The accumulation of sediment in the lee of ripples and dunes, and the thickness of bottomset deposits

Abstract

SUMMARYThe properties of bottomset deposits found in the lee of ripples and dunes formed in water depend on: (i) the diffusion and settling of grains driven over the crest of the sand body and (ii) the redistribution of grains over the bed due to the expenditure of fluid power in the recirculating eddy to the lee of the body. Experiment shows that the rate of grain settling in the lee of a sand body falls off hyperbolically downstream. The bottomset deposits of ripples and dunes also attenuate in thickness downstream, but reach a zero thickness commonly at 4–5 ripple- or dune-heights downstream from the crests. Bottomsets may consist partly or wholly of settled grains, but can also be formed when no sediment settles in the lee of a sand body.