Flash floods can occur under several types of ...
U.S. 1997: 11 die in
flash flood in Antelope ... Rock and Avalanche fall from
Western Part of Annapurna ...
Flash flood
From Wikipedia, the free encyclopedia
Driving through a flash-flooded road
A flash flood after a thunderstorm in the Gobi, Mongolia
A
flash flood is a rapid
flooding of
geomorphic low-lying areas: washes,
rivers,
dry lakes and
basins. It may be caused by heavy
rain associated with a
severe thunderstorm,
hurricane,
tropical storm, or
meltwater from ice or snow flowing over ice sheets or snowfields. Flash floods may occur after the collapse of a natural
ice or
debris dam, or a human structure such as a man-made
dam, as occurred before the
Johnstown Flood of 1889. Flash floods are distinguished from a regular flood by a timescale of less than six hours.
[1]
The temporary availability of water is often utilized by foliage with
rapid germination and short growth cycle, and by specially adapted
animal life.
Causes
Flash floods can occur under several types of conditions. Flash
flooding occurs when precipitation falls rapidly on saturated soil or
dry soil that has poor absorption ability. The runoff collects in
gullies and streams and, as they join to form larger volumes, often
forms a fast flowing front of water and debris. Flash floods most often
occur in normally dry areas that have recently received precipitation,
but may be seen anywhere downstream from the source of the
precipitation, even many miles from the source. In areas on or near
volcanoes, flash floods have also occurred after eruptions, when
glaciers have been melted by the intense heat. Flash floods are known to occur in the highest mountain ranges of the
United States
and are also common in the arid plains of the southwestern United
States. Flash flooding can also be caused by extensive rainfall released
by
hurricanes and other
tropical storms, as well as the sudden thawing effect of
ice dams.
[2][3] Human activities can also cause flash floods to occur. When
dams, constructed for hydro-electricity,
have failed, large quantities of water can be released and can destroy everything within its path.
[3]
Hazards
The United States
National Weather Service
gives the advice "Turn Around, Don't Drown" for flash floods; that is,
it recommends that people get out of the area of a flash flood, rather
than trying to cross it. Many people tend to underestimate the dangers
of flash floods. What makes flash floods most dangerous is their sudden
nature and fast moving water. A vehicle provides little to no protection
against being swept away; it may make people overconfident and less
likely to avoid the flash flood. More than half of the fatalities
attributed to flash floods are people swept away in vehicles when trying
to cross flooded intersections.
[4] As little as 2 feet (0.61 m) of water is enough to carry away most SUV-sized vehicles.
[5]
The U.S. National Weather Service reported in 2005 that, using a
national 30-year average, more people die yearly in floods, 127 on
average, than by
lightning (73),
tornadoes (65), or
hurricanes (16).
[6]
In
deserts,
flash floods can be particularly deadly for several reasons. First,
storms in arid regions are infrequent, but they can deliver an enormous
amount of water in a very short time. Second, these rains often fall on
poorly absorbent and often clay-like soil, which greatly increase the
amount of
runoff
that rivers and other water channels have to handle. These regions tend
not to have the infrastructure that wetter regions have to divert water
from structures and roads, such as storm drains, culverts, and
retention basins,
either because of sparse population, poverty, or because residents
believe the risk by flash floods is not high enough to justify the
expense. In fact, in some areas, desert roads frequently cross dry river
and creek beds without bridges. From the driver's perspective, there
may be clear weather, when unexpectedly a river forms ahead of or around
the vehicle in a matter of seconds.
[7]
Finally, the lack of regular rain to clear water channels may cause
flash floods in deserts to be headed by large amounts of debris, such as
rocks, branches, and logs.
Deep
slot canyons can be especially dangerous to hikers as they may be flooded by a storm that occurs on a
mesa miles away, sweeps through the canyon, and makes it difficult to climb up and out of the way to avoid the flood.
Significant flash floods
- 1889: Johnstown Flood, more than 2,200 people dead
- 1903: Heppner Flood of 1903; Oregon, United States: 247 dead, 25% of the city
- 1938: Los Angeles Flood of 1938, California, U.S.: 115 dead
- 1938: Kopuawhara Flood of 1938, Mahia Peninsula, New Zealand 21 dead
- 1952: Lynmouth disaster, England: 34 dead
- 1963: Vajont dam disaster, Italy: 1910 dead
- 1967: Flash flood in Lisbon, Portugal: 464 dead
- 1971: Kuala Lumpur floods, Malaysia: 32 dead
- 1972: The Black Hills flood, South Dakota, U.S.: 238 dead
- 1976: The Big Thompson River flood, which killed 143 people in Colorado, U.S.
- 1997: 11 die in flash flood in Antelope Canyon, a popular tourist attraction north of Page, Arizona.
- 2007: Sudan floods, 64 people killed.
- 2009: September 26 in Metro Manila primarily Marikina city, Taguig
City, and Pasig City; and many municipalities of the provinces of Rizal,
Bulacan and Laguna taking more than a hundred lives and leaving
thousands of affected residents homeless. It also submerged several
municipalities under feet deep of water for several weeks.
- 2009: October 1, Giampilieri, Messina, 37 people were killed. See also 2009 Messina floods and mudslides.
- 2010: Madeira archipelago, 42 dead
- 2011: Lockyer Valley, Queensland, Australia. 21 people dead, mainly in the town of Grantham.
- 2011: Philippines, Cagayan de Oro and Iligan City, 17 December 2011.
At least 1200 people killed as reported by Red Cross. See also Tropical Storm Washi
- 2012: Krasnodarskiy Kray, Russia. 172 people were killed by a flash flood that struck at 2 A.M. local time on 7 July. Main cities that were hit are Krymsk and Gelendzhik.[8][9]
- 2012: Uttarakhand, Uttarakhand, India: 822 dead
- 2012: Pokhara, Nepal - 32 dead + 30 missing [May 5, 2013, Nearly 3
weeks damming in Seti Gorge in Upper Seti Basin, Rock and Avalanche fall
from Western Part of Annapurna IV].
- 2013: November 17–19, Northeast Sardinia: 18 deaths, 3000 homeless. See also 2013 Sardinia floods
- 2013: Port Louis, Mauritius - 11 dead
- 2013: Argentina floods - 99+ dead
- 2013: Kedarnath, Uttarakhand, India: 5000 approx dead[10]
- 2014: Srinagar, Jammu & Kashmir, India: 300 Approximately Dead.[11]
See also
Further reading
References
Driving through a flash-flooded road
Nepal Monsoon
A flash flood is a rapid flooding of geomorphic low-lying areas: washes, rivers, dry lakes and basins. It may be caused by heavy rain associated with a severe thunderstorm, hurricane, tropical storm, or meltwater from ice or snow flowing over ice sheets or snowfields. Flash floods may occur after the collapse of a natural ice or debris dam, or a human structure such as a man-made dam, as occurred before the Johnstown Flood of 1889. Flash floods are distinguished from a regular flood by a timescale of less than six hours.[1] The temporary availability of water is often utilized by foliage with rapid germination and short growth cycle, and by specially adapted animal life.A flash flood after a thunderstorm in the Gobi, Mongolia
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