Solidified soil is made of dredged clayey soil mixed with cement. Generally, it is well known that the solidified soil is deteriorated in seawater by leaching of calcium. Therefore, the deterioration property of solidified soil has been investigated in this study. The test results revealed that (1) the deterioration amount of the test pieces with the constant ratio of water and cement and with the different water content became similar when the time exposed in seawater was same, and that (2) for the solidified soil with the unconfined compressive strength larger than approximately 10 MN/m², the deterioration will not cause.

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 We have devised the on-site reforming method to improve the seabed ground at the original position by the bucket attached to the ground improvement ship. In this method, it is possible to perform the process of excavating the seabed clay, mixing with the reforming material, and inputting the improved soil in situ, greatly simplifying the construction. In addition, since the inside of the bucket can be kept in a dry condition, it is possible to improve the strength quality of the improved soil and to suppress turbidity during construction. In order to clarify the feasibility of this method, we conducted laboratory experiments on 1/20 model.
 As a result, excavation of clay ground, mixing with reforming materials, and inputting the improved soil can be carried out, and feasibility of this method is considered to be high. On the other hand, in this experiment, the reforming material particle diameter of 1.18 mm or less was used, but in practical construction, the maximum particle diameter is about 40 mm. For this reason, evaluation of mixability in scale-up experiments using reformers of actual particle size is considered as a future task.

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 In order to construct a controlled waste disposal site on sandy seabed, bottom sealing by laying artificial sealing geomaterial made of marine clay has been developed. The method to give some necessary shear strength to the sealing material by adding “a small amount of cement” was studied. The conventional cement-treated soil was cracked due to the shear deformation and the hydraulic conductivity was increased. On the other hand, the hydraulic conductivity of clay with addition of a small amount of cement did not change even when subjected to shear deformation more than 20%. However, it should be careful that, with addition of small amount of cement, the hydraulic conductivity became lager than that of clay with no cement, because the void ratio became larger to the same consolidation pressure due to the bonding structure.

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 The lack of disposal facility of dredged clayey soils is making a problem in most of seaports. The self-weight consolidation analysis was carried out with a parameter of initial water content of disposed clay. It was shown that the selection of dredging method and transportation method of dredged soil makes a significant difference on the substantial volume of disposed soil and the lifetime of the facility. A rational approach to design the disposal facility is presented, where by combining the selection of dredging and transportation method and the pre- and post-disposal treatments of dredged clay the optimum method is determined based on self-weight consolidation analysis.

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 In order to use the premises of the off shore waste disposal site highly, it is necessary to construct piles into the bearing layer. In such a case, piles penetrate through impermeable layer. At that time, the pile is thought to bring the waste below the impermeable layer. In this study, for the waste of small particle size, the influence of the difference in rigidity between waste layer and underlying impermeable layer on waste dragging was investigated. For the waste of large grain size, the difference of bringing in due to the difference in eccentricity was investigated. As a result of experiments, it was confirmed that in the case of small particle size waste, the rigidity of the impermeable layer relatively decreases, so that the amount of waste brought increases, in the case of large grain waste, the penetration depth was found to be different according to the difference of eccentricity.

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 We have measured a time series of current velocity off Cape Shiono-misaki from April 20, 2016 to April 20, 2017 with a moored ADCP in order to investigate the characteristics of variation of the Kuroshio current in relation to ocean current power generator. The Kuroshio has taken a non-large-meander path for the measurement period. It is clarified from the measurement results that the currents at a depth of about 50m are characterized by the properties that the averaged velocity for one year is 100cm/s and the current direction is almost constant in the direction between the east and east-southeast.

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 The properties of the sea levels at Kushimoto and Uragami were examined using the data of current velocity measured at the station off Cape Shiono-misaki for one year. The high correlation with the current velocity concluded that the sea-level difference between Kushimoto and Uragami is a good index to monitor the Kuroshio velocity south of the cape. By analyzing the data of the sea-level difference, it was shown that the absolute velocity of the Kuroshio averaged for 10 years is 96.0 cm/s. Moreover, it was suggested that the Kuroshio velocity has an interannual variation at a period of 2.2 years and a seasonal variation with the maximum in August and the minimum in February.

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 In this research, we observed the tidal current using AD2CP targeting the Ohshima Ohashi bridge fourth bridge piers over Obatake Seto strait. Based on the observation results, the tidal current distribution and the turbulence distribution near the bridge piers were analyzed in detail. In consideration of the influence of the tidal current and turbulent flow near the bridge piers on the power generation device, the optimum installation position of the power generation device was selected.As a result, the feasibility of tidal current power generation at the point was evaluated.

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 In Japan, the power grid is regionally divide by utility companies, then the wind power potential is not effectively developed. The purpose of this research is to establish the stand-alone power generation system by means of offshore wind power generation in ports and coastal area. It is necessary to know the variance characteristics of demand of electric power in port facilities. This paper shows investigated the electric power usage in two ports those are located at the west coast of Hokkaido and the northern part of Kyushu. The time variance characteristics of electric power consumption in a port are estimated depends on wharf operation data such as cargo handling and so on. The difference of demand in the port facilities and supply by wind energy generation by use of offshore wind turbines is analyzed. The countermeasure to reduce the gap of demand and supply with the storage battery system is also discussed. And its reduction effect of carbon dioxide is analyzed.

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 This study proposes the WRF-observation hybrid method as a method to estimate wind-turbine hub-height wind speed from surface wind speed over the sea surface, and discusses the validity and problems of the method in comparison with a vertical one-dimensional method using the MOST-EKMAN model. The validation was conducted using in-situ measurements at the pier of the Hazaki Oceanographical Research Station in Kamisu, Ibaraki Prefecture. For winds from the sea sector, the WRF-observation hybrid method can estimate wind speed with a bias of 3.83 %, RMSE of 15.05 % and correlation coefficient of 0.95, which indicate higher accuracies than the MOST-EKMAN method and raw output of WRF. It is also found that the WRF-observation hybrid method tends to overestimate wind speed, and the main cause is that WRF exhibits too large vertical shears for winds from the land sector. In particular, this tends to occur in stable atmospheric conditions on the Hazaki pier.

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 For this paper, hydraulic model experiments and numerical computations were conducted to perform a basic verification of the technology related to new conceptual floating structure supporting high rise building. It was confirmed that the mooring system could withstand winds and waves with a 200-year return period in Tokyo Bay. However, it was also found that resonance might occur at around 3.0 Hz between the building and the floating body. In particular, this resonance could amplify the horizontal oscillation at the top of the building. In addition, around this resonance frequency, there could be large spectral components of shear stress and bending moment at the base of the building. It is important to consider these phenomena carefully in the structural design. There is also the problem of establishing a way to evaluate the resonance effect for the structural design.

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 This paper describes the motion characteristics and cargo handling efficiency of the Large-Scale Floating Coal Transshipment Station (LFTS). In considering feasibility of the LFTS system, it is important to know the cargo handling operation rate in the target area. LFTS can load 500,000 tons of coal and the draft will fluctuate greatly depending on the loading condition of coal. Accordingly, it is conceivable that wind load and the wave force including the slowly varying wave drift force affect the fluctuation greatly affect the fluctuation. Also, LFTS and bulk carrier are large-scale structures, the fluid forces acting on both affect each other, so the influence of hydrodynamic mutual interference between two floating bodies cannot be ignored. In this study, Grasp the motion response of bulk carrier under composite external force considering influence of hydrodynamic mutual interference, Based on the results, cargo handling efficiency was calculated, and the operating status of the LFTS system was grasped.

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 In this study, we carried out a conceptual design for member structures of a mooring buoy used at the ports of Nanboku-Daito Islands. A concept of the design is that a mooring buoy is hard to be affected by wave forces and easily exchanged even when damaged. As the result, we proposed a new type mooring buoy for simple maintenance. The proposed mooring buoy is a new type of an underwater float type mooring buoy. It uses multiple floating bodies (floats) held in water and two mooring ropes connected with a removable shackle. In consideration of maintenance, this mooring buoy is composed of some member structures that are easy to exchange when damaged. We confirmed that the proposed mooring buoy has sufficiently safe structural features against design wave forces by static equilibrium calculation.

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 In this study, we investigate the sensitivities of the aspect ratio (ratio of length to depth) associated with a connecting channel on seawater exchange in Shirahama Bay and Funauki Bay in Iriomote Island, Okinawa, Japan, using a simplified tidal current model. In the case of a control experiment with moderate aspect ratio, the tidal current in the connecting channel is activated leading to the difference of salinity among the two bays. In the case of large aspect ratio, the tidal current in the connecting channel is inactivated enlarging the difference of salinity among the bays. In the case of small aspect ratio, the tidal currents in not only the connecting channel but also the channels to the oceans are inactivated causing a reduction of salinity in both the bays. It is considered that the aspect ratio of the connecting channel effectively influences on seawater exchange and seed and fruit dispersal in both the bays.

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 In August 2016, the accident occurred that four swimming people curried away to offshore and die at Ishikari-hama beach in Hokkaido. The several other accident that the swimming people curried away occurred around the Ishikari coast in recently years. The current analysis in Ishikari Bay due to the seasonal wind was studied in the past research. However, the current dynamics due to the wind direction change in short time has not studied yet. Therefore, we tried to comprehend the feature of the current dynamics in Ishikari bay, expressly around Ishikari-hama beach.
 As research contents, we grasped the history of the accident around the Ishikari coast. In this case, we used the on-line database and extract the newspaper article about the accident at Ishikari coast. As the result, we comprehended the feature of the accident in Ishikari Bay. Secondary, we made the field survey at Ishikari-hama beach in July 2017. This beach has cusp topography. The interval spacing of cusp topography was about 100m, and the slope of the bottom was about 1/80. In the field, we pigmented the rip current by the sea water colorant, and the pigmented current was recorded as the aerial photography by the UAV. Thirdly, we confirmed the fluctuation of the current in Ishikari Bay due to the wind direction fluctuation. As a result, we comprehended that the current direction changed in several hours after the wind direction changed. Finally, we simulated the rip current and the wind driven current in Ishilari Bay.

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 In considering ocean resource development and disaster reduction in Japan, it is necessary to grasp the ocean environment around Japan, and analyses of the ocean condition such as the current structure and the change of water temperature. Therefore, in this study we analyzed the ocean environment for Japan Sea using the reanalysis data FORA-WNP30, which contains long-term (30 years), high frequency (daily) and high-resolution (1/10 degree) data. The reproducibility of water temperature and salinity in Japan Sea from FORA-WNP30 were evaluated and accuracy of the data was confirmed. Then, in order to grasp the ocean environment of Japan Sea, changes of water temperature and water flux at the straits of Japan Sea were analyzed. As a result, increasing trend of water temperature is large from sea surface to 300 m water depth in Japan Sea, being particularly conspicuous in autumn. The flux of each strait in Japan Sea have peak frequency at half and 1 year, respectively. The fluxes at Tsushima, Tsugaru and Soya strait are highly correlated. Because Liman cold current affects flux at Mamiya strait, the flux correlation with other straits is small.

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 In this paper, we conducted numerical analysis of coastal current change due to a construction of oyster reefs at the Shiotagawa river mouth in the Ariake sea. In the numerical model we developed, the fifth order WENO (Weighted Essentially Non-Oscillatory) scheme was applied to discretize advective terms in governing equations, and the two-way nesting approach with tideland treatment was introduced into the model. The changes of coastal current by reef construction were examined by comparing results with current state and between reef construction scenarios. Our analysis results showed that the time-averaged velocities could be decrease by the reef construction at the right bank of the river mouth. Moreover, our results suggested that the time-averaged velocities could be decrease by withdraw of existing oyster reefs at the right bank of the river mouth.

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 The object of this study is to predict the distribution of cesium deposited on the bottom of Tokyo Bay by means of the Hybrid Box Model linked with a diffusion model, released by Fukushima Daiichi Nuclear Power Plant. On the basis of the load fluxes from rivers, the distribution of concentration (separately for dis-solved cesium and small and large particulate cesium) in seawater and the mass of cesium sedimentation to the bottom of the bay were calculated by the models.
 Results were compared to the published observation data in order to examine the applicability of the used models. Estimated cesium concentrations in the sediment show good agreement with the observed data. From the analysis, it was estimated that 61% of the cesium inflow into the bay is deposited onto the bottom, and that 21% flow out of the bay. Cesium sedimentation is greater in the inner and middle parts of the bay, and decreases in the direction toward the bay entrance.

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 Inexpensive UAV systems are available to conduct environmental monitoring and aerial surveys in the terrestrial region. Currently, however, UAV application in aquatic and sub-aquatic environments is limited due to low visibility, light reflection on water surfaces, low shade on sand surfaces etc.. Despite these application difficulties, inexpensive UAV camera systems seem to have much potential. The authors therefore developed techniques for using these systems in coral, tidal flats, dune and beach systems, modelling of coastal structures such as fishing ports and concrete armor blocks, as well as monitoring of ecosystems. The research shows that the inexpensive UAV system has much more potential than expected and can be more applicable in coastal environments.

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 Tidal flats environment of the Yatsushiro Sea is a habitat of various rare species such as Black-faced spoonbill (Platalea minor). In the recent years, this tidal flats environment was getting threatened due to an increase in garbage disposal, dam and other factors. To deal with this problem a number of nature restoration projects were conducted by Yatsushiro River and National Highway Office in the Kumagawa river estuary of Yatsushiro city. One of such projects and its finding are presented in this paper. In the presented study we investigated topographic changes in the tidal flats using small UAV. Then the 3D modelling of the tidal flats topography was performed from the image taken by the drone.
 As the result, no significant changes in the topography around small island was detected. However, in 2017, the place tends to be deposited especially on the water-route. In the future, adaptive management will be necessary.

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 Ryujin-ike inlet is a small, unique in Oita Prefecture and opens to the Pacific Ocean. The inlet is known for Nankai earthquake tsunami deposition inside the inlet. The local community set a small dam at the throat of the inlet, expecting significant sea shell catchment. Following the construction of the dam, sea shell production inside the inlet was decreased. The small dam was set to control the amount of flood tide, however, the sedimentation at the landside of the dam generated a quasi-natural shoal, resulting in a greater reduction in flood tide than expected. As a result, the water ex-change and dissolved oxygen contents are declining to levels lower than the previous natural condition. Thus, to improve current water exchange at the inlet; the water exchange at the throat, water quality inside the inlet, and the inlet topography have been studied. The study shows that the tidal water exchange is limited only during the high tides of a spring tide period by a maximum of 2,100m³ nearly every two weeks.

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 We evaluated a surveying method that utilize UAV to develop habitat monitoring procedures for the endangered tiger beetle Cicindela lewisi. A study area was a sandy shore created for the purpose of mitigation of the loss of its original habitats. Our study showed that if UAV was utilized at an altitude of 30 m or less, it could estimate the habitat topography with practical accuracy. It was also revealed that this method could save labor and surveying time efficiently. It is suggested that the UAV monitoring method can make high frequent topographical surveys possible leading to steady progress in conservation of Cicindela lewisi.

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 In the Great East Japan Earthquake, many coastal and port structures were damaged by tsunami wave forces exceeding the design tsunami forces. For that reason, various kind of structures based on the concept of "resilient structure" in which deformation does not progress rapidly even if a tsunami exceeding the design one acts, have been proposed and some of them have already been practically applied. In this special session, four research papers were presented and a panel discussion was held for the purpose of reconsidering the fundamental concept of resilient structure, introducing design and construction cases considering resilient structure, and proposing new type structures. Through paper presentations and discussions, important findings and issues were extracted to adopt "resilient structure" in practical design and construction.

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 The special session on “Current status and perspective on the Northern Sea Route”, which is aiming at introducing current status of research topics on the Northern Sea Route, had been carried out. In the session, four research papers were presented and panel discussion was held. The session topic covered sea ice observation and forecast, navigation in ice covered waters, natural resource development, international regime, and maritime transport.

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