Performance of Tapered Submerged Vanes in Mitigating Local Scour Around Bridge Piers

Scour, defined as the erosion or removal of sediment from around bridge piers due to flowing water, remains one of the primary causes of hydraulic structure failures worldwide. Local scour around bridge piers poses a serious threat to bridge stability, particularly during high-flow events, as the development of downflow, horseshoe vortices, and wake vortices at the pier base leads to intense sediment removal and foundation instability. To address this challenge, the present study investigates the hydrodynamic behaviour and scour reduction performance of tapered submerged vanes installed upstream of a cylindrical bridge pier as an effective countermeasure against local scour. A combined numerical and experimental approach was adopted to evaluate the influence of tapered submerged vanes on flow structure and scour characteristics. Numerical simulations were carried out using FLOW-3D Hydro to analyse the three-dimensional flow field around the pier–vane system under steady clear-water conditions. The simulations focused on assessing velocity distribution, near-bed shear stress, vortex dynamics, and secondary flow patterns generated by the tapered vanes. Particular attention was given to the formation of leading-edge vortices (LEVs) and their role in modifying erosive flow structures near the pier foundation. Based on the numerical insights, a series of physical model experiments were conducted in a laboratory flume to quantify the scour reduction achieved by the tapered vanes. The experiments aimed to optimize the longitudinal and transverse placement of the vanes relative to the pier. The vanes were installed at a fixed longitudinal distance upstream of the pier, while transverse spacing was systematically varied to examine its effect on sediment transport and scour depth. Bed elevation profiles and maximum scour depths were measured after equilibrium scour conditions were attained. The results demonstrate that tapered submerged vanes significantly alter the near-bed flow field by generating localized leading-edge vortices that effectively deflect high-energy flow away from the pier base. This flow redirection weakens the horseshoe vortex and reduces near-bed shear stress in the vicinity of the pier. Among the tested configurations, the vane arrangement with a longitudinal spacing of 1.5D and transverse spacing of 2D exhibited the best performance, resulting in a 56% reduction in maximum scour depth compared to the no-vane case. Additionally, localized sediment deposition was observed upstream and downstream of the pier, indicating favourable redistribution of sediment induced by the vane-generated secondary currents. By integrating numerical modelling with experimental validation, this study provides valuable insights into the flow mechanisms and optimal placement strategies of tapered submerged vanes. The findings highlight their potential as a practical, efficient, and sustainable solution for mitigating local scour around bridge piers in alluvial channels.

Keywords: Scour, Submerged Vane, Horseshoe Vortices, Wake Vortices, Leading-Edge Vortex (LEV)