A two-layer eddy viscosity model to predict the near-bed hydrodynamic in vegetated flows

Flow-vegetation interaction in aquatic vegetation canopies affects various ecosystem services. The hydrodynamics within the bottom boundary layer in vegetated channels governs sediment transport, sediment-oxygen exchange, pollutant dispersion etc. However, the dynamics of the vegetated boundary layer is still poorly understood due to the challenges associated with direct flow measurement within the boundary layer. In this work we perform wall resolving Large Eddy Simulations (LES) to explore the boundary layer dynamics in flow through a dense (solid volume fraction, Φ = 0.09) array of rigid emergent cylinders for varying Reynolds Numbers (Re ∈ [8,20]x10⁴). The mean flow statistics far from the bed exhibit a self-similar behavior with Re. However, the flow within the boundary layer shows significant dependence on Re, which leads to variations in near-bed flow statistics. To elucidate the effect of Re on near-bed hydrodynamics, we perform quadrant analysis to identify the contribution of intense events to the generation of Reynolds stresses. We quantify the near-bed Reynolds Stress to develop a novel two-layer eddy viscosity model for vegetated flows for varying Re. This has numerous applications including, but not limited to, stream restoration, sediment transport, blue carbon, and microplastic transport.