3-D Numerical Investigation on Effect of Flow Structure and Water Level on Vegetation Distribution in an Open Channel

Abstract

The in-stream vegetation is recognized to have significant ecological and aesthetic importance in managing floods and restoring rivers. However, it also disturbs the velocity of running fluid by increasing the resistance of flow, and raises the water level because of reduced discharge area at times of flood. Therefore, it is very important to study the hydraulic characteristics of vegetation distribution, and this study carried out a numeric simulation for quantitative and qualitative analysis. The simulation applied Navier-Stokes solver based on PBM (Porous Body Model), LES (Large Eddy Simulation) and VOF (Volume of Fluid), and the estimated drag coefficients of vegetation with Reynold's number. A comparison between the measured and calculated water depth and depth-averaged velocity found that conventional and new experiments were highly consistent. A numeric water tank was also used in this study to discuss the hydraulic characteristics of vegetation by measuring the velocity and water level depending on different vegetation zones and incidental conditions. The result showed that full vegetation in an open channel reduced velocity and raised water level because of the drag of vegetation, while half vegetation on one side or at certain part of the channel substantially reduced the hike of water level. Therefore, vegetation should be distributed appropriately when applying that in river management or restoration after an accurate analysis on the hydraulic characteristics of vegetation distribution.