Over just two hours, the Guadalupe River at Comfort, Texas, rose from hip-height to three stories tall, sending water weighing as much as the Empire State building downstream roughly every minute it remained at its crest. The force of floodwater is often more powerful and surprising than people imagine.

Sisters Blair Harber, 13, and Brooke Harber, 11, were killed, along with their grandparents, when surging floodwaters ripped through the community. Their parents were staying in a different home at Casa Bonita and survived, according to the family's GoFundMe.