Accurate estimation of discharge hydrograph during flood events has been one of the most important issues in River Engineering. In this study numerical simulations of flood flows in a compound meandering channel are carried out using a 2-d numerical model to discuss the possibility to reproduce the discharge hydrograph only with the information on water levels. It is demonstrated that the numerical simulation with water level hydrographs at upstream and downstream boundaries can well reproduce the discharge hydrograph at the section in the middle reach and hence that the discharge hydrograph at upstream end is not always necessary. It is also shown that since discharge hydrograph is very sensitive to the magnitude of floodplain roughness, even a record of flood discharge at high water stage, not necessarily at the flood peak, may give good estimation of floodplain roughness, leading to highly accurate estimation of discharge hydrograph.

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To enhance the efficiency of mapping spatial distribution of surface soil material, we have developed and assessed a new mapping method of surface soil material using digital aerial photograph, image analysis and GIS. The method can map the spatial distribution of surface soil material schematically. The method can calculate attributions (Area, edge line) of every surface soil material quantitatively. The method is very useful for understanding relation between spatial distribution of surface soil material and vegetations.

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To examine the suspended-sediment transport from inland to costal areas in Tokyo Bay, we have monitored the suspended-sediment transport in main rivers flowing into Tokyo Bay, which are the Edo, Ara, Tama, Naka and Sumida Rivers. In the field surveys, we have installed an optical sensor for measuring turbidity and water samplers to measure the sediment concentration and particle size under flood flow conditions. The observed results reveal that the fine sediments of particles less than 71 μm are mainly transported in the main rivers under several flood flow conditions. The transports of finer and coarser sediments are relatively dominant in the Ara River and the Edo and Tama Rivers, respectively.

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In recent years, river flow measurement equipment such as ADCP (Acoustic Doppler Current Profilers) has come down in cost and instrumentation technology has improved. As a result, developments of new flow measurement techniques and data correction methods are actively advancing. We measured the flood flow of Typhoon No. 5 in the Shimanto River at Gudo point in 2007 using an unmanned boat equipped with ADCP. From the measurement results, we report on boat operation in high velocity currents, methods of correcting measured data, and accuracy evaluation methods concerning moving observation using ADCP.

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Secondary flow in a river was measured by a boat-mounted Acoustic Doppler Current Profiler. Three methods were tested, i. e., A) measuring in a fixed cross section with single back-and-forth, B) measuring in a fixed cross section with multiple back-and-forth, and C) measuring without fixed sections but randomly in the whole tested area. Reliability of the methods was examined via drawn primary and secondary velocity distributions. Applicability of the methods for a particular purpose was also discussed.
The method A, which is widely used for river discharge estimations, gives primary velocity fairly accurately. The method B gives the best results for secondary flow structure amongst the tested if the estimated time is good enough. The method C shows similar performance in accuracy as the method A, but it has an advantage of covering the whole flow field, even roughly, but with less time and efforts.

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Discharge can be considered one of the most essential hydraulic parameters to know about a river for managing it. Ordinarily, the H-Q equation is used to estimate the discharge from the level of a river. Certainly, this provides acceptably accurate estimates in the upper reaches of rivers. In estuaries, however, its accuracy is fatally degraded. In the initial part of this study, a river was divided into 15 zones in the traverse direction, and the discharge in each zone was compared with the actual discharge of the river itself to see what kind of cross section allowed the local discharge to show the best correlation with the river discharge. Then, ADCP were placed on the riverbed and longterm measurements of the flow speed distribution were taken for comparison with the discharge as indicated by actual measurements. A clear proportional relationship was obtained between the two sets of data. It is clear that the equation relating the data sets provides a far superior estimate of discharge over the H-Q equation.

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An acoustic velocity meter (AVM) has been developed to measure river discharge continuously. The AVM has breakthroughs as follows : 1) accurate time with GPS clock signals, 2) high signalto-noise ratio with tenth order M-sequence, 3) thrifty power consumption, reduction in size and weight. The AVM installed at the Ohtagawa diversion channel, where the water level and salinity change significantly, successfully measured the cross-sectional average velocity and discharge for a spring tide. In addition, the intrusion of saltwater was detected from the sound speed data of the AVM. The cross-sectional average velocity and discharge give close agreement with those deduced from an acoustic Doppler current profiler.

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We have recently developed a new river-discharge monitoring system with an H-ADCP measurement and numerical simulation in which a DIEX method is used to accurately interpolate and extrapolate the observed velocities in a cross section with satisfying dynamic principles. In the present study, we attempt to apply this system into the discharge monitoring in the tidal reach of the Sumida River. The measuring accuracy of the H-ADCP is strongly influenced by vertical density stratification and high turbidity conditions, showing that the range of the data assimilation in the DIEX method must be changed due to these conditions. The simulated discharge with the present system gives acceptable agreements with the observed results, indicating the fundamental applicability of the present system into the discharge monitoring in tidal rivers.

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Acoustic Doppler current profilers (aDcps) offer the potential for measuring suspended sediment concentration profiles. In recent years, aDcps operating at a few megahertz frequency have been able to measure velocity and backscattered signal profiles with a high degree of temporal and spatial resolution. Moreover, the blanking distance near the transducer becomes short. As a result, the aDcps may attain high-resolution measurements of suspended sediments in the bottom 1-2 m above the bed. However, a modification needs to be made to account for the complex beam pattern close to the transducer (near-field) . In the present study, the backscattered signal of an aDcp operating at 2 MHz is examined. The backscattered signal profiles corrected using the near-field function by Thorne give close agreement with suspended sediment concentration profiles on the tidal flat in an estuary.

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This paper deals with the applicability of the computational method to predict fluid forces acting on complicated-shaped solid objects included in free-surface flows. The computational method, MICS, predicts the fluid forces from the pressure and viscous terms of the incompressible multiphase fields. A solid object is represented by multiple tetrahedron elements and their volume fraction included in a fluid computational cell is estimated with a sub-cell method. The predicted results were compared with the measured fluid forces acting on a wave breaking block placed in free-surface flows. The validity of the computational method was shown through the quantitative comparison with the experimental results.

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It is important to evaluate the falling and accumulating processes of the complicated-shaped blocks dumped to river and sea bottoms to create artificial fishery area. This paper presents a computational method for multiphase fields with a T-type solid model, which allows us to deal with the movements and collisions of the complicated-shaped objects in free-surface flows. In the T-type model, an object is represented by multiple tetrahedron elements and contact-spheres are placed near the surfaces. Thus, the volume, mass and inertial tensors are accurately represented, while the computational load to treat collisions of the objects is quite small. It was shown that the accumulation of the multiple blocks dumped into a water tank was reasonably predicted by the present method.

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We have been investigating a sediment-laden flow used by a solid-liquid two phase flow model, in which motion of each particle is tracked by solving the Basset-Boussinesq-Oseen (BBO) equation. Hence, a modeling of interaction between solid- and liquid- phase was required, and consequently an accuracy of flow velocity field around particles was insufficient. In this study, we developed a model to solve the flow field around each particle with high resolution, and the Distinct Element Method (DEM) is applied to track each particle with taking interparticle force into account. After the performance of this model is confirmed in a basic test, a sedimentation process of particles in liquid was simulated.

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In dense vegetation, which is bent and swung by a flow because of its flexible structure, organized motion which is so-called honami can be seen. Flow field with vegetation layer is characterized by an eddy due to flow instability which brings velocity profile with an inflection point around the top of vegetation layer. A time-dependent and spatial change of vegetation density due to phase difference of swing motion of vegetation is known as one of the major characteristics of flow with flexible vegitation. In this study, the particle method is applied to analyse a flow with flexible vegitation with developing new model of flexible vegetation by introducing one-dimensional elastic body model.

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Because a frequency of heavy and concentrated rain may tend to increase in these days, danger of overtopping flow of river embankment becomes to be higher. Hence, it is strongly required to estimate a critical state of embankment failure under an overtopping flow in designing a river embankment. In this study, numerical simulations of an overtopping flow of an river embankment are carried out by a particle method. Hydraulic characteristics of a flow and forces acting on an embankment calculated by the particle method are compared with a hydraulic experiment. Furthermore, erosion process of an embankment due to an overtopping flow is simulated.

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Nature friendly hydraulic structures such as a rubble mound weir have attracted attention in recent years. Therefore, it is important to establish an analytical model to analyze the flow around such a porous weir. The aim of this study is to develop a destruction prediction model for the rubble mound weir under a gradual increase of discharge. The VOF (Volume of Fluid) method was used for the flow analysis around and through the rubble mound weir, and the DEM (Distinct Element Method) was used to express the failure process. A proposed VOF-DEM coupled model can feed back the movement of the DEM particles to the flow analysis of the VOF. It is confirmed that the proposed model can reproduce the step by step destruction of the rubble mound weir similar to the experimental results.

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A computational method has been developed to predict the movements of driftwoods transported by three-dimensional free-surface flows. A T-type solid model is introduced into the prediction method, MICS, which deals with a free-surface flow including floating objects as a multiphase flow field. In the T-type model, a driftwood is represented by multiple tetrahedron elements and its volume, mass and inertial tensors are accurately represented. The contact forces are evaluated with the contact-spheres distributed near the surfaces. The MICS with the T-type model was applied to experimental results and it was shown that the movements and accumulation of driftwoods are reasonably predicted by the present method.

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A new numerical solver is developed for the quasi-3D river flow model to simulate meandering river flows. This solver can investigate the flows in the arbitrary curved river channel, by means of the adaptive CIP-Soroban (CIP-S) scheme in a cylindrical coordinate system with support of a boundary fitted coordinate (BFC) system. Time development of water velocity in the convection phase is computed by the orthogonal curvilinear coordinate system without any transformation of the governing equations, whereas the continuity equation is solved by the BFC method, so that the mass conservation is fully satisfied and the water level is accurately calculated. From the verification of this solver of the meandering river flows with the pure BFC method, it is shown that the proposed numerical solver reasonably predicts the main flow profile in a periodically curved open-channel, and that the horizontal velocity profile both at the free-surface and at the bottom is reasonably predicted with the effect of the secondary currents in the curved section of the river.

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Boundary-fitted calculation methods have traditionally used the generalized coordinate system which is required the condition that the coordinate axes intersect. When meandering formation extremely develop, the channel eventually is short-circuited. Because of this, general coordinate system should not be applied to evaluate that problem. This study proposes a new boundary-fitted calculation method that combines a co-orthogonal coordinate system and a boundary-fitted cell system. To validate the accuracy of this method, it was applied to reproduce the flow regime of a meandering channel measured in a previous flume experiment. The calculation method was generally successful at reproducing the flow velocity distribution.

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A curved open channel flow is characterized by formations of cross-sectional secondary currents. The main structure of the cross-sectional flow is classified into the secondary current of 1st kind, which is caused by the centrifugal force. The outer-bank cell is generated near the corner between the surface and the outer-bank. Though the scale of the outer-bank cell is much smaller than the main secondary current, the outer-bank cell affects the erosion of the outer-bank. The previous studies showed that the outer-bank cell is initiated by two combinational effects, i. e., turbulence an-isotropy and the centrifugal force. Therefore, the criterion of the outer-bank cell is rather complicated. In this study, linear and non-linear k-E models are applied to the mild curved open channel flows studied experimentally by Booij (2003) . Only non-linear models could capture the outer-bank cell and could reproduce velocity and Reynolds stress profiles well. A 3rd order non-linear model slightly improved the accuracy. The computations with different curvature radiuses indicate that the linear k-E models can also generate the outer-bank cell in cases of very sharp bend. The threshold of R/H by the standard model for generation of the outer-bank cell was 22. The model with lower eddy viscosity could yield the outer-bank cell in the flows with larger R/H.

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In the applications of the Large eddy simulation (LES) to open-channel flows with roughness, water surface is usually treated as a fixed boundary by neglecting the effects of surface fluctuation generated by boil vortices or relatively large surface variations caused by the drag force at each roughness element. In the present study, in order to expand the applicability of LES to such general conditions, the bottom topography is treated by introducing the immersed boundary method and the free surface variation is simulated by introducing a density function. It was made clear that the developed model is capable to represent relatively large surface variations in the strip-roughness flows with various roughness spacings. The numerical results agreed fairly well with those obtained by PIV.

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Correct representation of the effects of the turbulence structure near solid boundaries is very important for successful large-eddy simulation (LES). In the present work, this so-called wall-layer modeling is done on commutation error terms near solid boundaries obtained by explicit filtering. These terms are ignored in conventional LES, but in the present work, these error terms are modeled using a dynamic procedure, making use of the scale-similarity of the modeled terms. It is found, by applying the procedure in LES of a high Reynolds number channel flow, that the dynamic modeling of these error terms makes it possible to gain the roughly same velocity profile as DNS results statistically, and moreover, to simulate the features of large-scale structures instantaneously.

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A two-dimensional numerical model for free-surface flows was constructed. The model was based on the high-resolution upwind scheme with MUSCL (Monotone Upstream-centered Schemes for Conservation Laws) technique, SMAC (Simplified Marker and Cell) method and a collocated grid system. The free-surface was treated by VOF (Volume of Fluid) method which was one of interface-capturing methods. The model was verified against experimental data of the dam-break flow propagating over a triangular bottom sill as well as flow at downstream from a groundsill. It showed that the model can reproduce the behavior of the dam-break flow and the flow at downstream from a groundsill.

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A computational method has been proposed to predict the interactions between free-surface flows and elastic bodies included in the flows. A solid model, whose deformations due to fluid forces are solved with a finite element method, is introduced into the MICS, a computational method for incompressible multiphase fields. A solid object included in the flows is divided into multiple tetrahedron elements, through which fluid-solid interactions are taken into account using a tetrahedron sub-cell method. The developed computational method was applied to the experimental results, which were obtained in an accelerated tank with elastic plates. As a result, the validity of the prediction method was confirmed.

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A new vertical two-dimensional numerical solver for a water flow in a reservoir is proposed. In the proposed solver, for a precise representation of small fluctuations of water surface and arbitrary curved bottom of lake, CIPSoroban method is employed. While advections are solved with a low numerical diffusion error by using Constrained Interpolated Profile (CIP) method, by using Soroban mesh system that enable to rearrange computational mesh points freely such as a Japanese abacus, the model can solve a time evolution of water surface and density flow with a high spatial resolution. In order to apply the method to a density current in a water reservoir, a three-dimensional k-E turbulent flow model is averaged in a direction crossing a reservoir and a set of averaged two-dimensional equations are derived. These two-dimensional governing equations are combined with the heat balance equations and time evolution of a water temperature is solved. The proposed numerical model is applied to the Shichigasyuku reservoir. It can restore a time evolution of a water temperature distribution reasonably.

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This study present a combined numerical model of a porous flow model that employ a non-Darcian resistance law and a 3-dimensional Large Eddy Simulation model in order to investigate 3-dimensional and temporal structures of flows around a rubble mound groin. A model's accuracy is cross-checked by comparing numerical results to observed results of an existing experiment, and model's results show good agreement in terms of time- and depth-averaged sense. Calculation results also imply that a permeable groin restricts growth of secondary flows in a constriction section. However, a combined model is not able to produce unsteady characteristics of flows that are caused by small scale and structured turbulences in a down-stream region of a groin.

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It is with much frequency that we can't get enough field data to define boundary conditions for hydraulic calculations especially in developing countries. The authors faced this kind of problem in a research on water exchange of the Neijiang, a tideland located in the lower reach of the Changjiang in China. This paper presents a process to estimate the boundary conditions for quasi-3D numerical simulation from limited available data: The water exchange of the Neijiang is controlled by the flow rate and the water stage of Changjiang which are highly changed in a day by tidal waves going up from the river mouth. In this study, 1-D unsteady flow model was constructed and calibrated by using the monthly flow rate at a far upstream station free from the tidal effect and the hourly data of tidal level at the river mouth, and the flow rate and the water level near the tideland necessary for the quasi-3D calculation were estimated. The results were checked by the water level data at one of the mouths of the Neijiang.

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Recently 3D laser scanner systems have been widely and effectively used to measure the physical environment of river. However, it is still very difficult to obtain submerged river bed topography. To overcome this problem, this paper proposes a new and practical method to interpolate the submerged bed elevation to compensate for the weak points of laser systems. First, we obtain the detailed bed data in an experimental channel by a laser scanner system. The performance of a geometric interpolation method using bed elevation and its gradient at water edges is discussed. Then we show the significance of water surface profile in estimating river bed profile through the comparisons between the interpolated and the measured data. And we formulate a new hydrodynamic interpolation method of river bed topography under water surface using water surface profile. The hydrodynamically interpolated submerged bed river shape is found to show good agreement with the measured data.

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We assumed two-dimensional advection-diffusion equation to be a basic equation and aimed to inspect the applicability of CIP method with tangent conversion through two benchmark problems. On the Skew Flow problem, we got superior results that CIP method with tangent conversion could catch a discontinuous border sharply without causing numerical oscillation. On the other hand, on the Rotating Cone problem, we got good results on the short time simulation but in the case of long time rotating cone velocity field CIP method with tangent conversion could not reproduce initial profile, so the room of improvement of the scheme is left.

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In this paper, we proposed a basin-scale distribution model for stream temperature prediction in a river network. The model used geomorphologic laws of river basins in order to connect channel segments from the sources to river mouth. In each segment, a theoretical solution derived from a thermal energy equation with Taylor-series approximation was applied to predict longitudinal variation of river temperature. The present model was able to predict the stream temperature distribution when the geomorphologic characteristics, the topological structure of the river network, and the meteorological and hydrological conditions were given. Comparison of the model prediction with the observation showed good agreement for the whole temperature increase from the source to mouth. However, more consideration, such as land use effects, will be needed for higher accuracy of stream temperature prediction.

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It is very important to predict the influence on the downstream from a dam reservoir by the effluent because of the river environmental protection of the future. In this paper, the stream temperature management system at the downstream from a dam reservoir was proposed. The 1-dimensional numerical model by the MacCormack scheme was used for prediction of the variation of the stream temperature, and the simple formula of the streambed heat transfer was introduced into the heat transfer equation in this model. The validity of the numerical model was shown from the simulated results for the field observation. Moreover, the applicability of the numerical model using the GSM-GPV was examined, and the stream temperature management system using the GPV was proposed.

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Water environment at tidal flat is maintained by the provision of groundwater in Ota River Floodway during a flood. In this paper, variation characteristics of groundwater quality in the tidal flat, located in 5.4 km upstream from Ota River mouth were investigated by river discharge and groundwater level in Ota Rive Delta. It is considered that salinity of the groundwater in the tidal flat was decreased by outflow of the groundwater in Ota River Delta. The high gradient of water level was formed by high ground water level in the rainy season and small amplitude of the tide under the ground of the delta. As a result, ground water in the delta is easy to flow into the tidal flat.

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The purpose of this study is to demonstrate the process of deposition and influence of human and natural impacts to sediment in Imazu tidal flat. In this study, various impacts on Imazu tidal flat were examined with the use of topographic, aerial photographs, rainfall record. Then, analysis of core sample's gradation, ignition loss, ¹³⁷Cs and ²¹⁰Pb was studied to clarify the age of sedimentation and historical change of environment of sediment. The results were as follows. The urban development around Imazu tidal flat has had worse influences on the sedimentary environment. The sedimentation rate of Imazu tidal flat was calculated 0.47-1.12cm/y since 1963, and in 1954-1963 was 1.56-3.56cm/y by the analysis of core samples. It was calculated that 5640-13440m³ sediment was discharged from catchment area annually, and 47520-333720m³ sediment flowed in Imazu tidal flat in 1953 by these results. It was assumed that this was caused by the flood in 1953.

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To clarify the deposition process in a riverine-type mangrove area which is directly influenced by terrestrial water with rich nutrients and high suspended-sediment concentration (SSC), we have conducted field measurements on suspended-sediment transport and deposition process in the Miyara River, Ishigaki Island, Okinawa, which has a typical riverine-type mangrove forest. The observed SSCs in the swamp are relatively lower than those in the creek under hydrologic events. The observed results reveal that the accretion rates of ground level are 3.1 and 1.3 cm/year in the upstream and downstream regions of the swamp, respectively. These facts demonstrate that the deposition rate of sediments are dominant in the upstream regions due to the huge environmental impact from inland and the mangrove swamp may capture a large amount of suspended sediments.

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The discharges of urban rivers in Japan are poor because of heavy water use and the water quality of them is better than those in 1970s but not desirable even today. They are also tidal, and the concentration of dissolved oxygen (DO) in the intruding saline water is very low. Therefore, the characteristics and dynamics of the water quality in them are very complicated. In the presenting paper field observation is carried out in order to clear the temporal and spatial characteristics of nitrogen, phosphorus and DO and the influence of tide and saline water in the rivers and canals which flows through the city center of Osaka. Two kinds of upstream waters flow into the area, and the water containing higher concentration of nutrients remains longer in the rivers. The water masses in which the concentration of DO is lowest are found in the saline water near the river mouths.

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In order to clarify formation process of water quality in tidal area of urban rivers, the field observation and its results of the salinity intrusion and spatial distribution of water quality in the tidal area of Kanda River, Nihonbashi River, Sumida River and Arakawa River are reported in this paper. From the results of field observation, following results are obtained; 1) BOD concentration show high value at Sotobori point and Upper stream of Sumida River and Arakawa River points. BOD Concentration of Arakawa River and Sumida River gradually decrease from the upper river side. 2) T-N and T-P concentration show high value at almost all observation points. 3) Salinity intrusion is a strong mixed type at high tide and weakly mixed type at low tide in Nihonbashi River. 4) After rainfall, dissolved oxygen concentra tion of Nihonbashi River is decreased, and it takes 6days to recover to initial concentration.

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In this study, the kind and the transport characteristics of floating garbage are examined in Hori River located in center part of Nagoya city. By field observation on floating garbage in Hori River, it was found that more than 70% in floating garbage is natural garbage, a lot of artificial garbage appears in downstream area and the most natural garbage are dead trees and grasses entering into Hori River. In addition, from investigation on floating garbage in water area of Matsushige lock, it was seen that water area of Matsushige lock affected prolongation of floating garbage in Hori River. By numerical analysis, it was seen that the transport characteristics of floating garbage in water area of Matsushige lock is the influence of water flow caused by density change of tidal phenomena in Hori River.

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Previous evaluation of pollutant loads for the basin of Tokyo Bay are not accurately treated with the influence of flood-flow conditions. In the present study, we attempt to clarify the nutrients and COD loads in the main influent rivers under hydrologic events. For this purpose, we mounted automatic water samplers at the Edo, Ara, Tama and Naka Rivers. The observed results indicate that specific relations between river discharge Q and water quality are found in each river. The pollutant loads in the Ara and Naka Rivers are dominant in flood and low flow conditions, respectively. The large amount of the nutrients and COD loads were transported under flood flow conditions in all rivers.

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This research is one of the field survey on the self-purification of the contaminated river water in a small town area, in which the undertaking of drainage works has been underconstructed during about 8-years. The field survey basin is about 5 km2 area and about 3.6km length of channel and then six-stations are decided for measuring points of water quality such as temperature, DO, conductivity, BOD, T-N, and T-P, still more volume of flowing water. The results obtained during 8-years are discussed about time series change characteristics. Especially, the purification effects of BOD, T-N, and T-P were maked clear by rate values of improvement relating to the diffusion ratio of drainage.

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Subsequent realization of the significance of diffuse sources necessitated the need for assessing the impact of land use characteristics on river water composition with alternative methodological approach. This study collected water samples from Saka River basin and the concentration of major ion s were analyzed. Proportion of land uses of the respective drainage basins were calculated from GIS data. The results were analyzed with the objective to find out the relationship between land use characteristics and water chemistry. Forest dominated sub-watersheds showed lowest ion concentrations. As the urbanization progressed, sub-watershed became to contain more ions. Urbanization induced positive significant relationships with Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl^-, SO₄^2-, TMI (Total Major Ions), while farmland with K⁺, SO₄^2-, TMI, and Industrialization with Na⁺, K⁺, Cl^-, TMI. These trends are distinguished more clearly using hexadiagram of the ion concentration and PCA scores for the sub-watersheds.

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In this study, water quality characteristics of citrus grove soil leachate were investigated. Citrus grove soil contains nitrogen and phosphorus in high concentrations due to the high amount of fertilization, and its soil pH is also very low. Therefore it is considered that not only nutrients but also some problematic materials such as Al and Pb for aquatic livings and ecosystem at the watershed can be contained in the leachate. It is also concerned that the materials can be discharged into the downstream site as a result.
It is observed that pH of leachate is in the range of neutral, and the concentration of Al is not at the level where the aquatic livings and ecosystem can be affected. However, some heavy metals can be discharged and nutrients can cause eutrophication. It is suggested that citrus grove can be a big n onpoint source of nutrients.

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This paper discusses the water quality formation in the headwater zone of a river with a dam reservoir at its downstreamend. Other result analysis indicates that, the released water from the purification center in the upstream affect very match influence the water quality of the reservoir influent most became clear. Moreover, it is understood the water quality formation of the valley can be classified with the land cover in the catchment. In addition, the necessity of the forest management was suggested from observed value of the TN and suspended solids on private ground. One of the source countermeasures that consider the water quality control of the reservoir is to pay attention to the fluctuation of the released water at the purification center.

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A large number of studies have been made on longitudinal changes of fish fauna, however, the relationship with the engineered viewpoint is little known. The purpose of this paper is to investigate relationship between longitudinal changes of fish fauna and segment classification defined from the viewpoint of flood control.
We focused on 15 rivers in Kyushu and run TWINSPAN analysis to divide the fish fauna longitudinally and compared segment classification.
The result of analysis showed that segment classification is largely corresponded with longitudinal changes of fish fauna and the values of longitudinal gradient which is the boundary of longitudinal fish fauna classification are 1/2000, 1/1000 and 1/100.

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SAKUTA ditch is the oldest irrigation channel in Japan. The first description is described in the Japanese Chronicle of Japan that is the Japanese oldest history book. SAKUTA ditch is located in FUKUOKA Prefecture. In other words it is the very precious irrigation channel which continues being used for more than 1500 years. According to the field observation results performed in SAKUTA ditch, it becomes clear that 24 species of fishes are existed. In recent years, however, there have been increasing demands from local residents for the creation of the convenient irrigation channel.
The objective of this study is to evaluate the fish habitat and to discuss the relationship between vegetation covered ration and physical environmental condition in SAKUTA ditch. The study results indicate that the density of fishes in channel is related to the vegetation covered ratio and the velocity distribution in the ditch. These results suggested that the water's edge structure and the vegetation covered ratio in channel are greatly influenced to fish habitat evaluation.

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We investigated the ecological influence of the Atago weir (Hirose River, Miyagi Pref., Japan) on the riverine benthic faunal community at 21 points in the upstream river section (?1000m) with locally varying hydraulic conditions (flow=-0.08-1.03m/s, depth= 19-179cm). The weir formed a semi-lentic environment (flow =-0.120.27m/s, depth =22179cm) in the upstream section for 700m river length. Silt layer partially emerged in the right bank side of the semi-lentic section. Density (N=33-5317/m²), taxa richness (S=1 - 27 taxa), and Simpson' diversity index (1-D=0.00 - 0.92) of the communities widely varied among the 21 points. The multiple regression analysis indicated that the spatial variations of abundance (N) and species diversity (S, 1-D) were mainly accounted for by physical environmental factors such as flow velocity, depth, and mean grain diameter of the sediment, etc.

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This topic presents the effect of water temperature on benthic invertebrate growth and assemblages at downstream site of the Dam in winter, in Japan. The surface layer water of dam was released, and the temperature was always 3-5 degrees higher than the upstream. This was because of tentative manipulation of dam. Life cycles of dominated species were faster and their body size were all larger in the downstream than the upstream. Kamimuria tibialis (Perlidae) as a predator grew faster. Also, its body weight was much heavier than in the upstream, even its body length is the same in the upstream. Periphyton biomass was also much higher, especially, filamentous species were dominated at slow current site in the downstream. Regardless of abundance of periphyton, Heptageniidae as a grazer were not increased compared with the upstream. Besides discharge control, water temperature changes invertebrate assemblages quickly. This result implies that restrict of the movement of species is need to consideration.

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Collection of benthic animals contributes to making biodiversity indexes in the Natori river basin. Biodiversity indexes are composed of alpha, beta, and gamma diversities. The relationship between biodiversity and habitat environment is investigated, and high diversity exists in the middle stream region and negative relation to agricultural areas. Furthermore elevation and agricultural land divided up 4 groups in the Natori River basin by nonhierarchical cluster analysis. At last, we discuss the relationship the gamma diversities.

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A new ecosystem assessment method based on exergy efficiency is proposed to evaluate health of river ecosystem. The exergy takes into account of both energy quantity and energy quality. In this method, ecological exergy efficiency, which is calculated by the ratio of organism exergy produced in system to exergy supplied from outside of system (photosynthetically active radiation exergy and organic exergy supplied by flood) is defined as an indicator of health of river ecosystem. This ecosystem assessment method is applied to natural riffle zone and riffle zone with bank protection in Genka River, Okinawa. The result shows that the exergy efficiency at the natural riffle zone is 0.84 and that at the riffle zone with bank protection is 0.13.

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The burst speed is the highest swimming speed of fish. Fish can migrate through fishways, when the maximum velocity in fishways is smaller than the burst speed. Therefore it is necessary to understand the burst speed of fish. In this study, an investigation on the burst speed of Zacco platypus under the condition that the body length and flow velocity are changed was conducted. The results show the swimming speed increases rapidly after starting swimming and acceleration decreases gradually. Finally, the swimming speed reaches to the burst speed. The burst speed divided by the body length decreases with an increase of the body length and increases with an increase of the flow velocity. The burst speed is generally known as a value ten times of the body length of fish. However, it was found that the burst speed of Zacco platypus is up to 30 times or more of the body length from the present experiments.

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There is the case to have to make the slope of the fishway steeper than the standard range, according to the geographical features condition. In this research, measurement of flow structure and observation of swimming behavior of Leuciscus hakonensis at the hydraulic model of the pool and weir type fishway with slope 1/5 were conducted. Main results are shown as follows; 1) Ascending rate of this species in TYPE C which has short pools in flowing direction is higher than in TYPE B which has big steps between each pools when the overflow depth equals 5-10 cm, ascending rate of this species over 9-10 cm in TYPE B is higher than in TYPE C when the overflow depth equals 15-20 cm. 2) The difference of flow structure doesn't necessarily greatly influence ascending rate of this species. 3) About this species, it is necessary to select TYPE B or C corresponding to the assumed range of the overflow depth.

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Schooling behavior of fish and interaction between a few individual fish in schooling have been investigated. However, swimming behavior of isolated fish has not been investigated. In this study, the swimming behavior of isolated ayu in the circular pools with changing the radius was recorded with a digital video camera. It was found that the swimming trajectory of ayu can be described by nodes and branches. The frequencies of the swimming distance and angle between each branch are modeled by the gamma distribution. The mean swimming distance of each branch divided by the body length is 2.51 and the mean angle between each branch is 72.5. The directions of angle between each branch do not depend on the swimming distance and also the angle just before the swimming.

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