Scour process, flow dynamics, hydrodynamic forces, around a series of repelling spur dikes

This experimental study examined the turbulence effects around spur dikes on scour dynamics under clear-water conditions. An experiment was conducted in a straight rectangular flume of length, width, and flow depth: 15, 0.91, and 0.70 m, wherein instantaneous flow velocity components were measured using an acoustic doppler velocimeter (ADV) across longitudinal and transverse directions over the evolved bed to evaluate Reynolds shear stress (RSS), drag forces, drag coefficient, turbulent kinetic energy (TKE), and vortex strength to capture the detailed hydrodynamics. The results indicate maximum scour occurred at the tip of the first spur dike. The RSS peaked at the base of the first spur dike, correlating with intense vortex activity and sediment mobilisation. Downstream, reductions in RSS, drag, and vortex strength corresponded to weaker turbulence; however, renewed vortex shedding between the second and third dikes sustained scour and sediment resuspension. Negative RSS values near the third dike indicated complex recirculation and vertical mixing that enhanced local deposition. TKE profiles mirrored the RSS trends, with the highest values near the first dike, driven by vortex formation and recirculation. The drag force and drag coefficient values consistently decreased across successive spur dikes. Similarly, vortex strength was much greater ahead of the first spur dike and decreased in the downstream direction. The findings provide new insights into the coupling between flow turbulence, vortex dynamics, and local scouring around the dikes.