Author(s): Terunori Ohmoto; Ryuichi Hirakawa; Hiroaki Taniguchi
Linked Author(s): Ryuichi Hirakawa, Terunori Ohmoto
Keywords: Dam removal; Reservoir sedimentation; Current velocity; Sand-bar
Abstract: Focusing on the river channel downstream of the Arase Dam, whose removal began in September, 2012, this study examined variations in sandbar size in the past (1966-2006) and tried to elucidate the structure of fine sediment deposition. Bed materials and the aerial photographs surveyed by the Prefectural government were used to investigate the change in the river channel. ADCP was used for the measurement of flow velocity and suspended sediment concentration. The particle size distribution of fine sediment covering gravel bed were measured by a laser diffraction scattering method. Field measurements clarified that the flow showed clearly discernible three-dimensional flow structures and the fine sediment deposited on gravel surfaces in the near-bank regions in the straight river. From the relation between the deposition of fine sediment and flow pattern, it has been suggested that the deposition of fine sediment is determined by secondary flow cells.
Year: 2015