Author(s): Muto Yasunori; Baba Yasuyuki; Nakagawa Hajime
Linked Author(s): Yasuyuki Baba, Hajime Nakagawa, Yasunori Muto
Keywords: Velocity measurements; ADCP; Real river; Groyne; Circulation; Exchange process; Boil; Wash load; Vegetation
Abstract: Velocity measurements were carried out in a river of straight reach with a series of groynes on one side of the main channel. A broadband Acoustic Doppler Current Profiler (ADCP) mounted on a small boat was used. The measurements were performed in the area of 60m times 200m, the channel width and the longitudinal distance of the straight reach including four groynes respectively, under three depth conditions including two submerged cases during floods. Flow patterns induced in the groyne fields, exchange processes between the main channel and the groyne fields, and relation among the flow dynamics, sediment movements and vegetations on the bank, are mainly of interests. As for the flow structure in one embayment, 2-D large circulation flow is dominant in the non-submerged condition, whereas a vertical vortex is formed just behind a groyne in the shallow submerged case, then these circulating patterns in the groyne fields are totally washed away in the deep submerged case. The exchange process is also governed by the 2-D circulation in the non-submerged case, whereas a weak depth-scale secondary flow cell formed in the junction region takes an important role in the submerged case. This secondary flow cell in the submerged case seems to drive a slow water body around the groyne towards the water surface, and then this water body shows a boil-like motion when reaches at the water surface. Sediment deposition in the embayment is strongly affected by the local flow structure around the groyne and the river bank. Patches of vegetations on the bank can be well correlated with the flow dynamics and the resultant sediment movements.
Year: 2005