The power of flash floods
AccuWeather's Emmy Victor shares just how powerful and dangerous flash floods can be.
Transcript
00:00 (upbeat music)
00:02 - Certainly when one gets up to inches per hour,
00:10 you're looking at the potential for flash flooding.
00:13 - During storms, keeping track of the rainfall intensity
00:16 and the volume of water per unit time
00:19 indicates if flash flooding is possible or likely.
00:23 Land elevation, soil conditions,
00:25 and ground cover also play a huge role.
00:28 - It would be very surprising to people in many places
00:33 what the magnitudes of the floods are
00:35 that are actually possible on the landscape.
00:38 - Flash floods are extremely powerful.
00:41 Victor Baker, professor of hydrology
00:43 and atmospheric sciences, says water flowing in a stream
00:47 typically runs an average of a few feet per second.
00:50 A flash flood flow could be 10 times that.
00:53 - If the water velocity is 10 times what you usually see
00:59 the energy is a hundred times what you usually see.
01:03 That is because energy goes up
01:05 with the square of the velocity.
01:08 - Fast moving water can be deadly.
01:10 It can also sweep away cars, roll boulders,
01:12 tear out trees, and destroy bridges and buildings.
01:15 - Think about what you normally see in a river
01:19 and what it does flowing along by your feet
01:22 and think of a flow more than a hundred times more energetic
01:28 and that is an example of why those two things,
01:31 why you have the problem from these floods.
01:34 - Flood waters also pick up massive amounts of debris
01:37 as they move, which can restrict the flow of water
01:39 and increase flooding.
01:41 Rapidly rising water can reach heights of 30 feet or more.
01:44 - So the water may back up behind that
01:47 and you may actually get a depth of water
01:50 five feet, seven feet deep,
01:53 just coming in all together, all at once.
01:55 For AccuWeather, I'm Emmy Victor.