The land nearest to the Mississippi River rises several feet above sea level. That about 50 percent of the city lies below sea level is the result of human activity, as Tulane geographer Richard Campanella details in an Atlantic Monthly article on the magazine's web site. (Photo at left by Baton Rouge Advocate.)
Campanella, the foremost authority on how New Orleans' unusual geography shaped its development, says New Orleans' land at first was entirely above sea level, as much as 14 feet higher on the ridge closest to the Mississippi River when the French began building the city there in 1718. The swamps and marshes nearer to Lake Ponchartrain were a few feet above sea level in the city's early days.
Areas of the city now below sea level began sinking as the result of drainage and flood-control projects began in the 19th century, as Campanella examines.
Falsely believed the cause of diseases like yellow fever, wetlands were drained, increasing the land's subsidence. Housing developments and commercial centers were built on the sunken land.
That made the city more susceptible to flooding and hurricanes, as shown by Katrina's devastation. Campanella describes metro New Orleans as a series of hollowed out bowls that fill with water during disasters like Katrina.
The subsidence can't be reversed, says Campanella, author of "Cityscapes of New Orleans" and other books, including a colorful history of Bourbon Street. A massive flood control project resulting from Katrina is under way, but Campanella warns that a more massive "moonshot" is required.
Campanella connects the city's man-made geographical problems to other complex processes threatening the city, such as the loss of coastal land and the intrusion of saltwater. While he seems pessimistic about the city's future, he says restoration of wetlands offers the best hope.