Flash Floods

You can plan or not plan and it doesn't make a hell of a lot of difference. What makes a difference is how much it decides to rain.

—Mark Twain, Life on the Mississippi

Flash floods are local events that occur very rapidly in semiarid mountainous regions. Following an unusually heavy rain (thunderstorm) in the headwaters of a mountain stream, the water comes roaring down the canyon in a wave often 10-15 feet high, a churning mass of water, rocks, mud, and debris with the power to rip up trees and crush buildings in its wake. In the United States common locations for flash floods are the Rocky Mountain region and desert areas in New Mexico and Arizona. Because of the high velocity of the water in the narrow stream channel, people living downstream may have little warning before the deluge hits. Consequently, there is limited opportunity for an organized response. The emphasis must be on saving lives rather than reducing property damage. Even when a few hours of warning time is available, it may be impossible to save real estate. The volume of water in a flash flood is so great that most structures in the path of the flood cannot be protected. The only thing to do when a flash flood is coming is get out of the way by heading to higher ground.

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