Two-dimensional discrete vortex method is applied to the flow at a confluence. Simulated results for mean and turbulent velocity characteristics together with the size of a recirculating region have a reasonable accuracy compared with open-channel experimental results. Unsteady large scale structure of the flow in the recirculating region including formation and decomposition of vortices is favorably simulated by this method. Generality of model parameters is examined for flows of different hydraulic conditions in a subcritical flow regime.

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Applicability of turbulence models to a two-dimensional buoyant surface jet is examined through comparison with experimental data. A k-ε turbulence model is found to overpredict the turbulent transport of the stresses so as to promote the vertical spreading of buoyant surface jet, because it cannot represent the anisotropy of turbulence. For taking account of the damping effects of the gravitational field and the free surface on the turbulence structure accurately, an algebraic Reynolds stress model (ASM) is examined with corrections to the pressure interaction terms at the free surface. The ASM tested produces a good agreement with measurements on the flow development and turbulence characteristics of buoyant surface jet. The predicted results also show the dependence of turbulence structure on gradient Richardson numbers.

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This paper presents a method for the estimation of transverse dispersivity in a homogeneous isotropic coastal aquifer where salt water intrusion takes place. An approximate solution of the concentration profile on the axis perpendicular to the fresh-salt water interface is derived from a similarity approach and compared with the concentration profile measured in a laboratory experiment. A two-dimensional numerical simulation on salt water intrusion and dispersion is performed using the dispersivities estimated by the proposed method. Numerically predicted concentration profiles agree well with the experimental data. It is concluded that the proposed method is practical for the estimation of transverse dispersivity based on the measured concentration.

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The behaviour of bubble plumes were studied in both a linear and a two-layered stratification. When bubbles were released downward flow formed outside the inner upward plume induced by bubbles, and different types of intrusions formed from the downward flow depending on the relationship between the stratification intensity and the bubbling rate. The inner plume's fluid diffuses outwards only in the zone where the downward flow exists.
The inner plume entrained the surrounding water and increased in size up to the critical level at which the drag force exerted by the bubbles is balanced with the negative buoyancy of the inner plume.
The efficiency of the input energy conversion to potential energy increases at first, shows peak, then decreases with increasing bubbling rate and decreasing stratification intensity.

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Laboratory tests were performed to evaluate the interaction of the flow between a main channel and floodplains. In the tests, prismatic channels similar to actual river courses were used. The experimental results showed that the increase in Manning's roughness coefficient due to the interaction could be predicted by estimating an apparent shear stress acting on a vertical plane along a interface between a main channel and flood plain. The mixing coefficient at the interface f can be almost constant and its value is around 0.17. On the basis of the prediction method obtained, the classification diagram for the estimation of the flow resistance in the compound channel was proposed, by which discharge capacity is calculated well in accordance with characteristics of river course, compared with the existing method. Further more, it becomes known how the resistance to flow varies with the change in the cross-section by river improvement works.

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The characteristics of seawater intrusion are examined on the various aquifer conditions. Numerical positions of fresh-saltwater interface are obtained with using Residual Flow Procedure that was proposed originally to solve unconfined groundwater flow. A simulated result of fresh-saltwater interface is confirmed by sand model test in case of two-layered aquifer. From the simulated results, the followings are clarified, that is; seawater easily intrude to the two-layered aquifers in case that the high permeable layer overlies on the low permeable layer. The intruded saltwater region is relatively small in case of both the stratified aquifers separated by a semi-permeable layer and the anisotropic aquifers having low permeability in vertical direction, but that is relatively large in both the two-layered aquifer and the stratified aquifer of which the upper layer is closed by the impermeable wall.

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LATERAL MODEL, a model of surcharged flow in urban sewer pipe systems, is presented. In this model, the pressure-control effect is considered which is caused by storage of stormwater in lateral pipes connected to a sewer pipe and has been ignored in traditional models. It is demonstrated that a pressure-wave celerity in the pipe systems is determined physically by the properties of the lateral pipes and the calculated values of the celerity using the properties almost agree with the empirical ones. The model is transformed into a practical model, SLOT MODEL, which is able to handle both openchannel and surcharged flows with the same flow equations. An equation for determining a width of hypothetical slot, which is a principal parameter in SLOT MODEL, is derived from comparing the flow equations of the two models.

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A new system was contrived to lift the heavier water from the bottom layer with an air bullet rising through a long shroud, and to destratify the sea or reservoirs. In this system, heavier water in the lower layer is lifted up through the shroud to the free surface, impinges on the free surface, spreads radially then plunges downwards. The mixing with environmental water is expected mainly during the fall process. First, the rising water behaviors such as the upward velocity have been analyzed and confirmed by laboratory experiments for the homogeneous layer. Second, the analysis has been extended to the two-layerd system, and important parameters, periodicity of the oscillation, rising velocity reduction have been obtained. Then using these results, the energy conversion efficiency has been predicted.

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A mathematical model which describes three-dimensional fully-developed flow in mildly curved channel is presented. The side boundary layer is included in the analysis, and the secondary flow is treated to be impervious at the side walls. It is found that the advective transport of fluid momentum due to secondary flow induces accumulation of longitudinal fluid velocity near the outer bank. The analysis makes it possible to treat the excess of shear stress at the outer bank due to curvature. The model is supported by available laboratory data.

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When a vertical dense jet impinges on the free surface, it spreads along the surface farther than is expected by the equivalence of the horizontal momentum and gravity, then plunges suddenly downwards. In this study, the mechanism of the widely spreading was investigated analytically and experimentally. At first, the spreading of the horizontal surface dense jet was obtained, then the idea was extended to the case of the vertical dense jet impinging on the free surface. The mechanism elucidated is as follows: The free surface of the horizontal jet depresses resulting from the velocity head there. The jet keeps to flow along the surface, until the excessive density of the jet exceeds the pressure decrease resulting from the depression.

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In recent years the sludge which has been piled up on the bed of urban rivers causes the lowering of the drainage ability and the water quality. But there is no effective idea for such problems.
The aim of this study is to wash away the sludge to downstream efficiently by discharging air into the water through orifices on pipes which set on river beds and producing the secondary flow.
This paper deals with the hydraulic behavior of the flow accompanied by induced aeration and the effect of aeration for the bed-material load.

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As the first step of refinement of fluvial hydraulics in mountain regions, velocity distribution, critical tractive force, and bed-load discharge under steady uniform conditions are investigated, though the flow and sediment behaviors in mountain regions are often unsteady and nonuniform. From gravel-bed flume data, the relation between the constant of the log-law and the relative depth is empirically formulated as a mathematical expression with one parameter; and resistance, critical tractive force and bed-load discharge formulae are deduced. The unknown parameter is determined in conformity for these formulations with the experimental data. As a result, the increase of dimensionless critical tractive force with bed slope is reasonably evaluated, and bed-load discharge for each bed slope is predicted with an improved accuracy.

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Distributed rainfall-runoff model was developed using radar rain as input. It consists of two submodels: one for direct runoff and other for baseflow. The direct runoff submodel is a distributed model which routes direct runoff in discretized element basin through a channel network to outlet using the kinematic wave model. In this submodel, watershed is represented by meshed square element basins connected by a channel network which is derived from altitudes at their central points by using newly developed algorithm for channel network computation. The baseflow submodel is a lumped storage-drainage model. This model makes it possible to take the effect of areal and temporal distribution of storm into account. Some experimental calculations are given to show this effect. Also sample calculations with respect to Uono River basin resulted in a good correspondence between predicted and observed hydrographs.

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In a stream composed sand and gravel, wavy patterns of sorting are often observed and they cause fluctuation of fractional bed-load discharge. In this paper, the formation mechanism of longitudinally alternate sorting is formulated as a linear instability analysis of bed-surface composition with a non-equilibrium bed-load transport model for each grain size of sediment mixture, and the condition that the longitudinal sorting falls unstable and predominant wave length of alternate sorting are predicted. As a result, alternate longitudinal sorting develops under the condition slightly above the threshold of motion of bed-material particles, and it always propagates downstream. The predominant wave length is subjected to the diameter of bed material, and thus its scale is the same order as small-scale bed forms. The theoretical results are consistent with the observed data.

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Effect of bank vegetation on the stable channel cross-section of straight gravel rivers is studied theoretically, in which singular perturbation and matched asymptotic expansion techniques are employed to derive the lateral distributions of depth-averaged fluid velocity and the bed shear stress. A condition of sediment incipient motion is imposed at the junction of the bed and the banks to derive the stable depth, and a formula for resistance to flow is used to obtain the stable width. It is revealed that a thicker vegetation yields a larger depth and a smaller width. Increasing discharge is found to increase the effect of vegetation. The analysis is found to agree reasonably well with available field data.

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Stochastic reservoir theory has been developed with correlated discrete inflows on a two-step transition model by Klemeš and on the basis of idea of joint probability of inflows and storage by Lloyd for Markovian inflows. Stationary distribution for any states of storage can be then calculated by the matrix algebra with the discrete representation for the amount of inflows and reservoir states.
Numerical calculation is carried out by the correlated Binomial inputs. The results coincide with the exact solution on a randam-walk theory by Phatarfod and the approximate solution on one by Nagao and et al. This approach can be easily applied to the experimental distribution for sample data.

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Only the average precipitation in a few hours preceding to the forecast usually has been used as input data for flood forecasting models. However, this method does not correctly evaluate the difference between expected value and actual observed value of discharge.
This paper proposes a method which evaluates the discharge and the water level in probability, by studying the forecast rainfalls probability distribution by means of Radar Rain Gauge (including Digitized Weather Radar) precipitation forecast methods, and by inputting the result into the run-off models as a group of forecast rainfalls.
The examination on the application led to the coviction that this new method can bring about practical and useful information.

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This paper is to discuss experimentally the wave forces acting on a submerged sphere in the two-component composite wave field. The measured wave forces are decomposed into the drag and inertia forces using the Morison's formula. The maximum wave force, the drag and inertia coefficients of individual waves defined by the zero-downcrossing method are mainly investigated in the relation to those of regular waves. Time variations of the water surface profile have significant effects upon the characteristics of the wave forces. The maximum wave force and inertia coefficient of the successive waves whose heights are increasing are shown to be larger than those of the successive waves whose heights are decreasing. Their variations become larger as the difference of the successive wave heights become larger.

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This study is to discuss the wave force acting on a submerged sphere due to the diffracted wave based on a numerical analysis. The hybrid method is employed to calculate the velocity potential of the diffracted wave.
The added mass coefficient, the force coefficients, the dominant range of the diffraction force are investigated in relation to the wave height distribution and non-dimensional parameters such as the relative sphere radius to the wave length, ka, the relative sphere diameter to water depth, D/h, and the relative submergence, d/h. The wave diffraction is governed by ka, D/h and d/h. The effect of wave diffraction to the vertical wave force is generally larger than that to the horizontal one. The added mass coefficient becomes larger with an increment of D/h and with decreasing of d/h for the same ka. When the change of wave heights is less than 5%, the diffracted wave has little effect to the wave force. The range in which the diffraction theory is applied in calculating the wave force is given graphically as a function of ka, d/h and D/h.

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A boundary element method using nonlinear potential theory has been developed for analyzing wave diffraction around large structure. To confirm the validity of the proposed method, the numerical results for solitary wave propagating through a three-dimensional wave channel are compared with analytical solutions in terms of wave profile and hydrodynamic pressure. The comparison shows excellent agreement regardless of H₀/h (H₀: wave height, h: water depth). Furthermore, nonlinear effects on wave loads exerted by solitary wave on a vertical cylinder are investigated by comparing the numerical results with first approximations given by Isaacson. The first approximations for horizontal force, overturning moment and wave run-up are appropriate with H₀/h being 0.1. It is, however, found that the first approximations for overturning moment are underestimated remarkably with H₀/h being 0.4.

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This paper is intended to discuss the wave force acting on a submerged sphere in a progressive irregular wave field. The measured wave forces are decomposed into the drag and inertia forces using the Morison equation. The maximum wave force, the drag and inertia coefficients of individual waves defined by the zero-downcrossing method and characteristics of the maximal wave forces are mainly investigated.
The variations of the successive wave heights and periods effect largely to the wave force. The inertia coefficients of x-directed wave force of the successive waves whose heights are increasing are shown to be larger than those of the successive waves whose heights are decreasing.
The probability distribution of the maximal wave forces in the case that the drag force dominates over the inertia force is not similar to that of the wave height. Then, the mean, mean one-third and mean one-tenth largest values of the maximal wave forces cannot be predicted with the mean, mean one-third and mean one-tenth highest waves, respectively.

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The wave-induced pore-water pressure acting on the bottom of a caisson and around the composite breakwater is analyzed by a poro-elastic theory, Biot's consolidation theory, using a finite element method. Effects of the stiffness and permeability of a rubble mound and the rocking of the caisson are examined. The spatial distribution of uplift force mainly depends on the permeability of the rubble mound. When the permeability is large, the distribution is almost linear at any phase of standing waves in front of the caisson. However, when the permeability is small, the distribution is not linear and the profile is different at each phase of standing waves; furthermore, it is affected by the magnitude of rocking of the caisson. The rocking of the caisson increases the upward pore-water pressure gradient which seems to increase the occurrence probability of a seabed liquefaction around the toe of rubble mound as one of the causes of scouring at the toe and sinking of foundation materials.

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In order to investigate the mechanism of topographic changes of the foreshore due to wave action, field data obtained at Ajigaura Beach once a week since 1975 were analyzed. Dominant factors determining foreshore changes are found to be energy flux of the deep water waves, grain size on the foreshore and foreshore slope. Accretion or erosion of the foreshore can be classified using these three parameters. Beach lamination process of the foreshore was investigated through the field observations at Ajigaura Beach. It is found that berm can be formed by some sublayers composed of coarse and fine materials or only by one layer composed of fine material. These changes can be elucidated by the wave climate change.

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High wave conditions in the East China Sea during Typhoon 8712 (Dinah) are hindcasted with the use of two kinds of shallow water wave prediction models based on the radiative transfer equation. The models give reasonable agreement with the observed data. It is demonstrated that huge waves brought about by Typhoon 8712 greatly altered the spatial distribution of maximum significant wave height generated by typhoons for the past 50 years in the East China Sea, and that the return period for maximum significant wave height which occurred off Nagasaki during a typhoon is over 100 years. It is also deduced from the computation of wave transformation that the violent action of huge waves exceeding the design wave height of the breakwater was responsible for the destruction of the breakwater in the Shin-Nagasaki Fishing Port.

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Influences of diurnal stratification on water qualities in a shallow eutrophicated lake is discussed with the reference of field observation conducted in Lake Kasumigaura in 1988. The following are pointed out.
Diurnal stratification makes a weak thermocline with the temperature difference of about 1°C, which prevents the vertical DO transport until the wind mixing erodes it out.
The temperature profile has double-thermocline occasionally when an old thermocline formed on the day before remains in the morning. Then, the old thermocline tends to stay near the bottom for several days because the wind mixing works on only the new upper thermocline. This means that the DO supply to the bottom is cut off for several days.
DO concentration near the bottom reaches zero when the old thermocline stays for three days. PO₄-P is released at a high rate from the bottom after DO concentration falls below 4ppm.

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This paper presents an analytical study on the behavior of front of flow immediately after breaking of a dam with water downstream. The basic equations in this problem are derived from the nonlinear shallow water theory, and they are solved numerically. This study stands an extension of Shimura's theory which treats the problem in case without water downstream.
It is confirmed that the qualitative tendency of solution is in satisfactory agreement with laboratory experiments.
The solution needs two initial conditions concerned with the slope and curvature of water surface, and they are induced by comparison between the analytical and experimental trajectories of the front.

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The turbulent structure of inclined wall plume is investigated experimentally. The velocity distributions are measured by the laser doppler anemometer. In order to obtain the density difference, the saline water was sampled by the siphon and then the concentration of salinity is measured by the conductivity meter. Thus, the mean flow properties of the inclined wall plume are obtained. The turbulent flow properties such as Reynolds stresses, kinetic energy of turbulence, viscous dissipation rate and eddy viscosity, are also obtained. These experimental results are compared with the similarity solutions obtained coupling with the κ-ε turbulence model. The agreement of experimental results and numerical calculations are fairly well except for the distribution of the viscous dissipation rate. It is concluded that the κ-ε turbulence model can explain well mean flow properties and turbulent structure of inclined wall plumes.

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The scattering of surface waves due to the multiple submerged breakwaters is examined theoretically using the method of matched eigenfunction expansions. The reflection coefficients are calculated for two and three trains of rectangular breakwater with equal spacing. The results indicate that strong reflection can be achieved even in intermediate water depth by means of placing multiple submerged breakwaters, especially when the width of spacing is taken several times that of breakwater.

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