Numerical Investigation of the Effect of Rigid Vegetation at an Inclined Bank, on Streamflow Hydrodynamics

Abstract

This study is a computational analysis of hydrodynamic alterations of flow such as secondary current, turbulent kinetic energy, and shear stress, in an open channel with an increased vegetation density at an inclined bank. Two arrangements of rigid vegetation at an inclined bank, linear and staggered, are investigated for five different vegetation density. The computational analyses are performed under constant flow and stable bed conditions. The variations of stream wise flow velocity, turbulent kinetic energy, and Reynolds stress along the main channel are evaluated and presented for each vegetation density. The results illustrated the impacts of vegetation density on the entire channel flow characteristics. These results are further analyzed based on average bed shear stress calculations. The main outcome of the study demonstrated that combined effect of inclined bank and effect of partly obstructed flow significantly generates Kelvin-Helmholtz type instability due to the presence of inflection point at different location along a vegetation cover. The calculated Reynolds stresses are higher at the main channel bed near the vertical bank, but shift to midflow depths near the boundary between the main channel and inclined bank. The turbulence kinetic energy profiles in the main channel and at the inclined bank exhibited results that were similar and parallel to the simulated stream wise velocities and Reynolds stresses. Furthermore, it is found that the ratio between bed shear stress and turbulent kinetic energy is almost 0.3 as the depth approaches the channel bed.