A flash flood is caused by sudden, excessive rainfall that submerges an area underwater within a few short hours. For many years, people have built homes and businesses in floodplain areas, land on the same surface level as the river. This increases the probabilities of property damage and loss of life from a flood's quick moving, often unexpected, wall of water.
In the western United States, the soil is generally dry, sandy and unable to absorb large amounts of water. Unexpected heavy rains from heavy showers and thunderstorms can quickly fill dry stream and river beds, sending torrents of water downstream.
Flash floods often occur when heavy rains continue to fall over several hours, inundating the soil with water past its point of maximum saturation. They can also happen as a result of a winter thaw or in connection with moisture from associated tropical storms and hurricanes.
Fast-moving water is extremely powerful. The result can be deadly to anyone residing in the water's path. The force of flash flood waters can also be extremely dangerous to motorists who, either unwittingly or trying to tempt fate, drive over water-covered roads and are swept uncontrollably downstream.
