This paper describes regionalization of probable rainfall that plays important role in water resources planning, especially in planning of flood prevention facilities. The authors compare some procedures for obtaining estimates of probable rainfall at arbitrary locations that have no observation. The procedures are: (1) simple mm regional regression analysis, (2) stationary kriging, (3) nonstationary (universal) kriging, and (4) regression-kriging combined analysis. Applying these procedures to the Yasu River basin (387km²) in Japan, they have obtained the estimates and the estimation accuracy for probable rainfall, compared them, and discussed incorporation of orographic effects.

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A two-dimensional numerical model, in which the curvature of stream line is taken into account to evaluate the intensity of secondary flow, is proposed. The advantage of this model is that it is possible to calculate bed variation even if movable bed is locally dry caused by evolution of bar. This model is applied to the prediction of bed variation in a meandering channel. The results agree well with the measurements. Furthermore, as a result of double fourier analysis it is found that the results have almost the same feature of bed configuration as measurements have.

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A theoretical macroscopic approach on energy dissipation in hydraulic jump in rough bed channel has been introduced in this paper. The study has been also performed experimentally using spot roughness, mainly under the condition of 10% intensity of roughness with a relative length L_R/h_b=28 for 4<F₁<10, where L_R: length of roughned bed, h_b: height of spot roughness elements. (1) An increase of about 20% in energy dissipation and also an average decrease of 40% in jump length are observed, (2) Between 30% and 60% of the increase in energy dissipation is a direct result of using spot roughness.

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Closed air cushion surge chambers have economically contributed to construction of hydroelectric power plants in Norway. To apply this type of chambers to our geological and topographical conditions in Japan, however, requires 1) the review of the equation for calculating the volume of the chambers, derived by R. Svee to secure the stability of oscillation in a hydraulic system, and 2) the feasibility study for minimizing the volume. In this paper, the portion R. Svee expressed by means of the governor equation that Thoma had used is expressed by applying a speed governor, the inertia of rotation part of a turbine-generator unit, the hydraulic characteristics of the turbine, and parallel running of power plants. Then the equation representing the stability of surge oscillations has been derived and generalized charts are nondimensionally illustrated to show the minimum volume of the chambers. Furthermore, in the course of this study, the stability equation for a hydraulic system not equipped with a surge tank has also been derived.

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Taking into account, the highly accurate and stable features of the finite difference of second order derivative the new refined scheme for advection is developed based on the concept of solving 2nd order wave equation instead of 1st order advection equation. Characteristics method is used in order to get accurate solution propagating downstream only. From Taylor series analysis and many numerical experiments, parameters involved in this method could be determined as functions of Courant number. Comparison of this scheme with the other various ones in model calculations and Von Neumann stability analysis prove its superior accuracy and stability. This scheme can easily be applied to multidimensional practical problem by separating characteristic curve each component directions. This proposed scheme uses only three computational grid points so that there is no need to pay much attention to the treatment at the boundary.

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The aim of this paper is to establish a method for estimating not only extreme waves generated by typhoons but also long-term wave conditions, based on the application of aspectral wave prediction model being termed a single point model on a grid system with high topographical resolution. The validity of the model is varified by reasonable agreement between computations and observations for the time variations of significant waves at several locations and the long-term wave conditions, or so-called wave climate, at Hamakanaya at the entrance of Tokyo Bay. Next, statistical analyses of the wave data at Hamakanaya hindcasted with the present model provide the estimates for the most extreme wave heights generated by typhoons in the past 55 years, the wave heights with the return period of 50 and 100 years, and the occurrence rate of waves for different directions which is one of the indices expressing the wave climate.

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Flow state around a square cylinder installed vertically in the wave field and the wave forces on the cylinder have been analyzed by using the point vortex method. The wake vortices due to flow separation from the cylinder corner in the wave field can be presented easily from this analytical method, and the wave forces calculated from this flow states agree roughly well with experimental values. Applying the calculated wave forces to Morison formula, the range of inertia coefficient becomes C_M=2.1-1.7 which is similar to the case of a circular cylinder, and that of drag coefficient becomes C_D=3-4 which is much larger than in the case of a circular cylinder.

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Wave-induced resonant displacement of pile-supported offshore platform is investigated theoretically and experimentally. The characteristics of resonance curves and the displacement curves of pile have been shown by using the theoretical solution of the displacement presented previously by one of the authors. The theory indicates that the resonance occures at the integer times natural period of the structure in each vibration mode. The displacements of the deck measured in experiments agree well with the theoretical values not only at the natural period but also at the twice and three times natural period corresponding to the first mode vibration. Suppression of the fundamental resonance has been realized also in the experiment by making the natural period equal to the wave period where wave length is twice as large as the leg span to cancel the wave force acting on each pile.

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Removal kinetics of gaseous H₂S in a packed-tower type deodorixation plant was studied. Deodorization in this type had two processes; sorption of gaseous H₂S and biological decomposition of adsorbed (absorbed) H₂S. The sorption rate and the decomposition rate interacted each other, and the proposed kinetic model included the interaction. In order to estimate the coefficients of the model equations, some experimental data were simulated by the numerical calculation. This model and the coefficient estimating method are very useful to evaluate the optimal conditions of the biological deodorization packed-tower and to estimate the removal characteristics of the complex of odor components.

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The oxygen consumption by bottom sediment containing organic matter was examined. The oxygen consumption by suspended sediment particles showed two stages. One of them due to chemical consumption continued for about 3 hours, another one due to biological consumption for 3 days. The rate constant of oxygen consumption was calculated. Its dependence on ignition loss, water temperature and so on was examined.
The experiment of oxygen consumption by sediment was carried out using an experimental flume. According to the multiple regression analysis the oxygen transfer coefficient showed positive relationships with following
(1) shear velocity acting on water sediment interface, (2) water content of sediment, (3) rate constant of oxygen consumption of sediment particles, and negative relationships with size of sediment particle.
A model which estimates the oxygen transfer coefficient by shear velocity, water content, sediment particle size and rate constant of oxygen consumption by sediment particles was presented. The oxygen transfer coefficient obtained by this model showed a close agreement with the experimental results.
In this study, the method of giving a general and quantitative estimation of oxygen consumption by bottom sediment was presented.

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This device is used as a purifier for urban small rivers of which the flows are scarce and the water is polluted. It dams up the river flow and discharged water flashes down the river course automatically. The flash-board overturns due to the hydrostatic pressure by storage water. In this paper, a method of determing dimensions of this device is illustrated for practical use. The hydraulic characteristics of the device such as flash discharge and the equilibrium water levels are made clear by the model tests in a laboratory and a field. The cycle of the perfonnance and the variation of water level can be simulated.

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This study aims at the prediction of released water from reservoirs to avoid water deficit, by using the transition probability of sequential 10-days averaged discharge on the basis of a bivariate log-normal distribution. After the soundness of the adopted distribution and Markoff chain were proved, the probability of release amount during 30 days were shown in some numerical values. This technique can bring practical prediction for the release amount by using the climatic information on future rainfall amount.

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