Deterministic coastal morphological and sediment transport modeling: a review and discussion

Modern coastal ocean modeling systems are now capable of numerically simulating a variety of coastal and estuarine problems and can thus provide useful information for managing coastal zones. Here we review state-of-the-art Eulerian implementations of bottom-up sediment transport and morphological change in coastal ocean hydrodynamic models. In order to investigate the fate of suspended sediment in coastal and estuarine waters as well as the evolution of sea or river beds, sediment dynamics need to be represented at a scale relevant to the numerical discretized solution, and significant effort is devoted to parameterize sediment processes. We discuss boundary layer hydrodynamics and the computation of the bed shear stress. We also focus on approaches used to represent near-bed processes such as bed load transport and sediment erosion and deposition. Sediment diffusivities, settling velocities, and cohesive processes such as flocculation all have an impact on suspended sediment throughout the water column. We then describe the implementation of process parameterizations in coastal hydrodynamic models, explicitly reviewing five widely used systems. The approaches implemented in these coastal models may present distinct strengths and shortcomings with regard to some important issues for coastal zones, both numerical and physical. While these detailed limitations need to be considered as part of model assessment, more general issues also hinder present state-of-the-art models. In particular, sediment transport is inherently highly empirical, which is further compounded by issues arising from turbulence closure schemes. We conclude by suggesting some possible directions toward improving sediment dynamics understanding and coastal-scale predictive ability