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A sloping-slit caisson breakwater, designed by the authors, was constructed at a fishery port using the new "precast-form caisson" (PFC) method. The sloping-slit caisson combines the advantages of an upright-slit caisson and a sloping-top caisson. It reduces wave forces by a front slit and a wave chamber. The downward force acting on the slope increases the caisson stability. It was found that the PFC method simplifies construction and saves labor in construction of the caisson.

The purpose of this study is to describe the characteristics of occurrence of coastal freak waves and to investigate their statistical and spectral structures. According to Ochi's definition of freak wave, 175 coastal freak waves were obtained from a long-term full scale wave data bank, in which there are more than 4500 wave records. The probability distribution of occurrence of coastal freak waves was investigated. The goodness-of-fit testing shows that the Rayleigh distribution is more appropriate for describing the occurrence probability of coastal freak waves when the ratio of its wave height to the corresponding significant wave height is more than 2.4. However, the occurrence probability of coastal freak waves remains below the Rayleigh distribution. The relationship between coastal freak waves and the related sea states shows that the occurrence possibility of coastal freak waves may significantly increase in the sea of grouping waves or in the wave field of bimodal spectra. Wavelet Transform was applied to the in situ wave records to investigate the energy distribution on the time-frequency domain. It justified the previous conclusions and demonstrated that the wave groups and superposition of the swell and wind wave energy, which occupies 70% of the coastal freak samples, play major roles of inducing the coastal freak waves.

An instantaneous dye-release experiment was conducted in a coastal field study. Dye was released into a longshore current field from the research pier HORS located in Hasaki, Japan. The release point of the dye was placed in a wave reforming zone which lay between a bar, where limited breaking occurred, and shorewards final surf zone, where all waves broke. Longshore current was present between the bar and shoreline. Deformation of the dye patch was observed efficiently and effectively with a moored video system. Some essential characteristics of the surf zone hydrodynamics and shear flow dispersion are explained from the results of video image analyses of the temporal variation of the dye patch distribution.

The wave-induced pressure gradient, ∂p/∂x, at the bottom is related to fluid acceleration and sediment movement in the surf zone. Following similar large-scale laboratory work by Suzuki et al. [2008a], this paper deals with the observations and analysis of bottom pressure gradients on a natural sandy beach. The cross-correlation coefficients between ∂p/∂x and the water surface elevation are high even in the surf zone, and the coefficients are higher than the coefficients between ∂p/∂x and the vertical velocity component or ∂p/∂x and du/dt. The observed nonlinear characteristics of ∂p/∂x are weaker than the laboratory experimental data but extreme values of ∂p/∂x are larger than the experiments. The distributions of exceedance probability of ∂p/∂x are evaluated using the two-parameter Weibull distribution. The modulus of the Weibull distribution is evaluated as a function of local significant wave height normalized by the offshore significant wave height. The exceedance probability distributions of ∂p/∂x show a broader distribution for the field data compared to the laboratory, but are, nevertheless, predicted reasonably well with the Weibull distribution.

At Waku fishing port in Yamaguchi Prefecture, Japan, which has a vertical breakwater at the mouth of the port, wave-dissipating blocks were installed in front of the breakwater to reduce the sea water spray generated at the breakwater. To clarify the effect of wave-dissipating blocks on the reduction of the salinity in the air, a large number of field observations were conducted at the port in the winter seasons from 2005 to 2011; the run-ups of the splash (heights and frequency), the wind (velocity and direction) and the salinity concentrations in the air were measured at about 30 observation points. The data obtained before and after the construction showed that the violent run-up of splash was efficiently blocked by fully covering the vertical breakwater with the wave-dissipating blocks. Consequently, the salinity in the air was also drastically reduced.

On a sand dune, a blowout is often formed owing to wind effect. The formation of a blowout was observed on November 25, 2016 at the Node coast facing the Pacific Ocean, where a blowout has been formed to leave a concave topography. Then, a model for predicting the formation of a blowout was developed using a cellular automaton method, in which two important factors of saltation and avalanche were taken into account. The results of the numerical simulation were compared with the measured results on the Node coast, and the predicted and measured shapes of the blowout were in good agreement.

Field observations were conducted to investigate the effects of physicochemical conditions on the distribution of the genus Halophila in subtropical Nakagusuku Bay (Okinawa, Japan). Four species belonging to the genus Halophila (H. ovalis, H. major, H. nipponica, and H. decipiens) were found growing in the study area. H. nipponica was most frequently shown in Nakagusuku Bay and H. decipiens was encountered less frequently, while H. major was mainly present at the same sites as H. ovalis. Statistical analysis using physicochemical data obtained at each observational site revealed that the distribution patterns of H. ovalis and H. major were independent of nutrient conditions, but were strongly affected by surface wave motion. The occurrence of H. ovalis was confirmed up to a depth of 8.3 m, and H. decipiens occurred below a depth of 9 m with H. nipponica where the organic content was high and wave motion was smallest among the observational sites. H. nipponica showed a preference for relatively high sedimentation and large amounts of organic materials and its distribution was independent of flow conditions. H. major grew together not only with H. ovalis but also with H. nipponica.