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Venice Floods After Dike Activation Fails

Monday, December 14, 2020

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Only two months after the newly inaugurated Mose flood barriers protected the city of Venice from acqua alta’s seasonal flooding, the city streets were reported to once again be underwater after the barriers failed to be activated last week.

According to reports, the barriers are only activated when tides are predicted to excel 1.3 meters (4 feet, 4 inches), however, on Tuesday, Dec. 8, while the tide was predicted to reach 1.25 meters, it ended up rising to 1.38 meters by the middle of the afternoon.

MOSE History

The Mose barriers were reportedly first designed in 1984 to protect the city against extreme weather—most notably, Venice’s flood on Nov. 4, 1966, which brought in 194 centimeters (6 feet and 4 inches) of water into the city. The barriers are named from the more functional Modulo Sperimentale Elettromeccanico, meaning Experimental Electromechanical Module.

Made up of 78 submerged gates positioned at the three mouths of the lagoon, the food barrier system was designed with the capabilities to be raised during acqua alta in order to protect the lagoon against high tides ranging from 110 centimeters to three meters. According to reports, these gates are split into four barriers, which include multiple gates to admit vessels through.

During low tides the gates are full of water, keeping them completely invisible in housing when inactive. In practice when the area is experiencing high tides, compressed air is introduced, causing the barriers to rise up and block the flow of incoming tides.

While the barriers were originally expected to go into service in 2011, La Stampa notes that the project underwent serious episodes of corruption, sanctioned in a trial which ended in 2017, revealing bribery to cover up work and project plans described to have poor design and even worse execution, having experienced a variety of construction delays.

In pushing through the variety of setbacks, in 2017, the project’s infrastructure was also reported to have undergone accelerated corrosion and technical problems. Having been partially installed roughly three and a half years prior an inspection in 2017, the Mose barriers were already reported to be showing signs of erosion from mold and mussels. Additionally, remaining barriers that hadn’t yet been installed in the water, were showing signs of rust from the salt air, despite special varnish applications.

Through further testing, it was discovered that some gates were completely unable to rise, while others couldn’t retract due to the accumulation of sediment. At the time, the infrastructure was also reported to have experienced several problems with the pipe system, was causing erosion of the lagoon bed and had also experienced the explosion of a housing structure.

If that wasn’t enough, a special 52 million-euro ($61.2 million) boat created to transport the gates for maintenance failed its first attempt at lifting one of the barriers for repairs.

In an analysis commissioned by the Administration of Public Works of Venice, the working branch of the Minister of Infrastructure, Mose risked structural failures due to electrochemical corrosion caused by the marine environment and due to the use of a different steel than that which was originally used during the tests. The analysis concluded that the 156 hinges connecting the gates to the concrete housing—each one weighing 36 tons—were at extremely high risk (a probability of 66%-99%) of being unusable.

While the project was originally expected to cost 1.6 billion euros, in 2017 that had already inflated to 5.5 billion euros, having missed its 2011 inauguration. Following the inspection report of that same year, reports claimed that the barriers would require another 700 million euros for repairs and at least 105 million euros per year for guaranteed function and maintenance.

In July of this year, the flood gates were tested successfully under the supervision of Italy’s Prime Minister Giuseppe Conte. To date, the project has been reported to cost over 7 billion euros.

Most recently, in October Mose was put to the test during the city’s first day of acqua alta or “high waters”—seasonal flooding caused by high tides.

In wake of a 135-centimeter-high tide forecast, Mose Commissioner Elisabetta Spitz confirmed the barriers would be activated that day, should levels reach predictions. They did, and the infrastructure proved successful.

Since its inauguration, the barriers have been activated a total of five times, including a three-day-long period at the beginning of December.

As part of the barrier project, next steps involve raising the city’s pavements in the lowest areas of the city raised to 110 centimeters and permanent defense walls construction near the existing flood barriers. Work is expected to be completed by December 2021.

At that time, Mose will also commence its trial phase and all project infrastructure will be handed over to the jurisdiction of the Italian state and controls will be handed over to the Venetian authorities.

Barrier Failure

With predictions of tides rising just 2 inches under what would have activated the barriers to lift, residents of Venice were left to deal with the flooding consequences of a low-balled estimate. As a result, half the city was under water, even reaching the raised walkways in St. Mark's Square, which CNN reports are usually cantilevered over lesser flooding levels.

According to Carlo Alberto Tessarin, on the board of the procurators of St Mark's, who oversees Byzantine Basilica of St. Mark, the structure—which dates back to the 11th century—suffered serious damages, in addition to neighboring restaurants, shops and businesses.

“We're underwater to a dramatic extent, the damage is serious,” he said. Adding that the church was still recovering from last year's flood, as the salt water has eaten away at the marble-clad interiors and even when dried, marble will continue to absorb the salt, spreading as far up as seven meters.

Since the event and with more bad weather in sight, the barriers were officially raised. Moving forward, Venice authorities report that they’re seeking more of a say in the decision of the infrastructure’s use, instead of having to go through the national government every time.

Currently, even with lengthy process of getting approval, the barriers reportedly take several hours to raise.

   

Tagged categories: EU; Europe; Flood Barrier; Health and safety; Infrastructure; Port Infrastructure; Program/Project Management; Project Management; Safety

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