I think the feds were in charge of the River levees and if the Mississippi changes course it is a bigger issue than new orleans having a flood. I don't know for sure but that is my guess.
I have a memory of people talking about Miss flooding NO and a decision to break the levee at Baton Rouge to protect New Orleans being discussed. It has enormous implications. The state Capitol is in BR and that is who would make that decision.
I don't know much about the 1927 flood but this may have been an issue then,,maybe someone else remembers.
We had a much smaller but similar situation years ago in San Diego..the Rodriguez dam in Mexico was full from rainwater and in danger of breaking..they let water out the spillways down the flood control channel to the US without giving enough notice downstream causing lots of damage... if the dam had busted it would have been ten times worse...