Many researches on non-contact flow velocity measurement methods such as radio wave velocity meters and image analysis have been conducted as a method of measuring the flow velocity and flow rate. However, preliminary maintenance is indispensable, and diffusion has not advanced as it is being developed. In the rainstorm of the northern Kyushu in 2017, the intermediary mountainous area was damaged, the river surveillance camera and the water level gauge were not installed and the flow velocity was unclear. Therefore, we focused on motion pictures taken by residents and conducted a study to estimate the flow velocity.

 In this study, the flow velocity was estimated from the motion picture taken by the residents of the disaster area using two methods, the float method and the weir raised height. As a result, it was found that it is possible to estimate the flow velocity using moving pictures taken by residents. However, with regard to values such as falling distance, it is necessary to examine a method to obtain accurately and to increase the accuracy of the estimated value.

 This paper examined a machine learning technique with the wavelet transform for classifying land cover conditions in UAV (Unmanned Aerial Vehicle) images of a riverine landscape. The UAV images were taken in a river course of Kurobe River, Japan. The UAV image analyzed was composed of a RGB, NDVI (Normalized Difference Vegetation Index), and a DSM (Digital Surface Model) of the river geomorphology made from a SfM (Structure from Motion) image processing of the UAV images. In a pro-processing of the machine learning, the DSM was decomposed into the low/high wavenumber components by a wavelet transform, and further its edges were extracted for effectively utilizing the hight difference information in DSM. The result of the machine learning showed that the F-measure had high enough above 0.91 in the dataset including all characteristic values from RGB, DSM, and NDVI into the machine learning algorithm.

 The validity of hydraulic computational results is closely related to the observed information and the analysis model. However, there are few study cases relationships between the density of observed data and the accuracy of computational results.

 In this paper, by using the elevation of numerical computational mesh in the general coordinate system which was made from three different densities measured by ALB, we discuss the measurement density of elevation for hydraulic computational analysis. Next, it was shown that the estimated hydraulic values and identification parameters to data assimilation in a Tone River reach changed according to the difference of the space density of the observation sites of the water level during the flood in October, 2017. We discuss the space layout of observation site for the data assimilation to the time-varying longitudinal water level distributions.

 The space-time image velocimetry (STIV) technique is one of the image-based techniques for measuring river flow rate using video images. However, there are cases where adequate measurement accuracy is difficult to maintain depending on the shooting conditions of the river surface, and robustness has been required as a measurement system. In this research, we classified factors that cause measurement errors into ten types and developed image filters mainly based wavenumber-frequency spectrum to improve the texture quality of STI. It was made clear that quality of STI can be remarkably improved with the filters and contribute to the robustness improvement of the measurement technique.

 In order to improve the accuracy of river discharge estimation, an anemometer, a radio anemometer and ADCP were used to obtain the data of wind speed, surface velocity and vertical velocity profile of the river. Field observations were conducted soon afeter the arrival of typhoon at the Goryo Bridge of Tone River. From another data set at the Heisei Bridge of Tone River, the roughness parameter z0 was evaluated by using the U2.25 which was the wind speed on the bridge. The deviation between surface velocity by using the radio anemometer and horizontal velocity at the highest layer of vertical velocity profile by using ADCP was defined the wind-driven current component. In conclusion, the linear relationship of ⊿u = 0.114*U10 was obtained.

 The authors proposed a calculation method of the bed load discharge using the bottom track velocity measured by ADCP and this study verified the effectiveness of the method by conducting an experiment with movable bed. First, we confirmed that the bottom track velocity measured by ADCP represents the sand velocity on the riverbed by using the STIV method. Next, a measurement method of the time variation of the sediment volume accumulated at the downstream end by SfM method using the interval photographed images of five digital cameras within 5% of accuracy was developed. As a result of the experiment based on these findings, the effectiveness was clarified since the time change of the bed load discharge estimated by the authors method and the measured value by SfM method roughly agreed.

 The sieve test is used to measure the grain diameter of bedload. However, the transportation of gravel from the field to the laboratory is expensive. And it has safety problems at torrents. We proposed an indirect grain diameter measuring method using contact time based on slope experiments, hydrostatic experiments and flume experiments. The contact time is the time during which the gravel is in contact with the elastic body. It was showed a relationship between grain size and contact time from these experiments. We clarified measurement characteristics of gravel number under slope experiments and flume experiments. Grain size distribution of bedload was shown qualitatively by using the equation of relationship between grain size and contact time considering experimental range.

 Despite the great success of the research of bedform morphodynamics, the three-dimensionality of the bedforms have still not been understood deeply. In this study, we perform numerical simulations of three-dimensional (3D) river antidunes using a combined model of a Boussinesq model, which is a depth-integrated hydrodynamic model with the non-hydrostatic effects, and a non-equilibrium bedload transport model. The model performance is tested with the experimental results of 3D antidunes. The results show that the model reasonably calculates the formation and development of 3D antidunes and subsequent formation of standing water surface waves. In addition, the results show a coexistence of the two different bedforms, namely, free bars and 3D antidunes. Some limitations of the model are shown, namely, the model can not reproduce the downstream-migrating 3D antidunes.

 This study examined the influence of turbulence model on 3D numerical simulation of sediment release from a conduit gate. The numerical model was validated in laboratory test and on-site test of sediment release. Comparison with measured flow velocity around a conduit inlet revealed that the k-ω SST model performed better than k-ε mdoel that is often used for turbidity transport simulation. The numerical simulation of on-site test showed that the buoyancy modified k-ω SST model is able to successfully suppress numerical diffusion of turbidity around water-turbidity interface. In addition, the buoyancy modified k-ω SST model was found to capture well the dynamic behavior of water-turbidity interface.

 The stability of river-bed structures near water drop works, is affected not only by the river flow forces but also seepage flows and seepage pressures, especially sucking out of fine soil grain due to seepage pressures diminishes foundation strength. In this study, we developed hydraulic and geotechnical modelling to evaluate stability of foundation around water drop works. Numerical modelling and Laboratory experiment facility were set up for the studies. It is shown that the stability can be evaluated with fluid force acted on the body, and/or seepage failure of ground.

 In recent years, river-bed degradation is proceeding in rivers. The river-bed degradation causes deterioration and damage of river crossing structures, such as weirs and groundsill, with backward facing step, and as a result, it is feared that bed protective works will be washed away due to a large flood flow. This study presents a preliminary approach to elucidate the fracture mechanism of river crossing structures using numerical 2-D simulations of undular jump and submerged jet flows under the fixed bed condition. The explicit moving particle simulation (E-MPS), which is one of the particle methods, is used in this study. In the E-MPS, the implicit computational scheme of the MPS for the pressure Poisson equation is solved by explicitly. The corresponding experiments are performed to investigate the applicability of the E-MPS method to the river hydraulic simulation. The results show that the E-MPS method may have a potential to demonstrate the flow characteristics of both undular jump and submerged jet flows.

 Accuracy and efficiency of a numerical approximation to the Basset history force that is the most time-consuming contribution in the so-called Maxey-Riley equation [van Hinsberg et al. J. Comput. Phys. 230 (2011) 1465] has been critically examined. An emphasis is placed on the impact of a time scale t_w on the simulation results. Compared with the traditional window method where the Basset integral is evaluated only over the latest period of size t_w, the method of van Hinsberg that approximates the tail of the Basset force kernel by exponential functions is found to give a better result by using a much shorter t_w. Since the prediction accuracy is quite independent of the choice of t_w, the method has a clear superiority to the traditional method in providing an accurate prediction with much less time and memory requirements.

 This study develops a numerical model for large wood dynamics in a braided river considering the root wad effect and anisotropic bed friction. The newly developed numerical model can precisely simulate the behavior of large pieces of wood using a 2-dimensional depth-averaged Eulerian flow model that calculates the water flow and bed morphology. We developed a Lagrange-type wood transport model and combined with the flow model, and the applicability of the combined model is examined in a comparison with experimental results. From the simulation results, we quantitatively calculate the Active Braiding Index (ABI), Bed Relief Index (BRI), and averaged values of deposition position and deposition angle. We then analyze the relationship between the bed morphology responses and the wood deposition patterns in terms of the root wad effect and input supply. The proposed model reproduces the prominent features of the flume experiment, indicating that the present numerical approach can clarify and predict the behavior of large pieces of wood in accordance with the bed morphology.

 This study conducted numerical simulation of 3-dimensional flow around the inverted syphon, in which upstream water level exceeds a design level. The results showed generation of a separation vortex near the top wall of the upper reach of culvert and indicated possibility of a huge head loss at this portion. As the result of comparative simulation of several proposals for improvement, we found that water conduction capacity of the inverted syphon was improved greatly, by chamfering the top wall of culvert inlet, at this chamfer, a part of upstream transition near the culvert was modified to closed type and its cross sectional area of flow was reduced gradually toward the culvert.

 In this study, a three-dimensional numerical wave tank “CADMAS-SURF/3D” with VOF method was improved for evaluating sloshing behavior and hydrodynamic pressure inside the reservoir generated by earthquake. Model experiments and numerical simulations were conducted in order to examine the validity of the numerical model.

 The experimental results revealed that the magnitude and vertical distribution of the hydrodynamic pressure are different depending on the relationship between the natural frequency of the reservoir and the earthquake frequency. The numerical model proposed in this study was shown to be able to reproduce the laboratory experiments appropriately.

 Flash flood forecasting is indispensable to construct efficient warning and mitigation of the increasing threat of flash floods in wadi systems. Flash floods modeling in arid region is hindered by the lack of appropriate hydrological models and data availability. Rainfall-Runoff-Inundation (RRI) model is applied in Wadi Samail as a case study for the most extreme flash flood events in Oman (1,000 year return period). Detailed sensitivity analysis were conducted for RRI model parameters indicating that the channel and hillslope roughness coefficients are the most significant parameters followed by the soil characteristics parameters such as soil depth, porosity and hydraulic conductivity. The most severe tropical cyclone in the recent history in Oman, Gonu-2007 and Phet-2010 were used to calibrate and validate the hydrological model. The results and the statistical analysis indicating that RRI model could efficiently simulate the extreme flash flood events in the arid wadi system. Where for model calibration, Nash-Sutcliffe efficiency (NSE) and Percent bias (PBIAS) indices equal to 0.93 and -14.3, respectively, and for model validation NSE and PBIAS equal to 0.86 and -12.0, respectively. Further improvements in RRI model is recommended to include the transmission losses and groundwater processes for better representation of the wadi system.

 A new numerical model for two-dimensional rainfall-runoff and flood-inundation flow analysis was constructed and dynamic rainfall-runoff and flood-inundation analysis of Akatani river basin in Kyushu-hokubu heavy rain in 2017 was performed by the model. A new procedure for a dry/wet boundary over a topography is incorporated into the model based on FDS(Flux Difference Splitting) solver. The model was also verified against observed water level and maximum inundation area. It showed that the proposed model can reproduce it with reasonable accuracy. A rainfall-runoff and flood-inundation process and were also examined based on the numerical results.

 This paper presents a new parallelization technique (DBA method) that is effective for large scale solid-liquid multiphase simulations in complex boundary geometries. This technique assigns plural blocks to every processing element and dynamically changing the assignment to balance computation load of processing elements. Simulations were performed on falling particles in the water and air by using the DBA method and the SB method that assigns a single block to every processing element. Computation efficiency of DBA method was examined from these simulations. The results showed that the SB method statically assigned computation resources to blocks of small computation load that made great load unbalance, while the DBA method reduced the load unbalance by dynamical changing block assignments to the processing elements and became faster than the SB method.

 Recently, renewable energy is required to diffuse due to energy situation. A project to install hydroelectric power plant was performed in order to effectively utilize unused energy in factory. This project has compared the performance between actual water turbine and model, and verified the accuracy of performance prediction for water turbine based on hydraulic model experiment. In this stady, 3D printing technology was applied to the production for water turbine model, and the accuracy of performance prediction were verified for actual water turbine based on hydraulic model experiment with 3D printing models. As a result, It was confirmed that the 3D printing model was freely produced complicated shapes which were difficult to reproduce by metal processing. Also it was possible to reduce the effort by using 3D printing technology. On the other hand, from the result of the comparison for the turbine performances, it suggested that the shape of model hardly affected the turbine performance, but the weight of model greatly affected.

 Countermeasures against an intake vortex are necessary to prevent problems such as a vibration of a water turbine generator in hydroelectric facilities. In order to study effects by position of the inclined wall, flow fields in the vertical intake facility with inclined wall have been measured by a visual observation and Particle Tracking Velocimetry(PTV). As a result, it is found to be important that whole flow fields are stabilize by the inclined wall and the space between the inclined wall and the inlet of the vertical pipe which is related the suppressing the swirling flow of free surface and the velocity of the middle and lower layer.

 In a horizontal channel, the characteristics of supercritical flow below a sluice gate have been investigated analytically and experimentally. For the developing flow, a method for calculation of the boundary layer thickness and the water surface is developed. The relation between the head loss and the energy thickness is clarified by using the energy equation in the boundary layer. The results of the analysis are in agreement with the experimental data. For the developed flow downstream of the critical point, the experimental investigation shows the length required to become equal velocity characteristics of the uniform flow, and the free-surface fluctuation is demonstrated.

 The formation of hydraulic jump is a useful method for energy dissipation below drop structures. When the jump is formed immediately below drops, the inflow codition (i.e., velocity priofile) might be affected downstream drop shape. This study investigated the effect of drop shape on velocity field in the jump under four different shapes. In conclusion, it has been found that the formation of separation zone at downstream face of the drop depends on drop shape, and that the inflow condition and the dacay of maximum velocity in jump associate with the formation of separation zone. For the development of main flow in jump, the relative drop height is more effective than the drop shape.

 The mathematical formulation to derive an approximate water surface profile for an undular hydraulic jump is described using the linearized Boussinesq equation with the eddy viscosity term. An approximate solution for a discontinuous hydraulic jump, which is composed of two distributions of the upstream and downstream parts, is firstly derived neglecting the vertical acceleration term in Boussinesq equation. Then, substituting the small deviation from a discontinuous jump profile into Boussinesq equation leads to a linearized equation which is applied to obtain the approximate solution of an undular jump. Extending the mathematical expression of a discontinuous jump solution, the simple equation is assumed as an approximate distribution for an undular jump and then the coefficients included in the basic equation are fixed considering the connection conditions of the upstream and downstream distributions at the origin. Finally, it is shown that the approximate solutions are in good agreement with the simulated results calculated using Runge-Kutter method.

 Turbulent open channel flow with strip roughness is one of the fundamental flows representing rough wall turbulence. This phenomenon and the relation between roughness spacing and flow resistance of relatively large water depth have been discussed so far. However, surface flow features under shallow water conditions have not been investigated in detail especially in the case of large roughness spacing. In this research, three dimensional water surface profile was quantified stereoscopically by visualizing water surface with fine sawdust. It was found that water surface shape changes complicatedly depending on hydraulic conditions. It was also found that in some cases, stationary wave patterns are generated where sharp wave peaks are arranged in a staggered manner. These stationary wave patterns have an amplitude of the same order as the water depth. Such water surface features have a similarity to those of triangular waves observed in anti-dune condition.

 Despite the remarkable improvements of flow measurement techniques and numerical models in recent years, the features of free surface fluctuations over rough wall turbulent flow have not been elucidated yet. In the present study, three dimensional measurement of time-dependent free surface profiles was performed in order to clarify characteristics of free surface over a shallow turbulent flow with a bed roughened by tightly packed glass marbles, by using the sampling moiré method. Some important results on statistical characteristics and decay charcteristics of frequency spectrum of free surface fluctuations were obtained.

 It is important for the calculation of river flows to evaluate the drag force acting on river structures and vegetation. But, the evaluation method of drag coefficient has not been revealed enough to be applied to non-uniform flows. In this work, laboratory experiments were conducted by using difference resistant elements in uniform, acceleration and deceleration flows.The drag coefficient was obtained as a function of Froude number from the experiments for uniform flows. In deceleration flows, the calculation results provided good agreements with the experimental results.However, the drag forces in acceleration flows were underestimated. This result is caused by the pressure reduction in separation area due to the existence of longitudinal pressure gradient. For the acceleration flows So, we proposed an evaluation method of drag coefficient for non-uniform flow. The method was validated through the comparisons with experimental water drpth plofiles.

 Firstly this study was carried out a hydraulic model experiment to clarify wash away characteristic of pell-mell placing block. As result, we confirmed that stability limit velocity of a foot protection block located in the midstream part faster than it of a foot protection block located in the upstream part under the influence of shielding effect. Then, we carried out a fluid dynamic force measurement experiment to clarify the factor that a foot protection block was caused by rolling by overturning moment. Especially, when the vibration component of overturning moment became maximum, we confirmed that rolling of pell-mell block occurred quantitatively.

 A predictive theory is developed to investigate the instability regime of a counter-current air-water flow in a pipeline. A temporal linear stability analysis is performed to ascertain the conditions that are required for perturbations to grow over a wide range of parameters (i.e., Reynolds number, slope of the bottom of the pipeline, air-pressure factor, ratio of the air to water flow depths). Our results indicate that the air pressure effect on the instabilities is more relevant for short waves at high Reynolds numbers, whereas long waves, which dominate the instability at low Reynolds numbers, are virtually unnaffected by changes in the air pressure.

 It was suggested that presuure variation generated by water hammer attenuated larger as a location of leakage was closer to downstream end in an experiment pipe. The damping of pressure fluctuation is closely related with energy loss during transient event in a pipe, so the mechanism in danping of it was investigated by analyzing energy loss due to friction and leakage flow theoretically. Besides, the validity of this mechanism was verified by numerical simulation, method of characteristics. Consequently, it was turned out that daming curve of pressure fluctuation due to friction could be reproduced in error by less than 1 percent for initial pressure variation and that of pressure fluctuation due to leakage flow could be reproduced in error by about 1 percent for it during about 20 seconds after water hannmer was generated.

 The experimental study was conducted to discuss the characteristics of the lateral over flow in the curved channel. The water surface profiles and the water velocities were focused in this study. The main results obtained in this study are as follows; (1) The longitudinal water surface profiles in front of the weir take the minimum water level, and the longitudinal velocity profiles is deference with respect to the relative weir height. (2) The transvers water levels at the outer side in the middle of the weir decreases as the discharge increases. Contrary, the water levels in the downstream edge of the weir increases. (3) The transvers velocity profiles in the weir region become smaller in the flow direction as the discharge increases. (4) The tendency of the ratio of the inflow discharge with the outflow discharge is difference with respect to the relative weir height.

 Characteristics of the flow structure of compound open channel flow with a circular main channel side wall (circular flow) are examined by using the velocity measurement method and the flow visualization method, and the flow properties of the vertical main channel side wall (vertical flow) were compared. As a result, under relatively high water depth condition, swirling flow pairing with oblique upward flow formed in vertical flow is formed also in circular flow, but it becames clear that it is weakened. In the low flow depth flow field, it becames clear that the flat swirling secondary flow formed in the vertical flow disappears in the circular flow. Under the condition of relatively high water depth, in the vertical flow, a large scale longitudinal vortical structure is linearly formed in a spatial-temporal concentrated manner at the tip of the floodplain, but on the side wall of the circular flow, a longitudinal vortical structure, it is inferred that the formation region meanders and that it affects weakening of the oblique upward flow and swirling flow.

 The cavity zone along riverside is expected to produce native habitats of various ecosystems and water-friendly environment. However, there is also a problem such as concern about deterioration of water quality because of a dead watet area. In this research, we have clarified the flow structure when the cavity aspect ratio changes for a flow field in which side cavity are continuously arranged in the downward flow direction. The flow velocity were measured by using PIV.

 As a result, it was clarified that the influence of the side cavity extended around the sidewall on the opposite bank side because of the flowing direction length of the cavity long in this experiment case. Furthermore, we also clarified how the turbulence generation term and the direct heat dissipation term change in the turbulent energy balance formula when changing the aspect ratio of the side cavity.

 In order to make clear the cause of deep scouring observed in The Kiso River, we focused on the generation mechanism of a large-scale planform vortex. The similar scour is generated in the experiments that simulate the field condition with convex bank and the boundary of fixed and movable beds. Next, 3D flow structures were investigated experimentally, under the condition with both the convex bank and backward step. In this condition, the deviated flow is extremely amplified in a deep zone and it causes strong planform vortex. This planform vortex provides rather high velocity near the bottom and this is considered to be one of the causes of the deep scouring.

 This study focused on grain size distribution of materials of riverbed, levee and substructure since river channel dynamics are characterized by nonuniform sediment transport of mixtures of gravels, sands and silts during floods. A multiple grain size model, which has not been applied very much for levee breach due to overtopping flow, was examined to discuss availability of the numerical model for hydro-morphodynamic process of river flood, levee failure and inundation. Numerical modeling with three sediment size classes corresponding to levee materials was carried out for overtopping breach test using a large-scale experimental flume located in Tokachi River (Chiyoda waterway). The numerical results of the levee breaching showed that the model could reproduce main features of breaching processes and morphological changes on riverbed and floodplain. The model with bedload transport formula by Ashida and Michiue in combination with hiding-exposure formula by Parker et al. estimated the time variation of breaching rate and discharges of river flow and inundation flow with good accuracy.

 In this study, the authors proposed the bedload velocity measurement method using celerity of water surface configuration due to dune. The method is constructed by using two definitions of bedload rate, one is for use dune’s height and its celerity u_w, the other is for bedload thickness and its velocity u_b. Comparison of the definitions shows bedlaod velocity is necessary for bedlaod measurement. The proposed method needs celerity u_w, wave heigh/depth ratio and water surface slope at crest. The estimated bedload velocity using the author’s method is plus-minus 50% by the measured value by ADCP. Among the factors, most dominant factor is u_w. STIV method is appropriate method for measuring u_w because the method can measure dominant dunes excepting bed small fluctuation.

 A turbidity current is a density flow the driving force of which is a density increase due to suspended sediment entrained in water from the bed. Turbidity currents have been found to have the lower layer with high sediment concentration with an equilibrium state because the turbulent diffusion is balanced with the settling of suspended sediment^1),2). In this paper, assuming that the high concentrated lower layer is in an equilibrium state, we obtaine the velocity and suspended concentration distributions in the depth direction, and the equilibrium thickness of the high-concentration layer formed in the lower turbidity currents. It is found from the analysis that the the thickness relative to the sediment diameter is determined by the three non-dimensional parameters: the settling velocity relative to the friction velocity, the particle Reynolds number, and the slope of the ocean floor. The high-concentration layer thickness relative to the sediment diameter increases with increasing the friction velocity relative to the settling velocity and the particle Reynolds number, and with decreasing the slope of the ocean floor.

 Ultrasonic attenuation spectrometer has attracted attention as a new measuring device for suspended sediment concentration and particle size distribution. It is necessary either to degass the samples nor to make measurement in a high frequency band where bubbles do not significantly scatter the ultrasonic waves since ultrasonic waves are greatly attenuated by fine bubbles. The ultrasonic attenuation spectrometer developed by the authors has a measurement frequency 1 to 10 MHz and fine bubbles may affect attenuation of ultra-sonic wave. Also, in the mountain rivers the water depth is shallow and the flow speed is high, so bubbles are likely to occur. In this paper we made measurement the attenuation characteristics of ultrasonic waves due to fine bubbles with diameters below 0.1 mm and verfied the effects of these bubbles on measurement of suspended sand concentration and particle size distribution in the measurement of mountain rivers.

 It is well seen that the places composed by straight channels and sharply curved channels on the wetland rivers, unlike rivers of alluvial area which have consecutive curves. A problem of the structure of curved meandering shape has already been dealt with by many researchers, and we can consider it in a systematic manner. On the other hand, structure of flexure meandering shape isn’t clear yet. In this study, we visualize surface current with dye and measure the flow rate of cross-section with one-dimensional LDV. Then flow on flexure point and around it is observed.

 This paper presents the experimental study on the downstream channel bed due to an oblique weir with an opening, paying attention to the effects of relative overflow depth on local scouring, 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 oblique weirs decreased with relative overflow depth and turned out strongly paired cellular secondary currents. In addition, the opening changed the place of strong local scouring from the channel side to the central region.

 The Ichikawa River is a second class river that flows down south of Himeji City, Hyogo Prefecture, where various river structures are installed. Among the river structures, there is a weir, the Hanada Weir, installed at an angle of 45 degrees to the direction of the river. To investigate the effect of the weir, surface velocities were measured by an image-based technique and they were used to evaluate the numerical simulation model successfully. From the numerical results by changing the obliqueness of the weir to the main flow direction, the existing angle was found to be preferable in view of the lowering of water level in flood conditions. With these viewpoints, the Hanada Weir has to have the similar structure even when the renewal of the weir is planned.

 Flood retarding basin which is one of the flood control hydraulic facilities is usually constructed in a strait site of the river. But due to the topographical restrictions, it is installed in the curved part of river.Although many research works have been conducted on lateral overflow in the straight river channel, knowledge of lateral overflow in the curved channel is not enough and discharge equation for curved channel is not established yet. Therefore, in this study we investigate the followings, (1) verification of the accuracy of the lateral overflow discharge using the river model experiments, (2) experimental verification of the lateral overflow discharge over the weir installed in straight and curved channel, and (3) the lateral overflow formula in the curved channel.As a result, lateral overflow formula with high accuracy was proposed.

 Dry masonry revetments had been used long time as traditional Japanese river revetments. From the landscape design and ecological view, there is still a lot of demand for dry masonry revetments. However, there is little knowledge about their strength and design method currently, it is difficult to select the method in case of revetment construction. For installation of dry masonry revetments, it is necessary to conduct scientific verification of the destruction behavior and strength of the method. We examined the outflow phenomenon of back filling sand material which is one of the fracture behavior of the dry masonry revetments by the hydraulic experiment. Following results are obtained. The outflow phenomenon can be prevented by filling the back filling gravel materials. The smaller diamater and the larger filling width of back filling gravel materials are the more effective to prevent the outfow phenomenon.

 Reservoir sedimentation is one of the most important problems for sustainable management of hydropower dams. Because of sedimentation in dams, little volume of the sediment flows at the downstream. Among several countermeasures, sediment replenishment is an effective option which can be environmental friendly at the downstream. In this paper, we considered the sediment replenishment of total approximately 680,000 m³ in 20 years. In the dam downstream environment, the changes of cross section, bed material size, algal biomass and benthic macroinvertebrates were shown the possibility of the effect of sediment replenishment. We found the potential of its increase in quantity of sediment replenishment.

 Because of the large rainfall event in 2017 around Kisyu area, one of the river named Akatani river was severely damaged. In the most of the mountainous area of the river, debris flow took place. In order to design the river to eliminate future damage of this kind, it is important to properly estimate the sediment transport rate from catchment area. This kind of study are classified as the sediment runoff. For this purpose, the authors proposed the RRIS model, which composed with Rainfall runoff, inundation, and sediment transport. The present study discuss about the case of Kawamata dam, whose sedimentation data are available. In the year of 1982, the Kawamata Dam catchment area experienced severer flood, which involve debris flow. The authors analyzed the timely changed of the sedimentation of the lake of Kawamata. Based on the analysis, large sedimentation are recognized between just after the Debris flow and few years. Thereafter, the sedimentation become much less. The authors tried to simulate this kind of sediment transport process with using RRIS model. The RRIS model simulated sediment-hydraulically reasonable results regarding to the sediment transport rate, riverbed variation, and spatially temporal changes of the bed material distribution. In addition to that, the RRIS model reasonably estimated the volume of sedimentation in the Lake Kawamata.

 The Aimoto weir interferes with the movements of gravel in the stony Kurobe River. This arises bed degradations and changes in arrangement of alternate bars downstream of the weir since 1995s flood. As a result, longitudinal dikes installed at flow attacking points are not able to work effectively. Therefore, we developed the sediment flushing channel paved with boulders for enhancing the discharge of gravels and cobbles through the sediment flushing gate of the cross-river structure. Our numerical results indicated that the sediment flushing channel was able to guide flood flow and gravels toward the sediment flushing gate. These effects mitigated the bed degradations and the changes in alternate bar patterns downstream of the Aimoto weir. Developed technique using the sediment flushing channel promotes recovery of stable meandering patterns of the alternate bars.

 Maintaining stable water levels during dry seasons is crucial for the irrigation of rice crops in the Vietnamese Mekong Delta (VMD) as agriculture, i.e. rice crops, is the main economic sector in the delta. Dry season water levels in the VMD are impacted by regulated flow discharges and river bathymetry. Hydropower dams, especially six mega mainstream dams in the upper Mekong River have caused tremendous reduction in the sediment budget of the VMD which, in turn, cause severe river bed degradation. Using in-situ bathymetric measurements and 2-D hydrodynamic modelling, this study investigates the alterations of water levels in the upper reach of the VMD as a combined impact of modified flow discharges and river bed degradation scenarios. Three thresholds of increased discharges associated with different degrees of river bed degradations were distinguished. Under low river bed degradation (< 1.5 m), water levels of dry seasons can be improved when the low-flow discharges increase by 10%. Under moderate degradation (1.5 m ≤ degradation ≤ 3 m), an increase of 20% of the low-flow discharge would help conserve the initial water levels. However, under high degradation scale (3 m < degradation ≤ 6 m), an increase of 50% of the low-flow discharge from upstream dams is expected.

 The discharge characteristics of suspended matter deposited on the river channel of Shira River along with the 2016 Kumamoto earthquake were examined. Suspended materials at the time of flooding on July 4, 2017 have the composition of TP / SS of about 0.1% and TN / SS of about 0.2% similar to the case of heavy rain in Kyushu in northern Kyushu in July 2012. Furthermore, the critical shear stress of clay particles of earth and sediment deposited in the river channel bending part from the resuspension experiment was about 0.3 N m^-2, and we clarified that clay particles of sediment deposited on the inner river bank will be resuspended in flood, as a resul of river hydraulic calculation. Therefore, in addition to the outflow of the forest soil in the upstream area in the normal state, the suspended matter supplied from the basin is discharged by sweeping / resuspensioning and resuspension of the riverbed sediment, which was accumulated in the riverbank after the earthquake

 The present study discusses influences of landslide numbers and water supply on debris flow characteristics using depth-averaged two-dimensional forms for mass and momentum conservation equations with Egashira's resistance law and erosion equation for debris flow. A small drainage basin within Akatani river basin where a lot of landslides and debris flow occurred due to a severe rainfall in 2017 is selected for discussion. Runout processes of landslides and debris flow are simulated numerically with several conditions for landslide numbers and water supply. Results show that peak discharge of debris flow and sediment runout volume increase with landslide numbers depending on flow path and the ratio of initial sediment volume, and that peak discharge of debris flow slightly increased with water supply. Therefore the effect of water supply on debris flow is not significant.

 Estimation of a damage of sediment-related disaster accompanied with flood, inundation, and sediment supply due to landslides is important to establish a prevention plan and/or evaluate the risk of them. In this study, we have developed a 2D Distributed Rainfall and Sediment Runoff/Inundation Simulator (:DRSRIS) with coupling the 2d rainfall runoff model, inundation flow model, and sediment transport model on the staggered grid which performs on the supercomputer. The model was applied to Haki area, Fukuoka Pref., Japan, where the Kyu-shu heavy rainfall in 2017 took place based on the sediment supply distribution estimated from the actual landslide data. The calculated sediment transport volume was underestimated, however, the calculated results almost corresponded to the inundated area obtained from the survey.

 In a bedrock river where high concentration sediment passes through the bedrock, erosion rate decreases with increasing sediment concentration even in the absence of gravel deposits. In this study, we propose a bedrock erosion formula focused on the work rate of bedload acting on bedrock surface to express this phenomenon. The work rate is the product of the shear stress and the velocity of bedload. Since the shear stress increases and the velocity decreases with increasing sediment concentration, sediment concentration can have conflicting two effects of promotion and inhibition of erosion. As a result, our model could reproduce the relationship between the bedrock erosion rate and the sediment concentration observed previous experimental study.