The non-linear k-ε model with the effect of the strain parameter and the rotation parameter is applied to 3-D calculation of the turbulent flow field around a surface-mounted cubic obstacle. In the construction of turbulence models, the condition of realizability is firstly considered in three types of basic flow patters, namely, simple shear flow, flow around a saddle point and flow around a focal point. Numerical simulation is performed under the conditions of the laboratory test by Larousse et. al. The model performance is examined through the comparison of numerical and experimental results. The present model can reproduce the complex 3-D flow structures with separation and reattachment around a cube.

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A large-eddy simulation tool is adopted to simulate the three-dimensional flow around the submerged spur-dikes. A numerical method is put forward to compute the three-dimensional flow with free surface and complex boundaries. The numerical method is established on the base of finite-volume/finitedifference method with staggered grid. A method of the equivalent Cartesian grid in a fluid cell, whosevolume is the same with that of the irregular fluid cell, is used to deal with the irregular cells and the eddy viscosity coefficient at the boundary cells in the flow field with complex boundaries. The water surface and the velocity distribution around submerged spur-dikes of simulation are compared with those of experiment. It is shown that the results of simulation are in agreement with those of experiment and it is possible to apply the numerical model to simulate the complex flow with complex boundaries.

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This study concerns the influences of standing waves on a circular free turbulent jet. A circular free jet oscillates and is in connection with the motion of standing waves. The motions of the jet oscillations are classified into three pattern by experimental data. As increasing the amplitude of the waves, the jet oscillations become vertically asymmetric and discontinuous. The oscillations of the jet is modeled by a coupled equation of the free jet with small amplitude wave theory. The simple jet-wave interaction model can be well described the jet oscillations. Furthermore, the spatial variations of the turbulence properties are investigated.

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A numerical model to predict the formation processes of dunes in open channel flows is developed. Flows and bed shear stresses over dunes are calculated by the depth averaged model considering the effect of vertical acceleration. Inotational condition of flows far from a dune bed and the acceleration/de-acceleration effect near a bed are included in the depth averaged model. Formation processes of dunes are simulated incorporating the nonequilibrium sediment transport model proposed by Nakagawa·Tsujimoto. Calculated results on the temporal development processes and shape characteristics of dunes are compared with previous theoretical and experimental studies. It is indicated that the calculated wave length caused by initial instability is coincident with the resonant relation of open channel flows over a wavy bed, and the wave length and height of dunes in the equilibrium state are dependent on the step length.

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The finite amplitude growth and stability of ripples and dunes is believed to be the result of the interaction between the complex turbulence field created by separation at the crest of the bed feature and bedload sediment transport. Numerical simulation of this turbulence field promises to provide the detailed qualitative and quantitative information of coherent structures that is required to model the sediment transport field over ripples and dunes. We present a high-order Godunov scheme, referred to as the CIP method, for the numerical simulation of turbulence over a 2-dimensional dune. Comparison of the velocity statistics of the numerical simulation with LDV measurements over 2-dimensional dunes in a flume is favorable. Analysis of the vorticity field reveals that the coherent turbulent structures produced in the shear layer are highly three-dimensional, and cross-stream velocities should be considered in future models of bedload transport over dunes.

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In order to understand the flow structure over sandwaves, 2-dimesional and 3-dimensional flow models are tested under the flow condition of flow over 2-dimensional sandwaves. CIP (Cubic Interpolated Psuedo-particle) method was introduced to evaluate the computational result with high accuracy. Computational results are compared with the velocity obtained by experiment. It was found that 3-dimensional turbulent structure is dominant even in the flow over 2-dimensional sandwaves. Direct numerical simulation of suspended sediment particle is conducted using data obtained by 2-dimensional and 3-dimensional flow model. A good agreement with theoretical profile is found only for 3-dimensional model. It is suggested that 3-dimensional treatment is required in calculating suspended sediment.

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Formation and migration of gully headcut is one of the complicated phenomena, which often appears in incised channels. Flume experiments have been conducted to investigate the flow field along and around the headcut. The fixed bed experiments with oblique headcuts show that the flow is concentrated to the head (upstream part) of the gully, which has been reproduced in numerical simulations for both of fixed and movable bed conditions. Headcut migration rate depends on the unit discharge along the brink and the change in elevation of energy-grade line passing the headcut. The initial shape of the headcutis an important parameter for the formation and movement of gully headcut. A sharp shape at the head of the headcut is required for the proper development of gully.

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The movable bed phenomenon constitutes a complicated system in which the flow, the bed-material load and the bed shape interact with each other. In the present paper, a study onthis mutual interaction system has been performed. However, an interaction between turbulent flow and bed-material load has not been so investigated, because it is very difficult to conduct turbulence measurements in sediment laden flows. In the present study, turbulence measurements were conducted using LDA in sediment laden open channel flows, and bed-material load was also measured by PIV.

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The paper deals with the concentration distributions of sediment particles in turbulent rectangular open channel flow. Special attention is paid on the effect of channel wall shear on the concentration profiles of sediment particles. Using the Reynolds strecc model, a mathematical model to describe the fluid and sic: din-mut motion in a prismatic open channel was presented. After confirming the validity of this model by laboratory experiments, sediment motions in a lateral cross section were discussed by this model. It was shown that the sediment particles flow downward with circularity trajectories like secondary current of fluid motion. Due to the settling of the sediment particles, the location of the center of the trajectory is somewhat near to the sidewall and to the bottom, compared with that of fluid motion. Experiments on sediment laden open channel flow, reported so far, were also reproduced numerically. In some cases of the reported paper, it was found that the circulatory motion of sediments spread almost over cross section. To the case of compound channels, the effect of relative height of the flood plane on sediment distributions were also investigated.

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Numerical simulation of the sediment transport based on the Lagrangian method is one of the most viable methods to investigate the complex mechanism of oscillatory sheet flow. Not only the flow unsteadiness with containing sediment particles, which respond to the flow acceleration and deceleration process, but also the interparticle collision of the moving particles complicate the simulation task. In this study, the sediment motion is simulated with the aid of the Movable Bed Simulatorcode based on DEM model in which the frequent collision of the moving particles is sophisticatedly modeled. And the particle diameter effect on the developing time-dependent process of sheet flow transport is investigated, using three different diameter sizes of sediment. The different tendency in sheet flow transport can be explained as a relaxation process related to the time lag of flow velocity and the sedimentmotion, which responds to the flow acceleration and deceleration. Also, the time lag of the sediment motion in the sheet flow layer is evidently influenced by the particle diameter size.

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Linear stability analyses for steep channel flows with movable bed of heterogeneous materials following a Talbot grain size distribution were performed in order to investigate peculiar characteristics of the bed forms.It was found that two kind of instability exist in the system such that one would be a bottom elevation instability and the other would be a sorting wave instability. Test experiments exhibited the formation of alternating gravel bars on the bed when the maximum growth rate of the bottom perturbation was greater than that of the sorting wave perturbation, and exhibited the formation of longitudinally and laterally alternating coarse sediment fractions when the condition was reverse.

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The fractional transport of graded sediment and the resultant sorting are the key factors to understand the sediment transport phenomena in alluvial stream. Ordinary approach is to apply the sediment transport law, which is proposed for the uniform sediment, for each fractions of graded sediment, with estimating the critical bottom shear stress based on the Egiazaroff s formula. In other words, the particle/particle interaction was not considered directly in the previous studies of the graded sediment; while the interaction between the different size sediments are predominant factor of the transport process of the graded sediment. In this study, the Movable Bed Simulator-the numerical code of granular material based on the Distinct Element Method-is applied to the fractional transport of graded sediment. The critical bottom shear stress and the fractional sediment transport rate estimated by the present code show satisfactory agreement with the previous experimental data. Furthermore, the velocity profile of the sediment particles and the thickness of the sediment moving layer are calculated by the present simulation to estimate the internal structure of the transport process of graded sediment.

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Cohesive sediment accumulated in an estuary contains fine sand and clay. To investigate the influence of the percentage of fine sand content on the erosion process of cohesive sediment, not only the erosion tests with vertical jets but also vane tests to measure yield stress were conducted. The percentage of fine sand content was varied between 0 and 80%. Both the yield stress of cohesive sediment and the critical condition of erosion are closely related with the adhesive water thickness of soil particles. The former is in proportion to the -5th power of the adhesive water thickness. The latter is in proportion to the -3/5 power of that thickness.

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The velocity and sediment concentration of sediment-water mixture flow change by the physical properties; e. g., mass density of solid and liquid phase, viscosity of liquid, interparticle friction angle of solid particle, etc. The laminar viscous term is introduced into the constitutive relations developed formerly by Egashira et al. to solve those. The effects of physical properties of solid and liquid phase on debris flow are investigated by means of experimental data as well as of numerical solutions for velocity profile, sediment concentration profile, flux sediment concentration and flow resistance. The results suggest that the present constitutive relations evaluate any changes of debris flow caused by physical properties of solid-liquid phase.

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Present study deals with transitional flow from debris flow to sediment sheet flow. An analysis method with two layer model presented here is derived on the consideration of an “interface” between flow layers of water and sediment and mass, volume and momentum fluxes through it. The model consists of mass and volume conservation of water and sediment including an equation describing level change of immobile bed as well as momentum equation of the both layer. Result of analysis agree well with those of previous experiments and can improve the defeat of single layer analysis.

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Several simulation models of debris flow have been presented. In these models, not only basic equations in these models differ from each other due to their approaches to flow mechanism, but also algorithms adopted in their numerical calculations are quite different. Therefore, they produce mutually inconsistent results even for identical phenomena. In this study, characteristics of these simulation models of debris flow are clarified by a one-dimensional simulation program under simple conditions, in which. We adopt two types of equations evaluating share stress at the bed with and without yield stress and three types of expression of erosion-deposition rate. The computed results reflect characteristics of the formulae for erosion-deposition rate in these simulation models.

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The viscous debris flow occurs frequently in the southwest of China. This natural event inflict damage on people or property. For the purpose of mitigation planning, it need to elucidate the mechanism of viscous debris flow. And then, it is necessary to analyze the motion of it.
On July 24th, 1997, a viscous debris flow was recorded with a digital video camera in JiangJia Gully, Dongchuan City, Yunnan Province, China. These images were saved as files formatted as BMP by computer interface board. Since the absolute coordinates of targets which were near the channel were surveyed by an infrared-light distance meter, the distance of a pixel of images about motion of debris flow is estimated in x and y direction, respectively. A new image analysis method, the auto-correlation method, is used to analyze the surface velocity of debris flow.
In this paper, the two results of image analysis are shown: one is the mean surface velocity change of central of several surges, another is the change of surface velocity vector in a fixed cross section. According to these results and the field experiment, it could be concluded that viscous debris flow is a kind of complex flow. It is a turbulence in the front of a surge; in the middle of a surge, it could be considered as a kind of cohesive flow; and due to the cohesion or yield strength, the flow almost stops in the end of a surge.

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The sediment transport from steep agricultural land through the watershed causes not only the deformation of river morphology but also the change of terrestrial and aquatic ecosystems. Hence, the sediment discharge equation due to rainfall runoff should be established so as to predict and to prevent the outflow of agricultural soils to the watershed. In this study the sediment discharge equation applied to the bare land was proposed based upon the experiments with the rainfall simulator and the previouslyobtained data. The sediment discharge equation inclusive of the protection effect of vegetation cover which was examined theoretically was applied to the actual field, and explained the order of sediment outflow from agricultural land by using the runoff process model simultaneously.

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In order to provide a robust tool to be used in runoff-erosion modeling, the present paper introduces new evolution steps in the SCE-UA genetic algorithm, which is based in the simplextheory. The new evolution steps were conceived in order to improve the efficiency of such an algorithm. Thus, they will theoretically expand the simplex in a direction of more favorable conditions, or contract it if a move is taken in a direction of less favorable conditions. Hence, these new evolution steps enable the simplex both to accelerate along a successful track of improvement and to home in on the optimum conditions. Therefore, it will usually reach the optimum region quicker than the previous version and pinpoint the optimum levels more closely. The new proposed algorithm is tested with special mathematical functions, as well as in the optimization of the erosion parameters presented in a physically-based runoff-erosion model. On the basis of these simulation results, the mean erosion parameter valuesare given, which agree with previous values reported to the same area. Thus, the new algorithm can be considered as a promising tool to optimize physically-based models as well as other kinds of models.

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It is very important for the prediction of sediment runoff into reservoirs and downstream of rivers to evaluate the behavior of sediment transport in a river basin located at high mountains. However, the difficulty for this study due to steep topographies and extensive research areas have hindered the accumulation of reliable data.This paper discusses characteristics of production, transportation and deposition processes of sediment in failed slopes and streams, and the overall situation of sediment balance of the basin, based on the on-site data such as aerial photographs and slope erosion data obtained from measuring sticks. The study area, Takase Dam basin, is surrounded by mountains higher than 2800 m in elevation. Characterized by steep topography and weak geology consisting of deteriorated granites, the area is one of the major sediment runoff areas in Japan.

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In this paper, a simulation method is developed to predict sediment runoff from a mountain region into a reservoir. In the model, the watershed is constituted by several slope units and channel network. A flood runoff in each slope unit is calculated by using kinematic wave runoff model, and sediment runoff in the channel network is simulated by using governing equations which correspond to each flow regime such as a debris flow, a immature debris flow, and bed load. The model is applied to the actual mountainous watershed, the Fudosawa and Nigorisawa River, Nagano Prefecture. The spatial and temporal variation of sediment discharge, bed elevation, and grain size distribution are calculated. Calculated sediment volume inflowing into the Takase reservoir approximately agrees with observed one.

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River catchment can be divided into a lot of sub-catchments. Prediction of sediment supply from each sub-catchment is very important for the planning of sediment control and river regulation works.
In general, longitudinal changes in lithologic composition of bed material are often observed, because each sub-catchment has unique characteristics in sediment supply.
The author focused this fact and proposed a method for the prediction of sediment supply from each sub-catchment by analyzing the change in lithologic composition of river bed material.
This method was applied for the upper area of the Fuefuli. river catchment, containing two large tributaries the lbkuwa river and the Koto river Through this observation, some knowledge was obtained;
-The amount of sediment supply changes according to the change of grain size. Andthis tendency in each sub-catchment is different from others.
-The topographical and geological nature in a sub-catchment effects on the amount of sediment supply from the sub-catchment.

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It is required to develop an appropriate sediment routing model for describing behavior of sedimentation in a whole river system. This research deals with a synthetic sediment routing model based on DEM (Digital Elevation Models). This kind of model has several subjects to be examined from the viewpoints on model construction such as computational time interval, tuning hydraulic parameters, effects of computational mesh scale on the results, pseudo channel network made from DEM and so on. Authors have hitherto been examined some of the subjects mentioned above in the mountainous Hayakawa River basin (509km²). In order to apply the model to larger river basin, the Fujikawa River basin (3, 571km²), a new method of automatical tracing of the channel network is adopted. In this paper, difference of channel networks between the conventional method and the new one is examined, and reasonable way of smoothing river bed as an initial situation is searched. The results of some cases of simulation on sedimentation in the basin is also discussed.

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The present study describes a method for predicting sediment runoff caused by erosion of sediment stored in river channels. The method is developed by combining a newly developed channel model, a rain-fall runoff model and a storage-type sediment runoff model. The channel model, which is based on a unit channel having two inflow points and one outflow point, can easily reproduce stream channels distributed in a drainage basin. A kinematic wave runoff method is employed in rainfall runoff prediction, and the sediment runoff model is developed by integrating partial differential equations for water and sediment with respect to the reach of unit channel. The present method can predict temporal and spatial change of water discharge, sediment discharge, sediment storage and sediment size when rainfall data are given as in-put. It is applied to the upper basin of Kumano river, and its applicability is verified by comparing the predicted results and reservoir sedimentation data.

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River bed-forms in mountain region are 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 rib’ bed forms. Low water channel and the surroundings have many kinds of vegetation and grain-size variation such as large gravel and small sand in the mountain region. Therefore, the mountain region gives good environments for living things. And, one more characteristic of the mountain river is that temporal variation is extremely large. In the present study, the stair-like or the transverse limb bed in mountain rivers with steep slope bed and with wide range of grain size of bed materials, was surveyed at a test field section of the Shigenobu river from1992 until 1998, and the characteristics of the bed forms and their change with time are discussed.

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Erosion process of cohesive sediment was investigated experimentally in the present paper. Series of experiments were conducted systematically to clarify the effects of following three parameters, containing percentage of clay, water content ratio and flow velocity exerted on the sediment sample, on the erosion rate. The relations between the erosion rate and each parameters were evaluated. The dependence of the erosion rate on the containing percentage of clay is found to be the most interesting characteristic, the mechanism of which was explained physically.

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Stability of river banks almost 10 m or more in their heights and movement of their failed soil mass are analyzed by a simplified Junbu method and the Newtonian law of motion. In analysis the bed near the bank slope was degraded drastically to make relative bank heights increase and water level was supposed in two cases: during and after flooding time. Then, calculation was carried out in cases of several river bank heights of 12-19 m. The outputs of analysis are values of the safety factor for bank slope, while acceleration, velocity, and movement distance for failed soil mass. Results show that bed degradation increases in relative banks height which have strong influence on the stability of river bank and the higher the river bank is, the farther the failed soil mass moves.

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There is a possibility of cohesive soil being used as a material of riverbank. For this purpose, it is important to investigate and estimate the erosive resistance of cohesive soils against the stream flow. Several studies on the erosion of cohesive soils have been made in recent years. In previous studies, the dynamic processes of bank erosion have been clarified. We have accumulated the knowledge about mechanism and process of erosion in cross and longitudinal directions. However, the knowledge is not sufficient in estimating the erosion amount and erosion speed.
The point of this paper is to examine the relation of flow velocity and erosion rate. Some hydraulic models were made to measure the flow velocity around eroded area in detail. One model reproduced faithfully the shape of erosion experiment to examine the longitudinal change in velocity, and another simplified the feature of overhanging bank to examine the effect of erosion angle. The important relations of flow characteristics and erosion mechanism are found as the consequence of those experiments.

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Channel forming process under the condition of no sediment discharge was investigated with both flum experiments and numerical simulations. In addition to the degradation of bed -elevation, natural channel can change its width relatively within short time, in the process. The experimental results revealed that the relatively short time for channel widening firstly occurs, and then the bed-slope gradually adjusts to the static equilibrium condition with no significant change of the channel width. The numerical model to simulate the channel forming process, which is constituted by the depth-averaged 2-D flow model with the non-orthogonal boundary fitted grid system and the bed -deformation model taking into account the collapse of the bed -material on side banks, can reproduce the process observed in the experiment.

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Formative condition and mechanism of a self-formed stream channel in a straight river course are studied in terms of flume tests and numerical analysis. The results support that a self-formed stream channel in a straight river course is produced in the formative domain of multiple row bars. In developing stage of self-formed stream channel, multiple row bars are produced firstly, and then transformed into alternate bars. Finally, a self-formed stream channel is produced. In addition, the developing of the mode (0, 2) for bed configuration promotes the formation of self-formed stream channel. Formation of equilibrium multiple row bars is investigated by means of numerical analysis under a wide range of hydraulic condition. The numerical results realize that any multiple row bar changes into a self-formed stream channel under the studied conditions.

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he present study describes field surveys of bed material, findings based on surveyed data and bed variation in a downstream reach, 0km to 37km, of the Kizu River. Field data realize that the river bed elevation changes longitudinally like riffle-pool bed profiles, coarse gravel are dominant in the riffle region, sand particles are deposited deep in the pool region, and sediment particles of pool region are transported from upstream as over-passing load or as selectively entrained sediment on riffle bed. The formula of grain size distribution which is employed in numerical simulation of river bed variation as the upper boundary condition of the study reach is proposed, taking account for the difference between grain sizes in riffle and pool regions as well as for characteristics of bed load transport such as over-passing load.

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Turbulence characteristics of open-channel flows with the vegetated zone are greatly affected by whether the vegetation is completely soaked or not. Structures in this kind of flows become not two-dimensional, but three-dimensional, when all part of the vegetation is in the water. In spite of many studies investigating these three-dimensional structures, little is examined concerning the structure near the water-surface. In this study, we simultaneously measured water-surface fluctuations and velocity in open-channel flows with the vegetated zone at the half channel width using an ultrasonic sensor measuring water-surface and a laser Doppler anemometer (LDA), and examined effects of the water-surface on three-dimensional turbulent structures. The experimental results revealed the characteristics of surface waves and correlation properties between surface waves and velocity fluctuations. Consequently, it was found how they contribute the transverse momentum mixing between the vegetated and non-vegetated zones.

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Comparative experiments were performed to examine generation factor of three dimensional structure in periodical large vortices at the boundary between a river flow and vegetation zone along the river. The first comparative experiment showed that the existence of the large vortices itself is most dominant factor rather than the effect of vegetation. The second one indicates that the important mechanism lies in the movement over the depth, not in the turbulence near the bed. And measurement of velocity fluctuations revealed that a strong upward flow is generated slightly behind the center of the vortex.

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It has been known that organized horizontal vortices are generated at the junctions of main channel and flood plains for two-stage channels, and they yield sediment transport between main channel and flood plains. In the present laboratory tests, it was found that the relations of the organized vortices and lateral suspended sediment transport in compound open channel flow with bank vegetation.
Numerical computations were performed by employing SDS-2DH turbulence model. For channels with bank vegetation, it was found that sediment transport is closely correlated with large scale horizontal vortices which are generated in the main channel and deposition rate takes a maximum value in the vegetation area.

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In a river, diffusion which is caused by horizontal shear has a great effbct on the environmental problem and in previous studies we made a shallow water flow equation including turbulent term on the basis of horizontal shear.In this study we propose a shallow water flow equation taking into accout Iignosa by using large eddy simulation theory and carried out experiments which types are high density, low density and middle density of lignosa. As results, in case of high density the water depth obtained by a equation including horizontal shear is more similar to the experimental results than a equation not including horizontal shear and in case of low density the water depth is consistent with the experimental results greatly by including horizontal shear.

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The roles of riparian vegetation have been noted from the view point of the river environment and flood control. Suspended sediment concentrations are measured in an open channel with cylinders installed across the whole channel width in their multiple rows. Cylinders are placed in stagger with their equal spacing on the bed.
Distributions of suspended load in an open channel with cylinders agree with Rouse distributions by using effective frictional velocities which are estimated by considering the drag force of cylinders. Flux distribution of suspended load in an open channel with cylinders is calculated. Flux of suspended load in an open channel with cylinders is found less than that without cylinders over the whole depth.

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Flow and bed evolution caused by a series of alternately arranged vegetation zones along the channel sides were investigated experimentally in the present paper. Because of the rise of water surface elevation just upstream the vegetation zone due to a sudden increase of local flow resistance, a secondary current is generated in the direction departing from the zone. And the locus of maximum velocity line is found to meander between each vegetation zone and its opposite side wall. The bed topography caused by this current in a movable channel is seen that a pair of both a deeply scoured portion and a deposited sand bar emerge in accordance with a generated flow field.

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Recently reverine trees in the course of gravel bed-river have extremely increased and enlarged their covered-area over bars and flood plain. Such a situation brings about problems of river management for the environmental aspects as well as the safety of rivers against flood. In order to clarify such problems, we should get the knowledge about the flow with vegetation-covered zones.
In this study, the applicability of a 2D-numerical flow model including vegetation drag effect is verified for the upstream reach of the river Watarase which has the averaged bed slope of about 1/150 and has the characteristics of the segment-1 reach with the excessive reverine trees. Calculated results are compared with the results obtained by the observation after flood and predict an increase in water-level depending on the vegetation density and predict the concentration field of suspended fine sand.

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Damage caused to herbaceous vegetation on two gravel bars by the 1998 and 1999 floods in the Nagata Reach of the Tama River can be divided into four types according to their damage extent. In Type 1 (severest), vegetation including roots was totally washed away. In Type 2 (second severest), all stems were sharply cut off at their bases and washed away, but their roots remained. In Type 3 (third severest), longitudinal strips of vegetation washed away and buried were formed in a Type4 area. In Type 4 (mildest), vegetation uniformly fell down intact in the flow direction (partly buried). Significant correlation between destruction type and Shields number for surface gravel suggested that different gravel movement caused different destruction types. By estimating possible gravel actions on vegetation, destruction processes to the four types were identified.

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It has been known that the growth of the vegetation on flood plain is much affected by the transport of substances by flood flow. Field observations were performed at Tama-river during July in 1998 and August in 1999, in which water qualities of flood flow, contents of organic matter and nutrients in the soil on flood plain and distribution of riverine vegetation were measured. The results of the observations show that the riverine vegetation on the left side flood plain was removed by the flood flow, which yields the decrease of contents of phosphorus and organic matter in the soil.

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Field survey was carried out in order to clarify such important ecological aspects of trees in Kinu-Rivar as appropriate felling of trees, tree planting, and management of trees. In this study, investigation was made as to realities of growth condition of trees, secular changes and characteristics of tree environment by differences in cannel characteristics, and hydraulic conditions.
And the following results were obtained as relations between the stages of growth speed of trees and dominant species, the direction of spread of trees, the effect of bed material characteristics, and the effect of inundation.

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The purpose of this research is to investigate the colonization process of woody plants, mainly Elaeagnus umbellata, on an alternating bar in a downstream reach of the Nakagawa River, Tokushima, Japan, and also to clarify their influences on hydrogeomorphic features and flood flows in the reach. Based on field vegetation survey and inspection of aerial photographs, it is shown that the colonization started in the late 1970s, and thereafter, the total cover-rate of the woody communities has been increased up to 50% after rather abrupt expansion occurred three times at intervals of about 6 years. The record of flood discharge indicates that seed dispersal of Elaeagnus umbellata due to autumnal floods is closely related to the above-mentioned abrupt expansion. It is found that the woody communities have caused characteristic changes in river-bed configuration of the reach and, through numerical calculations, that they have come to significantly raise the flood stage.

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An investigation of interaction between bed form and secondary flow in a compound meandering channel with straight floodplain banks for overbank was carried out. The mobile bed form in the main channel was measured by photogrammetry and the secondary flow was first visualized with a submergible video camera and then measured using three component laser Doppler anemometer. The results of the bed form and secondary flow during flood indicate that there exists a certain relationship between the bed form and secondary flow. The secondary flow induced by the floodplain flow in the main channel generates another secondary flow cell owing to the bed form change. Those secondary flow cells make sand bars crossing the main channel, particularly, in the cross-over region. Sediment transport rate reduces at an early stage of flooding owing to strong interaction between the floodplain flow and the main channel flow.

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Over-bank Flow in a straight channel with sinuous main channel is discussed based on experimental results. The main channel is a movable bed. The flow structure is characterized by secondary flow, and the secondary flow deforms the channel bed. Bed configuration was measured by a ultra-sonic level meter, and two components of velocity were measured by an electromagnetic flow meter. Secondary flow in a cross section was visualized by the neutral buoyant tracer method. The results indicate that three distinct eroded regions and two deposited regions on the bed are formed by the secondary flow in the case of overbank deep flow. At the downstream side of the ridge in the deposited region, secondary flow was newly produced.

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It has been observed from the previous investigation that the flow structure in the main channel changes and sediment transport rate decreases for meandering compound flow compared to bank-full flow. Because of this characteristics of the meandering compound channel flow, we have considered over loading sediment supply due to dam or bank failure in the channel that might cause large bed level fluctuation. In this paper, we have investigated the mechanism of bed level change for compound meandering channel experiment using steady flow and overloading sediment supply. The parameters for meandering compound channel bed fluctuation of this study include over loading sediment supply, planform of the channel and changes of relative depth. Additionally, we also have examined the characteristics of bed topography during flood period with unsteady flow condition.

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We have conducted laboratory flood experiments by applying the similarity law to real flood in meandering compound rivers. Comparing steady and unsteady flow in meandering compound channel with unsteady flow in meandering single channel, we investigated the hydraulic effects of plan and cross-sectional shapes of channel on flood flow.
In the case of a unsteady meandering compound channel flow, the discharge and velocity had two values for the same depth; on rising and falling stages. Comparing stage hydrographs for meandering compound channel and meandering single channel it was observed that, compound meandering channel had early response giving high values during rising stage and delayed response giving high values during falling stage. Also for both compound meandering channel and meandering single channel, increase of sinuosity and unsteadiness the maximum velocity occurred early on flood flow.

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Flow structures in a double meandering compound channel were studied experimentally. The double meandering compound channel is referred to as a channel whose levee alignment is meandering as well as main channel alignment. In this research, the levee alignment goes ahead of the main channel alignment by 32 degrees. The experiment was carried out varying the flow depth over the floodplain. The structures of the primary flow, secondary currents were detailed in this paper. As a peculiar phenomenon in the double meandering channel, dead water area was observed over the floodplain at different locations according to the flow condition.

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The purpose of this study is to perform large-eddy simulation for a solid-liquid multi-phase flow in a stratified field. The particular purpose of this model is to avoid extensive modification from the model by Tchen10) for a force due to the fluid pressure gradient. In order to verify the model, the concentration of the particles was compared between the computational results and the theoretical solutions. As result of this study, it is seen that a turbulent Shmidt number of 0. 42 is valid and that roll and boil occur by including the solid-phase into the simulation.

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In recent years, the high-density soft mud transport pipeline systems using a compressed air are utilizing in the field of marine construction works and coastal zone developments. This transport system is very useful for high-density slurry transport because it is easily to separating air from slurry. The purpose of this investigation is to clarify the mechanism of slurry transporting system using a compressed air in the experimentally. In the experiment, the air-liquid two-phase flows have been focused on liquid of low viscosity in long distance pipelines with narrow diameter and discussed the mechanism of generating, development and breakdown of water slug flows. As the results of experiments it was shown that the water depth of slug flow generating is nearly constant for all conditions of air-water mixing ratio in pipe flow.

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The relationship was evaluated between the increase of surface area and the gas transfer coefficient across the interface in two-layer flows by using cross-correlation coefficients evaluated from two sets of ultrasonic depth-measuring instruments in comparison with VTR. It was clarified that the surface area has little effect on gas transfer in smooth-bed flow against former studies. Furthermore, it became clear that the smaller-scale eddies contribute greatly to the greater gas transfer in open-channel flow than those in wind-wave. These findings can be used for evaluating gas transfer in actual river only by the spectrum of surface-wave.

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