definition of a flood is: an overflowing of water onto land that is
normally dry. The consequences of floods are sometimes very severe and,
during the 20th century, floods were the deadliest and most destructive
natural disaster in the United States.
American continent is mainly affected by five types of floods:
1. Heavy rains
can be responsible of "regional floods" as in the
Mexican states Tabasco and Chiapas. At the end of October 2007, heavy
rain related to a storm present in the Gulf of Mexico fell continuously
over the southern Gulf Coast during an entire week. The result was very
severe floods which covered some 70% of the state of Tabasco, including
the capital Villahermosa.
At least 20,000
people were forced to seek emergency shelters and 1 million people's
homes were under water. The floods caused profound devastation to
agriculture, which is the principal source of income in the state.
Indeed, the heavy rains occurred during the cocoa harvest (the state of
Tabasco is the largest producer of cocoa in the country). All the 2007
harvest were lost.
extraction of petroleum and gas, the construction of dams in the zone
and land erosion have all contributed to making this region more prone
to flooding. Deforestation has also allowed silt to deposit in rivers,
thus reducing their capacity and making floods more likely.
Some 70% of the
Tabasco low-lying state was thought to be under water,
including the capital Villahermosa - Source
2. Another kind of
flood is the "flash flood" which is defined as a
local flood of great volume and short duration generally resulting from
heavy rainfall in the immediate vicinity.
well known example of this kind of event in North America is the
Saguenay Flood, a series of flash floods that hit the
Saguenay-Lac-Saint-Jean region of Quebec, Canada on July 19 and 20,
1996. It was the biggest overland flood in 20th century Canadian
Problems started after two weeks of constant rain which severely
saturated soils, rivers and reservoirs. The Saguenay region is a
geological graben, which increased the effect of the sudden massive
rains of July 19. In the span of a few hours, 270 mm fell on the
region, the equivalent to the amount of rain usually received in a
storm produced the largest deluge ever seen in Canada this century. The
wave of water, rocks, trees and mud of 2.5 meters high ran through
parts of Chicoutimi and La Baie, completely leveling an entire
neighborhood. The enquiries have shown that the rain was the main cause
of this disaster but also that the network of dikes and dams protecting
the city was poorly maintained. The toll of the disaster rose to ten
dead, 488 homes destroyed, 1,230 homes damaged and 16,000 people
evacuated from the entire area.
3. Heavy rain can
also be the main cause of "dam and levee-failure floods"
like it happened on Hawaii Island in 2006.
The Ka Loko
Reservoir is a reservoir created by an earthen dam, on the island of
Kauai, Hawaii. Waters flow from Ka Loko Reservoir down to another lake,
then to the Waiakalua river and down to the Pacific Ocean. After
unusually heavy rain, the Ka Lokos dam bursted on March 14, 2006. The
flood from the dam went towards the town of Kilauea with a wall of
water reported to be between 6 to 20 m high and 60 m wide. The flood
killed 7 people and destroyed several homes.
conditions are the main cause of this disaster but several human
factors have led to the dam failure. Indeed, the dam was not properly
maintained nor inspected, and the owner of the dam performed important
works near the dam without permits. These unpermitted operations were
known by the administration but the works have not been stopped.
4. Each year, the Southern part of the continent is affected by
hurricanes which are sometimes responsible of "storm-hurricane
floods". A well known example of this kind of phenomenon is
the flood that covered the city of New Orleans during Katrina.
formed over the Bahamas on August 23, 2005, and crossed southern
Florida as a moderate category 1 hurricane, causing some deaths and
flooding before strengthening rapidly in the Gulf of Mexico. The storm
made its second landfall as a category 3 storm on the morning of August
29 in south-east Louisiana. The most severe loss of life and property
damage occurred in New Orleans, which flooded after the levee system
catastrophically failed. 80% of the city became flooded and at least
1,836 people lost their lives.
Satellite view of the Hurricane Katrina
(August 28 2005) - Source
5. It is also possible that a flood is not directly related to
precipitation. This is the case in northern regions where the ice
melting at the end of the winter sometimes causes "ice-jam
recently, the village of Eagle in Alaska was completely devastated by
floods. This village sits on the shores of the Yukon River in northern
Alaska in a very rugged region. The river winds out of the massive
Ogilvie Mountain range in the Yukon Territory of Canada and across
Alaska before dumping into the Bering Sea. This past winter, the snow
pack in the region close to the Eagle village, northeastern Alaska, was
higher than usual and the ice on the Yukon River was about 60 cm
thicker than previous years. In May, an unseasonably warm weather
caused rapid snow melting and ice movement on the Yukon creating the
perfect flood. Residents were awakened by the rising of the water level
which was so fast that they had to run away and leave everything.
The Yukon reached approximately 6 m above its previous highest flood
mark and the National Weather Service called the flooding "one of the
worst floods of record".
Photo by David Marunde
examples mentioned above are the results of extreme climatic conditions
but human impact often aggravates the consequences of the flood.
Katrina - NOAA
Significant Floods in the United States During the 20th Century - USGS
Measures a Century of Floods
The Great USA Flood of 1993 NOAA National
TheTop Ten Weather Stories of 1996 -
Environment Canada's World Wide Web Site
Wikipedia Hurricane - Flood
- Kaloko Dam - 2007 Tabasco flood - Saguenay_Flood
Yukon River Flood Devastates City of Eagle -
Sequim & Port Angeles News Online