Old River Control Structure such that the volume of the two rivers is split 70%/30%, respectively, as measured at the latitude of Red River Landing. This flow split was not based on science, but rather was based on the approximate flow allocation between the two rivers that existed at the time of construction. Water diverted at Old River flows into the Atchafalaya Basin, first entering the Red River, then continuing down the Atchafalaya River to the Gulf of Mexico, bypassing Baton Rouge and New Orleans (see diagram). The Morganza Floodway, between the Mississippi and the Atchafalaya Basin nearby downstream, is normally closed, but can
Morganza Spillway was 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%) The Governor of Louisiana, Bobby Jindal, had meanwhile sent a letter on May 4, 2011, to Robert Gates, the United States Secretary of Defense, requesting that the National Guard be deployed under Title 32 of the United States Code status to respond to record water levels in Louisiana, where there was "a significant probability that the U.S. Army Corps of Engineers [would]