Long before settlers decided that the shores of the Mississippi would be a nice place to raise a family, the river regularly topped its banks, heaping silt and mud onto surrounding wetlands. After a particularly nasty flood in 1927 that killed 300 people and left 600,000 homeless along the length of the river, city leaders in New Orleans decided to construct levees-some up to 25 feet high-to contain the swelling river during heavy rains. Residents had also been battling yellow fever, a viral
disease spread by mosquitoes. From 1817 to 1905, the epidemic killed 40,000. "So people decided to drain the swamps," says Al Naomi, senior project manager for the U.S. Army Corps of Engineers in New Orleans. With the levees in place and the swamps pumped dry, the city could now spread into areas that were once uninhabitable. "But when you take the water out of the swampy soils," he continues, "they start sinking."