1. The cause of flash flooding
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1.0 Introduction
Natural disaster can be the consequence of natural hazard or even from human
activities, which may lead to destruction of buildings, environmental problem even loss
of life. Malaysia is fortunate to be freed from natural disaster such as typhoon, earthquake
and volcano eruption.
However, our country does not escaped from the natural disaster totally as the
most occurring natural disaster in Malaysia is flood. In recent years, severe flooding has
occurred in several parts of Malaysia, both as localized flash floods and as basin-wide
floods on major river systems
Floods are the major disaster affecting many countries in the world year after
year. It is natural phenomenon that cannot be avoided occurring from time to time in all
rivers and natural drainage systems. It causes damage to lives, natural resources and
environment as well as the loss of economy and health. The impact of floods has been
increased due to a number of factors such as rising sea levels and increased development
on flood plain
Two major floods that occur in Malaysia are monsoon flood and flash flood.
Monsoon floods occur from cyclical monsoons during the local tropical wet season
roughly around the month of October to March. Flood occur when heavy rainfall that
prolonged for several days or intense rainfall over short period of time causing river or
stream increase in the water level that submerges the land. However, flash flooding
happens suddenly and without any warning.
Most flash flooding occurs due to slow-moving thunderstorm that repeatedly
moving over the same area or heavy rain from hurricane and tropical storms. It takes
about several minute to hours to develop. It also could occur when man-made structures
fail such as collapse of dam. Flash flood occurs six hours after heavy rainfall, mean while
flood is longer lasted a week or more.
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2. The cause of flash flooding
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2.0 Flash flood
Flash flood was one of the most common and destructive weather-related
phenomena that Malaysia experienced. In fact, due to the rapid development that the
country is undergoing, more incidences of flash floods were reported than before and
they were not confined to the monsoon seasons only but rather occurred at any period of
the year. Flash flood water moves at such a high velocity and usually carries a substantial
amount of debris. Several factors contribute to flooding is the rainfall intensity and
duration. Flash flooding occurs when a barrier holding back water fails or when water
falls too quickly on saturated soil or dry soil that has poor absorption ability. Flash floods
most often occur in normally dry areas that have recently received precipitation.
Figure 1. Flash flood in Kuala Lumpur
2.1 Cause
Flash flooding have many reason for it occurrence, one of them is the due to
clogging of drain. In Kuala Lumpur, the clogged drains and poor drainage system are the
main factors causing flash floods. The rubbish inside the drain prevents the smooth flow
of water. When heavy rainfall occur, the drain unable to support the amount of water thus
an overflow occur causing flash flooding.
Figure 2. Clogged drain

3. The cause of flash flooding
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Flash flood also could occur when man-made structure such as dam and levee
failed. All types of dams may fail with the sudden release of water into the downstream
drainage. Examples of dam failures such as in 1928, the Saint Francis Dam in Los
Angeles failed. The Johnstown, Pennsylvania dam, built of earthen material collapsed
after a period of heavy rainfall in 1889.
The Vaiont Dam in Italy failed when landslides that moved into the reservoir
behind the dam caused water to overtop the dam and in New Orleans, the levee systems
designed to prevent flooding failed during hurricane Katrina due to overtopping of levees
and floodwalls by the storm surge.
Figure 3. Saint Francis Dam. Figure 4. New Orleans levee.
Other than that, the increased of floods occurrences especially in urban area are
largely due to urbanization process that result in increase of impervious surface which
shortened the time of concentration and increase the magnitude of the runoff discharge. It
also decreases the amount of infiltration of the rainfall thus causing the water to
accumulate and flash flooding occurs.
Figure 5. The peak in urban area is higher due to impervious area and water flow
faster in concrete drain.

4. The cause of flash flooding
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It also occurs when the ground becomes saturated with water that has fallen too
quickly to be absorbed. The runoff collects in low-lying areas and rapidly flows downhill.
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
2.2 Effect
Floods make an enormous impact on the environment and society. Floods destroy
drainage systems in cities, causing raw sewage to spill out into bodies of water. Also, in
cases of severe floods, buildings can be significantly damaged and even destroyed. This
can lead to catastrophic effects on the environment as many toxic materials such as paint,
can be released into the rivers, and ocean, killing marine life.
Floods may also cause millions of dollars worth of damage to a city, both evicting
people from their homes and ruining businesses. Floods cause significant amounts of
erosion to coasts, leading to more frequent flooding if not repaired. Other than that, the
destruction of farms has cause the increase of vegetable price. The monsoon season in
other country has cause the imported price of greens soar.
2.3 Prevention
Flash flood cannot be stopped, however there are ways to prevent it from
repeating itself. Flood plains can be created and the stream also can be widened. It helps
by hindering the accumulation of water by providing a route for the drainage of water.
Also, the protection of wetlands helps to maintain a natural drainage system to provide a
place for the excess water to gather. Such devices allow the water to evaporate before it
can accumulate, creating flooding conditions.
Other ways of preventing floods include placing sandbags along the riverbank to
serve as levees and placing large rocks on banks to prevent erosion, which prevents
riverbanks from deteriorating, remaining high enough so that flooding will not occur as
frequently. Levees also impede the collecting of water. With a levee, a huge amount of
rain water can be accumulated before flooding occurs. However, one drawback to their
use is that if water is able to get past the levees, then the flooding is significantly worse
and causes several times more damage.

5. The cause of flash flooding
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Figure 6. Levee
In Malaysia, there are several project that been done in other to reduce the flash
flooding such as in Kuala Lumpur, Stormwater Management and Road Tunnel(SMART)
had been build to divert large volumes of flood water from entering the holding pond,
bypass tunnel and storage reservoir. This will reduce the flood water level at the Jalan
Tun Perak Bridge, preventing spillover. According to the Star Online, there are several
projects are implemented at various areas in Kuala Lumpur to reduce the flash floods. A
new retention pond in several areas in Kuala Lumpur and the drainage upgrading.
3.0 Conclusion
Flooding can cause many bad effect to our activities life, commercial or
industrials activities. However, floods can also bring many benefits, such as recharging
ground water, making soil more fertile and providing nutrients in which it is deficient. At
place that needed water, flash flood is a good way for water resources in particular in arid
and semi-arid regions where precipitation events can be very unevenly distributed
throughout the year.
There are ways to reduce the effect of flash flood to our life, such as
implementation of a flash flood guidance system. A key benefit of the flash flood
guidance system is providing early awareness of impending local flash flood threats.
Other than that, Floodplain mapping can be prepared now to delineate flood prone areas
on the map. Such kind of maps will help the civil authorities for quick assessment of
potential impact of the flood prone areas and initiation of appropriate measures can be
conducted for reducing the impact.
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6. The cause of flash flooding
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5.0 Reference
Musa Bashir, Basema. Flash Flood
Mohd. Safie Mohd., Dr. Buang Alias and Dzurllkanian Daud. (2006) GIS Analysis for
flood Hazard Mapping: Case Study; Segamat, Johor, West Malaysia
Zulherman M. Sosi and Susilawati Sulaiman. Analysis on Kuala Lumpur flood risk zone
http://www.kkr.gov.my (20 December 2009)
http://en.wikipedia.org/wiki/Floods_in_Malaysia (20 December 2009)
http://www.kjc.gov.my/people/ccm/webpages/resource/csum.htm (1 January 2010)
http://thestar.com.my/news/story.asp?file=/2008/9/3/central/1929494&sec=central
(19 December 2009)