Flood

Flood, Henry, 1732-91, Irish statesman. He entered the Irish House of Commons in 1759 and joined the fight to gain independence for the Irish Parliament. He lost favor with the nationalists, however, when he accepted (1775) a position in the government, and the leadership of the nationalists passed to Henry Grattan. Flood recaptured popularity when, following the repeal (1782) of Poynings's Law (see under Poynings, Sir Edward), he went beyond Grattan in demanding positive assurance of Irish legislative independence. But his opposition to Catholic Emancipation, which Grattan favored, once more reduced his following. Flood served (1783-90) in both the English and the Irish House of Commons, but he never regained his leadership of the Irish nationalists.

Flood, James Clair, 1826-89, American silver magnate, b. New York City. Having been apprenticed to a carriage maker, he left to join the California gold rush in 1849. The following year he returned to New York, then bought a farm in Illinois, but in 1851 he was back in California. In partnership with William Shoney O'Brien he operated a saloon and lunchroom in San Francisco until 1865, when the two men formed a successful mining partnership with J. W. Mackay and J. G. Fair to exploit the Comstock Lode.

Flood, in the Bible: see Deluge.

flood, inundation of land by the rise and overflow of a body of water. Floods occur most commonly when water from heavy rainfall, from melting ice and snow, or from a combination of these exceeds the carrying capacity of the river system, lake, or ocean into which it runs. Usually the combined flow of several water-swollen tributaries causes flooding along a river bank or shoreline. Accounts of floods that destroyed nearly all life are found in the mythology of many peoples (see Deluge). Not all floods are destructive, however. The annual floodwaters of the Nile and other larger rivers deposit fertile soil along the surrounding floodplain, which is used extensively for agriculture.

Flood Characteristics and Control

The rise and fall of the water level in a river is called the flood wave. Its highest point, or crest, travels progressively downstream. In the upstream portions of a river the flood crest passes quickly. Further downstream the greater volume of water causes slower passage of the flood crest, resulting in floods of longer duration. In many regions, annual floods follow the thaws and rains of spring; flooding also may occur because of thawing ice jamming narrower and shallower parts of a river. In the Arctic regions, especially in the basins of northward flowing rivers, the floods are caused by the thawing of the southern portion of the basin before the ice blocking the lower course of the river melts. Less predictable are floods resulting from ocean waves, called storm surges, pushed onshore by an advancing hurricane, and from sudden torrential flows, called flash floods, following a brief, intense rainstorm or the bursting of a natural or man-made dam or levee. In addition to the duration and quantity of rainfall, the nature of the soil (permeability; state of saturation) of an area affects the frequency of floods.

Generally, flood control measures along a river are attempted at both its headwaters and its low-lying floodplains. Runoff can be detained in the headwaters by planting ground cover on the slopes, building terraces to increase soil infiltration and prevent soil erosion, and building small check dams or retaining ponds to reduce the flow of water. Flood control on the lower floodplains involves building levees to contain the flow and straightening or dredging the channel to improve flow characteristics. Among the chief flood-control projects in the United States are the flood control works along the Mississippi River, the installations of the Tennessee Valley Authority, the Glen Canyon and Hoover dams on the Colorado River, and the systems of dams in the Columbia River basin (including Grand Coulee Dam) and in the Missouri River basin.

Notable Floods

A flood of the Tiber was recorded in 413 B.C. Records of floods on the Danube date from A.D. 1000. In China some of the world's most disastrous floods have been caused by the unstable Huang He (Yellow River). The river, which flows at or above the level of the bordering land, is contained in part by levees; however, because its channel has gradually become filled with deposited sediment, any appreciable increase in its volume causes the river to overflow and flood the surrounding area. The Netherlands, dependent on its dikes for protection from inundation, has suffered many disastrous floods from the sea and the Rhine and Meuse rivers. In 1970, 1985, and 1991, hundreds of thousands of people in Bangladesh were killed when the combination of high tides and a tropical cyclone (see hurricane) storm surge caused widespread flooding of the low-lying delta of the Ganges and Brahmaputra rivers.

In the United States the Johnstown, Pa., flood of 1889, in which thousands of lives were lost, was caused by the breaking of an earth dam above the city. Even greater loss of life occurred (1900) in Galveston, Tex., when tide and storm surges engulfed the city after a hurricane. The hurricanes of 1938 on the New England and Long Island coasts and Hurricane Donna in 1960 along the Atlantic coast from Florida to the Long Island Sound were also followed by storm surges. In June, 1972, extremely heavy rainfall associated with a tropical storm inundated the basins of the Chemung and Susquehanna rivers of New York and Pennsylvania, causing severely damaging floods in Corning and Elmira, N.Y., and Wilkes-Barre and Harrisburg, Pa. In July, 1979, Hurricane Claudette deposited a U.S. record of 43 in. (109 cm) of rain in Alvin, Tex., in 24 hours. The worst floods in the United States from river overflow were in 1913 on the Miami River (a tributary of the Ohio), in 1927 and 1973 on the Mississippi River, in 1935-36 on several New England rivers, and in 1993 when the waters of the Missouri, Mississippi, and some of their tributaries migrated well beyond the floodplains that are regularly submerged each spring to inundate parts of nine states.

High-water stage in which water overflows its natural or artificial banks onto normally dry land, such as a river inundating its floodplain. Uncontrollable floods likely to cause considerable damage commonly result from excessive rainfall in a brief period, but they may also result from ice jams during the spring rise in rivers, and from tsunamis. Common measures of flood control include improving channels, constructing protective levees and storage reservoirs, and implementing programs of soil and forest conservation to retard and absorb runoff from storms.

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A flood is an overflow of an expanse of water that submerges land, a deluge. 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 or lake, exceeding the total capacity of its bounds, with the result that some of the water flows or sits outside of the normal perimeter of the body. It can also occur in rivers, when the strength of the river is so high it flows right out of the river channel, particularly at corners or meanders.

The word comes from the Old English flod, a word common to Teutonic languages (compare German Flut, Dutch vloed from the same root as is seen in flow, float).

The term "The Flood," capitalized, usually refers to the great Universal Deluge described in Genesis and is treated at Deluge.

Principal types of flood

Riverine floods

• Slow kinds: Runoff from sustained rainfall or rapid snowmelt exceeding the capacity of a river's channel. Causes include heavy rains from monsoons, hurricanes and tropical depressions, foen winds and warm rain affecting snowpack.
• Fast kinds: flash flood as a result of e.g. an intense thunderstorm.

Estuarine floods

• Commonly caused by a combination of sea tidal surges caused by storm-force winds.

Coastal floods

• Caused by severe sea storms, or as a result of another hazard (e.g. tsunami or hurricane).

Catastrophic floods

• Caused by a significant and unexpected event e.g. dam breakage, or as a result of another hazard (e.g. earthquake or volcanic eruption).

For example: Tropical Storm Alberto, the famous 1994 storm, produced heavy flooding across Georgia, Alabama and northwest Florida and created between 400-600 million dollars worth of damage in the Southeastern US in 1994 United States Dollars

Other

• Flooding 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 same area.
• Dam-building beavers can flood low-lying urban and rural areas, often causing significant damage.

Typical effects

Primary effects

• 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 diseases.

Secondary effects

• 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.
• Trees - Non-tolerant species can die from suffocation

Tertiary/long-term effects

• Economic- Economic hardship, due to: temporary decline in tourism, rebuilding costs, food shortage leading to price increase etc.

Flood defences, planning, and management

In western countries, rivers prone to floods are often carefully managed. Defences 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 defences, 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. The defenses of both London and Venice will be rendered inadequate if sea levels continue to rise.

The largest and most elaborate flood defenses can be found in the Netherlands, where they are referred to as Delta Works with the Oosterschelde dam as its crowning achievement. These works were built in response to the North Sea flood of 1953 of the 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).

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 Saint Petersburg. Eleven dams extend for 25.4 kilometres and stand eight metres above water level.

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 during Hurricane Katrina 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 inches to twenty 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. These wetlands act as a sponge in storms and in 1995, when the floods returned, the government didn't have to expend resources in those areas.

In China, flood diversion areas are rural areas that are deliberately flooded in emergencies in order to protect cities

(See Crossing the Lines)

Flood clean-up safety

Clean-up activities following floods often pose hazards to workers and volunteers involved in the effort. Potential dangers include electrical hazards, carbon monoxide exposure, musculoskeletal hazards, heat or cold stress, motor vehicle-related dangers, fire, drowning, and 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 hats, goggles, heavy work gloves, life jackets, and watertight boots with steel toes and insoles.

Benefits of flooding

There are many disruptive effects of flooding on human settlements and economic activities. However, flooding can bring benefits, such as making soil more fertile and providing nutrients in which it is deficient. Periodic 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 Yellow River, among others. The viability for hydrological based renewable sources of energy is higher in flood prone regions.

Flood modelling

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 and Flowroute, 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.

See also

• Flood Risk Assessment
• Flood control in the Netherlands

References

External links

• Integrated Flood Management
• American Water Resources Association
• Catastrophic flood database
• Dartmouth Flood Observatory
• Decision tree to choose an uncertainty method for hydrological and hydraulic modelling, Choosing an uncertainty analysis for flood modeling.
• DeltaWorks.Org Flood protecting dams and barriers project in the Netherlands
• Europe floods 2006
• Flood Risk Management Research Consortium* International teaching module "Integrated Flood Risk Management of Extreme Events" (Floodmaster)
• Predictions Off for Global Warming Flood Risk - Study
• Protecting against the Next Katrina - Scientific American Magazine (October 2005)
• Category:Flood control at Appropedia, a wiki for non-Wikipedia (projects & practical "how to") content.
• Safecoast Knowledge exchange on coastal flooding and climate change in the North Sea region
• Social & Economic Benefits/Costs of Heavy Rain & Flooding from NOAA Social & Economics Benefits website initiative

Further reading

• 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.