flood, in hydrology


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 the like 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 some other larger rivers historically deposited fertile soil along the surrounding floodplain, which is used extensively for agriculture. The damming of the Nile and other rivers in modern times, however, often has greatly reduced this deposition.

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