Author(s): Akihiro Tominaga; Naoya Kojima; Tomomichi Kato
Linked Author(s): Akihiro Tominaga
Keywords: Riverside concavity; Spur dike; Reattachment; Recirculation; PIV; Flow structure
Abstract: A riverside concavity defined as the dead-water zone connecting with the main stream. Such a dead water zone tends to cause recirculation eddies and resultantly the deposition of suspended sediment. The function of spur dikes can be used to control the flow pattern in a concavity zone. In this study, effects of spur dike placed upstream side in a main channel on flow structures in a side concavity zone were investigated. The velocity was measured by using PIV method in a laboratory flume. Location distance of the spur dike from the upstream end of the concavity zone and the length of spur dikes were changed under two different discharges and their effects were considered. The flow patterns, magnitude of recirculation eddy and water exchange velocity in the concavity zone were changed by these parameters. The reattachment length of the separated wake zone behind the spur dike is important for the control of the flow structures in the concavity zone. When the reattachment point lies upstream of the downstream end of the concavity, the flow in the concavity is accelerated. When the reattachment point exceeds the concavity zone, the flow pattern in the concavity is extremely changed and the water exchange becomes very weak. The effects of spur dike are changed with water depth because the length of the separation zone behind spur dike is reduced in cases of submerged spur dike.
Year: 2014