Unsteady turbulent velocity profiling using an array of two Vectrino II Profilers in tidal bores and open channel flows

The propagation of positive surges in rivers and open channels is a highly unsteady turbulent process, with intensive sediment scouring and mixing. Despite its ecological and engineering significance, systematic physical studies of the unsteady turbulent characteristics of tidal bores remain limited. The present investigation performed ensemble-averaged velocity measurements using an array of two Vectrino II Profilers to investigate the vertical and transverse variability of the instantaneous velocity field during the propagation of breaking bores in open channel flows. Results highlighted satisfactory performances of Vectrino II Profilers in highly unsteady turbulent open channel flows. Rapid longitudinal deceleration, transient recirculation and large velocity fluctuations in all directions were observed with the bore passage. The vertical velocity increased then decreased with the sharp free-surface rise. The transverse velocity data highlighted drastic transverse motions of bores and existence of large vortical structures in the flow. Overall, the results suggested that the propagation of tidal bore is a highly unsteady turbulent process, and a three-dimensional phenomenon. The process was associated with large fluctuations in all velocity components, as well as formation of large vortical structures and intense turbulent mixing in the wake of the surge