Impacts of emergent rigid vegetation patches on flow characteristics of open channels

Abstract

This study examines the influence of emergent vegetation on flow dynamics in natural river systems using large eddy simulation. It specifically addresses alterations in flow velocity and turbulence characteristics within open channels with varying densities of vegetation. The findings reveal a marked reduction in flow velocity within vegetated areas due to the obstruction posed by vegetation and the dynamics of shear layers. The flow alteration manifests in two distinct phases: the formation of a stable wake region behind densely vegetated patches and a more gradual velocity recovery in areas with sparser vegetation. In non-vegetated downstream zones, flow velocity tends to stabilize over a distance. Regarding turbulence, the study identifies differing patterns: enhanced vortex structures and accelerated energy dissipation in sparsely vegetated areas, contrasted with reduced turbulence in densely vegetated patches. Quadrant analysis further elucidates that ejections and inward interactions are primary contributors to Reynolds stress within vegetation patches, whereas outward interactions and sweeps become dominant in downstream regions. These insights offer a deeper understanding of how aquatic vegetation shapes river hydrodynamics, providing valuable information for effective river management and ecological restoration strategies.