Abstract:
Groynes are hydraulic structures that protect against bank erosion, maintain water level by deflecting flow direction, and ensure navigation safety. They can be used for flood control, land reclamation, and provision of navigable depth. In addition, their functions can be changed along with the goals of river works and the nature of the stream. Groynes are flow diversion structures, commonly used in river engineering especially at river bends to prevent bank erosion and control river meandering. Today, various types of groynes have been installed as pilot projects encouraging competent authorities proceed with such option in the wake of pertinent needs. One is impermeable another one is permeable. In this study, permeable groynes in meandering channel are used.
The experimental study has been conducted in the open air facility of Water Resources Engineering Department, Bangladesh University of Engineering and Technology (BUET), Dhaka. Required data have been collected from 10 experimental runs in five different setups of the compound meandering channel. In each of those runs, velocities are measured at four cross-sections, and within each cross-section at four zones. Two depths of water (i.e. 20 cm and 15 cm) are considered in this study. Analyses are done for velocity distribution profile, velocity distribution coefficients (i.e. energy and momentum coefficients) and shear stress distribution.
In the present study, studies are carried out on velocity distribution profiles, velocity distribution coefficients and shear stress distribution. For zone-wise distribution of mean velocity, 20 cm and 15 cm depths, set-up 2 (i.e. 3 groynes at L spacing, L = length of the groyne) is the best option among all the set- ups. For zones 2, 3 and 4, set-up 2 produces minimum velocities throughout the cross-sections although zone1 produced minimum velocities for set-up 4 (i.e. 3 groynes at 3L spacing) for 20 cm depth case. For cross-section-wise distribution for both 20 cm and 15 depths, set-up 2 is the best option among all the set- ups. Regarding energy coefficient, for 20 cm depth, hence set-ups 1 (single groyne), 3 (i.e. 3 groynes at 2L spacing) and 4 seem to be the preferred options. For 15 cm depth, set-ups 2 and 4 seem to be the preferred options regarding energy coefficient. Regarding momentum coefficient, for 20 cm depth, set-ups 1, 2, 3 and 4 seem to be the preferred options. For 15 cm depth, set-ups 2 and 4 seem to be the preferred options regarding momentum coefficient. Regarding shear stress distribution, set-up 2 seems to be the best option with the lowest values among all the zones for both 20 cm and 15 cm depths.
