Floodplain

(Geol.) A plain formed by succe ive river overflows, extending to a considerable width on each side of a stream and made up of layers of mud, sand and gravel deposited by the subsiding waters. The F. of some streams is very wide and presents so level a surface that the stream winds through it in a serpentine course, its curves increasing in radius with increase of volume. By cutting away the bank on the concave side of the curve and depositing material on the other bank, the stream frequently shifts its channel, the curves occasionally forming nearly a circle, with a narrow neck of land intervening between their extremities. Such a neck is at times cut through by an overflow, and the river pursues a new "cut-off" channel; its abandoned channel becoming a stagnant "ox-bow" lake. Tributary streams coming from higher lands often follow the F. downward for miles before entering the main river. Plains of this character belong to many streams, notably the Mi i ippi, the Amazon, the Nile, and the Ganges. They are highly fertile, and are usually covered by swamp forests until cleared for cultivation. When occupied by man, overflow is provided against by dykes or levees.