Quasi-3D model to simulate flow in straight channels within vegetation patches

Graduate School of Advanced Science and Engineering, Hiroshima University, 1-4-1 Kagimiya, Highashi-Hiroshima City, Hiroshima 739-8527, Japan

^* Corresponding author: d222200@hiroshima-u.ac.jp

Abstract

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.