A simple method to predict the threshold of particle transport under oscillatory waves

Abstract

Abstract Various methods of predicting the incipient motion of sediments under oscillatory waves have been proposed in the past, but most require that at least the wave orbital diameter d o be known. Methods based on the oscillatory Shields parameter θ ws , need the wave friction factor f w in order to calculate the critical threshold velocity, for which d o is also required. Other existing methods not requiring d o are only applicable to quartz grains and yield highly inaccurate results. In this paper, a new dimensionless threshold orbital velocity, based on all the important variables playing a role in wave transport, is plotted against the dimensionless settling velocity. This yields a relationship that allows the prediction of the threshold velocity from the wave period and grain size alone. The method has the advantages that it is valid for grains of varying size and density in laminar or turbulent fluids of different density and viscosity, does not require the wave orbital diameter, and is more accurate than previous equations.