floodplain

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floodplain, level land along the course of a river formed by the deposition of sediment during periodic floods. Floodplains contain such features as levees, backswamps, delta plains, and oxbow lakes. Floodplains may be extensive, such as below the conflux of the Ohio and the Mississippi, where they have a width up to 80 mi (130 km). Rivers with extensive floodplains are the Nile, Ganges, Danube, and Po. Floodplains are generally very fertile, thus making them rich agricultural lands. The disadvantage of farming on a floodplain is the natural hazard of floods. In the United States there has been extensive house construction on floodplains in recent years, necessitating the construction of new dams to control small, annual floods.

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Floodplain

An area that has been built up by stream deposition, generally represented by the main drainage channel of a watershed , is called a floodplain. This area, usually relatively flat with respect to the surrounding landscape, is subject to periodic flooding , with
return periods ranging from one year to 100 years. Floodplains vary widely in size, depending on the area of the drainage basin with which they are associated. The soils in floodplains are often dark and fertile, representing material lost the to erosive forces of heavy precipitation and runoff . These soils are often farmed, though subject to the risk of periodic crop losses due to flooding. In some areas, flood-plains are protected by flood control measures such as reservoirs and levees and are used for farming or residential development. In other areas, land-use regulations, encroachment statutes and local building codes often prevent development on floodplains.

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flood-plain The part of a river valley that is made of unconsolidated, river-borne sediment and is periodically flooded. It is built up of relatively coarse debris left behind as a stream channel migrates laterally, and of relatively fine sediment deposited when bankfull flow discharge is exceeded.

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flood·plain / ˈflədˌplān/ • n. an area of low-lying ground adjacent to a river, formed mainly of river sediments and subject to flooding.