Until the 20th century, they kept to the high ground along the Mississippi River and on three nearby rises—the Metairie, Gentilly, and Esplanade Ridges. But in the early 1900s a brilliant city engineer, A. Baldwin Wood, invented massive pumps, up to 14 feet (four meters) in diameter, that were used to drain the great cypress "backswamp." The booming metropolis began spilling north toward Lake Pontchartrain. As the swamp soils dried, they shrank and compacted, slumping below sea level. In every flood since, the newer, lower neighborhoods suffered the most as the waters found their former haunts in the old swamp.

The great tragedy of Katrina is that the hard lessons learned in those earlier storms were blithely forgotten by all. After the great Mississippi River flood of 1927 wreaked havoc all along its course and came within a few feet of spilling over the river levees and inundating New Orleans, the growing city clamored for additional protection. Over the coming decades, the federal government erected a vast network of levees and spillways along the river and around the city, while giant new dams along the Missouri—the Mississippi's longest tributary—ponded water all the way to South Dakota. The system was billed as a triumph of engineering over nature.

Yet Gilbert F. White, considered the "father of floodplain management," came to a far different conclusion, one that Katrina drove home with a vengeance. As a young University of Chicago geographer, White had studied the delta after the 1927 disaster and realized that much of the suffering could have been avoided. "Floods are 'acts of God,' " he wrote in 1942, "but flood losses are largely acts of man." White and his colleagues argued that dams, levees, and other flood protections may actually increase flood losses because they spur new development in the floodplain, which incurs catastrophic losses when man-made flood protections fail. The phenomenon came to be known as the "levee effect."

Nowhere was White's advice more gleefully flouted than in the Lake Pontchartrain and Vicinity Hurricane Protection Project—the 125-mile-long (200 kilometers) system of levees and gates built by the U.S. Army Corps of Engineers to protect the city after Hurricane Betsy ravaged it in 1965. City planners and developers applauded as the corps not only strengthened existing levees around the city but also threw new levees far and wide, enclosing thousands of acres of undeveloped wetlands lining the new I-10 corridor. In fact, 79 percent of the estimated benefits that the corps initially used to justify the cost of the project came from the future development of those wetlands. Within a decade, Jefferson Parish had built 47,000 new housing units—modern-day Metairie and Kenner—while Orleans Parish added another 29,000 units, mostly in New Orleans East.

"It was basically a development scheme," says Oliver Houck, a Tulane professor of environmental law who has fought other corps projects. "They put it around New Orleans East, and the developers laughed all the way to the bank."

FROM ITS INCEPTION, the project was beset with technical problems, litigation, and political tinkering. What was supposed to be built in 13 years for 85 million dollars became a never ending 740-million-dollar project that was still ten years from completion when Katrina hit. The Government Accountability Office—the watchdog of Congress—had a field day, regularly criticizing the corps for cost overruns and delays.