A place for the US Army Corps of Engineers to dump water from the Mississippi River into Lake Ponchartrain to prevent flooding of the below sea level New Orleans.

The red crane in the distance is used to remove the wooden panels that contain the river in it's levee's when these planks are removed, the Spillway fills with the muddy water into the lake

For more information on the Bonne Carre see Pbase Coleen Landry's site
http://www.pbase.com/septembermorn/bonnet_carre_spillway