An Experimental Study of Longitudinal Velocity Distribution at Cross-over and Bend Section of a Compound Meandering Channel

Abstract

Generally, river flow can be schematized as compound meandering channel in which the longitudinal velocity distributions in the crossover and bend section are completely different and quite intricate. Engineers, Planners and Researchers are highly interested in predicting accurately as well as estimating quantitatively and reliably the longitudinal velocity distribution in a compound meandering channel. A laboratory experiment has been conducted in a compound meandering channel with symmetric cross-sections having floodplain width ratios (B/b) of 1.00, 1.67, 2.33, 3.00 and depth ratios (H-h)/h of 0.20, 0.30, 0.35, 0.40 using the large-scale open air facility in the Department of Water Resources Engineering, Bangladesh University of Engineering and Technology (BUET), Dhaka. Point velocity data have been collected using an ADV (Acoustic Doppler Velocity Meter) for different depth and width ratio at five different locations of a compound meandering channel. The traditional power law represents a vertical distribution of longitudinal velocity in open channel with maximum value at free surface and with zero at the channel bed. But the velocity distribution in the type of natural or laboratory compound meandering channel does not follow such velocity distribution. The longitudinal velocity distribution of a compound meandering channel shows two characteristics for all cases and depth ratios. In the bend section, velocity increases in the inner bend (convex) and decreases in the outer bend (concave). Similar nature is observed in the floodplain boundary for all cases and depth ratios. In the crossover of a compound meandering channel, velocity increases towards the mid-section and decreases in the boundary of the channel.