For a more selective management of the Mo.S.E

More selective management of Mo.S.E. could continue to protect Venezia and the other lagoon settlements from high water, while at the same time reducing the negative effects on salt marshes. This is what emerges from a study coordinated by the Department of Geosciences of the University of Padua and published in Nature Water, in which the University’s Departments of Land, Environment, Agriculture and Forestry and of Civil, Environmental and Architectural Engineering, the Istituto Superiore per la Protezione e la Ricerca Ambientale and the Università di Southampton also took part.
 

The effects of closures on salt marshes

Since 2020 the barriers have limited the inflow of tides through the inlets, keeping water levels in the lagoon lower. However, the closures also reduce the supply of sediments to the salt marshes, biodiversity-rich environments that store carbon, dampen wave motion and grow vertically thanks to the materials deposited during high tides and storm surges.

The researchers reconstructed with numerical models all 69 closure events that occurred between 2020 and 2023. According to the results, in 30% of cases an alternative strategy would have made it possible to avoid closure without compromising urban safety.The alternative AThOS strategy
“We compared three scenarios: the Lagoon with the inlets always open, the Mo.S.E. management actually adopted, and an alternative and optimised strategy called AThOS,” explains Alessandro Michielotto, research fellow in Geosciences and first author of the study. AThOS aims to “reduce the number and duration of closures”, while keeping water levels below the safety thresholds set for Venezia, Burano, Chioggia and the other lagoon settlements.

With the management adopted in the early years, the area of flooded salt marshes decreased on average by 27.5%, with peaks above 75%, while the average water depth fell by about 45%. “During the period examined, closures reduced sediment accumulation on salt marshes by 32%,” says Alvise Finotello, researcher in Geosciences . The loss is equivalent to an average reduction in vertical growth of 2.6 ± 1.9 millimetres per year, against a relative sea-level rise of about 4–5 millimetres annually.

The simulations also indicate that the annual duration of closures was on average more than double what was strictly necessary. “It would have been possible to avoid about 30% of closures, that is around twenty events out of 69 in total,” notes Luca Carniello, lecturer at the ICEA Department of the University of Padua.
With AThOS, the reduction in flooded salt-marsh area would have fallen from 27.5% to 2.9%, and sedimentation would have increased by 19%, recovering about 1.3 millimetres per year of vertical growth.

According to Andrea D’Alpaos, coordinator of the study and lecturer in Geosciences, Mo.S.E. management appears already to have progressively evolved: “The management of the barriers is not static, but can be improved over time in the light of data, accumulated experience and the effects observed.”
 

Towards adaptive management of Mo.S.E.

The outlook is therefore for adaptive management, capable of assessing when closure is truly necessary and of limiting its duration. “It is in this direction that there lies the concrete possibility of protecting both the city’s historical, cultural and urban heritage and the integrity of the lagoon ecosystem,” D’Alpaos concludes.