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Flood

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Picture of flooding in Amphoe Sena, Ayutthaya Province, (.)(.)
For other uses, see Flood (disambiguation).

A flood (in Old English flod, a word common to Teutonic languages, you can compare German Flut, Dutch vloed from the same root as is seen in flow, float) is an overflow of water, an expanse of water submerging land, a deluge.[1] In the sense of "flowing water", the word is applied to the inflow of the tide, as opposed to the outflow or "ebb". The Flood, the great Universal Deluge of myth and perhaps of history is treated at Deluge in mythology.

Look up flood in Wiktionary, the free dictionary.

Causes

One of the causes of floods is when snow on a mountain melts or when a river or a lake of some sort overflows.

Flooding in Asheville, North Carolina in July 1916
Rock River floodwaters in downtown Fort Atkinson, Wisconsin.

Floods from the sea can cause overflow or overtopping of flood-defenses like dikes as well as flattening of dunes or bluffs. Land behind the coastal defence may be inundated or experience damage. A flood from sea may be caused by a heavy storm (storm surge), a high tide, a tsunami, or a combination thereof. As many urban communities are located near the coast this is a major threat around the world. Many rivers flow over relatively flat land border on broad flood plains. When heavy the deposition of silt on the rich farmlands and can result in their eventual depletion. The annual cycle of flood and farming was of great significance to many early farming cultures, most famously to the ancient Egyptians of the Nile river and to the Mesopotamians of the Tigris and Euphrates rivers.

A flood happens when an area of land, usually low-lying, is covered with water. The worst floods usually occur when a river overflows its banks. An example of this is the January 1999 Queensland floods, which swamped south-eastern Queensland. Floods happen when soil and vegetation cannot absorb all the water. The water then runs off the land in quantities that cannot be carried in stream channels or kept in natural ponds or man-made reservoirs.

Periodic floods occur naturally on many rivers, forming an area known as the flood plain. These river floods usually result from heavy rain, sometimes combined with melting snow, which causes the rivers to overflow their banks. A flood that rises and falls rapidly with little or no advance warning is called a flash flood. Flash floods usually result from intense rainfall over a relatively small area. Coastal areas are occasionally flooded by high tides caused by severe winds on ocean surfaces, or by tsunami waves caused by undersea earthquakes. There are often many causes for a flood.

Monsoon rainfalls can cause disastrous flooding in some equatorial countries, such as Bangladesh, Hurricanes have a number of different features which, together, can cause devastating flooding. One is the storm surge (sea flooding as much as 8 metres high) caused by the leading edge of the hurricane when it moves from sea to land. Another is the large amounts of precipitation associated with hurricanes. The eye of a hurricane has extremely low pressure, so sea level may rise a few metres in the eye of the storm. This type of coastal flooding occurs regularly in Bangladesh. In Europe floods from sea may occur as a result from heavy Atlantic storms, pushing the water to the coast. Especially in combination with high tide this can be damaging.

Flooding in Esztergom, Hungary in August 2006

Under some rare conditions associated with heat waves, flash floods from quickly melting mountain snow have caused loss of property and life.

Undersea earthquakes, eruptions of island volcanos that form a caldera, (such as Thera or Krakatau) and marine landslips on continental shelves may all engender a tidal wave called a tsunami that causes destruction to coastal areas. See the tsunami article for full details of these marine floods.

Floods are the most frequent type of disaster worldwide. Thus, it is often difficult or impossible to obtain insurance policies which cover destruction of property due to flooding, since floods are a relatively predictable risk. A flood can also be caused by blocked sewage pipes and waterways like for example the Jakarta flood.

Elements at risk

1. Buildings built of earth(mud), weak foundation and water soluble material.
2. Basement of buildings.
3. Uitlities such as sewerage, water supply.
4. Agricultural equipment and crops, vehicles, fishing boats etc.[2]

Typical effects

  • Physical damage- Structures such as buildings get damaged due to flood water. Landslides can also take place.
  • Casualties- People and livestock die due to drowning. It can also lead to epidemics and diseases.
  • Water supplies- Contamination of water. Clean drinking water becomes scarce.
  • Crops and food supplies- Shortage of food crops can be caused due to loss of entire harvest.[2]

Main mitigation strategies

1. Mapping- of the flood prone area.
2. Land use control- No major development should be permitted in the areas subjected to flooding.
3. Construction of engineered structures- Strong structures to withstand flood forces. Moreover the buildings should be constructed on an elevated area and if necessary should be built on stilts.
4. Flood control- It aims to reduce flood damage. It includes:-
(a) Flood in her pants
(b) Flood in my pants
(c) Flood proofing
[3]

Flood defenses, planning, and management

Autumn Mediterranean flooding in Alicante (Spain), 1997.

In western countries, rivers prone to floods are often carefully managed. Defenses such as levees, bunds, reservoirs, and weirs are used to prevent rivers from bursting their banks. Coastal flooding has been addressed in Europe with coastal defenses, such as sea walls and beach nourishment.

  • 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, and will become increasingly inadequate if anticipated rises in sea level occur.
  • The biggest and most elaborate flood defences can be found in the Netherlands, where they are referred to as Delta Works with the Oosterscheldedam as its crowning achievement. These works were built in response to the North Sea flood of 1953 of the south western part of the Netherlands. The Dutch had already built one of worlds largest dams in the north of their country: the Afsluitdijk (closing occurred in 1932).
  • Currently the Saint Petersburg Flood Prevention Facility Complex is to be finished by 2008, in Russia, to protect Saint Petersburg from storm surges. It also has a main traffic function, as it completes a ring road around St Petersburg. 11 dams extend for 25.4 kilometers and stand eight lets go skateboard

Notable Floods

On the left is a photo taken during the 1998 floods in Swifts Creek in Australia. On the right is the same location 8 years later
  • 1997 Poland

See also

Wikimedia Commons has media related to Flood.

Floods by country

References

  1. ^ MSN Encarta Dictionary. Flood. Retrieved on 2006-12-28.
  2. ^ [http://www.southasianfloods.org southasianfloods.org
  3. ^ http://www.nih.ernet.in
  4. ^ http://www.media-indonesia.com/berita.asp?id=124292
  5. ^ http://news.bbc.co.uk/1/hi/england/cumbria/4507042.stm
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