Controlling and dredging the river rather than allowing it to migrate back and forth to the Atchafalaya keeps sediment/silt from replenishing itself. However, the delta was growing even into the 1960's (while we were losing some stuff elsewhere). The biggest problems were the canals that crisscross the marshes and allowed the saltwater to come in and kill the vegetation (marsh is estimated to reduce surge by 1' per mile) and the loss of barrier islands which gave immediate protection. Louisiana's coast hasn't been evolving for millions of years, because it's not that old. It's in the "tens of thousands" of years at best because it was all built up by river sediment (which naturally sinks and is replenished). There are actually some projects in their infancy to pipe out the silt into some of the barrier marshes with attempts to eventually seed them for the hold you get with vegetative roots. We'll see.
here's a shot of the southshore pre and post Katrina. Like I said, it's all pretty much open water now.
Steve
could we leave Mississippi out of this conversation please .... 
