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In order to explain the bed-load transport process by water flow, stochasticmodel is one of the useful methods which can describe the behavior of individualparticle of alluvial system.Most of the studies of bed-load thansport process by stochastic model has beencarried out only for the steady-uniform flow. But, the effect of flow unsteadiness onbed-load transport process should be considered in some real alluvial systems. Inthis study, stochastic model of the bed load transport process in unsteady butuniform flow characterized by oscillation-current coexitsing flow is proposed. Andthen, applicability of the present model is investigated by experimental results ofbed load behavior. Agreement of computed result with experiment is fairly good, and thus the unsteady uniform alluvial system can be described with the aid of thepresent model.

Many river engineers have hitherto suggested that there might exist cellular secondarycurrents in a straight river which had a pair of counter-rotating streamwise vortices with avortex diameter of about the flow depth. These cellular secondary currents create variousbed configurations such as sand ribbons which are alternating ridges and broad hollows andaligned parallel to the mean flow. Also, they may cause the three-dimensional flow patternsand sediment transportation in an actual river. However, the origin of the cellular secondarycurrent and its physical mechanism are quite unknown at present.In order to reveal the characteristics of the secondary currents and also their interrelationto the bursting phenomena occurring originally in the wall region, the present study hasexamined the turbulent structures in air duct flows with and without the cellular secondarycurrents. Considering that it was very difficult to measure precisely the secondary currentsin water flow because they were only a few percentage of the main flow, they could bemeasured by hot-wire anemomaters in two-dimensional air duct flow which correspondedsimilarly to open-channel flow. By systematically varying the bed configurations in whichthe longitudinal and alternate stripes of smooth and rough beds were set spanwisely, thegeneration and maintenance mechanism of the secondary currents were investigated.As the result, the strongest secondary currents were created when the width of the stripeswas equal to half of the width of the duct which corresponded to the flow deth in open-channel.The effects of the secondary currents on the mean velocity, turbulence intensities andReynolds stress were examined in detail, and then they could be explained well theoreticallyby means of (1) equation of motion, (2) equation of vorticity and (3) equation of turbulentenergy.Next, the effect of the secondary current on the bursting motion was examined by usingthe pattern-recognition method. Although the relative intensity of sweep to ejection motionswas affected by the secondary current, the bursting period was not varied. So, it issuggested that the bursting and cellular secondary current are phenomena different fromeach other and both of them coexist self-consistently.

Bed load transport process is characterized by irregular motion of individual sediment parti-cles, and such a property causes a various kind of alluvial phenomena. Hence, the statisticalcharacteristics of bed load movement based on the mechanism of motion of individual particlesare important to be clarified. In this study, the behaviors of individual bed load particles bothon a fixed bed and on an alluvial bed are observed and their characteristic quantities such asdistributions of particles velocities are measured elaborately, by making use of a movie cameraand a film motion analyzer. As the result of such measurements the bed load transport processcan be divided into following subprocesses. One is collision process with protrusions distributedon a rough bed and it gives the phenomena rapid variations. This process can be analyzed by aphysical model for collision, a statistical model for bed surface irregularity and some stochastictechniques. The other one is moving process of a sand particle without collisions. This can bedescribed by equation of sliding motion based on some experimental investigations and consider-ing some probabilistic characteristics.Such a study suggests that no methods but the combined type of deterministic approach andstochastic one can describe the bed load transport process and some trials were shown here.

In this paper dominant characteristics of the local scour near a cylindrical pier are investigatedon the basis of wide ranged experimental data. And an attempt is performed to explain its char-acteristics by making use of a simple model which is constructed in consideration of only the vortexof the stagnation plane and the continuity of the sediment in the same plane. Secondary, by dis-cussing the existing experimental results and proposals together with their applicability, anothermethod of estimation of the equibilium scour depth is proposed.

An investigation of three-dimensional turbulent structure, I.e.cellular secondary currentsor longitudinal vortices, is very important in hydraulic engineering because these currentscause three-dimensional bed shear stress, sediment distributions and bed configurations suchas sand ridges in straight rivers.The present study has carried out highly accurate measurements of secondary currentsin fully-developed open channel flows by making use of a powerful two-color Laser DopplerAnemometer (LDA) system with a direct digital signal processing. The primary and secon-dary velocity distributions, the maximum-velocity-dip phenomena, the bed and side-wallshear stress distributions and also the turbulence characteristics were made clear by varyingthe aspect ratio of channel. The effects of free surface on three-dimensional structurewere then examined by comparison with the data of closed duct flow. A strong free-surfacevortex is produced due to high an-isotropy of turbulence which is caused by the existenceof free surface. This vortex produces a velocity dip and also restrains the development ofthe bottom vortex. Although the bottom vortex may be divided into smaller ones with anincrease of the aspect ratio, multi-cellular secondary currents are not produced any longerin the central zone. The variation of bed shear stress, however, suggests strongly that multi-cellular secondary currents will be produced in all the cross section by a mutual interactionof the flow and sand ridges.

In non-equilibrium alluvial phenomena a strong interaction between the bed configurationsand the sediment motion plays an important role. As a typical event of the transport of bed loadsediment, the evolution of sand waves from an initially flattened bed was observed here by exper-iments. The time variation of stochastic properties of undulated beds was investigated. Theprocess of evolution of sand waves was described by a simplified kinematic model coupled withsome statistical techniques and verified by the experimental results. Furthermore, the distri-butions of the step length and rest period of sand movement over a duned bed were obtainedfrom bed profiled data, and the sediment transport rate calculated by use of these quantitiesshowed a fairly good agreement with the experimental results.

In order to unify the theories of bed load transport and sediment suspension, it is importantto investigate saltating motion of sediment particles. In case of sediment transport by flowingwater, successive saltation appears and it is composed of irregular individual saltation paths. Theirregularity and the succession of individual saltations are caused by repulsion events of saltatingparticles with a sand bed. Considering these effects, stochastic modelling of successive saltation istried in this paper, and respective subsystems composing the model are inspected by some funda-mental experiments using a film motion analyzing technique. Moreover, a series of numericalsimulation of bed load transport process is carried out based on the proposed model, and thestochastic characteristics of individual saltations and successive saltation are inspected. Verticaldistribution of existence probability of bed load particles is also investigated by this simulation, which may be important from view point of the objective of this study.

Numerical calculation techniques of turbulent shear flows are classified into two categories:one is K-e turbulence model and the other is large eddy simulation (LES). The standard K-emodel has been established at present to predict turbulent structure in closed duct flows, whileLES is being developed to predict coherent eddy structure in more simple duct flows. Thestandard K-e model cannot be, however, applied to open channel surface flows, because theturbulence near the free surface is more depressed than the closed duct flows.In the present study a new modified K-e model is proposed to predict reasonably the turbulentstructure in open channel flows with both of low and high Reynolds numbers. The numericalcalculations indicate a splendid agreement with the experimental data which were obtained bymaking use of hot-film and Laser Doppler anemometers.

For establishment of a reasonable hydraulic design of multi-diffuser by which various wastewaters such as sewage or warmed water can be efficiently diffused in river or sea, an experimen-tal investigation on the turbulent structure of two-dimensional dual-jet whose two nozzles wereset in parallel has been performed. By systematically varying the ratio of flow quantity of eachjet and the space between both nozzles, the mean velocity distribution and the turbulence charac-teristics of the dual jet have been investigated through hot-film measurements and visual obser-vations.Since the flow axes of dual jet were attracted and then merged each other, the flow fieldcould be divided into three subregions: (1) two-single-jet region (before mergence), (2) one-single-jetregion (after mergence) and (3) transition region between (1) and (2). The turbulent structure ofeach subregion could be described fairly well by a simple model in which two Gaussian profileswere combined under the conservation law of momentum flux. A noticeable fact has been alsoobtained from the characteristics of intermittency factor, macro-scale of turbulence and spectraldistribution that a coherent motion, so-called 'puff phenomenon', appeared near the edge of potentialcore of both single- and dual-jets.

In this study, bed form response to change of water discharge was investigated experimentallyand consequently, it was noticed that such an alluvial process was to depend much upon the geo-metrical properties of bed forms and their distribution. Therefore, the relationship between bedconfiguration and sediment transport was investigated by an experiment for two-dimensional scourand the geometrical properties of individual waves of sand waves were inspected based on bed profiledata.Next, using some techniques in the theory of stochastic process, the distributions of the scaleof sand waves were discussed. And in the last part of this paper, a model to describe the collapseprocess of sand waves due to suddenly decreasing of water discharge has been derived and wasverified by the experimental results.

bottomrackは水路床または堤頂部に設けられた流出孔であり, その流出特性から考えて流量変化の非常に激しい山間急流部で一定流量を取水・分水するのに適し, また流下土砂を調節する機能を有する。その型式としては流下方向の格子で構成されるもの, それと直角な方向の格子で構成されるもの, あるいは多孔板より成るものがある。Bott・mrack上での開水路流れの挙動については, 従来流量が場所的に減少する漸変流として解析されているが, 通常用いられるこの種の構造物上では水路条件および流量の不連続な変化によって急変流としての性状を示すことが認められている。その意味から本研究では, まずbottomrackにおける漸変流解析方法の適合性を実験によって明らかにし, 次に鉛直方向速度成分を考慮した場合の水面形特性を論じるとともに, 急変流性状を実験的に把握して解析の方向づけを与える。最後に水面変化が小さい常流遷移の場合について, 底部スリットからの流出量および主流の運動機構に関する理論的, 実験的考察を行ない, 分水工の一般的機能を論じる。, The behaviors of open cannel flow on bottom diversion racks and their dischargecharacteristics are investigated herein.The contents of this paper are as follows ; The first, the coefficients of dischargeare researched by experiment and applicability of gradually varied flow theory which isused widely for analysis of the water surface profile is discussed. The second, thefundamental equation including the terms of normal velocity is led and the characteristicsof abruptly varied flow on the racks are investigated by experiment. At the last, in caseof subcritical transitional flow, theoretical analysis of effluent and main flow behaviorsis described and verified by experiment.

The object of the study described herein is to investigate the performance of lateraldiversion works designed to secure a constant overflow rate.The contents of this paper are as follows The first, the characteristics of various elementsincluded in the fundamental equation on gradually varied flow of non uniform discharge aremade clear, based on the experimental analysis conducted by Dr. Iwasa and authors. Thesecond, dynamic expressions to give proper dimensions of the diversion works which satisfy thedischarge requirements are derived from fundamental eqnation. The thrid, the experimentalverification on the designed channels which show an effective performance is described.