Several factors contribute to flash flooding. The two key elements are rainfall intensity and duration. Intensity is the rate of rainfall, and the duration is how long the rain lasts. Topography, soil conditions, and ground cover also play an important role.
Flash Floods Occur within a few minutes or hours of excessive rainfall, a dam or levee failure, or sudden release of water held by an ice jam. Flash floods can roll boulders, tear out trees, destroy buildings and bridges, and scour out new channels. Rapidly rising water can reach heights of 30 feet or more.
Furthermore, flash flood-producing rains can trigger catastrophic mud slides. You will not always have a warning that these deadly, sudden floods are coming.
Most Flash Flooding is caused by slow-moving Thunderstorms, Thunderstorms repeatedly moving over the same area, or heavy rains from Hurricanes or Tropical Storms.
What is the difference between Flooding and Flash Flooding? The answer is that Flash Flooding occurs within six hours of the rain event, whereas Flooding is a longer term event and may last a week or more.
It is important to know your areas flood risk.
Who is most at risk from flooding? Those in automobiles when Flash Flooding occurs near them.
Watches and Warnings
Flash Flood Watch
Flooding or Flash Flooding is possible within the designated watch area. Remain alert to changing weather conditions. When your area is under a Flash Flood Watch
Flash Flooding or Flooding has been reported or is immanent. Take necessary precautions at once.
Flash Flood Safety Tips - Watch for rising water and prepare to move to higher ground.
- If you come upon a flowing stream where water is above your ankles, stop! Turn around and go the other way.
- Avoid low-lying areas and washes.
- Observe safety barriers near flood water. Many cars and trucks are swept away by rising water when drivers go around a barricade.
- DO NOT try to drive through a submerged road. It is often too difficult to tell how deep the water is.
- If your vehicle stalls in waters, act quickly. Leave the vehicle immediately and move to higher ground. Most cars and light trucks will begin to float in as little as two feet of water. Once the water gets deeper, the doors may be impossible to open.
- Keep children from playing in or near drains or culverts.
- Camp away from streams subject to flash floods.
- Follow all flood evacuation warnings.
- Never try to outrun a flash flood on foot.
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