The geomorphological changes of tidal flats adjacent to Shirakawa River mouth due to flush flood after earthquakes on April 14 and 16, 2016 were examined through field observation data. There was about 0.41m ground subsidence around field observation site. Therefore, the cross-shore bottom profiles could not return to the averaged profiles. The measured profiles were analyzed by the three parameters and the correlation among them was so high. The clinoform along the water-route propagated to off-shore approximately 150m during 2014 to 2016 after the earthquake. The estimated sediment discharge was 1.1*10⁵m³/yr/km², which correspond to four times during 1978 to 1997.

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 To clarify the characteristics of shoaling in a small fishing port, it is necessary to monitor the bathymetry frequently and persistently. This study focused on the shoaling of the Fukude fishing port, Japan, and long-shore sediment transport in the adjacent coast. The bathymetric information was collected from multiple small fishing vessels. The position and depth of the vessel during operation were acquired with a GNSS antenna and fish finder, respectively. The bathymetry was prepared to evaluate shoaling in the port and sediment budget for the coast. An assessment of the bathymetry monitoring data from 2012 to 2016 showed various rates of accretion in the port mouth and navigation channel. The rate of the shoaling ranged from 0.1 to 0.2 m/y in the inner part of the port due to supplying silt from the small river of which the mouth opened at the innermost part. Sudden changes of the depth at the port mouth were determined by ChangeFinder with AR model which is one of the data mining algorithms. There were several turning points of the changes with not only high-wave conditions due to typhoon but also calm waves. The longshore sediment transport rate in the adjacent coast was annually evaluated between 2014 and 2016.

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 In the Noshiro Port, in Akita prefecture, a sandbank is formed in the basin with sand transported into the port through an opening at the midpoint of main breakwater, whose shallow topography is more likely to obstacle to navigation. In order to consider countermeasures against the shoal due to sand inflow, we study the formation mechanism of sandbank based on the data obtained in the past, and quantitatively evaluate a feature of sand drift and its external forces by conducting a field observation on suspended sediment. Taking the result of these researches into account, we succeed in reproducing the sandbank by a multi-layer model of numerical simulation, with which an effective countermeasure is examined for decreasing the volume of sand deposition from a viewpoint of life-cycle cost for 50 years. As a result, a combination of submerged breakwater at the location of opening and a periodic dredging becomes more advantageous than a maintenance dredging only without a structure.

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 To conserve the shore adjacent to Fukui Port, the double crest submerged breakwater has been constructed. As a result, it is confirmed to reduce wave overtopping by installation of the submerged breakwater. However, stability of the seawall is concerned by scouring in front caused by the installation of the submerged breakwater. From the characteristic of the bathymetric change adjacent to the double crest submerged breakwater, the scoured sediment is observed to deposit near the submerged breakwater, indicating the two-dimensional phenomenon is predominant in bathymetric change. In the vicinity of both tips of the submerged breakwater, alongshore sediment is observed additionally. To evaluate the stability of the seawall, it is essential to predict the maximum scour depth, which is analyzed on basis of the bathymetric survey data from commencement of the construction to completion. Comparing the maximum scoured depth of each survey, the changing rates decrease with increase of the scour depth, which indicates that the changing speed of the maximum scoured depth is predictable as a function of scour depth. Precise prediction method of the maximum scour depth is proposed. And effects of the submerged groin are examined as well.

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 Sand wave is a consecutive wavy bedform on seabed with several meters in wave height and several tens-hundreds of meters in wave length. Where the crests of sand waves rise above the required channel depth, they prevent vessels from safe navigation. In Kanmon Route, several locations of sand wave formation exist and a prediction method of sand wave evolution is needed for efficient management of channel depth. In this study, a simple prediction model developed by Nakamura (2015) for sand waves in Bisan strait channel is employed, and the model is applied for sand waves in Kanmon Route. The prediction results show that channel deepening in the area of sand wave formation can reduce growth rate of the sand wave. It is also confirmed that the model is applicable for estimation to minimize dredging volume or for setting dredging frequency appropriately.

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 Hokkaido has a lot of fishing ports and the number of the fishing ports is about 280. Most of fishing ports in Hokkaido are located in the surf zone on the sandy beach. As a result, channel sedimentation has become a serious problem in many fishing ports. For example, a maintenance cost has been increasing every year. In general, when planning a coastal structure to control sediment movement, annual maximum wave heights was used as the external forces condition. However, channel sedimentation occurred in many fishing ports. Therefore, to understand channel sedimentation, in the autumn, wave, current, bed level change measurements were conducted at 4 observation points around Kuroiwa fishing port. From the results, We propose that not only wind waves height and period but also grouping waves (or long period waves) are important for channel sedimentation at fishing port. The point worth noting here is that during the grouping waves (or long period waves) developing, sand sedimentation had continued.

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 In general, when forecasting the shoaling of a navigation pass, only the nearshore current is considered as the external force of the drift sand. In the deep water zone, since the route is outside the surf zone, there is only a weak nearshore current and it is necessary to consider the wind-driven current. However, a prediction method considering the deep-sea wind-driven current has not been established. Observation data of current, calculated values of nearshore current and wind-driven current were compared. From this result, the mechanism of coastol currents in deepwater was understood. Next, we developed a method to predict the topography change in consideration of temporal changes of the nearshore current and the wind-driven current, respectively, when the wave height is high, to improve the reproducibility of the topography change. In addition, the external force used for prediction created seven models from the pattern of low pressure. From this, we propose a method which can almost predict the topography change.

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 Numerical simulations were carried out in order to analyze sediment transport and bottom topography change due to tsunami with large-scale eddy. This study, in particular, discussed the influence of shoreline condition and sand diameter on flow pattern, sediment transport and bottom topography change. The numerical results revealed that shoreline condition has a strong influence on large-scale eddy and sediment transport. Sensitivity analysis result also indicated that bottom topography change is sensitive to Manning's roughness coefficient in sediment transport simulation.

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 The purpose of this study is to examine applicability of numerical model of tunami sediment transport to quantitative assessment of resilience of coastal dikes with embankment at the back, which is one of the resilient structures of coastal dikes. For the purpose, simulation was carried out reproduction simulation to reproduce results of hydraulic model experiments, which were used to determine actual structure of coastal dikes. In addition , simulation was carried out actual-scale simulation of L2 tsunami caused by the Nankai Megathrust Earthquakes.
 In the reproduction simulation, the numerical model sufficiently reproduced a process of back slope erosion, proving that the model can be applied for quantitative assessments of the process. In the actual-scale simulation, the result showed that the height of embankment stays higher than the original dike even after tunami overflow, proving that the structure has sufficient resilinece effect. However, there are further challenges such as, improvement of reproduction of sand accretion behind the embankment, resolving uncertainty in parameter settings and verification of applicability of the numerical method to actual-scale processes.

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 This paper investigated the hydrodynamics around the river mouth and the deforemation processes of sand spit when overtoppong waves were observed due to typhoon based on images of the Tenryu river mouth in Japan recorded by a field camera with time interval of 1.2 seconds. Topography survey data and hydrodynamic data were also employed. It was found that short period waves frequently overtopped the sand spit where the elevation was low and the wave setup increased the frequency. On the other hand infra-gravity waves were the dominant factor of occurrence of overflow at high elevation area of the sand spit. This overflow lead to remarkable cross shore morphology change at wide area of the sand spit.

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 Recently, due to the development of 3D photogrammetry and UAVs, the UAV photogrammetry has been widely applied to various fields of study including coastal engineering field. The UAV photogrammetry has some important advantages for beach monitoring to enable us to frequently and easily observe morphology of beaches and also nearshore wave propagation. In this study, morphological changes on the beach around the Nanakita River mouth were observed with one week frequency of UAV flights. A conventional method of shoreline analysis was firstly applied to see the short-term recovery of shoreline positions after a big typhoon event in 2016. And also the effect of a tsunami event in November 2016 on beach morphological changes around the river mouth was discussed through the shoreline change analysis and 3D shape analysis. More than ten meters of shoreline change often occurred during this period. The surface of the right sand spit was eroded by the tsunami and the jetty had an effect of interrupting sediment movement.

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 Sediment transport mechanisms in swash, inner-surf and outer-surf zones have been investigated. The authors conducted field surveys in 2014 and 2015 during storm conditions in order to analyze the cross-shore and vertical sediment movements by using fluorescent sand tracers. However, there is a space to investigate sediment movements in the area from the swash zone to the outer-surf zone during calm wave conditions. In this study, the field experiments were conducted in the season of relatively mild wave condition. Five colored fluorescent sand tracers were installed on the seabed in the five different cross-shore locations, and sand cores were collected after surtain duration. Also, wave height, current velocity and wind speed were observed during the experiments. From the results we found that the onshore ward direction of the sediment transport was dominant in the surf zone. Although the sediment also transported offshore ward, the sediment was found until at the offshore end of the trough region. Even during the mild wave conditions, the longshore current velocity was relatively large in the area around trough and outer-bar crest. The sediment movement in the onshore region and offshore region of the outer-bar moved without the correlation, however, the outer-bar formed by both regions of sediments.

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 In this study, the characterisitcs of topographic change at Shichiri-mihama Ida coast, located in the southern part of Mie prefecture, was discussed by means of discriminant analysis based on shoreline change characteristics analyzed by network camera and wave data, and SfM-MVS analysis using UAV. As a result, the shoreline extraction using Sobel Gradient method enabled efficient shoreline extraction. By discriminant analysis evaulated in realtion to wave data, the usefulness of estimating adavance, retrogression and neutral events of shoreline behind artificial reefs at Ida beach was confirmed. In addition, SfM-MVS analyasis showed the effectiveness of artificial reefs installed in Ida beach to reduce erosion behind artificial reefs. Howerver, under long period wave condition, it was confirmed that the function of artificial reefs to decline erosion was decreased. Therefore, the consideration of coastal erosion against long period waves such as swells in contermeasures is implied.

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 Variation of shoreline position at the southern end of 17 km-long Kashima Coast, with Kashima Port at the north end and Hasaki Fishery Port at the southern end, has been observed with a X-band radar for 6 years. The radar captures hourly distribution of shoreline position approximately over 4 km. At the southern end, there is a 1 km long breakwater of the fishery port, which shelters southern incident waves. Further, the sandy beach is protected by headlands and a jetty from erosion. Shoreline positions of approximately every 2 days have been digitized from the radar images. Mean shoreline positions and shoreline inclinations of 4 sections bordered with headlands and jetty have been analyzed. Mean shoreline positions of all sections migrated seawards continuously during the observation period. At the farthest section from the fishery port, shoreline inclination showed a seasonal variation accordant with the wave incidence direction: sand between headlands is transported to the downwave resulting periodic changes in shoreline inclination. On the other hand, shoreline inclination close to the fishery port varied in a different manner due to sheltering effect of breakwater.

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 Niida River is well know to supply highly contaminated suspended ¹³⁷Cs originated from the Fukushima Nuclear Power Plant to the ocean. We examine the oceanic dispersal and inventories of the sediments and suspended ¹³⁷Cs in the ocean floor derived from Niida River, using the quadraple nested JCOPE2-ROMS 3D circulation model in a very high resolution configuration, coupled with a 3D multi-class sediment transport model, the iRIC-Nays 2DH river sediment model, the SWAN spectral wave model, and a static ¹³⁷Cs absorption model. We focus on the storm and flood event associated with Typhoon 201326 (Wipha) passed off the Fukushima Coast, which provoked an enomous amount of riverine fluxes, to quantitatively assess the accumulation and erosion of the sediments and resultant suspended ¹³⁷Cs inventories around the river mouth and nearshore areas.

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 Upon the results of a movable-bed experiment of a model scale of 1/50 on the function of an L-shape groin combined with a detached breakwater of pile structure, the contour-line-change model considering the effect of the change in grain size was applied. Three calculations were carried out while changing the shape of the L-shape groin. In all cases, experimental results were reproduced well by the numerical simulation with a sufficient accuracy. Finally, it was concluded that the contour-line-change model was applicable to the numerical simulation of the beach changes around the L-shape groin combined with the detached breakwater of pile structure on a coast where unidirectional longshore sand transport prevails.

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 At the tip of Ikujibana sand spit of the Shimoni-ikawa coast, four curved groins with pile structure have been constructed since 2005. On this coast, southward longshore sand transport prevails, and offshore sand transport also occurs because of steep seabed slope. After the construction of groins, a large amount of sand was deposited offshore of these groins. In this study, the Narrow Multi-Beam (NMB) data collected around Ikujibana between 1999 and 2014 were analyzed to investigate the sand deposition around groins.

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 When a setback-type floodway is constructed, a large pond may be formed between the berm and the mouth of floodway, causing a large impact to the surrounding beach. An excavation test to produce a pond in front of the floodway mouth was carried out immediately west of Numakawa-daini floodway on the Fuji coast, and the discharge of 0.17-0.2 m³/s was given by the suction of pumps. The change in water level of the pond, filtration, and the change in ground water level were measured. Under the condition of the discharge given in the experiment, the stream from the artificial channel rapidly infiltrated into the sand layer, resulting in rapid reduction in the surface flow velocity.

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 At the Numakawa-daini floodway located on the Fuji coast, sand originated from eastward longshore sand transport has been deposited into the outlet of the floodway, resulting in complete closure of the floodway. In this study, sand deposition inside the floodway owing to storm waves was investigated by field observation, and then a movable-bed experiment on the process of the deposition and the change in deposition given maintenance discharge was carried out. As a result, the deposition into the floodway was in a stable condition when the deposition reached the top of the floodway. Also, it was confirmed that the maintenance discharge was effective to decrease the amount of deposition of sand.

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 At the tip of Mihono-matsubara sand spit in Shizuoka Prefecture, the recycle use of sand, in which sand excavated from the shoreline is transported upcoast as the material of beach nourishment, has been carried out. However, since sand discharge into deep sea has still been occurring at present in this area, a method to reduce sand discharge into a deep sea is required. In this study, as one of such studies, the topographic changes around the Mihono-matsubara sand spit were investigated on the basis of the bathymetric survey data. Then, monitoring survey after the foreshore excavation for recycle use of sand was carried out.

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 On the Fuji coast, where Numakawa floodway of set-back type is newly planned to be constructed, the backshore has been eroding. In the planning of the location of the outlet of the floodway and the structural design of the floodway of the set-back type floodway, the effect due to such erosion must be considered. In this study, beach changes associated with extraordinary high storm waves in an area between Numazu port and Showa floodway including new Numakawa floodway were investigated. It was found that beach erosion was mainly triggered by offshore sand transport by storm waves.

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 Sand has been deposited on the west side of Chigasaki fishing port, and it is believed that part of such sand was transported offshore. On the Yanagishima coast west of fishing port, part of beach nourishment sand is also assumed to be transported offshore. In this study, an analysis using NMB survey data was carried out. It was found from the numerical simulation of nearshore currents that part of eastward long-shore sand transport was carried offshore, and from the analysis of grain size composition that none of the nourishment sand composed of coarse material was transported offshore.

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 The east part of the Shimoni-ikawa coast has been eroded due to the decrease in westward longshore sand transport, implying the occurrence of shelf erosion offshore of the coast. In this study, topographic changes on the offshore seabed were analyzed using the bathymetric survey data, selecting a coast with 6 km length between No. 160 where a submarine canyon develops near the shoreline and Miyazaki fishing port as a study coast. It was found that the shelf has been eroded. Furthermore, the contour-line-change model was applied to this coast. The observed topographic changes were well reproduced.

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 Southward longshore sand transport prevails south of the Kurobe River mouth on the Shimoni-ikawa coast. In recent years, the amount of longshore sand transport has decreased in this area because of the decrease in sand supply from the river. To maintain the beaches, sand supplied from the Kurobe River must be smoothly transported downcoast. Most important gateway is located at the Kurobe River mouth and Aramata area immediately south of the river mouth. In this study, the Narrow Multi-Beam (NMB) data collected since 1997 were analyzed to investigate bathymetric changes around the Kurobe River mouth and Aramata area, including offshore sand discharge via steep slope.

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 Owing to the previous studies on bathymetric features around the submarine canyons using the NMB survey data, it was found that three vertical submarine canyons develop near the head at a depth of around 100 m offshore of Seisho PA next to the Morito River mouth. Traces were left on the seabed on a steep slope at the east and west ends of the submarine canyon offshore of the Morito River mouth, from which sand discharges into the deep ocean. The formation of such topographic changes and offshore discharge of sand into a deep ocean have not yet been clarified. In this study, the BG model was used to predict such topographic changes. The possibility of offshore discharge of sand into the deep sea via a submarine canyon was shown by the numerical simulation.

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 Opak river mouth, located in Yogyakarta, Indonesia, has dynamic morphological features with active migration of the river-mouth opening. Several studies have been done around the location. However, processes of the river-mouth opening migration have not been fully understood. This research is aimed at elucidating the processes of the river-mouth migration. A series of aerial images of the study area were firstly analyzed to clarify the general tendency of short-term and long-term migration of the river mouth. A number of simulations were then conducted using an online-coupled model of Delft3D Flow and Deflt3D Wave (SWAN). The short-term behaviors of the migration was partially reproduced by the model, although the long-term migration was not well captured. The model results suggest that asymmetric features of tidal currents through the opening over ebb-flood and neap-spring cycles play a key role in the morphological evolution.

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 Poda and Po Da Nok Islands are located offshore of Krabi facing the Andaman Sea in the south part of Thailand. A shallow sea extends together with the development of a slender sand bar between these islands. Furthermore, there is another small island named Tup Island connected by sandy beach. Sand bars can well develop in this area because of the shallow sea. The wave-sheltering effect of these islands affects to another island. On August 2016, field observation was carried out to study the condition of sand bars, and numerical simulation using the BG model was carried out to investigate the interaction of three islands.

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 A three-dimensional parametric model was developed for the systematic migration of multiple sandbars on the Chirihama and Takamatsu Coast, Ishikawa, Japan. First, the principal modes of bar migration were extracted by an EOF analysis for the annual surveys over 11 years, and were approximated by a combimnation of simple functions for each survey line. Next, the alongshore variation of parameters in phase and amplitude variations were modeled by regression analysis. A three-dimensional parametric model was then established by synthesis of the approximate functions governing the cross-shore and alongshore variations. The comparison with field measurement demonstrated that the model is able to reproduce the main characteristics of the three-dimensional configuration and the spatio-temporal transition of the multiple sandbar systems. An ergodic feature is observed between the temporal and alongshore variation in mulitiple bar configuration.

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 The shoreline evolution of a multiple sand bar beach exposed to high-energy waves in Sea of Japan is investigated using the method of Empirical Orthogonal Functions (EOF). Seasonal to decadal variations in shoreline position are analysed by the EOF to find representative patterns of shoreline variability at Chirihama beach using a dataset of 15.5 km long coastline measured twice a year over 23 years. The first two modes explain 65% of the variation in the shoreline change, and mainly represent long-term trend and seasonal difference between summer and winter. Periodic shoreline recession and advance in about five years were identified by the EOF and spectrum analysis. The characteristic pattern of the spatial and temporal variations in shoreline change suggested middle-term shoreline evolution corresponding to offshore sand bar migration.

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 Recently the second channel of Lake Saroma was obstructed by coastal sediment, it is an accident that had never be seen before meteorological and oceanographic changes. In this study, we research coastal topographic variations around Lake Saroma with meteorological and oceanographic changes. Coastal topographic variations are simulated with 1-line model considered wave energy in wave direction, and sediment discharge from river is estimated by one-dimensional riverbed deformation model. As a result of the examination, the prediction accuracy of the shoreline change around the Lake Saroma improved, and it became possible to estimate the topographical change around Lake Saroma with meteorological and oceanographic changes.

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 Hai Hau Coast, Nam Dinh Province, northern Vietnam is an approximately 30 km long sandy beach, which is suffering long-term erosion in the last hundred years. The amount of erosion exceeds 1, 000 m, and several villages in the hinterland disappeared during this recession. On the other hand, at the river estuaries, north and south of the main part of Hai Hau Coast, satellite images capture formations of newly deposited areas, which are indicating that the rivers are still putting a huge amount of sand to the coast. This study tires to understand the formation process of Hai Hau Coast, and why it turned to erosive circumstance of nowadays, from literature survey, dating of sampled shells from the hinterland, and by a numerical computation of shoreline changes with one-line model. From literature survey, the area was so-called river dominated delta, and was continuously accumulating by the sediment input of old Red River. A large flood diverted the old Red River to the north and south, the present river estuaries, and the coast turned to so-called wave dominated delta, and the long-term erosion has started after this event. From the results of carbon dating of the shells, speed and amount of accumulation before the flood event were estimated. After the diversion, one-line model was applied to discuss the shoreline changes, which well reproduced the on-going erosion of Hai Hau Coast. The numerical result suggests that reclamation of the deposited sediments at the estuaries is one of the possible reasons of long-term erosion, which prevents feeding sand from the river to the coast.

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 Notsukezaki is the longest sand spit in Japan, located in the east region of Hokkaido, and the waves and morphology vary along the spit. In Notsukezaki, many groins has been developed for protection from beach erosion, and it is planned to develop groins in the future. The main purpose of this study is analyzing the bathymetric change characteristics around the groins by the survey results. We conclude that the dominant factors of the up-drift bathymetry of groins is the depth on tip and the height of the groins, and also, the dominant factor of the down-drift erosion of groins is the distance from the next to down-drift groin.

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 The controlling effect of longshore sand transport was investigated by the numerical simulation using the BG model, when various types of groins were installed on a coast composed of two grain size populations. It was found that groins of low-crown height and submerged-type groin are ineffective to control longshore sand transport, because coarse sand (gravel) is apt to be selectively deposited near the shoreline, and thus sand will be easily transported away over the crown of the groins. Furthermore, groin with an opening at the landward end was less effective to control longshore sand transport. This condition corresponds to the case in which the shoreline retreats on an erosive coast, resulting in the formation of an opening at landward end of the groin.

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 Laboratory experiments were conducted to investigate the effectiveness of foreshore nourishment with a mixture of sand and gravel. Deformation of a nourished bank on the foreshore was measured by using moderate and mild waves. Sands with three different sizes were used to form the nourishment bank. The effectiveness of the nourishment was discussed on the basis of measurements of bank erosion volume, shoreline change, subaerial beach width and submarine beach volume. The most significant erosion resistant performance was found for a mixture of three sands in equal proportion.

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 The performance of sand bypassing system introduced at Fukude-Asaba Coast in 2015 was evaluated by nearshore topography monitoring by using ARGUS cameras and UAV. Significant deposition was found in the subaerial area on the west of the outlet of the sand bypassing system, which appeared to be correlated with the variation in the incident wave angle. Beach recovery on the east of the outlet was analyzed by Empirical Orthogonal Function, which revealed the submarine deposition close to the shore in the area up to 1.5 km east of the outlet. Numerical simulation suggested that 40% of the bypassed sand was transported to the west of the outlet. Relocation of the outlet 1 km to the east was considered to be effective to increase the eastward transport.

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 The authors have studied the topographic changes and the changes in the vegetation zone on a marginal coast of a tidal flat, taking Banzu tidal flat left around the Obitsu River mouth in Tokyo Bay as an example. In this study, the exposure of a layer composed of cohesive material near the shoreline associated with erosion of the sand bar and the change in the seaward boundary of the vegetation zone on the marginal coast of tidal flat were investigated by field observations, and then a model for predicting the changes in seaward boundary of the vegetation zone was developed.

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 The 2011 Tohoku Earthquake Tsunami caused serious and devastating morphology changes along Southern Sendai Bay Coast in Miyagi Prefecture, Japan. There are some places in which there still exists tsunami affected topography change even after more than six years since the 2011 Tsunami. Although there have been several investigations dealing with topographical recovery in this region, no study has been made covering whole of the littoral system on Southern Sendai Bay Coast. This study investigates whole of the region of Southern Sendai Bay Coast with the length of 50km to find overall behavior of sand coast recovery. Serious erosion has been observed off Idoura Lagoon and in front of the Abukuma river mouth in order to supply sediment to the adjacent tsunami-induced erosion area.

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 Researches on sediment transport and the depositional process are important for understanding of the whole picture of nearshore disaster caused by the 2011 Tohoku-oki tsunami. In this paper, we analyze data from high-resolution seismic surverys, vibracoring, and bathymetric data assimilation, to describe processes of erosion and sedimentation by the tsunami on the shallow seafloor off the southern part of the Sendai plain where serious nearshore erosion occurred during the tsunami.
 Two well-defined and continuous reflectors (R1 and R2) were identified in the seismic profiles. Based on the geometry and distribution of the reflectors, charateristics of sediment cores, and change in bathymetric profiles, tsunami-generated sediment transport is considered as follows. The transport process was mainly controlled by backwash of the tsunami. The offshore-directed transport of beach sediments (medium to coarse sands) has generated the formation of the R1 erosion surface in water depths deeper than 8 m, followed by the generation of R2 caused by the erosion, transport, and sedimentation of coarse beach sediments (coarse sand to granule) in water depths shallower than ~10m. Both reflectors are not likely to deformed by wave-generated sediment reworking in water depths deeper than 9 m.

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 Tomamae fishing port is hindered the use of port areas and boat moorings behind the western outskirts by the overtopping waves, especially in winter season. However, in this port, comprehensive viewpoints including the formation of overtopping waves and environmental conditions which generate wave overtopping have not been revealed yet. In this study, in order to understand the wave overtopping in the western outskirts, field observation using a web camera was conducted, and various analyzes were made on the relationship between the overtopping wave phenomenon captured by the web camera and environmental conditions, including wave, wind and tidal level. Furthermore, conducting numerical simulation with CADMAS-SURF, on-site characteristics on wave overtopping were revealed.

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 In order to take countermeasures against salt damage of pier superstructure economically and efficiently, it is indispensable to clarify the wave conditions of splash generation at the vertical wall, and to grasp the characteristics of the splash. Using a series of images capturing splash generation process by a high speed camera, characteristices of splash such as the number of droplet, diameter and splashing velocity of each splashing speed, and so on are measured by the PIV and PTV technique and the relationship between splash and wave characteristics was investigated.

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 A novel numerical method is developed for simulation of fluid flow interactions with saturated porous media. The method is based on an enhanced version of Incompressible SPH (Smoothed Particle Hydrodynamics) method that solves Navier-Stokes and continuity equations and the effect of porous media is simply represented by considering linear and nonlinear resistance force terms similar to the studies by Ren et al. (2014) or Gui et al. (2015). However, one major difference is that in contrast to previous studies, in the developed method there is no numerical smoothing interface zone, thanks to the implemented enhanced schemes. The numerical method is validated through a set of benchmark tests, namely, flow in a U-tube with porous media (Peng et al., 2017), solitary wave attenuation over a porous bed (Gui et al., 2015) and solitary wave interaction with a submerged porous structure (Wu and Hsiao, 2013).

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 In this study, in order to clarify the transport process of splashes caused by wave-overtopping, model experiments were conducted using a two dimensional wind-wave flume. In the model experiments, splashes were visualized by the backlight technique, and taken by a high-speed camera. The splashes, e.g. the size, the number of splashes, etc., were measured by applying an image analysis technique to the videos. First, the appropriate conditions for visualization and the image analysis were examined and the validity of measurement results was confirmed. Next, the spatial change of the particle size distribution of splash was investigated for several specific individual waves in an irregular wave train. The transport characteristics of splash were clarified from the spatial changes of particle size distributions. The wave run-up height strongly affects the particle size distribution. In contrast, the wave overtopping quantity has little effect on the particle size distribution.

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 The upper flared shape seawall has a original curved shape at the front and reduces the amount of overtopping by returning waves to the offshore area. It can be applied to measures against storm surges in various places. In this study, in applying the upper flared shape seawall to the coast of Hokkaido. We did wave-overtopping experiments under conditions of strong wind and high wave, and compared with other conventional methods. As a result, the amount of wave overtopping of the upper flared shape seawall decreased compared with other methods. Even under wind conditions, the amount of overwinding was reduced by the trapezium loading wave dissipating works at the base front. Also, the upright wall on the top surface further reduced the amount of wave overtopping.

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 Traffic hindrances were often caused by wave overtopping under storm wave conditions on a coastal road of Route 231 at Hamamasu District of Ishikari City. In order to keep the safety passage of vehicles on the site, the necessary height of the wave splash barrier was designed based on the field data of wave overtopping. Hydraulic model tests with irregular waves of 1/40 scale were also carried out to obtain the wave force distribution acting the wave splash barrier. After the construction of the wave splash barriers, extreme storm waves, equivalent to the design wave condition, attacked the site on October, 2015. Because no damage was identified on the wave splash barriers, the applicability of the design procedures was confirmed for the prototype conditions.

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 In this study, a numerical model for calculation of fluid motion induced by an object penetrating the gas-liquid interface by combining the Immersed Boundary Method and the Level Set Method was presented. A new method of satisfying the boundary condition at the Lagrange points near the gas-liquid interface with high accuracy is described. After validating of tracing method of the gas-liquid interface by calculated result on sloshing in rectangular tank, it is presented that calculated result of the Strouhal number and distribution of time-mean velocity in wake of a circular cylinder agrees to experimental result with reasonable accuracy. Finally, calculated results of vortex pattern induced around a horizontally-oscillating vertical circular cylinder in stationary fluid under the condition of the Keulegan-Carpenter number = 9 and the Reynolds number = 1,000 is presented.

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 Local scour behind coastal embankments due to overflow has been known as a major cause of their failures under the 2011 tsunami. On the other hand, it was pointed that the scour holes caused energy dissipation to reduce the tsunami velocity behind. In this paper, the local scour behind the embakment model was measured in movable-bed experiments, and the measured shapes of the scour was related to the flow energy behind. Two different types of flow were observed around the landward toe of the embankment model, and induced different processes of the scour. Compared with the case without scour in a previous fixed-bed experiment, the flow energy behind the embankment was reduced by about 40% at maximum by the scour. Transition of the flow type didn't induce the change of the energy reduction rate. And the reduction rate depends on the normalized scour depth.

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 Simulation results of microscopic flow through porous media used Immersed Boundary method have been validated by comparison with previous experimental studies about the macroscopic pressure drop during passing porous media, the drag force acting on sphere body and so on. The constant rate of pressure drop in case of regular arrangement of porous media members shows suitability of conventional macroscopic method. However, the heterogeneity of pores caused by absence of a member of porous media would induce the difficulty of application of the conventional model. We discussed about the evidences of its difficulty by showing the pressure drop distribution inside porous media, the drag coefficient acting on each porous members, and the distribution of sectional average of intrinsic velocity in porous media.

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 Clarifying the effects of wave-dissipating block shape on the flow around the block is one of the effective ways to consider the shape characteristics of block in the performance-based design. In this study, hydraulic model experiments of flow around a block with three different shapes, installed in an open channel, was conducted for examining the shape effects of the block such as round shape, square shape and hollow shape, by measuring surrounding flow characteristics by the particle image velocimetry (PIV). The flow characteristics aound each block have been clarified by the dimensionless turbulence strength and the spacial distribution of the Reynolds stress. It has turned out that in regard to the ability to induce the turbulence, the square shape is higher than the round one, and hollow shape is higher than the square one. Furthermore, it was indicated that the wave height transfer rate of the different types of block can be estimated by considering the coefficients of shape characteristics and block breakwater porosity.

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 In the 2011 Tohoku tsunami, coastal urban areas were widely damaged by its huge hydrodynamic forces. However we have not fully revealed the huge tsunami hydrodynamic force acting on the structures. This is due to insufficient understanding on the relationships tsunami surge heights and shape of structure. When a huge tsunami strikes a uprigth structure, the tip of the tsunami runs vertically up the front face of the structure; herein, this phenomenon is called the tsunami jet flow. In response to the above background, this study aimes to improve the reproducibility of the tsunami water level fluctuation, by introduce dynamic contact angle to VOF model. It is found that the present model has certain accuracy on the reproducibility of the tsunami water level fluctuation.

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 Estimation formulas have been presented to evaluate tsunami wave pressure acting on vertical walls, in many cases, with comprising an inundation depth as a parameter. In actual design, the inundation depth is generally obtained from a tsunami simulation. While, the existing formulas do not consider the effect of the land-condition, e.g. slopes and obstacles. Focusing on the fact, in this study, hydraulic experiments are performed to examine the applicability of the existing formulas. In our results, the cases with supercritical flow showed a clearly sudden change of the inundation depth, which can distinguish incident waves from measured waves for an appropriate application to the estimation formulas. While, in the cases with subcritical flow, the inundation depth rose gradually and applying it to the estimation formulas leads an overestimation. We newly recommend to apply an inundation depth by a standing wave in front of the target wall for evaluation of the tsunami pressure, which corresponds to 1~1.2 times the hydrostatic pressure.

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