Tidal Flow Asymmetry and Discharge of Lateral Tributaries Drive the Evolution of a Microtidal Meander in the Venice Lagoon (Italy)

Abstract

Tidal landscapes are extensively characterized by the presence of meandering channels, the latter being important for the ecomorphodynamic evolution of these environments. It remains unclear whether changes in the relative strength of maximum flood and ebb currents (i.e., tidal flow asymmetries), together with the widespread presence of lateral tributaries, cause tidal meanders to evolve differently from their fluvial relatives. Here, we investigate the evolution of a meandering channel in the Venice Lagoon (Italy) that receives water from two major tributaries along its outer bank. Using a 2‐D numerical model, we first analyze the changes in local tidal flow asymmetries, both natural and anthropogenically induced, which occurred during the last 120 years. The effects of these modifications on the meander morphodynamics are then investigated by means of a 3‐D numerical model, and results are compared to modern and historical field data spanning more than one century. We show that under asymmetric tidal flows, tidal meanders develop depositional patterns according to the dominant flow direction, similar to that of fluvial meanders. In addition, the morphological effects of the nondominant tidal flow become increasingly negligible as tidal flow asymmetry increases. We also show that enhanced sediment and water fluxes from major lateral tributaries, sourced from wind‐wave exposed tidal flats, can critically influence the development of erosional and depositional patterns within tidal meanders otherwise sheltered from wind action by the presence of salt marshes.