A theoretical analysis was performed on the wave heights of alternating bars in alluvial channels. In the preceding analyses, the bed form had been assumed using a major component. These analyses were not so successful because the non-linear effects of the residual components of the bed form does not introduced.
The authors expressed the form of the alternating bars by the two components, and the order of amplitude of the two components were assumed to be the same. The analysis was performed up to the 2nd order of the amplitude. The results of the analysis were compared with flume data. It was found that the wave heights of the alternating bars agreed well with the observations.

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Hydraulic condition for alternate-bar formation in open channel flows with suspended sediment are determined by stability, analysis. It is shown that the condition for alternate bar formation in the flow with suspended sediment is much different from in the flow without suspended sediment. The theory demonstrate the effect of suspended sediment on the formation of alternate bars. When bed load and suspended load are present, the value of the neutrally stable stage is stable for the bed load only case and unstable for the suspended load only case. Thus, the two modes of transport produce opposite effects and the region where they balance identifies the neutrally stable case.

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This paper presents a new method to predict channel bed topography in meandering channels in a range of resonance of free and forced bars, in which previous models have not successfully predicted the finite bar topographies. Depth integrated version of three dimensional Reynolds equation is used to calculate the mutual effect of bed and channel geometry, while the intensity of secondary flow is calculated from the first order differential equation of the momentum equation in transverse direction. A new technique is introduced to take into account for the effect of channel width change caused by sediment deposition in inner bend range. Calculated results are successfully compared with series of experiments conducted in the resonant wave number range, and the validity of the new method is verified.

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Decreasing process of bar modes, which was found in basic experiments on plain bed and is regarded as a fundamental characteristic in formative process of multiple bars, is discussed with initial bar amplification of various modes evaluated by an existing linear stability theory. Specific features of multiple bar formation with micro scale bedforms are summarized from experiments carried out on a fine sand bed, where the mode decreasing process was also observed. Validity of the existing stability theory is examined to apply to prediction of changes in multiple bar modes on ripple-covered fine sand beds.

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The present study describes the deformation of alternating bars caused by a series of piles, based on the results of flume tests as well as of numerical solutions. A series of piles is composed of several piles which are straight arranged with proper separations and attack angle on the bars. The results show that alternating bars are well controlled and consequently a stream can be formed in a fixed region by placing a series of piles.

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It is well known that the local scour takes place around hydraulic structures such as bridge pier, weir or bed protection works especislly in rapid flow rivers. This phenomena is usually observed after the flood and there exists very few data with respect to the local scour during the flood, which is very important in hydraulic designing works.
Bed elevation during a flood was investigated in order to study the time dependent behavior of the local scour using an automatic riverbed elevation system which are set up along the thalweg downstream of the No.6 and No.7 bed protection works in Toyohira river.
Rapid erosion was observed during the raising stage of the hydrograph, and deposition was observed during the falling stage.
Besides, the result of caliculation by 1-D MacCorrak Method is compared with field data.

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This paper reports characteristics of local scour formed in downstream reaches of various types of bed protection works. Four types of bed protection works are used in experiments under a dynamic equilibrium condition to investigate time related changes in scour profiles, maximum scour depths and locations. The scour processes are also discussed in comparison with bed shear stress distributions measured in the maximum scour hole.
In addition, field observations of scour profiles were carried out at a downstream reach of hollow-squared blocks in the Manganji River in Hyogo Prefecture, and the observed scour profiles and velocity distributions were similar to those in the experiments.

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Some experiments on the local scour of bed in front of the wall by jet flow were carried out in a laboratory flume as a simplified model for the one in front of the revetment in bars bed channel. Experimental results revealed some of its fundamental characteristics, and a model based on these which can predict the local scour depth and its position in front of the revetment was developed. Inspite of bold simplifications and expansions, the results were practically satisfied.

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The flow in a curved reach causes the bed scour near the outer bank and resulting outer bank erosion. Making the outer bank slope milder is a useful means of bank protection. In a curved channel with milder sloping of outer bank, the theoretical and experimental works are conducted aiming at the improvement of flow and bed topography. The result of calculation coincides well with that of the experimental results with regard to the structure of three dimensional flow and the bed topography, and also making the outer bank slope milder in a curved channel enables us to reduce the bed scour near the outer bank without the rise of water level.

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The experimental results of 3-dimensional flow field and bed evolution around spur-dike is presented. And numerical simulation method for 2-dimensional bed evolution based on 3-dimensional flow model which is considered vertical pressure distribution is proposed. This numerical model takes into account non-equilibrium sediment condition. This model is applied for the experimental results and the simulation results are in good agreement with the observed data to some extent.

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This paper describes an investigation on a numerical prediction method to estimate local scour due to the cooling-water jets discharged from power stations. The method presented simulates the unsteady convection and diffusion processes of the warmed jets with a two-equation turbulence model within the calculation area being deformed by the local scour. The profile of the scoured sand bed is predicted by computing the amount of both the bed load and the suspended load in parallel with the simulation of the flow itself. The prediction method was applied to the experiments and its validity was reasonably confirmed.

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In recent years, the river bed level of our country has been degraded by dam constructions, and sand and gravel digging. The degradation has influenced the properties of alternating bars, by which the low-waterway is formed, and later, it is transformed by erosion. In this study, flume experiment surveys were carried out to investigate the changes in bar properties, and the formation and transformation mechanism of low-waterways by the thalweg, during a low water periods. Thus the authors determined the upper and lower limit conditions for the formation of a low-waterway.

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Control effect of common reed against bank erosion were studied at the Tama River. Erosion-resisting strength of river bank having a common reed were estimated by focusing on soil properties and reed roots. It was found that a common reed functioned so as to restrain the advancement of erosion. Erosion-resistance mechanism of a common reed was clarified by a laboratory curved channel which had a submerged vegetation model attached to the outer bank. Also, the resistance strength of common reeds was estimated by newly developed apparatus.

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River bed evolution during a flood event is modeled in a quasisteady approach using a 2-D depth-averaged numerical model. It is concluded that, with respect to the numerical solution, more significant are the accuracy of flow field computations and the precision achieved in approximating the bed geometry rather than differences in sediment transport rate formulas.

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The Karigane Bank in the Fuji River was constructed as a flood control works about three hundred years ago. The bank is located at the top of the alluvial fan near the river mouth. The purpose of this study is to get hydraulic evaluation of the flood control works maintaining the flow channel. Several sets of experiments with hydraulic models including mobile bed were conducted. In each experiment, surface velocity of flow, river bed configulation after runoff and flow patterns were measured, and effect of the bank system on maintenance of the channel was discussed. The results of this study showed that the existing formation of the works with the spur dikes could separate a flood way from the retarding areas in the channel and make the works an excellent flood control system.

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Sedimentation in reservoirs causes water to rise above the surface during floods. The influences of water rising will certainly extend year by year unless proper countermeasures for the productive deposition are taken. However, in fact, it costs much to not only dredge up the deposition from the reservoir, and transport them to disposal yards, but also public acceptance would be difficult.
This paper reports that the flushing by the current through the lowering water level at the TAKI reservoir in the TADAMI River in JAPAN, and the lessons from it, and how to dismount the massive depositions in the reservoir in order to lower its level.

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Grain size variations of bed materials with time and space during river bed degradation are measured in an experimental flume. It is observed that the bed surface sand becomes much coarser than the original sand mixture during the bed degradation. This coarsening of the bed surface sand is analyzed with a vertical sorting model of sand mixture in the moving layer on the bed surface, while the final armor coat formation during the parallel bed degradation is analyzed by the longitudinal sorting model.

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Experiments concerning physical properties of the mud enable us to treat the mud as a Bingham fluid, and also show that the yield shear stress and viscosity of mud are related to the water content. We make a hydraulic model of mud flow under the flowing water based on the governing equations for Bingham fluid, which takes into account the space- and time-distribution of water contents of the mud. Using this model, we analyze the velocity profile of mud flow and investigate the influence of shear stress acting on the mud surface and water content of the mud on the flowing-layer depth and mud velocity.

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Laboratory experiment is conducted using uniform sand of mean diameter 0.21mm under the condition that bed and suspended loads coexist. It is ascertained by the observation and the Garde·Raju regime criterion that sand waves produced on this condition are three dimentional antidunes and alternate bars with two dimentional antidunes.
Characteristics and flow resistance of these bed shapes are discussed on the basis of the results of experiments.

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Bed shear stress distribution along the bed surface is derived from boundary layer equation. Then, an effective shear stress for sand waves is expressed as integration of the bed shear stress distribution. As the bed load motion is influenced by fluctuation of flow intensity, the estimation methods of pick-up rate and average step length are proposed by considering these influences. The bed load distribution along a sand wave is calculated by using stochastic model consists of pick-up rate and step length. The results of application to experimental measurements are well good.

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Sand ripple profile in nearshore area in the Ogata coast, Niigata was measured under the stormy wave condition. A reproduction model test for the sand ripple in the Ogata coast was conducted in the twodimensional wave basin using the irregular wave similar to the wave conditions in the field, applying Ito and Tsuchiya's scale model relationship and time scale. Characteristics of sand ripple forms by model tests and in the field are discussed using dominant parameters such as the orbital diameter, the Shields number, and the sand grain Reynolds number that were obtained from sediment and wave conditions.

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In a compound open channel the flow velocity on the flood plain and in the main channel shows a marked differece, and a mixing zone exists between these two flows. The objectives of this paper is to study the fluid mixing in this region and compare the mixing with that in the 2-D mixing layer by using the flow visualization results on the water surface and in a transverse cross section of the flow. The analogy between the fluid mixing in a compound open channel and that in the 2-D mixing layer has been demonstrated from the results.

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In order to visualize 3-D turbulent structure of the outer region in an open channel flow, visualization technique using a vertical light sheet and particle tracers is used. Spatial structure of turbulent intensity, two-dimensional divergence and vorticity is obtained. On the basis of computed velocity component of long period, the mechanism of wall turbulence and the spatial structure of secondary flow is discussed.

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Instantaneous three-dimensional velocity fields in the wake of a hemisphere located on an open channel bed are obtained by using flow visualization in multi-sections and Mass-Consistent model. The instantaneous pictures of the coherent structure are taken at short time interval and their behaviors are investigated at high Reynolds number. The secondary hairpin vortex has been generated on the upstream side of the large hairpin vortex and coalesced into the large hairpin. The streamwise distances between hairpin vortices are irregular. The three-dimensional distributions of the instantaneous Reynolds stress and pressure are also shown.

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The transport equations for conditional Reynolds stresses and turbulent kinetic energy defined in turbulent flows with intermittency have been obtained. The intermittency considered may be based on any criteria that divide the flow into two mutually exclusive regions, including turbulent/nonturbulent intermittency, and intermittency defined by scalar. The derived transport equations involve terms representing the entrainment at the interface and the interaction between the two regions. Available experimental data have been examined in the light of the derived transport equations.

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The turbulent structures were investigated experimentally in open channel flows with strip roughness with various roughness spacing. The Reynolds stress distributed linearly in the outer region and the friction velocity could be evaluated from the gradient of its distribution. Using this friction velocity, turbulence intensities were well described in the same universal function as in smooth flows, but the streamwise turbulence intensity decreased near the bed. Mean velocity profiles coincided with the log-law involving the roughness function. The defect of the mean velocity became largest at the relative spacing L/k=8.

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The two-dimensional T-type confluence flow is numerically simulated by using k-ε turbulence models. It is found that standard K-ε turbulence model reveals severe discrepancies in predicting the confluence flow which is characterized by a large recirculating region. To analyze the reasons of the poor prediction, further studies are conducted by means of the low-Rynolds number version of k-ε model and an improved k-ε model proposed by Hanjalic and Launder for decelerated flows. By comparing the numerical results with the experimental results, it is understood that the wall functions used in the standard k-ε turbulence model and the inaccurate modeling of ε-equation are two main reasons for the poor predictions. Finally, some suggestions are proposed for the numerical simulations of the confluence flow.

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Field measurements on turbulent large-scale structure of a flood flow in the Hinuma river were conducted with 16-channels electromagnetic anemometers. The turbulent velocity components (u, v) at 8 points on a plane perpendicular to the mean flow have been sampled and recorded simultaneously by a A/D converter. The quasi-instantaneous 3D images of coherent structures in the flood flow were reconstructed from these obtained data by using conditional technique and a new method of data analysis. These structures detected near the river bed are low-velocity lumps of fluid and generate intermittently peaks of the high positive Reynolds stress. The high generation of the suspend load in the flood flow may be explained by these structures. Near water surface, coherent structures have also been found and they generated small-scale boils.

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A pair of aerial photographs of the flood flow in the Agano River on Sept. 25, 1966 was analyzed by the cross-correlation technique to obtain velocity vectors over the area of 1400×1000m of the water surface. About 250×350 velocity vectors were obtained at every 5.6m in streamwise and 2.8m in spanwise direction.
The interval and arrangement of the longitudinal low-speed band and high-speed band appearing alternately in the spanwise direction over the water surface were analyzed and two kinds of spanwise scales of large scale turbulence were found; one is about twice water depth and another is 4-5 times.

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Kinematic characteristics of large-scale eddies at a two-dimensional confluence are examined by using a correlation method, one of the image processing techniques. In this paper, a method for detecting and correcting erroneous velocity vectors, calculated by the correlation method is presented and it is used to obtain successive velocity fields of the water duct confluence flow of the discharge ratio Qr=0.2 and 0.4 at Re=3-10⁴. When a reverse flow region decreases, the results show that several small scale eddies are created and they are convected at a speed nearly equal to the mean flow velocity.

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Experimental and numerical investigations are carried out for waves with following and opposing currents. The flume bottom is covered by triangular strip roughnesses. The K-ε model is solved, for the large Reynolds number flow, with the Galerkin finite element method. Profiles and time series of the ensembleaveraged horizontal velocity are well predicted except in the very vicinity of the bottom. Magnitude but phase of the r. m. s. velocity fluctuations is reasonable predicted. Time-mean horizontal velocity and r. m. s. horizontal velocity fluctuation are also well predicted. The measured data give a much smaller von Karman constant which is not predicted by the model.

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Temperature fluctuations due to the interfacial waves were measured in a shallow lake within the range the between basic internal wave of buoyant frequency and the surface wind ripple. The frequency spectrum shows an inertial subrange. These waves are generated from amplified internal wave, and wind waves bring similar structure on the interface through the resonance mechanism with much slower interfacial ones. Diffusivity takes the peak at the bottom of the interfacial layer, and for such diffusivity profiles, the log+linear law for temperature is retained. Considering the first few mode of cellular motion, the fluctuation of buoyancy in vertical was found to be similar with the measured one.

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This paper describes thermal stratification in lakes, its property of flux by destruction, and water quality transportation from results observed in field survey for Lakes Hibara, Onogawa and Akimoto. Its main conclusions by the above-mentioned ways are shown in the following.
On the Whole, these lakes shows clearly not only thermal stratification in summer but also its destruction processes with the fall of water temperature. These lakes indicate a similar tendency of formation of thermal stratification in the vertical direction. Lake Hibara has clear processes of thermal stratification and of its destruction. Lake Onogawa has a tendency toward water stagnation. Lake Akimoto has a remarkable distribution for turbidity in the vertical direction.

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A gravity flow of granular bodies is considered as a model of main body of pyroclastic flow. Characteristics of the granular flow can be described by Kanatani's constitutive equations, which are obtaind in consideration of the energy loss caused by the only interparticle friction by the collison between the particles. Using above model, the 1991 pyroclastic flow at Mt. Unzen-dake were reproduced by the numerical simulation. The result of calculations roughly agree with the actual phenomena.

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Large scale pyroclastic flow occured at Mt. Fugen, Unzen volcano, on June 1991. The pyroclastic materials are suspended in air, so that the pyroclastic flow runs fast with relatively low resistance on the slope. In this paper, the fluid dynamical model of the pyroclastic flow is presented. The model is based on the thermal theory on the inclined wall, in which the effect of the of the air temperature is taken into account. The model can predict variations of the height, the speed of pryoclastic flow and the concentration of pyrocalstic materials.

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Nondimensional parameters governing rapid hyperconcentrated flows are derived by the comparison between intergranular-stress and inertia terms in the momentum equation. It is found that the ratio of flow depth to grain diameter and volumetric concentration of grains for the estimate of friction forces acting on a bed, and the ratio of tube diameter to grain diameter and concentration for that of drag forces on a tube are important parameters.
Relationship of friction and drag coefficients to these parameters is investigated experimentally. Dependence of drag coefficient on concentration and nondimensional tube diameter is found similar to that of friction coefficient on concentration and nondimensional depth.
For the larger concentration and smaller ratio of a characteristic length to grain diameter intergranular interactions play dominant role. For the larger ratio, on the other hand, the effect of turbulence of the hyperconcentrated flows becomes major.

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This paper discribes a numerical simulation method for the deposition of the debris flow with high content of fine and cohesionless sediment. The model assumes that the excess quanty of sediment than the equilibrium deposits with the settling velocity. The validity of the simulation method is proved by the experiment in which the steep channel abruptly debouches to flat area.

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The velocity and the shearing stress distributions in an open channel are of importance in order to design revetments or groins. In this paper, the interrelation between the velocity and the shearing stress in the various forms of cross-section is investigated with the trial calculation which is based on the assumptions obtained from the experimental results. The appropriate calculation method can be found for the practical use.

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In boulder-bed streams, large boulders jutting through the river bed play important roles in resistance to flow.
This paper deals with the drag force and the structure of flow around hemispherical roughness elements, which are models of large boulders. The separation length and the drag coefficient for a hemipherical roughness element were experimentally studied in the flows with various Froude number, spacings of roughnesses, or relative depth.

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Field measurements of velocity profiles for ice-covered streams were performed in Hokkaido. Surface conditions of the cover were classified into smooth ice cover, rippled ice cover and cover with frazil slush. Adaptability of logarithmic velocity distribution was first investigated. The friction factor fi and Manning's roughness coefficient ni were caluculated based on an assumption of the logarithmic distribution; average values ni for smooth and rippled cover were 0.012 and 0.021 respectively.

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Effects of the plane shape of a weir on the downstream flow structures are experimentally examined. Arched weirs having different curvatures, an arched one set in reverse direction and a straight type weir, are used for experimental study. Mean and turbulent velocity distributions and shear stress distributions are measured in the downstream region of each weir. It is found that arched weirs converge the flow to the center portion of the channel, while a reverse-arched type diverges the main stream to the side portions of the channel. Deduced structures of the flows are also presented.

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Skew arrangements of strip roughness induces a helicoidal motion of flow, and the transverse components near the free surface and near the bottom have different signs, which may restrict the zones where the materials are transported. In this study, the representative profile of the transverse velocity is analytically deduced from a simplified twodimensional model, and field measurement of turbulent flow over skew arrangements of strip roughness is conducted in an irrigation canal, which is often used for a conveyance of removed snow in winter. Furthermore, V and Δ type arrangements of strip roughness are investigated in order to apply such a helicoidal motion of flow to practical problems of effective conveyance of several materials.

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Part of cross section of streams is often vegetated, and faster flow over non-vegetated zone and retarded flow in vegetated zone neighbor with each other. In such situations, horizontal mixing of momentum dominates though the flow is three-dimensional. In this paper, numerical 3D calculation of such flows is attempted based on an algebraic stress model. One of the characteristics of the, present calculation is that the form drag is taken into account in the vegetation zone. The calculated results explain the flow structure surveyed by flume measurements, and particularly depth-averaged properties can be well described. The model-parameter which contributes the amplitude of cellular motion near the boundary of two regions is favorably neglected, which may imply that the cellular motion no longer dominates in the flow with vegetated zone.

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Appreciable surface waves appear for flow in an open channel with longitudinal zone of vegetation and they are expected to play an important role for transverse mixing. By flume experiments of flow with model vegetation, the characteristics of surface wave and the correlation properties between waves and velocity fluctuations are investigated to confirm that they contribute the transverse momentum mixing. By treating vegetated and non-vegetated zones as respectively one-dimensionalized channels but with boundary shear and transpiration through the boundary, the correlation properties are interpreted. Furthermore such a modelling of flow leads a linear instability analysis of water surface fluctuation of flow in vegetation zone.

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Coefficients of lateral momentum diffusion in open channel flows influenced by a series of groins were obtained from the detailed velocity profiles which were measured by LDV. The coefficients are not constant in lateral direction rather distribute with a peak in diffusion area of a groin. Magnitude of the coefficients are comparable or more less to compare with that of vertical momentum diffusion. It was found that the coefficients calculated from log-velocity distribution along the oblique line stretching from the shear layer of a groin correspond to the directly measured data.

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The snow removal system with an open channel is studied by the hydraulic approach. The fundamental equations are derived by adopting the two-phase flow analysis. The continuity and momentum equations are obtained for snow and water phase. Increment of shear stresses which is caused by the snow transport is taken into account in the model. The results obtained are the threshold condition of snow movement, the increment ratio of water depth and the maximum snow conveyance rate in an open channel. Some of these results are compared with the experimental data and the agreement between the theory and experimental data is quite satisfactory.

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A problem related to the capacity of snow removing by flowing water in ditch is treated. In this experiment, crushed ice was used instead of snow. The scale of the region of separation has been measured for the various plane forms of the elbow parts of ditch. The rise in ditch stage has been analyzed theoretically, and compared with the experimental values. The both results agreed approximately. The energy losses of the flow on the elbow parts of ditch is estimated. The limiting conditions of crushed ice trasportation by flowing water through the elbow parts of ditch has been studied experimentally.

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A model study of the formation of ice arching at the upstream faces of rounded bridge piers was conducted in a hydraulic flume. Polypropylene plastic was used to simulate square ice floes (10mm in thickness and 100mm in width). It was found that the conditions of ice arch formation at bridge piers were determined by ice covered ratio, ratio of span length and size of ice floes, and V²/gh (V: surface velocity, h: ice thickness).

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Eighty years have passed since systematic improvement of the Ishikari River started in 1910. Before the improvements, the Ishikari River was in a completely natural state, and caused floods every year due to its meandering stream. The goal of the improvements was to further the development of Hokkaido by rcelaiming the vast marshes along the Ishikari River. The improvement work involved channel improvement of river, mainly by (1) excavating short-cuts to shorten the river and lower the flood stage, and (2) construction of continuous embankments to prevent floods.
As a result, flood protection has improved remarkably and allowed the development of new residential areas. Flood prevention and reduction in water-levelsby the short-cuts have changed the Ishikari Marshes to fertile arable land.
This study will clarify how channel improvements in the Ishikari River executed for regional development contributed to a change in flood flows and decreases in floods.

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The spread of flooding water in a crowded urban district was simulated by incorporating prorerly houses, roads, and land information in the two-dimensional numerical model. It was shown by this numerical simulation that the time of flooding water advancement was mainly controled by the road network. It was also found by the model that the decrease in the innundation area and water depth became possible by setting drainage gate and tree zones, and raising the level of roads at appropriate places.

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