Analisi delle caratteristiche morfometriche e sedimentologiche di un meandro a marea in laguna di Venezia

Branching and meandering tidal channels, provide preferential pathways for the tide to propagate and for the transport of sediments within tidal systems, thus playing a critical role on their morphodynamic evolution. To address issues of conservation of tidal systems, exposed as they are to the effects of climate changes and increasing human interference, it is therefore of critical importance to improve current understanding of the origins and evolution of tidal meandering channels, together with their morphological characteristics, and the sedimentary structures emerging from their evolution. The present work addresses this important issue, focusing on the study of meandering tidal channels cutting through the San Felice salt marsh, in the northern part of the Venice Lagoon. The study is carried out by combining morphometric and sedimentological analyses, together with mathematical modeling. The planimetric configuration of a network of saltmarsh channels (determined through the use of a high resolution aerial photograph) was analyzed on the basis of a mathematical model that allowed us to quantitatively define the morphological characteristics of considered network. The sedimentological analyses were focused on a small winding channel, where 100 cores across 16 transects were collected. These analyses have allowed us to distinguish three main types of deposits: salt-marsh deposits, channel fill deposits and tidal-flat deposits. Their correlation has emphasized the presence of an erosive trend in proximity of the channel tip, whereas a depositional trend dominates the portion of the channel towards the outlet section. The occurrence of a lateral migration of the meanders that characterize the small channel is also observed based on the sedimentological structures. A mathematical model was then applied that allows one to describe the fundamental characteristics of the hydrodynamic circulation in tidal areas, such as the distribution of the bottom shear stresses, which control the erosion processes. The sedimentological analyses support modeling results, as well as conceptual and mathematical models of channel initiation previously proposed in the literature, according to which headward erosion is a major process in network development. The results show limited similarities between meandering fluvial and tidal channels, and suggest that the study of tidal meanders requires the development of specific theories and modeling frameworks, challenging the possibility of applying models developed for fluvial settings.