The paths of grain through wave-like bed forms

Abstract

From a knowledge of the topography of skin-frictionlines, the paths of transported grains relative to the ground and to bed features are presented for different kinds of wave-Iike bed form encountered in aqueous flows. In the case of a sinusbed (antidunes), the height of the forms and their propagation velocity can be used without correction to measure the rate of downstream transport of sediment involved in the movement of the waves. The flow over a ripple or dune bed is separated' however, and within the forms there occurs a sediment stream moving backward relative to the external flow direction. The rate of downstream transport of sediment involved in movement of the waves is in these cases a net rate depending on the ratio of the thickness of the forward-moving and backwardmoving sediment streams. Thus estimates of bedload transport rate based on the full heights of ripples or dunes can be in substantial error.