In response to the Mississippi River flood of 1927, the Lower Mississippi's most devastating disaster, Congress established a comprehensive flood control and navigation program, the Mississippi River and Tributaries (MR&T) project, in 1928.  Some 3,714 miles of levees have been authorized, with over 3,400 miles currently in place to contain flood flows. 
     The MR&T project includes four principal elements.  Levees contain flood flows; floodways remove excess flows from critical reaches of the Mississippi; channel improvements stabilize channels to provide efficient navigation alignment, increasing the river's flood-carrying capacity and protecting the system; and tributary basin improvements provide dams, reservoirs, pumping plants, auxiliary channels, etc. 
FACT: The MR&T includes four floodways that move excess flows from the river in order that the levee system may avoid undue stress.  One of these floodways, the Bonnet Carré Spillway, diverts the flood crests of the Mississippi River into Lake Pontchartrain to keep the river level lower at New Orleans.
FACT: Since 1928, the MR&T project has prevented nearly $226 billion in flood damages, for a total investment for construction and maintenance of only $9.6 billion.  Therefore, the program has returned over $23 in damages averted for every $1 spent on program costs.