NWS Dallas/Fort Worth Public/Media Guide - Flood/Flash Flood Safety

Flood/Flash Flood Safety

How do flash floods occur?
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.

The Power of Water
Most folks greatly underestimate the power of water, especially when the water is moving fast as during flash flooding. One cubic foot of water weighs about 62 pounds and typically flows downstream at 6 to 12 miles an hour. Water moving at 10 mph exerts tremendous force. If the water is one foot deep and moving at 10 mph, YOU CANNOT SAFELY WALK THROUGH IT. You will be swept downstream.

When a vehicle stalls in the water, the water's momentum is transferred to the car. For each foot the water rises, 500 lbs. of lateral force are applied to the car. But the biggest factor is buoyancy. For each foot the water displaces 1,500 pounds. Water one to two feet deep can provide sufficient buoyancy to decrease the weight of most automobiles and allow the current to carry it downstream. NEVER try to walk, swim, or drive through such swift water. If you come upon flood waters, STOP! TURN AROUND AND SEEK HIGHER GROUND.

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.

Be prepared before the flood...

Know your flood risk and elevation above flood stage of local streams and rivers. Do your local streams or rivers flood easily? If so, be prepared to move to a place of safety. Know your evacuation routes.
Keep your automobile fueled. If electric power is cut off, gas stations may not be able to operate pumps for several days.
Store drinking water in clean bathtubs and in various containers. Water service may be interrupted.
Keep a stock of food that requires little cooking and no refrigeration. Electric power may be interrupted.
Keep first aid supplies handy.
Install check valves in building sewer traps to prevent flood water from backing up into the drains of your home.
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, and
- flashlight, and
- extra batteries.

When you receive a FLOOD WARNING...
If advised to evacuate, do so immediately. Move to a safe area before access is cut off by flood water. Continue monitoring NOAA Weather Radio, television, or emergency broadcast station for information.

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 out 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.

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!
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 flowing streams.
If driving, be aware that the road bed may not be intact under flood waters. Turn around and go another way. NEVER drive through flooded roadways!
If the vehicle stalls, leave it immediately and seek higher ground. Rapidly rising water may engulf the vehicle and its occupants and sweep them away. 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 conditions.