A field experiment of beach nourishment using riverbed gravel of the Kurobe River, one of the origins for the formation of the Shimo-niikawa coast, was carried out at Shimo-iino area. The applicability of beach nourishment at the toe of the gently sloping revetment to recover the foreshore was investigated. In the field experiment, 1,000 m³ of gravel with the grain size d₁ = 20–100 mm and 5,000 m³ of gravel with d₂ = 100–200 mm were placed at the opening of the detached breakwaters, and successive movement of gravel due to waves was monitored by bathymetric survey and UAV. Because large gravel with d₁ = 20–100 mm and d₂ =100–200 mm had large equilibrium slope of 1/2.4, nourishment gravel was deposited to form a high berm. Then, gravel was transported alongshore by waves from the opening of the detached breakwaters to the location behind the detached breakwaters. Gravel beach was formed at the toe of the gently sloping revetment, implying the effectivity of gravel nourishment.

 Topographic changes in sand bars formed in the wave-shadow zone of the islands were investigated, selecting Gahi and Agenashiku Islands located in the strait between Zamami and Aka Islands of the Kerama Islands as the examples. On these islands, wave direction is restricted by their location in the strait, so typical seasonal changes of the sandbars occur. Gahi Island is located in the northeast part of the strait with a narrowest width of approximately 1.2 km between Zamami and Aka Islands, and Agenashiku Island is located 1 km east of Gahi Island. Both islands are surrounded by coral reefs with a wide sandy beach in the wave-shadow zone. The variation of sand bar formed on these islands was investigated using satellite images together with field observation on November 26, 2023. On both islands, waves are alternately incident from the west in winter and from the south in summer. It was found that the shape of the sand bars is in dynamically balanced condition under the seasonal change in wave direction.

 The north coast of Meedhoo Island located in Aduu Atoll in the Maldives is only one natural sandy beach remained on this island and it is important as the recreational beach for local residents. This sandy beach has been eroded and now it is in crisis. Upon this situation, shoreline changes around the inlet excavated near the northwest end of the island were investigated using satellite images taken between 2012 and 2023, together with the field observation of the beach situation near the inlet on July 14, 2023. It was concluded that longshore sand transport from the northeastern side to the west was accelerated by the excavation of the inlet, resulting in erosion along the north coast of the island.

 On the Shimizu coast, the offshore distance of the detached breakwater from the coastline markedly decreases near No. 9 detached breakwater, and the space for the passage of longshore sand transport is so narrow that longshore sand transport is difficult to pass through the detached breakwaters. In the previous studies, it was shown that the burial of the space between the detached breakwaters and the coastline is effective to facilitate northeastward longshore sand transport and longshore movement of sand body. In this study, the successive movement of sand body near the boundary between the Shizuoka and Shimizu coasts was reproduced using the BG model. Then, beach nourishment was planned to carry out in the vicinity of Nos. 8 and 9 detached breakwaters to enhance the movement of sand body. It was found that when beach nourishment using 3×104 m³ of sand is carried out near No. 8 breakwater, the shoreline advances up to the offshore end of the detached breakwaters within 10 years, enhancing northeastward longshore sand transport.

 On the Chigasaki-naka coast, beach nourishment has been carried out by forming an artificial mound for 380 m length. In this method, the seaward slope of the mound is eroded by waves to form a high scarp. This becomes a barrier for the access from the hinterland to the shoreline, and the scenic view is damaged compared with that on the natural beach. To avoid this situation, the height of the mound in the eastern part of the nourishment area was reduced from +6.9 m to +5.0 m and in the western half, material for the beach nourishment was pushed at a rate of 1×10 m³/yr shoreward after the reduction of the height of the mound up to +3 m. Then, the beach changes after these activities were investigated through the numerical simulation using the BG model (a model for predicting three-dimensional beach changes based on Bagnold’s concept). As a result, the length where high scarp is formed was reduced by half by the decrease in the longshore length of the beach nourishment area, whereas the beach profile similar to the natural profile was recovered in the western half.

 The changes in underwater topography occur during high wave conditions such as typhoons, advancing coastal erosion. Especially in steeply sloped seabed with submarine valleys, sediment carried offshore does not return to the shore. Understanding the characteristics of underwater topographical changes is essential for more effective and efficient coastal erosion control measures. In this study, we developed and manufactured measurement equipment using optical fibers capable of measuring underwater topographical changes even during high wave conditions. Field measurements were conducted on deep-sea steeply sloped seabed. As a result, a maximum decrease in seabed elevation of 0.08 meters was recorded during the measurement period due to high waves. Based on the calculated Shields number, it is estimated that sediment movement reached the suspended sediment to sheet flow condition. The measurement equipment using optical fibers was able to clearly capture minute changes in underwater topography in conditions where sediment movement reached suspended sediment to sheet flow, confirming its applicability in field settings.

 Numerical wave tank is a method for simulating interaction between waves and maritime structures. Creating a computational grid often requires a great deal of time and high-level technical judgement. We propose a practical method for making mesh to save time and consider. A proposed method is based on CADMAS-SURF, widely known as one of numerical wave tanks. Moreover, some schemes are added to handle breaking waves accurately. The validity of this method is verified by calculating existing hydraulic experiments with CADMAS-SURF. The results were confirmed to be valid. This method is expected to accelerate its use in design.

 Floating breakwater of square body has good effect of water-breaking performance with short wave period. However, the square body becomes larger the ensuring performance with long wave period and construction costs increase. This study clarifies the wave transmittance of single barrier floating breakwater with a vertical plate attached to the bottom surface of square body with hydraulic model experiments. The experimental results will be compared with analysis results using three-dimensional boundary element method. For future fishing farm expansion, we studied of single barrier floating breakwater is excellent water-breaking performance with short to long wave period and economically advantageous structure model.

 Although population, assets, and important infrastructure facilities are concentrated in the northern coastal area of Java Island of Indonesia as the most economically developed area, coastal disasters such as coastal erosion, tidal flood, ground subsidence, etc. due to coastal development have become apparent. On the other hand, most of coastal protection measures have been implemented as “after-the-fact measures” and “localized” measures after the coastal problems occur without a unified development plan for coastal protection and conservation. Individual measures implemented by each related organization sometimes causes further deterioration of coastal conditions. This study is aimed to prepare the basic idea and procedure for basic coastal protection and conservation plan to achieve the realization of systematic coastal protection and conservation implementation and management in cooperation with related organizations under a unified basic coastal protection and conservation plan based on the fully understanding of coastal process and characteristics such as waves and sediment transport mechanisms. It was also examined to prepare a concrete basic plan for coastal protection and conservation in three selected areas with different coastal characteristics on the northern coast of Java Island as a case study.

 On January 1, 2024, a tsunami was occurred by the 2024 Noto Peninsula Earthquake. In this paper, we analyzed the tsunami observed by tide gauges and wave gauges of NOWPHAS along the Japan Sea coast. The maximum height of this tsunami was 82.8 cm at Naoetsu (wave gauge). Spectral analysis revealed that the tsunami had peaks at about 8 and 15 minutes. At Toyama (wave gauge) and Fushiki-Toyama (tide gauge), the tsunami arrived within 2 to 3 minutes after the earthquake, suggesting the influence of submarine landslides in Toyama Bay. In Wajima (wave gauge), a rapid rise of the mean sea level after the earthquake was suggested. In Wajima (tide gauge), various events affecting the tide gauge were observed due to seismic motion, suggesting that the construction of a robust tide observation system against strong earthquakes is a future issue.

 To lift the coarse and heavy ores from deep sea, the carrier material（CM）circulation system was proposed to enhance the transportation efficiency and to reduce the amount of waste water. Therefore, the viscous characteristics of CMs（i.e., the relationships between the shear stress, τ, and the shear rate, ẏ）are one of the most important properties to evaluate the pumpability and lifting efficiency. In this study, a new tube-type viscometer, the falling head flow test（FHFT）was proposed for both Newtonian and non-Newtonian fluids of containing solid particles. Meanwhile, a pressure loss which is greatly generated at the elbows of FHFTs might have a serious influence on the measured viscous characteristics of CMs. To investigate this issue, FHFTs were conducted changing the dimensions of the experimental apparatus. The measured results demonstrated the values of the plastic viscosity, η_p are independent on the value of L_elbows/(h₀ + L). Moreover, they show an order of magnitude of variability for the value of L_elbows/(h₀ + L). In addition, the values of the yield stress, τ_y show no trend in the range of L_elbows/(h₀ + L) = 0.04~0.21, and they are scattered for the value of L_elbows/(h₀ + L). Therefore, it was judged the curved pipes of FHFTs have no influence on the measured viscous characteristics of CMs.

 To evaluate the environmental characteristics of the habitats of coastal marine organisms required for the long-term survival of their community, it is necessary to study the methods used to assess habitat suitability for organismal reproduction. In this study, we developed a method that involves use of a time-lapse camera to observe the breeding behavior of large decapod crustaceans, which is difficult to study by divers, and we confirmed its effectiveness by applying it to actual marine areas. Time-lapse cameras were installed by ingenious methods for about three days on tidal flats, in eelgrass beds, and in areas where there were port structures at three coastal sites in Tokyo Bay to record the occurrence and breeding behavior of large decapod crustaceans. Precopulatory mate guarding behaviors of blue swimming crabs (Portunus pelagicus), swimming crabs (P. trituberculatus), hermit crabs (Clibanarius infraspinatus), and other crustaceans were recorded from midnight to 9:00 a.m. We consider at least blue swimming crabs to be nocturnal. The effectiveness and safety of our time-lapse-camera–based approach led us to conclude that it was suitable for observing the breeding behavior of large decapod crustaceans at night.

 In the issues such as the declining international status of Japanese container terminals, the Ministry of Land, Infrastructure, Transport and Tourism (MLIT) has proposed an AI-based optimal terminal operation system as efforts to improve the operational efficiency of container terminals. The purpose of this study is to develop a digital twin system for AI container terminals to support operators' decision making. After studying the requirements and configuration of the digital twin system, we conducted a demonstration test of visualization and quantitative evaluation of container handling operations by linking an AI system and a container handling simulation model. From the simulation results, we confirmed that the simulation model correctly responded to an increase in the amount of work and was able to output information that contributed to operator decision-making support.

 Generally, wave observations are conducted using seabed-mounted oceanographic instruments or offshore cylindrical buoys equipped with RTK-GPS oceanographic instruments. In buoy-type RTK-GPS positioning, the baseline length between the onshore base station and the buoy observation station is limited to about 20 km at most, which may not provide sufficient water depth for wave observations in deep-sea waves. In this report, a demonstration test of a buoy-type oceanographic instrument that has been RTK-GNSS-enabled by adding the Quasi-Zenith Satellite System (QZSS) to GPS was conducted in the waters off Shirahama, Wakayama Prefecture. As a result, it was confirmed that the baseline length could be extended to 30 km without degrading the positioning accuracy, expanding the possibility of observing deep-sea waves. Furthermore, although some issues were found in certain areas, it was confirmed that the operational rate of wave observations and the quality of positioning could be improved.

 In the event of tsunami run-up into ice-covered rivers in winter season, ice floe transport and breakup due to collision with structures can be occurred due to tsunami run-up. This report presents two-dimensional hybrid horizontal model for analyzing such phenomenon. This model has one of particle method, namely, two-dimensional structural MPS method in the upper layer with two-dimensional horizontal shallow water equation in the lower layer. The driving force on each floe is added according to the information of flow field in the lower layer. Then the developed model is applied to some simple numerical test and is confirmed that multiple breakup patterns are obtained with parameters providing breakup behaviors.

 A reduction of greenhouse gas emissions is an important goal in the control of global warming. In coastal areas, the effects of carbon sequestration in seaweed beds are attracting attention. In recent years, studies of carbon sequestration in seaweed beds have focused on carbon storage in coastal areas. This study estimated CO₂ emissions from construction activities and the sediments dredged for sea-level reclamation as well as sediments temporarily placed on land while a navigation channel was being dredged. We measured the organic carbon in the dredged sediments as a function of depth at four points in the navigation channel and calculated the amount of carbon sequestered. We also estimated the amount of carbon dioxide sequestered in seaweed beds growing behind the breakwater based on a 17-year survey conducted from 2006. We estimated carbon dioxide emissions from dredging and reclamation per 125,810 m³ in Kushiro Port to be 1912.3 t-CO₂ and 957.1 t-CO₂ in the case of temporary placement on land and reclamation on the seafloor, respectively. The disposal of dredged material in the sea was thus expected to reduce CO₂ emissions by half compared to disposal on land. The carbon sequestration estimated from the initial carbon content was 5735 t-CO₂. CO₂ sequestration by seagrass beds was estimated to be 1.7 t-CO₂/year in this region.