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History And Facts About Floods in Venice: What Is The Acqua Alta?

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If you have heard about the famed lost underwater city of Atlantis, then acqua alta might seem similar to you with the city of Venice under high water.

Acqua alta is a natural phenomenon that happens when high tides occur in combination with long waves and winds. The term is only used when the water level rises over 35.4 in (90 cm) above the sea.

The phenomenon used to occur most of the time in autumn and winter. But in recent decades, the water level has been rising all around the year. The most affected part of Venice due to the flood is Piazza San Marco or St. Mark's Square, significantly the most famous region. Global warming has led to an increase in the occurrence of acqua alta. The melting of glaciers and ice caps has detrimental effects on the environment. It would be best not to confuse a typical flood with acqua alta. The water level must rise to a certain level to be called acqua alta.

The public is informed well in advance about any upcoming flood with the help of SMS services and newspapers. Sirens are activated a few hours before the flood to warn the people. The locals have got accustomed to this, and you may even see restaurants serving food to the patrons who sit on chairs kept in the water. Rubber boots are available in the city for everyone to use during acqua alta and are found even in souvenir shops around the city for tourists. It is almost a common thing for local people in their day-to-day lives.

If you found this article on acqua alta interesting, then you must check out similar articles on the first woman to fly around the world and first quarter moon facts.

How long does Acqua Alta last?

Acqua alta in Venice does not last for more extended periods of time. It will only stay for about three to four hours.

When some specific events coincide, favorable conditions for acqua alta happen. These might include the presence of a very high tide that occurs during a new moon or full moon phase, low atmospheric pressure, and a sirocco wind blowing in the narrow Adriatic Sea. The wind causes water to flood the Venetian Lagoon. The water level in Venice stays high for only some hours and goes down soon enough when the canals revert to their normal stage.

How often does Acqua Alta happen in Venice?

The phenomenon of acqua alta has existed for hundreds of years in Venice. The frequency of the high tides has increased with each passing year.

The first records of acqua alta date back even before the Middle Ages. Records of the phenomenon are found from the sixth century. The phenomenon became a topic of study towards the end of the nineteenth century. Scientists have been analyzing the floods to predict any upcoming acqua alta and prepare in advance.

The tide reaches above 31.5 in (80 cm) about 50 times a year, but it is called acqua alta only if it crosses 35.43 in (90 cm). This happens a few times per year, especially above 43.3 in (110 cm). Such high tide was once very rare, only once in four years, but nowadays, it might happen more than four times in one year alone. Minor flooding in Venice occurs at all times, and it is common for the people.

What month does Venice flood?

The phenomenon of acqua alta is quite common in Venice during the spring and winter seasons. It mainly occurs for a few days between October and January. At least it used to in the past.

Its frequency has changed in the past few decades due to climate changes. You might come across acqua alta even in September and April nowadays. But be prepared to witness this phenomenon any time of the year. While visiting the city in the winter and fall months, you must keep a pair of rubber boots in your traveling bag. This is even more important if your visit coincides with a new moon or a full moon as the tide remains high during this period. The phenomenon is not dangerous, and people try to visit Venice more during acqua alta since the views are very beautiful and unique, especially the reflection of St. Mark's Basilica.

What causes the Acqua Alta?

Since acqua alta is a natural phenomenon, it is caused due to high tide and a combination of winds and waves. The tide coincides with sirocco (south-east wind), low air pressures, and seiche (oscillating currents in the Adriatic Sea).

The wind prohibits the water outflow, and on such occasions, the waters rise and enter Venice. The sea is connected with the help of three harbor entrances that is called 'bacche di porto' in Italian,, which means port mouths. The entrances consist of Chioggia, Malamocco and Lido.

Tide control stations are scattered throughout Venice; the lagoon, open sea, and the city. Punta Della Salute is the place that serves as the reference point at the zero level. It has been in use since 1906. If the tide goes above 31.5 in (80 cm), it is known as acqua alta. The lower regions in the city are more affected during such scenarios.

Although it is primarily a natural phenomenon, there are some non-natural or manufactured reasons behind the increasing frequency of acqua alta in the past few decades. Porto Marghera is an industrial area in Venice that is part of the problem. When it was being built, a few lagoon areas were reclaimed. These areas had the function of serving as additional water basins. Furthermore, the people dug a deep canal to pass through oil tankers. The flow rate of the lagoon got increased by several degrees due to the canal. Some other construction works are also reasons behind the high floods. Mention might be made here of the Ponte della Libertà and the railway bridge. The city has lost about 11 in (28 cm) of altitude during the last 137 years because of these construction operations. Pumping natural gas and water from the ground due to industrialization is more contributing factor. Adding to these, climate change due to global warming has further increased the rate of floods. The melting of glaciers is a growing concern for the people of Venice.

Piazza San Marco faces the brunt of the high tide due to waters coming from the shallow Adriatic Sea.

Preventing The High Tides

The MOSE Project by the Italian government of Venice was supposed to provide solutions to acqua alta. Work went on for this project for a prolonged period of over ten years. The intention behind the project was to protect Venice by installing a system of dykes or flood barriers and rows of mobile gates that would control the water level. Hundreds of millions of euros were spent on constructing the defense system.

It was completed in 2014, but severe corruption complaints from environmental groups tainted the project. Two years later, in 2016, the project results were heavily criticized by UNESCO. The criticization came since the project overlooked the natural and cultural aspect of the Venetian Lagoon, threatening to subject it to irreversible damage. The multibillion infrastructure involves 78 remote-controlled MOSE gates that rise when required blocking high tide from entering the Venetian Lagoon. The argument against it is that the rising rates of acqua alta will ensure the gates be used more, thereby trapping the city's sewage in the lagoon, which would harm the environment.

A new MOSE barrier was activated for the first time on October third, 2020. It was successful in blocking a 51 in (129 cm) tide. On this historic day, the lowest part of the city around Piazza San Marco remained free from water. It has been used several times since then with the same success, but it has to be kept in mind that the MOSE is activated only when the conditions are severe. The flood barriers are saving Venice from the rising sea levels. The MOSE gates can be compared to Rotterdam's Maeslantkering protecting it from the North Sea or London's Thames Barrier. The salt marshes in the Venetian Lagoon have been cultivated to check the sea-level rise.

Preparing Yourself During Acqua Alta

Are you planning to visit Venice during the fall and winter months? Read on to know what to do if you encounter acqua alta and how to prepare yourself before going.

Rubber boots are essential when you pack your bags. Or you might even consider taking several plastic garbage bags along with elastic strings or bands to keep them in place. The mention of garbage bags might not sound elegant to you, but they are convenient when it comes to keeping your feet and shoes dry. Even if you forget to carry boots with you, do not worry. You can buy these boots in the Italian city itself. Plastic rain boots are also available in souvenir stalls and street hawkers. But remember that you might not find boots that fit if you have larger than average feet. The plastic boots should be used as a last resort as they are not great for the environment, and these are only a temporary solution. They do not last long. Try to avoid buying these from souvenir shops located around tourist hotspots such as Piazza San Marco, as they will cost you a premium. The best would be to carry wellington boots and overalls.

It is also doubtful that you will face trouble during your stay in Venice due to acqua alta since it is not dangerous at all. Even during 1966, when the record acqua alta occurred, and the whole of Venice came underwater, not a single person drowned. Raised walkways are built around the city in low-lying regions that allow the people to walk freely while keeping their feet dry. These are made of wood, and a map of the routes is available in most of the ACTV Vaporetto stops. Remember that these walkways can be used only if the water level is under 47.2 in (120 cm). Once the water crosses this height, you have no option but to use rubber boots or maybe disposable shoe covers.

A siren is sounded across Venice if the tide goes above 43.3 in (110 cm) to alert the people. The siren consists of one long sound as soon as the water level crosses 43.3 in (110 cm) and increases to four sounds if it reaches 55.1 in (140 cm). The sirens are activated much earlier if it is expected for the water to exceed 43.3 in (110 cm). You can be prepared in this way about any upcoming acqua alta. The local people are alerted through SMS services and phone calls. The internet can also help you view detailed forecasts across Vaporetto stops all over the city.

The most affected parts of Venice are the outer borders of Dorsoduro and Piazza San Marco (St. Mark's Square). You may have seen pictures of the St. Mark's square submerged in water with people sitting at café tables with their ankles in water as if it is usual for them. This is true that most of the well-known restaurants in St. Mark's Square remain open when an acqua alta occurs, and they take pride in that. You can join them and take a table yourself while away the time in the Italian city. Although the area looks very stunning at this time, you might want to avoid coming here if you wish to enjoy a moment alone from the crowd. Most tourists want to see the basilica from the lagoon side, and they all come to Piazza San Marco to get a glimpse of it. For a quieter experience that can also be unique, you can go walking along the delicately beautiful campi and calle of Dorsoduro instead. You may see some cafes and shops closing in regions under very high water, but most of the city remains active as usual. The locals go to their work or shop for groceries without paying any heed to the water. The buildings in Venice have been constructed in such a way for hundreds of years that the tides and the lagoon pose no barrier to them. The living quarters are always built on the first floor or above it.

If you want to avoid the water and enjoy acqua alta from a distance, head to one of the higher districts inside the city, such as Cannaregio. You can visit the many museums in Venice and enjoy acqua alta as you would embrace a rainy day anywhere elsewhere. While walking on the sidewalks beside canals, be careful as the edge between the canal and land is often unclear.

Acqua Alta Facts

The worst affected acqua alta happened in the last century on November four, 1966. The maximum height of the sea level rose to 76.4 in (194 cm) and was given the nickname acqua granda due to the unusually high tide. The historic day made many people homeless in Venice and caused serious damage to several Venetian buildings. The artistic heritage of the city also took a hit. Over 75% of shops in Venice either got destroyed or damaged. The city was devoid of any people for more than two days. The water was so high that boats sent to rescue people could not go under bridges to reach the homes. There was no electricity for days.

The second worst acqua alta occurred in 2019 November, with water reaching 74 in (187 cm). The disaster of 1966 ensured that electrical lines were now installed higher up, and the city did not have to face a power outage in 2019.

Here at Kidadl, we have carefully created many interesting family-friendly facts for everyone to enjoy! If you liked our suggestions for history and facts about floods in Venice: acqua alta, then why not take a look at history and facts about Clermont: The First Steamboat or the first woman to fly around the world?

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