Sheet flow sediment transport under waves with acceleration skewness and boundary layer streaming

The effect of acceleration skewness on sheet flow sediment transport rates qs― is analysed using new data which have acceleration skewness and superimposed currents but no boundary layer streaming. Sediment mobilizing forces due to drag and to acceleration (∼ pressure gradients) are weighted by cosine and sine, respectively, of the angle φτ · φτ = 0 thus corresponds to drag dominated sediment transport, qs―∼|u∞|u∞, while φτ = 90° corresponds to total domination by the pressure gradients, qs―∼du∞/d⁢t. Using the optimal angle, φτ = 51° based on that data, good agreement is subsequently found with data that have strong influence from boundary layer streaming. Good agreement is also maintained with the large body of U-tube data simulating sine waves with superimposed currents and second-order Stokes waves, all of which have zero acceleration skewness. The recommended model can be applied to irregular waves with arbitrary shape as long as the assumption negligible time lag between forcing and sediment transport rate is valid. With respect to irregular waves, the model is much easier to apply than the competing wave-by-wave models. Issues for further model developments are identified through a comprehensive data review.