A numerical model to compute the morphodynamic impact of a human intervention.

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Giovanna Vittori, Fengyan Shi, James T. Kirby

Friday 3 july 2015

14:30 - 14:45h at Mississippi (level 1)

Themes: (T) Sediment management and morphodynamics, (ST) Sediment transport mechanisms and modelling

Parallel session: 16B. Sediment - Transport

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In modeling the morphological impact of human interventions in the coastal region using a process-based model, the hydrodynamic conditions, often derived from regional scale models and sometimes incomplete measurements, may not be in equilibrium with the initial bathymetric profile before the intervention. In the numerical models, this lack of equilibrium causes a fast profile adjustment towards an equilibrium, which may bias the results aimed at evaluating the morphodynamic effect of the intervention. In this contribution, a method, named “concurrent correction method” (CCS) is described which uses the parallel computing technique and evaluates only the morphological impact of the intervention. The hydrodynamics and morphodynamics are assumed to be in equilibrium before the intervention. The morphological evolution is computed based on the change of sediment flux induced by the human intervention. The model can avoid the computational demanding spin-up period necessary to reach equilibrium conditions. In particular the CCM method is efficient for scenario testing with a large amount of morphological settings and hydrodynamic conditions. The CCM can be used in conjunction with any kind of sediment transport model. In this contribution, we used the sediment transport formulation proposed by van Rijn (1991) where a slope term was added to the original formula to take into account the effect of slope on sediment transport. The method has been applied to compute the morphodynamic development of a pit dredged offshore Cane South, SC. The seabed bathymetry was measured before dredging, after dredging and one-year after dredging in January 2009, April 2009 and March 2010, respectively. A corresponding morphological study has been carried out with the aim of looking at the near-field seabed evolution of the dredged area (Ramsey et al., 2014). The CCM provides better quantitative results compared to the measured data than those obtained with “conventional” methods.