re: What's to keep USACE from adjusting flow at ORCS to push the salt wedge downriver?

It wasn’t as big a deal back then because the river was not as deep. In the early part of the 20th century it was decided that the river be dug deeper to allow for bigger ships to go through the river.
Salt water is heavier than fresh water so it flows up river on the bottom. Since the bottom is lower, it allows the saltwater to creep up more.
Also the same amount of water flowing down the river in those years with a shallow bottom versus now with a deeper bottom had more force to keep the saltwater at bay in the gulf.

how many of our parishes get their drinking water from the mississippi river?

and 1988 say's hold my kentwood bottle