Numerical Simulation of Discontinuously Vegetated Open Channel Flow to Estimate Effects of Vegetation Condition on Flood Mitigation

This study investigated the velocity structures and turbulent characteristics in vegetated open channel flow using computational fluid dynamics software FLUENT, aiming to identify the optimal vegetation distribution for mitigating flood disasters. A three-dimensional Reynolds stress turbulence model was first validated with the experimental data and then used to investigate properties of flow through vertically double-layered and discontinuous vegetation patches that occupy both sides of an open channel with different patch patterns—linear and staggered. Results indicate that the flow velocities within the gap zones are reduced by the sheltering effect of vegetation patches, with a significantly greater reduction observed for the flow through the staggered patch pattern compared to the linear pattern. Flow velocities in the main channel increased by 29% in the linear pattern and 36% in the staggered pattern compared to vegetated zones. The staggered vegetation pattern compensates for reduced velocities in vegetated zones with increased main channel velocities, enhancing discharge capacity and water conveyance. This redistribution makes the staggered pattern more effective for extreme floods. Additionally, it reduces the velocity magnitudes, fluctuations, and turbulent kinetic energy in the vegetated zones compared to the linear pattern, benefiting aquatic life. Thus, staggered vegetation patches provide an effective flood mitigation strategy and promote positive outcomes for ecosystems and sediment deposition, highlighting the innovative finding of the study.