Flow Characteristics in a Two-Stage Vegetated Compound Trapezoidal Channel

In this paper, the impact of vegetation on various flow parameters that create a complex flow field between the main channel and the two-stage floodplains has been studied. A three-dimensional computational model of Reynolds stress turbulence code FLUENT (ANSYS) simulated the various flow and turbulence characteristics. The geometry consisted of a two-stage compound channel, in which the flow structure of both vegetated (with varying density) and non-vegetated cases was studied. The results showed that an array of vegetation along a two-stage floodplain imparted more flow resistance as compared to a single-stage floodplain which resulted in shifting higher velocities zone toward the main channel flow. Moreover, for a dense arrangement of vegetation, depth-averaged velocity increased from 16 to 28% for three different flow depths measured at the center of the main channel, i.e., Y/B = 0.2 (where Y represents the transverse direction and B is the channel width). Due to the gradient of secondary flow, velocities, and vortices between the main channel and both floodplains, transverse shear stresses were higher around the vegetation. Vegetated two-stage floodplains acquire low turbulence and Reynolds stresses, thus making them suitable for sedimentation and the formation of biological species.