Breaking down the force of water in the Texas floods

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.

- By MICHAEL PHILLIS Associated Press

The force of floodwater is often more powerful and surprising than people imagine.

Comfort offers a good lens to consider the terrible force of a flash flood's wall of water because it's downstream of where the river's rain-engorged branches met. The crest was among the highest ever recorded at the spot — flash flooding that appears so fast it can "warp our brains," said James Doss-Gollin, assistant professor of civil and environmental engineering at Rice University.

The Texas flood smashed through buildings, carried away cars and ripped sturdy trees out by the roots, dropping the debris in twisted piles when the water finally ebbed. It killed more than 100 people, prompted scores of rescues and left dozens of others missing. The deaths were concentrated upriver in Kerr County, an area that includes Camp Mystic, the devastated girls' camp, where the water hit early and with little notice.

Water is capable of such destruction because it is heavy and can move fast. Just one cubic foot of water — imagine a box a bit larger than the size of a basketball — weighs about 62 pounds (28 kilograms). When the river rose to its peak at Comfort, 177,000 cubic feet — or 11 million pounds (fivemillion kilograms) of water — flowed by every second.