In this study, a new rubble mound breakwater structure is proposed, which has a vertical cut on the side of the rubble mound breakwater as a temporary structure to be built on the sea during the construction of coastal facilities and structures. In addition, the structural resistiveness against wave action of the sloping breakwaters is clarified. Hydraulic model tests were carried out to determine the relative damage level of each structure depending on the wave number. Based on these results, I also studied the maintenance and management methods.

 It is proposed that the rubble mound breakwater (isosceles trapezoid mound), which is a temporary structure constructed on the shoreline in front of the construction yard during the construction of upright coastal dikes, should be an earth retaining work made of vertically stacked basket mats. A new rubble mound breakwater structure that can be installed on the seaward side of the shoreline is also proposed. The L-Type buttresses are embedded in the rubble mound breakwater, and the weight and frictional resistance of the rubble stone stabilizes the structure against sliding and overturning. The structural resistiveness against wave action of sloping breakwaters, which are used as breakwaters in relatively shallow water such as in the surf zone, is examined. Based on these results, as a new attempt, new formulae for calculating the stability number of the materials used in these structures were proposed by evaluating the relative damage level using DEM (Digital Elevation Model) data.

 Finally, the new formula for calculating the stability number proposed above is applied to the relative damage level analysis method. As a result, it was shown that it is necessary to calculate the stability number and predict the relative damage level for each material in the rubble mound breakwater structure composed of several materials.

 In April 2022, a pleasure boat sank on the Shiretoko Peninsula in a maritime accident in which all the crew members were missing. The search activities were conducted from the next day, however the search activities was difficult and has not been completed to this day. In this study, we assessed the situation in the sea area after the accident and considered the factors that made it difficult to find the missing persons. In the weather, the cold front passed through the area on the accident day, followed by a change in wind direction and a sudden increase the wind velocity and the wave height. Immediately after the search began, many crew members were found in the vicinity of the Shiretoko Peninsula, and this situation was grasped by the calculations of the virtual colorant diffusion. Furthermore, the current was calculated by the wind driven current and the tidal current. A few days later, the crew was found on Kunashiri Island and Sakhalin. According to the drift calculations, the winds at sea changed after the accident due to the influence of the high pressure located to the east of the area. And, the currents gradually spread in a northwesterly direction while oscillating from east to west over the waters from the tip of the Shiretoko Peninsula to the northern part of Kunashiri Island.

 Distant swells occasionally hit the southern Maldives, causing the development of long-period waves on the reef and resulting in a sudden increase in run-up height. Previous studies have indicated the existence of swells traveling from the Antarctic to the equatorial region of the Indian Ocean. In this study, we aim to clarify the propagation route and development process of these distant swells and discuss their predictability, particularly concerning extreme run-up events in the southern Maldives.

 To achieve this, we utilized ERA5 reanalysis data to calculate cross-correlation functions for the swell development index consisting of wave height and wavelength in the target area and swell wave height throughout the Indian Ocean. Our findings suggest that the swell tends to develop from southeastern Africa to southeastern Madagascar and eventually reaches the southern tip of the Maldives. We also demonstrate predictability by calculating energy fluxes across several inspection lines along the propagation route.

 Local subsidence damage on the airport taxiway right over the ground nearby the underground structure occurred during the 2011 off the Pacific coast of Tohoku Earthquake. The authors have clarified the relationship between accumulated shear strain in the ground and the amount of local subsidence of ground surface caused by the dynamic interaction between the ground and the underground structure from the results of shake table tests of a large model in 1g gravitational field in which an underground structure model was installed in a sandy ground. It was confirmed that seismic response analysis can reproduce the strain histories of the ground around the underground structure obtained from shake table test. In this study, a deformation analysis method for evaluating ground surface subsidence associated with dissipation of excess pore water pressure post action of seismic motion is discussed.

 Measurement of the decomposition rate of dried drifted eelgrass leaves in sand, sand mud, and muddy sediments of the Yamaguchi Bay (Yamaguchi City, Yamaguchi Prefecture) tidal flat were investigated. Each dried leaves discs were buried into four kinds of the sediment environments for 6 months at maximum. Dried eelgrasses disks were processed into discs with a diameter of 6 mm and placed in mesh bags with 2 mm opening. The experiment was carried out at the beach and tidal flats of Yamaguchi Bay. As a result, we were able to measure the decomposition rate until the eelgrass became less than 2 mm in diameter. We investigated the correlation between the dry weights of eelgrasses and the bottom sediment properties at each site. The leaching amount of the dissolved component by soaking into artificial seawater was also assessed. As a result of this study, it was found that the decomposition rate was suppressed in muddy sediments. Furthermore, permeability, oxidation-reduction potential (ORP), and 10 % particle size were negatively correlated with degradation rate.

 This study aims to prevent rocky shore denudation and effectively utilize cutting waste (wood powder) generated during timber processing. Against this background, we have been trying to develop a seaweed bed formation block using concrete containing wood powder fermented using yeast (hereinafter fermented wood powder). In this paper, we investigated the workability and strength of mortar containing fermented wood powder. Then we conducted basic experiments to estimate the number of yeasts and nutrients contained in one specimen. The results suggest that the maximum volume content of fermented wood powder was considered to be approximately 15%, which provides basic data for future concrete block fabrication.

 Wave observation in the port and harbor field is important in all phases of design, construction, and maintenance, and many cutting-edge observation techniques have been applied in the field, and many studies have been conducted on observation data analysis methods. In recent years, with the development of ICT technology, LiDAR (Light Detection and Ranging), which enables us to grasp three-dimensional shapes by using lasers, has been widely used, but there are few observation cases in the port field. In this study, we conducted field observations using the areal LiDAR and investigated its applicability and future potential for wave observation.

 Measurements taken at the shoreline show that when the waves break and run up the beach, there is a lot of water splashing on the structures and around structures such as caisson tips, steel pipe piles, and dissipating blocks, complex changes in the water surface could be acquired as an areal point cloud. In addition, in order to evaluate the acquired point clouds, we developed an evaluation method for the acquired point clouds by considering the grid partitioning dimensions and time division Δt. Wave observation methods based on non-contact surface LiDAR technology are expected to be used for future wave deformation research because they can measure wave breaking conditions in the field and complex water level fluctuations around structures at high densities, which have been difficult to measure in the past.