July 30 in Ellicott City, Md., began as a typical hot summer day. Founded in 1772 as a mill town along the bottom of a deep valley through which the Patapsco River flows, the city had seen plenty of serious floods. But July 30 proved to be anything but typical. That day, what the National Weather Service has called an “off-the-charts” thousand-year rainfall event (in terms of recurrence interval) occurred, creating chaos and destruction as flash floods ran through the middle of the city after more than 6 inches of rain fell in two hours. With little warning, Main Street became a turbulent river tossing cars, smashing storefronts, gutting small shops and leaving devastation, lost lives and massive sinkholes in its wake.