Bed Topography and Sediment Sorting in Channel Bend with Unsteady Flow

Abstract

Bed topography and transverse sediment sorting in an alluvial channel bend were investigated under unsteady-flow conditions with nonuniform sediment. Five experiments, each having the same initial sediment-size gradation but a different inflow hydrograph, were done in a 180° channel bend with a constant radius of curvature. In addition, bed elevations across various sections of the bend were measured, and bed-surface sediment were sampled at the peak and end of the hydrograph in each experiment. Experimental results indicated that the characteristics of the hydrograph have prominent influences on bed topography and transverse sediment sorting. Those cases with a higher ramping rate of the hydrograph have greater deposition heights near the inner bank and larger scour depths near the outer bank. Furthermore, the sediment is finer near the inner bank and coarser near the outer bank in cases with a higher ramping rate. The bed deformation and sediment-size variation correlated well with the unsteady-flow parameter defined in this study. Furthermore, regression relations for transverse bed profile, transverse variation of sediment size, and total amount of sediment discharge were established in terms of the unsteady-flow parameter.