Gravel beach shows more dynamic profile change than sand beach, and is vulnerable to erosion. An artificial reef may be a structure to reduce beach erosion. However, there are many cases still suffering from beach erosion after installation of artificial reefs, indicating that more studies about beach processes are required. This study aims to investigate shoreline change at Shichirimihama Beach by using WEB camera system and beach profile changes based on field observation. Results showed that high energy wave during typhoon is the main reason leading to the continuous shoreline retreat. High wave approaching from E-SSE direction leaded to the formation of berm on the top of beach face at the location without artificial reef. In the area behind artificial reef, berm formation was not observed and shoreline almost stood by at its orginal position. However, when highwave approached to the coast from S-SW direction, sediment on beach face was washed out and the shoreline reatreated on the entire study area. This results indicated that in Shichirimihama beach wave direction also plays an important role on beach morphology change

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 Granulated coal ash has been utilized for sludge to the enclosed bay as a beach sand alternate material and the water improvement effect is observed. In order to design the shoal by granulated coal ash, it is necessary to understand the moving characteristic of the granulated coal ash by flow and waves. However, the detailed moving characteristic in the shoal is not clear. So the moving characteristic at the time of installing granulated coal ash in a shoal is clarified by a hydraulic model experiment. Especially, This paper reports the experimental result about moving characteristic of mixed-sized granulated coal ash by the wave.

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 This study suggests the method for estimation of bottom sediment distribution in Suo Nada, the Seto Inland Sea, Japan. Some numerical simulations based on flow model evaluate the degrees of mud sedimentation and water accumulation. Regression equations are obtained by the results of simulation and observed data. The equations estimate the distributions of bottom sediment with accuracy. In this area, the bottom sediment distributions are determined by the degrees of mud sedimentation and water accumulation.

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 This paper presents the study of a cyclone frequency and a wave characteristic in Bay of Bengal. In recent, there were some damages by the wave and the storm surge caused by the landing cyclones in Bay of Bengal. In order to estimate the damages of wave and storm surge, it is necessary to investigate the frequency of the cyclones by using cyclone track archives and weather re-analyzed data.
 In this study, cyclone track archives and weather re-analyzed data were collected. And the analysis of cyclone tracks frequency was carried out and the wave prediction analysis based on the third generation wave prediction model (SWAN) were carried out. The results were presented the frequency and the wave scale in the typical area of Bay of Bengal.

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 We tried to clarify long-term global changes of semi-diurnal tidal amplitudes with the harmonic analysis. Analyses of tide-gauge data at about 200 stations in all over the world reveal that semi-diurnal tidal amplitudes are increased or decreased in many stations. This result shows that changes in semi-diurnal tidal amplitudes do not have a tendency unified global. On the other hand, mean sea level increasing in many locations is less likely to be affected by changes in semi-diurnal tidal amplitudes. The fact of many long-term trends of semi-diurnal tidal amplitudes are consistent suggests that these mechanisms are associated with ocean dynamics.

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 In this paper, the estimation method of mean sea level (i.e. MSL) from long-term records of tide gauge is shown by eliminating the influence of tide, atmospheric pressure and ground elevation. Then, for the discussion of sea level rise, time series of MSL are estimated at ten tidal stations in port area around Japan. At three ports in Japan sea side, MSL tends to increase clearly. At four ports in Pacific side, MSL tends to increase, but annual rates of elevation vary port by port. Each elevation rate of MSL estimated from latest records (during 2004-2013) is larger than that from whole obtained records respectively.

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 Basic performance of the SWAN model with 4 modes related to stationarity and dimension is investigated through numerical simulations under given uniform winds blowing normally to a coastline. The main accomplishments are as follows; (1) The stationary(st) and nonstationary(nst) modes yield a slightly different wave growth and the one dimensional(1d) and two dimensional(2d) modes give almost the same wave growth. (2) The Westhuysen et al.(2007) results regarding the relation between dimensionless wave energy ε^* or dimensionless peak frequency f^*_p and dimensionless fetch F^* are well reproduced by use of a st-1d mode with coefficient δ = 0 in the dissipation term. However, the ratio of peak period to moment basedmean period with -1 order is much greater than the empirical value of 1.05. (3) Wave growth is strongly affected by the choice of δ and time increment Δt used in nst mode. (4) Wave growth curves by nst-2d mode with δ = 1 are almost free from the given wind speed and provide overgrowth of both the Westhuysen et al.(2007) results and the empirical results, whereas the wave period ratio is much closer to an empirical value of 1.05. (5) The Toba constant B_T of 0.062 in 3/2 power law may be roughly reproduced by nst-mode with δ = 1, although the calculated coefficient varies within a range of ±5 % for mean of 0.070.

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 Wave hindcastings in the Japan Sea by the third generation model SWAN under input MSM winds conditions were conducted for April 3-4, 2012 Low Pressure System (LPS) and the virtually-modulated LPSs concerning strength, course and moving speed. Investigations of the largest maximum significant wave height H_maxM generated by each LPS show the following results: 1) the effect of time increment Δ_t used in wave hindcasting on H_maxM is significant and consequently use of Δ_t yielding the Courant number less than 1.5 for the lowest frequency and space increment is recommended, 2) a 15 % increase of wind speed in the Japan Sea yields H_maxM close to that based on 100, 000-year simulations, 3) the actual LPS took a course generating the largest H_maxM among the supposed LPSs, 4) 2/3 decrease in translation speed of the LPS gives the largest 1.1 m increase in H_maxM. A final conclusion is that the concerned LPS may have brought about extraordinarily high wave heights to the northeastern coastal area of the Japan Sea under actually-conceivable quasi-worst LPS conditions.

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 The nonlinear energy transfer plays a critical role in determining the energy distribution of directional spectrum. Numerous studies of the important role of the nonlinear energy transfer in the evolutions of wave spectrum have been clearly demonstrated in the frequency domain, however little is known about the characteristics of the nonlinear energy transfer in the directional domain. In this paper, we investigate the characteristics of spatial and temporal changes of the directional spectra in consideration of nonlinear energy transfer as a possible mechanism of the change of directional distribution in deep water depth. Numerical computations are performed by three different types of the third-generation wave model, WAM, where each of them is implemented with DIA (Hasselmann et. al., 1985), RIAM (Komatsu et. al., 1993) and SRIAM (Komatsu et. al., 1996), respectively, for the computation of the nonlinear energy transfer. The JONSWAP type spectrum and Mitsuyasu's directional function are applied to define the energy distribution of directional spectrum. The characteristics of bimodal directional wave spectra are also discussed.

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 Wave transformation describes the propagation of waves and water surface displacement from offshore to onshore. The magnitude of wave generation and wave set-up are dependent on a number of factors such as wind speed, water depth and tide level. This paper has investigated the characteristics of wave transformation in Manila bay along Roxas boulevard during extreme conditions specifically on typhoon events. Records of typhoon that struck Manila bay area for the past 40 years were used to generate the wave height and water displacement profiles through a numerical simulation model developed by Kraus and Larson (1991). Parameters such as water depth, wind speed and tide level were the input data in the simulation. Six transects were established up to a depth of 20m to describe the cross-shore profile fronted by breakwater structure and open sea. Results show that the wave height and water surface displacement are significantly higher in transects which are not exposed to any breakwater structure. A wave generated by a typhoon with a wind speed of 42 mps similar to that of typhoon Narsing in 1973 would definitely overtop the existing seawall situated along Roxas boulevard.

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 Kaetsu Coast is located on the middle north coast of Japan. This area has been suffering from various problems, including the progress of severe coastal erosion, frequent occurrence of rip current accidents, reduction of coastal habitats, and others. In order to cope with these problems, physical understanding of long-term wave characteristics is essentially important as basic engineering information. Accordingly, this study examines the long-term wave data observed at the Kanazawa Port in duration 1971-2012 in order to clarify the long-term as well as the seasonal characteristics in significant wave properties. On the overall, the seasonal variation in wave height, period, and direction is shown to be significant. The monthly-mean wave height and period are correlated with 2nd order polynomials very well. For the long-term variation, the annually-mean significant wave height indicates no significant trend. On the contrary, the Lepage statistical test detected an abrupt increase in the annually-mean significant wave period around 1990. In relation to these changes, the long-term variation in monthly-mean wave characteristics shows that the wave slope becomes smaller in the last two decades. The Mann-Kendall statistical tests demonstrated that the monthly-mean wave height and period in July have significantly increased during the study period. Several attempts have been made to correlate these features with climate changes.

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 The JCOPE2-ROMS downscaling oceanic modeling system improves mesoscale reproducibility by introducing a simple restoration to data which we call “TS (temperature and salinity) nudging”, where the prognostic temperature and salinity fields are weakly nudged four-dimensionally towards the assimilative JCOPE2 reanalysis (Uchiyama et al., 2012). However, there is not always an accurate reanalysis for assimilative oceanic downscaling models, and therefore alternative dataset should be prepared. Takano et al. (2009) proposed an empirical method to estimate 3-D thermal structure from the near real-time AVISO altimetry data along with the ARGO float profiling data. We view the derived empirical TS data (referred to as TUMSAT-TS) as a candidate for assimilation. A synoptic forward modeling of the JCOPE2-ROMS downscaling system is thus conducted to explore usability of this empirical TS dataset by carrying out with the TS nudging towards the TUMSAT-TS.

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 This study newly developed an air-sea-water quality coupled model in order to consistently analyze long-term and short-term variations of water structure in a coastal zone. The model was applied to Ise Bay area and its validity and utility were verified through the comparisons between the numerical results and observation data. As a result, it was revealed that the coupled model can simulate not only long-term variation such as formation and deformation processes of density stratification and dynamic process of hypoxia, but also complex water variation in a short period with high accuracy.

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 This study conducted tsunami propagation simulation due to the 2011 Tohoku Earthquake using the Coastal ocean Current Model (CCM), which is a quasi-three-dimensional ocean model with a terrain following multi-sigma coordinate system, so as to validate the applicability of the model for simulating tsunami propagation. Furthermore, the study numerically examined water structure variations in Ise Bay area under tsunami attack due to Nankai Trough earthquake using an air-sea-water quality coupled model including the CCM for coastal current calculation. As a result, the coastal flow induced by the tsunami caused an intrusion of oceanic water with high salinity during in a short period and the disappearance of hypoxia, which implied that the tsunami has a great impact on water structure.

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 We investigate with a detailed downscaling oceanic model on impacts of typhoon passages on upper-ocean cooling in and around the Seto Inland Sea, the largest semi-enclosed estuary in Japan. A sea surface heat budget analysis is conducted using the heat balance equation based on the outcomes of the innermost ROMS-L2 model results. After the mid September, the net heat flux at surface becomes negative to induce prominent surface cooling and cold-water formation in the upper ocean. The surface heat flux verying with the typhoons are characterized by decrease of short wave (solar) radiation and negative latent heat flux enhanced by strong surface wind stress and unstable condition of the lower atmospheric boundary layer during the typhoon passages. The latent heat flux is also strengthened by abrupt decrease of the near-surface atmospheric specific humidity after the typhoon passages.

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 The observation of atmospheric pressure fluctuation was carried out at Niigata University to predict generation of a gigantic tsunami. The atmospheric pressure changes were occurred by precipitation and a cold atmospheric current. The 3D numerical simulation of generation and propagation of acoustic gravity waves associated with tsunami was performed to investigate how acoustic gravity waves generate by the generation of tsunami. The negative atmospheric pressure wave was generated in the region where the subsidence of ocean floor occurred and propagated with decreasing its amplitude up to several hundred kms.

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 On the north shore of Lake Hinuma, Oyazawabana sand spit is formed owing to the wind waves from the east. Although this sand spit has been gradually eroded, beach was severely eroded by ground subsidence by 22 cm during the 2011 Great Earthquake together with the obstruction of longshore sand transport by a groin extended at the south end. In this study, beach changes around this sand spit was surveyed along with the sampling test of bottom material, and erosion mechanism was investigated. Furthermore, longshore sand transport rate between 2012 and 2014 was estimated to be 133 m³/yr.

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 Complex principal component analysis (CPCA) was applied to examine the medium-term geomorphological processes of the Mukawa coast in northern Japan, using an 18-year series of bathymetry survey data. The result of CPCA shows that the westward wave energy flux significantly influences on the geomorphological changes over the study area. The pattern of the geomorphological changes due to the westward waves emerged in the first mode of CPCA. The second mode of CPCA for the shallower region in front of the river mouth shows the pattern of geomorphological changes due to the river discharge.

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 El Puntal spit of 2.5 km length elongates at Santander Bay facing Gulf of Biscay in Spain. In extremely shallow sea of tidal flat on the south side of this sand spit, a small cay was deformed owing to wind waves in the bay, resulting in the formation of sand spits. In this study, the deformation of a cay and the formation of sand spits were investigated by the analysis of satellite images and site observation. The results were compared with those obtained by the numerical simulation using the BG model in the previous studies.

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 Nha Trang coast, which is located in the south central coast of Vietnam, is frequently affected by severe erosion in several months every year. Although the past studies have shown the shift of shoreline on this coast, detailed process of shoreline change is not clear. In this study, shoreline change in the north area, where the most serious erosion has been observed, is extracted from continuous images of coastal surveillance camera system. The seasonal shoreline variation on Nha Trang coast is one of distinct features and the change is characterized by seasonal variation of climate conditions. The retreat of shoreline in the north area and the advance of shoreline in the south area of Nha Trang coast occur during the northeast monsoon period with strong northeast winds and high waves. While in the remaining periods with the dominant of moderate winds and calm waves, shoreline advances in the north area and retreats in the south area.

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 The influences of sea level rise and wave intensification due to climate change have been studied recently. In regard with the influences on beach profile, number of studies have considered due only to sea level rise but not many studies due to change of wave characteristics have been conducted. In this study, the influence of both sea level rise and wave intensification due to climate change is investigated and compared around the structures. The study site, Uradome Coast, which has two submerged breakwaters and beach nourishment as erosion control. As a result, the beach profile change due to change of wave characteristic in future climate is estimated to be the same or more than that caused by sea level rise.

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 This study investigated topographic change of coastal dune and fill by tsunami overflow using hydraulic model test and aerial survey data.
 In case of hydraulic model test, wide crown width of body was restrained to decline speed of crown height. In addition, this study suggested prediction formula about speed of crown height decline by connecting shear flow of tsunami over flow and speed of crown height decline.
 Topographic change in Natori City before and after the Great East Japan Earthquake Tsunami suggested that wide crown width of body has erosion resistance by tsunami overflow.

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 In the Sangchan beach, coastal erosion had occurred due to human's development till ten years ago. However, since many countermeasures (Y-type groins and detached breakwaters) were constructed, although this coastal erosion came to an end, the recovery of the beach is insufficient. Therefore, in this paper, the safety at the Sangchan beach by existing countermeasures is confirmed and some improvement plans for raising the safety to coastal disaster are examined. The models of Ca et al. and Yamamoto et al. are used to evaluate the difference of coastal erosion between those plans to the present condition, and the equations of Van der Meer et al. and Yamamoto & Horikawa's are used to evaluate the difference of wave overtopping rates between those. As conclusion, the comprehensive comparison of examination results makes it clear that sand nourishment is the most proper countermeasure.

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 The fundamental issues of the beach erosion including the difficulty in social and comprehensive adjustments of the beach erosion were discussed through a case study, taking the Ichinomiya coast on south Kujukuri Beach as an example. On this coast, artificial headlands have been constructed since the 1990 as a measure against shoreline recession, but this caused further downcoast expansion of the beach erosion. Finally, it became difficult to escape from a vicious cycle of seawall construction - downcoast erosion - seawall construction - downcoast erosion, permitting further expansion of the erosion area. Such difficulties were analyzed, and the neccesity of the improvement of the relevant system was discussed.

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 On coral reef, complex flow fields are frequently developed by wind-driven flow and nearshore currents induced by breaking waves at the reef edge. Characteristics of sediment movement and beach transformation are different from silicate beaches owing to the differences in hydrodynamics and sediment properties. We conducted a field survey in an eroding artificial beach in Miyakojima Island to understand the mechanism of sediment transport and topography change in coral reef. It was concluded that strong currents observed in summer at the gap of the breakwater enhanced offshore-ward transport of sediments through the gap. The presence of continuous sand belt around the headland suggested the offshore sand loss due to northern wind in winter.

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 Severe erosion has occurred on Cua Dai Beach, Hoi An City, Quang Nam Province which is located in the central part of Vietnam. The erosion has been getting more serious in recent years. In this study, the changes of morphology are presented through analysis of satellite images. The propagation to the north of sandy beach wedge toe can be observed, indicating northward longshore sediment movement. Tourist facilities such as hotel, embankment, etc. have significant influence to the evolution of surrounding morphology. The reduction of sediment supply from river due to sand mining along the river or at the river mouth has been pointed out as the highly possible mechanism of erosion.

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 Coral cays formation mechanism has various reports and research, but observation data is almost less. So, coral cays formation field of wave field and flow field is still unknown. In this study, we discuss about external force of coral cays formation. In field survey we focused the ballast island on northern reef of Iriomote Island which is formed by only coral gravels. And, we performed numerical calculation to complement the external force field to coral cays formation. As a result, we understand that external force of coral gravel transport is caused by the waves than the flow on the reef. And, there has high potential of coral gravel transport, from bi-directional (NE and NW) waves on the reef center caused by interaction of the refractive wave of behind Hatoma shielding and two depressions near north ballast island.

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 Sandy beach of south Nagayama-no-hama Beach on Irabu Island was severely eroded owing to the effect of the construction of Irabu Bridge. Beach restoration was carried out on this beach to recover sandy beach. After the completion of the nourishment on south Nagayama-no-hama Beach, beach nourishment was also planned on the north beach. Numerical simulation using the BG model (a three-dimensional model for predicting beach changes based on Bagnold's concept) was carried out to determine the appropriate method.

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 Karasen beach is a recreational place, which used for clam digging, sea bathing etc. In April. 2012, almost area of the beach is covered by mud, and turned to dangerous such as being stuck in the mud. This phenomenon is very rare nationally. To determine the source of siltation, and to take measure, we conducted field survey, and numerical simulation.
 As a result, fine sediment is directly transported to the shore line by Chikusa river flood. On the other hand, fine sediment is deposited offshore. After deposition, tidal current and wave induced current will transport sediment to the beach. Based on the result, we proposed some measures, and make sure of the effect by numerical simulation, which quasi-3D current model is coupled with sediment transport model. From these study, we found that nourishment after dredging mud, and level the ground is the best way to escape from siltation.

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 This study on bimodal artificial reefs under construction at Kin-eicho coast of Niigata evaluated about wave attenuation by wave observation and beach stabilizing effect by bottom sounding.
 The comparison result suggests that wave height transmission coefficient of bimodal artificial reefs has higher tendency than the general artificial reef at Ariake coast because the crown width of bimodal artificial reefs at Kin-eicho coast are shorter. However, wave height transmission coefficient of bimodal artificial reefs satisfies a requirement of below coefficient of 0.6 required runup height against design wave.
 Effects of beach stability by bimodal artificial reefs have not been confirmed at the moment. The cause is due to the rapid flow offshore with sand from undeveloped section of bimodal artificial reefs.

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 Tottori Sand Dune Coast has been eroded starting around 1940s and the beach nourishment project has been carried out to restore the shoreline since 2005. In the project, the deposition sand at port and river mouth were dredged and transported to the erosional area. And then the sand was injected in the region offshore erosional area and the backshore area. The total volume of the sand was approximately 650,000m³ from 2005 to 2014. In this study, the effect of the project was estimated using the bottom sounding data and the shoreline data. The shorelines showed trend to restore after the beach nourishment project. From this study, it was found that although a part of injected sediments was moved to the Tottori port, recovery of the shoreline was maintained.

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 The purpose of this research is evaluation of 3 dimensional distributions of suspended particles with ADCP in and around Oshima Strait of Kesennuma Bay. The SS density was formulated based on a relation between rear scattering intensity of ADCP and FTU of water quality meter. Highest SS value was present above bottom west on the strait, and the current direction was west at mid-point of the strait. Transmitted SS to the west bay was up to ca. 200 g/sec, and ca. 50 % of the amount moved to the west bay mouth.

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 Hydrographic features of Yatsushiro-Kai, a semi-enclosed embayment in Kyushu, Japan, observed by a 10-year environmental monitoring between 2004 and 2013 by the Ministry of Land, Infrastructure, Transport and Tourism (MLIT), were closely examined. Stratification was stronger in the inner-most area than the middle where Kuma-River supplies a large amount of fresh water. Spatial characteristics of environment of Yatsushiro-Kai could be classified into nine categories, applying cluster analyses to bottom sediment and benthic community. One of the results of these analyses was shown that distribution of the benthic communities and the bottom sediment qualities was complex, especially in the inner-most area.

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 We have been developing a real-time current simulation system in order to clarify drifting process of marine litters supplied from a backland and to facilitate their removal. In this study, GPS buoy experiments were carried out to verify the accuracy of the system. Estimation scheme of wind velocity components are modified for better reproducibility. The system outputs were mostly able to trace buoy drifting in terms of flow velocity. The distance between neutral particle and observation buoy was 6.3km at maximum in results of release of four buoys. Computed horizontal flow velocity in the first surface layer, which are used for prediction in our simulator, and at 15cm deep can be used to predict buoy drifting better than that interpolated at sea surface.

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 Marine debris issues have gained a significant concern recently due to their impacts to coastal and marine environments. Knowledge on their abundance, distribution and seasonal variation are still limited in many aquatic environments including Kagoshima bay. This study was conducted in three phases from the year 2010 to 2014. Field study in Oosumi peninsula and along Kotsuki river was conducted on November, 2010 to investigate the abundance and distribution of micro size debris. Then, in Kagoshima bay three field studies were carried out to investigate spatial distribution and seasonal changes of marine debris along its coastline and on sea surface from the year 2011 to 2014. Kagoshima bay opens to the south of Kyushu island and is affected by Kuroshio current which probably carries marine debris into the bay. In addition there are several major rivers which carry debris into the bay. The size of the bay is similar to Tokyo bay, therefore field studies in and along its coastline can be representative study to reveal qualitative and quantitative characteristics of marine debris inside a bay in Japan. As a result, EPS fragments dominated the distribution in almost all surveyed beaches (over 90%). Rainfall and natural disasters (i.e. typhoon) contributed significantly to higher deposition levels of micro debris on beaches.

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 When the inundation area for the Nankai Trough Earthquake Tsunami is simulated, the assumed tsunami size and initial tidal level are usually fixed. However, those conditions would not necessarily be the same with the real tsunami. Therefore, it is important to simulate under various conditions and find high-risk locations for tsunami inundation. In this study, two-dimensional analysis of tsunami propagation under combinatorial conditions with the tsunami size and the initial tidal level were simulated. The model contains a two-way nesting scheme and can calculate tsunami propagation from the source to Osaka Bay in high speed with good accuracy. As a result, it was found that when the initial tidal level was lower than the mean sea level, the total inundation area is small even when a very large tsunami size is assumed. Also, as expected, the tsunami size and total inundation area were found to have a strong correlation. From these results, it was possible to identify critical locations where inundation occurred even under mild conditions.

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 Generally, two-dimensional tsunami analysis is used for the tsunami simulation. On the other hand, since huge computation time is needed, highly precise three-dimensional tsunami analysis is not usually used. In this study, the highly precise wide scale three-dimensional tsunami simulation has been carried out by the hybrid model in order to predict correctly the tsunami flood situation in a factory. This hybrid model combines two-dimensional tsunami analysis and three-dimensional tsunami analysis, and can perform a tsunami simulation efficiently from a wave source region to the factory of an object point. Moreover, the effect of the mitigation methods have been showed concretely against tsunami flood of important industrial factory using this simulation.

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 As long as enough high seawalls are constructed along the coast lines, industrial facilities in coastal areas can be protected against tsunami inundation. However, even when high seawalls exist, seawater will come into landside areas through water channels such as intakes, outfalls and drainage channels. Coming seawater will possibly induce inundation disasters, damaging electrical facilities and losing evacuation routes. In this study, an integrated numerical simulation model for inundations induced by tsunami overflows was developed. The simulation model consists of a 1-D pipe network flow model to simulate overflow volume from pits of a water channel and flow of the pipes and a 2-D inundation model to simulate inundation flow on the ground.
 The developed simulation model was verified with hydraulic experiments. In the experiment, an idealized coastal industrial area, equipped with a drainage water channel network, was set in a wave basin with 1/30 scale. It was found that although the simulation model doesn't consider the effects of surface tension forces, which act in this experiment to some extent, it reproduces the inundation areas and the time series of inundation depths obtained by the experiment, relatively well. If the surface tension forces are programmed into the simulation model, the simulation results will surely show better agreements with the experiment. However, surface tension forces can be neglected in the real scale and therefore, in the practical situation where surface tension forces are enough small, the simulation model is applicable. Since it has advantages of requiring less computational efforts compared with a 3-D simulation model, it is helpful to analysis the risks of tsunami overflow inundation and to contrive suitable BCPs.

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 In case a level 2 tsunami occurs, the wave height is expected to be higher than a design wave height of a seawall, as a result, the wave possibly overflows into the hinterland of the seawall. For the purpose of disaster reduction, we should examine the influence of the overflown tsunami on the buildings behind the seawall.
 We herein presented an approximate model to express collapsing behaviors of the seawall, as well as a numerical method to reproduce the overflow motions under the seawall collapsing situation. We examined the characteristics of the tsunami overflows and the seawall collapsing behaviors. Detailed discussion is made on the varying characteristics of the tsunami wave force acting on a hinter building with change of seawall collapsing motions.

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 A three-dimensional numerical model, which combines CADMAS-SURF/3D with a body-force-type immersed boundary method was constructed in this study so as to take into account the movement of a structure, prior to the development of a three-dimensional advection and diffusion numerical model of suspended sediment. The validity and utility of the model were confirmed by comparing between the numerical and experimental results in terms of outflow caused by a quick opening of a gate which was located between two water tanks with different water depths. The model is, therefore, said to be useful in developing a three-dimensional suspended sediment numerical model.

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 The inversion of geodetic datasets for the Niigata earthquake of 1964 was carried out to estimate the subfault displacements. The fault models by Abe and Matsuhashi were adopted for the Niigata earthquake and were devided into 10km×10km subfaults of which slip distributions were estimated so as to coincident with the crustal displacements. The maximum slip estimated is about 8m near the epicenter. The numerical simurations were carried out to evaluate the accuracy of a source inversion with crustal displacement data, and reveal that the accuracy depends on the distances between the locations of the fault and the observation point.

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 In the 2011 Tohoku earthquake tsunami disaster, the actual tsunami heights greatly exceeded the estimated heights and this underestimation resulted in serious damage in Japan. After the Tohoku tsunami, the Cabinet Office of Japan^4),5) reported a large slip zone (LSZ) and a super large slip zone (SLSZ) related to asperity and their assumed tsunami fault models. This led to organizations considering a new assumption in fault models. However, the resulting shapes or locations of LSZ and SLSZ differed from those reported by the Cabinet Office and organizations, and a standard method has not yet been decided. Seto and Takahashi¹⁾ proposed a model for analyzing multiple tsunami scenarios that considers the uncertainties in LSZ and SLSZ. However, that model did not allow considering multiple LSZ and SLSZ, uncertainty in the hypocenter, or uncertainty in the seismic magnitude. In the present study, a general model that considers all of the above uncertainties is proposed. The proposed model is applied to the Nankai Trough to assume multiple tsunami scenarios, and the detailed procedures for using the model are clarified. As an application to tsunami disaster mitigation by using multiple tsunami scenarios, the relationship between the predominant period and the tsunami source is examined. The predominant period is an important factor for tsunami disaster mitigation because it relates to both whether a tsunami warning should be cancelled and how the tsunami height will be amplified inside a port.

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 A tsunami induced by the Tohoku Earthquake (March 11, 2011) caused catastrophic damage on fishery ports along coastline of the Tohoku region. Restoration of damaged ports and investigation of tsunami countermeasures are still in progress.
 In the Fukui prefecture, where it is predicted to suffer from tsunami impact in the future, establishment of tsunami countermeasures is urgently necessary.
 We derived design tsunami forces for structures of fishery ports in the Fukui Prefecture by selecting a tsunami of the highest water level from a set of tsunamis that are predicted to occur with relatively high incidence. The set includes ones that occurred in the past and hypothetical tsunamis that are defined in other studies. In addition, tsunamis that are originally derived in this study by reducing magnitudes of largest class tsunamis are included in the set: the largest class tsunamis are hypothetical tsunamis that are considered to occur extremely rarely but have catastrophic damage when they do occur.

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 This study carried out the reproductive calculation for the submarine landslide model experiment that was conducted by Hashimoto and Dan (2008), adopted to kinematic landslide model (KLS model) and Watts model which calculates Tsunami wave propagation applying initial wave profile. Moreover, KLS model was modified to focus on synchronize the amount between collapse and deposition as ‘modified-KLS model’ in this study, which is designed to proceed collapse and deposition virtually simultaneously. As a result, KLS model does not have the advantage of tsunami height evaluation for the submarine landslide model since it becomes the Tsunami wave height of approximately 1.5-3.0 times in comparison with the experimental result. On the other hand, modified-KLS model and Watts model mostly reproduced the spatial distribution of Tsunami wave height.

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 In order to solve the problems of the inversion methods commonly used in the field of real-time tsunami prediction using the observation data of tsunami gauges, the ensemble Kalman filter method which is one of the data assimilation methods is applied to this filed. We tested its effectiveness by twin experiment in the area where DONET2 of JAMSTEC is set up. As a case study, using the case (3) model which the Cabinet Office supposes as earthquake tsunami model in Nankai trough, numerical calculation is executed in this study. As a result, it is clear that using the ensemble Kalman filter method, tsunami heights in the coast can be predicted in real time with good accuracy if the data are observed at tsunami gauges for 20 minutes. However, as long as DONET2 tsunami gauges are used, it is impossible to predict tsunami heights with good accuracy before arrival of tsunamis in the south of Wakayama and Tokushima Prefecture.

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 It is reported that protective barriers such as coastal dikes and roughness of ground surface may reduce tsunami wave force acting on land structures. The purpose of the present study is to develop an estimating method of reducing effect of tsunami wave force through hydraulic model tests and analytical model studies. The hydraulic model test applying Froude similarity's law with the scale of 1 to 100 was conducted in order to clarify the characteristics of wave force reduction by protective barriers. It was found out that tsunami wave force is reduced according to the height of costal dike, roughness of ground surface and the distance from the coast line. It was confirmed that drug coefficient changes according to the Froude number. A simple analytical method to compute the change of Froude number considering effects of discharge reduction and energy consumption was developed. The computed results are in good agreement with the experiment data.

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 In the case of multiple arrangement of cylindrical tanks, tsunami flow pattern becomes different from the case of a single tank by the interaction between tanks. Therefore, wave forces of tsunami on cylindrical tanks depend on the arrangement pattern and the distance between tanks. In this study, 3D-CFD has been carried out for tsunami flow around multiple arrangement of cylindrical tanks. The applicability of 3D-CFD has been verified by the comparison between the calculation result of 3D-CFD and the experimental result of Sakakiyama¹⁾. In addition, characteristics of tsunami flow pattern and wave pressure has been investigated from the calculation result of 3D-CFD and the experimental result of Sakakiyama¹⁾. The knowledge of multiple arrangement effects on tsunami force has been obtained from these results.

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 A flow phenomenon around a tank installed to coast in high Froude number range was discussed for suggestion of simplified safety assessment by using of 3D-CFD and experimental result of retrospective report. Validation of 3D-CFD was carried out with a tsunami flow and force under supercritical flow conditions. From the numerical result, we clarified that it was need to estimate not only hydrostatic fluid pressure but also reduction of static pressure caused by generation of dynamic pressure for tsunami force prediction. In addition, this value was best explained by dynamic pressure difference calculated from surface and bottom velocity. Formulated tsunami force prediction equation based on this study was in good agreement with experimental result.

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 Model experiments on hydrodynamic forces by run-up tsunami were carried out in a wave basin, where three types of tsunami were generated. Circular cylinders were used as models of oil storage tanks located at a storage area in a harbor. A force transducer was attached to the cylinders and three-component forces acting on the cylinders were measured. Measurement of water levels and velocities were carried our in the absence of a cylinder. Characteristics of the hydrodynamic forces were discussed by comparing wave and current fields. Impulsive forces were observed at an instance of collision with run-up tsunami. After the tsunami ran up, the water level rose for a long time and thus the drag and inertia forces became predominant. The effects of protection walls for oil spill and interaction with other cylinders were also discussed.

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 It is necessary to take account of transitional fluid force when tsunami collides against a pipe installed ashore. In this study, experiments by dam-break method were carried out to grasp characteristics of fluid force by tsunami acting on a horizontal pipe. The measurement results were compared with the results of CFD analysis, revised equation adding impulse force and fluctuating fluid force to Morison equation, and drag force equation shown in the guideline of Federal Emergency Management Agency (FEMA) to build a reasonable evaluation methodology of wave force by tsunami acting on a pipe, and to evaluate margins by each method. Consequently, evaluated maximum values of wave force to experimental results were 0.8 to 1.8 times in CFD analysis, 1.4 to 2.1 times in revised Morison equation, and 2.1 to 6.1 times in FEMA's guideline.

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