Wikipedia has a nice summary. The USACE is assuming the opening in the Morganza will be 21% of capacity. http://en.wikipedia....pening_.282011.29

Following this analysis, which showed that extensive flooding is expected in the Atchafalaya Basin regardless of the choice made regarding the Morganza Spillway, the Corps decided to start the 2011 diversion by opening the spillway a bit less than described in scenario 1a (21%, not 25%)[36]

Here are some larger maps of the projected flood depths from the source - http://www.mvn.usace...rre/missriver.asp

Even with opening the Morganza, many places downstream are still going to see record crests (though apparently not Baton Rouge and New Orleans) - http://www.google.co...yKaXb9nN5MgGXul_Q (1 page .pdf)

THE RIVER AT BATON ROUGE THROUGH NEW ORLEANS WILL CREST SOONER THAN UPSTREAM LOCATIONS DUE TO MORGANZA SPILLWAY OPERATIONS...AFTER CRESTS, STAGES WILL REMAIN AT THE SAME LEVELS AND NEW ORLEANS WILL FLUCTUATE NEAR FLOOD STAGE WHILE BONNET CARRE & MORGANZA ARE OPERATED

Fingers crossed...

Cheers,
Scott.