A flash flood is a rapid flooding A flood is an overflow of an expanse of water that submerges land. The EU Floods directive defines a flood as a temporary covering by water of land not normally covered by water. 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, of geomorphic low-lying areas - washes, rivers A river is a natural watercourse, usually freshwater, flowing toward an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including stream, creek, brook, rivulet, and rill; there is no, dry lakes Dry lakes are an ephemeral lakebed, generally extending to the shore, or a remnant of an endorheic lake. Such flats consist of fine-grained sediments infused with alkali salts. Dry lakes may be known as alkali flats, sabkhas, playas or mud flats. If the surface is primarily salt then they are called salt pans, pans, hardpan, salt lakes or salt and basins Depression in geology is a landform sunken or depressed below the surrounding area. Depressions may be formed by various mechanisms, and may be referred to by a variety of technical terms such as:. It may be caused by heavy rain Rain is liquid precipitation, as opposed to non-liquid kinds of precipitation such as snow, hail and sleet. Rain requires the presence of a thick layer of the atmosphere to have temperatures above the melting point of water near and above the Earth's surface. On Earth, it is the condensation of atmospheric water vapor into drops of water heavy associated with a storm A storm is any disturbed state of an astronomical body's atmosphere, especially affecting its surface, and strongly implying severe weather. It may be marked by strong wind, thunder and lightning (a thunderstorm), heavy precipitation, such as ice (ice storm), or wind transporting some substance through the atmosphere (as in a dust storm, snowstorm,, hurricane A tropical cyclone is a storm system characterized by a large low-pressure center and numerous thunderstorms that produce strong winds and heavy rain. Tropical cyclones feed on heat released when moist air rises, resulting in condensation of water vapor contained in the moist air. They are fueled by a different heat mechanism than other cyclonic, or tropical storm A tropical cyclone is a storm system characterized by a large low-pressure center and numerous thunderstorms that produce strong winds and heavy rain. Tropical cyclones feed on heat released when moist air rises, resulting in condensation of water vapor contained in the moist air. They are fueled by a different heat mechanism than other cyclonic or meltwater from ice or snow flowing over icesheets or snowfields. Flash floods can also occur after the collapse of natural ice Sometimes a glacier flows down a valley to a confluence where the other branch carries an unfrozen river. The glacier blocks the river, which backs up into a lake, which eventually overflows or undermines the ice dam, suddenly releasing the impounded water or debris dam A landslide dam, debris dam, barrier lake or quake lake if it is caused by earthquake, is a natural damming of a river by some kind of mass wasting: landslide, debris flow, rock avalanche or volcano. Some landslide dams are known to be as high as the largest existing artificial dam, or a human structure such as a man-made dam A dam is a barrier that impounds water or underground streams. Dams generally serve the primary purpose of retaining water, while other structures such as floodgates or levees are used to manage or prevent water flow into specific land regions. Hydropower and pumped-storage hydroelectricity are often used in conjunction with dams to provide clean, as occurred before the Johnstown Flood The Johnstown Flood occurred on May 31, 1889. It was the result of the failure of the South Fork Dam situated 14 miles (23 km) upstream of the town of Johnstown, Pennsylvania, USA, made worse by several days of extremely heavy rainfall. The dam's failure unleashed a torrent of 20 million tons of water (4.8 billion U.S. gallons; 18.2 million cubic of 1889. Flash floods are distinguished from a regular flood A flood is an overflow of an expanse of water that submerges land. The EU Floods directive defines a flood as a temporary covering by water of land not normally covered by water. 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, by a timescale less than six hours. The temporary availability of water is often utilised by plants with rapid germination and short growth cycle, and by specially adapted animal life.[1]

Contents

Causes

Flash flooding occurs when a barrier holding back water fails or when water falls too quickly on saturated soil Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics or dry soil that has poor absorption ability. 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, even dozens of miles from the source. In areas on or near volcanoes A volcano is an opening, or rupture, in a planet's surface or crust, which allows hot magma, ash and gases to escape from below the surface, flash floods have also occurred after eruptions, when glaciers A glacier is a perennial mass of ice which moves over land. A glacier forms in locations where the mass accumulation of snow and ice exceeds ablation over many years. The word glacier comes from French via the Vulgar Latin glacia, and ultimately from Latin glacies meaning ice. The corresponding area of study is called glaciology 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 southwestern U.S.

Hazards

The United States National Weather Service The National Weather Service , once known as the Weather Bureau, is one of the six scientific agencies that make up the National Oceanic and Atmospheric Administration (NOAA) of the United States government. It is headquartered in Silver Spring, Maryland gives the advice "Turn Around, Don't Drown" in reference to 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. Being in 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.[2] As little as two feet of water (60 cm) can be enough to carry away most SUV A sport utility vehicle is a generic marketing term for a vehicle similar to a station wagon, but built on a light-truck chassis. Usually equipped with four-wheel drive for on- or off-road ability, and with some pretension or ability to be used as an off-road vehicle, some SUVs include the towing capacity of a pickup truck with the passenger--sized vehicles.[3] 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 Lightning is an atmospheric discharge of electricity accompanied by thunder, which typically occurs during thunderstorms, and sometimes during volcanic eruptions or dust storms. In the atmospheric electrical discharge, a leader of a bolt of lightning can travel at speeds of 60,000 m/s , and can reach temperatures approaching 30,000 °C (54,000 °F) (73), tornadoes A tornado is a violent, rotating column of air which is in contact with both the surface of the earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. Tornadoes come in many shapes and sizes, but are typically in the form of a visible condensation funnel, whose narrow end touches the earth and is often encircled by a cloud (65), or hurricanes A tropical cyclone is a storm system characterized by a large low-pressure center and numerous thunderstorms that produce strong winds and heavy rain. Tropical cyclones feed on heat released when moist air rises, resulting in condensation of water vapor contained in the moist air. They are fueled by a different heat mechanism than other cyclonic (16).[4]

In deserts A desert is a landscape or region that receives an extremely low amount of precipitation, less than enough to support growth of most plants. Deserts are defined as areas with an average annual precipitation of less than 250 millimetres per year, or as areas where more water is lost by evapotranspiration than falls as precipitation. In the Köppen, flash floods can be particularly deadly for several reasons. First, storms in arid regions are infrequent, but they can deliver an enormous amount of rain in a very short time. Second, these rains often fall on poorly-absorbent and often clay Clay is a naturally occurring material composed primarily of fine-grained minerals. Clay deposits are mostly composed of clay minerals, a subtype of phyllosilicate minerals, which impart plasticity and harden when fired or dried; they also may contain variable amounts of water trapped in the mineral structure by polar attraction. Organic materials-like soil, which greatly increase the amount of runoff Surface runoff is the water flow that occurs when soil is infiltrated to full capacity and excess water from rain, snowmelt, or other sources flows over the land. This is a major component of the hydrologic cycle. Runoff that occurs on surfaces before reaching a channel is also called a nonpoint source. If a nonpoint source contains man-made that rivers A river is a natural watercourse, usually freshwater, flowing toward an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including stream, creek, brook, rivulet, and rill; there is no and other water channels have to handle. In addition, these regions may not have the infrastructure that wetter regions have to divert water from structures and roads, such as storm drains A storm drain, storm sewer , stormwater drain, drain (Australia and New Zealand) or drainage well system (UK) is designed to drain excess rain and ground water from paved streets, parking lots, sidewalks, and roofs. Storm drains vary in design from small residential dry wells to large municipal systems. They are fed by street gutters on most and retention basins A retention basin, is a type of best management practice that is used to manage stormwater runoff to prevent flooding and downstream erosion, and improve water quality in an adjacent river, stream, lake or bay. Sometimes called a wet pond or wet detention basin, it is essentially an artificial lake with vegetation around the perimeter, and, either because of sparse population, poverty or because residents believe the risk flash floods pose is not high enough to justify the expense. In fact, in some areas, desert roads frequently cross dry river and creek beds without bridges A bridge is a structure built to span a valley, road, body of water, or other physical obstacle, for the purpose of providing passage over the obstacle. Designs of bridges vary depending on the function of the bridge, the nature of the terrain where the bridge is constructed, the material used to make it and the funds available to build it. 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.[5] 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 A mesa is an elevated area of land with a flat top and sides that are usually steep cliffs. It takes its name from its characteristic table-top shape miles away, sweeping through the canyon, making it difficult to climb up and out of the way to avoid the flood.

Historical examples

See also

Further reading

References

  1. ^ "Definitions of flood and flash flood". National Weather Service. http://www.srh.noaa.gov/mrx/hydro/flooddef.php. Retrieved 2008-08-19.
  2. ^ "Watches, Warnings & Advisories—Flash Flood Warning". National Weather Service. http://forecasts.weather.gov/wwamap/wwatxtget.php?cwa=usa&wwa=Flash%20Flood%20Warning. Retrieved 2007-06-25.
  3. ^ "A Preparedness Guide to flash floods #1 weather-related killer in the United States". U.S. Department of Commerce The United States Department of Commerce is the Cabinet department of the United States government concerned with promoting economic growth. It was originally created as the United States Department of Commerce and Labor on February 14, 1903. It was subsequently renamed to the Department of Commerce on March 4, 1913, and its bureaus and agencies, National Oceanic and Atmospheric Administration The National Oceanic and Atmospheric Administration (NOAA, pronounced /ˈno.ə/, like "noah") is a scientific agency within the United States Department of Commerce focused on the conditions of the oceans and the atmosphere. NOAA warns of dangerous weather, charts seas and skies, guides the use and protection of ocean and coastal National Weather Service The National Weather Service , once known as the Weather Bureau, is one of the six scientific agencies that make up the National Oceanic and Atmospheric Administration (NOAA) of the United States government. It is headquartered in Silver Spring, Maryland, Federal Emergency Management Agency The Federal Emergency Management Agency, or FEMA, is an agency of the United States Department of Homeland Security, initially created by Presidential Order on 1 April 1979. The primary purpose of FEMA is to coordinate the response to a disaster that has occurred in the United States and that overwhelms the resources of local and state authorities, American Red Cross The American Red Cross is a humanitarian organization that provides emergency assistance, disaster relief and education inside the United States, and is the designated U.S. affiliate of the International Federation of Red Cross and Red Crescent Societies. July 1992. http://www.nws.noaa.gov/om/brochures/ffbro.htm. Retrieved 2007-06-25.
  4. ^ "Turn Around Don't Drown". http://www.srh.noaa.gov/tadd/. Retrieved 2007-06-25.
  5. ^ McGuire, Thomas (2004). "Weather Hazards and the Changing Atmosphere". Earth Science: The Physical Setting. Amsco School Pubns Inc. pp. 571. ISBN The International Standard Book Number is a unique numeric commercial book identifier based upon the 9-digit Standard Book Numbering (SBN) code created by Gordon Foster, now Emeritus Professor of Statistics at Trinity College, Dublin, for the booksellers and stationers W.H. Smith and others in 1966 0-87720-196-X. http://www.amscopub.com/images/file/File_67.pdf. Retrieved 2008-07-17.
  6. ^ Shadyside, Ohio Floods of 1990. NOAA The National Oceanic and Atmospheric Administration , pronounced /ˈno(ʊ).ə/, like "noah", is a scientific agency within the United States Department of Commerce focused on the conditions of the oceans and the atmosphere. NOAA warns of dangerous weather, charts seas and skies, guides the use and protection of ocean and coastal. (Report). Retrieved May 13, 2009.
  7. ^ "Flood Facts". QC Memory. http://www.qcmemory.org/Page/Flood_Facts.aspx?nt=266. Retrieved 2009-04-16.
  8. ^ "November 2006 Flooding". NPS. http://www.nps.gov/mora/parknews/november-2006-flooding.htm. Retrieved 2008-01-08.
  9. ^ "Flash floods kill 125 in Ethiopia". BBC. 2006-08-14. http://news.bbc.co.uk/2/hi/africa/4791813.stm. Retrieved 2007-07-03.
  10. ^ "Duck Creek Flooding Closes Davenport Streets". Quad Cities Online. http://www.qconline.com/archives/qco/display.php?id=391015. Retrieved 2009-04-17.
  11. ^ Arab News, Jeddah flood toll 106. SRPC. (Report). Retrieved December 02, 2009.

External links

Categories: Flood Categories: Bodies of water | Weather | Natural hazards | Water waves

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