Morphodynamic zones and three-dimensional changes of the intertidal beach at Egmond aan Zee, the Netherlands
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This thesis builds on the work of Price and Ruessink [T.D. Price, B.G. Ruessink., 2008. Morphodynamic zone variability on a microtidal barred beach. Marine Geology 251, 98-109] on the use of the relative occurrence of the morphodynamic zones to explain three-dimensional changes of the intertidal beach. A field campaign was conducted from 28 September to 31 October 2011 at Egmond aan Zee, the Netherlands, to map the intertidal beach morphology. It was found that low energetic wave conditions enhanced the intertidal morphology and caused onshore bar migration whereas high energetic wave conditions caused flattening of the intertidal morphology and offshore bar migration. Moreover, high energetic wave conditions with oblique incident waves were, in combination with an initial alongshore varying morphology, able to destruct the morphological pattern by the decay of a three-dimensional feature present in the initial beach morphology. The alongshore uniformity of the morphology and of the changes in morphology were tested using the approach of Plant et al. [N.G. Plant, R.A. Holman, and M.H. Freilich., 1999. A simple model for interannual sandbar behavior. J. Geophys. Res. 104, 157555-15776]. The alongshore uniformity of the morphology increased during low energetic wave conditions because morphological features, like the berm, bar and trough, enhanced. These morphological features did cause an increase in alongshore variation of the intertidal morphology, but their main pattern was shore parallel and induced, therefore, an increase in alongshore uniformity. The mapped morphology of the intertidal beach and a standard cross-shore wave transformation model coupled to an inner surf zone bore model were used to determine the morphodynamic zone distributions. The morphodynamic zone distributions showed an alongshore variation in intensity, induced by the alongshore variation of the initial morphology and caused, therefore, alongshore variation in the intertidal beach changes. It was found that, given the morphology, the alongshore variation in intensity of the morphodynamic zone distributions explain three-dimensional changes induced by the on/offshore bar migration and enhancing/flattening of the morphology. The destruction of the morphological pattern, induced by the decay of a three-dimensional feature, cannot be explained by the morphodynamic zone distribution as alongshore processes are involved.