View of the Bonnet Carre Spillway, Norco, Louisiana, USA, with the Dow Chemical petrochemical manufacturing complex in the background. The US Army Corps of Engineers opened the Bonnet Carre Spillway in 1931 to protect New Orleans from Mississippi River flooding. The spillway can divert flood water from the Mississippi to Lake Pontchartrain and then into the Gulf of Mexico, thus reducing water levels at New Orleans.