This paper proposes a gauge-radar rainfall composition method using Cokriging-type Sequential Gaussian Simulation (co-sGs). It estimates rainfall fields quantitatively consistent with ground gauged rainfall data keeping the spatial distribution pattern of radar rainfall. The method generates possible rainfall realizations with estimation uncertainty; the generated rainfall fields are to be used to evaluate the uncertainty of runoff prediction with a distributed rainfall-runoff model through a Monte Carlo simulation formulation. Application of co-sGs and its cross validation indicated that the generated rainfall has higher accuracy than one calibrated by Dynamic Window method currently used for operational purpose in Japan.

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This paper presents the development of a distributed rainfall-runoff prediction system considering flood control by dam reservoirs in the Yodo River basin. The simulation results show that the system can reproduce quantitatively flood control processes such as pre-release, peak discharge attenuation, and co-operative dam operations. According to multiple simulations with different magnitudes of rainfall, we found that one in 30 year event had exceeded the design high water discharge at Hirakata in 1960, while in 2000 one in 100 year event exceeded it because of the effect of flood control by dam reservoirs. The comparison of dam flood control effects under single dam operation and multiple dam operations indicated that a dam can attenuate peak discharge effectively for larger floods when other dams work together.

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Although the 6-point scheme proposed by Komatsu et al. is the 1st order scheme, computation results are obtained with high accuracy. The 6-point scheme is able to give numerical solutions with few clipping errors. However, there is a room for improvement for the reproduction of the semi-ellipse profile. We propose the 3rd order and 4th order 6-point scheme using the idea for the derivation of the 6-point scheme. Theses schemes are called the characteristics type high-order 6-point scheme. The high-order 6-point scheme obtained in this study is modified into the conservative form in order to incorporate the universal limiter. Theses schemes are called the conservative high-order 6-point scheme. The discriminator, which is an algorithm to distinguish between numerical oscillations and true physical maxima, is also introduced. The discriminator proposed by Asai et al. is modified in this study. A high-accuracy and high-resolution numerical method is proposed by introducing the universal limiter and the modified discriminator.

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Measurements of velocity and dye concentration in side-cavity that consisted of permeable walls were conducted by PIV and LIF. Measurements of flow properties were conducted by PIV. In contrast, a DV-camera was used to measure the dye concentration. The permeable flow from the inside of the side cavity was divided into 4 kinds of patterns, i.e., the patterns from the (1) upstream wall, (2) the side wall, (3) the downstream wall and (4) all walls. The aspect ratio (the streamwise length of the side cavity/the spanwise length of the side cavity) was set to 2 for all experiments. The Froude number was set to 0.27. In this study, the effects of permeable flow on flow patterns and dye concentration properties were examined. A large-scale vortex was generated along the downstream in the side-cavity. High concentration regions were observed upstream inside of the side-cavity. In contrast, low concentration regions were observed in the large-scale vortex. The large RMS value region of the concentration fluctuations was observed in both the interface region and the collision region between large-scale vortex and permeable flow.

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This study describes an experimental investigation on coherent structures and corresponding gas transfer phenomena beneath the air-water interface in wind-induced open-channel flows by using laser Doppler anemometer (LDA) with a wave-gauge sensor. In this study, the organized motions are investigated in detail by the linear filter technique and the time-frequency analysis using the wavelet transform, by which the wave-induced linear fluctuations are separated from the whole velocity fluctuations. As the results of experiments, it is shown that the coherent motions are observed significantly beneath the free surface due to the air-sheared flows, and that the gas transfer phenomena across air-water interface are governed by the organized motions beneath the water surface. It is pointed out that the main characteristics of coherent motions near the interface in these flows are similar to those of turbulent boundary layer with non-slip wall, and that the dependency of the gas transfer phenomena against the friction Reynolds number can be explained in terms of the frequency of the organized motions. This is because the high frequency motions are superior in the organized motions.

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A new simplified horizontal coordinate for computations of river flow, named a horizontal sigma coordinate, is presented to employ boundary-fitted grids along river channels like a generalized coordinate without losing the simplicity of numerical models such as Cartesian and orthogonal curvilinear coordinates. For this purpose, we introduce the sigma coordinate system normally used as vertical coordinates for ocean current and meteorological simulations into the horizontal coordinates in river-flow simulations. The fundamental performance of the horizontal sigma coordinates is confirmed through its application to river-flow simulations. The computational results demonstrate that the horizontal sigma coordinates may be one of promising tools for the numerical approximation in the horizontal direction with computational efficiency as well as higher numerical accuracy.

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A lot of discharge coefficients in subcritical open-channel flows with a side-weir have been suggested as yet. Subramanya & Awasthy found that discharge coefficients were affected by four parameters, i.e., the Froude number, relative flow depth, relative weir height and relative weir length, by making use of a dimensional analysis. However, previous discharge coefficients were obtained from the experiments under the condition that the parameters were not changed systematically. This is because it is quite difficult to conduct such systematic experiments. Recently, it is pointed out that the relative flow depth does not affect on the discharge coefficient so much in comparison with the other parameters. In this study, all four parameters except for the relative flow depth were changed systematically in subcritical open-channel flows with a side-weir. A new discharge coefficient is suggested. It was found that the accuracy of the present discharge coefficient is quite high.

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This paper aims to the accuracy improvement of a two dimensional flood flow numerical model by applying easily obtained vegetation characteristics that can be considered to use for future river management. Despite former works in which the effect of vegetation was included in the determination of Manning's roughness coefficient, in the new model, the resistance of the vegetation is introduced by adopting the concept of the drag force to deal with the deformed situation of the vegetation under flood flows. The vegetation density was distinguished by different types of plants, i.e. trees, bushes, bamboos and annuals. The resistance of annuals depends on the flow rate, therefore, the deformation of plants is considered as a decreasing factor of the resistance. The model was checked to confirm its applicability by comparing the analysis to the water surface profile and flow characteristics of the flood flow in the Asahi River and found a good agreement with the results.

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In order to design an environmentally-friendly river structure, the flow and fields around a rubble mound weir and groin were investigated. In a physical model experiment, the flow inside the structure was visualized by adjusting the refraction indexes between the working fluid and the rubble's materials. Velocity vectors were obtained by means of PIV. Mass and momentum exchange between the open channel flow and the rubbles' porous media were found to be predominant around the up- and downstream corners of the weir and the groin. Both the turbulent intensity and Reynolds stress were also significant in these areas due to intensive momentum exchange. On the other hand, in the structure, turbulence properties were mainly influenced by the arrangement of the rubble and pores in the structure.

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A new three-dimensional numerical method for large-scale river flow with a new mode-splitting technique and a parallel computation is developed. To remove the severe limitation of the computational time interval for the 3D calculation in previous mode-splitting techniques, we present a new mode-splitting technique with satisfying high numerical stability and reducing computational time. To examine the fundamental performance of the present model, the 3D computations of unsteady flows in straight and curved open channels are performed, showing that the present model may have high numerical accuracy and appreciable computational efficiency. The present model is also applied to the flood flow computation in the Edo River. The good agreements are obtained between the model simulation and field measurements. More importantly the computational time of the present model amounts to only 0.4% of that of the normal 3D model without the mode-splitting technique.

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This paper presents a theoretical model for prediction of undertow velocity profiles in the surf zone due to near-normally incident waves. The waves may be periodic or narrow-banded random waves, and the beach may be plane or barred. Both wave and surface roller models are based on simple energy balance equations. The undertow model consists of two-layer 2DH momentum equations, integrated above the wave trough level and over the entire depth. Coupled with a simple turbulent eddy viscosity model, analytical solutions are obtained for the vertical mean shear current profiles. Model predictions show excellent agreement with experimental observations which were not used in the model's development.

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Longshore current velocities measured once a day for 15 years with intervals of about 50 m along the 400-meter-long pier of Hasaki Oceanographical Research Station (HORS) were analyzed. The direction of the predominant longshore current velocity near the shore was opposite to that offshore. The causes of the cross-shore distribution of the predominant longshore current velocity were investigated with the offshore wave height and the alongshore component of the wind velocity.

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To evaluate accurately velocity and discharge in rivers from observed results at discrete points in a cross section, we present a new method for data assimilation in which observed velocities are properly incorporated into a river-flow computation. In the present method, we assimilate observed velocities into a shallow-water flow model, and then we can incorporate spatially the observed velocities in a cross section by satisfying dynamic principles. The present method is therefore referred to be here as a dynamic interpolation method. To confirm the fundamental performance of the dynamic interpolation method, we apply the present method to the spatial interpolation of velocities in a cross section using the simulation data for a river-flow computation and observed data. The interpolated results indicate that the present method can have higher accuracy for the evaluation of river velocity and discharge than the simple interpolation method.

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