– [Narrator] It's no secret. Venice has a flooding problem. (somber music) Here's St. Mark Square, it's
the lowest point in Venice. – It used to be flooded
only 40 times a year. – [Narrator] Now, it
floods 250 times a year. But Venice also gets larger floods that can cover this much of the city. – [Giovanni] In the past, this was a very exceptional case. – [Narrator] But since 2000,
it's happened 16 times.
In 2019, a catastrophic flood
cost the city over $1 billion. So we brought in engineer Giovanni Cecconi to discuss how Venice
can rein in the tides before it drowns. (somber music continues) These are the MOSE barriers
which Giovanni helped design and operate. – (Giovanni speaks foreign language) – [Narrator] They're
mobile storm surge gates that rise to separate the
Venetian lagoon from the sea. It's the city's $6 billion
solution to flooding. – This is the Venice Lagoon with the three entrances:
Lido, Malamocco, and Chioggia. – [Narrator] Two times a
day, the high tide comes in and fills the lagoon with water. The low tide then flushes
the water back out to sea. To block high tides, the MOSE barriers were
installed in each inlet. – This is the bottom of the canal in which the barrier are installed, and inside there is the flood gate. – Each gate is 66 feet
wide, 12 to 16 feet thick, and 61 to 97 feet tall,
making the tallest gate more than half the size of
the leaning tower of Pisa. So if forecast show especially high tides, the city raises the gates,
which takes about 30 minutes.
– The air is pumped
inside, it start floating. But because of the hinges, it will assume 50 degree position, keeping the sea higher and
the lagoon at the lower level. – [Narrator] Once raised, the barriers can maintain
a difference in water level from the sea to the
lagoon of about 10 feet. And for now, it's working. In 2022, a 5.5 foot tide was
forecasted to hit Venice, which could have flooded
82% of pedestrian walkways.
Because of the barriers,
locals and tourists only had to face wind and rain. But when the 78 MOSE
barrier gates are raised, they don't just keep water out, they also keep what's in the lagoon in. That's an issue because some of Venice's sewage flows into the lagoon and requires the tide to wash it out. And that's not the only problem.
– In 50-60 year, if
the sea level will rise more than two feet, the
MOSE will become useless. – [Narrator] This increase in sea level has led to more high tides, which has led the city to raise the gates far more often than originally planned, 66 times so far. But the sea level isn't just rising. Venice is also sinking. – Over the last century, the
city has sunk six inches. The sea level rose 4.3 inches. – [Narrator] Starting in the
1930s, water was pumped out from underground to support
industrial development, compacting the earth and
causing the city to subside. Though the city has stopped pumping, Venice is still sinking at a rate of one to two millimeters per year. So some scientists have a proposal, lift the city back up by
injecting water back underground – Below Venice, we have different strata of clay and sandy soil.
Sand is made of solid and water, and this water has a certain pressure. If you increase the pressure, the grain will increase in volume. And so you are very bound. – [Narrator] Scientists estimate that this could push Venice
up about 10 to 12 inches. And this idea has been implemented before. – [Giovanni] Here we are
in Long Beach, California. – [Narrator] Starting in the 1940s, water and oil were pumped out
from underneath Long Beach, sinking the city and
causing frequent flooding. – And here, there has
been a successful recovery injecting the water back into the wells. – [Narrator] But Venice and Long Beach aren't quite the same. Giovanni says Venice has a different type of soil than Long Beach and if Venice implemented this technique, it might not be as successful. – [Giovanni] If we pump water below ground and this produce an uneven
displacement on the surface, you can figure out what will happen. – [Narrator] The centuries old buildings and bridges could crumble. – And this has to be maintained forever. – [Narrator] Because if the
city stopped pumping water, – [Giovanni] This elevation that we gain will be lost as a souffle that was abandoned out of the oven.
– [Narrator] But there's
another engineering solution, a much larger one, a super levee. – [Giovanni] The super
levee will enclose the city inside this red line. – [Narrator] Ordinary
levees are embankments meant to block flood waters, but significant flooding
can flow over the top or seep through, breaking the levee and cascading into the
area it's meant to protect. Super levees solve this problem by creating a flood protection zone. They have a wide footprint
with a low-grade back slope. In Venice, it would be about 13 feet tall and extend almost 400 feet along the base. It makes them resistant to
water overflow and seepage. And even if water reached the top, it would flow slowly down the slope instead of cascading down, like it would with a standard levee. In Venice, a super levee
would divide the lagoon, forming a lake inside the boundary. – There will be a
permanent opening to allow the flushing of the city, so the water will enter continuously, and we can produce electricity here.
– [Narrator] Pumps would
help mimic the natural tide. – This will allow the the water to circulate inside the
city to keep the city fresh so we can swim again in the city. – [Narrator] And on
top, there would be room to build infrastructure. – Garage, transportation,
a bicycle route, trees. – [Narrator] And lastly. – We can relocate the tourism from the historical
city to the super levee. – [Narrator] Currently,
Venice has more beds for tourists than it has citizens. Giovanni believes a super
levee could alleviate the battle for space and
revitalize other industries in the city.
But this plan faces a hurdle. Construction of the MOSE
system was embroiled with corruption and delays. Building a super levee by
the time the MOSE barrier becomes ineffective would
require laws to change and the public's approval. – What we can learn from the past is, we need direct
participation of the people. So there will be not
Giovanni Cecconi super levee, but the super levee of
the people of Venice. – [Narrator] In the meantime,
Venice has found other ways to adapt to the rising tides. Glass barriers protect ancient monuments from the salt water, raised
walkways funnel crowds around, and Venetians wear waiters. – The history of Venice
is a 2000-year history of adaptation in which
the solution were found by trial and error.
I am optimistic because there
will be great transformation in the future..