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bedform The shape of the surface of a bed of granular sediment, produced by the flow of air or water over the sediment. The nature of the bedform depends upon the flow strength and depth, and upon sediment grain size. For fine to medium sand, the typical sequence of bedforms produced under conditions of constant depth and increasing strength of unidirectional flow is: no movement; ripples; sand waves; dunes; and an upper-flow-regime plane bed. In coarse sand a lower-flow-regime plane bed develops first, then ripples, followed by sand waves, then dunes, and an upper-flow-regime plane bed. At higher-strength flows, the upper flow regime plane bed is replaced by antidunes.