Newspaper archives are filled with accounts of surging waters, submerged plantations, quicksand, and close calls. In the Great October Storm of 1893, women were saved from drowning, the story goes, only when their long hair wrapped around tree limbs. “Down the bayou we are used to dealing with sudden adversity,” the poet Martha Serpas wrote in 2010. “We calibrate history by big hurricanes.”
The word “levee” comes from the region, too—from the French lever, to rise—but the technology itself comes from nature.
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Natural levees form gradually in response to floods. When high waters recede, they leave sediment on the banks. Those mud and sand deposits gradually build up into a buffer against subsequent floods. The idea behind manmade levees works the same way: They provide extra protection in areas prone to flood.
Today’s levees are designed to meet meticulous engineering standards. Inspection guidelines by the Army Corps of Engineers specify that urban levees should be built high enough to handle a 10-year flood, that is, a flood with a 10 percent probability of occurring in a given year.
But height, while critically important, is just one dimension of a technology that hasn’t ultimately changed that much over the millennia. Levee inspectors also look for signs of erosion, rutting or other pits that might indicate drainage problems. They look for cracking, slope stability, and signs of unwanted vegetation or animal burrowing. “Levee systems are complex because their successful performance relies on many different aspects working in conjunction with each other," said Tammy L. Conforti, the Levee Safety program manager for the U.S. Army Corps of Engineers, in a statement provided by a spokesman.
New Orleans now claims to have the best flood protection of any coastal community in the United States. “Today’s levee system is a far cry from the flawed structures that failed during Hurricane Katrina, devastating much of the region and killing hundreds of people,” the Times-Picayune wrote in 2013. “The new system was designed using better engineering, more advanced computer modeling and better construction materials. Just as important, it was designed to be a true system, and not just a system in name only as its predecessor.”
That may be true. It’s also been claimed before. “We have spent hundreds of millions of dollars to protect ourselves from water,” Louisiana Governor John McKeithen said in 1965, in the months before Hurricane Betsy devastated New Orleans, according to Craig Colten in his book, Transforming New Orleans and Its Environs. “We have built levees up and down the Mississippi,” McKeithen said. “We feel like now we are almost completely protected.”
And the city still wasn’t protected half a century later. When dozens of levees catastrophically failed throughout New Orleans in 2005, the strength of the storm surge was only partly to blame. It wasn’t just that water flowed over the tops of levees; the levees themselves disintegrated and in some cases shifted suddenly in huge sections. “Think of a layer cake,” Thomas Zimmie, a civil engineer at Rensselaer Polytechnic Institute, told the Times-Picayune in the weeks after the storm. “In the middle I’ve got my icing. All of a sudden, I push on the top of my piece of cake, and what it's moving on is this weak, slick icing. The whole thing moves.”