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, deltadelta
[from triangular shape of the Nile delta, like the Greek letter delta], a deposit of clay, silt, and sand formed at the mouth of a river where the stream loses velocity and drops part of its sediment load.
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 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 floodsflood,
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.
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. 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.
The Columbia Electronic Encyclopedia™ Copyright © 2013, Columbia University Press. Licensed from Columbia University Press. All rights reserved. www.cc.columbia.edu/cu/cup/
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Floodplain

 

the part of a valley floor that is flooded at high water but is above the low-water stage. A floodplain consists of two parts: a base of channel aluvium underlying a flood alluvial layer formed by the annual or less frequent deposition of silt by floodwater. Occasionally the foundation, composed of bedrock or more ancient alluvium, is exposed.

The most intensive accumulation of coarse-grained alluvium, forming crests and ridges, occurs in the parts of the floodplain closest to the channel. Farther into the floodplain fine-grained alluvium settles. Only silt particles are carried close to the high bank, where the floodplain is lower and swampy (terrace flood-plain).

As sediment accumulates on the surface of the floodplain, the banks of some sections are continuously undercut by the river flow, and bars are built up in other sections. As a result, the contours of floodplain change constantly. On the surface of the floodplain there are numerous hollows, which are traces of meanders (oxbows) and branches of the river that formed cutoffs and alternate with levees. The hollows attest to the channel’s meandering. In the parts of the valley where the alluvium accumulation primarily occurs, that is, in the lower course of the river, a solid channel levee often forms along the channel. The surface of the floodplain is frequently divided by a low scarp into a high floodplain and a lower one.

The floodplain is formed when the valley broadens as the result of lateral shifts in the river channel. Vast floodplains, reaching 20–40 km in width, are characteristic of large, level rivers with uneven flow. If the river flows in a tectonic trough, the width of the floodplain is determined by the dimensions of the trough.

The vegetation plays an important role in determining the relief of a floodplain. It helps prevent erosion and promotes the accumulation of alluvium. The center of the floodplain and the terrace floodplain are usually covered by trees and shrubs. Some floodplains are developed for agricultural use. In such cases, a large part of the land is used for meadows, which are among the best feed lands. The floodplain soils, regularly replenished with organic silts, are very fertile. During the flooded period, the floodplain is a spawning ground for fish.

Placer deposits of such useful minerals as gold, platinum, and cassiterite are found in the alluvial deposits making up the flood-plains of small mountain rivers. The sand and gravel are used as building materials.

REFERENCE

Makkaveev, N. I. Ruslo reki i eroziia v ee basseine. Moscow, 1955.
The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

floodplain

[′fləd‚plān]
(geology)
The relatively smooth valley floors adjacent to and formed by alluviating rivers which are subject to overflow.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
During Harvey's epic rain, as the water in the reservoirs got to a critical level, the Corps opened the dams from Addicks and Barker into Buffalo Bayou, flooding thousands of homes downstream of the reservoirs, many of which sat outside of designated floodplains.
While chairing the 54th Annual Meeting of Federal Flood Commission, Federal Minister for Water Resources Faisal Vawda urged the provinces and Federal line agencies for prompt approval of their respective floodplain management Acts and their strict enforcement to prevent the encroachment in the waterways on permanent basis.
Leandro Castello, assistant professor of fisheries at Virginia Tech, says: 'Floodplain forests are the principal sources of food [for fish] via provision of detritus, tree leaves, fruits and insects.' Indeed, for the economically important tambaqui fish (pictured above), which can fetch top prices in fish markets, fruits and seeds constitute the major food source during high waters when the species can enter new territories to feed and spawn.
An understanding of the roles presently played by local habitat conditions in the current distribution of freshwater mussels may support the identification of feasible approaches for restoring degraded freshwater mussel habitats in floodplains. In this study, how freshwater mussels use channels with artificial water level management was examined that are well connected with paddy areas with the aim of developing a future-expected model of the area.
A recent report from the European Environment Agency claims that more than 80 percent of Europe's floodplains have been barricaded by flood defenses, drained and built on; it predicts a five-fold increase in flood damage by 2050.
Preserving the integrity of floodplains is necessary for our own survival.
It asked the Ministry of Environment and Forests ( MoEF) why no environmental clearance is required for erecting structures in Yamuna floodplains? At the same time, Justice Kumar asked AOL, " As a conscientious organisation, tell us, did you conduct any environment assessment impact study on the river site before building there?
The full extent of potential building on Welsh floodplains is however likely to be much wider.
Members of the NFIP have to adopt and follow FEMA regulations and floodplain mapping.
(1989) stated that in Romanian language the meadow term is broader than the floodplain because it includes the non-flooded areas.
He said while in his statement that it is imperative to reduce deforestation in watersheds and encroachments on floodplains for agriculture, human settlements and other purposes.