A flash flood is the fastest-moving type of flood. It happens when heavy rain collects in a stream, dry wash, or road turning the normally calm area into an instant rushing current.
The quick change from calm to raging river is what catches people off guard, making flash floods very dangerous.
Any flood involves water rising and overflowing its normal path. But a flash flood is a specific type of flood that appears and moves quickly across the land, with little warning that it's coming.
Many things can cause a flash flood. Generally they are the result of heavy rainfall concentrated over one area. Most flash flooding is caused by slow-moving thunderstorms, thunderstorms that repeatedly move over the same area.
Flash floods, moving at incredible speed can roll boulders, tear out trees, destroy buildings and bridges, and scour out new channels. Walls of water can reach heights of 5 to 10 feet. You won't always have warning that these deadly, sudden floods are coming.
What to do:
- When a flash flood warning is issued for your area or the moment you first realize that a flash flood is imminent, act quickly to save yourself. You may have only seconds.
- Go to high ground immediately.
- Get out of areas subject to flooding. This includes dips, low spots, canyons, washes, etc.
- Avoid already flooded and high velocity flow areas. Do not attempt to cross a flowing stream on foot where water is above your knees.
- Do not drive through flooded areas. Shallow, swiftly flowing water can wash a car from a roadway. Also, the roadbed may not be intact under the water.
- If the vehicle stalls, abandon it immediately and seek higher ground. Rapidly rising water may engulf the vehicle and its occupants and sweep them away.
- Be especially cautious at night when its harder to recognize flood dangers.
- Do not camp or park your vehicle along streams and washes, particularly during threatening conditions.