Three dimensional mobile bed dynamics for sediment transport modeling.

摘要

The transport and fate of suspended sediments continues to be critical to the understanding of environmental water quality issues within surface waters. Many contaminants of environmental concern within marine and freshwater systems are hydrophobic, thus readily adsorbed to bed material or suspended particles. Additionally, management strategies for evaluating and remediating the effects of dredging operations or marine construction, as well as legacy pollution from military and industrial processes requires knowledge of sediment-water interactions. The dynamic properties within the bed, the bed-water column inter-exchange and the transport properties of the flowing water is a multi-scale nonlinear problem for which the mobile bed dynamics with consolidation (MBDC) model was formulated.; A new continuum-based consolidation model for a saturated sediment bed has been developed and verified on a stand-alone basis. The model solves the one-dimensional, vertical, nonlinear Gibson equation describing finite-strain, primary consolidation for saturated fine sediments. The consolidation problem is a moving boundary value problem, and has been coupled with a mobile bed model that solves for bed level variations and grain size fraction(s) in time within a thin layer at the bed surface. The MBDC model represents the first attempt to unify bed exchange and accounting mechanisms with vertically varying bed properties under a single mechanistic framework.; A suspended sediment transport solver, with parameterizations for noncohesive grain size settling velocity, erosion and depositions source sink terms has been extended to include parameterizations for cohesive grain sizes. Further, the consolidation model has been integrated into the mobile bed modeling framework. The new fine-grained sediment transport model, MBDC, was configured to simulate the flow, transport and bottom evolution within an expansion channel serving as an idealized conical estuary. MBDC model results, are compared with model results from literature, demonstrating qualitative agreement and model efficacy. The MBDC model approach, though requiring more site specific data for auxiliary parameterizations, yields a more complete physical and dynamic description of bed sediment transport processes.