Grain size sorting over offshore sandwaves: observations and modelling

Abstract

Offshore sandwaves are rhythmic bed patterns widely present in shallow shelf seas. Observations from the North Sea indicate a trend of coarser sediment with a higher sorting at sandwave crests. In this study, we present an extended model for sandwave dynamics that accounts for the presence and transport of non-uniform sediment. The extension involves an active layer as well as a fractional calculation of sediment transport, which includes hiding-exposure effects. Simulations of a growing sandwave for a bimodal mixture indicate a coarsening trend towards the crest, whereas in the sandwave troughs the sediment remains mixed. The model results show qualitative agreement with observations from various sites in the North Sea. 1