When high waves attack on an artificial reef, a wave breaking can occur around the artificial reef and a large hydrodynamic force can act on an armor block in the artificial reef. In previous researches, it has been reported that armor blocks are intermittently detached for a long time and a rubble stone consisting of a mound are flowed out from an area exposed by the detachement of block due to high waves. For this failure process of an artificial reef, a two-dimensional numerical simulation has been carried out previously, however, because the freedom of the motion of a block or a rubble stone are restricted in 2D field, the process was not perfecly reproduced. Therefore, in this study, we conduct a 3D numerical simulation on the failure process and compare the simulation result to the previous experimental result. In the simulation, the behavior of block which is detached and carried on behind blocks and the deformation of mound are shown well.

 A double parapet seawall is one of the countermeasures against inundation caused by wave overtopping and surge overflow due to storm surges. In order to evaluate the wave overtopping discharge of the double parapet seawall countermeasures, the authors have conducted hydraulic experiments and numerical simulations on irregular waves. The numerical results of wave overtopping discharge was underestimated by one order of magnitude compared to the experimental results. In this study, additional numerical simulations were conducted to clarify the causes of underestimation and to improve the accuracy of the overtopping simulations. The numerical results of the additional simulations show that the overtopping discharge is smaller because of the attenuation of the high-frequency component waves. Next, the effects of parameters such as the mesh size and the coefficient controlling the compression of the interface were examined. It was shown that attenuation of the wave height was reduced by setting the Courant number to 0.125. By setting the optimal parameters and turbulence model, the numerical results of the overtopping discharge were in good agreement with the estimated equation obtained from the experimental results.

 Quantitative knowledge on effect of wave absorbing works to mitigate wave runup height on coastal dikes and revetments is limited, and the height of coastal dikes and revetments with wave absorbing works is usually set by using the reduction rate of required revetment height based on acceptable wave overtopping discharge proposed by Goda. This study evaluates the effect of wave absorbing works on wave runup height, by comparing with the measured wave runup heights by hydraulic model experiments on revetments with wave absorbing works by Matsushita et al. and the estimated ones by Integrated Formula of Overtopping and Runup Modeling (IFORM) by Mase et al. The results show that the reduction rate of wave runup height by wave absorbing works is in the range of 40-80% and increases with wave steepness. Additionally, the results imply that using the reduction rate of required revetment height by Goda may underestimate the wave runup height by wave absorbing works when wave steepness is 0.02 or less and the ratio of water depth to wave height at the toe of revetment is 1 or more.

 This study reproduced the wave run-up of irregular waves under a strong wind blowing condition by using a gas-liquid two-phase flow model (OpenFOAM). The study also examined the applicability of the numerical model by comparing the effect of wind speed on wave run-up height with the results of hydraulic experiments. The numerical model showed that the wave run-up height of irregular waves increases with wind speed, and this phenomenon was observed in previous hydraulic experiments. The frequency distribution of wave run-up height of irregular waves obtained by numerical calculations partially matched the Rayleigh distribution, though there were differences in the peak values. The relationship between the representative values of wave run-up height obtained from the numerical model generally agreed with the relationship obtained assuming the Rayleigh distribution. The numerical model reproduced amplification of propagating waves due to wind actions, but the rise of mean water level due to wind actions was not be able to reproduce.

 To evaluate the hydraulic functions of the wave dissipating work, the resistance law was investigated by numerical calculations. First, as basic hydraulic functions, the reflection and transmission coefficients were measured by carrying out regular wave experiments. The model of wave dissipating work was set up as a rectangular cross-section with square timbers arranged in a regular pattern. Numerical calculations were performed using the numerical wave flume CADMAS-SURF. The linear and nonlinear resistive material coefficients α₀ and β₀ of the Dupuit-Forchheimer law (DF law), which is one of the resistive laws, were determined so that the experimental values are reproduced well. Calculations were also conducted with the square timbers of the wave dissipating work set up as a structure cell.

 Both calculations using the DF law and with square timbers as the structure cell were reasonally confirmed to reproduce the experimental values of the reflection and transmission coefficients. The effect of α₀ on the reflection and transmission coefficients was small, while the effect of β₀ was large. This indicates that the resistance of the wave dissipating works is dominated by the drag force proportional to the square of flow velocity.

 This study proposed a computational method to immerse kinematic and dynamic boundary conditions at ghost-cells within structures having arbitrary surface forms, given by three-dimensional point cloud data. This method was applied to problems of wave-structure interactions which occurred when water waves passed over a submerged breakwater composed by sphere-shaped armor blocks and tetra-pod models. We found fundamental mechanisms of wave energy dissipation through ejection of vortices from the pores before arriving waves and injection of them into the pores when waves passed over the structure. There were steady strong currents through the pores in the structure, which might affect local erosion on sea bed under the structure.

 For modeling of wave-dissipating blocks in simulations of wave overtopping, the so-called porous model has been widely used. The conventional model evaluates the fluid resistance by using semi-empirical experimental constants uniformly over the entire permeable area, and thus local flow velocities inside the block are not considered, resulting in poor reproducibility, especially under wave breaking where complex flows inside the block become more significant. In this study, a new permeable layer model is developed to reproduce the complexity of the local flows between wave-dissipating blocks. It explicitly describes the existence of the shielding area and void channel by distributing a modeled block composed of fixed particles, and simulations are performed by incorporating the model into the particle method, which is superior in reproducing breaking waves. Wave overtopping simultaion on wave-dissipating blocks is conducted to show the reproducibility of the overtopping flow volume, and further, the wide applicability of the model is shown through the simulation of the seepage process through the space between crushed rocks.

 This study deals with the influence of porosity and profile change of wave dissipating block layer on the wave overtopping and reflection by use of irregular waves. Two types of blocks with different porosity and the initial and deformed profile of block layer were used in the experiments and numerical computations. A model profile that consists of the depression of crest and the change of slope gradient was used as the deformed profile of the block layer. As a whole, the larger porosity of the block layer resulted in a smaller overtopping rate and reflection coefficient. Additionally, the overtopping rate increased and the reflection coefficient decreased by the deformed profile, then the difference of the overtopping rate by porosity of block layer became smaller than that in the initial profile.

 Breakwater with submerged mound was developed to secure a place for seaweed to glow, but it would be effective as a method of improving existing facilities in response to climate change. In this study, we aimed to clarify the effect of this structure on reducing wave energy(Reflectance, Transmittance, Overtopping flow rate, Water level rise). Verification was performed using hydraulic model experiments and numerical simulations. As a result, we summarized the knowledge to estimate the effect of wave control from structural and wave conditions.

 It is important to study effects of a transition from wave overtopping to wave overflow by storm surges and storm waves to estimate wave overtopping accurately. In the previous paper, the authors conducted physical modeling on the simultaneous occurrence of the storm surges and the waves on a vertical seawall, clarified the effect of mean water level change on the amount of wave overtopping, and compared the experimental data with the wave overtopping/wave overflow transition model. Although the potentially wave overtopping/overflow transition model can be applied to other seawall slope conditions, experimental data is limited to validate to the others than vertical seawalls. This study conducted experiments for 1:1 and 1:2 slopes, and the revised formula is proposed to estimate the overtopping discharge according to the seawall slopes. In addition, the model’s validity was evaluated by reproducing the experiment using a coupled storm surge, wave, and inundation model. The results showed that the coupled storm surge-wave-inundation model fairly reproduces the transition time series from wave overtopping to wave overflow.

 In this study, we estimated the wave overtopping discharge on airport island seawalls with multi-directional multiple reflection waves using the Boussinesq model (NOWT-PARI) and the direct fluid analysis method (CADMAS-SURF). The incident wave direction was set as the predominant wave direction, and the incident wave height was estimated from the superposed wave height at 0.7 wave length offshore from the seawall in normal direction and the reflection coefficient obtained by Goda's wave separation method. The validity of these estimates was verified by the calculation results using the Boussinesq model with a non-reflective boundary at the target seawall. Since the target seawalls are all multi-sectioned and covered with wave-dissipating structures, the effective crest height for oblique incident waves cannot be directly applied.

 Therefore, we applied the reduction rate of wave overtopping discharge for oblique incident waves, obtained from Goda's diagrams, to the wave overtopping discharge for perpendicular incident waves estimated by the direct fluid analysis method. This approach resulted in good agreement between the two methods, except in the case of alongshore wave overtopping.

 Flume-type anti-oscillation tanks have been proposed to mitigate the wave-induced motion of a towed floating caisson. The effectiveness of such anti-oscillation tanks has been investigated through hydraulic model experiments, field experiments, and numerical analysis requiring the input of physical parameters. In this study, a model that can compute complex behavior of free water in the tank and does not require physical parameters for a floating caisson was developed using the open-source software OpenFOAM and applied to existing hydraulic model experiments. From a comparison with experimental results, the predictive capability of the model was demonstrated in terms of natural periods and amplitudes of the heave and pitch of the caisson. Furthermore, it was found that the anti-oscillation moment induced by the motion of free water in the tank was mainly affected by the pressure acting on the bottom of the tank. This study suggested the usefulness of the developed model in assessing the effectiveness of anti-oscillation tanks.

 In this study, hydraulic model experiments and CFD analyses were conducted to confirm the behavior of a spar-type floating body during upstanding and tipping in the construction of a spar-type offshore wind turbine. Water was pumped or drained into a 1/100 scale model of a floating body, and the trim angle and the maximum acceleration of the floating body were measured. Experiments were conducted under various conditions, including with and without bulkheads and with and without ballast material. When water is pumped or drained with crushed stone or sand as initial ballast, The ballast material collapsed, resulting in a sudden upstanding or tipping, and the trim angle oscillated with a short period, resulting in a maximum acceleration of 0.245G. Numerical simulations were performed without ballast material using a 3-D computational fluid dynamics tool. A spherical moving grid around the floating body was used in the analysis, and the results generally reproduced the experimental results. Furthermore, it was found that the eccentricity of the center of gravity had a significant effect on the upending and tipping behavior of the floating body.

 The automated vacuum mooring system has been installed at Tsuruga Port, which is expected to speed up ships' berthing and unberthing, improve safety, and improve the efficiency of cargo handling by reducing the amount of ship motions. In this study, we conducted on-site demonstration tests on the RORO ships and the ferries and investigated the effects of introducing the system on improving work efficiency and reducing the amount of ship motions. In addition, we calculated the critical wave height for cargo handling of the RORO ship by using simulation of oscillation after verifying the ship motions by the measured value and considered the effect of reducing the amount of ship motions. The conclusions obtained in this study are as follows. (1) Under calm conditions, it was possible to berth the ferry using only the mooring system and fenders, and it was shown that the berthing work could be reduced. (2) The results of on-site demonstration tests and simulation of oscillation showed that it is possible to improve the critical wave height for cargo handling compared to mooring lines by introducing the mooring system, especially for surge, sway, and roll components.

 In this study, an experimental evaluation and reproduction simulations on the tsunami countermeasure using the additional anchor cable for large moored ship have been performed using the model ship as a 90,000DWT class coal carrier suffered by the 2011 Tohoku Earthquake Tsunami, based on revised several water tank tests under tsunami bore as well as our previous study. It was clarified that the slack mooring of the anchor cable as the tsunami countermeasure was restricted under tsunami wave height about 5 meters, and the tesnsion mooring might be considered under higher tsunami wave conditions.

 In this study, regarding a topographic change around a cylinder in a wave-current coexistence field, the authors investigated the reproduction of the phenomenon and its fast computation by a three-dimensional numerical analysis for a large-scale movable-bed experiment under forward current condition. In the analysis, we introduced a time interval Δ_tz for the topographic change that is larger than the time interval Δ_t for the flow, and accelerated the analysis by using the same number of calculations for the flow and the topographic change while allowing the analysis to progress through time in Δ_tz. As a result, under the experimental condition, no difference in scour was observed when Δ_tz/Δ_t was varied from 10 to 100, and the analysis was 100 times faster than the analysis using only Δ_t. In addition, comparison with experiment on the final scour situation showed that the numerical model reproduced the maximum scour position from the front to the sides of the cylinder and the shape of the scour. However, the maximum scour depth in the analysis was two-thirds that of the experiment approximatory, and the model could not reproduce the scour and sedimentation shape at the back of the cylinder.

 The Hydroplane Tsunami Barrier, which can be raised only by hydrodynamic forces, has been developed to prevent tsunamis and other waves from entering through openings in harbors. In order to investigate the behavior of the breakwater in actual conditions, it is necessary to combine a 2D planar tsunami propagation analysis from the wave source to the vicinity of the breakwater and a 3D behavior analysis of the area including the breakwater. In this study, the 2DH3D hybrid fluid-rigid-body coupled analysis method developed by Yoneyama et al. was applied to this breakwater to investigate its applicability as a preliminary step to the actual geometry analysis.

 We verified the accuracy of our method by comparing the analytical results with experimental hydraulic results in 2D and 3D cross-sectional domains. After the verification, we examined the relationship between the specific gravity and scale of the door body and the door body behavior. Furthermore, we showed that the computational accuracy can be maintained while minimizing the computational load by setting the grid spacing finer in the direction of the water depth and coarser in the direction of the breakwater's rise. We also showed that the breakwater works against long-period waves in a three-dimensional flow field where the direction of tsunami propagation and the direction of breakwater erection are orthogonal to each other.

 Recently, it has been reported that tsunami wave force containing bottom sediment increases more than the increment of hydrostatic pressure with the increase of fluid density. On the other hand, there have been few cases in which the relationship between the wave force increase and bottom sediment, density, wave shape, and other factors have been verified. In this study, hydraulic model experiments simulating tsunamis containing sand, silt and clay were conducted to confirm the existence and conditions under which the wave force increases by varying the location and type of structures under controlled conditions of fluid density and water temperature. The relationship between the shape and velocity of the tsunami tip and the maximum wave force was focused on, and the differences between the normal tsunami and those containing sand, silt, and clay were analyzed. The results showed that there were differences in water surface angles and their statistical variations, but no increase in wave force beyond the increment of fluid density was observed at the maximum time, including the maximum wave force.

 It is important to extract energy efficiently from irregular wave energy in wave power generation. In this study, to improve the power generation efficiency in the primary conversion of oscillating water column type wave power generation, hydraulic model experiments with irregular waves were conducted by installing a square cylinder simulating a power generation unit inside a wave-dissipating works formed by wave-dissipating blocks, and the characteristics of water level fluctuations inside the square cylinder were evaluated. The experimental cross sections were two cases, one with full-section covered type and the other with two-layer covered type, and wave height gauges were installed inside the square cylinder to measure water level fluctuations. Comparison of the waveforms between the incident waves and those inside the square cylinder showed that the short-period, low-height irregular waves were reduced inside the square cylinder, it was found that a low-pass filter effect of the wave-dissipating works. Comparison of the wave-forms between the incident waves and those inside the square cylinder showed that the short-period, low-height irregular waves were reduced inside the square cylinder, it was found that a low-pass filter effect of the wave-dissipating works. Comparison of wave spectral figures also confirmed the same effect. Comparison of the mean wave heights clarified that the vertical amplitude fluctuation in the square cylinder increased more than the incident wave height.

 When waves, tsunamis etc. that threaten the stability of port structures attacked, structure behavior prediction method for has not been established. In this study, we aim to evaluate applicability of the fluid simulation that breakwater caisson can move by applying the “fluid-rigid-body interaction analysis method” developed by Yoneyama et al. The results confirmed the following: (1) the fluid force acting on the breakwater caisson using this analysis method can reproduce the existing wave force calculation formula. (2) the breakwater caisson begin to move when Ratio of Strength against Action is 1 or more.

 This analysis method is considered to be a method that can reproduce actual phenomena well even under conditions where the stability of structures is compromised. Thus, it is considered to be one of the useful methods for examining of damage mechanism or disaster mitigation effects.

 According to the 2018 edition of the technical standards and commentaries for port and harbor facilities in Japan, the uplift pressure acting on a pier should be designed at a pressure equivalent to four times the wave height (4_ρgH), which is considered to be the upper limit for a perpendicular-entry case. However, this value is so large that it is difficult to design it . In the case of an actual pier, the wave incidence is often oblique, and Watabe et al. (2003) confirmed that the uplift pressure acting on the pier is smaller than that of a pier with waves entering perpendicularly. However, there have been few studies on the uplift pressure acting on piers with oblique incident waves, and design methods have not been established. However, there have been few studies on the uplift pressure acting on piers with oblique incident waves, and design methods have not been established. In this study, hydraulic model experiments were conducted at several angles of incidence wavs, including direct incidence waves, and the results were analyzed using the new method proposed in this study. As a result, it is clarified that the average uplift pressure over the entire pier decreases to 1/6 to 1/10 of that at oblique incidence angles, depending on the angle of incidence.

 On quay walls where multiple reflections of waves prevail, and continuous seawalls where wave shielding effects affect incident waves on adjacent seawalls, model experiments and numerical calculations, which are conducted by virtually removing target facilities to obtain incident waves, are unable. Therefore, we conducted a hydraulic model experiment using an experimental flume and a reproduction calculation using the Boussinesq model including a wave overtopping model and a wave pressure calculation formula. By applying Takayama’s approximation formula for the design diagrams of wave overtopping rate of vertical seawalls and Goda formula of wave pressure in reverse, the equivalent deepwater wave height, which is the input value of these, was determined by convergence calculation and compared with the known incident wave (equivalent deepwater wave height) at the target facility. As a result, we confirmed that incident waves with different wave heights or periods (equivalent deepwater wave height) can be estimated correctly from wave overtopping discharge and wave force, although these estimates from wave force are slightly underestimated.

 Cavity collapse caused by internal erosion of backfilling sand has occurred frequently at the back sides of coastal structures such as seawalls and quaywalls worldwide. To prevent the internal erosion-induced damage, it is crucial to detect cavities under the pavement at an early stage. In this study, prototype-scale model experiments were conducted to investigate the effects of asphalt and concrete pavement types and thickness on the accuracy of cavity detection using a ground-penetrating radar (GPR). The results showed that the type and thickness of the pavement greatly affected the detectable depth of the cavity using the GPR. It was difficult to detect cavities when they were formed and developed deeper than 1 m below the pavement surface, depending on the type and thickness of the pavement. In addition, by comparing and verifying the obtained GPR signal patterns at a certain periodic interval under the pavement, it was possible to accurately detect and identify the depth of cavity development at an early stage, namely from 1.0 m or deeper below the pavement.

 As a countermeasure against coastal internal erosion of ground behind seawalls and quay walls, a method using a two-layer filter, i.e. upper filter layer to prevent internal erosion of backfilling sands and lower filter layer with relatively large grain size to keep stability on backfilling stones, has been developed and put into practical use. The purpose of this study is to investigate the application of the above method to the restoration of the cavity collapse caused by coastal internal erosion. Two restoration methods were devised, depending on the depth of the location of washout, as follows. In the case of coastal internal erosion occurring deeper than the low-tide groundwater level, the two-layer filter is filled into the sinkhole due to the cavity collapse in the form of the lower filter layer being surrounded by an upper filter layer with appropriate layer thickness. On the other hand, in the case of coastal internal erosion occurring at a relatively shallow depth and when the ground around the location of washout is unsaturated during low tide, the two-layer filter is placed to cover the origin of the coastal internal erosion by excavating the residual backfilling sand in the sinkhole during the exposure period. Prototype-scale visualization tests showed that the two-layer filter with appropriate grain sizes can prevent recurrence of coastal internal erosion even under strong hydrodynamic forcing in both restoration methods.

 The seaward side of coastal dike is more vulnerable to high waves than the landward side because it is greatly affected by scouring in front of coastal dike. Therefore, designing resilient structures of coastal dike against high waves requires to estimate topographic changes in front of coastal dike. Hydraulic experiments, which are a method to estimate scouring depth, are difficult to conduct under many conditions because they are expensive and time consuming.

 In this study, we calculated wave-induced topographic changes in front of coastal dike using a three-dimensional coupled fluid-structure-sediment interaction model. The accuracy of the calculation was verified by comparing the calculated scouring depths and the measured scouring depths in large-scale hydraulic experiments. The results show that vortices and the maximum scouring depths in front of coastal dike can be well reproduced with the model.

 Bottom-mounted offshore wind power generation unit has a tower to support windmill. The tower on the sea bottom has risk of local scouring around the base of the tower by wave and currents, and scour protection works are installed around the tower as the countermeasure against the instability of the tower due to local scouring.

 This paper describes a study on the stability of scour protection works around the tower based on the results of wave tank experiment and numerical simulation.

 In the wave tank experiments, the damage level of scour protection works is investigated under several different conditions of wave height, wave period and current velocity. It is found as the experimental results that the wave condition with low depth-wavelength ratio have a higher possibility of the damage level of scour protection works.

 Three-dimensional numerical simulations have been conducted by using OpenFOAM, and the distributions of flow velocity and wall shear stress are obtained under the simplified wave and current conditions. Through comparisons between experimental and numerical results, it is indicated that the damaged area of scour protection works in the experiments have an association with the distributions of flow velocity and wall shear stress derived by numerical simulations.

 In raft-style oyster farming, oysters are suspended from rafts formed by multiple bamboos. Rafts have been damaged from typhoons, which is having a negative impact on ship navigation and the marine environment. Therefore, rafts made of highly flexible PE pipes have been developed with the aim of improving wave resistance. It is also expected to improve the growth of oysters. Therefore, we compared the raft's wave resistance and oyster growth performance with bamboo. A time-domain analysis was performed to comparatively evaluate the bending stress generated in regular waves. We also evaluated the durability of the PE raft during stormy weather. These results showed that PE was more durable than bamboo and had better growth performance for oysters. Furthermore, the PE rafts were also found to be more durable in stormy weather.

 The objective of this study was to determine the characteristics of seaweed attachment on floating structures constructed with the drifted pumice at the depth of 0-2.5 m. Blast furnace cement, tap water, and drifted pumice were mixed in a weight ratio of 1:0.5:2.2 to produce the pumice blocks (10 cm height, 10 cm diameter). The field experiments were conducted in Nagashima-cho, Kagoshima Prefecture. The pumice blocks were placed on Nov 13, 2023. After 22, 38, 58, 71, and 85 days of installation, the pumice blocks were collected. Wet weight of seaweed adhering to the top, side, and bottom of the pumice blocks was measured. The amounts of seaweed attached to the pumice blocks placed on the sea surface were highest at a depth of 0 m after 58-85 days of immersion, with seaweed densities ranging from 1.66-2.15 g/cm² on the top, and 0.19-0.29 g/cm² on the sides, decreasing to 0.10-0.17 g/cm² on the top, and 0.02-0.05 g/cm² on the sides at a depth of 2.5 m. The illuminance was highest at 0 m depth, and decreased with the depth. It is suggested that the pumice blocks are placed at a depth of 0 m for most suitable seaweed attachment.

 This paper examines the impacts of liquefied sediment flows on subsea structures through a series of centrifuge model tests. Additionally, a numerical analysis of a high-density liquid flow based on the Navier-Stokes equation was conducted to compare with the experimental results. A series of gravity flow experiments was performed under a centrifugal acceleration of 50 gravities, by varying the initial thickness of collapsed sediment and the distance from the sediment collapse point to the structure. The experimental results showed that immediately after the liquefied sediment flow impacted and acted on a subsea structure, the impact pressure rose rapidly and reached its peak, with the peak increasing with greater thickness and shorter distance. The predicted impact pressures obtained from the analysis considering the density of the liquefied gravity flow quantitatively matched the observed ones from the centrifuge experiments, indicating that the liquefied sediment flow acts on subsea structures as a high-density fluid that has a specific density of the liquefied flow. These results may facilitate the stability assessment of a subsea structure against liquefied sediment flow.

 Wave-seabed interaction models have been developed to assess wave-induced seabed responses. Although most of them employ a one-way coupling scheme, in which pressure computed from a wave model is applied to a seabed model, only a limited number of models employ a two-way coupling scheme, in which the feedback calculation is performed from the seabed model to the wave model. To investigate the effects of these two coupling schemes, a wave-induced response of the sandy seabed around a submerged breakwater and a composite-type breakwater was simulated using PORO-FSSI-FOAM, which enables both one-way and two-way coupling schemes. From numerical results, it was found that not only bottom flow velocity but also pore-water pressure and effective stress were affected by the coupling schemes. Furthermore, the difference between one-way and two-way was larger for the seabed with high permeability. This suggested that the two-way coupling scheme is essential for wave-seabed interaction models.

 In light of the ongoing global coral bleaching crisis, the mesophotic zone (MPZ) at depths of 30 to 150 meters, where water temperatures are relatively stable, is expected to serve as both a refuge and a resupply source for shallow-water coral genetics. To facilitate the establishment of a desirable coral ecosystem, this study employed a high-resolution ocean model for the coastal area around Okinawa Island, Japan, to investigate the advection-dispersion processes of coral larvae. A Lagrangian statistical analysis was conducted to evaluate the three-dimensional transport and population connectivity of the modeled virtual coral larvae between shallow areas and MPZs. The findings indicate that the degree of coral connectivity varies significantly depending on topographical features. Notable observations include asymmetry in coral connectivity between the east and west coasts, driven by the residual clockwise current around the island. Enhanced selfrecruitment was evident in shallow areas around the semi-enclosed Kin and Nakagusuku Bays, while significant accumulation occurred in both shallow and deep MPZ areas of the more open Nago Bay.

 We developed a double-nested downscaling oceanic circulation model with wave-current interaction coupled with a coral polyp model, that models photosynthesis, respiration, and calcification processes in coral reef ecosystem, for analyzing the impact of 11 typhoons that passed through in 2011 and 2012 on the flow field and coral reef habitat in reef areas on the coast of Okinawa main island, Japan. Bottom shear stress during typhoons in 2012, the year in which the overall coral reef coverage decline occurred, was greater than that caused by typhoons in 2011, suggesting that strong waves and currents caused by typhoons have contributed to the destruction and detachment of the coral reefs. The photosynthetic rate, respiration rate, and calcification rate of the coral reef ecosystem after the typhoon season were also weaker in 2012 than in 2011, suggesting that the habitat environment have been more severe for the coral reef ecosystem than the previous year.

 The hydrodynamics and water quality of the Seto Inland Sea (SIS) are strongly influenced by oceanic waters. In this study, we aimed to precisely extract oceanic influences by focusing on salinity as a conservative tracer and conducted a salinity budget analysis for the entire SIS using a long-term reanalysis data set based on a 3D ocean circulation model. The salinity fluxes through the strait transects were influenced by the Kuroshio path and exhibited a high degree of correlation with volume flux. This resulted in an increase in inflow from the Bungo Channel during winter and a decrease or outflow in summer. The changes in total salinity in the eight sub-basins also demonstrated a pronounced correlation with salinity fluxes. In particular, in the sub-basins west of Hiuchi-nada Sea, total salinity was found to increase with the salinity influx at Bungo Channel and decrease with the outflux. In contrast, in the eastern sub-basins, the salinity flux fluctuations were weaker than in the western sub-basins, indicating a notable east-west deviation. This includes smaller tidal residual currents and a lesser influence from the Kuroshio.

 The outflow process of harmful red tide Chattonella from Katakami Bay in the northwestern part of the Harima-nada Sea to the Bisan-Seto Sea area was investigated using actual measurements and a numerical flow model. The distribution of red tide was investigated in the bay and surrounding coastal area at least twice a month from June to August from 2018 to 2023. Although the timing of occurrence was different, red tide occurred in the bay in each year. In 2018, 2018, and 2023, runoff from the bay to the coastal area was observed, and before the runoff, river flow had increased due to rainfall. In particular, in 2018, due to the influx of freshwater caused by “2018 western Japan floods”, red tide reached the aquaculture fishing grounds of Bisan Seto, more than 50 km away. When Lagrangian particles were generated and tracked in the bay under the same conditions at the same time, they showed a distribution similar to the actual measurement results, suggesting the transport of harmful red tide across the Bay due to rainfall and flooding.

 The effects of long-term changes in surface heat flux and open water fluctuations on the water temperature in Tokyo Bay were investigated. Firstly, we developed a method to estimate the surface heat flux over Tokyo Bay, and focused on the equilibrium water temperature as an indicator of the effect of long-term changes in the surface heat flux. We find that the equilibrium water temperature tends to increase at the same level as the surface air temperature. We also reveal that not only longwave radiation but also shortwave radiation is responsible for the increase of the equilibrium water temperature. Secondly, the hydrodynamic simulations around Tokyo Bay were conducted for the recent period (2010-2020). The changes in open water temperature levels in the first and second half of this period may have influenced the winter surface water temperature fluctuations in Tokyo Bay.

 No examples of seawater CO₂ partial pressure observed over time in Osaka Bay, so it is necessary to estimate CO₂ partial pressure from TA, pH, and DIC based on the carbonic acid equilibrium relationship to understand long-term changes in the CO₂ absorption capacity of the bay area. In this study, seawater samples were collected from the coasts of Osaka Bay to verify the accuracy of CO₂ partial pressure estimation, and the CO₂ absorption capacity of Osaka Bay since the 1980s was determined from environmental statistical data. Comparison of the estimated values obtained by varying the combination of observed variables and the dissociation constant model with the measured values showed that the accuracy of estimates using TA decreased by up to 12% in estuarine areas affected by urban drainage, and the estimated values varied by up to 5.6% depending on the dissociation constant used for the same seawater. On the other hand, the overall CO₂ absorption capacity of Osaka Bay is increasing, not only in the inner part of the bay, which is known to have a high absorption capacity, but also at the mouth of the bay.

 To study the conditions of the characteristics of the sampling region under which tsunamis carry large amount of silty sediment, we referred the results of the previous survey. The relationship between the fine fraction content and indexes representing the characteristics of the sampling region were evaluated. The population density, enclosed index and river distance were selected as the indexes to represent the characteristics of the sampling region. The enclosed index was also taken into account the effect of ports. Through a hierarchical cluster analysis, the sampling regions with high enclosed index or population density and close river distance were classified as clusters with relatively large fine fraction content. The model that uses selected indexes to estimate the fine fraction content was suggested. Bayesian linear regression reveals the causal relationship between the fine fraction content and the explanatory variables multiplied by population density and enclosed index. These results demonstrate that the enclosed index and population density can be utilized as the indexes for quantitatively identifying regions where tsunamis are likely to carry large amount of silty sediment.

 Oxygen production in the photosynthetic process of phytoplankton coded in some biochemical models is limited by surrounding nutrient concentration, which does not directly affect oxygen production in the actual process. This study examined the validity of applying a model-process-modification using four-dimensional variational data assimilation method for Osaka Bay, and propose this approach as one of model improvement techniques driven by observations and data assimilation. The oxygen production-growth ratio parameter was defined as a state variable, and initial field estimation was conducted to evaluate the relationships between the parameter and other state variables. The assimilated results showed that the oxygen production-growth ratio was increased while dissoleved inorganic nitrogen decreased. The results partly support the validity of the modification of primary production in our model.

 As the measures to mitigate global warming have been internationally promoted in recent years, blue carbon has attracted attention as a source of carbon dioxide absorption. Several methods have been proposed to clarify the amount of carbon dioxide absorbed by seaweeds and seagrasses. However, the detailed contribution of each significant component has not been revealed. In a previous study, the parameter values of the DIC equation were estimated from laboratory experiments using eelgrass in Lake Komuke, Hokkaido, Japan. Still, the sensitivity to water temperature was evaluated too excessively. Our new DIC equation shows that water temperature may not significantly affect carbon emissions on respiration. In addition, the newly obtained parameter values were used to estimate the annual carbon dioxide uptake and compared with the previous studies, and the results were favorable. Furthermore, the box model was used to estimate the change in DIC within Lake Komuke, which allowed us to assess carbon absorption by the substantial eelgrass.

 In the Seto Inland Sea (SIS), despite the decrease in the inflow of chemical oxygen demand (COD) originated from terrestrial areas, the achievement rates of the environmental standards have been low. COD in SIS can originate from terrestrial areas, primary production, and the open ocean. Several studies have been conducted on COD for each originated source in SIS; however, COD composition for each originated source has not been revealed. It is nevertheless necessary to understand and quantify the sources of COD in order to clarify the limit of controllable COD in SIS. In this study, we analyzed the distribution and composition of COD by using a three-dimensional flow and water quality simulation with an ecological model, which classified organic matter into the terrestrial area, primary production, and the open ocean. The results showed that COD originated from terrestrial areas was mainly distributed around the estuary, and was rarely seen in offshore areas. COD originated from primary production was transported over a wide area not only the local area but also adjacent areas by advection and diffusion, and accounted for at least 30% of the total COD. COD originated from the open ocean was almost uniformly distributed within SIS (about 0.67 mg/L), accounting for at least 30% of the total COD. Based on these results, it is necessary to consider measures for COD management in SIS after understanding the amounts of COD originated from primary production and the amounts of COD originating from the open ocean.

 Coastal development has been underway with one of the objectives to prevent disasters and has resulted in changes to the wave field. Also, the changes may have affected oceanic flows since there are many effects of wind-waves on the flows, such as wind-wave-driven vertical mixing at the sea surface. In this study, numerical simulations have been conducted using an ocean-wave-water quality coupled model where the interactions between wind-waves and flows are taken into account. The calculation results showed that wave heights in the coastal area were decreased due to reclamations and harbor tranquility was improved. In addition, the decrease in wave heights weakened the vertical mixing of water through a decrease in turbulent kinetic energy and turbulent length scale at the sea surface. This effect due to wave field changes was not represented in the calculation without wave model coupling. Furthermore, the weakening of wave-induced vertical mixing in the coastal area prompted hypoxia.

 Understanding the spatial distribution (canopy height and biomass) of seagrass meadows is important for improving and utilizing the various environmental values of seagrass meadows. However, conventional survey methods for the spatial distribution of seagrass face the challenge of achieving both efficiency and accuracy. In this study, point cloud data analysis methods using a UAV equipped with a green laser scanner were applied to two seagrass meadows with different vegetation and environments (eelgrass beds in Hokkaido and subtropical seagrass beds in Okinawa Prefecture) to estimate the spatial distribution of seagrass meadows. In the subtropical seagrass meadow, the measured vegetation height was 16 ± 4 cm (mean ± SD), while the analyzed height was 17 ± 2 cm. The Cloth Simulation Filter was suitable for the analysis of the eelgrass beds (R² = 0.74, RMSE = 0.11 m). The spatial volume of vegetation estimated from the point cloud data was positively correlated with the wet weight of the vegetation. The slope of the regression equation differed between the two seagrass beds depending on differences in canopy height, shoot density and other factors.

 The purpose of this study is to clarify long-term changes in organic carbon content in two seagrass beds in Hiroshima Bay, The distribution range of seagrass varied and competing seaweeds were distributed in Jigozen, however there was almost no change in the distribution range of seagrass in Kojiro. The total organic carbon content in the sediment was high in areas where seagrasses were distributed, suggesting that the distribution of competing seaweeds also had an influence. The amount of total organic carbon in seagrass did not differ between sites, and seasonal fluctuations were greater in the rhizomes and roots than in the leaves. Seasonal fluctuations in the persistent organic carbon content in Jigozen were small, however it increased from May to August 2021 in Kojiro, when seagrasses flourish. The organic carbon content in the sediment in seagrass beds in Hiroshima Bay was influenced by the distribution of seagrass and/or seaweeds.

 The purpose of this study was to determine the biomass, production rate, and growth characteristics of reed over a nine-year period in Yodo River brackish salt marsh. Furthermore we conducted decomposition rate of leaves and steams to evaluate outfolw and decomposition in the carbon budget. The biomass of reeds have seasonal and annual variations, increased from spring to summer and decreased in winter. The growth and decomposition rate of reeds were high from spring to early summer. The decomposition rate of leaves and stems was correlated with soil temperature, and the decomposition rate of leaves was higher than that of stems, but all leaves were decomposed throughout the year, while stems remained undecomposed. The carbon storage rate of reeds, including production, respiration, outflow and decomposition processes, was 627 gC/m²/year, and the annual carbon storage rate in the saltmarsh investigated was estimated to be 26.3 tC.

 In coastal areas, organic matter (biogenic organic matter) produced and decomposed by plants, benthic animals and other organisms (biological activity) is deposited as bottom sediment. The elemental composition of organic matter in bottom sediments varies in a complex manner depending on biological activity, and understanding this variation may lead to the estimation of biological habitats. In this paper, changes in carbon and nitrogen composition (C/N ratio changes) due to biological activity were investigated based on redfield ratios. Bayesian inference machine learning was used to estimate C/N >12 in biologically active sites (where nutrient uptake by organisms is predominant) and C/N <8 in sites where undecomposed sediments (organic matter immediately after inanimate matter has been converted by mortality, excretion, etc.) accumulate. The results of this study show that the C/N ratio distribution of the coastal sediments can be used to evaluate the ecosystem in small areas of the coastal zone with different flow fields, and to identify areas of accumulation of undecomposed sediments and areas of high biological activity.

 In this study, monthly reed sample surveys were conducted from June 2023 to January 2024 to evaluate the carbon storage and sequestration in reed colonies at an artificial salt marsh (Osaka Nanko bird sanctuary) constructed in an urban waterfront area. As a result of measuring the size, biomass, and carbon content of each part of the reeds, it was found that the dry weight of the above-ground part of the reed was highly correlated with the product of culm height and terminal stem diameter. In addition, the total carbon content according to combustion analysis was 42% in the aboveground part, 40% in the dead bodies, and 38% in the underground roots, of which 39% in the aboveground part, 60% in the dead bodies, and 45% in the underground roots are persistent components.

 Based on the results of this survey, the annual growth rate of the reed community at Osaka Nanko bird sanctuary was estimated to be 1,638.4 dry-g/m²/yr, the amount of carbon storage was estimated to be 691.4 g-C/m²/yr, and the amount of carbon sequestration was estimated to be 272.0 g-C/m²/yr.

 Hard clams (Merterix lamarckii) are an important fishery resource fished in Japan. However, the catch amount fluctuates widely from year to year, and in some areas the amount is zero. Therefore, the relationship between the physical environment during the spawning and floating periods, which are important for the survival of hard clams, and the catch amount was examined using the FORA and results of long-term wave hindcast based on JRA-55.

 For the spawning of hard clams, low water temperatures and the occurrence of coastal upwelling are important factores, and a flow environment that allows the larvae to settle on the bottom is necessary. The favorable water temperature and current environment must continue for several years in order to increase the catch amount of the hard clams. The low catch on the Miyazaki and Ishikawa coasts may be due to high water temperatures, low occurrence of coastal upwelling, and a lack of suitable flow environments during spawning season.

 The purpose of this study is to evaluate the fish gathering on seaweed beds, fish reef seagrass bed and sediment area using environmental RNA/DNA in Hiroshima Bay by comparing with monitoring data by stationary cameras. In the artificial seaweed beds, fish reef blocks, seagrass bed, and surrounding sediment area in Shinto, Iwakuni City, Yamaguchi Prefecture, the average population of Sebastes inermis was higher than other fish species, however it was about one-tenth compared to September 2018 to December 2021. There was a positive correlation between DNA copy number and possibility of appearance of Sebastes inermis in artificial seaweed beds and sediment areas. However no correlation with RNA copy number could be confirmed. When fish were not detected, RNA was more often undetected than DNA, and environmental RNA was more accurate. The possibility of appearance of fish was low, it was not possible to quantitatively evaluate fish gathering in the oscillatory flow using environmental DNA and/or RNA in the oscillatory flow.

 To reveal the structure of gently sloping revetment that are suitable for crab habitats, we conducted a survey of crabs on different types of south-facing gently sloping revetment at the mouth of the Yoshino River in the summer of 2023. Crabs live in gaps in revetment, and the number of crabs and the distribution of carapace width varied depending on the characteristics of the gaps. For example, the majority of crabs on the revetment with narrow gaps were small, whereas on the revetment with wide gaps, the proportion of medium- and large-sized crabs was higher. Revetment with diverse gap widths and structures have the highest number of crabs, and crabs with various carapace widths were observed, making them suitable habitats for crabs. In addition, when the temperature reached a high temperature, crabs spent less time on the surface and took shelter in the cooler gaps. It was found that the habitat function for crabs differs depending on the shape of the revetment, and that the function of mitigating the effects of high temperature and dryness is particularly required in the summer.

 This study developed a framework for infrastructure assessment, including green infrastructure (GI) and gray infrastructure (GyI), and examined the impact of coastal infrastructure on humans and nature. The results of the survey showed that the well-being was related to the size of the hazard, and the smaller the hazard, the higher the level of satisfaction. The results also indicated that there is a limit to the level of satisfaction that can be obtained through urbanization, and that GI ecosystem services may lead to higher levels of satisfaction. The results of this study suggest the importance of considering the balance between GI and GyI in terms of both well-being and natural demand.