Preparedness - Flood
The rule for being safe in a flooding situation is simple: Head for higher ground and stay away from flood waters!
Flash Flood or Flood Watch
Flash flooding or flooding is possible within the designated watch area - be alert.
Flash Flood or Flood Warning
Flash flooding or flooding has been reported or is imminent - take necessary precautions immediately.
Urban & Small Stream Advisory
Flooding of small streams, streets and low-lying areas, such as railroads, underpasses and urban storm drains is occurring.
Flash Flood or Flood Statement
Follow-up information regarding a flash flood/flood event.
During the Flood
- Avoid areas subject to sudden flooding.
- If you come upon a flowing stream where water is above your ankles, STOP, turn around and go another way.
- Do not attempt to drive over a flooded road. The depth of water is not always obvious. The road bed may be washed out under the water and you could be stranded or trapped.
- Children should never play around high water, storm drains, viaducts or arroyos.
After the Flood
- If fresh food has come in contact with flood waters, throw it out.
- Boil drinking water before using. Wells should be pumped and the water tested for purity before drinking. If in doubt, call your local public health authority.
- Seek necessary medical care at the nearest hospital. Food, clothing, shelter, and first aid are available from the Red Cross.
- Do not visit disaster areas. Your presence might hamper rescue and other emergency operations.
- Electrical equipment should be checked and dried before being returned to service.
- Use flashlights, not lanterns, torches or matches, to examine buildings. Flammables may be inside.
- Report broken utility lines to appropriate authorities.
Flooding causes $37 million in damages annually in Colorado (Tornadoes cause just $1 million).
How Flash Floods Occur
Several factors contribute to flash flooding. The two key elements are rainfall intensity and duration. Intensity is the rate of rainfall. Duration is how long the rain lasts. Topography, soil conditions, and ground cover also play an important role in flooding.
Flash floods occur within a few minutes or hours of excessive rainfall, a dam or levee failure or a 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 also trigger catastrophic mud slides. You will not always have a warning that these deadly, sudden floods are coming. Most flood deaths are due to Flash Floods.
Most flash flooding is caused by slow-moving thunderstorms, as often occurs along the Front Range, thunderstorms repeatedly moving over the same area or heavy rains.
Occasionally, floating debris or ice can accumulate at a natural or man-made obstruction and restrict the flow of water. Water held back by the ice jam or debris dam can cause flooding upstream. Subsequent flash flooding can occur downstream if the obstruction should suddenly release.
Water weighs 62.4 pounds per cubic foot and typically flows downstream at 6 to 12 miles an hour.
When a vehicle stalls in the water, the water's momentum is transferred to the car. For each foot the water rises, 500 pounds of lateral force are applied to the car.
But the biggest factor is buoyancy. For each foot the water rises up the side of the car, the car displaces 1,500 pounds of water. In effect, the car weights 1,500 pounds less for each foot the water rises.
Two feet of water will carry away most automobiles.