A flash flood is typically caused by sudden, excessive rainfall that sends a river, stream or other body of water rapidly out of its banks. Often this occurs in a short amount of time, only several hours or even less.
They can also be caused by ice jams on rivers in conjunction with a winter or spring thaw, or occasionally even a dam break. The constant influx of water finally causes a treacherous overflow to begin, powerful enough to sweep vehicles away, roll boulders into roadways, uproot trees, level buildings, and drag bridges off their piers.
Most frightening is the rapidity with which the water rises.
In the western United States, the soil is generally dry, sandy and unable to absorb large amounts of water. Heavy rains from showers and thunderstorms can quickly fill dry stream and river beds, sending torrents of water downstream.
Fast-moving water is extremely powerful. The result can be deadly to anyone in the water's path. The force of flash flood waters can be extremely dangerous to motorists who unwittingly or unknowingly drive over water-covered roads - only two feet of running water are needed to sweep away a car.
Most people are unaware that:
- 80% of flood deaths occur in vehicles, and most happen when drivers make a single, fatal mistake trying to navigate through flood waters.
- Just 6 inches of rapidly moving flood water can knock a person down.
- A mere 2 feet of water can float a large vehicle even a bus.
- One-third of flooded roads and bridges are so damaged by water that any vehicle trying to cross stands only a 50% chance of making it to the other side.
- The Big Thompson Canyon Flood killed 140 people in 1976. It proved a tragic illustration of a sobering statistic 95% of those killed in a flash flood try to outrun the waters along their path rather than climbing rocks or going uphill to higher grounds.
There many be no time for a warning to be issued. You may have only seconds to escape. It could be a life-and-death decision for you and your family. If you suspect a flash flood is about to happen immediately climb to higher ground.
Avoid walking through any floodwaters. If it is moving swiftly, even water 6 inches deep can sweep you off your feet.
If in a car....
If you come to a flooded area, turn around and go another way. If your car stalls, abandon it immediately and climb to higher ground. Many deaths have resulted from attempts to move stalled vehicles.
Remember, it does not have to be raining for a flash flood to occur. Some of the most dangerous floods originate many miles away.