Understanding the interaction between flow dynamics and riparian vegetation is essential for effective river management and conservation of the river environment, including the river ecosystem. Numerical simulations have emerged as a valuable tool for this purpose, offering cost-effective and scalable approach. In this paper, we conducted a comparative analysis between the Bottom Velocity Computation (BVC) method for quasi-three-dimensional models, which is the enhanced depth-integrated model with sub-grid three-dimensional model, conventional two-dimensional model, and three-dimensional model to explore the three-dimensional (3D) flow effects induced by the presence of vegetation patches. The vegetation resistance evaluation method for non-equilibrium open channel flows was extended to two dimensions and incorporated into the equations for the BVC models to evaluate the interaction of the vegetation, three-dimensional eddy motion, and turbulence in a depth-integrated model. Our simulations focused on straight channels containing patches of vegetation. The results showed that the velocities within the vegetated areas were observed to decrease, while velocities in non-vegetated areas increased. Moreover, the BVC model showed consistency with experimental data compared to 2DC model. Specifically, the 2DC model tended to overestimate velocities in non-vegetated areas due to its inability to capture momentum transport from non-vegetated areas. This discrepancy highlights the importance of considering 3D flow effects for simulating flows in vegetated areas.
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