Interactions between bedforms and open channel flows through submerged vegetation

The presence of vegetation changes the flow and thereby modifies the river bedform. This study explores the characteristics of the bedforms and their interactions with the overlaying flow through submerged vegetation. Different types of turbulent flows are generated in a laboratory flume, and the bed topography and turbulent statistical parameters are measured. Results indicate that the bed morphology is characterized by the horseshoe scour holes around individual plants and the gully-ridge pattern in the wakes. These bedform features do not significantly influence the hydrodynamics in the free shear flow. However, the horseshoe scour holes, the gully-ridge pattern and sand ripples intensify the vertical variation of the flow velocity and promote the vertical momentum exchange in the bed shear flow. Besides, the horseshoe scour holes, the gully-ridge pattern and sand ripples persist in the 'quasi dual-flow' regime. These bedforms are found to promote momentum exchange and inhibit turbulent sweeping within the canopy layer. Above the vegetation canopy, however, these bed features are found to inhibit momentum exchange and promote turbulent ejection.