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FLOODING
AND FLASH
FLOODS
Produced by the National Disaster Education
Coalition:
American Red Cross, FEMA, IAEM, IBHS, NFPA, NWS, USDA/CSREES,
and USGS. |
Why Talk About Floods?
Floods are among the most frequent and costly natural disasters
in terms of human hardship and economic loss. As much as 90 percent
of the damage related to all natural disasters (excluding droughts)
is caused by floods and associated debris flows. Most communities in
the United States can experience some kind of flooding. Over the
10-year period from 1988 to 1997, floods cost the Nation, on
average, $3.7 billion annually. The long-term (1940 to 1999) annual
average of lives lost is 110 per year, mostly as a result of flash
floods.
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What Causes Floods?
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. Melting snow can combine with rain in the winter
and early spring; severe thunderstorms can bring heavy rain in the
spring and summer; or tropical cyclones can bring intense rainfall
to the coastal and inland states in the summer and fall.
Flash floods 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, and flash floods can catch people unprepared.
You will not always have a warning that these deadly, sudden floods
are coming. So if you live in areas prone to flash floods, plan now
to protect your family and property.
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 over what would occur on natural
terrain. During periods of urban flooding, streets can become swift
moving rivers, while basements and viaducts can become death traps
as they fill with water.
Several factors contribute to flooding. 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 important roles. Most flash
flooding is caused by slow-moving thunderstorms, thunderstorms
repeatedly moving over the same area, or heavy rains from hurricanes
and tropical storms. Floods, on the other hand, can be slow- or
fast-rising, but generally develop over a period of hours or days.
Learn about flooding and flash flooding in your area by
contacting the local emergency management office,
National Weather
Service (NWS) office, your
American Red Cross chapter, or your planning and zoning
department. If you are at risk, take steps to reduce damage and the
risk of injury or loss to your family.
Floods are among the most frequen and
costly natural disasters in terms of human hardship and economic
loss..most communities in the United States can experience some kind
of flooding.
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Awareness Information
Know the difference between
WATCHES and WARNINGS.
- A National Weather Service
WATCH is a message indicating
that conditions favor the occurrence of a certain type of
hazardous weather. For example, a severe thunderstorm watch means
that a severe thunderstorm is expected in the next six hours or so
within an area approximately 120 to 150 miles wide and 300 to 400
miles long (36,000 to 60,000 square miles). The NWS Storm
Prediction Center issues such watches. Local NWS forecast offices
issue other watches (flash flood, winter weather, etc.) 12 to 36
hours in advance of a possible hazardous-weather or flooding
event. Each local forecast office usually covers a state or a
portion of a state.
- An NWS WARNING
indicates that a hazardous event is occurring or is imminent in
about 30 minutes to an hour. Local NWS forecast offices issue
warnings on a county-by-county basis.
Many more WATCHES are issued
than WARNINGS. A
WATCH is the first sign a flood may
occur, and when one is issued, you should be aware of potential
flood hazards.
Be aware of flood hazards. Floods can
roll boulders, tear out trees, destroy buildings and bridges, and
scour out new channels. Flood waters can reach heights of 10 to 20
feet and often carry a deadly cargo of debris. Flood-producing rains
can also trigger catastrophic debris slides.
Regardless of how a flood or flash flood occurs, the rule for
being safe is simple: head for higher ground
and stay away from flood waters. Even a shallow depth of
fast-moving flood water produces more force than most people
imagine. The most dangerous thing you can do is to try walking,
swimming, or driving through flood waters. Two feet of water will
carry away most automobiles.
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Plan
for a Flood
Develop a Family Disaster Plan.
Please see the "Family
Disaster Plan" section for general family planning information.
Develop flood- specific planning. Learn about
your area's flood risk and elevation above flood stage.
Contact your local Red Cross chapter, emergency management office,
local National Weather Service office, or planning and zoning
department about your area's flood risk. 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.
If you are at risk from floods:
- Talk to your insurance
agent. Homeowners' policies do not cover flooding. Ask
about the National Flood Insurance Program (NFIP).
- Use a NOAA Weather Radio
with a tone-alert feature, or a portable, battery-powered radio
(or television) for updated emergency information.
- Develop an evacuation
plan. (See
"Evacuation"
in the "Family Disaster Plan" section.) Everyone in your family
should know where to go if they have to leave. Trying to make
plans at the last minute can be upsetting and create confusion.
- Discuss floods with your
family. Everyone should know what to do in case all family
members are not together. Discussing floods ahead of time helps
reduce fear and anxiety and lets everyone know how to respond.
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What to Tell Children
- If you come upon flood
waters, stop, turn around, and go another way. Climb to
higher ground. If it is moving swiftly, even water six
inches deep can knock you off your feet. Many people are swept
away wading through flood waters, resulting in injury or death.
- Stay away from flooded
areas. Even if it seems safe, flood waters may still be
rising.
- Never try to walk, swim,
drive, or play in flood water. You may not be able to see
on the surface how fast flood water is moving or see holes and
submerged debris.
- If you are in a vehicle
and become surrounded by water, if you can get out safely, do so
immediately and move to higher ground. Vehicles can be
swept away in two feet of water.
- Watch out for snakes in
areas that were flooded. Flood waters flush snakes from
their homes.
- Stay away from creek and
stream banks in flooded and recently flooded areas. The
soaked banks often become unstable due to heavy rainfall and can
suddenly give way, tossing you into rapidly moving water.
- Never play around high
water, storm drains, ditches, ravines, or culverts. It is
very easy to be swept away by fast moving water.
- Throw away all food that
has come into contact with flood waters. Contaminated flood
water contains bacteria and germs. Eating foods exposed to flood
waters can make you very sick.
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How to Protect Your Property
- 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.
- 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, making it less likely your home will 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
building sewer traps to prevent flood water 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 flood water 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 if these and
other damage reduction measures can be taken. 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.
Assemble a Disaster Supplies Kit
Please see the section
"Disaster Supplies Kit" for general supplies kit information.
Flood-specific supplies should include the following:
- Disaster Supplies Kit
basics.
- Evacuation Supply Kit.
- 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.
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Media and Community
Education Ideas
- Have your community join the National Flood
Insurance Program. Any community may join the NFIP. Check with
your local emergency management office for more information.
- Publish a special section in your local
newspaper with emergency information on floods and flash floods.
Localize the information by printing the phone numbers of local
emergency services offices, the American Red Cross chapter, and
the nearest hospitals.
- Interview local officials about land use
management and building codes in floodplains.
- Work with local emergency services and
American Red Cross officials to prepare special reports for people
with mobility impairments about what to do if an evacuation is
ordered.
- Periodically inform your community of local
public warning systems. Explain the difference between flood
watches and warnings. Let them know where to turn for emergency
broadcast information should they hear a warning on their radio or
television.
- Assist hospitals and other operations that are
critically affected by power failure by arranging for auxiliary
power supplies.
- Contact your local National Weather Service
office or emergency management agency for information on local
flood warning systems. River and rainfall readings are valuable to
local emergency management agencies and the NWS in assessing flood
conditions and taking appropriate actions. 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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What to Do Before
Flooding Occurs
- If it has been raining
hard for several hours, or steadily raining for several days, be
alert to the possibility of a flood. Floods happen as the
ground becomes saturated.
- Use a NOAA Weather Radio
or a portable, battery-powered radio (or television) for updated
emergency information. Local stations provide the best
advice for your particular situation.
- Listen for distant
thunder. In some types of terrain, runoff from a faraway
thunderstorm could be headed your way.
- If you are stopping your
vehicle, camp or park away from streams and washes, particularly
during threatening conditions. Flood waters can rise
quickly and carry you or your belongings away.
- When in or along stream
channels, be aware of distant events, such as dam breaks or
thunderstorms that may cause flash floods in the area.
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What to Do During a Flood
WATCH
- When a flood or flash flood
WATCH is issued:
- Listen continuously to
a NOAA Weather Radio, or a portable, battery-powered radio (or
television) for updated emergency information. Local
stations provide you with the best advice for your particular
situation.
- Everyone in a
WATCH area should be ready to
respond and 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. They will best be able
to tell you areas to avoid.
- If your residence is in a flood-prone area:
- Fill bathtubs, sinks,
and plastic bottles with clean water. Water may become
contaminated or service may be interrupted.
- Bring outdoor
belongings, such as patio furniture, indoors. Unsecured
items may be swept away and damaged by flood waters.
- Move your furniture and
valuables to higher floors of your home. If flood waters
affect your home, higher floors are less likely to receive
damage.
- If you are instructed
by local authorities, turn off all utilities at the main power
switch and close the main gas valve. In some areas, local
authorities may advise you to turn off utilities to prevent
further damage to homes and the community.
- Get your preassembled
disaster supplies ready. 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
truly feel your home is at risk from flood waters.
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What to Do During a
Flood WARNING
When a flood or flash flood WARNING
is issued:
- Listen continuously to a
NOAA Weather Radio, or a portable, battery-powered radio (or
television) for updated emergency information. Local
stations provide you with the best advice for your particular
situation.
- Be alert to signs of
flooding. A WARNING
means a flood is imminent or is happening in the area.
- 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.
- Follow the instructions
and advice of local authorities. Local authorities are the
most informed about affected areas. They will best be able to tell
you areas to avoid.
- If advised to evacuate,
do so immediately. Move to a safe area before access is cut
off by flood water. Evacuation is much simpler and safer before
flood waters become too deep for vehicles to drive through.
- Follow recommended
evacuation routes. Shortcuts or alternate, nonrecommended
routes may be blocked or damaged by flood waters.
- Leave early enough to
avoid being marooned by flooded roads. Delaying too long
may allow all escape routes to become blocked.
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Flood
Safety
- Stay out of areas subject
to flooding. Dips, low spots, canyons, washes, etc., can
become filled with water.
- If outdoors, climb to
high ground and stay there. Move away from dangerous flood
waters.
- 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 such swift water. Most 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 deep
can sweep you off your feet.
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What to Do
if Your Are Driving During a Flood
- Avoid already flooded
areas, and areas subject to sudden flooding. Do not attempt
to cross flowing streams. Most flood fatalities are caused by
people attempting to drive through water, or people playing in
high water. The depth of water is not always obvious. The roadbed
may be washed out under the water, and you could be stranded or
trapped. 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 of
water will carry away most automobiles.
- If you are driving and
come upon rapidly rising waters, turn around and find another
route. Move to higher ground away from rivers, streams, creeks,
and storm drains. If your route is blocked by flood waters 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.
- If your vehicle becomes
surrounded by water or the engine stalls, and if you can safely
get out, abandon your vehicle immediately and climb to higher
ground. Many deaths have resulted from attempts to move
stalled vehicles. When a vehicle stalls in the water, the water's
momentum is transferred to the car. The lateral force of a foot of
water moving at 10 miles per hour is about 500 pounds on the
average automobile. The greatest effect is buoyancy - for every
foot that water rises up the side of a car, it displaces 1,500
pounds of the car's weight. So, two feet of water moving at 10
miles per hour will float virtually any car. Many persons have
been swept away by flood waters upon leaving their vehicles, which
are later found without much damage. Use caution when abandoning
your vehicle, and look for an opportunity to move away quickly and
safely to higher ground.
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What to Do After a
Flood or Flash Flood
- Seek necessary medical
care at the nearest hospital or clinic. Contaminated flood
waters lead to a greater possibility of infection. Severe injuries
will require medical attention.
- Help a neighbor who may
require special assistance - infants, elderly people, and people
with disabilities. Elderly people and people with
disabilities may require additional assistance. People who care
for them or who have large families may need additional assistance
in emergency situations.
- Avoid disaster 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 waters, crumbled roads, landslides, mudflows,
and other hazards.
- Continue to listen to a
NOAA Weather Radio or local radio or television stations 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 flood waters remain around the building. Flood waters
often undermine 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 electric or waterline damage
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. Check with your utility
company now about where broken lines should be reported.
- 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 sturdy shoes.
The most common injury following a disaster is cut feet.
- Use battery-powered
lanterns or flashlights when examining buildings.
Battery-powered lighting is the safest and easiest, preventing
fire hazard for the user, occupants, and building.
- 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 travel 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 quickly leave the building. 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 sewage and
waterline damage. 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.
- Watch out for animals,
especially poisonous snakes, that may have come into buildings
with the flood waters. Use a stick to poke through debris.
Flood waters flush 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.
- After returning home:
- Throw away food that
has come in contact with flood waters. Some canned foods
may be salvageable. If the cans are dented or damaged, throw
them away. Food contaminated by flood waters can cause severe
infections.
- If water is of
questionable purity, boil or add bleach, and distill drinking
water before using. (See information on water treatment
under the "Disaster
Supplies Kit" section.) Wells inundated by flood waters
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.
- Pump out flooded
basements gradually (about one-third of the water per day) to
avoid structural damage. If the water is pumped
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.
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