The upper limit of Froude number for the undular jump formation has been investigated by many researchers, but a general agreement has not been obtained. The formation of undular jumps is affected by the inflow Froude numbei the development of the turbulent boundary layer, the aspect ratio, and the Reynolds number. In this paper, the effect of the Reynolds number and the aspect ratio on the undular jump formation has been clarified, and a general expression for the upper limit of Froude number has been established. The minimum scale of model required to apply the experimental results to a prototype design can be determined as Re≥65000. Also, if the aspect ratio is larger than 10, the flow condition of undular jumps can be regarded as a two-dimensional flow.

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The flow over a stepped channel can be divided into two regimes: nappe flow and skimming flow. It is indicated that for a nappe flow regime the energy dissipation occurs by jet breakup in air, by jet mixing on the step and that for skimming flow regime the energy dissipation is enhanced by the momentum transfer from main flow to skimming fluid near the steps. However, for the stepped steep channel where the wake vortices do not fill the entire cavity between the edges of adjacent steps, the flow structure was not clarified yet. In this study, the skimming flow characteristics in a stepped open-channel was discussed on the basis of experimental data of main flow velocity, pressure on channel bed and water depth. The authors found the correlation among them along the downstream distance from the step edge and clarified the three-dimensional flow structure embedded in the skimming flow from their spanwise variation.

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Fundamental properties of high velocity flows in a continuously meandering channel are studied analytically and experimentally. The linearized equations of the depth averaged flow model with the inertia term of momentum equation in the transverse direction, which is equivalent to Hasegawa's equation, is derived by use of the.power series expansion of transverse coordinate. Through the examination of the fundamental characteristics of the solution, it is shown that the resonance between the free surface variations and the channel meandering occurs with the increase of Froude number. The laboratory tests are carried out to verify the existence of resonance relation, changing the bottom slope of a channel. The comparisons of the analytical solution with the experimental results indicate that the resonance can be observed at the Froude number predicted by the theory and the amplitude of free surface variations in the experiments depends on the amplitude of the channel meandering.

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We might make a channel into a compound channel, as an effective way for the flood control and environmental reasons. Recently, even the river of steep gradient the river is often reconstructed into a compound channel. However, we have not enough knowledge how much safety we can secure, and what standard of cross section is easy for maintenance of a steep gradient river.
In this research, we have conducted experiments using meandering compound channel with different gradients. Especially, we investigated longitudinal and transverse profiles and fluctuations of water surface, depending on gradient of the channel. In case of steep gradient, we found that it is possible difficult to maintain the main channel unchanged, because of remarkable flow exchange between the main channel and floodplain, high velocity appeared near the bank, and large fluctuation of water surface.

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It is necessary to predict the effect of vegetation in the river channel on flood flow.
In this study, a flow field in a compound meandering channel with vegetation along banks is simulated numerically by using three dimensional model with spectral method, which is effective to simulation of the flow field without vegetation. Result of simulation is compared with that of experiment. Simulation can describe distribution of water level and of velocity above the level of flood channel, but cannot velocity distribution in the lower layer and secondary flow. This model may not describe properly the mixing between fluid of low velocity near the vegetation and that in main flow. Other turbulence model may be necessary to describe the three dimensional flow field with vegetation.

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Over-bank flow in a straight channel with a meandering main channel is discussed based on experimental results. The flow structure is characterized by secondary flow and fluid mixing between the main channel and flood plain flow. The secondary flow was directly visualized by a submergible video camera. The secondary flow shows spiral motions and affects the distribution of boundary shear stress and sediment transport. The relation between these structure and the traction process of bed materials is discussed on the basis of the distribution of tractive force visualized by a new method. In the experiments, we used light materials whose critical tractive force is equivalent to the mean shear stress on the bed.

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In compound open-channel flows, it is very important to clarify the interaction between main-channel and flood-plain induced by coherent vortices, so-called the secondary currents and “large-scale horizontal vortices”. These turbulent structures and coherent vortices are characterized by high shear layers generated by the shear instability between main-channel and flood-plain flows. In this study, secondary currents and three-dimensional turbulent structures were experimentally revealed on shallower floodplain by making use of a two-component fiber-optic laser Doppler anemometer (FLDA). Next, the bed shear stress on shallower flood-plain was evaluated from the accurate measured velocity profile in the viscous sublayer by making use of one-component fiber-optic LDA.

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Flow characteristics, such as secondary currents, Reynolds stress and turbulence energy, in the cross-section of gradually shallowed open channel flows were investigated with a hot-film anemometer. The wake strength parameter II decreases in the flow direction. It was confirmed that the value of n is determined by the pressure gradient parameter β. An exponential function describing the relationship between ri and β is proposed. The strength of the secondary currents decreases along the flow direction. The shape of iso-velocity lines in a cross section looks like the rectangular shape. The Reynolds stress takes a negative value near the water surface in the vicinity of the side wall.

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Three-dimensional measurements of open-channel flows were conducted by making use of two sets of laser Doppler anemometers. One is able to measure the u-v components, and the other is able to measure the u-w components. The Reynolds stress (-vw) could be first measured with high accuracy. The streamwise velocities which were measured by u-v measurement and u-w measurements were in a good agreement with each other. The third moments of the velocity fluctuations were agree well with the results of DNS (Direct Numerical Simulation). A new empirical formula, involving the van Driest damping function, expresses the spanwise turbulence intensity in the inner region.

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The inner layer and outer layer of unsteady smooth open channel flows were measured by making use of a twocomponent laser Doppler anemometer (LDA) under the condition that the unsteadiness parameter is very high. In such a situation the von Karman constant decreases in the rising stage and decreases in the falling stage. The friction velocity evaluated from the log law does not coincide with that evaluated from the linear formula in the viscous sublayer with an increase of the unsteadiness. In contrast, the characteristics of normalized turbulence are not affected by the unsteadiness so much; the van Driest's damping factor of the turbulence intensity of the streamwize is almost constant against the normalized time. The third-order moments of the turbulence agree well with those of the steady uniform flow.

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Image analysis methods have become a powerful tool for measuring turbulent flows in recent years. However, the accuracy of the methods in measuring turbulence quantities, e.g. turbulent intensities or Reynolds stress distributions, has not been examined in detail so far. In this research turbulence of a uniform open-channel flow was measured by using a PIV (Particle Image Velocimetry) technique and some PTV (Particle Tracking Velocimetry) techniques. In the case of PTV, the binary cross-correlation method and the recently proposedvector-grsdient-tensor method were compared by combining them with the particle masking technique or the conventional technique using a threshold value as the methods for image binarization. Images captured by a high-speed video camera with 200 fps were used and the mean and the turbulent properties were compared. It was made clear that the PTV techniques are superior to the PIV especially where velocity gradients are large and there are no significant differences between the PTV techniques.

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Supercritical flows sometimes occur during floods and shock waves can be easily found on the both sides of the pier. In order to know the influences of this type flow toward a pier, it is necessary to study on a flow around a circular cylinder in a supercritical flow. In this study we carried out experiments on a flow around a circular cylinder with the Froudc number of 1.98 and 2.06. Numerical simulations also were performed by using a shallow water flow equation in which the SGS effect is taken into account. As a result, the results of the numerical simulations agreed with those of the experiments, for example, Mach angle of shock waves and the intensified velocities behind shock waves.

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Large eddy simulation of fully developed turbulent flow in a compound open channel was carried out using the Smagorinsky model. The Reynolds number based on hydraulic radius and cross sectional averaged velocity is 5300. The mechanism of secondary flow is discussed by evaluating terms in the momentum equations for mean secondary flow. To clarify the important role of pressure gradients in driving the secondary currents, pressure is decomposed into several components that account for the contributions of convection, external force, the Reynolds stresses, and the viscosity. It is found that not only the Reynolds stresses but also the pressure gradients induced by the normal and shear Reynolds stresses play a major role in generating secondary flow.

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The processes of the production of turbulence statistics in cavity open-channel flows are investigated using the numerical flow field which is computed by Direct Numerical Simulation (DNS). The reliability of the results of DNS is confirmed by comparison which the results of turbulence measurements conducted by making use of a two component fiber-optic Laser Doppler Anemometer (LDA). The results indicate that turbulence structures in cavity open-channel flows are classified into six regions and these structures can not be reproduced by standard k-ε turbulence model, but Reynolds Stress Model (RSM) has the ability to do them.

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The non-linear k-ε model is applied to 3-D computation of unsteady flows around a square cylinder in open channels. Applicability of the non-linear k-ε model to the Karman vortices in the 2-D flow field is firstly investigated through the comparison of calculated results with experimental ones conducted in the closed water section by Lyn and the model constants are adjusted. Then, the 3-D computations of unsteady flows around a square cylinder in open channels are carried out focusing on the Karman vortices and the horseshoe vortices generated in the upstream region of a cylinder. The effects of the depth to the 3-D flow structures are also investigated through the comparison of the numerical results under the conditions of the different depths.

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A new method of modeling free-surface effects for the calculation of open-channel flows has been developed and validation calculation has been performed. The new model is built around the well proven k-ω Low-Reynolds number turbulence model with an explicit treatment of the free-surface fluctuation and the intermittency of the large-eddy structure interacting with the free surface. Also the equations for the mean free-surface position and the fluctuation of the free surface are derived and modeled. The results are seen to agree very well with recent direct numerical simulation results as well as experimental data of higher Reynolds and Froude numbers.

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Turbulence modulation in a flow with neutrally suspended particles has been experimentally investigated. The turbulent field generated by an oscillating grid was adopted as a basic turbulent field. Since there is no mean shear flow in it, the steady state can be easily attained. In the present study, the spatial characteristics, such as 1-dimensional wave number spectra and integral-length scales, in multiphase turbulent flows have been examined on the basis of measurements by traversing FLV. The main results are as follows:
When neutrally suspended particles exist in the flow, new eddies whose dimensionless wave number kd/2π is about 0.2 are generated. The eddies seem to be those of wake due to a relative velocity between a particle and ambient fluid because the value of kd/2π corresponds to the Strouhal number S_t found behind a rigid sphere in an uniform flow. Consequently, a wave number spectrum has a peak around kd/2π=0.2 if a comparably large number of spherical particles are contained in the flow.

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Various types ofwave-absorbing works have been developed to prevent coasts fromwave-induced disasters and have been used with remarkable success. However, the effective dissipation ofwave energy generates a large amount ofsea water spray. When it is transported landward by a strong wind, severe salt damage will be caused along the coastal region. In this study, the generation of spray from a typical wave-absorbing seawall has been investigated experimentally. A parapet installed on the top ofthe seawall is very effective for the reduction of spray quantity. A perforated seawall method, which is proposed as a new method to reduce the spray generation, has been also examined. As a result, the new method can decrease 30-50 % of spray quantity generated by the typical seawall method.

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The turbulence fields on both sides of an air-water interface were examined experimentally in windwater tunnel. The turbulent quantities in the air behave similarly to those in flows over flat plates in openchannels. As for the water side, wave component and turbulence component were separated by a spectral separation method. Turbulence component has universal characteristics on a 2-D gravity wave. It became clear that turbulent structure and energy budget on both sides are closely related with each other and that energy transfer through the air-water interface increases when the wind becomes larger.

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When the wind blows over the water, there occur drift currents and wind waves due to the wind shear across an air-water interface. At that time, mass transfer across a gas/liquid interface is of fundamental importance to environmental and geophysical sciences. Some studies about the wind-induced currents have been conducted in the field of coastal engineering and geophysical sciences. However, there are few studies about the wind-shear induced turbulence. The present study was undertaken with the goal of evaluating the relationship between the wind waves and the turbulent structures across the air-water interface in the laboratory wind tunnel.

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Tsunami causes erosion and accretion in a harbor or a bay, which may result in the collapse of structures and the damage of harbors. It is important to calculate the accurate sea bottom changes by Tsunami. The strong pressure gradient transforms the velocity vertical distribution in a strait or a bay mouth where the flow is accelerated and decelerated rapidly. It is necessary to study the propriety of the method that the bottom shear stress is estimated by the mean flow formula.
Characteristics of the velocity distribution and the bottom friction velocity of tsunami were carefully investigated by experiments in a narrow strait where the Shields number is more than 10. The velocity distribution becomes uniform in the acceleration phase, and the bottom friction velocity becomes large by the strong velocity gradient near the bottom. Based on the results, the method of evaluation of the bottom sheer stress by the log-wake law is proposed.

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A method to compute turbulent bottom shear stress from free stream velocity variation under irregular waves has been proposed for plane bed condition. The correlation has been assessed through spectral analysis of free stream velocity and bottom shear stress obtained from generated irregular waves and from k-ε model result respectively. A significant improvement in the prediction has been achieved compared to that proposed by the authors earlier. Turbulent friction factor and phase difference obtained through spectral analysis corresponds quite well to those from experimental data for sinusoidal waves and with corresponding available smooth turbulent friction factor descriptions. Proposed method presents a high degree of accuracy and is very convenient to use from the viewpoint of practical application.

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Field observation of heat and salinity on/in sand bar by using buried data-loggers was carried out in the Yasaka river mouth in Oita Prefecture in order to obtain environmental data of spawning ground of horseshoe crab Tachypleus tridentatus. Temporal changes in salinity and temperature on the surface and 15cm below the ground level have been measured at 20 minutes intervals since July, 1997. During the observation, large flood occurred on September 16 due to heavy rainfall of Typhoon 9719 and sand bar was partly eroded out due to flood flow. During this flood rapid decrease in underground temperature as well as rapid change in salinity was measured due to the exposure of the apparatus to the surface. Exact erosion time was observed, implying that this method can be applied to the observation of disintegration process of river mouth bar due to flood flow.

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Field observation of topographic changes of ebb tidal flat caused by the large flood associated with Typhoon 9719 was conducted at the Yasaka River mouth in Morie Bay in Oita Prefecture. Large amount of sediment deposited on the ebb tidal flat due to the flood of maximum discharge of around 1, 500m³/s. Topographic changes were measured with an accuracy of 1 cm along four survey lines across the ebb tidal flat as well as aerial photographing of tidal flat right after the flood. Flood ran aground of the tidal flat from the meandering main stream of the Yasaka River to form many sand dunes. Numerical simulation of two dimensional flood flows was carried out and observed results were well reproduced by this numerical simulation.

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Topographic changes off the mouth of the Tedori River flowing into the Ishikawa coast facing Sea of Japan were investigated by using sea bottom sounding data collected between March 1986 and March 1989. Twelve sets of contour maps off the rivermouth were compared including the ones obtained during the elongation period of rivermouth jetties, which had beenextended by November 1988. Extension of jetties caused large scale scouring around the jetties. On the Ishikawa coast extending between the Tedori rivermouth and Kanaiwa Port north of it, southward longshore sand transport dominates and countermeasures using many detached breakwaters had been conducted. Development of southward longshore currents carrying sand off this rivermouth jetties implies that this coast is still being eroded since there are no large rivers supplying sediment to this coast.

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To study sediment continuity from river to ocean deposition, some field investigations have been carried out in Mukawa River and ocean around its mouth. Investigation items are a density of suspended solids (SS) contained in river water in a flood, river water diffused in the ocean space, trapping deposited mss on bottom of ocean and particle-size analysis of coast sand. The results are below,
1) Among suspended load and wash load diffused in the ocean, the sedimentation with particle diameter bigger than 0.1mm sediment to within the limits whose distance from a mouth of a river is 2.5km.
2) The surface material of bottom of ocean is greatly influenced by suspended load and wash load, which are supplied from river at the time of a flood.
3) The main composition elements of coastal sand near a river mouth are the ingredient with a grain fine among riverbed material and big among suspended material.

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A current inside the spillway becomes the high-speed flow of the open channel in the pipe. It becomes pulsation flow when a ventilation section can't be secured and when an air velocity becomes bigger than the velocity of the current. It is necessary that pulsation flow isn't made to occur because it becomes the problem of the vibration and the noise in this case.
We thought that a ventilation section was secured in the center of the section, with circling, a current is made to fall, by combining the curve which is vertical to the horizontal curve, referring to the research which has a bending part in the horizontal part about the spillway. It was found out that the tendency of the quantity of entrained air varied in the surface of the water shape in the vertical pipe, and that the surface of the water shape in the vertical pipe could be classified in four by the difference in the hydrological regime of the horizontal curve. It became possible that it was predicted pulsation flow and that it was designed suitably by this. As for the tendency of the quantity of entrained air, it was found out that it became the same with the in-situ measurement as a result of the model test.

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Air entrained phenomena can often occur in hydraulic structures, for exmaple, headtank spillway of hydro power plant, intake channel, outlet channel, underground rivers, and so on. When the air goes out into the water surface of the outlet, the shock and the noise happen, and the structures may be destroyed at the critical moment. However, these are not enough studied. This study is an experimental investigation for pressure fluctuations created by the two-phase flow of air and water in a horizontal pipe, 100mm ID, on free outlet condition and water surface outlet condition. Measurements are also presented for the local void fraction, the local air velocity, and the local large bubble length using Optical Dual Probe Method. The effect of the outlet conditions was clarified on the pressure fluctuations at multi

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In an intake and discharge channel of an electric power plant or a LNG plant, surging phenomena of water may cause a siphon break or an overflow at pits, and then may give a damage to the facility. A new numerical simulation method to predict surging was developed. In the method, the “slot model” was applied to the pressurized flow, and the MacCormack's scheme is used to simulate the mixed flow condition of sub-critical and supercritical flow. The water level in a discharge basin which is usually set at the end of the discharge channel can be calculated simultaneously. The laboratory tests were carried out to verify the simulation model for three types of channels. Three types of channels were a pressurized channel, an open channel and a channel which had a vertical bend at the end. All the channels have a discharge basin at the end. It is shown that the model can simulate an unsteady surging phenomenon for almost all types of channels.

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A sand basin installed in the hydroelectric plant is designed so as to be able to settle sand beyond a grain size so that degradation of discharge ability of the water channel and abrasion of water pressured pipe and turbine can be restrained. However, performance of the power plant is lowered when sand flowing in a sedimentation basin is beyond the designed value because of frequent sand removal works. Instead of the conventional work using sand removal gate, we propose here a vortex tube method with which electric generation operation is not interrupted during sand removal work, showing some related design methods.

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In connection with hydraulic experiments of an intake channel of power plant, we present a numerical simulation by mean of which an accuracy of flow distribution and a reproduction of separation are examined. Conclusions are as follows; 1) Simulation results agree well with those derived from a rough wall log-law function at the rough wall pipe (n=0.014). 2) Best simulation results are obtained at longer training wall and at a use of L-type lattice pattern. 3) It is found that simulation method used here makes possible to reproduce numerically the phenomenon of separation appearing frequently in an intake water channel of power plant

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Flow structure and the criteria for formation of intake vortices have been studied experimentally and numerically. A particular emphasis is placed on the influence of the inflow property such as shear and nonuniformity on the flow pattern and formation of intake vortex. In the experiment, it is verified that when the inflow contains vorticity or circulation, an intake ' vortex can form. Computational study is made to see if the highly three-dimensional and vortical flow in the intake bay can be predicted. Although there still is a limitation as to the grid density that can be handled with present-day work stations, and intense line vortex cannot be predicted, weak recirculation of the flow can be aptly predicted by the present method.

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We used a hydraulic model test to study the mechanism that creates sound when a hydraulic jump-type energy dissipater is set underground. The test was performed using four types of models with different sizes and similar in shape and the factors ruling the generation of sound was studied. We evaluated the characteristics of the frequencies and the relation between acoustic power and hydraulic conditions. We also assessed the characteristics of sound circulation in an underground space and found that it can be explained by way of air column resonance. In addition, we made a basic study of the effectiveness of an acoustic filter in reducing resonance.

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This paper deals with development of a new numerical technique with high-accuracy and resolution for advection. The 6-point scheme, which is a numerical solver based on the characteristics method for advection, is modified in order to make it possible to be applied to the conservative advection equation. The modified 6-point scheme is named the conservative 6-point scheme. The universal limiter and a new discriminator are incorporated in the conservative 6-point scheme to obtain numerical solutions which are not only highaccurate but also free from numerical oscillations. It is found that the numerical technique presented in this paper is able to give good numerical results.

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Numerical models based on flux-difference splitting (FDS) technique are developed for simulating rapidly varied flows in two-dimensional space co-ordinates. A first-order accurate model using Roe's numerical flux and a second-order accurate scheme using Lax-Wendroff numerical flux are constructed. Roe's averaging for velocity and celerity ensures conservation and consistency while entropy satisfying solution is guaranteed by theoretically sound treatment. Flux limiters used in second-order accurate model yields oscillation-free results while maintaining high shock-resolution. The models' validity and applicability are demonstrated by comparing computed results with analytical and experimental results for some exacting hydraulic problems.

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The Lagrangian concept of the discretization of the Navier-Stokes equation, or the MPS method, which is generally called the Particle Method, is applied to the unidirectional flow with the periodic boundaries at its upstream and downstream ends. The MPS method is less affected by the numerical diffusion due to the convection term than the Eulerian methods, namely it has a superiority in the accurate calculation of the complicated behavior of water surface. The characteristics of the pool-and-weir fishway is investigated by using MPS method as the typical flow situation with the complicated behavior of water surface and the applicability of the periodic boundary condition. The plunging flow and the streaming flow, which are known as the two sub-modes of the flow in the pool-and-weir fishway, are reproduced well. The complicated unsteady behavior of the flow under the plunging flow mode is numerically investigated by the present simulation.

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A three-dimensional numerical technique is developed for gas-solid flows within a complicated-shaped domain using curvilinear coordinates. Since the present technique is based on the discrete element method, it can predict individual solid particle motion and particle-particle and particle-wall interactions. In particular, the conversion from a physical space into a mapped space enables us to evaluate efficiently particle-particle contacts and gas vorticity and velocity at the particle position. The present method is applied to gas-solid flows in a horizontal straight pipe and a horizontal curved pipe. As a result, it has been shown that the predicted flow characteristics reasonably agree with the experimental results.

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A numerical model is one of the useful measures to predict the characteristics of the environmental systems on the interface of different density water. In the last few years, some models were already proposed to calculate each problems like flow in the stratified closed water systems and the saltwedge, and realized beneficial results. However, these models also have some defects. For example, turbulent models are sometimes difficult to use actually because of its theoreticalcomplexity, and simple two-dimensional models can not calculate so accurately. So in this paper, the new two-dimensional numerical model is proposed, which use CIP-scheme in the calculation of advection phase, in order to calculate density flow more accurately without using complicated models, and its availability is confirmed by the comparison between the results of the calculation and that of the experiment under the same condition.

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A highly accurate numerical model for unsteady free surface flows, based on spatially averaged two-dimensional shallow water equations, is constructed. TVD-MacCormack scheme equipped with 4-step algorithm is employed as a numerical method. The capability of the model is tested against several exacting hydraulic problems that include the Stoker's analytical solution for a one-dimensional dam-break problem and the one-dimensional and two-dimensional experimental results for flood waves, propagating in a horizontal channel where equi-spaced solid cylinders are placed over full or half width of the channel, are initiated by instantaneous collapse of a dam.

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In overland flood flow analysis, the cartesian coordinate system has been commonly used for its easiness of mesh formation. However, in the application of it to urban area, blocking of inundated flow by buildings or spread of it along streets cannot be well expressed. In order to improve this, “Generalized Curvilinear Coordinate” and “Street Network Model” in which a network is constituted by links of streets and nodes of cross points are developed here. The results obtained by the three models including the catesian coordinate are studied and the merit of “Street Network Model” is designated.

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This paper treats a numerical analysis of overland flood flow intrusion into underground space in an urban area. A one-dimensional network model to express inundation flow in underground space linked with a horizontally two-dimensional overland flood flows by river bank collapse is developed and applied to Umeda underground market in Osaka city. A slot model is used for the treatment of the pressurized flow condition in underground space. The results obtained show that the model developed here can simulate the aspects of inundation flow into underground space fairly well.

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Artificial neural network is an advanced topic which provides hydraulic and environmental engineers with a strong tool for estimating missing information to be used for design purposes and management practice. In this study, a neural network is used to estimate the natural sediment discharge in rivers in terms of sediment concentration. This is achieved by training the network to extrapolate data collected from reliable sources. Selecting an appropriate neural network structure and a training algorithm as well as providing data to the network are addressed using a constructive algorithm called back-propagation algorithm (BPA). Sensitivity analysis is performed for flow and sediment parameters. The predicted sediment concentrations are agreed well with the measured ones.

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In order to assess the sediment transport in a whole water system, a synthetic sediment routing model based on the river channel networks obtained from the digital elevation map was examined. The sediment routing model was applied to the Haya River basin and the Abe River basin. Through the application using two kinds of scale of channel network element, and the diffelent catchment area, effects of these elements on the simulation of river bed variation were discussed. The results show that the river bed variation in the two kinds of scale, 250m mesh and 500m mesh, shows about the same behavior except upper part of the basin, and themodel has a possibility to be applicable.

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The difficulties involved in calibration of physically-based erosion models have been partly attributable to the lack of robust optimization tools. Recently, a global optimization method known as the SCE-UA has shown promise as an effective and efficient optimization technique for calibrating watershed models. This paper presents the essential concepts of the SCE-UA method and a physically-based erosion model, and then presents the optimization results in which the WESP model was calibrated. On the basis of these results, the recommended erosion parameter values are given, which should also help to provide guidelines to estimate them in other similar areas.

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Authors have analyzed the stable longitudinal distributions of river channels using the Network Model. It is very important for solving the problems, not only for river engineering but also for coastal or sabo engineering, dealing with sediment discharge to estimate annual characteristics of sediment yieldof rivers.
In this study, we estimate the longitudinal distributions of the mean diameter and the width of river channels in Ashibetsu, Kanayama and Houheikyou Dam basins. Then the results are analyzed by field data.

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It is an important subject to evaluate sediment transport rate in river management works. Especially in a large scale river like Ishikari, establishment of a tool to predict the sediment transport at the estuary is becoming urgent subject from environmental view point. The propose of this paper is to study the effect of the past experienced flood to the grain size distribution of bed material and sediment load. For this propose, data of suspended load observation was collected and the suspended sediment observation was conducted in the Ishikari River. Using these data, and a numerical model, the relationship between suspended sediment load and the discharge history is discussed.

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Authors proposed the network-moder for arguing a stable longitudinal profile on the basin. This model enables us to evaluate the longitudinal variations of dischare and sediment discharge, bed elevation, mean diameter of bed materials, width of channels and flow depth. In this model, there are some assumptions that discharge from the outer link in all the basin, sediment discharge from the outer link, inflow and sediment inflow from the side basin in the basin of branches are the same. In the real basin, those factors are complicated by geographical and geological configuration. So in this paper, those factors ate varied every unit river channel. The irnpnwed network-model is applied to the Takisato Dam basin. So, the sediment discharge at Takisato Dam is estimated. The animal volume of deposition could estimate extending conception of sediment discharge under dominant flow discharge. Estimated annual volume of deposition at sabo dams in the basin was verified with the value offield data.

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In this study, sediment transport along the Saru River after construction of Nibutani dam is studied. The Saru River is known for transporting large quantities of sediment during flood. Sediment transport observation was conducted during the flood in 1997 at several stations, from the river mouth to upstream of the reservoir. A numerical model to calculate sediment transport rate, grain size of bed material, and bed elevation is developed. The calculated sediment transport rate is compared with the observed results and the validity of the model is confirmed. It is suggested that the model can be a powerful tool for the long-term prediction of the river bed environment changes including the effect of the dam construction.

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Field observations were performed on the Mukawa Bridge located 2.6km upstream of the Mukawa River mouth during the 1998 snowmelt flood. Observations were made of water level, discharge, bed material and various components of water quality. The following became clear as a result of the investigations.
There is strong correlation in the concentration of the Nitrogen and the Phosphorus, which is adsorbed to by the suspended solids, with the average grain size of the suspended solids. Some water-quality components increase with discharge, and other components do not change with discharge. The waterquality components, which increase in concentration at the time of the flood, are primarily the undissolved elements. It seems that the rise in concentration of undisolved solids at the time of the flood was due to the suspension of flood plain and near bank deposits.

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It is an important subject to understand the turbidity and the water quality in the catchment area of a reservoir. This paper reports the characteristics of turbidity and water quality at floods in the catchment area of Shichigashuku reservoir from 1996 to 1998.
It was proved from continuous observations at floods that the turbidity also increases with the flow discharge. Functional relationships between the suspended loads and the flow discharge were obtained. The correlations between the characteristics of turbidity and water quality were discussed. It was understood that the water quality correlates well with the unresolved loads of turbidity.

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