Detention storages work for inundation contorol and water quality contorol. First flush is stored in the storage, treated after a rainfall event, and released to public water bodies like lakes, rivers, bays, etc. When rainfall forecasting by a radar is available and once a severe rainfall event is predicted, some amount of the stored first flush can be pre-released, and the resultant vacant capacity can be used for peak cut of the severe rainfall runoff to eliminate or reduce inundation volume. However large estimation error is inevitable in rainfall forecasting. In this paper, a basic study on on-line pre-release operation of a detention storage is reported, taking account of the large estimation error.

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The storage function method developed by Kimura is often used for short-term runoff calculation, and some on-line prediction methods which use this storage function method and the Kalman filter have been developed by several investigators including the authors. In this paper, the framework of our flood runoff prediction method is introduced and treatment of uncertainty of parameters of the storage function method is newly devised. In the new method, a number of filters with different parameters are run simultaneously, and the probability distribution assigned to these filters is updated by using the Kalman filter theory with real-time observation data. The results of application of this treatment show that the new treatment enhances the prediction accuracy.

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The possibility and the reliability of using Landsat TM 7 bands' data only to estimate monthly evapotranspiration (ET) over catchment areas were investigated through the regression analysis between the values of ET calculated from Morton or Penman equation and the data from satellites. The results for the Tokoro and the Abashiri River basin clearly indicated that such an approach was possible and reliable for grassland, forest and water area, and of the total 7 bands examined, four bands which belong to the visible light, near infrared, intermediate infrared and thermal infrared zone were most contributive and important, in the estimation of ET by using Landsat TM data only.

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The purpose of this study is to estimate the annual changes of monthly evapotranspiration (ET) in a river basin by using Landsat TM data, complementary relationship equation, and digital terrain model (DTM). This method was applied to the Tokoro River basin and the composited basin, which is consisted of the Bibi, Shukubai and Toasa River basin, in Hokkaido. It was shown that Brutsaert-Stricker equation was the most suitable among the complementary relationship equations for the estimation of ET, by comparing with the residual in annual mean water balance of Tokoro river basin. Net radiation contribute to the formation of basic annual variation of ET and advection term increase the ET in winter in above two study basins.

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A numerical analysis method is developed to estimate storage-level probability distributions in an actual reservoir with correlated inflows. A bivariate probability density model is adopted in order to estimate cumulants of a probability distribution for sum of two variables (inflows) mutually correlated. Using transition probability matrices obtained from the probability distribution functions for the sum variables, a calculation procedure of storage-level probability distributions for each period of five days through a year is shown. Moreover, the first passage probability and first passage time from an normal storage-level to a drought level are formulated and demonstrated for an actual reservoir.

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The importance of available fire-fighting water has drawn wide attention since the Hanshin earthquake in January 1995. On the other hand, as part of the flood control measures in Tokyo, many large reservoirs using underground space have been planned and implemented. Under this situation, it is necessary to consider using the reservoirs. Underground reservoir can store water during non-flood seasons, and the water thus kept can be used for eventual fire fighting. In this paper, underground reservoir's multi-objective uses are discussed, by analysing the monthly variations of the past 68 years' rainfall data in Tokyo.

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The global warming phenomenon has become of major interest in recent years. It has become of importance in respect of the water resources. This study aims at formulating the nonstationary time-series model for long-term variation of rainfall characteristics: the occurrance number and rainfall amount of one storm cluster taking account of monthly airtemperature. Mathematical models for rainfall characteristics consist of jump, trend, periodic and temperature components. Monthly rainfall changes for future 30 years in Tokushima and Niigata are shown.

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This study presents an application of neural network model to forecast of daily inflow series in a dry season with hydrological data at Makio dam basin area. The daily inflow and daily precipitation of a period before the day of forecast are used for the input to neural network. The lead time are one day and five days. In the case of one day, the average of relative error to data is about 20%. And in the case of five days, it is shown that the study of recurrent neural network with feed back is effective to progress of precision of forecast.

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This study aims at the prediction of daily inflow into a reservoir area by neural network model and information criterion (e. g., AIC) in a dry season. The calculation of network is carried out by the back propagation learning with a modified moment method. Comparison with this method and the usual linear regression method shows that neural network is effective in the reduction of error variance and in the increase of correlation between the estimation and observation of inflow data

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Recent research on climate and solar activity has suggested a close relationship between Northern Hemisphere land air temperature and sunspot cycle length. To find similar evidence for local data, we investigate 241-year monthly series of sunspots and temperature from south of Sweden. Three different sunspot cycle length and four different temperature data (same source) are used for the analysis. We find that different smoothing techniques yield different results. Results of the analysis display a certain relationship. We view that possibilities exist to better reconstruct temperature systems by regarding the solar cycle length.

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The eutrophication and the increase of phytoplankton occur at the many lakes polluted with inorganic and organic matter all over the world. The water quality at lake Abashiri, in which the water quality accidents called as “Aoko” and “Aoshio” in Japanease have often happend, have been simulated numericaly by using “Soumiya” model. In order to analyze numericaly the basic relationship between phytoplankton and zooplankton, the trajector of solution on the phytoplankton-zooplankton phase plane for Lotka-Volterra equation was used. It was shown that phytoplankton could be decreased largely by increasing zooplankton in the period of increasing phytoplankton.

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This paper describes spatial distribution of zooplankton inside lakes based on observational results. Lake A partially has vegetated bank, while Pond B is characterized by two different parts, an artificial shore and a naturally vagetated basin. Zooplankton was sampled at several points including near the vegetated bank and non-vegetated bank, together with phytoplankton concentration and other water quality parameters. It was found that the zooplankton concentration has a close relationship with vegetation and phytoplankton concetration.

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This paper describes the relation between comfort of shorelines and psychological and physiological human responses deduced from the measurement results of electroencephalogram (EEG) and electrocardiogram (ECG), and questionnaire on comfort sensation and other related sensations. Regression analysis showed that the comfort sensation depends on aesthetics of landscape, noise, smell and temperature sensations under specific situations. It was found that the content ratio of some components of EEG frequency spectrum has a plausible relation to the comfort sensation, and shorelines are relatively comfortable in psychological and physiological senses.

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Since November 1994 comprehensive field study has been performed in the Ara-River estuary three times to simultaneously measure the hydraulic and water-quality indices for 24 consecutive hours. The data are here analyzed to ultimately establish a method to protect the water quality in the area. For this purpose special emphasis is laid on the flux of water-quality indices, and the water-quality management is proposed with respect to such indices as COD, DO and TN that can be measured instantaneously.

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Techno rock is a concrete block which was originally designed as a protector of the riverbed during high water discharge. It is revealed that the block has a waterpurifying ability and a function of creating ecosystem in rivers. Experiments were performed to investigate how to enhance both dynamical and environmental abilities of the block.In order to protect scour or sedimentation, effects of attaching shades at the top and the inside a hole of the block were examined. Among several types of shades tested, two-shades type attached to the inside of the vertical hole were most effective to protect both the scour and sedimentation. Shades attached at the top of the upstream side reduced the scouring rate, whereas shades in the hole of the downstream side prevented the sedimentation.

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The urbanized areas in Japan have been subjected to the danger of inundation due to these location of the alluvial lowlands formed by flooding. Further, in recent years, the inundated areas have been increased by the rapid urbanization, in spite of the fact that the drainage system has been completely equipped for the established design level. In this paper, flooding model for urbanized area is proposed when the flood will exceed a design level. To put it concretely, Two-dimensional and One-dimensional approach are presented to analyze for the complicated flow condition mixing the sub-critical flow and the super-critical flow. The applicability of these models is explained by numerical study.

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This study describes two dimensional and one dimensional hydrodynamic models, to simulate watershed flow by treating surface runoff on a watershed of simple geometry. This model is formulated by a hydrodynamic system with the assumption of unsteady flow as steady flow which can reduce computation time. The numerical computation for this model is executed by use of the eight point implicit scheme. The Incremental Dynamic Programming (IDP) technique is adopted for the optimization of grid size during the computation. The model is applied to compute the routing of the floods in the Wichon IHP experimental basin located in southern part of Korea. Comparison of the results between the proposed model and the general type of two dimensional and one dimensional models indicate that the proposed model is nearly as good as, and computationally much faster than, the general two dimensional and one dimensional models.

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In order to make clear the physical explanation of the fast flow in macropores or soil-pipes, as a first step, a series of saturated and unsaturated flow experiments were carried out in vertical smooth cylindrical pipes. The objective of this study was to see the relationship between the degree of saturation and the flow rate inside the pipe. The pipes were of the order of mm. The equation for turbulent flow in pipes was modified. The following results were obtained from the experiments conducted:(a) several flow patterns occur depending on the degree of saturation, (b) flow rate for laminar film flow was affected by varying its thickness around the pipewall, and (c) proposed equations for turbulent flow can describe a highly saturated flow approximately.

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In this research, the effect of grain sizes on dispersion phenomena in unsaturated flow conditions were investigated. Miscible displacement experiments were carried out using three different but uniform sizes of glass beads as porous media. Mixing length theory concept was employed to analyze the experimental data. Mixing lengths were found almost constant to each media having uniform grain size distribution, in the lower range of moisture contents. They were however found increasing with increasing grain size of the media. The ratio of the mixing length to the grain size of the media was obtained almost constant. This constant number, named “Mixing Length Number” was found almost equal to 8. Applicability of the proposed model for dispersion coefficient based on mixing length theory was checked by experimental data.

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The convection and dispersion process in the large porous medium is investigated by applying mixing length theory. In which the eddy in turbulence is replaced by water passing through meandering water path in the media. The variability of pore water distribution is evaluated by two models.The one-dimensional convection-dispersion experiment was conducted. Based on the results dispersion coefficient and mixing length is estimated by this model, it is suggested that both structural and turbulent diffusion may occur in such a large pore.

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This paper studied finite difference numerical methods for threedimensional unsaturated subsurface flow model. The equation is mathematically classified as a type of heat diffusion equation. Therefore three-dimensional numerical methods for heat diffusion equation can be applicable to solve the flow equations. For the numerical methods, purely explicit method, ADE methods, and ADI methods are investigatedi n terms of accuracy, stability, and calculation time using analytical solutions for the linearized equation by Philip. As a results of comparison among the five numerical methods, ADE method proved to be the most excellent.

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Characteristics of heat and moisture transfer in porous pavement is investigated based on field observation and a numerical model. It has been found that the pore size in the pavement material posses a paramount importance for the transfer of water vapor. Ceramic porous pavements with small pore size inside can absorb a large amount of water from underlying soil, results in larger evaporation at the ground surface and lower surface temperature compared with other pavement. Usually the porous pavement surface is rather dry and the assumption of local equilibrium between liquid phase and vapor phase commonly used in numerical model for the computation of evaporation at the ground surface is not correct here. Thus, resistance to evaporation must be included in the numerical model to get good computation of evaporation. Due to evaporation, surface temperature and under surface heat storage of porous pavement is much smaller than impervious pavement.

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To evaluate the solute movement in an unsaturated soil, blue dye was injected to the field soil in Tunisia and both of the vertical and the horizontal cross sections below the injected region were observed. Since dye spreads along the preferential flows caused by cracks, the dye spreading patterns showed superior heterogeneity and the spatial correlations are significant only for small spatial scale. Concequently 2-dimensional convection dispersion equation can replicate an overall transport of solute but not replicate the detailed patterns.

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In lake Nakaumi, a blackish lake with enclosed waters, the velocity and salinity were measured. The measurements are made for a flow field and distributions of water temperature and salinity using ADCP and other equipments. Through these measurements, the following results are obtained.(1) The currents in enclosed waters depend on not only the change in tide level and water level at the center and inlets of the lake but also the thickness of pycnocline.(2) The pycnocline is subjected to tidal changes over a long time scale.(3) Some internal gravity waves changing thier oscillation period with tides and wind direction were observed.

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The three-dimensional velocities, salinity and temperature were measured at the mouth of Mutsu Bay in a spring tide by using ADCP's and STD's. The crosssectional distributions of velocities depict complicated flow patterns depending on tidal cycle and density field. There are no uniform velocity in the vertical direction. One tidal-averaged residual flow and density also indicated that the velocity fluctuations are affected by stratification and the earth's rotation. Their vertical profiles clarity existence of an internal wave in the longitudinal direction across the bay's mouth.

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The aim of this study is to disclose the characteristics of river efflux into a estuary by means of three-dimensional numerical analysis. The flow behaviors in estuary are governed by river efflux momentum and buoyancy force due to density difference between fresh and salt waters. The flow obtained by test simulation in a model estuary shows the plume or turbulent jets characteristics according to discharge and density. The increase of river discharge has similar effect with the decrease of density difference, in which the flow behavior resembles turbulent jets. On the contrary, the decrease of discharge or the increase of density difference causes the flow similar to a plume. Internal Froude number, the ratio of kinematic energy flux to density-deficit potential energy flux, is found to play an important role to macroscopic flow behaviors.

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The objective of this report is to discuss the flow characteristics in the Arctic Ocean (the Kara and the Barents) in connection with the marine contamination.
Using the observation data (water temperature, salinity) the author examined the water mass characteristics of the Arctic Ocean and compared the results with the results of flow analysis taking into account of river inflow, density structure in the sea, and investigated the present situation of flow. Additional research was also conducted on the relationship between the analytical results of this flow and the migration of cold larvae in the Barents Sea.

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Several of the mixing processes at density interfaces in highly stratified flow at the mouths of rivers flowing into the ocean bear close resemblance to mixing processes at the density interface seen in freshwater bodies, and can provide valuable insights into them. This paper addresses the mixing phenomena at the interface in the very highly stratified flow seen at the mouth of the Ishikari River during the dry season. It is shown that the chief factor influencing mixing across the interface is the wind, while factors disturbing the steadiness of the flow such as tide have but little influence. Furthermore, when the entrainment coefficient is examined as a function of wind speed, it is found that the surface salinity at any given river station can be accurately predicted. Turbulence structures are also discussed.

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In the Sendai river which is located in the southwest part of Kyusyu, Japan, the trouble that the salinity concentration of water drawn from the intake is more than the water quality standard of city tap water has sometimes occurred in recent years and it has called people's attention. In this paper, it is made apparent with the use of field data that all the trouble occurred in two or three days after the neap tide and that the fresh water discharge, the M. W. L. in the mouth of estuary and the pattern of tidal curve determine the situation of salinity intrusion and the mixing of salinity with the water taken. Evaluation of these dominant factors makes it possible for us to predict easily whether the trouble will occur or not in the future.

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Simultaneous measurements of three components of instantaneous velocity, salinities and water temperature have been performed during a spring tide in the Ota River estuary which demonstrates a large tidal range and density gradients induced by salinity. Data are collected at various distances from the bed. Stability influence of stratification changes widely during the tidal cycle. Around low water slack, the estuary is well mixed. On the other hand, the estuary strongly stratifies near the water surface after high water slack in the ebb tide. The longitudinal density gradient, which drives an upstream bottom flow, is essential throughout all tidal phases. Owing to the longitudinal density gradient, the ebb flows in lower layers are small and bed-generated turbulence is weak.

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In numerical calculations of salinity intrusion in a well-mixed type estuary like the Chikugo river, 1-D numerical diffusion model is in general used. It is quite important to evaluate the local dispersion flux precisely in this model.We tried to make up the evaluation method for this salinity flux by using some experimental data.
As the result of this study, the facts that the local dispersion flux cannot be described by the first derivative of salinity concentration only and that because the maximum density of salinity in the estuary is limited by the boundary condition of that at the sea the additional expression of flux described by the second derivative is necsssary are made clear. The use of new expression makes it possible for the 1-D model to perform the simulation well.

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From engineering aspects, the techniques for the prevention of the intrusion of salhie wedge are quite important. This paper proposed boundary layer control method using barrier settled on the river bed to reduce the length of the saline wedge. Various type of barriers were tested their effectiveness.
Theoretical and experimental study were conducted on the critical intrusion length of the saline wedge due to the barrier. Both results were compared and revealed good comparison. Eaves effect which attached downstream side of the barrier to control the motion of lower layer was also studied and found its effectiveness.

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In recent years the upstream intrusion of salinity in a tidal estuary has become a serious social problem for river environment and water resources. In view of taking water resources durably and preserving the ecology, artificial control methods for preventing the salinity intrusion are required. Setting up a mound on a river bed has been proposed and applied to real estuaries. So we experimentally examined the effects of the height and the position of mound in a well-mixed estuary. In addition, we proposed the method to make vertical mixing strongly by using a bubble plume to decrease the intrusion length of saline wedge and also examined its effect experimentally.

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It is well known that a few kinds of internal waves, which are generated by the hydrodynamic instability of shear layer, can be seen in a densimetric exchange flow. The mixing process due to these internal waves as well as the propagation process of a density front is reproduced numerically by means of N · S equation. It is, pointed out through the considerations of the numerical results that the typical flow patterns with both the Kelvin-Helmholtz and Holmboe instability waves can be simulated by using the numerical model, though the turbulence'model should be introduced to reproduced the characteristics of internal waves such as the wave amplitude and the length of mixing layer precisely.

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With visualization techniques it is observed that the vortex shear layer with large eddy was formed at a density interface in a stratified shear flow by progress of gravitational instability. It is also found out that large eddies entrain surrounding fluid into this layer and disperse mixed fluid intermittently toward upper and lower layer. The ensemble mean of this mixing process is defined as mutual entrainment velocity. The instability criterion of the vortex shear layer is determined based on experiments and field observations. Dynamical property of this vortex shear layer developed in the middle of two-layer stratified flows is analyzed to derive the mutual entrainment coefficients theoretically. Dependence of the mutual entrainment coefficients on the overall Richardson number of over and under-lying layers is clarified with the influence of the Reynolds number.

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The diffusion behavior of a forced plume discharged in the horizontal direction was investigated both experimentally and numerically. Velocity and temperature fluctuations in the plume were measured by FLV and thermocouple, respectively. The diffusion behavior was primary classified into two types, based on the effect of the bottom. In each case, a three-dimensional turbulent closure model (κ-ε model ) was applied to quantitatively simulate the behavior of the forced plume. The performance of the three-dimensional model was evaluated by the comparison of the numerical results with experimental measurements.

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Miscible conservative two-dimensional gravity currents traveling downslope, namely, inclined starting plumes and inclined thermals, are investigated in the laboratory, emphasizing on differences and similarities in flow characteristics of the flows. Using a large volume of experimental data, such gross flow properties as the dimensionless propagation speeds, the spatial growth rates, the shape factors, and the entrainment functions are quatified for the bottom slope angles ranging from 5° to 90°. The study is directed toward the comparison of entrainment functions of the flows.

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Flow characteristics of miscible conservative two-dimensional thermals traveling downslopes are investigated experimentally. A series of laboratory experiments is conducted for the range of bootom slope angles Θ=5-90°. With use of a large volume of experimental data, such important gloss flow characteristics as the spatial growth rate of maximum height, the dimensionless mass-centre velocity, the entrainment function, and others are quantified as functions of bottom slope angles.

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Flow characteristics of miscible conservative two-dimensional thermals traveling downslopes are investigated theoretically. An integral model is developed, using such empirical relationships as the entrainment function, thermal aspect ratio and others. A set of solutions for a fully developed state is obtained analytically and numerically. Resistance coefficient is determined semi-empirically. Comparisons between calculated and experimental results are presented as well.

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Dynamics of river inflow into a stratified reservoir is discussed by performing a k-εA turbulence model analysis. Several types of density currents found in a stratified reservoir are numerically reproduced;(1) plunging inflow at the upstream end of a reservoir, (2) surface density current taking place when fluid density of inflow is smaller than the reservoir water, (3) density undercurrents in the case of inflow density being larger than that of the reservoir water, (4) interaction between a thermocline and the inflow water mass, etc. It is confirmed that every types of the flows are successfully reproduced by the k-εA turbulence model. Some of the results are compared with the previous laboratory experiments and satisfactory agreements between the analysis and the experiments are obtained. The authors believe that some turbulence model should be taken into consideration in modelling reservoir hydrodynamics, which would be powerful tool in predicting reservoir water quality.

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This paper presents the analytical study on the hydraulic conditions of the plunging point of the negative surface buoyant jet discharged on the sloping bottom. Authors already found out four flow types of plunging phenomena and different hydraulic plunging conditions of each flow type experimentally. In this paper, analysis on two flow types, namely, the Density Wedge Type and Internal Jump Type were presented and used to explain the different results of the plunging conditions. Three-dimensional classification of each flow type was also done in the S-Fo plane.

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This study deals with the hydrodynamic behavior which relate to growing and accumulating process of freshwater red-tide due to Peridinium bipes blooming near the upstream end of a thermally stratified reservoirs. Hydraulic and ecological characterictics of the phenomena are estimated by field observation and numerical analysis. The results successfully explained development or keeping of the plankton population and its diurnal variation, which are concerned with circulative flow originated in plunging water and diurnal vertical migration of Peridinium population.

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Sea water intrusion into a brackish water lake is a stochastic phenomenon because the water levels of the ocean and the lake are incidentally fluctuated by weather condition. In this paper, a stochastic model is developed to simulate the time series of the water levels by using AR formulation in order to estimate the frequency and the intensity of the sea water intrusion into Lake Ogawara in a long term.
The result of the stochastic simulation for thirty years, together with the conservation law of salinity, successfully estimated the averaged salinity concentration in the lake.

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Lake Abashiri is a brackish lake located at Abashiri river mouth and forms two-layer structure of salt and fresh water. Here, we analyze the long-term. behaviors of the halocline, defined as boundary of the two layers, from time series of annual precipitation and discharge in Abashiri river basin. Using a echo sounder for taking photographes of the halocline, we could show short-terth behavior of the halocline caused by snow melt flood, strong wind and the intrusion of salt water to this lake from the sea during flood tide. We carried out numerical analysis regarding the short-term behaviors of the two layers in Lake Abashiri when the wind is blowing hard.

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Field Measurements were made on an inclined plume in Lake ogawara in 1992. The plume is a saline underflow of about 1 meter thick and several hundred meters wide along a bottom slope of 1/200. The scale and velocity of the flow are far larger than those of flume experiments so that the Reynolds number is very high.
The data are processed and analysed so that the entrainment rate and the Richardson number are estimated. The estimated values of entrainment coefficient is compared with a numerical calculation by k-ε model (Fukushima; 1988). Both results are on a same line which decreases rapidly when Richardson number approaches to unity. This fact suggests that the entrainment law for inclined plumes of large Reynolds number is somehow different from that of small scale flows in laboratory experiments.

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A field survey is carried out in order to examine water quality behaviors and thermal structure in a eutrophic reservoir, where very distinctive features are found in water quality profiles. Although temperature gradient is dynamically unstable in the bottom layer, thermal stratification has never been overturned even in a severe cold winter. On the other hand, electric conductivity is extraordinarily high in bottom layer to compensate density defect due to inverse thermal stratification. This suggests that there might be high concentration of dissolved materials and nutrients which are supposed to be originated from the reservoir bottom. In addition, dissolved oxygen is very poor in bottom layer. Based on the field survey it is investigated what kind of mechanism works to construct such a characteristic profiles of water qualities.

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The thermal ‘staircase’, a layer of constant temperature, was observed in seasonal thermoclines following the resuspension of cohesive sediments resuspension on the shore slope of Lake Biwa. When a moderate onshore wind blew, the bed materials were resuspended up to the mid thermocline with height of 2.5 m above the bottom, and settled down forming the staircase above the intrusion. As the consequence, the thermocline was divided into two layers by the staircase with a thickness of 0.7 m. To investigate the resuspension and settling process due to surface and internal waves in stratified lakes, laboratory experiments were conducted using a tank with a partial slope at one side. When the internal waves generated as the barotropic waves in the tank, the resuspension phenomena occurred frequently. Both surface and internal waves are essential for the resuspension process. In the stratified fluid, the distance and duration of suspended sediment transport are very long compared to that in the non-stratified one due to occurring of the intrusion into the stratified layer.

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As a drastic countermeasure to reservoir sedimentation and turbid effluence over a long term, a bypassing tunnel system is proposed and studied. In this paper, the effect of this system to improve the turbidity in a reservoir is discussed. We have succesfully reproduced the temparature and turbidity by adopting numerical methods and predicted the effect of the system according to several bypassing discharges.

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The relation between the vortex structures and the flow characteristics in the flow development region of a impinging plane jet was investigated using the technique of flow visualization. For the flow visulization, the laser induced fluorescent method and the dye-particle image velocimetry method were adopted. It was shown that the vortex motions hardly change by the flow impingement. Particulary, by the direct pressure measurements and the image processing analyses, the relation between the vortex motion and the pressure fluctuation was revealed.

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