The bathymetric evolution of the northeast part of the Ariake Sea and the Estuarine Channel of the Chikugogawa River was studied and the seasonal variations in the sediment phosphorus distribution in the region were analyzed. The tidal prism of a river mouth estuary determines the channel size of the main ebb tidal delta. The muddy bed of the estuarine channel was eroded by flood discharge, and the mixture of the bed materials and the discharged suspended sediments from the river basin deposited in the sandy delta.
The high concentrations of Al-P, Fe-P, residual organic P, and TOC in the fine sediment were continuously distributed from the sandy Chikugogawa river mouth delta to the muddy tidal flat in the front of the Rokkakugawa river mouth after the flood season. The size of the surface particles in the delta increased and the concentration of organic matter increased during the dry season.
These facts suggest that the fine silt and clay settled on the Chikugogawa river mouth delta are eroded by the tidal current, and a part of these particles return to the estuarine channel; the remaining particles migrate to the southwest sea area of the tidal flat. The suspended sediment around the delta is transported to the tidal flat that is offshore of the Rokkakugawa river mouth by estuarine circulation occurring in the innermost bay of the Ariake Sea.

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This paper presents the fundamental performance for measuring river discharge using an acoustic Doppler current profiler (ADCP) through field tests conducted in large-scale rivers. For measuring discharge, a down-looking ADCP near the water surface was moved across the river to collect data on the vertical distribution of horizontal velocities and water depth for the entire cross section. We compared water velocities and depths obtained with the ADCP and the lateral position of the ADCP with measurements obtained using conventional techniques and showed that the observed data obtained using the ADCP agreed well with data obtained using conventional methods. Discharge comparisons measured using the ADCP and a Price current meter revealed that the accuracy of the ADCP measurement was relatively lower and higher under conditions of low and high discharge, respectively. Based on these findings, we qualitatively clarified the application of the ADCP to the measurement of river discharge.

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In this paper, fluid behavior in conduit system is discussed in order to newly introduce AFC operation (operation of large-amplitude forced oscillation) into existing typical hydro-power plants with surge tank. And a dimensionless general-purpose diagram to help determine the capability of existing facilities is provided. Only three pieces of data on existing power plants are needed for this discussion: gross head, design water pressure, and head loss in headrace tunnel. Furthermore, non-linear forced oscillation equations for fluid movement in conduit system during AFC operation are studied in terms of chaotic dynamics. As a result, it is found that there is no occurrence of chaos in the range of practical use.

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This paper deals with a computational method for the movements of arbitrarily-shaped solid objects with collisions in three-dimensional free-surface flows. Since the mechanical interactions between objects and free-surface flows are adequately taken into account in the numerical method, no empirical coefficients, like resistance coefficients, are needed. An arbitrarily-shaped object is represented by tetrahedron elements, which are used to calculate its motion and estimate interactions with fluids, while contact-spheres are utilized for collision detections. The prediction method was applied to various experimental results and its validity has been demonstrated.

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