In order to build robust coastal dike against giant tsunamis, it is important to prevent tearing off of cover-blocks by lift forces produced by over-flowing tsunami. The stability of cover-blocks is affected by overflow conditions, cover-block's weight and slope gradient etc. In this study, we predict the distribution of lift force acting on the top of slope, and evaluate the relationship between safety-factor of cover-block and overflow depth. As a result, in the conventional dike, the cover-block tears off around at overflow depth 5.7m. On the other hand, the newly proposed type, which connected the cover-block and the crest concrete, has a high resist to the overflow depth of over 16.0m. Because this newly type increases the resistant moment of cover-block with accompanying overflowing water's weight on the crest in increase of overflow depth.

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RC buildings with piles had been expected to be resistant to tsunamis. However, pile-supported RC buildings were pulled up and toppled by the 2011 Off the Pacific Coast of Tohoku Earthquake Tsunami. Damage mechanism of the pile-supported RC buildings due to tsunami has to be found out for tsunami evacuation countermeasures with tsunami evacuation buildings. In this study, we focus on one of the pile-supported RC buildings in Onagawa town, Miyagi Prefecture that was pulled up, toppled and moved during the 2011 tsunami and find out its damage mechanism by using tsunami inundation simulation and tsunami response analysis. As a result it was shown that liquefaction by ground motion and reinforcement of ground surface by Tsunami made shear failure in the piles and after that the building topped and moved by Tsunami.

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This paper discusses the experimental findings pertaining to a failure of composite breakwaters brought by the instability of a foundation mound due to the seepage flow induced by a huge tsunami. Centrifuge tsunami testing using a drum channel was applied to reproducing the reduction of the bearing capacity of a mound under seepage flow leading up to the failure of the mound. The results show the occurrence of boiling and fluidization as well as the spread of the instability zone in the mound at the vicinity of the caisson as a consequence of the seepage, yielding the significant displacement of the caisson. The effects of the resiliency structure, which is placing rubble on the back of a caisson, are also examined in the light of stability of a mound as well as a foundation bed under the seepage flow.

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This study discusses the performance assessment framework of breakwaters against wave and tsunami action. As both of the performance assessment methods were established individually, relevance of the two methods are not necessarily clear. Authors proposed to regard performance assessment against wave action as serviceability assessment and that against tsunami action as safety assessment. Criteria for serviceability assessment should be determined by economical point of view and life cycle cost analysis should be used for that assessment. Authors also discussed on the performance assessment method against tsunami action whose magnitude is larger than that assumed in the design procedure. Some design examples are shown considering both wave and tsunami action.

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Wave presseures out of the surf zone are estimated by the maximum wave height corresponding to 1.8 times of significant wave heights according to Rayleigh theory. On the other hand, maximum wave heights for extreme waves increase under the effects of nonlinear four-wave interactions. Therefore, it is necessary to evaluate the effects on wave pressures of the deviation from Rayleigh distribution under extreme wave conditions. As results of the physical experiments and numerical simulations, it is possible to estimate wave pressures with the deviation from Rayleigh distribution if the occurrence frequency of maximum wave heights is considered.

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A method to predict disaster occurrence of costal structures is examined by refereeing the repeat disaster occurrences of coastal structures at locations close to each other. Significant wave height data from NOWPHAS is used to make a model of wave history, then maximum wave height during each storm, duration of storm and the flow rate of wave overtopping at the maximum wave height are used as key factors and the time function is also introduced to reduce wave energy and flow rate of wave overtopping at the time retroactive from the moment of disaster occurrence. The accumulation value of the wave energy and the flow rate of wave overtopping with the time function are carried out to judge of disaster occurrence of seawalls in Ishikawa coast, and the possibility of the index to explain the disaster occurrence is discussed.

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In a beach or a shallow area, there are a few cases that coastal dikes were destroyed directly by strong wave force. On the other hand, a lot of field cases show that scour and suction caused by the continuing action of waves bring their destruction gradually. Therefore, it is important for us to establish prediction methods of suction rate from within the coastal dikes. In this paper, we improve Ioroi et al.'s formula so that the suction rate is gotten with high accuracy by using the settling velocity of Rubey. Then, we reveal the influence of coefficient of uniformity and dry density to the suction rate using experimental data. Moreover, we examine how to get the suitable values of the flow velocity and the excess pore pressure using CADMAS-SURF, and confirm that the calculated values agreed with experimental values.

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The high-rise artificial fish reefs up to 20-40 meters have been developed in Japan. The tall reefs are not only composed of many members but also complicated structure compared to the traditional reefs. In general,the hydrodynamic forces exerted by waves and currents on the reefs can be computed from the empirical formula known as the Morison equation. But the adaptation of the equation for the tall reefs is not confirmed yet. Therefore both of physical model tests and theoretical considerations have been employed to investigate the wave forces exerted on the reefs. As a result,it is confirmed that the method adopted here may give an appropriate drag and inertia coefficients. It is also affirmed that the Keulegan-Carpenter number may be effective to explain the influence of the shape and distance of the members acting on the wave forces.

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Scouring due to tsunami causes a decrease in the bearing capacity of structures. Disaster of the breakwater with scour due to tsunami overflow was occurred at Hachinohe-port in East Japan Great Earthquake. The present study attempted to explicate the scouring mechanism due to overflow focusing on the tractive force and the pore water pressure in the sediment ground by using two-type geomaterials that is different permeability. As a result, scour was occurred with tractive force. The scour profile had same profile as proposed by Yeh et al. when sandy soil used. However, we found that the excess pore water pressure was generated in the ground due to jet flow, and liquefaction was occurred. Therefore, we need to recognize that the liquefaction-layer is generated due to overflow.

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The proving research of the offshore wind power has been continuing at the offshore of Choshi. The seabed of this area is composed of soft rock, but the scour resistance of the soft rock has not been revealed. Then we experimented the scour test using the core sampled from the site, and revealed the scour resistance property of the seabed. The specification of the scour protection was determined using the experimental results. Although the maximum wave height close to the design wave height was observed after the installation of the scour protection, the stability of the scour protection was confirmed by the data of sounding survey.

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When the hook of a crane-barge carries loads under wave condition, it is important to estimate motion of the ship, the hook, and the shackle for work safety. The hook and the shackle motions are mutually combined motions between the crane-barge, the hook and shackle swing. In this study, analytical model for coupled motion between crane-barge, hook, and shackle was proposed and verified experimentally; by a crane-barge model and by double pendulum model. In addition, analytical study for the development of reduction of the hook and the shackle swing motion method was conducted. By this analytical model, we proposed a way of reducing the hook and the shackle swing on a crane-barge under wave condition.

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Most breakwaters in Japan are caisson breakwaters. However, the lower is the number of caissons constructed in a year, the higher is the construction cost per caisson, because the cost of floating dock operation is fixed, irrespective of caisson number. Therefore, a construction method was developed in which breakwaters are constructed not of caissons but of connecting cellular blocks. This paper proposes a design method for connecting cellular blocks and examines wave force characteristics in the construction stage by using hydraulic model tests. It was found that the proposed construction method could cut the project cost by 15% and could cut the project duration by 3 years at the Port of Setana.

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Sediment microbial fuel cells (SMFCs) have attracted great attention for its high feasibility of renewable energy source and biodegradation technology. Here, we aim to experimentally evaluate the electrode distance effects in sediment by forced electron recovery based on variances in the profiles of sediment properties (pH, ORP) and the electrode potential. Large increases in ORP (or electrode potential) and decreases in pH were found near the anode electrode. The gradients of pH, ORP, and the electrode potential formed along with increases in the distance from the anode electrode. Based on the gradient profiles, the sediment located up to 8 cm from the anode electrode was affected by the forced electron recovery. This distance was 10-fold longer comparing to that of SMFCs operated with normal conditions.

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The overvoltage (voltage losses) of sediment microbial fuel cell (SMFC) is reviewed, and factors for improving the performance of SMFC are discussed through laboratory experiments. The SMFC performance (maximum power density P_MAX, exchange current density i₀, and limiting current density i_limit) obtained from the voltage-current density curves is investigated under different electrode conditions (material, burning) and many types of sediment. It was found that P_MAX, i₀ and i_limit were largest in the cases of burning electrode at 500°C, and when the sediment that has high content of unstable organic matter was used. These indicate that the overvoltage of SMFC can be effectively decreased based on these approaches, and it is also known that the rate-limiting factor of the SMFC performance is the electron exchange rate on the electrode.

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As there are some disadvantages in the measurement of redox potential (ORP) of sediment using conventional methods, we proposed a method based on the microbial fuel cell technology for evaluating the redox condition of sediment. Higher rate of electricity recovery by the microbial fuel cell technology was obtained from the sediment that had lower ORP, higher reduction capacity, and higher content of labile structural organic matter. Strong correlations between these parameters were found, ensuring that our method can be used to evaluate the ORP of sediment. Furthermore, our method makes it possible to continuously measure the redox potential of sediment in long period comparing with conventional methods.

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Connectivity evaluates stochastic processes of larval dispersal due to chaotic coastal circulations (e.g., Mitarai et al., 2009). In the present study, we quantify Lagrangian PDFs and connectivity using many Lagrangian particles released from 140 source sites in the modeled SIS circulation field in a double-nested, high-resolution ROMS configuration (Uchiyama et al., 2012). In winter, the fraction of particles transported to another region is about less than 40% except for both the channels, suggesting that particles largely remain in the release region. The regional connectivity is correlated with the seasonal variation of the mass fluxes at the straights between two neighboring regions. Particles released from Harima-Nada, representing larvae of marbled sole, are mainly transported towards the northern shore of Shodo Island, while particles arriving there originate mostly from the western shore of Harima-Nada.

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Spatial distribution and temporal variation of salinity, suspended sediment concentration (SSC) and chlorophyll pigments in the macro-tidal Chikugo river estuary, Japan, were measured for two weeks and investigated the effect of salinity mixing and the estuarine turbidity maximum (ETM) on the state of phytoplankton. The estuary was in a vertically well-mixed condition during spring tide with SSC exceeded 1,000 mg/l. The estuary changed to stratified condition during the neap tide with SSC of less than 20 mg/l. Chlorophyll-a (Chl-a) concentration was relatively low during spring tide and became high during neap. Pheophytin-a (Pheo-a) concentration was high during spring tide and it became low during neap tide. Chl-a rate in total phytoplankton concentration was 20–60% during spring tide and it reached 90% during neap tide. Peak concentration of Chl-a was located in the upper reach of the salinity front. It was found that the phytoplankton in the Chikugo River estuary mainly inhabit in brackish water below 1 psu. Good relationship between location of surface SSC maximum and Pheo-a length indicated that the detritus moved with suspended sediment, and development of the ETM and the deactivation of phytoplankton interact each other.

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Understanding of variances in properties of lipids plays an important role in considering the restoration of littoral environment. Here, loss on ignition (LOI) of sediment is investigated in combination with element analysis, n-hexane extract, and fatty acid analysis in order to provide a better understanding of variances in the lipid properties of sediment. It was found that the sediment that had large amounts of unstable organic matter (UOM) contained large amounts of lipids, and the lipid amount linearly decreased along with the decreasing amount of UOM. This ensures that the decomposition of UOM can be understood based on variances in the lipid properties. Furthermore, it is evident from our results that the decreasing amount of organic matter in transport processes differed from that in decomposition processes of accumulated sediment.

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In order to determine the behavior of red tide distribution by satellite remote sensing, we found out that the optical properties of Tokyo Bay significantly changes in terms of measured AOP (apparent optical properties) and IOP (inherent optical properties) in field observation. Based on the spectrum variation of measured reflectance, we developed the estimation model of high concentration of Chlorophyll-a (Chl-a). By applying the developed model to satellite images, the spatial variation of high concentration of Chl-a in the bay was discussed in this paper. As a result, Chl-a was gradually increasing from the coast of the bay. It was found that the increment of Chl-a is mainly dependent on the spatial variation of temperature when wind was weak and solar radiation was high.

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A large eddy simulation (LES) of the tidally induced bottom boundary layer process in the coastal ocean is carried out and the obtained results are used to examine the suspended particulate matter dynamics. Special attention is directed to the dependence of the vertical diffusive process of the particles on their size and density. We find that, presumably because the time scales of the particle response to water motions are much less than those of interest in this study, the magnitudes of the vertical velocities of particles are almost identical to those of seawater and fairly independent of their size and density. It is suggested that the vertical diffusivity coefficient of particles is of the same order as the vertical eddy viscosity or diffusivity coefficients derived from the velocity or temperature fields of seawater.

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Loss on ignition of sediments at different burning temperatures (ignition behavior) was conducted, and was compared with the total organic carbon, the organic carbon of unstable form organic matter (UFOM), and the organic carbon of humic substances, in order to classify the type of organic matter existing in littoral sediments of Hiroshima Bay. The results ensured that the origin of sediments could be classified based on the ignition behavior of the sediments. Importantly, the humic substance content determined from the ignition behavior denoted the same tendency of the measured value, ensuring that the ignition behavior can be used to classify UFOM and humic substances. It was also found that the ratio of loss on ignition at 300°C to that of 300-600°C could be used to classify the characteristics of sediment, as well as the C/N ratio.

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We have collected and organized the bottom sediment data that has been recently investigated in the Ariake and Yatsushiro Seas and have divided sea area of the Ariake and Yatsushiro Seas by cluster analysis using physical and chemical properties of sediments. As a result of consideration, It was suggested that in the mid-bay and mouth of the Ariake Sea, the suspension carried by the tidal residual current toward the mouth of the bay from the inner part of bay is deposited. According to distribution characteristics of total phosphorus concentration, we have found that deterioration of sediment environment is not only due to progress of siltation in the Yatsushiro Sea.

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Properties of organic matter existing in deposited sediments in littoral regions are identified based on the ignition behavior of the sediments. In addition, oxidation-reduction (redox) conditions of the sediments were evaluated based on the redox potential (ORP) and the oxygen reduction capacity (ORC). It was found that the proportions of unstable and humic organic matter could be identified based on the ignition behavior by excluding the clay-structural water content in the sediments. Moreover, a strong correlation between ORC and organic matter state was confirmed. The sediment that contained a high ratio of unstable organic matter to total organic matter made larger reductions in the dissolved oxygen concentration. Furthermore, it was possible to determine the amount of reduced substances based on ORC.

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Predicting behaviors of fine sediments is an important issue in terms of keeping navigation channels, an aquatic conservation and so on. So numerical models on sediment transport have been improved to achieve a high accuracy prediction. On the other hand, it is laboring to determine parameters for numerical models taking complicate behaviors of sediments into account. In the present study, a series of experiments was carried out to understand characteristics of a mud deposit. As the result of this study, it was possible that parameters associated with settling, self-weight consolidation and erodibility were determined by simple experiments with a settling column. In addition, the result of experiments by Gust Erosion Microcosm implies that a state of consolidation has no small effect on erodibility of mud deposits.

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We discussed a numerical model for oceanic dispersion and sedimentation of radioactive cesium-137 (Cs-137) in shallow water regions to clarify migration behavior of Cs-137 from Fukushima Daiichi Nuclear Power Plant. Our model considered oceanic transport by three dimensional ocean current, adsorption with large particulate matter (LPM), sedimentation and resuspension. The simulation well reproduced the spatial characteristics of sea surface concentration and sediment surface concentration of Cs-137 off Miyagi, Fukushima, and Ibaraki Prefectures during May-December 2011. The simulated results indicated that the adsorption-sedimentation of Cs-137 significantly occurred during strong wind events because the large amount of LPM was transported to upward layer by resuspension and vertical mixing.

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This study aims at investigating structures of ocean current, salinity and water temperature in Miyako Bay, Iwate, Japan after the Great East Japan Earthquake. Field observation using CTD was performed at 0.1 m vertical intervals for 28 locations in the bay in September 6, 2013. Ocean current, salinity and water temperature in Miyako Bay were reproduced using a coastal ocean current model, CCM. The comparison between the numerical and observational results was conducted to verify the model results. As a result, it was demonstrated that the model can appropriately reproduce the salinity and water temperature in the bay. In addition, the characteristics of the ocean current, salinity and water temperature in the bay such as isolated water mass with low salinity in the east-central part of the bay were revealed by numerical analysis.

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Water mass structure in a coastal area is significantly affected by meteorological forcing. Typhoons, in particular, have a great impact on the coastal water environment. The present study aims at numerically investigating the variation process of water mass structure in Ise Bay area under influence of Typhoon 0918 using an Atmosphere-Ocean-Wave-Water Quality coupled model and the four dimensional data assimilation with a tropical cyclone bogus scheme. As a result, the flow structure was found to be significantly changed by the effect of the typhoon, such as the formation of a vertical circulation flow due to strong winds. Furthermore, the numerical results revealed that the vertical mixing of water column was induced by the vertical circulation flow, resulting in the disappearance of hypoxia.

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This study aims at investigating of dynamic states of larvae of land hermit crab Coenobita brevimanus in Amitori Bay, Iriomote Island, Japan from the perspective of numerical analysis. An ecological investigation of Coenobita brevimanus was conducted to provide input data for a numerical model. Reproduction of coastal currents in Amitori Bay was done using a coastal ocean current model CCM. The dynamic states of larvae of Coenobita brevimanus were examined using particle tracking analysis based on the ecological investigation and the current field reproduced by the CCM. Coenobita brevimanus is speculated to employ a strategy to maintain the group of individuals by making most of the larvae stay around the release place.

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Upwelling events of bottom oxygen-depleted waters in the head of Mikawa Bay, known as the blue-tide or Nigashio, were documented and meteorological condition that causes the upwelling was discussed based on various field data. It reveals that onshore translation of bottom waters induced by moderate wind forcing of about 5m/s for several days and vertical mixing near the edge of tidal flats may be main causes of the upwelling phenomena. Time scale of bottom water translation and the effect of quick inversion of wind direction were also investigated by using a two-layer numerical model developed in the study. It was found that inversion of the wind direction causes quick movement of the water mass but does not show increase in the magnitude of rise of water.

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We investigated occurrence of blue tide in the field and experimented the effects of blue tide to Ruditapes philippinarum in the laboratory. Blue tide occurred several times each year on Omaemaha in inner part of Osaka Bay. Occurrence of blue tide corresponded weather condition. It could develop the relationship between ORP and pH in the field and estimate concentration of hydrogen sulfide in D.L. -1m inhabiting R. philippinarum. It was not recognized unequivocal effects of hydrogen sulfide to mortality rate of R. philippinarum under reductive environments. On the other hand, clearance rate of R. philippinarum was affected by hydrogen sulfide and did not recover early time.

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Distributions of dissolved oxygen and phosphorus concentrations were measured in a harbor area along the north coast of Osaka Bay. An anoxic water mass existed within a shallow depression in Koshienhama canal, where surfacing of anoxic water frequently occurs. Bottom anoxic water appeared beneath the surface chlorophyll maximum layer in a channel where sewage flows into. Total phosphorus concentration is higher in the upper layer than that in the lower layer, in contrast to total nitrogen concentrations. This suggests desorption of phosphorus from the bottom sediment. To pretend generation of hypoxic water, a countermeasure which uses buoyancy of river water was considered.

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It's important to understand the mixing effect of jet in density stratified field before applying water mixing technologies in actual site. In this study, we experimented on various types of stratified field and we measured the spatial distribution and temporal changes of density by using LIF method. The results of this study were as follows: (1) Entrainment parameter is affected only by velocity of jet. (2) Degradation of potential energy is affected by Froude number and initial potential energy of the field. We defined a new parameter including both Froude number and initial potential energy and it has a linear relation to the degradation of potential energy.

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Kabira bay on Ishigaki island is a tourist attraction, but in late years it is said that the water quality turned worse. The causes include sedimentation such as the red soil by anthropogenic activities, but are not sure. Then we investigated sediment conditions such as sediments thickness, deposition rates and sediment composition. Sediments thickness were up to 18 m. These sediments were deposited gradually over several thousand years, except bay inner part. Anthropogenic activities changed composition of sediments at bay inner part, but deposition rates were not change. Anthropogenic activities did not contribute for current sediment.

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Field observations were conducted to investigate physical environments and characteristics of turbid water in Kabira Bay. It was suggested that the anticlockwise circulation from the bay-mouth to central bay prevailed along the trench, however, during a period of high wind, wind-driven flow promoted vertical circulation. Wind-driven flow and cooling of surface water promoted vertical mixing in the water column, and thus, transported the high turbid water mass from the deeper to the upper layer. The flux of turbidity in the steep slope area along the trench was estimated to be directing toward the deeper layer, therefore, terrestrial fine sediments were estimated to be responsible for the high turbidity in the deeper layer.

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The field observation was conducted to verify the technique using the mesh-type artificial base for restoring a coral community in the Naha port where its population is thin. This base is installed some distance from the seabed to avoid sedimentation of silts on it and can enhance habitation of coralline algae. Therefore settled coral larvae can survive easily. More than 75 % survival rate of the settled coral was confirmed one-year after the base installation. The observed data revealed that the appropriate flow velocity is necessary to keep the suitable habitat conditions for coral. The HSI (Habitat Suitability Index) model including flow velocity as a SI (Suitable Index) for natural coral reef by authors can evaluate also the coral on the artificial base.

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Field measurement was conducted at the Omotehama Coast from 2008 to 2010 to grasp the influence of sand temperature affecting hatching and emergence success of loggerhead sea turtles. From the results of the nest depth measurement,it was found that the thickness of the egg cabin was relatively uniform despite the depth of nest. Negative significant correlation was found between high sand temperature (> 32 degrees Celsius) and emergence success on relocated nests. However there was no significant correlation between low sand temperature (< 24 degrees Celsius) and emergence success. Long-term exposure under the high sand temperature condition affects to emergence success.

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Barren ground is widely distributed in the sea area. The coastal structures to make the algae place have been constructed for about ten years. However, it is feared that the decrease in the effect of seaweed creation by the aged deterioration of the substrate. The occurring condition of Barren ground is that feeding pressure of sea urchin is greater than growth rate of seaweed. It is necessary to calculate the growth of the seaweed and the revenue and expenditure of sea urchin's food consumption correctly. In this study, the quantification of the seaweed biomass was examined by factors of environment with a remarkable change. Variability characteristics of the seaweed amount and a physical environment were clarified. Finally, the improvement of the calculation method of the amount of the seaweed was achieved.

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The eelgrass in Miyako Bay was greatly damaged by the tsunami. For future restoration of the eelgrass, we collected sediments from 110 stations in the bay and analyzed particle-size distribution and chemical composition in 2012 and 2013. The distribution of eelgrass was also measured at the same stations. The sediments on the south and west coast were suitable for eelgrass. On the other hand, the sediments on the east coast were coarser. The chemical composition indicated that we could not expect the supply of sand from the main river to the east coast. We estimated that the restoration of eelgrass on the east coast would be slower than on the west and south coast.

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The carbon sequestered in coastal vegetated systems (e.g. seagrass meadows) was termed “Blue Carbon” and has recently been highlighted as an option for climate change mitigation initiatives. However, relationships between air-sea CO₂ flux and environmental factors, varying tidally and diurnally, remained unclear. In this study, 48-hours continuous in situ measurements were performed in the Zostera meadow at Hashirimizu, Yokosuka. We statistically analyzed the observed data using the structured equation modeling (SEM). Specifically, we implemented the path analysis. The results indicate that wind speed was a direct factor for determining the flux, and the community metabolism (e.g. ecosystem production and respiration) was an indirect but important factor.

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It is thought that a salt marsh located at coastal urban area absorbs and emits large amounts of carbon dioxide (CO₂). In this study, a field investigation on CO₂ budget was conducted at Osaka-Nanko bird sanctuary, and CO₂ fluxes were measured at tidal flat, sea surface and reed field by using chamber methods in order to estimate CO₂ budgets of the salt marsh. The results of this study were as follows: (1) CO₂ fluxes of tidal flat and reed field were one order larger than that of sea surface. (2) It was estimated that CO₂ flux emitted from tidal flat was 3.26 g/m²/day and CO₂ flux absorbed by reed grass field was 1.53 g/m²/day in October 2013. (3) It was suggested from the result of seasonal change of fluxes that the absorbed amount of CO₂ becomes larger on summer than on autumn.

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In the previous study, a new method for transplanting zostera japonica which doesn't require much diving work was developed. This method is to put a biodegradability sheet close to living areas of zostera japonica and to move the sheet to the destination after zoster japonica grows enough on the sheet. Although the applicability of the sheet was already confirmed through a field survey, it was also observed that some zostera japonica are removed from the sheet after transplanting the sheet. In this study, laboratory experiments were conducted to clarify the requirements for zostera japonica to remain certainly on the sheet. The results of the laboratory experiments show that when the sheet is moved, more than 5cm of shoot roots need to remain and the moved sheet should be attached firmly to the destination ground.

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Variations of tsunami attenuation ability of coastal forests with stand age have been investigated by applying knowledge of forest ecology and tree morphology. The maximum resistance of a coastal forest against a tsunami flow is found to be realized at a certain age, because the size of individual trees increases with age whereas the resistance as the stand decreases with age as the result of self-thinning and heightening of tree crown area. Results on reaches of tree breakage show little difference for 20 and 40 years' old stand cases, because the individual tree durability momentum increases with stand age whereas the external momentum by tsunami flows also increases.

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This study aims to obtain better understanding of groundwater dynamics in coastal sandy-beach environment. The Teradomari-Nozumi Coast of the estuaries of Ohkouzu diversion channel was selected as field observation location. This sandy beach is formed by fluvial sediment supply through the above channel (maximum advance of shoreline is up to 600m). From these reasons, this coast is suitable as a study area for unconfined groundwater. The field observations and analysis of the beach groundwater for particular points along beach profile, revealed interesting characteristics include: strong correlation between groundwater fluctuations and rainfall events in a catchment area and so on. As a result, fresh groundwater supply in terms of steady flow theory is estimated to amount from 0.5 to 4.3 m³/day per meter of beach width.

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Groundwater circulation is one of important substance transportation process in delta area. It is affected by the variation of groundwater level and quality. To understand variation factors of unconfined and confined groundwater level and quality in Ota River Delta, the long term data were analyzed since 1975 to 2012. The confined groundwater level is varied with sea water level and upper river water level. Moreover, the sea water level in Hiroshima bay increases 20 cm compared with 1975 and the confined groundwater level increases 130 cm compared with 1975. The unconfined groundwater is varied with precipitation.

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Fresh water lenses are important water resources on oceanic islands. In this research, we examine the effective acquisition method of the fresh water by three-dimensional numerical simulation. Salt water just below the fresh-salt water interface is drawn into the fresh water well by pumping up fresh water. Then fresh water has yet sufficiently remained in the fresh water lens. In considering the effective water intake, the double pumping and water interception board methods were tried. In the model case of circular symmetry topography, the usefulness of the perpendicular double pumping method was confirmed. Seawater pumping amount of 2-4 times of fresh water pumping amount is necessary to obtain low-concentrated fresh water.

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In coastal parts of southern east area of the Miyagi pref., Watari land improvement district, planted areas of rice fields is less than half before the earthquake disaster because of the damage of tsunami. The decrease in planted area, namely, a decrease in irrigation water means a decrease in groundwater recharging. The decrease in recharging fresh water causes salt water intrusion. In this study, effects of the irrigation and drainage on salt water intrusion was investigated by a field survey and a simulation of one dimensional density stratified flows. As a result of investigations, salt water has been intruding into groundwater year by year. And it is expected to expand further in the future.

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The objective of this study is evaluate algal bed substratum by steel-making slag. We carried out construction of algal bed substratum by steel-making slag that of particle size finer than natural rock. When algal bed substratum was constructed, the value of the turbidity and pH was almost the same as the surrounding sea area. It could not be confirmed increase in pH when steel-making slag was submerged into the sea. The steel-making slag had been maintained as algal bed substratum after one year. The algal species and amount of the constructed bed by steel-making slag has been similar that of natural bed and constructed by natural rock.

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Lake Jusan is a brackish lake located in the down reaches of Iwaki River system and is a fishing place of Corbicula japonica. However, the annual catches of C. japonica have been fluctuated over time presumably because of aquatic environmental changes. To maintain sustainable fishery, it is necessary to understand the causal factors on reclamation processes of C. Japonica in relation to brackish environmental conditions of the lake. In this study, field measurements were conducted on salinity, water temperature, and distribution of larvae of C. Japonica. From the results, empirical formulation was made to estimate number of the larvae in the lake. By combining that formulation with numerical hydraulic simulation, a methodology was proposed to evaluate the influence of hydrological changes in the watershed on reclamation of C. japonica.

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To clarify capability of small scale artificial tidal flat (SAT) in urban area, we focused on manila clam production and investigated some SATs in Tokyo Bay. Manila clam production rate on a main SAT was comparable or higher than natural tidal flat in Tokyo Bay. But, manila clam was damaged by hypoxia seriously in late summer to autumn in one SAT which was main research area. Another one SAT, manila clam wasn't damaged hypoxia, because of the shallow area was widely than main SAT. Further, benthic microalgae was main food source of Manila clam in all SATs, and manila clam populations related to benthic microalgae abundance. It suggested manila clam production was affected directly benthic microalgae production, and benthic microalgae production on SAT was changed by design or maintenance condition of each SAT.

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Yatsushiro Bay, a typical closed bay on the west of the Kyushu Island, is a sea area where a vast tidal flat develops. Recently, various environmental degradations are reported to occur in Yatsushiro Bay, as red tidal and anoxic water. In this study, the ecosystem formation process by recovery of shoreline, in which the aim is to establish the technology that can artificially restore the tidal flat and the shoreline in front of embankment development and to recover and maintain the ecosystem, was investigated in Yatsushiro Bay. About eight months have passed since shoreline was constructed; benthos species have increased by the quadruple or more. The effect in the future can be expected by recovery of shoreline.

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