A discharge of air bubbles into water in a aeration tank generates a turbulent air bubble plume in a spiral flow. This paper discribes the mechanics of the air-bubble plume in a upward flow instead of the spiral flow. We measured the mean velocities and the streamwise component of the turbulent fluctuations with a miniature propeller current meter. It is found that the interaction of air bubbles plays very important role in the region close to the line source. The results of the analyses by the use of moment transformations for equations of momentum and volume conservation of bubbles are compared with experimental data.

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During heating season, hydrodynamic behavior of the thermocline in lakes and reservoirs is predominantly affected by the combined action of the stabilizing buoyancy flux due to solar radiation and the mechanical stirring due to wind shear stress. The present paper examines the entrainment process in such a situation experimentally and theoretically. In a physical model, the oscillating-grid turbulence and the stabilizing buoyancy flux are simultaneously supplied to the upper surface of a two-layer thermal stratification system and the resultant entrainment process is investigated. The entrainment rate is related to an overall Richardson number. The turbulent structure is also analyzed by considering the energy balance in the present system. Applying the entrainment law, we get an analytical solution of the equilibrium condition where the mechanical disturbance energy just balances the stabilizing effect of the buoyancy flux.

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It is important to investigate the characteristic of fluid forces acting on roughness elements of river beds and revetments. In this study, we investigate the velocity profiles over roughness elements, which are spheres or hemispheres sticked densely on the surface of the wind-tunnel bed, and the forces exerted on them, which can be calculated by measuring the surface-pressure distributions.
On the other hand, the existing critical shear stresses or tractive forces depend on not only the time-mean but also the instantaneous values of the boundary shear stress. But there are little reports on the probability density distribution of hydrodynamic forces on roughness wall. The temporal distribution of the drag forces exerted on densely placed spherical roughness elements is investigated experimentally.

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At a confluence, a separated shear layer accompanying a recirculating region is formed, which decreases the efficiency of the flow. In this study, the hodograph method is applied to the flow at a confluence to make clear the characteristics of separated streamlines. A free streamline and a boundary streamline which represents the center of a separated shear layer and the boundary between the combined flows respectively, are calculated for arbitrary confluence angles and channel width ratios. Also, a shape factor of a recirculating region is theoretically obtained with a reasonable agreement with the experimental results.

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The similarity solution of inclined wall plume is obtained analytically. The mathematical model used herein consists of the continuity equation of flow, the momentum balance equation in the flow direction, the diffusion equation of concentration, the equation of kinetic energy of turbulence and the equation of viscous dissipation rate of turbulence. It is shown that this set of equations has the similarity solution which can be solved numerically for each angle of the inclined wall. This numerical model is applied to the wide range of the slope angle, which includes the plume along the vertical wall for the special case and along the nearly horizontal wall. The velocity and concentration profiles of the inclined wall plume are explained well by the similarity solution.

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Multi-cellular longitudinal voltices dominate the three-dimensional structure of open channel flows and also produce the sand waves with longitudinal ridges and troughs which are called sand ribbons.
In this paper, the process of development of the sand waves was investigated in view of the interaction between the large scale eddies and the bed material, and the formation of sand ribbons was examined in detail.
Furthermore, the influence of secondary currents on the tractive force was estimated on the basis of Reynolds momentum equation to which the experimental results were applied. The results obtained show that the secondary currents have a significant effect on the tractive force.

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This paper presents a comprehensive assessment of the stream-tube model for two-dimensional solute transport in a natural river with steady discharge. Employing a transform of transverse independent variable from distance to cumulative discharge, consistent derivations are shown for model equations under unsteady and steady transport and for equations taking account of solute exchange with a deadwater zone. Analytical solutions for steady transport are presented as adequate approximations. Also solutions for solute with a first-order decay are obtained as modifications to those for conservative solute. Recent information on model coefficients are reviewed, in particular on the transverse dispersion coefficients. The paper concludes that some improvements are needed for Taylor's dispersion theory, which is the basis of the present model, in order to predict transverse dispersion properly in a nonuniform flow.

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Sediment discharge in alluvial channels with coarse and nonuniform bed materials depends strongly on the bed surface grain size condition. Sediment discharge is very small when the bed surface is covered with armor coat, while it increases sharply when the armor coat is destroyed during flood. In this paper sediment discharge characteristics of nonuniform sand bed during the increase and decrease periods of flood discharge are discussed experimentally in connection with the grain size distribution of bed surface materials, through which the sediment discharge formula of nonuniform sand and the process of armor coat formation are also discussed.

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Each of the particles transported as bed-load will rest on the bed after a certain passage, mostly due to being held up with the unevenness of bed surface particles and rarely to die-out of reflection energy during the impingement of the particle on the bed. In order to investigate the mechanism of this process, the uneven arrangement of bed particles are simulated stochastically, based on the observation by a video analysis, and a simulation model of bed-load movement is constructed. The validity of this model is verified by experimental data, and as a result, the characteristics of this process, that is Step-length and Moving-period, are clarified and the equation for estimation of these values can be developed as a function of dimensionless tractive force u/w₀. It is confirmed that the estimated values by these expressions agree well with the experimental values obtained by several researchers.

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In recent years, there has been an increased in the frequency of floods in small river basins within the Tokyo metropolis. From the disaster-prevention perspective. This is a serious problem. This phenomena is a result of the progress of urbanization works in the basins, like the increased in the basin area drained by the urban sewerage system. Thus the volume of rainwater flowing into the urban rivers have greatly increase.
The aim of this paper is to clarify the cause of this phenomena. It is an analysis of the relationships between, the basin area served by the sewerage system and its rate of increase, with the characteristics of the flood discharge from the basins. The analysis is based on actual data of flood discharge and rate of increase of the area served by the sewerage system in a basin.
The importance of the extent of the area of a river basin served by a sewerage system, in addition to the amount of impermeable area, on the time of concentration has been clarified.

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Nearly 10 years have passed since the Ministry of Construction installed radar rain gauge on Mt. Akagi and put it into operation in 1976. Radar rain gauges have since attested to their effects (realtime operability, large coverage area, comprehensiveness and the detection of local heavy rains) and 14 radars are in operation.
But only recently all the 14 became in operation and various methods are still being tested to identify radar constants (B, β, etc.) to convert received power reflected from rain into an amount of rainfall.
Foundation of River/Basin Integrated Communications (FRICS), has since its inception in October 1985 handled the work of studying to improve radar accuracy at the request of Regional Construction Bureaus as FRICS publishes radar data, etc. As a byproduct of this work, the authors have been able to prepare a method to identify radar constants. They hereby propose it and solicit readers' comments.

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Two types of the chemical changes of streamwater during storm runoff were found: Type I which recovers approximately the same concentration in the recession limb as the baseflow level prior to the runoff event; Type II which overshoots the baseflow level. Main solute belonging to Type I is SiO₂, and that to Type II is NO₃^--N.
To relate the element cycle in forest ecosystem to the streamwater chemistry, element content in forest soil was analyzed. This proves that silicon content in forest surface soil is somewhat lower than in deeper soil, while nitrogen becomes greatly enriched in surface soil. Besides, the difference between element contents in soil makes a change of vertical soilwater chemistry in SiO₂ and NO₃^--N concentrations, and consequently generates the chemical changes of streamwater through soilwater leaching.

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The water surface in the well for measuring the mean water level of the river is varied by the surface waves. And the same phenomenon is observed in the lagoon, namely its water surface is also varied by the tide. These two phenomena can be analized as the response by the periodical motion, and especially these are interest as nonlinear response phenomenon. This report shows the theoretical analysis and the corelations between the theoretical results and both the experimental data in the well and the observed data in the lagoon. The method for this theoretical analysis is useful for the nonlinear phenomenon which has the second order term of the velocity.

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An analytical procedure is developed for predicting the time-dependent impulsive force on vertical walls due to the collision of a bore. The impulsive force is estimated by using Cumberbatch's theory which treats the problem of a water wedge striking a wall. The comparison of the theoretical and experimental results shows that the present theory well estimates the total impulsive force and maximum impulsive pressure when the depth of water in the downstream region of the bore is sufficiently small compared with the height of the bore front.

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The diffraction of wave groups with a large offshore structure has been considered using the perturbation method of multiple scales. Second-order slowly-varying wave forces arising from such diffraction are then evaluated numerically for two types of incident wave envelope; one is the soliton envelope that is stable for the relative depth kh>1.36, while the other assumes simply sinusoidal profile. The numerical results for low-frequency wave force coefficients are presented for a circular and a rectangular cylinder and for a conical structure. It will be shown that the low-frequency wave forces become increasingly important in estimating the total wave forces as the value of kh decreases and as the value of diffraction parameter increases.

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Long-term beach changes and the topographic responses to the wave climate were analyzed based on the field data of the wave characteristics, grain size of the bed materials and beach profiles measured every week in a 11-year period between 1976 and 1986 at Ajigaura Beach in Ibaraki Prefecture. For the wave characteristics wave direction, wave height and wave period were observed. Eigenfunction analysis was carried out using the profile data. It was found that distinctive changes were observed before and after a period of 1982-83 in the moving average value of one year regarding shoreline position, wave climate and foreshore slope, and the periodic fluctuations of wave direction and shoreline position had totally changed since this time. It was concluded that the changes in shoreline position and foreshore slope were caused by the offshore sediment transport associated with the extraordinary high waves. In addition, the abrupt changes of the periodic fluctuations in wave direction and shoreline position closely correlated to the long-term changes of the oceanic and meteorological changes associated with the climate anomalies such as El Niño.

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Laboratory experiments using a fiber-optic LDV system and a small pressure transducer have been made to reveal detailed characteristics of velocity field in the surf zone and its relationship to sediment suspension with special reference to the three-dimensional large scale eddies referred to as “obliquely descending eddies”, the existence of which in the surf zone was recently revealed by Nadaoka et al. A conditional sampling technique has been used to find that large shoreward momentum at the upper layer of water is transported downward to the bottom by the large scale eddies with highly turbulent velocity fluctuation, Visual observation and concentration measurements of suspended sediment have shown that sediment suspension is mostly governed by such large scale eddies in a wide extent of the surf zone.

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This paper discusses the experimental determination of hydrodynamic coefficients of Morison equation for slender circular columns oscillating under sinusoidal wave action. Two types of columns are considered for study. Column-1 is a rigid circular column, hinged at the sea bed and the response oscillation is in the form of angular displacement. Column-2 is a flexible circular column, fixed at sea bed and the response oscillation is in the form of structural deflection. The columns are oscillated by sinusoidal waves in a two-dimensional wave tank and the responses are recorded. The hydrodynamic coefficients associated with the wave force equation are determined and are plotted against Keulegan-Carpenter number. The results are compared with the values given by other researchers and show a fairly good agreement.

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A new hybrid parametrical model for predicting ocean waves in deep water is presented in this paper. The model assumes that the directional energy of wind-sea defined separately for each direction grows in parametrical form according to the ideal generation condition and that each swell component propagates independently, undergoing energy dissipation. The model is formulated to estimate the time variation of directional spectra at a prescribed location through the computation along the straight wave rays focusing at the location. The computed results for test cases given in SWAMP show physically sound behaviour in each case and the hindcasted wave heights and periods during some typhoons in the Pacific Ocean are in reasonable agreement with the observed ones. These verify the consistency and applicability of the present model.

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Friction laws are obtained through hydraulic experiments on long waves running up on a dry bed. In the experiments, a bottom-running channel is used to yields a stationary wave and the water particle velocity is measured with an LDV. Similarity laws are found in the distributions of velocity and Reynolds stresses in the bottom boundary layer. The turbulence structure obserbed is quite similar to that in a turbulent boundary layer of a flow without free surface. Numerical simulations using the obtained friction laws successfully reproduce the tip profile of a wave as well as its run-up height.

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In order to predict wave shape and velocity of breaking solitons on gentle slopes, a momentum equation which includes nonlinear, dispersive and dissipative effects is derived. The Reynolds normal stress is modeled as the dissipative term by introducing eddy viscosity in which the mixing length is chosen as a product of surface elevation and distribution function of turbulence. This model shows good agreements on wave height attenuation, wave shape and velocity of spilling breaker with experimental results. It shows that the coefficient in the eddy viscosity is sensitive to the attenuation and the distribution function has roles in the initial phase of the breaking and in distinguishing breaker and nonbreaker.

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Using stochastic state space techniques, the authors developed a practical real-time stochastic flood prediction method for dam operation. Here we consider the series tanks model and the storage function model as the candidate for run-off model. In order to select a suitable stochastic model, predicted results are evaluated by a measure which is taken notice of accuracy in the rising part of a flood. The procedure of model set-up adopted here is applied for two dam basins: Tonoyama dam basin (294km²) and Tsunokawa dam basin (724km²). It is shown, by using the historical data, that the proposed method is practical and useful. The developed models are going to be utilized for real dam operation in near future.

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New sampling methods were tested at the outlet of electrostatic precipitator in municipal solid waste incinerators. These methods were based on the modified Method 5 sampling procedure reported by USEPA. The results showed that all congeners of PCDD/PCDF and precursors (CB/CP) except monochlorobenzen (M₁CB) were caught at the diethyleneglycol-filled impinger, which was cooled by the ice-bath under 5°C. M₁CB was caught at the activated carbon columns.

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It is an important subject to improve the urban rivers for flood protection. However, it is difficult in many cases to obtain the working spaces in the vicinity of the river channels. Therefore, the temporary stages are ofen constructed in the channels, and obstruct the flood flows. In order to reduce the backwater effects of such obstacles, the installation of pump system, by which a part of flood discharge is bypassed, are considered effective, and its applicability is investigated from the hydraulic view point.

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This paper presents a simple mathematical model of the turbidity current. The model consist of conservation equations for fluid mass and momentum and sediment volume. To describe the outline of the phenomena, we employed the boundary layer approximation and assumed the constant eddy diffusivity. The effect of the bottom shear and the resuspension of particles are neglected. In the numerical analysis, in addition to the finite difference method, the method of moment is also employed, which enables forward computation even in the case where the surface return flow is present. Flow velocity properties and sediment concentration distributions are given for various values of both dimensionless eddy diffusivity and the densimetric Froude number. Predicted velocity profile and sediment concentrations are compared with experimental data.

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The mechanism for maintaining turbulent secondary flows in ducts and open channels of non-circular cross section is examined from a theoretical standpoint. It is proven mathematically that no turbulence model based on isotropic eddy viscosity concept predicts secondary motion. Furthermore, necessary conditions for a turbulence model which includes driving mechanism of the secondary flow are briefly discussed.

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