Analysis of some key parametrizations in a beach profile morphodynamical model |
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| Institution: | 1. Water and Environment Research Group, University of A Coruña, Campus de Elviña s/n, 15071 A Coruña, Spain;2. Department of Civil Engineering, Aalborg University, Sofiendalsvej 11, 9000 Aalborg, Denmark;1. Research Unit for Water, Environment and Infrastructure Resilience (WEIR), Department of Architecture and Civil Engineering, University of Bath, BA2 7AY, UK;2. Coastal Research Lab., International Hurricane Research Center, Florida International University, Miami, Florida, 33199, USA;3. H R Wallingford, Wallingford, Oxon, OX10 8BA, UK;1. Department of Radiology, University of Pennsylvania, 3400 Spruce Street, 1 Founders Building, Philadelphia, PA 19104;2. Department of Orthopaedic Surgery, University of Pennsylvania, Philadelphia, Pennsylvania;3. Department of Pediatrics, The Children''s Hospital of Philadelphia, University of Pennsylvania, Philadelphia, Pennsylvania;4. Department of Biostatistics and Epidemiology, University of Pennsylvania, Philadelphia, Pennsylvania;5. Department of Biomedical Engineering, Stony Brook University, Stony Brook, New York |
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| Abstract: | A numerical process-based model to forecast beach profile morphodynamics has been developed. In the present paper, an analysis of various modelling approaches and key parametrizations involved in the estimation of the wave-driven current and the suspended sediment concentration is carried out.Several resolution techniques for the 1DV horizontal (i.e., in the x-direction perpendicular to coastline) momentum equation governing the Mean Horizontal Velocity (MHV) are analysed. In the first kind of techniques, the mean horizontal velocity is computed from the momentum equation, whereas the Mean Water Level (MWL) is computed using a parametrization of the depth-averaged momentum equation. Two boundary or integral conditions are thus needed. In the second kind, both mean horizontal velocity and mean water level gradient in the x-direction are the unknowns of the momentum equation, thus, three boundary or integral conditions are needed. Various additional conditions are discussed. We show that using a technique of the first kind is equivalent to imposing the difference between the surface and the bottom shear stresses in the 1D vertical equation. Both techniques lead to results that are in good agreement with the Delta Flume experimental data, provided the Stokes drift flow discharge is imposed as an additional condition. The influence of the breaking roller model and of the turbulent viscosity parametrization are also analysed.Suspended sediment transport by the mean current and wave-induced bedload transport are taken into account in the sediment flux. Three turbulent diffusivity parametrizations are compared for suspended sediment concentration estimations. A linear profile for the turbulent diffusivity taking into account the wave bottom shear stress and the surface wave breaking turbulence production is shown to give the best results. Using experimental data, we put forward the poor estimation of the bottom sediment concentration given by the three implemented parametrizations. We thus propose a new parametrization relying on a Shields parameter based on the breaking roller induced surface shear stress. Using this new parametrization, the bottom profile used in the tests keeps its two bars which disappear otherwise. However, the morphodynamical model still overestimates the bars offshore motion, a bias already observed in other models. |
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