Tsunami can yield extensive topographic change, which causes secondary damages such as collapse of coastal structures.Therefore, it is important to analyze the topographic change due to the tsunami. In this study, we investigated spatialvariation of sedimentation and erosion due to the 2004 Indian Ocean tsunami at the Kirinda port, Sri Lanka by using thebathymetric data before (Nov, 2004) and after (Feb, 2005) the tsunami. We also conducted numerical analysis of tsunamipropagation and sediment transport. The results show that the tsunami caused approximately 5m erosion or deposition, and the shoreline was moved approx. 100m toward the offshore. Morever, backwash that was redirected by coastal structuresplayed a main role of significant erosion around the wave breaker.

抄録全体を表示

Vecocity field in a harbor due to tsunami as well as free surface displacement was investigated experimentally to discussbottom topography change. Vortices generated near a breakwater head and inside the harbor were clearly observed. Mechanism of the bed topography change featured as an accumulation in the center of the habor and erosion in surroundingarea of the accumulation was explained with the velocity field and observation of trace of sand movement. Using ananalytical solution and the measured velocity as boundary conditions, an radial velocity component in Ekman layer wasestimated to be about 30% of the azimuthal one.

抄録全体を表示

Indian Ocean Tsunami 2004 made us to recognize of the power of the huge tsunami. To clarify the mechanism of failure due to tsunami and to make the assessment tool are important not only for the forecast of damage but also for the evaluation of evacuation towers. If the large tsunami occurs, large impulsive bore force may attack on. the land structure near the coastline. But, the behavior of structures against such power is still unsolved. In this report, the physical model tests are conducted to clarify the mechanism of failure of concrete wall due to the impulsive tsunami power. Several types of concrete walls and brick typ.walls with column are tested. From the results, the failure mode of walls against the impulsive tsunami power was clarified qualitatively.

抄録全体を表示

It may be possible to inform the tsunami warning such as tsunami wave height and arrival time just after an earthquake occurs, if we simulate many cases of the tsunami propagation in advance. However, it is not clear how the fault parameters influence on the tsunami of a specific site. This study calculated about 1200 tsunami propagation cases for the Akita Oil Storage Base to survey the influence of the uncertainty of the fault parameters. The tsunami wave height was related to the initial vertical displacement of the sea bottom although the location of epicenter varied the height. The arrival time was related to the distance from the epicenter and the magnitude of earthquakes.

抄録全体を表示

There are high risks that tsunamis may cause containers stored in ports to drift into sea/land areas. In this study, one of the main objects is to construct a simulation model which enable us make accurate prediction of the drift behavior of containers and its collision force. For the object, the field experiment for containers drifting and floating on sea surface due to tsunami. The field experiment was conducted in the inner harbor of the Shimizu Port, Shizuoka Prefecture. The container sunk completely to the sea bottom bed after floating for 24.15 hours. And the numerical simulation was conducted and the behavior of the container drift and collision force in Shimizu Port Area was estimated.

抄録全体を表示

When the oil storage tanks drift from their initial place by tsunami, they may cause severe troubles such as destruction of structures nearby and leaks of storaged oil. Model experiments revealed that the tsunami wave force and friction forces determine the slipping and drifting of the tanks, therefore we constructed a simulation model using the momentum equation for the prediction of the tank movement. The simulation results well represented the track of drifting measured by the model experiment. When the oil tanks start to drift, they tend to drift for several hundred meters unless they remain in the initial place by the force of static friction.

抄録全体を表示

This study proposes a calculation scheme which enables us to estimate the collision time and force of a container drifted by run-up tsunami. Simulated behaviors of the drifted container by a run-up wave are found to be in good agreement with the laboratory experimental results.A set of these calculated values are used as the initial values of the fluid-structure interaction analysis which simulates the collision of the drifted container. It is confirmed from these simulations that the added mass (water mass at the rear of the container) plays an important role on the collision and predicted collision force and time reached equilibrium state as the model accounts for adequate volume of water in the rear of the drifting container. Moreover, the effect of the added mass on the collision force and time is verified in full scale collision simulation.

抄録全体を表示

The fragility function of mangrove forest was proposed based on field surveys and the numerical analysis focusing mangrove forests affected by the 2004 Indian Ocean tsunami. The curve of growth for mangroves (Rhizophora spec.) was also proposed in order to estimate the change of the tsunami reduction effect depending on the age of them. Using these proposed functions, the numerical modeling was carried out to evaluate a tsunami reduction effect. As the results, we found that the mangrove forest with 10-year-old is mostly destroyed and the reduction effect rapidly decreases when the tsunami inundation depth exceeds 4m.

抄録全体を表示

A statistical analysis by using the filed data of damage of tree in a coastal forest due to a past tsunami was carried out, and the influence factor that contributed to damage of tree due to tsunami was extracted from a statistical analysis. And then, statistical models were developed by using the filed data. The statistical model for lodging rate explains the actual measurement value well by diameter of tree, root form, dn and tsunami inundation depth, The statistical model for destruction rate explains the actual measurement value well by root form, dn and tsunami inundation depth. In addition, actual probability of occurrence of tree damage and the probability of the present model used inundation depth from tsunami simulation were compared, and suitability of the present model was examined.

抄録全体を表示

We discuss the characteristics of the later-phase tsunamis accompanied with earthquakes along the Kuril trench, based on the numerical modeling of trans-oceanic tsunamis and the analysis of observed tsunami waveforms. The model results suggest that the later-phase tsunami is caused by edge waves or scattering waves from the seamounts, depending on the tsunami source location; tsunami energy radiated from south of 46° N can result edge waves andnorth of 46° N to 49°N can be scattering waves. Also, we found that analyzing the time evolution of Fourier spectra of observed tsunami waveforms can identify the cause of later-phase tsunamis and can be used to decide the timing of tsunami warning cancellation after it's issued.

抄録全体を表示

The following improvements on tsunami damage predicting are examined in order to decrease the tsunami damage: 1) It is checked that the destructive evaluation of buildings of a wide area due to tsunami can be efficiently performed with the numerical model which can calculate a flood of only land area with good accuracy and the gate type Rahmen model. 2) The limit of inundation height that human-beings can stand up to tsunami is obtained using data of a large-scale model experiment. This limit is determined by a slide and changes in the range of 20cm-40cm with sex and height. 3) When the overflow of tsunami occurs on the land area of a steep slope, a strong back-flow will occur. Therefore, a calculating method which can be used for the stable examination against it is also proposed.

抄録全体を表示

Numerical simulations for both tsunamis and storm surges on the coast of Okinawa Prefecture, which are expected to be the most dangerous cases, were conducted to evaluate the possible inundation area and potential damage. The detailed topographic model derived form filtered LiDAR observation data was applied to inundation simulation. Nonlinear long wave theory was used in tsunami simulation. The third generation wave spectrum model (SWAN) and VOF method (CADMAS-SURF) were used to calculate wave height and overflow volume, respectively, in storm surge simulation. The simulation results were compiled in inundation maps and computer graphic animations, and they were distributed to municipalities along the coast to promote tsunami and storm surge disaster prevention measures.

抄録全体を表示

While a typhoon is approaching, the necessity of disaster prevention works in ports is often judged from the highest storm water level in the storm surge simulation for several probable typhoon tracks. Since the actual water level seldom reaches the highest one predicted, the accumulation of such an experience causes carelessness in persons in charge of disaster prevention. The probability density distribution of the storm water level predicted is useful information for them to estimate the possibility of disaster in their ports. This study, therefore, simulated the storm surge in Seto Inland Sea for 109 typhoon tracks crossing or passing by the prediction circle of typhoon location and then discussed on the variation of the range and the accumulative probability density distribution of the storm water level with lead time until the typhoon arrival.

抄録全体を表示

Hurricane Katina (2005) brought enormous damage to coastal protection systems in southern portions of the states of Louisiana and Mississippi, USA. In efforts to recover the devastated areas, construction of new systems to protect the areas from possible storm surge in the future has been a very urgent task. In this work, we develop a coupled storm surge, wind wave, riverine flow and tidal current model being used to design the new protection systems. The computational model employs the finite element method for the riverine, tide and storm surge model and takes advantage of unstructured grids to obtain precise estimation of possible surge heights from 100-year level storms. Observed hydrographs and high water marks during the hurricane are used to validate the developed model. The validation shows that the model is capable of reproducing the storm surge induced by the hurricane with good accuracy. The model is also found to be useful to understand how the hurricane caused the unprecedented surge levels.

抄録全体を表示

The storm surge residual of 2.35m was recorded during Typhoon Anita (T7010) at Katsurahama in the Tosa Bay. The surge could not be explained by usual meteorological forces. The inclusion of the wave-induced radiation stress was necessary. This study examined the effects of waves and tidal variations for estimating the abnormal storm surge by using a coupled model between strom surges and waves together with the tidal variations, named as the SuWAT (Surge-WAve-Tide coupled model), and clarified those effects on the storm surge.

抄録全体を表示

In the modeling of air-sea energy transfer mechanism, it is the key to evaluate the wave energy dissipation transfer rate to mean current generation. We introduced the effective breaking dissipation stress factor, which indicates the contribution rate of dissipation stress caused by wave breaking to the total sea surface stress to generate the ocean mean currents. Numerical tests using the air-sea coupling model were conducted in this study to determine the factor (α=0.3) and the direct generation factor of mean current, β(U₁₀). Then the model was applied to storm surge simulation in the Bay of Bengal to confirm the model efficiency in the extremely shallow water.

抄録全体を表示

Storm surges generated by Typhoon T0416 and T0418 in the Seto Inland Sea were hindcasted by the SuWAT (Surge- WAve-Tide coupled model). To investigate the effects of meteorological data considered a topography around the sea on storm surges, the data obtained from WRF (the Weather Research and Forecasting model) was compared with it from a parametric model (Fujii and Mitsuta model). Our results indicate that storm surges simulated by the combination of WRF data and tidal variations showed better agreement with the observations than those by the analytical model with constant water level.

抄録全体を表示

The JAMSTEC offshore monitoring system located on the 2.3km-deep seabed near the sourse of the 2003 Tokachi-oki earthquake (M8.0) left us very precious observation records of ground motion and water pressure. Based on the records, findings on tsunami generation process estimated from the dynamic tsunami simulation are demonstrated in this paper. In contrast to traditional assumption, the tsunami generation process is made up of three components in terms of the water pressure. The first is short period vibration due to acoustic waves, the second longer period variation induced by Rayleigh waves, and the third a long-period tsunami.

抄録全体を表示

The 2007 Noto Hanto earthquake (Mj 6.9) occurred off northwest of Noto Peninsula, Japan on March 25, 2007. Associated with this earthquake, a tsunami was excited off northwest of Noto. And a mysterious small tsunami was also observed at Toyama off southeast of Noto Peninsula. This small tsunami arrived soon after the earthquake occurrence, and the wave height was about 10cm. First we estimated normal tsunami by the simulation considering vertical displacement of fault movement. Calculated waveforms roughly agree with the observed one except. for early arrival tsunami at Toyama. Next we assume the source region of the tsunami at Toyama from inverse propagation diagrams and finally attempt. to simulate this mysterious tsunami by considering horizontal displacement of the sea-bed in Toyama Bay.

抄録全体を表示

Hydraulic experiments were performed to simulate tsunami generation due to landslides, which consist of particles including glass balls, glass beads, natural rocks, acrylic rocks, and block ices, as well as packages of glass balls. The gate can be opened smoothly and quickly by pushing down two levers connected with the gate plate. The period of tsunamis due to glass-bead motion is longer than that due to glass-ball motion. On a mild slope, tsunami profiles depend on the diameter of the sliding glass balls. In shallow water, the slide distance of particles is shorter, the tsunami height becomes lower. The block ices can also generate large tsunamis, although the ice does not go deep under the water.

抄録全体を表示

In this study, it is discussed about the method to generate a strong flow by tsunami in a wave basin. The authors are tried to adopt the vertical jet system and measured horizontal water particle velocities. Before the experiments, numerical analysis has done, and the vertical distribution of horizontal water particle velocity is estimated to be almost the same. However, the horizontal water particle velocity in the vicinity of the bottom was a little small in the experiment. But it is negligible because the flow velocity is very large compared with the flow generated by regular waves. Moreover, by controlling the volume of the jet periodically, the oscillating flow can be generated. Therefore, it is concluded that the vertical jet system can apply to the large scale tsunami experiments.

抄録全体を表示

A method for estimating basic hydraulic quantities of inundated flow with floating bodies in the hydraulic experiments is presented and its validity is confirmed through examining quasi-steadiness of the flow, consistency among inundation depth of the flow, current velocity of the flow and void ratio of layer having floating bodies, and so on. Using the experimental data estimated by the presented method, applicability of the existing theory for estimating the moving velocity of floating bodies, i.e., the current velocity of inundated flow with floating bodies is examined, and it is concluded that the theory is useful in a practical situation. Fundamental characteristics of the inundated flow with floating bodies are also discussed through examinations of the experimental results and solutions of the theory.

抄録全体を表示

The 16 July (2007) Niigataken Chuetsu-oki Earthquake generated tsunami. The tsunami arrived at coast in the Japan Sea, and maximum tsunami amplitude close to epicenter was observed 27cm at Kashiwazaki and 32cm at Ogi. Furthermore, at Sakata far from the epicenter less than 200km, it was observed 24cm at 6hours after the main shock (JMA, 2007). There is a possibility of the occurrence of edge wave because of the epicenter near coastline and these observations. On the other, the ground change due to the earthquake has investigated in detail, and then, the fault model based on geology has been examined (GSI, 2008). In this study, numerical simulation about tsunami propagation based on the fault model of GSI, JMA and NIED was performed, and characteristics of tsunami propagation due to the shock have been examined.

抄録全体を表示

Empirical studies on wave setup at river mouths are important in terms of river mouth morphology change, navigation transportation, saline intrusion into river and water environment. The main objective of this study is to investigate the influence of water depth at the entrance to wave setup height at Iwaki as well as Yoneshiro Rivers facing the Sea of Japan, with especial reference to differences from rivers facing the Pacific Ocean. Frequent occurrence of wave set-up can be observed in these two river entrances due to storm waves during winter. By combining the results of the present and previous studies of Nguyen et al.(2007), a technical diagram is proposed as a relationship between wave setup height with offshore wave height and average water depth at river entrance.

抄録全体を表示

It has been suspected that the construction of the Isahaya sea-dike causes deterioration of aquatic environment in the Ariake Sea. Many studies on the aquatic environment have ever been conducted, but the causes have not been made clear yet. In this study, we examine the change of the tidal current due to the sea-dike by using the field observation data before and after constructing the sea-dike. As a result of the present study, it is clarified that the tidal current direction is changed and the M₂ tidal current is weakened in the head of the Ariake Sea by the sea-dike. In addition, it is concluded that properties of residual current might be affected by the sea-dike.

抄録全体を表示

The selective lumping scheme has been commonly used in the FEM analysis of tidal currents. The scheme is enable to get the numerical solution fastly and stably, despite it causes dull results because of introducing heavy artificial diffusion. A combination of the elements which satisfy the inf-sup condition should be used to modify the finite element analysis of tidal currents. In this paper, the finite element model in which employed the bubble-function element was developed and the analysis of tidal current in Ariake sea was carried out for the evaluation of the model. The analysis results were in good agreement with for the observed ones the tide levels and harmonic constants of tidal current.

抄録全体を表示

Tidal currents are one of the major attributes of flows in the sea. This paper describes the maximum likelihood method for the harmonic analysis of tidal currents. Assuming that measurements of tidal currents contain errors that follow the multivariate normal distribution, it can be explored the way to selecthe dominant components of tidal currents. Tidal currents were synthesized with harmoniconstants by numerical simulation, and AIC and BIC were employed to select the dominant components. As a result, BIC was a more reliable criterion than AIC when using many sample data. In addition, this method was applied to surface currents in Tokyo bay.

抄録全体を表示

Suspended sediments in estuaries play a significant role in understanding ecological and engineering problems. However, our knowledge for the transport processes of suspended sediments is insufficient, because the flow structures are very complex. To shed light on the effects of wind on sediment transport in Ohtagawa estuary, long-duration observations were carried out, using acoustic Doppler current profiler. In usually, the direction of the sediment transportation was toward upstream for the restricted freshwater discharge. When the wind blows downstream, the suspended sediment intrusion is encouraged. In flooded time, the direction of the sediment transportation was toward downstream.

抄録全体を表示

In order to clarify nutrient transport processes around the Kitan Strait, field surveys have been carried out every August from 1999 to 2004. The field surveys provided two very interesting results. The first is the development of stratification in the Kitan Strait. The upper residual current flows southward, while the lower does northward. As a result, there is a possibility that the lower nutrients in the Kii Channel intrude into Osaka Bay. The second is that such phenomena depend on the Kuroshio meandering. Although there are various conjectures about that matter, there are few researches. In the present study, the three dimensional baroclinic flow model with Lagrangian particles tracking method was used.

抄録全体を表示

Recently, eutrophication is serious problem in the Imari Bay because of an increase in load from the land and the food scatter of acuaculture. Therefore, red tides have been generated. Especially, a large-scale red tide gives the aquaculture and the ecology to the extensive damages. So, it is necessary to decrease the red tide. But, the generation mechanism of red tide is not understood in detail. So, to clarify the generation mechanism of red tide, we analyze the wind influences on a flow, which has great influence on generation of red tide in Imari Bay. As a consequence, it is clear that the northwind has generated a red tide because the wind weakened the water exchange.

抄録全体を表示

The drift numerical simulation model of the Seto Inland Sea with 0.5' mesh was constructed to search for problem of marine litter in the sea. The particles assumed to the floating litter were released from 13 rivers in these models and were traced for 30 days. As a result, the drift route, the arrival place, and the arrival time of the floating litter became clear. Moreover, the distribution of the amount of litter assuming proportion to the river discharge was calculated. A lot of amounts of the floating litter were distributed around the Okinose in the Osaka bay. They weredischarged from Yodo River. Also, the dispersion area of the floating litter was not proportional to the river discharge. This result was shown that the extension of the litter depended on the flow in the sea and the close of topography.

抄録全体を表示

The latitude of the Kuroshio stream axis is closely related to the intrusion of the Kuroshio water mass and the throughflow offshore from two open boundaries. The water densities at entrances depend on the intrusion difference of the Kuroshio water mass. A new data processing method, which accounts for various data of water quality measured at different observation points under different river discharge rates, is proposed to let the model be applicable to long-term and wide-area simulations. The throughflow depends on the boundary sea level difference and the density gradient between boundaries caused by the intrusion of the Kuroshio water.

抄録全体を表示

The current measurements have been carried out by NOWPHAS at several stations in the coastal area around Japan since 1996. In the data, temporal but simultaneous changes in residual currents were recognized at several stations in the Japan Sea side. In this study, the cross correlation analysis between current velocity and atmospheric pressure was made, and the migratory characteristic of low pressure distribution was investigated by tracing the negative maximum correlation area. As a result, it was found that the each station has an original migratory characteristic. For example, it was found that the generation of the strong current in the Sea of Japan side has close correlation with the low pressure migratory in northern area.

抄録全体を表示

This study presents the results of analysis of the field observations and the numerical simulation of tidal currents in the Kurushima Strait. The field data measured tidal currents at the two points near the Strait for fifteen days and measured vertical distributions of tidal currents in the west channel of the Strait for 10 hours in one day. The numerical simulation is performed by a multi-level model of tide and tidal currents as horizontal eddy viscosity terms, described with the Smagorinsky's formulas, are incorporated. The specific peculiarities of the complex coastal line and bottom topography of the Strait are taken into account in the model. The tidal current fields are reproduced by the model. Several components of tidal currents and the location of streaks, generated in the Strait, can be predicted by the numerical simulation.

抄録全体を表示

Recently, deterioration of the aquatic environment in the Ariake Bay has been a serious social problem. It is pointed out that a change of vertical mixing caused by decrease of tidal current led to the deterioration. In this study, in order to evaluate vertical mixing in the Ariake Bay quantitatively, in situ measurements on turbulent velocity shear by using a microstructure profiler were carried out. As a result of this study, it is recognized that values of eddy viscosity coefficient K_z in the area off Oura are 10^-5-10^-1m²/s. On the other hand, relatively large values of K_z are observed in the area off the Shimabara Peninsula, whose value was at least 10^-3m²/s. It is concluded that strong tidal current in the area off the Shimabara Peninsula can strengthen vertical mixing.

抄録全体を表示

A modeling method of long-term time series of waves and winds for evaluation of beach profile change was proposed. Statistical properties of parameters, representing storm waves, were analyzed and theoretical distributions were obtained together with correlations between those parameters. To check the uniformity of waves, meteorological and wave simulations were carried out. Those predictions were compared with the observations at the Naoetsu Port, and found to be well agreed each other. It was concluded that since spatial distribution of waves is uniform along the Joetsu Coast, the statistical variables can be given as input parameters for the concerned area.

抄録全体を表示

The wave forecast accuracy strongly depends on the sea surface wind accuracy. However, it is still common that we sometimes tune parameters in wave model according to the wind data used in the applications. In this study, we discuss the improvement of the wind energy input term as well as the drag coefficient of sea surface to be suitable for the wind data provided with a meso-scale meteorological model considered to be more accurate in applications to inner sea area. Some formulations for the term and the coefficient are examined to improve wave forecast accuracy by comparing the hindcasted results with the data observed during a few typhoons in Seto inland Sea, with some useful findings being discussed.

抄録全体を表示

In order to increase the forecasting accuracy of typhoon track and intensity, a new typhoon initialization method for mesoscale meteorological models is developed in this study. The new typhoon bogussing scheme is based on the potential vorticity inversion technique with a simple time-dependent axis-symmetric typhoon model, and can ingest a realistic high-resolution three-dimensional typhoon structure into low-resolution first guess fields, consistent with its environmental condition and atmospheric dynamics. Preliminary numerical experiments of Typhoon Bart (1999) using PSU/NCAR MM5 show that the new method is quite accurate compared with a traditional method operationally used, owing to the feature of having less dependence on empirical parameters and approximations.

抄録全体を表示

The sediment transport caused by tsunami was measured by a simple experiment. We measured the velocities and suspended concentrations caused by one solitary wave which is assumed as tsunami passing on the plane sand bed without breaking and splitting. It was found that there are phase lag between peaks of suspended concentration and velocity, and the time variations of vertical distribution of suspended concentration are in good agreement with approximated curve with exponential function. We found that the Brown's formula is inconsistent with the time variations of sediment flux measured in the experiment because it can't explain the phase lag between velocities and total sediment flux. The bed load formula by Ashida-Michiue shows a close agreement with amount of bed load.

抄録全体を表示

In this study, we investigated the sediment transport due to the 2004 Indian ocean tsunami along the natural coast at Hambantota, Sri-lanka. Bathymetry and topography surveys before and after the tsunami were conducted and the results showed significant erosion by the tsunami, especially around the places where shoreline discontinuations were observed. We conducted a numerical simulation of tsunami propagation as well as the bathymetry change induced by the tsunami. Furthermore, we also estimated the bathymetry change due to the usual sea waves at the coast. Our numerical results suggested that the tsunami has strong bottom shear stress at specific landform such as a river mouth and a cape. We also found that the sediment erosion and accumulation due to the tsunami had been mitigated by usual sea waves after the tsunami.

抄録全体を表示

The wave forcing term and a sediment transport model of sands were installed into the cohesive sediment transport model named “WD-POM” in order to calculate the morphologic change of intertidal flats due to tides and wind waves. Current fields and morphologic changes in the back of the offshore breakwater were calculated by using the improved model. Numerical results were agreed qualitatively with other experimental results. The model was also applied to the case of oblique incident waves on the uniformly inclined slope. The longshore sediment transport rate agreed quantitatively with the value estimated by using the longshore sediment transport formula. Furthermore, the improved model was applied to the Shirakawa intertidal flat in the Ariake Sea and current fields and morphologic changes were calculated.

抄録全体を表示

On the basis of cross-shore sand transport under the action of long period waves and standing waves reflecting from the seabed slope given by Bowen (1980) and Katoh (1984), a model for predicting the development of multi-bar system was proposed by applying the contour-line-change model. The increase in the intervals between the bars and the decay of the relative height of bars in the cross-shore direction were predicted well. The possibility of the recovery of the multi-bar system by beach nourishment using fine sand is also shown.

抄録全体を表示

Conceptual model for geomorphology and sediment transport due to tides and waves over intertidal mudflat has been proposed based on the field measurements of water depth, flow velocity and suspended sediment concentration from July 2004 to January 2008. Suspended-load flux and bed-load ability are expressed relative to the ratio of significant wave height to water depth. The maintenance mechanism for typical convex-upward profile over intertidal mudflat can be explained by the bed-load superiority for suspended-load using the conceptual model.

抄録全体を表示

In Awase area, Okinawa, two sandbars which extend perpendicular to the coastline are formed. This study intends to understand growth mechanism of the sandbars and to examine if the predicted sea level rise by global warming influences the sandbar formation. By analyzing sounding survey data, it is confirmed that the centroid of the sandbar is moving onshore with 26m/y and the volume is increasing with 500m³/y. These facts show that the sandbar gradually grows extending in the onshore direction. The onshore extension is caused by that the wave energy concentration on a shoal gathers coral sand and supplies them to the sandbar. It is also confirmed that high waves at high tide deform the sandbars rapidly. Therefore, the sandbar deformation by sea level rise is important and should be carefully examined.

抄録全体を表示

The spatial distributions of the cross-shore sediment transport rate for berm formation and erosion were examined using a 2.5-year data set of beach profiles. The investigation area was set from the maximum wave run-up position to the shoreline position at the mean tide level. The cross-shore sediment transport rates for berm formation and erosion were modeled with the offshore wave energy flux and the berm height, respectively. Moreover, the model was applied for the calculation of a one-month beach profile change. The results revealed that the model well predicts the beach profile change of the berm formation and erosion in a qualitative sense.

抄録全体を表示

Prediction of overwash occurrence can provide valuable planning information for local authorities, emergency services, and coastal residents. Based on those proposes a new empirical formula for predicting deposited washover volume was derived. The new formula was developed by modifying the assumptions of previous empirical models using new assump-tions based on the governing physical processes by taking into account the excess runup height over the beach crest and the duration of the overwash event. The empirical coefficient was calibrated using field data sets from United States. Verification of the model with a further fourteen field data sets was shown that the formula yields predictions are comparable to the measured field data with most of predicted overwash volumes falling within a factor of two.

抄録全体を表示

A sand bar has developed in Sanbyakken Area of Nakatsu tidal flat due to the accumulation of the fluvial deposit of the Yamakuni River. This sand bar has been extended eastward with time. Recently, rapid deformation of this sand bar occurred, and landward sand transport was generated by wave overtopping over the sand bar, while filling and destroying the salt marsh area behind the bar. During storm surges associated with T0711 attacked on September 17 and 18 in 2006 and T0704 attacked on July 16 in 2007, it was found that cross - shore sand transport with the rate of 21m³/m and 11m³/m, respectively, was generated by the overtopping waves.

抄録全体を表示

There are many kinds of model for predicting shoreline variation nowadays, which can be divided into two groups: process-based modeling (which is usually based on the sediment transport process and external forces) and another is mostly based on engineering computations which are not considered about the sophisticated or physically rigorous sediment transport process. One of the advantages of these models is short computing time due to not consider about sediment transport process. However, determination of empirical coefficients is the problems of these models. In this study, by applying long-term high-frequency field data on Sendai Coast with analytical analysis, a model for predicting the response of shoreline has been developed and verified.

抄録全体を表示

A model for predicting three dimensional topographic changes of a sand spit was developed by applying the BG model proposed Serizawa et al.(2006), which was originally developed based on the study of Bagnold (1964). The model was applied to the experimental results regarding the three dimensional deformation of a compound sand spit by Uda and Yamamoto (1991). Predicted changes were in good agreement with the experimental results, and the effectiveness of the model was confirmed.

抄録全体を表示

A model for predicting the formation, disappearance and recovery of a river mouth terrace was developed based on the contour-line-change model considering grain size changes. The topographic changes and grain size changes associated with the flushing process of a flood were first investigated, taking the mouth of the Abe River as the example. Predicted change in the river mouth terrace and grain size changes around the river mouth were in good agreement with the measured, showing the effectiveness of the numerical model.

抄録全体を表示