Effects of Vegetation Canopy Density and Bank Angle on Near-Bank Patterns of Turbulence and Reynolds Stresses

Vegetation growing on the surface of a streambank has been shown to alter the shear stresses applied to the boundary, but basic questions remain regarding the influence of vegetation and streambank configurations on near-bank hydraulics. In the present study, Froude-scaled flume experiments were used to investigate how changes in vegetation density (ratio of frontal area to channel area, including both stems and leaves) and bank surface angle influence near-bank turbulence intensities (RMSu,v,w) and Reynolds stresses (τuv and τuw) estimated using velocities obtained with an acoustic Doppler velocimeter positioned beneath the canopy. Results illustrate how, with increasing vegetation density, turbulence intensities and Reynolds stresses decreased along the sloped bank surface but increased at the base of the slope and within the main channel. The steeper bank angle resulted in greater vertical stresses on the bank surface than the shallower angle, but lateral momentum exchange was larger than vertical exchange along the base of the slope, regardless of bank angle. Leaves were an important influence on near-bank turbulence intensities and Reynolds stresses, whereas the influence of bank slope was small relative to the influence of vegetation density.