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.
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.
...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.
...Which levees are safe?
"without levee." It's a decision based on strict criteria: If a town can't prove that the engineering of its walls is able to repel a flood with a 1 percent chance of occurring each year, then FEMA doesn't consider it to be there.
That's a sober position, many believe, at a time when the arc of development is growing in dangerous flood plains. The "without levee" provision is akin to a red alert. Everyone behind the unaccredited wall is living in a race course for water, FEMA assumes.
