This says three main factors: 1.)sediment flow changes - we changed flow of Mississippi River to benefit a lot of upstream communities (for flood control/farming/maintaining river boundaries against nature's desire) - continuing to do so robs Louisiana of land mass 2.) subsidence - pumping out water aquifers and extracting oil (without replacing fluids) cause land levels to sink 3.) sea level rise

https://www.factcheck.org/2017/03/land-loss-in-louisiana/ All three together paint a pretty grim picture of the future of New Orleans.