Floodplain Vegetation Contribution to Velocity Distribution in Compound Channels

ABSTRACT: The flow in compound open-channel is characterized by a complex flow structure due to the interaction between the main channel and floodplain which is often home to a lot of kinds of vegetation. This paper describes the results of an experimental study on the influence of floodplain vegetation on velocity distribution in compound channels. For vegetation on the floodplain, rigid cylindrical rods 1 cm in diameter are used. The local flow velocities for different densities of vegetation were measured using a 3D acoustic Doppler velocimeter. The results showed that that after implanting the vegetation over the floodplain, the depth averaged velocity over the floodplain increases whereas it increases in the main channel. Also, the depth averaged velocity decreases in both the main channel and floodplain with an increase in the vegetation density. The maximum value of the streamwise velocity was found to decreases with vegetation density. While it was found that a major vortex forms in the main channel for smooth floodplain, two distinct vortexes (free surface and bottom vortexes) were observed for the tests with vegetated floodplain