ABSTRACT
Subaqueous grain flows are common phenomena in rivers and deltas. Grain flows occur at the downstream side of river bars and dunes in the channel and in deltas formed in lakes or shores (Allen, 1965). The slope is near the angle of repose and the flow is cohesionless. The sediments transported on the river bed may consist of various sizes of sand (D < 2 mm) and gravel (D > 2 mm). In such cases, sorting occurs in the grain flows, for example a downward coarsening. This leads to commonly observed downward coarsening deposits with stratification at about the dynamic angle of repose (Kleinhans, 2004). Since the capacity of the river flow to entrain and transport the sediment anew is inversely related to the grain size, the sorting patterns affect the sediment transport and hence morphological change of river channels (Parker et al. 2000).
