In recent years, the efficiency of work accompanying work style reform has become an issue, and dead-weight-type riprap leveling has been adopted for riprap leveling. However, there is a concern that the flow on the rubble mound caused by the falling dead-weight will scatter small rubble stones on the top surface, reducing work efficiency. As a countermeasure, we focused on reducing the generated flow velocity by providing holes in the weight. The purpose of this study is to clarify the phenomenon of the flow velocity generated by the dead-weight riprap leveling with the improved weight by examining model experiments, numerical calculations, and field demonstrations. From the measurement of the generated flow velocity in model experiments and the results of numerical calculations, it was found that by dispersing the flow into the upward flow, the horizontal flow, the flow that permeates the permeable structure, and the generated flow velocity could be reduced. The field demonstration tests of the implemented construction also confirmed that the generated flow velocity was reduced.

 Material transport in oceans is important for understanding e.g., distributions of microplastics and formations of marine environments. In order to investigate transport processes in the Japan Sea, this study conducted oceanic numerical simulations using the Regional Oceanic Modeling System with a Lagrangian particle tracking model. Particles were released from the Tsushima Strait in four seasons . Modeled results were validated with publicly available obsered surface drifter data (GDP). The GDP data are consistent with our numerical simulations, which implies that our regional numerical model well reproduces transport processes in Japan Sea. Particles released in winter and fall tend to distribute over a wide area, while those released in spring and summer are distributed along the coast. Submesoscale eddis enhance particle dispersions in th winter season.

 Towards sustainable conservation of eelgrass (Zostera marina) habitats in the Seto Inland Sea (SIS), a long-term numerical reanalysis was conducted with a high-resolution ocean circulation model coupled with a floating buoyant eelgrass shoot (viz., seed) transport model. A Lagrangian analysis quantitatively evaluated the population connectivity among eelgrass habitats considering their overgrown areas. A multigenerational connectivity evaluation model was then formulated based on Markov chains to investigate extensive, inter-basin shoot exchange among perennial eelgrass in the SIS over a period of nine years (nine generations). Although self-recruitment within the interior of the subbasins (bay and sea/nada) is predominant in a single year (one generation) connectivity, eelgrass shoots were found to pass over the straits and to expand their habitats to remote areas across generations. On the other hand, the Kurushima Strait plays a pivotal role in lateral shoot transport, segmenting the eelgrass habitats in the SIS zonally into two parts.

 While coral bleaching has been progressing worldwide in recent years, an extensive bleaching event occurred in 2016 around the Ryukyu Islands. Coral ecosystems inhabiting in the mesophotic zone (MPZ) at intermediate depths of 30 m–150 m, where water temperature is more stable and colder than that in the shallow-water zone (SWZ), are expected to serve as refuges for coral genotypes in the SWZ that has suffered from pronounced bleaching due primarily to high water temperature. However, the structure of the ecosystem linkage between the SWZ and the MPZ is still poorly understood. Therefore, we conducted a numerical analysis using a triple nested high-resolution ocean circulation model coupled with an offline 3-D Lagrangian particle tracking model that represents coral larval dispersal to evaluate population connectivity between the SWZ and the MPZ, to identify the relationship between vertical mixing effects in surface mixed layer duing the larval spawning period, and to examine the larval recruitment and their supply near the Sesoko Island at the west coast of Okinawa Island, where mesohotic corals have been observed.

 Hypoxic water masses have often been observed in the coastal area at the head of Osaka Bay and many studies have been conducted on its behavior. However, the relationship between wave conditions and hypoxia has not been clarified. In this study, the analysis of field observation data of water quality and wave conditions at Kobe Port was carried out. The results showed that there is relationships between wave height and variation in dissolved oxygen (DO) concentration. Numerical simulations were conducted using the three-dimensional flow-water quality-wave coupled model. In this model, the length scale of the surface-injected turbulence is related to the significant wave height and imposed as a surface boundary condition for turbulent mixing length. The model successfully reproduced the DO concentration and the numerical results suggested that wind-waves contribute to improve hypoxia through enhancing vertical mixing of seawater.

 In this study, we focused on the circulation of sulfides, iron, and manganese in the enclosed water area of Tokyo Bay. We conducted field observations and numerical analysis using a three-dimensional coupled model of the pelagic and benthic systems. Through load surveys of rivers, we created a quantitative formula for the forms of Fe and Mn in the Arakawa and Tama rivers and calculated the load of each river. Additionally, analysis of water and sediment samples in the bay revealed an increase in P_-Fe in the anoxic bottom layer where H₂S was present, suggesting that the formation of oxidized iron resulted from the reaction between H₂S and Fe²⁺. On the other hand, D_-Mn was found to be highly concentrated due to leaching from the sediment under anoxic conditions (ORP <-200 mV). In the analysis using the three-dimensional coupled model, there are challenges such as overestimation of H₂S in sediments and underestimation of D_-Mn in the water column. However, the model was able to generally reproduce the vertical distribution of DO, D_-Fe, H₂S in the water column, and D_-Fe, D_-Mn in the sediment.

 Material conservation is an important constraint in biogeochemical cycle analysis using numerical models. To assimilate data from a coastal physical-biogeochemical coupled model while ensuring material conservation, we implemented a four-dimensional ensemble variational method (4DEnVar) as a general-purpose method in the Regional Ocean Modelling System (ROMS) and evaluated the usefulness of 4DEnVar. Assimilation of sea surface temperature (SST) from the Japanese geostationary meteorological Himawari8 satellite, and temperature, salinity, chlorophyll-a and dissolved oxygen (DO) observed by monitoring posts, confirmed the improvement of the reproducibility of both physical and biogeochemical fields. In the future, we will study the correction with spatio-temporal distribution.

 The objective of this study was to determine the characteristics of seaweed attachment on floating structures constructed with the drifted pumice. 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 (15 × 15 × 5 cm). The field experiments were conducted in Nagashima-cho, Kagoshima Prefecture. 60 pumice blocks were placed on Nov 4, 2022 on the sea surface and seafloor, respectively. After 13, 27, 39, 67, 88, and 109 days of installation, 10 pumice blocks were collected from sea surface and seafloor, respectively. Wet weight of seaweed adhering to the top, side, and bottom of the pumice blocks was measured. The average amounts of seaweed attached to the pumice blocks placed on the sea surface were significantly higher than those placed on the sea floor. After 13 to 39 days, Enteromorpha sp. was observed on the top surfaces of the pumice blocks. Attachment of Ulva sp. was observed on the pumice blocks after 67, 88 and 109 days. The highest amounts of Ulva sp. were observed on the sides of the the pumice blocks placed on the sea surface. Installing the pumice blocks on the sea surface was expected to promote seaweed growth, which receives more solar radiation than the seafloor, and avoid covering by the sand after placing in the sea.

 This study was conducted to investigate the CO₂ flux at surface sea water of the Hyogo Canal over a 24-hour period and to evaluate the carbon storage of primary producers such as maicrophytobenthos, phytoplankton and Zostera marina. CO₂ was absorbed from the atmosphere to the water at surface sea water in four 24-hour investigation. The daily CO₂ absorption rate was estimated to be 260-736 mgCO₂/m²/day. The biomass of Z. marina was the most abundant among primary producers. The carbon storage rate of phytoplankton was similar to that of the sea surface, and the amount of carbon storage by phytoplankton was the largest with considering habitat area of each primary producer. On the other hand, the daily water quality fluctuation was small. These results suggested that the carbon storage of the canal is maintained by seawater exchange.

 The purpose of this study was to clarify the temporal variation of simultaneous and continuous observations of atmospheric and water surface CO₂ fluxes in brackish salt marsh. Atmospheric CO₂ flux was larger fluctuations than water surface CO₂ fluxes, with larger absorption from spring to summer. Water surface CO₂ flux was a small temporal variation, and emission during most of the day except for winter. Atmospheric CO₂ flux were highly influenced by solar radiation during the daytime and vertical wind speed during the nighttime, while water surface CO₂ flux were influenced by water temperature, tide level and discharge during both daytime and nighttime. These results indicate that the seasonal variations of atmospheric and water surface CO₂ fluxes in brackish salt marsh during day and nighttime are related to the meteorological conditions.

 There are two artificial reefs on the Iburi coast, Hokkaido, Japan. One is located off the coast of Shiraoi, where aggregations of Sabellariid polychaetes grow, and the other off the coast of Tomakomai, where this species is not found. We assessed and compared the characteristics of the bottom sediments of these two artificial reef areas. As a result, the silt and clay content rate in the seawater around the Tomakomai's artificial reef was 2.8 times higher than that around the Shiraoi's one. Laboratory experiments were carried out to investigate the ability to form the tube and the survival rate of this species in two different conditions. One is where the tube is buried in the bottom sediment and the other is where the tube stays in the suspended sand. The results showed that the survival rate of this species decreased significantly as the silt and clay content rate and the tube's burial depth increased. When the rate of sediment deposition into the tube exceeded the growth rate of the tube, it was speculated that this species died in it. The inhabit limit of this species was estimated using the estimating equation for the floating sand concentration in the breaker zone, which showed that the Tomakomai's artificial reef was an environment where the survival of this species was difficult.

 In order to develop a practical model of the attenuation effect of coastal vegetation, such as mangroves, on tsunamis and waves under various topographic conditions, researchers must focus on two key factors. Firstly, developing a three-dimensional model capable of handling breaking waves and turbulent currents is important. Secondly, it is essential to establish a modeling method that keeps computational costs low. Yoshida et al. (2022) showed that a mangrove forest could be modeled using the Dupuit-Forchheimer law (hereinafter referred to as the DF law) and that valid calculation results can be obtained even with a grid size about four times larger than the thickness of a mangrove tree trunk by appropriately setting the resistance coefficients. Therefore, this study aims to investigate the influence of the resistance coefficient and the grid resolution of the numerical model in applying the DF law on the accuracy of tsunami wave height attenuation reproduction for several experimental cases. As a result, the experiment could be reproduced regardless of the lattice resolution. The wave height attenuation effect by mangroves in the experiment was reproduced in the calculation using the DF law.

 The mortality rate of Pacific oysters cultivated in Hiroshima Bay has consistently remained elevated. Various factors, including elevated water temperature, decreased salinity, competition with other organisms, and depletion of oxygen from bottom sediments, have been proposed as potential causes of the oyster mortality. However, a definitive cause has yet to be established. This study aimed to address this gap by conducting a five-year field experiment to determine oyster mortality rates and investigating the relationship between water temperature, salinity, and oyster mortality in Hiroshima Bay spanning the years 1988 to 2020.

 The findings of this study indicated that the main causes of oyster mortality were a decrease in dissolved oxygen at depths of approximately 10 m and an increased number of spawning events triggered by high water temperatures at depth of approximately 0.5 m and 5 m. The mortality rate was higher in years with high accumulated surface water temperatures since 2000.

 In order to find a way to deal with the problem of less shade and less biodiversity on the gently sloping masonry revetment, a survey was conducted on the relationship between solar radiation and the distribution of intertidal organisms on the gently sloping revetment of the Yoshino River brackish water area in the summer. The amount of solar radiation on the south-facing revetment at the survey site was approximately 1.4 times that of the north-facing revetment, and it was found that the south-facing revetment is strongly affected by solar radiation, tends to dry out, and has a high surface temperature. Correspondingly, the number of species and the coverage of the organisms on the surface of the revetment were smaller on the southfacing side than on the north-facing side. On the other hand, since the moist environment is maintained in the revetment gaps, even on the south-facing revetments, the number of species and the degree of coverage are higher than on the surface, and the seaweed (Caulacanthus okamurai) can also grow. In order to reduce the influence of solar radiation on gently sloping revetments and increase biodiversity, it was shown that it is important to appropriately provide gap structures that can maintain a moist environment.

 The effects of dissolved inorganic nitrogen (DIN) inflow from rivers, DIN concentrations in Osaka Bay, and bivalves on oligotrophication in Harima-nada Sea were analyzed over one year by using a benthic-pelagic coupled ecosystem model. The analysis showed that an increase in DIN inflow from rivers and an increase in DIN concentration in Osaka Bay increase the amount of DIN discharged out of Harima-nada Sea and the amount of DIN consumed in Harima-nada Sea in terms of the annual nitrogen budget. However, an increase in bivalves increase the amount of DIN discharged in Harima-nada Sea, and increased the amount of DIN produced within Harima-nada Sea. All three measures increased DIN throughout the four seasons, and an increase in DIN inflow from rivers increased DIN in the surface layer of the Hyogo Prefecture coast, especially in summer, while an increase in bivalves reduced red tide especially in summer and autumn.

 Climate change mitigation consists of three functions: absorption of atmospheric CO₂ by the ocean, fixation of absorbed carbon through biological production, and sequestration of fixed carbon in deep sediments. Marine organisms, which are responsible for biological processes, are also affected by acidification. In this study, an ecosystem model that mechanistically understands, predicts, and evaluates these processes was applied to Tokyo Bay to analyze the interannual changes in climate change mitigation functions and their factors from the present day to the future (2000~2100 A.D.) in the urban coastal area based on changes in water temperature and atmospheric CO₂ under the RCP8.5 scenario. The results showed that (1) absorption increases after 2040 A.D. due to an increase in total alkalinity (TA), (2) fixation increases with an increase in zooplankton, and (3) sequestration decreases after 2060 A.D. due to dissolution of calcium carbonate.

 A prediction model for the eelgrass recovery after a tsunami was constructed using machine learning, as the model has not yet been established. Its usefulness in considering countermeasures was also investigated. The objective variable of the model is the rate of change in the eelgrass area relative to the area before a tsunami in each year from 1 to 7 years after a tsunami, and the explanatory variables are the eelgrass area before and immediately after a tsunami and information on the marine environment. A prediction model was constructed from information on the eelgrass distribution in Matsushima Bay after the 2011 Great East Japan Earthquake and Tsunami, using regression with a neural network to express the recovery trend. The model was applied to Ago Bay, Mie Prefecture, to predict the recovery of eelgrass. As a result, the relative recoverability of each location against future tsunamis was obtained. The result indicates that recovery prediction can be useful information in considering effective and strategic countermeasures before and after a tsunami.

 In water areas, environmental DNA (eDNA) monitoring is expected to be a useful method to collect biological information at single/multiple locations and continuously over the long-term, because it only requires sampling a small amount of water. However, in marine areas, it has been reported that the amount of eDNA varies depending on the sampling area and the sampling timing during a day with the tidal current variation. Therefore, in eDNA sampling, it is important to understand the influence of tidal currents. In this study, sea water samplings were conducted in order to understand the characteristics of the spatial and temporal distribution of eDNA associated with eelgrass beds, which are adherent organisms. The distribution of eDNA along the cross-shore direction were observed and the temporal change in the amount of eDNA were confirmed. The results showed that the distribution range of eDNA was approximately 100m wider than that of the eelgrass beds and the distribution varied with the currents. Additionally, the simulation with advection-diffusion analysis were conducted, where the amount of eDNA was represented with concentration value of virtual substance to qualitatively reproduce the spatial and temporal distribution. The simulations were conducted with the different current conditions, and it is suggested that spatially/temporally-appropriate sampling points can be selected.

 Dredged sediment can serve as organic matter storage when it is incorporated as a base material for construction of tidal flats. This carbon storing effect contributes to the reduction of greenhouse gas emissions. The field survey was conducted in July 2022 on an artificial tidal flat in Hannan District 2 in Osaka Bay, Japan. A total of four sites in the intertidal and subtidal zones within the tidal flat were surveyed. Vertical core samples (3 m long, 10 cm diameter) were collected using a vibrating core sampler. Laboratory analyses were conducted to measure grain-size composition, water content, soil particle density, loss on ignition (combustion temperature 300°C: IL₃₀₀; combustion temperature 600°C: IL₆₀₀), total organic carbon (TOC), total carbon, and corrosive substances. There were no significant trends in the lateral distribution of IL₆₀₀ in the dredged sediment layer (20 of 22 sites) sampled with the soil test cane. IL₆₀₀ in the samples from 20 sites at different locations were highly correlated with water content as well as with sampling depth in the mud; however, (IL₆₀₀−IL₃₀₀)/IL₆₀₀ varied little. We infer that the degree of degradation of organic matter was consistent across the study area. The spatial distribution of organic residuals on tidal flats constructed using dredged material was found to be unaffected by depth within the sediment, position in the intertidal or subtidal zones, or distance from the mid-breakwater. The estimated residual organic carbon in the dredged sediment utilized in this tidal flat was 82.5 ± 11.6 %.

 In the surface methane hydrate (MH) mining project, MH and mud drilled together with seawater will be pumped on board a ship, and only methane gas will be recovered in a gasification facility on board the ship. In this process, understanding the impact of turbidity on the surrounding environment and efficient discharge methods into the depression are important issues.

 In this study, in order to understand the turbidity of unwanted mud when it is discharged to the seafloor, we conducted a mud injection test using simulated deep-sea mud to understand the sedimentation characteristics of the mud when it is discharged. As a result, it was found that although the initial stage of the mud discharge is density flow-like, advection-diffusion behavior is dominant, and that the turbidity spreading is caused by the horizontal movement of the mud after it hits the seafloor and the upward turbulence after it strikes the tank wall. Numerical analysis using a three-dimensional flow model was used to qualitatively describe the behavior of the dumping mud.

 In the combustion method, a method for measuring the fixed amount of organic matter in organic mud, organic matter is classified into readily degradable and persistent organic matter using the combustion temperature (300°C) as an indicator. The coordination and desorption of organic matter to metal ions (persistent and per-decomposable organic matter) often involves the acceptance and transfer of electrons between the two substances, and potential fluctuations in the solution induce redox reactions of organic matter. In this study, we examined the combustion characteristics of organic sludge produced by battery reactions (redox reactions of organic matter that occur in the process of electron capture and insertion) to investigate the degradability of organic matter by battery reactions and to evaluate the ease and difficulty of organic matter degradation by battery reactions. The results showed that complexes (persistent) are formed when high energy levels are given to organic matter (electron insertion), which is easy to decompose.

 Because it is assumed that the dredged mud, which is material for tidal flat construction, will not diffuse into seawater, the organic properties of dredged mud have not been studied. In this study, dredged mud was collected in columnar form from two tidal flats with different elapsed times of dredged mud input, and the organic properties of each dredged mud were analyzed. There was no significant difference in apparent concentration of nutrients at the two sampling points years and decades after sand was covered on top of the dredge mud. However, the roles of dredged mud were confirmed from there was a significant difference in the content of nutrients bound to mud particles at the two sampling points, and active leaching of nutrients from dredged mud exposed to the water surface.

 Climate change impacts on waves can be quantitatively evaluated by conducting large-scale numerical wave simulations with typhoons extracted from the d4PDF dataset. However, due to an extensive number of typhoons in the d4PDF dataset, it is difficult to carry out wave simulations for all of them. Therefore, we propose a method for estimating the maximum significant wave height by developing a wave regression equation based on the results of a limited number of wave simulations, instead of performing simulations for every typhoon. The wave regression equation takes into account the time-varying wind field which is critical to wave growth. To validate the accuracy, we employed the k-NN model. Furthermore, we determined the minimum number of numerical wave simulations required to construct the wave regression equation.

 In existing storm surge inundation assumptions, the radius of maximum wind speed (R_w), the radius of maximum pressure gradient (R_p), and the radius ratio (R_p/R_w), which determines the scaling parameter (SP) is based on the values of historically significant cases. In this study, we investigated the spatial-temporal trends of R_w and R_p by analyzing the results of 49 cases of typhoons that made landfall in Japan. As a results, R_p tends to remain constant regardless of time, while R_w tends to fluctuate more than R_p. In addition, the radius ratio was around 1 at the peak time and 0.4-1.0 at landfall time. Therefore, the value of R_w varied with the lifetime of the typhoon. The two types of analysis (direction analysis / spatial analysis) of the factors contributing to the variability of R_w were conducted. It was revealed that the location of the maximum wind speed varies in various directions from the center of the typhoon. However, the magnitude of R_w does not vary. On the other hand, the location of maximum wind speed appears farther from the typhoon center as the typhoon structure collapses, and the direction also varies. Hence, spatial variability of wind field with typhoon structure collapse can attribute to uncertainty of R_w.

 In this study, pseudo-global warming track ensemble experiments for Typhoon Nanmadol (2022) are conducted using a dynamic coupled atmosphere-storm surge model in order to evaluate the direct and indirect effects of typhoon track, landfall, and global warming on typhoon intensity and storm surge in the Ariake Sea. It is estimated that Nanmadol crossing Kyushu raises the central pressure by about +20 hPa due to the effects of the landfall, and the effects of storm surge suppression at the Ooura Port is quantitatively shown to be about -0.62 m. According to the results of the pseudo-global warming track ensemble experiments, a future-climate typhoon moving northward over the sea west of Kyushu would enhance the risk of storm surge disasters due to 1) higher sea surface temperatures by the global warming, 2) lower attenuation by the local topography, and 3) higher wind speeds along the bay axis.

 The intensity characteristics of typhoons under special conditions were evaluated using an original climate experiment based on a model combining a slab ocean model with a global atmospheric climate model (MRI-AGCM) from the Meteorological Research Institute of the Japan Meteorological Agency. Seventy years of September average SSTs were analyzed, and cluster analysis was performed to compare the results with climate experiments as average September conditions. Climate experiments were also conducted and compared. In addition, a month-fixed EA experiment was conducted under present and future climate conditions (ssp585 scenario). The statistical characteristics of typhoons under the September 2018 condition, when Jebi caused extensive damage to the Kansai region, confirmed that many strong typhoons approached or landed in Japan, even considering natural variability. In addition, a trend of increase in the number of strong typhoons was obtained as a change in the intensity characteristics of typhoons by climate change.

 Pseudo global warming experiments (PGW) were conducted for Typhoon 1821 using the atmosphere model (WRF) and the coupled atmosphere-ocean model (WRF-ROMS), with the global climate models selected to focus on the future change in the atmospheric circulation. Changes in typhoon intensity, track, ocean response and disaster hazard were compared and evaluated between historical experiment and PGWs. The typhoon intensity increased, and the tracks were shifted in PGWs. Future changes in wind speed in the upper atmosphere were correlated with changes in track and translation speed, and typhoon intensity tended to increase with decreasing translation speed for WRF, while typhoon intensity tended to decrease for WRF-ROMS. The results of hazard assessment focusing on 1-hour and 12-hour precipitation showed that, on average, the hazard was enhanced in PGW, although there were changes in the areas affected by the hazard due to changes in typhoon track.

 This study shows future changes in the maximum potential intensity of tropical cyclones (TC) based on the MPI (Maximum Potential Intensity) theory. In addition, we have clarified the accuracy characteristics of TC intensity assessment depending on climate models and predicted future changes in TC intensity for each basin. The climate data used in this study is the HighResMIP (High-Resolution Model Intercomparison Project) experiment, including both atmospheric and atmosphere-ocean models, for 30 models. The spatial pattern between the reanalysis values from the observed data and climate models on the HighResMIP experiment in the present period generally agreed. The ensemble average MPI of the models for each basin, considering the inverse of RMSE as weights, indicated that the TC intensity will be strengthened to a maximum of about 940 hPa by 2050 in the WNP and NA. In the WNP, most of the models showed TC intensity will be stronger by 1 to 3 hPa in the future, while in the NA, 47% of the models showed MPI future change would be twice that of the WNP.

 Countermeasures against localized scouring at the base of monopile offshore wind turbines for offshore deployment of monopile offshore wind turbines. Although bag-type rooting materials and crushed stones have been studied as countermeasures, it is necessary to study other construction methods in pursuit of construction convenience and economic efficiency. In this study, the applicability of a stone cage as a scour prevention method was verified through hydraulic model experiments. The stone cage showed the same scour-preventing effect as that of the bag-type rooting material and crushed stone. The maximum scour depth increased in proportion to the clearance between the stone cages. On the other hand, the gaps between stone cages often caused local scouring around each cage, indicating the need to consider the gaps between stone cages when implementing the system.

 One of the methods proposed for preventing scour around the monopile foundation of an offshore wind turbine is to cover the seafloor surface with many round filter units. However, it has been pointed out that there is a possibility that these filter units may move, or the sand can be sucked out from the gaps around the monopile.

 In this study, we proposed an annular filter unit that can efficiently prevent these phenomena. A series of model tests were conducted to verify its basic fabrication and construction feasibility, as well as its performance in preventing scouring.

 The results demonstrated that the fabrication and construction would be feasible by appropriately selecting the formwork, using shape-retaining ropes, and installing appropriate amount of stone. It was confirmed that the hydraulic performance could be improved by covering the area of about three times the monopile diameter with the annular filter unit, and that the effectiveness in preventing scour could be enhanced by using round filter units or asphalt mats in combination.

 Offshore wind power generation is expanding primarily in Europe, and efforts to start offshore wind power projects are also progressing domestically in Japan. Among them, the coastal areas of Murakami City and Tainai City in Niigata Prefecture were designated as the promotion zone in September 2022, and procedures are currently underway to select a project operator. The average annual offshore wind speed within the promotion area in Niigata Prefecture is expected to be stable, however, the offshore winds increase in winter and calm down in summer, furthermore, the southern part of the sea area faces a plain, while the northern part faces a hilly area and may be strongly affected by the topography. Therefore, it is necessary to understand the differences in power generation capacity due to seasonal changes and differences in construction sites. Additionally, Niigata Prefecture has a vast coastal area, requiring an understanding of power generation capacity outside the designated promotion areas. Furthermore, it is considered important to grasp the differences from other promotion areas within Japan. In this study, we first investigated the characteristics of offshore winds in the designated promotion areas based on seasonal and spatial variations. Next, we compared the characteristics with other offshore are-as within Niigata Prefecture and other promotion areas. Offshore wind information was derived from the Japan Meteorological Agency's five-year surface data from numerical weather prediction, converted to a height of 100 meters above ground level at the wind turbine locations.

 The objective of this study is to use satellite synthetic aperture radar (SAR) data to obtain an initial understanding of the coastal damage distribution in the Marash Earthquake that occurred on February 6, 2023 in Turkey. The SAR data used are two images taken by the European satellite Sentinel-1 resampled to 30m spatial resolution on January 29, 2023 (before the earthquake) and February 10, 2023 (after the earthquake). We investigated the relationship between areas with large variations in ground roughness, building damage areas, and surrounding geology using the difference images of backscattering cross sections (NRCS) before and after these earthquakes. As a result, the area with large NRCS difference and the strong earthquake area (especially the northern part of the epicenter) were the same. Furthermore, the influence of snow and rain was small in the difference image of the SAR data this time, and the positive difference increased in the unconsolidated sediments layer area (the ground condition became rougher).

 In this study, the population change in sandy beaches across Japan were analyzed using hourly mobile network data for four years from 2019 to 2022 to obtain the characteristics of change in number of visitors to beaches. From the temporal changes in the monthly averages of the population in sandy beach meshes, the influence of seasonal changes and Covid-19 in the trend and fluctuations were different depending on the beach type. There are sandy beaches people comes from all over Japan and the same municipality. On the other hand, it is become clear that the lack of data due to restrictions on the available data concerning the protection of personal information makes difficult to obtain the actual population in places where the number of visitors is small.

 In coastal areas of our country, there are numerous tangible and intangible cultural assets, tourism resources, and local resources scattered throughout, which have become crucial assets supporting regional economies and cultural activities. As seen in recent major disasters like the Great East Japan Earthquake and the heavy rain disaster in western Japan, there has been an increasing opportunity for these traditional cultural assets and tourism resources to be compromised in coastal areas. In this study, we conducted spatial information analysis utilizing national geospatial data to verify the disaster risk of cultural properties, tourist resources, and regional resources in the coastal municipalities of the Osaka Bay region. As a result, it was revealed that the Osaka Bay region has a significant presence of regional resources, tourist resources, and designated cultural properties. Furthermore, it became evident that the proportion of tourist resources and designated cultural properties distributed in the coastal areas is higher than that of regional resources.

 The large-scale tsunami fires observed in the 2011 Tohoku Earthquake are expected to occur in future tsunami disasters, and the risk of death from fire is also a concern. Although studies have been conducted on the mechanism of tsunami fires and risk assessment, the relationship between tsunami fires and human casualties has not been clarified, and this is an issue that needs to be addressed when planning countermeasures. In this study, we analyzed the number of burnt victims based on the information of victims recorded in each postal code area. The results showed that the number of burn victims was limited to six postal code areas. In two of the six counties, burns were the dominant cause of death over drowning. The results suggest that the ease of secondary evacuation is one of the factors affecting the number of burn victims.

 In Japan, 2,000 to 3,000 drowning accidents occur every season at major bathing beaches. To prevent drowning accidents, beachgoers themselves need to be aware of the dangers of the ocean and avoid them. As a way to do this, bathing beaches provide daily risk levels regarding swimming conditions to beachgoers using beach safety flags in three colors. We have constructed an AI model that can predict the probability of drowning accidents with high accuracy and developed a new method for objectively judging swimming conditions based on the prediction results. On the other hand, when the AI model was applied to two beaches located on the east and west sides of the pocket beach, the prediction accuracy was low. This study quantitatively analyzed the reasons for the lower prediction accuracy for three beaches located on the Onjuku beach. As a result, it was considered that the reason for the low accuracy was that topographical features were not taken into account.

 In order to reduce the damage caused by traffic congestion, we develop a tool that promotes evacuating on foot by considering in advance what each individual will do to overcome the disaster. In developing the simulator, we considered the characteristics of car evacuees clarified by the past research and the situation in Ishinomaki during the 2021 Miyagi earthquake. This simulator shows the evacuation situation and traffic congestion in the Isinomaki area, shows how users evacuate when a big earthquake occurred or a tsunami warning is announced, and shows how long it will take to finish evacuating. The results obtained were as follows: 1) to show a video of what the evacuation behavior will be may lead to the promotion of evacuation on foot 2) since the simulator allows people to experience the traffic congestion in the Ishinomaki area, which can only be seen when occurred the disaster, showing the state of traffic congestion and which roads are likely to cause congestion may lead to the promotion of evacuation on foot.

 In some areas affected by the 2011 Tohoku Eartkquake, tsunami advisories and tsunami warning have been announced, such as the 2016 Fukushima-oki earthquake, the March 2021 Miyagi-oki earthquake, and the March 2022 Fukushima-oki earthquake. The authors have conducted a continuous questionnaire survey of coastal residents in Watari Town, Miyagi Prefecture, using a consistent sampling method. In this paper, by comparatively analyzing the actual situation of evacuation behavior in these four events, including the Tohoku Earthquake Disaster, we considered the relationship between changes in evacuation behavior over time, the time when the earthquake occurred and the scale of the hazard. As a result, differences in behavior related to 1) the scale of the earthquake/tsunami that occurred, 2) the time period of earthquake occurring, 3) the experience of the 2011 disaster and subsequent events, and 4) lifestyle changes were observed.

 This study proposes the use of Balloon-Type Evacuation Signs (BTES) to guide evacuees to Safety Evacuation Areas (SEA) in the event of a tsunami. An experiment was conducted in Wakabayashi Ward, Sendai City, to evaluate their visibility. The obtained results are as follows: 1) BTES has the potential to guide people to evacuate up to 1.5 km from SEA, covering the entire tsunami inundation zone in Wakabayashi Ward. However, it is important to ensure that people are aware of the meaning of BTES in advance. 2) The higher the altitude and the larger the diameter of BTES, the more noticeable it becomes to people. Nevertheless, within a distance of approximately 500 meters from BTES, there was less variation in visibility based on different altitudes or diameters. BTES should be designed according to the assumed evacuation guidance area for SEA. Although several issues need to be addressed before implementing BTES in society, this experiment revealed new possibilities of BTES as a novel evacuation guidance method.

 A field survey and calculation of topographic changes were carried out for Tsubasa Beach in Jonanjima Seaside Park as an artificial beach in suburbs of the city. In addition, considerations for the design of artificial beaches in an environment dominated by the action of wind were discussed. In the field survey, it was observed that windblown sand from the beach was deposited on the promenade located behind Tsubasa Beach, and it was an obstacle to the use of the beach. In the calculation, the current topography of Tsubasa Beach was reproduced, and the calculation was carried out considering windblown sand. As a result, beach sand was transported behind the beach and deposited there. In addition, it was found that the erosion tendency was shown in the beach area, and windblown sand to the back of the beach cause the loss of sand in the beach area. From these results, it was shown that it is necessary to consider topographical changes due to wind waves and sand movement due to windblown sand when designing artificial beaches in an environment with predominant wind actions.

 This study applies the hedonic pricing method to hotel room prices for hotels located near sandy beaches throughout Japan to measure the marginal effect of proximity to sandy beaches on hotel room prices. We investigated the geographic distribution of marginal effects by performing both ordinary least squares (OLS) and geographically weighted regression (GWR). The results showed that proximity to sandy beaches had a positive effect on hotel room prices, but the statistically significant range was obtained at the hotels around Okinawa Prefecture. In these areas, proximity to sandy beaches was shown to raise hotel room prices by approximately 13% to 28%. On the other hand, there are still issues to be addressed in setting explanatory variables in order to construct a valid equation for various socioeconomic influences.

 Both the shoreline recession by ground subsidence due to excess pumping of the underground water and that caused by wind waves incident from the easterly direction under the tropical monsoon weather were investigated, taking Pelalongan area on Java Island as a study area. In the study area, nine subareas were adopted on both sides of the Comal River delta and the shoreline changes in each area was investigated using the satellite images. Field observation was also carried out in Pekalongan area, and the ground subsidence was investigated on 19 August 2022. It was found that in this area, the ground subsidence reached approximately 1.6 m and the sinking area rapidly expanding. On the other hand, along the coast east of the Comal River delta, the mean wave incidence angle is as large as 22° clockwise, whereas on the west side, the angle increased up to 42°, causing the High-angle wave instability.

 The study of wave run-up on sandy beaches is important not only for beach preservation but also for the functional evaluation of coastal protection facilities such as seawalls and for disaster prevention in the backshore areas. The authors proposed a new method to quantify the temporal changes in wave run-up based on image data taken at the beach, but there are still issues to be resolved in long-term observations. In this study, wave runup height during the period from 2020 to 2022 was analyzed using image data taken at the Chigasaki Coast in Kanagawa Prefecture, and the relationship between wave runup height, waves, and tides at the target coast was investigated. The wave run-up height obtained by the image analysis and the existing wave runup formula have a correlation with a coefficient of determination of about 0.63, and the run-up height obtained by the image analysis was about 1.7 times larger. The higher the value of wave height, the higher the run-up tended to be, and this tendency was confirmed to be stronger when the tide level was higher than the average during the period.

 Longshore currents are one factor that determines the fate of sandy beaches. If we have a better understanding of the behavior of longshore currents, we can achieve a better prediction. In this respect, instruments are installed in shallow waters with considerable efforts to measure the longshore current. In this study, a Doppler radar velocimeter was installed at the research pier HORS, Hasaki Ocean Research Station, to measure the longshore current remotely for five months. We verified the measurement results with wave observation and float drift observation. The direction of the longshore current was looking to the downwave direction of the incident waves. It changed by the incident wave angle. The longshore current velocity's magnitude increased proportionately to the wave power but saturated when the wave power exceeded a specific value. This may depend on the evolution of the surf zone: During high wave periods, the breaking point locates far from the velocimeter.

 When estimating the concentration of CO₂ in water from the observed variables of DIC, TA, and pH based on the equilibrium relationship of the carbonic acid system, it is necessary to select an appropriate estimation pattern for the target water area from among several estimation patterns based on the combination of observed variables.

 In this study, water sampling surveys were conducted in different water areas in Osaka Bay, and the estimation error of each estimation pattern was confirmed by comparing the measured values of CO₂ using an originally developed analysis method with the estimated values calculated from observed variables, and the effect of the measurement accuracy of observed variables on the calculation results of CO₂ was examined through sensitivity analysis. As a result, we found that the pattern using pH as an observed variable had a smaller error in rivers and estuaries, while the pattern using DIC-TA had a smaller error in ocean areas near the open sea. The comparison of the rate of change of the estimated results in relation to the measurement error of each observed variable revealed that the influence of pH was larger than that of TA and DIC, indicating that special care should be taken in the observation of pH.

 In coastal areas, numerical models have been improved in accuracy through data assimilation using water quality measurements and HF radar observations. However, until recently, the limited spatiotemporal resolution of satellite data has hindered its utilization, resulting in few application cases. In recent years, there has been significant improvement in the spatiotemporal resolution of satellite data. Therefore, the use of data assimilation with satellite data is expected to be beneficial for closed water areas.

 In this study, data assimilation was performed using satellite-observed sea surface temperature (SST) through the reuse of the Green's function method in Tokyo Bay. The aim was to optimize the parameter values related to the heat balance within the numerical model and examine the impact on the reproducibility of water temperature. As a result, the root mean square error (RMSE) between the satellite-observed SST and the calculated water temperature from the numerical model decreased by approximately 26% at maximum, suggesting the effectiveness of satellite data assimilation in coastal areas.

 Distributed Acoustic Sensing (DAS), one of the fiber-optic sensing technologies, can observe strain along a fiber-optic cable densely in time and space. We conducted the DAS measurement using the submarine cable off Cape Muroto, Japan, with fiber length of 120 km. In this study, we elaborate long-period pressure fluctuations by examining the acquired dataset of both the DAS and the pressure gauge nearby during typhoons approach. The infragravity waves with a period of about 100 s were observed in addition to the ocean microseisms in the DAS measurement. Our in-situ observations suggest that DAS is sensitive to long-period pressure fluctuations and can detect pressure fluctuations induced by storm surge or tsunami.

 Development of automatic shoreline extraction methods based on SAR (Synthetic Aperture Radar) images using machine learning is ongoing. A large amount of shoreline position data obtained at the same time as SAR satellite observations is necessary for machine learning. In this study, we aimed to develop a method to generate correct shoreline position data efficiently and accurately from aerial images taken by UAV (Unmanned Aerial Vehicle). Field survey was conducted on two coasts to obtain UAV images and HandyGPS measured shoreline position. Difference of shoreline positions between the extracted one based on the obtained UAV images and measured on by HandyGPS was less than 3 m, which was thought to be sufficient for machine learning. The extracted shoreline was projected onto a SAR image, and it was visually confirmed that the extracted shoreline was highly accurate.

 In this study, a new image measurement technique for water surfaces is discussed through a planar wave experiment. The measurement system is composed of one projector and two digital cameras. For this measurement system, wave tanks are filled with white-colored water with white dye. Color pattern illumination, which has many color dots as a grid pattern, is projected from the projector to the water surface, and the light scattered just below the surface is recorded by the cameras. Including the projector as a single view for stereo analysis, we have totally three-views to determine 3D surface coordinates of each color dot. For robust automatic matching of color dots, normalized color difference vecotors are introduced as dissimilarity of the color patterns in the projected and recorded images. As the color dots scattered under water surfaces are recorded in this system, their recorded locations are shifted from the ideal locations with reflction exactly at the water surface. A method to correct the recorded locations is proposed and tested through the planar wave tank experiment. Progressive waves were successfully measured with the proposing technique, and obtained horizontal distributions of water levels were comparable to those by conventional wave gauges.

 Satellite imaginaries are expected as the base data for monitoring the deformation of rock reefs, because the most of important rock reefs locates in isolated islands. Satellite image classification and field surveys were conducted on rock reefs located in Inubousaki (Chiba Prefecture) and Bonten-no-hana (Kanagawa Prefecture), in order to establish a new monitoring method using satellite imagery. Four satellite image classification methods (K-means, threshold, maximum likelihood, and nearest neighbor) were applied to detect changes in the rock reefs captured via satellite imagery. The nearest neighbor method showed the most accurate results, and post-hoc detection using blue-band satellite imagery improved the accuracy of rock reef detection. Three-dimensional digital elevation models (3D-DEM) of the rock reefs were established based on the three-dimensional point cloud data acquired by a green LiDAR drone. 3D-DEM satisfactorily simulated the shapes of the rock reefs at the position where rock reef surfaces were covered by wave run-up. The accuracy of the geometric correction of the satellite images was the highest when the 3D-DEM was utilized as reference point data. The shapes of the rock reefs projected on the satellite image were estimated on 3D-DEM, considering the water level and sunlight direction when the satellite images were captured. The estimated shapes of the rock reefs were consistent with the shapes projected on the satellite images. The results suggest that 3D-DEM can provide good reference data when surveying the time-series erosion of rock reefs. Based on these results, a new rock reef monitoring method based on satellite imagery and 3D-DEM is proposed, and some recommendation for practical application are discussed.