There’s a spillway north of town that they will probably open to divert excess water away from the river channel & city. Hopefully, that will be enough. Look up the Bonne Carre(sp?) spillway.
You realize that the Bonnet Carre spillway empties into Lake Pontchartrain? And THAT has famously good levies.(Have they been improved enough lately?) I really don’t know, but it certainly depends on the volume of water and how long it takes the whole thing to arrive. If it drains south slowly, nothing will happen.
I don’t think it will have that big of an impact by the time it hits New Orleans. The river channel in LA can hold much more water than the river channel in MT, ND and SD.