The boundary mixing coefficients, which is used for estimation of boundary shear stress due to vegetation in quasi 2D simulations, in the Ototsu river is investigated numerically. Firstly, the relation between the boundary mixing coefficients <i>f</i> and vegetation density is examined through comparison of numerical resuts between quasi 2D and 2D simulations. From the relation, a value of <i>f</i> is found to be 0.08 in the Ototsu river. And it is shown that the quasi 2D model can reproduce the observation data of the water level in the three different flooding when the <i>f</i>=0.08 is used. The effects of deforestation to the boundary mixing coefficient <i>f</i> is also examined. It shows that deforestation is not effected significantly on the value of <i>f</i> in the Ototsu river.

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It is important to evaluate the effect of vegetations on the management of floods and river environment. In general, hydraulic effects of vegetation on flood flows are taken account by the permeability coefficient of vegetation and roughness coefficient, but these coefficients can not always be determined reasonably for various scales of flood and form of channel and vegetation. Objectives of this paper are to find a method assessing those coefficients from mutual relationship between flood, channel and vegetation.
For that purpose, we use the permeability coefficient of vegetation and roughness coefficient distributions determined by Fukuoka et al. 's analysis conducted on the Tone River and the Edo River floods, and find the relationship between these coefficients and vegetations and channel conditions.

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The rising backwater, which occurs due to the confluence of the Takahashi River and the Oda River, makes the water level rather higher during flood in the upstream of those rivers. The higher water level endangers embankments of those rivers. One of the possible means to reduce the water level is to relocate the present confluence site with the Oda River to the downstream site of the Takahashi River. This study aims to investigate the effect of the relocation of the confluence site using two-dimensional flow analysis. Numerical results under present river course condition were compared with the measured water level, and the effectiveness of the proposed analytical model was confirmed. It is also shown that the relocation of the confluence site has an effect to reduce the water levels of rivers considerably.

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The contour line change model was applied to predict the beach changes around artificial reefs built on the Shichiri-Mihama coast composed of coarse materials and facing the Pacific Ocean. The formation of a salient behind an artificial reef was reproduced well. On the basis of this numerical simulation, the model was further applied to the investigation of the improvement of the mouth of the Shihara River flowing into the same coast. In front of the mouth, an artificial reef is built to reduce the berm height. The appropriateness of this method in the reduction of the berm height, which is necessary for creation of a floodway, was confirmed by numerical simulation, if parallel jetties are further built to the shoreline to obstruct longshore sand transport on the shore face.

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The Naruse River mouth showed stable topography at least until 1996. However, sand bar on the left-hand side of the river mouth has been declining in recent years. The behavior of the morphology of the river mouth after the flushing of the sand bar has never been observed. In this paper, characteristic morphological change at the Naruse River mouth is shown with the use of aerial photographs and morphological maps. In order to determine the main factor of morphological change, numerical simulation of extended Boussinesq equations are applied. It is concluded that, the mechanism of the sand bar intrusion into the river is explained by wave overtopping over the left-hand side sand bar at the river mouth. Furthermore, sand bar height and width are important factors of sand bar intrusion.

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sophisticated measurement method to monitor gravel movements on the river bed. We have developed a tracer investigation technique on gravel movements that applied the IC-Tag technology.
This system is composed of an IC-Tag that is inserted in each gravel, an antenna, an amplifier and a logger. Through laboratory tests, basic characteristics of the IC-Tag such as readability in still and flow water, and under sand bed have been confirmed. We have also tested this system at the flushing operation of Managawa dam in 2005 and succeeded to find out flushed out gravels with IC-Tag in the downstream river bed.
In this paper, we present basic features of the measurement system and discuss results of laboratory and field experiments.

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In actual rivers, many aquatic plants are often observed and they have significant effects on hydrodynamic properties. In such vegetated open-channel flows, velocity profiles are largely changed in the vertical and spanwise directions. The vegetated canopies generate coherent turbulent motions that promote momentum and mass transports between over and within canopy. It is thus needed to investigate these turbulence characteristics and coherent motions in hydraulic engineering and river environment.
In the present study, we conducted a large eddy simulation in vegetated open-channel flows, and revealed numerically the turbulence structure and correlation properties in the whole depth region including within-canopy and over-canopy layers.

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The effects of low-water channel alignment and the position of vegetation on the behavior of flood flows in a compound open channel were investigated experimentally and numerically. The relative depth and position of vegetation were changed in experiments. The numerical model based on a finite-volume method on unstructured grid using flux-difference spitting technique was used in numerical simulations. Through the experiments and numerical simulations, it is found that the changes of flow pattern due to relationship between sinuosity and relative depth as well as the relation between a location of maximum velocity and vegetation in the channel were related to increasing of flow resistance and bank protection.

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Correlation between the oblique upward flow and coherent structure formed over flood plain in compound open channel flows was investigated by using flow visualization techniques. The results of velocity measurements using PTV show that the oblique upward flow and a pair of cellular secondary current are generated over the edge of the flood plain. This flow filed is characterised by two velocity shear structures (∂U/∂U, ∂U/∂z). Further, it becomes clear that longitudinal vortical structures exist over the edge of the flood plain for a long period. The vortical structure directly contributes to form instantaneous oblique upward flow and cellular secondary current.

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Open-channel flows with a relatively large-scale side cavity zone exhibits water surface oscillations in spanwise or streamwise directions. Although the side cavity zone is installed for improving the water-friendly environment, such oscillations, once occurred in the actual river in the urban areas, may cause flooding, resulting in a large damage in the residential area. In order to investigate the flow features associated with such surface oscillation, the authors have developed a 3D LES model that utilizes a density function for detecting air-water interface. With the developed model, it becomes possible to simulate water surface oscillation observed in the experiments. In this paper, the flow features related to the water surface oscillation as well as the local flow features along the interface between the main channel and the side cavity zone are investigated for the subcritical flows with relatively large Froude number.

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It is very important for the river management to grasp the hydraulic characteristics of flood flow in compound channels. The propagation speed of flood flow in compound channels has not yet been known, although that in simple cross-section channels was showed by Kleitz-Seddon. This study aims to clarify the propagation mechanism of flood flow and compare propagation speed from laboratory experiments with those of the theoretical expression derived for compound channels. As a result, theoretical formula provides a good expression for propagation speed of compound channels. Furthermore, we explain the effect of change in the channel cross-section on the flood propagation speed in rivers. Finally, we investigate propagation characteristics of various flood flows in the Tone River and Edo River.

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In this paper, the comparisons of the plane 2D flow model and the 3D flow model for the reproducibility of the local scour around a bridge pier is described. The river bed deformation model is the same in both flow models, and only the bed load is taken into consideration in this model. The FAVOR method and the collocated grid are applied in the 3D model, and the MacCormack scheme is applied to all models. The calculated results are compared about the initial flow, the shape of scour hole and the maximum scour hole depth. Moreover, the calculated maximum scour hole depth is compared with the field investigated results. From the comparisons of the calculated results, the 3D model can be reproducing the field investigated results rather than the plane 2D model, and the necessity of using the 3D model is pointed out for the prediction of local scour.

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In the Matsuura river digs the ground in the rice field of Azame down because there were for a long time a lot of floods, makes a flood plain there, and the natural regeneration business that starts restore the marsh is done. In this study, the flow including this Azame was analyzed by the numerical simulation.
As a result of the numerical experiment, it was understood to be suppressed even to about the half when the flood plain existed while flow velocity in the narrow section reached 4.5m/s in the current state without the flood plain river channel at the flow rate peak.
Moreover, the source location of the maximum flow velocity shifted to the left bank neighborhood though the peak at the flow velocity of the main current part in the flood plain downstream edge was suppressed by about 60% of the current state river channel.

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Nature friendly hydraulic structures made of natural stones such as ripraps have attracted attention in recent years. However, those structures are subject to failure problem under flood flow. Therefore, the authors proposed tied gravels to increase its stability against flood flow. Coefficients such as the drag and lift force are necessary in designing those structures. However, the authorized values for those coefficients are not established yet, the coefficients used for concrete structures are therefore applied in designing structures made of stones at present condition. This study aims to clarify the drag and lift coefficient for gravels and tied gravels experimentally.

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During a big flood in recent years, flood waters intruded into the staircase between ground and underground in an urbane area. Aerated flows are formed in the staircase. Drag force acts on bodies or human legs in a high-speed-aerated flow. The authors proposed a method for estimating the velocity and the depth on stepped channels. Flow resistance and total head in stepped channels were clarified under a wide range of angle of slope, step height, and drop height. On the basis of the flow characteristics of aerated flows, the expression for a drag coefficient on bodies in a high-speed-aerated flow can be reasonably presented. Also, the drag coefficient of a model leg is obtained using the previous results.

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Effects of regularly arrayed sphere roughness on flow resistance and turbulent characteristics in an open channel have been investigated over a completely rough-bed with uniform glass beads, where the sphere diameter were 15mm and 30mm. Detailed spatial measurements of streamwise and vertical velocity fluctuations were conducted using Particle Image Velocimetry (PIV) in a vertical plane along the completely rough bed surface. Experimental results indicated significant degrees of spatially regular variation in the time-averaged velocities, where the upflow velocity was much stronger than the downflow one and imhomogeneous turbulent characteristics were generated along the rough bed in case of the large ratio of the sphere diameter to flow depth. In addition, Reynolds shear stress and turbulent intensity showed minimum values at the ridge of roughness elements and maximum ones at the trough. These organized flow structure were caused by the vortex shedding generated by the roughness elements.

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The relation of time averaged conjugate depth and the characteristic of the length of hydraulic jump have been almost clarified. The time averaged pressure distributions around the end sill are also measured by several researchers. On the other hand, bed materials near the roller of hydraulic jump are sometimes picked up by the pressure fluctuations, so that it is quite important to investigate characteristics of the pressure fluctuations in and around the hydraulic jump. In this study, the fluctuations of bed pressure in and around roller and also instantaneous flow depth are measured with the pressure gauges and supersonic wave gauges, respectively. It was found that oscillations of roller influences on the instantaneous flow depth and bed pressure and also that the instantaneous bed pressure concerns with the instantaneous free surface fluctuations.

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Vegetation colonies are often observed to grow in stripe pattern or patches within many stream channel. In this paper, the influence that interaction of longitudinal vegetation zones gave to the flow resistance in an open-channel was examined experimentally. Laboratory experiments were conducted using a two-component electromagnetic current-meter to clarify the momentum transport between main flow and flexible artificial vegetation. Results showed that the flow resistance significantly depended on the lateral distance between longitudinal vegetation zones and the reason could be explained by the difference of convective momentum transport through the interaction between longitudinal vegetation zones.

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Laboratory experiments were conducted on local scour and bed evolution around a cylindrical pier. Not only with a traditional non-submerged pier, but some cases with a submerged pier were explored. Experiments were carried out in both static and dynamic scouring conditions. Shape of a scouring hole around the pier, as well as backwater caused by the pier, is of particular interest.
The shape of the scouring hole in the submerged conditions is similar to that in the non-submerged condition, thus the maximum scour depth appears in vicinal front of the pier. The maximum scour depth reduces as the height of the pier decreases. A refined equation for estimating the maximum scour depth including the effect of variable pier height is proposed and shows good performance in the range tested here. Backwater in the upstream is not so noteworthy in the submerged cases.

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It is very important to reveal the coherent structure in meandering compound open-channel flows for predicting the transport properties of suspended sediments in rivers in flood. However, flow-visualization techniques such as PIV and PTV, have not sufficiently been applied to such flows in previous studies, and thus, there is almost no detailed information on coherent turbulence in meandering compound open-channel flows. Therefore, in this study, we conducted some PIV measurements with high-speed CMOS camera. As the results, the time-averaged velocity properties and coherent turbulence structure were investigated and discussed.

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Groynes have been used for the stabilization of banks and for creating a navigation channel by confining the cross-sectional area, especially for large European and Japanese rivers. Therefore, turbulent flows and transport phenomena in groyne fields have paid attention to the appropriate design for bank protection and obtainment of enough depth in the main channel as well as the proper environment for ecosystems. In the present study, mean and coherent flow structures around single groyne under emerged and submerged conditions were experimentally discussed. In order to investigate the flow pattern around the single groyne, a scaled and schematized model was implemented and experiments were conducted by means of surface flow visualization technique and Particle Tracking Velocimetry (PTV). Furthermore, analytical techniques of proper orthogonal decomposition (POD) are applied to reveal typical pattern of coherent structures.

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Riverside embayment is often connected with primary river flow through a conjunction channel. It is important to maintain water quality in such a dead water zone during ordinary water-stage. In this study, we concentrated on the effects of length and orientation angle of the conjunction channel on flow structures and water exchange rate. The flow patterns in embayment zones were extremely changed by the orientation angle of the conjunction channel. When the length of conjunction channel is long relatively to the width, an isolated vortex was generated in a conjunction zone. This vortex fluctuates and penetrates intermittently into embayment zone. This indirect inflow generates consequential vortices but the magnitude of these vortices are considerably smaller than those caused by direct inflow. The water exchange rate was generally proportional to the velocity scale but it was affected by the vortex structures.

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To check the accuracy of coefficients of float, which are widely used in discharge measurements with float and image processing, we examine the coefficients of float by conducting ADCP measurements for flood flows in the Edo River and the Ara River. We compare the observed results for vertical flow structure with classical well-known velocity distributions such as logarithmic profile and Aki's theory which is used in the evaluation of the general coefficients of float. The observed velocity distributions are better agreements with the logarithmic profile than Aki's theory. It is noteworthy that the observed coefficients of float show a decreasing trend as water depth increases and the averaged coefficients of float are less than the general values. These results for the coefficients of float are also good agreements with those evaluated with the logarithmic profile.

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The branch block is a reinforced concrete block which consists of one trunk part and three branches part. In this study, basic hydraulic properties of the branch block bank protection were examined using the one-fortieth block model. Velocity measurements and flow visualization were carried out in a turbulent open channel flow in which the block models are set up along the side wall of the channel. The results of the velocity measurements show that the primary velocity over side wall is relatively low due to the strong secondary flow toward opposite side wall. Local low speed region were generated over the region of the junction of upper and lower branches of the block model. The results of flow visualization show that the large-scale longitudinal vortical structure is formed over the block model. It is inferred that these vortical structure contribute to generate characteristics of the velocity profiles.

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In recently years, the hydraulic design with nature has become the most important factor in planning river management. Some traditional counter measures for flood have become of special interest. The traditional measures can not fully control floods, however, the nature is not fully destroyed by them. One of the traditional measures is an open dyke system. The open dyke is the discontinuous bank of which upstream end is opened and connected to the downstream bank with small angle of10 to30 degrees. The open dyke has some functions by which the river water inundated through it to the surrounding flood plains during floods. However, these hydraulic characteristics have notbeen examined yet. In thispaper, the flow around the open dyke was investigated by the experiment. The result of this experiment shows hydraulic functions of it.

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It is important to reinforce the toe of levee back slope against failure by the overtoppingflow due to a flood exceeding the designed level. Inorder to control the running water from the back slope and toremove the inflowing water without delay, we proposed the toe protection works consisting of several units of drain ditch.
In this study, the flow pattern and the flow velocity have been investigated on the proposed the protection works byusing two model levees. As a result, it was considered that the behavior of flow on the toe protection works depends on the width of an unit of drain ditch. In the case of the drain ditch unit with the relative width of 2.15 and with holes, the flow velocity was markedly decreased. Such the effect was attributed to the dispersion of the flow. Furthermore, it was recognized that there was a difference in the flow pattern between two types of the drain ditches with a projection and without it.

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The ecosystem in the tidal region of a river tends to be diverse because of seawater intrusion. Such an ecosystem is observed in the Abashiri River in eastern Hokkaido. The downstream end of Lake Abashiri is about 7 kilometers from the Abashiri river mouth. The lower layer of the lake is saline water that has flowed upstream from the sea. Dissolved nutrient salts from the saline water layer make the lake a good fishing ground. However, in recent years, the damage to fishery of blue tide happens frequently because the fresh water depth of the lake became shallow. One solution is based on the comb-shaped weir traps that are used for catching fish in Abashiri River. Mesh structures that simulate weir traps were used in laboratory experiments to study the relationship between mesh porosity and salinity intrusion velocity. The following findings were obtained: The salinity intrusion experiment showed that when the mesh porosity is low, the flow velocity decreases before the water reaches the structure, and that the flow velocity does not differ greatly between before and after passing through the structure.

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Three-dimensional unsteady flow with localized areas with large vortices in the intake channel of a small-scale hydroelectric power station has been simulated numerically using a Large-Eddy Simulation (LES) technique. The method computes the motion of the free surface and a standard Smagorinsky model with wall damping is used as the turbulence model. With the total number of grid points of about one-third of a million, the complex and unsteady nature of the vortical flow can be reproduced reasonably well by marginally resolving the near-wall flow. Intake vortex of weak intensity can be captured and the flow conditions associated with appearance of vortices can be examined based on the results of the present simulation.

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A large eddy simulation (LES) of turbulent open-channel flow with strip roughness is performed together with the image analysis by the particle image velocimetry (PIV). In the simulation, an immersed boundary method is introduced in order to be able to simulate arbitrary channel bed topography. In addition, we used a sophisticated LES model to simulate the flow near the complicated boundary without using a damping function. The hydraulic conditions for the simulation and the experiment are restricted to a relatively small Froude number (Fr) flow, e. g. Fr less than 0.25, in order not to generate appreciable water surface fluctuation. The results show favorable agreements regarding the statistical properties such as the mean and the Reynolds stress distributions. Additionally, the instantaneous flow structure at the instance when a separation vortex hit the water surface is investigated, showing that the separated vortex ascends up to the water surface and locally decelerate the convection velocity of the surface profile.

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The speed of flood front under dry-bed condition with strip roughness is measured and investigated with experiment and numerical simulation. The influences of the roughness spacing and its height and on the flow conditions are especially investigated. It is shown that the factors affecting the speed are backwater effect by the head strip and flow restraint effect by other strips. One dimensional numerical model for flood flows simulation on strip roughness is developed. The model employs both effects and improves accuracy of shallow flow on large roughness.

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A numerical model for 2D inundation flows over a drying and wetting topography is developed. The model is based on Spatial Averaged Finite volume method on Unstructured grid using FDS technique for 2D Free-surface flows (SA-FUF-2DF model). A new procedure for a dry/wet boundary over a topography is incorporated into the model. The procedure modify the bed elevation of dry cell to satisfy zero flux across the cell edge between dry and wet cell when the non-physical flow is occurred. The model is verified against two experimental data of steady and unsteady flow over wetting /drying topography. It shows that the model can reproduce the complex behavior of the flows with reasonable accuracy as well as preserve the stable calculation and zero mass error.

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A computational method has been proposed to predict the flooded flows entering residential areas due to levee breaks and tsunamis. The focus is placed on the local free-surface flow whose momentum is so large that some buildings may be destroyed. The computational method is based on 3D MICS, a computational method for incompressible multiphase fields. In order to deal with complicated-shaped buildings in the areas, a tetrahedron sub-cell method has been newly introduced in 3D MICS. The arbitrarily-shaped bodies are represented as the assembly of multiple tetrahedron elements and their volumetric fraction in 3D computational cell is evaluated by the sub-cell method. A numerical model for the actual urban area near a river was set up and the artificial flooded flows were demonstrated with the present method.

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The purpose of this research is a real-time forecasting of a storm surge caused by typhoon. The lead time of forecasting was set six hours in consideration of time that it was possible to take shelter. Various parameters of the typhoon model used in the storm surge analysis were presumed by the neural network technique (BP method). The typhoon data which had passed the surrounding of Shikoku between 1991 and 2004 was used for the study data in the BP method. The numerical analysis of the storm surge for the T0514 typhoon was executed based on the predicted parameters by the BP method and the practicality of this forecasting system was examined by the comparison between observed storm tide and calculated one.

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Grid turbulence is one of most fundamental turbulence phenomena because it dose not have a velocity distribution in the main flow. This paper describes the computations of grid turbulence in shallow flows in open channels. Since the shallow grid turbulence is bounded by a solid bottom and a free surface, its fundamental turbulence structures are completely different from the three-dimensional grid turbulence. The vertical confinement of the flow suppresses the three-dimensionality and attains strongly two-dimensional features with inverse cascade of turbulence energy from small scale toward large-scale structures due to vortex merging. 2D depth averaged models and 3D models with linear and non-linear constitutive equations are applied to a shallow grid turbulence and the results are discussed through the comparison with the results of laboratory tests performed by Uijttewaal and Jirka (2003). In 2D computations, a modified non-linear 0-equation model could capture the fundamental aspects of flow phenomena including inverse cascading. In 3D models, an artificial disturbance at inlet boundary is necessary to generate inverse cascade.

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A new numerical solver is developed for a shallow-water flow model to simulate meandering river flows. This solver can investigate the flows in the curved river channel, by means of the adaptive CIP-Soroban (CIP-S) scheme in a cylindrical coordinate system. Time development of water velocity and free-surface level is computed by the orthogonal curvilinear coordinate system without any transformation of the governing equations, and the advection term is calculated by the high-accuracy CIP scheme. The numerical grid points of the waterfront line at the river bank are moved and tracked by the kinematic condition so that the grid points are always located on the line, and the rearrangement of the positions of the girds is easily conducted by the original CIP-S method. From the verification of this solver by the pure advection problem and by the numerical solution of the meandering river flows, in comparison with the CIP-S method in a Cartesian coordinate system and with the boundary fitted coordinate (BFC) method, it is shown that the proposed numerical solver reasonably predicts the main flow profile and water surface elevation and will be a promising numerical method as one of the practical solutions.

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A computational method has been proposed for shallow water equations, which is based on the prediction method for incompressible fluids on collocated grid system. In the proposed method, called MACS (MAC method on Collocated grid for Shallow water equations), the momentum equations are discretized with a C-ISMAC method and the water depth h is treated implicitly. The continuity equation is also discretized implicitly and its numerical solutions for φ = hⁿ⁺¹-hⁿ are obtained by solving simultaneous equations. The unit flow rates are corrected with the iterative computations based on the C-HSMAC method. The new treatment for the continuity equation is proposed and it enables us to predict dam-break problems, hydraulic jumps and sub-and super-critical flows stably and accurately without artificial diffusions.

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In this study, a numerical analysis and a laboratory experiment were carried out in respect to an open channel flow field with a movable bed in which a permeable groyne was installed. By comparing the agreement between the analysis and the experiment, the influence of the permeable groin to the open channel flow and movable bed erosion were discussed. The numerical method was expected to provide knowledge to the design of river structure such as permeable rubble mound groyne.

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In Recent years, flood disasters are frequently taking place where relatively steep slope rivers meet in the mountainous area. The cause of the disasters is mainly due to the sudden rise of water level at a confluence, which sometimes accompanies a hydraulic jump in the upstream region. In this research, a numerical simulation based on the shallow water equations and the unstructured grid system is performed to investigate the effect of the discharge ratio to the flow patterns and the riverbed change at a confluence. In order to simulate a river confluence in the mountains, the main channel slope is set at 1/80 with a tributary channel slope of 1/40. Laboratory experiments are also conducted to provide data with respect to water surface profiles and bed variation. Water surface velocity distributions are obtained by an imaging technique, LSPIV, using a high vision video camera. It is made clear that general flow features calculated by the simulation model agree fairly well with the experiments including the locations of hydraulic jumps and local scour.

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A numerical simulation method has been developed for describing the behavior of driftwoods motion and their accumulation process in channels with bridge piers. The present model has been composed of Eulerian analysis of depth-averaged flow motion and of Lagrangean analysis of driftwoods motion by using the extended Distinct Element Method (DEM), which can simulate the motion of driftwoods as the rigid body. The calculation results show time-depending process of driftwood accumulation in front of bridge piers including the effect of branch shape of driftwoods and also show the amount of dam-up water level due to jamming of driftwoods.

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When a lot of drift woods due to locally heavy rain flow into a mountain stream, a bridge is caused by serious damages. Damed-up drift woods may cause a flood, and piers and slabs of a bridge can be broken due to the collision with drift woods. Because such damages due to drift woods are recently increasing, it is necessary to consider the prevention against them. In order to make effective guidelines of prevention works, detailed mechanism should be examined. However, 3D numerical simulations of dam-up process of drift woods and resultant overflow around a bridge have not been carried out before. In this study, a numerical analysis by the MPS method is executed in the 3D field to simulate dam-up process of drift woods onto a small slab bridge in a mountain stream.

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To reduce damages of recurrent disasters of landslide in moutainside towns, a constant awareness of the disaster prevention is important. A dynamic and visual representation of a disaster would play an effective role to explain a danger of a landslide disaster. In the present study, numerical simulation of a landslide was performed using the three-dimensional Distinct Element Method, and an eloquent performance of this kind of simulator was represented by showing various angle of snapshots. Especially, a landslide considered with fallen trees modeled by the passively-moving-solid model was simulated because a usual landslide disaster contains fallen trees, and the simulation result showed a good agreement with an actual landslide in a tendency of accumulation form.

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A computational method has been proposed to predict the movements of arbitrarily-shaped solid bodies in a viscous incompressible fluid. This method is based on the 3D MICS, a computational method for incompressible multiphase fields. In this paper, the numerical procedures of solid-body movements are improved by introducing the quaternion that enables us to evaluate the rotating motions of solid bodies more accurately than the time-integration method. The proposed method has been applied to the assembly of tetrahedrons and it was shown that the fluid-body interactions are suitably treated. In addition, as a result of the computation of a falling rectangular body in water, it was confirmed that the position of the body and the falling speed are adequately predicted with the present method.

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Gravels and boulders cause a severe abrasion of a invert of concrete channel for removing depositted sediment in a reservoir. To understand the mechanism of abrasion is the key to design a channel and to make a maintenance plan of a channel. Although some experimental studies have been performed, it was difficult to measure the motion of gravels and boulders directly because of a highly-disturbed water surface. In this study, the 3D particle method with solid-liquid two-phase-flow model is applied to the flow in a concrete channel in which gravels and boulders are transported in a flow with a small relative depth. Detailed physical properties, a collision impact, an abrasion depth distribution, and so on, are estimated for the four different classes of particle diameters of sediment.

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Sloshing phenomena of liquid in rectangular and circular tanks with and without sloshing damper have been simulated using a CFD method, namely a large eddy simulation method with standard Smagorinsky model. The decay of the wave amplitude in free oscillation, the resonance frequency and the amplitude response characteristics to a single-mode excitation are found to agree well with the experiment in the basic case of rectangular tank. The effects of the damper net have been modeled by introducing resistance in the flow and have been found to reproduce experimental results. The response characteristics to a real seismic oscillation of fluid in a realistic cylindrical petroleum tank have also been calculated with favorable results.

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Erosion rate of soft cohesive sediment was investigated experimentally in the present paper. In this study, we developed a movable apparatus of erosion test, which was designed to conduct a field measurement of erosion rate. In order to check the validity and utility of this apparatus, the several series of measurements were carried out outside in large-scale experimental flume. It was verified that the results by this new measuring system has almost same order of accuracy as that by our standard test in laboratory. Effect of water temperature on the erosion rate were also evaluated quantitatively.

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The physical properties of fine cohesive sediment silted in reservoirs, such as organic matter content and particle diameter, vary among reservoirs. It causes the differences in their erosion processes. The main purposes of this study are to investigate which factor has a great influence on the erosion characteristic and to establish an index that describes the erosion property, which can be easily obtained by laboratory test.
Physical properties of fine cohesive sediments in several reservoirs have been measured, and it was found that humus content dominates their shear strengths. The measurement results on the critical shear strength and the erosion rate shows that liquid limit can be an important index of erosion property.

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The erosion process of cohesive sediment in an estuarine channel was studied using thermometers. Sixteen self-logging thermometers were attached to a fishing rod at intervals of 0.1m; 15 of them were sunk in a muddy bed and one was placed in river water. The progress of bed erosion was estimated from the difference in the water and mud temperatures. This is because the water temperature, which is essentially higher than the ground temperature, drops rapidly when flood discharge occurs. The bottom shear stress was calculated by ADCP's velocity profile; bed erosion occurs when the shear stress exceeds 1.8 N/m². The heat diffusion coefficients of the bed sediment were estimated using an equation of heat conduction. Their values suggest that the moisture content in the upper layer was greater than 200% and the lower layer comprised compacted silt.

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To realize long-term, continuous monitoring of deposition rate of sediments in rivers and coasts, we attempt to present a tipping-bucket type of sediment trap (TST), which was originally developed for measuring bed-load discharge in rivers at low cost. To check the fundamental performance of the TST, we conduct simple laboratory experiments for deposition of sediments. As field tests, we apply the TST to continuous monitoring for the deposition rate of sediments in three rivers. The observed results indicate that the TST can realize the continuous measurements of deposition in rivers. It should be also noted that the temporal variations of deposition rate of sediments during flood events may be observed clearly by using the TST.

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Hyper-concentrated flows like mud flow and debris flow have been frequently observed in an upstream region of a river basin. Such flows showed non-Newtonian properties but remain poorly understood concerning the impacts of their rheological properties on fully developed turbulent flow structure.
In this paper, we experimentally investigated the effects of non-Newtonian fluid on resistance characteristics and flow structure over gravel bed by using Particle Image Velocimetry (PIV). The results showed that Kaolin water mixtures in gravel bed open channel flows considerably changed flow structures and took the form of resistance decrease with Kaolin fraction C_v in the region of C_v<8% and followed by a subsequent increase in the region of C_v>8%.

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Results obtained from both of flume data and theories suggest that equilibrium bed slope in flow over an erodible bed are determined uniquely by sediment discharge rate when the movements of sediment particles are laminar and thus no suspended transportation take place. This means that the static friction force is dominant in debris flow and that sediment concentration is determined by shear stress balance on the bed surface as seen in our previous studies. On the other hand, if part of sediment particles in debris flow body is transported in suspension, sediment concentration will be larger and the equilibrium bed slope will decrease. These facts are supported by Egashira et al. 's and author's flume data and others' experimental data.
The present study discusses experimentally phase transition from solid phase to liquid phase based on experimental data and proposes thickness of laminar sediment moving layer and the methodology for the thickness if part of debris flow body is turbulent.

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