Tuesday, July 24, 2007

Flash Flood

A flash flood is a rapid flooding of low-lying areas (washes), rivers and streams, caused by the intense rainfall associated with a thunderstorm, or multiple training thunderstorms. Flash floods can also occur after the collapse of an ice dam, or a man-made structure, such as a dam. Flash floods are distinguished from a regular flood by a timescale less than six hours.

Flash flooding occurs when the ground becomes saturated with water that fell so quickly that it could not be absorbed. The runoff collects in low-lying areas and rapidly flows downhill. Flash floods most often occur in normally dry areas that have recently received precipitation, but may be seen anywhere downstream from the source of the precipitation (even dozens of miles from the source).

Flash floods are extremely dangerous because of their sudden nature. Being in a vehicle provides little to no protection against being swept away; it may make people overconfident and less likely to avoid the flash flood. More than half of the fatalities attributed to flash floods are people swept away in vehicles when trying to cross flooded intersections. As little as two feet of water can be enough to carry away most SUV-sized vehicles


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