Sediment flux based model of instantaneous sediment transport due to pure velocity-skewed oscillatory sheet flow with boundary layer stream

Abstract

Velocity-skewed oscillatory sheet flow transport is studied by an approximate model for instantaneous sediment transport resulting from exponential profiles of sediment concentration and velocity over a mobile bed. The phase lag effect, and asymmetry in wave friction factor, oscillatory flow orbital amplitude, roughness height, bed shear stress and wave boundary layer thickness are modelled so that the net boundary layer stream of pure velocity-skewed oscillatory flow can be obtained. The proposed model is found consistent with the previous classical formulas, and qualitatively refines a series of exponents of velocity power function for the approximation of instantaneous sediment transport rate under different flow conditions. The sediment fluxes can be well predicted with accuracy as that of a two-phase numerical model. The net boundary layer stream and sediment transport rates are also well predicted, especially the negative net stream and rates with large phase residual. The phase residual is shown a useful but insufficient factor in the net sediment transport in pure velocity-skewed flows. In addition, the net boundary layer stream resulting from velocity-skewed wave boundary layer development difference between onshore and offshore flow durations is an essential factor as well.