The vertical profiles of water current and temperature were measured in the Ogouchi Reservoir in order to investigate the mechanism of the water current control by the water preservation facilities.The constant current of 30 mm/s was observed around the vertical fence, it was suggested that these flows were a river inflow.And it was appeared that these flows were directed to the depth of 10 m by the vertical fences, and led to the layer which was the same temperature as the river inflow in center of the reservoir.As results of numerical calculation, the mechanism of the water current control by the vertical fence is reproduced, it was shown that water temperature was decreased in the upstream region of the vertical fence.It was suggested that it is possible to lead efficiently the river inflow by setting the withdrawal gate on the layer of the same temperature as the river inflow.

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Lake Inawashiro located in the center of Fukushima Prefecture is an acid lake which had sufficient self-purification mechanism and the water quality was extremely good. In recent years, however, water quality became worse due to pollution from the surrounding area. Previous studies of the authors reported a density current from field observation and also numerical simulation to reproduce the current in the lake. In this study, the numerical model has been improved by introducing the effect of wind to turbidity in order to achieve a higher accuracy. Furthermore, several hypothetical wind conditions are imposed to have a better understanding of this effect. It is found that the density current is highly influenced by the wind velocity. Simulation using relatively weak wind speed shows that the density current occurs at the center of the northern shallow area, whereas by increasing the wind velocity, the density current occurs in the east side of the shallow area.

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To clarify the mechanism of the physical environment of Lake Jusan, which is one of brackish lakes in Japan, we focused on movement of fine sediment, and performed field measurements. We measured sediment concentration and turbidity from 2007.6, to measure the sediment transport that flow in or flow out from Lake Jusan, and calculated sediment budget. We also collected and analyzed the bottom sediment. The results indicated that fine sediments supplied from the upper reaches are caught in Lake Jusan at certain ratio, and this system is influenced by frequency and scale of flood and bottom sediments resuspension caused by wind waves.

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As a countermeasure to water quality control as well as sedimentation due to turbid water inflows in a well-mixed reservoir, downstream control of inflowing dense water by means of placing a wall near a dam, is investigated experimentally. Effects of a fence placed upstream of the reservoir on plunge flows, controlled by a wall, are examined as well. It is found that the wall is capable of efficiently displacing the inflowing dense water out of the reservoir and maintaining the position of plunge point in stable condition. It is also found that the fence does not contribute to the displacing inflow water, but may contributes to stabilizing plunge point, dependent on the installed position and submerged depth of the fence.

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A field test of supplying oxygen-rich water into the bottom of dredged pits in Lake Nakaumi was performed in 2009. We used recently developed hypolimnetic oxygenators called WEP. In Yonago Bay, we selected two adjacent dredged pits, then installed and operated the WEP system in one pit for the experimental purpose. The other pit was used for the control purpose. The vertical profiling data of water quality in the pits showed the dissolved oxygen concentration was increased to 15-29 mg/L nearby the outlet of WEP system, and was kept at 5-15 mg/L in the experimental pit, on the other hand it was less than 5 mg/L in the control pit for 6 months of the experimental period (May - Oct.) in spite of the existence of tidal current. Moreover, we performed 3-D numerical simulations using ELCOM to evaluate the flow characteristics in the pits. They revealed that the water in the bottom of the pit stayed still but the water in the shallower layer there sometimes flowed out to the surrounding area.

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A numerical model was developed to calculate diffusive dissolved-oxygen (DO) transfer rate at rough sediment surface, considering vortex shedding in the water and biochemical reactions in the sediment. Calculational results showed that non-dimensionalized DO transfer rate (Stanton number, St) had a maximum value in the transitional region of surface roughness, in which the DO flux was two-three times larger than that at the smooth surface. Calculational results was significantly modified by considering non-steady variations in diffusive transfer rate due to step changes in DO concentration in the flushed region. Quantitative estimation of DO concentration at the sediment-water interface was also a critical procedure to evaluate St values.

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The spatial distributions of wind, wind-driven current, water-column current, and surface temperature were observed in a large meandering reservoir. Overall, it was found that the wind blew along the valley, and it was relatively strong in the center of the wide area. On the other hand, the wind was weak near the shore, in an inlet, and in the meandering area. A high water temperature was observed in places where the wind was weak. The diurnal current direction of surface water in the central area varied hourly, although the wind direction remained constant. The measurement of the horizontal current distribution at 11 stations indicated that all the velocity vectors do not run along the valley, and a vortex and divergent flow were produced by an underwater ridge. It is important to consider the horizontal distribution of wind and water current in order to control the water quality of a meandering reservoir in a mountainous region.

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Beach nourishment was carried out in the Ukishima region in Lake Kasumigaura to recover a sand beach. A spur dike extending in the direction of predominant waves from NW was attached to the existing groins to prevent the nourishment sand from flowing out at the downdrift end of the groin. After the beach nourishment, aerial photographs had been taken to investigate the shoreline changes and the monitoring surveys such as the bathymetric surveys and sampling of the lakebed material were carried out. It was confirmed that a dynamically stable beach was successfully formed by the construction of spur dike. Sand, the grain size of which is smaller than 0.35 mm, was transported into the zone deeper than Y.P.+0.2 m due to the sorting effect of waves.

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Field measurements on the terrace topography, velocity distribution of the river currents as well as the grain size distributions were carried out at the mouth of the Yumizutani River flowing into Lake Biwa to investigate the formative mechanism of a river mouth terrace. On the basis of these field data, the action of river currents to sand movement offshore of the river mouth was incorporated into the contour-line-change model. A model for predicting the dynamically equilibrium topography under the action of waves and currents was developed. The impact of river mouth improvement such as the construction of jetties at the mouth was also tested using the present model.

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The phenomenon that has been actualized due to the water quality deterioration because of the inflow of drainage and the industrial wastewater includes the phenomenon that is called water-bloom generated in the freshwater environment made a eutrophic. This is becoming a serious problem to secure the water.Mixing with the drinking water has already been confirmed, and the generation of water-bloom is becoming a big social problem, and fundamental measures have not been established yet.On the other hand, authors are proving the pressure to be a fast the pressure speed of the impact pressure by the water hammer and effective in the destruction of the blue-green algae.In this studies, the hydraulics flow characteristics of an effective water hammer pressure generator to the shredding of the water-bloom cell were examined.As a result, there was a boundary in the region where the water hammer was generated by length and the water supply head of conduit, and the water hammer pressure was able to be understood to be influenced according to the angle of the valve that generated the water hammer in addition in the water hammer generator.The demonstration in the locale was confirmed based on these and the scale etc. of an effective device to the doing water-bloom processing were able to be confirmed by continuous running.

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We carried out experimental study investigating the effects of physical treatment on dinoflagellate (Peridinium bipes) in order to develop measure to prevent freshwater red tide in reservoirs. Surface water in the reservoir occurring freshwater red tide was sampled for the physical treatments. We found that physical treatment caused cessation of swimming of P. bipes and subsequently effects on water quality and plankton composition. Immediately after physical treatment, almost of all cells of P. bipes stopped swimming behavior. However, one day after treatment, about 70% of cells restarted swimming. This ratio maintained 12 day after the treatment. Settlement of stopping cells led decrease in concentration of Chla and SS. Considering these effects, we discussed mechanism of effects of physical treatment on Peridinium dynamics and counter measure preventing freshwater red tide.

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The continuous monitoring of water quality at Nomura dam is carried out with a water-quality profiling system(YSI Inc.). It is equiped near the aerator and the effect of aeration on water quality is investigated. The sampling time and depth intervals are 2 hour and 1 m, respectively. The measuring items are water temperature, pH, turbidity, DO, Chl and the number of Blue-Green Alga per unit volume. Microcystis aeruginosa migrates up and down diurnally. Namely, it can be found near the water surface early in the morning and at midday exists at about 5m depth.

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This paper analyzes blooming mechanism of freshwater red-tide in an abolished-river which eutrophicated by seventy-years. Outbreaks of red tide of the river is depend on two phenomenon; the first one is the effect of secondary current generated by the wind along with the temperature rise, the second is the flow for the downstream by the release discharge from the power generation-dam in the downstream. Euglena spp. in euglena and Uroglena spp. in yellow-zooxanthellas is clarified to be the dominant species of the freshwater red-tide.

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Present work performed numerical simulations for jet-like, plume-like and off-source heated jet-like vortex pairs with standard k- model under OpenFOAM environment. It is shown that the total circulation of the eddy, which is considered to contribute to entrainment, increases due to buoyancy. Although eddy seems to be disrupted by the addition of heat away from the source, entrainment rate is reconfirmed to be increased in off-source heated jet. LES was also performed for pure jet, forced plume and off-source heated jet. Coherent vortical structures obtained under LES support the results gained from simulations of vortex pairs, and give more information on the relation between buoyancy and eddies.

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Controlling adverse density currents has been an important issue on water quality and ecosystems of brackish water regions. This study proposes to apply sluice gate for flexible control of density current migration in open channels. Hydraulic characteristics of density flows around a sluice gate are investigated by flume experiments employing the Particle Image Velocimetry technique and numerical calculations by a Large Eddy Simulation model. The results show that the behavior of density front migration under a sluice gate is dominated by internal Froude number of both fresh water and salt water layers, and entrainment of salt water in a downstream region of a dike is influenced by evolution of instantaneous flow structures in a fresh water layer.

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The formation of oxygen-poor water and the occurrence of hydrogen sulfide in estuary are caused by the sludge which contains a lot of organic substance. In order to examine measures against the water environment problems caused by the sludge, it is necessary to estimate bottom shear stress which is considered to be that exert influence on the behavior of bottom material. Based on our study, the bottom shear stress was estimated by the method of using the change of water level obtained by one-dimensional unsteady flow analysis and the density distribution obtained by field observation. The estimated bottom shear stress was validated by comparison with coefficient of eddy viscosity. In addition, the relationship between the bottom shear stress and the turbidity is discussed. The summary of the results is shown as follows; Increase in turbidity during flood tide is caused that the tip of saline wedge passes through a cross section; Due to increase in the velocity of toward downstream, the turbidity also increase during ebb tide.

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Dynamic motion of salt wedge was investigated in the Tone River estuary by field experiment and numerical flow simulation. In the field experiment, vertical profiles of salinity and velocity were measured from a boat pursuing the head of salt wedge along the deepest line of the channel. Being based on the collected data, characteristics of the velocity and the structure of the salt wedge front under transitional condition of flow rate and tide were discussed. Numerical flow simulation by using a vertical 2-D k-ε model reproduced the major characteristics of the motion of salt wedge obtained from the field measurement quantitatively: (a) dependency of the distance of salt wedge invasion on tide amplitude, (b) a time lag of the salt wedge motion behind the tide oscillation, and (c) asymmetric tendency of the motion of salt wedge at ebb tide and the flood tide.

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Prediction of water level in small rivers is great interest for flood control in an urban area located in the river mouth. The tidal river water level is affected by not only flood discharge but also tide, atmospheric pressure, wind direction and speed. We propose a method of estimating river water level considering these factors using an artificial neural network model for the Kanda River located in the center of Tokyo. The effects by those factors are quantitatively investigated. As for the effects by the atmospheric pressure, river water level rises about 7cm per 5hPa increase of the pressure regardless of river discharge under the conditions of 1m/s wind speed and north wind direction. The accurate rating curve for the tidal river is finally obtained.

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A series of spur dikes was constructed to reinforce an embankment at bends in the lower reach of the Kikuchi River. In recent years, eutrophicated fine sediment accumulation around spur dikes has caused a serious problem in estuary ecosystem. Therefore, Ministry of Land, Infrastructure and Transport has developed the renaturalization project of sand beach in the estuary. In this study, we have particularly investigated flow patterns and fine sediment transport around these spur dikes by using Stream-pro Acoustic Doppler Current Profiler (ADCP) and radio-controlled model boat equipped with Workhorse ADCP in the period of spring tide. The results show that these spur dikes weakened flow and SS transport in the concave, and strengthened them in the convex of the bend. In addition, fine sediment accumulation were discussed through streamwise distribution of SS transport in both cases of flood and ebb tide.

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Fine bed sediment in a river estuary is sometimes flushed by a freshet, and it affects bio-chemical condition in the estuary. The process of the phenomenon has not been much clarified yet because of the difficulty of measurements. This paper discusses the phenomenon by paying attention to black patterns of the water surface appearing on aerial photos taken in the Tone River estuary during a freshet. Sediment data suggests that the patterns correspond to deoxidized fine sediment raised from the channel bed. From correlations of the patters with bed topography and flow field obtained from stereo analysis of the aerial photos, the process is considered as follows: A turbulent spot caused by a local depression of channel bed triggers sediment pick up and intensifies vertical mixing, raising the sediment to the water surface. The transverse shear between the vertically mixed zone and the surrounding flow generates further turbulence, resulting in the expansion of the zone of vertical mixing and sediment rising.

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Accuracy of two kinds of wind data during 15 typhoons calculated at 9 sea stations of the Seto Inland Sea is estimated by comparing with wind data measured at those stations. One set of data is extracted from a 45-year wind data set for the concerned area which was made by Yamaguchi et al.(2009) using SDP overland wind data acquired by the Japan Meteorological Agency. The other is the wind data set made by Lee et al.(2009) applying a mesoscale meteorological model MM5. The degree of agreement between the time series of calculated and measured winds during a typhoon is evaluated by 7 error indices. Almost all mean values and standard deviations of the error indices suggest that the SDP data-based wind data shows a higher degree of accuracy than the MM5-based wind data.

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Serious Chilean Earthquake, rating magnitude of 8.8, occurred on February 27, 2010, and caused large tsunami waves in the Pacific Ocean after that. The main objective of this study is to investigate the tsunami wave propagation into rivers with different morphologies based on a range of details measurement data sets from 20 rivers. The analyzed results show that the tsunami wave can affect up to 22km upstream of river at the most. Furthermore, it is observed that there exists distinct difference of tsunami height in the river dependent on the different river mouth morphology. Thus, classification of the rivers has been proposed based on the rank of rivers and river mouth morphology.

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In this study, to clarify the relationship between water level variation and turbulence of flow, field observations were carried out in Omaehama beach, Nishinomiya City, Hyogo Prefecture, JAPAN. In each observation, wind speed and its direction, water level, wave height, flow velocity and its direction were measured in the vicinity of shoreline. The data of wave height was transformed to the velocity by using a liner filter theory and examined the effect of boat wave and wind one on turbulence of flow. The transferred velocity from wind wave was coincided with the turbulence of flow, however, that from boat wave was not so good. From the results of this study, we can see both boat wave and wind one are the significant factors of water level variation in urban semi-closed water area.

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In order to activate water exchange between a semi-enclosed bay and its open sea, a water purification method, called One-Way Pipe, is proposed. One-Way Pipe is a pipe attached asymmetrical structures inside, and can generate residual currents in oscillatory flow fields due to their directional resistance properties. This method is more economic and eco-friendly because it utilizes waves as energy sources. In this study, the optimum size and the position of the flange to generate residual currents were experimentally investigated under several wave conditions. Furthermore, the mechanisms for producing a unidirectional flow inside the pipe were discussed. The flange forms separation vortices behind it and generate a low pressure region behind the outlet of the pipe. This low pressure region due to separation vortices draws mass flow inside the pipe.

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Langmuir circulation is a large-scale secondary current, which is generated under the presence of wind-induced water waves. Many previous researchers have conducted various theoretical studies and numerical simulations, however accurate database of laboratory experiments is not still available. The main reason for this was due to the difficulty of the experimental set up, and most of the experiments were conducted with a point measurement such as LDA and ADV. Therefore the instantaneous and space-time correlation properties of Langmuir circulation have not revealed yet. In this study, stereoscopic PIV allowed us to conduct simultaneous measurements of all three velocity components on the cross sectional plane, and we obtained three-dimensional structure of Langmuir circulations, considering the relationship among three components and phase properties.

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For every time in summer season, hypoxic water mass has formed at the inner part of Hakata Bay. Field observation study has carried out at the inner part of Hakata Bay since 2004 with the particular aim of tracking the movement of hypoxic water mass. Hypoxic water masses form the end of June to September on this area because the consumption of oxygen in bottom water layers exceeds the re-supply of oxygen from the atmosphere. Under such hypoxic conditions, the seawater desalination plant has begun to use in 2005. After seawater desalination plant operation starting, hypoxic water mass tends to improve. In this research, the authors show the following result. After seawater desalination plant has begun to operate, the hypoxia around the mixed discharge water outlet tends to be improved.

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In order to make clear the mechanism to form the oxygen-depleted water at the bottom layer of the northern region of Kagoshima Bay, we carried out field observations at two representative positions. Then, we evaluated the processes to form the density stratification and vertical DO profiles by the numerical simulations based on the observational results. As a result, the following findings were obtained: 1) The seasonal change in DO concentration at the bottom layer of the observational position was controlled mainly by the seasonal change in the degree of density stratification. 2) Due to the relatively large depth, the stable stratification does not disappear until December and the most anoxic water is formed in winter in Kagoshima Bay.

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To clarify the present situation of water environment in the Uchikawa River in Toyama, field observations (water quality, flow velocity distribution and plankton sampling) have been carried out continually since 2009. Water quality in the Uchikawa River had been aggravated due to the development of well-drained paddy fields and new ports in and around the river basin from 1960s. Regardless of a water reclamation program, water quality in the Uchikawa River does not show a drastic improvement.Due to the effect of purification water from the Nishi-Uchikawa River, upward flows of seawater and vertical water quality changes in the Higashi-Uchikawa River were found from the investigation results of water quality. It was also found that the spatial distribution of plankton was influenced by the water flows. The existence of both freshwater and marine (brackish) algae in the river indicates that the resources subsidizing food web are provided through the multi-directional water flow.

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In order to clarify variability characteristic of water quality in tidal area of urban river, results of field observation at ordinary water (about the water quality change before and after dredging) and rainfall in the tidal area of the Nihonbashi River are reported in this paper. From the results of field observation, following results are obtained;1) The mean value of dissolved oxygen saturation of all layers decreased by 25.8% at the spring tide, by 20.4% at the neap tide before and after dredging. 2) BOD concentration decreased and T-P concentration increased after dredging. T-N concentration decreased after dredging at the low tide. 3) When total rainfall was 10.5mm in 7 hours, value of dissolved oxygen saturation did not change in all layers, and it increased by 20% after 7 days. 4) During daytime both air temperature and water temperature increased. On the other hand, during nighttime water temperature decreased in spite of air temperature increased. 5) Water velocity repeated reverse flow and uniform flow during a hour period.

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We surveyed suspended solids (SS) and heavy metal ions, such as iron, manganese and zinc in sediments, in order to evaluate contribution of sediments to heavy metal ions in the estuary. We found that SS increased in the estuary during low tide and this fact was concluded to be due to resuspension of sediments by a large tidal difference. The sediment samples were equilibrated with seawater at several concentrations, which were diluted with water. As a result, iron concentration dissolved into the mixed seawater was negligibly low. This may be due to the fact that iron exists as an iron complex with humic substances, which is insoluble into the mixed seawater by the salting-out effect. While, the concentrations of manganese and zinc dissolved into the seawater were found to increase with increase in salinity in the seawater, which was in good accordance with the results that the fractions of manganese and zinc in the exchangeable form in the sediment samples were higher than that in the other samples.

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Transportation and deposition of mud in tidal flats are closely associated with the tidal flats environment and the sludge-ization of tidal flats. It is thought that the transportation and deposition of mud are affected by the organic properties of mud, such as the amount and decomposition degree of organic matter. In this paper, an experimental investigation of the mud movement in packed sand was performed with mud in different organic properties. The experimental results suggested that the mud exists high amount of organic matter is easy to remain in the packed sand, and deposit in the pore of sand in loose state. In addition, it was also found that the deposition behavior of mud in the pore was not only affected by the organic properties but also the pore structure and the characteristic of infiltration flow.

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A setting-back of coastal dike to protect the wetland was carried out in 2004 near the mouth of the Maite River flowing into the Nakatsu tidal flat. Monitoring surveys, such as beach surveys and investigations in coastal vegetations, had been carried out between 2005 and 2009 after the setting-back.During the observation period, Typhoon No. 5 attacked the coast on the 2nd of August in 2007, resulting in the increase in tide level up to DL+4.7 m, which is a maximum since 2000. Due to the storm surge,shoreward sand transport occurred and a high berm with a height of 5.02 m was formed with the recession of the foreshore by 5 m. No changes were observed in the wetland and its environment was maintained despite the storm surges, suggesting that the setting-back is useful for protecting the wetland against storm surge.

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Mudflats have an important role as habitats of aquatic near-threatened species such as mudskipper. However, the study of mudflat environment is still limited especially in Okinawa. The objective of this study is to consider the method of conservation and restoration of mudskipper habitat in the main island of Okinawa. The prediction models of mudskipper′s habitat in individual mudflats and extensive distribution of mudflat for the habitat in the main island of Okinawa are developed using logistic regression analysis. The results indicate that the mudskipper′s habitat decreased by reclamation work in Nakagusuku Bay, and the mudflat suitable for the mudskipper′s habitat is limited to Nakagusuku Bay and Oura Bay in the main island of Okinawa.

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The study on embankment failure is essential to predict potential flood and flood risk management. Significance of soil type and state is essential for the prediction of erosion of embankment due to overtopping. The behavior of unsaturated soil is different from saturated soil. However, most of the existing embankment breach models do not consider infiltration of water inside the river embankment. Therefore, it is important to study erosion rate of unsaturated embankment of different sediments in different hydraulic conditions for the prediction of outflow discharge and hazard assessment. This study is focused on erosion of unsaturated river embankment caused by overtopping. Shear strength due to suction plays a vital role in erosion of unsaturated fine sediments. A new erosion equation is developed considering shear strength due to suction on an unsaturated bed. The shear strength of an unsaturated bed is correlated with a soil-water characteristic curve. The proposed model is tested for an embankment of different sediment sizes. The numerical model considering suction in erosion rate is capable to predict erosion rate of non-cohesive fine sediments as observed in the experiments.

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Recent progress of research on sediment transport, bed deformation and landform evolution was summarized in this paper. It can be much easier than before to conduct a numerical simulation of sediment transport event and bed deformation for the present, but there still remain essential problems. Unsteady and non-equilibrium effect of flow on sediment transport, the effect of cohesive sediment on the bed deformation process in river, and a sediment transport itself in case that the river bed is composed of sediment mixture with a very wide range of size distribution are such problems to be investigated in near future. In addition to this, some results of numerical simulation were illustrated in this paper in order to discuss how we can predict this kind of phenomenon in this research field.

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