It’s been some time since we carried anything on dam safety. This California story is scary. 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 Administration (corrected). This spring, the nation was riveted by images of blown levees and submerged towns in the Midwest along the Mississippi River.