The water in New Orleans' natural aquifer is modest in amount and even less appealing than the water in the river. The city consumes the effluent of nearly half of America, and, more immediately, of the American Ruhr. None of these matters withstanding, in 1984 New Orleans took first place in the annual Drinking Water Taste Test Challenge of the American Water Works Association.

The river goes through New Orleans like an elevated highway. Jackson Square, in the French Quarter, is on high ground with respect to the rest of New Orleans, but even from the benches of Jackson Square one looks up across the levee at the hulls of passing ships. Their keels are higher than the AstroTurf in the Superdome, and if somehow the ships could turn and move at river level into the city and into the stadium they would hover above the playing field like blimps.

In the early nineteen-eighties, the U.S. Army Corps of Engineers built a new large district headquarters in New Orleans. It is a tetragon, several stories high, and it is right beside the river. Its foundation was dug in the mainline levee. That, to a fare-thee-well, is putting your money where your mouth is.

Among the five hundred miles of levee deficiencies now calling for attention along the Mississippi River, the most serious happen to be in New Orleans. Among other factors, the freeboard--the amount of levee that reaches above flood levels--has to be higher in New Orleans to combat the waves of ships. Elsewhere, the deficiencies are averaging between one and two feet with respect to the computed high-water flow line, which goes on rising as runoffs continue to speed up and waters are increasingly confined. Not only is the water higher. The levees tend to sink as well. They press down on the mucks beneath them and squirt materials out to the sides. Their crowns have to be built up. "You put five feet on and three feet sink," a Corps engineer remarked to me one day. This is especially true of the levees that frame the Atchafalaya swamp, so the Corps has given up trying to fight the subsidence there with earth movers alone, and has built concrete floodwalls along the tops of the levees, causing the largest river swamp in North America to appear to be the world's largest prison. It keeps in not only water, of course, but silt. Gradually, the swamp elevations are building up. The people of Acadiana say that the swamp would be the safest place in which to seek refuge in a major flood, because the swamp is higher than the land outside the levees.

-- John McPhee, writing in 1987. Read more here.