Numerical Modeling of Flow and Sediment Dynamics Around an Isolated Submerged Flexible Vegetation

Abstract

This study investigates the hydrodynamics and sediment transport processes around an isolated submerged non-uniform flexible vegetation (FV) element in an open-channel flow using FLOW-3D HYDRO. The observed reconfigured FV shape is represented using a hybrid solid–porous configuration with a height-varying frontal area and porosity. Numerical simulations incorporate the RNG k–ε turbulence model, the saturated Forchheimer porous-media formulation, and Nielsen’s bedload transport formulation, and are validated against laboratory measurements of velocity profiles and bed elevation changes. Results show that FV induces a distinct three-layer flow structure, with a velocity deficit within the canopy and an accelerated shear layer at the canopy–water interface. Flow vectors reveal wake formation and coherent vortices that promote sediment mobilization, while turbulent kinetic energy (TKE) peaks above the canopy due to shear-layer instabilities. A C-shaped scour hole develops at the FV base, followed by downstream deposition, consistent with experimental observations. Although computational fluid dynamics (CFD) slightly underpredicts the maximum scour and deposition magnitudes, it effectively reproduces the centerline bed-elevation trends (R2 = 0.92) and key morphodynamic patterns with satisfactory agreement. The proposed robust and computationally efficient CFD framework demonstrates the capability of reproducing complex flow–vegetation–sediment interactions in vegetated channel systems and is applicable to river restoration, sediment management, and ecohydraulic design.