Suspended sediment erosion in laboratory flume experiments

Abstract

Laboratory flume experiments are used to examine the role of suspended sediment abrasion in bedrock channel erosion. A range of topographies was used, from a planar bed to a sinuous and scalloped inner channel. Experiments were run separately with bedload (used to form topography) and suspended load at a variety of water flows and sediment fluxes. Sediment samples were collected to determine mass flux and concentration profiles. Erosion was measured between each timestep and erosion rate determined for a variety of conditions. Rouse, Froude, and Stokes numbers were calculated from measured data for various timesteps to determine mode of sediment transport and flow characteristics. Flow was supercritical, and sediment was in suspension. Erosion patterns around imposed topography perturbations (a rock protrusion and a drilled pothole) were briefly examined. A hydraulic jump was used in one timestep to see the effect of the transition from supercritical to subcritical flow. Suspended sediment causes erosion in all bed morphologies. The amount and pattern of erosion are coupled to topography, but are not constrained by it to the same degree as bedload. As in the case of bedload, suspended sediment erosion is strongly coupled to sediment flux.