The climate is changing and water levels are starting to rise. It’s hard enough for the rest of the world to handle the situation, but the labyrinthine canals winding their way through Venice can’t afford any more flooding.

A 2004 photo of Piazza San Marco with flooding from high tides. Source: Wolfgang/CC BY-SA 3.0The historic city is sinking, the lagoon waters are encroaching, and residents are living in fear of “Acqua Alta,” the seasonal high tides that come in off of the Adriatic Sea. They’re turning to engineers for hope.

Flooding and problem-compounding structural subsidence are the twin threats. The geology of the region is fragile accompanied by a human element at work. Tourists arrive en masse to visit sights like St. Mark’s Basilica and the Rialto Bridge, exacerbating the issue. What those selfsame engineers have developed to counter the flooding is MOSE (Modulo Sperimentale Elettromeccanico), a mobile tide barrier.

Venice’s watery future seems bleak

The floating city is located on the northeastern coast of Italy and is renowned for its canals and stunning architecture. The beautiful architecture is sinking and the lagoon waters are on the rise.

Underneath those buildings, reinforcements have been installed to slow the sinking. Liquid grout has even been injected into the ground to stabilize the city, but that measure is a stopgap. Everything possible has been tried to stabilize the ground, leaving us to wonder what initiatives are being taken to lower the rising water levels.

The ambitious MOSE project

Italian engineers were never going to accept this bleak outlook, which is why MOSE was commissioned. In design, it’s a series of 78 mobile gates. They’ve been strategically installed across several narrow channels. At Chioggia, Malamocco, and Lido, the barriers regulate those Adriatic tides, preventing Acqua Alta from causing more flooding in the Venetian streets.Diagram of MOSE operations. Source: Magistrato alle Acque di Venezia - Consorzio Venezia Nuova/CC BY-SA 3.0

The MOSE project website gives an informative overview of the engineering solution, providing a small map of the inlet locations and gates. The project started in 2003 and has seen its share of challenges and controversies over the years. However, despite setbacks, the MOSE project is on course for completion. In fact, it’s already been put under pressure. Back in 2020, the partially completed tide barrier was deployed when storms pummeled the outer islands. The tide’s impact was held in check.

At any rate, other than the 6-billion-euro development and construction costs, plus those setbacks and accelerating flooding risks, it’s the mechanics of the project that draw the attention of engineers. How do these floating yellow gates operate when they’re deployed during a flood?

Diving into the gate mechanics of the Venice tide barrier

The MOSE project relies on conventional laws of physics. At heart, the Ministry of Infrastructure and Transport built the gates to rise via injected air power. They’re large, hollow steel boxes. Filled with water and submerged in their concrete seabed housings, they rise to the surface when compressed air is forced inside their hollow inner compartments.

Buoyancy is, therefore, key here. With each gate 20 meters in length and proportionately scaled to match the depth of each of the three channels, it takes the system somewhere between four and five hours to fully activate the tide barrier, so flood warning monitoring is crucial.

A full breakdown of one of these cycling operations has to be viewed from underwater, deep inside the Venetian lagoon. From the surface, the bright yellow squared-off gates just seem to pop into existence. Deep down toward the concrete seabed cradles compressed air is introduced into the metal, box-like gates via a sluice system. The water is displaced, and the barrier segments swing to the surface on hinges.

The 20-meter-wide gate boxes float on the surface like this for the duration of the high tide event, only sinking below the surface again when the flooding threat passes. Accomplishing this, they’re filled with water again and returned to their submerged concrete enclosures until next time.

The holistic vision of the Venice tide barrier

The devastating effects of high Adriatic tides and tourist-crowded streets need management. The MOSE project, floating upward on buoyant compressed air is one solution. To support it, the foundations of heritage buildings are receiving reinforcement, grassroots activism has partnered with governmental planning to ease the influx of visitors, and more engineering work is incoming.

By raising public quaysides and restoring the lagoon ecosystem, hopefully mitigating the effects of the high Adriatic tides, the waterways will experience some normalcy. Meanwhile, the addition of filtration units, early warning systems, and other technologically oriented defensive measures will work in concert with MOSE to preserve Venice’s architecture and history.

How engineers are protecting Venice’s past and future

Perceived as the cornerstone of their efforts, the MOSE floodgates are purposely designed to promote simple operability. Although tagged with that €6 billion bill, many of these costs are a result of delays and controversies. The actual design is straightforward and elegant. Water weighs down the container-like metal gates, keeping them in their concrete enclosures. Air is pumped into them when an early warning system signals a flood threat, and then they rise on hinges, floating as tide barriers.

The MOSE project represents a significant step in protecting Venice from the devastating effects of high tides. Once completed—no later than 2025—the system will provide a much-needed defense against rising tides, safeguarding the city's cultural heritage and ensuring its continued prosperity.

London has a similar system and other nations will be watching. Every country is going to be impacted by future high tides, not just Venice. It’s the historical lagoon city that’s at the thin edge of the climate wedge, facing imminent danger from worldwide tidal changes—waiting to see how well MOSE protects an ancient city for decades or more.