The weekend flooding in Tennessee that killed at least 21 people was more destructive than originally estimated, with about 120 homes washed off foundations, destroyed, or simply “gone,” officials said Tuesday. The scope of the damage came into sharper focus in hardest-hit Humphreys County, as rescue teams continue to search house-to-house with trained dogs for dozens believed still missing. “Our damage is much more massive than what we thought,” Humphreys County Sheriff Chris Davis told NPR in an interview Tuesday. It was already believed that hundreds of homes were water-damaged and uninhabitable, officials said after the storm brought 17 inches of rain in just three hours. Davis and other officials surveyed the damage from a helicopter late Monday, focusing largely on the hardest-hit town of Waverly, about 55 miles west of Nashville. “Yesterday we thought it was 20-something houses that had been removed from the foundations,” Davis said. “That’s not …