|
|
What Causes
flooding......
|
|
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.
|
|
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.
-
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.
Last modified: November 21, 2003
|
Driving in flood
conditions
-
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.
|
