A numerical model is proposed to investigate the finite amplitude bed topography and maigration characteristics in meandering channel. Migration characteristics of bar in meandering channel is investigated. The effects of geometric and hydraulic factors for finite amplitude bed topography are investigated using the proposed numerical model. By the results of the numerical experiment, a series of figures are presented, which show the effects of each parameter to the finite amplitude bed topography. A practical formura is proposed to estimete the finite amplitude bar height.

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The state of dymamic equilibrium must satisfy the following three condition; 1) Equal sediment discharge along the channel. 2) Stable channel cross-section with actively transported bed materials. 3) Hydroulic condition to confine the small sediment wave and the wave length of meander.The paper gave a concrete method to keep the three conditions and explained the applied results for the actual river.

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The Longitudinal profiles of bed elevation, the mean diameter of bed materials, the width of channel and the depth of flow in alluvial rivers were analysed theoretically. In order to close the system of equations the concept that the bed shear stress remain constant in the longitudinal direction was introduced, This was derived in the analysis for the stable cross sectional shape of channels.
The results of theoretical analysis were tested with the data of rivers in Hokkaido. The longitudinal profiles in rivers in Hokkaido fit to the theoretical one relatively well.

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Characteristics of river bed variation of the Kane River, which is a typical alluvial river, are discussed by using a large scale hydraulic model. The results show that the flow patterns and the river bed configurations for all cases of flood discharges are very disorderly. In order to get a better way of the stabilization of the main flow channel, some sets of layout of spur dikes are examined, and a new index is defined for quantitative evaluation of the channel stability. The index shows good agreement with the result of comprehensive observation of the river bed configurations.

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Equivalent roughness and flow resistance of erodible beds in open channel flow in the presence of sand waves are theoretically investigated. Based on boundary layer theory, the geometrical properties of sand waves are introduced as dominant factors affecting on flow resistance. Using linear stability analysis, dominant length of sand waves is obtained. Applying one dimensional wave equation and continuity equation for sediments, the height and steepness of sand waves are obtained. Suspended sediment effect is taken within the scope of study. The results of the presented model are significantly better than previous studies.

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Mountain river bed is characterized by steep slope, wide range of grain size distribution of bed materials and relatively small water depth to the bed roughness, which cause “stair-like” or “transverse limb” bed form. Flow resistance and bed form with transverse limb are discussed with data observed in a mountain river and obtained by experiments for the bed with sand-gravel mixture or fixed crosspiece roughness. The ratio, λ/Δ, of wave length λ to wave high Δ of limb bed in mountain rivers is about 10, in which case flow resistance is proved to become maximum by experiments. Flow resistance on the bed with relatively large roughness changes largely according to the flow patterns, and it becomes largest when the ratio, h_m/Δ, of flow depth hm to the roughness height Δ is about 1.7 for λ/Δ=10

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In natural rivers, it is commonly seen that gravel beds are delineated by sandy banks. A theoretical model to explain the “gravel bed sand bank morphology” of straight rivers is presented in this study. The theory of stable cross-section of gravel rivers is combined with that of sand-silt rivers by introducing the concept of an available function (P) of fine sands on gravel beds. The theory predicts the location of sand deposit in the channel for given center depth, slope and center value of P (available function).

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In braided channels, channels vary spatially and temporally, which results in the big variation of the sediment dischrge. It is important to know the channels pattern and process of stream channels variation. Channel patterns can be predict by the length and width of each stream channel. In this paper, two dimensional simulation model are employed to clarify the process of sand bar formation and channel diverging phenomenon in a gradually widening channel, in order to investigate the length of a stream channel. The results of the calculation are compared with the data obtained from flume tests to verify the numerical model.

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The effects of the protection works against the scour around bridge pier were studied experimentally, taking notice of their permeability. The scour around the pier is sufficiently diminished by the flush surface protection works. There are significant differences between the permeable and non permeable protection works in the scoured bed configuration and the flow structure behind the pier. The scour depth is smaller in the permeable case than the non permeable case. This is attributed to the reduction of the longitudinal vortices behind the pier by permeating flow.

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A numerical prediction method for local scour has been developed on the basis of the arbitrary Lagrangian-Eulerian (ALE) formulation, in which three-dimensional body-fitted coordinates (3D BFC) are regenerated for moving boundaries independently of the fluid motion. The governing equations, including transport equations for κ and ε, are discretized in a Lagrangian scheme and the convection terms are solved with third-order upwind difference. This prediction method was applied to the results of a three-dimensional local scour experiment and the sand bed profile was reasonably predicted.

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For the design of a groundsill, it is important to estimate the depth and area of local scour around it. In this study, we intend to construct a numerical simulation model which calculates a 2-dementional flow with MacCormack scheme and computes bed elevation by considering the non-equilibrium sediment transport. The result of calculation by this model is compared with the data observed from the hydraulic model test and they show rather good agreement.

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Protection works by stones or gravel against local scour of sand bed around river structures are effective only if the protected bed sand is not drawn out through the cover layer of stones or gravel which is stable against tractive force by the local flow. Hydraulic conditions for the effective protection works are studied experimentally. Bed sand can not geometrically move through the stones or gravel layer, when the ratio, D/d, of stones or gravel scale D to sand scale d is less than 2. The tractive force on the bed sand is exponentially reduced through the protection layer as a function of the ratio, LID, of the protection layer thickness L to D.

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This experimental study treats the local scour at downstream reaches of apron and drop channels under the wave type flow with a large-scale stationary wave.
Firstly, the occurrence conditions and flow configuration of the wave type flow are clarified. Next, the characteristics of the longitudinal and plane profiles of scour holes and maximum scour depth are discussed. In addition, the characteristics of velocity distribution in scour holes are discussed.

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Newly developed method to prevent the local scour in the region of outside bank of river bends is presented in this paper. Longitudinally inclined bar elements set on the outside wall generate the artificial secondary current, which regulates the inherently existing secondary current in bends. By using the effect of such secondary current regulation, the overdeepiiig point can be shifted toward the central region.

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Actual conditions of bank damage in some rivers of Tohoku district of the past decade were investigated. It was found that the nondimensional tractive force of flow and the ratio of high water channel width to radius of channel curvature, the ratio of low water channel width to distance of talweg from the channel bank are major factors determining the occurence of river bank damage. In order to make models to predict the location and type, scale of river bank damage multi-variable analysis (Quantification II) was carried out using some of these variables and a composed variables as factor variables. Among the obtained models, the model to predict location of river bank damage was highly evaluated by field data.

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The cavity behind bank protection occurs under stormy waves and flooding. In this study, we investigated the flow-out mechanism of back-filling sand under cyclic loading of water pressure experimentally and theoretically. As a result, it is clarified that cyclic seepage force which occurs around revetment under water pressure variation plays an important role to the movement of sand around revetment and also clarified by visualization technique that the sand around revetment moves like a circular arc. Furthermore, the effect of pressure distribution behind revetment and the effect of the porosity of bed on the flow-out phenomena are examined.

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Conventionally, the effectiveness of vegetation revetments is determined by experience, observation and investigation at the river site, rather than quantitatively in a hydraulic laboratory. But as more river improvement projects seeking to make better use of the natural environ ment are pursued, it is necessary that a more scientifically based understanding be achieved of the ability of vegetation to resist erosion, and the effects of vegetation on the hydrological regime and on suspended sediment.
In this study, bank erosion experiments were couducted using a large-scale experimental water channel with sodded slopes, in a study of the erosion-controlling effects of vegetation, and of the accumulation of suspended sediment, which adversely affects the growth of vegetation.

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The oblique strips installed on dikes control secondary circulation and reduce the local scouring at dike foot. These are discussed, the upper flow flux induced by the oblique strips, the most effective slanting angle, the protected area by this strips and the effects on the wave height of sand waves, near the outer side.

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Some model experiments were carried out in a laboratory flume in order to investigate the formation process of local flow and and scour and their mechanism in a steady condition at flow convergent parts along revetments in river channels, and effects of the revetment slope on these process and mechanism.
Experimental results revealed the flow in a local scour hole and its surroundings consists of a surface flow, a vortex flow at a flow convergent point, two spiral flows at its both side and a base flow, and that these flows contribute to the formationof a local scour respectively in corespondence with its strength.

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It is very important in Hydraulic Engineering as well as in River Environment Engineering to investigate turbulent structures in compound open-channel flows with flood plains. The present study is to conduct both the accurate turbulence mesurements with two-component fiber-optic laser Doppler anemometer (LDA) and the numerical simulations using three-dimensional algebraic stress model (3-D ASM). Both of them were compared with each other. As the results, numerical calculations including secondary currents were in a good agreement with accurate LDA database of compound open-channel flows. Of particular significance is the anisotropy of turbulence and the interaction between main channel and flood plain.

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This paper presents a qualitative and quantitative analysis of the flow in a single-flood plain open channel. A combination of the multi-section flow visualization technique and the Mass-Consistent Model (Sherman) are employed.This shows the mean and instantaneous 3-D behavior of flow interaction, momentum, mass and energy exchange between the main channel and flood plain.The results of mean flow are compared with the ones obtained by a propeller.Investigation of instantaneous flow structures have revealed that the high momentum flow in the main channel is interacted with the low momentum flow in the flood plain. Due to this interaction reversing flow comes out. This causes a subsidiary flow interaction with the surrounding flow in the flood plain. Moreover, comparison of different relative roughs of the flood plain and main channel show that a roughened flood plain generates a stronger secondary current in the main channel while turbulent quantities show larger values in the flood plain.

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Distribution of boundary shear stress and flow structure near the corner in a rectangular open channel are investigated. Boundary shear stress was estimated from velocity distributions obtained by LDA measurements and by using Preston tube, and also calculated by Naot-Rodi model. Flow structure near the side-wall was visualized by the hydrogen bubble method. Results shows that the secondary flow cells closely relate the distribution of boundary shear stress and coherent structure of wall region on the side-wall.

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This paper presents the developing turbulent flow in open channels with pile dikes by using SDS & 2DH turbulence model, in which the formula for the vertical component of the production of turbulence energy due to the bottom friction and the drag of pile dikes is modified. To test performances of the model, calculation examples are illustrated, and the depth-averaged velocities, vertical vorticity, turbulence energy as well as the Reynolds stress are reproduced reasonably well.

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This study reports the resultus of velocity measurements among groynes in River Chikuma.
Two large vortices contribute to flowing in, settling and heaping of suspended particles. The uppside vortex of the impermeable groyne has a characteristic life cycle. It has a negative correlation with fluctuation of a water level.
In time of flood, streamwise vortices released from lowerside of the impermeable groyne rise and flush humus mud on a river bed.

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The mass exchange phenomena between main flow and rectangular dead zone in open channel are investigated numerically by means of the plane 2-D shallow water flow equations. The Froude number dependency on the free surface oscillation and mass exchange rate is pointed out through the examination of the calculated results. It is shown that these characteristics can be explained by the simplified model concerning the movement and location of large vortices along the interface. The effect of dead zone scale and the properties of water depth variation at the interface are also investigated numerically.

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The surface flow structure of large scale vorticies at the rear of a cylindrical pier is studied for the flow of transcritical Reynolds number is over 10⁸. The field observation around AKASHIKAIKYOU OHASHI bridge pier was carried out. Water surface images are taken from top of the main tower using a video camera. And an image analysis method using a correlation method for the calculation of two dimensional velocity distribution of surface is examined. In the rear side of the pier, large scale vortices like Karman vortices could be seen by video and MEM spectrum of surface velocity fluctuation.

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The turbulent flow in a square channel with weak curvature in which Re number was beyond 10⁶ was investigated. The height of channel and the width are 5.5m and 4.8m, respectively. Numerical simulation by κ-ε model was also carried out. The calculated results except the turbulent kinetic energy were in a good agreement with the measured data in spite of a large Re number. Some interesting characteristics of turbulence in the duct were found by means of spectral analysis.The double structure of turbulence and the large coherent structure close to the inner-radius wall were recognized.

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The mechanism of sediment resuspension transport by wind driven current in a shallow lake was studied by means of a turbulence model where a shear stress by wave motion and a fall velocity of sediment described by a flocculation were included. The flow mechanism and the sediment concentration profiles depend on the aspect ration, and its tendency is similar to that in the field and experiment.Also the shear stress due to wave motion and the change of fall velocity due to a flocculation can not significantly affect the vertical profiles of sediment concentration.

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In order to examine mixing and turbulent mass transport processes in a wind-driven density current, a turbulence model analysis is performed. The system considered here is a 2-D semi-enclosed stratified basin whose downwind boundary is opened to an ocean; this flow system is analogous to the wind-enerated currents in a small inlet, a bay, etc., Focus is placed on water mass exchange rate across the open boundary, which is found to have a strong functional dependency on the so-called “overall Richardson number”. The present analysis give us useful information on what sort of hydrodynamic conditions could generate upwelling of polluted bottom layer fluid and water quality exchange between the basin and the external water area.

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Two-dimensional hydraulic and numerical experiments have been performed for clarifying the wind-induced upwelling and mixing phenomena in a two-layered stratified flow system exposed to wind stresses at the water surface. Both experiments make clear that the classification of four flow regimes proposed by Spigel & Imberger (1980) is a good agreement with both experimental results in terms of Wedderburn number and that upwelling phenomena of density interface occur only in the range of We less than 4.0. Both experiments are also carried out in the flume with an open downstream boundary in order to examine the phenomena appeared in semi-enclosed bay such as Tokyo Bay. The numerical experiments are quantitatively confirmed to show a good agreement with the results of hydraulic experiments.

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The influence of free surface on the characteristics of turbulence have been investigated experimentally. An oscillating grid was used to generate turbulence in a tank filled with water. The turbulence and the pressure disturbance were measured by both LDV and FLV and the pressure transducer, respectively. The results from the experiments showed that the vertical turbulence was converted into the horizontal one through the pressure fluctuation near the free surface. In addition, it is obvious that there are the dominant eddies contributing to the turbulent characteristics near the free surface as well as the energy exchange due to the pressure redistribution.

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Turbulent flow on mountain topography has been investigated experimentally. Special emphasis has been placed on the flow characteristics near a large-scale embankment that is often necessitated in the construction of large facilities like aircraft landing strips in hilly areas, that are typical of large-scale development in Japan. Experiments using scale model of real topography and idealized escarpment model were conducted. It is found that the wind blowing towards the slope is accelerated, but the turbulence does not grow due to the speed-up.The quantitative effects depend on the scale of turbulence in the oncoming atmospheric boundary layer and supporting experiments were also conducted to examine the scale effects.

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Near-wall region which consists of viscous sublayer and buffer layer in unsteadyopen-channel flows was measured accurately by making use of a two-component threebeam LDA system; the effects of pressure gradient produced by the time-variation of water surface and discharge were revealed experimentally. Friction velocities evaluated from linear formula and log-law formula coincided well with each other. However, the van Driest damping factor B which indicates the thickness of sublayer varied in the decelerating flows, whereas it showed an opposite manner in the accelerating flows.The von Karman constant K is nearly universal one even in strong unsteady flows. The normalized turbulence intensity was affected by the pressure gradient. The Reynolds stress and other statistical quantities were also changed from their universal distribution of zero pressure-gradient flows.

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It is very important in Hydraulic Engineering to investigate the response of velocity distribution and wall shear stress to abrupt changes of wall roughness in closed channels as well as in open channels. We (1991, IAHR Congress) have first revealed the overshooting property of shear stress and turbulence in the case of smooth to rough changes in open-channel flows. In the present study accurate LDA measurements over abruptly changed roughness have been conducted in asymmetric closed-channel flows. Of particular significance is a very large overshooting of shear stress in the case of smooth to rough changes.It was also stressed that the eddy-viscosity model is not valid and a refined stress model should be developed for computation.

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The rivers in Hokkaido, which are situated in a snowy and cold region, contain a large quantity of flowing frazil slush and accumulation of it.
We set an ice control structure to prevent inflax of frazil slush into the intake of hydroelectric power station for last three years.
This paper reports observation of hydraulic and meteorological conditions, the development of ice cover, velocity distribution under the ice cover and daily change of river discharge.

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The characteristics of the streaming are presented by considering the closure scheme based on one equation model in the turbulent boundary layer, where the Stokes' second order irrotational velocity profile is adopted at the upper boundary as the boundary condition along with the Batchelor's condition for the streaming. The calculated profile is compared with the existing analytical results based on zero equation models and the experimental data of van Doom (1981).
It is shown that the streaming velocity profiles differ from condition to condition of the relative depth, but the dependence on the roughness is weak.

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A wave friction coefficient applicable to short and long waves is theoretically derived for laminar and rough turbulent flow. This friction coefficient approaches the conventional wave friction factor for short waves with the increase of water depth and/or with the decrease of wave period. At another limit, it asymptotically approaches the friction law for steady current with the decrease of water depth and/or with the increase of wave period. A criterion is proposed to determine the condition that the bottom friction coefficient for steady flow can be used in place of that for waves.

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Laboratory experiments were performed in a climate simulator, where temperature, relative humidity, wind velocity and artificialinsolation can be controlled, to investigate man's physiologicalresponse and thermal comfort. The following results were obtained; 1) skin temperature decreases with wettedness, 2) variation ofmetabolic ratio with meteorological conditions can be ignorable and 3) thermal sensation can not be explained by increase of skintemperature, which conflicts with the former physiological models.

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A natural river space is needed by many people and conservationof it is eagerly needed. Recently in Japan, manyresearchers have tried to conserve the ecological environmentof a river. The purpose of this study is to investigate theinfulence of the changes of river environment and to builtan expert system of hydro-ecological model. A knowledge-basedexpert system for the prediction of hydro-ecological environmentof a river is presented.

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The Moisture Absorbent Textile (MAT) has been developed to control moistureloss from desert, i. e. evaporation. The evaporation quantity from a sand columnwith MAT, horizontally inserted at a upper part of capillary zone, is 39 % smallerthan that from a sand column without MAT. The decrease in the evaporation rateis attributed to the decrease in the vapor gradient over the dry zone. Its mechanism.is as follows. Due to the soil moisture, the swollen MAT makes the upward moistureflux across MAT low and the dry zone becomes thick. As a result, the watervapor density gradient over the dry zone, namely the driving force for the upwardmovement of water vapor decreases.

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For hydrological models, imformation of surface-soil moisture content interms of a large area is important. Then, using the microwave sensers'datum of satelites, such as E-ERS1 and J-ERS1, is expected in order toaquire soil moisture information of a large area. Nowadays, many studiesand experiments are under investigation for practice.
This study will deal with the Microwave Scattering Model for the relationbetween soil moisture content and backscattering coefficient on the baresoil. The backscattering coefficient value is affected not only by the soilmoisture content but by frequency, incident angle, surface roughness, andso on. We calcurated backscattering coefficient based on the theory in somepatterns, and compared the value of the theory with that of experiment.

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This paper is one of the serial study on underwater walking in flood disaster evacuation. By observing the underwater walking speed, the walking posture and people's psychology of every age group in the simulated flood flow, various conditions of walking in the stream are studied. The hydraulic condition of feasible safe evacuation for every age group is obtained.

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Evaluation of protective function of grasses covering a river bank against erosion due to flood flow is important for grasses to be used for the protective measures instead of concrete armoured bank. On the real river, however, transition of grasses takes place and the preffered kind of grasses may change from the turf being planted at the construction time. Thus the understanding of transition process is very important in such an evaluation of protective function of grasses. This study aims to investigate this transition process of grasses through a field observation in the Iwai River in Iwate Prefecture. Annual change in covarage rate of grasses was observed at river banks of various stages after the construction.

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A suspended sediment sampler was desiged for the flood observation. From the requirement on the feasibility of measurement at many time-space points in one flood, we have produced a light weight sampler with a manometer which memorizes information of the measurement depth. This was tested for the flood of September 1994 in the Abukuma river with peak discharge of 3, 000m³/s. The grain size distribution of sediment and concentration were analysed and show significant change during the flood. The concentration near the bottom is also estimated.

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