On the effects of vegetated bars on river hydrodynamics

In this work, we modelled the main interactions between the flow field and the vegetation settled on fluvial macroforms. The case study is a reach of the Arno River (Florence, Italy) near the confluence with the left tributary Greve River. We elaborated a 3D mesh grid and characterised the current vegetative condition of the reach according to both topographic and vegetation surveys. We evaluated the associated Manning coefficients and applied a two-dimensional hydraulic model (BASEMENT) for simulating scenarios of different vegetation maintenance conditions. The aim is to identify vegetation scenarios that maybe associated to a healthy ecosystem while considering the hydraulic constraints due to the river limited conveyance. We found that the dense and rigid vegetation, mostly growing in the absence of maintenance, induces higher bed shear stress on the right hand-side of the main channel, thus increasing erosion at the bank toe and eventually leading to failure of the riverbank.