The Role of 2DH Circulation in Sand Bar Migration Models

Abstract

A new, nonlinear equation for sand bar migration has been developed to study sand bar response to changing wave forcing. The bar system is represented by two parameters: the alongshore mean bar position (x(t)) and the amount of 2DH bar morphology present (a(t)). Cross-shore bar migration is driven by a physics-based sediment transport formulation, with the assumption that variations in the roller contribution to the undertow (and therefore the presence of wave breaking), along with the presence of 2DH morphology (assumed to cause horizontal circulation) are the two main contributors. The model was tested using video images from Palm Beach, NSW, Australia. Seven data sets, totalling 562 days and 11 major storms over a four-year period were used. The model was capable of reproducing sand bar migration over a variety of wave conditions with the presence of 2DH variability found to increase onshore migration rates during moderate wave conditions, a role that has often been assumed negligible.