Abstract

Most sediment laden flows in nature are produced by strong local gradients in terms of a hillslope or a pressure gradient. Describing these kinds of complex flows from an engineering perspective (e.g. by means of macroscopic sediment transport models) requires in-depth knowledge of the rheology of the sheared sediment beds and the fluid-sediment mixture. In the present work, we review a previously derived macroscopic model that relies on a two-phase flow approach for the fluid and the sediment phase, respectively, as a promising avenue to predict such a complex flow. We apply this model to data that was generated by means of highly-resolved direct numerical simulations of a sediment bed sheared by a pressure driven viscous flow. We show that the rheology obtained in the numerical results obeys the scaling that has previously been derived for neutrally buoyant particles in rheometer cells. A two-phase flow model that is based on these scaling relations is therefore able to reproduce the simulation results of sheared sediment beds with high accuracy. Finally, we provide a list of open issues for future research that will be key to improve our understanding of the sediment bed rheology. Those are the role of higher particle inertia, transient behavior of sheared sediment beds, and cohesion.