Investigation on streambed sediment and flow structure in the arase dam

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Terunori Ohmoto, Ryuichi Hirakawa, Hiroaki Taniguchi

Friday 3 july 2015

12:15 - 12:30h at Asia (level 0)

Themes: (T) Water engineering, (ST) River and coastal engineering

Parallel session: 15C. Engineering - Industrial

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As for the influence that the dam that is the river crossing structure gives to a physical environment in the river downstream region, that is, the river channel shape, the riverbed material, the sediment transport, and the stream regime, there are a lot of uncertain points. Moreover, the deposition of the microscope sand on the gravel bed are not researched enough. Degradation in the river ecosystem because of the control of the flow velocity decrease and the natural disturbance caused by smoothing the flood flow is pointed out in the gravel bed river in the dam downstream region. The growth of attached algae has been particularly serious affected because of factors such as biofilm separation, reduced frequency of renewal and the deposition of fine sediment. Focusing on the river channel downstream of the Arase Dam, whose removal began in September, 2012, this study looks at the sandbar behavior over the years before the dam removal began and tries to elucidate the structure of fine sediment deposits. With the aim of shedding light on the relationship between the deposition of fine sediment and flow, field measurement was conducted to investigate how the deposition of fine sediment on gravel varied in the cross-channel direction. The study area was defined at distances of 500 m to 700 m (19.2 km to 19.4 km from the river mouth) downstream from the Arase Dam. As a result, the sandbar area in the Arase Dam direct lower stream of the correlation with the dam annual maximum outflow rate was weak, and the influence from the amount of removal of the earth and sand deposited on the dam lake became clear.