A distributed rainfall-runoff simulation model based on the BGIS (Basin Geomorphic Information System) is developed. By using the BGIS, a watershed basin is represented as a set of slope elements of a quasi-three-dimensional shape by making use of cubic spline functions. On an approximated slope element, water movement is represented by combined surface-subsurface kinematic wave equations considering a change of slope gradient and slope width, and discharges from distributed slope elements are routed to a basin outlet through a channel network. BGIS is applied to the Shirasaka experimental basin (0.88km²) in the Tokyo University Forest in Japan, and runoff simulations are carried out.

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The cold region river forms a large quantity of frazil slush during winter period. In early March, the solid ice cover partially melts and remains along both sides of the river. Authors detect new phenomena, the discharge shows a daily oscillation in early March through field survey during 1992-1994 in Penkeniupu River.
This paper aims at analyzing physical mechanisms of such a daily oscillation and building its prediction model. Simulation results of the step-pool model considering anchor ice showed good agreement with the observed discharge.

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Experiments on the snow removal system using an open channel are carried out using the model snow lumps and the real snow lumps. Large amount of plastic balls are used in the experiments. Thus, the velocity profiles in the open channel flow with model snow lumps can be measured. The velocity profiles in a lower part occupied with water are approximated by the log-law. The speed of plastic balls is a little smaller than the velocity of water under balls. The snow transport rate, the inclease rate of the depth are also measured for the model snow lumps and the actual snow lumps experiments. These experimental results are snown to be explained by the theory developed by one of the authors.

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A theoretical model of the equilibrium cross-sectional shape of straight sand-silt rivers with permeable dikes is presented in this paper. The theory of self-formed sand-silt rivers is extended to include the case of channels with permeable dikes. It is found that the dike region tends to be completely filled with fine sand. It is also found, on the assumption that water discharge and river bed slope are conserved, that the equilibrium center depth is increased from 3% to 30% due to the effect of permeable dikes with common densities. With the aid of the theory of equilibrium longitudinal bed profiles, the present theory can explain the observed cross-sectional change; a 70% depth increase after the insert of permeable dikes.

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Gravel bed rivers transporting suspended sediment often have banks composed of fine sand (what we call “gravel bed sand bank morphology”). A theoretical model of the formation of “gravel bed sand bank morphology” is presented in this paper. The theory of equilibrium cross-section of sand-silt rivers is extended to include the case of gravel bed partially covered with fine sand. The theory shows that the location of sand deposition depends on the center depth, bed slope, sand size and sand supply. It is found that the bank regions tend to be filled with fine sand if center depth and bed slope are sufficiently large, and sand size is sufficiently small, and that the central bed region is covered with fine sand otherwise.

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It is essential to know the characteristics of granular chute flows to delineate the hazardous area of the pyroclastic flows or the snow avalanches. To contribute to such professional requirement, some kinds of granular chute flows are produced in an experimental flume to measure the mean as well as the turbulent particle velocities and solids concentration in the flow. Three kinds of characteristic behaviours are evident; i. e., laminar, laminar/dispersive and dispersive types, which mainly depend on the slope angle and the bed conditions. The theoretical constitutive equations for such granular flow which take the inelastic collision, the kinetic momentum transport and static skeleton stress into account well explain the experimental results.

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A numerical study has been performed for turbulent flow developing in a compound open-channel flow with variable-depth flood plain by using Reynolds stress model. In the calculation, govering equations are transformed from the physical plane to the calculation plane by boundary-fitted coordinate systems. Moreover, developing behavior of secondary currents is provided by the present method. The calculated results are compared with the experimental data available. As a result of this numerical study, it is found that the present method can predict well the cellular secondary currents, streamwise velocity and distributions of Reynolds stresses. As for the developing of secondary currents, the calculated results show that these flows change its profiles through interference between these flows and indicate the maximum value befor reaching the fully dveloped flow.

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Experiments of drag forces on a solid body in dry sediment and sediment-water mixture flows are made. The measurements of the drag forces show their significant variation with time. The forces are divided into a mean value and fluctuations. From the mean value a drag coefficient is determined. A nondimensional parameter governing the flow situation around the body is proposed. Drag coefficient depends on the nondimensional parameter. Frequency spectra of fluctuations for the mixtures and dry sediment are compared with those for clear water. The collisions of grains with the body play dominant role for the generation of drag forces in the flows with the smaller values of the parameter. The effect of turbulence becomes important in the flows with the larger values of the parameter.

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2nd order non-linear long waves have attracted special interest recently to be a driving force in several phenomena such as a harbour resonance, a slow drift oscillation of floating body and a formation of multiple longshore bars in a shallow water region along the coast. Kimura (1984) gave a convolution to give an averaged directional spectrum of the 2nd order long waves giving the first order directional wave spectrum. Since the convolution involves a complex integral kernal, long complex calculations are necessary. The present study deals with a simple modeling of the 2nd order long wave spectrum giving the 1st order directional spectrum used by Goda et al. (1975) in a shallow water region.

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A simple and inexpensive system is developed to generate an asymmetric oscillatory flow in a closed conduit, which simulates sea-bottom boundary layer induced by cnoidal waves. Easy-to-invoke modifications in the system may produce asymmetry of waves about horizontal as well as vertical axis, producing a wave profile encountered in the surfzone. The relations have been established between theoretical quantities and system parameters in order to facilitate practical application of the present system. Preliminary experiments have been carried out to check the validity of the system and excellent agreement has been found between theory and experiments.

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In this study, experiment and numerical analysis were explored for column in regular waves, the column which is supported by the base with nonelinear reaction charateristics, so that, in the case of chaotic vibration occurred, any condition for such occurrence and also its any charateristics may be acquired. As a result, (1) in case of column with two attractors, there exist the spheres of occurrence and extinction for chaotic vibration responding to change of wave height; (2) the experimental results and those of calculated ones are well consistent with each other in spectral and phase portraits, accordingly, prediction of chaotic vibration occurrence with numerical simulation seems to be possible.

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To develop the Tachibana Bay, Tokushima Prefectural Government investigates the safety related measures on the Nankai Tsunami in 1946. Due to land reclamation, the layout of the land is continuously changing. In this paper, using a numerical simulation, we clarify that the Tsunami will show quite different behavior as before.
Moreover we present a measure such that the change of the Tsunami's behavior will not have a bad affect with the surrounding areas.

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