| floodplain | Relatively flat surfaces adjacent to active stream or river channels, formed by deposition of sediments during major floods. The floodplain may be covered by water during floods: 100-year floodplain: That area that would be covered by water during the 100-year flood event. Historic floodplain: An area larger than the 100-year floodplain. (05 Dec 1998) |
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