Definitions for "Floodplain"
(1) A flat tract of land bordering a river, mainly in its lower reaches, and consisting of alluvium deposited by the river. It is formed by the sweeping of the meander belts downstream, thus widening the valley, the sides of which may become some kilometers apart. In time of flood, when the river overflows its banks, sediment is deposited along the valley banks and plains. (2) (SMP) Synonymous with 100-year floodplain. The land area susceptible to being inundated by stream derived waters with a 1 percent chance of being equaled or exceeded in any given year. The limits of this area are based on flood regulation ordinance maps or reasonable method that meets the objectives of the SMP (WAC 173-22-030(2)).
Lands along inland rivers and streams that are subject to periodic flooding. Lowland and flat benches along water courses that flood, on the average, at least once every 100 years.
Relatively flat area found alongside the stream channel that is prone to flooding and receives alluvium deposits from these inundation events.