Search

流れが高水敷に及ぶ洪水時の流れを対象に、低水路を移動床とした複断面蛇行水路において、2次流構造とそこに形成される河床形状との関係を、流れの可視化結果および速度計測結果を用いて検討している.対象とした流れは, 直線水路内に設置した低水路の蛇行度訂(=蛇行長/蛇行波長)が1.11と1.38の2種類の複断面流れであり, 本報告では, 高水敷粗度の影響について検討した.その結果, 高水敷上に一様粗度を設置した場合は, 同様の河床形状が滑面高水敷の場合より大きな相対水深で観察される, 帯状粗度を流れの構造を考慮して配置した場合は粗度の影響で河床形状に局所的な違いが見られる, などの知見が得られた。, Structure of overbank flow and bed form in compound sinuous channel with roughness on the flood plain are discussed based on experimental results. Visualization and measurements of velocity and bed form were conducted. Uniform roughness and a strip of roughness set on the bases of the flow structure were used.Secondary flow is most important in this flow. Uniform roughness affects on the water level, but not on the bed form. And then, a strip of roughness affects on the bed form, but not on the flow pattern on the water surface and velocity distribution. In the latter case, roughness on the flood plain reduces the surrounding velocity and this reduction causes the local modification of bed. The effect can be observed more clearly in the shallower case.

流れが高水敷に及ぶ洪水時の流れを対象に、低水路を移動床とした複断面蛇行水路において、2次流構造とそこに形成される河床形状との関係を、流れの可視化結果および速度計測結果を用いて検討している。対象とした流れは, 直線水路内に設置した低水路の蛇行度SI(=蛇行長/蛇行波長)が1.llと1.38の2種類の複断面流れである。両者の水路において, 基本単位と考えられるらせん状の2次流構造は同様であるが, 生成される数が異なる.その結果, 河床に形成される洗掘域・堆積域の列数も異なっている。, Over-bank flow in a straight channel with sinuous/meandering main channel is discussed based on experimental results. The experiment was carried out in a compound sinuous/meandering channel with movable main channel. Bed form measurements, velocity measurements and flow visualization in a cross section were conducted. The results indicate that there exists a certain relationship between the secondary flow and eroded and deposited regions on the bed. Two types of secondary flow were observed, one is the spiral motion induced by the shear stress between main channel and flood plain flows, and the other can be observed at the downstream side of the ridge in the deposited region. The separation of main channel flow behind the crest of sand bar produces this latter one.

複断面蛇行開水路流れの構造は, 相対水深(Dr=高水敷上水深/低水路水深)などの流れの条件, 蛇行度などの幾何条件に支配され, 複雑な様相を呈する。本研究では, 速度計測, 横断面流況の可視化, 掃流力分布の可視化, および河床形状の計測などで得られる結果を用いて, 流れの構造を検討するとともに, 掃流力分布との関係や河床の洗掘・堆積現象との関係について検討を加えた。その結果より, 低水路が固定床の場合の2次流構造, それが掃流力分布に与える影響, 移動床とした場合の構造の変化などを指摘している。, Over-bank flow in a straight channel with a sinuous main channel is discussed based on experimental results.The flow structure is characterized by secondary flow and fluid mixing between the main channel andflood plain flow. The secondary flow was directly visualized by a submergible video camera. The secondary flow shows spiral motions and affects the distribution of boundary shear stress and sediment transport. The relation between these structure and the traction process of bed materials is discussed on the basis of the distribution of tractive force visualized by a new method .We also made experiments in a channel of which main channel was movable bed. The secondary flow forms three distinct eroded regions and two deposited regions on the bed. Those regions are formed by the secondary flow.

1991年度から3ヶ年の予備的調査研究を経て, 1994年度よりインドネシア共和国中部および東部ジャワ島を中心に「洪水および地形変動による災害とその防御」に関する研究を推進している。主要なテーマは, (1)ジャワ島東部における洪水・土砂流出の評価と水害に関する研究および(2)インドネシアにおける海岸侵食に関する研究であって, これらは現地観測, 資料の収集・解析ならびに理論解析を駆使しながら推進され, これまでに興味あるいくつかの知見を得ている。本稿は, 1994年以後の研究によって得られた主要な成果について総括的に報告したものである。, This project has been conducted since 1994, with attention focused on flood and sediment hazards in central and east Java, Indonesia. It aims at developing methods for predicting floods and associated sediment phenomena such as sediment yields, river changes and beach erosions, including preferable countermeasures against flood hazards and coastal changes. Valuable results have been obtained from observations, data analyses and numerical simulations. This paper describes parts of them as well as the problems to be conducted.

This study was carried out as a joint work among the research sections of DPRI concerning with experimental hydraulics. Various methods and problems about the measurement, control and analysis in sediment hydraulics were discussed and some of them were improved in this study as follows:(1) Automatic measurements of sediment discharge including direct and indirect methods were improved. Indirect methods consist of sonar and ultra sonic image analyses.(2) A new measurement method of suspended load concentration using continuous pumping and weighing was devised.(3) A new type sand feeder for wet sand was devised.(4) A carriage system driven along arbitrary curves was devised and applied for the experiment on bed variation in a meandering channel.(5) A high-speed inteligent type carriage for the calibration of velocity meters was introduced and applied for the calibration of an electro-magnetic velocity meter.(6) An optical 3-dimensional bed profile measurement system using two theodolites and a personal computer was divised and applied for an experiment in an inclined wide flume.(7) An attachment made of paste for the ultra-sonic bed profiler was devised which extended its applicable lower limit depth to infinitesimally small one.(8) Picture processing by the cross-correlation was refined using CCD camera unit and a work station and applied for flood flow analyses. This technique was also applied to an automatic tracer tracking of video image and topography analysis.(9) A new algorithm for plane partitioning by triangles constituted by adjacent points was devived and applied to the linear interpolation of the data.

In this study, the characteristics of bed variation in meandering channels under unsteady flow conditions are discussed based on some experiments.In order to measure the bed profiles quickly along the lines parallel and normal to meandering bank lines, the carriage with an optical bed profiler was driven by two pulse motors which were controled by a personal computer.According to the obtained data, it seems that the bed profiles near bends are mainly controled by its plane form and does not change so much throughout the experiment except for the initial stage. This result coincides with that obtained by some field observations.

New measurement techniques for sediment discharge have been devised, employing both direct and indirect methods. In the direct method, two devices were made. The first one had a fixed inclined 0.3mm mesh screen, pump and baskets driven by a belt. Because of the choke of the sieve etc., the applicability of this system was limited in the range of Q

In this study, the property of erosion and deposition of cohesive soil was studiedfor the case of Kunigami Marge in Okinawa, Japan.According to the test using the method developed by the author et al, theerodibility of Kunigami Marge is summarized as u*c= 4 cm/s and E/u* = 0.8 x 10 5.Deposite property of Kunigami Marge depends not only on the concentration ofsoil but also on the property of the solvent. Namely, Kunigami Marge depositesforming a distinct borderface under the concentration higher than 3% in weight.Although it deposites faster in distilled water than in marine water under highconcentration, it takes longer time in the former than in the latter to complete thedeposition.According to the microscopic observation, this is explained by the sizedistribution of flocs, which is controlled by the electro-chemical properties ofinterface of soil particles and solvent.

An electrostatic chuck (ESC) is a type of reversible dry adhesive which clamps objects by means of electrostatic force. Currently an ESC is used only for objects having flat surfaces because the attractive force is reduced for rough surfaces. An ESC that can handle objects with rough surfaces will expand its applications to MEMS (micro electro mechanical system) or optical parts handling. An ESC consisting of compliant electrostatic inductive fibers which conform to the profile of the surface has been proposed for such use. This paper aims at furthering previous research by observing the attractive force/pressure generated, both theoretically and experimentally, through step-by-step fabrication and analysis. Additionally, how the proposed fiber ESC behaves toward rough surfaces is also observed. The attractive force/pressure of the fiber ESC is theoretically investigated using a robust mechano-electrostatic model. Subsequently, a prototype of the fiber ESC consisting of ten fibers arranged at an angle is employed to experimentally observe its attractive force/pressure for objects with rough surfaces. The attractive force of the surface which is modeled as a sinusoidal wave with various amplitudes is observed, through which the feasibility of a fiber ESC is justified.

Structure of overbank flow and bed form in compound sinuous channel with roughness on the flood plain are discussed based on experimental results. Visualization and measurements of velocity and bed form were conducted. Uniform roughness and a strip of roughness set on the bases of the flow structure were used.Secondary flow is most important in this flow. Uniform roughness affects on the water level, but not on the bed form. And then, a strip of roughness affects on the bed form, but not on the flow pattern on the water surface and velocity distribution. In the latter case, roughness on the flood plain reduces the surrounding velocity and this reduction causes the local modification of bed. The effect can be observed more clearly in the shallower case.

Over-bank flow in a straight channel with sinuous/meandering main channel is discussed based on experimental results. The experiment was carried out in a compound sinuous/meandering channel with movable main channel. Bed form measurements, velocity measurements and flow visualization in a cross section were conducted. The results indicate that there exists a certain relationship between the secondary flow and eroded and deposited regions on the bed. Two types of secondary flow were observed, one is the spiral motion induced by the shear stress between main channel and flood plain flows, and the other can be observed at the downstream side of the ridge in the deposited region. The separation of main channel flow behind the crest of sand bar produces this latter one.

Over-bank flow in a straight channel with a sinuous main channel is discussed based on experimental results.The flow structure is characterized by secondary flow and fluid mixing between the main channel andflood plain flow. The secondary flow was directly visualized by a submergible video camera. The secondary flow shows spiral motions and affects the distribution of boundary shear stress and sediment transport. The relation between these structure and the traction process of bed materials is discussed on the basis of the distribution of tractive force visualized by a new method .We also made experiments in a channel of which main channel was movable bed. The secondary flow forms three distinct eroded regions and two deposited regions on the bed. Those regions are formed by the secondary flow.

This project has been conducted since 1994, with attention focused on flood and sediment hazards in central and east Java, Indonesia. It aims at developing methods for predicting floods and associated sediment phenomena such as sediment yields, river changes and beach erosions, including preferable countermeasures against flood hazards and coastal changes. Valuable results have been obtained from observations, data analyses and numerical simulations. This paper describes parts of them as well as the problems to be conducted.

In this study, the characteristics of bed variation in meandering channels under unsteady flow conditions are discussed based on some experiments.In order to measure the bed profiles quickly along the lines parallel and normal to meandering bank lines, the carriage with an optical bed profiler was driven by two pulse motors which were controled by a personal computer.According to the obtained data, it seems that the bed profiles near bends are mainly controled by its plane form and does not change so much throughout the experiment except for the initial stage. This result coincides with that obtained by some field observations.

This study was carried out as a joint work among the research sections of DPRI concerning with experimental hydraulics. Various methods and problems about the measurement, control and analysis in sediment hydraulics were discussed and some of them were improved in this study as follows:(1) Automatic measurements of sediment discharge including direct and indirect methods were improved. Indirect methods consist of sonar and ultra sonic image analyses.(2) A new measurement method of suspended load concentration using continuous pumping and weighing was devised.(3) A new type sand feeder for wet sand was devised.(4) A carriage system driven along arbitrary curves was devised and applied for the experiment on bed variation in a meandering channel.(5) A high-speed inteligent type carriage for the calibration of velocity meters was introduced and applied for the calibration of an electro-magnetic velocity meter.(6) An optical 3-dimensional bed profile measurement system using two theodolites and a personal computer was divised and applied for an experiment in an inclined wide flume.(7) An attachment made of paste for the ultra-sonic bed profiler was devised which extended its applicable lower limit depth to infinitesimally small one.(8) Picture processing by the cross-correlation was refined using CCD camera unit and a work station and applied for flood flow analyses. This technique was also applied to an automatic tracer tracking of video image and topography analysis.(9) A new algorithm for plane partitioning by triangles constituted by adjacent points was devived and applied to the linear interpolation of the data.

In this study, the property of erosion and deposition of cohesive soil was studiedfor the case of Kunigami Marge in Okinawa, Japan.According to the test using the method developed by the author et al, theerodibility of Kunigami Marge is summarized as u*c= 4 cm/s and E/u* = 0.8 x 10 5.Deposite property of Kunigami Marge depends not only on the concentration ofsoil but also on the property of the solvent. Namely, Kunigami Marge depositesforming a distinct borderface under the concentration higher than 3% in weight.Although it deposites faster in distilled water than in marine water under highconcentration, it takes longer time in the former than in the latter to complete thedeposition.According to the microscopic observation, this is explained by the sizedistribution of flocs, which is controlled by the electro-chemical properties ofinterface of soil particles and solvent.

A handy test method of soil erodibility is developed. At first, drilling a hole from soil sur-face, poring water into the hole, we rotate a cylinder in the water. Then, the side wall of thehole is eroded by the circulating flow.Measuring the torque driving the cylinder and the shape of the hole, we can obtain therelation between the rate of erosion and the tractive force.For cohesive soil, this method is much more useful than channel test, although the rate oferosion obtained from the former is somewhat larger than that obtained from the latter.

The response of sand waves due to the time change of flow condition extending toboth the lower and upper regime was measured in a flume test varying flume inclination witha constant flow discharge. As a general tendency, it was found that in the lower regime theresponse seems to be slow and it appeared a remarcable time lag. On the other hand, inthe upper regime or transition, the response seems to be so quick that the bed form nearlycoincides with that for the steady state.Some hydrological and hydraulic data of several principal rivers in Japan were arrangedto estimate the bed configuration during floods, by means of a numerical simulation model.In some cases, the bed configuration is estimated to be dunes and the wave length and/orheight will differ considerably from those for equilibrium state.

It is important to clarify the dispersion process of river sediment because it is essential to predict and prevent the damage caused by contaminated sediment, and to detect the source of the contaminants from their spatial and temporal distribution. In this study, the dispersion process of bed load particles under the condition in which bed level changes with time is discussed. The distribution of elevation of bed particles, and the pick up rate for each elevation, were measured through flume tests; it was found that 1) The thickness of the active layer for flat bed conditions is about the maximum diameter of the bed material. 2) Coarser particles are apt to be more exposed than finer particles. 3) The pick up rate of the bed particles increases with the degree of exposure. The occurrence of the following phenomena were determined through flume tests, and explained through stochastic simulation, taking account of the time series of rest periods and step length combined with a conventional analysis of river bed variation. 1) On a bed of non-uniform material under high flow conditions, coarser particles move faster and disperse more widely than finer particles. 2) Bed level variation exhibits two opposite effects. The increase of the degree of exposure accelerates dispersion, but the reduction of shear stress decelerates it.

In this study, the authors invented a three-dimensional position finder, based on theprinciple of measuring three angles, using sine-cosine potentiometers. With this device, they surveyed in detail the stream formation process on a cohesive material bed.It has been found that even on steep slopes, the simple straight streams are seldommaitained, and the fall-like stepdowns as well as strong meanders are often formed.On the other hand, the sediment run-off from bare slopes was investigated from asediment-hydraulic view-point, based on the surveying of an actual residential developmentsite.

In this study, some measuring techniques of sediment discharge are discussed.In the previous paper, the author devised a direct measuring system composed of afixed sieve, a sand pump, rotating baskets and a load cell. In this paper, it is im-proved to a system composed of a trommel and a tipping bucket suspended by aload cell. For relatively small gravel and sand, this system works well.It is difficult, however, to apply direct measuring methods for coarser gravel, and it is necesarry to devise some indirect measuring techniques.Among some indirect methods, an acoustic one is discussed in this paper. Theoscillation of air confined in a pipe is detected by a microphone mounted on aninside wall of the pipe. The amplitude is proportional to the momemtum of theparticle which impacts the pipe. If the particle velocity is known or constant, it ispossible to estimate the particle mass from the amplitude with some calibration.Two sets of calibration were carried out using a small flume. It is expected thatthis method will be also applicable to field measurement.

In this paper, the delta formation process in a laterally wide basin wasformulated based upon the experimental results described in the previous papers ofthis series of research, and some numerical simulations were carried out to examinethe formulation.The results obtained are summarized as follows:The delta formation process is divided into three stages; in the first stage, thedelta develops mainly longitudinally; in the second stage, it develops mainlylaterally; and in the third stage, it develops in all directions keeping a nealy similarshape in average.In the first and the second stages, the flow expands on a delta plain withoutstream channels, which is well analyzed by a two-dimensional flow and bedvariation model. In the third stage, however, some stream channels are formed andmigrate on the delta plain, which is analyzed by a one-dimensional flow and bedvariation model.

Usually some cohesive materials are contained in bare slopes, where the rill-like streams are formed in the process of surface water erosion. For the prediction of the sediment run-off from such a slope, it is important to know the arrangement and scale of streams and soil property against erosion. In this study a new theoretical model is offered to obtain the shear distribution along the channel perimeter with an arbitrary corss section, and the erosion process of the cohesive material bed is investigated. The theory is examined by flume experiments using bentonite. Main results are as follows. The rate of erosion is related to the local shear. Shear distribution in a uniform flow is obtained by differentiating the area between the normals to the wall with the wetted perimeter. Bed unevenness in the lateral direction may be amplified or reduced according to the shape of the unevenness and the flow conditions. The criterion is obtained in the domain of a/H and L/H, where a and L are the wave height and length respectively and H is the water depth. A stream has an equilibrium cross section corresponding to the hydraulic conditions. When the rate of erosion is proportional to the shear velocity, the ratio of the water surface width to the maximum water depth is about 4 in the equilibrium state.

Time response of dunes due to periodic change of flow discharge was simulated throughsome flume experiments. Two kinds of hydrographs (triangular and sinusoidal) with severalperiods were used. As expected, dunes transformed with some time-lag for the change offlow discharge. Within some range of period, large loops were formed in the relation betweenflow discharge and wave height, wave length of dunes and flow depth. When the dischargevaried very quickly, the scales of sand waves hardly changed. A sinusoidal discharge hydro-graph seems to have a nearly equivalent role to the sand wave transformation as the triangularhydrograph with a considerably shorter period.

An equipment for automatic measurement of sediment discharge was devised. It consists of asand trap, weighing mechanism and conveyers.The sand trap is made of 0.3 mm mesh wire screen which is attached to the downstream endof a 50 cm wide flume. The sand particles gathered by the screen are conveyed to the weighingmechanism by means of a pump system. The weighing mechanism has five cups made of screen, which are cyclicly shifted in turn by a belt conveyer.In five positions, the functions of receiving sand, weighing, dropping sand washing and waitingare repeated every one minute.This device is applicable to the condition of the flow discharge between 1 and 40 1/s and thesediment discharge between 0.2 and 1 g/min for medium and coarse sand.

Some indices of risk due to the debris flows at a certain location in a basin such as the liabilityof occurrence, maximum discharge, total volume, etc. are discussed based on the systematic andmechanical considerations on the phenomena. Evaluation method of the indices under a par-ticular rainfall condition is proposed. The method is partly checked and proved valid, at theeast part of the Shodo island in cases of 1974 and 1976 disasters, concerning the relations between thevalues of the indices of liability of occurrence and the actual ratios of occurrence.

On a bare slope, complicated stream network consisting of rills and gullies is often formed. Inorder to estimate the sediment run-off from a bare slope hydraulically, it is important to know thedegree of concentration of surface water.In this study some experiments were carried out using cohesive material and artificial rainfall.On the other hand, a stochastic simulation model is developed in which the confluence process ofstreams based on their lateral movement is noticed.The most important difference of this process from that due to water supply at the upper end ofthe slope is that the inferior stream does not disappear at the joint but survives gathering the precipita-tion from the downstream catchment area.

The motion of bed load particles is so irregular that they disperse remarkably with time.In this study, some flume tests using painted tracer particles were carried out, in which thedispersive property of tracers changed variously with sediment feed rate.In analysing this process, a stochastic simulation model is proposed where it is discussedabout the degree of exposure of individual particle near the bed surface and about the variationof its pick up rate. The exponential distribution of step length is assumed. The result fairlyconforms to uniform material case but not to nonuniform one for present.