Instantaneous structures of both air and water layers were measured by using PIV method in wind water waves. Furthermore, turbulence structures at various phase of wind waves were evaluated by applying phase-averaged method. Reynolds stress distributions are much different with each layer. Reynolds stress contributions take a greater value on windward side of wave crest. It became clear that these phenomena are closely related to the generation mechanisms of coherent vortices both in air and water layers, which approach the wave periods in the faster wind velocity.

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A new method has been developed to resolve water-quality environment problems in water reservoirs utilizing flow characteristics of flow networks, defined as a system of mutually intersecting flow passage. In this paper, an experimental study was conducted to investigate flow characteristics in a new system of drainage ducts using X-shaped intersecting ducts in a reservoir model. Flow characteristics of the new drainage system are disclosed, which can be utilized to enhance a mixing and a suction effect in the intersecting ducts. It will lead to the improvement of problems for the selective withdrawal and the reservoir sedimentation.

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The experiments on the non-conservative inclined wall thermals using the mixture of water and nonuniform barium sulfate particles are carried out. The experimental results obtained may be compared with the numerical simulations. The new numerical model of an inclined wall thermal is proposed, in which the size distribution of solid particles is taken into account. The simulation model for inclined wall thermals of nonuiform suspended particles consists of the continuity equation, the mass conservation equation and the momentum equation. In the model, the dimensionless value α related to the entrainment coefficient E_w, and the form drag coefficient c_D are chosen as parameters. Comparing the numerical calculation with experimental results of inclined thermals, likely values of α and C_D are obtained.

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Characteristic behaviors of turbulent transition in the bottom boundary layer under irregular waves have been studied from laboratory data. It has been observed that flow transition under irregular waves is not only governed by instantaneous flow properties but also depends on the conditions in the preceding waves. While laminar-to-turbulent transition required a build-up of turbulent energy sufficient enough to produce traces of turbulence, for turbulent-to-laminar transition the turbulent wave was required to be followed by several successive smaller waves to allow total dissipation of turbulent energy. As a result waves with much higher Reynolds numbers show predominantly laminar properties, whereas, wave with Reynolds number as small as 5.0×10³ shows turbulent behavior. Use of conventional wave friction factor diagram, therefore, becomes unsuited to indicate flow transition under irregular waves. Also transition takes place over a much wider range of wave Reynolds number than observed for regular waves.

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Generation of water spray from wave-absorbing seawalls and its transport processes have been investigated by using a wind wave tank. Vertically-integrated spray quantities just behind the seawalls Q₀are much larger than those in a water region and increase with the increase of mean wind velocity Um and slope gradient. The leeward distributions of spray quantities Q can be expressed universally by using Q₀, Um and the gravity acceleration g. The values of Q/Q₀, decrease exponentially in the region of gx/Um²<0.5 because of the balance between advection and settling of large spray, where x is the distance from the seawall. In gx/Um²≥0.5, the decreasing rate of Q/Q₀, becomes very small due to the transport of minute spray.

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The aim of this study is to analyze the variability of sea surface temperature (SST) in the month of May 1990-1994 at the Kuroshio/Oyashio frontal areas. SST variations are examined using a combination of weather conditions and offshore water-mass distribution. A series of ocean thermal imagery (37-image) from Advanced Very High Resolution Radiometer (AVHRR) are analyzed to study influence of moving fronts on the coastal thermal environment. Multiple regression analyses are used to understand the relationship between independent variables (weather variation components and offshore condition) and coastal sea surface temperature (SST) as dependent variable. The regression results provide a good correlation between the predicted value and in-situ SST. Strong impact of variation in offshore circumstances on coastal SST distribution is clearly noticed especially at the edge of warm tongues and streamers of the of the Kuroshio flowing northward.

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Beach changes due to the elongation of river mouth jetties around the mouth of the Arakawa and Kinotodainichi Rivers in Niigata Prefecture are investigated. Topographic surveys off the river mouths were carried out seven times from 1988 to 1999. Since southward longshore sand transport prevails at this river mouth, south beach was gradually eroded after the extension of the jetties, whereas sand accumulated at the river mouth. The occurrence of scouring around the artificial reef and jetties, which was predicted by the previous study based on the topographic surveys, is confirmed in the real data. The effectiveness of an artificial reef constructed off the mouth of the Kinito-dainichi River to prevent sand deposition inside the river mouth is verified.

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Estuary water quality is greatly influenced by the ocean, particulaly the influences from ocean currents. Ocean currents have a very large thermal capacity, especially the Kuroshio and Tsushima warm currents. The Kuroshio, Oyashio and Tsugaru warm currents meet offshore from the Sanriku. Therefore, the water quality in bays along Sanriku coast can change with these three ocean current conditions.In this investigation, it was found that (1) for an average year, the coast southern limit of Tsugaru warm current (summer) and northern limit of Kuroshio current (winter) are about 40° N (Miyako), (2) Kuroshio waters intruded into Onahama are affected by the Kuroshio route at Hachijyojima (33.1° N, 139.78° E), (3) from the middle of September to January, yearly water temperature deviation is small.

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Generally, currents vary with density conditions. This paper describes mechanisms of currents around the mound at Ohfunato Bay in accordance with density difference between inside and outside the bay. It is revealed that mechanisms of currents are greatly related with the rainfall depend on the results of the field measurement in summer. Immediately after rainfall, low density water due to rainfall remains at the surface layer outside the bay. This water body mixes with the high-density water body at bottom layer outside the bay, and so the density of water body outside the bay becomes small. Under this condition, the inflow of low-density water at middle layer and the outflow of the bottom water inside the bay are stronger than usual. Thereafter, the density above middle layer inside the bay becomes small uniformly due to the inflow of low-density water. When low-density water body disappears outside the bay, the density of water body going into the bay becomes big.Therefore this water body comes to go into the bottom layer inside the bay. This current supplies oxygen to the bottom layer, thereby the depleted water body inside the bay recovers rapidly.

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Pollutant in a stagnant water area of a semi-enclosed bay has remained a serious water environmental problem. In order to activate tidal exchange, Komatsu et al.(1993) proposed a method, “Pond Method”, which can surely create a one-way flow by operating two water gates with tide. In the Karatsu Port, located in the northern part of Kyushu Island, a waterfront development on the basis of excavation of a canal has been planned. In this paper, we try to apply the Pond Method and other water restoration methods to the Karatsu Port and investigate the effects of these methods by the numerical simulation. As a result of this research, it was made clear that the ratio of the residence time by Pond Method to one by the excavation of the canal is only 3.2% and that this method is extremely effective for the field of a very weak tidal current.

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Nowadays water pollution caused by eutrophication in a semi-enclosed bay has been a serious problem. In order to solve this problem, a method has been proposed to activate the water exchange between an inner bay and its outer sea area by using Bottom Roughness with directional resistance properties. In this paper, a possibility for practical use of this method was examined from many angles. First, the basic effect of Bottom Roughness on substance transport was examined by a laboratory experiment Next, 2-dimensional numerical simulations were carried out to estimate the validity of this method in the Nagoya Port that has a complicated topography. Lastly, it was it-ported that four kinds of Bottom Roughness were sunk to investigate their influence on the scour of seabed and the water environment. From these results, it becomes clear that this method is efficient to improve the water quality in real sea areas.

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In this study, 2-dimensional numerical simulations were carried out in order to make clear the mechanism of salinity intrusion in a well-mixed type estuary. As a result, the following findings were obtained; 1) It was made clear that there are twin tide-induced residual circulations in the sea area near the river mouth. 2) The substance transport mechanism in a model estuary was clarified by means of the particle tracking simulations. 3) The results of numerical simulation, which can correctly reproduce the salinity intrusion in the laboratory experiments, show that the tide-induced residual circulations contribute to not only the salt balance near the river mouth but also salinity intrusion length as a tidal pumping effect.

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Omura Bay in Nagasaki Prefecture, which is almost isolated from the outer sea, is famous for the very low exchange rate of sea water. In the present paper, the authors carry out the tidal flow simulation using the simulation system improved with the automatic control method, and it is discussed that the effect of seabed configuration on the exchange rate of sea water in Omura Bay. At first, it was estimated that the current rate ranges from 0.2 to 0.4%. Secondly, the authors performed the simulation tests with the modified seabed configuration which is cut the sea mount and buried the deep basin, respectively or simultaneously. It was confirmed that there are little changes of tide, the averaged rates become higher than current one and the water mass pattern nearby the bay mouth stretches into the depths of the bay.

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The formation process of three gyres in Lake Biwa, as observed using ADCP, has been simulated by using Large Eddy Simulation (LES). Two different dynamic subgrid-scale (SOS) models-Dynamic Mixed Model (DMM) and Mixed Scaling Formulation Model (MSFM)- are employed to describe stratified non-isotropic SGS stress due to the large disproportion between horizontal and vertical gridspacing in the computational grid.
The driving force of gyre formation is assumed to be differential heating due to heat volume differences between middle-lake and shoreline areas. This condition was created in the simulation by setting the initial temperature distribution in the lake based on field observations. Significant gyre formation patterns are calculated by LES both with DMM and MSFM. Due to the huge disproportion between horizontal and vertical grid spacing, the isotropic SGS model (such as the Smagorinsky Model) does not perform well.

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Experiments by a two-dimensional wind flume were performed to investigate the wind-induced density change and the growth of a wedge-shaped intermediate density layer in a closed stratified water. The vertical distributions of density and velocity were measured near the upwind end while the mixing-layer deepening was visually estimated at the end of the flume. Three digital video cameras were used to take the temporal density changes and the image was analyzed by the digital computer, The luminance profile obtained by the image processing technique is in agreement with the density profile measured by the electric conductivity meters. The intermediate density layer is formed by an accumulation of mixed fluid at the start and gradually increase the thickness and length due to wind-induced circulation in the mixed layer. The temporal velocity distribution in the mixed layer depends on the density difference and the mixing-layer deepening.

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This paper presents a theoretical study of the steady wind-driven currents in a semi-enclosed rectangular basin of uniform depth. Linearlised equations of motion and f-plane approximation are used. Horizontal component of winddriven current has been obtained for a general steady wind system by means of Fourie analysis. Solution is composed of both wind drift and slope current. Calculation reproduced a flow structure similar to the existing field data.

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In a brackish lake the occurrence of the density stratum by the vertical distribution of water temperature and salinity exerts an important influence on the water quality. Therefore. in a lake where there might be a occurring of strong density stratum. the mathematical model that predicts the break of density stratum should be developed and the characteristics of the break of density stratum must be examined with the model.
In this paper, the 1-D mathematical model that predicts the hourly change of water temperature and salinity distribution in the shallow brackish lake is developed. And using the model. the influence of water temperature and salinity distribution on the characteristics of the break of density stratum is investigated analytically. Furthermore. the influence of the shape of the lake is evaluated. Finally. the frequency of the break of density stratum is discussed from the results of numerical simulations under various stratum conditions with actual wind data in the past.

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Lake Nakaumi has a strong pycnocline. The interface oscillation characterizes the flow in the lake. Wind and tide are external force causing the interface oscillation. These external forces are classified by the diurnal period components from that over the day period components. We studied the interface oscillation and the flow which originates due to this oscillation in Lake Nakaumi. It was deduced from the results that;(1) The interface oscillation in the Yonago bay is different from that in the central part of the lake. Yonago bay has longer period and larger amplitude interface oscillation than the central part of the lake.(2) The astronomical tidal current is dominant near the Nakaura gate. But the flow due to the land and sea breeze is strong in the central part of the lake.(3) As the interface oscillation originates by the strong wind in the central part of the lake, it can easily propagate into the Yonago bay.

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The Takase River is important in the southeast of Aomori Prefecture and its estuary is typical tidal river. Mixing of salt-water intrusion in compound channel is very complicated. The field measurement is performed to study the mixing characteristics in the compound channel of the Takase River estuary. The salinity concentrations are measured by the thermometers and by the salinometers in 29 stations of the field. The water temperature is changed into the salinity concentration. The results of this study showed that patterns of the horizontal salinity mixing in the compound channel at flood tide is different from those at ebb tide.

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Two-dimensional numerical model is developed. The effect of diurnal inequality and river discharge on the mixing of density current in estuary is investigated. Numerical results coincide almost with observed ones for the higher isohaline but for the lower isohaline the difference between numerical and observed results is large. The effect of the diurnal inequality on saline intrusion is classified into two patterns. This classification is explainable by the new parameter, which is defined by the tidal amplitude. When the river discharge exceeds 1000 m³/s, the intrusion of saline water is almost stopped.

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To predict the water temperature in lower reaches of urban rivers, field measurements and model development were performed for simultaneous transport of water and heat in a stream. Detailed information on river flow and heat transport under tidal motion was obtained through an intensive measurement in the lower reach of the Ara River. Based on the knowledge of time variations and cross-sectional profiles of the flow and the stream temperature, a onedimensional dynamic model is developed to predict flow and water temperature in tidally affected urban streams. The model takes into account of tidal motion, longitudinal dispersion, water exchange with tributaries, wastewater effluent and the heat exchange between the atmosphere and the stream water. Using the calibrated model, effects of heated water discharge on the stream temperatures due to the district heating and cooling system were estimated for a possible scenario in which the river thermal energy is used through the water heat pump technology.

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In this study, field observation was carried out in the Old Kitakami River. As a result, most of the mixture form was of weakness mixing, and it was shown that the saline wedge was almost stopped at the riffle at the 6km site. The result of the bottom sediment survey, proved that the property of the bottom sediment is different in the upstream and downstream of the riffle. Next, numerical simulation was done according to the two-dimensional k-ε turbulent model. Simulation result of the saline wedge stopping at the riffle was reproduced in good agreement with the observation result Finally, by changing the flow rates, it was shown in the simulation that features of the saline wedge differed in the upstream and downstream of the riffle. These results suggest that the saline wedge is frequently stopped by the riffle in ordinary water discharge, and then, mound is formed by suspended solid settling on the top of the saline wedge.

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In this study, the flow characteristics in downstream area of the Nagara river estuary barrage are estimated by means of observed data obtained from ADCP (Acoustic Doppler Current Profilers) and observation plane for water quality. The investigation results are summarized as follows. The flow in downstream area of the Nagara river estuary barrage in inflow of the tide is affected by the situation of density in mouth of river. In the case of existence of low density water in mouth of river, the flow becomes two layer flow because of existence of high density water in bottom. In the case of existence of high density water in mouth of river, the flow get into deep area of river. In the case of the ebb tide, down stream flow pass upon high density water. In the spring tide, inflow of the tide pass to the Ibi river because the water level in the area from the Nagara river barrage to joint point with the Ibi river more rapid increase than the Ibi river.

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In recent years, spur dikes are expected to demonstrate various functions. Permeating flow through the spurdike can control the flow field, structures of separation vortex and bed configuration around the spur dikes. In this study, velocity fields behind the solid, straightly permeating and inclined permeating spur dikes are measured and compared. The resistance and scour depth at the head of the spur dike are reduced by the permeating flow through the dike. Spur dikes with inclined permeating flow were proved to have several advantages. The inclined permeating flow reduces the strength of the separation vortex, keeping almost similar deceleration effect and reattachment length. Furthermore, it decreases the turbulence intensities behind the spur dike and maintains relatively lower velocity over a long distance behind the spur dike, even in the case of movable bed.

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It is important to clarify three-dimensional flow structures and instantaneous vortex structures in order to understand the mechanism of sediment transport and water quality exchange in spur-dike regions. In this study, characteristics of organized vortex structures around the submerged spur dikes were investigated by using PIV method. The velocity vectors were obtained in several slices of vertical and horizontal plane. The instantaneous flow structure in the region between spur aces is quit different from the long-time averaged flow structures. The vertical vortices and transverse vortices interact with each other and the flow indicates strongly three-dimensional phase. Two-dimensional PIV analyses of vertical and horizontal planes can catch the fragment of instantaneous vortex structures.

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Natural vegetation plays important roles on river environment. It is needed to find the way of managing vegetation aiming at the harmony between flood control and environment. Considering the vegetation as groins, we studied the flow and bed topography around permeable groins to determine the structure and arrangement of vegetation groins from the standpoint of both flood control and environment.
The experiment showed that the groin interval to length ratio, L/D=2.0 and groin height to water depth ratio, hg/h=0.90 gave good representation for flood control and environment. The three dimensional numerical model provided good explanation for experimental results of the flow and bed topography in the channel with permeable groins in series.

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This study examines measuring methods of drag coefficient, lift coefficient and equivalent roughness that are necessary for mechanical design of revetment blocks set on river banks. The setting method of blocks and the influence of the Reynolds number on drag force and lift force are examined by checking the experimental results. A standard testing method which is capable to estimate the characteristics of blocks, taking the error of mesurment into account and the treatment of fluctuation of hydraulic force on the block are shown in this paper.

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Bridge piers are often built near by. It is very important to estimate the hydrodynamic forces acting on piers and maximum scour depth around them for their safety and economical design. In this paper, two cylindrical piers were set in a straight channel of movable bed that were apart at a distance of four times of their diameter in the longitudinal direction of flow. Based on the detail measurement of the pressure, velocity and bed variation around the cylinders, the structure of flow and the fluid forces were clarified. Fluid forces and maximum depth of scour were compared with the case of single pier experiment.

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Groins are used as structures against bank erosion in curved channels. The arrangement of groins has been studied by the statistical, experimental, and numerical methods. Recently they are also focused as structures making favorable environment in rivers. The arrangement of groins should be thought by the function of groins. For this purpose, the numerical model, which represents accurate flow and bed deformation around groins, is needed.
Considering the practical use, we have studied on quasi three-dimensional numerical model. We introduced groin arrangement and hydrodynamic forces in this model to estimate the effects of groin. The result shows the general features of the flow and bed deformation. Drag coefficient C_D and lift coefficient C_L of hydrodynamic force were determined without measuring these forces. In this paper, we made clear the characteristics of hydrodynamic force on the submergible groin in series about the various groin arrangements by measuring forces directly and flow around the groin, and obtained drag coefficient C_D and lift coefficient C_L.

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The reservoir sedimentation, in mountain rivers with steep slope like in Nepal is characterized by the water level profile with a hydraulic jump. The sediment deposition is observed ina small, steep laboratory flume with a dam, which causes a hydraulic jump in the reservoir. The bed configuration is two-dimensional without sand waves, or three-dimensional with sand waves dependingon sediment sizes in the reservoir downstream of the hydraulic jump. The delta deposition is found progressively moving toward dam as well as sediment deposition toward upstream, which start from the section of the hydraulic jump. The location of the hydraulic jump is shifted to upstream side from the initial section, after the bed elevation raises due to the sediment deposition. The longitudinal bed profiles averaged over channel width can be simulated well by one dimensional analysis with the application of hydraulic jump. The simulated bed profiles and water levels were found to coincide with the observed ones for each discharge and slope of the channel.

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Effect of the depth of trench on diffusional mass transfer from bottom sediment to flowing water in a rectangular trench is formulated as a function of flow velocity and the aspect ratio of the trench. Laboratory experiments are carried out in order to investigate the relation of the diffusional mass transfer for sediment bed in a rectangular trench with the water flow and the depth of the trench. The experimental results have shown that release flux of dissolved substance increases as the flow velocity increases in almost all experiments. It is also found out that release flux increases as the depth of the trench decreases. These results suggest that diffusional mass transfer is influenced by turbulent structure in a rectangular trench. It is considered that exchange of the water body near the sediment-water interface for the upper layer water becomes more frequent as the flow velocity increases or the depth of the trench decreases, so that release flux increases.

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Freshwater red tide blooms are formed at the reservoir tail in many cases. Dinoflagellates such as Peridinium and Ceratium are usually causative species. These species are unique in being able to swim toward light (phototaxis). This ability makes it possible for them to swim upward during a day. Density currents formed around a plunging point of river water at the reservoir tail seem to help them accumulate around the plunging point. We have surveyed flow structure, water quality changes and diel distribution variation of red tide causing Peridinium bipes at a reservoir tail to investigate the mechanism which leads to a long term continuation of red tide bloom. A continuous surface flow directing upstream was measured at the reservoir tail and P. bipes's accumulation at the water surface and upward migration during a day were observed. Most individuals remain at the surface even during night; however, some settled down and were transported downstream by plunged river water which contains available nutrients. This partial settling seems to allow them to take up nutrient from river water without being flushed out throughly

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The estuary and its adjacent coastal area is a hot spot acting as filter as well as a reactor between land and ocean. The functions are associated with several processes such as biological, biochemical, geochemical and physical ones. As the biological process, nitrification and denitrification occur both near the surface of sediments and in watercolumn. Nitrous oxide (N₂O), greenhouse effect gas, is one of the intermediates, in the nitrification and denitrification processes. The gassing the atmosphere is low in concentration, about 320ppbv at present it, however, has been increasing by 0.8 ppbv annually. We study that emission of N₂O from sediments in the bay obviously changed due to various change of sediment water quality, making use of sediment-water quality model, at Tokyo bay and Hakata bay. This model was simple layer model, consisted of nitrification, denitrification and oxidizing organic compound. Simulation results showed that emission of N₂0 from sediments were high rate due to upper water quality changing, not only nutrient concentration but water temperature and oxygen consumption. Emissions of N₂0 from sediments at bay head of Tokyo bay were much more than other three stations of Hakata bay.

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Tidal flat plays an important role in the water purification of a coastal region. In orderto investigate the nutrient budget on a tidal flat, field observations of water quality have been made on Wajirotidal flat at the east side of Hakata Bay in summer. The nutrient flux between sediment and seawater were estimated. Nutrients are removed from seawater in the daytime, and dissolved inorganic nitrogen and phosphate are released from sediment to seawater in the nighttime. The tidal flat functions as a sink for net budgets of nitrogen and phosphorus in the daytime, but as a source for phosphorus and as a sink for nitrogen in the nighttime. Since the uptake and release rates of nutrients per unit bed areadepend strongly on the quantity of solar radiation and DO concentration, they have spatial and temporal variations.

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Field survey was conducted in Pasig River flowing through Metro Manila, the national capital region of the Philippines in order to get the basic information about flow and water quality for the future planning of river environmental management. Salinity, water temperature, DO, Turbidity, and Chl-a were measured with a water quality meter every 1km or 2km along the channel center line in the reach of 25km between Manila Bay and Laguna de Bay. The spatial structure of flow and water quality in the reach are estimated from these data. BOD was analyzed for water sampled at several stations. The rate of BOD load and the pollutant runoff coefficient are also roughly estimated.

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As part of a major effort to understand and quantify the eutrophication process in Lake Yanaka, characterization of the lake is carried out by combining extensive survey and analysis of existing data with field measurement of both flow and water quality parameters in Lake Yanaka.
Peak concentrations of chlorophyll a and its relation with phosphorus, oxygen, inflow and outflow, and the observed flow patterns are the main focus of this paper. Various featuresof water quality conditions in the lake are elucidated, and particularly, the mechanism of phytoplankton blooms in Lake Yanaka is explained with supporting evidence

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The problem that oxygen depletion observed in eutrophic natural lakes and reservoirs damages natural benthonic organisms and induces nutrient release from the sediment is becoming serious. For this problem, we proposed a method which transports surface water including a large amount of dissolved oxygen (DO) to a bottom layer in which DO is not usually enough. The effect of injection of surface water into hypolimnion on water quality restoration by this system has already been proved. In this study, we investigate the degree of water quality restoration in case of intermittent injection of surface water into hypolimnion by field experiments and numerical experiments.
From numerical experiments, we find that it is expected that the water quality can be restored, even if the period of supplying surface water is shorter than the period of supplying no surface water.

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A water purification system was developed and installed in the lower layer of a eutrophic reservoir. A preliminary test was conducted in order to examine its performance. The aerator generates fine air bubbles of several ten micro millimeters, so-called micro-bubbles. Dissolved oxygen, temperature, electric conductivity and other water quality items have been measured in every two weeks after starting the micro-bubble aeratin in March 1999. Despite continuously operating the system, total amount of dissolved oxygen in the reservoir has decreased so far, from which the air discharge is estimated to be less than oxygen consumption due to decomposition. Nevertheless, DO concentration in the lower layer is higher than that observed in the last four years, while DO in the surface layer has been kept less than that in the last four years. These results suggest that the system functions for aerating water body to some extent, except that the air discharge is not sufficient for complete aeration, yet.

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Laboratory experiments were performed to consider flow characteristic and oxygen supply by a bubble plume in two-layred stratification which density and anoxic. Experimental results are follows. Flow shape varies initial airflow rate. This confirms by vertical density and DO distributions. Oxygen supply are confirmed to compare entrainment volume whether it involves gas exchange or not from upper or lower layer. The efficiency of oxygen supply was evaluated to use the oxygen volume of increase and provided oxygen volume, As a result influence factors are provided airflow, bubble diameter, initial height of density surface and flow shape. Allowing for them, evaluation factor was introduced. Value of experimental and evaluation are in a 1 to 1 ratio in a logarithmic faction

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In Watarase Reservoir, a eutrophic shallow lake, fish kill phenomenon has been occurred especially during spring and summer. In this study, the dominant factor of this fish kill was investigated not only from ecological view point but also from that of water quality and movement. It was shown that the primary production of phytoplankton in this reservoir is high enough to feed fishes whose standing crop is high. Field observation with fish finder indicated that almost fishes exist in deep area near the bed. And it was concluded the sudden fall of dissolved oxygen at night, which is caused by stirring mud with strong wind, is one of the important factor of fish kill.

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There are sulfate ion and nitrogen ion that acidify raindrops in rainfall. Those chemical ions are taken in rain by rain in or wash out. Until now, the authors have been investigating through measurement of acid rain in local area. And it is made clear that there are a seasonal characteristic of acidity in Tochigi region.
In this study, it is examined a characteristic of distribution about ion concentration or amount of fallout in rainfall. As a result, there is a tendency that sulfate ion concentration is high in summer, but low in winter on the whole of Tochigi region. And a rate of contribution of the origin of sea salt is not so much. But, there is a tendency that potassium ion is high in winter, but low in summer in Nikko. As a rate of contribution of the origin of a salt is a few, it is assumed that the origin of potassium ion and sulfate ion are in inland area

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The load of total nitrogen (TN) and total phosphorus (TP) in stream water was surveyed at 23 points in the Nagara River Basin (2000km²) located in the central part of Japan. Multivariate analysis was applied to relate the TN and TP data to the conditions of land coverage such as geologic feature, type of land use, population density, percent of sewered population, etc. The load of TN and TP was largely governed by the distribution of human activities such as industrial wastewater discharge, agricultural production, population density, domestic animal density.

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A mathematicaml odel of NO^-₃N runoff process from a forested mountain basin is developed, based on a tank model comprising a surface tank with soil water storage systems, and a ground water tank. The model takes account of three elementary processes of NO^-₃-N in the forested mountain soil. They are infiltration and advection, solute exchange between mobile water and immobiler egions, and nitrification by microorganisms in the soil. The process of former two are modeled as a function of the rainwater movement and soil moisture saturation calculated by the tank model.The latter process is modeleda s a functiono f soil temperaturec alculatedb y a soil temperaturem odel. The model is applied to annual observations in 1992 obtained in Shirakawa-tani fo restedm ountainb asin (main species Japanese cedar) located on Shikoku island in Japan. The model describes the seasonal change of NO^-₃-N streamwater concentration well, through a year.

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To investigate the influence of chemical fertilizers on groundwatear and surfacewater neighboring tea plantations in central Shizuoka prefecture, a time series of chemical compositions and nitrogen isotopic ratios within local wells, springs, rivers and ponds were studied.The pH of spring and pond water in some areas maintained basic acidity with neither any noticeable changes in nitrogen isotopic ratios nor any disappearance of nitrate within the ponds and low concentrations of chlorophyll and phosphorus.Therefore, the activities of photosynthesis in the ponds of this area were very low due to low concentrations of phosphorus. However, the pH of spring water in the other areas maintained basic neutrality to alkali with high concentrations of C²⁺_a and SO^2-₄ and low concentrations of NO^-₃ because of soil and fertilizer improvement.Concentrations of Al, Co, Ni, Zn and Mn ions in the groundwater and surface water increased with the decrease of pH values.Then, soil and fertilizer improvemenit si important.

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To investigate the river and ground water chemistry in the snow area, chemical composition and oxygen and hydrogen isotopic ratios of water in the Wagagawa basin were studied. During spring season, most dissolved component in river water was diluted by spring runoff. However, NO^-₃ concentration was maintained high because NO-₃ concentration in the snow was high. Spring and hot spring water contained a lot of SO^2-₄. High SO^2-₄ concentration was thought to depend on hydrothermal activity which induced copper sulfide deposits.δ D andδ ¹⁸O were measured in order to estimate the origin of water. All waters were on two kinds of meteoric line.δ ¹⁸ and δ ¹⁸O in the snow were thought to be higher than those of summer precipitation. Those of hot spring were extremely low. Therefore, the origin was thought to have arisen from precipitation at high altitude or past precipitation when the temperature was colder than that at present.

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Data assimilation of surface current obtained by oceanic radar into 3-D baroclinic models is examined in Osaka Bay. Oceanic Radar is one of remote sensors that are possible to measure spatial distributions of near surface velocity. The observed currents include the effects of wind stress, waves, tides and buoyancy and so on. These data sets should be useful to the data assimilation of numerical simulations. The blending and nudging methods are applied and the decay of velocity in the vertical direction, a log law is added to blending. Assimilated currents and salinity distributions are compared with measured results of ADCP and STD. As a result, the blending was better than the nudging. RMS value of velocity differences between assimilated by blending and observed by ADCP in surface layer was 0.12cm/s.

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To investigate remediation and enhancement of polluted marine environment, an environmental monitoring have been carried out at a special floating laboratory in Kaita Bay. This monitoring includes meteorological observation, current profiling and water quality measurement. The results indicated that sea-land breeze, which is common phenomenon around the coast of the Seto Inland Sea, greatly affects the marine environment of Kaita bay. Especially, time variation of chlorophyll-a at 4m depth had apparent diurnal oscillation that had good correlation with the movement of thermal stratification, which might be driven by sea-land breeze. The correlation between this oscillation and existence of sealand breeze had a statistical significance.

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The environmental management after human action is significant to eliminate and minimize the negative impacts on environment at developing area. In this study, the information distribution system of tidal current is proposed in order to support the environmental management in real time. Firstly, the numerical simulation model was developed to predict the temporal changes of tidal current and water stage at Isahaya Bay and Shimabara Bay, and the accuracy of predicted results was discussed in compared with the observed results. Following, the information system was built usingfree software. The predicted results of current by numerical simulation were distributed from thissystem by means of the internet in real time. This kind of system is likely to become very useful toolnot only for the water environmental management but also for the prevention of natural disastersaround the coastal area.

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The water level in the Lake Nakaumi is predominated by that of the Japan Sea, and is affected not only by tide but also by meteorological factors. In this paper, wehave studied effects on water environment of the Lake Nakaumi by typhoons: Firstly, we have classified the typhoons according to the tracks following toward Japan and have shown thewater level fluctuations in the Lake Nakaumi while typhoons pass Japan. Secondaly, we have evaluated the water exchange while typhoon9719 has passed near the Lake Nakaumi. This study shows four types of typhoons depending on their tracks The water levels in the Lake Nakaumi aie effected by the type of typhoon. It is also observed that the volume of water exchange by the typhoon9719 in Lake Nakaumi is nine times as large as that of during ordinary condition.

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It depends on flow patterns formed in pool-and-weir fishways whether fishes succeed in the access to upstream or not. However we had not focused on the relationship between the flow patterns and the swimming behaviors which is a key element concerning about the fish accessibility. As a result, although the pool-and-weir fishways have been installed in many weirs, we could not have evaluated the efficiency. With these backgrounds, eight two-dimensional flow patterns were formed by changing the pool length and pool depth, and swimming behaviors was observed in each flow patterns in this research. It was confirmed that there are three obvious swimming routes to access a upstream pool, and significantly it was certain that one route is more successful to access than the other routes. The result shows that the flow patterns in the pool could provide a fundamental element concerning about fish accessibility and that we have to design the pool length and depth to keep the successful route.

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