Sediments have become a serious problem in the management of the Hitotsuse Dam Reservoir (reservoir capacity: 261,361,500 m³), Miyazaki, Japan. The prevention of sediments in reservoirs remains a challenge, because the catchments can contain many landslip areas and the strata architecture is complex. In this study, we investigate the source of the sediments in the reservoir using mineral analysis. The core sample was collected by a boring machine from a 16 m sediment depth. To assess the nature of the particles, landslide soils accumulated in catchments of the Hitotsuse Dam were sampled and analyzed. Energy dispersive X-ray fluorescence (ED-XRF) and X-ray diffraction (XRD) were used to determine the component composition and mineral composition of the sediments, respectively. Cluster analyses were performed to evaluate the similarity in the component and mineral compositions of each sample. Component and mineral compositions of core samples indicated high similarities with the landslide soil to three samples out of 60 samples taken at 22 points. The points of three samples locate along the same stratum. It was strongly suggested that the sediments were continuously supplied from the same stratum located in the upper river basin. This method has the potential to determine the substances that release sediments in reservoirs and the location of the substances in the soil. Appropriate countermeasures to reduce the accumulation of sediments can then be taken at those specific locations.

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