Author(s): Fereshteh Bagherimiyab
Linked Author(s):
Keywords: Fine sediment; Suspension; Accelerating and decelerating flow; Acoustic Doppler methods; PTV (Particle Tracking Velocimetry)
Abstract: In order to simulate fine sediment dynamics over an armored bed in a river during the passage of a flood wave, quasi-instantaneous profiles of velocity and sediment concentration were taken simultaneously and co-located using acoustic Doppler and imaging methods. Flow visualization and PTV measurements were made in parallel. Systematically higher friction velocities were observed in accelerating flow than in decelerating flow for comparable mean flow velocities. This indicates that the same change of relative submergence generates different flow dynamics in both flow ranges. In the final phase of the accelerating flow range, fine sediment suspension from the bed started in bursts and rapidly created nearly stationary ripples. Vortices shedding from the ripple crests produced most of the sediment suspension in the form of events, making suspension intermittent. Due to the ripple structure, high sediment suspension continued to occur during the decelerating flow even though the flow velocity decreased.
Year: 2011