Author(s): Su-Chin Chen; Je-Weiliao; Hsun-Chuan Chan; Yi-Chiung Chao
Linked Author(s):
Keywords: Submerged vegetation; Critical velocity; Turbulence intensity; Acoustic Doppler velocimeter (ADV)
Abstract: This study experimentally investigated the effects of bending submerged flexible vegetation on the characteristics of flow and configuration of deposition. Bending submerged flexible vegetation was produced using a plastic pipe and films which were 20 cm long. The experimental flow velocitieswere performed for three sediment critical velocities (Vc) experiments, 0. 8 Vc, Vc, and 1. 2 Vc. Vertical distributions of time-averaged velocity and turbulent intensity at various streamwise distances were measured with an acoustic Doppler velocimeter (ADV). The flow characteristics around the bending submerged vegetation were analyzed. The results show that the velocities reduced around the vegetation as the water flow passed through it; in particular, the flow velocities reduced dramatically in the middle and at the end sections of the vegetation because eddies develop at the front of the vegetation and flow along the vegetation toward downstream. It induced the turbulence intensity and the flow kinetics disappeared gradually. A scour hole formed, which was affected by the local scour at the front of the vegetation; the sediment was then transported downstream as the flow conditions on Vc, and 1. 2 Vc. The sediment deposited on the low velocity zone was influenced by the disturbance to diminish the turbulence intensity under the vegetation; in addition, the dune forming appeared progressively. The dune height, the length of the deposition zone, the horizontal distance of the dune crest increased with an increasing flow rate.
Year: 2013