Flow field alteration due to permeability and subcanopy flow for emergent vegetation

The present experimental study investigates the effects of emergent tree-like vegetation on the flow field. Two major flow alteration mechanisms are noted, namely the flow through a porous element and the subcanopy flow. Firstly, a simple artificial porous element simulated the vegetation to deduce the pertinent physical mechanisms. This element comprised a hexagonal array of circular cylinders, which was placed on top of a wooden rod to simulate the tree-like canopy or directly to the flume bottom to simulate reedy vegetation. The results show that the porosity in the "reedy vegetation" leads to a long flow recovery distance, mainly due to the steady wake region, which inhibits the lateral mixing. However, the subcanopy flow in tree-like vegetation disrupts this effect by enhancing the vertical mixing. Subsequently, the flow through a natural tree-like plant (Cupressus Macrocarpa species) is assessed with the aid of the previous findings.