floodplain

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.

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

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.