Also found in: Dictionary, Thesaurus, Financial, Wikipedia.


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.
..... Click the link for more information.
 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.
..... Click the link for more information.
. 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 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.


Makkaveev, N. I. Ruslo reki i eroziia v ee basseine. Moscow, 1955.


The relatively smooth valley floors adjacent to and formed by alluviating rivers which are subject to overflow.
References in periodicals archive ?
amp; Gray; (Eastern) False Rue Anemone; Floodplain woods; Infrequent; C = 5; BSUH 17575.
It said: "Since 1906 there has been a dramatic increase in the urban area encroaching on the Rheidol floodplain.
Although the combination of advances in managing navigation pools and a rising concern about the effects of navigation structures on floodplain species has resulted in experimentation with a pool drawdown strategy that would provide a 30-day summer growing season for floodplain plants, this is inadequate for the decurrent false aster, since it requires approximately 120 days to complete its life cycle, from seedling to production of seeds.
This includes 73 hectares of new or restored wetland habitat, the reconnection of 85 hectares of active floodplain and 5,700m of riverbank brought under positive management.
The Government Accountability Office (GAO) upheld the appeal in December, agreeing that NOAA did not fully address the floodplain issue.
The 100-yr floodplain is a regulatory standard used by federal agencies to administer floodplain management programs; it is also the basis for insurance requirements in the National Flood Insurance Program (NFIP).
The report adds: "It is important to reinstate areas of functional floodplain which have been previously developed.
Another part of the material was collected in the upper Parana river floodplain (22[degrees]50'-22[degrees]70' S and 53[degrees]15'-53[degrees]40' W), specifically in Patos, Guarana and Garcas Lagoons, Baia and Ivinheima rivers and Pau Veio Glade, during March, June and September, 2004 and March, 2005 (Figure 1).
Members of the NFIP have to adopt and follow FEMA regulations and floodplain mapping.
PNW Restoration, Engineering and Geomorphology Practice Lead Sky Miller will present Nooksack River Floodplain Evaluation along with Paula Cooper of Whatcom County.
PESHAWAR -- WWF-Pakistan raised serious concerns over the increased frequency of massive floods and urged the government to reduce the impacts of environmental hazards through better management of critical watersheds and floodplains.
floodplain, the low terrace and the middle terrace.