[scythe]

I think you've got this backwards. Sometime in the 15th century, the Mississippi's course drifted westward and crossed with the Red River (now called the Atchafalaya River) at Turnbull's Bend. From that point forward, according to the laws of hydrology, the Old Mississippi was inevitably doomed. The ACoE's ORCS acts to prevent the Mississippi from being completely diverted along the Atchafalaya.

It's the parts of the delta which are fed by the Old Mississippi which are disappearing, and this is a totally natural process. The same river is what serves the port of New Orleans. The natural course of the river can only be temporarily stayed; it will find a way around the ORCS eventually. If the river is allowed to flow naturally, the majority of Southeast Louisiana, including New Orleans and Lake Ponchartrain, will disappear under the ocean.