Conditional probability distributions of runoff discharge and water storage at a flood control reservoir given several hour lead forecasted rainfall intensities are theoretically derived using expectation techniques based on the linearized relationship of storage function between rainfall and runoff intensities and on the continuity equation between runoff (inflow), outflow, and water storage of the flood control reservoir. By this theory, significance of rainfall forecasts with various levels of accuracy is investigated.

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This paper aims to physically explain the storage function S=kQ^p, one of the typical lumped models, on the basis of fundamental equation of saturated-unsaturated flow given by Richards with fundamental relationships of soil water properties, i. e. water retention θ-φ and peameability K-θ. At the first stage of this paper, outflow properties are examined using a two dimensional saturated-unsaturated flow model. At the second stage, the relationship between parameters (k, p) of storage function and basin properties are made clear. Result s show that the parameter k is dependent on the slope properties (slope dimension and soil properties) and the parameter p is the inverse of β which is the exponent of K-θ relationship shown by Kozeny.

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Stormwater detention facilities have been used to reduce stormwater runoff from urbanized areas. They are recognized as a means to reduce peak flows of downstream rivers, and it is needed that the planning of them are done on a watershed-wide basis. In this paper a method to estimate the effects of runoff control of stormwater detention facilities on a watershed-wide basis, and the results of its application to a small river are presented.

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This study develops a quasi-three-dimensional model which practicality and economically calculates secondary flows by substituting the average water depth velocities U and V (U downward and V transverse) obtained from the two-dimensional shallow water flow model into the equation of motion in the three-dimensional downward and transverse directions.

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Radio current meters, which are installed on bridges or similar locations, emit radio waves at the surface of the river water and measure the surface velocity from the reflected waves using the Doppler effect. Fieldtest of Radio current-meter has been done on the Uono river for flood discharge measurement during snowmelt flood seasons in 1990 and 1991. In addition, 4 radio current-meter were set on the same bridge in 1991. All of the data were analysed and the estimation method of discharge from surface velocity data obtained, was proposed. The flow velocity and its direction (velocity vector) at a given point can also be obtained from the observation of the water surface at the point from two points on a bridge. Rooping characteristics of H-Q relation could be measured on the Furu-River.

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Critical condition that snow can move or not in an open channel flow is investigated theoreticaly and experimentaly. A theory of snow movement conditions is derived from force balance of large snow chunks for flow direction. In order to comapred with the theory, the experiments are carried out for several snow conditions and hydraulic conditions. The theory can predict the movement of several size of snow chunks under several bed slopes and surface materials of the bed.

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The turbulent characteristics of flow with spatial change of bed roughness in open channels are described by a relaxation model with an impulse response for Reynolds-stress distribution. The applicability of the model to the flow with an abrupt change of bed roughness are inspected through flume experiments and field measurements. The applicability to the flow with longitudinally cyclic changes of bed roughness is also inspected by flume experiments. Furthermore, a numerical calculation of the flow with an abrupt change of bed roughness is conducted based on a k-ε turbulence model, and the physical background of the relaxation model is supplemented.

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In order to evaluate the impact of bridge piers in a river on their downstream channel and hydraulic works, it is necessary to develop some effective numerical methods for estimating local scour as the supplement of the hydraulic model experiment. This study is intended to construct a three-dimensional numerical simulation model for the local scour around a bridge pier by improving Fukuoka's three-dimensional model in the computation of water flow and considering appropriately the non-equilibrium sediment transport in the calculation of bed variation. It is shown that the numerical simulation model can obtain, with adequate accuracy, solutions that are in good agreement with the experimental results of the local scour from the large-scale hydraulic model.

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Through the investigation of sedimentation in electric power reservoirs, macroscopic tendencies toward domestic sedimentary features are grasped from the yearly changing conditions and the sedimentation rate, relating to various factors of the drainage basins and reservoirs. They are divided into three types of sediment accumulation changes; and the specific sediment accumulation needs to be estimated by its types. It also indicates that factors relating types and specific sediment accumulation, and the relation between types and reservoir plannings.

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This paper aims to establish the systematic estimation method of the wave force acting on the submerged sphere. First, the stochastic characteristics of the vertical wave force showing irregular time variation even under the regular wave train are discussed, in which the Weibull distribution is employ to express the appearance probability distribution of the period and maxima of it. The mean values of the Weibull parameters are given in this paper so that the mean values of such vertical wave forces can be evaluated. Then, the validity of the simplified Morison and modified Morison equations are discussed and the ranges in which the simplified estimation methods are applicable are given graphically. Based on the present study, the wave force acting on a submerged sphere under any conditions becomes to be evaluated with the simple and reliable estimation method.

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When tsunami attacks islands, there are some cases to damage the islands heavily by the trapping phenomena. Thus, a theoritical solution on the trapping of long waves by conical islands is obtained, which considers the effects of both infinite radius of islands and refraction by slopping beach. Characteristics on variation of spacial distribution of water elevation, characteristics on variation of runup height around coastal line, and characteristics on frequency response of maximum runup height are examined through the theoritical solution, then the condition in which the influence of trap is strongly appeared is demonstrated. The heights of tsunami traces in Oki-island and Okushiri-island can be explained satisfactorily by the present theory.

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A water quality simulation computer system was developed to utilize detailed environmental information on a watershed effectively and rapidly for planning of river basin management. The system was composed of a personal computer and mainframe computer. A water quality simulation model and display system of environmental information worked on the personal computer. The database on a watershed was constructed on the mainframe computer. The system was applied to the Oyabe river. The water quality observed in 1989 was well simulated with reasonable parameter values, although there were disagreements for some tributaries. The functions, which enabled effective utilization of the system, were also shown.

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The mechanism of gravity dewatering process in sludge drying bed is analysed using the consolidation theory. In order to ensure the accuracy of simulation, it is very important to evaluate the compressibility and permeability of water treatment sludge under low compressive pressure. The result shows that cake layer formed above media has poor permeability, and dewatering rate is limited. The destruction of this cake layer by aeration and/or mechanical stirring to maintain high dewatering rate is the principle of high speed sludge drying bed. The performance of this process is investigated experimentaly, and gravity dewatering equation under completely mixed condition is derived. The dewatering performances of two processes are compared, and it becomes clear that high speed sludge drying bed can treat higher sludge loading than conventional method.

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A long-range transport model for East Asia was developed to estimate wet deposition of sulfate. The results obtained by the long-range transport model were evaluated through comparison with observation data of acidic deposition. The observation was conducted at 21 stations throughout Japan for one year. The calculated amount of wet deposition of sulfate in Japan was 0.22Tg/y in S equivalent, while the observed one was 0.29Tg/y. The long-range transport model can predict almost 80% of the observed wet deposition. The contribution of the sulfur oxides from volcanic eruption to wet deposition amounted to about 20%.

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