Bed Surface Grain Size Evolution under Unsteady Flow Conditions in a Degrading Channel

Abstract

Abstract Laboratory flume experiments were conducted in order to identify the temporal evolution of bed surface grain size properties by unsteady flows under zero sediment feeding conditions. Purposely designed sediment beds were composed by well-sorted gravel and sand, for each case, detailed data of the bed surface composition were collected. It is found that for all cases, the final sediment bed in the whole reach always shows a coarsening feature, and the coarsening process is much more developed near the inlet boundary. Further, the time variation of the percents of gravel and sand are observed increase or decrease alternately during the experiment and finally close to their initial percents. Besides, the experimental results show that there is no direct correlation between the flow unsteadiness and the coarsening degree of the final bed.