This observation was carried out to improve water quality in the tidal reach by aeration where pollutant settles down and accumulates on a river bed because of low river velocity. We found out by field test flow, an airlift type is usefull to improve water quality as remedy of these problems in such reach.A few typical results are presented mainly refering to the dissolved oxygen in the placid water by using the circulated flow of the airlift.

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Temporary cofferdam used in river improvement work causes the backwater. In flood time, this backwater increases the risk of overflow over the bank. To diminishthis backwater there are two method. One is kinematic method which is to diminish the flow resistance by using smooth shutterings in shape and rough-ness. The other is dynamic method which is to diminish this backwater by adding momentum ofaccelerator. We carried the mock-up test of dynamic method using the propellers of work-ship as accelerator, and as the result the water level fall down 10 cm. The result exhibited good agreement with the momen-tum principle. This paper presents the result of mockup test.

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The performance of an open-channel electromagnetic flow meter in concrete-lined and natural channels was investigated. It was found that a good correlation between the induced potential and observed discharge can be derived for the concrete-lined channel, without considering the effect of electric conductivity of water (ECW). However, the effect of ECW is important in the natural river. To significantly improve the accuracy of measurement, a parameter functionally-related to water stage was used. Pollution of the electrodes over a period of time seems to alter the system characteristics. Hence, periodic calibration of the parameters is required to maintain a constant performance-level.

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Field measurements of turbulent velocity were carried out in rivers and channelswith electromagnetic anemometers. A set of two probes of the instruments could detect the three components of flow velocity simultaneously, and thus the turbulent characteristics of flows which were almost one order larger in scale than laboratory flumes could be measured. The following flows were investigated:(1) uniform flows:(a) with sufficient submergence, (b) with small relative submergence, (c) over vegetated bed;(2) flow with abrupt change of bed roughness; and (3) flow in a stream with vegetated region (transverse velocity profile was discussed). The obtained data are compared with those previously obtained in the laboratories, and discussed.

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We have made the field observation of turbulent flow in the tidal portion of Teshio river, using a two-dimensional LDV system of our making. The turbulence energy and Reynolds stress were higher in an upper layer than in a lower layer due to surface wave with the frequency of 0.3 Hz, but there existed the velocity fluctuation of 1 Hz in the whole depth with about equal intensity. Turbulent intensities of vertical velocity component were proportion to that of horizontal velocity component.

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One can say at present that the basic structure of open-channel turbulence has been almost revealed through experimental data of high quality using laser Doppler anemometers in laboratory flumes. However, these experiments have been conducted at moderate Reynolds numbers, say Re=10⁴. Then. it is not so clearwhether the laboratory data of open-channel turbulence can be applied to river turbulence at very high Reynolds numbers.
In this study, the to measurements of the Biwa-Sosui River at Re=8x10⁵ have been conducted using three-component electromagnetic flow meters. As the result, it was first found that multi-cellular secondary currents really existed in the river at high Reynolds numbers. The features of secondary currents in rivers were in a good agreement with those in laboratory flumes.

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A handmade automatic system is developed to observe hydraulic phenomena of a reservoir. The system is composed of a personal computer, which collects data and controls traverse equipments, the hardware, measurement instruments and the software. Special attention is paid to the controller. The system enables one to get the vertical hydraulic profile of the reservoir through one year exceptice covered period.
The obtained water temperature distribution shows stratification and mixing characteristics affected by wind, the sun radiation, and the atmospheric temperature.

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A Thermal Video System is used to measure instantaneous temperature distributions due to the heated water horizontally discharged into the still water surface. The images are translated into digital data with which several characteristics of the surface plumes are discussed. Coefficients to express the distribution aregiven in terms of the densimetric Froude number. Contours of the temperature variance and their three-dimensional expression show the generation area of the major eddies, interference and breaking of the eddies and general paths of broken eddies. It is found that mean temperature distribution deviates from the Gaussian distribution.

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The promotion of sediment suspension in a laboratory flume is discussed. Due to strong upward flow behind a spherical obstacle fixed at the bottom, bed materials are transported as suspended load. Horse-shoe vortices in front of the obstacle generate scour hole around it, and arch-shaped vortices behind the obstacle produce ripples in its near downstream area. Sand particles are entrained by the coherent vortices even after the scour hole has developed, which is detected by the distributions of suspended sediment. The obstacle placed in front of a weir can increase the amount of the suspended sediment passing over the weir.

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Sand bed instability due to non-equilibrium suspended sediment is analyzed. Non-equilibrium suspended sediment concentration distribution is described by using the convolution integral model for turbulent flux distribution of suspended sediment of which impulse response is determined from the transition process of the Reynolds stress distribution of open channel flow with abrupt change of bed roughness. The results reveals the effect of non-equilibrium suspended sediment on sand bed instability by comparing them with the analysis based on non-equilibriumbed-load transport model.

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In this paper a mathematical method to calculate longitudinal and vertical flow velocity and non-equilibrium concentration of suspended load in open channels with a trench is discussed. This method is based on 0-equation turbulence model and two dimensional diffusion equation of suspended sediment. Using this method, the velocity profiles and the concentration distributions are simulated for some trenches with different ratio of the depth to the length. These results show that the flow structure that consists of main flow and circular flow can be simulated precisely and the concentration can not be calculated correctly without the estimation of two dimensional flow structure.

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It is often found that a coarse surface layer exists in the outer-bank region, and a finer one in the inner-bank region in natural stream bends. This phenomenongenerally results from the sortingof graded bed load. A method for the calculation of bed load discharge is proposed, in which the effects of bed slope and flowdirection on sediment transport have been taken into accounts. Furthermore, a two-dimensional numerical simulation modelis developed, which is useful for predicting of the spatial and temporal variations of grain size distribution as well as of the bed configuration. Discussions are made on the sorting process and the effects of grain size distribution on the bed topography.

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In braided channels which often form in mountain streams, sediment discharge varies spatially and temporally with the variation of channels. Results obtained from flume tests show that merging and diverging phases of channels occur alternately and repeatedly in space and time, which bring about the periodic change of sediment discharge. In order to estimate the sediment discharge averaged temporally, the average width of the channel should be known. We propose a new method predicting the width of channel in terms of the concept of the self-formed channelwhich is similar to the criterion of alternating bars formation.

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The threshold condition of the incipient motion of coarse materials in mixed-sediment beds is studied with respect to spherical particles.
First, the influence of protrusion and relative depth on the fluid force is clarified experimentally.Secondly, a general equation for the threshold shear velocity is deduced throughthe theoretical consideration of the escape of the coarse particle from a hollowconsisting of the finer sediment. The equation explains very well the experimental results of the threshold condition of isolated spheres.

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The interaction between the sorting process of sand mixtures and the developmentprocess of sand waves is discussed by using the sorting model at the crest of sand waves. In this study, the first, we discuss the developmental property of sand waves with sorting of sand mixtures. The second, propose the sorting model considering the movement of sand particles around the crest which defines the wave height. Finally, consider the physical model for the interaction between the particles and the sand waves, and the intrinsic particle size.

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Bed load transport and grain size variation of the surface layer of a river bed with gravel and sand mixture are discussed based on flume experiments with equilibrium conditions of sediment discharges. The bed surface layer tends to be coarser than the substrate at low rates of sediment transport, but it becomes finer at higher rates. The bed load transport rate can be calculated based on the availability of each size grains in the surface layer, because the mobility of grains is due to fluid forces acting on the exposed grains. The coarsening and finingmechanism is also discussed qualitatively.

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To clear the difference among the liquid, the mass of sediment particle flow andthe extreme content flow of clay, this report treats with the non-uniform flow of those flow. By the energy analysis for those fluid, the normal depth and the critical depth are defined as same as liquid. However, those flow has the non-flow part in the layer, because those fluid has the frictional angle or the yield shear stress.
To divide of the non-flow parts, the equilibrium gradient is introduced. The upper parts on the equilibrium gradient which is drown from the behind corner of the obstacle move with the normal depth.

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The step length often plays an important role in fluvial processes. In this study, two types of motion, sliding and saltation, are employed as models of bed-load motion to evaluate the step, and a common framework to describe the step length is presented based on the two models. An application of equations of motion islimited to the individual microsteps, a succession of which forms a step length, and the succession of the microsteps is subjected to the irregularities of sand beds. Thus, the framework is synthesized in a stochastic manner, but the constituent parts are described deterministically. The present study makes it possible to estimate the mean step length and reveals the applicable ranges of the respective models of bed-load motion.

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Real fluvial system is non-uniform and unsteady, therefore, the nonequilibrium sediment transport model should be developed in a spaceand-time plane, in order to describe the real fluvial phenomena precisely. In this study, the convolution integral formed sediment transport model is developed along a temporal axis. The sediment pick-up rate, which is one of the fundamental parameters of the model, is estimated by means of a numerical simulation of incipient rolling motion, with particular reference to the effects of flow unsteadiness. The result of the simulation is compared with the experimental data of sediment particles' motion in an oscillation-current coexisting field to confirm the applicability of the method proposed.

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The scouring process of sand bars due to overflow is experimentally, theoretically and numerically studied. The bed load formula of Meyer Peter-Miuller is extended to include the effects of local slope and pressure gradient, by using the experimental results. The equation of motion is derived to describe the sand motion under non-equilibrium condition. Numerical computations based upon these relationships simulate very well the temporal change of the measured profiles of sand bars.

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It is emphasized that there are no significant differences between the dynamics of debris flow and bed load so far as bed shear stress is large enough for forming a grain sheet flow. The constitutive equation, which is developed for debris flows, is applied in order to discuss the characteristics of bed-load such as the depth of bed-load layer h_s, particle-concentration c (z) and velocity-distribution of bed-load layer u (z). A bed-load formula is developed by integrating the product of u (z) and c (z) from 0 to h_s. According to this, non- dimensionmal bed-load rate is proportional to τ^5/2_*.

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Various problems on the global enviroment become the center of public interest in the world. These problems are complicatedly connected with the increase of CO₂, the destruction of ozonic layer, the dcrease of forests and the expansion of desert lands etc. This paper deals with a method to evaluate quantitatively the effect of forests on the hillside land slide, as one of the abovementioned problems. A new coefficient Cp to express the effect of tree roots on slope stability is proposed in this paper.

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There occurs rapid deposition from debris flows at the mouth of mountain canyon because of rapid flattening of the slope. First, grain movement in debris flow in the deposition process is investigated experimentally and theoretically. From the measurement of the locations of deposited grains in the experiments, their mean, standard deviation and correlation coefficient are determined. The equation for the period of grain movement and the mean location of deposited grains are derived. Finally, by using the results of grain movement deposition profile is calculated.

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Sediment discharge and concentration are experimentally investigated for debris flows caused by denser fluid and by plain water, respectively. Denser fluid is represented by the mixture flow of sand and water. The former debris flow is found to carry more gravels than the latter. Gravel discharge and concentration increase with the decrease in the sand grain diameter. This can be explained by critical fluid velocity for gravel movement in the mixture flow. For the estimate of the critical velocity the drag force is also investigated. The value of the drag force in the mixture flow of very fine sand is close to that in plain water. Therefore, such mixture flow is found to behave like a single fluid.

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The objectives of the present study are to clarify the physical mechanism regarding to the formation and downstream variation of particle size distribution of bed materials in rivers. In the field observation carried out, we measured the abrasion rate of many cobbles put on river bed during snowmelt flood and their downstream migration distance. The numerical simulation of the newly proposed equation shows the relative importance of the two mechanisms of selective sorting and abrasion due to the differences of the geological features of bed materials.

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It is very important in river management works to take into account the influences of the vegetation to the flow during the flood. Logarithmic or parabolic law can be a good assumption for the vertical profile of downstream velocity distribution in open channel flow without vegetation. However, these assumptions cannot be applied to the flow through the vegetation because of the strong effect of the resistance caused by trees.
In this paper, the vertical distribution of flow through the vegetation is predicted theoretically. The bed drag coefficient has to be changed in order to calculate the depth averaged downstream velocity accurately.

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Hydraulics in vegetated streams increasingly becomes important for designing comfortable river environments. In this study, suspended sediment transport is investigated. Firstly, the turbulent structure of open channel flow over a vegetated bed is studied by means of both experiments and numerical analysis based on k-A turbulence model. Secondly, the turbulent flux of suspended sediment is estimated by assuming a similarity between the change of turbulent flux distribution of suspended sediment due to the presence of a vegetated layer and that of turbulent momentum flux (Reynolds-stress distribution). Based on the above, the concentration distribution of suspended sediment of flow in a vegetated-bed channel is predicted against the vegetation density.

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Flows and sediment transport in compound channels with trees on flood plains were investigated experimentally using flow visualizations and measurements.Time-averaged velocity profiles, characteristics of large scale eddies produced by the shear instability and the mechanism of the sediment transport were considerably changed by vegetation. The deposition of suspended sediments occurred locally at the certain points, and its location was determined by the arrangement of trees.

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The evolution of local scour with time, caused by a submerged hydraulic jump downstream of an apron, is investigated on the basis of the sediment continuity equation as well as the experimental evidence that the configuration of scour holes in the progressive stage possesses the properties of geometric similarity. A semi-theoretical analysis of one aspect of the phenomena of the problem is presented. Calculated results are compared with available data.

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The report treats with the control of the local Kscour in the out side of the bend channel. When the skewed rectangular roughness elements placed on the embankment, the local scour decrease and the bed profiles in the cross section change nearly plan. The upper direction flow induced by the skewed rectangular roughness elements reverse the direction of the secondary current near the bed. The mechanism of the scour decrease is discussed as the velocity Vθ is in uniform and the centerfrugal effect decrease.

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This paper describes experimental results of local scour downstream of a bed protection work with hollow squared blocks under a dynamical equilibrium condition of bed load. Variations of profiles and the maximum depths of scour holes with time were discussed, and compared with those under a static equilibrium condition and experimental results of a bed protection work with smooth bed. Flow characteristics, such as, velocity distributions, bed shear stress and pressure on the scoured bed were also measured at several stages of scour. Non-equilibrium caluculations of bed load using the bed shear stress measured could simulate well the variations of scour hole in the early stage of the scour.

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The mechanism of sediment control of side weir is investigated with attention focussed on bed load and bed variation, using a rectangular flume with main and side weirs.
Discussions are made on the energy-loss due to local flow around the weir, the relation between the sediment rating curve and bed variation, the diversion ratio of sediment and the dividing discharge ratio. Such sediment phenomena can be evaluated roughly in terms of one dimensional analysis.

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The turbulent velocity components (u and v) at 11 points on a plane perpendicular to the meanflow in a reciprocating oscillatory turbulent flow have _been recorded simultaneously by 11 X type hot-wire probes. Using conditional sampling technique and a new method of data analysis, we reconstructed the quasi-instantaneous three dimensional image of large-scale structure. The new method of data analysis consists of two steps. The first one is the spatial inter- and extra-polation of velocity components u and v by the method of “ virtual load” and the second is to regulate them together with the third velocity component w so as to satisfy the continuity equation by the mass conservation technique.

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From the spectral point of view, the generation, growth and decay of fluctuations accompanying large-scale structure in an oscillatory turbulent flow are discussed analyzing the experimental data obtained by multiple-probe hot-wires We found that fluctuations with structures are weak at the beginning of flow deceleration phase but grow rapidly, both in low and high frequencies range, with advance of the phase. These high frequency disturbances are generated at the positions where the high-shear layer appears. Fluctuations accompanied by turbulence structures near the wall get weaker and weaker with advance of the phase which could be account for by the reduction of the ensemble-averaged shear.The average height of the structure gets taller and taller during flow deceleration.

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Laboratory experiments have been performed to study non-linear vortex-excited vibratidn of a circular cylinder in planar oscillatory flow. The relationship between the transverse response of the test cylinder and the frequency ratio fnw/fd (fnw: natural frequency of cylinder in water, fd: frequency of oscillatory incident flow) are obtained for four values of Keulegan-Carpen ter number (KC KC=10, 17, 25, 50). The non-linear phenomena caused by the fluid-structure interaction in this vortex-excited vibration are discussed.

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The method of calculation of high velocity flow with free boundary is developed by means of the method of characteristics. The basic equations used here are the plane two-dimensional flow equations in the steady state. These equations are transformed into the characteristic form. It is shown that the position of free boundary is determined as the intersection of stream line (λ1-line) and another characteristic line λ2 or λ3. The hydraulic variables along the free boundary are also calculated by using the relation satisfied along λ1- and λ2-line or λ1- and λ3-line. The numerical method shown here is applied for some typical high velocity flows with free boundaries studied by Rouse and Knapp. The calculated results are compared with the previous experimental results in order to verify the method of calculation.

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Flume experiments were carried out in order to study the velocity field in the boundary layer under wave and wave-current combinations. These included both smooth and rough of flat and sloping beds. The particle velocity was measured by an LDV. The particle velocity on the sloping bed was found to follow the logarithmic law of wall as for the flat bed. However, significant differences in the time mean velocity and the mass transport velocity for the combined wavecurrent flows are found. The comparisons in terms of the friction factor and roughness parameter were made with several theoretical models.

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The stability of the seabed under wave pressure is an important problem in the design of pipelines, anchors and offshore gravity structures. Recently, many studies of wave-seabed interaction are reported. However, in most cases, such studies discusses on the seabed response to the sinusoidal pressure variation. The aim of the present paper is to study the effect of the finite amplitude wave pressure variation on the seabed response. The seabed response are analyzed by the finite difference method with the Biot's equation for the consolidation in the vertical, one dimensional model. The effects of the wave steepness, the relative depth, the amount of air and water, the permeability and the compressi-bility in the seabed response are investigated by various example.

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Purification of polluted sea water in deep bays is essential from the viewpoints of coastal environment. Development of artificial fishing grounds is also desirable from the standpoint of coast fisheries. These two social problems need commonly the development of technology to generate net flow in coastal region and to control it. We are demonstrating how to gain the difference of water head by overtopping waves into a coastal structure, and how to discharge the overtopped sea water into a bay or deep sea by using the head difference. This study is concerned with the maximum quantity of wave overtopping gained when two-dimensional regular waves climb up a sloping bed. The maximum quantity can be evaluated by using non-dimensional empirical diagrams.

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The behavior of solitary waves on density interfaces over sloping bottom is studied numerically. Such solitary waves are caused by tidal flow, and propagate towards shore or river mouth where density stratified flow is formed due to the difference of temperature or salinity. The main concern is whether solitary waves can propagate further upstream changing their polarity, or collapse or are reflected on the slope. A method of numerical analysis to treat such a complex flow including oneand two-layered region, free surface, density interface, and open boundary is also discussed.

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The effect of water conduction by a pump system on water quality of urban rivers was investigated. The object river system of this study is the Shinmachi river system which flows through the center of Tokushima city. By using field observations and a numerical analysis of Holly-Preissmann method, it was found that the concentration of BOD in the Suketoh river decreases from 14.7 ppm to 7.7 ppm when the pump system was operated only in the ebb tide.

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In order to evaluate the buffer capacity of watershed to acid deposition, it is necessary to make clear both the pathway of precipitated water and the accompanying chemical change of the water. We observed temporal variations in the chemistry and ¹⁸0 content of the streamwater during a storm and divided the discharge into baseflow and precipitated water. The streamwater chemistry is explained by assuming the temporal variation of baseflow chemistry.The following 2 mechanisms are supposed:(1) soilwater, which has different chemistry and buffercapacity from groundwater, is the source of storm runoff.(2) soilwater and/or groundwater chemistry changes in the pathway to stream.

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Behavior of later Quality and Sediment in Estuary region is influenced by Floods and Tide, There is a complicated phenomenon. Estuary region is catchment area for run-off of rain fall, living waste water, and Basic flow of urban small riers is extremely small quantity.
There fore, precipitation and sedimentaion is easily in estuary region. Pollution load is on the increase in fooding.
This paper is result of investigation to use numerical analysis of a dementional unsteady flow equation and diffusion equation and datas of observation about behaviors of water pollution and bottom deposits at tidal reach in urban small river.
The following was clarified by this research about at area of sediment in quantitative with relation to tractive force

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Acid rain is a water pollution event and is a typical instance of the interenvironmental pollution which is induced in return for the purification of atmospheric pollutants such as sulfur dioxide and nitrogen oxide. These pollutants are absorbed into and dissociated in rain drops to increase hydrogen ion, i. e., rain acidity. A mathematical model for the scavenging and dissociating of sulfur dioxide to form acid rain has been developed. The model simulation shows that both of rainfall intensity and initial pH have important effects on the acid rain formation.

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The cooling effect of plant (forest) and water surface (lake) on the thermal environment in urban area was studied by the field observations and numerical experiments. At first, field observations were carried out at the three sites, that is, around a single tree, the Senzokuike Pond and the Meiji shrine. In all the cases, the cooling effect of forest or pond was shown remarkable, and the cooling ratio per the unit area decreased in proportion to their scales Secondly, 3D numerical experiments were performed to investigate the heat and momentum transfer from the water surface. The results show that the differences of roughness height between water surface and surrounding area have much effect on the mechanism of heat and momentum transfer.

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The variability of surface heat flux depends strongly on the materials heat absorption and storage rates. During summer days, the temeprature in the materials and long-wave radiation from the surface were measured together with surface long-wave radiation, atmospheric and solar radiation etc. Among materials, asphalt slabs absorb highest radiation energy, and increase their temperature. Eventually, they radiate heat as high as 700W/m², which is 150W/m² higher than that of concrete slabs. In addition, the heat absorbed during daytime is released into the atmosphere during night and causes so-called “tropical nights”.

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Recently, evaluation of environment involving so many factors is required in relation to the global environmental problems. Prospective means of Remote Sensing for environmental investigation are applied herein from such three points of view; Vegitation Index is related to run-off and evapotranspiration using the corresponding data of the National Digital Land Information, Heat-island phenomena is mitigated by the existence of vegitation or water surface, and pattern of lake current is analyzed by turbid water flown into the lake, applying MOS-1 image.

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Aoshio, upwelling of anoxic water, often appears in the bottom of Tokyo Bay from summer to autumn. Since many observations have revealed that the wind-driven flow moving off-shore may induce the stratified bottom water of anoxia to move ashore, basic two-dimensional experiments have been performed to clarify the upwelling and mixing phenomena of two-layered stratified flow system exposed to wind stresses at the surface. It is confirmed that the prediction of Spigel and Imberger is a good agreement with the flow visualization results of upwelling phenomena.

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The purpose of this study is to make an improvement plan of water hazards caused by AOSHIO, the ascending of the anoxic water from the bottom to the surface, at the Lake Abashiri in Hokkaidou.The field observation shows the following results;
1) The lake is vertically divided into two layers, the lower layer with salt waters and the upper with fresh waters.
2) The interface between two layers shows the regular oscillation of internal waves on gentle wind.
3) The interface shows the uniform decline toward the wind direction on strong wind.

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Natural periods of surface and internal seiche in Lake Suwa and Lake Nojiri are determined using a numerical model and from the field observation data of water temperature and free water level. The finite element technique is applied to the surface seiche and is also extended to the internal seiche.
The natural periods computed from the numerical model and those obtained from observation data are almost equal. The natural periods of first mode of the surface seiche in Lake Suwa and Lake Nojiri are about 1350s and 490s respectively, and those of the internal seiche in Lake Nojiri vary from 220 to 270 minutes.

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