The violent force of flash flooding

Flash floods carry thousands of tons of force. Here's what makes them so destructive. AccuWeather's Leslie Hudson has more.

Transcript

00:00Water's power can be deceptive. A few inches of rain can escalate into a deadly flash flood

00:09in minutes. In Central Texas, the 275-mile stretch known as Flash Flood Alley is among

00:16the most dangerous in the U.S. On July 4th, over 10 inches of relentless rain pounded the Texas

00:22Hill Country, sending the Guadalupe River surging 26 feet in under an hour. Hydrologist

00:29Gregory Waller says a number of factors combine to create this flash flood disaster. This wasn't

00:35just meteorology and hydrology. This was a, you know, convergence of all the bad things

00:43to make this a catastrophic event. Flash floods don't just hit hard, they last. While tornadoes

00:49pass in minutes, flash floods can wreak havoc for hours with the extreme volume and force

00:55of the water and more. We had 150,000 of these cubic feet going through. So you could equate

01:02it like a column of 18 wheelers of mass coming down that river system, knocking everything

01:09out. The other issue is it's not necessarily the water. It's what is the water also bringing

01:14with it? It picks up debris. It picks up a log, which becomes a medieval battering ramp.

01:19It picks up, you know, a car, a vehicle, a house that creates more surface area and more

01:25force. At peak flow, the Guadalupe River pushed over 4,200 tons of water per second. Just a

01:31few feet of fast moving water can unleash more pressure than an EF5 tornado. They're both catastrophic,

01:38even though the damage looks similar. You know, a tornado is 100 plus miles an hour, 200 plus

01:44mile an hour winds, but only for a few minutes. You know, we're talking about a volume of water

01:48that even in a fast responding river system, it's two to three hours to go up, two to three

01:54hours to come down. Wind has mass, it's moving, it's picking up debris, but water has a lot more.

02:00Waller says warmer temperatures and shifting rainfall patterns are making severe weather events

02:05more frequent and more dangerous. When we use the term emergency, this is a level that you may have

02:12to do more than the normal safety protocols in order to survive. We're talking catastrophic damage at

02:18this point. And it requires another level of preparedness and reaction.

02:22For AccuWeather, I'm Leslie Hudson reporting.