Up to now, utilization of the coastal waste landfill site remains at low level. In the advanced use of these sites by large structures, it is necessary to drive some foundation piles through the barrier clay layer. But in the actual field, there is concern that waste will be pulled into the clay layer or leaked to outside by piling. So in this research, we conducted a series of experiments examining the effect of pull-in prevention on pile tip shape and coat the absorbent polymer to pile surface by model experiment and X-Ray CT scanning. According to the experiments results, it was found that the pulled-in waste can be reduced by sharpening the tip of the pile. Also, on a pile that has an outer edge at the tip like a pile that has reinforcement band, it was found that the pulled-in waste can be reduced by coating the swelling material on pile surface.

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 To evaluate the applicability of various stability estimation methods to submarine slopes during earthquakes, centrifugal model tests at 90 G with 45 m and 75 m water depth were conducted. Industrial clays with similar strength characteristics were used to prepare slope models instead of natural submarine clay. On a tilting table, pseudo static forces were applied to the slope and the seismic coefficient at the onset of failure was investigated. The shape of slip surface was also determined.
 The slip surface was found to be similar to the toe circle failure and was shallower than the critical slip surface estimated by slope stability analysis. Other differences include a slightly larger seismic coefficient at the onset of failure, and deeper water. A slice analysis was conducted on the slope with the obtained slip surface using strength parameters obtained in the direct shear tests. The results indicate that the modified Fellenius method is capable of simulating the test results well.

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 The aim of this study is to reveal a useful method to increase lateral resistance of existing coupled pile. The authors conducted three kinds of lateral loading tests of coupled pile; centrifuge model test, large-scale model test and X-ray CT scanning model test. This paper describes a method to stabilize ground surrounding coupled pile using cement treating technique. The paper also describes experimental results of the model tests to evaluate effects of several conditions in terms of geometry, depth and strength of cement-treated soil on the lateral resistance of coupled pile. The paper introduces the most promising method to stabilize the ground intermediating between the two piles of coupled pile with its mechanism of increasing the lateral resistance based on the experimental results.

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 Dredged clay stabilized by cement has been widely utilized as a geomaterial. Intensive research has been conducted to understand its strength behavior. However, the influence of sand content on the mechanical behavior of cement-treated dredged clay has given less emphasis. The sand content of dredged clay is varied depending on the source. This study examined the correlation of various sand and cement content to the liquid limit and the strength behavior of dredged clay at a different curing period. It was found that to know the liquid limit after mixing with cement is useful to evaluate the liquidity or flow characteristics of cement treated clay. The liquid limit of cement-treated clay increased gradually up to 10% cement content and decreased at increasing cement content. The cement-water ratio can be used as a parameter to estimate the strength of cement-treated clay composed with different sand content. Even though various amount of sand was added to cement-treated clay, the strength seems to be not correlated with the sand content which is not more than 70 %.

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 Marine dredged clays treated with agents lime have been used as reclamation and filling materials. Dredged clays contain the various organic matters to affect the physicochemical properties. This study aims to evaluate the effects of humic acid on the strength development and microstructure of cement-treated marine clay. It was found that the strength development was governed by the cement and humic contents. In addition, a specific cement content, at which the strength reduction due to humic acid are overcome, existed for a given humic acid content.

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 In order to investigate the applicability of a simple underwater repair method to a place where damages such as cracks and lack of corners in concrete structures underwater occurred, concrete specimens were installed in the submerged areas, and examined the filling of the grout to cracks and lack of corners.
 For repair of cracks in the underwater, we adopted a simple construction method by installing a rubber sheet and injection of plastic grout, and the injection situation was evaluated by core samples. It was confirmed that the repair of the lack of corners were filled by pouring the high flowing and anti-washout underwater grout into the damaged portion.
 This paper shows that it can be used for repairing cracks in underwater parts of concrete structures and repair for lack of corners by test of real size specimens and actual ocean condition.

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 Fiber-Reinforced Mixture of Dredged soil and Steelmaking slag (FRMDS) has been developed as, for example, an impervious material used to fill waste reclamation sites in Japanese coastal areas. Recent studies have revealed that the mixed fiber resulted in higher deformability of FRMDS.
 The principal goal of this study is to reveal deformation characteristics of FRMDS and possible factors to influence them. The authors conducted the unconfined compression tests (UCT) of FRMDS to evaluate effects of mixing ratio between fiber and steelmaking slag on the deformation characteristics. The results of stress-strain behavior and visual observation during UCT indicates a failure mode of FRMDS can be categorized into four different types depending on the mixing ratio and curing period; I. Brittle Failure Type, II. Stable Failure Type, III. Ductile Failure Type and IV. Strain Hardening Type. In other words, the deformation characteristics of FRMDS are expected to be predicted by properly controlling the mixing ratio and curing period. The paper describes a schematic diagram of the failure mode partitioned based on the mixing ratio.

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 The establishment of a disposal site costs a great deal of money. Therefore, it is necessary to dispose of more dredged soil in existing and new disposal sites. The objective of this research is to increase the amount of disposed soil available for disposal by lowering the water content ratio at the time of input by "pretreatment before input". In order to evaluate the effect of drying on the volume reduction, a drying shrinkage test was carried out. Drying characteristics of dredged soil was confirmed by the change of typical soil constants. And, the drying speed remarkably improved by heating. As a conclusion, this study showed that the volume of dredged soil decreases linearly in a wide range of water content.

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 In a design, soils are separated the sand and the clay, and it is evaluated by different methods. However, there is actually soil called intermediate soil, in the present situation that is struggling in its handling. On the existing ground, since soil particles with different particle sizes and properties are mixed in the soil, it is problem the act of treating a matter separately mixture sand, sand and clay. Therefore, it is desirable to conduct a unified evaluation of mixed soils mixed with various types of soil as mentioned above. In this study, in a design, focusing on the rigidity which is one of the important elements, mixing natural clay and silica sand in various proportions, making the specimen has granular structure by sand by a method of compacting with a predetermined energy, doing bender element test, and attempt evaluate shear modulus and fines of sand-soil mixture.

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 This study investigates the performance of geotechnical filter on mitigation of internal erosion of earth structure in costal facilities. Gravels with various particle size distribution were examined as the candidate material for geotechnical filter. In addition to the filtering (clogging) effect with the reclaimed sand, the stability of the geotechnical filter against the riprap was evaluated by a series of shaking table test. Furthermore, the modelling test revealed that the geotechnical filter mitigates the damage of geotextile due to both aircraft load and seismic motions.

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 In the new runway and water passage under construction at Naha Airport, the water passage is composed of box culverts. To clarify the propagation of wave pressure inside the box culverts, a large-scale hydraulic experiment and a numerical simulation were conduc6ted. The results of the study clarified, the following matters. Wave pressure propagates rapidly inside the water passage, and propagates not only inside the box culverts but also inside the mound and backfill-stones area surrounding the box culverts. Wave pressure inside the backfill-stones area can cause migration of backfill soil through breaks in the geotextile sheet used to stabilize backfill.

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 After the Tohoku Pacific Ocean Earthquake in 2011, GRS (Geosynthetic-Reinforced Soil) coastal dykes are proposed to be strong dykes against overflow of tsunami. The authors have studied the resistibility of GRS coastal dykes against overflow through hydraulic experiments with several types of GRS coastal dykes. The authors showed that shape of GRS coastal dykes and inner structure of them affect the resistibility of overflow. But the mechanism of improving resistibility of GRS coastal dykes are still not realized. In this research, the authors conducted a series of hydraulic experiments on the resistibility of geogrid covering the surface of GRS coastal dykes against erosion. The results of experiments showed that laying geogrids on the surface of the ground was remarkably effective in decreasing erosion of geo-materials. In addition, it was proved that geo-material erosion with geogrid cover was related to the grain size of adjacent geo-materials.

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 In seismic performance evaluation of pile supported wharves, the evaluation which calculated bending moment reaches full plastic moment or not is mostly performed with bilinear elasto-plastic model of M-φ characteristics (the full plastic moment is applied as the maximum bending moment). Since local buckling occurs in steel pipe piles with a large diameter-to-thickness ratio, which are used frequently by economical design, strength declines without reaching full plastic moment. There is a concern that has become a dangerous design. On the other hand, strength of steel pipe piles with a small diameter-to-thickness ratio continues to increase modestly even after yielding, and they have toughness against deformation. These effects cannot be evaluated in the M-φ characteristics. Therefore, we have tried to formulate strength and deformation characteristics of steel pipe pile by using three dimensional FEM analysis using shell elements.

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 To achieve economical seismic improvement of wharf structure economically, utilization of the existing structure is an effective method. In this research, we focused on a structure composed of a new pile, an existing pile, and strut members, which connected the new and existing piles. A new pile was built horizontally in the center of the existing pile to support the superstructure. The existing pile was cut off at its head and connected to the new pile; therefore, the existing pile was only utilized for support of the horizontal forces on the new pile. We investigated the basic deformation characteristics and their effects through both a model experiment and a numerical analysis. The shaking table test shows this wharf structure have comparable seismic resistance as the standard wharf model, which was designed to proof level-two earthquake ground motion. The existing pile transferred forcing to the new pile through the strut members, which reduced the maximum bending moment of new piles. Through dynamic finite element analysis, we confirmed that the experimental results can be reproduced. We then analyzed the sensitivity of the strut members' specifications. By appropriately selecting the rigidity, we showed that reinforcement was obtained through balanced distribution of force on an existing structure.

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 The pier-type structures used in ports are frequently constructed using steel-pipe piles with a large diameter-to-thickness ratio (D/t) of 100 to suppress construction costs. The results of previous research, however, revealed that the values of these piles obtained for the full plastic moment using the cross-section calculation in design exceed the actual value. Therefore authors had performed experiments and numerical analyses using steel-pipe piles with large D/t in order to propose new modeling of the relationship between the bending moment and curvature reflecting the effect of D/t on deformation performance.
 In this research, we evaluated the influence of the proposed modeling for steel-pipe pies with large D/t based on analytical results of seismic response analyses of a pile-type structure subjected to the level 2 earthquake motion.

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 Deep embedded and large diameter steel pipe piles have been popularly used in the port facilities nowadays for supporting large vertical load, because of growing size of port facility or changing structural types. Estimation of bearing capacity of large diameter and deep embedded piles are complex problems such as bearing capacity is increased because of deep embedment and bearing capacity is decreased because of decrement of plugging effect by using large diameter piles. In this report, focusing on pile plugging phenomena, pile plugging mechanism was investigated under the sandy ground with different relative density. Open ended model pile penetration experiments were conducted and plugging ratios and incremental filling ratios of each experiment was compared and the effect of relative density of the ground to these parameters. Finally, product of coefficient of lateral earth pressure and friction coefficient inside of the pile was estimated. Then inner friction force distribution was estimated. As a result, inner friction around the toe of the pile is large and it rapidly decreases along with upward of the pile under different relative densities.

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 It is important to properly predict deterioration process of structures to reasonably make a maintenance plan and management of pier structures. In this research, we consider the effectiveness of the proposed stochastic degradation prediction considering based on actual structural inspection data. Uncertainties to be considered are chloride ion concentration on concrete surface, apparent diffusion coefficient, corrosion occurrence limit of steel material, construction error. In particular, a deterioration prediction model considering as a probability field with respect to chloride ion concentration and apparent diffusion coefficient, which are considered to have spatial correlation is proposed. Finally, the contributions of uncertainty on deterioration prediction are discussed.

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 It is necessary to conduct two-dimensional nonlinear earthquake response analysis many times in order to evaluate the seismic reliability of a pile supported wharf. This study aims at proposing a simple estimation method of the seismic reliability of a pile-supported wharf considering the variation of input seismic motion. The simple estimation method uses three results of two-dimensional nonlinear earthquake response analysis in order to evaluate the mean value and standard deviation of the residual displacement and the maximum bending moment of the wharf. It was shown that the method well evaluates the probability distribution of the residual displacement and the maximum bending moment of the wharf with enough accuracy.

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 Steel pipe piled piers are exposed to severe corroding salty environment and they should be more appropriately maintained. However, few researches have been conducted on the residual structural and seismic performance of corroded piers. The objective of this study is to clarify the effect of corroded steel bar at the RC superstructure and the junction area between superstructure and the steel pipe on the structural performance of the entire pile-supported structure. This study has been developed through the laboratory loading tests and numerical analyses. From the experiment and analysis, it is confirmed that corrosion on the superstructure has impact on the residual structural performance. However, corrosion on the reinforcement bar in haunch has minor impact on the whole behavior.

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 This study aims at proposing a simple evaluation method of seismic performance of pile pier supported wharf considering the effect of the ground deformation. The proposed method is based on a frame analysis referring the pile deformation evaluated by the two-dimensional earthquake response analysis. Estimated bending moment generated in piles by the proposed method was compared with that by the two-dimensional finite element earthquake response analysis and the applicability of the proposed method was discussed.

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 Partial factors for verification of piled pier stress concerning ships' approach were introduced in the 2007 technical standards for port facility. The partial factors are constant regardless of the design water depth. However, since the statistical properties of the ships' speed depends on the ships size, the failure probability of the piled pier stress is influenced by the design water depth.
 The purpose of this paper is to propose suitable partial factors reflecting the statistical properties based on actual measured ship's berthing speed, for verification of piled pier stress. We also proposed an analytical method for reliability analysis on the mode applying with modeling of the fender, response surface method, and MCS.

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 Reformation projects for existing protective and mooring facilities in harbors have recently shown rapid increase to meet new requirements due to changes in social and economic situations. Accordingly, it is required to setup a design framework that is not the same as those for a new construction, but there are no guidelines available how to execute facility reformation design.
 In this paper, we collected 262 facility reformation projects nationwide in Japan and performed case analyses focusing on motivation and methods of reformation. As a result, we showed the current situations of existing port facility reformation that was urgently responded to the requests corresponding to the change in social situations. Also, we clarified typical problems during reformation design such as changes in verification methods from the originals and difficulty in structural performance evaluation of an existing structure. In addition, we showed the basic of the reformation design and the prospects to solve the problems for the reformation design of existing port facility.

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 The inspection and diagnosis of the lower part of the pier is the concerning problem due to the poor working environment and labor shortage. In order to address this problem, we have developed the inspection and diagnosis by using radio control boat. The camera attached with radio control boat captures image and these images are studied by various images processing method for the inspection and diagnosis. In addition, we have developed a method that automatically determines the degree of degradation from the captured images. These results are compared with the expert judgment this has been applied to the construction since 45 years. In this paper, the usefulness of the inspection efficiency and the degradation judgment from the proposed development method has been discussed.

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 In the case of reinforced concrete (RC) superstructure of piled pier, the appropriate timing of remedial measures is decided based on the prediction result of the time when the chloride ions concentration at the cover depth reaches 2.0 kg/m³ for corrosion onset of steel bar. However, the threshold conditions for corrosion onset should be determined considering with several factors, such as environmental conditions, materials and mix-proportions, from the corrosion theory viewpoint.
 In this research, the influences of coexisting ions in seawater on current density of steel bar, chloride ions penetration and pH of pore solution were experimentally investigated as the first step of developing highly accurate prediction method for chloride induced deterioration. As a result, the following findings were obtained. The current density of steel bar was quite small under high pH like sound concrete structures, even if the chloride ions concentration at the steel bar surface reached 3 % same as seawater. However, the current density became high under low pH value and existing of ions in seawater, even if the chloride ions concentration at the steel bar surface was very small. Moreover, the both diffusion and advection of chloride ion was suppressed.

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 Under marine environment, corrosion rates of steel materials depend on oxygen supply rate to the steel surface. Therefore, it is said that corrosion rates are mitigated if the steel surface is covered by rock-fill or seabed soil. However, the relationship between the corrosion rate and the environmental condition in front of the steel structure is still unclear and corrosion rates of steel materials which covered by rock-fill or seabed soil are not evaluated correctly. In this study, dissolved oxygen diffusion coefficient of solution or materials which exist in front of the steel material was measured by the electrochemical method to evaluate the oxygen supply rate to the steel surface. Then, the relationship between corrosion characteristics and oxygen supply rates was investigated. As the result, it was fond that the particle size and void ratio of the material which covers the steel surface control the amount of dissolved oxygen diffusion coefficient. A high correlation was found between corrosion rates and dissolved oxygen diffusion coefficient.

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 Generation of caves under pavements in the coastal area often causes serious accidents, however, those caves are not visible in general. Therefore, it is very important to establish an efficient method for the detection of caves under pavements. This paper aims at discussing the detection method of caves by use of microtremor. Microtremor observation was conducted at Sakaisenboku port where caves were generated. From the single point observation record of microtremor, both horizontal component and vertical component of microtremor were analyzed and it was found to be difficult to detect the caves by the single point observation record of microtremor. Next, array observation record of microtremor was analyzed using the spatial autocorrelation method. Phase velocity at the points with cave was found to be larger than that at the points without cave. As the results, maximum array radius for the detection of caves under pavements were found to be 3.6 meter in this study.

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 The reinforced earth method has been used in many land construction works, based on its high seismic performance. On the other hand, it has not been applied to the construction of port facilities. Our group studies how to apply this method to sheet-pile quay wall, and it can become a cost-effective quay wall, compared with the conventional one. In this study, a series of centrifuge model tests were conducted under a centrifugal acceleration of 50g by changing length, height, and number of reinforcing geogrids connected with sheet piles. Displacements of sheet pile and ground, tension forces of geogrid, and bending moments of sheet pile during seismic motions were discussed in the paper. The results showed high performance of this method, and the specification of a sheet pile can be reduced because of its low bending moment.

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 The fishery of Wakayama prefecture is the core industry and many fishery ports are put in place around the Kii peninsula. In this study, we extract the present states and problems by questionnaire survey for the fishermen's union and examine the characteristics of the anticipated tsunami damage such as inundation depth, temporal limitation time for evacuation of fisher-boats against tsunami by using the announced simulation results. As a result, the consciousness of regional differences on Nankai Trough Great Earthquake and tsunami, stagnation of cooperation between other organizations and oblivion of past disaster information were confirmed. Moreover, the importance of pre-making rule on evacuation of fisher-boats against tsunami was pointed out.

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 This study examined actual drifting ships caused by the 2011 off the Pacific Coast of Tohoku Earthquake Tsunami in Otsuchi and Kirikiri fishing port coasts in Iwate prefecture, Japan. Moreover, this study calculated reproduction simulations using actual drifting ships, and investigated the disaster risk of drifting ships by tsunami in this area. The analysis of actual drifting ships showed that the distances from the coastline to the final position of drifting ships have a correlation with whole length of ships. We proposed the verification method using these correlations, this method indicated applicably to actual field in reproduction simulations. In the risk analysis using numerical simulations, we showed that whole inundation area is exposed to the risks by drifting ships, the area behind road embankments is at lower risk.

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 Field coastal forests surveys were conducted in Miyagi Prefecture, which was inundated by the mega tsunami associated with the 2011 earthquake off the Pacific coast of Tohoku. In the field, standing and fallen trees were judged; and the tsunami depths, tree-trunk diameters, and tree heights were measured. Based on the relation between the tsunami inundation depth and the tree-trunk diameter, the tilting limit condition was determined. It was critical in determining whether the trees remained standing or fell. The tilting limit condition agrees well with the result that was obtained by a survey conducted on 184 forest trees by the Miyagi Prefecture Forestry Promotion Association. The effect of the growth of the ground soil property (sand- and gravel-based soils) of trees on the tilting limit condition was discussed. When the data for standing and fallen trees obtained from the relation between the tsunami inundation depth and tree diameter were plotted, the survey data was found to be one of the reasons for the scatter. It was also confirmed that the characteristics of the growing soil of trees had a considerable effect on the tilting limit of trees.

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 For tsunami mitigation, suitable arrangement of multiple tsunami measure structures is very important. The objective of this study is to estimate effect of a combined position of coastal forest and embankment on tsunami flow pattern and fluid force acting on tree by the hydraulic model experiment.
 When the coastal forest is in the lower stream side of the coastal embankment, the fluid force acting on trees becomes large, and the coastal forest is expected as resistance to tsunami. However, when a coastal forest and an embankment are near, there is a risk of trees breakage in the front face of a forest.

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 In this study, the simplified motion calculation method of the impact velocity is proposed for tsunami debris. Additionally, the hydrodynamic characteristic of tsunami debris and the surrounding flow characteristic are investigated by CFD for the calculation method. From these results, estimation models of them are proposed. The calculation result of the proposed motion calculation method showed that the impact velocity become smaller than the flow velocity of tsunami. Furthermore, the result showed that the influence of hydrodynamic coefficient and surrounding flow characteristic, on the impact velocity.

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 In the previous coastal surveys, coastal change has been analyzed by looking at “shoreline” changes in general. In this survey, coastal change between 1970s and 2000s were analyzed comprehensively by comparing “area” of land cover (sandy/muddy beach, sandy vegetation, coastal forest, coastal facilities and others (housing, agricultural field, etc)) behind the sandy/muddy beach shoreline which lays 7,600km in Japan's coast. As the result of the survey, it was revealed that the cover area of sandy beaches and sandy vegetation has decreased and the one of coastal facilities and others has increased by 2000s. Also, it was understood that the morphological changes of beaches occur mutually with shoreline change as well as land cover changes behind shoreline by quantitative analysis. Those results are clearly shown in the land cover maps created for 6,500 beach areas which were divided by similar sand drift systems.

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 On the tidal flat offshore of Kanda City facing the Suo-nada Sea, an isolated sand bar develops. This sand bar forms a sand body on the tidal flat under waves, and it deforms while maintaining a semicircular shape. On October 17, 2014, the north end of this isolated sand bar approached the land, and a flood/ebb tidal delta was formed owing to the flood/ebb tidal current at the opening between the tip of the sand bar and the land. Then, due to the second field observation on September 17, 2016, severe beach erosion occurred immediately before the attachment of the tip of the sand bar to the land, and finally the mergence of the sand bar to the land occurred, causing large-scale beach changes.

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 On the lakeshore south of the Nagase River mouth in Lake Inawashiro, typical lakeshore changes due to high-wave-angle instability can be observed, because the shoreline runs approximately in parallel to the incident wave direction. In this study, the shoreline evolution due to the instability was investigated using satellite images and field observation. As a result of the study, three sand spits were found to develop on the shoreline of the sand body, and the mean velocity of the eastward movement of sand spits were 66 m/yr. This velocity was in good agreement with the velocity of 68 m/yr calculated from the satellite images taken between 2010 and 2015.

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 On the Moriya coast located in south part of Boso Peninsula, a small river flows into the sea, and the mouth of this river is stably fixed at a location behind the rocks located at the central part of this pocket beach. Because the wave-sheltering effect of the rocks were seemed to be the cause that the river mouth was fixed behind the rocks, field investigations were carried out at the river mouth to measure the topographies of the beach and river mouth, and the wave-sheltering effect was calculated by using the angular spreading method. The primary cause of the formation of a river mouth behind the rocks is found to be due to the decrease in the wave diffraction coefficient behind the rocks.

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 In recent years, severe coastal erosion in river mouth delta has been observed worldwide. To discuss such development of river mouth delta and shoreline retreat, an analytical solution of a one-line model, which is based on linearlized diffusion equation, may be used. By superimposing the solutions, it is possible to study various conditions and useful for understanding the essential phenomenon. However, the existing analytical solution for development of river mouth delta is restricted for rivers pour into an infinite length of the sandy beach. For this reason, it is impossible to take into consideration the influence of the edge of the beach such as capes and coastal structures. In this research, therefore, a theoretical study on a river mouth delta, which develops in a finite length sandy beach, has been investigated. It is found that the influence of the boundary does not appear when the dimensionless time t^* is less than 0.3, and the existing solution can be applied. When the dimensionless time is sufficiently large, it shows a simple delta development process in which the parabolic shaped shoreline moves in parallel. At this time, the longshore sediment transport rate decreases linearly from the river mouth to the boundary. This theory was verified using laboratory experimental data from Refaat (1990).

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 On Nha Trang Coast in South Central Vietnam, the retreat of shoreline has become obvious in recent years. However, investigations discussing the coastal erosion mechanism in this area are insufficient. Therefore, a video camera system was installed in this area and started monitoring the shoreline change continuously from May 2013. Based on the camera's image data of over 3 years until August 2016, this study investigated the characteristics of beach deformation on the Nha Trang Coast. According to the video monitoring, the shoreline retreats in winter when the northeast monsoon waves are prevailing, and the beach is recovered in the summer due to calm waves from east or southeast. Then EOF (Empirical Orthogonal Function) analysis was utilized to decompress the dominant processes of shoreline variation along Nha Trang Coast, and found that the first component, which accounts for 93.8% of contribution rate, corresponds to seasonal shoreline change. Moreover, in order to confirm the periodical characteristics of shoreline change, this study approximated spatial and temporal eigenfunctions by using simple linear regression and Fourier series expansion, respectively. It was also found that the seasonal shoreline variation was observed within 350 m of the northern end of this coast.

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 Fongafale Island in Tuvalu country, of which land was formed by the accumulation of coral gravels and sand with low elevation of 3 to 4 m from seawater level, was subject to serious coastal disaster risk, such as wave overtopping, coastal erosion, etc. The pilot Project of gravel beach nourishment was undertaken in Tuvalu to examine the applicability and effectiveness as coastal protection measures taking into account the enhancement of beach use. The continuous monitoring has been carried out to examine the change in beach profile and its stability against wave action by comparing to the full-scale reclamation project which was carried out at nearby coast. The results show the high stability of beach profile and less outflow for filling gravels and sand.

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 Beach has been eroded at the Cai River mouth flowing north of Nha Trang, resulting in disappearance of all sandy beaches on both sides of the river mouth. The satellite images taken between 2002 and 2015 and the storm event occurred in 2008 were analyzed together with the field observation in 2015 and 2016. Most important cause of the beach erosion was due to sand excavation from the sand bar on the right bank to obtain material for land reclamation on the left bank. Another factor of the erosion was the movement of sand in the upstream direction along the left bank. A measure for the restoration of sandy beach using training jetties was also shown on the basis of the example at the Dam Nai Bay entrance.

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 Sandy beach at Hiroura in Lake Hinuma has been eroded owing to wind waves and ground subsidence by 20 cm during the 2011 Great Earthquake. As a measure against beach erosion, beach nourishment using 2000 m³ of riverbed material from the Kuji River was carried out in January 2013. Field observations were carried out on January 12, 2012 before the nourishment and September 30, 2014 after the nourishment to investigate the effect of the beach nourishment. In August 2016, four typhoon hit the area, causing the rapid rise in water level of the lake together with storm waves, resulting in severe beach erosion. In this study, the damage after 2016 typhoons was investigated on the basis of the field data. It was found that the lakeshore was severely eroded due to increased water level and high waves caused by strong wind.

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 Sea level rise and wave characteristics change under climate change have been reported. In generally, the beach profile change on climate change is simulated using Bruun rule considering only sea level rise. However the wave characteristics change was predicted. And the impact assessment of wave characteristics change has been carried out by several researchers. In this study, the shoreline change under climate change considering sea level rise and wave characteristics change were investigated at Tottori Sand Dune Coast. It is found that change of shoreline retreat is proportional to sea level rise, and the shoreline change with wave characteristics change is smaller than the shoreline change with sea level rise.

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 Impact of high tide and high waves due to typhoon No. 10, 2016 was discussed through field surveys under and after the typhoon event. From visual observation and debris carried in the event, maximum run-up height on Sendai Coast was estimated to be about T.P. 4 m. Severe erosion of embankment toe along the coast line near Sendai Port was observed. Due to overtopping of high waves over sand dune, some amount of sediment was transported into Gamo Lagoon.
 20 ~ 30 m retreat of shoreline was observed through shoreline analysis based on aerial photographs taken before and after the typhoon. In one or two months after the event, shoreline positions almost reached to the positions before the typhoon mainly due to the contribution of the cross-shore sediment transport. However, the recovery was relatively slow in the area around Gamo Lagoon and Idoura Lagoon where the wave overtopping over the sand dunes were observed during the field survey. In addition to a river mouth and detached breakwaters, some structures revealed to coast line due to the erosion by the 2011 tsunami have effect to block the longshore sediment transport to induce faster recovery of the shore-line on the up-drift side of the longshore sediment transport.

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 In 2012, a groin with a low crown height was constructed together with beach nourishment at the Harai River mouth on the Kutsuo coast. After the construction of a groin, longshore sand transport toward the mouth was blocked by the groin, resulting in severe beach erosion at the river mouth bar on the left bank of the river, which had been extending for a long time. At Kutsuo fishing port on the right bank of the river, the deposition of sand which was originary transported offshore by the river currents and then transported by waves continued, resulting in the deposition of the navigation channel. The beach changes around the Harai River mouth was investigated using satellite images and field observation was carried out. Finally, the results were compared with the results of the movable-bed experiment.

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 At Mihono-matsubara on the Shimizu coast, a plan was determined to build L-shape groins in place of the ordinary wave dissipating breakwaters using concrete armor units as a measure against beach erosion with the improvement of the coastal scenery. This L-shape groin employs the detached breakwater with pile structures as the head part of the breakwater. Before the construction, it was required that the controlling effect of longshore sand transport is clarified. To this purpose, beach changes around the L-shape groins to be constructed on the Shimizu coast were predicted using the contour-line-change model including the effect of sand back pass from the north end of the Shimizu coast.

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 The causes of beach erosion on Shichiri-ga-hama Beach were investigated by the comparison of aerial photographs and the analysis of shoreline change. Narrow Multi-Beam survey was carried out to investigate offshore seabed topography in detail. As a result, the main factor of beach erosion was assumed to be due to the imbalance between eastward longshore sand transport turning around Point Inamuragasaki and the sand supply from the Yukiai River. The beach material excavated from the backshore was temporally placed near the shoreline during the construction period of Route 134 on this beach, and this substantially effected as beach nourishment, implying the effectiveness of beach nourishment.

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 A movable-bed experiment with a scale model of 1/50 was carried out to investigate the function of an L-shape groin. As a measure to reduce the construction cost of an L-shape groin, the reduction in the number of the concrete blocks to protect the upcoast side of the groin and the removal of part of the breakwater connecting the tip of the groin to offshore breakwater were investigated. Finally, it was concluded that the reduction of part of the breakwater was possible, and the landward end of the groin was not exposed to waves, even when extraordinarily high waves are incident to the coast, suggesting no need to protect the landward end of the groin.

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 The gently sloping revetment is stable when the toe of the revetment is buried beneath the sandy beach. However, when the toe of the revetment is exposed to waves as a result of beach erosion, fill material under the revetment is drawn out through the gap between the toe and sandy beach, resulting in the damage of the entire gently sloping revetment. Furthermore, when the toe of the revetment is exposed to waves, the revetment tends to be slippery because of the attachment of marine organisms, causing the increase in danger of the falling. In this study, the recovery method of sandy beach in front of the gently sloping revetment using gravel nourishment is discussed as a measure to improve the waterfront function, taking Kemigawa Beach in Tokyo Bay as an example. Numerical simulations were carried out using the BG model.

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 The grain size distribution from aerial photos taken using an unmanned aerial vehicle (UAV) at the Shichiri-mihama coast, Mie Prefecture, Japan was estimated using an automatic object detection software tool for granulometric analysis for fluvial gravel beds, BASEGRAIN, and its accuracy was examined from comparison with sieve analysis. Furthermore, the spatio-temporal distribution of the medium grain size estimated from orthomosaic images generated using a structure-from-motion (SfM) technique was examined and discussed. Results indicated the characteristics of the spatio-temporal distribution of the medium grain size at the Shichiri-mihama coast. This suggested that BASEGRAIN can be applied to gravel beaches to assess their grain size distribution.

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 The field experiments were conducted to investigate the characteristics of sediment movements during a short time duration. The focusing area is from the swash zone to the offshore side of the bar. At the Hasaki coast, Japan, five colored fluorescent sand tracers were installed on the seabed at different cross-shore locations, around every 50 m, from near the shoreline to the offshore side of the bar. During the experiments, seven times of seabed surface sediment samplings were conducted every 10 m of cross-shore distance from 1 hour to 144 hours after the installation of the fluorescent sand tracers. From the analysis, the sediments in the surf zone were spread in the area from near the shoreline to the onshore side of the bar within one hour after the installation. The fluctuation of the centroid of the fluorescent sand distribution was correlated with that of the wave breaking point. The sediment movements at the offshore side of the bar had a correlation with the value of the offshore wave energy flux.

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