Venice Flooding: Why Is Venice Sinking?

Venice, the picturesque Italian city built on a network of canals and underwater channels centuries before, is no stranger to flooding. The city’s sea level location and intricate waterways make it particularly vulnerable to rising tides and heavy rainfall.

In recent years, Venice has experienced some of the worst floodings in its history, causing significant damage to buildings, infrastructure, and tourism.

On November 12, 2019, Venice was hit by a tide of water over 1.8m (5.9 ft) high. At its peak, more than 80% of the city was underwater. It was the second-worst flood ever recorded in Venice.

This article explores the causes and consequences of Venice’s frequent floods and the measures being taken to protect this beloved city from future disasters.

Facts	Details
Historical Flooding	Venice’s location, natural causes, and human causes are three primary factors. Acqua alta (high water) is a phenomenon where high tides and strong winds push water from the Adriatic Sea into the Venetian Lagoon, causing flooding.
Causes of Flooding	Three primary factors: Venice’s location, natural causes, and human causes. Acqua alta (high water) is a phenomenon where high tides and strong winds push water from the Adriatic Sea into the Venetian Lagoon, causing flooding.
Rate of Sinking	Over the last century, Venice has sunk by more than 9 inches. Annually, the city naturally subsides by an average of 1mm.
Cost of Flooding	In 2019, damages from flooding, including harm to structures, businesses, and lost tourism revenue, were estimated to exceed €1 billion.
MOSE Project	A system of mobile flood barriers designed to protect Venice from high tides and storm surges. Comprising 78 gates, the project began in 2003 and faced multiple delays. It is expected to be completed in December 2023.
Potential Solutions	Techniques like soil consolidation and soil stabilization have been considered to raise or stabilize Venice. However, these are expensive and complex solutions.
Future Predictions	Sea levels globally are rising at an accelerating pace. Venice could serve as a global hub for climate change solutions, guiding other coastal cities.

Why Does Venice Flood?

Venice is known among tourists for its beautiful canals and picturesque waterways, but it is also notorious for its frequent flooding.

Three major factors are at play for this slowly sinking city: Venice’s location, natural causes, and human causes.

1. Venice floods mainly occur due to a phenomenon called acqua alta (high water), which occurs when high tides and strong winds push water from the Adriatic Sea into the Venetian Lagoon. This excess water seeps onto the main island and causes Venice to flood.
2. Venice’s naturally occurring sinking problem, combined with the average sea level rising, results in the city facing a major problem and not just for the historic old Venetian buildings.
3. A combination of factors, including natural geological processes, groundwater extraction, and the weight of buildings on soft soil and shifting tectonic plates, cause Venice’s subsidence issues.

While the flooding typically only affects a small portion of the island, most notably St. Mark’s Square, which is just 55cm above the current average sea level.

“When you are this close to the upper limit of the tidal range, any meteorological event can be hazardous and cause an extreme flood,” says Piero Lionello, lead author of a report into the impacts of flooding on Venice for Natural Hazards and Earth System Sciences. “Small increases can have a large impact.”

Storm surges like the one in November 2019 have become uncomfortably frequent in recent decades.

When Did Venice Start Sinking?

Venice has been sinking since it was first settled in the 5th century and floods have been recorded since the 8th century. However, the sinking rate has increased significantly recently.

According to official city records, there have been 324 high-water events since 1872. More than half (187) have happened in the past 30 years.

In the 20th century, Venice began groundwater extraction from soil. The groundwater extraction caused the soil to compact and sink, leading to increased flooding in the city. In addition, the construction of large buildings and the dredging of canals further destabilized the soil, exacerbating the problem.

Is Venice Sinking?

Venice has sunk by over 9 inches in the last century alone. While this might appear minimal, it intensifies the flooding challenges. Even minor sea level rises can harm iconic structures like St. Mark’s Basilica considerably. Since its inception, Venice has sunk approximately 4 feet (1.2 meters).

Annually, Venice naturally sinks by an average of 1mm. This and the escalating sea levels due to climate change amplify the city’s susceptibility to flooding and erosion. This continuous soil deterioration compromises the integrity of buildings and infrastructure, heightening their risk of damage during floods or seismic events.

Venice’s average sea level is around 32cm higher now than it was when official records began in 1872. While they disagree on the amount, Scientists have a consensus that climate change is hastening this rise. A study from Natural Hazards and Earth System Sciences in 2021 indicated that Venice could see sea levels elevate anywhere between 17cm to 120cm by the year 2100.

How Much Does Flooding Cost Venice?

In the significant flood event on November 12, 2019, over 80% of Venice was submerged by nearly 6ft of water.

Subsequent floods that year led Mayor Brugnaro to estimate the damages, including harm to structures, businesses, and revenue losses from tourist cancellations, to exceed €1 billion.

This rising water isn’t just a short-term concern; it’s eroding Venice’s architectural heritage.

Many Venetian structures were constructed with waterproof basements using white Istria stone. Yet, the upper sections were crafted from bricks and mortar. The previously waterproof sections can’t fend off the current water heights.

The bricks absorb the sea’s salt. In humid conditions, this salt attracts moisture, and when the walls dry, the salt forms crystals. This repetitive process is gradually wearing down Venice’s brick and mortar.

How Does the City Deal with the Flooding?

Efforts are being made to address sinking and flooding by limiting groundwater extraction and using lightweight building materials, but it remains a significant challenge for Venice’s future sustainability.

However, Venice isn’t the only historic city facing higher tides. Neighboring Venetian islands, Murano, Burano, Lido, and others, are struggling with coastal flooding.

MOSE Project

The MOSE project is a system of mobile flood barriers designed to protect Venice from high tides and storm surges intensifying due to global warming.

The system consists of 78 gates, weighing around 300 tons, positioned at the three inlets to the Venetian Lagoon. When water levels rise above a certain threshold, the gates can be inflated with compressed air to form a barrier against the next incoming tide of water.

The MOSE project has been under construction since 2003 and was originally scheduled for completion in 2011, but it faced numerous delays and cost overruns.

However, when fully operational, it is expected to significantly reduce the risk of flooding in Venice and safeguard the city’s cultural heritage and economy.

Even incomplete, and as recent as November 2022, the MOSE project is actively helping prevent flooding. MOSE might be exactly what the city needs to mitigate the effects of high tide, but it doesn’t combat the true problem the city faces: climate change.

The project isn’t without its critics. According to National Geographic and other outlets, the system appears to have a long-lasting negative effect on the marshes that keep the Venetian Lagoon alive.

Venice’s MOSE flood barriers will be completed in December 2023, and we will learn more about how it can stop flooding and stem rising sea levels.

Can Venice Be Raised?

Technically, it is possible to raise Venice to some extent. However, it would be a very difficult and expensive engineering feat.

One approach to raising the city would be to pump water underneath its foundations to lift it. This technique, known as soil consolidation, has been used in other parts of the world to raise sinking buildings and infrastructure.

However, Venice’s size and complexity, along with its historic buildings’ fragile nature, would make such a project very challenging. If the city isn’t raised in unison, it could cause Venice’s buildings to experience structural damage.

Another approach could involve injecting grout or other materials into the soil underneath the city to stabilize it and prevent further subsidence. This technique, known as soil stabilization, has been used in other parts of Italy.

However, any attempt to raise Venice would be very expensive and would require a great deal of planning and coordination. It would also likely require the relocation of residents and businesses while the work is being done. It would also stop tourists from traveling to Venice, causing the city to lose its most precious revenue generator.

As a result, most experts believe that the best approach is to protect the city from further subsidence and rising sea levels through measures such as flood barriers, land use planning, and sustainable development practices.

As long as global warming continues, the Adriatic Sea will likely experience rising tides that plague Venice.

The Future of Venice

Sea levels are on the rise globally, and the pace of it is accelerating with each passing year. Venice is a clear warning sign highlighting the imminent threats of climate change and coastal flooding.

While the future of Venice looks bleak, the city is in a unique place to tackle these challenges as they have been for centuries. Venice might just become a global hub of climate change solutions as the rest of the world looks on.

The MOSE project and other efforts politically, economically, and technologically may guide other coastal cities to act before the changes are irreversible.

Update 09.13.2023

According to a report from NPR, UNESCO is deliberating on adding Venice to its list of endangered world heritage sites due to the combined effects of over-tourism, construction, and climate change.

UNESCO feels that the efforts by Italian authorities are insufficient.

Frequently Asked Questions about Venice Sinking

How Far Has Venice Sunk?

According to recent measurements, Venice has sunk about 9 inches (23 cm) over the last century, and the rate of subsidence is estimated to be around 0.08 inches (2 mm) per year. In addition, sea level rise is expected to accelerate in the coming years due to climate change, which could worsen the problem for the city.

What Is Underneath Venice?

Underneath the city of Venice, there are a series of wooden piles that have been driven deep into the ground. The piles, which are made of oak and larch wood, are driven through the layers of clay and silt that make up the Venetian lagoon until they reach the underlying bedrock.

The piles serve as the foundation for the floating city’s buildings, and their placement and spacing were carefully calculated to ensure stability and prevent sinking. The wooden piles are protected from decay by salty water and lack of oxygen, which creates an environment that inhibits the growth of microorganisms.

In addition to the piles, a series of interconnected canals and waterways run underneath Venice. These canals serve as the city’s sewage and drainage system and provide a means of transportation for both people and goods. The Grand Canal and smaller canals are unique features of the city and contribute to its distinctive character and charm.

How Deep Is the Water Venice Is Built On?

Venice is built on a series of small islands and islets that are located in a shallow lagoon in the northern Adriatic Sea.

The water in the canals and channels within the city is relatively shallow, with an average depth of around 1 meter (3.3 feet). However, the canals are subject to fluctuations in water level due to acqua alta, tides, storms, and other factors, which can cause flooding in the city’s low-lying areas.

When Was the Worst Venice Flood?

The worst flood in Venice occurred on November 4, 1966. The flood, known as the acqua alta or high water, was caused by a combination of factors, including high tides, a severe storm, and the city’s sinking into the marshy Venetian lagoon.

The water level reached a peak of 194 cm (76 inches) above sea level, causing extensive damage to buildings, homes, and businesses. St. Mark’s Square was flooded with over a meter of water, causing significant damage to the Basilica’s interior and precious artwork.

The flood of 1966 was a wake-up call for Venice and the Italian government, leading to the development of a major program of measures to protect the city from future floods, including the construction of the MOSE project, a system of mobile flood barriers that can be raised to protect the city during high tides.

Venice’s sinking and flooding are complex problems requiring innovative solutions to protect this iconic city from further damage. While projects like MOSE and other sea barriers can help to prevent flooding in the short term, addressing the underlying causes of subsidence and rising sea levels will be crucial for ensuring Venice’s long-term survival.

Whether through investments in infrastructure, sustainable development practices, or scientific research, it is clear that protecting Venice will require a concerted effort from governments, international organizations, and concerned citizens around the world. Only by working together can we save Venice and ensure that this unique and beautiful city remains a vibrant part of our cultural heritage for generations to come.

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