Theories for linear and regular waves are usually employed to analyze the wave transformation in the coastal zone, but irregularity and/or nonlinearity cannot be neglected in many situations. In the present paper, a new and general set of wave equations which is named nonlinear mild-slope wave equation is derived to take into account the dispersion and nonlinearity within an arbitrary accuracy. Then, the theoretical characteristics of the wave equations proposed so far are discussed by showing that they can be derived as special cases of the present equations. Sample results of numerical calculations of the various wave equations are given to show the effect of irregularity and nonlinearity, and comparisons of the numerical results with field data are also given. Finally, a future scope in the analysis of wave transformations is presented.

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People's interest in rivers seems to concentrate on the close-to nature work. However, it has not yet attained the stage estimating the erosive resistance of grass-covered levee which is one of the most important close-to nature work of rivers. In order to estimate the erosion threshold of grass-covered levees and to use as basic reference data in levee design, we performed erosion experiments on the grass-covered flood channels under certain hydrauric conditions, grass and soil properties. Erosion resistance of grass-covered surface and erosion limit are shown to be expressed in terms of bed-shear stress, erosion time, soil and grass properties. The applicability of this predicting method is confirmed by flood data and levee overflow experiment in situ.

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Horizontal large eddies and water level fluctuation appear periodically near vegetations in river flow. To estimate the flow pattern and water level fluctuation 2D-numerical model was developed. Experiment and 2D-numerical analysis of the river flow were performed focussing on the lateral mixing due to horizontal large eddies. The computational results of flow pattern and water level fluctuation agreed with experimental results. As the result, it became clear that flow pattern and distribution of shear stress in the river flow with vegetations can be estimated accurately, by the mothod presented in this paper.

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By the hydraulic model test, it was shown that flooding water over a crowded urban district flowed along major roads in the direction of the mean ground surface slope. Also, the Manning roughness coefficients in roads and housing areas were estimated. We developed the numerical model with a general non-orthogonal coordinate system that properly incorporated the roads in the model. The validity of this model was confirmed by comparing with the result of the hydraulic model test. Structural and non-structural measures against inundation were proposed based on the results of the hydraulic and numerical models.

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In this study, the mechanism of transverse mixing in open-channel flow with longitudinal zone of vegetation along side wall is investigated. Flume experiments with idealized vegetation zone are conducted. As a result, the followings are postulated: transverse mixing is caused by rather organized and low-frequency fluctuation of transverse velocity, and it is maintained by association of water-surface fluctuation. By hydraulic analysis where vegetated and non-vegetated zones are treated separately as two neighboring one-dimensional flows but considering the alternate transverse flow at the interface between them, the phase relations among respective velocity components and water-surface fluctuation are explained.

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This paper discusses field observations and model results for temperature and concentrations of dissolved substances in Myojin-ike, a saline lake. Myojin-ike is itself composed of three smaller interconnected basins, the largest of which is connected to the sea of Japan by a pipe. Results from water quality analyses and hydraulic measurements indicate that there is a fair amount of exchange of nutrients between the lake and sea and from groundwater. A simple model is presented that incorporates these exchanges. Calculated and observed concentrations for salinity, SiO₂, PO₄-P and [NO₂-N+NO₃-N+Org. N] show good agreement.

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The various coherent structures, such as kolk-boil vortices and the streaky structures, are often observed in the flood rivers and estuaries. The behavior of these structures is quite different between the rising and falling stages of the flood period. The unsteadiness effects of flood flows cause the these difference of turbulence. Therefore, it is important to investigate the turbulent structures in unsteady open-channel flows. In this study, the turbulent structures over smooth and rough beds were accurately measured by making use of LDA in unsteady open-channel flows. The unsteadiness effects upon the structures, mean velocity distribution, bed shear stress and turbulence characteristics and also the effect of secondary currents on them, were examined theoretically and experimentally.

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Taking into account of shortage and pollution of raw water in the case of drought, an optimal design method of a water supply system with a buffer reservoir for raw water and advanced treatment facilities is proposed to fill a quantitative water demand as well as to meet a water quality requirement concerning hygienic safety and palatability. To minimize the sum of the construction cost and the operation cost of the system and to elucidate the characteristics of the system through the cost analysis, a formulation and a procedure to solve the optimization problem are given. A contour chart of the minimum cost of the system for various conditions of water supply is shown. The uncovered characteristics of the system and the contour chart are helpful to obtain the consent of water users to an introduction of the system.

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A fish death accident was occurred in a drainage canal from a reclaimed land. Decrease of salinity caused by a gate repairs and lack of oxygen cased by rapid increase of temperature were thought to be the cause of the accident. In addition, our investigation showed the possibility of pesticide inflow. The effects of these factors were estimated by experiments using mullet. The current simulation model of the canal was also constructed. Then SSEM, a Shallow Sea Ecological Model, was extended to simulate the pesticide inflow and salinity change. The extended SSEM revealed that the decrease of water quantity, the decrease of salinity and the pesticide inflow caused the accident. To decrease the pesticide amount down to one fifth, the accident might not be occurred.

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