We collected a large number of field data for the vertical velocity profile, measured with acoustic Doppler instruments like ADCP, under flooding conditions in large actual rivers and then compared the observed results for the vertical velocity profile and the coefficients of float with classical well-known theories and empirical formulas to evaluate the accuracy of the coefficients of float, which are the ratio of the depth-averaged velocity to the surface-layer velocity measured by floats. The observed velocity distributions and coefficients of float were in better agreement with the logarithmic velocity profile than Aki’s theoretical formula. Due to these results, the coefficients of float generally used in Japan, which are evaluated in line with Aki’s theoretical formula, were larger than the coefficients of float calculated by the measured velocity distributions. Based on these findings, we proposed how to evaluate the coefficients of float.

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  This paper proposes a location equilibrium model incorporating household income distribution. We applied this model to Neyagawa riverbasin, in Osaka, to evaluate social costs and benefits of landuse regulation strategies based on flood risk assessment. The result of the cost-benefit analysis shows that the impact of the landuse regulation strategies on a low income group would be greater than higher income groups. Net benefit of landuse regulations becomes maximum at the regulation level of 5 year flood return period. When regulations based on more than 25 years flood return period are conducted, the net benefit becomes negative. These results reveal that it is beneficial to prohibit the area with high flood frequency from being used for housing.

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  Cost-benefit analysis of landuse regulation strategies was performed to evaluate their applicabilities. The study basins were Osaka and Tokyo regions, Japan’s two largest cities. In this research, two different kinds of landuse regulation strategies were considered: landuse regulations that prohibit use of area predicted to be inundated under or above floor level with a design rainfall event. The former is called a strict regulation and the latter a weak regulation. It was deemed from results that the weak regulation had broader applicability than the strict one for both regions because net benefit of the weak regulation tended to be positive for a wide range of design rainfall events. However, for Osaka region, the strict regulation based on a design rainfall of 5 years return period was shown to be the most effective because it gave the largest net benefit in all regulations. For Tokyo region, results showed that the weak regulation had some applicability while the strict one did not; this is because economic damages in this region are mainly expected to be caused by flooding above floor level.

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  This research investigated the social costs/benefits and applicability of a building regulation strategy based on flood risk assessment. The study areas are Osaka and Tokyo regions, both of which are the highest population density areas in Japan. The investigations showed that the social benefits of building regulations exceeded the costs in both regions and the total benefit for Osaka region was larger than that for Tokyo region. This result indicates that the building regulation strategy has a degree of applicability as a countermeasure for flood hazards and it is more effective in Osaka region than in Tokyo region. The building regulation strategy was also compared to a land use regulation strategy. The results showed that the total benefit of the building regulation strategy was larger than or almost same as that of the land use regulation strategy. It suggests that the building regulation strategy has the same degree of applicability with the landuse regulation strategy.

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  The formation process of depositional landforms on a 2-D permeable plain was studied numerically. In this paper, such landforms are called a micro-scale alluvial fan. The purpose of this study is to develop a numerical model which enables us to simulate this formation process. To understand the formation mechanism more precisely is also the purpose of it. The Slope collapse model was applied in order that the local slope angle does not to exceed the angle of repose. And the modified version of bed load transport function was introduced so as to consider the gravity effect associated with the slope angle in longitudinal and lateral directions. Water flow was computed on the basis of both the 2-D shallow water equations for surface flow and the 3-D Richards’ equation for subsurface flow. Comparison was made between a computed result and that of the experiment by Sekine et al. (1998). As a result, it was verified that the numerical model works fairly well, and the formation process of micro-scale alluvial fan can be simulated reasonably. The process is closely related to the channel deformation process, that is, channel migration, disappearance of the channel, and a new channel formation.

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  This study analyzed relationship between deposition process of coarse particulate organic matter (CPOM) and flow structure around river bank in a gravel bed river.
  At first, the movement of CPOM behind the protrusion of a river bank was investigated. This field experiments revealed that the flow near the riverbed in main stream was entrained behind the protrusion of the bank and the flow near the surface behind the protrusion returned to the main streamline. Therefore, suspended materials near the riverbed in the main streamline are entrained and deposit at the center of circulation.
  Based on this result, litter patches were classified into several types by focusing on whether the litter patches collect suspended material or floating one. Then, deciduous leaves were collected from each litter patch, and type of tree, mass, decomposition rate, and attached macro invertebrates were analyzed.
  Consequently, following forming process of litter patches was clarified. The depth where CPOM suspended, which depends on type of tree, determines the place of CPOM deposition. Then, type of tree and physical environment of the litter patch determine the suitability of habitat for macro invertebrates. Finally the species and the number of macro invertebrate and the deposition period determine the decomposition rate of CPOM. Thus, the quality of CPOM is different among several litter patch types.

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  To examine the effectiveness of time domain reflectometry (TDR) for finding the interface between fresh and salt water layers, the possibility and accuracy in measuring the interface level were investigated with a two-rod TDR probe of 48cm. In the TDR waveform, reflection coefficient values indicate the magnitude of electrical energy of a microwave step-pulse given by TDR cable tester. The level was estimated by analyzing the waveform feature that the coefficient value will abruptly reduce at the interface due to energy absorption by salt water. In the experiment, to reproduce various groundwater qualities in a coastal aquifer, the electrical conductivity of fresh water was arranged from 0.0005 to 0.4 S m^-1. The fresh water was set to the upper layer than salt water of 5.2 S m^-1 in the experimental column. In the situations where the conductivity or layer thickness of fresh water was large, the energy loss into the water prevented us from measuring the level. However, when the thickness is thin for the high conductivity condition, the interface could be more detectable due to reduction of the loss. The root mean square errors for the measured levels were less than 1cm under static hydraulic conditions even if the measured levels fluctuated. These results may suggest that the proposed method for detecting the interface is effective.

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  This paper examines the resonance characteristics of the wave power generation device, which consists of pulley(s), wire(s), floats(s), counterweight(s) and ratchet mechanism. The resonance analysis model introduces the relative displacement between the water level and the float’s position into the applied dynamics model for the system in operation. The applied dynamics model is mainly composed of the equations for generator, equations for driving pulley motion and equations of the heaving float motion into which are introduced the exciting wave force, the added mass and the wave damping force. The equations of the natural frequency, the ratio of the frequency of water wave to that of the natural frequency, the damping ratio and magnification ratio have also been given. Moreover, the behaviors of the average occurred electric power and maximum wire tension have been examined for wave periods around the natural period of the system. Concequently, in order to design the optimum conditions of the device, the appropriate magnification ratio is evaluated.

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  The MPS (Moving Particle Semi-implicit) method has been proven useful in free-surface hydrodynamic flows. Despite its applicability, one of its practical problems is the high computational load. By the way, Graphics Processing Unit (GPU), which was originally developed for computer graphics acceleration, now provides unprecedented computational capability for scientific applications.
  The main objective of this study is to develop a GPU-accelerated MPS code with using CUDA (Compute Unified Device Architecture) language. Several techniques have been shown to optimize calculations in CUDA. In order to promote the acceleration by GPU, particular attentions are given to both the search of neighboring particles and the iterative solution of simultaneous linear equations in the Poisson Pressure Equation. In this paper, dam break flow calculations have been carried out by the GPU-accelerated MPS method, and the accuracy and performance of GPU-based code are investigated by comparing the results with those by CPU.

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  Profiling and mooring measurements were carried out in Genka Bay, Okinawa, Japan to study the characteristics of the internal tidal current and its associated cooling system. The study results show that the depth-averaged current flows nearly parallel to the coastline. There is also an existence of a cross-shore internal tidal current according to the vertical structure of the horizontal current. This current influences on the bottom water temperature transmission from offshore to nearshore bottom water and changes the vertical temperature profile even of nearshore regions and thereby establishes a unique cooling system. Spectra of the baroclinic and bottom water temperature also congruent the internal tide based cooling system in GB.

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  Sedimentation aspects have a major role during the design of new reservoir projects because life of the reservoir mainly depends upon sediment handling during reservoir operation. Therefore, proper sediment management strategies should be adopted to enhance the life span of reservoirs. Basha Reservoir is one of the mega water resources projects which are being planned to construct on the Indus river. Under this study, the efficiency of four sediment management strategies were evaluated by using the RESSASS model. The reservoir management strategies considered for sediment simulation of Basha reservoir include the normal operation, raising of MoL, draw-down the MoL (flushing) and controlling the sediment inflows. Under normal operation, the model predicted the life span of Basha reservoir around 55-60 years. But by raising of Mol 2.0m/year implemented after 35 years of operation may add 10-15 years more to the life-span of the reservoir. However, by adopting the flushing operation to draw-down the MoL at El.1010m initiated after 35 years of operation, it may also add about 15-20 years more. Moreover, the results obtained by considering 50% reduction in sediment inflow due to implementation of river basin management projects upstream of Basha within 30 years of reservoir operation, depicts that the life of the reservoir will be more than 100 years. It is therefore concluded that proper sediment mitigation measure can significantly enhance the life-span of planned reservoirs.

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