Turbulent flow characteristics over gravel bed channel with submerged vegetation patches

This experimental research investigates the turbulent flow dynamics in a narrow open channel with submerged finite uniform patches of flexible and rigid vegetation placed along the sides of the channel at equal intervals. A Sontek FlowTracker 2.0 Acoustic Doppler Velocimeter was used to collect instantaneous velocity data to evaluate essential turbulent flow attributes, including velocity profiles, Reynolds shear stress, higher-order moments, and turbulent bursting events. The findings indicate that the maximum intensity of the turbulence occurs at the inflection point immediately above the plant's canopy. Vegetation greatly affects the flow structure, reducing velocity in the vegetation zone and increasing velocity above the vegetation canopy. Compared to the upstream non-vegetation zone, the depth-averaged flow velocity increased by 24% above the canopy, diminished by 19% below the canopy, and increased by 12% in the downstream non-vegetated zone in flexible vegetation. For rigid vegetation patches, the depth-averaged flow velocity increased by 23% above the canopy, diminished by 25% below the canopy, and increased by 5% in the downstream non-vegetated zone as compared to upstream non-vegetation zone. Quadrant analysis revealed the occurrence of sweeps and ejections more nearer to the vegetated bed. Furthermore, the arrangement and placement of the vegetation patches were pivotal in diminishing flow velocity and affecting momentum transfers between vegetated and non-vegetated zones. These findings indicate that submerged flexible and rigid vegetation significantly modifies flow patterns, increasing turbulence and dispersing turbulent loads. The research enhances comprehension of flow-vegetation dynamics in natural channels, impacting riverbank stability and ecological habitat management.