Inadequate flood protection from suspect US levees

Evan Lehman in Scientific American via ClimateWire: Levees are as varied in the United States as the people they guard. They're shaped like snakes, rings and spurs that can be tough, flimsy or a century old. No one knows for sure where all of these earthen walls are, who built them or what type of rocky mixture lies shrouded inside their bulk. Some help protect homes from flooding, while others ring industrial zones containing chemical plants and refineries. Many stop rivers from turning into lakes on farms that abut the riverfront.

They shadow the diverse landscapes they protect. But these widely disparate levees do share at least two common traits -- they are all steadily weakening from water's efforts to go under, over or straight through their earthy embankment. Very few were built to protect against the more powerful storms expected by climate scientists and the flooding that will accompany them.

Now, after years of treating suspect levees with remarkable caution, federal flood officials are recalibrating the way they view the risk to communities lying behind these walls. Government officials say it's driven by better scientific methods used to measure precise flood hazards. But critics believe it could result in still more homes being built in the path of runaway water.

"I do think it's a huge concern," said Shana Udvardy, who directs flood management policy for American Rivers. "The risk is, people are going to believe they're safe when they're not." At last count, there were roughly 30,000 miles of levees across the country. String them together and they would wrap around the world, and then some. Here's another way to harness their ubiquity: For every McDonald's restaurant in America, there are more than 2 miles of levees.

And most of them, almost 70 percent, are not trusted by government flood officials to do their job. The Federal Emergency Management Agency (FEMA) said in 2010 that 20,350 miles of levee walls are "not accredited" -- meaning that those who live behind the barriers are assumed to be threatened by a "high risk" of flooding....

Boys climbing on a levee in New Orleans, shot by Carly Lesser & Art Drauglis, Wikimedia Commons via Flickr, under the Creative Commons Attribution-Share Alike 2.0 Generic license