Analisi dell'evoluzione morfodinamica di un meandro a marea in laguna di Venezia

The present work deals with the morphodynamic evolution of a meandering tidal channel in the San Felice salt marsh, in the North-Eastern part of the Venice Lagoon. This study aims at improving the current knowledge on the evolution of tidal meandering channels and their morphological characteristics. Towards this goal, we carried out sedimentary facies analyses and morphometric analyses. The comparison of aerial photos highlighted that the portion of the marsh through which the studied channel develops, experienced relevant changes in the last 70 years. Interestingly, we observed that morphological changes at the marsh scale, lead to an increase in channel width and to a decrease in channel sinuosity in the considered period, thus challenging the validity of the assumption of increasing tidal channel sinuosity in time. The sedimentological analyses focused on two tidal bars along the study channel, where 52 cores (1-3 m deep) across seven transects were collected. These analyses allowed us to distinguish between salt-marsh, top-bar, bar and channel lag deposits. The depositional architecture found through these analyses showed an overlap of outer bank bar sediments on point bar sediments. This means that sediment deposited on the outer side of the channel which can be interpreted as a signature of the progressive decrease in the sinuosity. Mathematical models were used to study the morphometric features of the tidal meandering channel. Model results allowed us to quantitatively analyze the decrease in channel sinuosity, the increase in channel width, and the increase in the tidal fluxes which shape the channel. Other relevant geomorphic features like the spatial distribution of bottom shear stresses on the marsh surface and the drainage density of tidal networks were analyzed to quantitatively evaluate the effects of morphological changes which characterized the study area. Interesting differences between tidal meanders and their fluvial counterparts emerge