Navigating the first years of flood regulation in the Venice Lagoon - a delicate balance between humans and nature

Coastal areas, such as deltas estuaries and lagoons, are highly dynamic environments shaped by the interplay of depositional and erosional forces. While providing a multitude of valuable ecosystem services, spanning from wave-energy dissipation to habitat provision and carbon sequestration, they also serve as important hubs, supporting large populations. 
However, communities living along low-lying coastal environments are currently threatened by rapidly rising sea levels and the intensification of the extreme events, which increase the flooding risk.

To reduce the risk of floods, different engineered structures (e.g., flood-gate barriers) have been adopted worldwide. Here, we present a study delving into the first years of operation of the Mo.S.E. system, the mobile storm-surge barrier system activated in the Venice Lagoon starting from October 2020. The research aims to investigate the impacts of the flood regulations, exploring the potential counter-effects of water level reductions on the lagoonal ecosystems.

During storm surges, floodgte barriers at the three lagoon inlets are raised to temporarily disconnect the lagoon from the open sea, keeping water levels below a prescribed safety threshold to avoid the flooding of the city of Venice. However, the intertwined action of wind waves and reduced water levels may generate an intensification of the eorional processes across the tidal flats. The reduced water levels negatively affect also salt-marsh sedimentation. Although erosion processed can increase the suspended sediment volume within the tidal basin, lower water levels reduce salt-marsh flooding depths and duration, and the sediment deposition over marsh surfaces.

We also explore a hypothetical scenario considering an optimized flood regulation procedure, aimed at reducing the duration of flood-gate closures. Slightly higher water levels, prescribed by the optimized regulation, would allow sediment deposition over salt-marsh surfaces without compromising the preservation of urban areas from flooding.

Our findings offer valuable insights, underscoring the paramount importance of promoting effective defensive intervention policies. Our results might help to identify feasible solutions that better balance the preservation of  coastal urban areas with the protection of natural coastal ecosystems