A great demand for the guarantee of“safety and reassurance”of foods is extremely high among consumers, fuelled especially by the outbreak of O-157and BSE problem. This paper presents the strategies for establishing environment and hygiene management in fishing ports, making Shibetsu fishing port of Shibetsu into advanced example. We suggest a couple of solutions; the first isthe rationalization of the fish landing area centered in the port of Shibetsu by zoning the water and land areas according to the expected hygiene level.The second is the installation of a roof covering over landing and handling areas to keep fish catch fresh as well as the area sanitary. These solutions give good effects on the local economy whiling enhancing the Shibetsu fisheries brand.

View full abstract

In this paper, a marine phytoplankton trapping system, which is composed of a seawall-like structure with a function of the wave pump (wave-current conversion device), a deposition tank and an open channel, is proposed with an aim of improving seawater quality and utilization of phytoplankton as biomass. Time-averaged flow fields induced in this system by wave action are analyzed by meansof a 2-D numerical wave tank taking the κ-ε turbulence model together with the VOF method developed by Hirts and Nichols. A series of laboratory tests on flocculation of marine phytoplankton by using PAC and γ-PGA are made and the sizes of flocks as well as their terminal velocities are measured. Based on the result of these analyses and tests, quantities of trapped phytoplankton are estimated.

View full abstract

To evaluate the water quality of sea areas in Japan, the public observation data on water quality were collected. And, the index of the water quality, which has obtained from the five factors (COD, TN, TP, DO and coliform group) at 952 observation points by the principal component analysis, was proposed. And, the relative water qualities at the 952 observation points were evaluated with the water quality index. The evaluation shows that the water qualities are relatively bad in sea areas near the big cities and in large harbors. Then, the relationship between the water quality index and physical conditions of bay (bayopening-width, tides, average-bay-depth, etc.) were investigated about 56 bays. Except some bays of very bad water quality, it was found that the water quality becomes good with the increase of bay-opening width.

View full abstract

This paper deals with nutrient dynamics caused by sediments resuspensioin noxygen-depleted offshorea rea.I ti sconsidered that ammonium (NH_4^-N) adsorbs to sediments and nutrient cycling varies with decomposition of particle organic matter in resusupend sediments in laboratory experiments. As a result, for one thing, Water-sediment partition of NH_4^-N which indicates sorbable amounts is formulated using dissolve oxygen in water column. For another, as well as thetime when it is stationary culture when it is suspension culture for sediments, concentration of NH_4^-N variation in water column is related C/N ratio in sediments and it is indicatetd hat concentration of NH_4^-N variation have a seasonalitypattern from laboratory experiments.

View full abstract

Braid adsorbent having functional group of amidoxime is a promising material for the recovery of uranium dissolved in the seawater. This braid adsorbent was made by polyethylene multi-fibers which were fictionalized by radiation-induced graft polymerization and subsequent chemical treatment. There was correlation between the grafting time and the degree of crystalline orientation of the fiber. The braid adsorbent obtained was moored at the offing of Okinawa Island. The adsorption of uranium increased three times when the stacks of cloth adsorbent was soaked in seawater at the offing of Aomori prefecture. It was found that the braid adsorbents could improve the efficiency of contact between the adsorbent and the seawater. Moreover, the mooring system has possibility which reduced the cost for the recovery of uranium from seawater.

View full abstract

The density of uranium in the seawater is only 3 mg/m³, but its total amount is 4.5 billion tons. In the last report, the braid type adsorbent was proposed with its mooring system for the collection of the uranium from the sea. And, it was shown that a high performance of the adsorbent and a big fall in weight of the mooring system are feasible and there's no problem of the adhered creature. In this report, it is shown that 134 km² of mooring basin is needed for annual product of 1200 tons of uranium. In addition, 6000 km² and over of suitable basin for the collection of the uranium is shown between Okinawa Islands and Tosa Bay.

View full abstract

We designed a wave warning system for installation on a waterfront amenity seawall with a wave-dissipatingfunction. This system can visually warn people on a breakwater against wave overtopping by water spouting fromoutflowp ipes. We clarifiedt he basic performanceo f the inflowa nd outflowp ipes, whichw ere installed on the body and superstructureo f the wave warning system respectively. A hydrologicalm odel experimentw as conductedt o optimize the shape of the inflow pipe, the ratio of the diameter of inflow pipe to that of outflow pipe, and the location of inflow pipe installation.

View full abstract

A technique is presented for rapid detection of sea bed sediment property using a free-falling type accelerometer. The measurement of deceleration during the penetration of the instrument into the sea bottom sediment allows for detection of the vertical profile of the sediment strength. Comparing output data from the system obtained in the field measurement with analyzed results of core-sampled s edimentss hows good detection of vertical structures of sediment properties, such as water content. There is high inverse correlation between the measured bearing strength and the water content especially for sediments with higher mud (silt and clay) content. Based on these measured data, this system appears to be utilized for spacial and temporally frequent monitoring of sedimentary environment.

View full abstract

In this paper, the wave observation system by arrayed buoys whose three dimensional movements are measured precisely by the kinematic GPS is proposed. Firstly, the general concept and system configuration of this observation system are described. The proposed wave observation system measures the three-dimensional movements of each observational buoy relative to the fixed reference station by the kinematic GPS. Because the distance between the reference station and each buoy is about several kilometers at most, the measurement error of the kinematic GPS can be estimated less than a few centimeters. The data of each observational buoy are sent to the reference station by radio telemetry system, and then the data are used to estimate effective information about wave such as period, wavelength, height and direction. Finally, it is shown that this proposed system is able to estimate the propagation directions of waves of the same period propagated from various directions by high resolution and analyzing ability.

View full abstract

Intensive field observations have been conducted in Zanpa Area of Okinawa Island offshore to figure out the characteristics of the vertical profile of tidal current. In the bottom layer, due to the steep slopping shelf along Zanpa Coast, amplified tidal currents have been found, as we can observe in an air flow passing over a hill. Despite the effects of bottom friction, current velocity becomes higher in the bottom layer through the effects of abrupt contraction of the depth. This trend of the current velocity-increasing is observed only near the hedge of the shelf. The vertical distributions of water temperature and salinity concentrationalso show the existence of up-welling flow near the hedge of the shelf.

View full abstract

[in Japanese]

View full abstract

The similarity law of the wind velocity in wave-overtopping experiments is not known. Then, in this study, the correspondence of the wind velocity in the wave-overtopping experiments to the one in the real coast was investigated experimentally based on the results of the field observation of wave-overtopping conducted by Fukuda, et al.(1974) in 1971-1972 at Niigata east port. Wave-overtopping rate, incident waves, wind direction and wind velocity, etc. were obtained in that observation. The experiments were conducted by using two-dimensional wave tank using the 1/45 reduced scale model. Generating the wave and the wind at the same time, wave-overtopping rates were measured. And the rates in the experiments were compared with the ones of the field observation. It was found that the wind velocity in the experiment becomes about 1/3 of the wind velocity of the real coast.

View full abstract

Artificial reefs have been used to protect coastal erosion, and are now replacing detached breakwaters. When we establish a submerged breakwater or an artificial reef, it is known that a topography change sometime causes score around them. According to the analysis result using the bottom sounding carried out before and after construction, if it have the openings, the erosion generated in the center of opening or the offshore. The transmission wave to the shore side across the reefs changes as return flow, and is flowing out into the offshore field. It is important that evaluation of the flow strength near the bottom to predict geographical feature change due to the structure establishment. Moreover, the size of an undertow has a close relation to opening width. This research performed the numerical calculation of the flow distribution around the opening for the artificial reefs established at a certain spot, and considered the flow velocity distribution of the return flow around the opening.

View full abstract

There are a lot of researches on the run-up of waves which propagate onto plain beaches. The results from them have been contributing to the estimations of wave run-up height for the real planning of maritime structures and the managements of coastal zones. Contrary to this, however, not enough knowledge has been given on the run-up phenomena of long-period waves on complex beaches, because of the difficulty of numerical simulations of breaking and run-upping waves and restrictions of experimental equipments for long-period waves.
Koshizuka has developed a numerical simulation method for breaking and run-upping waves on a beach, based on the particle analysis. This Koshizuka's method is applied to analyze the run-up height of long-period waves such as Tsunami or solitary wave. The results are verified by Synolakis's experimental data for the run-up heights for the plain beach.

View full abstract

The real-time prediction of the storm surge at each port and coast is necessary to mitigate the coastal disaster. The storm surge can be computed in a few hours or less with a numerical model based on long wave approximation by an ordinary personal computer, while the maximum storm surge can be quickly calculated with a simple empirical equation based on the past storm records. In this paper, the storm surges at major points in east Seto Inner Sea, including Osaka Bay, and Tokyo Bay are predicted with the both methods and their results are compared with the measured. As the result, the magnitude of the storm surge by the empirical equation was sometimes larger than the measured and the time, of the peak was sometimes earlier by a few hours. For the exact computation of the storm surge, the spatial grid interval for the numerical model should be around 1.8km for the major points on the coast of Osaka Bay, 0.6km or less for the central Seto Inner Sea, and around 0.6km for Tokyo Bay The run of a typhoon should be started on south from the north latitude of 31 deg for the storm surge prediction of these bays.

View full abstract

Global warming and its accompanying sea level rise will be serious issues in the future. According to the Intergovernmental Panel on Climate Change (IPCC), a global average sea level rise of 9cm to 88cm is projected for 1990 to 2100 and a steady increase of sea level for all of the scenarios considered is expected. In the coast regions, coast disasters caused by storm surge coupled with sea level rise are likely increased. To examine adaptation strategies against the increased coastal hazards, it is important to understand the characteristics of storm surge events. The aims of this study are to determine the most dangerous typhoon conditions in the Suo sea, to compute the maximum storm surge height, and to estimate the possible inundated areas by using GIS.

View full abstract

Three-dimensional experiments are conducted in a wave basin in order to investigate deformation of submerged breakwater and change in hydraulic performances with its deformation. Transmission coefficient is used as an index of the hydraulic performance of the submerged breakwater. The crest height at the submerged breakwater head decreased in a few cases. However, the authors show that the value of the transmission coefficient did not increase in many cases even though the submerged breakwater was deformed. The authors also show that the incident wave with longer wave period deforms the submerged breakwater more and the rubble stones from the eroded area are accreted at the region of 0.25 L_1/3 from the submerged breakwater head.

View full abstract

A numerical analysis model for solving non-linear wave-structure interactions, based on the coupling of a Boundary Element Method (BEM) which is applied to the region far from the structure where the fluid motion is less non-linear and a Volume Of Fluid (VOF) method which is applied to the region around the structure where the fluid motion is highly non-linear, is developed.
Two methods were combined under the principles of continuities of the velocity and the pressure. The validity of the method was checked comparing the numerical results with the experimental ones for surface oscillations around a submerged breakwater. Consequently, combined method can calculate wave field including wave breaking, with the same accuracy of VOF, and with much shorter CPU-time.

View full abstract

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 dissipater to the sea with comparatively large tidal difference, performance of the dissipater for various water levels is examined extensively. As a countermeasure to the variation of performance with tidal difference, we propose two different types of dissipaters, i. e., a vertically inclined wall unit and a combination of different draft wall units along the shore. Effectiveness of such dissipaters is examined experimentally and theoretically for various water levels.

View full abstract

We have proposed a triple-walled breakwater with different draft depths, which is supported by steel piles. It aims to reduce both transmitted and reflected waves for comparatively long waves such as swells. In this study, performance of such a breakwater in obliquely incident waves is examined experimentally and theoretically. Effect of partition or separation walls between the breakwater units on the performance is extensively examined. It is confirmed that the triple-walled breakwater is effective for obliquely incident waves in the same manner as the normal incidence. In oblique waves, however, the installation of partition walls is strongly recommended to reduce the reflected wave for comparatively long waves.

View full abstract

The breakwater and revetment constructed in the wave breaking zone are normally covered with wave-dissipating concrete blocks in front of the upright structure to decrease wave overtopping, transmitted wave and to reduce wave pressure acting on the wall. There is the upright structure with detached wave-dissipating concrete blocks, which is a kind of structure described above. In general, the detached type may be more effective measures to decrease overtopping and/or transmitted wave than the covered type. The problem is that the both of overtopping rate and transmission coefficient of the detached type cannot be estimated quantitatively. Moreover the wave pressure acting on the wall is unknown for steep bottom slope. In this study, we examine the performance of the two detached type models for bottom slope of 1/10 by physical model test and numerical simulation. The volume of fluid method is employed in numerical simulation. As a result, we can obtain the rate of overtopping, transmission coefficient and water elevation in wave chamber. It is also found out that the wave pressure acting on the wall is impulsive.

View full abstract

Flaring Shaped Seawall (FSS) can drastically reduce a crest height and wave overtopping volume in comparison with a conventional upright one, and a top area of the FSS can be used effectively. In this study, hydraulic experiments and numerical simulations for the FSS on the mound have been carried out using a twodimensional flume model. As a result, the wave overtopping rate and flow velocity by the numerical simulations are in agreement with those by the experiments. Good agreement between numerical results and experimental ones is found in not impulsive wave pressure. However, it is necessary to investigate an impulsive wave pressure furthermore.

View full abstract

This paper presents the results of examination on wave transmission over a low-crest artificial double reef which is made of wave dissipating concrete blocks. In the experiment, the ratio of the submerged depth of crown of reef to the incident wave height, R/H_I, was set in the range of 1.10 to 4.98. The relative width of the reef against wave length, (B₁+B₂)/L varies from 0.76 to 2.16. The relative spacing of the structures against wave length, l/L has a variation form 0.23 to 1.30. In the case of total width of double reef, B′(=B₁+l+B₂) is equal to width of single reef, B₀, K_T of double reef is almost equal to K_T of single reef. K_T decreases following an increase in B/L, and K_T becomes the minimum value in the case of l/L=0.23 or 1.10.

View full abstract

To increase calmness at Furubira Fishery Port in Hokkaido, Japan, construction of an east groin was planned. One requirement for the groin was to efficiently controls invading waves from the outside of the port and reflected waves from inside. A permeable double slit-caisson structure was selected for its permeability and ability to dissipate waves on both sides. A groin with such a structure dissipates waves on both its seaward-facing and portward-facing sides, allowing it to reduce reflective waves and increase calmness inside the port. A hydraulic model test using a two-dimensional wave channel revealed that incorporation of holes in the internal wall of the caisson affords wave-dissipating ability against long-period waves.

View full abstract

To analyze the wave reflection and transmission from slit type structures, it is indispensable to estimate energy loss at slits. Several methods estimating energy loss have been proposed. However, most of the configurations have been treated are uniform shaped structures such as a row of cylinders.
Recently, structures of non-uniform configuration are often constructed as, say, seawater exchangeable breakwaters. Therefore, it is necessary to construct a new method suitable for non-uniform shaped structures. In the present study, a concept of complex blockage coefficient is adopted in the Boundary Integral Method, BIM, with some modification. Comparison of the BIM-results with experimental results and numerical results by the Volume Of Fluid method, VOF, shows the validity of the present method.

View full abstract

The curtain wall type intake is often used in the intake of the thermal power plant and the nuclear power plant. Because wave force acting on the steel pile which supports the water interception board is large, the cost of construction of this structure is high. Therefore, we designed the curtain wall that has the hinge in the upper part of the water interception board. The water interception board of this curtain wall synchronizes with the wave and wave force acting on the steel pile can be greatly decreased.
In this research, we executed the hydraulic model test intended for this upper hinge type curtain wall. As a result, we understood a basic character of this curtain wall, such as the power to act on the hinge and the dynamics of a water interception board. And we executed the outline design of this curtain wall from the experimental result, and compared the life cycle cost with a past curtain wall. The reduction in about 17% can be expected of the life cycle cost of this curtain wall compared with a past one.

View full abstract

The piled pier with the wave control screen has been newly proposed in order to be able to suppress the wave up-lift which affects the slab. The physical model test with two-dimensional wave flume has been conducted to find the optimum layout condition of screen and to obtain the external design condition for this type of pier. Further, CADMAS-SURF (Super roller flume for computer aided design of maritime structure) has been applied prior to the physical model test in order to know the outline for characteristics of horizontal and up-lift force. As result, it has been presented that the wave control screen was greatly effective to suppress the wave up-lift, and that the mathematical wave flume model was useful the qualitative analysis such as pre-study of physical model test.

View full abstract

The concrete blocks used for coast, ports and fishery harbours have been made as a function for every use. Authors developed the new type armor block with not only the effects of armor but the effects of wave attenuation and eco-reef for fish, and have studied about the using the block as armor block of the artificial reef especially in the case of applying to the deep sea area.
The paper mentions, in the case of applying this new type armor block to the face of the slope of embankment and armor block of submerged breakwater, the execution of hydraulic model test for the purpose to dear the stability number to analyze proper necessary weights on terms and condition of significant wave height etc.

View full abstract

Since rubble foundation of composite breakwater in construction has no armor layer, the stability of rubble stone for waves is generally low. Thus, it is important to know the stability and the extent of damage of rubble foundation in the view of construction. In the present study, hydraulic model tests were conducted to investigate a relationship between a stability of rubble foundation and crown height of rubble foundation. In the case of irregular waves, these results suggest that the extent of damage of rubble foundation and Ursell's number on the rubble mound correlate to a high degree. Added to this, it is shown that the method combined CERC's equation with CADMAS-SURF proposed by Matsumoto and Takahashi (1998) is valid for estimating a mass of rubble stone for regular waves.

View full abstract

Many thermal power plants and nuclear plants apply curtain wall intake method that utilizes the deeper, i. e. the colder sea water to efficiently cool down the power plant system. In general, the curtain wall structure consists of rigid PC shielding wall and steel pipe piles that supports the PC wall. In order to retain the structural resistance to large waves and various subsurface conditions, the curtain wall structure tends to become large and therefore increase the construction costs.
We thus propose a membrane certain wall which is expected to reduce the construction costs. Since the membrane curtain wall itself is light and flexible, it also reduces the wave force acting on the wall and therefore enables us to apply relatively simple structures to support the curtain wall.
In this study, we conducted the hydraulic model tests to explore the characteristics of wave force acting on the membrane curtain wall. Through the experiments, we tested several membrane curtain walls with different structures and examined their structural effects on reduction of the wave force.

View full abstract

Through hydraulic model experiments, we clarified the characteristics of wave transformation and wave pressure acting on an upright wall of the breakwater on the ultra-steep seabed and come up with the countermeasures in order to avoid an impulsive pressure or alleviate such an exceptional wave pressure.
The results of the study are as follows: As for wave transformation, wave height doses not increase on the ultra-steep seabed. Wave pressure as well as the generation ratio of an impulsive breaking wave pressure decreases as the breakwater moves forward to the offshore. There hydraulic phenomena are related to the ratio of wave height to water depth and mean bottom slope. In the case of a sloping breakwater, the generation ratio of an impulsive breaking wave pressure diminishes and its size reduces to a half that of an upright wall. The transmitted wave height of a sloping wall is almost equivalent to that of an upright wall.

View full abstract

This research investigated the difference in the characteristic of wave forces which acts on the superstructure by the existence and the scale of lower caves. The section form of sloping breakwater where settlement of wave dissipating blocks was taken into consideration was set up, and analysis using numerical wave flume (CADMAS-SURF) was carried out. As a result, horizontal wave forces acting on the superstructure increased with damage progress, and it is found out that sliding stability damages the damage section 2. Moreover, when the cave under superstructure exceeded 1 m, it became clear that sliding stability is damaged also for the basic section. The deformational limit of the dissipating blocks to the sliding stability of superstructure and the size of the cave under superstructure were clarified. These results are contributed to repair propriety judgment of wave dissipating blocks covering sloping breakwater.

View full abstract

One of the important characteristics in the propagation of ship waves is to reduce the wave height with the increasing distance from the sailing line. In addition, the transformation due to wave shoaling and refraction must be considered in case that ship waves propagate on a sloping coast. In the present study, a method to estimate the maximum wave height has been proposed on the basis of results of numerical simulation for ship waves that are generated by a ferry sailing along the coast with straight, parallel depth contour lines. The proposed formula of the maximum wave height is the product of the relative shoaling coefficient, the relative refraction coefficient, the relative damping coefficient and the characteristic wave height defined at an appropriate distance from the sailing line. The coefficients are calculated by using the finite amplitude wave theory for shoaling and Snell's law for refraction. The damping coefficient is calculated so as to be proportional to -1/5^th power of the distance from the sailing line. The maximum wave height estimated by the proposed method agrees well with the one by numerical simulations.

View full abstract

Various factors affecting the velocities of longshore currents induced by obliquely incident random waves are examined through numerical calculation and literature review. Several models of the random breaking process are used for mutual comparison. These models produce some differences in the estimate of wave height decay in the surf zone, and the differences cause large changes in the longshore velocities. Efficiency of horizontal mixing also depends on the wave breaking model employed. The eddy viscosity formulation by Larson and Kraus (1991) is found better suited to random waves than those by Longuet-Higgins (1970) and Battjes (1975). Introduction of surface rollers in numerical models is necessary in shifting the longshore current profile toward the shoreline and brings forth appreciable strength of longshore currents at the trough of a barred beach. Compared to significant consequence of the selection of wave breaking models, eddy viscosity, and surface roller strength, a questionof linear or nonlinear formulation of shear stress along the seabed seems trivial.

View full abstract

In this study, to gain an assessment referring to the number of waves of irregular wave used in the laboratory tests, the influence of wave signal length on the damage level of armour layer is investigated by the experiments. Furthermore, the statistical properties of the high wave and its wave grouping relating to the damage of armour layers are investigated by changing the wave signal length.
The appearance probability of high wave exceeding the critical wave height that brings about the damage of armour model has been analyzed using the Rayleigh distribution. It may be found from this analysis and experiments that 600 waves give a tentative criterion for the number of waves of irregular wave train used in the laboratory tests. Furthermore, to explore a better insight into the criteria for the number of waves, statistical evaluations of the run length of the high wave exceeding the critical wave height in every irregular wave train are provided.

View full abstract

The long period oscillation (LPO) with high amplitude (1m) and period less than 5-minute was observed at Shimohaya Bay in Wakayama Prefecture in a storm. The sea wind gustiness and wave group observed at the offshore area had the nearly same period as the LPO. We had the numerical simulation of the LPO, assuming that the LPO was generated by only groupness effect of breaking waves. The results showed enough intensity of amplifying of long wave by topographic resonance (6-minute long wave was amplified more than 10 times in Shimohaya Bay). However, the high amplified point was not restricted in Shimohaya Bay by the simulation.

View full abstract

Transmitted waves due to overtopping and due to waves which pass under the caisson in a discharge flume is sometimes a problem for stable operation of pumping works. The currents make influence on not only the transmitted waves but also the incident waves. The phenomena, therefore, might be quite complicated. To understand the phenomena, the hydraulic model tests were carried out. The transmitted waves due to overtopping in the currents sometime quite larger than the transmitted waves without currents. To simulates the transmitted waves, a new methods is proposed. The methods are based on the Bousinesque equation. The mechanism of the flow under and over the caisson are modelized by a simple pipe flow and non-linear long wave equations. The method is quite capable to represent experimental results.

View full abstract

Laboratory examinations were undertaken to clarify the deformation behaviors of water proof sheet, applied at a seepage control structure in an offshore waste disposal site. We examined a pressure resistance of PVC sheet which is installed upon backfilling stones of gravity-type bulkhead. As the result, the more the penetrating point of stone is smartened, the more the maximum strain occurred near the point. Pressurizing for 24 hours on a backfilling slope modeled actual seepage control structure in a waste disposal site, PVC sheet was deformed due to unevenness of backfilling stones, however, no breakage was observed. Local large strains (more than 10 %) were measured upon large degree of unevenness near the penetrating point of a stone. Those results indicate that the behavior of waterproof sheetdeformation during the penetration of a backfilling stone could be applied to the evaluation of waterproof sheet deformation due to unevenness of backfilling slope in a controlled waste disposal site.

View full abstract

The Technical Standard for Landfill Sites was amended in 1998 by the Prime Minister's Office and the Health and Welfare Ministry. Under this guideline, Manual of Design, Construction and Management at Coastal Disposal Site was issued by Waterfront Vitalization and Environment Research Center. This manual mentions some attentions when designing, constructing and maintaining disposal sites at sea. In addition, the technical subjects which are wished to be solved are also included. A damage detection system is one of them.
The authors are developing a damage detection system applicable in coastal disposal sites. This paper explains some results of a demonstration test of the damage detection system applicable at coastal disposal sites.

View full abstract

The standard of impervious structure about a disposal site was defined by the law 1999. However, with the past technology about impervious sea wall, it is very difficult to construct this type of structure meeting this law. Then, we proposed new structure and material about impervious sea wall, which maintains the performance of water interception over long period. This research paper reports the result of the field experiment about impervious sea wall structure with clayey water interception material.

View full abstract

More and more use of coastal areas for waste disposal has recently been expected because land-based disposal facilities have faced acute decrease of remaining capacity and large-scale facilities are possibleonly at coastal areas. While environmental consideration requires sever structural safety for the facilities to protect ambient area from contamination. This study quantitatively investigates sealing performance of embedded steel-plate cell as bulk-head for waste disposal by experiments and three-dimensional seepage flow analysis. Joint between cells is focused.

View full abstract

[in Japanese]

View full abstract

A mesoscale meteorological model, ANEMOS, was applied for wind hindcasting around the Seto inland sea area throughout the year of 2000. Then, coastal waves around the area were hindcasted using a third generation wave model, WAM. In this paper, we examined the accuracy of the hindcasted wind data as well as wave data in the Seto inland sea area by comparing the measured wind and wave data, and discussed the usefulness of the hindcasted data for practical applications. In addition, we introduced a wave hindcasting database equipped with a convenient graphical user interface.

View full abstract

The third generation wave model WAM, which was originally developed for simulating waves in deep and large open sea area, is applied for Tokyo Bay with introducing some modification and tuning suitable for simulating waves in inland sea area. The wave parameters as well as directional wave spectra in Tokyo Bay are simulated for 4 years from 1998 to 2001 with sea surface wind data computed by using a mesoscale meteorological model. Simulated monthly, seasonal and yearly wave conditions are compared with the observed wave conditions, and applicability of WAM for inland sea area is discussed with demonstrating its high utility.

View full abstract

A Boussinesq model which can calculate breaking waves in surf zone has been developed. The eddy viscosity coefficient in the momentum diffusion term for reducing the wave energy due to wave breaking should be estimated appropriately in order to reproduce the wave transformation in surf zone. In this study, wave breaking models are proposed by combining a bore model with models for distributing turbulence energy in time and space domains. The accuracies in the breaking wave calculations are verified by results of model experiments with reef and bar-trough bathymetries.

View full abstract

The purpose of the present paper is to establish the theoretical predictions for the vertical distribution of undertow inside a surf zone. The basic equation is based on an eddy-viscosity model and on an assumption that the average shear stress over a wave motion could be described in terms of the different linear function of the vertical distance from the sloping bottom at the two separate regions, which are the upper side and the lower one of the level of the wave trough. The coefficient of eddy-viscosity ν_t could be described in terms of an function of the vertical distance from the sloping bottom, just because the created vortices and turbulence in wave breaking will be spreading downwards from the water surface while decaying instantly. As a result in comparison of the results of our numerical analyses with Okayasu et al.'s flume tests, it is found that the change of ν_t has much effect on the characteristics of vertical distribution of undertow, especially near the bottom and surface, and is also shown that the surface vorticity has greater effects on characteristics of the vertical distribution of the undertow than any other factor.

View full abstract

The undertow is one of important factors which causes the disastrous erosion of beach. So far, the problems of this phenomenon have been treated both theoretically and experimentally by many investigators especially for elucidating the mechanics of transport of sediment. In order to establish the theory of undertow, it is essential to estimate quantitatively the vorticity of large-scale vortices induced on the water surface by breaking waves, because it is also one of main boundary conditions for solving the basic equation of undertow. Many theoretical estimation methods of the surface vorticity have been presented. Several ones are chosen for discussions and compared with each other in this paper. As a result, the calculation results of the surface vorticity by Nadaoka et al.'s method and Hirayama et al.'s one have a resemblance, and in comparison of the vertical distribution of undertow calculated by these methods with the experimental ones by Okayasu et al., it is shown that the surface vorticity has great effects on the vertical distribution characteristics of undertow.

View full abstract

This paper describes propagation of nonlinear water waves through a density-stratified fluid. The governing equations for a multilayer fluid system have been derived by vertical integration in each fluid layer with nonlinear boundary conditions satisfied on the interfaces. These equations, which can treat fluid density distribution inside each layer, are also applicable to compressible fluid motion with additional sets of equations concerning fluid density and pressure. Numerical computation was performed for surface and internal long waves in the vertical section using the simplified set which consists of the continuity equations and Bernoulli's equations for incompressible fluids having horizontally distributed density. The surface and internal waves progressing through the density stratified region, where the lower layer water is heavier than the upper, are simulated and the changing rates of wave height areobtained. The wave profiles change in space and time because of energy transfer between the surface and internal waves, which repeat transmission and reflection through the density stratified region, resulting in generating longer and shorter period waves.

View full abstract

Analysis of air bubble entrainment process in breaking wave is very important in the elucidation of breaking mechanism. Although some experiments have been carried out to investigate the processof air entrainment, this phenomenon still remains many uncertainties. In this study, hydraulic experiments have been performed to measure shapes of wave surfaces and vorticity due to wave breakings. As a result, it has been proven that both “ripple-like turbulent” and non turbulent regions exist together in the front surfaces of breaking waves and air bubbles are found to be entrained through the “ripple-like turbulent region”. Finally, the formation of the “ripple-like turbulent region” can be recognized by vortices produced due to wave breakings.

View full abstract

Komatsu et al.(1997) have proposed asymetrical bottom structure, that is “Bottom Roughness, ” as a new method to activate tidal exchange between a semi-enclosed bay and an outer sea. On the other hand, it is expected that vertical mixing is enhanced by the upwelling produced by the Bottom Roughness. The Bottom Roughness have been installed in the Isahaya Bay since September, 2002 as a field test to fix on soft ground peculiar to the Ariake Sea. In this research, in situ observations to measure time series of tidal current and water temperature at fixed points near the installed Bottom Roughness were carried out in order to examine degree of vertical current and vertical mixing. As a result of this research, it becomes clear that the Bottom Roughness can produce the downwelling when the current flows in the forward direction, meanwhile the upwelling is produced by the backward flow.

View full abstract