Grain Size Change of Bed Surface Layer and Sediment Discharge in Rivers with Gravel and Sand Mixture

Abstract

Bed load transport and grain size variation of the surface layer of a river bed with gravel and sand mixture are discussed based on flume experiments with equilibrium conditions of sediment discharges. The bed surface layer tends to be coarser than the substrate at low rates of sediment transport, but it becomes finer at higher rates. The bed load transport rate can be calculated based on the availability of each size grains in the surface layer, because the mobility of grains is due to fluid forces acting on the exposed grains. The coarsening and finingmechanism is also discussed qualitatively.