Bathymetry data obtained for 16 years around a large-scale submerged breakwater on the Niigata coast were analyzed. A local scour has developed shoreward of the submerged breakwater and expanded according to the extension of the breakwater. The maximum scour depth reached about 4 m. However, in the area protected by the submerged breakwater and groins, the influence of the scour is confined just shoreward of the breakwater, and the scour does not have a strong influence on the beach stability near the shoreline. Furthermore, in contrast to detached breakwaters, the submerged breakwater did not show erosion but a small level of accretion seaward of the structure.

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Numerical simulation of the alongshore sediment transport in the form of bedload around a groin has been carried out under conditions of various combinations of regular waves and bottom slopes. A formula for the groin blockage efficiency against alongshore bedload has been presented as the function of the ratio of the depth of groin head to the height of offshore wave, and its scope has been extended stochastically against a random wave and wave climate. The groin blockage efficiency is expressed in terms of the ratio of the depth of groin head to the seasonal mean of significant wave height or the energy-averaged significant wave height. The information will benefit a rational design of groin systems in control of alongshore sediment transport.

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This study was performed to reproduce the storm surge generated by Typhoon 0416 over a large area at Seto Inland Sea by using a meteorological model and a multi-sigma coordinate ocean model and to demonstrate hereby the importance of winds over offshore and inland seas and inflow of seawater from offshore to inland sea. It was demonstrated that tidal level calculated by an Atmosphere-Ocean-Wave coupled model agrees well with the observed one at all the locations over Seto Inland Sea. Additionally, the calculations based on the conventional method using a parametric typhoon model and a usual sigma coordinate ocean model were performed to compare the results with those computed with the coupled model. As a result, it was shown that the parametric typhoon model underestimates the wind effects and the usual type sigma coordinate model overestimates the inflow of seawater from offshore, and the meteorological model and the multi-sigma coordinate ocean model are necessary to reproduce high-accurately the storm surge over a large area.

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To realize an accurate and continuous monitoring for river discharge at low cost, a new monitoring system with an H-ADCP measurement and river-flow simulation is developed. The H-ADCP can measure velocity profile at a horizontal line. In the numerical simulation, the measured velocities are interpolated and extrapolated in a cross section with satisfying dynamic principles. The present computational method is therefore referred to as a dynamic interpolation and extrapolation (DIEX) method. To confirm the fundamental performance of the present monitoring system, the H-ADCP measurement was done at the middle reach of the Edo River and the river discharge was evaluated with the present method. The simulated velocity and discharge were compared with the results measured with an ADCP and a price current meter. The results indicate that the simulated velocity and discharge give good agreements with the observed data, demonstrating the fundamental validity of the present monitoring system for river discharge.

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In this study, numerical simulation of suspended sediment transport was conducted on the basis of the equation of motion in mass point system. LES turbulence model was introduced to simulate a coherent structure of turbulent shear fow which is composed of a series of ejection and sweep. Several hundred of sediments were traced in such a flow field, and their trajectories were analyzed statistically. Diffusion coefficient of sediment was evaluated numerically on the basis of diffusion theory by G.I. Taylor, and was compared with the value of turbulent diffusion coefficient. As a result, these two coefficients were found to take approximately same value, which coincides with the assumption of traditional analysis.

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SI (Suitability Index) model is applied for grasping habitat features of water creatures and goshawk in the Natori City. Geographical information system data with hydrological simulation contribute to making of SIs. Habitat area of species examined is estimated from habitat suitable index (HSI) in the whole Natori River basin using past survey data. We can obtain the agreements between actual habitat and estimating one and the predictive values for each species are more than 0.85. HSI results can give us quantitative information of effective factors in habitat. Species in stream area are affected by hydrological fluctuation more than mean velocity change, so that, hydrological simulation data plays an important role for estimation of habitat.

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We have proposed a methodology accessing watershed environment in view of ecosystem. Habitat suitability index on actual habitat places investigated by field survey is calculated from numerical map information and hydrological simulation. This index is used to discuss influences on habitat in the cases of landuse change and climatic change, and to evaluate biodiversity. The results show that urbanization affects habitat of lentic species, accipiter gentiles habitat is corresponding to high biodiversity areas, and most of high biodiversity area exist in the middle stream region. The methodology proposed is useful for understanding the distribution of the watershed environment quantitatively.

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In this paper, we experimentally investigate hydromechanical behavior of water surface ripples by using the simultaneous image measurements of an open-channel turbulent flow and the free surface. We also try evaluating the performance of the water surface ripples as a visualization tracer quantitatively for the local remote sensing technology for river flows. It is found out that the behavior of the water surface ripples can be explained very much well by using the theory of wave-current interactions in which the propagation velocity of water surface ripples is treated as the group velocity of waves propagating upstream in the open channel flow. An equation that estimates the mean bulk velocity through using the representative wave number is derived by taking the wave energy conservation into account, and its validity is confirmed by the experimental data. It can be expected from the obtained results that the performance of the water surface ripples as a passive visualization tracer in a river flow is limited since the water surface ripple has its own propagation velocity, and a correction based on the wave theory as treated in this paper should be needed for accurate river velocity measurements.

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The standing wave pressure is the predominant force in designing deepwater breakwaters. When the design of breakwaters is conducted by means of the reliability based design, some values denoting the reliability of the quantitative estimation of the standing wave pressures will be required in order to obtain a reasonable dimension for the breakwater. In the present study, a comparison between the computed results using the forth order approximation based on the finite amplitude theory and the experimental results is made to obtain those values. Consequently, both the bias of the experimental results with regard to the computational results (=0.91) and the standard deviation (=0.10) are found.

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The gas convectional resistance of the culm in P. australis was analyzed with Darcy-Weisbach type equation. The head losses are occoured mainly at the node diaphragms and basal pith cavity. The friction losses at the inner walls excluded basal pith cavity are inversely proportional to the Reynolds number. The head losses coefficients at the node diaphragms are linearly proportional to a root of the kinetic heads. Therefore new head loss coefficients were defined. This research made clear the physical aspect why Darcy’s type equation is able to apply on the convection of the culm in P. australis. The mathematical model constructed in the present study was in good agreement with the experimental results.

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This paper introduced observed high frequency sea-bed pressure data obtained from the Japanese nation-wide coastal wave observation network (NOWPHAS) just before the attack of the 2007 Noto-Penisula-Earthquake tsunami and the 2005 Off Miyagi Prefecture Earthquake tsunami events. Duration time and frequency spectrum analysis was conducted with the K-net earthquake vertical acceleration data near-by. Coastal sea-bed pressure observation has a high potential for future tsunami disaster prevention, for the observed pressure is the direct result of the earthquake to the sea-water. Improvement of the NOWPHAS system is recommended with the additional acceleration sensor and soft-ware system change.

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