Forensic Engineering - The Ripple Effect: The Fate of Freshwater in the Twenty-First Century - page 185

Experts say—only half-jokingly—that there are only two kinds of levees: those that
have failed, and those that will fail. They fail for many reasons: shifting rocks, falling
trees, or burrowing muskrats; getting hit by a ship or the tremendous pressure exerted
by floodwaters; or because of the weight of storm surges overtopping them, or burrow-
ing through them, or tunneling under them—any one of which can lead to catastrophic
flooding.
Levees exist in every state in the nation. The Federal Emergency Management
Agency (FEMA) , which is responsible for identifying flood hazards, estimates that
levees protect 55 percent of the American population, or about 156 million people. The
US Army Corps of Engineers (USACE, or the Corps), which is responsible for build-
ing and maintaining federal levees, has estimated that the United States has approxim-
ately one hundred thousand miles of levees. But more than 85 percent of US levees were
privately built , ad hoc, by farmers, developers, or businesses. No one really knows how
many of them exist, where they are located, who is responsible for their upkeep, and
what their integrity might be.
Many US levees were built 100 to 150 years ago out of whatever material lay close
at hand, such as sand and seashells dredged from the bottom of a canal, which are not
structurally sound. During construction, other materials—such as rocks, tree roots, and
human detritus (such as piles of garbage or old boxcars)—get swept up and entombed
inside levees' banks. These materials tend to shift and weaken the structure over time.
Private levees are not inspected by the Corps and are often not well maintained, fre-
quently leak, and are sometimes breached.
In a 2007 inventory of the levees that it oversees, the Corps found that 177 of
them—about 9 percent of federally inspected levees —were “expected to fail”; 122 of
the levees were at risk of “catastrophic failure.” California, with 37 at-risk levees, and
Washington State, with 19, were the worst off. But the list included levees stretching
from Washington, DC, to Hartford, Detroit, Omaha, Albuquerque, Los Angeles, and
Honolulu.
A weakened levee can suddenly give way with little or no warning. At four o'clock
one morning in January 2008, the residents of Fernley, Nevada , a dusty town east of
Reno, were awakened by the sound of a rushing torrent. Stumbling into the night with
their flashlights, residents were shocked to discover that a thirty-foot section of levee
along the Truckee Canal had ruptured. Within minutes, the breach had released enough
water to swamp 450 homes, force 3,500 people to evacuate, and cause millions of dol-
lars' worth of damage. Some residents found their predicament difficult to comprehend.
“We live in the desert, you don't think of [a flood] happening here,” a Fernley resid-
ent said. But there it was: water several feet deep in their basements. The exact cause of