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Floods and
Flash Floods
As land is converted from fields or
woodlands to roads and parking lots, it loses its ability to absorb rainfall.
Urbanization increases runoff two to six times more than what would occur on
natural terrain. During periods of urban flooding, streets can become swiftly
moving rivers, while basements and viaducts can become death traps as they fill
with water.
Flooding occurs in known floodplains when prolonged rainfall over several days, intense rainfall over a short period of time, or an ice or debris jam causes a river or stream to overflow and flood the surrounding area. Floods can be slow- or fast-rising, but generally develop over a period of hours or days.
Most flash flooding is caused by slow-moving thunderstorms, thunderstorms repeatedly moving over the same area, or heavy rains from hurricanes and tropical storms. Flash floods take from several minutes to several hours to develop. Flash floods generally occur within six hours of a rain event, or after a dam or levee failure, or following a sudden release of water held by an ice or debris jam. Flash floods can occur without warning.
Floods can roll boulders, tear out
trees, destroy buildings and bridges, and scour new channels. Floodwater can
reach heights of 10 to 20 feet (3 to 6 meters) and often carries a deadly cargo
of debris. Flood-producing rains can also trigger catastrophic debris
slides.
NOAA Weather Radio is the prime alerting and critical information
delivery system of the National Weather Service (NWS). NOAA Weather Radio
broadcasts warnings, watches, forecasts, and other hazard information 24 hours a
day over more than 650 stations in the 50 states, adjacent coastal waters,
Puerto Rico, the U.S. Virgin Islands, and the U.S. Pacific
territories.
ACTION
MESSAGES
If you are at risk from floods, you
should: • Find out the
elevation above flood stage of your home, outbuildings, and pastures or
corrals. Knowing
the elevation of your property in relation to nearby streams and dams will let
you know if forecasted flood levels will affect your home.
• Find out if local streams or rivers flood easily. • Talk with members of your household about the possibility of floods and flash floods and what to do to stay safe if one occurs. Knowing how to respond will reduce fear and save precious time in an emergency. • Find out about the flood evacuation routes in your area and develop a flood evacuation plan for your household. (See “Evacuation, Sheltering and Post-Disaster Safety.”) All members of the household should know where to meet each other, where to evacuate to, and what route(s) to take if they have to leave. Making plans well in advance will help you avoid last-minute confusion. • Find out if you are located in a floodplain, which is considered a Special Flood Hazard Area. If you are, you are still eligible for flood insurance. Check with your city or county government (start with the Building or Planning Department) to review the Flood Insurance Rate Maps, published by the Federal Emergency Management Agency (FEMA). If your home is especially vulnerable, consider relocation. • Talk to your insurance agent. Homeowners' policies do not cover flooding. Ask about the National Flood Insurance Program (NFIP) (www.fema.gov/nfip). • Use a NOAA Weather Radio or listen to local stations on a portable, batterypowered radio or television for updated emergency information. • If you live in a frequently flooded area, stockpile emergency building materials. These include plywood, plastic sheeting, lumber, nails, hammer and saw, pry bar, sand, shovels, and sandbags.
• Avoid building
in a floodplain unless you elevate and reinforce your home.
Some
communities do not permit building in known floodplains. If there are no
restrictions and you are building in a floodplain, take precautions to make it
less likely your home will be damaged during a flood.
• Keep insurance policies, documents, and other valuables in a safe-deposit box. You may need quick, easy access to these documents. Keep them in a safe place less likely to be damaged during a flood. • Raise your furnace, water heater, and electric panel to higher floors or the attic if they are in areas of your home that may be flooded. Raising this equipment will prevent damage. An undamaged water heater may be your best source of fresh water after a flood. • Install check valves in plumbing to prevent floodwater from backing up into the drains of your home. As a last resort, when floods threaten, use large corks or stoppers to plug showers, tubs, or basins. • Construct barriers such as levees, berms, and flood walls to stop floodwater from entering the building. Permission to construct such barriers may be required by local building codes. Check local building codes and ordinances for safety requirements. • Seal walls in basements with waterproofing compounds to avoid seepage through cracks. • Consult with a construction professional for further information about these and other damage-reduction measures. Check local building codes and ordinances for safety requirements. • Contact your local emergency management office for more information on mitigation options to further reduce potential flood damage. Your local emergency management office may be able to provide additional resources and information on ways to reduce potential damage. • Ensure that any outbuildings, pastures, or corrals are protected in the same way as your home. When installing or changing fence lines, consider placing them in such a way that your animals are able to move to higher ground in the event of flooding.
• Heavy
rain for several hours, or steady rain for several days, can saturate the ground
and cause a flood.
• Distant thunder indicates a distant thunderstorm that could send runoff your way. Runoff can produce a deadly flash flood that appears with no warning, particularly in certain types of terrain, for example, in an arroyo or streambed.• Other distant events, such as a dam break or the sudden unclogging of an ice jam, can cause flash floods.
• Use a NOAA
Weather Radio or listen continuously to a local station on a portable,
battery-powered radio or television.
• Be ready to act quickly. Floods and flash floods can happen quickly and without warning. Be ready to act immediately. • Be alert to signs of flooding, and, if you live in a flood-prone area, be ready to evacuate at a moment's notice. Floods can happen quickly and you may need to leave with little or no notice. • Follow the instructions and advice of local authorities. Local authorities are the most informed about affected areas and the most knowledgeable about areas you should avoid. • If your home is in a flood-prone area: -Fill plastic bottles with clean water for
drinking. (See
“Stocking
and Storing Food and Water”) Water
may become contaminated or water service may be interrupted.
•
Consider a
precautionary evacuation of your animals, especially
any large or numerous animals. Waiting until the last minute could be fatal for
them and dangerous for you. Where possible, move livestock to higher ground. If
you are using a horse or other trailer to evacuate your animals, move early
rather than wait until it may be too late to maneuver a trailer through slow
traffic.-Fill bathtubs and sinks with water for flushing the toilet or washing the floor or clothing. Adults can use this water for bathing, but young children should not bathe in water that has been stored in glazed tubs and sinks because over time lead can leach into the water from the glaze. -Bring outdoor belongings, such as patio furniture, indoors. Unsecured items may be swept away and damaged by floodwater. -Move your furniture and valuables to higher floors of your home. If floodwater affects your home, higher floors are less likely to be damaged. -Turn off utilities if told to do so by authorities. Authorities may ask you to turn off water or electric utilities to prevent damage to your home or within the community. Most of the time they will tell you to leave the gas on because, if you shut if off, a professional is required to turn your gas back on, and it may be several weeks before you receive service. -Turn off propane tanks. Propane tanks may be damaged or dislodged by strong winds or water. Turning them off reduces the fire potential. -Unplug small appliances. Small appliances may be affected by electrical power surges that may occur. Unplugging them reduces potential damage. -Keep your previously assembled Disaster Supplies Kit near. You may need to act quickly. Having your supplies ready will save time. -Fill your car's gas tank, in case an evacuation notice is issued. If electric power is cut off, gas stations may not be able to operate pumps for several days. -Be prepared to evacuate. Local officials may ask you to leave if they conclude that your home is at risk from floodwater.
• Use a NOAA
Weather Radio or listen continuously to a local station on a portable,
battery-powered radio or television.
• Be alert to signs of flooding. A warning means a flood is imminent or is happening in the area. • Bring your companion animals indoors and maintain direct control of them. Be sure that your pet disaster kit and your family Disaster Supplies Kit are ready to go in case you need to evacuate. • If you live in a flood-prone area or think you are at risk, evacuate immediately. Move quickly to higher ground. Save yourself, not your belongings. The most important thing is your safety. • If advised by authorities to evacuate, do so immediately. Move to a safe area before access is cut off by floodwater. Evacuation is much simpler and safer before floodwater becomes too deep for vehicles to drive through. • Follow the instructions and advice of local authorities. Local authorities are the most informed about affected areas and the most knowledgeable about areas you should avoid. • Follow recommended evacuation routes. Shortcuts or alternative, non-recommended routes may be blocked or damaged by floodwater. • Leave early enough to avoid being marooned by flooded roads. Delaying too long may allow all escape routes to become blocked. • If you evacuate, take your animals with you. If it is not safe for you, it is not safe for your animals.
• Stay out of
areas subject to flooding. Dips,
low spots, canyons, washes, etc. can become filled with
water.
• Climb to high ground and stay there. Move away from dangerous floodwater. • If you come upon a flowing stream where water is above your ankles, stop, turn around, and go another way. Never try to walk, swim, or drive through swift water. Many flood fatalities are caused by people attempting to drive through water, or people playing in high water. If it is moving swiftly, even water six inches (15 centimeters) deep can sweep you off your feet.
• Avoid already
flooded areas, and areas subject to sudden flooding. Do
not attempt to cross flowing streams or water covered roads. As little as six
inches of water may cause you to lose control of your vehicle. The National
Weather Service reports that nearly half of all flood fatalities are vehicle
related. The depth of water is not always obvious. The roadbed may be washed out
under the water, and you could be stranded or trapped. Also, standing water may
be electrically charged from underground or downed power lines. Rapidly rising
water may stall the engine, engulf the vehicle and its occupants, and sweep them
away. Look out for flooding at highway dips, bridges, and low areas. Two feet
(0.6 meters) of water will carry away most vehicles, including SUVs and pickup
trucks.
• Stay away from underpasses. Underpasses can fill rapidly with water, while the adjacent roadway remains clear. Driving into an underpass can quickly put you in five to six feet (1.5 to 1.8 meters) of water. • Turn around and find another route if you come upon rapidly rising water. Move to higher ground away from rivers, streams, creeks, and storm drains. If your route is blocked by floodwater or barricades, find another route. Barricades are put up by local officials to protect people from unsafe roads. Driving around them can be a serious risk.
• Get medical
care at the nearest hospital or clinic, if necessary. Contaminated
floodwater can cause infection. Severe injuries will require medical
attention.
• Help people who require special assistance—infants, elderly people, those without transportation, large families who may need additional help in an emergency situation, people with disabilities, and the people who care for them. • Stay away from damaged areas. Your presence might hamper rescue and other emergency operations, and put you at further risk from the residual effects of floods, such as contaminated water, crumbled roads, landslides, mudflows, and other hazards. • Continue to listen to NOAA Weather Radio or a local radio or television station and return home only when authorities indicate it is safe to do so. Flood dangers do not end when the water begins to recede; there may be flood-related hazards within your community, which you could hear about from local broadcasts. • Stay out of any building if floodwater remains around the building. Floodwater often undermines foundations, causing sinking. Floors can crack or break and buildings can collapse. • Avoid entering any building (home, business, or other) before local officials have said it is safe to do so. Buildings may have hidden damage that makes them unsafe. Gas leaks or damage to electric lines or water lines can create additional problems. • Report broken utility lines to the appropriate authorities. Reporting potential hazards will get the utilities turned off as quickly as possible, preventing further hazard and injury. • Avoid smoking inside buildings. Smoking in confined areas can cause fires. • When entering buildings, use extreme caution. Building damage may have occurred where you least expect it. Watch carefully every step you take. • Wear long pants, a long-sleeved shirt, and sturdy shoes. The most common injury following a disaster is cut feet. • Use
battery-powered lanterns or flashlights when examining
buildings.
DO NOT USE CANDLES.
• Examine walls, floors, doors, staircases, and windows to make sure that the building is not in danger of collapsing. • Inspect foundations for cracks or other damage. Cracks and damage to a foundation can render a building uninhabitable. • Look for fire hazards. There may be broken or leaking gas lines, flooded electrical circuits, or submerged furnaces or electrical appliances. Flammable or explosive materials may have traveled from upstream. Fire is the most frequent hazard following floods. • Check for gas leaks. If you smell gas or hear a blowing or hissing noise, open a window and get everyone outside quickly. Turn off the gas at the outside main valve if you can and call the gas company from a neighbor's home. If you turn off the gas for any reason, it must be turned back on by a professional. • Look for electrical system damage. If you see sparks or broken or frayed wires, or if you smell burning insulation, turn off the electricity at the main fuse box or circuit breaker. If you have to step in water to get to the fuse box or circuit breaker, call an electrician first for advice. Electrical equipment should be checked and dried before being returned to service. • Check for damage to sewage and water lines. If you suspect sewage lines are damaged, avoid using the toilets and call a plumber. If water pipes are damaged, contact the water company and avoid using water from the tap. You can obtain safe water from undamaged water heaters or by melting ice cubes that were made before the pipes were damaged. Turn off the main water valve before draining water from these sources • Watch out for wild animals, especially poisonous snakes, that may have come into buildings with the floodwater. Use a stick to poke through debris. Floodwater flushes snakes and many animals out of their homes. • Watch for loose plaster, drywall, and ceilings that could fall. • Take pictures of the damage, both of the building and its contents, for insurance claims. • Watch your animals closely. Keep all your animals under your direct control. Hazardous materials abound in flooded areas. Your pets may be able to escape from your home or through a broken fence. Pets may become disoriented, particularly because flooding usually affects scent markers that normally allow them to find their homes. The behavior of pets may change dramatically after any disruption, becoming aggressive or defensive, so be aware of their well-being and take measures to protect them from hazards, including displaced wild animals, and to ensure the safety of other people and animals.
• Throw away
food and drinking water that has come in contact with floodwater, including
canned goods. It
is impossible to know if containers were damaged and the seals compromised. Food
contaminated by floodwater can cause severe infections.
• Discard wooden spoons, plastic utensils, and baby bottle nipples and pacifiers if they have been covered by floodwater. There is no way to safely clean them. • Disinfect metal pans and utensils by boiling them in clean or properly treated water. • If water is of questionable purity, boil the water or add bleach to it, and then distill the water if you will be drinking it. (See “Food and Water Safety During/Post Disaster”) Wells inundated by floodwater should be pumped out and the water tested for purity before drinking. If in doubt, call your local public health authority. Ill health effects often occur when people drink water contaminated with bacteria and germs. • Avoid drinking or preparing food with tap water until you are certain it is not contaminated. Floodwater may have contaminated public water supplies or wells. Local officials should advise you on the safety of the drinking water. • Pump out flooded basements gradually (about one-third of the water per day) to avoid structural damage. If the water is pumped out completely in a short period of time, pressure from water-saturated soil on the outside could cause basement walls to collapse. • Service damaged septic tanks, cesspools, pits, and leaching systems as soon as possible. Damaged sewage systems are health hazards.
• Have
your community join the National Flood Insurance Program (NFIP). Any community
may join the NFIP. Check with your local emergency management office for more
information.
• Ask your local newspaper or radio or television station to: -Do a series on
the dangers of floods and flash floods.
-Do a story featuring interviews with local officials about land use management and building codes in floodplains. -Highlight the importance of staying informed about local weather conditions. -Run public service ads about how to protect lives and property in a flood. Help the reporters to localize the information
by providing them with the local emergency telephone number for the fire,
police, and emergency medical services departments (usually 9-1-1) and emergency
numbers for the local utilities and hospitals. Also provide the business
telephone numbers for the local emergency management office and local American
Red Cross chapter.
• Work with officials of the local fire, police, and emergency medical services departments; utilities; hospitals; emergency management office; and American Red Cross chapter to prepare and disseminate guidelines for people with mobility impairments about what to do if they have to evacuate. • Periodically inform your community of local public warning systems. Explain the difference between flood watches and warnings. • Help hospitals and other operations that are critically affected by power failures to obtain auxiliary power supplies. • Contact your local National Weather Service (NWS) office or emergency management agency for information on local flood warning systems. Advanced warning provided by early detection is critical to saving lives. Automatic flood detection systems are available commercially for flood-prone communities. • Publish emergency evacuation routes for areas prone to flooding.
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