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The numerical model is an extended research version of Delft3D. Delft3D is a comprehensive numerical model suite, which includes a wave driver, hydrodynamic flow, sediment transport, and morphologic response modules (http://www.wldelft.nl/d3d/). The extensions to Delft-3D include a more sophisticated wave driver and sediment transport model to account for the effects of wave groupiness and corresponding infragravity waves on the near shore morphology (Reniers et al., 2000; Ad Reniers is presently a National Research Council Post-doctoral fellow at the Naval Postgraduate School under the direction of Prof. Thornton). The new wave and roller module, operating on the time scale of wave groups, are coupled to a depth-averaged flow model using the non-linear shallow water equations to predict the time dependent flow field. Sediment is stirred by the short-wave orbital motion and wave breaking induced turbulence, which is then transported by the mean and infragravity flow field. Divergences in the sediment transport pattern result in bed-level changes, which in turn affect the hydrodynamics. This is all done within the same time-step (as opposed to the modular set-up commonly used in Delft-3D). Typical wave periods associated with the infragravity waves are in the order of twenty seconds to a number of minutes. The spatial scales associated with the infragravity waves can be of the same order as the observed patterns present in the bathymetry (O(50) m and larger (Holman and Bowen, 1982), hence their potential importance in the near shore morphology.
|Figure 1. The bathymetric evolution (changes with respect to the initial infinitely long, plane sloping beach in m) after approximately 12 days showing a barred beach (denoted by the dark blue) intersected by irregularly spaced rip-channels (qualitatively similar to field site conditions shown in Figure 1 of the ripex homepage). The average rip-spacing is in the order of 250 m. The arrows are mean current (averaged over sea-swell band) velocities showing rip currents.|
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