if the sea wall collapses in a major way one-third of the city will be submerged at normal sea level heights. If it happens during a major Hurricane all of FEMAs horse and all the Kings men will not be able to save that wall again.
A twelve foot increase in sea height during a long slow moving hurricane with 17-18 foot waves could put the entire city under water if a large chunk the seawall is taken out. It will at that point be the largest disaster in the history of the United States. Think about it, we need a defense plan there.