Unified modeling guidance based on a sedimentation parameter for beach changes |
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| Authors: | Robert J Hallermeier |
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| Institution: | U.S. Army Coastal Engineering Research Center, Fort Belvoir, VA 22060 U.S.A. |
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| Abstract: | Review of four available proposals for designing coastal movable-bed models demonstrates that each suggested model-scaling law contradicts all the others. Accurate laboratory models providing the separate empirical bases, however, all appear fairly consistent with the new design guidance developed here. This formal development considers sediment excursions under wave action by means of a parameter including bed slope and the threshold of sediment movement. The consequent relationship for sedimentation similitude between model and prototype indicates that appropriate model sediment and horizontal scale depend on the selected vertical scale along with wave period and prototype sand characteristics. Explicit forms derived from the general design guidance recover two expressions resembling those previously reported by E.K. Noda (1972) and by P. Vellinga (1982); the route towards Noda's result indicates that guidance is not appropriate for small models of large situations, but the present development yields an independent basis and a needed refinement for Vellinga's empirical results. Considerations of sedimentation similitude are also shown to be supported by successful new laboratory models using sand profiles developed in a large wave tank as prototypes. Spatial distortion seems to be the advisable strategy for small models but proper distortion is rather modest with prototype materials, according to present results. |
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