is an overflow or accumulation of an
expanse of water that submerges land. In the sense of "flowing
water", the word may also be applied to the inflow of the tide
.Flooding may result from the volume of water
within a body of water, such as a river
, which overflows or breaks levees, with
the result that some of the water escapes its normal boundaries.
While the size of a lake or other body of water will vary with
seasonal changes in precipitation and snow melt, it is not a
significant flood unless such escapes of water endanger land areas
used by man like a village, city or other inhabited area.
Floods can also occur in rivers, when the strength of the river is
so high it flows out of the river channel, particularly at bends or
meanders and causes damage to homes and businesses along such
rivers. While flood damage can be virtually eliminated by moving
away from rivers and other bodies of water, since time out of mind,
people have lived and worked by the water to seek sustenance and
capitalize on the gains of cheap and easy travel and commerce by
being near water. That humans continue to inhabit areas threatened
by flood damage is evidence that the perceived value of living near
the water exceeds the cost of repeated periodic flooding.
The word "flood" comes from the Old
, a word common to Germanic languages
(compare German Flut
, Dutch vloed
from the same
root as is seen in flow, float
). The specific term "The
Flood," capitalized, usually refers to the great Universal
described in the Bible
, and is treated at Deluge
- Slow kinds: Runoff from sustained rainfall or
rapid snow melt exceeding the capacity of a river's channel. Causes
include heavy rains from monsoons,
hurricanes and tropical depressions, foreign winds and warm rain
affecting snow pack. Unexpected drainage obstructions such as
landslides, ice, or
debris can cause slow flooding upstream of
- Fast kinds: include flash floods resulting
from convective precipitation (intense thunderstorms) or sudden release from an
upstream impoundment created behind a dam,
landslide, or glacier.
- Caused by a significant and unexpected event e.g. dam breakage, or as a result of another hazard (e.g.
earthquake or volcanic eruption).
A muddy flood is produced by an accumulation of runoff generated on
cropland. Sediments are then detached by runoff and carried as
suspended matter or bedload. Muddy runoff is more likely detected
when it reaches inhabited areas.
Muddy floods are therefore a hillslope process, and confusion with
mudflows produced by mass movements should be avoided.
- Floods can occur if water accumulates across an impermeable
surface (e.g. from rainfall) and cannot rapidly dissipate (i.e.
gentle orientation or low evaporation).
- A series of storms moving over the
- Dam-building beavers
can flood low-lying urban and rural areas, often causing
- Physical damage - Can range anywhere from
bridges, cars, buildings, sewer systems,
roadways, canals and
any other type of structure.
- Casualties - People and livestock die due to drowning.
It can also lead to epidemics and waterborne diseases.
- Water supplies - Contamination of water. Clean drinking water becomes scarce.
- Diseases - Unhygienic conditions. Spread of water-borne diseases.
- Crops and food supplies - Shortage of food crops can
be caused due to loss of entire harvest. However, lowlands near
rivers depend upon river silt deposited by floods in order to add
nutrients to the local soil.
- Trees - Non-tolerant species can die from
- Economic - Economic hardship, due to: temporary
decline in tourism, rebuilding costs, food shortage leading to
price increase etc.
In many countries across the world, rivers prone to floods are
often carefully managed. Defences such as levees
, and weirs
are used to prevent rivers from bursting their banks. When these
defences fail, emergency measures such as sandbags or portable
inflatable tubes are used. Coastal flooding has been addressed in
Europe and the Americas with coastal
, such as sea walls
, beach nourishment
, and barrier islands
Remembering the misery and destruction caused
by the 1910 Great Flood of
Paris, the French government built a series of reservoirs
called Les Grands Lacs de Seine (or Great Lakes) which helps remove
pressure from the Seine during
floods, especially the regular winter flooding.
London is protected
from flooding by a huge mechanical barrier across the River Thames, which is raised when the water
level reaches a certain point (see Thames Barrier).
Venice has a
similar arrangement, although it is already unable to cope with
very high tides.
The defences of both London and Venice
would be rendered inadequate if sea levels were to rise.
largest and most elaborate flood defences can be found in the
Netherlands, where they are referred to as Delta Works with the Oosterschelde dam as its crowning achievement.
were built in response to the North Sea flood of 1953
southwestern part of the Netherlands. The Dutch had already
built one of the world's largest dams in the north of the country:
the Afsluitdijk (closing occurred in 1932).
the Saint Petersburg
Flood Prevention Facility Complex is to be finished by 2008, in Russia, to protect
It also has a main
traffic function, as it completes a ring
around Saint Petersburg. Eleven dams extend for 25.4
kilometres and stand eight metres above water level.
for over 150 years, has been controlled by various actions of the
Vienna Danube regulation,
with dredging of the main Danube during
1870-75, and creation of the New Danube
elaborate system of floodway defences can be found in the Canadian
province of Manitoba. The Red River flows northward from the United States, passing
through the city of Winnipeg (where it meets the Assiniboine River) and into Lake Winnipeg.
As is the case with all north-flowing
rivers in the temperate zone of the Northern Hemisphere, snowmelt
in southern sections may cause river levels to rise before northern
sections have had a chance to completely thaw. This can lead to
devastating flooding, as occurred in Winnipeg during the spring of 1950
. To protect the city
from future floods, the Manitoba government undertook the
construction of a massive system of diversions, dikes, and
floodways (including the Red River Floodway and the Portage
Diversion). The system kept Winnipeg safe during the
1997 flood and which devastated
many communities upriver from Winnipeg, including Grand Forks,
North Dakota and Ste. Agathe, Manitoba
. It also kept
Winnipeg safe during the 2009
In the U.S., the New
Orleans Metropolitan Area
, 35% of which sits below sea level,
is protected by hundreds of miles of levees and flood gates
. This system failed catastrophically,
in numerous sections, during Hurricane
, in the city proper and in eastern sections of the
Metro Area, resulting in the inundation of approximately 50% of the
metropolitan area, ranging from a few centimetres to 8.2 metres (a
few inches to 27 feet) in coastal communities. In an act of
successful flood prevention, the Federal Government of the United
States offered to buy out flood-prone properties in the United
States in order to prevent repeated disasters after the 1993 flood
across the Midwest. Several communities accepted and the
government, in partnership with the state, bought 25,000 properties
which they converted into wetlands
wetlands act as a sponge in storms and in 1995, when the floods
returned, the government did not have to expend resources in those
, flood diversion
areas are rural areas that are
deliberately flooded in emergencies in order to protect
Many have proposed that loss of vegetation (deforestation
) will lead to a risk increase.
With natural forest cover the flood duration should decrease.
Reducing the rate of deforestation should improve the incidents and
severity of floods.
Egypt, both the Aswan Dam (1902) and the Aswan High Dam (1976) have controlled various amounts of flooding
along the Nile river.
Clean-up activities following floods often pose hazards to workers
and volunteers involved in the effort. Potential dangers include:
water polluted by mixing with and causing overflows from foul
sewers, electrical hazards
, carbon monoxide
or cold stress
exposure to hazardous materials
Because flooded disaster sites are unstable, clean-up workers might
encounter sharp jagged debris, biological hazards in the flood
water, exposed electrical lines, blood or other body fluids, and
animal and human remains. In planning for and reacting to flood
disasters, managers provide workers with hard
, heavy work gloves,
, and watertight boots with
steel toes and insoles.
There are many disruptive effects of flooding on human settlements
and economic activities. However, floods (in particular the more
frequent/smaller floods) can bring many benefits, such as
recharging ground water, making soil more fertile and providing
nutrients in which it is deficient. Flood waters provide much
needed water resources in particular in arid and semi-arid regions
where precipitation events can be very unevenly distributed
throughout the year. Freshwater floods in particular play an
important role in maintaining ecosystems in river corridors and are
a key factor in maintaining floodplain biodiversity.
flooding was essential to the well-being of ancient communities
along the Tigris-Euphrates Rivers,
the Nile River, the Indus River, the
Ganges and the
River, among others.
The viability for
hydrological based renewable sources of energy is higher in flood
While flood modelling is a fairly recent practice, attempts to
understand and manage the mechanisms at work in floodplains have
been made for at least six millennia. The recent development in
computational flood modelling has enabled engineers to step away
from the tried and tested "hold or break" approach and its tendency
to promote overly engineered structures. Various computational
flood models have been developed in recent years either 1D models
(flood levels measured in the channel) and 2D models (flood depth
measured for the extent of the floodplain). HEC-RAS, the Hydraulic
Engineering Centre model, is currently among the most popular if
only because it is available for free. Other models such as TUFLOW
combine 1D and 2D components to derive flood depth in the
floodplain. So far the focus has been on mapping tidal and fluvial
flood events but the 2007 flood events in the UK have shifted the
emphasis onto the impact of surface water flooding.
Below is a list of the deadliest floods worldwide, showing events
with death tolls at or above 100,000 individuals.
||1931 China floods
||1887 Yellow River
||1938 Yellow River
||Banqiao Dam failure, result of Typhoon
Nina. Approximately 86,000 people died from flooding and
another 145,000 died during subsequent disease.
||Indian Ocean tsunami
||India (mostly in
Nadu), Thailand, Maldives
||1935 Yangtze river flood
|more than 100,000
||St. Felix's Flood, storm
||Hanoi and Red River Delta flood
||1911 Yangtze river flood
- O'Connor, Jim E. and John E. Costa. (2004). The World's
Largest Floods, Past and Present: Their Causes and Magnitudes
[Circular 1254]. Washington, D.C.: U.S. Department of the Interior,
U.S. Geological Survey.
- Thompson, M.T. (1964). Historical Floods in New
England [Geological Survey Water-Supply Paper 1779-M].
Washington, D.C.: United States Government Printing Office.
- Powell, W. Gabe. 2009. Identifying Land Use/Land Cover (LULC)
Using National Agriculture Imagery Program (NAIP) Data as a
Hydrologic Model Input for Local Flood Plain Management. Applied
Research Project. Texas State University - San Marcos.
- MSN Encarta Dictionary. Flood. Retrieved on 2006-12-28. Archived 2009-10-31.
- Glossary of Meteorology (June 2000). Flood. Retrieved on 2009-01-09.
- Stephen Bratkovich, Lisa Burban, et al., "Flooding and its
Effects on Trees", USDA Forest Service, Northeastern Area
State and Private Forestry, St. Paul, MN, September 1993, webpage:
- See Jeffrey H. Jackson, Paris Under Water: How the City of
Light Survived the Great Flood of 1910 (New York: Palgrave
- Amanda Ripley. "Floods, Tornadoes, Hurricanes, Wildfires,
Earthquakes... Why We Don't Prepare." Time. August 28,
- "China blows up seventh dike to divert
flooding." China Daily. 2003-07-07.
- Bradshaw CJ, Sodhi NS, Peh SH, Brook BW. (2007). Global
evidence that deforestation amplifies flood risk and severity in
the developing world. Global Change Biology, 13:
- United States National Institute for Occupational Safety and
Health (NIOSH). Storm and Flood Cleanup. Accessed
- NIOSH. NIOSH Warns of Hazards of Flood Cleanup Work.
NIOSH Publication No. 94-123.
- WMO/GWP Associated Programme on Flood Management "Environmental Aspects of Integrated Flood
Management." WMO, 2007
- Dyhouse, G. et al. "Flood modelling Using HEC-RAS (First
Edition)." Haestad Press, Waterbury (USA), 2003.
- United States Army Corps of Engineers. Davis, CA. Hydrologic
- BMT WBM Ltd. Spring Hill, Queensland. "TUFLOW Flood and Tide
- Cabinet Office, UK. "Pitt Review: Lessons learned from the 2007
floods." June 2008.
- Worst Natural Disasters In History