Flood Barrier Successfully Protects Venice
For the first time in decades, the city of Venice put its flood barriers into practice, successfully keeping the city dry during its first day of acqua alta or “high waters”—seasonal flooding caused by high tides.
The barriers, also known as Mose (Italian for Moses), are named from the more functional Modulo Sperimentale Elettromeccanico, meaning Experimental Electromechanical Module.
According to reports, the Mose barriers were 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 (six feet and four inches) of water into the city.
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.
Venice gets 78 #floodgates to save the #city from future floods Venice is one country that has been experiencing heavy...Posted by The Live Media on Wednesday, October 7, 2020
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.
Most recently, 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.
In wake of a 135-centimeter high tide forecast, on Oct. 3, Mose Commissioner Elisabetta Spitz confirmed the barriers would be activated that day, should levels reach predictions. They did, and the infrastructure proved successful.
“Today, everything is dry. We stopped the sea,” City Mayor Luigi Brugnaro told reporters at the time. “Lots of bad things have happened here, but now something wonderful has happened.”
According to CNN, St. Mark’s Square in the city (which usually floods at just 90 centimeters), remained fairly dry with only large puddles swelling around the drains. It was also reported that while tides rose to 132 centimeters outside of the Mose barriers, tides measured only 70 centimeters within the lagoon.
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, where all project infrastructure will be handed over to the city.