New Orleans' levees: Past, present, future

How did the levee system around New Orleans come to be? And can it be improved to prevent the city from becoming flooded in a future storm? We look at the history -- and future -- of the levees around New Orleans. Guests: Craig Colten, author of "An Unnatural Metropolis: Wresting New Orleans from Nature," and professor of geography at Louisiana State University in Baton Rouge; and Philip Davis, NPR correspondent.