Experimental Study of Flow Characteristics in a Compound Meandering Channel

Abstract

Most of the river flows in Bangladesh can be characterized as compound meandering channel in which the flow characteristics are very complex. Engineers, Planners and Researchers are highly interested in predicting accurately as well as reliably the quantitative estimates of flow parameters in a compound meandering channel. Experiments have been conducted in a compound meandering channel with symmetric cross-sections having floodplain width ratio 1, 1.67, 2.33, 3 using the large-scale open air facility in the Department of Water Resources Engineering, Bangladesh University of Engineering and Technology (BUET), Dhaka. The aim of the research was to explore the physics of flow phenomenon in the compound meandering channel with varying floodplain width. Point velocity data have been collected using an ADV (Acoustic Doppler Velocity Meter) by four runs in every setup (four setups) at five locations of a compound meandering channel. The analysis of velocity profile and isovels show that the velocity is increasing in the inner bend and decreasing in the outer bend of a bend section in a compound meandering channel. Maximum and minimum velocity is obtained nearest to the inner bend and outer bend respectively. But in the crossover section maximum velocity is obtained nearest to the mid section of a compound meandering channel. There is a significant effect of depth and width ratio on the percentage of flow in a compound meandering channel. The percentage of flow in the main channel is decreasing with the increase of depth ratio and the percentage of flow in the main channel is increasing with the decrease of width ratio. Shear stress is increasing with the increase of depth ratio. Low magnitude of boundary shear stress is obtained at the outer bend as compare to that at the inner bend. Due to non-uniform distribution of velocities over the channel sections of a compound meandering channel, velocity distribution coefficients are introduced. The value of energy and momentum coefficient of a compound meandering channel decrease with the increase of depth ratio at the same relative width ratio.