There's a dam on the lower Mississippi called the Atchafallia Dam (and most likely I spelled that wrong, so look it up yourself if it bothers you). It exists to insure that the Mississippi River flows past New Orleans and not down the Atchafallia River, which is where the River wants to go and which, if it followed its inclination, would leave New Orleans no longer a seaport.

The Mississippi River will eventually flow down the Atchafallia. Not right now, not perhaps in the next century, but it will.

Given enough time, Nature will utterly destroy everything Mankind has done. And Nature doesn't care if it's a garbage dump, the Citadel at Halifax, St. Peter's in Vatican City, or the Canadian Railways. Mankind could bring about the Nuclear Winter, and Nature -- red of tooth and claw and completely uncaring -- would simply start over. Nature is patient, and utterly ruthless.