Exporting calamity: Katrinas for everyone; Coming soon to a coast near you.

• Author: Tidwell, Mike

When the malevolent waters of Hurricane Katrina destroyed most of New Orleans, Americans across the country began asking two basic questions. How in the world did this disaster happen? And, Can the same thing happen where I live?

Surprisingly, in all the coverage since the storm, the media have answered the first question largely incorrectly and the second question not at all.

The main reason Katrina became a mega-disaster was not because of flawed hurricane levees and poor evacuation plans. These were just symptoms of a larger disease. Katrina destroyed New Orleans because, over the past 100 years, the Gulf of Mexico moved about one meter higher in relation to the city. The land itself, thanks to human activities, sank about two-thirds of a meter in relation to the Gulf while the Gulf waters rose-again because of human actions--about 30 centimeters.

That one-meter rise over the last 100 years wiped out a staggering 400,000 hectares of coastal wetlands and barrier islands between New Orleans and the Gulf. A land mass larger than Rhode Island simply turned to water. The result, by August 29, 2005, was to create a watery flight path for Katrina to slam into New Orleans, like a plane into the World Trade Center. The old landforms that had traditionally slowed down the surge tides of past hurricanes in Louisiana--the marsh grasses, the coastal islands--were almost all gone. Without them, only a fantastic fortresslike city could hold back such assaults. Sooner or later New Orleans was bound to lose, no matter how big the levees grew or how much bottled water was stored at the Superdome.

So why did the land sink in the first place, and the ocean rise? Because of something I call the Law of Unintended Consequences. The land sank because the lower Mississippi River no longer flows free. After 7,000 years of annual flooding at its mouth, which deposited along the Louisiana coast staggering amounts of sediments and nutrients drained from two-thirds of the continental United States, the lower Mississippi River doesn't flood anymore. From the crude early levees of the French settlers to the massive control structures of the Army Corps of Engineers, the lower Mississippi has been utterly tamed. It obediently stays within its banks all the way to the continental shelf and deposits its soil into the deep water of the Gulf of Mexico rather than along the Louisiana coast.

The pre-existing coastal land, meanwhile, then does something seemingly strange: it...