New Orleans: The Big Easy On the Brink

If a flood of Biblical proportions were to lay waste to New Orleans, Joe Suhayda has a good idea how it would happen. A Category 5 hurricane would come barreling out of the Gulf of Mexico. It would cause Lake Pontchartrain, north of New Orleans, to overflow, pouring down millions of gallons of water on the city. Then things would really get ugly. Evacuation routes would be blocked. Buildings would collapse. Chemicals and hazardous waste would dissolve, turning the floodwaters into a lethal soup. In the end, what was left of the city might not be worth saving. "There's concern it would essentially destroy New Orleans," says Suhayda.

Suhayda, a water-resources expert at Louisiana State University, is the kind of guy who could have given Noah a computer model of all 40 days and 40 nights of rain, including the Ark's soft landing on Mount Ararat. So it is real cause for concern that he has joined the chorus of scientists and environmentalists who are saying that the watery threat to New Orleans is extreme--that in the worst-case scenario, in fact, there might not be a city of New Orleans left standing by the end of the century.

New Orleans has always had a complicated relationship with the water surrounding it. Everyone told the first settlers this was the wrong place to build a city. It is wedged precariously between the mighty Mississippi and Lake Pontchartrain, and most of it was once swampland. Aggravating the problem is the fact that much of New Orleans is below sea level, so that after a good rain, the water just settles in. There is now a decent pumping system, which helps. Old-timers, however, still talk of the days when, after a bad storm, bodies washed out of the cemeteries.

What is threatening New Orleans is a combination of two man-made problems: more levees and fewer wetlands. The levees installed along the Mississippi to protect the city from water surges have had a perverse effect: they have actually made it more vulnerable to flooding. That's because New Orleans has been kept in place by the precarious balance of two opposing forces. Because the city is constructed on 100 feet of soft silt, sand and clay, it naturally "subsides," or sinks, several feet a century. Historically, that subsidence has been counteracted by sedimentation: new silt, sand and clay that are deposited when the river floods. But since the levees went up--mostly after the great flood of 1927--the river has not been flooding, and sedimentation has stopped.

The upshot is that New Orleans has been sinking as much as 3 ft. a century. That's bad news for a city that is already an average of 8 ft. below sea level. Making things worse: sea levels worldwide are rising as much as 3 ft. a century on account of global warming. The lower New Orleans plunges, the worse it will be when the big one hits.

New Orleans' other major man-made problem is that its wetlands and its low-lying barrier islands are disappearing. The Louisiana coast is losing 16,000 acres of wetland each year, mostly as a result of population expansion into once pristine areas, destructive oil and gas drilling, pollution and land loss through lack of sedimentation. As it turns out, wetlands and barrier islands aren't just nice to look at; they are also a key natural barrier to hurricanes. (Every 2.7 miles of wetland absorbs a foot of storm surge.) As the wetlands go, the chance of a hurricane blowing the city away grows.