Why does Venice flood, how often does it flood, is it sinking and what defences are there?

Here we explain why Venice has flooded, what defences there are, and if the city is sinking.

Why does Venice flood?

Venice experiences a phenomenon "acqua alta" or "high water" due to exceptional tide peaks in the Adriatric Sea.

The tidal peaks reach their maximum level in the Venetian Lagoon, which runs around and through the city, causing flooding in the region.

The causes of the tidal peaks are down to a number of factors, including the movement and phase of the moon, wind strengths and direction as well as rain level and rising sea-levels.

On October 29, Venice was inundated by an exceptional high tide, which put three-quarters of the city under water.

The peak level was the highest reached since December 2008, according to Venice statistics.

Tourists and residents alike donned high boots to navigate the streets of Venice after strong winds raised the water level over five feet before receding.

The water exceeded the raised walkways normally put out in flooded areas in Venice, forcing their removal.

Transport officials closed the water bus system – except to surrounding islands – because of the emergency.

Venice's St Mark's Square was closed after the water level reached 5.1 ft – the fourth highest level ever recorded.

Is Venice sinking?

According to LiveScience, the rise in sea-level isn't the only thing that has Venice's famous canals rising every year because the city is subsiding.

Previous studies had that suggested the city's subsidence had stabilised but it has been claimed that the city is tilting to the east.

Scientists tracked the elevation of Venice and its surrounding lagoons over a ten year period and have said that on average, the city is sinking up to two millimetres every year.

It's thought the subsidence is due to plate tectonics as the Adriatic plate, on which Venice sits, is subducting beneath the Apennines Mountains and causing the city and its environs to drop slightly in elevation.

How often does Venice flood?

Exceptionally high tides in Venice occurs once every four years, on average.

However minor flooding in the city happens around four times a year and usually within the winter months.

High water can sometimes last only for a few hours but it is dependent on which part of the island is hit by floodwaters.

What defences are there?

Venice Mayor Luigi Brugnaro said a series of underwater barriers that are being erected in the lagoon would have prevented the inundation.

According to the Associated Press, Brugnaro said he had asked to talk with Premier Giuseppe Conte to underline the urgency of the project, nicknamed Moses, which would raise barriers when the tide reaches 43 inches.

Residents and businesses typically reinforce their doors with metal or wooden panels to prevent water from entering the bottom floors, but photos on social media showed shop owners using water pumps this time to try to protect their goods.

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