In Cambodia, agriculture is the important industry which engages many people. However, the water supplied only during rainy season is the source of water for agriculture. To use the limited water resources effectively, it is necessary to apply the water-resource management based on the meteorological prediction and the river runoff prediction. As the factor of these predictions, the soil moisture plays a key role in water and thermal transportation to the atmosphere, and the contribution of river runoff property. On the other hand, the soil moisture distribution with the paddy field scale is helpful in the agricultural activity and management. Therefore, Synthetic Aperture Radars (SAR) is expected to observe soil moisture with high spatial resolution in large area. The purpose of this study is to validate the algorithm for soil moisture estimation by using multi-polarization data acquired with the Phased Array type L-band Synthetic Aperture Radar (PALSAR) onboard the Advanced Land Observing Satellite (ALOS).

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Nitrogen load and river water chemistry in a fruit-rich watershed were estimated by numerical simulation. The study area was the Zakurogawa River Watershed. The proposed method could calculate monthly emission factor of nitrogen in orchard. Therefore, seasonal variation of TN load from the watershed and TN concentration in the river could be simulated. The TN load from orchard occupied about 79% of the total and the monthly loads were larger from autumn to spring. These would depend on the amounts of fertilizer and precipitation. Consequently, it was revealed that the TN concentration in the river was controlled by seasonal variation of the TN load from orchard.

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Floodplains have been affected by human impacts on a global scale. Restoration projects of floodplain have been conducted all over the world. The Azamenose which locates on middle and lower part of the Matsuura river is one of the projects in Japan. As there is little knowledge about floodplain restoration, it seems to be important to conduct scientific monitoring and estimation on some restoration project sites. The purposes of this study are to examine seasonal fluctuations of water quality in Azamenose, and to identify effective factors of the fluctuations. At first, we observed seasonal fluctuations of water quality (water temperature, water level, pH, DO, nutrients). Secondly, we observed coverage of aquatic plants in the field. The results indicated that the main factors of water quality fluctuations were flood and vegetation. We considered that flood increased nutrients level and decreased water temperature in Azamenose. Moreover, we speculated that DO level decreased drastically in summer due to the rank growth of water chestnut (Trapa japonica).

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A laboratory experiment on denitrification was carried out in order to develop a technology for treatment of leachate from municipal waste landfill. The authors have already collected fundamental data from a previous experiment on denitrification in a confined test tank. The present experiment was performed in a circulating test tank with inflow load. It was investigated how parameters such as carbon, phosphorus, denitrification bacteria and inflow nitrogen load influenced on denitrification rate. It was found that phosphorus is an important control factor in addition to carbon in leachate denitrification. A negative functional dependency of denitrification rate on inflow load was also confirmed, which provides useful information for development and planning of a treatment plant capacity. A design concept for the leachate treatment was proposed based on the experiment.

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The landscape of a river sandbar is composed of several elements, including vegetation, bare areas, side-pools and so on. For sandy river management, it is necessary to determine the contributing factors for the ecosystem functions of alternate bar segments. In recent years, it has been reported that sandbars have a water purification function involving denitrification driven by sub-surface flow, but the details are still unknown. The objective of this study was to develop a model that could be used to examine how the nitrogen is trapped and retained by several elements of a sandbar in an alternate bar reach. We also developed a framework to analyze the temporal change in the denitrification by using a numerical simulation, aerial photos, and a water quality information system. The main results of this study are that the temporal change in the denitrification ecosystem function in a sandbar reach can be quantified using the proposed model and the denitrification activity has increased over the past 35 years. In addition, it was clearly shown that differences in the vegetation distribution and sandbar shape affect the nitrogen dynamics. Thus, the numerical simulation has made it possible to determine the most effective vegetation patterns to maximize the ecosystem function in a sandbar.

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Annual SS (Suspended Solids) load from the Hiromi river to the Shimanto river was estimated based on the 33-months continuous daily observation data. The water quality of the Shimanto river, which is often called "the last clear stream of Japan", is observably deteriorated especially during rice transplanting period. Suspended load prediction models were established and the effect,of rice transplanting activities to the rivers' suspended load was also estimated. Results showed that the amount of annual SS load to the Shimanto river from the Hiromi river was 9.8x10⁶ kg and if drainage from paddy fields during rice transplanting is completely stopped, the amount could be reduced by 8.0-12x10⁴ kg SS.

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In the previous studies, SS concentration is found to be associated with rainfall intensity by using exponential function. However, it is not clarified how high turbidity is provided from fields and forests areas. Therefore production and transportation of suspended sediment was investigated by sampling surface soils in 18 domains over an entire river basin. Chemical decomposition analysis showed that the transportation rate of suspended sediment was related to the type surface soil. Turbidity measurement in fields and forests and chemical decomposition analysis enables to develop a method which can be used for the evaluation of the relative suspended sediment transportation rates from each domain of a river basin to its downstream end.

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Unit load method has been widely used in evaluation of pollutant load from watershed to lake or inner bay. However this method has several issues for accurate evaluation of pollutant load. In this study, we present a new approach for evaluation of unit load averaged over infiltration basin under low-flow conditions using longitudinal variations of pollutant load and point source using GIS. For this purpose, we conducted water sampling and discharge measurement in Takasaki River, flowing into Lake Inba-numa. The results indicate that unit load averaged over infiltration basin of Takasaki River in spring and summer was quite lower than that in autumn and winter. The tendency of the seasonal variations of unit load is closely related to land use of plowed field.

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It is pointed out that dissolved silicate is an essential matter for diatom and an important factor affecting ecosystems in estuaries. We made field measurements and analyses for water quality and material flow, especially dissolved silicate in the Yodo River Basin with sewerage systems and waterworks systems. Dissolved silicate concentration in Uji River is about 1 to 2 mg/L, and the spring-blooming in Lake Biwa causes a significant decrease in the concentration. The dissolved silicate concentration in water and sewage plants is hardly changing in the treating process. Moreover, underground water pumped up for tap water contains rich dissolved silicate, and is greatest source of dissolved silicate in the basin.

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Swimming behavior of a school of fish in running water has not been investigated. Recently, Onitsuka et al. investigated on the swimming behavior of isolated or a couple of fish in running water. In this study, the swimming behavior of a school of ayu, consinting of 3 fishes, in running water was investigated. It was found that the streamwise length of a school increases and the spanwise length of that decreases with an increase of the flow velocity and also that the swimming speed in the streamwise direction increases with an increase of the flow velocity. The turning angle of swimming trajectory decreases with an increase of the flow velocity. The individual distance becomes larger when the velocity is increased.

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Behavior of the fish has been investigated so much. However, the effects of the side-wall on the fish behaviors have not been investigated. In this study, the swimming behavior of isolated ayu in a rectangular open-channel flow was recorded with a digital video camera with changing the velocity. It was found that the fish behavior is affected by the side-wall where the distance from sidewall is less than one time of body length of ayu, so that this area was defined as the side-wall area. The mode value of the ground distance, ground speed, swimming distance and swimming speed in the side-wall area is smaller than those in the universal area, and also that the angle of refraction in the side-wall area is constant, irrespective of flow velocity.

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Automatic passing fish detection system using RFID (Radio Frequency IDentification) technology was developed to provide information on movement and behavior of Ayu fish (plecoglossus altivelis) within a fishway. In this study, movements of Ayu fish were deduced from detection signals of sensing antennas placed at each remote location to be monitored. To accomplish this, a newly application software which help controlling multiple RFID readers, determining fish locations and logging the detection status was developed. Using developed system, the effect of decreasing light levels on the behavior of Ayu fish within the fish tank was examined. It was found from the result that most of Ayu fish ascended or descended the channel response to the change of light levels and their location was associated with water velocity.

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In Sendai River system in Tottori Prefecture, 33 weirs have been obstacle to upstream migration of Ayu fish. The Eino weir is one of the most important places for the migration. At the immediately downstream of the weir, a lot of Ayu fish have been stagnated outside the entrance of permanent fishway, and this might be caused by the position of the fishway and the existence of the flow passing over weir. The same situation has occurred at around half of the obstacle points. In this study, the authors proposed a new portable fishway that is installed parallel to the weir axis in order to adjust the position and the slope of the fishway easily. The field observation confirmed that the installation of the fishway enabled the upstream migration of Ayu fish stagnated at the immediately downstream of the weir. Flow characteristics in the fishway were made clear. Also, the total number of the days when Ayu fish could migrate through the fishway was predicted by hydrological approach.

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Through the ages, the pool-and-weir-fishway have been installed in many rivers in Japan. As time advances, fish-ways fail to function adequately because they are deteriorated, broken or changed flow in the downstream.The main purpose of this study is to make clear the problems of fish-ways and to find better resolution methods to solve it. Therefore, we carried out the model experiment by using the open channel where a pool-and-weir-fish way had been set up.As a result, a promising method to cope with the local scouring and circulation flow at the downstream of fish-way is studied by the model experiment.

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River-crossing structures such as dam and weir cause fragmentation of aquatic habitats, which often prevents migration of aquatic fauna. In this study we evaluated such effect of fragmentation on probability of occurrence of freshwater fishes in several sections of Sagami River, Japan. Logistic-regression model describing the relation of habitat properties to presence/absence of each 41 fish species was statistically fitted to their distribution monitored from 1993 to 2005. The model considered six habitat properties of each section: basin area, longitudinal slope, isolation period, river width, upstream connection and downstream connection. As results, different habitat properties were selected for the model of each species and the correctly predicted ratio was over 75% for 28 species. These models imply the effect of fragmentation on fish distribution in the Sagami River and can be applied in several ways for river environment management.

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The construction of erosion control dams and the alteration of riparian forest are known to have strong influences on the density of salmonid fish that dominate in mountain streams. Our objective was to elucidate the indirect effect of the dam construction and riparian alteration on stream invertebrates through the alteration of salmonid fish (Oncorhynchus masou ishikawae) density. The densities of two dominant invertebrate species, Baetis yoshinensis and Baetis thermicus, were low at study sites with high O. masou density. In conclusion, our study suggested that human activities indirectly affect stream invertebrates via changing fish abundance in mountain streams.

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We conducted a field survey in 8 tributaries of the Shigenobu River to elucidate the influence of catchment land use on fish and invertebrate assemblages and feeding habit of fish. Fish and invertebrate assemblages were dominated by high-temperature and pollution tolerant taxa in agricultural streams. Dominant omnivorous fish, Phoxinus oxycephalus jouyi, selectively fed on periphyton in agricultural streams while it utilized various food items in forest streams. We concluded that changes in water temperature and nutrient concentration would generate synchronous changes in community structures of fish and invertebrates and, moreover, fish feeding, along the forest-agricultural gradient.

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It is important to make clear seasonal changes of fish habitat quality in rivers. There are still many unsolved question in fish habitat quality, because this consists of quite complex system. In this study, field surveys of seasonal changes of fish habitat quality were conducted through nine months in Itabitsugawa river which belongs to class B river. It was found that Carassius langsdorfi moves from pool to riffle through winter to summer. Zacco temminckii and Zacco platypus evade Carassius langsdorfi in all seasons, because the body length of Carassius langsdorfi is larger than that of Zacco temminckii and Zacco platypus. Further, Zacco temminckii evades Zacco platypus which is larger than 8cm of body length.

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Our target species, Ryukyu-Ayu (Plecoglossus altivelis ryukyuensis) are thought that they are facing on distinct because of high water temperature in estuary of their habitat on their juvenile stage. It is necessary for conservation to evaluate how that condition effect on Ryukyu-Ayu. The aim of this study is to investigate an impact on their habitat suitability caused by development in estuary. To evaluate this we tried to apply the result of survival experiment on Ryukyu-Ayu larva to actual sites. This means we built statistical model to estimate 24 hours survival rate (ESR) from the experiment results and calculate ESR using field observation data of water temperature and salinity. The results show The ESR in habitat of artificial estuary is less than 40% even though more than 80% in all observation point in natural estuary and that carry out 1 deg water temperature falling can provide about 20% ESR rising.

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Since a lot of estuarine fish inhabit the Chikugo River and fishermen carry out drift net fishing, this river is unique among the rivers in Japan.The relationship between the catch number of the estuarine fish, i.e., Coilia nasus, and the salinity, temperature, suspended sediment concentration (SSC), and tidal current was investigated. The salinity, temperature, and SSC were measured at a station 14.6 km from the river mouth. The tidal current was calculated by conducting a one-dimensional dispersion simulation. A drift net was floated over the cross-section of the river between 14.6 km and 16 km from the river mouth, and the fish catch number was recorded for every cast. The catch density of Coilia nasus was higher in June when the water temperature was 23^oC, salinity was 0.07 psu, SSC was 20 mg/l, and freshwater discharge was 90 m³/s. It was suggested that Coilia nasus was swimming in a low-salinity and low-SSC region near fresh water. Data on the catch per unit effor during the semi-diurnal tidal cycle showed that higher catch rates were obtained 30 min after slack high tide, when the current velocity was 0.4 m/s.

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The Shiretoko Peninsula which is located between Sea of Okhotsk and Nemuro Channel enable us to observe a connection with the ocean and inland easily, the having many kinds variety of the creature was recognized, and it was registered with natural world heritage. In Shiretoko, the nutrient of the ocean is found to be transported to inland by birds, salmon and trout. It is expected that drift ice brings nutrient from the northern part of Okhotsk Sea to Shiretoko during winter, which results in the sound ecological system and the great biodiversity in Shiretoko Peninsula. However, it is not clarified how much nutrient is brought by drift ice to Shiretoko exactly. In this study, we thus aim to estimate how much nutrient is transported from inland and drift ice to the ocean and how much is brought back to inland from the ocean by using isotope analysis.

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Vegetation overgrowth along river networks in Japan has been a serious engineering problem for both flood protection and ecological conservation. For proper riparian management under the severe circumstances of the global climate change, it would be necessary to predict the vegetation dynamics for long-term duration. In this paper, we try to expand the stochastic process model, developed for predicting the vegetation dynamics in a river channel, to the whole river network by employing a stream ordering system, i.e., Shreve's link magnitude. In the model, the flood discharge was stochastically simulated using a shot noise process, whose model parameters are examined to relate the link magnitude of a river network. The results of Monte Carlo simulation for several cross sections in the Kako River confirm that the present model is able to predict the vegetation dynamics in the whole river network. Moreover, responses of the vegetated channels are stochastically evaluated in terms of the changes of river discharge and channel geomorphology.

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In this paper, solar shading effects using NDVI and discharge estimation correction are considered for refinement of a stream order network model which can predict basin-wide distributions of stream temperatures. As a result, the network model is able to take into account seasonal variations of the shading effect by vegetation and also improved the accuracy of hydrological quantities in river discharge and stream width estimations. Comparison of the network model prediction with the observed stream temperatures in the Ibo River Basin in Japan showed very good agreement for the temperature distribution structures along the river network for almost all seasons, excluding an autumnal month. More considerations for higher accuracy in this month and sensitivity analyses of the model parameters are needed in the future research work.

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In this study, various applications of aerial photograph analysis were proposed to detect the large scale and long term dynamics of riparian vegetation. By comparing the aerial photographs taken at neighboring shooting date, expansion and destruction rates of vegetation, age of vegetation and critical discharge dividing expansion and destruction of vegetation can be estimated in addition to the surface cover types and vegetation cover rate. The results of the analysis show that the vegetation expansion and destruction rates are considerably large in the study site whereas the vegetation cover rate has gradually increased during last 40 years. The vegetation expansion was expected to occur during the period that the annual maximum discharge had been less than 4000~6500 m³/s.

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Forestation on floodplain is now a world-wide issue from a river engineering viewpoint. Based on a field data analysis of river morphology, discharge and land cover in the last decades, a main cause of floodplain forestation was found to be decreased frequency of floodplain inundation after sequent channel restoration works. In order to perform an adaptive river management, a uniform flow analysis of vegetated channel is carried out for several cross sections from middle to downstream. It is investigated how floodplain excavation and thinning of tree vegetation modify flow structure and tree destruction during flood events. It is discussed based on the analysis what is a proper management strategy in order to create a safe and attractive river environment.

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Growth and detachment of the attached-algae in river bed is one of the key factors in ecological system in the river. The detachment process of the algae can be categorized into three types, namely 1 Natural detachment due to aging, 2 Detachment due to flow and bed material load and 3 Detachment caused by rolling of the bed material. To evaluate the detachment processes during flood, we conducted a series of field survey in a site in the Johge River. In the period this survey had been conducted, a flushing discharge and a flood due to typhoon were observed. The chlorophyll-a densities on the bed material before and after floods were measured. Based on the field survey results, the detachment processes of algae are evaluated, and a new model to estimate an amount of detachment during the flood is proposed.

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We conducted in-situ measurement to find effects of stream discharge variation on attached algae on three types of substrates at four stations, which are located at both lower and upper reach than dams, in the upper Chikugo River, so-called the Ohyama River, in 2011. During the measurement period (May-June), a single small scale flushing occurred. Thus, we especially analyzed effects of the small flushing on amount and species of attached algae. As a result of the present research, the followings are clarified: i) Attached algae on the natural stones in the lower stream from dams grew mature and decreased much more than the upper one, ii) There is a significant difference of adhesion of attached algae between a natural stone and an artificial substrate under stable flow regime in the lower stream from dams, and iii) Small flushing of 20-30m3/s can show an effect of exfoliation of attached algae in some degree in the river.

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This study focuses on the problem of "mosquito swarm" along urban rivers. Different from general biological methods (capture, counting and photograph), we adopted a fluid dynamical approach to investigate the temporal-spatial distribution of mosquito swarm. First, a novel device composed of multiple laser sheets is developed as a mosquito counter in order to quantify the density of the swarm. Second, filed observations are done in Nomi River by utilizing this laser device as well as the other conventional meteorological observations. The followings are the major results obtained: (1) Mosquito swarms are apparent only about 1 hours before the sunrise heavily on one-sided (sunlit side) along the river. (2) The hot-sopt of mosquite swarm seems to exist ; the cross sections of urban street perpendicular to the river. The locations were roughly fixed with slight perturbations. (3) The suitable temperature to make swarm is about 22.5ºC.

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Little past progress has been made in the evaluation of the impact of dams on the environments of the rivers downstream from the dams, because the impact manifestation mechanisms are complex and the impacts themselves are not easy to abstract. We have conducted field survey to investigate the change in river bed between upstream and downstream of 15 dams. Riverbed material seems coarser at any immediately downstream sites due to the trap of sediment behind dams; however, downward grain size change pattern was different among rivers. So then we applied the statistical analysis to its patterns and classified 15 dams into six groups. And we evaluated their feature by comparing it with the calculated grain size which is estimated from the shear velocity.

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This topic presents the effect of trial impoundment of dam on secondary productivity of Stenopsyche marmorata (Trichoptera) at immediately downstream of Takizawa dam, in Japan. S marmorata has very high productivity among all invertebrate species and bivoltine life cycle. Production statistics for S.marmorata in Nakatsu-gawa river calculated by the increment-summation method and the instantaneous growth method, respectively. Values for non-wintering generation, wintering generation and annual production during individual years for the entire study period are given separately. Annual productions were 26.09/23.75 g/m² for 2006-2007, and 46.18/58.11 g/m² for 2007-2008 by increment method / instantaneous method. Because of the minimum outflow were maintained during the long period of trial impoundment, the survival rate of the fourth and fifth instars of larvae were significantly higher than the other study. Also, its individual body weight was heavier than the others. The biomass and productivity strongly depend on river gravel bed size distribution and flowing phytoplankton from the dam.

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Bypass tunnel is one of the important water quality management facilities in reservoirs. There are two types of bypass tunnels. One is bypassing turbid water and the other is bypassing clear water to the downstream of a reservoir. However, these systems are quite new and we do not have sufficient information. In order to evaluate the effect of bypassing of clear water on water quality both in reservoir and downstream, we applied a three-dimensional water quality simulation model, ELCOM-CAEDYM developed by CWR, to Urayama reservoir in Arakawa River basin. The comparison of the model results between an actual bypass operation and a scenario without bypass operation showed that the bypass operation has improved SS in downstream of the reservoir remarkably. Moreover it revealed that the bypass has improved other water quality parameters not only in downstream but also in reservoir.

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Flocculants made of natural volcanic ash soils can be used to purify turbid water in reservoirs. Imogolites in the flocculants seem to play an important role when the flocculants are applied. To clarify the mechanism of imogolite-induced flocculation, we studied the flocculation and charging of latex particles as a function of the ratio of the concentration of imogolites (CI) to that of latex particles (CL) at three different pH. The mechanisms at each pH are found as follows. At pH4, flocculation occurs only around CI/CL=0.01, where the particles are uncharged found from electrophoretic mobility. Thus, the mechanism at pH4 is charge neutralization. At pH6.5, the suspensions flocculate when CI/CL is higher than 0.01; the particles flocculate due to charge neutralization as well as sweep flocculation, by which latex particles are enmeshed by the flocs of imogolites. At pH10, where imogolites and latex particles bear negative charge, the suspensions flocculate when CI/CL exceeds 0.1. Only the sweep flocculation acts at pH 10.

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Flood inflow is one of the factors which give influences to flow and material transport in closed water body. In this study, flows induced by flood in Isahaya flood regulation pond were predicted using a numerical simulation model composed by rainfall-runoff model and hydrodynamic model. In advance of the simulation, applicability of these models to Isahaya regions were examined. Simulated results shows that flows were formed in this pond by inflow of flood and gates operation to control the accumulated water level. On the other hand, at the water area apart from river mouths, effects of wind on flow are not negligible. This means that, in order to clear the material transport processes in this pond, influences of inflow of flood as well as wind should be considered in the wet weather condition.

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Detailed investigation of three-dimensional structure of wind-driven currents due to secondary circulations is needed to an accurate estimation of material transport on lakes and oceans. In this study, the convenient method to observe this structure by using the web camera, H-ADCP and Workhorse is proposed and the spatially-periodic profiles of horizontal wind-driven currents were obtained by using the method. Furthermore, surface velocities in the high-speed zones were estimated by applying the logarithmic law and the friction coefficient. From the results, the maximum surface velocity is about twice of 3.5% of U10, which is used in the general estimation of wind-driven surface currents.

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Vegetation communities are often observed to grow in stripe pattern or patches within many stream channels. In such a situation, hydraulic engineers should examine an appropriate vegetation management system paying attention to flood control and vegetation ecosystem. On the other hand, the cavity zone along riverside is expected to produce native habitats of various ecosystems and water-friendly environment. However, effects of side cavities on flow resistance and turbulent flow structures are ambiguous. In this paper, the flow resistance and momentum transport in an open channel flow with permeable and impermeable side cavities in longitudinal direction were examined experimentally. Velocity fluctuations were measured by using a particle-image-velocimetry (PIV). Results showed that the flow resistance significantly depended on the aspect ratio of cavity. And we revealed the effects of the vegetation permeability on turbulent flow structure.

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An investigation of three-dimensional turbulence structures at open-channel confluence with zero or ten degrees was conducted experimentally by using a flow visualization technique. Measurements were performed with the aid of a high-accurate image analysis method of particle image velocimetry by illuminating vertical and horizontal sections with a laser light sheet. Evolution of secondary flows for zero and ten-degree confluence showed a significant difference even though the difference of the angle is rather small. For example, increase of tributary channel discharge for a ten-degree confluence generates a large scale secondary flow that extends to the whole channel width, which was not predicted before the experiment. In addition, the extent of confluence effect in the downstream direction was also examined.

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Flow state around hydraulic structures such as groin and weir composed of connected stones is very complicated. Therefore, more accurate approaching velocities must be used in designing these structures considering the structure's stability against flood attack. In this paper, three-dimensional flow simulation for hydraulic structure composed of connected stones was carried out to get more proper approaching velocity and its applicability was investigated. Numerical results can explain fairly well the water level and velocity profiles around permeable hydraulic structure composed of connected stones. Furthermore, the obtained approaching velocity is considered accurate enough for design use.

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Boulders are sometimes placed in rivers to enhance an ecological function by making scour hole and downstream deposition. At first, flow structure around single large hemispherical roughness was investigated in emerged and submerged conditions. The effect of large roughness on the flow variation was larger for submerged cases than for emerged cases although emerged cases have lower velocity. Then bed deformation was observed around a large spherical roughness put in the movable sand bed. Roughness was moved upstream and sank because of the front scouring due to a horse-shoe vortex. The deformed bed configuration with sunken spherical roughness attained a stable situation. The maximum scour depth was almost 0.5 - 0.6 of the roughness diameter. The scoured volume became larger in the side-placement cases than the center-placed cases.

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Several groynes were constructed about 300 years ago to protect the banks of Japanese rivers, which are characteristically steep and short. To investigate the effects of groynes on the Shigenobu River in northwestern Ehime Prefecture, a field investigation was conducted to measure the sizes of groynes and the sizes of stones on the surface of the groynes as well as the bed morphology around the groynes. In addition, particle tracking velocimetry and numerical analyses of the three-dimensional flow and bed variation around the groynes were conducted. It was found that flow patterns, such as patterns of mean velocity and Reynolds stress, and the bed variation around successive groynes were affected by the particular arrangement of groynes. The study proposes a simple arrangement of river structure for stable bed morphology.

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Complex three-dimensional flows around river confluences are characterized by the secondary flow as well as primary flow, and it also causes intense local scouring and deposition. So, numerical simulation models which include effects of three-dimensional flows are required to calculate flows around a river confluence.In this study, first, we evaluate reproducibility of several functional forms describing vertical velocity distributions of flows around a river confluence by using measured data by Rhoads et al.(1995). Second, we develop a bottom velocity computation method with water surface velocity equation using the general coordinate system. And then, the validity of the model is discussed through the comparison with the measured results.

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Numerical simulations for flood flows in a symmetrical river confluence were performed using a quasi-three dimensional numerical model. The vertically averaged and moment equations was used as governing equations to allow for the incorporation of pre-assumed linear distribution of horizontal velocity and quadratic vertical velocity and pressure distributions. The model is based on finite volume method using HLL (Harten, Lax and van Leer(1983)) numerical flux, which is one of a Riemann solver. The model is verified against two experimental data of flows in curved channel and in symmetrical river confluence. It shows that the model can reproduce the complex behavior of the flows with reasonable accuracy.

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This paper describes the applicability of a multi-level grid type turbulent shallow flow model (KMR: Kinematic Mesh Reconstruction) to an unsteady open channel flow around a bridge pier. The KMR model employed a two-dimensional depth-averaged URANS (Unsteady Reynolds Averaged Navier Stokes) type shallow flow equations. As a turbulence model, a second-order non-linear 0-equation model proposed by Kimura et al (2009)1) is adopted. The turbulence structure in a shallow open channel flow is characterized by vortex merging and up-cascading. To predict efficiently a large spatial difference of the turbulence scale, computational grid is divided and merged automatically and dynamically at each time step. The model is applied to a shallow flow around a square bridge pier model and the accuracy of computational results on vortices behavior, velocity profile and water surface elevation is examined through the comparison with a previous experimental result. Numerical results showed that the present model could capture excellently the fundamental aspects of the flow around a bridge pier with less CPU time than the fixed grid computation.

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Numerical computation of river flows have been employed the general coordinate system to adjust a river plane form. An adjustment flexibility of the coordinate system is better but it is difficult to generate a grid system in order to compute stably because grid system is not determined uniquely. This study develops a new boundary fitting method introducing the hierarchical quad-tree grid system for computation of confluence and bifurcation in natural rivers. The numerical model with the quad-tree grid system apply to compute flow pattern in experiment flume and in natural river with bifurcation and confluence , the computed results agree with measured result of the flume and natural river well.

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Recently, maintaining biodiversity in rivers is required as a part of nature-oriented river works. Wandos made artificially in rivers are one of the measures to secure biodiversity. Transport of suspended solids at the water surface of wandos to river stream is known to be controlled by large scale vortices.In this study, firstly transport rates of expanded polystyrene particles as uspended solids at the water surface of a wando in a rectangular channel were examined. The results of experiments in the rectangular channel indicate that the transport rate of expanded polystyrene particles decreases with the increase in Froude number. Secondly, a formula on the transport of expanded polystyrene particles was proposed as a function of Froude number and the ratio between the length and the width of wando.

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It is important from the engineering point of view to predict the collapsing process of river embankment and behavior of overtop flow for reducing disaster during flood. We performed some considerations on refinement of a two-dimensional computational model based on shallow flow equations to predict more accurately the front overflow levee breach phenomena. We tried to introduce a levee erosion model instead of sediment transport model to evaluate the deformation of the levee. In addition, intermittent behavior of the bank collapse is modeled. A calibration of the numerical model is made through the comparison with field experimental data. Recently, a real-scale experiment on a front levee breach was carried out at the Chiyoda Experimental Channel in Hokkaido, Japan. We performed the computation under the same conditions in the experiment. The computational results showed that the present refined model can predict fundamental aspects of the front levee breach phenomena. breach phenomena.

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Flood control capability of a dry dam which is a flood control dam without a slide gate in a spillway was quantitatively estimated for a hydraulic bore. In recent years a dry dam has been reviewed and planned in some sites since impacts on natural environments of a dry dam are relatively small. A dry dam may have several noticeable characteristics. For example, it should reduce damage from a hydraulic bore which happens if landslide occurs and a natural sedimentation dam formed by sediments and rocks collapses or they fall into a dam reservoir filled with water. In this study, flood control capability of a dry dam for a hydraulic bore was investigated using a dimensional analysis and numerical simulations. As a result, this study enables us to estimate the quantitative flood control capability of a dry dam for a hydraulic bore.

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A dry dam becomes to be recognized as an effective river structure to control flood with reduction of sediment deposition in a reservoir as well as conservation of river environment. However, hydraulic characteristics and sediment transport behavior around a dry dam have not been clarified yet. This paper presents a one dimensional (1D) and a three dimensional (3D) numerical models, which can simulate flow structures and sediment transport for a dry dam. The computation with the present 1D model could predict reasonably the peak discharge cut effect during flood. It also could predict accurately the deposition patterns and sediment sorting upstream of the dam. On the other hand, the 3D model could simulate realistically a flow through a tunnel and a flow over the dam crest. The 3D model also implies the existence of three-dimensional recirculating flow inside the reservoir, which will affect the flow behavior and sediment transport near the tunnel during flood.

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Drag coefficients of bodies in aerated flows have not yet been shown clearly. For design purposes, it is necessary to clarify the drag force acting on various bodies in high-speed aerated flows, such as baffle piers on chutes, or boulders in mountain rivers. Also, it is significant to know the drag force acting on human legs in aerated flows, because of the refuge from floodwaters entering the staircase between the ground and underground spaces in an urban area. In this paper, the general expression for the drag coefficient of various bodies in aerated flows is reasonably established on the basis of flow characteristics of aerated flows. Also, in stepped channels, drag coefficients of various cylindrical bodies and a model leg are obtained from aerated flow characteristics.

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In this paper, instability of flow due to break of symmetry between sag of the valve body and flow direction was analyzed on the basis of momentum theory in axis symmetric flow field, and characteristics of fluid force acting on the valve body (deviation fluid force to the valve shaft center) are clarified. The analysis result shows that fluid force is proportional to sagging of the valve edge. Till the valve opening is around 60%, the working angle is upward, that means sagging of the valve body is suppressed. When the valve opening is beyond 70%, the working angle is downward, that means sagging of the valve body is increased. Moreover, validity of the analysis result is examined by comparing it with the measurement result in discharge.

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Hydraulic model tests and numerical simulations were executed to determine shape of stilling basin type energy dissipator of the A Headworks that local scour occurred at the downstream of apron in. As a result, length of horizontal portion of the pool of the dissipator should equal 25m that is maximum value of length of the entire pool in past cases, and depth of the pool should equal 30% of maximum value of water level difference around gate, in ordet to get the highest performance about dissipating energy on a lean budget for limited time. In addition, it is not easy to control undular jump by changing the length of pool, more effective means is to change the depth of pool, under the conditions of this study.

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