Flow dynamics and velocity decay in vegetated leaky barrier wakes

Leaky barriers serve as a soft-engineering approach for river management and have become indispensable for river restoration and bank stabilization. In this study, we idealized multiple full-span leaky barriers as horizontally arranged cylindrical arrays with uniform diameters (d) and equal spacing (0.5d). Flow field visualization was conducted using tracer techniques, and particle image velocimetry was employed to quantify the effects of blockage ratio on wake structures behind these barriers. Results demonstrate that flow deflection induced by barrier obstruction generates a primary jet through basal gaps. The maximum velocity of the primary jet (u¯max) increases with the blockage ratio (ψ), reaching 2.82–4.43 times the average velocity of the incoming flow (U0). The primary jet retains initial velocity at x/d≤0.5, decaying linearly within 0.5<x/d<2.4. Within 2.4<x/d<8, the decay rate diminishes due to jet merging and weakened adverse pressure gradient. Multiple secondary jets emerge within inter-cylinder gaps and are deflected by the low-pressure zones downstream of cylinders. These jets coalesce before merging with the primary jet. Coherent vortex bands with elevated vorticity develop near wake shear layers, significantly enhancing turbulent kinetic energy in these regions. Jet interactions modulate velocity decay patterns in both primary and secondary jets. This work reveals fluid-barrier interaction mechanisms, advances hydrodynamic understanding of leaky barriers, and evaluates their ecohydraulic implications for riverine ecosystems.