The Hydraulic design manual on energy dissipators has been reported on the basis of the experimental results on velocity characteristics of jumps, jump length, sequent depth ratio of jump, and etc. But, in these results, the effect of aerated inflow on characteristics of jumps has not been considered. Because, an aerated flow on smooth channel chutes has not been formed in experimental models even if the boundary layer of supercritical flow is fully developed. This paper presents the effect of the aerated inflow on characteristics of jumps in a sloping channel. The experiment reveals that the different flow condition is observed between aerated and non-aerated inflows. For an aerated inflow, the jump length can be reduced, and the maximum velocity at each section decays in a short distance when a downstream depth and a channel slope become large. The present study gives a significant point for the hydraulic design of an energy dissipator with a jump formation.

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Hydraulic jump of high-Froude number flow entrains air bubbles with high concentrations, thus scattering lowfrequency sound to the environment. In the present study, the frequency of the sound scattered from a dissipater of a spillway was predicted by the Helmholtz equation derived from a phenomenological equation of multi-phase flow. This low frequency sound was considered to be generated by the oscillation of the bubble cloud in the region of dissipater with high void ratio.
Based on the Helmholtz equation for sound wave, the eigen-value problem was solved analytically for the simplified models of the dissipater and numerically for the more practical model. The eigen-frequencies obtained from these models were compared to the experimental results and shown to be well-predicted by the present method.

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The vertical 2D movable bed simulator, which has been a key tool of the computational mechanics of sediment transport, has a limitation in describing some of details of sediment transport phenomena. Because all of sediment particles have their center of gravity on the same vertical plane, the 2D model cannot describe the effect of the particles existing in an external space of the calculated vertical plane. This limitation of 2D model brings some problems, which comes from a geometrical arrangement of particles, especially on the simulation of grain sorting. The framework of 3D movable bed simulator, which is based on the distinct element method, is shown herein. A dam-up process of sediment body moving on a uniform slope by fixed vertical columns is simulated to show some part of performance of the present model.

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The three dimensionality of grain sorting is investigated from a viewpoint of computational mechanics. The vertical sorting of mixed size grains under the uni-directional flow is simulated by the 3D numerical movable bed, which is based on the Distinct Element Method. The results of 3D model are compared with that of 2D model, to clarify the significance of the three dimensionality in the vertical grain sorting. The active transverse motion of grains is estimated through the time series of the gravity center of each class of grain by 3D model. Although the detail of the grain sorting, such as the transverse motion of grains, cannot be describe by the 2D model, the time series of volumetric ratio of each class of grain calculated by the 2D model shows fairly well agreement with that of 3D model.

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There occurs significant gully erosion and sediment runoff by rainfall on the slope of the Mt. Unzen Fugendake. This causes a large increase of bed elevation and sometimes great damage to the houses in the downstream area of the slope. In order to prevent the disasters, the prediction of the runoff of sediment and water is an important problem. It is necessary to understand the process of erosion and variation of a gully to estimate the runoff of sediment and water from the mountain slope.
The purpose of this study is to investigate discharge of sediment and water, sediment concentration, bank erosion and bed variation in the lateral erodible straight channel at steep slope.
From the experiments it is found that bank erosion causes an increase in discharge of sediment and water and sediment concentration in the channel.

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With problems caused by sediment manifesting themselves in recent years, the need for comprehensive sediment management has been rising increasingly. To solve these problems, the appropriate monitoring of sediment transport is imperative. Observation of bed load shifting near river beds, however, is difficult because it is prone to the influence of river flows and river-bed contours. For this reason, experiments on sound pressure generated by bed load were conducted using an experimental channel in this study. As a result, the underwater sound pressure was confirmed to be in proportion to the amount of drifting sand. It was possible to derive an experimental formula for bed load with single particle size of 3mm or larger.

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In the present study, we derived a model of yield stress of coagulated suspensions by developing our viscosity model previously proposed. Evaluated values of yield stress by the present model showed good agreement with the experimental results by Buscall et al., who measured yield stress of polystyrene latex suspension coagulated with 0.1 M BaCl₂ solution, where the electrical repulsive force between particles is negligible. From the analysis, it is expected that flocs become compact in higher values of volume fraction and prolonged shearing makes flocs compact.

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Erosion rate of cohesive sediment has been investigated experimentally to understand the effect of some major factors, such as the clay content ratio, the water content ratio, a water temperature and etc., on the erosion rate. Based on the experimental results, a simple erosion rate formula was also developed. In the present study, several check tests were conducted to verify the validity of the previous results. Soil mechanical test was also conducted to evaluate the shear strength of the test sample. Correlation between the shear strength (cohesion) and an erosion rate was explained in the present paper.

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A numerical model of hillslope erosion was constructed in the present study. A collapse model was newly developed and introduced so as to keep the local slope angle be equaled to or less than the angle of repose at any time in numerical computation. Also the effect of gravity associated with the slope angle in longitudinal and lateral directions on sediment transport rate was considered. The velocity field of sheet flow emerging on the slope was evaluated by solving the shallow water equations numerically with the aid of the CIP method. The numerical analysis was conducted with focussing on the hillslope erosion process, the effect of vegetation on it, and the sediment yield rate.

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The sediment control throughout the watershed is regarded as one of indispensable tools from the environmental viewpoint of landscape managements in the watershed. The purpose of this paper is to develop the previously-proposed sediment routing model into the framework which can predict the sediment runoff in spring and early summer in cold and snowy region on the basis of the effects of freezing and thawing on both the rainfall runoff and sediment runoff. The model proposed in this paper was applied to the Kuchoro river catchments whose large amount of yielded sediment has a considerable influence on the landscape of Kushiro Mire. Comparing the features of sediment runoff in spring with that in autumn may indicate the possibility that the coarser pore by frost and thaw suppresses the occurrence of surface flow and subsequently reduces the surface erosion, while the decrease in soil strength increases the sedimentoutflow due to riverbank erosion.

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Suspended sediment and nutrient transport were monitored during one year in two areas, one is the upper reach of a river which flow into Lake Hinuma, one is the estuary which is outlet of the lake. SS and particulate phosphorous (P-P) concentration can be estimated by turbidity using their correlation. The measurements of suspended load in the tidal channel were made using an acoustic Doppler current meter and turbidity meters. The amount of the sediment which is the difference between the sediment load monitored in the river and in the tidal channel during one year corresponds to the annual sedimentation rate in Lake Hinuma which was estimated by geological approach. The flux of P-P flow into the lake during floods reached 60% of the total phosphorous in one year. It is assumed that most of these P-P deposits in the lake and dissolved phosphorous released from P-P makes phytoplankton grow up.

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A serious sediment disaster occurred in the Camuri Grande River basin due to heavy rainfall on December 16, 1999 in Venezuela. In this paper, efficacy of countermeasures such as sabo dams in the ravines and channel works on the fan of the Camuri Grande is evaluated by numerical simulation methods. Efficacy of sabo dams is estimated by using a one-dimensional model, in which a very wide grain-size distribution of the riverbed material as well as several flow types such as a debris flow, an immature debris flow and a turbulent flow is taken into account. Efficacy of channel works is evaluated by using two-dimensional model, where a finite volume method using unstructured meshes is adopted. Efficacy of Sabo facilities are found to be evaluated reasonably by this method.

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Many numerical simulations of debris flow have been conducted. However, not only basic equations of debris flow are quite different respectively, but also the numerical analyses are conducted by researchers due to their approaches to the flow mechanism. The present study describes a method of one-dimensional numerical simulation, based on a flow model suggested by Egashira and Miyamoto. The results show the treatment of sediment entrainment, especially, the treatment of the front parts of debris flow by taking the dynamic condition on the bed surface into account.

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Present study deals with deposition-erosion process of debris flow with transition between fully dispersed debris flow and sediment sheet flow. A two layer is derived to unify these two kind of flows. An “interface” is introduced between upper layer which is mainly consist of water and lower layer which is mainly consist of sediment. This model consists of mass and volume conservation of water and sediment including an equation describing level change of immobile bed as well as momentum equation of the both layer. Numerical analyses were carried out to explain experiments of deposition-erosion process of debris flow and sediment sheet flow on the rigid or movable bed. Calculated results agree well with experimental data for wide range of condition.

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Deposition process of debris flow has not been examined in detail in a region around a point of abrupt slope reducing though the process is very important for disaster prevention planning. Several experiments were carried out to investigate the process by measuring profiles of free surface, interface if it appears and bed and by tracing sand particle locus. The experimental results were compared with those of computation of a two-layer model proposed by the authors to show good agreement in case of movable bed surface condition in upstream reach and some discrepancy with fixed bed there. This discrepancy was somewhat improved by modeling the equation for equilibrium bed slope

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Recently, many grid-type Sabo dams have been constructed. These dams have functions to pass through sediment transported during normal floods and to store hazardous big boulders transported by a debris flow. In this study, we pay attention to the sedimentation processes of debris flow by a grid-type Sabo dam, and flume experiments and numerical simulations are carried out using stochastic model of blocking by a planer grid-type dam. In this study, the model is expanded into the three-dimensional model and processes of the debris flow generation, development and sedimentation by a grid-type Sabo dam is expressed by the model. This model is found to be very useful to clarify the function of the grid-type Sabo dam.

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Transverse ribs are popular existences in a mountain river, those are composed of the transverse lines of large cobbles across a stream. For intension to apply the rib-step morphology to a fish-way, knowledge is desired on the configuration structures of rib-steps. Present paper describes results of field survey for the Gunbetsu River to clarify plan forms, rows of cobbles etc. of the ribs, and also deals with configuration features of experimentally formed ribs in a laboratory channel. From the both results, followings were found: Plan form of a transverse rib is not necessarily straight but curved line with S-shape or M-shape is more popular. The former transverse ribs are formed by comparatively large cobbles, while the latter transverse ribs are composed of the cobbles with various diameters. Correlation with respect to the diameters of adjacent cobbles is not strong, which shows the order of cobble diameters is rather random.

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Hydrodynamic mechanism of suspended load in open channel flows over woody plants was investigated based on the results of laboratory experiments. In the experiments, three-dimensional distributions of equilibrium sediment concentration were minutely measured in uniform flows over tree models uniformly arranged in a staggered manner. It was clarified that so-called dispersive flux plays an important role in the mass-conservation relationship of suspended load, and also that the diffusion coefficient of suspended sediment is almost proportional to the kinematic viscosity of flow. The experimental results of vertical profiles of horizontally averaged sediment concentration were accurately reproduced by a numerical model that includes an empirical model for the dispersive flux and a κ-ε turbulent flow model for the diffusion coefficient.

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On the transition process of dune formation, it is known that a hysteresis is observed that the critical Froude number at which dunes disappear when discharge increases is larger than the critical Froude number at which dunes reappear when discharge decreases. In this study, in order to explain the hysteresis observed in the dune transition, a weakly nonlinear analysis is performed with the use of the growth rate expansion method. The analysis leads a nonlinear amplitude equation, which shows that when wavenumber is 0.1-0.4, the type of bifurcation appeared in the dune transition is subcritical for σ=0.8. This result implies that there is a possibility that the hysteresis is caused by the subcritical bifurcation.

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Large-scale scouring was generated by the 1998 flood of the Shokotsu River resulting in revetment damage. The main channel was filled up by deposition during the 1981 flood of the Toyohira River. The cause of this scouring of the floodplain and deposition in main channel was considered for the purpose of understanding the impact of flood to channels. It seemed that the scouring and deposition was caused by the formation of double-row bars. In general, the nondimensional shear stress at the floodplain is smaller than at the main channel. Therefore, it seems that the floodplain is hard to be scoured. However, when the elevations of floodplain surface and main channel bed are not so different, a lot of deposition and scouring in channel is caused by multi-row bars during large scale flood. This phenomenon is shown in this paper using actual river data.

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In recent years circumstances surrounding river sciences have been greatly changing. It is noted that a river not only safely discharges water particularly during flood, but it plays an important role in creating an environment that is beneficial to people and a larger ecosystem. Therefore, new attempts to restore regulated rivers to their original, natural forms are underway.
In this study, restoration of a river that had been straightened to its original meandering course was conducted in simulation. To obtain basic data for understanding the flow regime and behavior of sandbars at the completion of restoration works, a model experiment was carried out.

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In the previous researches on the sand bed stability with finite amplitude and growth of alternate bars, it is assumed that flow changes over time due to the unsteady flow do not affect the generation of alternate bars. Hydraulic experiments on the formation of alternate bars under unsteady flow conditions are conducted in this paper. The wavelength and wave height of alternate bars differ significantly between unsteady and steady flow conditions and between rising and falling stage of the water level due to the flood wave. Unsteadiness is typical of actual formative conditions for alternate bars, especially for gravel bed rivers. Results suggest that finite amplitude effects of the flood-wave on alternate bar formation are not negligible when investigating their behavior under unsteady flow conditions.

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Sand bars in rivers have important effects on river meandering, which cause change of flow and disasters in rivers. There are a lot of studies on bars under steady flow. But unsteady flow (ex. artificial flood) has been considered to restore river environment. It has become more important to predict bed topology under unsteady flow.
In this paper, we calculate changes in riverbed by using 2-D shallow water equation model. The points of this simulation are boundary condition and shape of flood wave. Periodic boundary condition was applied to unsteady flow analysis. We compare with the result of numerical simulation and experiment results. Knowledge on boundary condition in the simulation can be gotten in this research.

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Temporal and spatial variation characteristics of braided streams between straight confining walls are studied by means of flume experiments and numerical simulations. Results are summarized as follows.(1) The number of streams produced in a straight channel depends on the width-depth ratio; the number of streams increases with the width-depth ratio.(2) The geometry of streams shows self-similar characteristics which suggests the possibility that the streams promote restoration of natural riverine ecosystem.(3) Small-scale bed geometry significantly affects the formation of large-scale bed geometry. In addition, stabilization mechanism of bars is discussed focusing on unsteadiness of flow and growth of vegetation. The results suggest that decrease of maximum water discharge promotes bar stabilization.

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Development of emerged mid-channel bar is very important in the formation of braided stream. Numerical model is one of the powerful tools to predict the flow and bed topography in braided streams, however, it is very difficult to simulate the flow and sediment transport at the boundary of emerged bars. In this paper, a numerical model is tested under the condition of emerged bars are developed, in which a technique is tested to take into account for the emerged bars. The calculated results are favorably compared with experiments of the formation of braided streams. The formation of braided stream and transformation of bar mode is discussed using the results of the calculation.

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The Yoshino River cohesive soil sample experiment showed two types of eroded bank; near-watersurface and under-water-surface. Flow field of the near-water-surface eroded bank was examined through physical bank model experiment and numerical analysis. In this paper, the flow fields near and inside of the both eroded banks are investigated. It shows that flow properties of the near-water-surface and underwater-surface eroded bank shapes are different, which signifies two different erosion mechanisms of the bank shapes. The numerical model, which was used to simulate near-water-surface eroded bank flow fields, could not reproduce the flow field of under-water-surface eroded bank because of its confined flow inside the eroded bank. A 2-D numerical model is developed incorporating SIMPLE method for the under-water-surface eroded bank. This model could reproduce the flow fields of successive model eroded banks of near-water-surface and under-water-surface for two different erosion stages.

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Movable bed experiments with large-scale bed forms and bifurcated channels were conducted by using a steep slope channel and heterogeneous bed materials in order to investigate mechanisms of stream channel change and sediment transport in a mountain river. From the experimental results and observation, it was found that a bifurcated channel in a mountain river has unstable mechanism such a mainstream changes alternately from one to another at the nodal point of bifurcated channel, and that bed evolution and sediment discharge in the lower reach are obviously influenced by the mainstream alternations. For interpretation of the mechanism, a simple mathematical model was introduced, which was derived from the sediment continuous equation. Self-excited change of a mainstream due to the change of sediment transport rate at the nodal point was shown by the model without considering influence of alternating bar migration.

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According to previous studies of compound meandering channel flow based on laboratory and natural streams data, two different flow characteristics have been identified; simple meandering channel flow and compound meandering channel flow. The existence of both characteristics depends on sinuosity, depth ratio and other parameters. These results become important information to design river structures and for river improvement. However, quantitative evaluations of the effect of plan shape, cross-sectional shape and hydraulic condition on the flow characteristics have not been investigated well. In this paper, we conducted experiments with small sinuosity channel (s=1.028) to study the effect of sinuosity and main channel width and relative depth. Thereafter, we compared our laboratory results with field data from 10 Japanese compound meandering rivers so that the effect of plan shape was analyzed. Finally, it showed that classification of the different flow characteristics of compound meandering channels were based on the representative parameters sinuosity, depth ratio, location of maximum velocity filament and maximum scouring depth at meander apex section.

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Cylindrical holes, so-called the pothole, are often found on the exposed bedrock in riverbed and riverbank. The formation process of pothole gives us a suggestion for considering an abrasion of concrete hydraulic structures. A sand by-passing tunnel as a measure against sedimentation in dam reservoir suffers the damage of abrasion caused by colliding cobbles. This paper intends to show the framework for evaluation of abrasion induced by colliding cobbles, through the simulation of pothole formation. The MPS method, which has a good performance in the simulation of rapidly varied flow with fragmentation and coalescence of water, is extended by adding the moving solid module as a model of a cobble. The motion of cobble driven by the stream in a pothole is tracked to evaluate the collision impact of cobble to the wall of pothole.

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It is commonly observed that, in pocket beaches, river mouths are located at either end of beaches adjacent to one of the headlands. Izumi et. al. presented a linear stability theory to explain the instability of river mouths in pocket beaches. The theory shows that river mouths cannot stay stably in the central region of beaches but can stay only within regions near either end of beaches when the capability of longshore sediment transport is not sufficient compared with the load of river sediment supply. In this study, a series of experiments are performed to study the instability of river mouths with the use of a simplified physical model. It is found that river mouths are always unstable at the center of beaches even without the shielding effect of headlands on the wave energy; thus, the shielding effect is not essential for the instability. Contrary to the theoretical results, river mouths are unstable at the beach center even if sediment supply is not sufficiently large.

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It is important to know quantity of wash load for the integrated sediment management from upstream through downstream river basins. Generally, both continuous turbidity measuring and bottle sampling are used for suspended-sediment concentration measurement in rivers or reservoirs.
Here, we have developed a new suspended sediment concentration measuring system with differential pressure transmitter (hereafter, we call SMDP). The SMDP has advantages in long-term and high turbidity measurement because differential pressure transmitter is measuring density of water directly. A floating type and a water circulating type are available, and both of them have shown good performances through field experiments at the Miwa dam, the Tenryu river and the Kurobe river.

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Reservoir sedimentation has strong influence not only on the function of reservoir but also on the balance of sediment through the river system. Although various methods for controlling reservoir sedimentation are available, the effectiveness and applicability are limited. Therefore, some new methods should be developed. We propose a new flushing system that is a combination of a by-pass tunnel and a sub-dam. The sub-dam is a small dam constructed at a little downstream of the upstream end of reservoir and equipped with a gate and an introductory channel. During a flood, the sub-dam is submerged beneath the reservoir water, and sediment is deposited upstream of the sub-dam forming a delta. After the flood, water stored upstream of the sub-dam is drained away through the by-pass tunnel. Then, the delta is eroded by the flow introduced from the gate of the sub-dam. The eroded sediment is transported into the by-pass tunnel. Efficiency of the introductory channel to control erosion process is investigated by flume tests. Two-dimensional numerical simulation is also carried out to reproduce the experimental results.

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Sediment accumulation in reservoirs is one of the serious problems in the dam management works in Japan. In this paper, two series of experiments are conducted to simulate the sediment release from the dam reservoir with an operation of water surface elevation of the reservoir. Onedimensional numerical calculation is tested using the experimental condition. It is found that the one-dimensional model can predict the behavior of the sediment movement. However, it is suggested that two-dimensional model is required to predict more accurate sediment movement.

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The bed profile of sediment deposition in a reservoir with a sand-mixture is studied in a steep channel. Following the findings on experiments in a laboratory flume for the mixture of fine and coarse sediment, the deposition profile is numerically simulated. The one-dimensional continuity equations of flow and the sediment transport are applied to calculate the bed profile of the mixture corresponding to the water surface profile. Due to the minimum energy at the critical condition of flow, a sub-critical region below the jump and a super-critical section above the jump are formed. The deposition of sediment occurs in the sub-critical region, where the flow velocity decreases. The difference of mobility of each grain size is considered in the sand-gravel mixture, where the sediment sorting in the part of the sediment deposition is occurred. The modification factors are introduced on the transport mode of individual particles in the sand-gravel-mixture.

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Discharge measurement is one of the most important subjects for river planning. The measurement through floating device, which is a typical method as the Lagrangian method, is being adopted extensively. Most of the rivers in Japan are compound meandering channels, which have complex flow field. Many of these rivers have phase difference between main channel and levee, and the flow fields due to phase differences become more complex. Therefore, we have to check the accuracy of the discharge measurements of those compound channels.
In this paper, we have presented the method of three-dimensional analysis of compound meandering channel. And we have checked the accuracy of discharge measurements. It is observed that the measurement values of those channels with phase difference have large errors. Those errors might be reduced by increasing the number of floating devices in the flood channel.

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Field measurements of surface flows on a river by using a helicopter were carried out. Image Velocimetry (IV) is applied for measurement of surface flow of the river. The images are taken by a video camera which is built in the helicopter. For tracers of surface river flows, the “Senbei” is selected because of its decomposable in natural situation.

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A pulse-to-pulse coherent acoustic Doppler profiler (HR-NDP) operating at 1.5MHz has been used to measure accurate vertical profiles of turbulence parameters, such as Reynolds stresses and eddy viscosity, and to test the parameterization of dissipation rate and stability function S_m in the model of Mellor and Yamada (M-Y). The HR-NDP and STD were deployed during the summer of 2001 for 18 hours in a tidal river. Reliable data with the HR-NDP were corrected with 3s intervals at the cell-size 3cm in the range 10-160cm above the bottom. Density profiles with the STD were taken nominally every 10min. In the near-bottom layer, the production rate deduced from the HR-NDP correlates with the M-Y closure-based dissipation rate, but the empirical constant B₁ is larger than that conventionally used in the model. The stability function S_m deduced from the HR-NDP does not agree with S_m of M-Y model.

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A new one-dimensional velocity measurement method using image analysis was developed. In this method, image intensity distribution for a line specified in the mean flow direction on a flow video image was cumulated in the temporal direction, thereby creating a spatiotemporal image with a striped pattern indicating the mean velocity on the specified line. The striped pattern is created due to the convection of image intensity conveyed by the mean flow. This method is applicable to river surface images videotaped from a riverbank during flood. Since the images are distorted the spatial resolution in the far field is relatively low; however, the presented method showed a favorable performance in the measurement of flood surface flow of the U River. The result was compared with that by the large-scale particle image velocimetry (LSPIV) and the new method's superiority was verified. Also a method for improving mapping relationship between the CRT coordinates and the physical coordinates was demonstrated.

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Hydrodynamic force exerting on a squre pillar placed in steady free surface shear flows were investigated experimentally. The angle of attack α of a suare pillar and the ratio of channel width B/d (blockage-ratio) to pillar width were changed in the range of 0deg;-45deg; and 3-30, respectively. It is found that the drag coefficient C_d of a squre pillar decreases with B/d in the range of B/d=3-14, and the values of C_d at a given α becomes constant when B/d≥14 when provided that the Reynolds number based on pillar size, namely R_ed≥2.0×10⁴. The values of C_d at a given α in a shear flow are different from those in uniform flow. Diagrams to describe the relationships between C_d and α as well as C_d and B/d are presented.

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The behavior of the flood flows in a floodplain with structures and hydrodynamic force acting on structures are investigated experimentally and numerically. The depths and the surface velocities of flood flows are measured by using image analysis and PTV, respectively. The hydrodynamic force is determined by a special device based a 2-component load cell. The model verifications of a numerical model based on FDS technique and unstructured FVM for 2D flood flows (FUF-2DF model) against these experimental data are made. It shows that the model can reproduce the complex behavior of flows and hydrodynamic forces acting on structures with reasonable accuracy.

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A criterion of walking in a stream of flood flow or inundated flow awoke wide interest especially after the disaster at Kurokura river in 1999. In this paper, generalization of critical walldng standard in a stream was made by using experimental results and the walking criterion applied in Ohi river in the17^th to 19^th century which is considered to be valuable in the sense of historical approval. Critical datum at Kurokuea river is also attached importance to the result. Some considerations were then made to the basis of evaluation of the proposed criterion and to some rescue methods based on the walking criterion studied in this paper.

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A flood of the underdrain and an inundation into underground space in urban area are ones of the primal targets of urban flood-relief measures. Complicated behavior of a water surface serves as a key on analysis of rapidly varied flow, which characterizes the flow in the underdrain waterway under a heavy rain. Herein, an inundation of underdrain waterway and sewer pipe and resultant motion of cover material are simulated by the MPS method, which is the Lagrangian gridless model of water flow, with a module of passively moving solid. The blown-up manhole cover by water jet and the lift-off of concrete cover materials of underdrain waterway with the increase of water pressure are well simulated.

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Construction of underground big rivers for peak cut of runoff forces researchers to investigate the problems of unsteady flow in a conduit at a heavy rain storm and improve the analytical methods for the flow. The important problem in this flow lies in transient phenomena between part-full and full flow, which have been reported by author to be strongly related with the shape of pipe inlet. But the effects and the transient properties are not incorporated sufficiently in the analytical methods. In this paper, the transient properties are investigated according to the hysteresis of the relation between head water level and discharge, and a hydraulic model is proposed to simulate the transient flow in the conduit.

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To predict 3-D particle's motion in swirling flows, a numerical model was proposed on the basis of theoretical equations of motion and rotation for a particle as well as the velocity distribution model for swirling flows. The velocity fluctuations, which were assumed to be the Markov process, were also taken into account. 3-D particle's motion in horizontal swirling flows was measured using imaging processing techniques. The validity of the proposed model was confirmed through the comparison with the experimental results. The effects of particle diameter and particle density on the particle's motion were investigated. The relation between the forces acting on the particles and the particle's motion were examined.

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To promote time and effort savings and to increase efficiency in experiment, numerical simulations have been applied in various cases. In an intake structure with a gradual expansion, streamline approaches wall and separation occurs due to Coanda effect. Using the standard κ-ε turbulence model, such a behavior in an intake structure cannot be well reproduced, especially in a separation region. In the present study, revived version of κ-ε model proposed by Abe et al.(1992) is applied to a flow in an intake structure with a gradual expansion. The results using this model show good agreement with laboratory experiment.

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Most of investigations on bottom boundary layer are for sinusoidal waves. In this study, flow properties in bottom boundary layer under irregular waves has been investigated from experimental data for rough bed condition. A method has been proposed to calculate instantaneous turbulent bottom shear stress from the variation in free stream velocity under irregular waves for rough bed condition. Instantaneous free stream velocity and a friction factor for significant wave or each waves included irregular wave have been introduced. Instantaneous bottom shear stress computed by the proposed method has been compared with experimental data. Proposed method presents a good agreement and has been found to be very convenient to use from the viewpoint of practical application.

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The relationship between principal components of water quality and biodiversity was investigated based on the water quality and benthic community survey of the Kano-river in Central Japan. The data of benthic community survey were involved in “National Censuses on River Environments” by Ministry of Land, Infrastructure and Transport. In this study, we used a reference model for estimating the relation between the number of individual biological group (i. e., species, etc.) under particular environmental condition and biodiversity indices. Our results showed that the values of biodiversity indices increased as the scores of principal components of water quality decreased when the score was bigger than a certain value, but did not change remarkably when the score was smaller than the value. This trend was similar to that of model estimation if weaker groups are supposed to be dominant under good environmental condition.

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A field observation was conducted to know water quality and soil in a mangrove swamp. The sediment characteristics, the water qualities and the ground water height were measured in a mangrove swamp in Ishigaki Island. It was found that the concentration of dissolved phosphorus in the groundwater of the mangrove swamp takes a larger value than that in the main channel, while there is no significant difference in the concentrations of dissolved nitrogen between the groundwater of the mangrove swamp and the main channel. During a high tide, the seawater containing a large amount of oxygen inundates the mangrove swamp, and therefore the concentration of dissolved oxygen in the groundwater of the mangrove swamp increases around the peak high tide. The supply of oxygen from a coastal area supports biological activity in the mangrove swamp.

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This paper deals with the characteristics of water quality loads from the watershed in a snowy and cold region. Specifically, an attempt was made to estimate the water quality load factors from the Ishikari River watershed, where the land use consists of forests, farm land, urbanized area, etc. The water quality loads were supplied by non-point and point sources. The point loads were estimated on the basis of statistical data such as population, while the non-point loads were related into the land use and their characteristics were investigated.
As a result, the water quality load from each source could be monitored throughout the entire watershed, thus it was determined that it is of practical use to evaluate water environment related to land use.

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In order to evaluate the relationship between land use and river water chemistry, inorganic ion concentrations were monitored in the Kishi and Zakuro Rivers. The drainage basin of the Kishi River is mainly covered with forest and the orchard is widely distributed in the lower stream of the Zakuro River. In the Kishi River, the concentrations of Ca²⁺, Mg²⁺, K⁺, HCO₃^-, SO₄^2- and NO₃^- gradually increased down the stream. On the other hand, the concentrations of Na⁺ and Cl- did not changed in the upper and middle streams and sharply increased in the lower stream where the residential area and paddy field made rapid progress. In addition, the concentration of NO₃^- increased and the others decreased with increasing flow rate due to rainfall. Contrary to this, in the Zakuro River, the fertilizer used in orchard has affected the concentrations of NO₃^-, SO₄^2-, Mg²⁺ and Ca²⁺

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