This is the Venice we’re all familiar with.
And this is the version that’s a little less ideal.
Over time the city famous for its canals, bridges and architecture
has also developed a reputation for flooding. Yes, it’s always been prone to the water,
but the frequency and seriousness of its floods has gone up a few notches in recent years.
To solve the problem, the city invested in a one-of-a-kind new defence system.
Costing billions and featuring some amazing engineering,
its task is to stop this unwanted water problem once and for all.
But it’s not gone entirely to plan. Far more expensive than first predicted and now
decades in the making, the scheme has been marred by corruption,
environmental opposition and questions about its long-term effectiveness.
In the face of a changing climate this is a story that any coastal city needs to hear
and remember as we build the future - both for its triumphs and its tribulations.
Built in the middle of a lagoon, Venice has been susceptible to a natural phenomenon
known as acqua alta, or ‘high water’ since its founding in the fifth century.
It’s where a combination of weather factors take place at the same time - a high tide,
low atmospheric pressure and strong winds blowing in from the Adriatic Sea.
The result is flooding and though it’s been a part of life here for centuries,
it’s now becoming an existential problem.
What used to happen just a few times a year began occurring more than 60 times a year by the end of
the last decade - and 2019 saw the worst flood in over 50 years, with 80% of the city under water.
Combine this with rising sea levels, more extreme weather events,
a city that is gradually subsiding - albeit very slowly - and Bond,
James Bond sinking buildings and you have a situation that needs an urgent fix.
That’s where this near-€6BN or USD $7BN flood blockade comes in - now finally
up and running 18 years after construction began.
Called the Mose system, it’s formed of 78 gates - each
20-metres-wide - that rise up out of the water when flooding is imminent.
These pop-up barriers are located at three points along the coastal
cordon that separates the lagoon from the Adriatic.
The two lower inlets - Malamocco and Chioggia - have one barrier each,
while there are two at Lido in the north where a new artificial island fills the gap between them.
When they’re not needed, the gates are filled with water and lie
submerged in giant reinforced concrete housings - allowing boats to pass overhead.
To raise them, compressed air is sent into the gates. This forces the water out and causes
them to rotate on their massive 42-tonne hinges, eventually breaching the surface.
Once empty of water they form a barrier high enough to block even
the highest tidal waters from getting through.
They can resist a three-metre-high tide and are designed to be effective
even if sea levels rise by as much as 60 centimetres in the future.
Once the tide passes, the gates are refilled and they flip back to their closed position.
They can be raised in about half an hour, and the sinking process takes around 15 minutes.
Because each barrier has multiple gates and they can be controlled separately
the whole system is flexible depending on the size of the tide and other conditions.
The way the gates work may be clever, but it’s the enormous housings, or caissons,
that are perhaps most impressive from a construction point of view.
These immense structures, which are as big as apartment blocks and weigh
many thousands of tonnes each, had to be manufactured in three separate
locations before being dropped into huge trenches on the seabed.
There are also two shoulder caissons at all four barriers,
which connect the housings to the mainland.
These allow workers to reach the system’s inner mechanisms
via service galleries that run underneath each barricade.
At Chioggia and Malamocco different methods were used to launch the caissons into the water.
Those manufactured on the Chioggia side were constructed in a dry dock,
which was filled with water, causing the finished structures to become almost buoyant.
Barges armed with huge cranes were then used to pick up the caissons
and manoeuvre them to their resting place.
Over at Malamocco, the units were moved by massive rolling platforms mounted on tracks.
Once at the water’s edge,
a crane lifted them in before barges and tugboats arrived to take them away.
Across all three sites, when it came to lowering the caissons, hydraulic dampers
in each corner helped to absorb the force of these massive structures hitting the seabed.
Even when Mose is deployed there’s still a way for vessels to get through.
Locks were built alongside the barriers to ensure
some boats could still come and go even when the gates are up.
It’s a clever flood defence system that could also make a difference around New York City,
on San Francisco Bay or in Sydney Harbour in the years ahead - but before these cities add the idea
to basket, it’s important to ask a fundamental question: does the system in Venice actually work?
Well, the good news is it passed the first major test. In October 2020, Mose successfully
protected the city from a 1.3-metre-high tide and it has performed multiple times since.
But this doesn’t mean flooding has been stopped entirely. In December, it was unable to prevent
an unexpectedly high tide from sweeping in and drenching the city once again.
But, this was not the fault of the system. Weather forecasters underestimated how high
the water would get, so authorities kind of didn’t think to switch it on.
It was far from the first blunder for the project.
In 2014, dozens of officials including the city’s mayor were arrested in a corruption scandal,
with millions of Euros in bribes thought to have changed hands over the scheme.
Its final cost is now around €4BN higher than originally predicted
and that’s without the estimated €100M required each year to maintain the system.
Opponents have voiced their concerns about Mose’s impact on the lagoon’s ecological systems,
as holding back water in this way could lead to depleted oxygen levels. This would get worse the
more the barriers are used, and it’s likely they will be seen more frequently as sea levels rise.
Others have cast doubt over it actually being able to withstand
the higher water levels that are expected to occur later this century.
The time it’s taken has also been heavily criticised. The system might be new, but it was
designed in the 1980s, when attitudes to climate change were less serious than they are today.
Many also question whether it’s as effective as much older and
less expensive defences like the Thames Barrier in London or Rotterdam’s system.
Whether the pessimists are proved right or not, this is what the people of Venice are
putting their faith in for years to come and for many it will be a huge relief.
It might not turn out to be the perfect solution, but the main thing is that it works - at least for
now - and it stands as a powerful case study for other cities facing rising sea levels to look to.
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