During a scenario earthquake with MW9.0 along the Nankai Trough, not only strong motion but also huge tsunami is predicted in Shizuoka Prefecture, Japan. In this study, first, seismic waveforms at station sites for ground motion observation in the coastal area were estimated based on the SMGA models considering local site effects. Using non-evacuation time based on the time history of instrumental seismic intensity, the effect of the estimated strong motion on tsunami evacuation was then discussed. Finally, in order to evaluate evacuation time from the strong motion estimation sites to designated refuge places, walking experiments were carried out. The constructed relationship between the evacuation time and the non-evacuation time will be useful for conventional seashore preservation in Shizuoka Prefecture.

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 Beach topography around the L-shape groin on the Shimizu coast was measured in detail, and the topography was reproduced using the BG model. Measured characteristics of the topography were well reproduced. Furthermore, the effect of controlling longshore sand transport by the L-shape groins was investigated numerically with changing the longshore length of the head part of the L-shape groin as 90, 120 and 150 m. The ratio of longshore sand transport relative to that with no groin were Q/Q₀=0.78, 0.75 and 0.73, respectively. The difference in reduction effect of longshore sand transport was minimal.

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 There has been concerns about catastrophic storm surge disaster under the intensification of typhoon and sea level rise due to the global warming. In the case that the subsidence of ground level occurs after earthquake, there is possibility of further huge inundation disaster. Thus, it would be of importance that countermeasures against storm surge after earthquake is taken because the occurrence possibility of Nankai trough huge earthquake is feared. In this study, storm surge inundation simulations were conducted under the circumstance that Second Muroto typhoon or virtual Super Muroto typhoon hits Osaka Port after Nankai trough huge earthquake. As a result, coastal area would have had much higher risk for human and property in the case that coastal and riverine facilities fail to function.

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 Measures for tidal disasters are required as a adaption against climate change, though the methodology for above measures is still developing. Uncertainty of future climate change was one of technical hazards for their execution of adaption. In this study, at first, both of international and national adaption policy was reviewed. Then, tidal inundation simulation is carried out with consideration of future climate change. These results of simulation are used to discuss to reveal the recent hazards to develop disaster risk reduction method against climate change, such as risk-monitoring, estimation, evaluation and management (both prevention and mitigation).

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 The operation of tidal gate constructed in river is difficult when heavy rain is forecasted because flood risk is significant. The delay of operation caused overflow by storm surge in Yatsushiro Bay at August 2015. One of the reason was unexperienced high speed of water level rise. In this study, we analyzed the mechanism of this phenomena and compared to past storm surge events. Then we assessed the variance of water level rise speed from virtual tropical cyclone scenario. Finally, typical tropical cyclone tracks causing high water level rise were selected. Then one viewpoint to assess the possibility of dangerous storm surge event was shown.

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 The aim of this study is to evaluate the changes in the characteristics of central atmospheric pressure and speed based on the differences in typhoon tracks and to develop typhoon models necessary for preparing prediction maps for the largest storm-surge inundation areas.
 The study reveals two features. The first is that the atmospheric pressure of typhoons that pass through the western region of Tsushima straits is higher than that of the eastern region and that the minimum pressure for the region spanning the latitudes between 34°N to 38°N is 940 hPa. The second observation is that the speed of movement is preferably either 96 km/h (the second Muroto Typhoon) or 73 km/h (the Ise Bay Typhoon) in some coastal areas spanning the Hokkaido, Tohoku, and Hokuriku regions.

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 The Technical Cooperation Project was undertaken in Mauritius to examine the applicability of coastal conservation/protection measures against coastal disaster as an adaptation measure for future climate change. The demonstration project of gravel beach nourishment was implemented at the specific coastal area with the low elevation land to prevent wave overtopping to the hinter area. The contiguous monitoring has been carried out to justify the effect of this type of measures. The result shows high applicability on protection function and improvement on coastal use and environment.

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 Coral cays formation mechanism has various field surveys, experiment, and numerical simulations, but observation data for transport feature of coral gravel and topographic change is almost less. In this study, we conducted field survey in ballast island on northern reef of Iriomote Island which is formed by only coral gravels. Then, we discuss about external force and transport feature of coral gravel in the reef. As a result, we understand that external force of coral gravel transport is caused by the waves than the flow on the reef and Shields number is around 0.03, these results correspond with the past study. The movement of colored coral gravel showed that wave from east and south gathered coral gravel in the reef to ballast island. Then, we measured the amount of gravel which trapped in the sediment-trap on lower end of the reef slope. Thus, coral cays are formed and maintained by transport of gravel to island and flow out to reef slope.

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 National land of Tuvalu was formed by coral gravel and sand. Although the island is vulnerable to high wave and beach erosion due to a narrow and low elevated land, proper coastal conservation measures had not been implemented because of the difficulties of procurement of materials and equipments. Gravel beach nourishment was proposed as a coastal conservation measure to improve three functions; protection, beach use, and environment using sustainable materials in Tuvalu. Gravel beach and groins were designed with consideration of these three functions as well as the reduction of required volume of materials. Environmental education was conducted to the public to improve their awareness on beach environment, and to enhance their voluntary participation to beach management and a certain effect by the education was confirmed through interview survey to stakeholders.

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 We focused on a coastal structure of bamboo fence installed at the upper Gulf of Thailand, and tried to evaluate the performance of the fence in terms of wave damping. Moreover, laboratory experiments were conducted to find out effective arrangements of the fence. From the field survey data, wave damping ratios were approximately 20 % at the beginning. The performance of the ratio, however, was decreased due to the deterioration of the bamboos. The laboratory experiment data showed that wave damping ratios become up to 45 % in cases of shorter wave periods with longer wave dissipation distances and cross arrangements of modeled bamboo sticks. As wave periods become longer, the effectiveness tends to be less, and regardless of the dissipation distance and arrangement of sticks, the wave damping ratios are limited to the level of around 10 %.

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 It is common to realize in literatures that shoreline position extracted from unknown capture time aerial photograph or satellite image (hereafter referring both kinds as image) has not been corrected to tidal effect. One of reasons is due to missing capture time of satellite image which was collected from open sources or captured a long time ago. However, the correction of tide for shoreline position extracted from image is highly required for studies in the field of coastal morphology changes. Especially, in the developing country, where field data is very limited, shoreline data extracted from satellite image plays more important role. There approaches, which can estimate the capture time of image based on the solar height and the length of shadow of vertical object on the horizontal surface on the earth, are introduced in this study. The capture time estimated from solar height has much smaller error compared to that from length of shadow. This error is acceptable for the tidal correction purpose. The temporal variation of shoreline positions of cases without and with tidal correction has been shown.

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 Each year, there have been many storms and strong monsoon waves that caused significant change of coastal morphology in the coastal zones of Vietnam. In the central of Vietnam, Nha Trang Coast also has a severe shoreline erosion problem, especially beach in the northern area of southern Nha Trang Bay disappears in several months every year. In this study, seasonal variation of morphology in this area is investigated. The detailed process of morphological change is presented based on analysis of fifteen-minute time-averaged images from northern and southern camera of video monitoring system. In addition, on the basis of the camera images analysis for surf zone characteristics, depth of closure is identified in consideration of different wave conditions between the northeast monsoon season and the non-monsoon season; hence the estimation of closure depth based on width of surf zone is also proposed in this analysis. Following that, longshore sediment transport rate for corresponded seasons is computed.

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 In the Khlong Wan coast, coastal erosion had occurred due to the construction of two offshore fishing ports till nine years ago. Although 11 detached breakwaters were constructed, the recovery of the beach is insufficient. Especially, the opening area between the groin of the old fishing port and one detached breakwater is dangerous to coastal erosion and wave overtopping.
 Therefore, in this paper, the mechanism of the coastal erosion was confirmed by the examination using one-line simulation. Then, the safety at the most dangerous section (320 - 400m in longshore distance) by existing countermeasures was clarified and three improvement plans for raising the safety to coastal disaster were examined. The models of Ca et al. and Yamamoto et al. were used to evaluate the coastal erosion and scour during one storm surge, and the equations of Van der Meer et al. and Yamamoto & Horikawa's were used to evaluate the wave overtopping rates. As conclusion, the comprehensive comparison of examination results made it clear that the sand nourishment is the most proper countermeasure.

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 Golden Beach in south Taiwan is widely known and has been attracting many beachgoers. In recent years, this beach has been eroded and measures to restore the sandy beach are required. The cause of the beach erosion was investigated on the basis of bathymetric survey data. In the study area, northward longshore sand transport, which was induced by the wave-sheltering effect of Anping Harbor, prevails, and the rate of transport was estimated to be 1.25×10⁵ m³/yr with the conditions of the depth of closure (h_c) of -6 m, the berm height (h_R) of 2.2 m, and the characteristic height of beach changes (h) of 9.2 m.

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 Field observation was carried out on a land-tied island extending near Bip Island in Van Phong Bay in Vietnam. It was found that this land-tied island extended by the deposition of sand supplied by southward longshore sand transport along the west coast of Bip Island, and its amount was estimated to be 655 m³/yr on the basis of the investigation using satellite images as well as the field observation. A sequence of beach changes showed that sand supply from the north coast of the island is the major factor for the extension of the land-tied island.

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 Beach was severely eroded on the Hitotsumatsu coast located in the south part of Kujukuri Beach during the typhoons in October 2014. In summer in 2015, four typhoons hit the coast, causing further erosion on the Hitotsumatsu and Ichinomiya coasts immediately north of the Hitotsumatsu coast, and sand dune was eroded. On both coasts, the sandy beach width has gradually reduced owing to successive erosion, and storm waves hit these coasts under the condition, resulting in severe erosion which cannot be solved using the ordinary protective measures. In this study, field observation was carried out to investigate the field conditions, and future measures were discussed.

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 Three typhoons hit the Tojo-Maebara coast during summer in 2015, resulting in severe erosion. To investigate the cause of the beach erosion, field investigation regarding longitudinal profiles using a RTK and grain size distribution along the shoreline were carried out. The shoreline changes were also analyzed using aerial photographs. It is found that the erosion of the coast, which was triggered owing to the wave-sheltering effect of the fishing port breakwater constructed at the south end of the pocket beach, still continues at present and the water depth in front of the shoreline increases, causing damage of the gentry sloping revetment on this coast.

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 Beach has been severely eroded on the Kawarago coast in Hitachi City, and a famous bathing beach disappeared. To investigate the cause of the beach erosion, the shoreline changes between Oose fishing port and Kawarago Port were investigated using aerial photographs as well as a field observation on December 26 in 2015. Bathymetric survey data obtained between 1982 and 2013 around Kawarago Port were analyzed. The major cause of the beach erosion was the sand deposition behind the detached break-waters constructed south of Oose fishing port, and the secondary is the ground subsidence associated with the 2011 Great Earthquake.

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 Shoreline changes on north Kujukuri Beach and beach changes around Iioka fishing port were investigated using aerial photographs and bathymetric survey data. The sand transport rate turing around the tip of the Iioka fishing port breakwater from Byobugaura sea cliffs was estimated to be 6.2×10⁴m³/yr between 1980 and 1990. It has reduced 1.3×10⁴m³/yr between 1990 and 2009. The former value was in good agreement with the rate of the deposition of 6.2×10⁴m³/yr on the Shimonagai and Yokone coasts located in the wave-shelter zone of the Iioka fishing port breakwater. Thus, all sand supply from the Byobugaura sea cliffs is assumed to deposit on the Shimonagai and Yokone coasts, resulting in the exhaustion of sand supply to downcoast.

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 Beach changes around the Katagai River mouth in Toyama Bay were investigated using satellite image and bathymetric survey data gathered between 1968 and 2014, together with the field observation in May 2015. Immediately south of the Katagai River mouth, a steep slope is formed in the submarine canyon offshore of the shoreline, and sediment supplied by floods of the Katagai River was once deposited and then it discharged into the submarine canyon. The rate of longshore sand transport across the river mouth was estimated to be approximately 6000 m³/yr.

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 We conducted the field observations and the calculations on current field by tide and wave to grasp the influence of the formation of the bar on river mouth. Study site is Akashi river mouth, Hyogo Prefecture in Japan. Akashi river is one of the typical urban river, the bar at the river mouth repeat appearance and disappearance. From field observations on recent four years study, it is clarified the right bank bar often developed than left bank one. However, from the result of the past aerial photographs , it turned out opposite result to recent four years study. From the results of the tide calculation, it is clarified that the current velocity by tide has small difference in before and after breakwater construction. On the other hand, the result of the wave simulation, it is clarified the current velocity decreased due to breakwater construction. In addition, it became clear that wave is more remark-able to give the bar of the Akashi river mouth because the tide has very smaller current velocity than wave.

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 A new floodway is planned to be extended in the vicinity of the junction of the Numakawa and Takahashi Rivers on Ukishimagahara Lowland behind the Fuji coast because of the high possibility of flooding. In this plan, setback-type floodway was planned to prevent sand from depositing inside the floodway, by which the location of the gate is positioned in further landward compared with the ordinary-type floodway. On the other hand, a culvert-type floodway has been successfully constructed near Numazu, and it resembles to the setback-type floodway. Therefore, the beach changes around these structures were compared, and the difference in beach changes around two-type floodways was studied.

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 The movement of sand body was investigated using the bathymetric survey data, and the effect of beach nourishment was verified on the Shizuoka-Shimizu coast. It was found that the sand body moved downcoast given the sand supply of 1.8×10⁵m³/yr from the Abe River. The beach nourishment using the riverbed material of the Abe River was effective as a measure against beach erosion. However, it was estimated that the deposition of coarser material on the beach face causes the slowdown of the movement velocity of sand body.

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 We developed a new inversion method to estimate a fault model of seismic sources from geodetic data, using Akaike's Bayesian Information Criterion. The inversion method provides not only the distributions of fault slip, optimal hyper-parameters, but also strike and dip of a fault by minimizing ABIC. The estimated strike and dip agree well with the true values of them through the numerical experiments. The distributions of fault slip were compared with the target distribution and show generally good agreement with them. The geodetic data inversion based on Bayesian formulation for the Tohoku-Oki earthquake of 2011 was carried out. As a result, the calculated horizontal displacements reproduced well the observed horizontal displacements and tsunami wave forms.

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 Lattice Boltzmann Method (LBM) is the one of the new and efficient Computational Fluid Dynamics (CFD) solvers. It has become an alternative powerful method compared with the other conventional CFD solvers. In the current study, we developed a robust tsunami simulation model by applying enhanced LBM for shallow water equations with treatments of the bed slope in the external force term in the Lattice Boltzmann equation.
 The proposed model is verified by the comparison with the conventional tsunami numerical model which is based on the Finite Difference Method (FDM). As a result, LBM results are in good agreement with the FDM results. The results imply that LBM based on shallow water equations has sufficient applicability of tsunami propagation and inundation.

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 The high water marks resulting from the Great East Japan Earthquake Tsunami around Matsushima Bay were noticeably smaller than those in other nearby regions. It has been suggested that the islets in the bay may have reduced the tsunami height but a quantitative analysis on the reduction effect has not been undertaken. In this study, we evaluated the tsunami height reduction factor by numerical analysis where topographic details of the islands were removed in stages and the water depth at the entrance to the bay was increased. Comparison of the results showed that the relatively shallow water depth as well as the islets in the bay contributed to a reduction in the tsunami height on the order of 4 m and delay of tsunami arrival to the coastal areas around the bay by up to 10 minutes in some areas. In addition, we showed that an appropriately sized breakwater (length: 6.5 km, crest height: T.P.+6.0 m) at the mouth of the bay can obtain the same tsunami reduction effect as the one given by the actual topography in the bay.

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 In order to evaluate tsunami wave forces acting on land structures, it is necessary to know an inundation depth and a water depth coefficient of the tsunami. In the past, the value of 3 has been used as the water depth coefficient. However, based on the field survey after the 2011 off the Pacific coast of Tohoku Earthquake, it was found that the water depth coefficient can be reduced according to the distance between the land structure and its corresponding coastline.
 In this paper, we show that from research results in the past, the water depth coefficient is dependent on the Froude number. Next, we present a simple evaluation model based on the energy grade line method that can express the change of the Froude number from the information on the inundation depth in tsunami hazard maps. We conducted hydraulic model experiments in accordance with the Froude similarity law of the assumed scale 1/100, to confirm the validity of the evaluation model. Finally, we show the Froude number is reduced depending on the distance from the coastline and the elevation related to the land structure, and the ground roughness.

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 Estimation equations for the viscosity of water containing suspended sediment were proposed, and flow fields under a uniform flow and a tsunami were investigated using a numerical model combined with the estimation equations. Numerical results showed that the maximum tsunami force on an onshore structure was affected by the change in the density and viscosity due to suspended sediment, suggesting that it is essential to consider the effects of suspended sediment in assessing the maximum tsunami force.

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 There are many researches on disaster mitigation and countermeasure for a tsunami cuased by Nankai Megathrust Earthquakes in the future. Owing to the topographic feature of Ise Bay and Mikawa Bay, the tsunami coming from Pacific Ocean has to pass through Ise Bay mouth to intrude into the bays. Tsunami information around the bay mouth can be considered as a prior information of tsunami arrival in the bays. In 2014, GPS wave gauge had been installed off Ise Bay mouth so that it will be possible to obtain the tsunami information in advance. This study aims to grasp the characteristics of a spatial distribution of the maximum water level and its arrival time in Ise Bay and Mikawa Bay by numerical simulations of tsunami propagation coming from the ocean. As a result, higher water level and shorter arrival time of maximum water level are indicated around the top of Chita peninsula in the bays. Furthermore, the northwest part of Ise Bay is also exposed by high water level. In Mikawa Bay, the western part has high risk than the eastern part for tsunami disaster. The distribution of tsunami risk in Ise Bay and Mikawa Bay is investigated in this study.

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 This study compares the characteristics of shoreline change, i.e. erosion and recovery, of damaged coasts in Indonesia and Thailand due to the 2004 Indian Ocean Tsunami, with those of a damaged coast in eastern Japan due to the 2011 Great East Japan Tsunami. The results shows two major characteristics: (i) sand bar erosion and recovery at different positions and (ii) serious coastal erosion and insufficient recovery. In addition, the coastal recovery, having been observed until around one year later from the tsunamis, has not been observed after one year at all the coasts damaged due to the 2004 and 2011 tsunamis. These indicates that the coasts that insufficiently recovered after the 2011 tsunami would not recover at least in decades.

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 This study analyzed topographic change using aviation laser survey and aerial photography due to the 2011 off the Pacific coast of Tohoku Earthquake Tsunami. The study area was from Aomori to Chiba prefectures in the tsunami inundation zone. The results suggested the relationship between the amount of erosion and tsunami height. Besides, the fill in Asahi city, Chiba prefecture, was eroded locally by the tsunami. The factor was investigated by topographic analysis using aviation laser survey, aerial photography and numerical simulation.

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 For elucidating the sand movement characteristics at Namiita coast, in situ and flume experiments were conducted. Field experiments which used colored sand were conducted from Dec. 2014 to Feb. 2015 and from July - Oct. 2015. For both seasons, colored sand (d₅₀=0.6 and 1.0mm) has been confirmed to move not only offing direction (within the shallow region from the critical water depth for the sediment movement) but also shore direction from the setting point. If similar material will be used for the beach nourishment, there is a possibility to contribute to the re-formation of sandy beach.
 Flume experiments with considering different submarine topography (before and after 2011 Tsunami) and wave conditions were conducted. By using experimental results, change of submarine topography through the year was clarified. Even submarine topography after 2011 Tsunami, a tendency of sedimentation was confirmed to be maintained around beach line. These results suggest that sandy beach in Namiita coast might be reformed by conducting beach nourishment.

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 Tsunami debris has potential to induce damages of buildings and tsunami fire. However, methods to evaluate the risks of tsunami debris have not yet been established. This study attempted to make data sets for numerical simulation about tsunami debris. The data sets were estimated range, volume and weight of tsunami debris due to the great east Japan earthquake. The range of tsunami debris was estimated using aerial photography. The volume and weight were estimated from the reports of local government. The situation of tsunami debris was difference in areas. Comparison of the estimated results of tsunami debris between the three areas, Rikuzentakata-city, Kesennuma-city and Watari-town, showed that coastal dikes restrained tsunami debris moving offshore. Additionally, tsunami debris was distributed in a wide range in case of the wide inundation area.

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 In this research, a damage forecasting method which considered indeterminacy of each tsunami drift was developed. I aimed at the drift starting water depth, the drag coefficient and the additional mass coefficient as the typical parameter which indicates the special quality of the drift and did by this research. The variability was considered by the numerical simulation which considered indeterminacy. A drift process by an influential presence in a building was compared in the actual cite.

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 This study focuses on the impact of debris-flow interactions on the inundation characteristics around the nearshore area. Laboratory experiment was first carried out to investigate the behavior of cubic wooden chips placed on the inundated area. Image-based analysis was applied to extract the quantitative characteristics of inundating flow and behavior of wooden chips. Numerical model was developed based on non-linear shallow water equations with dispersive terms. Behavior of each wooden chip was computed based on the equation of motion with hydrodynamic forces specified by Morison's equations. Influence of wooden chips on the inundating flow was accounted for in the momentum equation by adding the force acting on the chip as a reaction force and increase of hydrostatic pressure due to floating debris. The developed mode reasonably represented the observed behavior of floating wooden chips and the validated model was further applied to investigate the characteristics of flow-debris interacting fields.

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 In the 2011 off the Pacific coast of Tohoku Earthquake, at many places, coastal dykes fully collapsed by deep over-topping tsunami deeper than the dyke height. In this study, the resistance of coastal dyke against deep over-topping tsunami current was evaluated by performing a series of model tests using constant-height water flow. The effects of the following factors were evaluated; the slope of upstream and downstream slopes; the thickness of surface gravel layers; the opening size between the slope protection panels; and the length of geogrid layers reinforcing the embankment; and the connection between the reinforcement layers and the panels. It was found that GRS coastal dykes having the following structures can exhibit high resistance against erosion of the backfill caused by deep over-topping tsunami current, thereby a high stability: the upstream slope is gentle while the downstream slopes is steep; the surface gravel layer is thick enough; the opening between the slope protection panels is small enough; and the geogrid layers are arranged over the full width of the embankment and the reinforcement layers are connected to the panels.

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 Damage to coastal forests in southern Miyagi Prefecture caused by the mega tsunami associated with the 2011 earthquake off the Pacific Coast of Tohoku was surveyed nine months after the disaster. Specifically, the relationships among tsunami inundation depth, tree diameter, tree height, and whether the tree was standing or fallen were examined in coastal forests. The findings revealed that the relationship between the tsunami inundation depth and the tree diameter (tree age) was critical in determining whether trees remained standing or whether they fell over. A tilt-condition expression for trees was introduced using two moment-equations of the theoretical moment of the drag force due to tsunami flow and the moment of the pulling-down test for trees based on forestry methods. In the tilt-condition expression for trees, values of C_D=1 and F_r=0.53 for the drag coefficient and Froude number, respectively, agree well with the critical condition identified for whether trees remain standing or fall over in the field.

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 The three-dimensional behavior of a floating sloping-top caisson was investigated using hydraulic experiments. Experimental results showed that a decrease in the relative caisson width resulted in an increase in the amplitudes of the heave and roll under no-mooring conditions and an increase in the amplitudes of the surge, heave, roll, and pitch under tension-mooring conditions. Furthermore, it was revealed that the mooring lines reduced the amplitudes of the sway and heave, which was a different trend from vertical two-dimensional hydraulic experiments with different mooring conditions. This suggested that the appropriate modeling of mooring lines is essential in assessing the behavior of a floating caisson.

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 This paper describes a large scale floating coal stockyard (LFCS) proposed in the paper and hydroelastic characteristics of it in regular waves. The LFCS with 590 m long and 160 m wide is capable of storage of half a million t maximum and off-loading of coals. It is expected to improve transport efficiency of coal sources in Kalimantan regions because of installing such as the LFCS offshore. At first, structural sections of the LFCS which must store huge weight of coals were designed and stabilities to deformation due to loading of coals with several cases of arrangements on the LFCS were discussed. In addition, stress distributions according to the arrangements were statistically analyzed with FEM. Applying a hydroelasticity analysis method with the Green function method combined with FEM for structural deformation, we investigated hydroelastic motions with various conditions of the arrangement. From the results, although the hydroelastic motions are different due to the loading arrangements and weight, its effect and the difference are not always large.

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 In Japan, a structural performance evaluation method for wave-dissipating concrete blocks has not yet been established. In this study, surcharge load acting on the block sitting in the bottom-layer of wave-dissipating works was investigated through model experiments against permanent action and variable wave action. Based on the results of model experiments, surcharge loads by permanent action could be approximated by a gamma distribution. And, it is related to the relative density of wave-dissipating works and buoyancy of the blocks. Surcharge load by wave action in the case of small wave height are affected by the variation of buoyancy, while in the case of large wave height, surcharge loads are affected by the contact force of blocks by wave force propagations. The amplitude of the surcharge load by wave action is proportional to the wave height.

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 In The 2011 off the Pacific coast of Tohoku Earthquake, coastal area breakwaters of the Pacific Ocean were suffered extensive damage by tsunami attacks. A method for reinforcing an existing caisson type breakwater against tsunami attacks with a steel pipe piles behind the breakwater and filling rubbles between breakwater and piles were proposed. Horizontal loading experiments on model breakwaters were conducted on dry sand condition to develop a design verification method on steel piles used in this reinforcing method. Flexural rigidity of a pile and number of piles used in an experiment were changed. Resistance increment of the caisson was mostly affected by total flexural rigidity of piles in a unit length along breakwater length. The paper also discussed force acting on piles from the caisson side. Clarifying the distribution and intensity of the force acting on the pile can make an effective design verification method of piles to be used in this reinforcement.

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 For investigating the basic performance of the third generation wave model SWAN(version 40.91ABC), wave computations are conducted under both uniform winds and actual storm(2014 April 3-4 Low Depression) conditions, in cases where any of the wave growth and decay terms, sea drag coefficient(C_d) formulas, space resolution and time increment are changed. The main results are as follows. In uniform winds conditions, 1)the relation between dimensionless energy ε^* and dimensionless fetch F^* depends significantly on an applied growth and decay formula and any of ε^* obtained from different formula is greater than the empirical relation-based ε^* , 2)the Janssen formula yields the greatest ε^* of the three formulae used and the effect of C_d formula on the ε^* − F^* relation is negligible, 3)the effect of U₁₀ on ε^* − F^* relation is hardly found and a slope value in the relation between peak period and moments-based mean period is close to an empirical value of 1.1. In storm conditions, 4)the effect of either C_d formula or wave growth and decay formulas on the maximum wave height is significant, in cases where any of SWAN with various input parameter conditions yields reliable estimates of wave heights and periods, 5)the effect of space resolution on wave heights and periods is hardly detected but the effect of time increment is significant in the Janssen formulation case.

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 In a spectrum-based wave model, estimation of the surface displacement-based (significant) wave height H and (significant) wave period T is conducted by multiplying the square root of 0th spectral moment m₀ by a constant value such as α =4.004 and multiplying a -1st moment/0th moment ratio m_-1/m₀ by another constant value such as β =1.000 respectively. But analyses of numerically-simulated samples and measurement samples indicate that these coefficients of α and β may depend on any of the spectral width parameters Q_P, κ₀₁ and so on and that each of them can be approximated by use of Q_P- or κ₀₁-powered linear expression with an upper limit of α =4.004 or β =1.000. The constant value case for α and β definitely yields greater estimates of wave height H and period T than the variable value case. This leads to either rectification of overestimation in wave hindcasting toward more proper estimation or degeneration of proper estimation to underestimation. The former tendency in Typhoon 1106 case and the latter tendency in Typhoon 0918 case were confirmed through detailed comparison between SWAN-based hindcasts and measurements for wave heights and periods at many GPS buoy stations deployed along the offshore areas of the Pacific coasts of Japan.

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 A wave hindcasting system, which consists of the JMA(Japan Meteorological Agency)-provided MSM(Meso Scale Model) winds data sets and the third generation model SWAN, is applied to estimate wave conditions generated by the recent powerful typhoons such as T1102 and T1216 in the East China Sea connecting to the Pacific Ocean. The following results are obtained: 1) The MSM wind speed data is generally in reasonable agreement with the measurement data at each of 14 lighthouses located along the islands in the East China Sea, although the former tends to give 10 to 20 % greater value than the latter. The wind direction data is in close agreement with the measurement data at each lighthouse. 2) The SWAN model yields satisfactory estimates for wave heights at each of the coastal stations deployed along the islands but slightly less satisfactory estimates for wave periods. 3) Estimates of strong typhoon-generated wave heights depend significantly on the use of a drag coefficient formula or a wave growth formula.

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 The present paper examines the applicability of the third-generation wave models WAM and WAVEWATCH III (WW3) to the estimation of design waves and to the prediction of ocean waves, by verifying the reproducibility of waves derived from those models. Wind wave and swell are simulated by two wave models for 6 abnormal weather cases (ex. typhoon, low pressure and winter storm waves) and typical seasonal cases in summer and winter. The accuracy of the wave simulations by the wave models in a particular focus on the swell are revealed by comparison between the wave simulations and the observations of the GPS buoy and the seabed gauges mounted in the nearshore coast of Japan, in NOWPHAS system. The results show that in most abnormal weather cases the peak wave heights and wave periods for WW3 show better agreement with the observations than those for WAM, and in several cases the wave heights by the models little overestimate the observed ones. Causes of the overestimation should be clarified to improve the prediction accuracy of the models.

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 For maritime constructions, it is highly important to obtain reliable wave predictions for safety operation and work executable judgment. Advanced wave prediction method based on WAM model has recently been utilized in many marine construction sites. However, accuracy of the wave prediction under mild wave climate is not clear. This study investigates accuracy reduction factors of the WAM model based on the comparison between hindcast calculation and field data, with special reference to low wave condition. From this comparison, it is found that spectra obtained from the WAM model gives overestimation at high frequency region (0.3-0.4Hz), which might be induced by overestimation of wave height and also by underestimation of wave period in this region. Thus model improvement is required for high-frequency waves in order to increase prediction accuracy for lower waves.

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 In order to improve the wave estimation precision targeting bay area, it is necessary to improve the estimation accuracy of sea surface wind as the external force condition. The method proposed in this study, pseudo-consideration of the influence of land terrain in the calculation results of the previous model, which is a method of finding the inner bay sea surface wind. This method is effective to improve the accuracy of the case of performing the sea surface wind estimate and waves estimate of the bay area with the previous model.

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 We compare the calculated characteristics of the Weather Research and Forecasting model (WRF) and the previous model, we examined the applicability of WRF to the study of design offshore wave. As a result, we have confirmed that WRF is useful as a new sea surface wind estimation model. Further, we have confirmed the usefulness of the SWAN as a model alternative to wave transformation calculations based on energy balance equation method.

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 High waves, so-called ‘Yori-Mawari Wave’ are caused by low pressures through passing Japan Sea in winter several times in a year. In particular, on February 2008 a huge swell with a maximum significant wave-height of 9.92 m and a maximum significant wave-period of 16 s was observed at Toyama Port. For the dangerous damage, many studies of hindcast and prediction were carried out and the accuracy of wind wave models of the third generation is improving. The estimation of significant wave-height and -period at Fushiki and Toyama Ports have been worse yet, though those was considerably well at Wajima and Naoets points where are bounded by the open ocean.
 Because an above problem remains unclear, in the present study the refracton-deffraction due to complicated topography around/in Toyama Bay was investigated numerically using Simulating Waves Nearshore (SWAN) that is a third-generation numerical wave model. As a result, it was found that an appropriate horizontal resolution improved the significant wave-height and -period in the hingcast run.

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 Numerous efforts have been made for the improvement of nonlinear energy transfer computation. Until now, the DIA method is generally used for evaluating nonlinear energy transfer S_nl in the practical wave model because of its low computational cost. Tamura et al. (2008), suggested SRIAM developed by Komatsu (1996) to be incorporated into the operational wave model. The performances of the wave model were significantly improved by using SRIAM. However, the computational cost is still 20 times larger than the existing operational wave model using DIA. Therefore, we modified SRIAM by reducing the number of the resonant configurations. It was found that 9 numbers of configurations produce the nonlinear energy transfer approximately well as compared to the original SRIAM which has 20 numbers of configurations. This method is then called as the Reduced SRIAM (R-SRIAM). The configurations of R-SRIAM show that the quasi-singular quadruplets contribute the most to the nonlinear energy transfer than the regular quadruplets. Hence, we proposed the efficient number of resonance configurations by selecting only from the quasi-singular quadruplets to be included in the calculation, which is called as the Alternative Multiple DIA (AM-DIA) method. The reduced number of the resonant configurations makes the computational method of the nonlinear energy transfer more economically acceptable.

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