This study is concerned with breach discharge from straight channels. Such breach characteristics as flow direction of breach flows, effective length of breach section were verified experimentally. It is found that breach characteristics of submerged outflows differ substantially from those of complete outflows. The analysis is directed toward the improvement of Honma’s overflow discharge formulas in terms of breach characteristics obtained in this study. It shows that the improved formulas can predict overflow discharge in both complete and submerged outflows with good accuracy.

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Effects of the groves against flood hazards on dyke breach flows and the hydrodynamic forces acting on a structure are investigated experimentally. It is found that depending on Froude number at the broken point of the embankment, characteristics (size of tree, density and length of forest zone) of the groves and the distance of groves from the broken point, different type of the flows, namely, submerged outflow,forced hydraulic jump and jump-spray are observed. The regime of the flows is distinguished by the ratio of specific force of the flows to retarding force due to the groves. It is also found that the primary mechanism for reduction of the hydrodynamic forces acting on a structure is due to increase of flow depth downstream of the groves.

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Vegetation communities are often observed to grow in stripe pattern or patches within many stream channels. In such a situation, hydraulic engineers should examine an appropriate vegetation management system paying attention to flood control and vegetation ecosystem. In this paper, the flow resistance and momentum transport in open channel flow with discontinuous vegetation in longitudinal direction were examined experimentally. Velocity fluctuations were measured using a particle-image-velocimetry (PIV). Results showed that the flow resistance significantly depended on the longitudinal length of cavity between vegetation zones and the reason could be explained by the difference of momentum transport through the interaction among main flow, discontinuous vegetation and cavity.

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Railway and road embankments on a flood plain affect the propagation of inundation flow. In inundation simulation, the embankment in the flooded area is treated as the solid wall that inundation flow is able to overflow. However, the embankment involves the potential to be damaged during a severe flood event, and the breakage of the embankments causes not only physical damage but also a reduction of transportation function. In this study, the damage to the embankment of the Kishin line during the flood event in August 2009 is analyzed. The topographic and hydraulic conditions of the embankment failure are discussed.

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The energy loss at manholes in a storm sewer network is often compared with the friction loss in pipes under a surcharge flow. It is important to estimate the energy loss at manholes exactly in the design of a storm sewer network and in a flood-analysis. Some researchers have already investigated the energy loss at three-way manholes. However, the relationship between the energy loss and the water depth in manholes has not been enough studied yet. In this study, the effect of the water depth and the ratio of the flow rates in the lateral and in the downstream pipes on the energy loss at a three-way circular manhole was investigated. This study also proposed a modified formula for energy loss coefficients described in Urban Drainage Design Manual, USA (2001) for the three-way manhole.

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Recently, locally heavy rainfall occurs frequently at highly urbanized area, and causes serious personal accidents, so importance of flood forecasting system is growing in order to reduce damage of inundation. However, flood forecasting that secured lead-time for evacuation is extremely difficult, because the rainfall flows out rapidly.
In this study, the numerical simulation model that can finely express inundation mechanism of urban drainage areas was applied with the most recent available data and analysis tool. The influence of the factor (i.e. sewer system, overland and rainfall information) which affected inundation mechanism was evaluated through the sensibility analysis with this model, and evaluation results show some requirements of model condition and information on time and space resolution of real-time flood forecasting.

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A new simple inundation evaluation method based on the support vector machine, which is one of machine learning methods, using inundation and rainfall records in the past as training data, is proposed. Formulation on the application of the support vector machine to the inundation evaluation is fully described. The system, in which the inundation evaluation method as well as visualizing tools is implemented, has been developed. By comparison of the inundation hazard predicted by this system and the actual inundation that occurred recently, the effectiveness and applicability of this system are discussed.

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Numerical simulations of flooding event in the Iizuka-city area in the Onga river basin was performed by a numerical model for rainfall-runoff in watershed and flood inundation process in urban area with flood disaster-reduction system such as sewer network and drainage pump station. The rain-fall runoff was simulated by a distributed hydrological model. The flood flow in rivers and inundation flows on the ground were simulated simultaneously by the 2D free-surface flow model. The dynamic network model for free-surface-pressurized flow combined with the Preissmann slot was used for the sewer network. The effects of flood disaster-reduction system and inundation processes in Iizuka-city under different rainfall patterns were examined based on the numerical results.

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This paper deals with the development of an integrated model for rainfall-runoff/flood inundation simulation and economic loss estimation, especially focusing on Sayo Town, Hyogo Prefecture, Japan where there was a severe flood disaster due to a heavy rainfall event on 9-10 August 2009. Firstly, the rainfall over the Sayogawa river catchment at the time is analyzed by using the composite radar and Radar-AMeDAS reanalysis data by the Japan Meteorological Agency in addition to the ground observation data. Second, the rainfall-runoff and flood inundation processes are simulated using the integrated model with the Radar-AMeDAS reanalysis data. The simulated inundation area shows the good agreement with the inundation record. Then, the economic loss estimation based on the simulated inundation area and depth is carried out and compared with the prospected value reported by the municipal government. The house/building economic loss estimated is 20.4 billion Japanese Yen, which agrees well with the reported value 18.5 billion Japanese Yen.

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We have evaluated relationship between sediment hazard, regional geomorphic properties and heavy rainfall in Tokyo. It tried to clarify regional characteristic of the sediment hazard by using spatial numeric information. The antecedent precipitation index was used sediment analysis as heavy rainfall condition. The results obtained are as follows; 1) It was clarified that the sediment hazard have a greater tendency to long term rainfall than short term heavy rainfall. 2) It shows a regular relationship between relief energy and antecedent precipitation index in case of sediment hazard evaluation excepting the complex geo geological condition.

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Evacuation movement of persons from an inundated underground space was investigated in this study. Numerical simulation was conducted under the two conditions; (1) the persons were guided to evacuate in a recommended manner or (2) they escaped through the nearest stairs without guide. Simulation was also conducted in order to make clear the effect of evacuation announcement. It was confirmed that the guide was effective to make an orderly and safe evacuation movement. And the announcement was also effective to make persons escape more rapidly to a ground level in case that it was made at just the right time. This kind of computation must be needed before we make a plan of the announcement.

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Frequency of rainfalls over the capacity of drainage system is increasing and underground inundations occurred in some Japanese cities in recent years. It is an urgent matter that managers of underground spaces plan for safe evacuation of users. In order to make the plan, they should know when and from which entrances the rainwater will flow into there. In this paper, inflow discharge was calculated by using 1D-2D urban drainage model in a drainage basin where one of mega-underground mall is located. And appropriate counter measures were investigated. From the results, it is found that peak discharge of inflow appears behind the rainfall peak and that the delay time is from 0.5 to 2.5 hours and depends on the rainfall conditions. It means that several rainfalls should be considered for planning of counter measures and evacuation.

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Torrential rainfalls have been observed frequently in recent years and these rainfalls caused inundations in urban and rural areas. Intensity of such rainfalls were sometimes excess over the design rainfall of drainage systems and rain was running over the road. In these floods, some portion of rainwater intruded into underground spaces and the users faced the danger of underground flooding. In this paper, underground flooding in a mega-underground mall were investigated by using 2D shallow flow model with structural mesh and evacuation from there was also studied with the criteria of safety evacuation obtained by evacuation tests. The results show that flooding processes and safety of evacuation are quite different in the two cases with and without the consideration of drainage system. It means that the inflow conditions into underground space are depend on calculation results of rainwater flooding.

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The objective of the study is to understand the method that is appropriate for the inundation flow analysis. In the case of flooding in a densely populated urban area, the inundation flow concentrates in open spaces such as roads. This tendency is prominent especially in the alluvial fan areas, because the momentum of the flow is large due to high gradient. Therefore, it is necessary to express these characteristics adequately in the inundation flow analysis. In this study, the inundation flow analysis method was verified using a physical model experiment and improvements were made to the flood simulation model. By incorporating the influence of buildings in the continuity equation, the simulation model could replicate reasonably the results obtained by the physical model experiment.

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In this paper, in order to verify the stormwater exchange model between ground surface and sewerage system in integrated urban inundation model, we conducted experiments of urban inundation using a flat basin with a sewer pipe and rainfall supplier, and those results are compared with numerical simulation results. From the comparison between them, it is obvious that stormwater drainage and overflow discharge in urban area can be estimated exactly by using step-down formula and overflow formula in steady flow cases. In unsteady flow cases, however, calculated inundation water depth on the ground surface responses to piezometric head of the sewer pipe too quickly than experimental results, which requires much smaller values of the coefficients in those formula.

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Low-lying agricultural reservoirs under the pressure of urbanization in Japan are subject to increasingly higher risk of inundation disaster due to the change in the runoff characteristics by decreasing the area of paddy fields and the recent increase in the frequency and magnitude of heavy rainfall events. The objective of this study is to develop an inundation analysis model specifically aiming at low-ying agricultural reservoirs. The model developed in this study is composed of three modules: runoff calculation module in which the runoff from each landuse cell is calculated using water balance analysis, channel network module in which the flow in the channel network is calculated by a one dimensional unsteady flow analysis, and inundation flow module in which the behavior of overflown water is demonstrated using topographically adjustable cells. One of the unique characteristics of this model is the runoff from landuse with different attributes are reflected in the course of calculation in a realistic but concise manner as the origin of runoff. As a result of applying the model to a study field, inundation process was verified to be reproduced well.

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Numerical simulation of a flood event is made, using a one-dimensional Boussinesq equation model. Flood generation factors and occurrence conditions are employed for model calibration. The simulated results are verified by comparison with video images of surface waves taken during the flood period. The numerical simulation is used to study the mechanism whereby the surface waves are generated. The numerical model seems to be able to accurately reproduce the water waves that occurred during flood period in 1981. The simulated results show that the surface waves grew when they came into phase with the antidunes. The simulated results confirm that the phenomenon is related to Froude number.

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A depth averaged flow model is commonly used to simulate flows in rivers or lakes. However, it is not applicable to the case three-dimensional flow structures are predominant. To improve the model performance, several refined depth averaged models have been proposed, by incorporating the effects of secondary currents, flow acceleration/deceleration and vertical acceleration. Nevertheless, a horseshoe vortex in front of a bluff body cannot be reproduced in depth averaged flow model. In this study, a modeling of a horseshoe vortex is carried out theoretically, by including the effects of flow acceleration/deceleration and the development and attenuation of secondary currents. For verification of model, the proposed model is applied to the flows around a square cylinder and compared with the results of three-dimensional numerical simulation. The results showed that the present model can capture the fundamental features of horseshoe vortex.

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This study describes the methodology on an inverse estimation of the bed roughness coefficients in open-channels with flood plains. The coefficients are identified by an adjoint shallow-water model and an optimal control theory. Several twin experiments were carried out with the synthetic data in order to validate the method. The data assimilated consists of values of the water level and depth-averaged velocity. The results showed that the coefficients can be accurately predicted with the velocity data, while the estimation fails with the water level data. This is because the cross-sectionally distributed bed roughness does not always influence the lateral profile of the water level, but the local velocity field. Namely, the relation between the lateral profile of the water level and the bed roughness turns out to be non-unique in open-channels with flood plains.

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A meandering compound open channel flows show a complicated three-dimensional flow structures because of the combined effects of the secondary currents of the first kind, and the horizontal vortices at the junction between the main channel and the floodplain. The secondary current of the first kind is generated by the unbalance of the centrifugal force and the lateral pressure gradient. The horizontal vortices are generated due to the shear layer instability. Clarification of the flow is important for both flood control and river environment. URANS computations have more computational efficiency compared with LES or DNS. The applicability of 3D CFD model based on a URANS non-linear k-epsilon model was examined through the comparison with the experimental results by Sanjo et al, in which detailed steady and unsteady flow structures have been illustrated clearly through PIV measurement. The present URANS computations could reproduce the secondary flow patterns excellently. The horizontal vortex shedding observed in the experiment could also be captured though shape of the row of vortices was not replicated well.

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Turbulent flow around a channel bend has been computed by Large Eddy Simulation (LES) method. The bed forms of the channels considered are contoured like those of natural rivers with pointbars and the calculation results are compared with those of flows around a similar bend with a flat bed. The simulated flows are of laboratory-scale flows and no special near-wall model is applied but the results show important features of the flow around a bend and a reasonable agreement with the available experimental results. Particularly, the secondary flows near the outer bank along with the main secondary flows induced by the streamline curvature are reproduced well and the effects of the bed form on these flow and the turbulent characteristics are reproduced.

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In non-intrusive river flow measurements such as imaging or radar techniques, water surface irregularities in turbulent flow condition is assumed advected with the surface flow. The surface irregularities are usually considered to be induced by turbulence originated from boil vortices generated near the rough bed. However, the relationship between bottom roughness and water surface fluctuation is not well understood so far. Therefore, we conducted experimental and numerical investigations with relatively simple bed roughness composed of hemispheres. Particle tracing velocimetry (PTV) technique is applied in the experiment and the large eddy simulation (LES) with immersed boundary method (IBM) is used in the simulation. It was made clear that the numerical simulation reproduces the water surface fluctuation fairly well and advection speed of surface pattern can represent the surface flow velocity.

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The importance of flow and turbulence to the ecology of aquatic benthic organism has been widely reported. Aquatic vegetation is one of environmental variables that influence turbulence and the ecological condition of rivers. Coherent motions are generated near the vegetation edge and these large-scale eddies control the vertical exchange of mass and momentum between the over- and within-canopies. Therefore, it is of great importance to reveal the coherent eddies in vegetated flows. However, the transition from boundary-layer flow upstream of the canopy region to a mixing-layer-type flow within the canopy has not been fully investigated. So, in this study, turbulence measurements were conducted intensively in vegetated open-channel flows by using PIV. Velocity profiles were measured at 33 positions in a longitudinal direction to examine the evolution mechanism of the coherent structure near the vegetation edge. The present PIV data confirmed efficiency of mixing layer analogy and provide insight into spatial evolution of coherent structure.

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PIV and LIF techniques were conducted to reveal relationship between sedimentation and mass exchange property in a groyne field. It was found from the PIV measurements that different bed-form conditions, that is to say, with and without bed slope, yielded corresponding gyre formations. The other experiment, the LIF results allowed us reasonably to evaluate transfer velocity of dye through boundary between mainstream and dead water zone, They suggest that mass exchange properties have significant relations with horizontal gyres, thereby, with the conditions of bed slope. The results normalized by turbulence intensity and length scale of gyre were in good agreement with a large-eddy model.

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When a rectangular side cavity section is installed to a relatively narrow open-channel flow, water surface oscillation is generated within the side cavity and main channel. However detailed experimental examinations of the three-dimensional flow field for these hydraulic structures have not been conducted so far. So we measured the three-dimensional local flow structure by applying the particle image velocimetry technique (PIV) to multiple vertical and horizontal cross-sections. Numerical analysis by three-dimensional large eddy simulation (LES) is also performed for comparison. It was made clear that the LES yields comparable results to the experiments in terms of the three-dimensional flow structure and surface oscillation.

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Three dimensional flow structures were measured by using PIV to clarify the mechanism of sediment deposition caused in a riverside embayment with various shape configurations in a compound open channel. The 3-D flow structures were deformed by the step angle and they were related well to the deposition configuration. The upstream-oriented backward facing step causes the reattachment downward flow and the secondary flow in the center of the riverside embayment zone. Total amount and bed configuration of sand deposition were correlated with the typical 3-D flow structures.

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The effects of entrance barriers along an embayment mouse were investigated in order to contain sand deposition in an embayment zone. The velocity and sand deposition were measured in an open channel with a trapezoidal embayment. The entrance shielding methods were changed in length, height and location in a systematic way. Both bed load and suspended load were considered in the present experiments. As a result, typical flow structures were made clear and the restraining effect of sand deposition was observed by control of entrance configuration. The amount of sand deposition decreased in proportion to the shield factor. However, it was noticed that the configuration of sand deposition was varied by the location of barrier. The velocity strength in an embayment is also correlated to the volume of sand deposition.

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In the present study, an ADCP flood measurement and 3D flow analyses were conducted around the Gudo point near the Shimanto-river bridge which is located at 9.5km upstream from the mouth of Shimanto River in Shikoku-island Japan, to reveal the details of flow structure around the bridge. There are some river structures such as bridge piers and bed protections around the bridge. There is also a large local scouring in the right bank side of the bridge. The scouring has progressed for a long period to 10m depth below water surface. In order to estimate the accurate discharge, detail flow structures considering with the complicated surroundings are needed for river management such as flood control. As a result, flood-flow velocity and bed profile were successfully measured by the ADCP and 3D flow was analyzed far downstream area from the bridge.

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This paper is concerned with the reproduction of flash floods with high Froude number. In order to reproduce unsteady super-critical flows, it is common to give two hydrographs of depth and discharge based on the method of characteristics. Since we pointed out recently the possibility and the computational method to reproduce flood flows for sub-critical flows using one depth hydrograph, the theory and method are extended to unsteady super-critical flows in this paper. Non-linear analytical solutions with boundary hydrographs at the upstream end are firstly derived. Then, it is proved that the boundary hydrographs at the upstream end can be reproduced inversely, using the solution of one depth hydrograph at one site.

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It is important to clarify the formation, break and flow of river ice on frozen rivers. The aim of this study is to clarify ice break and flow phenomena during river ice breakup, as these phenomena are the initial stages of ice jam. With regard to the break of river ice, we developed a method of judging ice break by comparing the stress caused by the flowing water and flowing ice, and the allowable bending stress of the river ice. The ice flow is expressed using the continuity equation that considers the change in amount of ice, and the equation of motion that considers the effect of the flowing water. This one-dimensional mathematical model showed that although there is a problem with the reproducibility of ice jam, it is possible to reproduce ice break and flow phenomena by comparing the freezing conditions from the results of the calculations, with those of aerial images of the actual river.

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To discuss river management and maintenances against recent changes in various circumstances surrounding rivers, such as river environments, rainfall characteristics and social conditions, it is necessary to clarify the manner of floodwater storage in the channel. This paper presents an unsteady two dimensional numerical method using water levels measured in a mainstream to compute flood flows in river systems with several lateral inflows, such as tributaries and pump stations. The method is applied to the Asakawa River flood at August 2008, and installation methods of water level observation stations are discussed. And the method is applied to the Ushizu River flood at July 2009, and influence of inflows from pump stations in low-land area on flood flow is evaluated.

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Forestation on flood plains is a world-wide engineering issue in middle to downstream reaches in many rivers. This brings not only degradation of flow conveyance capacity but also irreversible changes of ecological system in rivers. In order to obtain information on tree vegetation behavior during flood events, field data of flow fields and tree vegetation collapse were collected in Kako River, where willows are heavily vegetated on the flood plain. After starting a H-ADCP flow measurement in 2009, small to medium size flood events frequently occurred, which enables us not only to verify an analytical model to reproduce flow fields in and out of vegetations but also to examine tree vegetation collapses after flooding. The analytical solutions on velocity profiles as well as flow force acting on trees were in good agreement with the H-ADCP measurements and tree damages, respectively.

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Horizontal large eddies caused by the instability of shear layer between main channel and flood plain were investigated for two rivers by aerial photo analysis and numerical flow simulation. One river (A) has flood plains on both sides of main channel, and the other (B) has one flood plain with a comparatively narrow main channel. Transverse velocity at the edge of flood plains caused by eddies were obtained from aerial photo analysis, and eddy lengths were determined by zero-up cross of the velocity. A flow model of quasi-3D was applied to the large eddy computation under the actual flow conditions. Scale and intensity of eddies obtained from the computation agreed very well with the results from aerial photo analysis. In addition, the both results suggested that rows of eddies in river-A were less stable with frequent merging and splitting than in river-B. A series of numerical experiments showed that the eddy stability is controlled by the ratio of the transverse scale of eddies to the width of main channel.

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The flow around a bend of a real river reach during floods has been simulated by a Large-Eddy Simulation (LES) method in order to investigate the detailed flow characteristics and their effects on the gravel bars that exist on the inner banks of the meandering river reach. The hydrodynamic effects of flood flows near the gravel bar are thought to be closely related to the conditions for plant communities of diverse species to be maintained. The present numerical simulation, that represents the bed bathymetry to about 15 centimeters in the vertical direction, is found to reproduce the observed water level and slopes of a few hundred meter long reach for given discharges of a few hundred tons/sec. The simulated results include the three-dimensional velocity distributions and the bed shear stress along with the instantaneous secondary flow features and provide important information to study the hydrodynamic effects of flood flows on the gravel-bar plants.

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In case a gate installed at the end of discharge conduit is vibrating during discharge, or an air valve is vibrating during water-filling operation into the conduit pipe between main gate and auxiliary gate, and vibration period tv is larger than tc (water hammer propagation time) that is equivalent to the phenomenon of slow closure, there is a possibility that water hammer oscillation in the discharge conduit could be induced. In this paper, by using two case examples, vibration phenomena transmitted to each part are analyzed, on the basis of water pressure fluctuation and pressure wave propagation due to occurrence of water hammer oscillation.

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In this study, we present a new assembly manhole to connect drainage pipes with a large hydraulic head difference. The manhole consists of spiral channel along the sidewall and spiral stairway around the center axis for maintenance. To investigate hydraulic characteristics of this manhole, we have performed laboratory experiments using hydraulic models of 1/15, 1/10 and 1/7.5 scales. We have measured velocity and surface elevation in the spiral channel and air pressure inside the manhole. A simple prediction model for the flow velocity was also developed by utilizing the Manning formula. The velocity and the water level along the spiral channel were reasonably estimated by the present model. The positive and negative air pressures were observed when the connecting pipes of upstream and downstream were in full depth. With the aid of the Froude similarity, we have confirmed that the velocity and pressure are allowable for the design of the prototype structures.

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Aeration by free surface vortex in hydro-electric facilities has been investigated for many years. The studies on free surface vortex have been mainly conducted by model experiment that required many works and costs. Combination of image velocimetry and numerical simulation is a powerful tool for estimation of occurrence of aeration by free surface vortex. The knowledge of aeration by free surface vortex is necessary to designing the hydro-electric facilities quickly and efficiently. In this paper, the technique to measure the velocity field and free surface profile simultaneously has been developed by using image processing techniques. The developed technique is applied to experiments on the aeration by free surface vortex in order to clarify relationship between free surface profile and circulation of flow fields. The results show some interesting phenomena related to aeration by free surface vortex.

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Stepped channels are effective for dissipating the energy of supercritical flow that occurs at steep channels. Generally, stepped channel flows are characterized as aerated flows. For design purposes, it is important to know the aerated flow characteristics such as the aerated flow depth, the air-concentration ratio, the aerated flow velocity, and the energy head in skimming flows. Recently, the authors showed the aerated flow characteristics for the quasi-uniform flow region of skimming flows under a wide range of channel slopes. However, for the nonuniform flow region, the aerated flow characteristics have not yet been shown clearly. In this paper, an equation for the calculation of the aerated flow depth has been developed in the nonuniform aerated flow region. Also, the aerated flow characteristics have been clarified in the nonuniform aerated flow region for a channel slope of Θ=55°.

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This study describes gas transfer beneath air-water interface and related turbulence transport below the free-surface in open-channel flow with small aspect ratio. Simultaneous PIV-LIF measurements were conducted by using dual high-speed camera system which allowed us to evaluate gas transfer flux accurately on the basis of eddy-correlation method. It is found that the present transfer velocity becomes larger compared with previous experimental data obtained in the large aspect ratio condition. Furthermore, time-variation of bulge structure of dissolved gases and surrounding velocity vectors were visualized in order to understand turbulence contributions to gas transport.

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In recent years, it has become necessary to develop suitable methods for restoring natural rivers. The authors have examined more nature-friendly hydraulic structures made of connected natural stones. Although such structures are excellent in environmental aspects, design standards for such structures have not been established yet because the structures comprise natural stones with various shapes. Furthermore, the design flow velocity is not clarified when the proposed connected natural stones were used as a groin and other hydraulic structures. At present, 1.2–1.5 times large velocity of the representative mean velocity is used as the design velocity. Therefore, in this study, the hydrodynamic force for solidly connected natural stones, and the velocity field around such structures were examined experimentally. Experimental results clarified not only the hydraulic characteristics of the flow around the groin, but also the drag and lift coefficients of the connected stone. An efficient design method for the solidly connected stone was proposed.

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The flow induced forces on a cube and a strip roughness placed submerged on the bed in open channel flow were measured by using the three-component load cell. The flow around the cube were measured by using a laser doppler anemometer and a particle image velocimeter and were simulated with a k-epsilon; turbulence model. The drag and lift force coefficients of the cube and strip roughness in the open channel flow with free surface become large with increase of the ratio of cube height h and water depth d (h/d). The equivalent roughness k_s for the strip roughness were also estimated by the measured drag forces acting on a strip roughness.

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Field Measurement of Self Potential Method using Copper Sulfate Electrode was performed in base of riverbank in WATARASE River, where has leakage problem to examine leakage characteristics. Measurement results showed typical S-shape what indicates existence of flow groundwater. The results agreed with measurement results by Ministry of Land, Infrastructure and Transport with good accuracy. Results of 1m depth ground temperature detection and Chain-Array detection showed good agreement with results of the Self Potential Method. Correlation between Self Potential value and groundwater velocity was examined model experiment. The result showed apparent correlation. These results indicate that the Self Potential Method was effective method to examine the characteristics of ground water of base of riverbank in leakage problem.

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Multispectral remote sensing methods of water depth can potentially play an important role in shallow water bathymetry. However, they have not been widely used because they require auxiliary information about optical properties of target water area for each image in order to build or calibrate the prediction model. In this study, we examined the inter-image compatibility of the prediction model of the popular method by Lyzenga et al. using three QuickBird images of different water areas. As a result, predicted and measured depths were found to be highly correlated regardless of the combinations of the image used for calibration and the image predicted. The interchangeability can be utilized to reduce the amount of the auxiliary information necessary to apply the method, and therefore to improve its feasibility.

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River bed material is normally heterogeneous, and the grain size distribution shows some features of each rivers. The information of distribution is, therefore, important factor in river engineering, and several traditional methods is practically used. Image processing method with digital photograph is modern analysis by using computer and replaced traditional analog photograph method. In image processing, however, optical distortion brings measurement error. We present a calibration of the distortion with optical theorem. In laboratory experiment with balls supposed river bed gravel, the theoretical calibration is considered to be appropriate. In field experiment, actual coefficient to calibrate distortion is estimated. In consequence of the investigation, it makes image processing method more accurate.

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The sieve test is a method of measuring grain diameter for erosion control studies using a sieve made from a wire mesh. However, it is expensive to transport gravel from the field to the laboratory. Therefore, we looked for an easy, economical method of measuring grain diameter. We proposed a simple method for measuring the grain diameter in the field. Our method uses the contact time between the gravel and an elastic body. We determined the contact time between glass balls, gravel, and a hard plastic polyacetal board and found that the grain diameter was proportional to the contact time. Experimentally, there was a good correlation between the contact time and grain diameter. In addition, the count of the number of pieces of gravel was accurate. The contact time was measured and converted to the grain diameter. The resulting grain size histogram of the gravel determined in the experiments matched the material studied. Application of this method in the field is possible.

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The authors conducted bedload-discharge measurement using an Acoustic Doppler Current Profiler (ADCP), a modified Toutle River-2 bedload sampler (TR-2β) originally fabricated by the United States Geological Survey (USGS), and a water-sediment sampler modified based on a suspended sediment sampler. Results from field measurements during minor flooding at two different sites show that 1) not only TR-2β but also the water-sediment sampler is necessary to observe the size distribution of sediment particles, though appropriate volumes of bedload discharge cannot be obtained by those two sediment samplers in contrast to shear velocity. They also show that 2) ADCP performed better in the measurements than the sediment samplers. Additionally, the authors described the characteristics of bedload discharge as being unsteady and showing a cross-sectional distribution. Finally the authors proposed an observation method based on the findings and suggested the applicability of the current methods in terms of hydraulic condition.

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Monitoring of river is significant both in flow management and river usage. Although river monitoring systems have been installed in many rivers in Japan, most of the existing system do not record images and utilize them for quantitative measurement of the flow. Already proposed methods for quantitative measurement include image analysis techniques such as large scale particle image velocimetry (LSPIV) or space-time image velocimetry (STIV) proposed by the authors. However, there still resides skepticism about the accuracy of the methods. Therefore, we conducted concurrent measurements with ADCP to verify the performance of the image analysis techniques. At the same time, we established a quasi-real time system of discharge measurement by introducing a novel image collection system with high image compressibility.

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The authors have been developing an accuracy-evaluation method for flood flow observation with an Acoustic Doppler Current Profiler (ADCP). Several field measurements were conducted under severe ADCP measurement conditions characterized by high velocity and highly-frequent water-surface vibration. This paper described main factors which influence the accuracy of velocity/water-depth measurements and reviewed previous observation results. To finalize the development of the accuracy-evaluation methods, the authors conducted field measurements under severe conditions with highly sophisticated devices and verified the method with high-quality datasets. Finally it was applied to previous flood observation results obtained in the Shimanto River.

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Stream flows in steep gradient bed form complicating flow configurations, where co-exist super-critical and sub-critical flows. Computing numerically such flows are the key to successful river management. This study applied CRD schemes to 1D and 2D stream flow computations and proposed genuine ways to eliminate expansion shock waves. Through various cases of computing stream flows conducted, CRD schemes showed that i) conservativeness of discharge and accuracy of four significant figures are ensured, ii) artificial viscosity is not explicitly used for computational stabilization, and thus iii) 1D and 2D computations based upon CRD schemes are applicable to evaluating complicating stream flows for river management.

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Accuracy of a highly precised Moving-particle semi-implicit (MPS) method, proposed by the authors, is compared with that of the traditional MPS method on the static fluid pressure and water wave propagation. The MPS method is modified with a precise estimation of the gradient. In a static fluid analysis, a good accuracy is obtained in the modified MPS for static pressure than in the original MPS. In case of progressive water wave propagation analysis, the oscillation of wave pressure can also be simulated with high accuracy. The study suggests that the proposed method for the gradient operator can contribute to improve the accuracy of the MPS method.

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