In the probabilistic assessment of the maximum tsunami water level, large-scale parameter studies are required to comprehensively account for uncertainties associated with earthquake occurrence. Therefore, reducing the computational cost of tsunami simulations for individual parameter settings is desirable. In this study, a deep learning (DL) model was developed to impute coastal water levels, serving as a surrogate for part of the tsunami simulation process, based on fault parameters and event locations. Tsunami propagation over virtual submarine topography was simulated for 2,592 cases with varying fault parameters to generate a foundational dataset for DL model training. By appropriately optimizing the hyperparameters, the DL model demonstrated sufficient accuracy and stability, confirming its potential as a reliable imputation-based surrogate method for tsunami simulation results.

 In predictions using sequential data assimilation ensemble Kalman filter/smoother, there are cases where the accuracy worsens if there are too many observation points, so it is necessary to clarify how to select observation points to improve prediction accuracy. The observation points were selected based on the idea that if the predictions at offshore observation points are good, the prediction accuracy will also improve in coastal areas. In other words, the observed waveforms and data assimilation waveforms for 5 minutes after the earthquake occurred at the offshore observation points were compared using Root Mean Square Error (RMSE) and correlation coefficient (R), and observation points with poor waveform agreement were removed. As a result of verification in two cases of the simultaneous occurrence of a historical earthquake and a submarine landslide in the Nankai Trough, the average RMSE of the 60-minute time waveform at 22 coastal points decreased by 0.06m and 0.13m in 5-minute data assimilation after removing observation points with RMSE of 0.14m or more in the waveform comparison at DONET observation points, and it was confirmed that data assimilation accuracy can be improved by selecting observation points based on waveform agreement.

 In conventional tsunami prediction using a sequential data assimilation ensemble Kalman filter, the initial wave source of past earthquakes has been used as an ensemble. In this study, multiple ensembles were set up by perturbing the initial wave source obtained from the magnitude and epicenter of the earthquake, which are real-time earthquake information available immediately after the earthquake occurs, using the earthquake similarity law. Data was assimilated for 5 minutes from the earthquake occurrence at the DONET observation point in the Nankai Trough using three ensemble settings: empirical information only, real-time information only, and considering both information, and predictions were made for 18 coastal points. Verification was performed using tsunamis from the 1946 Nankai earthquake, the 1944 Tonankai earthquake, and Cabinet Office Case 3, and the results showed that the prediction accuracy of the ensemble setting of the initial wave source using both information was the best in all three cases, and the RMSE of the 60-minute time waveform averaged 18 points was 0.11m, 0.25m, and 0.40m, which was an improvement over the conventional method.

 Tsunami on the northern coast of Noto Peninsula uplifted by the 2024 Noto Peninsula Earthquake is not well understood because of (1)difficulties of tsunami field survey due to the destruction of roads to access the northern coast, (2) seawall effect of the uplifted coast, and (3) difficulties of distinguish between traces of the tsunami and wind waves which have almost the same trace height, etc.

 This study aims to understand the actual situation of the tsunami on the northern coast. Therefore, first, places judged to have tsunami trace are identified through inspection of aerial photographs and video pictures taken immediately after the tsunami attack, and then heights of the tsunami traces are measured. Effectiveness of the method is comfirmed by applying the method to places where the tsunami trace heights are already obtained. Next, a simple static tsunami model which has initially a uniform water level rise caused by a uniform coastal uplift in the cross-shore direction over a uniformly sloping beach is proposed and analysed theoretically. It is indicated through a theoretical analysis based on the nonlinear shallow water theory that the water of the uniformly raised area in the static tsunami model just flows out offshore and does not oscillate on shore. This phenomenon is comfirmed from a CCTV footage taken at the Wajima port and so on. These suggest that main part of the tsunami on the northern coast is originated from somewhere else. Aiming for a rough estimate of the initial water level rise in the static tsunami model, a field survey on the distribution of the upper end level of the reef whitening, i.e. vertical displacement is also conducted along the northern coast.

 The tsunami generated by the 2024 Noto Peninsula Earthquake reached the coastal region of Niigata Prefecture, where it was observed at several ports including Naoetsu Port. Upon tsunami arrival, resonant phenomena—such as phase differences and amplification of wave heights—occurred more prominently inside the ports than offshore. This study aims to elucidate the tsunami response characteristics of ports in Niigata Prefecture resulting from the Noto Peninsula Earthquake and to identify the resonance conditions for tsunamis in these ports by investigating the periods of past tsunami events.

 First, the periods and wave heights of the observed tsunamis were calculated using data collected from both inside and outside the affected ports. Then, the natural periods up to the third mode and the amplification factors of each port were estimated using analytical formulas. Furthermore, numerical simulations were conducted to assess water level fluctuations within the ports during tsunami arrival. By varying the input tsunami periods in the simulations, the resonance characteristics and amplification behaviors of each port were evaluated.

 Finally, the relationship between the source regions of past tsunamis and the tsunami periods upon reaching the Niigata coastline was analyzed. Based on this, the tsunami source areas and periods most likely to induce resonance at each port in Niigata Prefecture were identified, and potential mitigation strategies were discussed.

 A moment model fully coupled with a turbulent flow model was used for computing transitional features of solid-fluid flows induced by polydisperse particles settling in still water in this study. We discussed the variations in particle number density, particle / fluid velocity, and resulting vortex structures. A vortex ring, generated by settling behavior, entrapped particles, resulting in a typical mushroom-like distributions of particle number density. The polydisperse particles are classified through settling process, depending on the initial volume fraction. We found a three-dimensional vortex structure composed of the vortex ring wrapping counter-rotating vortices stretched vertically, which highly influenced particle motion including re-suspension when it approached the bottom.

 The generation of waves by the entry of solid particles into water, such as in mountain collapse triggered tsunamis and landslide tsunamis, involves the complex interaction between solid and fluid phases. Wave generation arises from the deformation of the interface when the solid phase enters the fluid phase. The authors previously performed a two-dimensional numerical simulation using an entirely Lagrangian meshfree coupled fluid-sediment interaction solver (MPS-DEM method), which is effective in handling problems including large interface deformations. However, actual landslide tsunamis are three-dimensional phenomena, necessitating a three-dimensional model. In this study, the previous two-dimensional model is extended to a three-dimensional model, and the reproducibility of the wave generation phenomenon caused by the solid phase entering the water is investigated. As principal calculations, simulations of wave generation experiments are performed that involve the collapse of a rectangular particle column and the entering of solid particles with sliding down on a slope. From the calculated results, it is confirmed that the use of an apparent volume correction model is essential to reproducibility, as also shown in the case of 2D calculations, and that the proposed MPS-DEM solver demonstrates satisfactory accuracy for 3D calculations.

 This study evaluated tsunami inundations in estuarine regions in the Nobi Plain, Aichi Prefecture, considering both tsunamis and river discharge (normal / 95 days specific discharge) as well as the sea level rise. The maximum error in tsunami arrival time within the model was 8 minutes, and the error in average tsunami height at six inner bay locations was within 1 m. The impact of climate change-projected sea level rise (0.2 m / 0.5 m) in 2050 under the SSP2-4.5 scenario was assessed. The results showed that differences in river discharge (normal / 95 days specific discharge) were negligible in inundation characteristics. However, when the sea level rise was considered, the inundated area was extended up to 51%, and the average inundation depth increased by 41%. Furthermore, in scenarios where tsunamis and sea levels rise overlapped with high tides, the inundated area expanded by approximately 3.2 times compared to current assumptions.

 In areas such as the Nobi Plain, which is situated at zero meters above sea level, there is a concern that inundation may be prolonged due to the necessity for artificial drainage. Moreover, it has been posited that the risk of storm surge inundation is increasing due to global warming. Evaluating the duration of inundation by storm surge under future climate conditions is necessary. This study aims to predict the duration of inundation by performing inundation calculations that consider the local drop in water level due to drainage, as per the mass conservation law. The inundation calculations are conducted for the Nikko River area in Aichi Prefecture, Japan, assuming the maximum possible storm surge under future climate conditions. The effects of the difference in drainage treatment between the conventional method and the proposed method on the inundation duration are examined, and its validity is discussed. The findings indicate that the traditional method requires 12 days to eliminate inundation on the right bank of the Nikko River, whereas the new process requires nearly 20 days. This discrepancy is attributed to the conventional method's reliance on an inundated area, which leads to an overestimation of the reduction in water level due to drainage.

 Tsunamis ascending a river may acquire a higher propagation speed and travel longer distances than tsunamis traveling on land, resulting in flood damage even inland. In this study, we conducted a comparative study based on 3D numerical results on the effects of the magnitude of river flow on inundated area. We targeted a simple topography including a river channel with a uniform cross section connected to the sea. After creating a river flow and obtaining a steady state, we generated a tsunami to calculate inundated area on the land, as well as the tsunami height and propagation speed of the river tsunami. For the present conditions, as the river flow velocity was increased, the tsunami height increased, whereas the propagation speed of the river tsunami decreased. Regarding the inundation, as the river flow velocity was increased, the inundated area increased, although the inundated zone was limited to the area close to the river mouth.

 One type of Natech (natural hazard-triggered technological accident) involves the secondary impact caused by chemical substances that leak from industrial facilities into rivers during earthquakes and subsequently spread due to tsunami run-up.

 In this study, based on previous research, a two-dimensional/three-dimensional hybrid numerical simulation was conducted to account for the effects of density-driven flow and tsunami propagation. The distribution of leaked chemicals was visualized in both horizontal and vertical directions, and the influence of differences in chemical density and release location on diffusion behavior was evaluated.

 The results revealed that higher-density chemicals are more strongly affected by density currents, tend to diffuse into lower layers, and are more influenced by riverbed topography. In addition, regardless of the release location, chemicals were found to accumulate near the upper right bank. Furthermore, a hazard map was developed for the post-tsunami scenario, providing valuable insights for improving the impact assessment of water intake facilities.

 In the 2011 Great East Japan Earthquake, the so-called “black tsunami”, which involved bottom mud and sludge, were observed. It is required to reveal generation mechanism of black tsunamis, in order to examine their effects on tsunami loads. In this study, moving bed experiments using a mud model with a grain size of a few μm were performed and summarized the erosion thickness based on the pressure gradient in the downstream direction and the vertical distribution of water content ratio of the bottom mud. The failure limit of the bottom mud due to Tsunami flow was estimated by comparing the yield shear stress of the bottom mud model. As a result, the failure limit of bottom mud can be estimated from the relationship between the bottom shear stress of the Tsunami flow and the yield shear stress of bottom mud. Furthermore, the erosion depth of mud becomes significantly larger when the bottom shear stress of the flow becomes larger. An estimation equation for mud erosion under tsunami flow was proposed.

 Large-scale scour can occur around the head of breakwaters when huge tsunami hits. Although previous studies have reported the instability of wave-dissipating block-covered breakwaters caused by such scouring and the possibility of the breakwater sliding due to such instability, effective countermeasures have not yet been established. In this study, the stability and scour prevention effects of armor blocks installed directly from the mound to the sandy bottom were verified through large-scale experiments in order to directly prevent scouring of the seabed and mound, which is the origin of damage. The results of the experiments using the high weight of the armor blocks revealed that the mechanism of damage is that the blocks are induced to slide in a plane toward the center of the scour hole that occurs in the uncovered area of the sandy substrate. The effective extent of block placement in relation to the scour hole in the uncovered area was also investigated.

 Rock bags and filter layers are being considered as a scour protection measure for monopile foundations of fixed offshore wind turbines, with long-term stability also being important consideration. In addition, the similarity law of the sediment is an issue in a movable bed experiment. Recently, Dean number has tended to be use, but the particle size cannot be avoided from becoming smaller in model experiments, and fine sand is also concern about the cohesiveness. In this study, the long-term stability of the countermeasure was examined through a movable bed experiment. Moreover, the effects of model scale and sediment size on scour were also verified using fine sand (d₅₀ = 0.05 mm). As a result, once the top of rock bags settled to the same level as the foundation ground, scour became gradual, and the rock bags was stable. Under this condition, the effect of the filter layers decreased. Furthermore, when using fine sand, it should be noted that the scour depth increases and the bed erosion like cray was caused during a significant external force.

 A number of studies on offshore wind monopile foundation local scour have recently been carried out in support of the work of Sumer et al. (1992, 2001a) on dimensionless maximum scour depths. According to Sumer et al. (1992, 2001a) the maximum scour depth is expressed by the KC number and the wave flow non-dimensional velocity U_cw, but it is considered that the intrinsic experimental conditions, in particular the bottom grain size, experimental scale and monopile diameter, also have an influence in practice.

 Therefore, a review was made of recent national and international papers on scour experiments on offshore wind turbines, including the aforementioned Sumer et al. Experiments were conducted under a wide range of conditions, with experimental scales from 1/9 to 1/130, sediment grain sizes from 0.06 to 0.58 mm and monopile diameters from 1 to 130 cm, and although Sumer et al. (2001a) showed that the maximum non-dimensional scour depth due to wave and flow was correlated with the KC number, in many experiments the maximum non-dimensional scour depth was in the large range Sumer et al. (2001a) suggested that the KC number may be overestimated.

 Based on the constructal law, which states that natural flows evolve to facilitate more efficient movement through a given medium, we assumed a dynamic equilibrium state of sediment transport during uprush and downrush in the swash zone. From this assumption, we theoretically derived a relationship between the foreshore slope and sediment grain size. By incorporating existing formulas for run-up height and setup height, we obtained simplified expressions for this relationship. The simplified formulas were unified and expressed as functions of wave height, surf similarity and wavelength.

 Because it is difficult to directly identify wave characteristics and other factors influencing changes in foreshore slope and sediment grain size at the site, we proposed a new joint probability density function for wave height and foreshore slope to estimate both parameters statically.

 As wave height increases, the expected vales for the foreshore slope and their standard deviations decrease, consistent with observed site characteristics. The expected values of foreshore slope correspond well to the experimental data where wave conditions are known, however, it remains challenging to determine wave conditions from the field data alone. Sediment grain size estimated from the expected foreshore slope was significantly influenced by the prior sediment condition. The method performed well when representing transitions from fine to fine grain size but was less accurate for transitions from coarse to fine. This remains a topic for future investigation.

 The groundwater level affects the sediment transport process in swash zones, and researchers have investigated the relationships between the sediment transport process and infiltration/exfiltration flow across the beach surface. The authors have elucidated the seepage effect with the numerical simulations resolving each sediment grain. However, water contents inside the unsaturated zone of beaches were ignored; thus, details have not been revealed about the effects of capillary force induced by suctions among sediment gaps on the sediment transport process.

 In this study, the authors embedded the capillary force model in the Lagrangian solid-liquid two-phase flow model and combined it with the saturated-unsaturated seepage analysis. Two-dimensional sediment transport simulations considering the unsaturated zone investigated the effects of unsaturated sand on the run-up distance and sediment transport rate. The results showed that small water content inside unsaturated beaches can affect the updated shoreline position, and the capillary force can reduce the sediment transport rate on the foreshore region.

 The transport of sediment by water flow is often estimated by solving transport equations for either the density of the sediment-laden fluid or the sediment concentration. However, in many cases, the reproducibility of real phenomena is ensured by tuning diffusion coefficients, which raises concerns that such approaches are not always fully consistent with the underlying physical mechanisms. Meanwhile, several sediment transport models based on the fluid forces acting on sediment particles have also been proposed. However, many of these models assume a one-way interaction from the fluid to the sediment particles, typically under the assumption of low sediment concentrations. Although discrete models that directly calculate the fluid forces acting on individual particles have also been developed, they tend to suffer from extremely high computational costs. In this study, we investigate the applicability of a mixture model that accounts for both the sediment volume fraction and fluid forces to address these issues in sediment transport modeling. The validity of the model is examined through verification using dam-break flow as a representative test case.

 When considering measures to conserve tidal flats or to prevent their shrinkage or disappearance, it is essential to understand local sediment dynamics. In this study, we estimated the amount of suspended sediment transport using the results of field observations (flow velocity, water level, turbidity, and underwater camera) for approximately 20 hours and the results of grain size analysis of local sediment samples. The underwater camera images showed that the sand ripples moved in one direction. In contrast the suspended sediment repeatedly moved back and forth during the observation period, and a large amount of sediment movement occurred instantaneously in the opposite direction of the sand ripple movement. The total amount of suspended sediment movement was estimated to be 5.90 g/m for the first observation and -51.51 g/m for the second observation, based on the grain size analysis results of the field samples. It was confirmed that not only the direction of the instantaneous movement of the suspended sediment was different from that of the ripples, but also the amount of movement during the entire observation period could be different from that of the ripples, depending on the oceanic conditions.

 In the Philippines, coastal road has been constructed on the shoreline at many coasts not only to reduce traffic jams but also to prevent storm surges. By this method, sandy beach as a buffer zone has disappeared at many places. To investigate this issue, field observation was carried out in August 2024 at four river mouths along Albay Gulf and on the San Roque coast near Legaspi in the south part of Luzon Island. It was found that the shoreline receded due to the blockage of southward longshore sand transport by the construction of groins. On the San Roque coast, waves are incident from the counterclockwise direction normal to the shoreline due to the wave diffraction affected by a protruded peninsula. Under this wave condition, a coastal road was extended along the shoreline, resulting in the disappearance of the sandy beach. Wave overtopping became severe due to the excess seaward advance of the coastal road, and finally the installation of concrete blocks along a long coastline was needed to prevent wave overtopping.

 The flushing through the floodway, change in water level around the floodway during a flood and sand deposition at the opening of the conduit due to storm waves were investigated under the conditions that the upstream gate of the No. 1 channel of the Numakawa-daini floodway is opened or closed. The temporal changes in sand deposition associated with the wave run-up in front of the downstream end of the conduit were monitored at 10 min intervals using two time-lapse cameras. When the gate at the upstream end of the floodway is closed, a still water area was remained near the downstream end of the conduit, so sand deposition into the conduit was prevented during the wave run-up. When the upstream gate is opened, the still water area in front of the downstream end of the conduit was buried with sand. However, the incident wave height during the field test was not so high as approximately 2 m, full closure of the conduit was avoided under the tide level and wave height during the field observation. The sand deposition inside the conduit due to incident waves with a higher wave height was remained to be solved.

 Coastal erosion of beaches in Japan is progressing, and this trend is expected to accelerate further due to future sea level rise. It is essential to understand past shoreline changes to consider effective countermeasures, and there is a growing need for regular, nationwide-scale monitoring. In this study, we developed a system to automatically extract shorelines from past to the present day from publicly available satellite imagery of all beaches in Japan (806 beaches with a total length of approximately 4, 800 km) By incorporating geographic information on beaches into the open-source program CoastSat, which interfaces with Google Earth Engine for satellite scene selection and shoreline extraction, we were able to acquire large-scale shorelines across the country automatically. Analysis of shoreline changes from the 1980s, when publicly available satellite imagery became available, to the present revealed erosion and accumulation trends that were generally consistent with previous reports, thereby confirming the validity of the proposed system.

 The Oshinden coast is located west of the Maite River mouth flowing into the Nakatsu tidal flat. In the past, in the area between the Oshinden coast and the Maite River mouth, sand was transported by eastward longshore sand transport generated by waves incident from NW in winter, and sand deposited at the mouth was flushed away during the floods at the Maite River. With this, sand dune next to the river mouth was severely eroded. The sandy beach next to the Maite River has been a spawning ground for Horseshoe crab and its hinterland has been a habitat for endangered species, so that the protection of the area was needed. Since 2016, therefore, a river mouth jetty was extended to prevent sand from transporting in the river mouth and protect the sandy beach next to the river mouth. As a result of this improvement, a sandy beach recovered immediately west of the jetty. In this study, field observation was carried out at this river mouth to monitor the effect of the measure. Longitudinal profiles across the foreshore were measured using an RTK-GNSS as well as the sampling of seabed material in April 2024. An UAV survey of the tidal flat near the river mouth was also carried out. Finally, we proposed a method to naturally form a spawning ground of Horseshoe crab, sandy beach and coastal vegetation by the deposition of sand originated from tidal flat.

 On the Hishinuma coast, a method to promote beach restoration through the continuous beach nourishment (sand engine nourishment) in a designated area was adopted instead of the conventional beach nourishment method, and beach nourishment using this method was started in 2024. Previous studies on this method were based on the model calculations and the appropriateness of the method has not been confirmed yet with the comparison with the real topographic changes. Since the sand engine nourishment was conducted at the Hishinuma coast in recent years, its effect was investigated using the Narrow Multi-Beam (NMB) survey and oblique images taken by an UAV. Furthermore, the BG model (a model for predicting 3-D beach changes based on Bagnold’s concept) was also applied to the measured topographic changes. Then, the difference in the effect of beach nourishment when the particle size of the nourishment material was changed was examined by the numerical calculation, and the effect of sand engine nourishment was made clear.

 A regional sediment transport model by using RRI model, gRSM and WDM-POM was constructed. By applying the model to Yamakuni River Basin and Nakatsu Intertidal Flat and using field observation data obtained by authors in 2017, the validation of constructed model was conducted, and the estimation of sediment movements due to the flood in 2012 was made. Furthermore, by the estimation of future hyetograph by using the d4PDF data, the forecasting simulation was conducted. In conclusions, the qualitative valication of constructed model was done and the similar mud concentration distributions with numerical and observation results in 2017 were confirmed also in numerical results of 2012. Finary, the future forecasting simulation based on the d4PDF data revealed the similar siltation with the results of 2012 and 2017. Detailed investigation will be conducted in the future work.

 Effects of the river boudanry position on sediment transport simulations in the coastal zone by investigations of the salt wedge and the turbidity plume movements due to the river flood around the rivermouth were discussed by using the numerical model WDM-POM constructed by authors, which was the quasi-3D regional sediment tansport and morphodynamic change model. Numerical simulations with the river boudanry at rivermouth or at non-tidal zone in the upstream of river were conducted by changing river boundary conditions of salt consentration S. In conclusions, the salt wedge intruded to the river at the low-discharge, although it could not intrude to the river during the large river flood. By considering of the intrusion of the salt wedge, turbidity plume movements at both of the outside and the inside of rivermouth were so different from those in the case of no salt wedge that it was quite important to conduct simulations with the combined numerical domain of the river and the coastal zone.

 The change in foreshore area along the east Enshu-nada coast was investigated using the aerial photographs. The foreshore areas in area I between Tenryu River mouth and Fukude fishing port and area II between Fukude fishing port and the Kikukawa River mouth decreased by 9.3×104 m² and 8.9×104 m², respectively, during 2010 and 2024. When multiplied the change in these foreshore areas by the characteristic height of beach changes of 12 m on this coast and divided by the elapsed time of 14 years, the rate of decrease in sand volume in areas I and II were estimated to be 8.6×104 and 8.2×104 m³/yr, resulting in the rate in decrease in sand volume of 1.68×105 m³/yr in areas I and II. The decrease in foreshore area I is due to the imbalance between eastward longshore sand transport and the rate of sand supply from the Tenryu River. In contrast, regarding area II, not only the imbalance in longshore sand transport but also the loss of sand by windblown sand are assumed to occur. Furthermore, in area III located at the eastern side of the study area, the foreshore area decreased by 5.01×105 m² due to erosion between 1962 and 2010, resulting in exhaustion of shoreline sand.

 A peninsula located at the western tip of the African continent hosts the city of Dakar, with a hook-shaped shoreline extending along its southeastern side. A port is planned to be constructed in Ndayane, 38 kilometers southeast of Dakar, requiring coastal impact assessment. This study analyzed shoreline changes using satellite imagery and field surveys at three sites: Ndayane, Rufisque and Saly. In Rufisque, wave directions varied seasonally, and shoreline changes were driven by offshore sediment transport. In Ndayane and Saly, southward longshore drift was dominant, with stronger dominance in Saly. These results indicate that seasonal shoreline changes due to wave direction occur in the region, but their impact is limited.

 While the construction of offshore breakwaters has stabilized the shoreline near the Nankoku section of the Kochi coast, the time required for the effects of restored sediment supply from the Monobe River remains uncertain. To understand sediment dynamics, we investigated the temporal changes in beach cross-sectional areas along various survey lines through bathymetric surveys. The results revealed that the formation and shoreward migration of offshore bars are recurrent, with sediment accumulating in the troughs behind the bars. Additionally, sediment transport near the shoreline differs significantly from that offshore. Near the shoreline, sediment transport is inhibited by four discharge channels, including the Ushirogawa discharge channel. Conversely, offshore, significant sediment accumulation was observed on the west side of the Daini discharge channel, with a gradual accumulation trend over a range of approximately 1.6 km east from the New Kochi port. However, a decrease in cross-sectional area was noted over a range of approximately 1.6 km across the Higashisawa discharge channel.

 When oil storage tanks are destroyed by a tsunami, they can cause widespread tsunami-induced fires. The behavior of oil storage tanks induced by the tsunami involves the interaction between the structure with fluids inside and the fluid outside the structure. The objective of this study is to establish a simulation method that simultaneously handles the behavior of multiple fluids regions and colliding structures.

 A new Fluid-Structure Interaction (FSI) model is developed by integrating the computational fluid dynamics (CFD) software OpenFOAM with the physics engine Bullet. In OpenFOAM, released by ESI- OpenCFD, there is a solver called overInterDyMFoam, which enables two-phase fluid-structure interaction simulations using the overset mesh method. overInterDyMFoam is improved to calculate multiple fluid domains. In addition, the overset mesh method is also improved using an Immersed Boundary Method to handle fluid behavior near collisions. To calculate the behavior involving contact and collisions, a physics engine Bullet is employed. Bullet is modified to be able to handle structures with fluid, and the effect of the fluid inside is given as a change in the mass distribution. This method is more stable and more appropriate than the method of giving it as an external force, especially when it involves a collision.

 While a tsunami after a big earthquake acts on a structure, aftershocks are likely to occur. However, we do not consider the superposition of aftershocks and tsunamis when we design port structures. Some design methods are suggested for those situations, but there are currently challenges in establishing a numerical analysis method. In this study, using a fluid-rigid body coupled analysis method installed considering seismic motion and the porous body model methods, we evaluate the analysis method can apply to the superposition of earthquakes and tsunamis. The results are confirmed below: (1) Regardless of whether the tsunamis overtop the structures, the maximum forces acting on the structure in numerical analytical value are approximately the same as the sum of design value of the tsunami and the earthquake. (2) The numerical analysis method we suggested can evaluate the forces and displacement of structures subjected to the combined forces of earthquakes and tsunamis. (3) From numerical analysis result, the combined force of earthquakes and tsunamis is explained by the sum of the forces when each phenomenon acts independently.

 In the 2011 Great East Japan Earthquake, the tsunamis scoured the ground behind coastal levees at the toe, causing their breaches, and resulting in extensive flooding damage. Understanding the failure process of coastal levees caused by tsunamis could lead to enhancing the resilience of coastal levees. This study used the open-source simulation code DualSPHysics to simulate the failure process of coastal levees with the coastal levee as a movable bed. The results showed that the foundation lost its bearing capacity due to tsunami scouring, causing the coastal levee and armor blocks to slide together. This caused gaps to form in the slope, and the armor block was peeled away by the tsunami. However, not all of the armor blocks were torn off, and the maximum scour depth remained at about half that of the experiment, leaving issues regarding the detachment process of the armor blocks and the scouring process.

 Field surveys of biodiversity in tidal flats are often limited the high-frequency, multi-site observations by high work costs. This study investigates a simplified monitoring approach by focusing on birds, which occupy the apex of tidal flat ecosystem structures. Fixed-point cameras were used at multiple locations within the artificial tidal flat of the Osaka Nanko bird sanctuary and the Kogi River artificial wand to capture images of avian activity, and seasonal surveys of benthic organisms and sediment characteristics were conducted. A deep learning-based model for automatic bird classification was developed to identify species, number of individuals, and spatial distribution from the captured images. Relationships among avian presence, benthic distribution, sediment properties, and inundation conditions were analyzed, and decision tree analysis revealed the environmental factors associated with bird occurrence. The findings suggest that avian activity patterns can serve as effective indicators for simplified environmental monitoring of tidal flat ecosystems.

 In Japan’s national greenhouse gas (GHG) inventory, the accurate estimation of CO₂ absorption by seagrass and macroalgal beds is required. To achieve this, it is necessary to measure and analyze the biomass on a nationwide scale with high accuracy, wide spatial coverage, and sufficient data density. However, conventional dive surveys make it difficult to conduct large-scale measurements, and estimating the biomass from satellite or aerial imagery is also challenging.

 In this study, we used a hybrid UAV equipped with a green laser scanner capable of long-duration flights to survey the entire Lake Komuke in Hokkaido (256 ha). The acquired point cloud data were processed with noise reduction and classified into water surface, vegetation, and seafloor. The spatial volume of vegetation was then calculated across multiple spatial resolutions (1–50 m), incorporating vegetation coverage based on point cloud density, and compared with in situ measurements of wet weight of the vegetation.

 A strong positive correlation was observed between calculated spatial volume and measured wet weight (R² = 0.85 at 20 m resolution), indicating that the method enables high-accuracy estimation of total biomass across the entire lake area.

 The Platinum electrode (PtE) measures potential in seawater, indicating the oxidation-reduction potential (ORP). When reductant (Red) is introduced around the electrode, the electrode potential decreases. Because dissolved oxygen (DO) is consumed in the oxidation of Red, forming an anoxic state in the water column. Continuous measurement of the electrode potential enables us to understand the introduction of Red and the process of anoxia in the benthic habitat. In addition, the potential of the carbon electrode (CfbE) responds to the activity of attached organisms, making it possible to evaluate the biological habitat. This study aimed to link the potential changes of PtE and CfbE with the physical and biological phenomenon in the water of intertidal flats. The changes in potential, DO, salinity, and temperature were measured using electrode and water quality measurement devices near the seawall. The change of potential in PtE was mainly dominated by tide changes in the intertidal flat. While that in CfbE was linked with biofilm formation, indicating the condition of the benthic habitat. Therefore, changes of potential in PtE and CfbE can be used to clarify the ecosystem state of intertidal flats.

 Although it is widely known that the stability of various wave-dissipating blocks differs, differences in their wave overtopping reduction effects are often not considered, and Goda’s overtopping discharge charts are commonly used in practice. In contrast, the EurOtop manual proposes a method for estimating wave overtopping discharge using a roughness factor (γ_f) for each block type. This study conducted wave overtopping experiments under the same wave conditions as in our previous research series, and γ_f was obtained for two types of blocks. The results showed that even for the same type of block, variations in seabed slope and the cross-sectional shape of the wave-dissipating blocks caused significant differences in γ_f, indicating that the γ_f estimation method in EurOtop does not adequately represent the overtopping reduction performance of blocks. Therefore, a correction based on layer thickness area was applied to experimental results using the same block type but with different cover types, crest widths, and layer thicknesses. As a result, the corrected γ_f values become nearly consistent, suggesting the potential for a unified evaluation of block performance in wave overtopping reduction.

 There are from 1,300 to 2,000 rescues every year on patrolled beaches of Japan. Rip currents account for 48 % of the natural factors of drowning accidents. In generally, it is difficult for beachgoers to recognize rip currents. In order to reduce rip current accidents, it is necessary to clarify the actual level of beachgoer’s knowledge and ability to recognize rip currents. In this study, it was investigated to clarify the recognition ability of rip currents with different beaches, locations, weather and wave conditions, rip current characteristics, and viewpoints using Virtual Reality (VR) and the eye-tracking. In addition, in order to quantitatively evaluate the rip current knowledge and clarify whether knowledge leads to differences in recognition, a knowledge survey was conducted for participants. Three gazing data were used in the analysis as follows; Number of visits in the rip current area, Total duration of visit, and Time to first fixation. As a result, rip currents that generate under the calm wave conditions and the fixed rip were not well known and were difficult to recognize. Almost all participants could recognize the permanent rip from a viewpoint where the entire that could be seen. It was also found that even those participants with knowledge had difficulty recognizing the calm rip and the fixed rip, and were not always able to recognize the flash rip and the permanent rip more quickly and confidently. It was thought that the results can be used to improve measures to prevent rip current accidents.

 Two pressure gauges have been installed at the seafloor in the the Nankai Trough in 2024. The pressure gauges have been connected to the DONET seafloor network and started for long-term observation. One of the challenges in the long-term observation of pressure gauges is sensor drift, i.e., the phenomenon in which the output value deviates from the calibrated value over time. In this study, we analyzed the in-situ data to evaluate the long-term stability of the pressure gauges. As a result, the sensor drift of the pressure gauges can be approximated by the combination of an exponential function and a linear function, and was estimated to be −0.0066 cm and +0.0236 cm per day. The pressure gauges were previously pressurized at 20 MPa for 20 days in the laboratory experiment. Although the sensor drift in the laboratory experiment was overall overestimated, the directions of sensor drift were consistent, suggesting that the laboratory experiment is effective for predicting sensor drift.

 Approximately half of all drowning incidents are caused by rip currents. To prevent such accidents, AI-based rip current detection systems have been in operation on five beaches, providing real-time hazard notifications to lifeguards and beachgoers. This systems have significantly reduced rip current incidents at the monitored beaches. However, the detected information is limited to the fixed camera view, making it difficult for users to spatially recognize the location of rip currents. Therefore, we developed an AR ap-plication that visualizes rip currents areas linked to the existing detection system. In this study, a suitability of the AI model created on the adjacent beach for detecting rip currents on the study coast was confirmed. Then, the accuracy of converting image data to GPS coordinates, and the accuracy of AR-based rip current visualization were evaluated. The results showed a GPS conversion error of 4.1 meters, and an AR visualization error of 9.9 meters. The maxi-mum error relative to the center of the detected rip current area was approximately 14 meters, which is considered acceptable for rip currents awareness.

 This study summarizes the findings of an experiment that examined the application of UAV equipped with a scanner that emits green laser light to monitoring during construction at a dredged soil disposal site. The experiment showed that while increasing the sensitivity of the laser light improves the bathymetry capability of the green laser light, lowering the flight altitude leads to a decrease in bathymetry capability and surveying accuracy due to the effects of noise. It also revealed that by conducting surveys on a high-density route using UAV that can navigate for long periods of time, it is possible to prevent data loss in shallow areas and further improve bathymetry capability. Using the results of surveys using a UAV based on these findings, we were able to demonstrate how 3D data can be used in construction management at a tidal flat creation site.

 In Aki fishing port, facing Tosa Bay, it is known that runup of tens of meters scale has occurred on the offshore breakwater during mainly typhoon season. In this study, we have been taking images continuously, using a fixed camera newly installed in a building about 300 meters away. In addition, a method was investigated to measure the spatio-temporal distribution of wave runup from the taken images. As a result, we observed the highest runup height of about 40 meters from the offshore breakwater, and about 80 times of runup per hour during Typhoon Shanshan in 2024. Furthermore, it was confirmed that the spatio-temporal distribution of wave runup could be roughly measured, by using the conventional method of binarizing the difference in luminance values between frame images. On the other hand, when the boundary between the sky and the sea is unclear, like in stormy weather, it is difficult to measure runup by the method. Therefore, it is required to correct by visual confirmation of the movies.

 Instead of costly and labor-intensive in-situ shoreline observations, utilizing satellite imagery for shoreline monitoring is highly desirable. In this study, we employed CoastSat (Vos et al., 2019), an automated shoreline extraction tool, to extract and analyze the shoreline positions of Hasaki Coast in Ibaraki Prefecture from 1984 to 2024. Comparison with in-situ survey data from HORS revealed that the RMSE of shoreline extraction by CoastSat was 11.3 m. Moreover, when shoreline positions were averaged over 4 months and 1 year, the RMSE values decreased to 6.77 m and 4.66 m, respectively, indicating that this approach can detect shoreline changes over a wide range of timescales—from seasonal fluctuations to long-term trends. Analysis across the entire Hasaki Coast successfully captured the key characteristics of its shoreline dynamics. These findings demonstrate the feasibility of using CoastSat for long-term shoreline monitoring at Hasaki Coast, with promising potential for application to other coastal regions in the future.

 In Japan, the progress of port loading and unloading facilities is lagging behind internationally, even though the 2024 logistics problem caused by the declining birthrate and aging population has occurred. The development and revitalization of ports is one of the important themes in coastal and harbor engineering. In this paper, we present Japan’s efforts concerning automated loading and unloading, and then propose a method to evaluate the installation potential of Automated Container Terminals, namely ACTs. ACTs, which automate gantry cranes and transport vehicles, are expected to dramatically improve operational efficiency and resolve the issue of labor shortages. We set four evaluation criteria for the potential of ACT installation: demand and supply, geographical conditions, economic effects, and land traffic conditions. We attempted specific evaluations for the regional ports of Kagoshima and Shibushi, as well as the ports of Nagoya and Tokyo, located near large cities. The present method can also be applied to the evaluation of various port functions other than logistics.

 For harbors at remote islands supporting regional exchange and logistics on sea routes, it is necessary to keep enough harbor tranquility in normal wave condition. However, during storm to suspend services of shuttle ferries, both calling and anchorage are not supposed in harbors at remote islands while they are expected in mother ports in main islands. Therefore, in this study, the conditional cargo handling rate for shuttle ferries approaching remote islands is newly proposed with not only allowable cargo handling wave heights but also an allowable ship navigation wave height which is defined in offshore. The purpose of that is to estimate the harbor tranquility of remote islands to know a required improvement level of maritime structures by excepting days out of service from the calculation of cargo handling rate.

 The improvement of harbor tranquility of remote islands by sheltering with maritime structures from offshore waves and considering mitigation of allowable cargo handling wave height can be expected in case that the conditional cargo handling rate is less than 100 %, while it is required to improve navigation performance to reduce skipping a port in case that it reaches 100 %.

 Beach erosion is a major problem in Bali, Indonesia, where beaches are valuable tourism resources. Continuous monitoring of shoreline morphology is essential not only for mitigating erosion but also for reducing the impacts of coastal hazards such as wave overtopping. Fixed-point camera systems provide a cost-effective and sustainable approach for long-term monitoring, and the generalization of such methods is of increasing importance. Although previous studies have explored shoreline detection techniques, few have achieved full automation, and none have addressed automatic shoreline extraction from field imagery containing obstructive elements such as boats on shore. In this study, a fixed-point camera was deployed along the northern coast of Bali, and an algorithm was developed to automatically detect the shoreline based on edge detection techniques that incorporate brightness distribution and hue information. Validation results indicate that the proposed method achieves sufficient accuracy under a wide range of environmental conditions.

 This study presents field observations of wind waves and the wind speed immediately above them using an unmanned aerial vehicle (UAV). Measurements were conducted approximately 200 meters offshore along the eastern shore of Lake Biwa, in water depths of about 3 to 4 meters, where waves had propagated and developed over a long fetch of 12–28 km. A UAV equipped with an anemometer hovered at various altitudes to obtain the vertical profile of mean wind speed. Additionally, spectral analysis of the time variation in surface brightness, captured by a downward-facing camera on the UAV, was used to estimate the significant wave period from the peak frequency of the brightness spectrum. The friction velocity and roughness length derived from the wind profile were generally consistent with previous observations. The significant wave height estimated via Toba’s 3/2 power law, using the calculated friction velocity and-significant wave period, showed reasonable agreement with values estimated by the SMB method.

 The objective of this study was to quantify the CO₂ balance and ecosystem services associated with the construction of green seawalls (biologically symbiotic seawalls) as part of efforts to expand blue infrastructure that contributes to global warming mitigation and the realisation of biodiversity in coastal areas. The CO₂ emissions associated with construction work were calculated for two existing green seawalls. The reduction in CO₂ emissions was also calculated on the assumption of the use of low-carbon materials and fuels. Furthermore, scenarios for the future growth of seaweed and seagrass were created, taking climate change into consideration, and CO₂ absorption over a 50-year period after construction was estimated. The findings demonstrated that the blue carbon ecosystem's ecosystem services surpass the offset costs of CO₂ emissions (post-reduction) associated with the construction of green seawalls by promoting the growth of seaweed and seagrass.

 Encapsulating dredged sediment by using it as a base material for constructed tidal flats is one potential way of sequestering greenhouse gases from the atmosphere. However, few studies have assessed the effectiveness of carbon sequestration in the subtidal zone of constructed tidal flats. In this study, we conducted field surveys at Oshima tidal flat, Hannan 2 tidal flat, and a shallow area to estimate the carbon retention and methane production at each site. The mean carbon retention rate in the subtidal zone ranged from 77.4 ± 3.8% to 84.7 ± 2.2% on Oshima tidal flat (which has a sand cap); the carbon retention rate in the subtidal zone was higher than that in the intertidal zone. In the intertidal zone of the constructed tidal flat of Hannan District 2 (the shallow area), the average carbon retention rate ranged from 65.2 ± 3.2% to 79.9 ± 3.6%, which was lower than that of the subtidal zone of Hannan District 2 (the tidal flat area) where sand capping was implemented. Although the dredged sediments encapsulated in the constructed tidal flats were under reducing conditions, methane production was negligible due to the presence of sulfate ions in the pore water.

 In recent years, there have been signs of oligotrophication in enclosed inner bays such as the Seto Inland Sea and Mikawa Bay in Japan. In this study, we conducted a fertilization experiment using molten slag, which is used as a fertilizer for rice plants, on a sandy tidal flat in Mikawa Bay. Molten slag alone and slag mixed with cattle manure and rice husks were used as fertilizers. The fertilizer was packed in jute bags and buried on the beach. The quality of pore water and seawater was measured about three months after the start of the experiment. The pore water at the molten slag point, mixed with cattle manure and rice husks, showed high levels of inorganic nitrogen, inorganic phosphorus and silicate. On the other hand, the pore water at the molten slag only point had higher values of inorganic phosphorus and silicate than the non-fertilized point. During the early part of the flood tide, the pore water released nutrients into the seawater. To capture clams, gravel bags were placed at the fertilization points. Clams in the gravel bag at the fertilized point grew more during the summer and fall than clams in the gravel bag at the non-fertilized point.

 In recent years, pumice strandings have caused significant disruptions to coastal fisheries and maritime traffic, highlighting the need to better understand the transport and deposition processes of floating materials in swash zones. This study quantitatively investigated the behavior of pumice particles under waveinduced swash conditions using large-scale flume experiments and numerical simulations based on the Smoothed Particle Hydrodynamics (SPH) method. In the physical experiments, a modified Multi-Object Tracking technique(MOT) was applied to capture pumice trajectories, and the influence of bottom topography was evaluated using two-sample t-tests. The results showed that in concave areas, pumice velocity was significantly lower than in convex regions, with approximately five times more pumice particles stranding and a 0.83-fold shorter maximum run-up distance. Numerical simulations further revealed that particle behavior was strongly influenced by the number of pumice stones.