Most of seawalls in Tokyo Bay Area are upright seawalls. These seawalls are severe for marine organisms to live because their environmental conditions are extreme in terms of eutrophication and oxygen depression in summer and fresh water inflow in rainy days as examples.In order to increase biodiversity, we placed two types of seawalls to provide marinecreature with a habitat. One was placed in front of the upright seawall having three functions-tidal flat, tide pool and reef. The other was placed inside rubble mound seawall having small tidal flat.As the result, some of creatures, which do not live on normal seawall, lived on or in both of the seawall. It's found that changes of seawall's form can increase species of marine organisms.

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Komatsu et al.(1997) have recently proposed a new water-purification method in a semi-enclosed coastal area. By means of this method, to activate the tidal exchange between the inner and outer sea area, installing many bottom structures “Bottom Roughness” controls a pattern of tidal residual current, which have an unsymmetrical 3-dimensional shape. In order to confirm the effect of the present method in an actual coastal area we started prototype test since May 2000 in New Nagasaki Fishery Port, Nagasaki, Japan. In this prototype test, 60 units of bottom roughness, whose height and width were 4m respectively, were installed on the bottom near two mouths of the port in May 2001. In this paper, some processes to apply this water-purification method to New Nagasaki Fishery Port were reported.

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We investigated the mechanism of the entrainment of sediment into a small harbor with channel-type breakwater through experiments in a wave basin. It was found that the significant sediment entrainment took place when the mode of oscillation in the harbor became the 1^st mode. In the case where the incident wave period was shorter than the period that caused higher mode oscillation in harbor, only a little amount of sediment entrainment took place. The separated eddies from the top of sub breakwater played very important roll in the entrainment of sediment into the harbor. It is also found that the small jetty attached at the top of sub breakwater could effectively prevent the entrainment of sediment into the harbor. The opening of the channel in breakwater could also reduce the amount of entrainment of sediment at certain condition of incident wave period.

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A numerical simulation in estuary including a tidal flat is carried out with the Movable Land-Sea Boundary Method that land boundary changes according to the ebb and flood. We developed a new method controlling two problems, namely, conservation of water mass, tidal curve on shallow water area. By comparison of other two methods, our present method controlled about 1-10% as to conservation of water mass. And tidal curve was expressed naturally without any impact of numerical treatment. Then, we carried out a tidal current simulation for evaluation of flow field in Sanbanze. In Sanbanze, there are some passage that is 5-12m depths and some emergence areas in spring tide. The topography condition is very complicated. Simulation results agreed with current direction in each tidal cycle and the locations of emergence areas. However, the scale of emergence areas was larger a little than observation data, since computational grid was large compared with a spatial scale of the tidal flat. From the above examination, application to the tidal flat of our present method was confirmed.

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Every year, a lot of fluid mud is deposited into the river-fishing port of the Ariake Sea, the function of ports is reduced. Therefore, it is necessary to solve the mechanism which fluid mud deposits into the fishing port. Moreover, it is necessary to create the controlling port depth method, and to be applyed to the target fishing port.
As a result of the investigation about a fluid mud deposition mechanism, fluid mud was conveyed as high-concentration cloudy water from the sea at flood tide, and since having sedimented and deposited in the port was presumed, it was presumed that it was the fluid mud deposition phenomenon by siltation.
Six controlling port depth methods of construction were devised.It was proved by local experiment that there is capability to remove mud about these six methods. At the river-fishing port in the Ariake sea area, the flow figure which judges which should be chosen from six methods was created.

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A beach erosion has been a serious problem. As countermeasures against a beach erosion, a sand fill method and permeable layer works have been recently considered, instead of revetments, detached breakwaters, and artificial reefs. In this research, movable bed experiments with regular and irregular incident waves were carried out to study beach stability effects by porous concrete blocks as a permeable layer. Erosion reduction effects were seen in the vicinity of the shoreline when water permeability block was used, and sand depositions were seen on the fore shore.

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Relation between protection of coastal forest and coastal erosion was investigated, taking Nakamurahama beach in Niigata Prefecture as the example. On this beach coastal forest was excessively expanded close to the shoreline and earth dike was built to protect coastal forest itself against wind-blown sand in winter. The amount of 88% of all the narrowing of natural sand dune was caused by this activity and the rest of 12% was due to the shoreline recession by erosion. Thus, this natural beach has been rapidly altered to artificial coastline armored with concrete revetment. In order to change the situation, overall land management is required instead of local optimization by sector-by-sector activities.

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Beach erosion due to the exhaustion of longshore sand transport was investigated, taking Momosakihama beach in northern Niigata Prefecture as an example. On this coast, longshore sand supply from the upcoast has been greatly decreased, causing the shoreline recession. As a measure against shoreline recession, gently sloping revetments were built, but all these structures were destroyed. Detached breakwaters were also built, but almost all sandy beaches disappeared. In order to solve the beach erosion problem, coastal engineers should appeal to open public regarding not only the engineering issues but also the ones related to social system obstructing the solution of the erosion problem.

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About 30 years have passed since artificial beaches were built in Japan, and some maintenance problems were appearing in these beaches. This paper reports on the shoreline erosion of an artificial beach “Inage-no-Hama” in Chiba pref. The artificial beach is constructed in the reclaimed land, and there land subsidence is progressed in present. Beach profile change is analyzed by wave and land subsidence characteristics. As a result, it is found that beach erosion is strongly related to the land subsidence and the erosion rate by subsidence is about 30 percent against by waves.

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Using a vertical array of four streamer-type traps, the on-offshore sand transport rates were measured in the swash zone on three beaches. At the same time, water velocity and water level were measured. The vertical distribution of sediment concentration was obtained from the measurements. Concentration of onshore sediment transport was uniform from bottom to the upper part. The corresponding distribution for the offshore transport rate indicated that the sand transport was concentrated in the bottom layer.

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The Candi Dasa coast located in the eastern part of Bali Island in Indonesia was a famous coastal resort with the well-developed coral reef along the coastline. In recent years, coral mining has beenwidely carried out for getting construction materials, resulting in the deterioration of the coast. After the coral mining, wave action to the beach increased and coral sand was washed away. Various measures using twenty Tshapegroins and seawalls were taken, but the situation is getting worse. This study investigates the causes of the beach erosion of this coast by using aerial photographing, sounding and field observations.

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Relation between shoreline and beach profile changes at coasts with dominant longshore sand transport was investigated based on the combination of aerial photographs and field observation. Field observation was carried out at coasts between Kazusaminato and Isone Point in Chiba Prefecture. Beach topography around a groin was classified into four patterns based on the parameters such as the crown height and the landward length of the groin, which control obstruction rate of longshore sand transport of the groin.

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Large-scale beach erosion and accretion triggered by the construction of an offshore breakwater on the Ajigaura and Naka coasts in Ibaraki Prefecture was investigated through field observation and analysis of aerial photographs.The shoreline retreated largely outside the wave shadow zone, leaving gravels on the foreshorezone by selective erosion of bed materials and devastating famous bathing beach of mild slope. In contrast, in the wave shadow zone, a large amount of fine sand accumulated. The measured shoreline configuration was well predicte by the Hsu model to forecast a stable shoreline. On the Naka coast, the same phenomenon was occurred and seawall was heavily damaged.

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In recent years, coastal erosion has emerged as a nationwide problem. Toward comprehensive sediment management that promotes coastal conservation, the mechanism of wide-area sediment transport needs to be understood. Research on sea sand drift has thus far targeted relatively shallow sea areas, such as the breaker zone.For wide-area sediment management, however, study should be extended to include the role of grain size in sand drift and to include sand drift in deep-sea areas. As part of this research, an field survey was conducted in the Ishikari coastal wide-area in winter, when significant wide-area topographical changes occur. As a result of the field survey in the outer breaker zone, a large sediment transport was found.

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The relationship among shorelines, sand bars and stable points of the sandy beach on the field survey result around the new port of Ishikari Bay was discussed in this paper. Conclusions are as follows:(1) The volume of erosion is the maximum at the wave steepness H₀/L₀=0.030-0.035.(2) The on-offshore movement of sand bar is influenced by the position of sand bar crest at the windward of harbor, and the shoreline is moving with the sand bar at the leeward of harbor.(3) The site of the artificial reef is decided by the scale and the position of sand bar.

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In the first of a series of experiments on coral recruitment by in situ mass culture, transportation, and settlement of reef-building coral larvae in Okinawa, Japan, gametes and embryos from slick on the sea surface after mass spawning in early summer, 2002 were collected and cultured in eight floating culture ponds (2.0mL × 2.0mW × 1.0mD each) at Akajima until the planula larvae were competent to settle into the substratum. In May, about 2 million larvae were transported by boat to a seeding experimental station at Naha Port, a distance of 50 km east of Akajima. Similarly, in June additional 1.2 million larvae cultured in a 1-ton rearing tank were transported to the same seeding station. Divers then released the larvae over concrete blocks surrounded by a vinyl cloth with windows in a mesh screen or by a nylon mesh enclosure. The number of polyps settled on the concrete blocks was monitored 4, 7 and 9 months after seeding and compared with a control outside the mesh enclosures. The results exhibited an enhancement of coral larval recruitment and demonstrated the applicability of this restoration technology in the rehabilitation of coral reefs in defined areas where natural recruitment is limited.

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Seaweed communities have been observed on the eastern shore of Ishikari Bay in a rocky area north of the Ishikari River estuary. Spawning by herring (Clupea pallasi) was confirmed in sea areas in the bay where Phyllospadix iwatensis cluster in the seaweeds vegetation.
The Ishikari River flows into the Ishikari Bay. The river catchment area accounts for one-sixth of Hokkaido's area, and this river is typical of those in Hokkaido. It is thought that the water that flows out from the Ishikari River influences the growth of seaweed vegetation on the eastern shore of Ishikari Bay.
We investigated the seaweed distribution and the water quality on the eastern shore of the bay. Many species of seaweed were found to be inhabiting the Ishikari River estuary, and many perennial seaweeds were found to distribute in those area. Laminaria religiosa, a large annual alga, predominates offshore of the estuary. A relationship was confirmed between seaweed distribution and salinity, and seaweed distribution and nutrient concentration.

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As a study of deep seawater utilization, application for possible improvement of seawater quality in an enclosed harbor area was examined by a numerical analysis. The effect of direct discharge of deep seawater is compared with that of surface water discharge. Although deep seawater turned out to be more effective than the surface water, rather large discharge at least 100, 000m³/day was required to achieve a significant improvement of water quality. As an another possible improvement of water quality using deep seawater, nutrient absorption by seaweed community in the enclosed area was evaluated.

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Effects of building a harbor on the surrounding river environment are studied by choosing the Toyama harbor, which had been constructed by digging the Hojyouzu lagoon with surface area of 1.8 squares Kilometers. The Uchikawa River of 2km length to the Japan Sea has connected the lagoon. Current feature in the river as well as water qualities before and after the harbor construction are compared. Hydraulic analysis indicate that before the harbor construction the water level at the lagoon changes 3hr behind the sea, and, ratio of tidal difference at the lagoon to the sea is approximately 70% These generate two ways current in the river, which functions keep the river water environment at satisfactory level. The harbor construction takes away the water level difference between both ends of river, and the river become stagnant.Consequently BOD of 25 mg/l as well as DO of 15 mg/l is observed at the Uchikawa River.

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Temperature distributions were measured at the Susuki coast in Shizuoka Prefecture and the Kamoda coast in Tokushima Prefecture in order to investigate the relation between temperature in the sandy beach and hatching success of loggerhead turtle Caretta caretta. Temperature in 50cm depth was positively correlated with beach profile and the correlation rate depended on the condition of vegetation. Hatching success was low in nests located at the upper part of the beach. High sand temperature might cause high mortality of eggs.

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The purpose of this study is to clarify the effect of improvement work of man-made tide pool at Tannowa-Hakotsukuri artificial rocky coast on marine organisms. This work fills the tide pool with gravel and cuts off a part of upper edge of the side walls in tide pools. Then, the field observations on marine organisms arecarried out in the man-made tide pools.
As a result, the number of species of marine organisms increases as compared with the number before the improvement work. Especially, the diversity of marine organisms is improved at the tide pool which is far from the low water shoreline. Moreover, porous concrete, concrete with slits in surface and covered with porous mats are recommended for the construction material of man-made tide pool.

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Experimental ecosystem remediation with ecocycle management on seaside park pond where water bloom occur in summer season as its eutrophication, was conducted using mesocosm system. MgO was supplied as chemical remediation materials (CRM) to control T-P concentration. Results were concluded as follows; 1) MgO sprinkling leads the smallization and the properization of ecocycle on seaside park pond, 2) the dominant species of phytoplankton was transited by MgO sprinkling from cyanophyceae to bacillariophyceae, 3) MgO sprinkling treatment was proved to be essential for on-site purification on enclosed and eutrophicated water bodies.

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As a water quality purification measure for areas such as lakes, a sand capping method by sand-upwelling system was developed. This method involves welling up clean sand from below contaminated sludge by using a water jet. The disposal of sludge and the acquirement of pure sand are not necessary like dredging and conventional sand capping works. Besides, the ecosystem will hardly be disturbed by this method.
A scale model test and field tests at Lake Suwa were carried out to study sediment purification effects, sand capping conditions and turbidity range. As a result, it was demonstrated that sand capping was succeeded by this method.Some characteristics of this method were revealed, the thickness and the area of the sand capping depended on the jet discharge rate and the sand diameter, the turbidity range was very small caused by this method. After seven months later, the field observation was carried out in Lake Suwa. The thickness of the sand capping layer and the aerobic environment were maintained. Also, many Limnodius appeared in the sand capping area.

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Improving and conserving the coastal environment and promoting proper use of the coast by the public were added to purposes of the Seacoast Law as well as shore protection. However, there are many issues to be settled for actualization of the purposes because some matters are in trade-off among shore protection, environmental conservation, and promotion of proper public use, and technical knowledge about coastal management considering natural environment is insufficient. Discussion on “Coastal management harmonized with nature” was conducted in a study group established by Sea Coast Division, River Bureau, Ministry of Land, Infrastructure and Transport. This paper shows the results of the discussion which involve its general idea, its basic policy, and important matters in its process.“Coastal management harmonized with nature” will be the standard of the future coastal management in Japan.

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The Japan Ocean Industries Association (JOIA) has been conducted the feasibility studies on the floating offshore wind power facilities. This paper summarizes the present state of the foundation types of the offshore wind power facilities in Europe as well as the studies of the JOIA, especially the concept of the struct-urety pes and the mooring systems of the floating structures. Also the studies on the optimal structure type in the water depth between 20m and 200m are presented.

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It is essential for Japan to investigate the possibility of a floating type wind farm on the ocean. A SPAR type structure is selected as a base of a 2MW-wind turbine set at sea of the depth 100m. An equation for the wind load on a rotor is deducted and the inclination of the SPAR is estimated. Then, after the motions among waves calculated by applying Morison's equation are examined with experimental results, the maximum inclination of the SPAR due to irregular waves is estimated as well. The total inclination seems to be allowable for the wind turbine generating. It is also found that the mooring point on a SPAR at the level of the gravity center is better for SPAR motion than the point at the level of sea surface.

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As the technology of wind turbine generators (WTG) has been largely developed, so we much depend on their turbine makers in designing. However the environmental conditions in Japan are significantly different from those where this technology originated; for example the magnitude of variability of sea conditions. Therefore we studied for the combinations of stresses due to wave and wind using time domain structural analyses subjected to fluctuating wind and wave loadings. In the study, the maximum stresses due to wave alone, ones due to wind alone and those due to both wave and wind were determined with the NOWPHASE data measured at off Miyazaki during typhoon number 18 in 1999. Furthermore we conducted Rayleigh forecasting of maximum stresses using the means stresses, and their standard deviations obtained from simulated stress histories. Making clear the relation between stresses due to wind and wave, this paper concluded that the maximum stresses may be simply the sum of both maximum stresses.

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In order to lessen vibrations caused by wind and wave loads, and rotational forces of blades acting on an offshore wind turbine, as well as oscillations by earthquakes, we studied to clarify the effect of seismic isolation and vibration -control mechanism attached to such a tower-like-structure. The scale model tests (1/55) were conducted for a blades-nacelle-tower-foundation structure of a 1500kW wind generator at the top. Two kinds of isolation rubbers are fixed onto the foundation againste arthquakes, whiles loshingd ampers are set to top of tower beneath a nacelle against the other vibrations. Both free and forced oscillation tests by rotating three blades were carried out for the models mounted either mechanism respectively. Meanwhile a response experiment of the model with sloshing dampers was carried out in a wind tunnel to determine the damping constants by comparing with the modal analysis. The paper describes the effects on vibrationreduction by these mechanisms as comparison of magnitude of responses and damping ratios.

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While many articulated buoyant towers connected to a gravity base with a universal joint have been constructed for navigational aids on the sea bottom, such as in Tokyo bay, Japan's Coast Guard has planned to develop advanced navigation aids system to mark ships navigation routes by laser lights. This kind of heavy duty tower would also require added its stability and motion characteristics for the winds and waves. Therefore we conducted a 1/20 scale model test to measure wind loads acting to the deck of the tower and inclinations of the tower by using a wind and wave tunnel. In this study, first we obtain drag coefficients for wind loadings on the deck as well as added mass coefficients of the tower by the natural free oscillation test. Then we compared test results with time domain analyses to determine the inertia and drag force coefficients of the tower. The paper also describes the transverse oscillation due to steady and fluctuating wind, wave loadings and combined wind and wave loadings.

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The DEMATEL (DEcision MAking Trial and Evaluation Laboratory) method and ISM (Interpretive Structural Modeling) were used to elucidate the factors responsible for an insufficiency in the number ofnew recruits to the fishing industry and to determine the effectiveness of strategies to overcome this problem. The contribution of each factor to the problem of insufficiency in the number of new recruits to the fishing industry and the correlations between these factors were analyzed using the DEMATEL method. Then ISM was used to stratify the cause and effect relationships between factors by utilizing a direct effect matrix derived by the DEMATEL method. The validity of the DEMATEL method and ISM were examined on the basis of results of analysis using the DEMATEL method and the results of analysis of cause and effect relationships using ISM.
Moreover, the effectiveness of each strategy for solving the causes of the problem was evaluated, and the overall effectiveness of a strategy to resolve the problem including the total effect of all of the factors, as determined by DEMATEL, was evaluated.

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In this study, the mass-flow of material in individual industries in fishing area is analyzed to show material balance, and to extract the problems in establishment of the recycling-based society. The analysis counting nitrogen as the index material results in following facts. The material flow in this area is not like closed-cycle caused by 3 problems, input mass exceeds shipment in agriculture, inflow material exceeds catch and outflow in lake Saroma, a larger part of raw material changed into wastes in marine product processing industry. To establish the society, 6 ways of measures are thought up, such as fertilizer and feed production from scallop viscera, fishing field development, promotion of lake water exchange and so on. The approximate costs to balance in lake Saroma is estimated and compared to the benefits (losses in case no measure were taken).

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The shoreline of the Teradomari and Nozumi coasts extending around the mouth of the new Shinano River, which was a floodway excavated in 1923, had been advanced due to the rich fluvial supply from this river. However, in recent years, natural sand dune was largely narrowed due to the beach erosion associated with formation of wave shadow zone caused by the extension of the breakwater of the Teradomari Port. Furthermore, excess progression of coastal forest occurred. Thus, natural scenery of this coast is rapidly changing to an artificial poor coastline. These situations were analyzed by comparison of aerial photographs and field observation.

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Preventive method of beach erosion and accretion triggered by the formation of wave shadow zone associated with extension of port breakwater is investigated through the field observation, taking the Shimohara fishing port in Tateyama City in Chiba Prefecture as the example. This phenomenon is well-known in coastal engineering, but in Japan this kind of beach erosion and accretion have been repeatedly reported. In order to solve this problem, not only the research in engineering method, but also improvement of the environmental assessment system are required so as to include the prediction of topographic changes in the items of environment assessment.

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Relation between beach erosion and the development of coastal forest was investigated by comparing past aerial photographs, taking the Heisa-ura coast in Chiba Prefecture as the example. Sand dune has been well developed at this coast due to the strong wind-blown sand in winter in the past. In order to prevent the damage due to wind-blown sand, coastal forest has been extensively planted. However, excess development of coastal forest in recent years as well as the construction of earth dike along the coastal forest caused shoreline recession by the excavation of beach sand to supply the construction materials. Appropriate land management isrequired between the coastal forest area and the shore protection area in order to avoid devastation of natural sandy beach.

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After the East Groin of Ishikari Bay New Port subsided, we gathered data on the average caisson height and on the significant wave height measured at the surface where the water depth was 24m in the sea offshore of the port. These two types of data were compared to investigate the relationship between the subsidence and waves. Also, we examined the causes of the subsidence and countermeasures based on the results of post-subsidence surveys, including an onsite survey. The examination revealed that when high waves cause subsidence that progresses to some extent, there was no major subsidence after that extent. The post-subsidence soil survey confirmed that the scour occurred after the subsidence. The onsite survey indicated that mat installation was an effective countermeasure against scour.

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Hydraulic model experiments on the stability of rubble mound foundation of composite breakwaters against wave action were conducted in a large wave flume, where the failures of rubble mound were reproduced. Sliding of the caisson was also occurred by the decrease of friction coefficient due to the settlement of rubble mound even the initial sliding safety factor is larger than 1.2. Numerical calculations of expected settlement due to mound failure using Monte Carlo simulation were also conducted in order to compare the experimental results. Calculated settlement was larger than experimental one because the elastic deformation of rubble mound foundation was not taken into account in the calculation.

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A numerical model is proposed for the pore pressure build up in soil around a pipeline subjected to horizontal cyclic loading. The model is based on results of centrifuge tests, and the effect of various factors on the pore pressure build up is investigated through some examples using the proposed numerical model. Itis found that the pore pressure build up component due to horizontal cyclic loading depends significantly onthe initial settlement ratio as well as the ratio of horizontal to vertical load. It is also shown that a peak appears in the pore pressure build up response when the initial settlement ratio is larger than about 0.2.

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This paper describes model test results of suction foundations on the stability and the applicability of a proposed design method.
The model tests are conducted by applying static horizontal loads to structures using suction foundation in a soil tank to investigate the performance of suction foundations subjected to horizontal loads. The model test results are also used to examine the design method of the suction foundation. The model tests show the horizontal displacements of the structures using the suction foundation against the horizontal loads become small with the increase of the penetration depth of the suction foundation. And the failure loads estimated by the design method conform to the model test results.

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A new material (FA mortar) which is mainly made of coal ashes is investigated experimentally and numerically for the use of sucking prevention behind the backfill of a caisson in place of a sheet.The validity is confirmed in the present study and based on the investigations, the test execution has been conducted in Naha Port.

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This paper is prepared to propose fundamental points to be considered for design of caisson walls against breaking impulsive wave pressures. This have been obtained through field surveys of damages which have occurred over the past 30 years due to breaking impulsive wave pressures, and through a analysis of extent, characteristic, cause etc. of such damages. It was found, as a result of our study, that there is a relationship between actual failure level and cracking moment and safety factor (ratio: initial cracking moment against actual bending moment), and that this brings about a possibility to establish a practical design method, applying Goda pressure formula in consideration of the impulsive pressure coefficient (Takahashi et al.) ³⁾ .

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A simplified theory to calculate the total wave pressure exerted on a slope of mound breakwater is proposed. Its applicability is examined by comparing the theory with the results of numerical computations. Discussionis also made on the properties of the pressure attenuation inside the core of breakwater. Throughout this study, it is clarified that the theory will assist the design of a rubble mound breakwater to be built on a soft subsoil by providing an estimate of wave force on the breakwater and the subsoil.

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Permeable mounds made with concrete armor units are placed in front of some of the cooling water outlets of steam or nuclear power generating stations in Japan, which not only diffuse discharge flow, but also prevent the channel systems connected to outlets from severe wave effect. Both high and low water levels at the upstream side of the energy dissipating mounds should be determined for the design of such channel systems. However, the prototype values of the loss coefficient of armor units have not been reported. A new method to determine the coefficient from the values of up-and downstream water depths and discharge per unit width is proposed, and applied to a set of prototype data. An evaluation of prototype loss coefficient for tetrapods and the method to calculate upstream water depth are shown. The drag coefficient of tetrapods to be used in the dynamic equations in the combined porous body and VOF model is mentioned as well.

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The hydraulic characteristics of block mound seawall with single armor layer are investigated by 2-D model tests. The differences in thickness of armor layer are discussed on wave reflection, wave overtopping and wave force on crown wall. Based on the test results, the necessary height and width of the crown wall can be obtained for the design conditions. The stability of HAMA-BITE, newly developed block for single armor layer, is examined by wave force and stability tests. For thepractical design of block mound seawall with single armor layer, the stability number of HAMA-BITE is formulated as the function of the relative damage level and the number of wave action.

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The seawater exchangeable breakwaters may be useful to exchange the seawater and supply oxygen for improvement and preservation of seawater and sediment quality. In this study, we propose a modified curtain-wall type seawater exchangeable breakwater and examine its performance by physical model tests and numerical simulations Both the damping wave model and the volume of fluid method are employed in numerical simulations. The main feature of a modified breakwater is to place a submerged horizontal plate in the water chamber, which plays an important role to reduce both the reflected and transmitted waves for the wide range of wave frequency. It is also found out that the modified breakwater can cause aeration and vertical mixing by wave actions

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We have already presented a new type of reflection wave dissipater which has a curtain wall in front of the vertical seawall.The mechanism of the dissipater is to enhance vortex flows around the lower edge of curtain wall by the use of piston mode wave resonance in the water chamber. In order to expand the usage of the new type dissipater, performance of the dissipater in obliquely incident waves is examined extensively, including normal incidence of waves.The dissipaters adopted in this study are a single water-chamber type and a double water-chamberty pe. The latter is intended to expand the effective range of wave period. Applicability of the numerical analysis based on the damping wave theory is also examined precisely for both the normal and oblique incidence of waves.

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The water pollution in the harbor is one of the most crucial topics today. A permeable breakwater and a seawater exchange breakwater have been developed in order to settle the water pollution problems in a harbor. Recently, a new procedure for improving seawater property using vertical mixing is proposed.
In this study, we investigate the characteristics of vortex induced large-scale circulation and mixing around a curtain-walled reflection dissipater. The mechanism of vortex appearance around a curtain-walled reflection dissipater is investigated through a numerical simulation and hydraulic experiment.

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Pontoon-type floating breakwaters have been adopted everywhere in Japan. Especially for improving the ability of reducing transmitted waves for comparatively long waves by the floating breakwater, various studies have been carried out. In this study, to improve the high reflective feature of the pontoon breakwater for comparatively short waves and also to expand the effective range of wave period for the reduction of transmitted waves, we apply the two additional devices to the pontoon breakwater; vertical-barrier-type reflection dissipaters and submerged horizontal plates. The formerd evice is intended to reduce reflected waves from the pontoon for comparatively short waves. The latter is to expand the effective range of wave period. There are two dissipation mechanisms presumed in this model. One is to enhance vortex flows around an outside vertical barrier by the use of piston-mode wave resonance in the water chamber. The other is effective usage of radiated waves by the oscillating floating body, especially for comparatively long waves.

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In order to settle the water pollution problems in a harbor, various resolutions, such as a permeable breakwater and a seawater exchange breakwater, have been proposed and developed. In this study, usage of a permeableb reakwater as a resolution of the water pollution problem is examined. A double-walled breakwater is used as a permeable breakwater, which is consisted of an inclined plate array as a front wall and a curtain wall with some spacing near the seabed as a rear wall. We have already presented the wave transmission and reflection characteristics about the double-walled breakwater.
In order to clarify the water exchangea bility about the double-walled breakwater, the 3-D experiment about a model harbor is carried out. The mass flux by wave actions through the harbor entrance and the spacing beneath the double-walled breakwater is examinede xtensively. We also observe the mean flow pattern around the permeable breakwater for various wave conditions.

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A water-exchanging slit caisson can exchange water inside of the harbors to reducee nvironmental pollution. In order to clarify the hydraulic characteristics of the water-exchanging slit caisson, three-dimensionanl numerical simulation was carried out, and quantities of exchanging water through the hole and wave transmitting coefficient were calculated. And the results were verified by using model experiments. It is confirmed that the quantities of exchanging water were related to the period of wave. So the numerical simulation is useful to predict the hydraulic characteristics of the caisson.

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This paper describes i nteraction of surface/internal water waves with floating/submerged platforms by considering nonlinearity of fluid motion and flexibility of oscillating structures. The model represents a multilayer fluid system interacting with horizontally very large and elastic thin-plates, where the set of governing equations is derived by vertical integration in each fluid layer with nonlinear boundary conditions satisfied on the interfaces. Numerical computation is performed for surface/internal long waves and floating/submerged plate oscillations in the vertical section. Resonated pressures beneath a floating plate on the sea surface in a two-layer system are obtained in forced oscillation cases by taking into account different order of wave height to water depth ratios. In free oscillation cases surface and internal waves interacting with a floating or submerged plate structure are calculated. Progressing waves are also simulated under floating structures whose flexural rigidity changes spatially.

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