On a multi-phase modeling framework for sediment transport

Understanding sediment transport in the heterogeneous environment, including river, beach, estuary, shelf and submarine canyon, is crucial to the preservation and restoration of coastal ecosystem. A multi-phase modeling framework is developed in order to study sediment transport driven by a variety forcing (current, tide, wave and gravity-driven flow) with a range of sediment characteristics. As an example, constitutive relation for intergranular interaction (particle stress) based on kinetic theory of granular flow is adopted in a two-phase model and is shown to be capable of modeling wave-induced sheet flow transport in the sandy-beach environments. Recently, to further model typical fine sediment transport processes of long timescales (e.g., tidal), spatial inhomogeneity, and multiple sediment classes, the two-phase model is rationally simplified. The simplified model is much efficient yet robust to retain essential mechanisms of fluid-sediment and intergranular interactions. Adopting rheological closure based on viscous suspension, preliminary results indicate that the model captures field observed lutocline behavior of fluid mud under tidal flow and wave-supported gravity-driven fluid mud on the continental shelf.