In order to evaluate the impact of the natural environment on tidal flat organisms, it is necessary to understand the spatiotemporal distribution of environmental factors and tidal flat organisms, and to confirm their mutual relationships. In this study, we used deep learning to determine the number of individuals and their habitat locations from image data of click crab burrows taken in tidal flats.

 As a result, we succeeded in detecting click crab burrows, and the detection accuracy was approximately 70% in cases where detection was attempted using both burrows and sand balls as features. In addition, in the habitat distribution based on location information, although the area is slightly smaller than the actual measurement in the field, the distribution shape is similar. Therefore, it is considered to be an effective method for understanding distribution characteristics in vast tidal flat surveys.

 In the areas affected by the Great East Japan Earthquake, restoration and reconstruction efforts are progressing at a rapid pace, including the construction of giant sea walls. They target local economies and industries, and do not give sufficient consideration to the restoration of natural environmental spaces. As a result, the rich fishing village scenery before the earthquake is being completely lost. In recent years, the idea of ``pre-disaster reconstruction'' in areas that have not experienced a disaster has become widespread as a form of regional disaster prevention. In this study, we applied this idea to the natural environment, and based on the results of GIS analysis using open data, a questionnaire survey of fishing port managers, and a literature review, we proposed a procedure for formulating a pre-disaster recovery plan.

 The mechanical properties of soft dredged soil are improved by the solidification reaction caused by the mixing of converter steelmaking slag. Depending on the amount of calcium and silica leached from the steelmaking slag and the dredged soil, the strength of the dredged soil may not be sufficiently improved. In this study, the effect of magnesium oxide as an auxiliary material for converter steelmaking slag mixed soil was examined. The results showed that the addition of magnesium oxide significantly improved the strength of converter steelmaking slag mixed soil, even under material conditions with low calcium and silica leaching. From the results of several instrumental analyses, it was inferred that this improvement in the mechanical properties was due to the formation of new reactants and densification.

 Coastal erosion is one of the major coastal problems in Indonesia. A fishing port was constructed 5 km updrift side from the Pebuahan coast in the western part of Bali Island. Significant coastal erosion occurred on the downdrift side of the fishing port after construction. On the other hand, sand accumulates on the updrift side year after year and the accumulated sand has already invaded the inside of the fishing port. As a measure to protect against coastal erosion on the downdrift side by blocking littoral drift, seawall measures have been carried out. But that is clear that the problems of coastal erosion on the downdrift side and sedimentation problems at fishing ports have not been resolved. Therefore, this study aims to confirm the feasibility of sand bypassing from the updrift side of the fishing port to the downdrift side as a new erosion control method through long-term satellite image analysis field surveys and numerical analysis.

 In the technical standard and commentary of port and harbor facilities, the performance verification of structures against seismic forces is based on the time history waveform of input seismic motions, and there is not enough knowledge about how to give variations in reliability analysis. In this study, we proposed a method to generate a large number of pseudo-seismic motions by considering the covariance evaluated from the variations and seismic motions of the design input earthquake motion evaluated at each frequency. The frequency distribution of the design seismic intensity of the pier is obtained from the pseudo-seismic motions, and it is assumed that the design seismic intensity of the pier follows a lognormal distribution in the reliability analysis. The generalization performance was improved by improving the parameter estimation method of the RSM. It was also confirmed that the failure probability changes accordingly.

 This paper reports the results of Sampling and Cone Penetration Test (S&CPT) conducted in medium dense sand (N value = 10 to 30) and its applicability. This test method allows conventional Cone Penetration Test (CPT) and continuous soil sampling simultaneously. In the previous study, demonstration tests were conducted in soft clay (N value < 2) and loose sand (N value < 10), and several issues regarding sampling performance and workability was found. To overcome them, the structure of the sampler was modified, and the demonstration test was conducted on medium dense sand. As a result, the following conclusions are drawn. 1) It is possible to obtain several meters of continuous soil sample in medium dense sand by using an appropriate shoe to prevent soil blockage at the tip of the sampler. 2) The time operation for S&CPTs requires no longer than 2 to 3 times that for CPTs, thus the workability of S&CPTs are extremely high.

 The application of dredged sediment is required to supply nutrients into the construction of artificial tidal flats.Several previous studies demonstrated that Granulated Coal Ash (GCA) -induced changes in the physicochemical properties of tidal flats promoted the supply of nutrients in coastal sediments. The purpose of this study was to investigate the GCA-induced changes in the physicochemical properties of dredged sediment. The field investigation was conducted to observe the environmental changes of the tidal flats due to GCA in an artificial tidal flat created by dredged sediment behind the breakwater of Hiroshima Bay. The results showed that high water content was retained in the dredged sediment. On the other hand, GCA promoted the decomposition of organic matter in the dredged sediment, increasing the porosity of the surface on the tidal flats.

 Endowment of wave energy in the sea around Japan is estimated as 35,000,000 kW and is never small. But the wave energy technology has not become in practical use. All of the systems ever proposed and studied or developed are operated in seme-submerged condition, and therefore, they cannot keep the position against the wave force exerted with low cost. In this study, check valve type wave energy converter, which solved the above problem, is investigated. Hydraulic consideration was made about the energy available, and the model experiment was made supposing the operation at the sea off Niigata area. This study enabled us to evaluate the available energy considering the factor for the decay of pressure variation under water and the factor influenced by the fact that the length of the region of check valve array is shorter than the wave length. Also, the effective head in the theoretical hydraulic power calculation was found to be 0.7 times the total head. This result was applied to the calculation of the available energy in the real sea.

 One of the liquefaction countermeasure methods is the gravel drain (GD) method using highly permeable crushed stone to reduce the amount of excess pore water pressure during liquefaction and to accelerate its dissipation. On the other hand, flat shell piles are more likely to be damaged. On the other hand, shell drain (SD) piles constructed with flat shell particles have been reported to be more effective as liquefaction countermeasure piles than GD piles, because the drainage performance of SD piles is less affected by sand contamination than that of GD piles. In addition, shells are lighter than crushed stone, and the application of SD piles may reduce the amount of post-seismic ground settlement. In order to confirm the effectiveness of SD piles in reducing post-seismic ground subsidence, which is considered to be effective against repeated earthquake ground motions, this study experimentally clarified the effectiveness of SD piles in reducing post-seismic ground subsidence by comparing the amount of ground subsidence after vibration with that of GD piles in 1G field shaking table experiments.

 The Net Buffer Method substantially suppresses the risks of internal erosion and collapse behind seawalls and quaywalls by caisson joint wave reduction. In this study, a six-year follow-up study after the application of the Net Buffer Method to three Major Ports and Strategic International Ports in Japan was conducted, involving three typhoon events. The results of the field surveys, observations, and the in-situ sampling and tests demonstrate the effectiveness of the Net Buffer Method as preventive maintenance and recurrence prevention measures against coastal internal erosion and collapse. Notably, the Net Buffer Method has proven itself effective in preventing collapse under multiple strong earthquake motions as well as severe wave conditions than those that led to collapse in the past.

 In this study, a method is proposed to estimate the presence or absence of damage to mooring facilities in a port area by using velocity-PSI values calculated from seismic waveforms (on the ground surface) at each port, which are obtained from the Strong Motion Earthquake Observation in Japanese Ports. The definition of "damaged" is defined as the case where there is damage at least at one facility in the port where the observation point is located. The estimate method consists of: 1) a table for on-site engineers that classifies the velocity-PSI values in stages and explains the presence or absence of damage to mooring facilities and the degree of damage assumed for each classification, and 2) an earthquake fragility curve that expresses the possibility of damage to mooring facilities in each port using the velocity-PSI values as an indicator. This method was applied to the evaluation of damage in the Noto Peninsula earthquake, and a certain degree of applicability was confirmed.

 To construct sustainable socio-economic activities through the stable supply of renewable energy, ocean development for offshore wind power generation is being advanced. In Japan, a country prone to earthquakes, there is a need for the development of seismic design methods that not only ensure safety against earthquakes but also contribute to cost reduction through structural rationalization. This research conducted model vibration experiments using a large underwater shaking table to verify the seismic behavior considering the dynamic interaction between monopile foundations and saturated sandy soils, and performed reproduction analysis with the three-dimensional effective stress analysis method "analysis code FLIP ROSE 3D" to assess its applicability as a seismic evaluation method. The analysis results largely replicated the bending moments in the submerged and emerged parts of the monopile from the model shaking table experiments, as well as the response acceleration and displacement at the pile head, thereby confirming its applicability as a seismic evaluation method.

 Seagrass beds play vital roles, serving as habitats for fish and shellfish and contributing to oxygen production. However, recent environmental changes driven by climate change and human economic activities have disrupted the delicate balance of ocean ecosystems, impacting seagrass beds and increasing the grazing pressure from sea urchins and other vegetative organisms. This disruption has led to overgrazing by sea urchins, resulting in a decline in commercially valuable seaweeds like kelp and an increase in the proliferation of economically less valuable sea urchins. This study develops a mathematical model of the symbiotic relationship between sea urchins and kelp, conducting theoretical analyses to propose a management plan aimed at maximizing final profit. The findings suggest that in scenarios where minimizing kelp feeding damage is crucial, it's essential not only to delay the reduction of feeding pressure management levels but also to avoid excessive reductions, allowing for adequate kelp growth.

 The Kako River is the longest first class river in Hyogo Prefecture. The Kako River weir started operating in 1989, and the weir and the dams of upper and middle reaches of the weir started operating integrally in 1992. This study tried to quantify the river flow decrease and to examine the influence on the environment of the estuary by development of water resources at the Kako River basin. The study found that the river flow from the Kako River mouth to the sea decreased by 20% per year under the mean precipitation after integrally operating start of the Kako River weir and the dams. The decrement of annual mean of surface salinity concentration, the decrement of surface salinity concentration on flood season and the increment of dissolved inorganic nitrogen on flood season on the station near the Kako River mouth became smaller. It is thought that it is important to take into account the influence on the environment of the estuary and the fishery production by development of water resources.

 In the towing operation of caissons by tugboats, the caisson is subject to motion due to waves and towing. Therefore, it is important to understand the motion characteristics of the caisson during towing to ensure the safety of the operation. In this study, we investigated the effects of head waves, following waves, and beam waves on the motion characteristics of the caisson during towing through model experiments. As a result, the heave amplitude ζ_amp resonated at Ti^mod / T_h ≈ 1.0 with head waves and beam waves, while the total amplitude of pitch β_amp increased significantly at Ti^mod / T_p ≈ 1.0 with following waves. Furthermore, the periods of heave and pitch matched the apparent incident wave periods acting on the caisson. Regarding the caisson's motion characteristics due to wave direction, different characteristics were observed with following waves. In the case of following waves, it is inferred that the caisson is influenced by towing on the front side and by wave action on the back side, thus exhibiting different motion characteristics from head waves and beam waves. In the future, we aim to further investigate this phenomenon using numerical analysis.

 In the coastal area of Konagai Town, Isahaya City, Nagasaki Prefecture, clam death occurs during summer. Based on recent results of clam survival rate and dissolved oxygen concentration, the short-term mass mortality of clams in the summer of 2021 is due to anoxic water bodies. On the other hand, it was suggested that asari clam may be dying slowly due to factors other than the anoxic water bodies. The peak spawning period was inferred from the developmental stage of the gonads, and the condition factors suggested that a decrease in stored energy during spawning may cause death. It was suggested that spawning and water temperature are closely related to survival, and there was concern about the effects of changes in seawater temperature. As a means of confirming the relationship between changes in seawater temperature and spawning, the total temperature from the day of lowest recorded water temperature to the next spawning was calculated to be 2, 174 ℃. It is necessary to verify the relationship between spawning and water temperature using this as an indicator in the future.

 On the Ishikawa coast, it is confirmed that the shoreline retreated 200 m in about 80 years from 1892 to 1970. In response, the foreshore is being restored by the construction of a group of detached breakwaters to prevent erosion. However, erosion has been progressing offshore of the detached breakwater even after the erosion countermeasures were taken, and offshore erosion is also progressing at depths deeper than 15 m, which exceeds the depth limit for wave-induced sediment transport. In this study, we collected beach sand samples at intervals of about 2 m from a water depth of 5 m to a maximum of 30 m along 10 side lines along the Kaetsu coast, and calculated correlation coefficients at each site based on grain size analysis, constituent element analysis by X-ray fluorescence analysis, and constituent element ratios, in order to understand the characteristics of offshore marine sand and discuss sand drift mechanisms.

 In order to accurately predict the development of storm surges for effective gate operations in the inner part of the Ariake Sea, we investigated the impact of different computational parameters in the numerical model on the estimated values. Our study aimed to provide insights for constructing storm surge numerical models in this region, focusing on the influence on the maximum surge deviation and its temporal variations around the maximum storm surge deviation. As a result, we found that setting the computational range to encompass the precursor waves improved the accuracy of reproducing temporal variations during storm surge development. We also clarified that the deviation remains unchanged until the grid resolution within the Ariake Sea reaches 600 meters or less, but beyond 1,000 meters, the estimated values decrease. Additionally, we identified significant differences between meteorological forcing from the Meteorological Research Institute's Meso-Scale Model (MSM), which reflects the influence of land, and a simple empirical typhoon model, with variations in their tendencies depending on the typhoon. Furthermore, stability in the computed results was achieved by setting the vertical layer number to five or more.

 Rock debris (particle size: 0-300mm, permeability coefficient: 2-3×10^-1cm/sec) was planned to be used for the seafloor replacement part of the Shinmoji (Phase II) sediment disposal site. There was a concern that the dredge soil in its turbid state would permeate into the rock debris layer, allowing the flow-out of muddy water into the sea, requiring the placement of a sand prevention sheet. Here, we conducted a series of experiments on the seepage of the turbid dredge soil into the rock debris layer to examine whether the rock debris has filtering and clogging effects to effectively deter the muddy water outflow. The results proved both effects, leading to a new cross section without such sheets in the field. The new cross section was adopted in practice and subsequently field observations were performed on the SS (suspended solids) concentrations from 2022 to 2023. The results confirmed the effectiveness of the rock debris layer to prevent muddy water outflow at the water sediment disposal site.

 While waves diffracted on breakwaters and multi-reflected in a harbor area act on harbor facilities, it may be difficult to estimate the progressive wave height on quay wall, which is applied to Goda formulas of wave pressure. In design of the parapet installed on quay as a countermeasure for inundation due to wave overtopping, estimation of vertical distribution of wave pressure must be required on stability check as same as design of breakwaters. Therefore, in this study, the vertical distribution of wave pressure is directly calculated by using a Boussinesq model (NOWT-PARI Ver5.2), which is widely used for harbor tranquility analysis in abnormal wave condition.

 Although a newly developed wave pressure equation which is installed in the Boussinesq model can estimate the vertical distribution of dispersive wave pressure, it is realized that the model overestimates one of nonlinear standing wave pressure overall and especially around water surface and must be modified in detail to estimate wave power limitedly acting on the parapet located above settle water surface.

 A new measurement system using optical fibers has been developed for the accurate placement of steel pipe sheet piles in construction projects. Conventional control methods do not assume deformation of steel pipe sheet piles in water or soil, but in reality, deformation may occur due to the weight of the piles and the influence of the ground. This technique directly measures the deflection of steel pipe sheet piles, and its applicability was verified through field demonstrations and laboratory operational checks. A combined optical fiber and laser measurement system was welded to steel pipe sheet piles to measure the direction and amount of deflection in real time. Initial field demonstrations confirmed the deformation of the steel pipe sheet piles in response to changes in soil properties. Additional field demonstrations on long steel piles showed no deflection during the measurement but presented new challenges unique to long steel piles. Further work will be done to verify the accuracy and improve the measurement system to more accurately determine the deflection.

 In this study, a portable ship motion measurement system with a sample period of 100 Hz was developed using a small IMU (inertial sensor). The accuracy and practicality of the system were also investigated. The amount of rotational motion was calculated in the object coordinate system as Euler angles (Yawing, Pitching, Rolling) using an extended Kalman filter with the rotational angular velocity as the input signal and the rotation angle calculated from the acceleration and geomagnetic field as the observed value. The amount of translational motion was calculated as displacement in the absolute coordinate system using GPS and acceleration data converted to the absolute coordinate system by taking Yawing into account. Ground experiments were conducted to verify the accuracy of the measurement of the amount of rotational motion, and the true and measured RMSEs of Yawing, Pitching, and Rolling were 13.26°, 0.09°, and 0.05°, respectively. Sea trials were also conducted using a small ship to measure the amount of ship motion during the voyage and confirm the applicability of the system.

 A carrier material circulation system that transports ore in a capsule is proposed as a system for pumping deep-sea mineral resources. An experimental study was conducted to determine the dimensions and shape of a capsule suitable for this system. The following four points were found. (1) The transportation efficiency of bentonite suspension, which is assumed to be used as CM, is several times higher than that of water, and is further improved when sand is added. (2) The larger the diameter of the capsule, the higher the transportation efficiency, and this trend is remarkable for the capsules with high density. (3) The transportation efficiency is slightly lower for capsules with a larger height-to-diameter ratio. (4) Spiral ribs are disadvantageous for vertical upward transport of heavy capsules.

 In order to enhance wave attenuation, a method of widening only the wave dissipating blocks of horizontally composite breakwaters may adaptively respond to the high uncertainty associated with future climate change without removing the existing wave dissipating blocks due to raising the crest level of the breakwater. Hydraulic model experiments acting irregular waves with 1/50 scale were conducted on widening the wave dissipating blocks to explore the potential generalization of this improvement method. The crest width of the wave dissipating blocks was varied for three types to disclose the wave transmission and the sliding stability of the caisson. The stability of existing wave dissipating blocks was also examined by varying their mass to determine the critical wave height at which block displacement occurs. The experimental results indicated the possibility of maintaining performance equivalent to before the improvement by only widening the wave dissipating blocks without raising the crest of the breakwater, even after increasing the design wave height.

 The arrival of a typhoon has a significant impact on the decision of whether to proceed with marine construction, but the chaotic nature of typhoons makes deterministic forecasting difficult. Although ensemble forecasting has been studied for the prediction of precipitation intensity and storm surge by clustering the members to increase the accuracy rate over time, there are few examples of its application to wave forecasting, especially for the purpose of determining whether construction is feasible or not. Therefore, the authors conducted a basic study of wave forecasting by clustering the paths of multiple typhoons, categorizing, and averaging the wave estimation results for each cluster, and using the results to understand wave trends by path and to predict the probability of each scenario for use in decisions on whether to construct or not and to evacuate. As a result, it was found that the wave heights calculated differ according to the different scenarios that are included in the ensemble. Clustering typhoon paths from the most recent ensemble forecast and comparing them with typhoon information is expected to be utilized as a decision-making tool.

 It has been reported that the density-increasing effect and early dissipation of excess pore water pressure by short piles of crushed stone and the hammock effect of geosynthetics edge restraint by crushed stone can reduce the amount of sinking during liquefaction in thick sub-layered residential land. In recent years, as we are shifting to a recycling-oriented society, there has been research on the use of shells, a by-product of marine products, as a civil engineering material. In this study, focusing on the hammock effect, the applicability of using shells as edge restraints for geosynthetics and an effective hammock mechanism were verified through pull-out experiments and 1G-indoor shaking table model experiments. As a result, the applicability of shells as geosynthetic end-constraints and the effective hammock mechanism were clarified.

 The surveying method using UAV-SfM/MVS produces high-resolution ortho mosaic images that provide information on both the elevation and changes in gravel beach components. In addition, gravel size can be useful to understand the process of topographic change on gravel beaches. This study focuses on the machine learning model 'GRAINet' and its ability to estimate the size of gravel grains on Ida beach. A map of the distribution of gravel grain sizes was created, and changes in the spatio-temporal distribution of topography and gravel grain size were investigated. The results suggest that the demonstration data should be verified by comparison with the sieving test at the target site.

 There have been no prior studies or field applications employing a staggered arrangement of stone gabions as mound covering material for composite breakwaters. In this study, we conducted 1/40 scale irregular wave experiments utilizing stone gabions arranged in a staggered pattern as mound covering material for composite breakwaters. Stability assessment employed the dimensionless average sliding amount D’, as proposed by Shimizu et al. (2023), to represent the average mound offshore sliding amount for each stone gabion model. Our findings suggest that, compared to lattice arrangements, staggered arrangements may potentially prevent the sequential movement of stone gabion models. Additionally, stability numbers at D’ values of 0.05, 0.10, and 0.15 were approximately 0.3 larger in experiments with lattice arrangements compared to those with staggered arrangements. Under the experimental conditions with spaced arrangements of stone gabion models, the stability numbers for lattice and staggered arrangements (Ns) remained generally consistent, indicating they fall within the range of experimental accuracy.

 Wave dissipating blocks experience a reduction in wave dissipating function due to damage or movement. Finding damaged areas on wave dissipating blocks visually is difficult, so automatic extraction would be very useful. A machine learning model was constructed to apply instance segmentation to ortho-mosaic images obtained by UAV-SfM/MVS surveying to identify wave dissipating blocks from the images. In addition, learning conditions that increase the discrimination accuracy of the machine were examined. The areas where the blocks changed were extracted based on the difference between the areas of wave dissipating blocks before and after the disaster. The results indicate that the two types of blocks could be identified individually from the ortho-mosaic image. The difference in the block area between the observations allowed identification of the planar change in the wave dissipating blocks.

 In offshore wind power generation, ocean currents are considered as an external force. The guidelines for offshore wind turbines define ocean currents as blowdown currents, underwater currents, and beach currents, and propose a linear distribution that reaches zero at a depth of 20 m for blowdown currents and a 1/7 power law from surface to bottom for underwater currents as the vertical distribution. Although the vertical distribution of the current is important because it affects not only the stability of the foundation but also the scour, the 1/7 power law tends to overestimate the vertical distribution of the current compared to the estimated current, for example. In this study, we first focused on the simultaneous vertical profiles of ocean currents and compared them with the estimated currents and, although there are only a few examples, with observation records. The results showed that many of the vertical distributions were consistent with the exponential-type vertical distributions used in Ekman theory, and that the 1/7 power law tended to overestimate them.

 A wave-power generation system with waterwheels installed in the chamber of a vertical-slotted breakwater has already been proposed and developed for the last decade. An empirical formula for estimating the acquired power that the wave system is constructed under a constant water depth has also been proposed. In Japan, however, breakwaters are generally constructed on mounds. Hence, it is necessary to evaluate the performance of the system considering the effect of mounds in practical use. In this paper, the boundary integral method is applied to the analysis of the wave field around the breakwater on a mound for estimating the velocity through the slit, and an estimation method of the acquired power considering the effect of the mound is established.

 In order to develop a method to estimate the turbidity distributions from the aerial images of muddy water in offshore construction projects, the relationship between the color of captured image and the turbidity of muddy water was experimentally investigated using a small container. The results showed that the relationship between the color difference, which indicates the difference between the colors of images of turbid water with different densities, and the turbidity is similar even under conditions with different water sources, ocean colors, and illumination levels, and that the relation of the change in color difference to the turbidity shows a curve shape such as a power-law approximation where the larger the turbidity, the smaller the ratio of the color difference to the turbidity. This result suggests that it is possible to construct an index for evaluating turbidity from turbid water photographic images regardless of the bottom sediment or sea area in a limited area such as an offshore construction area, i.e., an area where the sea color is uniform. In addition, we confirmed that the range of color difference tends to become narrower as the illuminance becomes lower regardless of the material or bottom color, suggesting that it is useful to construct a turbidity evaluation index corresponding to the illuminance or to formulate the degree of illuminance.

 The Hybrid Caisson (HBC) can be expected to have anti-toppling effects and expand its applicability to soft ground through footing. However, currently, the effect of footing is not considered, and HBCs are designed using the same process as reinforced concrete (RC) caissons.

 Therefore, in this study, we aimed to calculate the uplift and downward pressures acting on the footing using a particle method capable of reproducing the behavior of nonlinear fluids, as the wave pressures used in HBC design occur during complex fluid behavior such as overtopping waves and breaking waves.

 By comparing the experimental results of existing studies by Ezaki and Sakai with our calculated results, we confirmed that the permeable mound placed under the HBC can achieve uplift pressures close to experimental values by setting the fill rate to 70%. Additionally, the possibility of economically efficient cross-sectional design considering footing was suggested, as the downward pressure acting on the footing was obtained to be higher than the uplift pressure.

 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, fine-grained sand around the piles will be mixed into the voids of the crushed stones during liquefaction, which will reduce the effectiveness of the countermeasures and increase the liquefaction damage. It is reported that drain piles constructed with shells are effective in preventing the deterioration of drainage performance because finegrained sand around the pile does not easily get mixed into the pore space of the shells even when subjected to vibration. If shell drain piles are to be used in the implementation, it is important to quantify the effect of pile diameter on sand mixing during earthquake. In this study, 1G-field shaking table model tests were conducted for four different pile diameters. The experimental results showed that the length of sand mixing into shell drain piles becomes more remarkable as the pile diameter increases and that the length of sand mixing into shell drain piles was smaller than that into gravel piles.

 The creation of seaweed beds is an important issue for the recovery of fishery resources and the maintenance of ecosystems, and has been attracting attention in recent years as it contributes to the promotion of blue carbon. In this study, we investigated the feasibility of using fermented wood powder mixed into mortar as a block for seaweed bed creation. First, the viability of yeast in the mortar was examined through laboratory tests. Then, the mortar specimens mixed with fermented wood powder were immersed in the sea for exposure tests, and the growth of algae was examined. The results of the laboratory tests showed that the yeast could survive for at least 13 weeks in the mortar by forming the fermented wood powder into clumps of about 25 mm in size. In the exposure tests, the mortar specimens containing fermented wood powder had significantly more laminaria japonica than those without fermented wood powder.

 Numerical analysis is an effective tool for evaluating large deformation in seabed soils and its effectson surrounding structures, such as leg penetration of SEP vessels, subsequent pile foundation installation and leg withdrawal. One of the representative numerical methods used for large deformation analysis is the Material Point Method (MPM), which is a hybrid of the grid method and the particle method. In this study, a solid-liquid two-phase coupled 1-point axisymmetric MPM simulator based on the u-U formulation considering soil-water-structure interaction was originally developed. The formulation and program were validated by comparison with theoretical solutions, and centrifuge model experiments of leg penetration and withdrawal of a SEP vessel were reproduced and analyzed to verify the applicability of this method to the problem of large ground deformation associated with steel penetration. The behavior of leg penetration and withdrawal and the surrounding ground, such as the region of predominant plastic shear, were qualitatively reproduced, and issues for quantitative evaluation were extracted.

 Based on Goda et al.'s (1975) wave overtopping rate estimation chart, we calculated the wave overtopping rate and required crest height when the sea level rises. As a result, the wave overtopping rate increased with sea level rise, and in many cases, the overtopping discharge became 0.04 m³/m/s with a rise of 0.6 m. In particular, for seawalls covered with wave dissipating blocks, when the water depth is shallow, the wave overtopping rate increases rapidly, and a rise of 0.6m exceeds the seawall's disaster limit rate of 0.2m³/m/s. The increase in wave overtopping rate was particularly noticeable when the water depth was shallow at the wave-dissipating seawall. In addition, the increase in wave overtopping rate was more pronounced when the wave period was shorter. Because the crown height of a seawall with a short wave period is relatively low, it is relatively susceptible to the effects of sea level rise. The shallower the installation water depth, the greater the required crown height when the water level rises.

 During the event of an earthquake, there is a significant concern regarding the discharge of hazardous substances stored at industrial facilities into rivers. This concern is exacerbated by the possibility of these substances reaching the intake points of water purification plants due to the upstream movement of rivers caused by tsunamis, thereby affecting the process of water extraction. The current study specifically addresses this issue by hypothesizing the release of hazardous substances in the vicinity of the Yodogawa Dam area during a Nankai Trough earthquake, an event predicted to have a high probability of occurring in the near future. By employing various scenarios, the study aims to forecast the potential impacts on water intake at a purification plant.

 The findings from this investigation reveal several key insights. Firstly, hazardous substances discharged more than approximately 1000 meters downstream from the dam are unlikely to reach the intake point, thereby posing no significant threat to water extraction processes. Secondly, an increase in the volume of hazardous substances released results in a higher maximum concentration in the water; however, the influence on the duration of water intake stoppage remains relatively minor. Additionally, the study highlights a distinctive behavior in cases where multiple hazardous substances are released simultaneously, as opposed to the release of a single type of substance. Others’ outcomes are mentioned in the main text.

 These outcomes underscore the complexity of hazardous substance dispersion, which is influenced by a multitude of factors. Consequently, this complexity necessitates a comprehensive approach to analyzing the impact on water intake. The study concludes that in order to accurately assess the implications of hazardous substance discharge on water purification processes, it is imperative to conduct diverse analyses under realistic conditions.

 Although it has been reported that rubber-tired gantry cranes (RTGs) in harbors were not damaged in the 1995 Hyogo-ken Nanbu earthquake, their seismic behavior has not been well clarified yet. Therefore, model shake table tests were conducted to investigate the behavior and stability of RTGs. As a result, although large values of acceleration response were observed in the legs during vibration, large stress of structural member leading to failure were not observed, which is consistent with the fact that no damage was observed in RTGs during the Hyogo-ken Nanbu Earthquake. Although large acceleration response values were observed due to the influence of higher-order modes, the high frequency component was not observed in the member curvature, indicating that the contribution of low-frequency modes was significant.

 We developed a fish reef capable of effectively sustaining the function of creating biological habitats over extended periods, even in high-turbidity brackish water dominated by sessile bivalves. These fish reefs were characterized by their simple structure, consisting only of ropes attached to plastic frames. We tested the hypothesis that “the attachment of bivalves to the ropes creates habitats for gobies” in on-side aquarium experiments. We found that (1) the attachment and growth of bivalves on the ropes created rough surfaces and shadows within the fish reef, attracting juvenile Dusky Triple-tooth Gobies Tridentiger obscrus, and (2) the juvenile gobies entered and settled in the internal spaces of the fish reefs. The gobies utilized the rough outer surfaves of the fish reefs, even when the sessile bivalves entirely covered the fish reefs. Furthermore, as the bivalves were detached, the spaces within the fish reef for the gobies to enter were restored.

 Sediments dredged from navigation channels have been used as a foundation for artificial tidal flats and as backfill for depression-type, subaqueous borrow pits. The goal of this study was to determine the rate of sequestration of organic carbon and production of methane in the dredged sediments used as backfill for a subaqueous borrow pit. A field survey was conducted in September 2023 at the restoration site of a depression-type, subaqueous borrow pit in Mikawa Port, Japan at two sites: St. 1, where no sand capping was applied, and St. 2, where sand capping was applied. Vertical core samples were collected using a vibrating core sampler. Laboratory analyses were conducted to measure, the particle size distribution, water content, loss on ignition (600°C; IL), total organic carbon, and methane in the sediment. The IL was used as an indicator of organic matter to calculate the rate of sequestration of organic carbon in the dredged sediments. The initial values used to calculate the sequestration rate of organic carbon were taken from an earlier survey conducted in 2008. The sequestration rates calculated for St. 1 and St. 2, 117% and 106%, respectively, exceeded 100%. The initial IL value for the dredged sediments in the 2023 survey (estimated from the relationship between the silt/clay ratio and the IL of the dredged sediments at the time of the 2008 survey) was higher at St. 1 (96.9%) without sand capping than at St. 2 (83.3%) with sand capping. Depending on construction conditions, the rate of sequestration of organic carbon may be higher when dredged sediments are used as backfill for a subaqueous borrow pit than when they are used as substrate for tidal flats. The amount of methane produced in the dredged sediments was small compared to the carbon sequestered in the dredged sediments used as backfill for the depression-type, subaqueous borrow pit.

 The purpose of this study is to clarify the relationship between the actual regulatory status of “INOCHIYAMA” and its maintenance period and cost focus on the coastal area of Enshunada, Shizuoka Prefecture, where severe tsunami damage is foreseen due to a Nankai Trough Earthquake.

 As a result, it clarified following; (1) In the “Urbanized Area”, public land (parks) and donated land (mountain forests) can be easily used to construct “INOCHIYAMA”, but issues include the cost and construction period of applying for permission under the Urban Parks Act and taking measures to prevent forest collapse. (2) In the “Urbanization Control Area”, public land (school land) and farmland are likely to be used for construction of “INOCHIYAMA”, but the issue is the construction period required for development permit applications based on the City Planning Act and farmland conversion procedures based on the Agricultural Land Act. (3) In “non-delineated areas”, residential land, farmland and protected forests are likely to be used for the construction of “INOCHIYAMA”, but the issue is the construction period required for farmland conversion procedures and application procedures based on the Forest Law.

 The purpose of this study is to clarify the sea-scape characteristics and formative factors when traveling by car on the road, focus on the Boso Peninsula area of Chiba Prefecture, where includes many coastal roads among the registered cases of Scenic Byway Japan. As a result, it clarified following; (1) Sea-scape can be seen at a total of 503 locations on the coastal roads in 121 road sections of the Boso Peninsula area. (2) Derivation of nine sea-scape types view from the similarity of sea -scape characteristics, (3) The formative factors of nine sea-scape types derived from "Road cross slope", "Road alignment" and "Roadside objects".

 The formation and maintenance mechanisms of coral reef islands have been studied through field observations, movable bed experiments, and numerical analyses, and it is qualitatively understood that coral gravels are accumulated to form coral cay above the water surface under certain natural conditions. However, locations that satisfy such conditions are limited. To promote such local accumulation process of coral gravels, authors proposed a gravel trap system using permeable boards.

 In this study, we improved the trap system by adding a sloping bed in front of the trapping board and also by partially adding a permeable roof structure along the trap board, and conducted the field verification test of the improved trap. As a result, it was confirmed that the slope of the trap enhanced the accumulation of coral gravels and the roof structure worked to reduce the loss of trapped gravels. The amount of coral and debris deposited in the trap was confirmed by SfM analysis based on images taken by an underwater camera, and the trend of coral and debris deposition was consistent with wave direction when the wave-associated near-bottom Shields parameter exceeds its critical value for initiation of motion of coral gravels.

 In maritime construction management, judgment based on weather and sea condition forecasts is highly valued, but it is currently difficult to predict weather and sea conditions completely using existing technology. Therefore, ensemble forecasts, which capture meteorological phenomena probabilistically, have started to be utilized. The Japan Meteorological Agency increased the spatial resolution of the Weekly Ensemble Numerical Weather Prediction Model GPV (Japan) from 0.5625 degrees to 0.375 degrees since March 2022. In this study, we conducted wave calculations using the wind data included in the Weekly Ensemble Numerical Weather Prediction Model GPV (Japan). By evaluating the impact of high-resolution forecasting on wind and wave predictions, we examined the application of this high-resolution forecasting in maritime construction management. As a result, there were fluctuations in wind speed after the increase in resolution, and an increasing trend was observed in the rate of change of ensemble-averaged wave height data. When utilized for construction feasibility and ship evacuation decisions, an improvement in accuracy was observed.

 In recent years, due to expectations for the introduction of renewable energy to prevent global warming, offshore wind power generation business is attracting attention. The area around Noshiro Port, located in Akita Prefecture, has high expectations for offshore wind power generation projects. Plans are underway for multiple offshore wind power projects, including those within the port area. One of the environmental impact assessment items for Noshiro Port is water quality (water turbidity). As more offshore wind power generation projects are planned in Japan, regular surveys of the marine environment are required before and during construction. In this research, a method for estimating the area distribution of SS concentration over time in the vicinity of Noshiro Port in Akita Prefecture was investigated by synchronizing the satellite observation date and the field observation date of SS concentration for only one scene. These results effectively showed the planar and time-series change trends in the SS concentration distribution in the target sea area, and the applicability of monitoring SS concentrations in port construction was considered.

 As demand for renewable energy increases, there is an urgent need to identify issues related to the construction of floating offshore wind farms. In the construction of spar-type floating wind farms, a construction method in which wind turbine components (towers, blades, and nacelles) are suspended from a hoist vessel and mounted on a spar-type floating structure is considered. To determine whether work can be performed during such construction and to calculate the operation rate, it is essential to understand the amount of motion under conditions where multiple floating structures interfere with each other. In view of the above background, the purpose of this study is to contribute to the construction planning of future floating offshore wind turbine farms. Hydraulic model experiments were conducted to simulate the three-stage process of mounting a wind turbine suspended from a hoist vessel onto a spar-type floating structure to determine the amount of motion of each structure and the tension acting on the suspension line, and some considerations were made.

 In this study, the distribution of ground safety factor on a peatland coast was estimated for the Bengkalis island, Indonesia. A simplified model of the cliff topography that occurs after coastal erosion on an almost horizontal peatland coast was used to create a simple equation for estimating the ground safety factor around the coast based on the arbitrary location from the coastline, the distance from the waterway and the peat layer thickness. Using the equation, this study estimated the distribution of the ground safety factor as of 2013, clarified that there was a significant difference in the mean value of the ground safety factor between the landslide-affected areas and non-landslide-affected areas after the time of the estimation.

 In this study, a hydraulic experiment was conducted using a circular wave tank to compare a new linked wave board device with a traditional wave generator, assessing the efficacy of the new device and the impact of wave height from spiral waves on coastal sediment transport and morphological changes. The introduction of the new wave device improved the stability of wave height, allowing independent adjustment of wave height and wave period. When wave height was high, a pronounced tendency for erosion and deposition to occur alternately was observed, suggesting that the enhancement of littoral flow due to strong fluid motion and the contribution of long-period wave components from obliquely incident waves were the causes. Conversely, with low wave height, morphological changes were relatively mild, and it was found that littoral flow generated near the offshore side of the shoreline could induce morphological changes. These differences demonstrate the significant role of wave height in influencing longshore sediment transport and morphological changes.

 The frequency distribution characteristics of typhoon forecast errors were clarified based on 173 past typhoon forecast data of Japan Meteorological Agency. As the lead time of tropical cyclone disaster increased, the base of the error distribution widened, and the distribution characteristics changed depending on latitude, season, and intensity of tropical cyclone. As latitude increases, the variability of forecast errors in central pressure and track decreases, while the variability of forecast errors in forward speed increases. The forecast error distribution of central pressure is smallest in summer, indicating relatively high accuracy. Additionally, there is a tendency for forecast errors to be more variable in stronger typhoons than in weaker ones. Even with the bias values estimated from historical typhoon forecast error data used to correct the forecast results, significant improvement in forecast error was not achieved. A statistical model simulating the error distribution was used to validate the 2023 typhoon forecast case, indicating that missed hazards could be improved.