In the late 1990s, "the development and conservation of environment" was added to the legal objectives of both the River Law and the Coast Law. However, there have been significant differences between rivers and coasts in the approach to environmental management since then. Therefore, we extracted issues in coastal environmental management from the perspectives of planning, design, and surveying, and discussed the direction of their solutions, by comparing with the nature-oriented river management. Identified issues in the planning include setting quantitative environmental targets, and securing sandy beaches and setting back coastal dikes under the effects of climate change in the planning. The issues in the design include organizing environmental points of concern and ensuring good beach environments through multi-purpose facilities. The issues in the surveying include collecting nationwide data from the national census of beach-inhabiting plants and animals, and establishing a system for detailed data examination by experts.

 We projected future changes in design forces for coastal infrastructure in the central region of Tosa Bay under the climate change scenario RCP2.6, and proposed protection levels along the coast while considering adaptation measures. Utilizing a simplified estimation formula derived from 100 typhoon cases extracted from d4PDF, we determined that the storm surge deviation will increase by 12%, necessitating an increase in the design high tide level by 0.74 meters compared to the present, corresponding to an exceedance probability similar to the current coastal protection plan. Conversely, the 30-year probable wave height increased by 2%, remaining within the range that does not necessitate modifications to the design wave height. Calculation of the required coastal dike height using these design forces revealed that certain coastal areas may fall short by up to 1.17m from the current height. We prioritized adaptaion measures for coastal sections based on dike height deficiencies for storm surges and high waves by 2100, the timing for facility updates, the timing when dike heights become insufficient, and the conditions of the hinterland.

 To elucidate the mechanisms underlying wintertime phytoplankton primary production that modulates the intensity of the subsequent spring bloom in the offshore region of Enshu-nada Sea, a six-year numerical reanalysis was conducted using a three-dimensional physical–biogeochemical coupled model (ROMS-NPZD). Primary productivity exhibited pronouced contrasts between the northern and southern flanks of the Kuroshio path, with wintertime spatial variability strongly influenced by variations in the Kuroshio path. The wintertime carbon-based primary production was estimated at approximately 4.0 × 10⁶ tons during meandering phases and 3.6 × 10⁶ tons during non-meandering phases of the Kuroshio, indicating an enhanced carbon uptake of about 0.4 × 10⁶ tons due to the meandering state. Furthermore, empirical orthogonal function (EOF) analysis was conducted to assess the contributions of seasonal wind-induced coastal upwelling and localized upwelling induced by anticloclwise cold-core eddies and bathymetric features such as submarine ridges. The results suggest that wintertime primary production in the offshore Enshu-nada region is regulated by the synergistic interplay of Kuroshio path variability, seasonal wind forcing, and topographic modulation.

 Understanding water exchange times is critical for effective water quality management in coastal areas. In this study, the mechanisms and timescales of water exchange in the Seto Inland Sea and each sea area were investigated using a high-resolution three-dimensional hydrodynamic model coupled with a Lagrangian particle tracking method. Results indicated that 90% of the water in the Seto Inland Sea is exchanged over a period of 546 days, with an average residence time of 225 days. The contributions of throughflow and freshwater inflow within the sea to the overall water exchange were found to be relatively minor. In Harima-nada, many particles were transported to adjacent sea areas by eastward flows driven by winter monsoon conditions. In this region, frequent generations of submesoscale eddies enhanced vertical transport in the winter season. Conversely, during the summer season, particles tended to remain within a cold bottom water dome that formed in the central area, potentially affecting material and nutrient cycling following the breakdown of stratification.

 There is a growing demand for the development of an analysis database for aquatic environment studies that integrates observed data and numerical simulation results using data assimilation techniques. Such a database would contribute to the analysis of current water temperature and salinity distributions in both coastal and estuarine areas. In this study, we have developed a physical quantity analysis database for Ise Bay by assimilating observed water temperature and salinity data into the numerical simulation results of currents using a regional coastal data assimilation method based on the ensemble Kalman filter. The database covers 12 years from 2011 to 2022. The root mean square error of water temperature and salinity in the analysis database was 0.7°C and 2.2, respectively, in the surface layer of the inner part of Ise Bay, representing an improvement of 0.7°C and 1.0 when compared to the numerical simulation results. This database enables users to analyze specific events of interest in the aquatic environment of Ise Bay.

 Riverine water and treated wastewater, which contain large amounts of dissolved organic matter and nutrients that significantly impact the marine environment, flow into coastal areas. Therefore, it is essential to develop monitoring techniques with high spatiotemporal resolution to observe their dynamics. In this study, we conducted marine observations using a automated vessel in the estuary of the Hiro Bay and the Kurose River watershed in Hiroshima Prefecture, focusing on a refractory substance, colored dissolved organic matter (CDOM), and surface salinity to capture the dynamics of riverine water and treated wastewater. As a result, we successfully identified water masses characterized by high concentration CDOM and low salinity in the estuary, influenced by river outflow from the Kurose River, where a sewage treatment plant is located midstream, and wastewater from a sewage treatment plant facing to the estuary. The CDOM observations in addtion to salinity can suggest the potential to assess the influence of river water and treated wastewater on coastal marine environments.

 In this study, fixed-bed experiments were conducted on black tsunamis with sludge and other sedimens contained in the water to confirm the changes in inundation depth and wave force for tsunamis with different fluid densities and viscosities. In the experiments, fresh water, turbid water with varying density and viscosity, and salt water with varying density only were used, and models of seawall were set up in a two-dimensional open channel and impacted on the seawall with matching maximum tsunami heights and waveforms at the shoreline regardless of the fluid type. As a result, when the fluid density and viscosity are high, the inundation depth increases while the wave force decreases, but when only the fluid density is high, both inundation depth and wave force tend to increase. This is inferred to decrease the wave force because the fluid's viscosity dampens the tsunami energy. Numerical CFD simulations using OpenFOAM were conducted to reproduce the above experiments.

 A method for real-time storm surge prediction has not yet been fully established. This study developed a time-series prediction method for storm surge water levels using Bidirectional Long Short-Term Memory (Bi-LSTM), a type of deep learning model. The Bi-LSTM model was constructed using hourly atmospheric pressure and wind speed data from nine meteorological stations along the paths of typhoons that approached Osaka Bay as input, and storm surge anomaly at Osaka and Kobe ports as output. As a result, the model achieved correlation coefficients of approximately 0.7 to 0.8 and RMSE of less than 0.15 meters for the entire time series at both ports. Furthermore, the optimized and trained Bi-LSTM model was applied to the storm surge prediction for Typhoon Jebi, and its accuracy was evaluated through comparison with observed data, demonstrating its applicability to real-time storm surge prediction. A comparison between the prediction results of Bi-LSTM and conventional LSTM also confirmed the superiority of Bi-LSTM approach.

 The actual flooding of urban areas in northern Tokushima Prefecture due to the storm surge caused by the Second Muroto Typhoon in 1961 was examined by collecting victim testimonials, news footage, and official documents, as well as conducting a storm surge inundation analysis. The storm surge inundation analysis was carried out on Tokushima City and Komatsushima City. For topographical data, 5m DEM data was used, corrected with the 1/5000 National Land Base Map surveyed in 1965. Levees were considered as linear structures, and breaches were taken into account as much as possible. The outside water level was the tide level of Komatsushima Port, and inland flooding due to heavy rain was also taken into account. The actual damage at 23 locations was made clear from the testimonials and video materials. The results of the storm surge inundation analysis were able to explain well the actual flooding damage obtained from victim testimonials and news footage.

 This study investigates four typhoons that generated pronounced storm surges in Tokyo Bay. Forecast experiments for both typhoon tracks and storm-surge height were performed on a vector supercomputer (2.45 TFLOPS per vector engine) using an optimized Weather Research and Forecasting (WRF) model code. Simulations were initialized at one-day intervals from roughly four days to one day before landfall. The results show that forecasts initialized two days or less before landfall—corresponding to the late-recurvature and post-recurvature phases—achieved relatively high accuracy for both typhoon tracks and surge-peak timing. In two-day-ahead forecasts, surge-peak timing errors ranged from 1 to 6 hours, and in every case more than 80 % of this error could be explained by Along-Track position errors of the prelandfall typhoon center. Under the present conditions, forecasts initialized approximately two days in advance using eight compute nodes—with a parallel efficiency exceeding 50% (60% in this case)—successfully predicted the storm surge peak before its actual occurrence. Further case studies involving additional typhoons are needed to establish the generality of these findings.

 Wave downscaling (DS) utilizing AI technology offers an enhanced resolution for low-resolution wave grid point values (GPV), potentially enabling more effective utilization of datasets like ERA5. This study employs the CorrDiff model, a diffusion method, to upscale coastal area wave data in the Hokuriku region, using ERA5 GPV (0.5-degree grid) as input and a coastal wave model GPV (CWM; 0.05-degree grid) as output. We conducted a long-term wave downscaling spanning from 1940 to 2024 using the developed model, validating its accuracy through comparison with observational data. Through extreme value statistical analysis, we investigated the secular changes in the 50-year probability wave height (H₅₀) derived from these estimations. Notably, the trends in H₅₀ varied significantly across locations, with pronounced trands observed at three sites: Niigata-Oki, Toyama, and Wajima. A comparison of the H₅₀ distributions between 1955 and 2009 indicates a notable long-term change in wave direction. This study demonstrates the capability of AI technology to perform long-term, high-resolution wave downscaling, facilitating extreme value statistical analysis based on extended-term, low-resolution wave GPV datasets.

 Weibull distributions have been employed as candidate distributions of extreme wave heights population. However, it doesn't make sense from the viewpoint of statistical theories because these Weibull distributions applied to wave heights are not one of the extreme value distributions for maxima but for minima. Though Weibull distribution is well-known as an extension of the Rayleigh distribution for random wave height in wave group in coastal engineering, it is not obvious to use Weibull distributions in the frequency analysis of extremal wave heights. We study here on the tail properties of Weibull distributions by means of asymptotic expansion to elucidate the practical roles of Weibull distributions, which will be a key to solve the Procrustean bed problem in the design of massive natural force defense, and we also propose a method to check the compatibility of Weibull distributions and the extreme value distributions in the penultimate and ultimate senses.

 Probabilistic tsunami hazard analysis employing the tsunami simulation analysis such as nonlinear long wave model is computationally expensive due to the large scale parameter studies required to evaluate the uncertainty of the phenomena. To solve this problem, we attempt to reduce the computational cost by using the machine learning based emulators. Applying Gaussian process regression as an emulator, we interpolated the simulation results of megaquake tsunamis occurring along the Japan Trench to obtain tsunami hazard curves and quantitatively evaluated the difference from the case without interpolation. As a result, it was confirmed that the interpolations by Gaussian process regression can obtain the tsunami hazard curves with sufficient accuracy while reducing the computational cost. It was also found that the sampling method of the learning data has a significant influence on the predicted values by Gaussian process regression compared to differences in the kernel functions used.

 Meteotsunamis frequently occur along the western coast of Kyushu, triggered by atmospheric pressure waves propagating over the East China Sea. A notable meteotsunami in March 2019 caused vessel capsizing and inundation damage on the western Kyushu coast. Despite their potential to damage ports and coastal urban areas, the relationship between meteotsunamis and meteorological or bathymetry conditions is not fully understood. This study analyzed mesoscale weather prediction data to investigate the meteorological conditions that caused recent significant meteotsunami events. Atmospheric pressure waves were then modeled, and meteotsunami simulations were conducted. The results showed that water waves trapped at the western edge of the Okinawa Trough propagated while amplifying due to the Proudman resonance. Additionally, resonance in the Goto Nada Sea contributed to amplification in Nagasaki, while the shallow continental shelf influenced meteotsunami amplifications near Makurazaki. Furthermore, numerical experiments under various atmospheric pressure conditions showed a clear dependency of meteotsunami amplitude on the propagation direction and crest length of the atmospheric pressure waves. These findings highlight the potential for a meteotsunami forecast using meteorological datasets based on real-time estimation of the location and crest length of atmospheric pressure waves.

 This study aims to clarify the field applicability of a time-dependant Boussinesq-type wave model to inundation events caused by storm surges and waves, which are projected to become increasingly severe in the future. The model applied in this study was a modified version of the Boussinesq-type wave model (NOWT-PARI Ver. 5.3), capable of simulating wave overtopping and inundation on quay surfaces associated with time-varying tidal levels. The model was applied to the inundation at Shimizu Port that was caused by storm surge and high waves during Typhoon Hagibis in 2019. The Boussinesq-type model, given time series data of offshore wave conditions and observed tidal levels at Shimizu Port as boundary conditions, successfully reproduced the observed inundation extent and depth. Furthermore, the model was able to calculate inflow and outflow discharge across quay edges, and the simulated flow patterns on the quay surface were consistent with those inferred from damage observations.

 The purpose of this study is to evaluate the tsunami forces acting on a seawall when there is a topographical feature, such as a sand dune, in front of the seawall. To achieve this, hydraulic physical model experiments were conducted using tsunamis with realistic periodic characteristics, and the effects of the tsunamis were measured and analyzed in detail. The results confirmed that while the flow conditions in front of the seawall change depending on the presence or absence of sand dunes, the maximum value of the tsunami force does not significantly change. Additionally, it was confirmed that the vertical distribution of the maximum wave pressure at all times and the wave pressure at the time of maximum tsunami force both correspond to the hydrostatic pressure equivalent to the maximum inundation depth in front of the seawall. These experimental results are consistent with existing literature, and although the experimental conditions of the tsunami and sand dune topography in this study are limited, calculating the tsunami force using 1.5 times the hydrostatic pressure of the maximum inundation depth in front of the seawall, which exceeds the experimental results, can provide a higher evaluation of the tsunami force due to sustained wave pressure. This approach is considered applicable in the practical design of seawalls.

 In the southern part of Okinawa Island, numerous coastal cliffs are composed of Ryukyu limestone, particularly in areas subject to intense wave action. These cliffs are often undercut at their bases by wave erosion, forming sea cliffs with well-developed notches. While the collapse mechanisms of such cliffs due to self-weight have been increasingly clarified, those triggered by tsunami loading remain insufficiently investigated. Given the widespread distribution of tsunami boulders in the Okinawa region, understanding this mechanism is essential for estimating the magnitude of past tsunamis. In this paper, we conduct numerical simulations to evaluate the stability of sea cliffs under both self-weight and wave forces. The results indicate that sea cliffs that do not collapse under their weight exhibit greater resistance to wave loading as their height increases, but may still fail depending on the wave height.

 Breakwaters with submerged mound have been installed at fishing ports throughout Japan in anticipation of the growth of seaweed. Although breakwaters with submerged mound are expected to dissipate a large amount of energy due to the effect of the submerged mound, there have been few cases of quantitative evaluation of their performance. In this study, the wave force characteristics of breakwaters with submerged mound are clarified through hydraulic model experiments.In addition, we propose a new correction factor in the Goda equation, which is commonly used as a wave force calculation method, so that the results of this experiment can be used in the design of breakwaters.

 The results show that the wave pressure distribution on the vertical wall of a breakwater with a submerged mound is similar to the model assumed by the Goda equation and can be evaluated with the new correction coefficients.It was also found that the wave force on the breakwater with submerged mound is significantly smaller than that on the vertical wall when the top of the submerged mound coincides with the water surface, but the effect decreases as the water depth above the top of the submerged mound increases.

 This study deals with the influence of porosity and profile change of wave dissipating block layer on the irregular wave forces. Two types of block with different porosity and the initial and deformed profiles of the block layer were used in the experiments and numerical computations. As a result in the cases of the initial profile, the acting wave forces are similar for the two blocks in the experiment. In the result of numerical computations, the wave forces are smaller slightly for the block with larger porosity. In the cases of the deformed profile, the wave forces increased in both blocks and the rate of increase between the initial and deformed profiles is higher in the block with larger porosity. Additionally the experimental and calculated values of the wave force were in good agreement for the initial profile.

 Coastal upwelling has a significant impact on marine environments and fishery resources by transporting cold nutrient-rich water from deeper layers toward the surface. To evaluate effects of coastal upwelling around the mainland Japan, this study employed a regional ocean physical-ecosystem coupled model, ROMS-NPZD. Coastal upwelling occurs on the east side of the mainland Japoan in response to intensified southerly winds during summer (summer-monsoon). Combined effects of vertical advective upwelling and enhanced vertical mixing due to wind forcing result decrease in temperature by approximately 3°C in coastal regions. Significant phytoplankton bloom appears several days after upwelling events. Coastal upwelling predominantly occurs along the east coasts in a north–south direction. In particular, significant upwelling off the Boso and Joban coasts also influences nutrient and phytoplankton distributions in the offshore Kuroshio downstream.

 This study presents coastal upwelling and it effects along the east coast of the mainland Japan using satellite observations data, sea surface temperature and chlorophyl a concentration, from HIMAWARI. Sea surface temperature along the coast decreases as increase in southerly winds, indicating typical coastal upwelling responses along the east coast. The magnitude of coastal upwelling is explained by the southerly wind magnitude due to summer monsoon. Observed results also show that phytoplankton concentration is increased by coastal upwelling. Responses of coastal upwelling to wind forcing vary within horizontal scales of O(10) km. Coastal upwelling is enhanced when the wind direction is paralell to the long coast line. In addition, our results suggest that sea surface temperature cooling owing to coastal upwelling may reduce air temperature in adjacent coastal regions.

 Internal Kelvin wave and Internal Poincare wave affects the energy partitioning defined as the ratio of Kinetic Energy (KE) and Potential Energy (PE). However, the effects of Wedderburn number (W_N) and wall boundary on the energy partitioning of geostrophic current had not been elucidated in the rectangular basin. Therefore, this study aim to elucidate the effect of W_N and wall boundary on the energy partitioning of geostrophic current by analyzing them from theoretical solution. This study showed that KE/PE in enclosed basin increased with decrease of W_N for 2.0≤ W_N ≤3.0. In addition, comparing the KE/PE in enclosed basin with the KE/PE in domain without east-west wall, KE/PE is less than 1 in the enclosed basin, but KE/PE is greater than 1 in the domain without the east-west wall. Therefore, east-west wall likely to convert the given energy into the PE in the enclosed basin. This study helps us to understand the effect of interaction between W_N and wall boundary to the geostrophic current.

 Hydrodynamics in highly open coastal areas is influenced by various forcing factors, including waves, wind, tides, internal waves, offshore currents, among others. This study aims to assess the hydrodynamic processes and underlying mechanisms through a 15-day field observation conducted in the summer of 2023 at the tip of the Hazaki Oceanographical Research Station (HORS) at Kashima-nada Coast, Japan. During the observation period, a shift in wind direction occurred following the passage of a low-pressure system accompanied by a cold front, leading to a southward coastal current that persisted for several days with pronounced diurnal variability. Based on its spectral characteristics, phase velocity and the internal Rossby deformation radius estimated from the JCOPE2M reanalysis data, we speculated that diurnally forced internal tides generated along the continental shelf slope were amplified near the coast and evolved into nearinertial internal Kelvin waves propagating alongshore with the coastline to their right. These internal Kelvin waves are likely to exert a significant influence on nearshore circulation and resultant marine environment, even within the surf zone during calm periods.

 The correlations between the annual maximum wave power, generated by typhoons and cyclones off Tomakomai Port, and the Arctic Oscillation (AO) and the Pacific Decadal Oscillation (PDO) indices were investigated, and the following results were obtained.

 (1) In the time series of correlation coefficients between annual maximum wave power, generated by typhoons and cyclones, and AO and PDO indices, there are periods when significant positive correlations appear continuously for each index. (In the following, it is described as two periods.)

 (2) The years with significant positive correlations do not overlap between typhoons and cyclones, nor between AO and PDO indices.

 (3) Comparing the two periods, the difference in the location of typhoons when they generated annual maximum wave power of 100 kW/m or more is attributed to the difference in the timing of maximum typhoon movement speed over the Sea of Japan.

 (4) Comparing the percentages of explosively developing cyclones among the cyclones that generated annual maximum wave power of 100 kW/m or more for the two periods, the percentage associated with the PDO index is twice that associated with the AO index.

 (5) There is a possibility that the correlations between the annual maximum wave power, generated by typhoons and cyclones, and AO and PDO indices are attributed to changes in the power of the Pacific High and changes in sea surface temperature in the South and East China Sea.

 Future changes in storm surges and high waves due to climate change along the Tottori coast were examined by using 5 km-mesh d4PDF data under a +2K warming scenario. Comparisons with long-term reanalysis datasets JRA-3Q and GPV revealed that the model bias in atmospheric pressure and wind speed is larger in the Sea of Japan compared to the Pacific Ocean. It was also confirmed that storm surges caused by typhoons will increase more on the western side of the Tottori coast, which is strongly affected by winds that cause Ekman transport. Furthermore, it was found that high waves caused by non-typhoon atmospheric depressions will show little or no change in the future, while those caused by typhoons will increase by up to 7% in height. The mean wave direction in the future will change clockwise by about 2° for both typhoons and atmospheric depressions.

 This study applied the radius of maximum wind (R_w) estimation method, based on the angular momentum conservation principle proposed by Avenas et al. (2023), to typhoons in the Northwest Pacific. An enhanced approach was proposed that accounts for the temporal variation of typhoon structure. By incorporating the time-varying maximum wind speed and gale-force wind radius, the method provided dynamically consistent R_w estimates suitable for operational forecasting by the Japan Meteorological Agency. When validated against R_w derived from Synthetic Aperture Radar (SAR) observations, the proposed method reduced the root mean square error (RMSE) by approximately 27% compared to existing estimates from the IBTrACS dataset. Furthermore, storm surge simulations were conducted for six recent typhoons that caused storm tide anomalies exceeding 1 meter in Mikawa Bay, Aichi Prefecture. Results show that the proposed method improves the RMSE of peak storm surge predictions by about 30% compared to conventional approaches relying solely on central pressure. These findings demonstrate the potential of the proposed method to enhance the accuracy of both typhoon analysis and storm surge forecasting.

 Ocean waves excite microseisms. There is a potential to estimate typhoon-generated high waves, which are difficult to observe, from continuous seismic observation. We estimated typhoon-generated high waves using the relationship between typhoon-generated high waves and secondary microseisms in F-net Abuyama station. We analyzed statistically observed seismic waves by F-net, ocean wave observation by NOWPHAS, and ocean wave hindcasting data by WAVEWATCH III in summer season and assessed the relationship between microseisms and typhoon-generated high waves. The correlation between the observational significant wave height and secondary microseisms energy is more than 0.7. The correlation between 0.1Hz-0.15Hz secondary microseisms energy and simulated significant wave height is high and typhoon-generated high waves have a high correlation with low frequency microseisms energy. We constructed a statistical model that can assess typhoon-generated high waves from secondary microseisms and estimated ocean wave height when the typhoon is close to Japan.

 In this study, Typhoon No. 9 of 2020, which caused abnormal sea levels in the western part of the Sea of Japan, was investigated to elucidate the causes of the abnormal tide and to assess the sensitivity to typhoon track shifts. Using the WRF atmospheric model and the GeoClaw storm surge model, we conducted reproduction simulations of the abnormal sea levels and performed typhoon track shift experiments by laterally displacing the typhoon path up to 48.2 km eastward and westward. When the typhoon track shifted eastward, the wind direction after the typhoon's passage changed approximately 10 degrees toward the north. In all cases, water transport due to the Coriolis force was observed from the Tsushima Strait and the northern offshore area of the San'in region. The maximum tidal anomalies at Sakaiminato and Hamada changed by up to ±15% and ±16%, respectively, with the largest variation occurring when the track was shifted 24.6 km westward. Along the northern coast of Kyushu, wave energy flux originating from the Tsushima Strait affected the surge height, while along the northern coast of the San'in region, wave energy flux passing off the eastern coast of the Korean Peninsula influenced the surge height.

 In this study, directional wave spectra observed every 20 minutes by an ADCP installed on an offshore observation tower were analyzed to classify energy distribution characteristics and dominant wave directions, followed by a correlation analysis with wind data. Wave system separation was conducted using the WITS method, where cases in which the first component accounted for more than 75% of the total energy were defined as Unimodal, and others as Complex-field. Unimodal wave systems were dominant in the northwest direction within a wave age below 30, whereas in the southwest direction, data were distributed across a broader wave age range, with a higher occurrence rate of Complex-field systems. Additionally, the relationship between nondimensional fetch and nondimensional significant wave period theoretically follows a 1/3 power law. The observational data showed a smaller slope than this theoretical value for waves from the northwest, while a larger slope was observed for waves from the southwest.

 A river mouth delta is formed along the north shore of Lake Inawashiro in Fukushima Prefecture, as a result of the sedimentation of sand supplied from the Nagase River flowing into this lake. Along the south shoreline of the river delta, wind predominantly blows from the west in winter, that is, the same orientation of the lakeshore shoreline. Therefore, the shoreline deformation due to High-angle wave instability occurs. In this study, long-term shoreline changes along the lakeshore were investigated using satellite images and the three-dimensional topography was measured in October 2023 by UAV survey. Longitudinal profiles along 21 transects across the sandbar in the lake were also measured by an RTK-GPS. Furthermore, wind waves to cause beach changes were calculated by the SMB method. Based on these data, the formation and deformation of the sandbar along the lakeshore was investigated.

 At Numakawa-daini floodway located on the Fuji coast, sand is deposited inside the conduit during storm wave conditions, resulting in difficulty in the drainage. In this study, the difference in sand deposition under the open or closed conditions of the gate located at the upstream end was investigated using two-dimensional wave flume test, taking this floodway as an example. The experimental results showed that the amount of sand deposition when the gate upstream end is closed greatly decreased compared with that when the gate is opened. The BG model (a model for predicting three-dimensional beach changes based on Bagnold’s concept) was applied to the experimental results and the calculation results were compared with the experimental results. It was found that the results of experiment and numerical simulation were in good agreement. It was concluded that sand deposition when the gate at upstream end of the conduit is closed greatly decreased compared with that when the gate at upstream end is opened.

 A seabed of very steep slope develops close to the shoreline at Ikujibana of the Shimoni-ikawa coast. Therefore, pile-typed groins have been constructed as a measure against erosion. Seven groins supported by steel piles were arranged in a curvilinear shape. Recently, a cone-shaped erosion occurred near No. 2 groin. To investigate this topographic change, NMB survey and sounding using a lead were carried out around the groin, together with the acquisition of the oblique images using an UAV. As a result, it was found that the seabed elevation significantly decreased between January 1, 2024, and May 22 after the Noto Earthquake occurred on January 1, 2024, with the maximum decrease in seabed elevation up to 6 m. However, until November 2024, the seabed elevation gradually increased again. Although the longitudinal slope before the erosion was as steep as 1/1.8, the slope became 1/3.3 after the erosion. Since the steep slope of 1/1.8 is approximately equal to the critical slope when submarine landslide takes place, the seabed of steep slope became unstable, and its stability was assumed to be lost by an external factor such as the earthquake, causing the seabed landslide.

 The coast between Oarai and Kashima Ports has a closed cell in terms of littoral transport. Therefore, when sand is deposited at Oarai Port, beach south of the port becomes erosive. On the basis of aerial photographs and bathymetric survey data, the rate of sand accumulation at Oarai Port and the rate of erosion on the Otake coast were determined. It was found that the shoreline change in Oarai Port between 1965 and 2024 was 830 m and the increase in foreshore area of ΔS was 8.8×10⁵ m². Denoting the shoreline change as ΔY, the sand accumulation area of a triangular shape on the lee of offshore breakwater was shown by ΔS = 10³ ΔY. Furthermore, the depth of closure and the berm height at Oarai Port were determined to be h_c = 9 m and h_R = 2 m, resulting in the characteristic height of beach changes of h = 11 m as the sum of them. Since the increase in foreshore area ΔS was 7.7×10⁴ m² at Oarai Port between 2019 and 2024, this increase rate of the foreshore area is multiplied by the characteristic height of beach changes h and divided by the elapsed time of 5 years, the recent accumulation rate of sand was estimated to be 1.7×10⁵ m³/yr. Similarly, the rate in decrease of the foreshore area on the Otake coast between 2009 and 2016 is multiplied by h, the erosion rate was estimated to be 5.4×10⁴ m³/yr. Thus, sand accumulation in Oarai Port and erosion on the Otake coast simultaneously continues at present.

 The Hojo River floodway in Tottori Prefecture frequently experiences river mouth closure due to sandbar formation. Based on the observation that flushing begins promptly when the river water level exceeds the sandbar crest, we investigated a method to facilitate flushing by artificially creating a notch in the sandbar. Field experiments were conducted to evaluate a technique that discharges pumped water onto the sandbar to induce a single notch. Results confirmed that discharging water onto the seaward slope or near the crest edge effectively transported sand seaward. Moreover, gradually shifting a discharge point with a flow rate of 0.08m³/s from the seaward side toward upstream enhanced the efficiency of notch formation. Numerical simulations further suggested that simultaneous discharge from two points, sequentially moved from seaward to upstream, can efficiently form a notch within a short period. This method shows promise as a practical countermeasure for river mouth closures in small and medium-sized rivers.

 An uplift of about 4.0 meters formed a marine terrace along the northwestern coast of the Noto Peninsula following the 2024 Noto Peninsula Earthquake. Instances of seismic uplift affecting sandy coastlines are exceedingly rare, and the deformation processes of such uplifted coastal environments remain unstudied. The long-term evolution of a sandy beach uplifted by an earthquake represents an extremely rare and important event, as it enables the tracking of coastal geomorphological changes from a clearly defined initial condition that previously did not exist in the field. The objective of this study is to monitor the long-term morphological changes of the sandy beach at the uplifted Kaiso Coast, focusing on the influence of oceanographic and meteorological conditions including wave action, tidal levels, wind, and precipitation through monthly drone-based topographic surveys. Drone-based topographic surveys of the Kaiso Coast approximately one year after the uplift confirmed that the shoreline had retreated by about 20 meters over the year, due to deformation of the beach caused by wave and winds in winter, and by tidal levels and rainfall.

 The Yamamoto Coastal, Nakahama area, has been subject to coastal erosion due to the interception of coastal drift sand. This construction area aims to restore the sandy beach by means of headland maintenance and beach nourishment.Based on the following constraints and issues, this study clarified, based on the results of surveys and bottom sediment surveys, that beach nourishment can be efficiently and environmentally implemented by using the headland opening, which is exposed to waves at the same time as the beach nourishment, because the beach nourishment material is naturally classified in the sea by wave energy.Limitations of beach nourishment: (1) The offshore area is the fishing ground of the Uva mussel, and it is necessary to consider the growth of Japanese surf clams, Pseudocardium sachalinensis. (2) The soil excavated from the lower Abukuma River channel, which is the source of sediment supply, has a wide grain size range of silt, clay, and large gravel. Beach nourishment challenges: When beach nourishment was applied from the headland screening area, silt/clay clods and gravels remained in the surface layer of the beach.

 Shichiri-ga-hama Beach in Kanagawa Prefecture has eroded in recent years. In the previous study, the cause of this erosion was pointed out to be the sand discharge turning around Inamura-ga-saki Point which bounds the east end of Shichiri-ga-hama Beach, resulting in the loss of sand of the beach. It was pointed that sand was transported turning around the point when high waves are incident from the westerly direction. However, its verification of the waves and nearshore current was remained to be observed. Wave gauges were installed offshore of the point and inside the submarine canyon west of the point to measure both the wave height and wave direction. The wave records were referred GPV data as well as the calculation of the nearshore current field to compare the measured and calculated velocity. On 28 November 2024, waves were incident from N200°E and under the condition, eastward and southward offshore currents developed, respectively, at a location offshore of Inamura-ga-saki and a point inside the submarine canyon. The measured and calculated results were in good agreement. Due to the calculation results, counterclockwise circulating current developed in the west vicinity of Inamura-ga-saki, and this area was in accordance with the location where the seabed elevation decreased in recent years.

 A model for predicting topographic changes considering both the action of offshore current by a flood and waves was developed, applying the BG model to the Oi River mouth. The reproduction period of the calculation was set to be between 2009 and 2022 given averaged wave data determined from the wave observation during the observation period. In the calculation, the equilibrium slope of the foreshore was set to be 1/10 and composed of coarse sand of d₂ = 1.0 mm, whereas in the offshore area, the slope was assumed to be 1/100 and composed of fine sand of d₁ = 0.2 mm. Furthermore, we assumed that the sand inflow from the river mouth was assumed to be 2.4×10⁵ m³/yr and the discharge ratio of d₁ and d₂ was set to be 3:1. As the distribution of the offshore current, a large intensity was assumed at the central part with gradually decreasing distribution on both sides. The calculated and measured shoreline configurations on both sides were in good agreement. In the field, an extensive erosion occurred on the right side of the river mouth, which was reproduced by the numerical simulation. The formation of a river mouth terrace was also reproduced well.

 Selecting the coast north of the Ohi River mouth on the Suruga coast, the topographic changes were numerically reproduced using the BG model. The measured and calculated beach changes between 2009 and 2022 in Ohigawa and Yaizu areas of the Suruga coast were in good agreement. Beach erosion was severe in the area north of the Wadahama coast located at the north end of the Suruga coast, and sediment produced in this area discharged into a steep slope in Tajiri area southeast of Kogawa fishing port. On the other hand, in the south part of Ohigawa and Yaizu areas where a continental shelf is well developing, the seabed of a gentle slope offshore of the detached breakwaters is gradually eroded, resulting in the decrease in seabed elevation. In the prediction, the beach erosion at the Wadahama coast can be greatly reduced if beach nourishment is carried out at a rate of 11.3×10⁴ m³/yr. However, such nourishment material is finally discharged into the deep ocean via a steep slope.

 At Minato Oasis facilities, events are held to promote interaction among local residents, tourists, and cruise passengers, and resting spaces are provided for visitors. Since the onset of the COVID-19 pandemic in 2020, many functions of Minato Oasis were suspended due to the global spread of the virus. However, in recent times, efforts to revitalize the facilities in the post-COVID era are being considered. In this study, a survey on infectious disease Business Continuity Planning (BCP) was conducted targeting the administrators of 135 Minato Oasis locations across Japan. The study clarified the current issues and countermeasures necessary for BCP development at each Minato Oasis.

 When jacked-up SEP vessels are used to lift monopiles from a floating barge during the construction of offshore wind power generation facilities, it is necessary to estimate the dynamic amplification factor (DAF) due to barge oscillation. In this study, the dynamic analysis software OrcaFlex was used to simulate a hydraulic model experiment of a monopile hoisting operation by a SEP vessel. The simulation covered operations both inside and outside a harbor, and its applicability as a construction simulation was verified. The analysis modeled the wave field, the floating structure, the mooring system, the suspended load, the configuration of the hoisting equipment. From the analysis results, it was verified that the model could reproduce the behavior of the floating structure during the hoisting process and the characteristics of the DAF, which depend on the barge's dynamic response characteristics, as observed in the experiments. The results demonstrate the utility of the construction simulation, enabling the evaluation of safety and operating rate in actual construction scenarios.

 The force of a tsunami drifting object impacting a coastal structure is considered to be affected by the force of the surrounding fluid in addition to the mass, impact velocity, and stiffness of the drifting object. In this study, the added mass coefficient of a boat impacting from the bow and side directions was investigated by numerical simulation based on the Haehnel and Daly collision force evaluation formula used in the FEMA guidelines. The values of the added mass coefficient obtained from the analysis were generally distributed in the range of 1 or less, similar to the added mass coefficients of driftwood and containers in the guidelines. It was confirmed that the added mass coefficient was affected by the effective axial stiffness at the time of impact, which is consistent with the trend of previous studies on the impact time of ships.

 In evaluating the impact of tsunami-borne debris collisions on coastal structures, it is essential to determine the possibility of collision and establish collision conditions. This requires accurately understanding the drifting process of debris. Previous hydraulic experiments have revealed that the movement of debris is influenced by factors such as wave breaking, the initial position of the debris, and its physical characteristics. However, analytical verification is considered effective for a more detailed analysis of how these different conditions affect the drifting process. Therefore, in this study, the three-dimensional fluid-rigid body coupling analysis method developed by Yoneyama et al. was conducted in order to reproduce existing experiments on debris movement. Through this, the applicability of this analytical method for estimating the drifting process of tsunami-borne debris was confirmed. Furthermore, the effects of differences in debris characteristics on their drifting process were examined using this method.

 In this study, an experimental study on the tsunami countermeasure using the additional anchor cable with a sinker for moored large ship have been performed using the model ship as a 90,000DWT(Dead Weight Tonnage) class coal carrier suffered by the 2011 Tohoku Earthquake Tsunami, based on several water tank tests under tsunami bore as well as our previous study. It was clarified that the slack mooring of the anchor cable using a sinker restricted the surge motion and tension of the mooring line, but the tension of the anchor cable increased in case of the submerged sinker placed on the bottom. On the other hand, the sinker installed at the ship’s bow in hanging induced a reduction of the tension of the anchor cable as well as that of the surge motion and the line tension.

 Compound flooding, caused by the superposition of river floods and storm surges, is a growing concern. Numerical simulations for assessing this risk are sensitive to analytical settings, including riverbed topography data and boundary conditions. This study investigates the impact of varying these conditions on the accuracy of river water level simulations for Typhoon Lan (2017) in the Arakawa River, Tokyo Bay. While our model reproduced upstream water levels with high accuracy, significant errors persisted downstream. The choice of riverbed data proved to be a critical factor, improving pre-peak water levels by 10-20 cm when using high-resolution datasets. Nevertheless, the minimal improvement in downstream accuracy indicates a need for further model refinements, such as enhancing meteorological field predictions and incorporating drainage processes.

 This paper reveals internal mechanism of safety factors in the design of existing breakwaters from viewpoint of their maintenance that has become of great importance in recent years. Design method using safety factor had been used until 2007, when “Technical Standards for Port and Harbor Facilities” was revised in which reliability-based design method was employed. Therefore large amount of breakwaters exist in Japan, which had been designed using safety factor method. Finding out probability density function of the ratio resistant force to acting force, which is equal to safety factor and both of the forces are random valuables, we can calculate failure probability of their structures in a discipline of mathematical statistics.

 The Takamatsu Port Asahi District Quay is designed as a seismic-reinforced quay with a vertical pile deck type mooring quay structure. Large-diameter steel pipe piles are used for the foundation piles of this quay due to the high axial force caused by earth pressure and ship traction forces. However, when a φ1, 300mm open-ended pile was driven at the stern part of this quay, it was found that there was insufficient axial bearing capacity (mainly at the pile tip). Based on this experience, dynamic load tests were carried out to find a pile specification that can provide sufficient axial bearing capacity by testing four different types of piles: a standard open-ended pile (straight pile), a tip-reinforced cross-ribbed pile, a tip-reinforced grid-ribbed pile, and a tapered pile

 This paper reports the axial bearing capacity obtained from these four types of test piles, which were driven by the vibro-hammer method up to the front of the bearing layer, and the remaining bearing layer portion was driven by the impact method, under the same conditions as in the actual construction.

 Wave loading led to bearing capacity failure in caisson-type breakwaters. In this study, ductility of the breakwater was improved by enhancing resistance to toe pressure by the caisson through partial solidification of the mound under the caisson. Two-dimensional distinct element analysis was conducted to examine how the improvement zone at the mound and the width of the mound shoulder influences the caisson’s behavior. When the improvement zone beneath the caisson was made sufficiently wide, the caisson tilt was significantly suppressed. However, when that zone was too short, the solidified soil was lifted and displaced by toe pressure, which led to an increased tilt of the caisson. It was also observed that a wider mound shoulder reduced the relative impact of a short improvement zone. These findings indicate that an appropriate balance between the extent of improvement and the mound width is critical for the measure’s effectiveness.

 This paper examines the impacts of liquefied sediment flows on subsea structures, such as cables and mooring foundations, through a series of centrifuge model tests. Additionally, a numerical analysis of a high-density liquid flow based on the Navier-Stokes equation was conducted to compare with the experimental results. A series of gravity flow experiments was performed under a centrifugal acceleration of 50 gravities, by varying the height of the collapsed sediment and the effective density of the sediment. The impact of the flow on the structure was evaluated using the peak pressure at the time of collision and the impact force over the duration of its action on the structure. It was found that the impact on structures could depend on the vertical effective stress of the sediment before collapse. The predicted impact pressures obtained from the analysis considering the density of the liquefied gravity flow quantitatively matched the observed values from the centrifuge experiments, indicating the potential to evaluate the impact of liquefied sediment flows on structures based on the expected extent of the sediment failure.

 When large wave pressures act on seawalls or quaywalls, damage to anti-sand sheets and joint plates can occur, potentially causing the suction of reclamation sand. Suction prevention works require ensuring water permeability to allow transmission of wave forces and enhancing stability through increased weight of materials to prevent damage caused by wear due to fluttering or abnormal tension of materials resulting from waves and tidal differences. In this research, we applied rubber chip mats made from waste materials generated during production processes to seawall joints as a new suction prevention method that achieves both void structure and high weight, which has been difficult to combine conventionally. To confirm its effectiveness in preventing suction, we conducted large-scale hydraulic model experiments simulating the suction of reclamation sand in seawall models to investigate the necessary thickness of rubber chip mats corresponding to the acting wave forces. The experiments demonstrated that a 36mm thick mat completely attenuated the wave pressure from passing waves of approximately 1.0m in height, successfully preventing suction of the upper sand layer.