The objective of this paper is to show a theoretical approach to the determination of optimal order of channel routing within a channel network. The channel network with tree structure, widely used in distributed hydrological modelling, is studied. In addition to tree structure, the structure of drainage system which indicates the relation of upstream subnetworks is used to represent its logical structure. Under the basic rules of channel routing, namely from upstream to downstream, the theory about optimal order of channel routing is established, and an algorithm to obtain this order automatically is developed by considering the logical structure of channel network. The result shows that for a channel network with Horton-Strahler order ω, necessary and enough number of buffers storing series of discharge is only ω.

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The present study describes sediment discharge over the side weir and bed variation in a straight open channel, which are associated with sediment problems of a bypass channel. Energy losses due to the useage of side weir are discussed experi-mentally in the case that total flow discharge is drained from the weir. Sediment discharge over the side weir and bed variation are predicted well in terms of one dimensional governing equations and the results of the energy losses. It is basically important to estimate how water and sediment are diverted to a side weir in the case that part of the flow discharge is drained over the side weir. A simple method for predicting the diversion ratios of sediment as well as of flow water is developed. Calculated results of the ratios coincide with experimental data.

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In this paper, the flow dynamics of three-dimensional thermals is invesigated experimentally and theoretically. The variations of the maximum height, the maxiumum width and the speed of the three-dimentional thermals are measured by the experiment. It is shown that the non-dimensional height and speed are both dependent on the non-dimensional time. Next, the fundamental equations are developed for the three-dimensional inclined thermals. The theory consists of the equations of the mass concervations of water and salinity in the thermal, the momentum equation, and the equation of the thermal width. The numerical integral of the basic equations described well the experimental results of the height and the speed of the inclined thermals.

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A numerical model to simulate the turbulent flow in shallow water has been developed to reproduce horizontal large-eddies without loss of practical applicability, and thereby, to present a new framework to properly evaluate horizontal mixing of mass and momentum. The present computational method has been applied to a time-dependent computation of longshore currents. The results show the development of large-scale eddies around the breaker line and their subsequent merging as a strongly nonlinear process, demonstrating the importance of these eddies in the horizontal-mixing mechanism.

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SDS & 2 DH model developed recently by the authors to simulate turbulent flow in shallow water has been applied to horizontal large-eddy computation of river flow with transverse shear caused by a vegetationlayer. The development of horizontal large-eddies around the inflexion point in the mean flow profile and their succesive merging process are reproduced by the present computation with the good agreements with the experiments in the mean velocity and Reynolds stress profiles as well as in the large-eddy configuration. The existence of bottom friction, as compared with usual turbulent free shear layer, is found to significantly affect the evolution process of large eddies and hence their role in the related momentum transfer.

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As new models supersede the conventional wave forecast methods, the multiple regression wave forecast models described in physical parameters are developed. In the models, ocean wave separated into wind waves and swells, and assumed that propagation speed of each wave component is constant. From this assumption, the governing equations of the models are expressed as linear algebraic equations. For the verification of models, wave forecast is carried out.
It is clarified that the models show good accuracy and solve the difficulties of the existing wave forecasting models.

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Nonlinear resonance in a low-frequency range induced by incident wave groups is investigated numerically using the multiple-scales perturbation method. In the numerical analysis, the length of the harbour is assumed smaller than the long wavelength, but no other restrictions on the horizontal dimensions are imposed. Numerical results of the amplification factor for a rectangular harbour basin are compared with the experimental results. The agreements are, however, not satisfactory partially due to the difficulties in handling spurious free long waves. Random-wave numerical calculations are also carried out assuming the first-order spectrum of JONSWAP shape. The narrow-band approximation implied in the present analysis is found to be very acceptable in long-period harbour response problems.

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Stochastic simulation of bed-load particle is a useful means to estimate the probability density function of the moving period which plays an important role in non-equilibrium bed-load transport process along a temporal axis. First, the motion of a bed-load particle is simulated under various kinds of hydraulic conditions in oscillation-current coexisting flow. Secondly, the bed-load discharge is evaluated by integrating the non-equilibrium sediment transport formula, by using the result of the simulation. Finally, the formula of bed-load discharge within a half cycle of oscillation and that of a net rate of bed-load transport are proposed with particular reference to the effect of relative strength of current to oscillation.

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Wave induced scouring around a large-scale offshore structure is investigated by a series of model experiments. Scour patterns are compared and classified for various shapes and types of structures, and with those in front of breakwaters. The influence of the structure's being submerged and the foundation's being not embedded also examined. Scour and accretion at the side of a cylinder is related to the gradient of the velocity amplitude caused by waves. The relationship between maximum scour depths and the incident wave height are obtained.

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Role of the sediment cloud is very important in sediment suspension over ripples in an oscillating flow field. In this paper, sediment suspension over ripples is divided into two subprocesses: (i) entrainment process from a bed by forming a sediment cloud, and (ii) diffusion process of sediment particles released from the cloud. Osillation-current coexisting flow is simulated by k-εmodel of turbulence, and the motion of a sediment cloud is traced on the simulated flow field. Numerical analysis of sediment suspension is performed by a diffusion equation with a source term, where a sediment cloud is regarded as a moving source of diffusion.

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Simulation of multicomponent adsorption equilibria based on IAST-Freundlich model was executed for the evaluation of the overall isotherms which represent the behavior of the sum of all components. Batch adsorption isotherm was found to differ quite regularly with the change of the initial overall concentration. Batch isotherms plotted for the fixed overall removal rate and the column isotherm were described by Freundlich equations and the value of Freundlich exponent 1/n was essentially identical for all these isotherms. From these findings, two dimensionless overall isotherm models and a modified isotherm model were derived to compensate the difference of the initial overall concentration.

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The production of polyhydroxyalkanoates (PHA) from alkanoic acids by several activated sludges was investigated. The productivity and composition of PHA polymers were strongly dependent on the composition of wastewater (carbon sources) and the process of wastewater treatment. The screening of PHA accumulating bacteria from different activated sludges was carried out. The isolated microorganisms were divided into two groups. One group of microorganisms produced copolymers of 3-hydroxybutyrate (3HB) and 3-hydroxyvalyrate (3HV), P (3HB-co-3HV), from propionate, and the other produced the copolymers P (3HA) of 3-hydroxyalkanoates of C₅-C₁₂ from propionate under aerobic conditions. The isolated microorganisms from aerobic/anaerobic activated sludge showed high activities of taking phosphate under aerobic conditions but did not accumulate PHA under anaerobic conditions.

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