In the official explanation of technological standards for offshore wind power facilities in Japan, it is mentioned that the numerical wave tank “CADMAS-SURF” is one of the method for generating time series profiles of nonlinear irregular wave and its computing loads can be reduced by using a coupling method, which is proposed by Hirayama and Nakamura (2015), with one of the Boussinesq-type wave equation model “NOWT-PARI”. In this study, the coupling method named “Single component wave approximation” is modified and its applicability to calculation of wave shoaling on slopping bathymetry is discussed.

 The rip currents and coastal currents are basic phenomena for understanding water accidents and beach deformation. The dynamics and morphology of rip currents, especially the origin of cell structures, are still unclear. Since it is extremely difficult to control these phenomena experimentally, we devised a method to obtain temporal mean fields by a numerical calculation method and applied the method to calculate the time average field of the rip currents and the coastal flows every moment of calculation time step. The incident waves were limited to the direction perpendicular to the shoreline, the topography was uniform in the coastal direction, and the regular waves were applied for about 1 hour to confirm the generation of beach currents in the offshore direction. The visualized results of the time averaged currents have offshore direction, which show good agreement with the previous knowledge. It was confirmed that the interval of occurrence(wave length) of rip current cells was consistent with the previous studies, and that the water level fluctuation was due to wavesetdown.

 CADMAS-SURF (CS) is a computational fluid dynamics model for the analysis of incompressible single layer fluid. CS uses the VOF method to represent the free surface and the free surface boundary velocities are extrapolated from the fluid interior. In CS, linear extrapolation is the standard method, but causes numerical instability under strong velocity gradients. On the other hand, zero-gradient extrapolation, which has relatively high numerical stability, causes the wave damping and the inaccuracy of wave breaking. Therefore, in this study, “variable gradient extrapolation” was implemented, which compensates for the disadvantages of conventional methods. Variable gradient extrapolation improves numerical instablity under strong velocity gradients, reduces the damping of wave height and also represents wave breaking on uniform gradient slopes, good agreement with Goda (1970). Variable gradient extrapolation could be expected to be utilised as a method that is superior to the conventional extrapolation methods.

 This study focuses on the size effect of simulated pipe to the terminal velocity of free-falling solid body in a vertical pipe with highly viscous fluid. The Navier-Stokes equations are employed as governing equations and Moving Particle Semi-implicit (MPS) is chosen as the numerical method. A rigid body model for solid is also applied. The solver of the Pressure Poisson Equation (PPE) is GPU accelerated. The moving speed of “inlet particles” on the bottom is dynamically adjusted according to the solid’s vertical velocity, so that the inlet velocity can represent the solid’s terminal free-falling velocity in cases with normal boundary conditions. Numerical experiments of both 2-D and 3-D are conducted. Various parameters such as density, viscosity and ore’s diameter are also considered. The results show that the inlet velocity increases as the simulated pipe’s width or height gets larger.

 Estimating of wave breaking point using 3D numerical calculations is important for wave-resistant design and for research on phenomena related to breaking wave. In this study, the transformation of breaking wave for three types of seabed slopes was calculated for different grid condition. The accuracy of the wave breaking point for each grid condition was verified by comparing them with breaker index and previous experiments. As a result, using a z-directional grid width that divides breaking wave height into approximately 20 divisions and a x-directional grid width approzimately 2 times the a z-directional grid width, breaker depth can be calculated with an error rate of ±20 % from breaker index. wave breaking points can be calculated with the same accuracy as in previous experiments. Therefore, we showed that wave breaking point can be evaluated with the same accuracy as the breaker index and previous experiment.

 It has been pointed out that air-sea heat flux model is possible to be improved by accounting for the effect of the spray evaporation due to large contribution of latent heat of sea spray to the air-sea heat transport. This study conducted an image experiment to measure the density as well as refractive index of the air around a droplet levitating in an air flow. The air density around an evaporating droplet cooled by the latent heat and advected by the air flow was successfully visualized using the background oriented schlieren technique. It was confirmed that thinning of the thermal boundary layer of a droplet corresponds to the acceleration of the spray evaporation.

 In this study, numerical computations of planar focussing short-crested wave breaking have been performed. Evolution of the surface forms and vortex structures produced in breaking waves depending on the wave period and crossing angles, are characterized in comparison with those observed in the previous long-crested wave breaking. An organized rib structures of vortices with counter-rotating vorticity, were found to be produced at the crossing location which literally extend in divergent wave crests. Spatial oscillations of the wave height observed in the crossing wave field, were also investigated through spatio-temporal spectrum analysis in this paper.

 One of the issues for particle methods is the energy conservation. The lack of energy conservation can induce unphysical attenuation of wave height in a wave analysis; however, because previous particle methods have insufficient energy conservation, a long-distance wave propagation has not been able to be simulated in particle methods. In addition, because smaller waves gradually attenuate during a propagation, it was difficult to simulate irregular waves. Therefore, this study proposes a perfectly energy-conserved particle method with using the IDS method and a modified algorithm. The proposed model is verified through two benchmark tests: a standing-wave and a solitary-wave simulations. In both simulations, the calculated results using the proposed model agree well with the theoretical solutions. Then, the application of the proposed model to an irregular-wave simulation is examined. It is shown that irregular waves generated in a flat-bottom wave flume do not attenuated even at a further point from a wave maker.

 Evolution of planar surface forms of initial waves formed in wind tunnel experiments, measured by diffusive light photography, was discussed in this study. The initially created crossing small ripples evolve into larger waves with uniform wave crests with longer wave length propagating in the direction of wind, while a variety of wave forms are taken during the evolution; parastic capillary waves on the wave face, local ejection of the wave crest, resulting in spume drops. The energy transfers among frequencies and wavenumbers during the wave evolution were discussed on the basis of spatio-temporal spectrum.

 Wave response due to topography plays a dominant role in long wave behavior such as tsunamis. Understanding tsunami response functions in real bathymetry can lead to a better prediction of early warning system. This study estimated response functions of tsunamis due to bathymetry, targeting on the Pacific coast of Japan. The estimation method was based on the linear wave theory and its spectral convolution. Ratios of tsunami waveform spectrum at an onshore point to one at an offshore point were obtained from a large ensemble of synthetic tsunami scenarios. The characteristic response features were elucidated by the geometric mean of the spectral ratios. The spectral peaks of these response functions in bays agreed with ones derived from an approximate estimation theory. Besides, the detailed frequency-dependent responses were estimated.

 According to recent investigations on the bottom boundary layer development under tsunami, wave boundary can be observed even at the water depth of 10 m, rather than steady flow type boundary layer. Moreover, it has been surprisingly reported that the tsunami boundary layer remains laminar in the deep-sea area. For this reason, the bottom boundary layer under tsunami experiences two transitional processes during the wave shoaling: (1) flow regime transition in a wave-motion boundary layer from laminar to the turbulent regime, and (2) transition from non-depth-limited (wave boundary layer) to depth-limited boundary layer (steady flow bound-ary layer). In the present study, the influence of these two transition processes on tsunami wave height damping has been investigated using a wave energy flux model. Moreover, a difference of calculation results by using the conventional steady flow friction coefficient was clarified.

 We investigated on a series of bubble bursting processes, including a formation of a rim bounding liquid film on a bubble cap, extension of the hole on the film, evolution of concentric vertical jet, on the basis of high-speed micro image measurements. We also discussed linear stability of the motion of the rim on the flim, causing a formation of fingers on the rim and generation of film drops. The ascending velocity of the concentric vertical jet, produced after collaps of the bubble cap, and the drop diameters are parameterized in terms of Bond, Laplace and capillary numbers. The effects of surfactant to the parameterization are discussed through the experiments using purified water and seawater.

 Although extratropical cyclogenesis is associated with the baroclinic instability, their explosive development is contributed by release of the latent heat in a moist air over the ocean. It is concerned that intensification of explosive cyclones occurs due to the rise in sea surface temperature in a future climate This study characterizes future change of the explosive cyclones classified by their trajectory types by using the data in the future climate database, d4PDF, and then discusses on the statistic surge level induced by the winter cyclones. The acceleration of the cyclone development might contribute to increase the static surge levels in a relatively low latitude area.

 In recent years, it has been concerned that the storm surge will be severe more than the past due to the climate change by the global warming. Once storm surge occurs and starts flooding, the damage will rapidly spread on low-lands and lead to many problems, though, because of the topographical features, most of the population and major properties are accumulated in those dangerous area in Japan. Hence, the storm surge prediction will be important more and more, on the other hands, it is difficult since storm surge is strongly affected by even small differences of the typhoon tracks. For inventing the storm surge prediction system which the uncertainty of the typhoon tracks can be taken into consideration, two types of the ensemble weather forecast were used as input data for the system. In this paper, the storm surge deviation predicted by the system was verified with comparing used ensemble weather forecasts and the observed data. Besides, the gaps between the results predicted by two types of the ensemble weather forecasts were also investigated.

 This study shows how the worst class of typhoons and related storm surge height along major bays in Japan will change based on MPI (Maximum Potential Intensity) theory and MPS (Maximum Potential Storm surge height) model. The climate data used in this study is HighResMIP (High-Resolution Model Intercomparison Project) experiment, which includes high-resolution and atmosphere-ocean models. In the Northwestern Pacific, the maximum future changes in MPI were observed in September in 30-40°N latitude band, with an enhancement of -6.1 hPa by 2050 under the RCP 8.5 scenario. The largest change in MPS was observed in Osaka Bay, increasing +0.56 m by 2050. This result indicated that it is important for adaptation measures to consider storm surge changes in addition to sea-level rise.

 Spatial dependence of extreme wave heights should be taken more in consideration for disaster reduction plan in several viewpoints of the accumulating risk affected by the magnified typhoon due to the climate change. Accordance will be an useful index for the multivariate extremes, which is defined by the proportion of the identical cases of occurrence factors for the componentwise annual maxima to the total number of years. We first rearrange the dependence properties of bivariate extremes, and then we introduce the nested models for cross occurrence rate of three locations of extreme wave heights as one of the simplest models to connect the combination of bivariate extremes to the trivariate extremes without any additional parameters. Application of the nested model to annual maxima of wave heights at three locations: Omaezaki, Shimizu and Shimoda is demonstrated in comparison with one of the Husler-Reiss three parameters model.

 It is important to understand the tidal characteristics of ports and harbors. The design tide level is often based on a stochastic tide level with a specified return period, and long-term tide level observation records are required, but the statistical years of the data are often insufficient, so extrapolations must be made. In this study, we attempted to understand the characteristics of tidal levels in Japan mainly from the viewpoint of the probability of tide level anomaly by organizing tide level data (1998-2020) from JMA tide stations along the coast of Japan. The statistical years of the tide level data are also discussed. As a result, the values of probability tide level anomaly and the optimal distribution function tended to be similar in the vicinity of similar topography, and the optimal distribution function was often Weibull distribution. Although statistical data over a long period of time is necessary to examine probability values, even if the period is short, if the MIR criterion is lowered by the extreme value statistics, there is a possibility that the estimation error can be equalized.

 Wave predictions are referred to in various fields such as fishing, surfing, ship navigation, and maritime construction. Marine construction management is greatly influenced by the accuracy of wave forecasting. Wave predictions are made based on the spectral wave model forced by meteorological information. Recently, wave prediction by artificial intelligence has been developed. However, most wave predictions by meteorological or artificial intelligence models are short-term predictions. In order to make a construction plan for marine construction, it is desired to estimate the wave height and frequency of construction several months ahead. This study carried out a monthly ensemble wave height forecast using the statistical wave model. It was found that the results of the ensemble wave prediction approximately agree with the observed wave data. However, the accuracy of the results in the long-term prediction is inferior.

 The use of neural networks for wave forecasting has the advantage that it does not require deep domain knowledge and can be implemented at low cost for each region. However, reanalyzed Grid Point Value (GPV) data of weather fields are frequently used as explanatory variables for neural networks that hinder real-time wave prediction. In this study, we constructed a neural network using AMeDAS and NOWPHAS observation data for real-time wave prediction and predicted the wave height and period at Kobe Port. The combination of explanatory variables and SHAP values allowed us to explain, to a certain extent, the contribution of each explanatory variable to the prediction accuracy. The results showed that information on the wind at an appropriate distance on the upwind side was important to improve the prediction accuracy and that the contribution of historical information on waves (wave height and period) was extremely high, and in particular, the wave height could be predicted with sufficient accuracy for practical use.

 Wave predicting is in high demand for process control in the implementation of offshore construction work, such as the construction of offshore wind power generation facilities. A number of deep learning models have been developed in recent years for wave prediction. However, many of these models are pinpoint wave predictions at NOWPHAS. When applied to construction work, those models cannot be used when the work is far from NOWPHAS observation points or when the work vessels or materials are moved long distances. When predicting multiple locations using models from previous studies, it is necessary to create the model for each location, which is labor-intensive. In this study, we developed the two-dimensional wave prediction method using the deep generative model, which is a type of deep learning, with the aim of accurately predicting waves at multiple locations with a single model.

 Modeling various global environments requires accurate calculations of air-sea momentum transfer. However, the accuracy of field measurements affects some parameters of the calculation formula, such as the drag coefficient. Therefore, a high-precision and high-frequency measurement method that can measure wind speed and wave conditions simultaneously is needed. In this research, we propose a method for estimating wave conditions (wave period, wave height, and wave direction) using the motion of the small-buoy which is designed to synchronize with the waves. Proposed method is able to reduce sensor error and integration error by sensor fusion of two IMU sensors based on geometric constraint of buoy motion. A windwave tank experiment shows that the proposed method can accurately estimate wave conditions.

 For long-term coastal monitoring, deep learning was applied to images from fixed cameras installed on the coast to estimate wave conditions. Datasets created from images of the Shichiri Mihama Ida coast in Mie Prefecture and the Hasaki coast in Ibaraki Prefecture and wave information obtained from NOWPHAS were used to compare wave estimation accuracy. Results showed that the machine provided good estimates of significant wave heights and the angle of the image suitable for estimating significant wave heights differed from coast to coast. Although the machine tended to underestimate the significant wave height, it was able to reduce this tendency by capturing images in a different direction of the incident wave. The accuracy of the estimation was further improved by using images taken from multiple shooting directions.

 A huge volcanic eruption occurred at Hunga-Tonga Hunga-Ha’api in Tonga on 15 January, 2022. The volcanic meteotsunami was observed globally according to the propagation of atmospheric shockwaves such as Lamb waves. The present study attempted the numerical analysis using the Princeton Ocean Model to investigate the effect of the upper wind to the so-called Proudman resonance caused by the coupling of atmospheric pressure waves and ocean long waves. Under the no wind condition, the computed wave height was as small as 50-60% of the wave height of the in situ observation by NOAA DART bouy systems. However the computed waves under the jet stream conditions was higher by 1.3-1.5 times of the no wind conditions at Shikoku-Oki and by 2.5-3.0 times at Tohoku-Oki. Power spectrum of the sea level elevation showed that waves with the period around 10 minutes were much more enhanced with the against winds, rather than the Lamb wave.

 The eruption of the Tonga volcano that occurred in January 2022 caused large water level fluctuations and damage to the coast of Japan due to the propagation of atmospheric pressure waves. In considering future coastal disaster prevention, it is necessary to understand the impact of this meteotsunami. In this study, the propagation path and atmospheric pressure waves were estimated using the measured values of atmospheric pressure, and the characteristics of the water level change due to the atmospheric pressure waves were investigated. In this study, numerical calculation considering the propagation of atmospheric pressure waves and sensitivity analysis for the propagation velocity of atmospheric pressure waves were carried out, and it was confirmed that there was a water level rise of about 1 m along the coast of Japan from the assumed propagation of atmospheric pressure waves. The water level rise of meteotsunamis caused by atmospheric pressure waves in coastal areas is smaller than the water level rises of tsunamis and storm surges caused by earthquakes. However, it is a value that cannot be ignored in terms of disaster prevention, indicating the need to consider damage estimation in consideration of this effect in the future.

 On January 15, 2022, a large-scale eruption occurred at the submarine volcano Hunga Tonga-Hunga Ha'apai near the Tonga Islands, and sea-level changes were observed around the world. The sea level fluctuation is assumed to be caused by atmospheric-oceanic resonance due to the Lamb waves and atmospheric gravity waves associated with the eruption. However, the details of the atmospheric pressure fluctuation and propagation process associated with this eruption are still unclear at this time. Therefore, in this study, we examine the effect of atmospheric-oceanic resonance by performing sensitivity analysis for tsunamis propagating from Tonga to Japan by varying the amount of atmospheric pressure variation and propagation velocity of the waves, which are considered as Lamb waves and atmospheric gravity waves. In this event, the amplitude of the wave was amplified by the Proudman resonance, and a significant sea-level change was considered to have occurred at Amami Oshima. Furthermore, Proudman resonance is also assumed to have occurred at multiple locations due to the combination of pressure waves with the same velocity as the phase velocity of the long ocean wave in the passing ocean region.

 Tsunami intrusion into river is investigated in this study. Investigation and analyses were conducted based on water level measurement data and distance from the river mouth at several rivers in Miyagi Prefecture during the 2022 Tonga Volcano-Tsunami. These data were used to discuss the influence of river mouth morphology on the tsunami height and propagation distance. In addition, an empirical method is applied for estimating dissipation coefficient. The value from the present study shows good comparison with an empirical formula proposed by the authors based on field data during the 2011 Tohoku Tsunami.

 The water waves caused by volcanic eruption in Tonga in 2022 reached Japan several hours earlier than the forcasting. To obtain fundamental understanding of the phenomena, we conducted numerical experiments on the propagation of water waves in one dimension and atmospheric gravity waves in two dimension. From the temporal change of the wave profile depending on the wave-sound velocity ratio, the growth of the water surface due to Proudman resonance was confirmed. The arrival time of the waves calculated with the actual topography was in good agreement with the observation, and the time difference from the forecasting was explained.

 A major explosive eruption from Hunga Tonga-Hunga Ha'apai in Tonga occurred on January 15, 2022. This eruption caused tsunami, and many tsunamis were reported along the Pacific rim including the coast of Japan. This paper shows the outline of the observed results on atmospheric pressure and water level at the bay mouth of Tanabe bay, Wakayama, Japan, and the comparative findings on the characteristics of water level fluctuation measured under different conditions.

 In the observed results at the offshore observation tower at the bay mouth of Tanabe bay, atmospheric pressure fluctuation of about 2hPa was measured after around 7 hours of the eruption, and a 0.35m tsunami was measured between 0:00 a.m. and 1:00 a.m. on January 16. Water level data measured at the bay mouth of Tanabe bay contains several components with different frequencies. The dominant component is the natural period of Tanabe bay and its period is around 40 minutes. Additionally, fluctuation components from 10 to 20 minutes are included during the peak of water level variation. The fluctuation components from 10 to 20 minutes are also observed in water level data measured by offshore buoy after the eruption in Tonga. On the other hand, the fluctuation components from 10 to 20 minutes are not found in water level data of tsunami due to distant earthquake in 2015. This result means that water level fluctuation components from 10 to 20 minutes is a characteristic component of tsunami excited by atmospheric pressure variation due to the eruption in Tonga 2022.

 In the present study, we used a pressure standard (i.e., a pressure balance) and a thermally controlled bath to reproduce the seafloor environment at a depth of 2, 000 m and examined the pressure fluctuations during an earthquake. Two different types of pressure gauges, i.e., the quartz resonant pressure gauges and the silicon resonant pressure gauges were pressurized by the pressure balance. Pressure fluctuations at a frequency range lower than 0.1 Hz have the same characteristics regardless of the type of pressure gauges, while pressure fluctuations at a frequency range higher than 0.1 Hz are different by 10 dB in amplitude. Compared the experimental data with the in-situ observation data, the amplitude caused by the Rayleigh wave was coincided. However, the pressure fluctuation predominated at 0.1 Hz was not reproduced in the experiment, suggesting an unique phenomenon exhibited only at the seafloor.

 This paper examines the behaviour of subaqueous gravity flows of liquefied sand in a set of centrifuge model tests. The behaviour of gravity flow is mainly governed by the gravity acting on the sediment. The centrifuge model testing technique is a realistic means of reproducing a submarine gravity flow, and furthermore, drum-type centrifuge does not have side walls of the channel, so that long-distance flows could be observed. A series of wave tests was performed under centrifugal accelerations of 30 or 50 gravities. In the experiments, sediment gravity flow with a velocity of 2.0m/s was reproduced in the drum centrifuge channel. The sediment flow, which corresponds to fine sand in a field, proceeded long distance with a constant velocity, resulting in a flow of more than 340 m on the prototype scale (the length of the experimental channel). The grain size distribution of the deposited sediments out of the gravity flow of mixed soils was also investigated.

 The 2011 Tohoku tsunami accompanied a large amount of silt and clay along the Sanriku coast and supplied them substantially onto the inland area. Such a tsunami containing silty materials could contribute to increasing coastal and human damage. However, characteristics of tsunami-induced suspension of silty materials and their effect on tsunami flows have not been sufficiently understood. This study conducted a laboratory experiment of sediment transport on a silty bottom and developed a numerical model to investigate the detailed processes and mechanisms. Results from the experiment indicated that a wave-induced flow suspended more silty materials for higher fluidities of bed materials. A vortical flow induced by wave breaking further contributed to enhancing the sediment suspension from the bottom. The sediment processes were reproduced by the numerical model with two empirical parameters of sediment entrainment calibrated with the experimental result. The numerical model reasonably reproduced a local scour on the bottom as well as the concentration of suspended materials.

 Black tsunamis that engulfed bottom sediment were observed during the 2011 Great East Japan Earthquake, and there is concern about the effects of such tsunamis. In order to properly design coastal structures against tsunamis, it is necessary to quantitatively evaluate the impact of changes in density, viscosity, etc. due to the inclusion of bottom sediment. Most of the previous studies on the concentration of sand suspended by tsunamis have focused on relatively large grain size sand, and few studies have focused on bottom sediments with grain size of a few micrometers, such as mud and sludge. In this study, we conducted a moving-bed experiments on fine-grained bottom sediments, focusing on the sediment roll-up characteristics that lead to black tsunamis. The results suggest that the thickness of flow-induced fluidization of the bottom sediment surface layer differs depending on the water content of the bottom sediment, and that viscosity, which is strongly related to the water content of the sediment, is one of the factors controlling the thickness of fluidization.

 To assess compound flood risks from first-class to small-sized rivers, it is essential to develop a model that can solve the entire process in a unified manner. However, there have been few studies due to discontinuities between ocean and hydrological models and technical issues (meteorological field and wave modeling). The present study developed an integrated atmosphere-ocean-river model (SuWAT-River) by constructing a system that automatically converts river discharges into water levels. The water level of the rivers of Toyogawa (first-class river) and Yagyu and Umeda (small and medium-sized rivers) due to Typhoon Trami (2018) was reproduced with the high accuracy by SuWAT-River. Results of sensitivity experiments revealed that the water level rise due to storm surges and flooding was 7.3 and 3.2 times higher in the Yagyu River and Umeda River than in the Toyogawa River, respectively. Furthermore, these small and medium-sized rivers are extremely risky because the storm surges and flood peaks are superimposed on the estuaries.

 To improve the accuracy of storm surge forecasting, it is desirable to improve the typhoon forecasting accuracy. The typhoon forecasting model WRF has a high degree of freedom in setting its calculation conditions. In this study, we conducted sensitivity analyses of the WRF’s calculation domain settings, initial and boundary conditions, and physics options, which have a large impact on typhoon forecasting due to the differences in their settings among model users. Here we show that (1) horizontal resolution has a greater impact on typhoon forecasting than location of calculation domain, (2) the choice of analysis data used for initial conditions of WRF has a greater impact on typhoon forecasting than lateral boundary conditions, and (3) the relationship between forecast start time and variability of storm surge forecasting due to differences in the setting of physics options of WRF. These results are useful for evaluating the uncertainty in typhoon and storm surge forecasts caused by differences in the WRF’s calculation conditions. In the future, introducing more sophisticated data assimilation (e.g., 4DVAR, EnKF) in typhoon forecasting seems necessary to improve the typhoon and storm surge forecasting accuracy.

 We conducted a combined probability assessment of earthquake ground motion and tsunami damage for buildings in the entire city of Osaka, considering individual structure types. First, numerous finite fault models were synthetically generated along Nankai Trough. Each fault model has a different slip distribution with similar wavenumber characteristics to historical subduction earthquakes. Subsequently, strong-motion and tsunami simulations were performed for all generated fault models, and the dam-age probabilities to buildings in Osaka City were estimated. In estimating the damage probabilities, wooden and non-wooden buildings were distinguished. The spatial distributions of ground motion and tsunami damage probabilities showed different characteristics. Estimating damaged buildings at different magnitudes showed that the increase in the expected number of buildings damaged by tsunamis was significantly larger than that by earthquakes as the magnitude increased. Additionally, the combined damage probabilities of ground motion and tsunami damage were significantly different from the individual ones, indicating the importance of assuming both types of damage in coastal urban areas.

 Coastal and harbor structures on the Sea of Japan coast are mainly designed for winter storm waves, but there is a significant risk of tsunami disasters. In recent years, tsunami prevention/mitigation measures have been in progress by local governments based on potential tsunami sources identified by the Japanese government. Since the tsunami magnitude varies significantly along the coastline, it is required to examine if existing structures work against tsunamis as well. This study estimates run-up heights by winter storm waves (seas and swells) and tsunamis and compares them along the long coastline to discuss the dominance of the two forcing factors. The overview of the run-up heights suggests that the Sea of Japan coast can be roughly divided into three segments depending on the relative significance of the two factors.

 In Dokai Bay, where no inundation disaster due to storm surge has been reported so far, two inundations occurred about 9 hours at 2-hour intervals after the closest approach of Typhoon Maysak in 2020. In the future, it is expected that the possibility of inundation disaster by the same mechanism as in this case occurring again will increase due to the rise of sea level caused by global warming and the increase in the strength of typhoons. Therefore, in this study, the mechanism of storm surge occurrence was examined using numerical simulation. Two hours before the peak of the tidal level anomaly, the tidal level anomaly of the entire Tsushima Strait including Dokai Bay becomes negative and the oscillation begins. The rise in tide level due to this oscillation was the main cause of the first inundation. The second inundation was caused by a combination of positive tidal level anomaly caused by Ekman transport and high tide.

 Numerical experiments on tsunami force acting on a fixed bridge girder and tsunami erosion of bridge-abutment backfill were conduced to investigate the characteristics of the tsunami force and its estimation equations. Numerical results showed that an increase in horizontal force and a decrease in vertical force became smaller after the erosion of the backfill and the foundation under the girder. This suggested that it is essential to take into account the effects of the erosion of the backfill and foundation in assessing the onset of the girder movement and the downward lift force acting on the girder.

 The individual Drag Force Model (iDFM), a subgrid-scale model that treats groups of buildings in a grid as drag forces, is developed and coupled with the AMR method, in which the computational grid size is refined in time and space, to develop an efficient numerical model of storm surge inundation over metropolis including different scales phenomena. The results of the structure resolving model, which treats buildings as topographic features, were used as true values for the inundation calculations, and a comparison of the inundation characteristics was conducted. The reproducibility of the momentum flux in the area where buildings are densely built and the flow velocity is generally reduced is good, but the reproducibility in the area where the momentum flux and inundation depth increase locally along the road is an issue to be improved.

 The study area was a sea area where an upright seawall and an upright coastal dike were installed on a complex semicircular topography centered on a bay. In addition to two-dimensional cross-sectional hydraulic model tests and tsunami simulations, three-dimensional tsunami simulations were conducted to confirm the effect of three-dimensional current on tsunami wave force by taking into account the complex topographical characteristics, and the validity of the existing tsunami wave force calculation formulas was verified by comparing with experimental and simulation results. As a result, it was found that undular bores and breaking bores were not generated even when the topographic characteristics and uncertainties of the tsunami height and the tsunami duration were taken into account, that there were no significant differences among experimental or simulation methods, that the tsunami wave pressure distribution based on the existing tsunami wave force calculation formulas enveloped all wave pressure data. And, it was also found that the existing tsunami wave force calculation formulas were on the safe side because the tsunami wave pressure coefficient remained at the same level as the hydrostatic pressure even when the Froude number of the progressive tsunami wave exceeded 1.5.

 During the Great East Japan Earthquake and Tsunami, radioactive substances leaked from the Fukushima nuclear power plant, causing loss of properties and serious environmental pollution. In order to prevent similar nuclear power plant accidents, it is necessary to consider tsunami damage under various conditions. The purpose of this study is to ascertain the influence of the presence of a sand dune in front of a seawall and the sediment transport on tsunami waves by conducting simulation analysis and comparing the results to hydraulic experiments, to provide data with a reference value to protect the nuclear power plant behind the seawall. In this study, based on the 2DH-3D hybrid tsunami behavior analysis model, an analysis model that can take into account the suspended load and bedload of the sediment, the tsunami density changes, and sand dune deformation has been developed. The validity of the numerical analysis is verified by comparing the results with hydraulic experiments. The results of this study indicate that 1) the developed analysis model appropriately reproduces the experimental results such as the wave force acting on the seawall; 2) under the circumstances of the long-period wave targeted in this study, it was discovered that the sediment transport did not have a large effect on the wave force; 3) the cause of 2) is presumed to be that the deformation of the sand dune is small when the tsunami reaches the seawall.

 Aiming for the advancement of tsunami load, historical and/or prospective tsunami scale evaluations, empirical formulas for evaluating frictinon factor K of inundation flow and density ρ of inundation water under a movable bed, which are available to tsunami run-up theory, are proposed using experimental data increased (expanded) the amount (range) by carrying out additional experiments on ρ and run-up of inundation flow, and verification data of the theory under a movable bed are provided. Series solution with a higher universality to the run-up of tsunami inundation flow with sediment over a uniformly sloping bottom, in which both K and ρ depend on time, is derived under conditions depending on initial stored water depth h₁, bottom slope i, sediment diameter d₅₀, and examples of the solution are shown. The solution is applicable to the case that ρ is independent on time, i.e., the case of inundation flow without sediment under a movable or fixed bed. Including the case of inundation flow without sediment, validity of the solution to the tsunami run-up is also verified through a comparison with the verification data on run-up distance.

 In this study, in order to improve the calculation accuracy for predicting the formation of sediment deposition on land induced by tsunami run-up, a bedload layer model is introduced into a tsunami sediment transport model and its improvement is carried out. The bedload layer model assumes the existence of deposition and mobile layers of sediment on a fixed bed. Validation of the model on a flat-bed experiment shows that the introduction of the bedload layer model improves the reproducibility of the phenomenon compared to a typical model. In addition, the possibility of highly accurate prediction of the phenomenon is demonstrated by changing the equilibrium bedload layer thickness and consideration of non-linear changes in the sediment discharge depending on the sediment volume in the target area. However, from the application to the slope-bed experiment using other particle sizes with the same parameters as the flat-bed, it is indicated that further studies are needed to reproduce the phenomenon in other particle sizes.

 New guidelines have been developed in response to the damage caused by the Tohoku-Pacific Ocean Earthquake Tsunami. Moreover, A great deal of knowledge has been obtained regarding the evaluation methods of tsunami loads acting on-land structures.However, not many studies have been conducted on tsunami wave forces on structures from the pushing wave to the receding wave of a tsunami, such as wall wave forces and buoyancy forces.In this study, a model experiment was conducted using a large wave tank capable of measuring tsunami waves from the pushing to the receding wave range, and tsunami wave forces were measured by changing the aperture of the structure. The experimental results were used to evaluate the feasibility of using the conventional estimation equation for tsunami wave force.

 A tsunami that struck Sulawesi Island in Indonesia in September 2018 caused enormous damage to the city of Palu. On the other hands, some historical tsunamis, which assumed to be caused by a submarine landslide were observed at tide gauges along Japanese coastal area as well (ex. Suruga Bay Earthquake in 2009). Therefore, the risk of tsunamis from submarine landslides should be appropriately assessed, particularly in Japan, where the seabed is steep and there are many faults.

 In this study, we apply a 3-dimentinal slope stability analysis model of submarine landslides to reproduce source of the tsunamis which were assumed to be caused by submarine landslides in 2009 Suruga Bay Earthquake. Risk distribution evaluation for submarine landslides is conducted based on bathymetry, soil condition and seismic intensity. Furthermore, a two-layer tsunami simulation are applied to the tsunami reproduction. Consequently, the observed waveform, which could not be explained solely by the fault pattern, was reproduced correctly.

 It is important to conduct a probablility assessment of landlslide tsunami, because dynamics of landslide tsunamis have uncertainties. However, practical applications for probabilistic framework of landslide tsunami have not been well established. The objective of this study is to propose a probabilistic assessment of landslide tsunami for Palu Bay, Sulawesi island, Indonesia. A Monte Carlo approach was employed to randomly generates a large number of landslide source models based on 2018 Palu tsunami data. Numerical simulations of landslide tsunami were also conducted by using the random models. Moreover, the concept of aleatory uncertainty among the probabilistic methods for earthquake tsunami which conventionally used in Japan and expected average interval of the earthquake were used to calculate a tsunami hazard curve. As a result, it was indicated that design tsunami height of 5 m in Palu city equivalent to reproduction periods of 100-200 years.

 Recently, tsunamis associated with 2022 Tonga volcanic eruption also occurred, and the need for volcanic tsunami simulation has been called for. The purpose of this study is to investigate how to reproduce historical volcanic tsunamis with complex generation mechanisms and insufficient observational information. In the past, the landslide model (code: TITAN2D) was used to reproduce 1792 Mayuyama collapse tsunami, but further study is needed on the setting of soil parameters for practical use. We attempted to reproduce the collapse behavior of 1640 Komagatake eruption tsunami, obtained the input conditions for tsunami simulation. Furthermore, the influence of soil parameters on the results was evaluated separately for land and sea areas, with results suggesting what is important for the reconstruction of historical events.

 In addition to the deterministic tsunami assumptions based on historical tsunamis, a probabilistic approach has been developed for hazard assessment by considering large number of tsunami scenarios. In coastal areas where tsunamis are feared to strike, if levees are raised only based on assumed tsunami height, raised levees may affect the daily life, bread-and-butter job, and use of beach. This study evaluated the maximum inundation depth using a probabilistic tsunami hazard assessment method for the southern coast of Tokushima Prefecture, and the efficient coastal levee height was quantitatively estimated by a costbenefit analysis of coastal levee raising considering the future changes in population and business locations in the hinterland. The results show that the net benefit of levee raising is positive in the areas where population and assets are concentrated and industry is developed. It is confirmed that there are some areas where the benefits can be expected even if the temporary height of levee is raised lower than planned height.

 This study proposes an evaluation method including the countermeasures to secure an acceptable survival probability against natural disasters those were tsunami and storm surge along coastal zones. This study showed that the integrated mortality risk can be calculated for multiple water disasters of a wide range by using the method proposed in this study, and the effectiveness of risk integration can be also expressed. In addition, we confirmed that it is possible to set an acceptable risk as a reduction target for integrated risk and to consider appropriate disaster reduction countermeasures according to the reduction target.

 In order to reduce human casualties from tsunamis, it is important to take soft measures in addition to hard measures. For safer evacuation, it is effective to consider the tsunami inundation area and the arrival-time of tsunamis. Therefore, the purpose of this study is to examine an influence of the tsunami arrival-time prediction error on the evacuation behavior. We conducted an evacuation simulation using the numerically calculated values and the arrival time of tsunamis predicted by the machine learning model. In the route selection method used in this study, the mortality rate increased as the evacuation start time became later due to the tsunami arrival time error, confirming the effect on evacuation behavior.