The authors proposed a numerical model of the precipitation considering cloud micro-physical processes and aerosols by improving the term related to condensation and evaporation of cloud water in the model proposed by Routledge and Hobbs (1983), and simulated the orographic rainfall considering the existence of aerosols. The maximum value of rainfall intensity at the ground surface becomes weaker with increase of the number concentration of aerosols. In order to compare the parameterization regarding cloud formation and the phenomena occurring actually in clouds, the authors have constructed the experimental facilities with quasi-prototype scale. In comparison with the results of prototype scale experiments conducted by the authers, the validity of our precipitation model is confirmed.

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Runoff models can be divided into two groups: distributed parameter models and lumped parameter models. These two groups of models have been developed independently. The relationships between these two models were studied in the early 1970's. Since then, many types of storage function runoff models have been derived from the Kinematic Wave model and the unsaturated flow model. However, the characteristics of the various storage function runoff models have not been evaluated sufficiently. This paper focuses on the Kinematic Wave model and three storage function runoff models derived from the Kinematic Wave model and shows the evaluation method based on the frequency response and the stochastic response.

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Numerical modeling of flow including the calculation of hydraulic transitions is a useful tool when planning river engineering works. The Flux Difference Splitting Scheme, FDS, has been developed to simulate flow with shock waves in numerous aerodynamic applications. FDS incorporates the theory of nonlinear characteristic waves and the concept of numerical flux. This method can also be applied to open channel flow, thus producing a robust algorithm capable of calculating flow at supercritical, subcritical, and transitional Froude numbers. In this paper, an FDS model for two-dimensional open channel flow is developed and applied to several different hydraulic conditions. Comparison of calculated results with theoretical and experimental results is favorable.

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This paper describes turbulent structures in cavity open-channel flows. Turbulence measurements were conducted by making use of a two-component fiber-optic Laser Doppler Anemopmeter (LDA), where the Froude number, the Reynolds number and the aspect ratio of cavity shear layer changed. Next, Large Eddy Simulation (LES) and flow visualization by Particle Image Velocimetry (PIV) were carried out for two cases of experiments of which turbulent structures shows the characteristic behaviors. As the result, the effects of changes of Froude number, Reynolds number and the aspect ratio of the cavity shear layer, also the relationship of coherent structures were revealed and discussed.

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A linear stability analysis of downstream-driven channel inception is performed in this study. The analysis shows that, in the case of mild slope where flow is subcritical, perturbations grow only if the wavelength is on the order of 6-100 times as large as the critical depth devided by the friction coefficient (D_c/C_f) and that the characteristic wavelength which maximizes the growth rate of perturbation scales 10 times D_c/C_f. Evaluating the friction coefficient as on the order of 0.01, an estimate of incipient channel spacing on the order of 1000 times the Froude-critical depth is obtained. It is also found that the possibility of channel inception decreases as surface slope or the critical bed shear stress relatively increases.

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In order to make clear the physical mechanism of aoshio in Lake Abashiri, the present authors carried out field observations in which flow characteristics and the behaviors of density interface were focused on. We found that the density interface oscillates in the first mode of internal seiche, and wind-driven current that form two vertical circulation occurs, when strong wind is blowing on the lake for long time. Furthermore, the influences of the topography of the lake, the inflow discharge from the upstream rivers, and internal seishe on wind driven current in this lake are made clear.

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It was determined by oxygen isotopic and chemical composition analysis that most of the rainfall which fell in the upper stream of the Ishi river basin did not run off directly but rather ran off after it had infiltrated into the ground. Therefore, in the Ishi river basin upper stream, no remarkable change in water quality occurred even despite fluctuations in rainfall amounts. However water quality was changed by types of land use. The sulfur of SO₄^2- found in the upper stream water was estimated by sulfur isotopic ratios to have mainly come from the Izumi formation. The Ca²⁺ and HCO₃^- found in the upper stream water were thought to have come from CO₂ gas and feldspar contained within the soil of the forests during weathering. Ca²⁺, HCO₃^-, NO₃^- and SO₄^2- of river water in orchards and rice fields were thought to have come from fertilizer. The Na⁺, Cl^-, Ca²⁺, HCO₃^-, NO₃^- and SO₄^2- found in the river water of housing sites were thought to have derived from sewage.

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The conventional design method of the storm sewer network has two critical problems, i. e., the manhole energy loss is not considered in the design code, and the reasonable design is not easily obtained satisfying many kinds of design conditions. This paper presents an optimal design method of the storm sewer network considering with the manhole energy loss. The manhole and pipe diameters are determined by the optimality criteria method based on the minimization of the friction loss of pipe and manhole energy loss while the pipe slope and other conditions are known. Then the pipe slope is determined by the genetic algorithm based on the minimization of a cost performance function.

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Experiments were conducted to verify the validity of the BEM-FEM and poro-elastic FEM models, developed by the authors, for composite breakwaters. The BEM-FEM model is confirmed to predict well the wave field. The poro-elastic FEM model uses an equivalent nonlinear Darcy coefficient of permeability and runs under the surface pressure computed by the BEM-FEM model. The poro-elastic model computes the pore pressure in the porous media more accurately than the BEM-FEM model. The transmitted wave characteristics along with the dynamic behaviour of the composite breakwater and seabed are investigated. A study is conducted to find out the parameters causing a high pressure gradient at the offshore toe.

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