Impact of Vallisneria natans on flow structure

In order to study the impact of submerged vegetation on flow structure, flume experiments were conducted to measure the mean velocity, the Reynolds stress and the turbulence kinetic energy of flow with Vallisneria natans canopy. Influenced by Vallisneria natans canopy, a logarithmic profile is generally presented above the canopy. As a difference exists in the vertical distribution of frontal area, a region with counter velocity gradient and a local velocity maximum appear inside the canopy. The Reynolds stress reaches maximum around the top of canopy and decreases gradually in both upward and downward. Due to the existence of counter velocity gradient, negative stress and a local stress maximum are produced within the canopy. Turbulence produced by shear stress makes turbulence kinetic energy reach maximum around the top of canopy and transmits vertically towards the bed. Restricted by the limited distance of the vertical transportation of turbulence, wake production becomes the major source of turbulence, and the turbulence kinetic energy diminishes dramatically at the bottom of canopy.