In 2050 80 percent of the salt marshes of the Venice lagoon will be definitively submerged. It’s the fault of subsidencesea level rise but also the Moses he’s putting his own spin on it. This is according to research from the Institute of Geosciences and Georesources of the Cnr of Padua recently published in the scientific journal «Science of the Total Environment». «The MOSE is necessary and there is no question about it – stated Luigi Tosi, research director -. However, when it was designed many decades ago there was little knowledge of the possible consequences. Now we have the technology and the tools to say in which direction to act. How do you fix it? We have to plan salt marshes nourishment, exactly like we do with beaches.” Otherwise, in the space of a few decades, 16 kilometers of salt marshes that now emerge between 25 and 50 centimeters above sea level and 18 kilometers of those that now barely emerge at 25 will be submerged. This is shown by the progression of the data collected in the last twenty years and developed by the Cnr research team with an eye to the future and also to the contribution of the MOSE.
The numbers of the phenomenon
The projection of acceleration of the prevalence of water on the emerged land speaks of 30 centimeters more in the space of thirty years. «The rise of the sea statistically from the 1990s to today has a progression of 3.5 millimeters per year and the lowering of the ground in Venice varies from 1 to 4 millimeters per year – continues the researcher -. But the data is much more accentuated in the northern lagoon and in the southern area compared to the area involving the historic center of the city”. The map developed by the team clearly shows the vulnerable areas, those in which the orographic variety risks being canceled out: they vary from bright pink to scarlet red and are all concentrated in the northern lagoon and in the southern area, between Fusina, Chioggia and Malamocco. Inhabited Venice will be spared but surrounded. «The sea rise is homogeneous for the entire Adriatic. Subsidence, however, is not – continues the research manager -. If we add the two data, we are talking about 4-6 millimeters per year.” Vulgarly speaking, the city and lagoon sink half a centimeter per year on average but it can also reach 6.5 millimetres.
Action and obstacles
Rise of the Adriatic and sinking of the land they can only be stopped with global action on the climate which still seems distant. One thing, however, is possible at a local level. «The salt marshes are fed by the tides: when they are submerged, sediments accumulate on top of them and thus maintain their size. But with the Mose, there is no longer this movement”, they explain from the Cnr. It is also widely documented and observed that sand and debris tend to accumulate where they are not neededor: in the lagoon canals, close to the arches of the Liberty bridge and in other places where they cause problems. For a long time it was not possible to sort them elsewhere because the old sludge protocol provided for stringent rules and the only thing that has been able to grow in recent years with that slime is the artificial island of the seabed at the mouth of the Malamocco canal known as Tresse. From the vicious circle of port and navigation problems where debris is in excess and morphological debasement where it is scarce, It’s time to take it to the next level. «We need to urgently intervene to nourish the salt marshes — urges Tosi —. And we need to start now because it will take years before the effects can be appreciated.”
