By Dr. Robert Thorson
Let bayous be bayous. If the land beneath New Orleans wants to be a bayou, then I suggest we let the levees, dikes and pumps fail. Let Old Man River do its delta thing.
Let the City of Jazz become the wonderful swamp that nature intended. All that’s necessary is for urban residents to evacuate the land permanently, instead of every time a strong hurricane bears down on the Mississippi Delta.
In the eleventh hour of Sept. 15, New Orleans was spared a direct hit by Hurricane Ivan. The storm veered east, pounding Mobile Bay instead. The 1.3 million people who had evacuated returned. One of these days, however, they’ll come back to a sea of slippery mud resembling brown butter, a sign that nature is reclaiming its natural course.
Eight miles of “mountain butter.” That’s the way the writer John McPhee described the foundation of New Orleans in his 1989 book, “The Control of Nature.” Real butter melts in the hot sun. Mountain butter — Mississippi silt washed down from the Rocky Mountains — is different. It doesn’t melt. Rather, it slowly compacts, bringing the land surface down with it. This is terrible news for New Orleans, which sits as much as 10 or 15 feet below the Mississippi. Actually, it’s worse than terrible. It’s an impossible situation. With sea level rising steadily, New Orleans will someday go under. It’s a modern-day Atlantis in the making.
Think Venice, Italy (but add in deadly hurricanes), to have some idea of what we’re dealing with. Venice was also built on a river delta, beneath which are thousands of feet of mountain butter with a European flavor. Before human settlement, Venice stayed above sea level because the river deposited layers of fresh mud to replace the elevation lost by compaction. After settlement, humans kept the river away with dikes and pumped the underground water, causing the land to sink. The Italian answer? Abandon the lower floors of buildings, let the roads go under and switch from wheeled transport to gondolas.
Much of New Orleans has also sunk below sea level. But instead of letting the Mississippi replenish the land with sediment, or letting the sea come in, the U.S. Army Corps of Engineers has shunted the river away, rimmed the bowl-shaped zone of subsidence with giant concrete dikes and installed sump pumps to suck away excess water. Things seem fine until hurricanes threaten, because each one dumps torrents of rain into the bowl and sends a storm surge against its perimeter. One of these days, waves pounding high on a levee will “melt” a pat of mountain butter, causing the dikes to fail and the sea to rush in. At the same time, the artificially elevated Mississippi River will back up and likely pour in from the north. New Orleans will become a new Venice, at least for a few miserable days.
The basic problem is a conflict between geological certainty and financial inertia. The Mississippi Delta has grown steadily since the days of the dinosaurs, mostly from sediment shed from the northern High Plains. When too much sediment accumulated in one place, the river simply shifted its course, inaugurating the growth of a new delta lobe somewhere else and ushering in an interval of subsidence on the abandoned lobe.
This is what nature has in mind for New Orleans. Yet, this is what’s now being prevented by a federally subsidized engineering infrastructure that becomes more costly as the city sinks further and the river rises higher to deliver its load of mud farther away. Geologically speaking, New Orleans becomes a worse place to live every year.
For a more familiar example, consider a community of homeowners who have built their houses on a cliff that, over time, has eroded. My recommendation would be for them to enjoy the view while they can and then move the houses back when they threaten to fall over the edge. I recommend something similar for New Orleans, which has already sunk beneath the brink of sea level. There is no fair and reasonable alternative but to move the city to higher ground.