We studied the effectiveness of measuring impedance of soil in the experiments as the method of real time measurement of water content and ion concentration of soil water. We composed an impedance measurement system of a soil column controlled by computers, and made experiments for measuring them at a constant temperature. We concluded that susceptance divided by the angular frequency indicated a water content independent from ion concentration or a soil particle size, and that the further measurement of conductance made it possible to trace the change of ion concentration. We also proposed a simple method to make calibration curves. We think that the measurement method developed in this study is very effective in tracing unsaturated phenomena in a soil column.

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This paper presents a numerical model for predicting solute transport with multicomponent chemical reactions in subsurface. A non-linear least square estimation by Levenberg-Marquardt method is adopted for obtaining numerical solution of the chemical reaction term in the convection-dispersion equations. To test the reliability of the model, laboratory experiments are performed under the conditions of continuous injection of KCl solution into the undisturbed soil columns. It is concluded that the accuracy of model predictions can be improved by the suitable selectivity coefficient and the spatial distribution of cation exchange capacity for the soil being considered.

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For adequate river management, flood fighting and flood control in urban small river basins, it is important to understand the characteristics of short time rainfalls in small catchments, including rainfall's migration, their rise and declime, as well as the time-space distribution. Concentrated shorttime thunderstorms and widespread longtime rainfalls of typhoons are the main cause of flooding in urban small river basins. In this study, the characteristics of short time, 5-30 minutes rainfalls within 23 square km area of thunderstorms and typhoons are studied based on the densely-observed data from the gauging station network in Tokyo. The possibility of short-term rainfall prediction is considered from the analysis of these characteristics.

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The method using the mean velocity profiles was developed for the resistance law of open channel with the v-grooved ribret surface. First, an approximation to the virtual origins were estimated by the closest match between the measured velocity profiles and the velocity profile calculated using several values of van Driest's damping coefficient. Then, the profiles of the mixing length were evaluated from the measured velocity profiles. The present method can be applied to the other kind of roughness. However, although the linear profile of the shear stress in the open channel flow can be employed, other techniques are required to apply the present method for boundary layer flow.

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Characteristics of turbulent structure of corner region affected by channel meandering are investigated using LDV measurements and DPTV (Dye streak pattern Particle Tracking Velocimetry) which visualize dye streak pattern and particle path line simultaneously. First kind of secondary flow develope opposing to second kind of secondary flow of corner region in straight open channel flow. The developement of secondary flow results in arrising of large-scale coherent structure which contribute to generate large-scale shear structure with different characteristic for the left and right side wall region.

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A VITA (variable interval time averaging) conditional sampling is carried out in older to find out organized motions of thermal plumes in a convective boundary layer (CBL). The experimental data are collected in a stratified flow wind tunnel which has been specially designed so as a realistic CBL to be experimentally reproduced. Through examination of conditionally averaged time series and vertical profiles of turbulent components and their stochastic characteristics, it is discussed how thermal plumes contribute to heat and mass transport in the CBL. The present analysis successfully picks up characteristic organized events such as predominant warm updraft in a heated surface layer, weak cold downdraft around feet of thermal plumes, buoyantly accelerated upward motions inside of a mixed layer, negative turbulent heat flux associated with cold updraft in an entrainment zone and so on. Based on the short time averaged thermal plume structure which is most responsible in turbulent diffusion of heat, momentum and air mass in a CBL, a physical model study of atmospheric process is expected to be performed in the stratified flow wind tunnel with correct hydrodynamic similarity.

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Rivers meander with various curvature. Many rivers have a compound cross section composed of main channel and flood channel. In such a compound meandering channel, there occurs exchange of flow between main channel and flood channel. Thus, the compound meandring channel flow shows hydraulic phenomenon different from that of in-bank flow.
In this paper, a large-scale experimental channel of flat rigid bed with compound meandering was used to meansure flow in detail. This experiment clarified the hydraulic characteristics of compound meandering channel flow, such as three-dimensional flow structure, discharge of a main channel, growth and decay processes of secondary flow, and so on.

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The effect of external cyclic forces, such as climate, atmospheric and astronomical phenomena, on internal currents in enclosed lake was studied. Present study shows that (1) Salinity at the bottom is related to seasonal change of water level in the lake, and change of salinity at the bottom is propagated to upper layer with three months behind the times, (2) The day scale change of internal currents have a great influence on water level and wind of the lake with change of pressure distribution, (3) Nature of internal wave is changed according to strength of atmospheric and astronomical phenomena.

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The large scale inclined plume was observed in Lake Ogawara. It had a far larger scale of the motion and velocity than those in the laboratory experinatal flume, so that its Reynolds number was 105. The entrainment coeffcient and the Richardson number were estimated from the data and those were compared with other laboratory experiments of inclined plume. Both results were on a same curve which decreased rapidly when the Richardson number approached to 1. They imply that the entrainment law for inclined plume with high Reynolds number may be different from that of small scale flows.

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In open-channel flows, anisotropic turbulence is observed due to the existence of free surface. Open-channel flow has its own peculiar coherent structures and turbulence characteristics. In actual flooded rivers, the kolk-boil vortex is often observed on the water-surface and generated behind discontinuous boundary such as dunes and steps. It is important to examine the interaction between non-uniformities by unsteadiness effect and streamwise variation of bed shape. In the present study, the turbulent structures in unsteady open-channel flow over dunes were measured by means of fiber-optic LDA system. The mean-flow structures such as time variation of free-surface profile, bed shear stress and the turbulence statistics were discussed by comparing with backward-facing step flows. As the results, such mean properties can be explained by the effects of unsteadiness and spatial acceleration/deceleration which is caused by the shape of dune bed.

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In open-channel flows such as rivers and estuaries, various coherent vortices are often observed and greatly affect sediment transport. These coherent structures often occur especially in flooded fluvial rivers. The hydrodynamic behavior of flood structures is quite different between the rising and falling stages of flood period. In the rising stage, the concentration of suspended sediment increases owing to the kolk-boil vortex because the rising stage corresponds to the growing period of dunes and because separated vortex from the dune collides intermittently at the next dune and washes out bed materials around there. Therefore, it is very important to investigate unsteadiness effects on the coherent structures in unsteady open-channel flows so that the growing process of the dunes and the behavior of the suspended sediment can be explained dynamically. In the present study, the specific behaviors of coherent vortices over dunes were accurately measured by means of simultaneous use of two sets of LDA. The differences of convection properties on coherent vortices between the rising and falling stages were discussed by evaluating the conventional and conditional space-time correlation structures.

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The accuracy of GAL model, recently developed by the authors for a new formulation of dispersed-phase motion in a multiphase turbulent flow, is examined for numerical simulation of convective transport. To reduce numerical diffusion inherent in the previous scheme of reallocation procedure of the GAL model, a new reallocation scheme is presented. The performance of the GAL model with the new scheme is confirmed through numerical simulation for simple cases of convective transport and comparison with the computational results obtained by 1st-order upwind scheme, QUICKEST method and 6-point scheme. Among these the GAL model with the improved reallocation procedure is found to have relatively higher accuracy, being comparable to 6-point scheme. More importantly the improved GAL model has high numerical stability even for the flow condition of Courant number greater than one, and can precisely simulate evolution of a distribution with a sharp front.

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Field data obtained in Suruga bay at the depths of about 20m were analyzed to describe the dynamics of waves and currents during the typhoon 9617. Large swells with periods longer than 15s dominated in Suruga bay for a couple of days before the passage of the typhoon. At the passage of the typhoon, strong winds from NNE were developed, which generated local wind waves in the bay and induced the upwelling of cool water near the head of the bay. The upwelled cool water region propagated to the western coast with strong current oscillations. Numerical simulation with a three-dimensional σ coordinate model demonstrated that the baroclinic motion was resulted by the propagation of internal Kelvin wave which was excited primarily by the continuous blow of strong winds.

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In order to evaluate the permeability of bedrock in the area of Kaore Dam and Kaore-anbu Dam, the quality of groundwater and the behavior of isotopes around the dams were investigated at the time of initial filling. The travel time of the groundwater to move from the reservoir to the boreholes in the inspection gallery of Kaore Dam, obtained from the change of ion concentration, was as long as 7 to 20months. This result indicated that the permeability of the base rock of the dam was sufficiently improved by grouting. Also, the result of multivariate analysis using isotopic data showed the arrival of the reservoir water to the temporary drain tunnel. It was suggested that electric conductivity and nitrate that can be measured in the field were effective as indicators of the arrival of the reservoir water.

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In order to evaluate the permeability of bedrock in the area of Kamioosu Dam, the quality and temperature of leakage water were investigated at the time of initial filling. The travel time for water to flow from the reservoir to observation weirs of the leakage water and boreholes in the inspection gallery, estimated from the change of ion concentration by time, were 2 to 20months. The travel times of leakage water collected at the riverbed, obtained from the change of ion concentration and the heat transfer/diffusion analysis, were 4 to 9months. These results mostly agreed with the travel time of 2 to 10months obtained from the unsteady seepage analysis using design values as input data.

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The continuity equation for water flow with enclosed pressurized air in underground diversion channel is derived by considering the compressibity of water and enclosed air, and the elasticity of the tunnel wall material. The pressure wave propagation speed in such a water flow is obtained from the continuity and dynamic equations. It is shown that the enclosed pressurized air causes a remarkable reduction in the wave speed.

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