As the rain infiltrates the ground, the runoff of the rain flows into the river. It is difficult to know accurately the amount of rain that infiltrated the ground and the saturated amount of rain under ground as well as a period of conversion from infiltrated rain into a runoff. Thus it is very difficult to forecast stream flow by modeling a runoff process. The runoff analysis (e. q. tank model) is useful to forecast stream flow. In this study, we construct a system of runoff analysis by using neural network, which can be effective to solve non-linear and pattern classification problems, using the same data used in the tank model by KOZUE, and then compare to the results of the tank model. We evaluated the efficiency of the system using neural network on runoff analysis.

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In Lake Biwa area, there are some quantitative hydrological data in historical years, such as monthly water level data recorded by Feudal Zeze Clan in Edo Era. This paper proposes the estimation procedure of areal duration precipitation at historical flood of Lake Biwa, using the water level records at the beginning and the end of the flood, and the hyetograph reconstructed from weather records of old diaries. Furthermore, this procedure is applied to the recent floods and the reliability of reconstructed flood is evaluated. As results, this procedure is effective especially for large floods, and the precision of the water level data at peak is important for reliability of the estimated value.

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In order to keep both safety and amenity in Neya River Basin, East Osaka, where the rapid urbanization has been advanced, this paper discusses the efficiency and availability of the flood control facilities. Firstly the seasonal rainfall characteristics was estimated. Secondly this paper discusses the time-dependent characteristics of cut-off effects of peak flood discharge by the model rainfall. Finally the possibility of the practical control concerning the flood control and water reuse as the general service water is studied in order to get the higher stage of water environment expecting both the safety and amenity in the middle of 21 century.

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A method to generate a Gaussian and log normal random field is presented. The method is based on a matrix factrization technique of decomposition of a covariance matrix into its squre root matrix approximately by using the Chebyshev polynomials. When we generate a Gaussian or lognormal random field with N_x×N_y points covered by a mesh of a rectangular grid, the algorithm presented here requires only 3N_xN_y entries to be stored.

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In general, a groundwater aquifer is hydrogeologically non-uniform due to its inherent formation. Although numerical simulation of mass transport plays an important role for prediction and remediation of pollution, studies on macroscopic dispersion from a hydrogeological point of view are insufficient. In the present paper, a method for estimating the parameters used in a geostatistical model of logarithmic hydraulic conductivity is proposed and applied for a tracer test carried out in the aquifer of Horkheimer Insel, Germany. The macroscopic dispersion coefficient obtained by the present method agrees well with the one observed in the tracer test. It is shown that the present method is useful for evaluating the non-uniform hydrogeological structures and the macroscopic dispersion.

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The purpose of this paper is to study the effect of dam construction on the middle reaches of alluvial rivers. The Nibutani dam was constructed on the Saru River, 21.4km upstream of its mouth in 1996. In this paper, the flow and sediment transport system is studied along the Saru River including field resoluts from the Nibutani dam and its reservoir. The sediment transport rate, bed material distribution, and bed elevation changes were investigated before, after and during a flood. A numerical model to predict the sediment transport rate and river bed changes are proposed and verified using the data obtained by field measurements. This study clarifies the effect of the dam on the river, and many useful information for river and dam management works are obtained.

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Numerical models based on Flux Difference Splitting (FDS) with the Roe numerical flux and with the Lax-Wendroff numerical flux for 2D flood flows are developed. From verification against existing experimental data for hydraulic jump and through numerical experiments on such typical sample problems as a circular jump and dam-break flow, it is found that the latter is superior to the former in accuracy, whereas the former to the latter in limitation for applicability in severe condition. Based on these findings, a flood model, that takes the advantage of these two models, is proposed and verified against existing experimental data of 2D flood wave due to partial dam-break on dry bed.

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Experimental tests and theoretical studies were made to investigate properties of small-scale bed topography that are step and pool systems widely observed in mountain streams. The findings are 1) the grain size distributions of the bed surface materials sampled in the typical mountain streams show the type of Talbot distribution, which is known to give the closed packing for heterogeneous materials; 2) the Talbot type grain size distributions of bed surface materials with an exponent n=1/2 to 3/4 is essential to the formation of the bed topography; 3) formulas for estimating a wave length and a wave height of the bed topography were proposed; in addition, 4) flow on the bed topography were classified into four types from experiments and with application of the Bernoulli equation. Based on the results, a design method of a new fish-way, of which shape and structure can be substituted spacing and height of a natural small-scale bed topography, was proposed. The fish-way proposed here have strong points that it can not only provide a habitat for fishes but also can draw off sediment in the pools by the own running flow.

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Fundamental properties of high velocity flows in a continuously meandering channel are investigated with comparisons of the results of previous experimental and analytical studies. Substituting a simple functional form assumed for hydraulic variables into the 2-D depth-averaged flow equations, the non-linear algebraic equations concerning amplitudes and phase lags for the depth and velocity distributions are derived. The mechanism to increase resistance coefficients of mean flows are included in the analysis. The results of non-linear analysis, which were obtained through the error analysis of algebraic equations, indicate that in the case of a meandering channel with small curvature radius, the Froude number can not exceed the value at the resonance relation due to the increase of flow resistance, and the relation between the amplitude of depth variations and the Froude number can be approximated by the linear theory in the range of the smaller Froude number than the resonance one.

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The experiments on snow drift were carried out using the low temperature wind tunnel at Shinjo Branch of Snow and Ice Studies, NIED in Shinjo, Yamagata Pref. The wind veloctiy profiles were measured by the hot film anemometer and the snow drift flux profiles were measured by the snow paricle counter (SPC). The size distribution of snow particles were also measured by SPC. These results obtained by the experiments show that the higher the measuring position is, the smaller the size of snow particles is. The numerical analyses were made using the non-Boussinesq κ-ε turbulence model and the results were compared with the experimental rersults. The numerical results of the velocity profiles show the typical profile in a boundary layer. The snow drift flux obtained by the numerical analysis agrees well with the experimetal results near the bed. The velocity profle in snow drift is expressed by the log+linear law.

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Turbulent structures in the mixing layer between the main-channel and the concave are analyzed using wavelet transforms. The flow is measured by a particle image velocimetry. The continuous wavelet transform of the velocities successfully detects the characteristics of the large-scale vortices along the mixing layer, such as the spatial scale, frequency, advection velocity and occurrence interval. The joint probability distribution of the scale and the frequency shows that there is a linear relationship between them. Then, the longitudinal and vertical amounts of the kinetic energy is clearly decomposed into the components according to the respective frequencies by using the multiresolutional analysis. The frequency ranges are classified into three groups that are characterized by the energy distributions of the components. These results strongly support the applicability of wavelet transforms to this flow.

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It has been known that the shear instability generates large horizontal vortices at the junctions of main channel and flood plains for two-stage channels. The present laboratory tests show that the horizontal vortices appear for flow with small relative depth. For channels with bank vegetation, horizontal periodic vortices also appear for small relative depth, and it was seen that the vortices in the main channel is predominant.
Numerical computations were performed by employing SDS-2DH turbulence model, and the results obtained agree reasonably well with the experiments. The model can predict the wavelength of horizontal vortices, the lateral distributions of the Reynolds stress, temporally-averaged longitudinal flow velocity, etc. The numerical simulation, which was performed for lateral transport of suspended sediment, has revealed that the transport is closely correlated with the large scale horizontal vortices.

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Hydraulic characteristics of flow in open channels with spur dikes were studied both theoretically and experimentally. Series of laboratory tests and 2-D numerical computations were performed by varying the interval of spur dikes. It was found that the mass and the momentum exchange rates between the main flow region and the spur dike region are influenced by the interval. Especially, momentum transport is much affected by the interval in equilibrium region. For the case in which the interval of spur dikes is nearly equal to the scale of separated eddies from the first spur dike, the eddies move downstream without changing their structure, and consequently the momentum transport in equilibrium region between the main flow and the spur dike region takes a maximum value.

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A numerical method is developed to analyze the hydroelastic responses of large-scale floating structure under waves. BEM is applied to evaluate the fluid motion and FEM to analyze the deformation of structure. By satisfying the continuity of the pressure and displacement on fluid-structure interface, the dynamic wave-structure interaction is simulated. A time domain solution under arbitrary wave condition is obtained just by prescribing the conditions on wave generation boundary for each time step, and this method is applicable to the cases with varied sea-bottom configuration and distributed structural mass or stiffness. The effect of space and time discretizations on the convergence and stability of solution for regular, random and solitary waves is discussed by comparing among numerical solutions. The validity of the present method is verified by comparing with experimental results for the three kind of waves mentioned above. Furthermore, the fission of a solitary wave under a large-scale flexible floating structure has been observed both in numerical analysis and experiment.

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A numerical model is developed for 3-D floating body motion in nonlinear waves, solving the B. E. M. on the velocity and acceleration potentials. Then the movement of the element nodes on the free water surface is evaluated to coincide with the 3-D motion of water particle by the Mixed Eularian and Lagrangian method (MEL) and their movement must strictly satisfy the dynamic boundary condition. Based on the six-degrees of freedom motion solved, the movement of the element nodes on the floating body surface is evaluated and updated. The validity of this numerical model is verified through the comparison with the theoretical solutions of nonlinear waves, the nonlinear 2D-B. E. M. and experimental results. This numerical model is extended for the 3-D floating body motion in a semi-closed mooring basin surrounded by breakwaters with the opening and discussed.

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Sigma coordinate system employed in many coastal ocean models may have considerable errors in computing horizontal diffusion and horizontal pressure gradient in case of steep bottom slopes. In the present study, for more accurate calculation of coastal current and pollutant transport, a dual-sigma coordinate system is presented for a correct calculation of the horizontal diffusion and the horizontal pressure gradient without appreciable increase in computational load. This coordinate system, by introducing a horizontal interfacial plane, separates the flow field into the upper layer, where appreciable vertical variation in density may usually exist, and the lower layer on an uneven seabed; in each of which the sigma coordinate system is employed. This new coordinate system is applied to some simple cases to examine its fundamental validity and performance, demonstrating that the dual-sigma coordinate system may have much higher accuracy than the sigma coordinate system.

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Characteristics of wave forces on a three dimensional body on a submerged breakwater have been investigated experimentally. Maximum wave force has been found to depend greatly on the location of the structure and its shape. In the vicinity of the leading crown edge, the plunging breaking occurs and the impulsive breaking wave force acts on it. The variation of the maximum wave forces are formulated based on Hiroi's and Goda's formulae. Moreover, the Morison equation has been modified to consider the varying water surface, and the calculated wave force using the velocity and acceleration at the front face is confirmed to reproduce well the experimental result. The numerical prediction method based on the VOF method has been also developed to estimate the velocity and acceleration of breaking waves on a submerged breakwater. With the use of these computed values and recommended drag and inertia coefficients, the Morison equation can give good estimation of wave force even in a case that the impulsive breaking wave force acts on the structure.

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The characteristic of vortex wake around a vertical flat plate with the separation from its sides has been clarified by using PIV. Then, a discrete vortex method combined with BEM is presented to simulate the flow field around the plate, and wave force equations are newly derived to estimate the wave force acting on it. Comparing the experimental values with the numerical ones, both agree well, which has verified the validity of calculation method presented in this paper.

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Field measurements were performed to investigate the effects of Kuroshio Warm Water Intrusion (KWWI) to the mouth of Tokyo Bay on the three dimensional characteristics of currents and material transport in the bay mouth in winter. When KWWI occurs, the bay water with low temperature and low salinity flows toward the ocean in the surface layer, the Kuroshio Warm water with high temperature and high salinity intrudes into the bay in the intermediate layer and the coastal water with low temperature and high salinity flows toward the ocean in the bottom layer. The depth of the KWW intrusions into the bay depends on its density relative to the vertical density profile at the bay. The KWWI transports heat into the bay effectively which is five times as large as the winter-averaged heat flux.

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To understand the fundamental and overall characteristics of thermal environment in coastal areas, a comparative analysis based on a set of long-term data of water temperature variation has been performed for the Tokyo Bay (semi-closed bay), the Kashima coast (open coast) and the Kasumigaura (lake), which are located under similar weather conditions. The results show that, all through the year, the water temperature variation in the Kasumigaura is governed by the heat flux through the water surface such as solar radiation, whereas that in the Kashima coast is dominated also by the horizontal convection. In Tokyo Bay, in summer, the water temperature variation in the surface mixing layer in the time scale more than one week is mostly governed by the vertical heat flux through the water surface. Since the heat is accumulated in the surface mixing layer and its average depth is comparable to that of the Kasumigaura, the subsurface water temperature in the Tokyo Bay exhibits nearly the same variation with that in the Kasumigaura. In winter, on the other hand, the horizontal heat flux through the baymouth from the Pacific Ocean influences the water temperature even at the head of Tokyo Bay.

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Field observations were carried out for the purpose of understanding the characteristics and the movement of suspended sediment which was carried by flood and then resuspended in the reservoir. From the analysis of water quality, the correlation of turbidity to SS and T-P was clearly defined, which can be useful for estimating the amount of SS and phosphorus flowing into the reservoir.
The current in the reservoir during the flood is numerically simulated using 3-D k-ε turbulence model, the result of which reproduces the turbidity profiles and the sedimentation distribution. These were in accordance with the measurement, and the model presented in this paper will give valuable information for the management of reservers.

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The recent studies on gas transfer at water surfaces are summarized. The contents of proceedings of the International Symposium on Gas Transfer at Water Surfaces, which were held three times in the last few decades, are classified depending on subjects in order to analize the movement in the research field. Some interesting topics in the proceedings of the Third International Symposium held at Heidelberg in Germany are presented. Research activities in Japan are also briefly summarized.

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