Assessment of Delft3D Morphodynamic Model During Duck94

摘要

Cross- shore wave transformation, nearshore current, and morphology model predictions using Delfi3D are compared with comprehensive observations acquired on a barred beach at Duck, North Carolina over a wide range of conditions. The Delfi3D 2- DH model utilizes shallow water equations to phase resolve the mean and infragravity motions in combination with an advection diffusion equation for the sediment transport. Model coefficients and the effect of small changes in the wave incidence angle were examined for model sensitivity. The wave transformation model is dependent on the breaking parameter gamma, which determines organized wave energy dissipation. Gamma was found to increase as a function of offshore Hms. However, this is robust and a model skill of .89 was obtained using a constant gamma = .425. The manning number n affects the current bed shear stress and determines the model current magnitude having an optimal value of n 0.02. The model is not overly sensitive to the value of n. The asymmetry coefficient alpha(w) determines the amount of onshore sediment movement. The rip channel created by mean currents on a short time scale is not affected by alpha(w) whereas bar evolution requires more time to develop allowing alpha(w) to affect morphology. A values of .25 gave the best results. Further research is needed to calibrate this parameter. Small changes in wave angle can cause significant errors for currents when complex bathymetry is present and the waves are near shore normal. Overall the model is robust with sensitivity to small changes in near normal wave angles over complex bathymetry.