Extensive beach erosion is observed around a large-scale structure constructed on the coast. However, the extent of impact of coastal topographic change seems to be larger than expected in research in the past. In this study, the influence of large-scale structure on coastal erosion was investigated through experiments and numerical simulation of shoreline change. Significant extension of coastal erosion area around a large-scale structure was observed in laboratory experiments when external currents or waves with alternately changing incident angles were introduced. The development of circulation currents and the arrest of sand in the sheltered zone were considered to be the essential mechanisms.

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This study deals with bathymetric changes around artificial reefs (AF) which have been constructed along Tottori sand dune coast. Three types of AF groups are investigated applying ARGUS method. In one AF group with a wide alongshore interval, sand bars which are a part of the local alongshore bar system appear between the intervals. In AF group with small intervals, offshore concave sand bars appear between AF intervals inside the AF line. Rip channel appears shore side of each bar and the channel changes the direction toward the center of each AF after it meets with the neighboring channel. A large alongshore sand bar appears from one of the AF interval outside the AF line. It may show that there is a sand movement from inside the AF line.

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Countermeasures against channel shoaling at the Tomamae fishery port on the west side of Hokkaido, have been deemed necessary. Therefore the sediment transport characteristics must be properly understood. In this study, field observations in terms of wave dimensions, flow, and such like , were conducted to find that the sediment behind the artificial reef and around the shoreline had been transported by the longshore current and rip current. Based on these characteristics, a calculation method was developed. It consisted of a two-dimensional analysis of the advective diffusion equation considering vertical distribution of the suspended sediment concentration. The calculation results were in good agreement with the measured flow velocities, flow directions and changes around the sea bottom.

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Two extremely large events of berm erosion were observed during the field experiments carried out at Hasaki by employing twenty some ultrasonic gages near the shoreline between Jul. 12 2002 - Jul. 21 2006 and Jul. 24 2008 - Oct. 29 2008. One was caused by a Typhoon waves and the other by a winter storm. Both erosions show complete disappearance of berm profile within a few hours when large waves with significant long period waves attacked well-developed berm profile during rising tides. However one of them shows erosion advancing onshore-ward creating beach cliff like profile while the other show almost instantaneous erosion of whole berm profile. Both erosions stopped when beach profiles become uniformly mild slope.

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In this study, the authors experimentally investigated the formation of cuspate topography and the effect of the initial topographic perturbation on the alongshore uniform barred beach with a 1/20 slope.The cuspate topographies appeared only in the cases which we generate the accretion-type waves.The perturbation added in the initial topography disappeared gradually and the positive-feedback mechanism was not observed in this study.This result indicates that the formation of cusp with positive feedback mechanism may need other certain wave condition.

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Rising of sea level together with the increase of wave height during a single extreme storm event might give storm waves more possibility to get over the beach crest and bring the sediment further inland direction especially at a low barrier island. Therefore, it is important to estimate the total amount of deposited sediment on a barrier island after storm and propose any suitable countermeasures to prevent the sand deposition into the bay or lagoon. From 8^th to 10^th of October 2009, an extreme typhoon number 18 attacked the Nanakita River mouth area and there was a lots of sediment deposited inland. This study is to analyze the deposited sediment and to evaluate the effectiveness of present overwash prevention construction in the Nanakita River mouth area by using the field observation data. The estimated sediment deposition shows well agreement with the result of empirical overwash formula.

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Relative importance of tidal motions and river discharges for the sediment transport was evaluated using field measurements and data analysis on an intertidal flat adjacent to the Shirakawa River mouth. Monthly-averaged sediment budgets during flood periods indicated the different pattern at the closest point to the river mouth. Sediment is transported to north during non-flood period while transported to south during flood period at this point. The basinscale tidal motions are found to be important for the sediment transport during non-flood period. The phase relationships between the peak river discharge and tide level during the flood are most important for the sediment transport on the intertidal flat adjacent to the river mouth in the fetch-limited closed bay.

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The aim of the paper was to understand the mechanisms of sediment transport due to water level changes under wave actions. Because in low-energy beach, the effects of tidal level fluctuations become increasingly important and could affect beach profile. Measurements of bed profiles, sediment grain size and wave conditions have been carried in the field and an experimental water flume. The size of berm increased under depositional waves on the flood, and the offshore bar moved further seaward on the eddy under erosive waves. With the rise and fall of the tide, the sediment sorting has been developed horizontally and vertically, therefore, the grain size and the porosity inside the bed would change.

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The shoreline position in alongshore direction around the Nanakita River mouth was measured from aerial photograph which have been taken every 2 months in 20 years. Empirical Orthogonal Function analysis was used to decompose the data into the dominant mode of shoreline variability for left and right side of river mouth. The results were also examined in relation with wave parameter and river discharge. The first mode shows the same shoreline movement between left and right side which reveals cross-shore process. The analysis of second mode and its correlation with river discharge reflects the influence of long-shore process. This mode also reveals the influence of river mouth in interrupting the long-shore sediment transport. The higher modes reflect the formation of beach cusps in relation with wave parameter.

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Field observations of grain size distribution of the foreshore and backshore material were carried out in Oiso area on the Seisho coast on July 30 and September 4, 2009 immediately after the storm waves due to Typhoon 0911 to investigate the sorted deposition of gravel and sand. The foreshore and backshore material was sampled along with the grain size analysis. After the storm waves with the significant wave height of 2.1 m medium and coarse sand was found to be re-deposited on the backshore over the berm composed of gravel.

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This study is concerned with the development of a 3D morphodynamic model for considering wave-current interaction. The wave action conservation equation for waves and the quasi-3 D nearshore current model with the surface roller model were employed. Firstly, in order to investigate the influence of the interaction into the morphodynamics, three model tests associated with a detached breakwater, submerged breakwater and sand bars with rip-channel were carried out. Secondly, the presented model was applied to the beach evolution after offshore nourishment, so called "shoreface nourishment", conducted at the Egmond coast in the Netherland. From the model tests and the comparison with the field measurement, the validity of the presented model was founded.

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The sediment routing process in natural beach-dune systems plays an important role for sustaining the topography of sandy beach. Recent practices of coastal protection, however, tend to suppress sediment transfer between a coastal dune and the fronting sandy beach, reducing resilience of the beach subject to severe wave forcing. This study explores linkage between the beach and dune processes. The resistivity explorations and surface-wave prospecting performed on the coastal dune identified the sedimentary architecture of it, in conjunction with examination of existing borehole logs. Notably, there occurs a buried deposit of old sandy dune below the current beach surface. Furthermore, the examination of ten vibrocores retrieved from the seabed suggests that the deposit of well consolidated old dune extends out to the sea.

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Basic features of coastal evolution on Chirihama Beach, Japan, have been investigated using a set of field surveys. The results on the shoreline survey show long-term eroding trend during the last twenty years. The cross-shore profile survey records show that the seabed slope has been decreasing more recently. The typical profile configurations are characterized by the presence of multiple bars. An EOF analysis has been conducted on the periodic movements of these bars. The net offshore migrations of bars have been repeated with a return period of approximately 4 years. It is also shown that the transition from double bar to triple bar configuration accompanies the temporal retreat of shoreline. The alongshore variability of the behavior of multiple bar system has also been examined.

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Sandy beach shows gradual topographic change with long-term and short-term variations corresponding to the conditions of waves and tides. Because of the irregularity in the profile change, it is difficult to investigate the characteristics of shoreline change in detail. In this research, long-term survey of the beach profiles has been carried out on three different coasts almost every week for more than ten years. The topographic data were analyzed and the characteristics of the long-term and seasonal beach profile change were discussed using the statistical methods and the empirical orthogonal eigenfunction method (EOF).

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Beach changes of the northern Shimizu coast were investigated on the basis of the bathymetric survey data collected since 2006 between the artificial headland No. 4 south of L-shaped groin and transect No. 1 crossing Shimizu Port breakwater. Maximum longshore sand transport of 6.2×10⁴m³/yr was measured at a location of X=1.5 km of the coast. Because of the steep slope, all these sand transports were found to be discharged offshore with the rate of 6.2×10⁴m³/yr between 1998 and 2002, 6.6×10⁴m³/yr between 2002 and 2006 and 4.2×10⁴m³/yr between 2006 and 2009. Offshore sand loss also occurred in an area between X=0 and 0.3 km behind the Shimizu Port breakwater.

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At the northern end of the Shimizu coast, a steep slope and submarine canyon develop and approximately 6×10⁴ m³/yr of sand has been discharged into the deep sea through the steep slope every year, resulting in the net loss of sand. To prevent sand from discharging into the offshore zone, the recycle use of sand at the north end of the coast was considered. The effect of sand excavation near the shoreline at the north end of the coast was investigated using the contour-line-change model. It was found that minimum volume of excavation was 2×10⁴ m³/yr for the erosion not to expand to the surrounding coast under the condition that longshore sand transport is 6×10⁴ m³/yr.

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Uda et al. (2009) proposed a model for predicting beach changes due to rapid offshore sand transport during the storm wave conditions, assuming that the equilibrium slope of sand is reduced. In this model, the equilibrium slope was assumed to decrease regardless of the grain size, even though the beach material has a wide grain size range between gravel and fine sand. The sampling test after the storm revealed that gravel was remained on the foreshore and only medium sand was transported offshore. Therefore, the change in equilibrium slope corresponding to each grain size was incorporated in the contour-line-change model. The predicted and measured results were in good agreement.

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This study investigates physical mechanisms of eastward extension of the sand spit at the Tenryu River mouth. Shoreline profiles of the sand spit, extracted from successive still images recorded by a field camera, were first compared with hydrodynamic characteristics such as waves, river flows and tides. Color sand and gravels were used as tracers to capture the characteristic movement of sediments on and around the sand spit. Tracers placed in the swash zone around the middle of the sand spit moved westward while the ones around the east end of the spit moved eastward. Clear difference between sand and gravels was also observed especially in their moving directions. Image and numerical analyses were finally carried out to investigate the hydrodynamic characteristics that caused such characteristic movements of sediments.

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On the Chigasaki coast, beach nourishment using coarse material has been carried out since 2004 to recover the sandy beach. To investigate the daily changes of the nourished beach, photographs have been taken from a fixed point. The 51 photographs taken at 1 s intervals were selected under the conditions that the tide level is within M.S.L.±0.1 m, the significant wave height is less than 0.5 m, and the photograph was taken between 8 and 12 am. The weighted average of these photographs was obtained to clearly determine the shoreline position. The imageries were produced from these photographs by the geometric transformation method. The change in shoreline position after the beach nourishment was monitored using the imageries

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An X-band radar was employed to observe morphological behaviors at the mouth of River Tenryu, Sizuoka, Japan, for 2.5 years from June 2007. Land area of the river channel showed a seasonal variation: it increases in the summer seasons and decreases in winter. The river mouth widens by floods and narrows at ordinary flow periods. Phase difference between water levels in the river and ocean decreases generally in summer and increases in winter. Also, a coefficient representing flow resistance in the estuary showed a similar seasonal variation. The sand bar at the river mouth migrated towards inland in 2009, and water depths of the sea bottom in front of the river mouth estimated by analyzing wave motions captured during storms became milder from 2007 to 2009, suggesting overall coastal slope decreased during the period.

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In October 2009 the category-5 typhoon T0918 hit the Japan Pacific Coast and significant topographic changes occurred along the Enshu-nada coast due to the storm waves. Significant wave height was more than 10m and rapid landward migration of the sand spit of the Tenryu river mouth was observed. Based on X-band radar image analysis spatial and temporal changes of overtopping waves and corresponding sediment flux across the sand spit were revealed. Spatial concentration of the sediment flux can be explained by the nonlinear relationship between wave height of overtopping waves and corresponding sediment fluxes. A sediment flux model was developed based on the relationship. Maximum flux was estimated by the model to be 51 m³/m/hour. It happened when high waves and high tide were observed simultaneously.

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The Kochi coast formed by the fluvial sediment supply from the Niyodo River has been eroding and the water depth immediately offshore of the shoreline has increased, resulting in increase in the damage potential against wave run-up. The beach changes of this coast were investigated using the bathymetric survey data along with the grain size analysis of the seabed material. On the basis of these field data, the mechanism of increase in water depth owing to the offshore sand movement associated with the storm waves and offshore sand mining were analyzed using the contour-linechange model.

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This study investigates long-term change of terrace morphology and longshore sediment transport around the Tenryu River mouth based on bathymetry data of past 50 years. Based on the sediment budget around the terrace and the assumption of little sediment supply from the river in recent years, CERC formula was calibrated to estimate the longshore sediment transport rates at both east and west boundaries of the focusing area. Obtained boundary conditions then yielded distribution of the longshore sediment transport around the terrace and estimations of sediment supply from the river. These results and additional numerical analysis clearly showed increasing impacts of the detached breakwaters and indicated that the terrace morphology in 1984 may be required for dynamic equilibrium of the sediment budget around the river mouth.

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Sediment movement dynamics were investigated on the basis of sediment analyses sampled on the watersheds and the downdrift coasts of the Mimigawa River, the Niyodo River and the Ohkohzu Channel, in which significant anthropogenic activities have been introduced in the last centuries. Sand and gravels were sampled on more than 150 locations along the rivers and coasts. Spatial and temporal changes in sediment movement were described from the sediment retention rates in reservoirs, roundness of gravels as well as the distributions of mineral and luminescence properties of sand particles.

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Bottom sounding and sediment sampling were carried out before and after 1975 and 2001 floods. Discharged sediment was estimated by riverbed change calculation. The grain distribution except the fine grain components equal to or less than 80μm almost coincided with the grain distribution of river terrace. Total deposition volumes calculated from the change topography of river-mouth were estimated by the coarse components more than 80μm of discharged sediment. The mean volume for 30 years of the coarse discharged sediment are 6.8*10⁵ m³/year. The volume of river terrace increases rapidly for big flood and decreases slowly for several years.

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Sediment transport processes in the Tenryu-Enshunada watershed were studied in terms of feldspar luminescence properties, i.e., thermoluminescence (TL) and optically stimulated luminescence (OSL). Spatial variation of sample TL/OSL intensities indicates various sediment origins along the river route, as well as the evolution and transport process in the whole fluvial system. A relationship between TL and OSL intensities was found for all samples. Indexes were proposed for identifying the riverine and coastal sands. Underground sedimentary constitution at river-mouth sand spit and estuary terrace was specified based on these criteria. After distinguishing the effect of partial bleaching on age dating for both riverine and coastal samples, depositional age at estuary terrace was estimated.

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A series of laboratory experiments were conducted on the performance of coarse sand nourishment on a fine sand beach. Beach profiles were measured for two cycles of high waves and moderate waves. The movement of coarse sand nourished on the shore was found to be classified in terms of the C parameter proposed by Sunamura and Horikawa (1974). Coarse sand nourishment was found to be effective, even in the case coarse sand was moved offshore, since coarse sand contributed to the decrease in offshore-ward sand transport rates thorough the stabilization of the sand bar at the breaker point.

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On the Jinkoji coast facing the Pacific Ocean, beach nourishment using 8.7×10⁴m³ of gravel with grain sizes ranging from 3 to 15 mm had been carried out by April 2008. After beach nourishment, a stable beach was formed between the artificial headlands. In response to the success in recovering a sandy beach, beach nourishment was also planned for the Komiyasaku coast south of the Jinkoji coast along with the Oritsu coast, which is a famous recreational beach. In this case, beach nourishment using gravel is considered to have been avoided for recreational use. Taking these conditions into account, beach nourishment using medium sand was planned. A stable beach topography produced by gravel nourishment was reproduced numerically using the BG model, while incorporating the effect of changing the grain size into the model, and the effectiveness of the model was confirmed. Then the model was applied to gravel nourishment along the Komiyasaku coast and to beach nourishment using medium sand at the Oritsu coast.

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The Shonan coast facing Sagami Bay has been eroding since the 1970s. Now that the steady procurement of nourishment sand has become difficult in Japan because of the limited sand resource, the effective use of sand presently deposited on a coast has become important. For this purpose, regional sediment management considering not only sand volume but also the sand grain size is important. In this study such sediment management for maintaining beaches was considered, taking the Shonan coast as an example, and applying the contour-line-change model considering the changes in grain size.

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Method controlling the diffusion of gravel in foreshore nourishment using short groins and small-scale detached breakwaters were investigated, taking into consideration the fact that the gravel movement concentrates on the foreshore. When beach material composed of mixed grain sizes is nourished on the foreshore, the discharge of the gravel component may be reduced when these structures are installed, while supplying fine sediment to downcoast. The mechanism was investigated using the contour-line-change model considering the change in grain size under the conditions beach nourishment is carried out on a dynamically equilibrium beach with a constant longshore sand transport.

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On the Hamamatsu-shinohara coast facing the Pacific Ocean, beach has been severely eroded, resulting in the shoreline recession of 210 m between 1962 and 2004. As a measure against beach erosion, beach nourishment using the mixture of sand and gravel was begun in 2005. Since then, 3.5×10⁵m³ of sediment was supplied to the coast. In this study, we proposed a model for predicting the movement of gravel by waves. The predicted and measured results were in good agreement.

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Laboratory experiments were performed on the stability and the erosion control performance of a submerged sand pack breakwater. Design criteria for the size and the shape of the sand pack were proposed in terms of B/do and F/W. Successive action of inertia force and drag force under atilt broken waves was found to be critical for the stability. Erosion control performance was verified by a series of beach profile measurements in which the shoreline retreat and the decrease of beach sand volume were both mitigated by a submerged sand pack structure introduced at the bar location. Characteristics of local scour around the structure was also investigated by a wave basin experiment.

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This study investigates process-based functions of sand-filled-geotextile bags as coastal stabilization works through laboratory experiments. An image-based technique was newly introduced to automatically extract bed profiles and this technique enabled us to acquire high-frequency and high-resolution data of bed profile changes, which provide instantaneous local cross-shore sediment transport rates. Sand-filled geotextile bags, installed inside surf-zone, showed essential functions not only to mitigate erosion but also to trap sediment without causing significant impacts on natural beach processes. Experimental analysis revealed that principal factors of observed shoreline stabilization are wave energy dissipation and asymmetric profiles of the time-varying suspended sediment concentrations around the sand bags.

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In this study, monitoring the nourished sand longshore movement was performed based on the feldspar luminescence measurements, including both Thermoluminescence (TL) and Optically Stimulated Luminescence (OSL). Nourished sand presents larger TL/OSL properties than the natural beach sand. Investigation on the spatiotemporal distribution of post-filling beach sand luminescence features provides the opportunity for assessment on the nourished sand movement characteristics, which was demonstrated from the present field studies along the Miyazaki coast and Shounan coast. Comparing these two techniques, it was found that the OSL technique is suitable for study on short-term sediment movement within a limited area; whereas, TL technique can be applied to the long-term and large-area nearshore process estimation.

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Groins are facilities to control the sand drift for maintenance and the recovery of the shoreline. In Japan, impermeable groins with the concrete block are general. However, groins of the timber piles remain in the Netherlands, and there is a possibility to adopt permeable groins as a construction method also in Japan according to the needed function of littoral drift control. Moreover, the permeability of the groins is a control element as well as the length of the groin in moderately easing influence of the longshore sediment transport control to the downstream. The model experiments were done in a tank aiming to clarify control function of the permeable groins on littoral drift.

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This paper proposes a new method of the environment monitoring on coastal sediment. To clarify the temporal-spatial variation of median grain size and effect on coastal vegetation, we applied the method for determining grain size from digital camera images of sediment proposed by Rubin to the sediment at the sandy beach in the Narugashima Island which is located at the mouth of Osaka bay, Japan. We also applied EOF (empirical function) analysis to the temporal-spatial data of median grain size which was obtained by above method and extracted the principal component which rules sediment dynamics. From the results of estimation of the amount of wind-blown sand, the sediment tends to move in north- south direction in summer season and in east-west direction in winter one, respectively.

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The invasive mussel dominates the vertical seawall structure which composes much of the coast. A large volume of oxygen is consumed after dropping the mussels themselves to the bottom during the summer period. In this research, it was suggested the inhabiting situation at inside of the mussels association. The inside association was composed by young shells. They are less 20 mm of body size. The obesity rate is lower and the mortality rate is higher than the outside. The cause of dropout was considered for constructing the multi layered mussels on the seawall. The inside of association becomes heavy condition for living. With the changes in temperature and salinity, some individuals at inside association decrease adhesive to the seawall, and drop out with the integrated living mussels.

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The morphology of sand cays developed in Miyako Island and Kumejima Island, Okinawa Prefecture, Japan, was investigated. The variation of submerged sand area, potential zone for sand cay formation, was found to be well correlated with a typhoon index, proposed to quantify the influence of typhoon on sand cay morphology. The analysis of sediments sampled around sand cays indicated the importance of the presence of beach rocks in the formation of the sand cay.

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The numerical analysis by LES was carried out for the current and topography change around the Shiogama(namely the deepest region) near Ushi Shima. The flow accelerates and diverges radially during the eastward current and converges during the westward current near the top of slope around Shiogama. The anticlockwise vortex is formed at the eastern zone of Ushi shima and this accords with the measured results. As the result, the bottom is accreted at the eastward zone of Ushi Shima.

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Bathymetric data in a wide coastal area were derived from frequent monitoring using fishfinder and GPS data logged during fishing operation in Enshu-nada Sea. The offshore bathymetric changes in near critical depth were evaluated by the annual changes of contour line positions along the cross-shore direction and these standard deviations. The analysis revealed long-term trend with short-term fluctuation in the sea bottom changes associate with the frequent monitoring data. We found that slow erosion appeared in the offshore area except around river mouth and inlet was indicated.

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A Boussinesq type numerical model was developed which can simulate both wave fields and current fields around permeable detached breakwaters. The validity of the model was verified through measurements of waves and nearshore currents in hydraulic experiments investigating reflection and transmission capability. The porosity of the structure was accounted by a friction term incorporating turbulent resistance. The combination of turbulent friction model and anisotropic diffusion type wave breaking model turns out to reproduce not only the wave fields around the detached breakwaters but also nearshore current fields behind the structures well.

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Recently, the Bouyancy-driven vertical piling breakwater, which is proposed as a barrier for tsunami in original, is expected to apply as a drastic measure for harbor tranquility. In this case it is very important to consider its permeability for wind waves because it has a narrow gap between individual piles. In this paper, a sponge layer model and a porous layer model, those are often applied to partial wave reflection boundaries, are used as a permeable boundary in a Boussinesq wave model, and harbor tranquility is evaluated in an actual harbor. The porous layer model can reproduce both transmission and reflection rate with a standard gap but not with more wide or narrow gap. A numerically installed such breakwater can increase harbor tranquility in a whole year, but it is not enough in more severe seasons because its transmissivity is not so small.

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Wave runup is an important factor for coastal levee design and flood defence activities along the coast. A calculation method of wave runup height often used for facility design is based on model experiments with relatively-steep slope (steeper than 1/30). We proposed new calculation equations of wave runup height for very gentle slope (milder than 1/30), and verified the equations and other methods by field observations in three coasts. The field verification results that our equation can precisely calculate wave runup height in a gentle-slope coast, and that calculation method of wave runup height should be selected based on sea bottom slope and wave steepness.

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Recently, coastal disasters due to swells induced by heavy storms increase at any harbors. The wave overtopping rate of long period swell banded narrow spectra is different from that of wind wave because of the characteristics on the wave grouping and the wave height distribution. In the study, the model experiments were conducted to measure the wave overtopping rate of the long period swell on seawall and to propose the countermeasure to be able to be efficiently decreased the wave overtopping rate. As a result, it is possible to estimate the wave overtopping rate of the long period swell by applying the existing design method and to reduce the wave overtopping rate of long period swell by placing the permeable dethatched breakwater formed in concrete blocks in front of the seawall.

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This study deals with modeling for profile change of rubble mound seawall based on the experimental results. The model profiles are given by composite sine curve corresponding to the degree of deformation of the structure. The model profiles agree well with the measured profiles. The model profiles are also used in the experiments and numerical model to evaluate the change of the wave dissipation performance. The reflection coefficient and overtopping rate are used as the indices of the performance. The measured reflection coefficient decreases but the overtopping rate increases with damage progression of the seawall. The computed reflection coefficient is almost constant and the overtopping rate shows opposite tendency from the experimental result.

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Experimental Study is conducted in horizontal 2-D wave basin to investigate the wave dissipation performance of Double Barrier Floating Breakwater (DBFB), which is restrained by vertical piles. The results are compared to that of fixed breakwater. The pressures on the front and lee sides of breakwater are examined in order to evaluate a drag coefficient, C_d and a hydrodynamic-mass coefficient, C_m of DBFB. The transmission coefficients are then estimated from these hydrodynamic coefficients under various conditions. The applicability of the formula proposed by Harms(1979) are also discussed.

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Generally, it is extremely difficult to determine the exact wave-overtopping rate by random waves because of the irregularity of waves. In this study, the influence of the number of waves acting a seawall on the wave-overtopping rate was investigated by conducting a large number of computations with a numerical simulation model "CADMAS-SURF" based on VOF method. The main conclusions obtained from the results of numerical experiments are: 1) it is necessary to measure about 500 overtoppings to obtain the convergent wave-overtopping rate in a wave train. 2) However, if the appearance frequency distribution of overtopping quantity by individual waves is sufficiently expressed with an exponential distribution, the reliable wave-overtopping rate can be obtained, even if the number of overtopping is about 50 or 60 times.

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At Waku fishing port in Yamaguchi pref., which has a vertical breakwater at the mouth of the port, dissipation blocks were installed in front of the breakwater to reduce the sea water spray caused at the breakwater. In this study, to clarify the effect of dissipation blocks on the reduction of the spray caused at the vertical breakwater, field observations were conducted at Waku fishing port in the winter seasons before and after the construction: the wave run-ups (heights and frequency), the wind (velocity and direction) and the salinity concentrations of the spray at 30 observation points were measured. The observed data showed that the dissipation blocks can effectively reduce the sea water spray caused at a vertical breakwater.

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An upright seawall with floating panels was proposed in this study in order to mitigate wave overtopping disasters induced by storm surge or high wave. Laboratory experiments were carried out using a two-dimensional wave flume for confirming the effectiveness of the floating panel as a countermeasure against wave overtopping and examining the dynamic behavior of the floating panel. As a result the floating panel was found to have a great reduction effect of wave overtopping under regular wave action as well as infragravity wave action by following the water surface elevation in front of the seawall. It was also confirmed that the phase lag between the behaviors of the floating panel and the water surface increases as wave period approaches the natural period of the vertical oscillation of the floating panel.

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On October 21, 2007, the vehicle accident to which the windshield was damaged by wave action occurred on a coastal road along the Japan Sea. In this study, the situation when the accident occurred was clarified by the hearing such as those who drove and the road administrator. Wave overtopping rate and vertical wave force acting on the vehicle were reproduced by two dimensional hydraulic model tests with irregular waves. The hydrodynamic pressure that acted on the windshield was formulated by using the speed of the vehicle. The hydrodynamic pressure is proportional to the second power of the speed of the vehicle, and the influence of the angle of the windshield became clear. The limitation of the speed of the vehicle is also proposed to evade the vehicle damage.

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