As early as the 1970s, Italian authorities began contemplating how to save the city from the water masses, and since 2020, Venice has a unique solution in place: a 1,560-meter-long chain of flood barriers, known as MO.S.E.
However, seawater is an aggressive environment for many materials. Following the first full-scale trial of the system, it was discovered that key parts of the barriers had started to corrode.
Nicolas Larché, Site Manager at Institut de la Corrosion, a subsidiary of RISE, was hired to inspect the corroded elements of the MO.S.E. barriers and develop a plan of action. He has witnessed up close the destructive forces of nature and humanity's struggle to master climate change.
“The authorities in Venice called us in to understand how the corrosion had occurred, and our preliminary investigation revealed that it was due to an initial incident. Seawater had accumulated along certain tensioners and stagnated, causing corrosion on several surfaces,” he explains.
Thorough inspection yielded positive results
The MO.S.E. barrier consists of 78 hollow gates, which are filled with water when the barrier is lowered. In the face of a flood threat, compressed air is pumped into the gates from underlying plants, or galleries, to drain them of water. This raises them above the surface, protecting the city from up to three meters of water rise. After the commissioning, the seawater that inadvertently had penetrated the galleries had begun to wear down some of the tensioners (hinges) responsible for keeping the gates in place. This insight, along with data indicating atmospheric corrosion inside the galleries, raised concerns.
In collaboration with Euro Anticorrosion Service, EAS, Nicolas Larché optimised and utilized a precise 3D laser technique for measuring and tracking the progression of corrosion. The data was used to quantify the barrier's lifespan and maintenance requirements. They also installed sensors to continuously monitor the corrosivity of the atmosphere near the tensioners. Air conditioning systems were installed in the galleries to purify and dry the air. The tensioners were also treated with a layer of moisture-repellent grease.
Finally, they took samples from the tensioners, which are subjected to very high loads during tidal movements, and conducted tests to simulate how well they withstand the force and frequency of tides, in presence of existing corrosion.
The result was rather reassuring. Despite existing corrosion, the barrier is expected to last for at least another 100 years, provided that all the data is correct, and the circumstances remain roughly the same.
“To be on the safe side, we also conducted a simulation where we doubled the tidal frequency and increased the load with 30 percent. The simulation showed that even then, the lifespan would be over a hundred years. But, of course, we must regularly check that our hypothesis is correct, so we will conduct routine inspections to track the evolution of the corrosion,” says Nicolas Larché.
An effective solution for Venice
The conclusion is that Venice's solution works well for Venice, as long as the corrosion is closely monitored and actively counteracted. But Venice is just one of many cities heavily affected by rising sea levels. What can we learn from MO.S.E. and its challenges?
“Venice is very unique, it's a city out in the sea, in a small lagoon. Seawater can only enter the city through three main gates, making the barrier system possible. Copying the concept in other locations would probably be difficult, but it is not unthinkable that some form of physical barrier could be constructed in places with a similar configuration,” says Nicolas Larché.
Rising sea levels are just one of several problems the world is now facing due to climate change. The increase in temperature has also led to other types of corrosion problems.
“In terms of corrosion, global warming is of great significance. Temperature is a key parameter. A project the Institut de la Corrosion is currently working on concerns corrosion issues due to growth of Sargassum seaweed. The increase in its growth can be due to rising temperatures and human pollution. Sargassum seaweed floats into the coasts where it dries and dies. In the process, it acidifies the environment and releases toxic gas. The atmosphere becomes extremely corrosive and can affect the durability of surrounding metallic structures.”
Important to act
So, how should coastal communities act in the future to tackle the challenges posed by climate change? Nicolas Larché explains that he is not a climate expert, but he believes that authorities worldwide should review the inspection frequency to align it with climate change. This way, problems can be detected and predicted before it's too late.
“RISE and Institut de la Corrosion can investigate how temperature changes or rising water levels affect infrastructure and provide advice on appropriate measures. We can also help continuously adapt existing anti-corrosion systems to new climate conditions. In addition, we actively develop methodologies to study the effect of corrosion and anti-corrosion systems on the environment. Thus, we do not only study the impact of the environment on the materials, but also consider the impact of the materials on the environment.”
Photo:
Pexels, Matt Hardy
