Experimental investigation on dispersion mechanisms in rigid and flexible vegetated beds

Vegetation in channels strongly affects flow structure and turbulence, with consequences on the hydrological storage of nutrients and chemical tracers, the shelter of stream biota as well as the trapping or transport of sediments. At the same time, all these phenomena are inevitably subjected to alteration of hydrological conditions in fluvial systems due to climate change. The present study intends to provide a thorough investigation into the processes of transport and dispersion induced by flow turbulence within the vegetation structure. Specifically, velocity measurements in vegetated channels were intensively conducted and analyzed in the case of both flexible submerged and rigid emergent canopies. The experiments aimed to: (i) highlight the differences in the hydrodynamic structures induced by different plant types and configurations; (ii) study the spatially varying dispersive properties and turbulent behavior of the current, attributable to different plant density, submergence and stiffness. Further, the spatial variability of velocity and turbulence distributions was taken into due consideration. The experimental results showed how longitudinal and transversal hydrodynamics and transport differ, depending on vegetation configuration and stem properties.