High tide flooding in Venice is one of the city’s unique features. It’s nothing more than a high flood peak, affecting the city only during autumn and winter – mainly in November and December.

But since the beginning of the 20th century the situation has gradually got worse. Why?

What happens during high tide flooding in Venice?

In every sea, tides rise for 6 hours and fall in the following 6. The peak causing acqua alta (high tide flooding) therefore occurs in the middle of the rising phase.

  1. How is high tide flooding measured?

High tide flooding is measured according to the mareographic zero at Punta della Salute. When the highest tide expected is above 110 cm, people are warned. But since 97% of the surface of Venice is around 100 cm above the sea level, the level of water is a major problem only in the lowest areas of the city.

  1. The case of Saint Mark’s Square

The only problem is that the lowest area in the city is Saint Mark’s Square. An exceptional high tide flooding – i.e. above 140 cm – thus means 60 cm of water in the heart of Venice’s old town.

  1. How to protect Venice?

Here’s why building the mobile barriers of the MOSE system – whose control system can be seen at the “Punto Mose”, in the northern area of the Arsenal – was fundamental: to protect the artistic and cultural heritage of the cities on the lagoon, but most of all their inhabitants.

Then why is high tide flooding getting more and more critical?

Why is high tide flooding a serious problem for Venice?

The reasons are six:

  • in the last decades, floodings have become more frequent and grown in intensity: there’s a higher risk of disasters like the record flooding of November 1966 – the tide reached 194 cm – happening again;
  • as well as difficulties for citizens and their houses and shops, tides cause a slow deterioration of the buildings and the ecosystem in this area;
  • Venice risks being flooded because of two reasons: first of all, due to the historical phenomenon of subsidence, which sees the city slowly sinking; secondly, the rise of the Mediterranean sea level, related to the climatic events we all know;
  • erosion is the consequence of diverting river courses from the lagoon and, in the post-war period, of removing sand and gravel from riverbeds. This means that the amount of sand brought to the sea by rivers has decidedly shrunk;
  • in the last 60 years, the countryside has been gradually abandoned: uncultivated fields are much less easily eroded than cultivated ones, so the sea receives a smaller amount of sediments. And, as a consequence, the sea moves forward;
  • the greenhouse effect, causing glaciers to slowly melt and, as a result, sea level to rise.

So, whether danger is upon us or not, Venice and the other cities on the lagoon need to be protected.

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