Investigating natural and anthropogenic impacts on the hydrodynamics of the Venice Lagoon (Italy), a numerical approach

The ongoing threat to coastal areas is well documented worldwide. The dynamic equilibrium of these landscapes is governed by the interaction of erosional and depositional processes and it is therefore critically affected by the intertwined effects of increasing anthropogenic pressure and climate changes, such as the increasing rates of sea level rise (SLR) and the intensification of extreme events.
The various human pressures which affect coastal areas can have several impacts on their evolution. As an example, the Venice Lagoon, the largest brackish water body in the Mediterranean Sea, has been extensively affected by human interventions, such as the diversion of the major rivers in the Renaissance period, the excavation of navigable channels, and the construction of jetties at the inlets in the 20^th century. In addition, after the November 1966 flood event, when water levels reached the maximum value ever registered in Venice (194 cm above the Punta della Salute reference datum) and heavy rainfalls caused the surrounding rivers (Piave, Brenta and Sile) to overflow, some defensive structures were designed and later adopted to reduce the flooding risk of the city of Venice and the surrounding floodplain. As an example, the levee which separates the Sile River and the Venice Lagoon was modified by building a spillway allowing the river flood to debouch into the lagoon. More recently, the mobile barrier system, known as Mo.S.E., designed to protect the city of Venice and the surrounding urban settlements from flooding has been activated, regulating the high water levels due to storm surges. However, the impacts of such defensive structures on lagoon hydrodynamics and morphodynamics remain poorly understood.
In this work, we applied two numerical models to investigate the potential effects of increasing anthropogenic pressures combined with a changing climate, on the hydrodynamics of the Venice Lagoon. The two-dimensional wind wave tidal model, coupling a hydrodynamic module with a wind wave module, allowed us to evaluate the effects of SRL (based on IPCC projections) on the lagoon hydrodynamics. In addition, the model allowed us also to analyse the possible effects of the repeated activations of the Mo.S.E. system on lagoon hydrodynamics and on the related ecosystem services, comparing regulated and non-regulated present and future scenarios. Finally, an integrated three-dimensional hydrodynamic model, was used to account for changes in water density (e.g., changes in water salinity) in the above described scenarios, thus monitoring the dynamics of salinity gradients under extreme conditions, driven by freshwater inflow through the Sile River spillover.