LINKAGES BETWEEN FLOW, MORPHODYNAMICS AND VEGETATION

Riparian areas are typically colonized by a wide variety of vegetation species and types, including woody trees, bushes, and shrubs. The presence of vegetation has a significant impact on the flow field, playing a key role in shaping river morphological evolution. The stems, branches, and leaves of riparian vegetation alter the flow dynamics, modify turbulence patterns, and affect bed shear stress and sediment processes. These vegetation-induced effects are further expected during overbank flows and floods, as the threshold for sediment mobility is often exceeded, resulting in dynamic changes to bedforms, bars, and channels. The combined influences of flow dynamics, sediment transport, and vegetation create a complex interplay within river environments. Understanding these intricate interactions is of utmost importance for accurately modeling the morphological evolution of channels and implementing effective management strategies for river environments. This thesis is based on experimental activities conducted to investigate the flow dynamics and sediment transport characteristics in river environments featuring leafy flexible vegetation and large-scale bedforms. The experimental setup encompasses both mobile-bed and fixed-bed conditions, representing the final morphology of mobile-bed scenarios, enabling a novel analysis of flow characteristics, turbulent fields, and resistance composition in the different conditions. The obtained results highlight the notable influence of leafy flexible vegetation on controlling bedform geometry and sediment transport processes. Surprisingly, contrary to previous studies, the data demonstrate that the presence of vegetation increases dune celerity, consequently enhancing sediment transport. This effect is likely attributed to the increased turbulence caused by the presence of leaves. To model this process, a turbulence-based model for predicting bed-load transport is corrected using the new dataset. Under mobilebed conditions, this study reveals deviations from the linear superposition principle of the hydraulic resistance in setups incorporating leafy plants. This indicates the introduction of non-linear effects in the combined contribution of dune and vegetation form drag to the overall flow resistance. Accordingly, in fixed-bed conditions, direct measurements of the hydraulic forces exerted by both dunes and leafy flexible plants yield similar results, confirming the initial hypothesis. This study demonstrates that the presence of leafy flexible vegetation significantly influences the hydrodynamics and morphodynamics of river systems, affecting bedform geometry and sediment transport processes. These findings deepen the understanding of the intricate interactions among flow, sediment transport, and vegetation within river environments, offering valuable insights for the development of improved river management strategies. A crucial aspect of this advancement involves the abandonment of rigid cylinder models in favor of more realistic representations of flexible vegetation.