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Venice’s MOSE flood barriers rise for the first time

Parting the Lagoon

Venice’s MOSE flood barriers rise for the first time

Boat traffic on a dreary Venetian day (Sinziana Susa/Unsplash)

It’s about time: Last week, the $6.6-billion MOSE project, started in 2003 (but envisioned all the way back in the ‘80s) to protect Venice from flooding, successfully raised its gates for the first time.

When complete, supposedly in 2021, MOSE will consist of 78 yellow sea gates intended to swing into action during Acqua alta, or high water, when the Adriatic Sea inundates the Venetian Lagoon and causes dangerous flooding throughout the city. With climate change-induced sea-level rise, well, rising, and Venice sinking, the system is needed more than ever. At the end of 2019, Venice was submerged after experiencing its worst flooding in 50 years, with parts of the ancient city left under six feet of water, including the 925-year-old St. Mark’s Basilica.

The MOSE barriers are intended to sit at the bottom of the lagoon, fill with air when needed, rise, and subsequently seal three inlets leading to the Venetian Lagoon at noncontiguous points, which they successfully accomplished for the first time on October 3. Officials had predicted that tides on that day would reach 4.27 feet—not historic, but more than enough to flood the city. Although water levels only reached 2.3 feet on October 3rd, MOSE’s first deployment went off without a hitch.

The system is designed to accommodate floods of up to 10 feet (3 meters), which is well beyond historic records (though not outside of the realm of possibility in a wetter, warmer world). Aside from the obvious dangers in having a city flood, the MOSE project is intended to keep Venice’s water levels consistent to ensure the long-term health of the historic buildings there: If the canals rise and retreat, the non-waterproofed brick above the waterline is eroded by salt, allowing water to infiltrate the foundation and erode the sediment between the wooden piles and the building’s stone base.

While the technical specifications are seemingly sound, concern has been raised over the frequency of MOSE’s deployment. While only needed a handful of days per year at the time of writing, it’s estimated that the barriers could be deployed up to 187 days under a worst-case sea level rise scenario between 2050 and 2100. If that happens, the Venetian Lagoon would be essentially cut off from the Adriatic Sea, preventing pollution from flushing out of the city and depleting the lagoon’s oxygen levels.

Still, the test last week was a momentous occasion; the MOSE project was supposed to have been completed in 2019 but missed that target due to cost overruns, construction delays, and corruption within the Italian government.

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