The main purposes of this study are to investigate the influence of shear stress and sediment properties (sediment type, water content, viscosity and yield value) on the resuspension rates of a cohesive bed in streams, and to estimate theoretically the rate as a function of those parameters. Three clays and six muds with several different water contents were used as bed material. From the results obtained by dimensional analysis of experimental data, we concluded that the cohesive bed should be regarded as an aggregation of cohesive sediment for the resuspension phenomenon. A dimensionless resuspension rate function for cohesive sediment was deduced by establishing the equation of motion for a sliding sediment and considering the fluctuation of tractive force. This function showed good agreement with the experimental results.

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Because of recent changes in river environments and the subsequent increase of disasters of hydraulic structures caused by local scour, it is important to make a physically reasonable model for local scour with sufficient applicability. An analytical model to describe scouring process at front foot of a bridge pier is derived based on reasonable estimations of the vortex intensity and the subsequent sediment motion. The model is so available that it is possible to analyze the responding properties of scouring to the fluctuation of sediment discharge as an important aspect of the changes of river environments. The fluctuation of sediment discharge caused by the migration of dunes is a typical example, and a coupling of the derived model with a model for dune migration makes it possible to predict the fluctuation of scour depth and the maximum scour depth as a design criterion.

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On the basis of flow force conservation the two-dimensional buoyant surface discharge of a light fluid over a stagnant ambient fluid can be classified into four regimes: a fully entraining buoyant jet, a jet/jump combination, a direct jump, or a flooded jump. A depth-discharge diagram for such entraining flows is presented to assess these different transition paths between a supercritical discharge and an imposed subcritical downstream condition. Certain flow instabilities are predicted to occur at downstream Froude numbers of 1 or 1/2, respectively. Comparison with various experimental data, including additional data by the authors, confirms the flow force conservation theory. Furthermore, a more detailed analysis of the spatial development of a buoyant surface jet is made using an entrainment formulation with buoyant damping for closure of the governing equation. The predictions compare favorably with experimental data.

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This paper discribes the mechanics of the flow laden with cohesionless small particles as mud flow. The velocity profile and the motions of the particles in the flow are observed so as to show that the generally accepted fluid models such as the Dilatant, the Bingham, etc., cannot exactly explain the flow. It is found that both the collision between the particles, and the turbulent mixing of the fluid mass containing particles play very important role in the mechanics of the flow. A new model to explain the flow is proposed and examined by the experiments.

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Mechanism of particle suspension is investigated experimentally and theoretically in the flow over a rough bed. Particle motion and turbulent flow near the bed, which is visualized by dye, are photographed simultaneously, and the forces acting on the particles when they are lifted up from the bed and are moving in the flow are discussed from the results. Further, the structure of turbulent flow on the rough bed, which is visualized by hydrogen bubble technique, is investigated about the periodicity and time scale of upward flow. A stochastic model of suspended particles is formulated from the mechanism of particle suspension, the structure of turbulent flow and equation of particle motion. This model is applied to the analysis of critical stage, the process of vertical dispersion and step length of suspended particles.

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The equation of multivariate maximum entropy distribution is evolved for the hydrologic frequency analysis, and its characteristics, which include the applicability to hydrologic data, are investigated in detail.
It is proved that the maximum entropy distribution is based on the same level as Pearson's system of frequency-curves because it derives some distributions which are wellknown in statistics. The general equation of multivariate maximum entropy distribution with the restriction of arbitrary function g_r (·) is obtained by Lagrange's method of multipliers. In the case of the moment problem, the parameters of the distribution are identified by the iteration method. When three-variate normal distribution and hydrologic data are adopted as the populations, the conformity of multivariate maximum entropy distribution is investigated in connection with low-order moments, and it is proved that 3M (2, 2, 2, 2) is in a good agreement with actual data.

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The behavior of a vortex ring impinging on a density interface is investigated both analytically and experimentally. On the surface of the vortex ring, a secondary vorticity is produced not only by the discontinuity in velocity between inside and outside of the vortex ring, but also by the difference between the direction of the gravity force and the density gradient. The generation of the secondary vorticity is analyzed by means of the vorticity equation, then the deformation and the motion of the vortex ring are investigated with respect to time. These results clarify the basic mechanism of some important behaviors of vortices on a density interface.

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A method to calculate suspended load is proposed for equilibrium and non-equilibrium conditions. The diffusion theory is conventional for these problems, but it is difficult to decide the concentration at a reference level and the diffusion coefficient of particle. In the present theory which is based on the stochastic analysis of motion of suspended particles and pick up rate, suspended load can be predicted without these parameters, and it is found to be useful in calculating non-equilibrium suspended load.
Pick up rate is studied for nonuniform sediment theoretically and experimentally by considering sheltering effect of gravels, and suspended load can be calculated for uniform and nonuniform sediment. Equilibrium concentration distribution and concentration at reference level which are calculated from the present model are compared with the previous results. Then, this method is applied to calculating non-equilibrium suspended load with armouring process.

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Mathematical models for defining stable straight rivers are presented, in which poorly-sorted coarse bed materials are transported without altering their channel cross-section. Introduction of lateral turbulent diffusion in the momentum balance equation makes it possible to obtain a bed shear stress distribution which allows a mobile bed and immobile banks. A condition of threshold at junctions of the bed and the banks and a resistance formula are used to obtain the stable depth and width, respectively. Laboratory tests are conducted by changing size distributions of bed material but keeping the same median size, which reveals that the channel cross-section is considerably affected by the size distribution. The theory predicts the effect of mixtures very well, and it is also applied successfully to actual rivers. Rational regime relations are presented based on the analysis.

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The principle of Time Marching Approach, defining the steady flow in pipelines as the flow in the limiting case where the transients finally converge, is explained theoretically in this paper. The speed of convergence in TMA depends on the spectrum radius of the coefficient matrix related to the characteristic finite difference equations for the linear partial differential equations, which are derived through perturbation from the steady flow equations, and a new method is proposed to converge rapidly to the steady flow.

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This paper discusses the uncertainty of the estimated population parameters in the hydrologic frequency analysis. Firstly, the changes of the distribution shape and the probable variate of a fixed recurrence interval are investigated using the observed hydrologic data. Next, when the population parameters of the normal distribution are regarded as the random variables, the method of estimation of the decrease degree of the uncertainty, which is measured by the entropy of the distribution in unknown expectation-known variance and unknown expectation-unknown variance, is developed in some detail. Besides, applying this method of estimation to the observed hydrologic data, the validity of this method is investigated. Finally, the possibility of the application of this method to the non-normal population is suggested briefly.

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An analysis is provided for the spatial variation of the strength of secondary circulation in laminar flow through curved channels. The process of interaction between the main and the secondary flow is definitely shown through experiments. A mathematical model for computing the longitudinal variation of secondary circulation is developed reflecting the effect of the interaction. Experimental results support this model. Because of the important effects of secondary circulation on the river flow profile, techniques used in this model will provide usefull improvements in computational methods for river flows.

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A mathematical model for defining the bed topography and the bed material size distribution in uniformly-curved bends is developed, in which the coarsening of sediment size toward the outside is predicted and the bed topography is calculated coupling with the lateral sorting. The major agency for sorting is that coarser grains feel a larger ratio of transverse gravitational force to fluid force than finer grains. It is revealed that the sorting reduces the depth of scour considerably in the outer area of bends. The model is tested with a laboratory test, and it is applied to an actual river, both of which support the present theory.

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An analytical procedure is developed for predicting the surface profile of a bore in a channel of constant water depth caused by the breaking of a dam. The velocity field of bore is assumed to be analogous to the conventional plane turbulent wall jet in a coordinate system moving with the bore. The model is analyzed as a quasi-steady flow, and the flow equations are satisfied in depth-integrated form. The validity of the solution is examined through comparison with the results of laboratory experiments. It is found that the present procedure is applicable to bores over a relatively smooth bed.

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An experimental work is performed to examine the characteristics of internal fluctuations in two-layer thermal strata induced by the combined action of grid-oscillation and heating from below. The interfacial layer depth and the vertical deformation of interface are expressed as a function of Péclet number and the overall Richardson number which are defined from the grid-turbulence scaling velocity. Based on these results, it is found that the relative intensity of temperature fluctuationn at the thermocline is proportional to Péclet number as well as to the inverse of Richardson number. It is concluded that the mechanical turbulence plays more predominant roles on the internal fluctuations than the thermal convection. However, the thermal stirring effectively contributes to the mixing process because of its buoyancy flux effects.

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A two-dimensional computation method for open channel flows is developed reflecting the effects of secondary flow. Among the assumptions in the analysis, the vertical velocity profiles of the main flow and the secondary flow are assumed to remain similar, and the general distoreted velocity profile is expressed by the composition of them. This method has been verified using available data. The scheme of computation is very simple so that computation by personal computer is feasible.

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Engineering application of groundwater simulation models is to decide the efficient allocation of limited groundwater resources. Linear response model analysing confined groundwater flow was combined with linear programming (LP) to formulate the method of optimal groundwater withdrawal allocation. For this purpose, linear response coefficient ω^p_{i, j} was introduced as the parameter of linear response model. Linear transformation of the model with the parameter ω^p_{i, j} directly became constraints in the LP formulation. Objective function was written to maximize the total withdrawal of an area. Thus the LP method of optimal withdrawal allocation was formulated applying the model. Some cases of optimal allocation problem at Lowland, Tokyo were solved using the method.

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Two methods of analysis for two-dimensional motions of a floating body moored in a vibrated, restricted region are developed assuming the irrotational fluid motion and the small amplitude motions of waves and a floating body. One method is the boundary element method. The other is the method based on variational principle derived from the Hamilton-Kelvin principle. In the latter, we can obtain the explicit solution by assuming that the water surface moves up and down in keeping a horizontal plane.
As a result of calculation for rectangular cylinders, it is found that (1) the calculated values by two method are in good agreement at low frequency range (2) four types of resonant oscillation exist in the motions of the floating body.

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A theoretical analysis using an integral equation derived for the unknown horizontal velocity component in a pervious wall is proposed for estimating the reflection coefficient of wave dissipating caisson with multitudious vertical pervious-walls in an oblique sea, and various factors related to wave and structural conditions having influences on the reflection coefficient are investigated for the double vertical slotted-walls caisson. The theoretical results are compared with the experimental data for a normal incident wave. The optimum structural conditions to minimize the reflection coefficient and the difference in the wave dissipating characteristics between the single vertical slotted-wall caisson and the double one are also discussed in the paper.

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This paper proposes a calculation model of random wave transformation on a uniform slope for frequency distributions of the wave height, the percentage of breaking waves in the wave height distribution, and representative wave heights in shallow water including the surf zone. Input data are a deep-water wave steepness, a probability density function (pdf) of the wave height and a bottom slope. The pdf is divided into 400 segments with each representative value of the wave height and the appearance probability. It is assumed that each segment consists of an individual wave of which the wave height changes equivalently to a monochromatic wave having the same height and period. The transformation of random waves is estimated by superposing the calculated wave height of an individual wave with its appearance probability. The predicted results by the present model agree well with those of the laboratory experiments.

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This paper presents an analytical study on the hydraulic characteristics of a surging front on a gently sloping beach caused by tsunamis forming a partial clapotis, based on the conventional shock relations. The validity of the solution on the height of surging front is examined through comparison with the results of laboratory experiments. It is found that agreements between the theory and the experiments are very well. The solutions are affected by the run-up height of the tsunamis. Therefore, it is also discussed analytically. The comparison of the theoretical and the experimental results shows that the theoretical result well describes the run-up height of tsunamis with a relatively large reflection coefficient.

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It is well known that truncated error of long wave simulation by the finite difference method appears as the dispersion or dissipation effects and causes numerical damping of wave height. In the present study, the truncated error of tsunami numerical simulation is investigated by using exact and approximate solutions of descretizated equations. As a result of one-dimensional initial value problem, it is clarified that numerical error varies dependently of Fourier spectrum of initial wave profile and resolution Δx/L and the value K(=√gh·Δt/Δx) are important parameters to estimate truncated error.

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This paper presents a numerical model of nearshore currents due to irregular waves. The radiation stress is estimated by a current-refraction model for irregular waves, in which the energy dissipation by wave breaking is modeled through the use of a saturated frequency spectrum in shallow water. The model is in reasonable agreement with measured wave height and mean water level variation, and observed nearshore current patterns. Next, the model is applied to the computation of wave transformation and nearshore currents on a uniformly sloping beach and on model topographies with complicated contour. The comparison with the results based on a regular wave model shows that wave irregularity has a smoothing effect on the offshore distributions of wave height, mean water level variation and longshore current, but that it does not have much effect on nearshore current patterns.

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Characteristics of sea-breeze fronts are investigated by field research and laboratory experiments. Field research was conducted at the Kasumigaura Lake where a sea-breeze front shows its plane figure through water surface ripples. Experiments were carried out using water tank with heating device below the inland part. Both front structures observed at the field and the laboratory water tank are closely similar to each other. A consideration is given to the celerity of sea-breeze front as a function of the initial density gradient and the density flux from the bottom.

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Wave reflection and transmission by an open-bottom airtight chamber for an active wave control system are investigated with consideration of compressibility of the air in the chamber. The hydrodynamic interaction of incident and scattering waves with the internal air of the chamber is formulated by employing linear potential theory and the equation of ideal gas state. Numerical results are presented to show the effects of internal air pressure upon the characteristics of wave reflection and transmission in various structural configurations. Model tests have been carried out in a two-dimensional wave flume. The experimental results are in good agreement with the numerical predictions. This paper also discusses an active wave control system to attain an optimum running condition by controlling the internal air pressure.

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A simple expression is presented on the capability of storage-treatment systems to reduce non-point pollutant runoff load. The effectiveness depends on capacities of the facilities and probabilistic properties of the runoff, such as the interval, duration, volume and concentration of the runoff events. Assuming the compound Poisson process for the runoff time series, the exact expressions of the ratio of treated load in terms of storage and treatment capacities are theoretically derived on the neibourhoods of all boundaries of the domain on which the problem is defined. Then, an approximate expression over the whole domain is presented of which the value and the first order derivative coincide with those of the exact ones near the boundaries. The accuracy is checked by means of Monte Carlo simulations.

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The die-off process of coliform group was investigated in AIT-oxidation ponds in parallel with the laboratory tests. More than 99% of coliform group was removed in AIT-oxidation ponds. A major type of coliform group in the influent was E. coli., while Klebsiella spp. took place of E. coli. in the effluent. E. coli. was more sensitive to the environmental conditions in AIT-oxidation ponds than Klebsiella spp. and C. freundii.
The model for predicting the coliform group density in the facultative pond was proposed and the die-off rate coefficient was estimated. In case that a factor affecting the die-off process of coliform group was expressed by the sum of the sunlight effect, the dissolved oxygen effect and the pH effect, a better estimatin of the coliform group density was obtained. And then the estimated die-off rate coefficient was 2.56 (1/day) around 30°C.

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A regional waste disposal system consisting of four subsystems, i. e., intermediate treatment (incineration), transportation, land reclamation and leachate treatment, was optimized by the dynamic programming technique. The sum of construction and running costs was employed as the objective function to be minimized under maintaing the COD concentration of effluent below a certain level.
The optimal system under the study comprised incineration of the whole waste, reclamation by the sectionally controlled filling, and biological leachate treatment followed by the adsorption by activated carbon. The cost of incineration is the largest portion as much as 86% of the total cost. The effects of parameters such as the transportation distance, the amount of waste disposed, and the efficiency of biological leachate treatment on the optimal system design were also examined.

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A mathematical biofilm model considering diffusion and decomposition of a single substrate was developed, and simplified approximate relationships between net removal rates and normalized biofilm parameters were obtained theoretically. Long term experiments on acetate treatment with methanogen attached biofilm reactors were carried out, and removal rates were analized by using the present model. Variations of biofilm parameters which specified treatment characteristics were represented as a function of the attached biomass. By using these parameters, treatment characteristics of methanogen attached biofilm reactors are simply and accurately evaluated.

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A new type of fixed wheel gate has been developed for regurating gate of high head dam. Through a series of experimental and theoretical analysis, it has been clarified that the new type of gate was applicable in real gates and was proved stable in dynamic behavior against vibrations due to the fluctuating water pressure without any divergences. The stability has been evaluated both by model tests and numerical analysis. The structure has been analysed by a model subjected to the distributed loads which were measured on a model of new type gate through laboratory tests. The static loads are also measured and analysed same as dynamic loads. The results about the responces of gate vibration system by dynamic loads which are measured in model tests, show good coincidence with the measured data in field gate. Therefor the method as shown here gives good solutions for estimating the forced vibration phenomena of gate system.

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Energy loss of air flow due to water-valve which will be utilized in a wave-power-generation system is experimentally studied. Conclusions are; 1) the difference between steady and unsteady flow is not recognized; 2) flow loses its energy by two factors; one is threshold pressure head which is equivalent to submerged depth of vertical pipe and the other blowing out of air into water; and 3) the loss by later one is proportional to the 0.5 power of velocity in case of low velocity and to the 1.6 power in case of high.

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