From the New York Times:
People tend to underestimate the power of floods: six inches of fast-moving water can knock you down; two feet of water can float most cars away. Floods kill an average of 127 Americans a year — more than tornadoes or hurricanes — and cause more than $2 billion of property damage annually, according to the National Oceanic and Atmospheric Association.
This spring, the nation was riveted by images of blown levees and submerged towns in the Midwest along the Mississippi River. But an even more threatening situation looms in California, especially around the San Francisco Bay Delta. The delta is the link between two-thirds of the state’s fresh-water supply — which originates in the Sierra Nevada and the rivers of the north — and two-thirds of the state’s population, which resides in the south.
Starting in the 1870s, farmers began building 1,100 miles of levees around the delta to control floodwaters and create farmland out of tule marshes. Today many of those levees are old, decrepit and leaking. Jeffrey Mount, a geologist at the University of California, Davis, predicts that there is a 64 percent chance of a catastrophic levee failure in the delta in the next 50 years.
For more, see: California’s Next Nightmare