Field observations were carried out for a flood intruding into the Shichikashuku reservior. The measurements can be classified into three types:(1) measurement of the turbidity of inflow water, (2) survey of the flow structure of turbid water in the reservoir, (3) measurement of the precipitation amount in the reservoir. The results show the characteristics of movement of wash load in the reservoir.
The current in the reservoir during the flood is numerically simulated using 3-D k-ε turbulent model in order to reproduce the turbidity profiles and the sedimentation distribution. The calculation results were in accordance with the measurement, and the model presented in this paper will give valuable information for the management of the reservoir.

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Surface erosion is increasingly caused by forest clearance for cultivation and urbanization. It is commonly observed that gullies formed at the edge of plateau surfaces tremendously accelerate surface erosion. It is accordingly important to study the mechanism of gully formation and the effects of vegetation in order to reduce soil erosion. This paper presents a mathematical model as to how vegetation effects on gully formation in terms of a linear stability analysis. It is suggested that vegetation decelerates gully development by reducing gully spacing and flow intensification. It is found that a slight increase of critical shear stress due to vegetation prevents gully formation effectively.

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Head-cuts are classified into two typical patterns. One is the case where the direct erosion from the vertical face dominants. Another one is the case where the bed-scour induced head-cut dominants. In this study, the later pattern was treated. In the bed-scour induced head-cut, the most important factor to determine the migration rate of the head-cut would be bed-scour rate. The sediment transport phenomenon in an impinging jet is very complicated. In this study, firstly, a sediment transport model considering with the jet impingment effect was proposed. Secondly, the bed-scour induced head-cut was modeled. The model was verified by a head-cut experiment. Using a calibrated empirical parameter, the simulated head-cut migration phenomena are in good agreement with the experimental result.

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This study deals with local scour downstream of bed protection works in order to establish a reasonable design method for the bed protection works. A relation between bed shear stress and maximum scour depth in the scour hole under dynamic conditions of bed load was derived using Newton's second law of motion. Comparing the relation with the results of experiments carried out using several kinds of bed materials, the effect of riprap works for reduction of scour depth was discussed. An equation to predict equilibrium maximum scour depth was also proposed and verified by using experimental data sets of several researchers as well as our own. The calculated values of the equilibrium maximum scour depth agreed with measured ones in the experiments.

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Some features of flow and scouring around spur-dike-like structures (or abutments) are discussed based on experiments under clear-water scouring. A simplified analytical model for the prediction of the maximum scour depth around these kinds of structures is developed by considering flow concentration to a restricted region in the scour hole. The model predicts scour depth at sloped-wall as well as at verticalwall abutments, being verified by the available data and previous formulae. Finally, a model constant for flow concentration is identified by the inversion of experimental data, and an interpolated analytical model for the maximum scour depth under low and high tractive forces.

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In order to prevent the increase of disasters of hydraulic structures caused by local scour, it isi mportant to estimate the performances of protection works around hydraulic structures. Based upon the experiments and field data and field data, the design criteria for protection works mostly have been proposed. Recently several analytical researches have been carried out to clarify the mechanism of reduction of local scour depth due to protection works. In this study, after we conducted the flume experiment on the effect of porous protection works, we proposed the physical model of performances of porous protection works. The proposed model almost explained the reduction rate of the local scour depth when the porous protection works are constructed.

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In debris flows over erodible beds, kinematic bed conditions such as velocity and velocity gradient are determined from the dynamic condition that the driving force must be equal to the yield stress at the bed surface. On the other hand, debris flows over rigid beds depend on the conditions; bed slope, sediment discharge rate, static friction angle of sediment and friction angle of grain to the bed surface. In present study, the differences between debris flows over erodible beds and ones over rigid beds, and their transitions are clarified theoretically by solving velocity profile, sediment concentration profile and flow resistance and experimentally by using flume data.

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The size of a debris flow will increase if bed material is entrained into the flow body. The erosion velocity or entrainment rate can be predicted if the torrent bed sediment is the same as that of debris flow body. However, such cases are rare. The present paper describes the entrainnig characteristics of bed sediment into debris flow body based on flume tests. Experimental results show that the entrainment/erosion velocity decreases with the sediment size ratio, d/d₀, in which _d is the bed sediment size and d₀ is the grain size of the supplied debris flow. The critical grain size of entrainment depends on the relative flow depth, h₀/d₀, in which h₀ is the debris flow depth.

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In the numerical models of irregular successive saltation, the collision of saltating particle with bedmaterial particle is treated as the collision between two rigid bodies. While, on the movable bed, not only the bed-material particle colliding with the saltating particle but other particles in the neighborhood of the colliding particle are affected by the collision. In other words, the consideration as the granular material is required on the modeling of collision process on a movable bed.
In this study, the distinct element method is applied to collect the basic information on the collision process on a movable bed. The characteristics of the coefficient of restitution is investigated based on the numerical information for various kinds of conditions. The effect of the movable bed on the saltating particles are also examined based on the simulation of the successive saltation with taking the characteristics of the coefficient of restitution into account.

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Spatially and temporally averaged constraints on the extraction of momentum at the sediment boundary are inadequate to describe the episodic and spatially variable nature of bedload sediment transport. A model is proposed for the instantaneous transport of bedload sediment i a turbulent boundary layer having an arbitrary near-bed structure. The instantaneous force on individual grains is calculated. based upon a function for the reduction of velocity caused by upstream, protruding grains. Instantaneous forces calculated in this manner are in agreement with the highly spatially-and temporallyvarying drag forces measured of particles in sediment beds. When coupled with a simulation of the motion of all grains comprising a three-dimensional bed, the dynamic boundary condition predicts reasonable transport rates.

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Erosion process of cohesive sediment was investigated experimentally in the present paper. Flow velocity and the containing percentage of clay are the control parameters depending on which the erosion rate and the eroded thickness change considerably. The characteristics of this process were made clear quantitatively through a series of systematically arranged experiments, though the ranege of the experiments were restricted. The results of this study are purely fundamental but will be important in future understanding of both a bank erosion and a topographic change in delta formed around a river mouth.

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A three dimensional numerical model was developed to examine characteristics and mechanism of flows and bed deformation in a compound meandering channel. In this paper, it is shown that characteristics of flows and bed deformation in numerical results changes with the relative depth. When the relative depth is low, characteristics of flow is close to those of a single-section meandering channel because the exchange rate of the fluid between a main channel and flood channels is not yet large. When the relative depth is high, flows and bed topography show the characteristics of those in a compound channel obtained in a physical model with movable bed and numerical model with fixed flat bed. The river bed in a meandering compound channel is scoured along a main flow area by the secondary flows which go outside of the main flow area over the river bed.

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Longitudinal bed profiles and sedimentary bed-forms, one experiment without any groin and five with impermeable submersible groins in series experiments, were investigated in a 27.5m long straight channel in different arrangements of groins. Spectrum analysis of longitudinal profiles near and even very far from groin head showed large amplitude spectral peaks in the region of higher wave numbers. This indicated the groin bed's more irregular sand waves and non-equilibrium sediment transport than no groin bed having same the hydraulic conditions. The bed-form height and bed-form length followed a separate distribution function. The former fitted Rayleigh distribution well and the latter had Normal distribution. The van Rijn empirical formulae for bed-form height and bed-form steepness were modified, and bed-form height and length of groin bed might be estimated from the modified equations.

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The purpose of this study is to clarify the influence of woody riverine-plants on stream flow and bed-load rate. Characteristics of flow and bed-load rate were investigated based on results of flume experiments conducted by the authors. In the experiments, two types of model plant were used. One was a shrub-type, imitating bush trees such as pussy willows, and the other, a tree-type consisting of stem and crown parts. Verification of model parameters included in a one-dimensional k-ε turbulent flow model was perfomed using velocity measurements taken in the experiments. This model was applied to the estimation of effective tractive-stress of bed-load rate. The relationship between measured bed-load rates and estimated effective tractive-forces was represented well using Ashida-Michiue's bed-load formula.

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Compound channel with a series of vertical drop spillways in low water channel is popular countermeasure for flood and sediment control works in Japan, especially in steep slope rivers. The main river flowing through the city of Sapporo, Toyohira River, has 8 low head dams in low water channel with a few hundred meters of interval. It is desired from engineering viewpoint to evaluate hydraulic functions, effect and existing problems in such compound channel rivers. In this paper, a numerical model to simulate flow and bed deformation in compound channel with a series of vertical drop spillways is depveloped. Calculated results are compared with the results obtained in moveable bed experiment.

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We experimentally studied the location and depth of channel bed scouring along meander channel banks in thirty four different types of meander channels with various sets of wavelength and bend angle. The results are as follows:(1) The location of bed scours along side banks moves downstream gradually in whole reaches of weakly meander channels with the migration of alternate bars.(2) The location and shape of scours are stabilized along downstream banks of convex curves in meander channels with larger bend angles than critical ones.(3) Above critical angles scouring becomes deeper as bend angles become larger.(4) The depth of stabilized scours in short wavelength meander channels is large because their critical bend angles are larger than those in long wavelength meander channels.(5) When the location and shape of scours are stabilized, scouring depths are minimum in meander channels with slightly larger bend angles than critical ones.(6) As larger quantities of water are discharged, scouring depth becomes small in smaller-angled channels but it becomes large in larger-angled ones.

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It is important subject for controlling flood to estimate erosive resistance of natural riverbank. Several studies on the erosion of consisting of cohesive soil have been made in recent years. In those studies, only cross sectional erosion depth has been paid attention to. But, bank erosion depth increases with widening its area. And, failure of overhanging bank comes about by large erosion area.
The point of this paper is that expansion mechanism of erosion area is examined. Indoor erosion experiments were given using undisturbed floodplain soil of the Yoshino River, Shikoku, Japan. In addition, overhanging banks are reproduced by hydraulic model to examine the longitudinal change of flow characteristics. As the consequence of those experiments, erosion process of cohesive bank and mechanism of failure of overhanging bank are clarified.

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In steep alluvial rivers, braided channels are often produced due to the formation of multiple raw bars. It is important to predict the long term bed variation as well as channel shifting for river for river regulation works.
In this paper, the Abe river is chosen for discussions. The field data show the river bed has aggraded since the year 1967, and a typical draided channel is formed. The applicability of a two-dimensional numerical model is verified for local erosion and deposition in braided areas and outer-bank erosion in curved regions. In addition, it is found that the method can predict a complex bed configuration, which is caused by an artificial change of the upstream reach.

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The river-bed configurations were measured by a echo-sounder attached to a cross-type float under floods in the Hii River which is the typical sand-bedded river in Shimane Prefecture. At the same time, time series of photographs were taken of the flow patterns on the flow surface, and the vertical distributions of the velocity and turbidity were also measured.
In this paper, by using the data, moving velocities of dunes were obtained at every stage of the floods, and approximate estimations of discharge rate of bed load and suspended load were tried.

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The present study deals with simulation model of cohesive bank erosion that was developed by use of results of field observation at the Yoneshiro river. The model uses the prediction method of fluvial erosion rate of cohesive soil which is applicable to natural banks, only one soil property, tensile break stress is measured. So that, there are no need to adjust the parameters which is concerned to fluvial erosion rate. By the comparison of field observation and simulation results, spatial variation of soil properties related to erosion resistance is one of the most essential factor to increase the simulation accuracy.

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The present study describes a long-term sediment budget, two-dimensional bed variation and temporal change of bed surface, which are based on field surveys and observations. The long-term bed analysis shows that river bed in the reach 0km to 22km aggrades at annual rate 2 to 4cm, and sediment is delivered to the coast at volume of 10⁵m³ a year. These are also predicted by numerical simulation with one-dimensional governing equations. In addition, the migration of braided streams will play an important role in local scours if flood flow peaks are not so large.

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Step-pool morphology, which is one of the most important environmental elements in mountain rivers, has been recently incorporated into channel works. From an ecological point of view, it is desirable that the materials are not covered with cement and the structure is allowed to be changeable. When we design the step-pool structure in such a sense, we should know the deformation process of the structure in floods and the critical discharge for the disappearance of the step-pool bed form. Therefore, we surveyed the changes in the step-pool structure due to the floods in the Gamata River. The structure was changed with the combination and division of the steps, but not completely destroyed by the floods. The formation and deformation process of the step-pool structure have been explained theoretically using the hydrological data.

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In order to identify the process of formation and the form characteristics of step-pool systems in mountain streams, movable bed experiments were conducted by changing the rate of flow, the channel gradient and the bed materials. The findings are 1) the Talbot type grain size distributions of bed surface materials with an index n=1/2 to 3/4, is essential to the formation and stabilization of step-pool systems; and 2) medium-scale bed undulation, which is similar to alternating bars as often found in alluvial rivers, can develop in mountain streams, and formation of the medium-scale bed undulation subsequently promotes the formation of a step-pool system. In addition, 3) a law of resistance of flow during the formation of step-pool systems was specified, and formulae for estimating a wave length and a wave height of a step-pool system by using the resistance law were proposed.

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Temporal responses of sand waves, mean flow depth and reach averaged sediment transportation rate due to periodic change of flow discharge were investigated on the basis of flume tests using the graded and the uniform sediment. They were also predicted by taking the reference grain size for sand wave transformation into account. The predicted results were verified with the experimental results. From the results of experiments and predictions, it was found that the width of loop in the graphs of dischargewave height and discharge-flow depth for the graded sediment were smaller than that for the uniform one under same flow discharge condition. Therefore, time lag of response for the graded sediment is smaller than that for the uniform one. And, the peaks of wave length, wave height and flow depth indicated the positive time-lag to the peak of flow discharge, while the peak of sediment transportation rate indicated the negative time-lag to it.

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The characteristics of alternate bars have been vigorously studied under steady flow conditions in straight and regular meander channels. However, in order to consider bed variation in actual rivers, it is important to clarify the bar deformation due to the changes in various channel conditions. Therefore, this paper deals with the behavior of alternate bars under several different channel conditions (e. g. the existence of a curved section and side-wall structures in a channel, and changes in the rate of sediment supply from the upstream) by means of experiments and numerical analyses. The changes of channel conditions leads to the different bar wavelength, bar height, and migration speed. Using the numerical results, the mechanisms of these phenomena are discussed.

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Bed topography of a mountain river is seen to be composed by three different scale undulations of large scale unit, meso-scale unit and small scale unit. Of the three, small scale unit was identified with step-pool systems in the recent investigations. However, the origin and the properties of meso-scale unit are not yet elucidated though it has been suggested to correspond to an alternating bar. For the explanation of the mesoscale unit, experiments of alternating bar generation were conducted by using a steep gravel bed channel and the bed forms were compared with actual bed topography of a mountain river. The experimental results showed that meso-scale bed topographical unit is just an alternating bar formed by gravel and stones: The alternating bars generated in the experimental channel, on which step-pools were superposed, revealed the very similar properties to those of the compared river.

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In open channel fows with bed-load transport, mean flow properties, turbulence intensities and Reynolds stress profiles are affected by the bed-load motions. In this study, LDA measurements over flat movable sand bed were conducted with high accuracy. The sediment transport was also measured simultaneously. It was found that the mean velocity gradient near the bed decreases with an increase of the bedload transport rate. Both the horizontal and vertical turbulence intensities, also increase in the inner layer as compared with those of rough fixed-bed open channel flows. Reynolds stress profiles near the bed deviate systematically from the triangular distribution which is theoretically valid in a two dimensional uniform open channel flow.

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We have tested the suitability of two non-linear analyses of the geometric and migration characteristics of alternate bars formed between rigid vertical walls of a straight channel. The development of alternate bars were predicted. The wave height obtained by an analytical method is higher than that obtained by a finite difference method (FDM). The difference is caused by higher wave number components in the simulated flow. The difference in the migration velocity between these analyses is large, which is caused by the difference of the bed geometry structure. It is found that the secondary flow which is estimated in the FDM by the stream line curvature affects the wave height very much. The wavelength of alternate bars produced by a bed disturbance located in the upstream end of the computational domain was found to be close to the wavelength obtained by a linear analysis.

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In this study, we propose an image processing technique for measuring the temporal and spatial distribution of the suspended solid concentration in water. An equation, which relates luminance in the image to the concentration of the suspended solid in water, is derived by applying the radiative transfer equation that represents the effect of the multiple scattering of light as well as that of the light attenuation. The optimized values of the coefficients in its equation are experimentally determined from luminance of image on the uniform concentration condition. In order to examine the accuracy of the present method, the concentration distributions are measured with the quasi-uniform concentration in water. The result of measurement shows that this method is useful for estimating the rather high concentration of suspended solid.

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Effect of roughness elements on diffusional mass transfer from bottom sediment to flowing water is formulated as a function of flow velocity and characteristics of roughness element such as height and distance. Laboratory experiments which use strip roughness are performed in order to investigate how the diffusional mass transfer from bottom sediment to flowing water is exerted by the effect of roughness elements. The experimental results show that released flux of dissolved substance increases as the flow velocity increases and that it also increases as the distance of roughness element decreases. These results suggest that exchange of the water body near the sediment-water interface for the upper layer water becomes more frequent as the flow velocity increases or distance of roughness element decreases, so that the released flux increases.

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The average settling and rising velocity in homogeneous turbulent fields of a spherical particle have been examined. The velocity field of homogeneous isotropic turbulence is simulated by Kraichnan's technique. Both experimental and numerical results are shown. From experimental and numerical results, it is found that both light and heavy particles tend to be delayed by relatively weak turbulence. The results also show an increase in the average settling velocity when turbulence intensity is relatively strong. In the experiments, the rising velocity for a light particle decreases greatly with increasing relative turbulence intensity. An decrease by a factor of 0.05 is observed in the grid turbulence. The increases and decreases in the simulation are small in comparison with those in the experiments.

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Pressures generated during the initial moments of vertical entry of a circular cylinder (10.1cm radius) into a water bath at 10m/s were measured near the water surface by 2.5mm diameter pressure transducers mounted in the sidewalls of an impact chamber, at distances of 0, 1, 2, and 3cm from the centerline. The incompressible theory of water entry agrees very closely with results for a smooth projectile. The theory is also found to apply to drop impact on a surface during this initial phase. Results are also presented for projectiles roughened by a fixed layer of beads. The presence of a bead layer whose thickness is 5% of the projectile radius drastically reduces the peak pressure, from 55 bar for a smooth projectile to about 20 bar. The decrease in peak pressure should not influence the amount of soil eroded during impact, which depends more critically on the extent of the region of stresses that exceed the soil's shear strength.

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The hydrodynamic force acting on a vertical thin-plate has been studied experimentally and numerically under conditions in which the flow is subcritical and the variation of water surface is very small. The pressure acting on the upstream and downstream faces of the plate has been characterized and an experimental formula for the drag force has been proposed. The pressure magnitude and distribution on the plate has been calculated numerically by using the two dimensional incompressible Navier-Stokes equation under simplified conditions. The hydraulic condition for predicting the pressure and the drag force on the plate has been shown, and the velocity field around the plate has been discussed.

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This study describes experimental investigations into the non-linear vortex-excited vibration of a circular cylinder in steady and uniform flow in open chanel with emphasis being placed on the amplification of fluid forces caused by the fluid-structure interaction. The dynamic transverse responses of a spring supported circular cylinder were investigated in the range of reduced velocity Vr=4 to 10 for several values of reduced damping Ksa. The value Ksa of deduced damping was adjusted by using a electromagnetic damper. Hydrodynamic forces, drag and lift, acting on the vortex-excited circular cylinder freely vibrating in uniform flow were measured by using a load cellinstalled in the test cylinder and a load cell supporting the test cylinder. The variation of amplification of the hydrodynamic forces acting on the vortex-excited vibrating cylinder in comparison with the hydrodynamic forces acting on the cylinder stationary mounted at the reduced velocities Vr and amplitudes of transverse vibration of cylinder were evaluated quantitatively.

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Honami is a well-known phenomenon observed in paddy and wheat fields. However, the mechanism of Honami generation is not completely solved. Several theories published hitherto are divided into (i) gust attack theory, (ii) resonant oscillation theory induced by turbulence of air flow, and (iii) a recently proposed one the instability wave theory generated between air and conopy flows.
In order to shed a light into the phenomenon, a numerical simulation considering large deflection of plant stalk has been performd. Turbulent air and conopy flow is computed by LES model by Kanda and Hino (1994). The waving oscillation of plant stalk is simulated by a row of elastic cylinders.
Within a limited range of this simulation condition, the result seems to support the gust-attack theory, although the conclusion does not exclude the possibility of other mechanisms.

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Vegetation in a river may affect the 3-D flow structures and can control the local scour and accumulation in curved open channels. In this study, three-dimensional mean flow structures were measured in a curved open channel with various vegetation arrangements. Furthermore, experiments were conducted in a movable bed and the effects of vegetation on the local scour were examined. The secondary flow is generated only in the region outside the vegetation zones and the lateral scale of the vortex structures in bends are reduced. The main flow indicates complicated behaviors affected by the strong lateral shear, centrifugal force and momentum transport by the secondary flow. In movable beds, the secondary flow develops fast and becomes about 1.5 times larger than that in fixed beds. The vegetation changes the bed configuration through the change of mean velocity field.

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It has been known that shear instability generates large horizontal vortices at the junctions of main channel and flood plains for two-stage channels. In the present laboratory tests, it was found that the vortices disappear due to subdepth scale turbulence for flows with relatively large value of h/H. For channels with bank vegetation, horizontalp eriodicv orticesa lsoa ppear, for which it was seen that the vorticesi n the main channeli s predominant.
Numericalc omputations were performed by employing SDS-2DHt urbulencem odel, the results o f which agree reasonablyw ell with the experiments.

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As the construction of sea dyke has come to finish on April 14, 1997, the 35.5 km² area of original Isahaya Bay has been separated from sea, and will be changed to land in near future. It is considered that the spatial distribution of tidal flat around the Isahaya Bay is severely affected by the progress of reclamation project. Thus, numerical simulations were carried out in order to examine and evaluate the influences by an enclosure of bay. Calculated results show that the shoreline in the Isahaya Bay varies as the decrease of water exchange between inside and outside of the sea dyke. Moreover, because of the decreased velocity of current, deposition is occurred in front of the dyke. These results imply that the possibility of an appearance of tidal flat, and its area is influenced by the control of gates. It consequently indicates that adequate attention should be paid to preserve and create the tidal flat.

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The Suez Canal is an important water-transport route all over the world. Two hydrodynamic issues related to the flow within the canal are worthy of consideration: sedimentation in the northern section of the canal and high velocity current in the southern section of the canal. To address the sedimentation issue, a large program of dredging works is being undertaken. A numerical model is presently being developed to simulate flow in the canal with a special attention paid to the south part. This model is the focus of the present study. The model is a two-dimensional depth averaged finite element model utilizing independent open boundaries at the north and south ends of the canal. The radiation and modified long wave boundary conditions are compared. Due to its accuracy and flexibility to suit different forcing conditions, the radiation boundary condition shows superiority over the modified long-wave formulation. The simulation results reflect most of the physical phenomena observed in the canal.

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Nowadays, water pollutions in many semi-enclosed bays have been a very serious social problem. In order to solve this problem, we have proposed the method to activate the water exchange between a bay and its outer sea area by using bottom roughness. In thisstudy, we developed two types of bottom roughness and examined their resistance properties experimentally. At first, the bottom roughness which could create the tide-induced residual current normal to the main tidal flow was improved. Then, it was made clear that the bottom roughness with the shape of a quarter sphere had the property to produce directly the tide-induced residual current not only in the parallel direction but also in the arbitrary direction to the main tidal flow. Finally, it was confirmed from the results of the numerical experiment that the combination of these bottom roughness could efficiently make a stronger residual circulation.

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A variational data assimilation using the adjoint equations is applied into a one-dimensional oceanic Ekman layer model to estimate some physical parameters of the ocean model. At first, the effects of the computational conditions such as data intervals in time and space, and initial values of control variables to the model results were investigated through the identical twin experiments in which the pseudo observation data generated by the oceanic model were used. Next, the in-situ current data measured in the sea off Fukushima were assimilated into the model. The results showed the vertical eddy viscositiy coefficients were in order of 10^-3 (m²/s) and the surface wind drag coefficient was about 1.0x10^-3.

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Since ADCP (Acoustic Doppler Current Profiler) has been widely used in estuarine and coastal waters, barotropic or baroclinic features can be clarified accompanied with three-dimensional computation. Newlydeveloped VHF (Very High-Frequency) Radar is based on the fact that VHF Radar sea-echo on the sea surface makes resonant Bragg scatter and is possible toprovide spatial distribution of near surface velocity in about 30 cm depth from sea surface. In the present study, VHF radar measurements were carried out in order to compare with ADCP results in the head of Osaka Bay. As a result, reasonable agreements were found.

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Omura Bay in Nagasaki Prefecture, which is called a double-closed bay, is connected with Sasebo Bay through very narrow channels. The authors had applied satellite remote sensing technique to confirm the exchange condition of seawater between these bays. This method is capable of investigating only the surface current. In this paper, the numerical simulation system was improved in order to simulate actual tides by using three-element control function. The results of satellite remote sensing were compared with the outcome of the simulation system. It follows that the results of satellite remote sensing and the outcome of the system corresponded well when the axis of coordinates which is rotated 34 degrees from circles of latitude and longitude and eddy viscosity in the 40m2/s to 60m2/s range were used for the numerical simulation.

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The Japan Sea is a semi-enclosed water body with complicated geometry and a narrow strait of Tsushima through which sea current enters. As for the surface current of the Japan Sea, tidal component is weak followed by the sea current component. In wintertime the strong seasonal wind blows over the Japan Sea to induce the surface current. The purpose of this paper is to develop a method to estimate the surface current in winter quantitatively. Firstly the observed data of wind and surface current off the Noto Peninsula is analyzed to obtain the predominant flow direction of Northwest and the magnitude of the wind driven flow of about 15cm/s. Secondly, the numerical model to calculate tidal flow and sea current is developed with the obtained maximum tidal flow of about 15cm/s and sea current about 3cm/s of the Noto Peninsula, confirming the predominance of the wind driven current.

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A Russian Tanker sank in Japan Sea on February 2, 1997 and the spilled oil is dispersed along the Japanese Coastline. In this incident, the spilled oil flowed west over 300km for 15days. It has been known in the Japan Sea that in winter the wind driven current is dominant over the tidal flow and sea current. This study, therefore, explores the relation between wind and surface current using the measured data off the Noto Peninsula as well as the calculated geostrophic wind. The wind data is analyzed to obtain the predominant wind direction of NW and the deviation from the gcostrophic flow. The auto-correlation study of wind and surface current gives the correlation scale of 20h and 13h for wind and current respectively. The cross-correlation study gives the wind-to-current response time scale of 5h.

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It is very difficult to evaluate the river discharge at a tidal portion, because the discharge can not be calculated directly from the water level due to influence of tide. A new measurement system of discharge and salinity flux at a tidal portion using an acoustic Doppler current profiler is proposed in this paper. To estimate the system, field measurements were carried out at 5.5km from the mouth of the Takase River. The results show that velocities measured by the acoustic Doppler current profiler near the center point of cross section are proportional to mean velocities, and that mean salinities can be also calculated from the salinities of upper and lower layers near the center point. Amounts of salinity intrusions evaluated by this system agree well with the results observed in lake Ogawara.

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The salt wedge in the Ishikari River has become very long due to dredging activity. Studies of the salt wedge have suggested a new coefficient in addition to the interfacial friction coefficient, which has been widely used in research. On the basis of detailed observations of time-dependent changes in the interface of long salt wedges, the method we are proposing can be used not only to explain how the shape of the salt wedge changes due to tide, but also will allow useful predictions of time-dependent changes in the shape of the interface in response to flowrate and sea level.

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Field measurement and numerical simulation were carried out in order to investigate development and movement of the low oxygen water mass in the Tone River below the estuary barrage. The measurement data shows that low oxygen water frequently generated in the front part of salt wedge, and then developed downstream in the salt wedge gradually.
Next, in order to simulate the characteristic behavior of the low oxygen water, the standard k-ε turbulence model is adopted in the numerical model of salt intrusion. Furthermore in addition to the k-ε model, DO-transport equation and BOD-transport equation are introduced for the purpose of simulating the characteristic behavior.
Comparing the calculation results with the measurement data, the characteristic behavior are reappeared well.

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Efficiency of a prevention method on saline wedge intrusion in rivers using an air curtain (a two-dimensional bubble flow) was experimentally investigated from a viewpoint of a flow mechanism. The behavior of saline wedges in the presence of an air curtain is governed by the three external forces: the buoyancy of an air curtain A, the intrusion force of a saline wedge B and the inertial force of a fresh water flow R. It was found that the flow behavior could be classified into three types both by A/B dominating the rising discharge of salt water due to an air curtain, and by A/R dominating the strength (circulation) of a convection cell induced by an air curtain in its upstream side. In addition, the efficiency of this method was evaluated using the newly introduced parameter α through the discussion on the appearance conditions of the three flow types.

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In this paper, the flow dynamics of the inclined wall thermal with suspended solid particles are investigated experimentally and theoretically. The flow vectors in and around the thermal are obtained by the picture analysis of the video-taped data. The simulation model consists of the conservation equations of the fluid mass, the solid particle mass and the momentum. Characteristics of the inclined suspension thermals are simulated well by the present model. The satisfactory numerical results are obtained such as the longitudinal variations of the height, the speed and the volume of solid particles in the thermal.

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