Study on the functions of hydraulic structures and riverbed evolution for the basin-wide sediment managements

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In order to execute appropriate basin-wide sediment managements, it is necessary to know the processes of sediment yield, transport, and deposition. In this research, observations of sediment yield were done and found that in the central Japan, freezing and thawing of the ground influence the amount of sediment yields and it has little correlation with rainfall which will not generate landslides. A rainfall and sediment runoff model and a prediction model of surface landslide were developed where the time variation of moisture contents was taken into account, and the validity of the models was checked by the observed and experimental data. In the sediment transport process, it is very important to discharge sediment downstream from check dams and reservoirs appropriately from the view point of amount of sediment and the diameter. Therefore, a numerical simulation model was developed which can express the jamming process of the big boulders into junglegym-type check dams. The model was found to be valid by the experimental data. Moreover, sediment flushing and sluicing from the reservoir become very important due to environmental problem as well as the problem of the decrease of reservoir functions. The new method to remove the sediment deposited in the reservoir downstream was developed and the availability of it is checked by the experimental data Due to the sediment supply from upstream, middle and downstream regions of the riverbed will be strongly influenced resulting in the variation of the river topography. In order to evaluate the effectiveness of hydraulic structures in the river, a numerical model was developed to simulate the flow and local scour around hydraulic structures. The model was found to be valid by comparing the computed results with experimental data. The functions of traditional riparian works such as Bandal-like structures were also investigated.