Flow structure around a row of vertical rods in a floodplain

This paper presents the results of an experimental study to determine the effect of a row of vertical cylindrical rods on the structure of turbulent flow inside a symmetrical rectangular compound open channel. The coherent turbulent flow structure or bursting events and associated shear stresses play an important role in sediment entrainment and bed instability in an open channel. Therefore, in this study, three-dimensional bursting analysis is used to find the turbulent flow structure at the edge of a floodplain. The study used a model of a symmetrical rectangular compound channel in which ratio of the main channel width B to the floodplain width b was 1·5. A row of cylindrical wooden rods was installed on the floodplain bed at different distances d from the edge of the floodplain (d/b = 0, 0·1, 0·2, 0·3 and 0·4). Three-dimensional flow velocities were measured using an acoustic Doppler velocity meter (micro-ADV). For different experimental tests, the contribution probability of bursting events to the Reynolds shear stress was computed at different points of the flow depth. Minimum values for the contribution probability of shear stress were found for internal, external sweep and ejection events at the edge of floodplain for d/b equal to 0·1. Furthermore, the transition probability of internal, external sweep and external ejection events for d/b = 0·1 decreased at the intersection of the floodplain and main channel. Although scaling of the experimental results requires further study for application to wide rivers, these findings may be useful in practical applications for narrow rivers.