Floodplain

A floodplain, or flood plain, is flat or nearly flat land adjacent to a stream or river that experiences occasional or periodic flooding. It includes the floodway, which consists of the stream channel and adjacent areas that carry flood flows, and the flood fringe, which are areas covered by the flood, but which do not experience a strong current.
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Noun
1. a low plain adjacent to a river that is formed chiefly of river sediment and is subject to flooding
(synonym) flood plain
(hypernym) plain, field, champaign

The flat or nearly flat land along a river or stream or in a tidal area that is covered by water during a flood.

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