Double Layered Vegetation for Flood Mitigation: A CFD Study on Flow Resistance

Abstract

This research addresses the use of vegetation as a bio-shield for mitigating flood water flow. Mostly single-layer vegetation is often used; this paper investigates whether double-layered vegetation would be more effective. A numerical model using Computational Fluid Dynamics (CFD) in ANSYS Fluent was explored to simulate water flow through various vegetation setups. The model was built on the Volume of Fluid (VOF) method and was validated against experimental data. The behavior of single- and double-layered rigid vegetation under different vegetal density conditions and flow rates has been investigated in this study. Results demonstrate that an increase in water level upstream, which indicates significant flow resistance, is strongly enhanced by dense and double-layered vegetation. The flow velocity within and directly behind the vegetation zone is strongly reduced. However, the most important finding is the sharp increase in the water speed in the gap regions beside the patches. Generally, double-layered vegetation can slow down the flow and dissipate its energy; hence, it is less likely to be damaged. It is concluded that a vertically double-layered vegetation system is more resilient and efficient in being a bio-shield for mitigating flood impacts on riverbanks and coastal areas than a single layer is. Future work may focus on the optimization of the arrangement of the vegetated patches, considering gaps with inclinations, to better control high-velocity zones for improving the design in real-world applications.