Temporal Variation of Suspended Sediment Concentration for Waves over Ripples

Variations of suspended sediment concentration over ripples in regular waves were described using an existing numerical model system. Nielsen’s (1992) empirical formula for sediment entrainment rate from the bed surface was used with an additional scale factor in the model system. The model system was applied to two typical laboratory experimental conditions selected for description of the variation of suspended sediment concentration. The flow model results are described with regard to wave orbital velocities, vorticity, shear stress, and pressure. The suspended sediment model results show that the suspended sediment concentrations have four or more peak values in a wave period depending on flow and sediment conditions. The model results suggest that the suspended sediment concentrations have four peaks when the ratio of the orbital excursion length amplitude and ripple length is close to 1, and more than four peaks when the ratio of the orbital excursion length amplitude over the ripple length is larger than 1. The computed temporal variations of the suspended sediment concentration for Bosman’s (1982) case were compared with measurements, and agreements between them were reasonably good. The computed profiles of the wave-period average suspended sediment concentrations also agreed well with measurements near the beds for the two experimental conditions.