Mean Flow and Turbulence in Compound Channels with Vegetated Floodplains

The study of flow in compound channels with vegetated floodplains is essential to assessing the development of the stage-discharge relationship and sediment and pollutant transport. The present study experimentally investigated mean flow and turbulence characteristics in a prismatic compound channel. The experimental program consisted of vegetated and non-vegetated floodplains with different relative depths. The results show that vegetation had a significant effect on the flow characteristics of streamwise, lateral, and vertical velocity and Reynolds stress. For a given relative depth, the conveyance capacity of the channel decreased up to 31% for a vegetated floodplain over a non-vegetated floodplain. Although, the depth-averaged velocity varied significantly across the main channel, it was fairly constant over the vegetated floodplain. Strong secondary currents and lateral momentum transfer between the main channel and its floodplain led to high gradients in the depth-averaged velocity, bed shear stress, and turbulent kinetic energy at the interface.