If you were in Venice back in November 2022 you might have seen
these glass barriers. They're protecting St. Mark’s Basilica from floods.
It’s a striking measure to combat the city’s most pressing problem:
it’s sinking, and has been for years. But hold on a minute – if you’ve watched
our channel before you’ll remember that Venice JUST spent decades building a $7BN
sea-defence system that finally started working in 2020. Well,
as this footage shows that big expensive megaproject isn’t turning out to be so mega .
So what’s the deal here? Why does Venice still need additional methods
to protect parts of the city? And if a $7BN system isn’t enough to save it…what will?
People travel from all over the world to see Venice’s scenic canals and architecture,
but the city may not be around to visit for much longer.In the worst-case scenario experts predict
it could be underwater as early as 2100, as buildings sink further into the soil and
climate change causes sea levels to rise. The city gets a lovely preview of that
future every so often during when a high tide known as acqua alta sweeps in. Now,
Venice has pretty much always had to deal with this type of flooding. But in recent decades,
it’s become much more frequent and intense, and the city is paying the price.
Venice is suffering its worst flooding in 50 years.
Sound bite: Venice floods dozen of time a year …locals tell us this is not normal . These walls
are just the latest step in Venice’s long-running battle to hold back the sea. You see, the place
is essentially floating on water: it’s built on top of a lagoon and its foundation is mostly mud.
The first settlers lived in houses made of wood and clay – both fairly lightweight materials,
but as things expanded better engineering tactics were needed.
To create a stronger foundation, long wooden piles were driven into the ground until they
reached hard clay five to six metres down. Each pile was closely placed together with rock packed
in between which prevented the silt from rising. From here, wooden platforms and stonework were
placed on top. That worked for a time, but by the 16th and 17th centuries, the constant flow
of sediment from the main rivers flowing into the lagoon had essentially turned it into a swamp. To
solve that issue, engineers boldly diverted the rivers around the lagoon and straight out to sea.
Just a couple of hundred years later, the barrier islands that divide Venice Lagoon from the
Adriatic Sea were reinforced with a 10-kilometre sea wall in an attempt to withstand storms.
Then following the devastation of the 1966 flood, the city installed
a network of raised walkways of 110-cm. But as you’re probably guessing, none of
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Now, let’s get back to Venice before it sinks. What
you’re looking at here is the city’s latest and most expensive flood defence system yet:
a $7BN mechanised barrier called MOSE, that promised salvation from a watery fate. After
decades of controversy and planning, it finally began operating in 2020.
Here’s how it’s supposed to work.
A series of 20-metre wide metal barriers have been strategically placed around the
lagoon's inlets. They sit in huge concrete caissons that were prefabricated on land
then dropped into trenches on the seabed. Each of these massive concrete segments features a
service tunnel that all connect back to land, allowing access for inspections.
When not in use – the hollow barriers are filled with water and submerged.
But when a high tide is forecast, compressed air flows into the gates,
pushing the water out. This causes the gates to rotate on their hinges
and rise above the surface, blocking the incoming tide from entering the lagoon.
Then when water levels lower again, the gates
fill back up and drop back beneath the surface, allowing ships to pass.
Over the last few years, MOSE has stopped a lot
of potential flooding that would’ve previously washed out the city.
But it has some drawbacks.
First off, construction took ages. It was designed way back in the 1980s and was supposed to start
working in the 2010s – but the system didn’t go online for another decade. Since then,
our understanding of climate change and its expected effects has evolved massively,
and the forecasted scenarios that MOSE was built for are now outdated.
So parts of the city still see flooding: like St. Mark's Square which becomes a rather grand lake
whenever the tide goes more than 80 cm above its regular level. Annoyingly for businesses
and historic landmarks, city officials will only raise the MOSE system when tides hit 110
cm – bringing in protection for about 86% of the city. If the threshold was lower,
the gates would need to be closed 80-100 times a year; a frequency it isn't equipped to handle
yet. That’s why, despite a new $7BN system, Venice still has to use glass barriers like this. They’re
five metres long, around 1.3 metres high and stop rising tides from sweeping into famous buildings.
Each one is fixed onto armoured concrete that extends two metres underground and
works alongside a series of pumps and valves that prevent backup in the drainage system.
When it’s not flooding, there are openings within the walls. Then when the tide hits,
they’re sealed off. It’s only supposed to be
a temporary measure until something more long term is devised – and the walls and
pumps can stop up to 1.1 metres of water, something MOSE isn’t optimised to do yet.
That’s right: the $7BN system can’t keep up with the simple aquarium walls.
So, having waded through all this context you’re probably wondering why they don’t just lower the
flood threshold and raise that big expensive MOSE thing more often. Well, brace yourself,
because one of the big reasons is that MOSE is not cheap to operate. Every time the barriers go up,
it costs over $320,000 – largely going on power and teams of people. You have to send 80 people
through the lagoon in order that they are just there in order to manually work on these machines,
in order to pump air in there and so on. So it's not just press of the button, but 80 people going
out, staying there maybe for two days because you have bad weather, weather situation, they cannot
come back and so on. To be clear, MOSE isn’t fully complete yet and this cost will probably go down
over time. It’s technically still in experimental mode and is due to finish sometime in 2023.
Eventually, it could be optimised and run with a smaller crew, allowing it to be raised more often.
But that doesn’t necessarily mean they’ll use it more.
Then remember, if you close the lagoon, there is no ships that can pass. So you don't have
industrial ships, you don't have passenger ships, you don't have commercial ships like the fishery,
the fisher boats. They cannot go out anymore or cannot come in anymore.
With 27% of the city’s economy relying on these ships, pushing back the floods also means pushing
away income from trade. The system does feature locks alongside its gates to allow some ships
to pass, but it hugely impacts capacity. To make things worse, MOSE isn’t a permanent fix.
Georg estimates the system might be pushed to its limit by around 2050 or 2060 depending on
how quickly sea levels rise, and how often they need to close the gates.
He believes there are better, longer term options the city could take;
like raising everything further above sea level by pumping water into underground wells.
There's geologists that were working on these kinds of projects and they showed…
that you can raise Venice between 30 and 35 centimetres. When we started
to measure the sea level at the end of the end of the 19th century,
we fixed the average water level at zero. … So if you can raise Venice again by 30, 35 centimetres,
you basically go back into the past by 120 130-40 years. Raising land like this
is something scientists have been considering for years, and it’s been used in places like Taipei
and Tokyo to mitigate sinking and store gas. But don’t expect to see it in Venice anytime soon.
Critics say that because the city injected so much money into the MOSE system it's the
one they'll have to run with, for now at least – though that view might of
course be forced to change should the waters truly come to threaten Venice’s existence.
This beautiful city has been in a battle with the very tides that enable its success for centuries,
often engineering a way around the water and finding a path forward.
But in a world that’s now changing faster than ever before it’s realising that billions of
dollars and glass sticking plasters simply aren’t enough. The result is one of our planet’s most
breathtaking cultural landmarks being plunged into an increasingly desperate race for survival
that it seems to be losing. This video was made possible by
Masterworks, you can learn more about that in the link below. There’s also the chance to dive deeper
on Venice’s flood defences and the other topics on our channel over on The World’s Best Construction
Podcast – available right now wherever you get your podcasts. And as always, if you want to
learn more about where construction is headed, make sure you’re subscribed to Tomorrow’s Build.