Development of a beach deformation model based on transport mechanisms of mixed grain size sands due to waves and currents

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Most of existing beach deformation models have been developed on the assumption of uniform sediments and therefore failed to simulate the transport as well as the deformation of mixed grain size sands. The objective of this study was to establish a beach deformation model of the mixed grain size sand applicable to the actual field.In the surf zone, atilted waves and the undertow are developed significantly. By performing a series of laboratory experiments in an oscillatory flow tank, we observed transport mechanisms of the mixed grain size sands and obtained numerous data of the sediment transport rate for the condition of the atilted waves including currents. The results showed the coarsening and the -mixing on the surface layer. From these, we successfully developed a sand transport model considering the interference mechanisms of the different grain size sand and the applicability to the prototype scales.Moreover, we proposed a numerical model of beach deformation of the mixed grain size sand combining the sand transport model with waves and currents models. The validity of the model was verified with laboratory experiments in a wave basin for the conditions of a detached breakwater and groins.