Floods and Flash Floods
Floods are a natural and inevitable part of life along the rivers of our country. Some floods occur seasonally when winter or spring rains, coupled with melting snows or torrential rains associated with tropical storms, drain small tributaries and fill river basins with too much water, too quickly. Other floods are sudden, resulting from heavy localized rainfall. These flash floods are raging torrents which rip through river beds, urban streets, and mountain canyons after heavy rains, sweeping everything before them.
U.S. Floods and Flash Floods
The transformation of a tranquil river into a destructive flood occurs hundreds of times each year throughout the United States. In fact, floods and flash floods are the number one weather-related killer in the country. No area of the United States is completely free from the threat of floods. On the average, each year over 300,000 Americans are driven from their homes by floods and flash floods; 135 people are killed; and around $2 billion worth of property is damaged or destroyed.
In the Spring and Summer of 1993, extended, heavy rainfall caused record flooding in much of the Upper Mississippi River Basin. The Mississippi and Missouri Rivers were closed to shipping before and after the flooding, and millions of acres of productive farmland were flooded in the Midwestern United States. Property damage alone exceeded $10 billion.
Utah Floods and Flash Flood Statistics
In Utah, over 360 flash floods and more than 170 snowmelt floods have occurred since 1853. Also, since 1950, 26 people have been killed by floods or flash floods in Utah, making such floods the second greatest weather-related killer in the state (after lightning). Click on the following site for Statistics on Utah's Floods and Flash Floods.
Runoff from melting mountain snow causes "snowmelt floods." Such runoff usually reaches its peak in May or early June. Sometimes this runoff causes flooding along lower mountains and valley streams. In the Spring of 1983, rapid warming during the last week of May and the first part of June, caused rivers to rise dramatically throughout Utah. State Street, North Temple Street, and 13th South Street in Salt Lake City were tuned into rivers with sandbag boundaries. Interstate 15 in Juab, Utah and Millard Counties was inundated in places by water from swollen rivers and lakes. Rivers throughout the state carved deep crevices into canyon roads, leaving many summer recreation areas inaccessible for camping. The hardest-hit areas were in Juab, Utah, Beaver, and Uinta Counties. In addition, a massive mudslide blocked the Spanish Fork River in Utah County, trapping water behind the slide which eventually covered the town of Thistle with water.
The Danger of Flash Floods
Utah is occasionally subjected to locally heavy rainfall associated with summer thunderstorms. These heavy but short-lived storms can produce local flash floods in dry stream channels, as well as in perennial streams which create very dangerous situations for anyone caught in the path of the surging waters.
In Utah, flash floods typically occur when slow moving thunderstorms produce torrential rainfall. These floods can roll boulders, uproot trees, wash away roads and automobiles, 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. Often there is no warning that these sudden, deadly floods are coming.
Most flash floods in Utah have only caused limited damage, but a few have been very destructive and deadly. For example, on June 10, 1965, a flash flood killed seven people in the Sheep Creek area of Flaming Gorge in Daggett County. The National Weather Service account of this tragic event reads as follows:
"One June 10, 1965, a husband and wife and their three children and two nephews drowned in a flash flood in Sheep Creek Canyon in the Uinta Mountains of Daggett County. They were camped in Palisades Campground along the snowmelt swollen waters of Sheep Creek. Heavy rains in the area turned the creek into a raging torrent."
Flash Flood Forecasts and Warnings
To protect yourself from flash floods, know when they may occur, what the warning signs are and what to do if you are caught in a flash flood. Be aware of the latest forecasts and warnings through NOAA Weather Radio and commercial television and radio broadcasts. To take full advantage of weather forecasts and warnings when there is a high potential for flash flooding, learn what the following terms mean:
A Flash Flood Warning is issued when flash flooding has been reported or is imminent. If you are in the warned area, take immediate action to save yourself. You may only have seconds!
A Flash Flood Watch means that the potential for flash flooding is high within the watch area. Be alert to signs of flash flooding and be ready to evacuate immediately, if necessary.
A Flash Flood Statement is issued to provide follow-up information regarding a flash flood event.
Be Prepared for a Flash Flood
Be Prepared for a Flash Flood
Know your area's potential for flash floods. For information, call the National Weather Service, Red Cross chapter, or local emergency management agency. In Utah, areas most prone to flash flooding include steep, narrow canyons and washes in southern and eastern Utah, any location near streams or rivers (especially those located downstream from a dam), and other low lying areas. Be aware of the latest weather conditions and listen for Flash Flood Watches and Warnings. NOAA weather radios, which may be purchased in stores, provide continuously updated weather forecasts and warnings for all of Utah. The average transmission range is 40 miles depending on topography, and there are several broadcast locations throughout Utah. It may be best to purchase a radio that has both a battery backup and a tone-alert feature which automatically alerts you when a watch or warning is issued. Watch and warning information is also available on the Emergency Broadcast System through local radio and television broadcasts.
If you are caught in a flash flood situation, follow these safety rules:
Head for higher ground and stay away from flood waters! Also stay out of areas that flood easily, such as dips, low spots, canyons, washes, etc.
Listen for distant thunder. Runoff from a faraway thunderstorm may be headed your way.
Monitor the water level of nearby streams for rapidly rising water.
Never try to walk, swim, or drive through swiftly moving high water. Six inches of fast moving flood water has the power to knock you off your feet, and a depth of two feet can float your car! If you come upon flood waters, stop, turn around and go another way.
Never camp along streams or in washes. Many flash flood deaths in Utah are due to people camping in these areas when a flash flood occurs.
Also, here are some automobile safety tips:
Never drive through flooded roadways! Many flood fatalities are auto related! In your automobile, look out for flooding at highway dips, bridges and low areas. The depth of water can be deceptive as the road bed may not be intact under flood waters.
If your vehicle stalls, leave it immediately and move to higher ground. Rapidly rising water may engulf your vehicle and its occupants and sweep you away. Remember, it’s better to be wet than dead!
Be especially cautious at night when it is harder to recognize flood dangers.
Do not camp or park your vehicle along streams and washes, particularly during threatening weather conditions.
Finally, here is some advice on actions you should take after a flash flood has happened:
Stay away from flood waters.
If fresh food has come in contact with flood waters, throw it away.
Boil drinking water before using. Wells should be pumped out and the water tested for purity before drinking. If in doubt, call your local public health authority.
Use flashlights, not lanterns, torches or matches, to examine buildings. Flammables may be inside.
Report broken utility lines to appropriate authorities.
Much of the information for this section originally appeared in the copyrighted book Utah's Weather and Climate, edited by Dan Pope and Clayton Brough, in 1996. UCCW Directors have received permission from the copyright owners of this book to reproduce such information on its website and to revise and updated it where appropriate.