Floodplain

Any land area susceptible to being inundated by floodwaters from any source.

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:

A generally flat, low-lying area adjacent to a water body that is subjected to inundation during high flow or rainfall events. The relative elevation of floodplain areas determines their frequency of flooding, which ranges from rare, severe, storm events to flows experienced several times a year.