The authors have been developing a non-wave overtopping type seawall with a deep circular cross section (referred to a flaring shaped seawall (FSS) ). The seawall effectively controls waves by reversing incoming wave's motion on its curved face. This seawall creates a safe and useable space on top with a lower crest height compared to a conventional upright seawall. The basic characteristics of the FSS, such as wave overtopping, wave force and wave reflection, have been investigated through a series of experiments. Practical construction of the FSS has been scheduled in Beppu bay. However, because in practical situations wind is blowing, it is necessary to investigate the effect of wind on an FSS. In this study, the hydraulic model used in the experiments is scaled down from an actual site and we predict the wind effect on water spray and wave overtopping when the planned FSS is constructed on site.
Hydraulic characters of a Flaring Shaped Seawall (FSS) with a slit type wave absorbing structure installed on a mound are investigated through experiments with a two-dimensional wave tank. A row of circular columns is arranged in front of the seawall in order to reduce breaking wave pressure without disturbing an excellent checking effect of a wave overtopping. A critical wave height, which is defined as a maximum wave height on which no wave overtopping occurs at all, was measured on different incident wave conditions as well as mound shapes. The wave pressure distributions on the seawall, the wave reflection coefficient, and wave-overtopping rate were also measured. The reduction effect of the breaking wave pressure by the slit type wave absorbing structure is discussed under various incident wave conditions. And then, influences of the slit type wave absorbing on the wave reflection coefficient and wave-overtopping rate are also discussed in this study.
Seawalls constructed in rough sea areas are exposed to huge wave forces especially having a steep slope sea bottom in front of the structures. Hydraulic model experiments were conducted in a wave flume in order to investigate the characteristics of wave forces and wave overtopping for seawalls. Wave forces on seawalls constructed in deep water area can be estimated by Goda formula, while in shallow water area having a steep slope in front of the structure are often subjected to impulsive breaking wave force much larger than the force calculated by Goda formula. Wave overtopping quantity for the front wall can be estimated by Takayama formula, while the overtopping quantity for the rear parapet is proportional to that for front wall.
Wave forces and wave pressure acting on an axisymmetric caisson with slanting upper wall were investigated through hydraulic experiments and theoretical analyses. The vertical distributions of horizontal wave force were well estimated by the Morison's formula with velocity distribution calculated by the nonlinear wave theory and variable inertial force coefficient calculated by the diffraction wave theory. The horizontal wave force calculated by the linear diffraction wave theory is larger than the experiment results. The theory to evaluate the vertical wave force acting on the bottom of the caisson was developed based on the 2-dimensional infiltration equation. The vertical wave force is found out to change according to the water permeability of the sea bottom.
The present design procedures for the breakwater with footing ignore a wave pressure acting on the footing under the assumption that the compressive force on the upper face of the footing can be cancelled by the uplift force on the bottom face of the footing. This assumption is acceptable, but the experiments have confirmed that the compressive force becomes much lager for the case of long footing than the uplift force and works to stabilize the breakwater. We have proposed two empirical formulas for the distributions of uplift and compressive pressures. However, the validity of the formulas was not confirmed for random wave experiments. The present paper describes the confirmation of their validity thorough the experiments in random wave and numerical simulations. The empirical formulas are slightly improved.
The multiple functions of the fishery industry and fishing villages are stipulated as follows: “The national government shall take necessary measures to ensure that the fishery industry and fishing villages will discharge diverse functions other than fishery product-supplying functions. ”The Fisheries Basic Plan was devised in the following year, that is, in 2002, based on this law. To improve aspects regarding multiple functions among the measures to be taken, the Plan stated that an understanding of the multiple functions should be promoted and that ideal measures intended to advance these functions should be examined. In the Fishing Ports and Grounds Improvement Law and the Long-Term Plan for Improvement of Fisheries Infrastructure, which were devised concurrently, it was specified that improvements to the infrastructure should be promoted to ensure that multifaceted functions would be served. In this study, how multiple functions and their surrounding elements are recognized in Hakodate City, a fishing area, were analyzed through the mutual relationships of respective elements.
Input-output tables are useful in analyzing problems and tasks based on the industrial and economic structures in fishing villages. Therefore, such tables were compiled for five regions in Hokkaido (Rausu, Akkeshi, Nemuro, Tomamae and Minamikayabe) and the far reaching economic effects resulting from changes in the industrial structure and the creation of new industries to address regional problems and measures aiming to address other future problems were calculated by inputting variables into the tables. This research aims to highlight the common challenges facing fishing villages and fisheries in addition to the unique issues confronting each fishing village by comparatively analyzing the characteristics of the present industrial structure for the aforementioned five regions, so that the most effective measure for each region could be assessed.
In our fight against global warming, the ocean plays a vital role as a carbon dioxide sink. It is believed that marine and terrestrial (e. g. forest) areas absorb approximately half of the CO2 emissions caused by human activities (7.1 billion tons worldwide). On the other hand, fisheries cause large amounts of CO2 emissions in energy consumption among other production activities, and the carbon dioxide emission intensity of marine fisheries ranked 10th among all industries in 1990 (Center for Global Environmental Research, Independent Administrative Institution National Institute for Environmental Studies). This research aims to estimate the far reaching effects of reduced amounts of carbon dioxide discharged directly and indirectly by comprehensively evaluating CO2 balance and reflecting the result in the input-output table, as in Fig. 1, which are designed to analyze the fisheries environment, in which CO2 emissions from energy production are high.
Several types of wind countermeasure had been set up until now in fishery ports. To try to apply thinned woods for windbreak in fishery port, wind tunnel tests were carried out to obtain wind reducing effect of windbreak using thinned woods. Measurements of mean wind velocity were made in the lee of model fences. The test cases were three cases of model fences on breakwater with impermeability of 50%, 66%, 80% and one case on flat floor with impermeability of 66%. Results of the model tests showed that the case of impermeability 66% was most effective in comparison with three types of impermeability, and that the case of model fences on breakwater with impermeability of 66% was more effective comparing the case on flat floor with the same impermeability. By using these results, appropriate design for windbreak applying thinned woods would be conducted.
After back pain and lumber compressive force are introduced as indexes for physical load in working environment at sea, a new method is proposed to evaluate them during ship motion. It is applied to fishermen working on a purse seine. In the case of considering acceleration of ship motion, the lumber compressive force is larger than that ignoring acceleration, and it was found that the workers over 60 yeas old are continually exposed to the compressive force over the threshold limit values, 2300N, indicated by Jager et. al.
This study aims to clarify the impact of implementation of the traceability system for fishery products and hygiene installations of fishing port. In this study, the traceability system using “QR” code is installed to cultured algae products on a trial in the Fukushima fishing port. The cultured algae products was delivered to a retailer and questionnaire survey was conducted to consumers who bought the algae products. From the trial implementation, the effectiveness of the traceability system for fishery products using “QR” code is examined, focusing on the actual procedures through the distribution and satisfactory results of the consumers. And traceability system is an effective method to inform consumer of hygiene management information on fishing port.
The thermal control and traceability system of marine products from ocean to consumption area and consumers via long-distance transport has been developed in order to enhance the reliability and safety of fishery products. In this study, the improvement in the quality and hygiene management is examined in Rausu fishing port of Hokkaido as an example into.
The fishing ports which equipped the pumping system of deep-sea water for the purpose of sanitation control and fish farming of cold water have increased. It considered using a large-scale entrainment process of a buoyant jet for a water quality improvement of the fishing port. We suggested a new hastening method of seawater exchange by discharging the cold water from the bottom layer of the fishing port to the harbor entrance. The jet area formed by the cold-water discharge to the open area turned into stratified region when the distance from the outfall, which is standard by momentum flux and buoyancy flux, got 20-30 times longer, and most of the part of the stratified region vanished when it got 200-400 times longer. Large-scale entrainment process of a buoyant jet was presumed to be what generates 101-102 times as much large-scale sea water exchange compared with outflow discharge.
The purpose of this research is verifying whether it being possible to improve the environment of the fishing ground in enclosed water by tilling. This experiment was conducted in the fishing ground of the freshwater clam in Lake Shinji. The tilling machine used for this experiment moves with the pressure of air. In order to verify this experiment effect, the tilling area and the non-tilling area were set up. The contents of investigation are water quality, a sediment, and benthos. Investigation was conducted once before the tilling experiment and carried out twice after the tilling experiment. The following thing was checked as a result of comparing a tilling area with a non-tilling area about the contents of investigation. (1) The sediment of the bottom of a lake in a tilling area came to be soft during a fixed period. (2) The sediment of the bottom of a lake in a tilling area would be in the oxidation state during a fixed period. (3) It was suggested that growth of the freshwater clam in a tilling area is promoted. The above thing showed that the environment of the sediment of a fishery had the effect of a certain amount of improvement by tilling.
To obtain figures and tables for environmental assessment on diffusion caused by dumping dredged materials from fishery ports into the ocean, study on past records on volume of dredging and dumping materials were carried out. The cases for numerical simulation on diffusion were selected by examining the study on past records. The simulation was conducted for conditions of three types of dredged materials, three water depths, three current speeds and one representative median diameter. As the results of the simulation, figures of maximum concentration, maximum diffusion distance, affecting time on diffusion for 2mg/L and 10mg/L conditions were obtained. After specifying sorts of fish around the dumping area and fishing time, a trial of prediction on diffusion and assessment for dumping dredged material were conducted by using those figures.
The scallop shells have continued to stack in the open. And Scallop shells are going to increase every year. The purpose of this research is considering recycling use of scallop shells. It considered mingling and using scallop shells for friction-increasing mat. It examined for the relation ship between the weight content of crashed scallop shells, and a movement limit wave height of caisson by model experiment. Using this wave height, it found a frictional resistance coefficient by the GODA formula. It turned out that a friction coefficient exceeded 0.7 by the size of crushed shell 2-5mm for the case of 50 or less % of weight content.
In order to use scallop shells of a fishery by-product effectively for the back-fill material of a quay, we are investigating the internal friction angle of the sand which mixed the crashed scallop shells by consolidated-drained tri-axial compression test. In our second report, we checked that the sand which mixed the crashed scallop shells is applicable to back-fill material. However, it turned out that how to mix sand and a shell influences unit mass and internal friction angle. This time, we investigated the internal friction angle of the mixture sand which changed the mixed method and the injevtion method of materials at making a specimen. As a result, when the maximum grain size of crashed shell is about 10mm and the rate of shell mixture is about 25%, it is thought that we can use the sand which mixed the crashed scallop shells for the back-fill material, by carrying out consolidated-drained tri-axial compression test and grain size analysis before and after compressiontest.
Recently, marine products are cultivated and preserved in the inside the harbor. Therefore, organic matter like feces of fishery products and remainder of feed is deposited at the bottom of aqua farm, and sediment is polluted. On the other hand, the promotion of utilization of the scallop shell exhausted 200, 000t during year is a regional problem in Hokkaido. Then, we constructed the artificial reefs of scallop shell at the bottom of aqua farm and created detritus feeder's habitat, and aimed at the establishment of prevention technology of environmental deterioration that used detritus feeder's physiological function. In the main discourse, we compared shell reef's community and a peripheral benthic community, and examined the characteristic. As a result, the biota by a species different from a peripheral benthic community was formed in the shell reefs. Therefore, the installation of the shell reef obtained the characteristic of enabling the immigration of the benthos in the point of habitat creation.
The origin of longshore sand supply to the Kujukuri coastal plane with a 60 km length was investigated through field observation. This coast is surrounded by sea cliffs at northern and southern ends; Byobugaura and Taito cliffs. Main supply source of sand to this coast is the Byobugaura cliff, but the south boundary condition of littoral transport related to the formation of the Kujukuri beach was not clear. This study shows that the southern end of littoral transport is not the southern sea cliff, but it expands up to the watershed of the Isumi River.
Long-term shoreline changes of the Yoshizaki coast located around a mouth of a tributary of the Suzuka River flowing into Ise Bay were investigated on the basis of the comparison of past geographical maps and aerial photographs. The characteristic height of beach changes was evaluated to be 4m from the bathymetric survey data. Longshore sand transport rate of 2×104m3/yr was obtained from the shoreline changes multiplied by this characteristic height of beach changes in the natural condition. In recent years, this longshore sand transport of the coast was totally exhausted and a long shoreline was separated into several pocket beaches.
A guideline of the comprehensive sediment management in littoral system including rivers, being main supply source of sand to coasts, was made to simultaneously solve not only beach erosion, but also surplus accumulation of fine sand inside the fishing ports, ports and river mouths. The method of sand recycle (sand back pass) is proposed instead of local optimization using hard structures against beach erosion. To overcome ordinary inconsistent measures under the sector-by-sector system, unique target to preserve coastal land was set in entire Tottori Prefecture. The plan was put into practice in 2005.
Beach changes around the mouth of the Hino River flowing into Lake Biwa were investigated through the comparison of aerial photographs. In the past, a large river mouth delta developed at the mouth of the Hino River, but in recent years rapid shoreline recession occurred. Two causes of beach erosion were found. The first is the dredging of the river bed including the mouth, resulting in decrease in sediment supply from the river. The second is the water level control, in which water level of the lake is raised in winter to obtain water resource and this accelerated erosion by the combined effect of strong wind in winter.
For sediment management of a consistent water system, the sediment transport maps in the river engineering field and drift sand distribution maps for the coastal protection plan in the shore engineering field zealously have been made in late years. Furthermore, we can't make the sediment management plan of a consistent water system that is connected from river to sea until we grasp the sediment transport of river mouth part which is joint of river and shore. In this study, we investigated the height of change in topography based on the surveyed topographical data of fives times just after a flood around Abe River mouth in 2004. Furthermore, We considered the relations between the external force such as the river discharge or the wave height and the sediment transport of the Abe River mouth area.
Lakeshore erosion due to waves transmitted through the entrance channel of a lake and the formation of a sand spit around the entrance were investigated through the field observation at lakes facing the Ohotsuku Sea. Waves transmitted from the ocean to lake diffract into a lake and propagate apart from the entrance channel, losing wave energy and resulting in longshore sand transport. Due to this longshore sand transport, sand is transported from the vicinity of the entrance channel to far side and the lakeshore adjacent to the entrance channel is eroded. The shoreline deforms to be normal to the incident wave direction, resulting in the formation of a sand spit. This mechanism was explained by the shoreline change model.
Numerical models for predicting topography change caused by sediment transport so far are generally carried out by using representative grain size. But actually bed material in the field often has wide grain size distribution. In a beach where grain size distribution is wide, the direction of bed material transport depends on its grain size because the mode if transport of fine bed material is different from that of coarse bed material in the cross-shore direction every now and then. The purpose of this study is to simulate sorting process of the bed materials in the cross-shore direction due to difference of transport direction between fine and coarse materials and topography change by applying SBEACH model. Simulated grain size distributions gave qualitative explanation for the observed one by the hydraulic model tests.
A model for predicting three-dimensional beach changes around a gently sloping revetment was developed using the contour line change model. Wave sheltering effect of the revetment itself at downcoast corner was taken into account to predict a concave shoreline at the corner. The effect obstructing longshore sand transport due to a gently sloping revetment can be quantitatively predicted by the model. Results of the prediction were compared with a movable bed experiment. Both agreed well, and it was confirmed that this model becomes a useful tool to predict three-dimensional beach changes around a gently sloping revetment.
Old maps, such as Inoh Maps and other historical ones, are prospective which might be used for determining the changes of coastal geographical features in the past. It is expected that long-term geographical changes can be known provided that the accuracy of an old map is satisfactorily high. In the present study, the changes of geographical features in Nobiru Coast, Miyagi Prefecture and Matsukawaura Lagoon, Fukushima Prefecture are examined by comparing historical and latest maps. Furthermore, long-term sediment budget analysis is carried out for the Nobiru Coast.
In northeastern Brazil, large-scale sand dunes are formed by wind-blown sand caused by unidirectional strong wind. This characteristic of wind induces a strong littoral drift with more than several hundred thousand cubic meters per year in the northeastern coastal region in Brazil. In this condition, wind-blown sand acts to the sediment balance as a source or sink in the coastal region. This study aims to investigate sediment balance in the coastal region under the condition of existing of large-scale sand dunes and littoral drift using the statistic weather and wave data, aerial and satellite photographs.
This study investigates the coupling field of grouped wind waves and their associated long waves in the surf and swash zones. Based on the calculated wave fields, the contributions of the wind waves and the long waves on the sediment mobility are discussed. Spatial variations of the incident grouped wind waves propagating over a plane slope are calculated based on time-dependent mild slope equations. Generation of the long waves is reproduced based on a time-varying breakpoint model proposed by Symonds et al. . In order to obtain the long wave solutions extending over the landward region from the still water shoreline, calculations using non-linear shallow water equations are connected to the Symonds' model invoking a moving boundary treatment. The Shields parameters under composition of the grouped wind waves and the associated long waves are evaluated to assess the mobility of the bottom sediment. The results show that the long waves have greater sediment transport ability over the grouped wind waves in the swash zone.
A considerable amount of wind-blown sand intrudes into the inland crossing over wind-breaks with several meters high although wind-blown sand on a flat sand surface concentrates near on the sand surface. For explaining this phenomenon, we offered a hypothesis that wind-blown sand flowing downwind is entrained into a local current which generates around wind-bleaks, flied high up and crossed over wind-breaks. To verify this hypothesis, a wind tunnel experiment of sand crossing over a non-permeable fence is carried out. The experiment showed evidence that the local current exaggerated motion of blown sand near the fence and increased the amount of crossing over the fence. To examine the hypothesis further, additional experiments are carried out. The results showed the fact that the hypothesis could be acceptable.
Many researchers have gained key knowledge from existing quantitative measurements of the vertical profiles of suspended sediment concentration in coastal zones. Despite these advances, there still remains much to be solved concerning the distribution of the time and space-dependent concentrations of suspended sediment that accompanies wave-driven transport, as well as the way in which the distribution of suspended sediment concentration varies with the changes in the equilibrium beach profile. This study investigates variations in the temporal and spatial distributions of suspended sediment concentration that induce changes in the equilibrium beach profile. High concentrations of suspended sediment in beach profile Type I and Type II have been recorded in the zone of breaking waves in the ocean half-wavelength region between a bar and trough. The distinction in suspended sediment concentration between Types I and II is clear: suspended sediment concentrations are higher in Type I than in Type II throughout the observed region.
The level-one earthquake ground motion is going to be presented as time histories by the seismic hazard analysis considering source, path and site amplification effects. Site amplification factor is calculated by the spectral inversion of the strong motion record. However, it should be noted that strong motion record is not obtained at all the port areas nationwide. In such cases, site amplification factor applied at port areas is obtained by the modification of that at inland sites. This study aims at discussing the effect of the modification of the site amplification factor on the evaluation of the level-one earthquake ground motion from the viewpoint of the deformation of quay walls.
In order to introduce the performance-based design framework into the design of quay walls, it is necessary to stipulate the allowable displacements of the quay walls as one of the performance requirements. This paper aims at presenting the allowable displacement for gravity type and sheet pile type quay walls against the level-one earthquake ground motion. We conducted series of earthquake response analyses by using the level-one earthquake ground motion obtained by the earthquake hazard analysis and evaluated the displacements of the quay walls for each structural type. We proposed the average displacements as the allowable displacements of the quay walls.
On March 20th, 2005 an earthquake with a magnitude of 7.0 struck the port of Hakata in the northern Kyushu. A design seismic force of the earthquake motion is estimated 0.2 while the present design seismic force is 0.05 for a many of facilities at the port. The damage has been found throughout the port. This paper presents a comprehensive review of damage of Hakata port. The facility damage is analyzed in terms of structural design, construction age and level of availability of the facility. As the result, the facility displacement has a close relationship with the structural design. An occurrence of apron holes is resulted in the structural design and the construction age. This study also shows that the damaged facilities over 30cm displacement and 10% of apron hole are out of use.
It is necessary to evaluate the forthcoming earthquake ground motion precisely from the viewpoint of coastal earthquake disaster prevention. In this study, we focus on the reproduction of the seismic intensity at Takamatsu port by the past destructive earthquake. Site amplification plays the key role in the reproduction of the seismic intensity at coastal areas because of the basin effects. In this study, we modified the site amplification factor based on the horizontal over vertical spectral ratio of the microtremor record and succeeded in reproducing the seismic intensity.
It is important to know whether a coastal dike maintain its functions to protect the hinter-area against disastrous tsunami accompanying giant earthquake. However, it has been thought almost impossible because the length of dikes is extensive and the level of techniques needed for the evaluation is high and complicated. There is, therefore, an urgent demand for a practical seismic performance evaluation technique. The authors have developed and propose a simple technique depending on the results of hydraulic experiments as well as numerical analyses, taking into account the shape of a coastal structure and ground conditions.
Tsunami-induced wave pressure and tsunami force acting on containers on an apron are investigated with a three-dimensional numerical simulation based on MARS (Multi-interface Advection and Reconstruction Solver) as well as hydraulic model experiments for the measurements of runup height on the apron and tsunami force acting on the containers. It is consequently found that the numerical method allows the good estimations of both the runup height on the apron and tsunami force acting on the containers. It is also revealed that the maximum runup height in front of the containers gives the maximum wave pressure on the containers with hydrostatic pressure approximation, however impact pressure on the lower part of the containers may exceed this hydrostatic water pressure.
This paper introduces a newly developed real time tsunami detection system using offshore water surface elevation data obtained from GPS buoys or seabed installed acoustic/pressure wave gauges. In order to eliminate high frequency components caused by wind waves and swells, shape of the numerical low-pass-filter was determined with consideration of its real-time efficiency. To eliminate lower frequency phenomena caused by astronomical tides and other causes such as water temperature change, 6 days continuous passed data were found to be necessary to obtain harmonic constants of the 4 principal tide components and averaged sea level. Miss-fixed and data-loss phenomena, which may appear in the GPS buoy observation, were also considered to elaborate the automatic system. Proposed system was checked with the actual offshore tsunami observation data caused by the 2004 Tokaido-off and 2005 Miyagi-off earthquake tsunami events, and the applicability was well confirmed with exception during a huge typhoon caused abnormal waves and sea-level events.
A big difference between the Andaman Sea coast and the coasts in the western countries of the Indian Ocean was found in damage state caused by the Indian Ocean Tsunami. It is thought that geographical features of the coastal cross-shore section affect the characteristics of the tsunami deformation and the damage situation of the coastal structures. In this paper, the model experiments were conducted to clarify the difference of deformation, breaking, runup or pressure of tsunami by the characteristic of the coastal cross section. The wave steepness and water depth on the reef are closely related to generation and development of dispersive solitons, and it is clarified that the impulsive breaking wave force takes place at the breaking of individual soliton. Tanimoto's empirical formula can be applied to estimate the wave force of tsunami on coastal structures when the dispersive solitons almost disappear due to these breaking or no dispersive solitons occur.
The research on the properties and inundation effects of tsunamis has been much advanced recently, but the research on the damages of port facilities and vessels moored at them due to tsunamis has not been pursued sufficiently. It is essential for the reduction of the damages to take effective measures under the abundant knowledge of the damage mechanism. The experiments on the motions of a vessel moored at a wharf or a dolphin type facility in tsunamis were performed to investigate the characteristics of tensile forces of mooring ropes and impact forces on mooring fenders. The sway motion is predominant and the other two motions of roll and heave are too small to affect the mooring forces. The impact forces of the vessel on the fenders are closely related to hitting speed of the vessel.
Several processes of tsunami generation and growth due to seabed deformation of submarine earthquakes have been simulated using the 3D numerical model based on the Reynolds-averaged Navier-Stokes equations or the 1D numerical model based on the nonlinear shallow-water-wave equations for incompressible-fluid motion. The initial wave profiles of tsunamis generated by the uniform uplift of seabed were compared between the results through these two models. The tsunami-earthquake cases where the seabed deformation changed its place along the horizontal direction were also treated to evaluate the profile and height of steady tsunamis propagating outside their wave-source areas.
In recent years, some fishery areas have frequently suffered major damages due to earthquake tsunamis. The purpose of this study is to identify the problems and to propose countermeasures against these disasters in fishery areas. We examined some cases with earthquake tsunami damages, and analyzed the results. The result has shown the importance of three main actions to take measures against these disasters. The first is to secure safety of local population, workers, and visitors. The second is to improve the disaster prevention level of fishing ports and fishing villages. The third is to secure marine products distribution function in time of disaster.
Based on documents investigation, we examined a disaster scenario of power plant which hit by tsunami. In addition, we paid our attention to drifting ships due to tsunami and examined an evacuation method of a ship as a part of examination of countermeasures against tsunami disaster for a model harbor. The disaster scenario and a evacuation flow of a ship which we showed by this report become a help of examination of countermeasures against tsunami disaster.
The 2004 Indian Ocean Tsunami took a heavy toll of lives among beach users. Accordingly, we have to recognize the absolute necessity of countermeasures against Tsunami for bathing beach. The purpose of this study is to examine present problems in crisis management of bathing beach for Tsunami disaster. We sent out questionnaires to lifesavers at 31 bathing beaches, and analyzed the results. As a result, we see that if an appropriate system of shelter is constructed, it will be possible to highly decrease the damages at a lot of bathing beaches. And we suggest that it is important to construct a cooperative relationship with lifesavers and coast management entities etc.
As to estimate the effect of the coastal defense facilities against tsunami disaster, the simulations for both tsunami inundation and evacuation applying to the case of the bay Kesennuma were conducted to evaluate the number of the casualties caused by tsunami quantitatively in this study. The facilities expected to prevent the tsunami disaster are composed of the water gates, parapets and level raising of quaywalls which have been already constructed at the location or are experimentally introduced in the simulation. After calculating a time series of the inundation height and water particle velocity for each case, we applied the results to the evacuation simulation and evaluated the number of casualties for various ages and various starting time of the evacuation. Finally, assuming the probability density function on the starting time of the evacuation from tsunami and population ratio about ages at the area, we successfully obtained the expected number of the casualties in case the coastal defense facilities are disposed or not, and verified the mitigation effect of such constructions.
We have proposed the flap type gate for protection against storm surge and tsunami, and the studies for its hydraulic and hydrodynamic characteristics and design method of it are in progress. In this paper, two-dimensional hydraulic model tests on the scale of 1: 50 were carried out in the flowing water tank with the bore generator, and wave pressure and gate behavior required for designing of the flap type gate were revealed. Besides, function and performance of the flap type gate were examined in terms of disaster prevention against hydraulic bore by tsunami.
The flap type gate has been developing as storm surge and tsunami countermeasure. Because the flap type gate closes a harbor quickly, it is thought to be effective as a tsunami countermeasure. However, there are some uncertainties in the hydraulic and hydrodynamic characteristics against tsunami. In this paper, two-dimensional hydraulic tests were carried out on the model of scale 1/60 in the water channel with wave maker, and wave pressure and gate behavior of the flap type gate were investigated. As a result, it confirmed that a modified flap type gate was effective as a tsunami countermeasure.
The flap type gate against storm surge and tsunami has many superior points in comparing with existing coastal structures for prevention of disasters. However, the flap gate has the problem that the gate itself sways because of waves from the open sea and generates waves into a harbor. In this study, a new flap type gate was designed, and the wave transmission characteristics on a new gate were investigated through a two-dimensional hydraulic experiment with the model of scale 1/35. The obtained results indicated that the transmission waves due to sway of the gate were reduced.
As for the necessity of planning of an artificial tidal flat, it is argued in various opportunities, and many studies about construction technique and biological investigation have been done. Accumulation of a result of biological investigation may become an evidence to evaluate the tidal flat environment, but it is not easy to evaluate the environment in tidal flat from a observations of the habitat, because of a large change of tidal flat environment around the river mouth. In this study, a usage of biological findings are examined and the relation between the habitat segregation and variation of tideland materials characteristics.