Drifting vessels in ports under Tsunami can worsen damages to the ports, by causing collisions between vessels or vessels running aground on piers. The Japanese Ministry has been implementing an initiative to facilitate emergency evacuation of vessels from ports, thus it is significant to examine water facilities for such quick evacuation by referring to the actual vessel movements under Tsunami.

 The purpose of this study is to provide a good reference for ports to examine measures to support smooth evacuation, by analyzing vessels movements (from the occurrence of the Eastern Japan Great Earthquake until the completion of the evacuation) observed at Tomakomai, Kashima, and Kawasaki ports, under the utilization of AIS data.

 In recent years, many cavities have been discovered at the back sides of reclaimed sea-walls in harbors and if expansion is progressed without detection, those cavities may result in serious accidents eventually. Generally, the causes of those cavities are varied, ranging from is-sues with the structural and material difference of seawall, natural environmental background and construction history of each structure.

 Although Ground-Penetrating Radar (GPR) and scoping surveys are common techniques to detect those cavities, these conventional methods require specialized knowledge to confirm the existence of cavities correctly and cannot provide crucial information of the internal conditions which help to determine the underlying causes of the cavities.

 To address these challenges, the authors developed a 3D modeling system that install a small gimbal camera and cloud computing. Then, our field experiments with this system confirmed that it is capable of acquiring detailed images and 3D profiles of the cavity interior, allowing for a better understanding of the process of cavities.

 The purpose of this study is to evaluate the effects of preservation of tidal flats associated with bridge construction in the Tama River estuary. Part of the tidal flats in front of the nature reserve area, which had been removed by the construction of the bridge piers, was backfilled after the construction. In order to promote earlier recovery of the ecosystem, the surface sediments of the dredged tidal flat was temporarily placed on land and used as the sand capping materials of the restored tidal flats. In addition, steel sheet piles were driven into the sediments at the edge of the dredged area, so as to minimize erosion of the bankside residual part of tidal flats. These conservation measures were based on an adaptive management scheme, in which the effects of construction and responses to unexpected natural hazard were monitored and examined whether prompt or appropriate improvements of the construction would be necessary. The monitoring results showed a rapid recovery of the same benthic communities as the surrounding tidal flat. The driving of steel sheet piles had a certain protective effect on the surrounding tidal flats, although a large-scale flooding event caused wide range of topographical disturbances during the construction. The damage still remains. Therefore, it is necessary to make an overall evaluation based on long-term investigation including these effects.

 The purpose of this study was to clarify physical and ecological impacts of the dredging work associated with constructing bridge piers, and those by a large-scale flooding event in the Tama River estuary. Based on the results of periodic environmental surveys conducted for about four years, we analyzed the effects of dredging work and the largest flood in the past on the topography and ecosystem of the tidal flat. As a result, it was inferred that the sediment environment and benthic communities of the tidal flat were not greatly affected by the dredging work. Whereas, remarkable topographical and sediment environmental changes were observed due to the largest flood in history. Benthic communities, mainly composed of opportunistic species, appeared immediately after the flooding, which indicate that the population of organisms would recover relatively quickly against large-scale physical disturbances. However, long-term investigations are required to determine whether the same communities as before the flood, in which large, long-lived benthic organisms such as bivalves appeared stably, could be formed.

 In this study, we analyze the characteristics of the long-term variability of waves globally and around Japan using ERA5, which provides long-term global wave estimation data from 1959 to 2022. The accuracy of ERA5 wave height estimation around Japan was verified, and the distribution of probability wave heights was calculated globally and for the sea area around Japan. We also determined the secular trend of annual maximum wave heights.

 Although ERA5 tended to underestimate wave heights, the overall estimation accuracy was high, and ERA5 was judged to be a practical wave database. The distribution of the estimated 50-year probability wave heights for both globally and for the area around Japan was generally consistent with the results of previous studies. The annual maximum wave heights tended to increase globally and also around Japan on the Pacific Ocean side and the East China Sea area.

 Gravel drain method is one of the liquefaction countermeasures, which used permeable crushed stones to suppress the rise of excess pore water pressure and to increase the dissipation rate. However, gravel drain piles have a high void ratio and great drainage performance, and it is concerned that fine sands around the piles may mix into the voids of the crushed stones could prejudice suppressing the rise of excess pore water pressure into various liquefaction damages. On the other hand, the effective use of scallop shells, which are a by-product of the fishery industry, is being attempted towards the creation of a circular society, but their applications are limited, and the used amount is still very small. Meanwhile, a shell layer construction using flat-shaped shells has been reported to be difficult applied for fine sand on top to mix into the voids of the shells even when subjected to vibrations.

 Based on the above, we conducted a small vibration table experiment in the 1G field (gravitational field) with different relative density (D_r) and acceleration, to study crushed shells-based drain piles (hereinafter referred to as shell-drain piles) which is expected to reduce the drainage performance due to sand contamination during liquefaction. The experimental results showed that, compared with gravel lane piles, crushed shells-based drain piles have the effect of inhibition of sand mixing at the time of liquefaction and inhibition of deterioration of drainage performance due to sand mixing.

 This field experiment revealed that ark shell Scapharca broughtoniie grew well (increase from 37.8 mm to 62.0-65.6 mm in length in 449 days) in the suspended culture cage where glass bottle cullets (Crystal Stone Sand; CSS) were used as substrate. The CSS discharged from public life in large quantities was thought to be available for the substrate of aquacultures of marine bivalves. In comparison between CSS and Anthracite, no significant difference was observed in shell length at the same depth. In case of the same substrate, the shell length was significantly higher at 3m than 1m depth for Anthracite although there was no significant difference in the shell length among two depths for the CSS. Monitoring of sea environments, especially dissolved oxygen, is crucial for the sustainable cage cultures of clams in the enriched coastal area like Osaka Bay.

 Beach has been severely eroded on Ajigaura Beach in Ibaraki Prefecture. As a measure, a sand back pass method was adopted, by which 10,000 m³ of sand is excavated from the north end of the beach a year and sand is transported upcoast for beach nourishment. However, nourishment sand was quickly transported to the original location while losing the effect of the nourishment. This method requires a large cost for transportation of sand, so the continuation of this method is difficult. Instead of this method, a method to create a stable beach by constructing an impermeable detached breakwater was considered by the numerical simulation using the BG model (a model for predicting three-dimensional beach changes based on Bagnold’s concept).

 Suction bucket foundations for bottom-fixed offshore wind turbines are a form of foundation that is expected to reduce construction costs. While cost reduction is required in future offshore wind power development, there is an urgent need to develop technology for foundations that can support large wind turbines. For large wind turbines, a structural type supported by a multi-legged foundation is considered to be effective. As the legs of multi-legged foundations are relatively close to each other, there is concern about mutual interference with scouring phenomena. On the other hand, the rock bag protection method is well known as a scour prevention method. In this study, the characteristics of scouring phenomena for various types of foundation structures, including the suction bucket type, were determined. The bottom velocity around the foundation was determined by numerical analysis, and it was suggested that the scouring area could be estimated from the bottom velocity ratio around the foundation. Furthermore, the effectiveness of scour prevention works for the suction bucket type was confirmed, and cost reductions were expected due to a reduction in the number of prevention works installed.

 A three-dimensional numerical analysis was conducted using a three-dimensional coupled fluidstructure-sediment-seabed interaction model (FS3M) to investigate the motion of a floating caisson towed along a straight line under regular waves. Numerical results showed that the heave and the pitch of the caisson tended to fluctuate with the same period as the apparent incident wave period observed from the caisson. Furthermore, the amplitude of the heave increased when the apparent wave period matched the natural period of the heave. The natural period of the pitch was affected by towlines; thus, the amplitude of the pitch increased when the apparent wave period matched the natural period of the pitch considering the towlines. The time-averaged value of the tension force acting on the towline increased with increasing the incident wave height and during heave and pitch resonances.

 The relationship between two discretization methods and tsunami behavior for finite-difference simulations of tsunamis based on nonlinear shallow water theory is analyzed. Methods for determining whether a tsunami waveform contains numerical oscillations are investigated. It is shown that short-period oscillations that affect the maximum tsunami elevation appear as a result of numerical instability caused by steepening of the wavefront. It is also shown that the magnitude of the numerical viscosity caused by the truncation error associated with the discretization of the governing equation has a strong correlation with general nonlinear indices. Furthermore, the effect of the local viscosity term to effectively suppress the oscillations is verified.

 In this study, as a method of maintaining the performance of the wave-dissipating block sloping breakwater, the transmission coefficient with berm is examined by hydraulic model experiments and numerical calculations. As a result of the experiment, the transmission coefficient increases under the condition of the lower crest compared to the sloping breakwater of the basic shape, and it is improved by berm. By installing two layers of wave-dissipating blocks up to the still water surface, the transmission coefficient is equivalent to that of the basic sloping breakwater. As a result of the calculation, it is possible to reproduce the result of the experiment in general. When R_c/H_I > 1, setting the characteristic value of the block further improves the accuracy with respect to the experimental results.

 Oxidation-reduction potential (ORP) measures energy level of redox reactions in solution, and can be used as qualitative index to evaluate water quality in tidal flats with high biological activity. Conventional ORP sensors measure activity of ions that have passed through a membrane with internal electrodes, thus continuous monitoring at field is difficult. A carbon electrode, which directly measures the redox reaction without a membrane, captures redox reaction of dissolved and suspended substances such as ions, algae, and organic matters that adhere to the electrode. In this study, a carbon based ORP sensor was installed in a tidal flat to evaluate the water quality in a place with high biological activity. The results confirmed that unique potential characteristics appeared depending on the presence or absence of biofilm on the electrode surface, suggesting the possibility as new water quality parameter.

 In addition to the increasing size of wind turbines, the outer diameter of monopile foundations tends to increase in Japan due to the need to consider the effects of seismic loading, which makes installation by SEP vessels, hammer blows, and factory fabrication a challenge. In this study, we propose a structure in which a larger cylindrical underwater seismic control panel is installed around the monopile, partially submerged in water, and the panel vibrates horizontally with the monopile when subjected to external forces, reducing the cross-sectional force of the monopile through the interaction of the panel and water. To confirm the seismic behavior of the proposed structure, underwater shaking table experiments were conducted with and without ground. As a result, it was found that the seismic performance of the proposed structure is particularly high for the second-order mode of wind turbines. It is also shown that the water resistance force acting on the structure increases due to the water surface fluctuation within the seismic control panel.

 At Numakawa-Daini floodway flowing into the Fuji coast, the formation of the stream during flushing and rebuilding process of a berm in front of the outlet of the floodway was numerically predicted using the BG model (a model for predicting three-dimensional beach changes based on Bagnold’s concept). Given the topography after the flushing on 19 October 2021, topography after the flushing was calculated while simplifying the topography around the floodway as far as possible, and then the recovery of foreshore profile was predicted, given the calculated topography as the initial topography.

 The blockage of the movement of a sand body occurrs on the Shimizu coast located northeast of the Shizuoka coast. On the other hand, sand back pass, by which sand is excavated at the north end of the Shimizu coast and is transported upcoast for the beach nourisment, has been carried out the Shimizu coast and the sandy beach of the Shimizu coast has been barely maintained by this activity. It is required to recover the condition, in which sand supplied from the Abe River is naturally supplied to the coast, for the shore protection to be sustainable. Therefore, beach changes associated with the movement of a sand body were investigated using satellite images and an UAV, togeter with field observation. It was found that sand movement was blocked by the installation of detached breakwaters of short offshore distance.

 Nusa Dua and Tanjung Benoa Beaches extend along the east coast of Bukit Peninsula located in the south part of Bali Island, Indonesia. On these beaches, beach erosion has occurred due to the spatial imbalance of northward longshore sand transport. Satellite images of Nusa Dua Beach show that sand transport through the opening behind an island occurred, resulting in erosion in the south part of the island. On the other hand, on Tanjung Benoa Beach, northward longshore sand transport was blocked by groins and the beach was eroded due to the shortage in sand supply. To consider the shore protection of these coasts, UAV images of the coasts were taken on 24 March 2021 and field observation was carried out at Nusa Dua and Tanjung Benoa Beaches on 7 September 2022. Appropriate measures against beach erosion were considered to be sand bypassing and sand back pass, respectively, instead of the selection of hard measure.

 Aiming to develop a filling control method for underwater grout joints of jacketed offshore wind turbine foundations using a two-hole RI meter, we conducted a two-stage laboratory experiment to verify the applicability of the two-hole RI meter and the measurement accuracy of this method. As a result, it was confirmed that the distance between a pair of guide pipes into which the gamma-ray source and detector are inserted should be set at 300 mm to 400 mm, and the measurement time should be at least 3 minutes. It was also confirmed that the RI meter should be inserted vertically downward at least 150 mm to the grout joint in water. The measurement accuracy was confirmed to be ±0.017 t/m³, taking into account statistical noise due to catastrophic oscillation of the gamma-ray source and measurement error due to horizontal displacement of the RI meter. By upgrading this technique, it’s shown that this technique can be used to quantitatively control the filling of underwater grouting materials.

 An improvement of an existing 3D topographic measurement method was used to measure the temporal topographic change of a gravel beach using a hydraulic model experiment. The existing method had low reproducibility of the 3D model, limiting the data that could be used to examine topographic changes. The effect on the reproducibility of the 3D model was verified by changing the imaging equipment to increase the processing speed of the images and by changing the imaging conditions by irradiating the gravel beach surface with lighting and lasers. The analysis conditions that best improve the reproducibility of the 3D model were also examined. As a result, the measurement accuracy of the gravel beach topography before and after wave generation was improved, and the measurement error was suppressed to the millimeter level. Furthermore, the improved image processing speed makes it possible to measure the development process of landforms during wave making and the topography of arbitrary cross sections over time.

 In the previous study, a method of observing both beach topography and the distribution of marine debris deposited on a coast was developed based on field observations before and after a storm at the Onuki coast south of Oharai Port. In this study, field observation of the deposition of marine debris was carried out on the Shichiri-Mihama coast in Mie Prefecture. A method to predict the distribution of marine debris deposited on a coast was newly developed, taking the effect of wave run-up to the deposition of marine debris on the beach into account. The observed and predicted distributions of marine debris were considerably in good agreement.

 The deformation of a slender coral cay with an aspect ratio of 9.3 (Nagan-nu Island) located 15 km west of Naha was investigated using satellite images and field observation was carried out on 31 October 2021. Field survey using an UAV was carried out on 28 August 2022, and the deformation mechanism of this coral cay was investigated while comparing with results of the wave observation by NOWPHAS Naha. Since this island has a slender form, overflow over the island from north to south or south to north occurred corresponding to the wave incidence from the north or south, respectively. However, the overall topography was in dynamic equilibrium.

 The effect of a training jetty to control sand deposition at the river mouth was investigated, taking the mouth of the Minato River that flows into Uraga Strait in Chiba Prefecture as a study area. Because the size of this river is small, sand deposition at the mouth due to waves is remarkable, whereas flusing of sand by floods often occurs, and the river mouth topography is in dynamically equilibrium state. The variation of the rivermouth bar was investigated using satellite images and field observation was carried out on 22 June 2022. Moreover, cross sections of the rivermouth bar were measured using a GPS-RTK along three transects across the rivermouth bar as well as the sampling of riverbed material. At this river mouth, when the shoreline of the rivermouth bar completely attached to the training jetty and the direction normal to the shoreline became equal to the wave incident angle, the sandbar became stable.

 At the Hamamatsu-Goto coast next to the Tenryu River mouth, a groin has been constructed and beach nourishment was carried out between 2012 and 2020 using 7.3 ×104 m³ of the riverbed material of the Tenryu River to widen the foreshore at a narrow beach in front of the seawall, where once wave overtopping occurred. Monitoring surveys of the beach changes, such as the bathymetric surveys around the groin and UAV measurements, were conducted after the extension of the groin to evaluate the most appropriate depth of the groin. In this report, the intermediate results of the monitoring surveys were reported. It was found that the beach width has increased owing to the beach nourishment as well as the recovery work of the detached breakwaters and the construction of the groin.

 Artificial tidal flats made of granulated coal ash(GCA) have been created in Hirosima coastal area and the effect of GCA on tidal flats environment has been evaluated. In previous research, we clarified the improvement of the sediment and biological environment in tidal flats with high organic mud deposits. In this study, we investigated the environmental improvement effect of bottom sediment in tidal flats where mud with low organic content accumulated, clarified the effect of increasing benthic organisms including clams, and the effect of improving the primary productivity of tidal flats (increase effect of microalgae). In addition, we compared the difference in living organisms depending on whether or not GCA on the tidal flats, and clarified that the GCA has the effect of constructing a various ecosystem.

 Effects of granulated coal ash (GCA) on coastal sediments have been estimated to be (1) humification, (2) granulation of clay particles, and (3) polymerization and saponification of fatty acids. However, these effects have not yet been demonstrated through chemical analysis. In this study, analytical procedures were proposed to verify these effects. The purpose of this study is to clarify humification of soil organic matter due to organic complex formation by GCA. The analysis procedures include alkali decomposition, acid decomposition, n-hexane extraction, etc., and demonstrated composition of persistent organic matter by GCA.

 Accretion was frequently observed at floodway located in the Niigata coast, especially associated with high waves in the winter. The cost to dredge the deposited sand has been high until now, so it is required to consider the counter-measures to decrease the sand accretion. Considering the appropriate method to reduce the sand deposition by using the numerical simulation, it is necessary to increase the accuracy of numerical simulation. In this study, XBeach was employed to simulate the accumulated sediment volume and bathymetric changes near the floodway. Comparison of the simulated sediment volume with the dredged sediment volume revealed that the simulation result was in fairly agreement or underestimated compared with the observation. Additionally, the wetslp parameters were examined to increase the accuracy of the simulation. The sensitivity results showed that the wetslp was set to 0.24, which was lower than the initial value of 0.3, improved the accuracy of simulated volume accumulated at the floodway. It is still needed to carry out further evaluation, this study shows possibility of simulation of accretion in floodway by using XBeach.

 On Shichiri-ga-hama Beach of 2.7 km stretch, beach has been severely eroded in recent years. This study aims to investigate the cause of erosion of this beach. Field observation was carried out to measure the relative height between the crown of the pedestrian bridge showing the previous level of the sandy beach and the present sandy beach. From this relative height, the thickness of the eroded sand layer and the rate of erosion were estimated. Satellite images were compared to study the expansion of exposed rock in the nearshore zone, and the comparison of site photographs taken on 28 November 2015 before erosion with the present ones was also made. In the previous studies, accurate bathymetry of Shichiri-ga-hama Beach was not measured. So, the measurement using the airborne laser bathymetry (ALB) was carried out in January 2022 to study the characteristics of the seabed topography.

 Along the coastline of 6.4 km length between Chigasaki fishing port and the Hikiji River mouth, eastward longshore sand transport prevails together with a large amount of windblown sand being transported inland during winter. Beach nourishment has been extensively carried out as a measure against beach erosion on the Chigasaki coast, and part of sand was transported inland to deposit along the cycling road of the coast, causing damages to traffic. Numerical simulation on both windblown sand and sand transport due to waves was carried out using a model combined the BG model with a cellular automaton method.

 Lake Komuke, which faces the Sea of Okhotsk in Hokkaido, has improved its environment since it became a permanent lake mouth after constructing a flow levee in the Showa 50s. However, although the flow levee built in the Showa 50s is ageing and is undergoing renewal, the width of the mouth may change when the flow levee is improved or renewed, and the change in the width of the mouth may affect the environment inside the lake. Therefore, in this study, we evaluated the influence of changes in the width of the mouth of the lake, focusing on salinity and the amount of dissolved inorganic carbon on the lake environment as water quality items that affect the lake environment using the three-dimensional environmental fluid model Fantom. As a result, we proposed a construction method using existing sheet piles that can improve the flow embankment and channel revetment without changing the width of the mouth of the lake.

 Steel slag-dredged soil mixture is widely used as a construction material for tidal flats and shallow areas, as a reclamation material, and as a refilling material for subaqueous borrow pits.

 Grabs are often used when dumping steel slag-dredged soil mixture into the sea. However, in construction using a calcia drop-mixing vessel, it is considered efficient to use a tremie pipe, which can reduce the transportation and dumping of calcia-improved soil, into the sea. On the other hand, when steel slag-dredged soil mixture is dumped into the sea using a tremie pipe, turbidity may occur and the tremie pipe may be clogged.

 Therefore, we developed an underwater dumping system for steel slag-dredged soil mixture, which consists of a tremie pipe with slits on the side and a hopper with a V-shaped drop part for the steel slag-dredged soil mixture. Through experiments, it was confirmed that the newly developed tremie pipe can reduce turbidity and increase strength by dropping and mixing the steel slag-dredged soil mixture. The maximum turbidity of the tremie pipe with slits was reduced to about 40%, and the amount of turbidity generated was reduced to about 10% compared to the normal tremie pipe.

 The maximum storm surge is generally estimated using the strongest typhoon among those that have approached and hit to Japan. Although return periods of the central pressure of the strongest typhoon in Tokyo, Ise and Osaka bays are estimated as 500 ~ several thousand years, those of storm surges induced by the typhoon are unknown. This study estimated return periods of the estimated maximum storm surge in Nagoya and Omaezaki which are induced by the strongest typhoon, using hourly data of observed sea surface elevation. Because the observed data include abnormal tides other than storm surge, such abnormal tides were excluded from the observed data. The estimated return periods were about 4,000 years in Nagoya which has frequently experienced severe storm surge, and about 28,000 years in Omaezaki which hasn’t experienced severe storm surge much so far. The return periods depend on characteristics of the sea area other than typhoon’s characteristics.

 Several marine structures with pile foundations have been proposed over the years, and such structures are subjected to repeated horizontal loads in numerous directions and at various load levels under the effects of waves or winds. Additionally, the behavior of piles subjected to load perpendicular to the pile axis is affected by the pile embedment lengths. This study focused on the ratio E_r, which is the ratio of L and l_m1 (L is the length of embedment of a pile and lm1 is the depth of the first zero point of moment of a long pile), and investigated how the behavior of single piles subjected to repeated horizontal loads changes depending on the E_r. The pile head deflection at the maximum load was getting increased when a pile was repeatedly loaded in one direction. On the other hand, it was getting decreased when a pile was repeatedly loaded in alternating directions. The rate of change of the pile head displacement per number of repeated loading cycles was almost independent of E_r for E_r≧1.0, whereas for E_r<1.0, it changed significantly compared to E_r≧1.0. In addition, focusing on the bending moment distribution, for E_r<1.0, it changed little in both one direction and alternating direction repeated loading experiments, while in the case of E_r≧1.0, it changed with repeated loading.

 In countries and areas where oceanographic phenomena like waves are not observed, ad hoc coastal structures are designed based on experience. This study applies various kinds of analytical data to the coastal master plan of Davao City, the Philippines, where observation data are scarce.

 The study conducted downscaling wave analysis using the WAVEWATCH III-SWAN coupled model with long-term wave hindcasts to obtain probability waves for the target coast. This study also conducted storm surge analysis as compensation for the missing period of tide observations to derive probability tide levels. The results of evaluating the planned road revetments’ function with such analytical data clearly indicated that the armor units of the revetments were stable, but the elevation of crown heights was insufficient in some sections. Finally, a master plan including an action plan by 2045 was developed based on the results of this study.

 To promote the low-carbonization of the port structure construction, it is necessary to use low-carbon materials. The effect of applying low-carbon materials should be evaluated throughout the construction process from the production of raw materials to the completion of construction in order to take into account procurement conditions, construction conditions and so on. Also, for effective implementation of low-carbon materials, it is necessary to estimate the effect of CO₂ emission reduction in the upstream side such as the design stage in advance, but the estimation has many uncertainties since the details of the construction work have not yet been determined.

 In this paper, the effect of steel-making slag concrete on CO₂ emissions in the whole construction process is evaluated, reflecting the actual situations of the construction. Also, the amount of CO₂ emissions was estimated by assuming the upstream side, where there are many uncertainties. The influencing factors for the utilization effect throughout the construction process were investigated and the effects of various error factors on the accuracy of the estimation were verified.

 In this study, different evacuation start times were considered in the evacuation simulation from the tsunami caused by the Great East Japan Earthquake in the Shikaori area of Kesennuma City, Miyagi Prefecture. The evacuation completion rate and the number of deaths were quantitatively evaluated. As a result, in the case of later the evacuation timing for local residents, the higher number of deaths and the lower evacuation completion rate were calculated. In addition, there is a nonlinear relationship between staggered evacuation and the number of deaths, showing that temporal dispersed evacuation is one of the effective methods for efficient tsunami evacuation. Also, the result of the present study shows that different evacuation timing and early evacuation is of important for local residents to decrease the number of their deaths and to decrease the evacuation completion rate.

 In Amitori Bay of Iriomote Island in 2022, corals at a deep reef slope from the reef margin to 40 m below sea level were surveyed using quadrats. The coverage and bleaching rates were evaluated based on species identification, yielding the following major results.

 (1) Corals observed for this study were classified into 12 families, 34 genera, and 85 species. (2) Coral bleaching in 2022 was similar to large-scale bleaching that occurred in 2016. (3) At depths of 3 m and 10 m, species diversity was high; the dominant species were not discernible. The rates of bleaching also varied widely among species. (4) The dominant species were distinct at depths of 20, 30, and 40 m. (5) The vertical distributions of most species were limited to less than about 10 m or to 10–20 m. (6) Results of this study might not be fully evaluated by classification according to genus or shape.

 Short-term and medium-term wave forecasting is essential for process control in offshore construction projects up to one or two weeks in advance. In addition to physical models, statistical models, such as deep learning models, have recently been used for wave forecasting, and weather forecast values are used to accurately forecast waves several days in advance. However, the accuracy of wave forecasting decreases with an increase in forecast lead time due to the uncertainty of weather forecast values, making it challenging to accurately forecast waves one week ahead or longer. In this study, ensemble wave forecasting was conducted using Bayesian deep learning based on approximate Bayesian estimation, that takes into account uncertainties in weather forecast values and model representations. Compared to the deterministic wave forecast of the existing model, the 11-day wave forecasts of the proposed model improved the forecast accuracy by an average of 10 % ~ 20 %.

 Sampling and Cone Penetration Test (S&CPT), which enables simultaneous sounding and sampling, was proposed as a simple and economical ground investigation method in seafloor. To improve penetration performance, sampling performance, and workability, the structure of samplers was improved, and field experiment was conducted on sandy ground. As a result, we succeeded in collecting several meters of slightly disturbed continuous soil samples from sandy ground with N values as high as 20. The working time required for penetration and withdrawal of the sampler and probe was about two times longer than that of the cone penetration test (CPT). Thus, the workability od S&CPT was much higher than the standard penetration test (SPT) and/or the undisturbed sampling by sophisticated drilling.

 The selection of months for offshore wind farm maintenance was discussed by using high surf advisory or warning information. High surf warnings and advisories from 2013 to 2022 were obtained from Disaster Prevention DB, and information whether warnings or advisories were announced every six hours (advisory information) was calculated at six locations. Significant wave heights from 2010 to 2020 by WAVEWATCH III were used to categorize an information comparable to the advisory information. Classification approaches by threshold (Ex1) and by using neural network (Ex2) were investigated to show that the accuracies by both approaches were about 0.9, except for one site. Monthly averages were calculated for the number of the daily advisories or warnings from the Disaster Prevention DB, Ex1 and Ex2. Some areas showed distinct seasonal variations in the monthly averages, suggesting that the cost advantage is greater when the monthly averages are smaller.

 Zostera beds are attracting attention as blue carbon, which is the field of CO₂ fixation in sea areas. When creating a new Zostera bed, it is often difficult to find an appropriate candidate site. Therefore, it was considered to set the artificial ground at an appropriate depth in the sea. Small-scale containers containing Zostera marina seeds and sand were suspended at a predetermined water depth in the actual sea. As a result, Zostera marina germination was confirmed from the containers placed 1.0-3.0 m below the surface of the water. In addition, seeds were reproduced from the second-year plant. It was suggested that a long-lasting Zostera bed could be created by the hanging Zostera bed creation method.

 We have found out fluctuations of benthos and fish fauna in the coastal area with oyster-shells laid down, and analyzed their food web with stable isotope for three years. The species number and diversity (H’) of benthos and the individual number of fish within the period were respectively 18.2±10.3, 3.1±0.7 and 4.8±6.3 (/m2); represented 3.5, 2.2 and 7.5 times as many as those in the control area without shells. δ¹⁵N/δ¹³C ratio gradually increased with trophic level, from mud on the laid shells (9.1±0.5 ‰ / - 20.2±0.8 ‰), benthic mollusks (12.2±1.7 / -18.1±2.3), arthropods (13.2±1.5 / -17.1±0.9) to fish caught in laid area (16.4±1.0 / -16.2±0.6), respectively. These results support benthic fauna richness made on /in laid shells contribute great to fish habitat growth.

 Underwater placing tests were carried out on high fluidity concrete with a slump flow of 50 cm that met the mixing conditions required for underwater concrete to investigate its applicability in water and to evaluate its flowability and quality in water using core specimens. The results showed that high fluidity concrete using air-entraining and water-reducing admixture containing thickeners or air-entraining and water-reducing admixture can be applied in water in the same way as underwater concrete, and that its underwater flowability allows a greater quantity of concrete to be placed at one time than underwater concrete, thus contributing to increased productivity. It was also shown that the use of air-entraining and water-reducing admixture containing thickeners in high fluidity concrete has a small effect on the flowability in water, but seem improve the resistance to material separation, thereby reducing the strength variation associated with flow in water.

 Drifting objects flown out from the Pacific Ocean side of the Tohoku region by the Kuroshio Extension tend to be either blocked by the Emperor Seamount Chain or move eastward by eastward winds. If the winds around the Emperor Seamount Chain tend to be southward, the drifting objects will move southward, away from the Emperor Seamount Chain, and move toward Japan by westward winds. If northward winds continue while the drifting objects moves toward Japan, the drifting objects will move northward and return to the Kuroshio Extension region. It has been revealed by observations for the first time that drifting objects can make large-scale circumnavigation during more than one year on the western side of the Emperor Seamount Chain, even without crossing the Emperor Seamount Chain, by ocean currents, winds and the Emperor Seamount Chain.

 In the 2007 revision of the Technical Standard for Port and Harbour Facilities and its Commentary, the concept of performance-based design was presented. The 2018 revision clarified the concept of improvement design of existing facilities and the promotion of effective utilization of existing stock. In designing a new jacket-type pier in front of an existing revetment (double steel pipe sheet pile structure with long piles) consisting of long and short steel pipe sheet piles in the outer area of the central breakwater of the Port of Tokyo. We evaluated the effect of long piles and attempted to establish performance criteria. As a result, it was confirmed that the long piles exerted resistance force during a level 2 earthquake and reduced the stress generated in the piles of the new pier. This paper presents an economical design by effectively utilizing the structural form of the existing port facilities within the framework of performance-based design.

 The Suez Canal blockage in 2021 highlighted uncertainties and business risks of the recent international maritime transportation including those caused by cyber-attacks on various maritime systems. The Tokyo Bay Central Access Channel is a vital gateway to Tokyo bay area ports which maintain the production activities and the people’s lives in the Kanto region.

 This study, by focusing international container trade and domestic unit load cargo transportation, searches an alternative transportation route and estimates the generalized cost involved when serous blockage should happen at the Tokyo Bay Central Access Channel. It is concluded that more than 70% of the foreign containers to/from the Kanto region needs to be detoured through port of Sendai-Shiogama and Ise-Bay area ports, which are requested to accommodate the number of containers to their capacity limits, and the transportation cost increases by about 2.93billion yen/day (32 percent).

 The sediment transport model XBeach was applied to existing hydraulic experiments on topographic change of a gravel beach to investigate the influence of parameters related to sediment transport and evaluate the predictive capability of the model through comparison with experimental results. Numerical results showed that the reflective type of beach profile change can be obtained by increasing a factor for landward bed-load sediment transport (uprushfac) greater than unity and decreasing a factor for seaward bed-load sediment transport (backwashfac) less than unity to take into account the effect of in/exfiltration across the beach surface. It was also found that the reflective type of beach profile change cannot be computed simply using the groundwater module. Furthermore, the accuracy of the spatio-temporal change of the beach profile can be improved by calibrating the static friction angle of the sediment (re-poseangle) in addition to the factors of bed-load sediment transport.

 Lake Saroma is the largest brackish water lake in Japan. In January 2012, the second inlet of Lake Saroma had a disaster that buried the channel. In this study, waves, river sediment runoff, topographical changes, and shoreline changes were organized. It was concluded that the cause of the burial disaster in 2012 was the remarkable response of topographical changes to the large-scale flooding of the Tokoro River and eastward waves. In addition, using a 1-line model, future predictions were made assuming a scenario in which the largest river flood in history and eastward waves overlap. This indicates the danger of the environment becoming severe.

 Significant wave height forecasting is needed to determine whether or not a ship is navigable and offshore construction work is feasible. The wave forecast is usually carried out by using global or regional operation numerical ocean surface wave model. In addition, the artificial neural network has been also used for wave forecasting. However, almost all neural network wave forecasting has been carried out on the specific location and the 2-dimensional wave forecasting has been not so much performed. In this study, we attempted to forecast a two-dimensional wave field using convolutional LSTM, using numerical values of a third-generation wave estimation model SWAN as training data. The results shows that 2 dimensional wave forecasting in the lead time of 1~3 hours are conducted in high precision, while the wave forecast in the lead time over 12 hours were not carried out with high precision.

 One of the issues of offshore wind power generation systems already in practical use in harbor areas is the countermeasure against scouring of foundations. In recent years, many studies have been conducted on the application of foot protection bags to prevent scouring of the foundations of mono-pile support structures, and their effects on scouring prevention have been clarified. On the other hand, it is necessary for the foot protection bags to be stable against waves and currents, but so far the study has been limited to individual conditions. In this study, with the aim of proposing a method for calculating the required mass of foot protection bags, a hydraulic model experiments were carried out on the stability of foot protection bags laid around a mono-pile. As a result, it was clarified that the effect of relatively gentle currents such as tidal currents and ocean currents is small, and that the effect of waves is dominant on the stability of foot protection bags. In addition, we confirmed the effects of water depth and wave period, and proposed a design diagram of the stability number Ns of the foot protection bags against the relative water depth h/L.

 Coast around Japan is rich in wave energy. In this study, we propose a method in which a pair of positive and negative pressure-resistant containers placed under the water surface are connected with pipe to produce unidirectional flow in the pipe under the wave condition. Since it can be placed underwater like a submerged dike, it is expected to be able to acquire energy during high waves with a low possibility of damage due to wave force of high waves. A prototype model was placed in a wave-making tank with two-dimensional configuration, and the flow velocity generated in the pipe connecting the pair of pressure resistant containers was measured. It was confirmed that it is possible to obtain a stable flow velocity under the regular wave condition, and that it is possible to increase the generated flow velocity with the increase of the wave height. In addition, it was clarified that the average flow velocity of about 65% of the regular wave can be obtained under the irregular wave condition, although the flow velocity becomes unstable.