Wave trasformation on pebble beach and deformation of the beach

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Recently gentle slope sea dikes with permeable slope instead of steep slope concrete dikes have been constructing widely. The reason is that the former have effective function to reduce wave run-up and reflection from the dike and give room for creating new ecosystem on them. In this study, hydraulic function of permeable gentle slope sea dikes constructed using pebble is first investigated. The deformation of the sea dike is also examined in the laboratory and in the field.Deguchi and Sawaragi carried out experiments in 2-D wave tanks to examine wave transformation, run-up on the model sea dikes of various slope and surface elements. It is found that waves dissipate their energy on the permeable slope and decay their height and consequently the depth of wave breaking and the wave breaking height decrease remarkably. The rate of decreases becomes large with the increase in the size of the pebble on the slope and with decrease in the slope. Especially, wave run-up height on the permeable slope is less than a half of the on the impermeable slope. Then they constructed numerical model for predicting wave height and wave run-up on the permeable slope by applying a non-linear unsteady Dary's law for the fluid motion in the permeable layr. The predicted results coincide fairly well with the measured wave height and run-up.Ono and Deguhi investigated 2-D deformation of the sea dikes made of pebble in the laboratory and 3-D topography change in the Marble Beach constructed using pebble of marble and locating on the southern part of Osaka Bay. It is found that a so-called depoitional type profile change took place by net onshore pebble transport. The both equilibrium profiles of the pebble slope in the field and experiments coincide with the Dean's profile.