Several factors contribute to flash flooding. The two key elements are rainfall intensity and duration. Intensity is the rate of rainfall, and 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 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, thunderstorms repeatedly moving over the same area, or heavy rains from hurricanes and tropical storms.
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.
Identify where to go if told to evacuate. Choose several places...a friend's home or a motel in another town, or a shelter.
Know your area's flood risk. For information, call your local National Weather Service office, Red Cross chapter, or local emergency management agency. Check your homeowner's or renter's insurance. Homeowners' policies do not cover flooding. Contact your insurance agent to find out how to get flood insurance.
Even 6 inches of fast-moving flood water can knock you off your feet, and a depth of 2 feet will float your car! NEVER try to walk, swim, or drive through such swift water. If you come upon flood waters, STOP! TURN AROUND AND GO ANOTHER WAY.
Flooding along rivers is a natural and inevitable part of life. Some
floods occur seasonally when winter or spring rains, coupled with melting
snows, fill river basins with too much water, too quickly. Torrential rains
from decaying hurricanes or tropical systems can also produce river flooding. Winds generated from tropical storms and hurricanes or intense offshore
low pressure systems can drive ocean water inland and cause significant
flooding. Escape routes can be cut off and blocked by high water. Coastal
flooding can also be produced by sea waves called tsunamis (tsoo-n
-m z), sometimes referred to as tidal waves. These waves are produced by
earthquakes or volcanic activity. NOTE: Coastal flooding caused by the storm surge
associated with hurricanes is described in publication NOAA/PA 78019, "Storm
Surge and Hurricane Safety." As land is converted from fields or woodlands to roads and parking lots,
it loses its ability to absorb rainfall. Urbanization increases runoff 2
to 6 times over what would occur on natural terrain. During periods of urban
flooding, streets can become swift moving rivers, while basements can become
death traps as they fill with water. An arroyo is a water-carved gully or normally dry creek bed. Arroyos
can fill with fast-moving water very quickly. Flash flooding at this arroyo
in Arizona took only 58 seconds to develop. Floating ice can accumulate at a natural or man-made obstruction and
stop the flow of water. distant thunder runoff from a faraway thunderstorm could be headed your
way.
water rising rapidly
look out for..flooding at highway dips, bridges, and low areas.
by listening to NOAA Weather Radio, commercial radio, and television
for the latest flash flood/flood WATCHES, WARNINGS, and ADVISORIES. NOAA WEATHER RADIO IS THE BEST MEANS TO RECEIVE WARNINGS FROM THE
NATIONAL WEATHER SERVICE. The National Weather Service continuously
broadcasts updated weather warnings and forecasts that can be received by
NOAA Weather Radios sold in many stores. Average range is 40 miles, depending
on topography. Your National Weather Service recommends purchasing a radio
that has both a battery backup and a tone-alert feature which automatically
alerts you when a watch or warning is issued. The rule for being safe in a flooding situation is simple: HEAD
FOR HIGHER GROUND AND STAY AWAY FROM FLOOD WATERS! Families should be prepared for all hazards that affect their area. NOAA's
National Weather Service, the Federal Emergency Management Agency, and the
American Red Cross urge each family to develop a family disaster plan. Where will your family be when disaster strikes? They could be anywhere
at work, at school, or in the car. How will you find each other? Will you
know if your children are safe? Disasters may force you to evacuate your
neighborhood or confine you to your home. What would you do if basic services
water, gas, electricity or telephones were cut off? Follow these basic steps to develop a family disaster plan... I. Gather information about hazards. Contact your local
National Weather Service office, emergency management or civil defense
office, and American Red Cross chapter. Find out what type of disasters
could occur and how you should respond. Learn your community's warning
signals and evacuation plans. (1) Post emergency telephone numbers by phones;
Flooding Takes Many Forms...
Flash flooding occurs within 6 hours of the rain event.
Flooding is a longer term event and may last a week or more.
RIVER FLOOD
COASTAL FLOOD
URBAN FLOOD
FLASH FLOODING IN ARROYOS/WASHES
ICE JAM
Environmental Clues...
Listen for...
Look out for...
Nearly half of all flash flood fatalities are auto related!
In your automobile...
MANY FLASH FLOODS OCCUR AT NIGHT...BE PREPARED TO TAKE QUICK ACTION.
How can a foot or two of water cost you your life?
Before the flood...
What can do:
- Do your local streams or rivers flood easily? If so, be prepared to move
to a place of safety. Know your evacuation routes.
Assemble a disaster supplies kit containing: first aid kit, canned food
and can opener, bottled water, rubber boots, rubber gloves, NOAA Weather
Radio, battery-powered radio, flashlight, and extra batteries.
What YOUR community can do:
STAY INFORMED ABOUT THE STORM
What to Listen For...
When a flash flood WATCH is issued Be alert to signs
of flash flooding and be ready to evacuate on a moment's notice.
When a flash flood WARNING is issued for your area,
or the moment you realize that a flash flood is imminent, act quickly to
save yourself. You may have only SECONDS!
Go to higher ground Climb to safety!
When you receive a FLOOD WARNING:
During the flood:
After the flood:
FAMILY DISASTER PLAN
II. Meet with your family to create a plan. Discuss the
information you have gathered. Pick two places to meet: a spot outside
your home for an emergency, such as fire, and a place away from your neighborhood
in case you can't return home. Choose an out-of-state friend as your "family
check-in contact" for everyone to call if the family gets separated.
Discuss what you would do if advised to evacuate.
III. Implement your plan.
(2) Install safety features in your house, such as smoke detectors and
fire extinguishers;
(3) Inspect your home for potential hazards (such as items that can move,
fall, break, or catch fire) and correct them;
(4) Have your family learn basic safety measures, such as CPR and first
aid; how to use a fire extinguisher; and how and when to turn off water,
gas, and electricity in your home;
(5) Teach children how and when to call 911 or your local Emergency Medical
Services number;
(6) Keep enough supplies in your home to meet your needs for at least three
days. Assemble a disaster supplies kit with items you may need in case
of an evacuation. Store these supplies in sturdy, easy-to-carry containers,
such as backpacks or duffle bags. Keep important family documents in a
waterproof container. Keep a smaller disaster supplies kit in the trunk
of your car.
A DISASTER SUPPLIES KIT SHOULD INCLUDE:
IV. Practice and maintain your plan. Ask questions to
make sure your family remembers meeting places, phone numbers, and safety
rules. Conduct drills. Test your smoke detectors monthly and change the
batteries at least once a year. Test and recharge your fire extinguisher(s)
according to manufacturer's instructions. Replace stored water and food
every six months.
LOCAL SPONSORSHIP: NOAA/PA 92050 ARC 4493