re: Mississippi River diverging: When do we finally let it go down the Atchafalaya?

Nature might eventually force our hand. The big problem is that only about 1/3 of the current water volume would be going down the current channel, and that would cause saltwater to backflow into the NOLA metro area and ruin the supply of drinking water.

You'd also have to move not only over 1,000,000 residents of NOLA plus all the people who would be displaced by the new course of the river, but also a couple of airports, several universities, some of the oil and gas infrastructure, the Port of New Orleans, etc. It would likely cost hundreds of billions of dollars that we don't have right now.