| In muddy estuaries, the suspended sediment concentration can vary greatly with depth. Sometimes there is a near-bed, high concentration region, termed a fluid mud layer, which plays a dominant role in the total sediment transport. The movement of fluid mud has been cited as the most likely cause of rapid sedimentation in channels located in muddy estuaries. However, most existing cohesive sediment transport models represent only the upper low concentration suspension and neglect the presence of fluid mud.; A time dependent, laterally-averaged cohesive sediment transport model, FM2D, which simulates estuarial hydrodynamics, the vertical and horizontal suspended sediment structure, and the formation and movement of fluid mud was developed as part of this research. FM2D is an unsteady finite difference model that uses a staggered lattice grid to solve the governing equations to determine the spatial and temporal variations in the field variables. The FM2D model, which is composed of hydrodynamic, dissolved salt transport, cohesive sediment transport, cohesive sediment bed (which includes a finite strain consolidation module), and turbulence closure modules, can simulate barotropic and baroclinic circulation driven by tides, wind, and density gradients due to dissolved salt and suspended sediment.; The vertical suspended sediment structure in estuaries is defined by three characteristic regions: an upper low concentration suspension layer, a fluid mud layer, and a cohesive sediment bed. The formation of fluid mud is due to rapid erosion and/or rapid deposition. Fluid mud has been found to behave as a non-Newtonian fluid in many previous studies, and is modeled as a Bingham plastic in FM2D.; Partial verification of FM2D was accomplished by comparing the predicted flow field and concentration distributions of suspended sediment with analytical solutions, a laboratory experiment, and available field data from the Charleston Harbor estuary in South Carolina. |
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