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 2011 event) had been opened by the Corps of Engineers. The Corps estimated the flow rate at . However, on May 25, new estimates from the U.S. Geologic Survey (USGS) described a much higher rate of , resulting in the closure of 3 bays by May 26, and additional closures by May 29, bringing the total to 11 bays with an estimated diversion rate of . The Corps continued to evaluate the flow and close additional bays as appropriate. By June 6, the number of open gates had been reduced to seven, and by June 8, only two gates were