The reliability of the estimated parameters is evaluated by using the entropy to posterior distribution in the 2-parameter lognormal distribution. When λ and ζ are parameters representing the expectation and the variance of the hydrological value transformed into logarithm respectively, the following cases are discussed.(1)λ: unknown, ζ: known, (2)λ: known, ζ: unknown, (3)λ, ζ: unknown. In each case, the posterior distribution of the unknown parameter (s) is derived from Bayes Theorem, and its entropy is developed. This model is applied to monthly rainfall, and the increase of the reliability, accompanied by the increase of the number of data, is investigated.

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This paper compares various parameter estimation methods for three hydrologic frequency analysis models: three-parameter log-normal (3LN), the Gumbel (EV1), and the generalized extreme-value (GEV) distributions. Ten methods for 3LN including the maximum likelihood, moments, probability weighted moments (PWM), Ishihara-Takase, improved Iwai, sextiles, and least-squares are evaluated through Monte Carlo simulation studies in terms of the root mean square error (RMSE) of the estimates of the quantiles (T-year events). Six methods for EV1 and four methods for GEV are compared in the same manner. The merits of the methods are discussed in relation to the sample size N.

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This paper describes a probability model of heavy storm patterns with multi-local peak intensities. The definition of a storm cluster and a storm part leads that their occurrences follow Poisson and logarithmic series probability distributions, respectively. Using combined Freund's bivariate probability distribution functions gives the joint probability distribution of depth, duration and local peak for a storm part. The joint probability distribution function of total duration, local depths and local peak intensities for a single storm cluster with multi-storm parts is derived from those of storm parts.

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Flow series is considered by combination of the following two components. The one for the domain of smaller quantity of flow is a simultaneous correlated binomial distribution, the other for the larger quantity of flow is an independent binomial or Poisson distrubution. The whole flow model is composed of the linear combination of the distribution functions for those two models. The decision of boundary for two components and the selection of optimal model are judged by AIC (Akaike's Infomation Criteria). Through the analysis on the simulated data, the estimated results for the model are well coincident with the original parameters. In addition, by applying the model for the observed flow data at the drainage of Makio Dam, the decision of boundary and the characteristics of divided flow are considered as the reasonable results.

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The authors introduce a fractional function for adaptation of a hystogram of hourly rainfall data for 13 years at Musashikoganei. Then, using the above fractional function, they develop relationship between infiltration capacity of infiltration facilities and ratio of infiltration to annual rainfall. And an example of estimation of efficiency of infiltration facilities at houses is shown for Kokubunji experimental basin.

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The purpose of this study is to investigate the structure of residents' evaluations of the urban river and the frequency of visits to river space.
Questionnaires were conducted to residents around the Muromi river and the Naka river. The structure of evaluations and the frequency of visits were analysed statistically based on residents' past experiences, socialities, and their original images of the river environment.
The results are as follows: 1) The relation between residents' experiences and the socialities, and the evaluations of the Muromi river, is similar to that of the lowest reaches of the Naka river. 2) Residents who have higher evaluations of the quality of the river in their past memories, tend to have lower evaluations of the environment of today's Naka river. But residents who have higher evaluations of the past river, tend to have higher evaluations of the environment of today's Muromi river. And these tendencies are closely related to the difference of variation in the water quality levels during the past 30 years between the Muromi river and the lower reaches of the Naka river. 3) Residents who participate in the improvement of the environment of the Muromi river, tend to visit more frequently to the river. Residents around the Naka river also have this tendency.

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The questionaires are collected from the Komatu river basin in 1985 and 1989 to investigate the inhabitant senses for the river environment in an urban area. These data are anayzed by the Quantitative and Mathematical Methods. From the analysis, the followings are clarified: i) The inhabitants prefer the familiarity with water to the flood control. ii) The preference is essentially unchanged with time and depends on their inhabited district. ii) They are sensitive in the sense to the improvement of their life circumstances.

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The purpose of this study is to investigate the evaluation of a river environment in a city. A questionnaire survey was executed to the inhabitants around Ikemachi river in Kurume, and Komatsu river in Miyazaki, in which the water is conducted by pump. We discuss in this paper the inhabitants' evaluation of the two rivers under the impact of large rivers on environmental improvement.
The findings are as follows: 1) The inhabitants' evaluation responds to the river improvement which is worked to the small urban river, but is influenced by the sense of closeness to the neighboring large river.
2) There seems to be a tendency that the people who have more sense of closeness to large rivers don't like the immoderate artificial work for urban small rivers.

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Riversides have become a place for leisure, and several kinds of projects have been progressing in Japan. At the same time, we, Japanese, frequently experienced heavy rainfalls which caused many deaths and enormous property damage. It seems to be apparent that the problems of disaster prevention and of river environment are related to one another, so that these should be discussed on the whole for to be solved.
In this paper, the necessity of management of the river environment taking public awareness into consideration is described, based upon the results of ‘Survey of Awareness for River Environment’ carried out at Wallingford in 1989 and ‘Survey of Awareness and Practice for Flood Disaster Prevention’ at Nagasaki in 1988.

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Not only Flood control functions, Water utilizatoin functions but also Functions of River Environment has been to very important. Because of, River environment function has influence on Life environment, Mental climate of human being. Firstly, In the present report, We wish to describe the Water Familiarization Functions. We had divide for form of bank, Materials of bank, Water quality, Water quantity, Bioiogical indicator etc. in environmental factor of River for a Synthetic river environment statement.
How to Statement of River environment is methods of numelical system and Principle component analysis. An object of River is 25 rivers in Tokyo and, We had draw maps of Synthetic River environment statement by the charts. As a result of We could extract a preponderant rivers for improvement of river environment and countermeasure of river purification from 25 rivers.

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This paper discusses a hydro-environmentalconsideration on a river planning with an urban development. The low flow regimes of the K river in the Tama New Town after the urban development is successfully assessed wiht the dally hydrological model proposed by Ando et al. The ncomments and counterplans are considered in order to achieve the purposes of the river plan for the K river.

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The Shinmachi river flows in the center of Tokushima city and is composed of 7 tidal branches. The water pollutant level of this river is still high because of a large quantity of domestic wastewater. The pump system, which was constructed by Tokushima Prefectural Office for introducing clean water from the Yoshino river, has been in operation since 1980.
The aims of this paper are to ascertain the characteristics of flow in the Shinmachi river to valuate the amount of clean water introduced by the pump system and to investigate the effective operation of the pump system. By using field observation and a numerical analysis of an implicit type finite difference method, it was found that 70% of clean water from the Yoshino river flows into the Suketoh branch and the remain flows into the Shinmachi river. In the spring tide, clean water can be introduced most effectively when the pump system is activated only in the ebb tide.

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Anticipatory release operation against floods for multi-purpose reservoirs was proposed as a vehicle to incorporate the recent remarkable progress of precipitation forecasting techniques into better utilization of available reservoir storage.
The accuracy of precipitation forecasts was expressed by a set of standard deviations of absolute or relative prediction errors, σ_s, σ_e, σ₁ and σ₁ * that are respectively for the time that precipitation starts, the time that ends, differences between successive precipitation forecasts and differences of realized precipitation from the immediately preceeding prediction.
Numerical simulation was conducted for a hypothetical two-reservoir system of a typical scale, which revealed that the anticipatory release operation brings about an extra efficiency and reliability to the reservoir system by reducing flood damages of which the magnitude depends on the accuracy of precipitation forecasts. This is equivalent to the increase of an extra storage to the system.

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Although the methodology of the on-line rainfall-runoff forecasting has been established basically, there are still many important problems when it is really utilized in river management offices.
This paper especially focuses on the problem that the style of on-line rainfall-runoff forecasting information should be easy to be woven into existing management systems, and provides a new algorithm of on-line forecasting for it.
Our method can give the information on the whole hydrograph including the probability that the time to peak of discharge has passed the current time, the probability distribution of the total volume of future discharge, the probability that flood will surpass the warning water level, and the probability distribution of flood peak time and peak volume.

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It is one of the most important research topics in hydrology to investigate the physical and statistical characteristics of precipitation in a basin. The objectives of the present paper is to show some features of precipitation observed by the raingauges installed along the mountain slopes. The relation between the rainfall amount during the observation period and the elevation of the raingauges is shown in the present paper. Further, the relation between rainfall intensity and observation period is discussed. The rainfall amount during longer than 1 day increases linearly with the elvation. The rainfall intensity dicreases with1/√T which T is the observation period.

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A computation method of rainfall distribution to be utilized for short-term rainfall prediction based on the analysis of a heavy rainfall event which arose during Baiu season in Japan, and a method of extracting information required to utilize this computation method in a real time from three-dimensionally scanning radar are presented.

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Snow surveys just after snowfall events and radar observations have been conducted to study the snowfall distribution in the Chuetsu district, Niigata, Japan. It was shown that the snowfall distribution is mostly dominated by orographical factors-the main effect being that of ground-forced-induced ascending current of air. A three-dimensional numerical model of the atmosphere incorporating orography was used to estimate the regions where the ascending current of air can occur. They are in a good corespondence with the snowfall regions derived from radar data.

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A numerical model is proposed to predict the distribution of snowfall considering the effect of snow transportation by winds. This model consists of;(1) calculation of wind velocity vectors (3-D potential flow) over an arbitrary terrain (using Digital Terrain Data), and (2) calculation of snow particle transportation by wind. Influences of parameters in the model on numerical results are examined and reasonable values for the parameters are selected. Based on the above model, several examples of snowfall distributions on the ground are obtained from the distribution of snow particles observed at 2000 m above the ground by a radar rainrauge.

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Three-dimensional wind field are computed. The initial condition is givin by interpolation of the observed surface date and the gradient wind estimated from the pressure distribution, provided that the wind profile consists of the surface boundary layer, Ekman layer and free atmosphere. the optimum value of α=0.13 which is the ratio Gaussian precision moduli is determined so as that this ratio is equal to the ratio σ₁/σ₂, σ_i (i=1, 2) being deviations of the observed field from the desired adjusted field.

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The physical processes of unsteady flow in tidal reiver estuary are studied experimentally. These flows may be treated as two-layer flows without mixinng at or through the interface. Treating these flows as such requires to provide the interfacial shear known. Then, finding interfacial shear coefficient, this experiment by hydraulic model shows that the profielofs composed of four typical patterns are P, A, Z and B and are likely to vary with tide stage of their stratification. Further, the data obtained on the interfacial shear are compared to the results by the former researchers in Fig.10. Patterns of P & Z are shown to be good agreement with the former's results, but A & B are not compatible with this approximation. Flowing states depended on the river run-off are evaluated and shown to be the same results.

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Interfacial wave is an underwater undulation under certain density structure of the sea. When interfacial wave enters to a slope, its wave height changes, its shape deforms and after the breaking it runs up as a bore. By test channel experiments adaptability of the small amplitude wave theory to estimate wave height is studied and obtains as a limiting condition, energy transporting velocity-wave ratio Cg/C=0.9, that is, the limiting facter is lower layer thickness. This thickness can be defined as a breaking condition of interfacial wave. After breaking, the bore proceeds decreasing its height. Relation between bore height and its velocity, internal Froude number Fi=0.46. Bore height is estimated by energy loss using Harleman's resistance coefficient τ.

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The authors have performed an inviscid stability analysis of two-layer flow with tanh stream velocity distribution, considering perturbations of second order. Results of the analysis show good agreement with measurements of the phase relationship between concentrated vortices directly above and below the interface which were due to shear instability, and interfacial waves. Also, these analytical results lend increased credence to the growth mechanisms for Keulegan waves and Cycloidal waves over linear theory as mathematical models.

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Three types of mixing (stratified, partially mixed, well-mixed) observed in tidal estuaries are well known. Although its importance for engineering aspects, hydraulical classification is not yet completed because of the lack of knowledge of physical mixing mechanism on density interface by tidal currents. The behavior of unsteady saline wedge and mixing of the interface due to tide are studied experimentally. The large scale and strong mixing are observed at the flooding tide period which may cause partially or well-mixed type. This phenomena is explained to be caused by density currents which progress toward river mouth from the sea. The experimental results such as upper and lower depth and velocity change with time, position change of the tip of the wedge with time, et. al., are presented and discussed.

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This paper presents theoretical and experimental study of selective withdrawal from two-dimensional and two-layered systems. To estimate critical withdrawal condition precisely, it is most important to determine the configuration of density interface. It is studied theoretically dividing into two regions. One of them is the region far from intake and possible to predict as density wedge such as saline wedge because of viscous effect. The other one is the region near the intake and possible to assume similarity of interface configuration because viscous effect is less important. The model to predict configuration of density interface is developed using concepts mentioned above and verified by experimental results.

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Recently air bubble plume has been suggested as a method of water quality purification. In this study, air bubble characteristics, flow induced by air bubble rise and destratification by the flow have been investigated by field test.
As the results of the study, following concequences were obtained.
1. Bubble diameter is 5-7cm.
2. Bubble velocity is 50-150cm/s and can be expressed by way of function of air supply.
3. Volume flux ratio can be explained by the equation which is induced in field in which there is not stratification. But there is the maximum value of volume flux ratio.

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This paper presentes the results of experimental and theoretical investigations on the chracteristics of two-dimensional inclined bubble plume. The inclined bubble plume forms when bubbles are released from air line source oriented perpendicular to a horizontal flow. For the measurement of velocity, a propeller-type current meter is used and an air volume fraction is measured using a conductivity probe. From the result of measurements, we find that the inclined bubble plumes are divided into two categories. The velocity and the angle of inclination of bubble plume are obtained theoretically, applying the equations of continuity, momentum and volume conservation of air bubbles to a model based on the assumption which turbulent diffusion is neglected for simplicity. This theoretical result is compared with our experimental data.

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The two-layered stratified flow past a cone is studied experimentally, Tne aim of this paper is to investigate the dependence of the flow on the Reynolds number and the Richardson number, the effect of the level of the interface on the flow and the spatial distribution of the internal wave. The result is that the flow does cot change when Re number and Ri number change within 800<Re<1800, 20<Ri<100, but that the level of the interface greatly affect it, And the internal wave is measured by an electric conduction meter and is found to be boomerang-shaped.

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A three-dimensional, primitive equation model that describes the spreading behaviour of a frontally bounded river plume is presented. First, the scheme is successfully confirmed to apply the thermal plume in a cross flow through comparison with field data obtained in the thermal plume discharged from Widows Creek steam plant. Secondly, computations for the growth of river plumes discharged into a uniform cross flow are presented and discussed for a variety of crossflow velocities. These results demonstrate the dynamics of river plumes, especially the formation of frontal structure.

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A theoretical model is presented that describes deepening-of the diurnal mixed layer under the action of wind. The model is an extention of DIM (Dygamic Instbility Model) which is applicable for the situation where turbulence produced by shear instability at the base of mixed layer. Coaparative considerations of existing results lead to an idea that the meanings of self-similarity must be followed up for a reasonable modeling. Present study therefore adopts some assuaptions on self-similerity not only of density and velocity profiles but also of energetic balance. Consistency of these assuaptions is described through a simple imaginary mixing model associated with K-H instability mixing. The resulted model successfully predicts the entrainment rate observed by authors in Lake Kasumigaura.

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The annual cycle of surface heat exchange process and thermal structure in lakes were examined by performing a model analysis. The annual variation of the meteorological conditions were described in terms of annually varying equilibrium water temperature as a single harmonic sinusoidal function of time. The water temperature field was expressed by using an integral mixedlayer model and its stratification and destratification processes were evaluated by our developed entrainment laws. The present analysis enables us not only to get the thermal structure solution but also to analyze the surface heat flux or heat balance of the water body. We found dimensionless parameters which govern the annual variation patterns of thermal structure as well as surface heat exchange. Using these parameters, classification of thermo-dynamic phase in lakes was performed, in which three categories of lakes, i. e. stratified lakes (or thermo-dynamically deep lakes), moderatelymixed lakes and well-mixed lakes (or thermo-dynamically shallow lakes), are found.

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The effect of suspension of nearly neutrally buoyant particles on the turbulent characteristics in oscillatory flow has been studied experimentally. Vertical distribution of concentration of particles at various phases of a cycle of oscillation was measured by means of image-processing by the use of a laser slit-beam. It has been shown that although the turbulent structure becomes more complicated by the inclusion of particles, essential part of turbulent characteristics of oscillatory flow is maintained.

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The turbulent structure of density underflow is investigated by theoretically. The standard k-ε turbulence model is adopted in the numerical model. The partial differential equations are discretized by the SIMPLE method in order to carry out the numerical calculation. The turbulent properties such as kinetic energy of turbulence, Reynolds stresses, viscous dissipation rate of turbulence and eddy viscosity are simulated by the numerical analysis and compared with the experimental data. The whole reservoir is considered to be the calculational domain. Thus the inverse flow resultant of the entrainment of the upper water can be taken into account. It is shown that the numerical model explains well the mean flow properties such as the distributions of velocity and relative density difference.

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The characteristics of vertical forced plume in a uniform cross flow of stably linear stratified environment are studied both numerically and experimentally. The empirical formulas for the diffusion characteristics of vertical forced plume (trajectory, dilution, etc.) are presented experimentally. The three-dimensional numerical model is used to quantitatively simulate the behavior of the vertical forced plume in these ambient conditions. The performance of the three-dimensional model is evaluated by comparison of numerical results with experimental measurements. By using numerical model, the production and disappearance of vortex pairs are discussed as plume flow downstream.

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Hydraulic characteristics inside the depressed density interface induced by vertical impinging jet is studied experimentally. The relationship between the integral time-scale and predominant period of interfacial fluctuation is found to be similar to the experimental result with oscillating grid. The most turbulent energy is occupied by the component of predominant period. From measurement of flow velocity, the intergral time-scale is proportional to Brunt-Baisala frequency and the predominant period. The characteristic length scale defined by the predominant period and turbulent intensity is almost identical to root mean square of interfacial fluctuation at the edge of interface and to nominal width of jet at initial position of interface. The characteristic length-scale mentioned above is closely related to the entrainment process at the edge of interface

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This paper proposes an integrated model of the behavior of a buoyant jet injected into a uniform cross-flow. Governing equations are the integral conservation equations of volume, mass, cross-streamwise and its perpendicular components of momentum. The ordinary differential equations to predict the variations of cross-sectional area, mean velocity, and the trajectory of a jet axis are derived from the governing equations. Entrainment rate is estimated by considering the vortex induced flow of the ambient fluid.

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Characteristics of turbulence in a flow with suspensions of neutrally buoyant and sinking particles are investigated experimentally. The turbulent field generated by an oscillating grid was adopted for measurements. Since there is no mean shear flow in it, the steady state can be easily attained.
A variety of sedimentation velocities of particles are provided by using salt water, the density of which can be easily controlled. The turbulence is measured by LDV and the effect of sedimentation velocity of particles on turbulent properties are discussed. It should be noticed that increasing sedimentation velocity of particles results into smaller turbulent intensity.

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Recently large-scale projects of land reclamation, such as Kansai International Airport, have been on the rapid increase. Direct dumping of soils with bottom-dump barges enables us to reclaim lands in short time economically. The method of construction, however, includes very serious technological problem to be solved, that is diffusion of turbidity. The purpose of this study is to clarify the diffusion process of turbidity especially by the flow field which falling-behavior of soils induces through hydraulic experiments. The results show that the induced flow plays an important part of initial diffusion of turbidity.

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In this paper, the spread of continuously spilled oil on a uniform flow are dealt with experimentally and theoretically. The laboratory experiments were performed in a circulating water channel. The oil was continuously pored onto the surface of uniform water current from the small outlet. The plane view of the spreading oil slick was observed. Mathematical model is developed on the basis of two-layer model and kinematic wave theory. Thus the governing equation of the front velocity of oil slick is derived. Calculations of the advance of the slicks show similar tendency to experimental data.

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Experimental investigatins on the fluid forces acting on two circuler cylinders in tandem arrangement were carried out. The Reynolds number and the distance between the cylinders were varied in the range 1×10⁴<Re<8×10⁴ and 1≤1/d≤6. As a results of systematic investigation on drag and lift forces measured at the same time, fluctuation of fluid forces are divided into four patterns according to their charactristics. It was found that the intermittent changes of time-mean drag and intensity of fluctuating drag and lift occure in the range 1/d=3-4 at front cylinder and 1/d=2.5-4 at rear. This discotinuous changes of fluid forces is caused by the abrupt change from one stable flow pattern to another. The results were summarized in several figures from which one can obtain the timemean and the intensity of fluctuating drag and lift and the Strouhal number.

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Two sets of lysimeter with wind tunnel were constructed, one of which was grassed (40cm height) and the other of whichwas turf (5cm height). Close relationship between CO₂flux and insolation, humidityflux and vapor pressure difference, heatflux and humidityflux has been observed. Grass shows much effect of moderating the cliaate, but not turf, because of their difference in evapotranspiration rate and shelttering effect.
Numerical simulation using NEO-SPAM (soil-plant-air-model) has been performed to see the effect of the allocation of vegetation. Vegitation is more effective in moderating the climate if the separation of vegetated zone are shorter, and leaf area density is important in terms of both the shelttPring effct and latent heat effect.

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An analytical procedure is developed for predicting the surface profile and momentum distribution of a flow immediately after opening a gate rapidly. The basic equations are derived from the nonlinear shallow water theory, and they are solved numerically. The comparison of the theoretical and experimental results shows that the present theory well estimates the surface profile of the front part of flow.

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In some new diversion dams, sand and gravel were accumulated under gates by floods. But occasionally accumulated sand is flushed by sluice outlet at closing gates after flood. Analysis of this process by two methods (field surveys and flume experiments) clarified as follows:(1) To flush accmulated sand, the difference of water levels at upstream and downstream of a gate should be five times as large as the maximum size of sand or gravel.(2) In a dam on a sand-bed river, flushing sand by sluice outlet is so easy to occur that controllable gates are easily closed after flood.(3) In a dam on a gravel-bed river, gravel flushing is difficult. Therefore, even if gravel can be flushed, gates will get damaged by collision of gravel.

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The distributions of hydraulic pressure acted on the gate bottom in vibration were measured and the damping coefficients of hydrodynamic forces were analysed for three typesof gates. The study involves forced oscillation tests and it is concluded that the flat bottom has two kinds of modes of negative damping caused by vortex in the lower range of reduced volocity (Vr) and by separated stream line in the higher range of Vr. The beveled edge (α=+15°) has the negative damping only in the higher range of Vr and another one (α=-15°) has none. Hydraulic discussions for these results were given.

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The author has outlined three-dimensional characteristics of nappe oscillations for explaining the effect of spoilers. Full-scale models have provided the common tendency of Sound Pressure Levels of the Low Frequency Air Vibration under the increase of the overflow depth of weirs Various combinations of the opening of weir nappes have confirmed the effect of spoilers for restricting the oscillation within narrow limits as well as dicreasing peak Sound Pressure Levels. The author has also proposed the measure to estimate Sound Pressure Levels about the weir width, hight, overflow depth and the distance from the weir.

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This paper describes an experimental investigation into the non-linear vortex-excited vibration of a cylinder in planar oscillatory flow with emphasis being placed on the amplification of the forces acting on a cylinder caused by the fluid-structure interaction. The experiments were carried out using a water tank which has an internal dimension of 1.0m long and 0.5m deep by 0.5 m wide, and is oscillated in true harmonic horizontal motion. The result shows that the amplifications of the in-line force and transverse force acting on a vortex-excited cylinder are large in the range of Keulegan-Carpenter number (KC) about 5 to 10. It implies that the fluid-structure interaction is large in this range of KC numver. The differences between the flow pattern around the vortex-excited cylinder in resonance condition and those around the rigidly mounted cylinder are observed in the case of KC=8.4.

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Instantaneous two-dimensional velocity fields behind a backwardfacing step in open channel were successively investigated by the use of flow visualization and digital image processing. Instantaneous spatial distributions of fluctuating velocity vectors, pressure and spanwise vorticity were presented and discussed. Space-time distribution of the longitudinal velocity close to the channel bed and the temporal variation of spanwise vorticity were estimated in order to clarify the low-frequency unsteadiness in the separation bubble. The low-frequency unsteadiness seems to be dependent on the strength of spanwise vorticity in the reattachment zone.

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This paper describes the influence of the air-entrainment on the deflected jet from plunging nappe induced by open channel step flow and the characteristics of the deflected jet from inclined submerged jet. The characteristic values such as maximum velocity, representative width of the deflected jets, and so on, are related to air-entrained discharge. And the air-entrained deflected jets are connected with the inclined submerged jet through the density Froude number Fd. By the experimental equations, those correspondences are clear. Furthermore, it becomes clear on the basis of the calculated results of the boundary layer growth of the deflected jets that the tractive forces are considerably reduced more than h_* = 0.5.

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Sudden-contractions are often seen in a river channel, by natural features and manmade structures such as weirs. In Japan, the flood routing is usually carried out by the storage-function method, but the weak point of this method is that we can not estimate the parameters if some changes are occured in the channel. On the other hand, we can not obtain the f l ow characteristics at sudden-contraction, even if using the strict unsteady flow equations. The cause of this fact is assumed to be existence of some control-conditions at contraction. We find out this conditions by experiments, and develope the method of calculation of flow characteristics at contraction using these control-conditions. Lastly, we confirm the usefulness of this method by applying to a natural river basin.

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A convex or concave boundary of the flow cross section causes a three-dimensional flow.Such a three-dimensional flow has an effect on flow structure which is very difficult to deal with. As the first step to study, a flow charastatic of variation due to the shape of cross section and Reynolds number is clarified experimentally.Furthermore, in consideration of its practical application to rivers, the hydraulic characteristic of compound channel with floodplane or berm of levee is studied.

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The three dimensional open channel flow in the continuous bends is calculated by means of a numerical method of the differential scheme for the horizontal plane, the finite differential scheme for the vertical direction and the fractional step scheme in the time. The calculated results are in good agreement with experimental results for the vertical distribution of both main flow and secondary f l ow over whole region of the bend channel.
It is found that the error occurs on the calculated bottom shear stress when we divide the vertical direction using the same elements. The better dividing method for vertical direction is proposed.

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