flash flooding in jordan and in the neifgouring.ppt

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1. Flash Flooding
Flash Flood:
#1 weather-
related killer in
the United
States!

2. What is a flood?
What is a flood?
A flood results from
days of heavy
rain and/or
melting snows,
when rivers rise
and go over their
banks.
The "State Street River" (floodwater from City Creek) rushes through
downtown Salt Lake City, Utah, in May 1983. Rapid melting of a record-water-
content snowpack caused the most widespread flooding in the State's history,
resulting in damages totaling $621 million.
State Street River

3. What is a flash
flood?
A flash flood is a life-
threatening flood
that begins within 6
hours —and often
within 3 hours—of
the rain event.
Floodingis a longer
term event and may
last a week or
more.
What is a flash flood?

4. A floodis typically
associated with a
defined body of water,
but flash floods can
occur in normally dry
areas with no visible
stream channel.
What is a flash flood?

5. What is a flash flood?
Consequently, included
in the flash flood
definitionis the rapid
inundation of normally
dry areas, roads,
underpasses, and
buildings.

6. Most flash flooding is caused
by slow-moving
thunderstorms,
thunderstorms repeatedly
moving over the same area,
or heavy rains from
hurricanes and tropical
storms.
What is the cause of
flash flooding?
Midwest flooding caused by rain storms, August 2007

7. Hurricane induced flood
Katrina, 2005: New Orleans, LA
Floyd,1999: North Carolina
Hurricane Floyd,1999
Hurricane Katrina, 2005

8. Flash floodscan
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.
Panther, WV,
May 8, 2002 --
Heavy silting
happened on
many creeks and
rivers as a result
of the violent
flash flood that
struck southern
West Virginia on
May 2, 2002.
Clear Fork Road,
WV, July 14,
2001 --This
house was torn
apart by the
flooding of the
nearby Clear
Fork Creek.
How dangerous could flash floods be?

9. Flash flood-producing rains
can also trigger
catastrophic mud slides.
You will not always have a
warning that these deadly,
sudden floods are coming.
How dangerous could flash floods be?

10. Flooding Types
River Flood:Flooding along rivers is a natural and inevitable part of life. Some floods occur
seasonally when winter or spring rains, coupled with melting snows, fill river basins with too much water,
too quickly. Torrential rains from decaying hurricanes or tropical systems can also produce river flooding.
Coastal Flood:Winds generated from tropical storms and hurricanes or intense offshore low
pressure systems can drive ocean water inland and cause significant flooding. Escape routes can be cut
off and blocked by high water. Coastal flooding can also be produced by sea waves called tsunamis ,
sometimes referred to as tidal waves. These waves are produced by earthquakes or volcanic activity.
Urban Flood:As land is converted from fields or woodlands to roads and parking lots, 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, while basements can
become death traps as they fill with water.
Flash Flooding in Arroyos/Washes: An arroyo is a water-carved gully or normally dry creek
bed. Arroyos can fill with fast-moving water very quickly. Flash flooding at this arroyo in Arizona took only
58 seconds to develop.
Ice Jam:Floating ice can accumulate at a natural or man-made obstruction and stop the flow of water.

11. How do flash floods occur?
Several factorscontribute
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
coveralso play an
important role.

12. Rainfall and Runoff Relationship
Flash floodsare rapid-onset
hydrologic events that can be
very difficult to forecast. A
combination of high rainfall
rate with rapid and often
very efficient runoffis
common to most flash flood
events. Ice jam formation
on riverscan also play a role
in rapid-onset flash flooding,
particularly upstream of the
ice jam.

13. Soil Influences
The three critical soil
properties to consider when
assessing the risk of flash
flooding are soil moisture,
soil texture, and soil
profile.
Soil moistureis often
considered the most
important soil factor for
rapid runoff and flash
flooding. There is some
validity to this reasoning in
that if the soil is saturated
there is no room for
additional rainfall to
infiltrate, and all rainfall
becomes runoff regardless
of the soil texture.

14. Flash floodsoccur
with intense rainfall
rates that often exceed
the soil's infiltration
capacity even when
the soil is dry.
When rain is very intense...

15. Soil Influences: Soil Texture
Certain soil texturessuch
as clay, and to some extent
silt, can be associated with
low infiltration rates and
result in rapid runoff during
intense rainfall. Therefore,
runoff from intense rainfall
is likely to be more rapid
and efficient with clay soils
than with sand.

16. Soil Influences: Soil Texture
Although sandy soils
permit greater infiltration
of intense rainfall, rapid
runoff can occur if there
is only a thin layer of
soil.For example, if an
impermeable layer of
rock underlies a thin
layer of soil, that soil
layer can saturate
quickly and result in
large amounts of runoff.

17. Flash flooding facts
1. Flood can occur nationwide.
2. Flash floods are the #1 weather-related killer in the U.S.
3. Nearly 80% of all flash flood fatalities are auto related!
4. Many flash floods occur at night....be prepared to take quick action.
5. A mere 2 feet of water can float a large vehicle or even a bus. This is
why you should never drive through flooded roads. Just 6 inches of
rapidly moving flood water can knock a person down.

18. FLOOD WATCH -means that an overflow of water from a river is
possible for your area.
FLASH FLOOD WATCH -means that flash flooding is possible in
or close to the watch area. Flash Flood Watches can be put into
effect for as long as 12 hours, while heavy rains move into and
across the area.
FLOOD WARNING -means flooding conditions are actually
occurring in the warning area.
FLASH FLOOD WARNING -means that flash flooding is actually
occurring in the warning area. A warning can also be issued as a
result of torrential rains, a dam failure or snow thaw.
Watch and warning

19. What should we do in case
of flooding?
The rule for being safe in a flooding situation is simple: HEAD FOR
HIGHER GROUND AND STAY AWAY FROM FLOOD WATERS!
When a flash flood WATCH is issued Be alert to signs of flash
flooding and be ready to evacuate on a moment's notice.
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!