All real hydrologic processes are more or less stochastic. While the dynamics for a runoff process are described by differential equations, strictly speaking, runoff phenomena are best expressed by stochastic differential equations. In this paper, the differential equations whose solutions give the first four moments of discharge from storage function model are proposed under the condition that rainfall input from a random process is independently distributed. The validity of these equations is cross-checked by a simulation method. It is possible to estimate the probability density function of discharge by using the obtained first four moments.

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Conflicts of interests in actions of country groups against global warming are evaluated in this paper. The main objective of the study is to improve a design process of players' prefernce vectors, based on conflict analysis: Traditional preference of outcomes is replaced by that of particular options of players in conflict analysis. The simple criterion to judge preferable order of options for each player is explicitly provided. And, by introducing basic principles of cost distribution as a value judgement system, we are able to analyze the conflicts among players' actions which reflect their different characteristics.

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Interparticle collision plays a very important role in bed-load transport with high concentration. The motion of bed-load particles are traced simultaneously in the numerical simulation of granular assembles. The results of present simulation has clarified that the interparticle collision brings the irregularity to the trajectory of individual saltation, which is the deterministic one depending upon only the initial velocity just after a repulsion at a bed surface. Such a change in the structure of bed-load layer due to the interparticle collision are investigated by comparing the results of the characteristics of the existing probability density and the velocity profile of bed-load particles with those estimated without interparticle collision.

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Laboratory tests were performed for flow over flexible, artificial vegetations attached to the bottom of an open channel. It is found that the Reynolds stress generated at the boundary of the vegetation is transported upward by ejection and downward by sweep, respectively. The organized vortex generated at the top boundary of the vegetation is closely associated with the transport of the Reynolds stress, and honami(waving of the flexible vegetation) is observed to be produced by the movement of the vortex. The periods of vortex generation predicted by a linear stability analysis agree well with the observed periods of honami generation. The instantaneous three-dimensional profile of the organized vortex was measured by employing PIV method and MASCON model, and it was visualized by using Application Visualization System.

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In compound open channels, the interaction between main channel and flood plain flow is the most important problem to be clarified. This interaction affects the resistance to flow and sedimentation on the flood plain. To carry on the research of the interaction, it is necessary to investigate the flow structure in the mixing zone between main channel and flood plain flow. In this paper, the three dimensional structure in the zone is visualized in horizontal, lateral and transverse cross section of the flow by the neutral buoyant tracer method and the hydrogen bubble method. The results show the existence of two kinds of vortex there, the one is the lateral vortex induced by the velocity difference of the two flows, and the other is the longitudinal vortex induced by the strong secondary flow which is observed near the external corner of the flood plain.

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Numerical simulation has been carried out for the fully developed turbulent flow of compound open channel by using Reynolds stress model. Since special attension is also paid for the boundary condition of free surface, modified boundary condition is adopted in this calculation. Moreover, the generation mechanism of cellular secondary currents is examined by calculating production terms in vorticity equation. Calculated results are compared with the experimental data available. The most characteristic feature is that the secondary currents proceed from the junction between the main channel and flood plain to the free surface. The present method can predict well not only this phenomenon but also the distributions of Reynolds stresses. Regarding to the generation of cellar secondary currents, calculated results suggest that the production term involving normal stresses plays an important role in generation of secondary currents along the free surface.

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Time scale of sediment suspension is estimated based on the numerical simulation of the suspended particle in flow with vertical random oscillation. Turbulence is simulated by superposing the oscillations of various frequencies together in taking account of energy spectrum of the turbulence. The settling velocities under regular and irregular oscillations are estimated. On the basis of the characteristics of the vertical displacement of particle, the time scale of the motion of particles is estimated respectively. The approximated formula of the time scale for calculation of suspended sediment is proposed by summarizing the results of the present simulation.

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An initial stage of diffusion of turbidity in direct dumping of soil using hopper barges with bottom doors was studied both through laboratory experiments and theoretical consideration. The two-dimensional experiments were carried out to observe turbidity clouds as a mechanism of the initial diffusion process by a flow field generated by a swarm of soil particles falling vertically in water. A semi-empirical model based on results of the experiments was developed and applied to the experiment.

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A method for the estimation of component waves, which form a monochromatic composite wave field, is proposed. The wave field is decomposited with progressive waves, where their progressive directions are given; and their amplitudes and phases, which specify the component waves, have to be determined. The least square method is employed to calculate the amplitudes and phases. Parameters of the estimation are tested by computing the component waves of a composite wave field, which is simulated by superposing 3 progressive waves. Then the method is applied to the analysis of the wave field around a semi-infinite breakwater.

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This paper proposes a methodology to estimate the occurrence of impact breaking wave forces on composite breakwaters, by utilizing a neural network which is said to be useful to deal with the data of which a cause-and-effect relationship is ambiguous. Experimental data of Tanimoto et al. (1981) were well classified and arranged with respect to the occurrence of impact breaking wave force by the neural network.
Since the network was constructed by the experimental data of which condition was limited to some degree, the network is not applicable to all cases of composite breakwaters; however, the methodology proposed here is general. Adding other data, we can develop the more suitable network.

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In this study, the authors set up a contact bed in the upper part of UASB (Upflow Anaerobic Sludge Blanket), named UAHB (Upflow Anaerobic Hybrid Blanket). Experimental results indicated that: (1) The contact bed not only promoted the granulation during the period of start-up, but also improved the organic matter removal. (2) When effluent is not recycled acidogenic bacteria exist mainly in the lower part and methanogenic bacteria mainly in the upper part. This reactor developed is a new kind of UAHB reactor which possesses the features of two-phase anaerobic digestion. The mechanisms of granulation in UAHB process were also discussed.

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Conventional biological nitrogen removal processes require large reactor volume as comared with conventional activated sludge process and need large space for facilities. When required to retro-fit conventional activated sludge facility to biological nitrogen removal facility, it is very difficult to secure a site for expansion and also expansion reqires large capital investment especially in crowded metropolitan area. To cope with these problems, we have developped new nitrogen bioreactor using immobilized nitrifying bacteria which are concentrated in polyethylene glycol pellet. Keeping these pellets in the nitrification tank of single-sludge pre-denitrification process, simultaneous high-rate nitrogen and BOD removal has been realized without further expansion of conventional activated sludge process facilitiy; the retention time of the reactor is the same of conventional activated sludge process even at a low water temperature as well as 10 degrees centigrade.

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