Toward a numerical analysis of a drowning process in a water flow, a new numerical flow simulator solving a fluid dynamics and human body motion is developed. The CIP-CUP scheme for a multi-phase flow and the link model for a human body motion are combined. While a human body is modeled as a group of solid bodies, in order to represent a fainting human's motion, a new technique to limit the angle between connected two solids is proposed. The present model is applied to a human drowning in a rectangular pool. The calculation result shows that the present model enables a qualitatively reasonable interactions between human body motion and fluid flow.

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 The presence of ice hinders the operation of small hydropower plants in cold regions like Mongolia. In order to study this problem, we propose a numerical model for analyzing the liquid-solid phase changes that occur in a free surface flow. This model is formulated using the lattice Boltzmann method (LBM). The single phase free surface model, along with the immersed boundary condition, is used to model the free surface flow and solid phase. The thermal lattice Boltzmann (LB) equation is combined with a non-iterative enthalpy based formulation to simulate heat transport and phase changes. These models are integrated in a way that holds physical relation. The performance and accuracy of the model is validated using experimental evaluations. The formation of open water in the down stream channel of the hydropower plant is successfully simulated to demonstrate the performance of the model. Results indicate that the proposed model can be used for studying measures to control downstream ice in hydropower plants. It can also be applied to study the ice phenomena in open channel flows.

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 The simulation with 2-D (Two-dimensional) model and 3-D (Three-dimensional) model is a popular method to study open channel flows because it is very effective from the aspects of economy and efficienty. However, the applications of 2-D models sometimes cause serious discrepancies between the computational results and real phenomena. Recently, Nanson (2010) measured the velocity profile in a natural meandering river and discovered that, a secondary flow can be weak even though in a sharply curved and deep channel. The study related to weak secondary flow is unfamiliar in this field and the applicability of simulation models on such flows is not known well. In this study, we thus deal with both 2-D and 3-D numerical models to clarify the flow structures related to the secondary flows at a sharply curved meandering channels. We considered two different types of sharp bends in rivers, one is relatively wide and extremely shallow bend, and the other is relatively narrow and deep bend. In those two bends, it has been reported that the secondary flow is relatively weak. We apply both models to the two bends and clarify the different mechanisms of flow structures as well as the applicability of each model.

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 This paper describes some theoretical considerations on reproducing unsteady flood waves in supercritical flow state using one depth hydrograph given at one site in the downstream section of a river course. Based on the method of characteristics for shallow water equations, the analytical solutions of linearized equations were previously derived for the region just downstream of the upstream boundary. In this study, the analytical solutions are derived for the region far from the upstream boundary and are verified through the comparison to the results of numerical analysis. It is pointed out through the theoretical consideration of the derived analytical solutions that depth and velocity hydrographs at the upstream boundary can be reproduced in principle using a depth hydrograph at one site in the downstream region. Further investigations are still required to develop a practical computational method to reproduce flood flows in an actual river using only a water stage hydrograph observed at one site.

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 One of the characteristic features of turbulent open-channel flows is the free-surface pattern shows time-dependent variations subject to the effect of turbulence. However, the free-surface dynamics is not fully understood especially regarding the advection feature of surface variation. Hence, Direct Numerical Simulation (DNS) that allows the deformation of free surface was conducted to investigate the influence of the Froude number and the Reynolds numer for turbulent flows with a smooth wall. It was made clear that the advection feature is a superposition of the effects due to turbulence and surface waves. In addition, the contribution of each mode was found to be dependent on the Froude number.

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 CRD scheme is a numerical computational method based on the multi-dimensional characteristic theory. Our previous studies have adopted a CRDz scheme, using a bed variation model to avoid unphysical expansion shock occurance. Another result also showed that a 2-D CRD scheme can also drastically reduce the occurance by modifying the mesh shapes. However, its mechanisms have not been revealed. This study analyzes relationships between mesh shapes and expansion shock occurrence under dam-break flows. Results showed that expansion shock occurrence can be avoided when flow direction and mesh are allocated non-perpendicularly, since information is distributed both to subcritical and critical numerical points. This scheme could also work under bank-overtopping flows, indicating its applicability to discontinuous flows.

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 Study on flood flow and bed variation analysis for rivers with steep slope are few in spite of the importance. This paper studies a method to give the upstream boundary conditions to calculate flood flows and bed variations in the Hime River, evaluating the inflow discharge and sediment supply from the upstream by using several observed water level hydrographs and observed bed variation. The method proposed for the bed variation analysis in stony-bed rivers is applied. This paper presents the framework for calculating flood flows and bed variations using time series data of water surface profiles during a flood in a steep slope river.

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 Numerical methods for 1D unsteady flow analysis and discharge and roughness coefficient estimations using time variation of water level in channel with arbitrary shape were constructed. These methods used 1D shallow water equations as governing equations, method of characteristics curves and flux-difference splitting scheme as a numerical technique. The stage hydrographs were used as boundary conditions at up- and down-stream for 1D unsteady flow analysis. The time variations of water surface profile were used as input conditions for the estimations. These methods were validated against numerical results of non-uniform flow and experimental data of non-uniform and unsteady flows in expanded channel. It shows that proposed methods can predict the discharge hydrograph and the estimation method can predict the roughness coefficient with reasonable accuracy.

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 This paper presents a practical forecasting method for water level in sewer by using a machine learning. A physical model is usually used to calculate water levels. However, it takes a lot of time to calculate them. This is a serious issue for sewer management in real-time in an emergency. In this paper, this issue is solved by using the machine learning. In addition, we proposed hybrid forecasting which also learns the results of physical simulation because the machine learning cannot predict unprecedented case. As a result, the calculation time and accuracy in proposed forecasting are improved.

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 A 1D unsteady flow analysis method and an estimation method for discharge and Manning's roughness coefficient using time variation of water level in rectangular channel were constructed. These methods were based on 1D shallow water equations and its characteristic form. The time variation of water level was used for 1D unsteady flow analysis as boundary conditions. The time variation of water surface profile was used for the estimations as input conditions. These methods were verified against numerical results of non-uniform flow and experimental data of non-uniform and unsteady flows in rectangular channel. It shows that proposed methods can predict the discharge hydrograph and the estimation method can predict the roughness coefficient with reasonable accuracy.

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 In this study, we developed a hydraulic analysis method using particle filters in order to improve the estimation accuracy of the hydraulic phenomena of a river channel network. This method enabled us to estimate the time-space fluctuation of conveyance and the time-space distribution of the water level and discharge using the observation information. First, we verified the validity of the method by twin experiments and considered the differences in observation information which are used in particle filter. Next, we verified the efficacy of our developed analysis method by applying flood flow in the lower basin of the Shinano river channel network.

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 Considering the dynamic boundary condisition at free surface (zero tangential stress) was the fundamental problem for applying the General Bottom Velocity Computation (GBVC) method to the flow over hydraulic structures with large water surface deformations. The zero tangential stress condition causes generation and flux of vorticity at the free surface. We formulated these processes and developed GBVC-FSV method. GBVC-FSV method was applied to the flow over a vertical sill. A comparison with the results of GBVC method indicates that GBVC-FSV can calculate the flows with large water surface deformations more stably.

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 To measure velocity distributions around a microbe, the three dimensional Particle Tracking Velocimetry (3D PTV) with a differential interference contrast (DIC) microscope and a single camera has been developed. In this method, the properties of out-of-focus image of a particle are used for estimation of distance from particle to focal plane. In the out-of-focus image of the particle, a ring like image is generated around the center of the particle image and the diameter of the ring like image increases with the distance from the particle to focal plane. Experimental results show that the diameter of the ring like image is proportional to the distance from a particle to the focal plane. The proposed method has been applied to measurements of three dimensional motion of particles around an Euglena in water.

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 Although there are many researches regarding strip roughness effects on flow resistances, researches under shallow flow conditions have been rarely conducted. In this study, we conducted shallow water experiments by varying roughness spacing, bed slope and the Reynolds number, and categorized water surface patterns into 4 patterns, that is, Flat surface, Nomal Jump, Periodic hydraulic Jump, and 3-Dimensional standing wave. In addition, we successfully showed region segmentation figures for each water surface patterns by using SVM(Support Vector Machine) algorithm. This approach enables us to estimate water surface patterns approximately.

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 Authors have already formulated energy loss coefficients of the three-way circular drop manholes in consideration of six dimensionless variables for structural elements of pipes and manhole, and hydraulic parameters. However, any calculation formula of the energy loss for drops between two opposed inflow pipes and an outlet pipe has not existed yet. In this study, the energy loss for a three-way circular manhole with drops between two opposed inflow pipes having different diameter and an outlet pipe was examined. From the experimental results, the influence that drops between the inflow pipes and the outflow pipe and the water flow velocity of an inflow pipe gave, to the pressure head of another inflow pipe was clarified.

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 The riverside concavity zone is often buried by substantial sediment deposition. In this study, a training dike is equipped just upstream entrance of a concavity zone in order to suppress and remove the sand deposition. The effects of a training dike on flow structures and sediment deposition in a side concavity were investigated numerically and experimentally. The length, orientation angle and location distance of the training dike were changed and their influence were examined. The amount of deposition in a concavity was reduced in almost cases by the effect of sweeping flow produced by the training dike, but it happened to be increased in bed-load dominant cases. With an increase of the angle and the velocity strength of induced flow by the training dike, the deposition in a concavity zone becomes small.

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 This study utilizes pressure sensors embedded in the model bed material placed in the river bed to estimate the pressure distribution around the bed material. As a proof of concept, two pressure sensors were utilized in this study. Channel experiment was conducted to understand basic characteristics of the proposed method. Field measurement in a cobble-bed river during a small flood was conducted and time-series change of pressures in the upstream and downstream side of the model cobble were analyzed to discuss turbulent fluid force acting on the bed material during the small flood when the bed cobbles were immobile but smaller fraction of bed material was partially transported.

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 Scouring or depositing downstream of submerged weirs with an opening is a sediment phenomena resulting from the interaction of the three-dimensional turbulent flow field around the structure and the moveable sand bed. This paper presents the experimental study on the downstream channel bed due to weir with an opening, paying attention to the effects of relative overflow depth on local scouring around the structure, sand bars and three-dimensional flow patterns. The experiments were conducted under the clear-water scour condition for an equilibrium scour hole. The experimental results show that local scouring and sand bar development downstream of the submerged weirs decrease with relative overflow depth and turn out strongly paired cellular secondary currents.

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 The characteristic of the lateral over flow was investigated with the curved channel which has the constant radius of curvature R. the curved channels with R=0.50m and 7.0m were used. The main results obtained from this experiments are as flows; (1) The lateral over flow discharge is proportional to the power of the over flow depth. The power is around 3/2 if the lateral wire is set near the entrance of the curve channel. The value of the power decrease as the location of the lateral wire is installed downward. (2) the ratio of the lateral over flow discharge with the inflow discharge does not well depend on the location of the weir from the entrance to the middle part of the channel. In downstream wise from the middle the ratio decreases. (3) The ratio of R=0.50m is larger than that of R=0.70m. (3) We applied the lateral discharge formulation we proposed in 2016 to the experimental data. It has a good accuracy except near the entrance and the exit of the curved channle

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 In flood flows of curved rivers, a risk of the river bank and the bed erosion are increased. To avoid the risk, it is necessary to control the primary velocity. In this study, four types of zigzag roughness, which are upward step type, downward step type, vertical type and composite type, were focused. Characteristics of the velocity profiles of the curved channel flows with zigzag roughness were investigated using an electromagnetic velocity meter. The results indicate that individual velocity profiles are formed corresponding with zigzag roughness. The four types of zigzag roughness contribute to a low speed region near the side wall and secondary current. In particular, it is possible that composite type roughness can avoid a contact with high speed fluid to the water colliding front and the outer bank of the curved channel.

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 For the hydraulic design of steep stepped channels, it is important to elucidate the aerated flow characteristics of skimming flows in nonuniform flow region. An analytical equation for calculation of the aerated flow depth is developed for the nonuniform aerated flow region, and the surface profile and specific energy are calculated using this equation together with the continuity equation for the air phase. For a wide range of channel angles and relative step heights, the results agree with the experimental data both for uncontrolled inflow and pressurized inflow conditions.

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 In this paper, the roll waves flow velocity and periodic properties are reported based on the experimental results. The internal velocity profiles were measured using the PIV technique and the surface elevation were also measured by the ultrasonic distance meter to examine the periodic properties. The velocity profile of the roll waves flow is faster than the log-law profile. The dimensionless velocity gradient which calculates from the roll wave period, shear velocity and viscous sublayer thickness has strong relationships with Re number. Furthermore, the wave celerity of the roll waves shows like free fall phenomenon.

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 Water levels and flow velocities in the vicinity of model spur dikes were measured in a laboratory flume under clear-water overtopping and non-overtopping flows. Spur dike height and flow depth were varied in the experiments and found to significantly influence the distributions of the flow velocity. For overtopping flows, the ratio of the flow depth to the spur dike height was found to be an important control on the water level and flow rate reduction near sidewall. A preliminary technique is proposed to predict the water level and flow velocity for spur dikes perpendicular to the bank.

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 The present study focuses on a DO recovery process in wando zone connected to a main-channel. Our field survey results in that the DO is larger in opened condition to the mainstream than in closed condition. This implies that mass exchange between the mainstream and the wando is significant to maintain proper water quality. Hence, we conducted laboratory experiments in which time-variation of the DO value and horizontal velocity vectors were measured in the model wando, and proposed a prediction formula of the recovery time related to reaeration through free-surface and DO supply from main-channel.

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 The cavity zone along riverside is expected to produce native habitats of various ecosystems and water-friendly environment. However, effects of side cavities on flow resistance and turbulent flow structures are ambiguous. In this paper, effects of aspect ratio of side cavity on open-channel flow with submerged permeable and impermeable side cavities were examined experimentally. Velocity fluctuations were measured by using a particle-image-velocimetry (PIV). We revealed the flow resistance could be explained by the difference of momentum transport through the interaction between the side cavity and main flow region. Moreover, we clarified that the momentum transportation form shows strong three dimensions in the overflow casese compared with the non-overflow casese.

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 We tried to develop climate class due to external load database on climate change. And It used verification of Japanese reservoir water index(Eutrophication frequency ratio, and turbidity) to find out relation to external load production.
 Dtail resuts are as follows: 1) There is a lot of external load at Bload-leaved deciduous forest, Plannning area. 2) The external load volume show a weak association between eutrophication index. 3) The external load volume correlate strongly with turbidty.

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 In this study, to examine the affinity of sand color in basins-scale, field observations, image analysis and hierarchical cluster analysis were conducted. Sampling sites were 29 rivers and 42 beaches around the Kii channel, Kinki region, Japan. It is confirmed the rare sand color such black can be tracking factor for sediment transport in this area. Moreover, it is clarified at least 5 color indexes are required to present the trend of sand color in this area.

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 Most bedlaod discharge rate is evaluated using effective friction velocty. The effective friction velocity is introduced imaginary, therefore, the values and bedload discharge which uses the values have been not evaluated in a river. There are two reasons, one is that bedload discharge observation is conducted in a point and short time, the other is that there is no method to evaluate effective friction velocity in rivers. In this paper, method to estimate bedload discharge and effective friction velocity using bottom track velocity measured by aDcp and Egashira's bedload discharge rate is proposed. Two measurements are conducted to validate our method, sand pit measurement and sand waves measurement. In former measurement, the method is validatd by comparing with deposited bedload volume. In latter measurement, the method is validated by comparing with bedload discharge estimated by migration speed and height of sand waves.

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 This study aims to analyze hydraulic resistance with field observation data obtained by acoustic Doppler current profilers. We focused on the τ*-τ*' relation proposed by Kishi & Kuroki, and compared it with the observed data. They showed a quite good agreement in the Hime river and the Chiyoda experimental channel. In addition, the τ*-τ*' relation and the observed data in the Shinano river also showed a reasonable agreement although they have a bit difference in terms of the slope of the τ*-τ*' relation. One of the reasons of the difference is likely to be the value of R/d in the field which is much higher than that of precedence researches. In contrast, observed data in the Jamuna river and the lower Mekong river showed a totally different tendency from the τ*-τ*' relation. It is inferred that high concentration of suspended sediment and high R/d value cause the difference. To conduct a prediction of roughness in the Jamuna river and the lower Mekong river, a new τ*-τ*' relation was derived with the observed data. It is showed that the new τ*-τ*' relation is capable to predict roughness coefficient reasonably by taking R/d into consideration.

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 The authors constructed the Rainfall Runoff Inundation and Sediment transport model (RRIS) with implementing the sediment transport and riverbed elevation change to the RRI model. In order to verify the RRIS model, the authors applied the model to the Kawamata Dam catchment. The Kawamata dam experienced the heavy rainfall by typhoon, which cause the Debris flow. Because of the Debris flow, large volume of sediment accumulated in the Dam lake as well as the catchment. Before and after the rainfall event, sediment runoff characteristic changed. This study is the first attempt to try to simulate this kind of sediment runoff caracterisits. For this purposes, authors selected the one of the largest event, and simulate the sediment runoff processes. The authors successfully conducted the numerical simulation, and correlated the relation between volume of the sediment runoff and the sediment size distribution.

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 The presence of polders in southwestern Bangladesh leading to gradual silting up of rivers which, in turn, has resulted in serious waterlogging rendering large tract of land uncultivable. The current practice to solve this issue is temporarily de-poldering by cutting embankment. It allows natural movement of sediment-borne tidal water into a selected beel known as tidal basin and allows deposition of sediment. Sedimentation determines the life span of basin and the rate of raising the land. It is essential that better understanding of sedimentation process is required. One significant hydraulic fact is that the faster the flow is, the more sediment it can carry with it. One of the key governing factor of the flow is opening size of link canal. In this research, attempts have been made to inspect the effectiveness of tidal basin management investigating different opening sizes of link canal through laboratory experiments and preliminary numerical simulation. Our finding shows sediment carrying capacity is a function of velocity. Moreover, only increasing the opening size of link canal will not allow more sediment to deposit in selected tidal basin. It is also found in experiment that near the embankment, where tidal flow enters during high tide and leaves during low tide, vortex like formation tries to erode the material which in real case also happens. Developed numerical model has good agreement with experimental results and can be used to better understand effectiveness of tidal basin management.

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 Streamwise canyon of the roughness layer in armored bed of the dam-downstream river actually relates to the movement of sand. Wind tunnel experiments were conducted by changing the spacing of the rib structure of the roughness to clarify the bottom shear force in the streamwise canyon where flow is accelerated. The result shows that when the spacing is large, velocity near the bottom is high and the velocity is in logarithmic distribution. On the other hand, when the spacing is small, the velocity is in dog-legged distribution. The result indicates that separated eddies from the rib structure could narrow the flow accelerated region in the streamwise canyon. In addition, the average values of the shear force correction coefficient k have been obtained from 1.0 to 0.8 by using observed friction velocity and calculated one, and by calibrating the amount of bed load transport.

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 While sediment is needed to build aquatic habitats and reintroduce nutrients for submerged vegetation, too much sediment can easily cause ecosystem and safety issues. Sediment buildup can damage the drainage ability or navigability. In addition to the problems cause by load quantity, sediment can easily introduce pollution and other contaminants into a waterway, spreading the pollutants downstream¹. As contaminants do not degrade (or degrade very slowly), they can be a source of environmental issues for long periods of time, even if they are not frequently resuspended. The most problematic contaminants in both bedded and suspended sediment are metals and persistent bioaccumulative toxics (PBTs), such as pesticides and methyl mercury². Sediment remediation may involve dredging to remove the deposited and contaminated sediment from the waterway¹. The dredging method has some disadvantage points like it costs a lot of money or it cannot be used in urgent cases, therefore a new method which can encounter those disadvantages should be developed. A new tool, which named “Bamboo Spike Ball” or “BSB”, is invented with the hope that it can remove sediment in a cheaper cost and can be used in urgent cases. BSB basically is designed by using stone, clay and bamboo which are cheap and eco-friendly materials. Bamboo spikes are tied surrounding stone in a sphere shape so that BSB can roll along the channel by flow force effect. PIV technique was used to figure out the effect of BSB to erosion characteristic on bed. The result showed that while BSB was rolling, under the effect of the collision force of BSB's spike and turbulent flow caused by BSB's structure, significant amount of sediment was removed in compare with case which river bed is affected by flow only.

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 Mixed-size debris flow impact against a vertical structure was simulated by a numerical movable bed channel. The simulation result brought that the average impact on the structure was affected by the gravity force on debris flow deforming in front of a structure as well as the momentum flux of debris flows coming from the ustream. Momentum flux of the simulated debris flow varied moderately with respect to time. However, the particles of simulated debris flow segregated while flowing down and large particles gathered around the front of the flow. The frequency of large impact of particle collisions was therefore high in the initial stages of the impact and become low immediately due to decreasing of size of coming particles. It was clarified from differences of vertical velocity between moving large particles and small particles that large particles moved upward actively where the flow surface transitioned to mild slope in the downstream direction.

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 A new approach to simulate the mass failure process in riverbanks is developed and verified by experimental work. Both planer and circular failure modes can be expressed by this approach. The proposed approach is capable of distributing the collapsed bank material. Failure mechanism of riverbanks is described, failure plane is determined, shape of collapsed material is proposed, and travel slide distance is estimated. Eight experimental cases were conducted to investigate the processes of mass failure that follows the hydraulic erosion of an artificial riverbank with different heights and slopes. Deformations, developed cracks, plane of failure, and shape of deposited material were recorded. It is watched from experimental results that there exist many cracks are developed and thus many planes of failure are found, while in numerical simulation only one failure plane exists. The difference between simulated and experimental results may return to the large deformation of collapsed bank material which can't be simulated by simplified assumptions. Further improvements to the proposed approach are needed.

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 Dike failures are recently occurred during floods, and cause sever damages. For disaster mitigation, it is of great importance to reproduce dike failure process accurately and consider countermeasures. The objectives in this study is to develop a numerical model to predict the dike failure process due to seepage flows. By coupling the open channel flow model to simulate simultaneously overtopping and seepage flows around a dike with the soil deformation model based on GIMP method, a numerical model is proposed. Moreover, a hydraulic experiment is carried out and the applicability of numerical model is examined through the comparison with the experimental results.

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 Rivers in Japan are so steep that urban cities where the human and material assets are concentrated are exposed to the crisis. In order to reproduce the levee breach with numerical analysis, we tried to investigate it experimentally, in which the body of levee is contained cohesive sediment. Two series of movable bed experiments were conducted about simulated levee breach with cohesive sediment by overflow. As a result of this study, we found that the process of erosion and collapse of sidewalls along the flow passage are different between sand levee with cohesive sediment and that without it. Finally, it becomes clear that downward erosion and lateral one are affected by cohesiveness being related to each other closely.

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 Natural bedrock channels show diverse erosional morphologies. In this paper, we study experimentally the formation process of multiple incisional grooves which is not been investigated yet. We conducted flume experiments, the flume consisted of weak mortar to imitate bedrock. The mortar bed is eroded because of abrasion caused by saltating sand. We observed the relationships among the groove number, the water depth, the bed slope and the distribution of lateral flow velocity. We also focused on the merging process of multiple grooves.
 Our experimental results indicate that the groove number depends on water depth, but does not depend on the bed slope. The multiple grooves are formed due to turbulence-driven secondary flow. Since the size of secondary flow cells scales with water depth, it is reasonable that the groove number per channel width would also scale with water depth. There are two patterns in the merging process; one is caused by the fluctuation of bedload direction, the other is caused by lateral bank erosion of multiple grooves.

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 When the layer of soft rock which exists under a gravel bed is exposed at river beds, the degradation speed of bed becomes very high. In recent years, river structures have been become unstable due to erosion of soft rock bed. A linear stability analysis is conducted for understanding the bed shape of soft rock rivers. The stability analysis in this paper reproduced the bed configuration of soft rock partially covered with sediment. It is found that the wavelength of the bed configuration of soft rock partially covered with sediment becomes long compared with the wavelength of an alternate bar.

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 Understanding the differences between characteristics of alluvial and bedrock meanders is the need of hour. In this paper we have performed some numerical calculations in order to, first make an effort to observe the change in migration of bedrock channel in response to change in sediment cover and sediment feed rate. After realizing how sediment availability effects bedrock meanders, we tried to compare characteristics of alluvial and bedrock meanders under similar hydraulic and physical conditions.

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 To understand more detailed phenomena from our previous study on bedrock exposer expansion under condition that bedrock is smooth and alluvial cover thickness is about half of bar height, flume experiments were conducted. In the case that bedrock was smooth and flow was maintained for longer hours than our previous study, the result showed that bedrock exposures along bar front were expanded to downstream on mid and upper side of flume and bedrock exposers along bar front were reduced on lower side of flume. This phenomenon was also confirmed by our previous study. Thereafter, new bars were developed on the upper end of flume and this new bars development caused exposing bedrock along bar front and these new bedrock exposers expanded to downstream. As this new bedrock exposer expanded to downstream side, expanded bedrock exposers on the immediate downstream of new bedrock exposers reduced. Thereby, as characteristics of bar wave lengths under condition that alluvial thickness is thin and bedrock is smooth, bar wave length is not stable. In another case that bedrock was as rough as alluvial cover materials, the results showed that bedrock expansion was reduced in comparison of the previous case. However, bedrock exposer rates were not notably different because total length of alternate bar is almost same between each case.

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 Degradation of exposed bedrock takes place in many rivers worldwide, posing problems of current high interest for river management. Erosion in bedrock rivers is often caused by abrasion from moving sand particles, which is directly linked to the distribution of the alternating zones of exposed bed rock and bed covered with sediment. Erosion by abrasion is active only in a portion moderately covered with sediment. Where there is no sediment and bedrock is completely exposed, no abrasion takes place. And where the bed is fully covered with sediment, no abrasion takes place as well because of the cover effect of the sand.
 In the present work, we study experimentally the occurrence of bed degradation in an annular covered flume flow with a simulated bedrock. In curving bedrock channels, due to secondary flow, sand accumulates in the inner bank while the bed is exposed in the outer bank. In the experiment, patterns of topo- graphic changes along the bed could be observed. We correlate the experimental results with expected flow patterns and erosion processes.

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 In the upstream of Ishikari River whose riverbed is formed with gravels on the soft bedrock, recently, the sudden riverbed degradation has been observed, which may cause damages on revetment works and bridge piers, or losses of sermon`s spawning beds. Therefore, the Asahikawa Development Department which manages the river has conducted some hydraulic experiments to establish a countermeasure for the riverbed degradation.
 While the former experiments clarified the effectiveness of the countermeasure, the authors, for further study, conducted an experiment which reproduces soft bedrock erosion. The experiment consists of two stages, which are the pre-experiment for choosing the soft bedrock material to reproduce the one on site, and the large-scale experiment to evaluate the countermeasure. The experimental results indicated that the countermeasure is safe against the bedrock erosion, and the erosion encourages roughness jump and sand deposition.

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 The new waterway projects such as shortcut and gravel extractions have been carried out all over the country. The shortcuts have lowered river water surface elevation at the time of flood and they suppress the flooding. On the other hand, the riverbed elevations rapidly decrease due to bed slope changed artificially and canyons are formed in several rivers. However, little is known about how riverbed degradation occurs or how the canyon is formed by change of the bed slope. In this study, we conducted numerical simulations to evaluate the deformations of alluvial bed and peat bed in bed slope being changed. The results suggest that the bed slope become constant on the alluvial bed and the erosion proceeds at the bare peat bed, they also propose the upstream migration of the peat bed slope is what forms cyclic steps morphology. Moreover, we carried out numerical simulation of reproduction of Yubari river bed degradation by shortcut. We confirmed the possibility of the reproduction using the peat bed model.

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 The Kako River flows through Hyogo Prefecture. The influence of runoff due to barrage water and the Mino River tributary, combined with a meander in the river upstream from the large barrage on the Kako River (Kakogawa Barrage), has promoted the development of a sand bar on the river bank opposite the confluence. The sand bar, which has hardened, currently deflects the passage of water back to the left bank and has decreased the usable water surface area of the river. The objective of this study was to survey the river topography in the vicinity of the Mino River confluence and identify the factors responsible for sand bar development. In addition, movable-bed modeling of the channels at the tributary junction was performed to assess the influence of the barrage water and the river meander upstream on river flow, and to consider the effect of the spur dike installed for control of a sandbar. The numerical calculations were analyzed using the two-dimensional flow analysis software, Nays2DH, to verify the experimental results and to investigate how they can be applied.

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 Recently, technology of numerical simulation has developed. Numerical simulation can describe sediment transport and flow around sand in detail. However, these simulations are difficult to indicate the sediment flow along river, because much information and heavy simulation are needed to calcrate in. Numerical simulation method for mixed sediment transport which used in much of previous studies is still useful in order to grasp sediment movement along wide area.
 One of problems in conventional simulations for sediment transport is that it is not able to describe sediment transport in both flood stage and low flow stage. So this paper treated simulation method for calculating sediment transport by using the rate of volume occupation of sand and cobble and water without fixed porosity.

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 In the gravel bed river, serious damage of such as levee failure may be caused by lateral bank erosion with the channel change. Therefore measures to control the channel widening are often carried out by setting such as the low-water channel revetment. However, some influence of channel widening restriction on the characteristics of channel plane is not clear yet. In this study, we examined focusing on the influence that the sediment supply is insulated from the bank when restraining channel widening by the fixed wall. Our movable bed experiments showed the process of increases in the watercourse wavelength along the bank by the influence which has no sediment supply from the bank, and the possibility that the quantity of sediment supply from the upper reaches reduce or promote that influence.

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 The objectives of this research are to confirm the floodplain vegetation distribution on braided channel and its effects on channel morphodynamics by means of laboratory experiments. The results showed that high density vegetation on sandbars led channel decreasing and meandering as well as previous researches. In contact, when seeds were distributed by flow from the inlet section of the flume, seeds were settled in wide areas on sandbars and formed longitudinal vegetation-patches lines. These vegetation patches changed channel formation much complicate due to the increasing in the number of small scale channels. This mechanism could be one of the process to form a bed morphodynamics called Island Braiding.

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 This study presents sediment transport characteristics and sediment related problems in the Ayeyarwady River first and the proper use of dikes to keep the navigable flow depth in a main channel of braided channels is discussed. The study reach is 25 km long around Mandalay City along the Ayeyarwady River in Myanmar. The depth integrated two dimensional bed deformation analysis has been performed to understand the change of the flow pattern and bed deformation characteristics in braided channels. The bed deformation analysis is carried out under two conditions such as with dike and without dike installation. In case of the simulation with dikes, installation of the dikes in bifurcated channels is effective to suppress the temporal change of the main channel which is used for ship navigation. It is considered that these dikes would be effectively reduced the dredging frequency.

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 In the Hii River with braided channels, developments and deformations of sand waves during a flood affect flood flows and sediment transports. The Hii River floodway has a settling pond at the river bifurcation point for reducing sediment discharge to the downstream. For managements of the Hii River bifurcation section and the floodway, reduction of inflow sediment discharge into the floodway is required. The General Bottom Velocity Computation method was employed for computation of flood, which took account of time series of observed water surface profiles. We estimated flood discharges, bed variations and sediment transports in the river bifurcation section and the floodway during the flood of Sept. 2012. In addition, we propose reduction measures of inflow sediment discharge into the floodway.

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