Study on the flow characteristics in embayment with spur dikes

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Takeshi Takemura, Hirokazu Sumi, Tomoaki Nakamura, Akira Oda, Minoru Ochiai

Friday 3 july 2015

12:30 - 12:33h at North America (level 0)

Themes: (T) Hydro-environment, (ST) Ecohydraulics and ecohydrology, Poster pitches

Parallel session: Poster pitches: 15F. Environment - Ecohydraulic

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Spur dike, one of the hydraulic structures, is used for the purpose of preventing the erosion of the river bed or river bank by changing the direction of flow. Sometimes embayment is formed for such as scour or deposition of sediment occurs around the spur dikes. The embayment is used by some fishes, benthos or etc. Therefore, it is important to maintain condition continuously in embayment, however, it is difficult. In this study, flow structures in embayment with spur dikes are investigated using two-component electromagnetic velocimetry and flow visualization technique. The embayment was made with two spur dikes and the aspect ratio (W/L) of it set 3 (width of embayment along streamwise direction: W, length of spur dike cross-stream direction: L) or 5. We used four types spur dike model, two impermeable spur dikes (Type-1), Type-1 with an impermeable flat plate 1/3B in length located along boundary between spur dikes (Type-2), replace the impermeable spur dike to permeable one on the upstream side (Type-3) and Type-3 with an impermeable flat plate 1/3B in length located along boundary between spur dikes (Type-4), in the experiments. In addition, the alphabet A or B (indicating the difference in aspect ratio) added at the end of the model name. Flow characteristics in embayment are investigated by flow velocity, momentum exchange rates between the main flow region and in the embayment, and flow visualization. As an experimental result, the mean flow velocity and RMSD of Type-3-A is about 1.53 times and 1.09 higher than Type-1-A respectively. Moreover, it is confirmed that there are few large fluctuation in flow in embayment. We investigate these four models carefully and reach a conclusion that the model Type-3-A is easy to maintain because of reduces the size of recirculation by permeability flow velocity from spur dike at upstream side.