Variations of Bed Surface Sediment Size in a Channel Bend

Abstract

Variations of sediment size and its gradation of the bed surface layer in a channel bend with nonuniform sediment are investigated experimentally. Four groups of sediment with the same initial median diameter (D _o ) but different initial size gradation (σ _o ) have been used for experiments which were run until the equilibrium bed topography was achieved. Analyses of experimental data have yielded the following results: (1) The time of equilibrium for bed evolution decreases as σ _o increases; (2) the median size of sediment (D) for a given section in the bend increases with increasing distance from the inner bank towards the outer bank, and it also increases with increasing σ _o ; (3) the value of D/D _o along the inner bank decreases with increasing σ _o , and it also shows a gradual decrease in the upper half of the bend and a slight recovery in the lower half; and (5) the transverse variation of σ value exhibits a general trend increasing from the inner bank towards the outer bank.