The Projected “MOSE” Barriers Against Flooding in Venice (Italy) and the Expected Global Sea-level Rise
Paolo Antonio Pirazzoli and Georg Umgiesser
Three meteorological and surge events that occurred during the last decades are analysed, simulating that a relative sea-level rise of 0.5 m (average IPCC prediction for the year 2100 + local subsidence) has taken place and that the MOSE gates (the planned mobile protection against flooding of Venice) could have been in operation. In all cases considered, flooding would have occurred in the lowest parts of Venice, lasting for dozens of hours, in spite of raising the street level. Problems would start for a sea-level rise of about 20-30 cm, or even today for a repetition of the 1966 event. This is both because the projected gates are not watertight, and rainfall and river discharge contribute to raise the average water level in the lagoon. Therefore, the MOSE would be inadequate to protect Venice in the case of a near-future sea-level rise. Temporary “diffuse” interventions seem preferable to the MOSE gates, because they would be safer for the environment and bring back the frequency of flooding to the very acceptable level of about one century ago. They could even avoid floods completely by using movable containers that could be temporarily sunk to completely close the inlets when necessary. This would make possible to gain at least a few decades, thus giving time to narrow the large uncertainty ranges of present-day estimations. Only with a closer assessment of near-future sea-level rise will it be possible to decide which type of “hard” defence would be eventually necessary to save Venice and its lagoon. Anyway, a stricter control of water pollution should be a priority intervention.