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Recently, the problem of wave overtopping has been studied experimentally in horizontally two-dimensional wave field. The properties of wave-overtopping rate for the multi-directional random waves were shown by Sakakiyama and Kajima(1996) and Tomita et al.(2000). On the other hand, in the numerical approach, Moriya and Mizuguchi(1996) calculated wave-overtopping rate for the obliquely incident regular waves along a semi-infinite seawall by utilizing the Boussinesq equations and the wave-overtopping formula of Kikkawa et al.( 1967). However, the validity of that model is not confirmed for random waves. In designing drainage facilities behind the seawall, we are required to estimate maximum wave-overtopping rate as well as time-averaged one, considering multi-directional random wave field…

Authors carried out field survey of the disaster due to the Dec 2004 Indian Ocean Tsunami at Kirinda fishing port in Sri Lanka. We observed severe scour at the harbor mouth, where used to be covered by large amount of accumulated sediments. In order to investigate the physical mechanisms of this observed feature, we conducted a numerical analysis that computes tsunami propagation, sediment transport, and resulting beach topography changes. Model predictions successfully explained the topography change observed in Kirinda and indicated that the back-rushing flow, which concentrated at the harbor mouth, played significant role to cause extensive scours in Kirinda fishing port.

Comprehensive field measurements on waves, currents and beach morphology were performed at south Kasimanada coast facing the Pacific Ocean where significant beach erosion has been experienced in recent 30 years. Anthropogenic impacts on coastal sedimentary processes were described on the basis of grain size distribution and dating of vertical sediment cores sampled in the nearshore area. Headland structures, constructed from 1984, are found to contribute to trapping fine sand and stabilizing the shoreline. The dating of sediment stratum by using Pb-210 method revealed that the sediments at the water depth of 20m were found to be fresh within the 50cm thick surface layer. Historical change in sedimentary processes for the last 50 years were presented.

A flap-gate breakwater for tsunami and storm surge protection was previously developed through hydraulic model experiments and numerical simulations. In this study, applicability of the flap-gate breakwater through a field experiment is shown. Although the field experiment is carrying out at Yaizu fishing port in Shizuoka prefecture, Japan, some technical investigations have been obtained. Feasibility of maintenance and characteristics of age deterioration and corrosion will be verified through continuous experiments to be conducted in the future.

Long-period waves induce low-frequency oscillations at a port. It has been reported in Japan that such oscillations cause significant disturbances in cargo handling and mooring of ships. Typical long-period wave absorber, such as porous ones, requires a large structural width of more than 50 m. Hence, small ports find it difficult to use such absorbers. We have developed a new type of longperiod wave absorption structure whose width is considerably smaller than that of conventional ones. The performance of this novel structure is highly effective in the case of long-period waves. In this research, we investigated the wave-absorbing mechanism of this structure by performing hydraulic model experiments and numerical simulations. Furthermore, we investigated the improvement of the structure to achieve high performance for waves of various periods.