Abstract:
The estimation of the bed shear stress is a crucial step in many sediment transport formulae since, when bedload
is dominant, sediment transport can be parameterized in terms of the bed shear stress. In this work, the
performance of a new bed shear stress estimator for nonlinear waves is analysed. The effects of velocity and
acceleration skewness are incorporated in the time-varying bed shear stress using two parameters: the index of
skewness or nonlinearity, r, and the waveform parameter, φ. The results are compared with two different data
sets obtained in the Aberdeen Oscillatory Flow Tunnel, under accelerated-skewed oscillatory flows. When
applied to a typical bedload formula, the new expression considerably improves the prediction of the net sand
transport rates. A sensitivity analysis for the phase-lead between the bed shear stress and the outer flow indicates
that the new expression provides the best trends between predicted and measured transport rates when compared
to other parameterizations. This work provides further insights in the correct prediction of sediment transport
modelling, accounting for the effect of nonlinear wave shapes.
