The role of seasonality and plant morphology on wake characteristics behind a patch of natural-like riparian vegetation

Behind a riparian vegetation patch, wake characteristics including a region of reduced flow velocity and increased turbulence may promote sediment deposition and further vegetation growth, thus understanding riparian vegetation-associated flow and wake characteristics is crucial to studying and developing predictive models for hydromorphological processes. Through flume experiments we explore the flow structure downstream of a circular vegetation patch of complex morphology to investigate the impact of seasonality and reconfiguration on wake features. To this end, three cases including one leafless, and two foliated plant patches representative of riparian species were tested under two flow conditions. The findings reveal the presence of leaves and branches to affect the mean and turbulent flow fields generating additional mixing as compared with models based on rigid cylinders. Due to the complex volume distribution in the vertical direction, three-dimensional flow structures were attained downstream of the riparian vegetation with the vertical flow forcing generating mixing that inhibited formation of the von Karman vortex street. In contrast, the flow structure downstream of the leafless patch was similar to that obtained for rigid cylinders with the occurrence of two-dimensional flow field. The differing plant morphologies affected the reconfiguration process consequently impacting wake size. The main differences were obtained for the lowest bulk flow velocity tested with the plant patch comprising longer leaves that streamlined and aligned with the flow resulting in smaller wake width than the elliptical leaves plant patch.