Mose system protects Venice from flood risk

A sophisticated dam system built to protect Venice from flooding withstood the challenge of an exceptionally high tide this week as heavy rains swept across Italy.

Weather bulletins had forecast a tide of 170 cm (5.58 ft) for Tuesday – near record levels – raising an alert for potential flooding that could have left large areas of the lagoon city under water.

However, the Mose, a system of 78 flood gates rising from the Venetian lagoon floor, was activated in advance overnight, shielding the city from the high waters seen at sea.

Over the years, the city has been affected by regular high tides, or “acqua alta” in Italian, as in 2029  when the city was devastated by the second-highest tide ever recorded.

The occurrence is caused by a combination of factors exacerbated by climate change, from rising sea levels and unusually high tides to land subsidence that has caused the ground level of the city to sink. 

“If the Mose barriers had not been there, Venice would have been catastrophically under water,” Italy’s Transport Minister Matteo Salvini said.

Designed in 1984, the multi-billion project is aimed at protecting Venice from tides of up to 3 metres, well beyond current records, but over the years, the project has been plagued by corruption, cost overruns and prolonged delays.

The Mose scheme, both an acronym for the project’s name in Italian and a reference to the biblical prophet Moses, first began operating in October 2020.

After decades of initial controversy, the building of the MOSE began in 2009, with the last “fin” installed in June 2019, on the Lido side of the Treporti island.

The Venice lagoon is notoriously shallow – the average depth is just 1 metre (3.3 feet). But the inlets from the Adriatic are much deeper: Malamocco, the entrance to the industrial port is 14 meters (46 feet) deep, for example. Although they didn’t alter the depth of the inlets, engineers excavated the seabed along all three to make room for the concrete ‘cases,’ which fit flush along the seabed.

High tides are expected to last well into Thursday this week, with a tide of up to 140 cm forecast.