Mose have defended Venice 44 times since the start of its use on October 3, 2020, with 20 saves in the first year, 13 in the second and 11 in the autumn-winter season. However, there are some problems to solve and work to complete. The studies conducted in these first two years of use have highlighted some critical issues in the use of the worksuch as the impact on sediment inflow and oxygen starvation, which must be carefully evaluated by the control room that decides when to raise dams.
The lowering of the seabed
The picture presented on January 12 by researcher Luigi Tosi at the Corila conference on the results of 4 years of work on the Venice-2021 research program is worrying. In addition to sea level rise, which could reach a range of 28-55 centimeters in the event of emissions containment or 63-100 centimeters in the worst-case scenario, there is also the problem of subsidence. Currently, the lagoon bed is sinking by 3.5 millimeters a year and by 1.5 in the city of Venice, but by 2050 it is expected to decrease by 6.5 millimeters per year. This means that the seabed could drop by about four inches in 30 years. For this reason, Luca Zaggia of Ismar-Cnr, who coordinated the first part of the conference on the risks of the lagoon which is increasingly becoming an arm of the sea, hoped that the lifting rules of the Mose will soon change to limit these impacts.
The protection of Piazza San Marco
A recent positive news is the start of the works to protect Piazza San Marco, which once completed will make it possible to raise the Mose when the water level in the lagoon reaches 90 centimetres, compared to the current 70. The reason is that the closure of the inlets reduces sedimentation by 25-30% per year, but if the alert threshold were 130 instead of 110 (as currently in the experimental phase), the reduction would be only 10%. When the water in the lagoon is shallower, the seabed is more exposed to the waves and the sediments are raised into suspension. The defense of Venice is not in question, but there are counter-effects on the morphology of the lagoon that need to be corrected. Help to limit the loss of sediments could come from the new sludge protocol, which according to the estimates presented by Marco Marani of the University of Padua could limit it from the current 614,000 cubic meters per year to 178,000.
The anoxia problem
The work carried out by Corila in recent years has been of great quality, which has led to the publication of a hundred articles in various scientific journals, underlined Pierpaolo Campostrini, Director of Corila. With regard to MOSE, the institutions present at the final round table declared that they were available to collaborate to resolve the problems encountered. At the moment there are no alarms, but only phenomena that are being studied, for example anoxia could be a problem if Mose were to close even in the summer.
The vulnerability of Venice
Venice’s vulnerability is not only linked to its geographical position and the rise in sea level, but also to overtourism, i.e. unsustainable tourist flows that contribute to the transformation of the city’s social fabric. According to a study by Ca’ Foscari University, the optimal number of visitors per day would be 52 thousand peoplebut in the spring of 2022 a peak of 100,000 visitors was reached.
For years, the passage of large ships in Venice has been one of the main causes of wave motion, which has caused significant damage to the lagoon. After the failure of the Clini-Passera decree of 2012, in 2021 the Council of Ministers established the entry ban for ships over 25,000 tons. This decision, described as historic by the then minister Franceschini, made it possible to prevent Venice from being included in the list of UNESCO sites in danger.
The proposal to lift the city
Over the years, several proposals have been presented to safeguard Venice from rising sea levels and damage caused by waves. The study “Venice shall rise again” by Giuseppe Gambolati and Pietro Teatini from 2013 proposes to raise the city by injecting fluids (pre-treated salt water) into the underground geological sedimentary layers hundreds of meters deep. The simulations carried out indicate the possibility of raise Venice by 26 centimeters at an estimated cost of 80 million euros.
Measures to protect housing
The Municipality of Venice is taking measures to protect the residential area of the city and counter overtourism. On the one hand, they are promoting initiatives to encourage tourists to stay longer in the city, on the other they are evaluating the introduction of higher entrance fees for those who visit the city for just one day. Since 2021, tourist flows have been monitored by the administration through the Smart Control Room, which provides daily estimates on the presence and origin of visitors.
