FEW YEARS AGO, I took a flight from New Orleans to the spot known as the Bird’s Foot, where the Mississippi splays into three, clawlike distributaries and finally empties into the Gulf of Mexico. The plane was a four-seater, and it flew low enough that I could make out all the features of the ground below, or what passes for ground these days. Southeast of the city, Louisiana barely exists anymore; mostly it’s just open water. What keeps the Mississippi in its channel are two sets of enormous levees, one on each bank. From
