In forest soils, there exist a large amount of dissolved organic matters, such as humic acid, result from decomposition of litters. Organic matter, as well as NO_3^-N, is one of the most effective tracer for separating run-off components from discharge. We separated this organic matter into some molecular weight groups using gel chromatography, and mainly investigated their changes during short period of storm run-off. In this report, it is showed that the concentration of organic matter with high molecular weight changes very quickly, while ones with lower molecular weight and NO_3^-N changes very slowly, during storm run-off. Using these results, further more, another concept for separating run-off components was considered.

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Laboratory tests were performed to evaluate the lateral momentum transfer in shallow water flow. In the tests, media with very high porosity were put on a part of a test channel in such a manner that lateral discontinuity in velocity was made. The experi-ments showed that the periodic generation of large scale eddies had an essential role on the lateral turbulent mixing. The mixing coefficient f, which expressed intensity of the momentum transfer, was calculated, and relation between the coefficient f and properties of the media was determined. On the basis of the mechanism of the mixing due to the large eddies, prediction methods of the coefficient f were developed, by which added flow resistance due to the lateral turbulent mixing can be calculated.

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The dynamic response of a two-layered stratified lake subject to wind stress is investigated theoretically and experimentally. A model lake of constant depth and width is considered. The motion of the water is assumed to be two-dimensional in the vertical longitudinal section. The fundamental differential equations for the currents in each layer and the elevations of the surface and interface are solved for an instantaneous rise in constant wind stress. The response of the lake of a successively variable wind stress is calculated by shifting in time and superposing of the solutions for constant wind stress. The availability of the theory is examined by comparison of the experiments and field obsevations with its theoretical simulations.

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The proper evaluation of water utility is essential for a resonable operation and planning in a reserviors system. Such evaluation is mainly based on a discharge-series released from reservoirs. This study aims at the analitical deduction of joint probability of discharge-series and application for a two-reservoir system. This analysis is carried out by extension of two-step transition model previously proposed by the authors. In case of series connection of reservoirs, a joint probability of discharge-series upstream is combined with that of infow-series down-stream. In case of parallel connection, a joint probability of discharge-series from one reservoir is combined with that from the other. Some numerical example is given for the case of series-connection, and the usefulness of this technique is shown for allocation problem of reservoirs capacities upstream and downstream.

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Mathematical models for defining cross-section of self-formed straight sand-silt rivers are presented, in which sediments are actively transported everywhere as bed load and suspended load. A balance of lateral bed load and lateral diffusive transport of suspended sediment is imposed. to maintain a stable channel cross-section. Singular perturbation technique is employed to solve the sediment balance equation, from which a relation for stable depth is derived. A resistance formula for dune-covered bed is used to obtain stable width. It is revealed theoretically that the channel-center depth relative to sediment size is approximately proportional to S^-0.82 for natural sand-silt rivers. The analysis is found to agree reasonably well with laboratory and field data.

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Discretizing the linearized characteristic equations of gradually varied unsteady flows using the backward difference method in time and the Galerkin's method in space, a numerical model for a single channel is first set up and then the system model for channel networks in flat land is graph-theoretically formulated in terms of connection matrices. This formulation is developed to facilitate the systematical computation on digital computers for large-scale complex networks. The numerical results obtained by the present method are compared for verification to observation data. The agreement between the computed and observed water levels for a flood time is satisfactory. It is further shown that this method is more advantageous than the 4-point implicit method in regard to the time required in making the computations.

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A numerical wave-absorption filter has been developed for open boundary condition in the analysis of nonlinear and irregular wave evolution. The filter is composed of a simulated sponge layer and Sommerfeld's radiation condition at the outer edge of the layer. The wave-absorption characteristics of the filter have been investigated by applying to the linear potential theory and to a two-dimensional nonlinear boundary element model. In both cases, the filter is found to be applicable for a wide range of wave parameters. In order to realize a practical ‘Numerical Wave Tank’, the present model also incorporates a wave generator in the computational domain composed of a series of vertically aligned point sources. Numerous numerical experiments demonstrate that the present approach is effective in generating arbitrary wave profile without reflection not only at the open boundaries but also at the wave generator.

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This study is based on the numerical solutions derived with BIM for fully nonlinear two-dimensional irrotational free-surface flows. The solutions compares extremely well with the exact solution of the steady solitary wave on a uniform bottom and the experimental measurements of a solitary wave up to breaking over a bed containing a submerged obstacle and a sloping bottom.
The interaction between a solitary wave and a rectangular step takes a variety of forms, depending on the single parameters ξ_s which means the rate of the depth change due to the step to the wave-height of the incident solitary wave. The parameter uniquely governs i) the critical incident wave-height which determines the presence of the breaking caused by the step, that is, whether or not an incident wave breaks, ii) the location of the onset of the breaking and iii) the wave-height at the location. These breaking criteria are expressed in regression equations dependent on the parameter.

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The domestic wastewater flows into urban small rivers and it pollutes water quality of the urban small rivers. Especially the untreated domestic wastewater from the catchment area with no sewerage works influences water quality of the urban small river significantly.
This paper deals with an estimation of improvement in the water quality of urban small river by treatment facilities of the domestic waste water with the mesh analysis model. The mesh analysis model can estimate flow rate, flowing pollutant loads and water quality in any cross section of the river. The mesh analysis model can estimate changes of flow rate, flowing pollutant loads and water quality by urbanization, sewage works construction, settlement of household wastewater treatment tanks, which purify sewage and domestic waste, and etc.
And the mesh analysis model represents a reduction in the pollutant loads by self purification with runoff rate of pollutant load between a mesh and the next mesh. We estimate an effect of construction of sewerage works and arrangement of the household wastewater treatment tanks for improvement in water quality of Sanda river. The concentration of pollutant load is reduced by the constraction of sewerage system in downward of the catchement area and the amount of pollution load decreases from 1/3 to 1/2 of it before sewage works construction.

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The effects of data conditioning on the mass and drag coefficients (C_m & C_d) are reviewed by two geometric and one numerical interpretations. Two geometric analyses of data conditioning proposed by Dean demonstrate that when the Dean eccentricity parameter E equals unity, the data are equally well-conditioned for determining C_m & C_d. For simple harmonic data, the Dean eccentricity parameter may be shown to be proportional to the Keulegan-Carpenter parameter, K; ie., E=√3K/2π². When E=1.0, then K≈11.40 and the Dean error ellipse is a circle with zero eccentricity. The matrix condition number of the 2×2 matrix used to determine C_m & C_d in a best least-squares sense becomes unity when K≈13.16 and E≈1.15. Two sets of experimental data are compared with the two geometric and one numerical analyses.

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