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Severe Weather Awareness - Flash
Floods and River Floods
The Number ONE
weather-related killer in the United States
Flooding kills
almost twice as many people each year as tornadoes and hurricanes
combined!
Unlike hurricanes,
floods are a threat in every state.
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Flooding can take many forms including river floods, coastal floods, urban floods, and flash
floods. |
Ed Hayden
Goldsboro News- Argus
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Tom Herde
Boston Globe
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David Vann
The Sentinel-Record
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| River flooding...like coastal flooding...are long term events and may last a week or more. |
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Flash flooding and urban flooding are short-term events ... usually
occurring with 6 hours of the beginning of heavy rain.
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Photo by: Brian Strickland News-Argus
Goldsboro , N.C. |
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How do flash floods occur? The two key elements are:
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rainfall intensity
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duration
Topography, soil conditions, and ground cover
also play an important role.
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Flash floods occur within a few minutes or
hours of excessive rain or a dam or levee
failure. 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. |
Photo by: David Vann
The Sentinel-Record
Hot Spring, AR
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Most flash flooding is caused by slow-moving thunderstorms,
thunderstorms repeatedly moving over the same area (called
"training"), or heavy rains from hurricanes and tropical storms.
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| Urban Floods are the result of land being converted from fields and
woodlands into roads and parking lots.
As land is paved, 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 and
basements can become death traps as they fill with water. |
Photo by: Kaye Farmer
News-Argus
Goldsboro, N.C. |
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Nearly half of all flash flood deaths are auto
related. Even 6 inches of fast moving flood
water can knock you off your feet and at a
depth of 2 feet will float your car.
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Water weighs 62.4 pounds per cubic foot and is
typically flowing downstream at 6 to 12 miles
an hour.
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When a vehicle stalls in the water, the water's
momentum is transferred to the car. For each
foot the water rises, 500 pounds of lateral force
are applied to the car.
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The biggest factor is bouyancy. For each foot
the water rises up the side of the car, the car
displaces 1,500 pounds of water. In effect, the
car weighs 1,500 pounds less for each foot the
water rises.
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Two feet of water will carry away most cars -
1,000 pounds of lateral (or side force) plus
3,000 pounds of buoyancy!
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Clues to potential flash flooding:
- Distant thunder - runoff
from a faraway thunderstorm could be heading your way
- Look out for water rising
rapidly
- In your car look out for
flooding at highway dips, bridges, and low areas.
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Before the flood...
- Know your flood risk and elevation
above flood stage
- 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 other containers. Water
service may be interrupted or water
contaminated.
- Keep a stock of food that requires
little cooking and no refrigeration.
- Keep first aid supplies on hand.
Keep a NOAA Weather Radio, a
battery-powered radio, emergency
cooking equipment, and flashlights in
working order.
- Install check valves in building sewer
traps to prevent flood water from
backing up into the drains of your
home.
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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. |
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River Flood Watch
- River levels may reach or rise above
flood stage
- Be ready to move to a safe area if necessary
- Stay tuned to NOAA Weather Radio or local radio and TV for possible warning
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River Flood Warning
- Rivers will rise above flood stage
- Take all precautions necessary to protect your life and property
- Move to a safe area if you are in the flood area
- Stay tuned to NOAA Weather Radio or
local radio and TV
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Flash Flood Watch
- Heavy rains are possible
- Be ready to move to higher ground immediately if flooding occurs
- Stay tuned to NOAA Weather Radio or
local radio and TV for possible warning
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Flash Flood Warning
- Flash flooding has been reported or is
imminent
- Move to higher ground immediately
- Never drive through floodwater on roadways
- Stay tuned to NOAA Weather Radio or local radio and TV
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The rule for being safe in a flooding situation is
simple:
Head for higher ground and stay away from flood
waters!
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Flood and Flash Flood warnings are sent to
local radio and television stations and are
broadcast over your local NOAA Weather Radio serving the warning area. These warnings are
also relayed to local emergency management and public safety officials who can activate local
warning systems to alert communities to the danger.
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Contact us if you'd like a free copy of
Flash Floods and Floods...the Awesome Power - a preparedness brochure produced by the National Weather Service, Federal Emergency Management Agency, and the American Red Cross.
Related Web Sites on Flooding:
Credits:
Thanks to the Goldsboro NC News-Argus for allowing us to use pictures from
Hurricane Floyd flooding
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National Weather Service
Weather Forecast Office Columbia
2909 Aviation Way
West Columbia, S.C. 29170-2102
(803)822-8135
Webmaster: caewx@noaa.gov
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