Vivian Spencer, an elementary school principal in Waverly, Tenn., watched helplessly from atop her gymnasium’s bleachers as floodwaters rose several feet high around her on Aug. 21.

Spencer, along with her daughter and two more adults stranded with them, placed calls for help on social media before losing electrical power and cellphone service. Three hours later, friends rescued them by boat. Even then, swift currents and chunks of pavement loosened by the floodwaters struck and almost capsized the vessel.

Still, it could have been worse.