Bonnet Carré Spillway — The Valve That Saves New Orleans

About thirty miles upstream from New Orleans, the Bonnet Carré Spillway is the emergency valve that has kept the city dry for nearly a century. When the Mississippi rises to dangerous levels, the Army Corps of Engineers opens the spillway's three hundred fifty steel bays, diverting water across six miles of low wetlands into Lake Pontchartrain rather than letting it pile up against New Orleans' levees.

The spillway was built between nineteen twenty-nine and nineteen thirty-one, a direct consequence of the Great Mississippi Flood of nineteen twenty-seven, the disaster that killed roughly five hundred people, flooded sixteen million acres, and finally broke the American faith in levees alone as flood control. Congress authorized a new system of relief structures and spillways, and Bonnet Carré was the most critical: the last line of defense for the largest city on the lower river. Engineers first opened the bays in nineteen thirty-seven, and the spillway has performed its function more than a dozen times since. It is a Civil Engineering Historic Landmark, the pivot on which New Orleans' survival has repeatedly turned.