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Nova travels to the storied city of canals and explores the many problems facing Venice as well as a number of intriguing solutions
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00:00Ah, Venice.
00:10To Italians, she's known as La Serenissima, the most serene republic.
00:16For 1,200 years, the city has performed a magical balancing act.
00:22Not quite land, not quite sea, Venice seems to float in its own world.
00:28A world that at first glance appears immune to the passing of time.
00:36The 900-year-old St. Mark's Basilica presides over a giant public square
00:42that's changed little since the days of Casanova and Vivaldi.
00:49But in recent years, the illusion that is Venice has begun to crack.
00:55And this idyllic city has been showing a darker side.
01:03The trouble began on November the 4th, 1966,
01:07when an extremely high tide swept into Venice and refused to leave.
01:15For 15 hours, Venice was inundated by the sea.
01:23In historic St. Mark's Square, the water was four feet deep.
01:29Luckily, no one was killed.
01:31This place was a disaster zone.
01:38In a single day, the city and the world were forced to face a harsh reality.
01:45Venice was sinking into the sea.
01:50Today, flooding has become a fact of life.
02:02Instead of floating above the water, the 15th and 16th century buildings are often filled with it.
02:09And the ancient bricks are gradually dissolving away.
02:16Venice is at a critical point.
02:19The problem of flooding must be solved right away.
02:22But how can Venetians stop the flooding?
02:28Not only is the city sinking, but sea level is rising, here and all over the world.
02:37It's happening.
02:38It's happening now.
02:39Venice is a trigger.
02:40Venice is the first major city in the world to face sea level rise,
02:44because it's built right at sea level.
02:47The Venice you know today cannot be preserved as it is today.
02:54It was built on a salt marsh at sea level, in a sinking area, and unfortunately sea level is rising.
03:04Is Venice's long and happy marriage to the sea destined for disaster?
03:09Or can the city of canals somehow be saved?
03:14Sinking city of Venice.
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05:15Several times a year, sirens sound along the canals of Venice.
05:24They can mean only one thing.
05:28The water is coming.
05:30Between October and January, the lowest parts of Venice flood almost every day, and much
05:47of the city is inundated half a dozen times.
05:50During this wet season, Venetians rarely venture far without their rubber boots, and sometimes
05:59even that's not enough.
06:00They call it aqua alta, high water.
06:10It's this sort of slimy, murky water, which isn't very pleasant, but it also contains
06:16quite a bit of pollution.
06:19So, you really don't want to stick your hand in this water or have this water in your
06:25entry to your house, in your hallway.
06:33Schools can't run.
06:35Boats have troubles getting under the bridges.
06:37There's a whole series of dysfunctional things which happen with aqua alta.
06:45It's not just inconvenient.
06:48The tide is insidious, creeping into every building, without regard for its historical
06:53value.
06:56Salt water eats away at floors and walls no matter what century they were built in, or
07:02what genius architect designed them.
07:06The front of St. Mark's Basilica, perhaps the most famous Venetian landmark, is adorned
07:11with stones from around the Mediterranean.
07:15All of it is being corroded by floods, almost on a daily basis.
07:23Venice is famous as the city of romance, the city of Casanova, where lovers forget their
07:30worldly woes.
07:35It was once an extremely rich and powerful city, built by merchants and bankers who controlled
07:41a shipping empire throughout the Mediterranean.
07:46Her wealth and beauty flowed directly from the sea.
07:53So, how is it that the water is now threatening to undo all that it made?
08:00In the case of Venice, it comes down to location, location, location.
08:08If you were planning to build a city, you could hardly pick a less practical spot.
08:17At the northern tip of the Adriatic Sea, historic Venice sits on what's actually several dozen
08:22islands within a 200-square-mile shallow lagoon.
08:29A long chain of barrier islands guards the lagoon from the sea, but three openings in the
08:34chain allow ships, and the tide, access to the city.
08:41Flooding occurs when exceptionally high tides break through these inlets.
08:45Normally, the tides are controlled by the moon, but the sun also plays a role.
08:55These astronomical tides are easily predicted, and they aren't very extreme.
09:00The difference between high and low tide in Venice can be as little as an inch or two, or it
09:07can be more than three feet during a fuller new moon.
09:11But you can't blame the moon for Venice's flooding problems.
09:19The aqua alta, those extreme high tides, are caused primarily by the weather.
09:26Strong winds out of the south driving Adriatic waters to the north, and forcing it into the
09:30lagoon, and causing flooding.
09:33So, predicting aqua alta is really based on predicting storms.
09:38And it's not that easy.
09:43Bad weather was the cause of the 1966 deluge.
09:48Wind and low pressure created a giant storm surge that pushed water into the lagoon and
09:54wouldn't let it out.
09:57The flood was a complete surprise.
10:01Since then, Venice has paid much more attention to the weather and its effect on the tides.
10:08Out on the Adriatic, 12 miles from shore, this platform collects data 24 hours a day.
10:22Temperature and humidity, wind speed, atmospheric pressure, anything that contributes to a storm
10:28surge.
10:28All this information is relayed to a team within the city.
10:34If flooding is predicted, then alarms go off.
10:39Given enough warning, Phoenicians can minimize the damage.
10:45Doorway barriers keep some water out of ground floor shops and apartments.
10:48But for most of the city, there's no stopping the sea.
11:00These events are becoming more frequent.
11:04A century ago, St. Mark's Square, the lowest point in Venice, flooded about nine times a year.
11:09Nowadays, it happens about a hundred times.
11:25Buildings in Venice were constructed to withstand some contact with the sea, but these floods
11:30are pushing them beyond their limits.
11:32To understand why, just look at a typical Venetian foundation.
11:44Here, a canal has been pumped dry for repairs, revealing a few of the secrets of the city's success
11:49and some of its major weaknesses.
11:57Strip off the outer layers of the foundation, and you'll find a forest of wooden pylons.
12:02These logs were pounded through the soft mud, 10 or 15 feet, to the bedrock below.
12:11Surrounding the pylons are several layers of water-resistant stone.
12:17As long as the sea washes against this lower level, the structure above is well protected.
12:23But now, the flooding is rising beyond the stone foundation, to the building itself,
12:30which in most of Venice is made of brick.
12:32The bricks, sometimes coated in stucco, are soft and porous, and much more vulnerable
12:40to corrosion.
12:45Chemists at the University of Venice are studying how this works.
12:47It's very interesting to see the effect of water on the sample, which is no different from
12:56what happens to the walls in Venice.
12:59I'm immersing the brick in a few millimeters of water that contains a small quantity of salt.
13:03The salt travels up through the brick.
13:11As the water dries, the salt crystallizes.
13:14With every new flood, the salt dissolves once again and bores a little more into the brick.
13:21Eventually, the brick will crack and crumble away.
13:30This is what's happening inside all the walls of historic Venice.
13:34Almost everywhere, ground floors are damp and moldy.
13:46Many residents have moved upstairs.
13:51Or out of town.
13:52Since the 1950s, Venice has lost over half its population.
14:00Today, fewer than 70,000 people live here.
14:07Residents are trying to escape the flooding.
14:09But they're also running away from the tourists.
14:16About 15 million tourists pour into tiny Venice every year.
14:22And most of them stay less than a day.
14:30They drive prices up.
14:32On everything from food to rubber boots.
14:35So, every day, Venice becomes less of a living city and more like a museum.
14:45A museum which is often very, very wet.
14:51But does it have to be this way?
14:56Just look at the Netherlands.
14:57The whole country is below sea level and not a drop gets in.
15:00I don't see why we, who are nearly three feet above sea level in St. Mark's Square,
15:06are not able to stop this water.
15:16The Netherlands used to be one of the most waterlogged nations on Earth,
15:20with more than half the country below sea level.
15:22Since the 1600s, legions of windmills have powered water wheels
15:29that lift water up into canals.
15:34These channels flowed back to the sea,
15:37which was held at bay by earthen dikes.
15:40But this system was not foolproof.
15:43In January 1953, hurricane force winds and an unusually high tide
15:54blasted the Dutch coast, collapsing the protective banks.
16:021,835 people were drowned,
16:06and 70,000 were left homeless.
16:09A third of the Netherlands was underwater.
16:13Over the next 50 years,
16:24the country spent billions walling itself off from the North Sea.
16:32But for Rotterdam, the biggest port in the world,
16:35a permanent barrier would have spelled economic disaster.
16:38And so, the Dutch came up with this.
16:44Two mobile gates that can swing out to block the river
16:47whenever the North Sea gets out of hand.
16:52To withstand the full force of the sea,
16:55the structures must be gigantic.
16:59Each gate has a steel barrier seven stories tall,
17:03which holds back the water.
17:04The arms are as long as the Eiffel Tower is high.
17:12The gates are far from subtle.
17:15But Pierre Wellinga, environmental scientist, is still a fan.
17:19When the North Sea is rough, we are very vulnerable.
17:23And we had the choice between raising all the dikes,
17:27three, four, five meters,
17:29and rebuilding part of the old cities,
17:32or a one-time mobile barrier.
17:35And the population was much in favor of this mobile barrier,
17:39because it is safer and it has less effect overall on the landscape.
17:48When the sea is calm,
17:50the barriers rest in canals on the riverbank.
17:56If a major storm is predicted,
17:58the huge arms will rotate towards the center of the river
18:01until they almost meet in the middle.
18:03Then the barriers fill with water and sink into the riverbank.
18:12Finished in 1997,
18:14the gates haven't been tested against a real storm yet.
18:17But it's predicted they will be needed on average once every ten years.
18:21The Dutch system of dams and gates has been hailed as an engineering marvel.
18:30But could it work for Venice?
18:33What I know of Venice,
18:35the people and the visitors do not like to see such a massive structure.
18:41And the design, which is now discussed for Venice,
18:44is a more elegant solution.
18:46The Venetian flood plan calls for several sets of mobile gates
18:52placed at the three large entrances to Venice's lagoon.
18:57Most of the time,
18:59the steel gates lie flat
19:00in a special housing on the bottom of the inlet.
19:04When extremely high tides threaten the city,
19:07compressed air is pumped into the hollow gates,
19:10causing them to tilt upwards to the surface.
19:13Each gate measures about 65 feet wide,
19:18about 12 feet thick,
19:20and 65 to 100 feet tall.
19:24They're designed to hold back a high tide
19:26more than 6 feet above normal.
19:30When in use,
19:31they're supported by the water on both sides.
19:34After the tide recedes,
19:36water flows into the gates,
19:38sinking them back into place.
19:39If the hollow gates look flimsy,
19:45take a peek inside.
19:48Each gate is supported by an internal steel framework,
19:52weighing between 300 and 400 tons.
19:56The design of the mobile gate system
19:59is very innovative.
20:01When it's in use,
20:03the elements of the barrier
20:05are allowed to swing back and forth
20:07with the waves.
20:09In this way,
20:10much of the wave force
20:11is transmitted back to the water on both sides.
20:15And very little force
20:16is transmitted to the foundation
20:18and to the supporting structure.
20:20So in this aspect,
20:22I think it's very, very clever.
20:27Many engineers believe
20:28these mobile gates
20:29represent the salvation of Venice.
20:31There's just one problem.
20:35They don't exist.
20:37Except in computer simulations like this.
20:46Since the flood of 1966,
20:49Italians have been talking
20:50about how to protect Venice.
20:52And then one third.
20:55Talking.
20:56And talking.
20:59But somehow,
21:00they've been unable to make a decision.
21:03Instead,
21:04the gates have become
21:05a political hot potato.
21:07Tossed from one administration
21:09to the next.
21:10And that's meant
21:11a lot of tossing.
21:13Since 1966,
21:15there have been more than
21:1635 different governments in Italy.
21:18The politicians
21:20who are sitting in Rome,
21:22who essentially
21:22have control of this,
21:24who are coming and going
21:25almost on a yearly
21:26or two-year basis,
21:27do not have a clear focus
21:29on this.
21:30They will not be in office
21:31when this is done
21:32because it will take 10 years.
21:34And this helps to explain
21:35why you have
21:36this sort of inertia.
21:42It's not that nothing
21:43has been done.
21:45Every now and then,
21:47there's a flurry of activity.
21:49Like in the late 1980s,
21:51when engineers rolled out
21:52a full-size prototype
21:53of a single gate,
21:55which was attached
21:55to a large derrick.
21:58The whole contraption
22:00was ceremoniously
22:01hauled along the coastline
22:02to gain public support.
22:07On television,
22:10they talked about this thing.
22:12It's the first time
22:13I've seen it.
22:13after years of inaction,
22:28Venetians were
22:28understandably skeptical.
22:30Oh, no, look.
22:33As far as efforts
22:34to save Venice go,
22:35up to now,
22:36they haven't tried very hard.
22:38They've doubled up
22:38a lot of the money
22:39meant for saving Venice,
22:41but they've done very little.
22:42We hope that now
22:43things go well
22:44with these mobile gates.
22:45Okay, the politicians,
22:48they make project.
22:52Blah, blah, blah, blah.
22:53All the Venetian people
22:55now wait.
22:56Today, 14 years later,
23:03the Venetians
23:03are still waiting.
23:07Construction of the gates
23:08has not even started.
23:11This is particularly frustrating
23:13to engineers
23:13like Andrea Rinaldo.
23:19Especially in this country,
23:21science and technology
23:22take a backseat
23:23to politics.
23:24It's never intentional.
23:29It happens everywhere.
23:31But in a humanistic country
23:33like this,
23:34what an MIT professor says
23:35and what a gondolier says
23:36is basically the same thing.
23:40And if I say this,
23:41it's because I've been
23:42burned on this before.
23:47Initially,
23:47the gate plan required
23:48years of testing.
23:51No existing mobile gates
23:52operate in this way,
23:53popping out from the seafloor
23:55by means of compressed air.
23:59To make sure
24:00the concept would work,
24:01engineers spent
24:02four years
24:03fine-tuning
24:04the technical design
24:05of the single gate module.
24:06Then, to test the whole system,
24:15they set up several scale models
24:17of the lagoon inlets,
24:18complete with mini mobile gates.
24:22Tiny ripples simulate
24:24the effects
24:25of a mighty sea storm,
24:26and the response
24:27of the barriers
24:28is carefully noted.
24:31During the testing phase,
24:33engineers did find
24:34a potential problem.
24:37When test waves
24:38hit the gates
24:39in certain patterns,
24:40adjoining gates
24:41rocked in opposite directions,
24:43creating holes
24:44through which floodwaters
24:46could flow.
24:48This, I believe,
24:50was uncomfortable
24:51to the designers.
24:53But there have been
24:54improvements of design
24:55by changing the dimension,
24:57so this problem
24:58is solvable.
25:01By making a few minor changes
25:03in the size
25:04and angle of the gates,
25:05the engineers are confident
25:06they'll avoid this problem
25:08and the gates
25:09will do their job.
25:11That is,
25:12if the gates
25:12ever get built.
25:17Paolo Pirazzoli
25:18was born in Venice
25:19and has been fighting
25:20the gate plan for years.
25:22In theory,
25:29the mobile gates
25:30with optimal weather conditions
25:32could put an end
25:33to high tides.
25:34But only in theory,
25:35because it has
25:36a lot of problems.
25:39It is an extremely
25:40complicated project.
25:41It's fragile and expensive
25:42in terms of its construction
25:44and maintenance
25:44and it would have
25:45a negative impact
25:46on the environment.
25:52environmentalists
25:54make up the biggest block
25:55against the gates.
25:56They worry that the gates
25:58will be closed
25:58too often
25:59and will damage
26:00the lagoon ecosystem.
26:03Some insist
26:04that Venice
26:04and the lagoon
26:05would be better off
26:06left to Mother Nature.
26:08But the gate engineers
26:10don't buy that argument.
26:15In recent years,
26:16there's been a growing sense
26:17among people
26:17that every intervention
26:19in a lagoon
26:20and in a city
26:20is considered tampering.
26:22manomissioni
26:23all these interventions
26:24are generally called
26:25the disaster of doing.
26:34It's hard for me
26:35to agree with this
26:36because it's clear
26:37that everything
26:38that we see today
26:39in the Venetian lagoon
26:41is the result
26:42of an artificial system.
26:47It's not the product
26:48of natural evolution
26:49but of a massive interference
26:51from humans.
26:56It's true.
26:57Humans have been tampering
26:58with Venice
26:59and its lagoon
26:59for hundreds of years.
27:05Today,
27:06Venice is a collection
27:07of built-up islands
27:08connected to the mainland
27:09by an artificial causeway.
27:11But 16 centuries ago,
27:13it was a very different place.
27:15A bunch of marshes
27:17surrounded by a shallow mix
27:19of fresh and salt water.
27:25The earliest settlers
27:26were probably running away
27:28from Attila the Hun
27:29and other barbarians.
27:31They picked this spot
27:33precisely because
27:34it was so inconvenient.
27:36foreign invaders
27:39gave up trying
27:39to get there,
27:41figuring it wasn't
27:41worth the trouble.
27:46Only the locals
27:47knew the location
27:48of channels
27:48deep enough
27:49for seafaring vessels.
27:53Safe from invasion,
27:55the ambitious Venetians
27:56developed a monopoly
27:57on trade and shipping
27:58in the eastern Mediterranean.
28:01This is what made Venice
28:03is rich and powerful.
28:08But by the 14th century,
28:09nature threatened
28:10to undo
28:11the city's cozy place
28:13in the lagoon.
28:20The big turning point
28:21happens in the middle
28:22of the 14th century.
28:27It seems that
28:28reeds and swamps
28:29are invading the lagoon
28:30and menacing the city.
28:33The swamps corrupt the water
28:36and bring disease
28:37and death.
28:38And in addition,
28:39they make the city
28:40vulnerable to attack.
28:45Several rivers
28:46which ran into the lagoon
28:47were depositing
28:48large amounts of silt.
28:51Only a foot or two deep,
28:52the lagoon was becoming
28:53even shallower
28:54and more swamp-like.
28:57Mosquitoes
28:58and malaria
28:59were rampant.
29:00many feared the lagoon
29:03would fill in completely
29:04and Venice
29:06would lose
29:06its best system
29:07of defense.
29:10So,
29:11the Venetians
29:11decided to take control
29:13of their destiny.
29:14essentially,
29:20there is a decision
29:21to proceed
29:21systematically,
29:22to adjust
29:23everything that
29:24surrounds the lagoon
29:25and to heal
29:27the relationship
29:27between water
29:28and land
29:29through constant control.
29:33After much debate,
29:35the Venetians launched
29:36an enormous
29:37public works project.
29:40Over the course
29:41of two centuries,
29:42they built a series
29:43of large canals
29:44diverting the major rivers
29:46around the lagoon
29:47so the silt
29:48would be deposited
29:49elsewhere.
29:52The plan worked.
29:54The lagoon
29:54stopped silthing up.
29:57But,
29:58the Venetians
29:58were left
29:59with another problem,
30:00one they could not
30:01solve so easily.
30:03Their city
30:04was sinking.
30:05In fact,
30:09Venice had been sinking
30:10since the very beginning.
30:14The Alps
30:15are partly to blame.
30:17The weight
30:17of this mountain range
30:18is bearing down
30:19on all of northern Italy,
30:21slowly driving it
30:22into the sea.
30:25But,
30:26even more damaging
30:27to Venice
30:27is what lies below.
30:30Underneath Venice
30:31is a salt marsh.
30:33Venice is sitting
30:35on several layers.
30:37The uppermost
30:37and thinnest
30:38are the lagoon sediments.
30:40Fairly muddy
30:41and,
30:42in part,
30:42salt marshes
30:43and that's what
30:44Venice was built on.
30:45Below that
30:46is nearly a mile thick
30:47of river sediments.
30:50Those sediments
30:51are slowly compacting.
30:55In effect,
30:57Venice is sitting
30:57on a giant sponge
30:59filled with water.
31:01As the weight
31:01of Venice pushes down
31:03on the sediments,
31:04it squeezes
31:05some of the water out
31:06and the sponge
31:07gets thinner.
31:09To make matters worse,
31:11the seas have been
31:12slowly rising
31:13for centuries.
31:15This is what
31:16the people of the lagoon
31:17have had to contend with
31:18since they first arrived
31:20on these marsh islands
31:21nearly 2,000 years ago.
31:27Remnants of their
31:27long struggle
31:28can be found
31:29on the island
31:29of Torcello,
31:31northeast of Venice.
31:34The land here
31:36has sunk so low
31:37only a handful
31:38of residents remain.
31:44Beneath the foundations
31:45of this 900-year-old cathedral,
31:47archaeologist Albert Ammerman
31:49has uncovered evidence
31:50of how the old lagoon dwellers
31:52dealt with flooding.
31:53What we can always see
31:56in the archaeological record
31:57is the gradual,
31:59progressive buildup
32:01of the land surface.
32:03We can see
32:04five or six floors
32:06with just one
32:07after the other
32:07six inches a foot
32:09gradually being built up.
32:11Flooding would always
32:12be a problem.
32:13So their way
32:14to deal with it
32:15was essentially
32:16to come in
32:17and continually
32:18be adjusting
32:19the ground level
32:20upward,
32:21layer after layer
32:22without the constant
32:25drone of water pumps,
32:27the entire pit
32:28would be a giant
32:29swimming pool.
32:30But everything here
32:31was once high and dry,
32:34safe above the tides.
32:35Well, the earliest
32:37evidence that we have
32:39is a walkway
32:40made of Roman tiles
32:42and that goes back
32:43to about 200 A.D.
32:45We're in Roman times
32:45and this is found
32:47at five feet
32:48below sea level today.
32:50Anything built
32:54on these marshes
32:55would eventually
32:55sink into the sea.
32:58So, when a building
32:59was too often flooded,
33:01the Venetians
33:02would either
33:02raise up the floor
33:03or they might
33:04tear the whole thing
33:05down and build
33:06a new structure
33:07on the old foundation.
33:10But at some point
33:11in the past,
33:13the Venetians
33:13abandoned the strategy.
33:14One of the fascinating
33:17things is that
33:18since essentially
33:191800,
33:21the time of Napoleon,
33:22the fall of the
33:23Venetian Republic,
33:24they have stopped
33:25doing that.
33:26Venice has become
33:27in some sense
33:28a museum.
33:29It's become fossilized.
33:30The life of the city,
33:32also the notion
33:32of preservation,
33:33heritage,
33:34stops people
33:35from doing
33:36what was the thing
33:37that Venetians
33:38always did.
33:39That is,
33:39build up
33:39the ground level.
33:40It's been a long time
33:46since the ground
33:47in Venice
33:47was raised
33:48on a regular basis.
33:51When these homes
33:52were built,
33:53their front steps
33:53would have stood
33:54well above
33:54the highest tide.
33:58Now,
33:58coated with green algae,
34:00they're visible
34:01only at low tide.
34:05Some believe
34:06that if Venetians
34:07want to fight
34:07off flooding,
34:09they should follow
34:09the example
34:10of their ancestors.
34:10The ground level
34:15has been increased
34:16many times in the past
34:17with demolition
34:18and reconstruction.
34:21Today,
34:23of course,
34:23it's not possible
34:24to demolish,
34:25but you can still
34:25make some increases
34:26in ground level
34:27that will be comparable
34:28with architecture
34:29and landscape.
34:37Raising the sidewalks
34:38and walls
34:38of the canals,
34:39perhaps by a foot
34:41or less,
34:41could go a long way
34:43to protect the city
34:44from moderate high tides,
34:45the most common
34:46cause of flooding.
34:51When it's done well,
34:52as here in one section
34:53of Venice,
34:54the change is hardly
34:55noticeable.
34:58Some people say
34:59that this should be
34:59the priority for Venice,
35:01not the mobile gates.
35:02that will solve an enormous proportion
35:06of the flooding problems.
35:07It won't solve all
35:09the flooding problems,
35:10but it'll probably solve
35:11half or three-quarters of them.
35:12And you could do that
35:13over the next ten years.
35:16It will cost money,
35:17but it will solve the problem
35:18very seriously
35:19in that immediate time scale.
35:21Plans are in the works
35:27to slightly raise the ground
35:29in the lowest parts of Venice,
35:31including St. Mark's Square,
35:33where the labyrinth
35:34of elevated walkways
35:36is an all-too-familiar site
35:38during the winter months.
35:42Most critics of the gates
35:44support this approach,
35:45and some have suggested
35:46an additional strategy,
35:49narrowing the three inlets
35:50to the lagoon.
35:53The smaller the opening,
35:55they argue,
35:55the less water
35:56can enter the lagoon
35:57and the lower the tide.
36:01Depending on how drastic
36:02the change,
36:03it could lower the tide
36:04by 8 to 12 inches.
36:12With narrowing
36:13of the arbor's mouths,
36:15the aqualta would have
36:15to reach almost
36:16four and a half feet
36:17to cause flooding.
36:18And this level
36:19is reached only once
36:20every three years.
36:25This means
36:26that we would have
36:27the same frequency
36:28of aqua alta
36:29as we had a century ago.
36:35But narrowing the inlets
36:37would not be
36:38a completely reliable
36:39defense against aqua alta.
36:42It could only work
36:43for tides that flow
36:44in and out of the lagoon
36:45fairly quickly
36:46on a cycle
36:47of just a few hours.
36:50But there are
36:51some extremely high tides
36:53that linger,
36:54like the one in 1966.
36:56The high tide
36:57flowed into the lagoon
36:58and stayed for a day.
37:01In a situation like this,
37:03whether the inlet
37:03is wide or narrow,
37:05the floodwaters
37:06will eventually get in.
37:07We have studied that in detail
37:10and we came to the conclusion
37:13that it only works
37:14with low tides,
37:16but with exceptionally high tides
37:18that last for, say,
37:1924 hours.
37:21Even making the mouth
37:22more narrow
37:23does not work at all.
37:25It would be
37:26a worthless solution.
37:29Narrowing the inlets
37:30is considered
37:31a soft solution
37:32for Venice
37:33and has been endorsed
37:34by some environmentalists.
37:36But its effect
37:38could be less than kind
37:39because it would reduce
37:41the amount of clean
37:42seawater
37:43flowing into the lagoon
37:44with each tide.
37:45Today, the lagoon
37:50is the largest
37:50saltwater marshland
37:52in the Mediterranean
37:53and is cherished
37:54by Venetians
37:55as a place
37:55of natural beauty.
38:01It's known throughout Europe
38:03as a bird-watching mecca.
38:05Tens of thousands
38:06of birds stop here
38:07during their annual migrations.
38:11They feed on the plentiful
38:13fish and shrimp
38:13that thrive
38:14in the shallow,
38:15salty lagoon waters.
38:18If the flow
38:19of new seawater
38:21into the lagoon
38:22is reduced,
38:23these creatures
38:24will be deprived
38:25of oxygen
38:26and nutrients.
38:30In addition,
38:31without the cleansing
38:32action of the tides,
38:34one of the lagoon's problems
38:35may rapidly
38:36get much worse.
38:39Pollution.
38:41Well, the water
38:42in Venice
38:43has quite substantial
38:46levels of pollution.
38:48There's raw sewage.
38:49I have a boat in Venice
38:51and I take people
38:52around in the boat.
38:53You can actually see
38:54soap suns coming
38:55out of people's
38:56washing machines.
38:57You can see worse things
38:58coming straight
38:59from their houses.
39:03Venice has no
39:04municipal sewage treatment,
39:06equipment, so most homes
39:07pipe their sewage
39:08into the canals.
39:14On top of this,
39:16there are the factories
39:16at the nearby industrial complex
39:18of Port Marghera,
39:19which only recently
39:21stopped dumping chemicals
39:22into the water.
39:23and there's also
39:26agricultural pollution,
39:28fertilizers that flow
39:30down the Po Valley
39:31and into the lagoon.
39:35All this pollution
39:36is swept out of the lagoon
39:38and into the sea
39:38every day,
39:39twice a day,
39:40by the tides.
39:41If narrowing the inlets
39:45would be harmful,
39:47then what kind of damage
39:48would be done
39:48by the mobile gates,
39:49which would close off
39:50the lagoon completely?
39:54How long would the gates
39:55actually be closed
39:57when high seas threaten?
40:00Recently,
40:01nature provided the engineers
40:02with another opportunity
40:03to test their gates' performance,
40:06at least virtually.
40:10On November 6,
40:112000,
40:12tidal charts in Venice
40:14called for a modest high tide,
40:16just a few inches
40:17above the mean.
40:19Later that day,
40:20meteorologists forecast
40:21that a storm
40:22would push the tide
40:23two and a half feet higher,
40:25which would cause
40:26some flooding.
40:28But the storm
40:29took a sudden turn
40:30for the worse.
40:31And by 9 p.m.,
40:33the tide had risen
40:34to four feet,
40:35enough to flood
40:3693% of the city.
40:42Afterwards,
40:43researchers created
40:44a computer simulation
40:45of the storm
40:46to see how effective
40:47the mobile gates
40:48might have been.
40:49The gates would have been shut
40:53for nine hours,
40:54and the water level
40:55in the lagoon
40:56would have reached
40:57not more than
40:57two feet,
40:58three inches.
40:59The engineers believe
41:02that once the gates
41:03were opened again,
41:05tidal flushing
41:05would soon clean out
41:07any built-up pollution.
41:08But what about
41:10repeated closures
41:12over the course
41:12of an entire season?
41:14What effect would these
41:15have on water quality?
41:18According to Pierre Vellinga,
41:20who was on a government panel
41:21which evaluated the gates,
41:23not much.
41:24Well, I'm a professor
41:25in environmental sciences
41:27myself,
41:28and we have taken
41:29the concerns
41:30of the green people
41:31very serious.
41:32But when we studied it,
41:33we came to the conclusion
41:35that the closure
41:36of the barrier,
41:37say, 10, 20 times a year,
41:39has about the same effect
41:41as when you have
41:42lower tides in summer.
41:45The claim
41:46that these mobile gates
41:48would really be bad
41:49for the environment,
41:50we could not find
41:51any ground for.
41:56If the gates
41:57were in place today,
41:58they would probably
41:59be closed on average
42:00about seven times a year.
42:02Even most environmentalists
42:04agree this is not a problem.
42:06But what will happen
42:10in the future?
42:11Remember,
42:12Venice is sinking,
42:14and the sea is rising.
42:16Won't the gates
42:16have to be closed
42:17more often?
42:20That depends on
42:21how much the city sinks
42:22and the sea rises
42:24in the next hundred years,
42:25the expected life
42:26of the mobile gates.
42:28Figuring that out
42:29is tougher
42:30than it might seem,
42:32because in the middle
42:33of the last century,
42:34Venice started to sink
42:35at an unusually high speed.
42:40The problem was soon
42:41traced to Port Marghera,
42:43where factories
42:43were pumping large amounts
42:45of groundwater
42:45out from deep
42:47under the city.
42:48The groundwater wells
42:50were active
42:51from the 30s
42:51through the early 1970s,
42:54I believe,
42:54and when they were stopped.
42:56And they were stopped
42:57because it was realized
42:58that it was actually
42:59drawing the city down
43:00at a faster rate
43:01than it would be
43:03sinking naturally.
43:06The pumping
43:07was a catastrophe
43:08for Venice.
43:09In less than a century,
43:11the city lost
43:12about nine inches
43:13against the sea.
43:14But when the pumping
43:17stopped,
43:18the sinking slowed down
43:19drastically.
43:23In the last couple
43:24of decades,
43:25Venice sank very little.
43:28No one knew
43:29how fast Venice
43:30would sink in the future,
43:31so the gate planners
43:32chose several
43:33possible scenarios.
43:37One scenario
43:38was very conservative,
43:40predicting that Venice
43:40would sink
43:41less than two inches
43:42in the next hundred years.
43:44before long,
43:47this choice
43:48was coming under attack
43:49and from an unlikely source.
43:52We found
43:53that the scenarios,
43:54the projections
43:55that they were using
43:56in these impact studies
43:58were completely wrong.
44:01There were fundamental flaws.
44:04Albert Ammerman
44:05is an archaeologist,
44:06not an engineer.
44:07But together
44:08with marine geologist
44:10Charles MacLennan,
44:11he had uncovered
44:11controversial new evidence
44:13about the change
44:14sea level of Venice.
44:16There was no motivation
44:17on our part
44:18to study
44:19or evaluate
44:21the mobile gates.
44:23Our initial purpose
44:24was really
44:25to look at the archaeology.
44:27Inadvertently,
44:28we learned about
44:31sea level
44:32in the lagoon of Venice.
44:33By carefully measuring
44:35and dating
44:35and the different levels
44:36of ancient buildings,
44:38the team tried
44:38to determine
44:39how fast
44:40the seas in Venice
44:41have been rising
44:42throughout her long history.
44:44The result of this
44:45was we could see
44:46the average rate
44:47of change
44:48was five inches
44:49per century.
44:51The team believed
44:52the gate planners
44:53had been too optimistic
44:54about Venice's
44:55rising sea level.
44:57And they began
44:58to question
44:59some of the planners'
44:59other conclusions,
45:00particularly
45:01their predictions
45:03about global warming.
45:07Global warming
45:08is a contentious issue,
45:10especially when it comes
45:11to its effect
45:11on sea level.
45:17Hollywood films
45:18have had a field day
45:19with the doomsday scenarios
45:21resulting from
45:21melted polar ice caps.
45:23Waterworld,
45:29starring Kevin Costner,
45:31depicts a future
45:32where dry earth
45:33is a hot commodity.
45:36Jerks!
45:40And Steven Spielberg's
45:42A.I. transforms
45:43Manhattan
45:44into a waterlogged
45:45ghost town.
45:46If New York
45:53is going to look
45:53like this,
45:54then Venice
45:55is a goner, too.
45:59But we don't have
46:00to melt all the ice
46:01on Earth
46:02to have problems.
46:05Even with a little bit
46:06of global warming,
46:08the oceans will expand.
46:10That's what water does
46:11when it's heated.
46:12And if the oceans
46:13get bigger,
46:14there's nowhere
46:14to go but up.
46:17But predicting
46:18how far up
46:19and how fast
46:20is extremely tricky.
46:22We sometimes think
46:24that the oceans
46:25are like one tub
46:27of water
46:28and when it gets hotter,
46:31the water expands
46:32and rises.
46:34But if the climate
46:35changes,
46:36then also the wind
46:37changes
46:38and the storm
46:40surges change.
46:42So the water
46:43will be pushed up
46:44differently
46:45in different parts
46:46of the world.
46:48Official estimates
46:49for global sea level
46:50rise in the next
46:51hundred years
46:52are all over the map,
46:53from four inches
46:54to three feet.
46:56Exactly what's going
46:57to happen in Venice
46:58is anybody's guess.
47:03The gate planners
47:03estimated a probable
47:05rise of about
47:06eight inches,
47:07meaning that the barriers
47:08would be closed
47:09just a few times
47:10a year.
47:10For this kind
47:12of sea level rise,
47:13it's probably
47:14necessary to close
47:16the gate
47:16approximately
47:1712 times a year
47:18or 45 hours
47:20per year.
47:22The length
47:23of closure
47:24is very,
47:24very small
47:25compared to
47:26the time
47:27when tidal
47:28flushing
47:28can be effective.
47:30But gate critics
47:31think that these figures
47:33are too optimistic.
47:34if one accepts
47:36notions about
47:37global warming,
47:38what reasonable
47:38scientists around
47:40the world think
47:40will happen
47:41is that over
47:42the next hundred
47:42years,
47:43the midpoint range
47:45of what they think
47:45will happen
47:46is that there'll be
47:47an 18-inch rise.
47:50If that happens,
47:51then you're going
47:52to have aqualta
47:53all the time,
47:54and then you're going
47:55to have an emergency
47:56situation.
47:57The problem
47:59that I see
48:00with the mobile gates
48:02in the Lagoon of Venice
48:03is that the closing
48:05may have to be
48:06too frequent
48:07and for too long
48:08duration each time.
48:10What we're talking
48:11about is in a bad year,
48:13out in the later years,
48:14maybe after about
48:152060,
48:162070,
48:17you could have
48:18day after day,
48:19week after week,
48:20some days even
48:21two closings.
48:24Ammerman and
48:25McLennan fear
48:26there were so many
48:27closings,
48:28pollution inside
48:29the lagoon
48:30could build
48:30to dangerous levels.
48:35But what will
48:36pollution levels
48:37be like 60 years
48:38from now?
48:41Aerial surveys,
48:42along with sampling,
48:43have shown that
48:44water quality
48:45in the lagoon
48:45has improved somewhat
48:46over the last decade.
48:51And it would be
48:52nice to think
48:52that at some point
48:53in the next 60 years,
48:55Venice will
48:56build a sewage
48:57treatment facility.
48:59But if the worst
49:01case scenarios
49:02for global warming
49:03come true,
49:04it won't matter
49:04how clean or dirty
49:05the water is.
49:07There will simply
49:08be too much of it.
49:13For some,
49:14this is reason enough
49:15not to build the gates.
49:16Well,
49:18in the next 100 years,
49:19Venice has undoubtedly
49:20got a serious problem
49:21because all the projections
49:23for sea level rise
49:24indicate a rise of around
49:2650 centimeters
49:27to 100 centimeters.
49:29And that is going to mean
49:30that a mobile gate solution,
49:31which has been put forward,
49:33will be impossible
49:34to implement.
49:38But when others
49:39consider the rising seas,
49:41their conclusion
49:41about the gates is...
49:43Well,
49:44exactly the opposite.
49:45Because we know
49:46so little
49:47and we think
49:48the lagoon is precious
49:50and Venice is precious,
49:52the mobile gates
49:53is like a precautionary measure.
49:56It will be very useful
49:58for at least 100 years.
50:00And if sea level
50:01comes quicker
50:02than you think,
50:03at least you have a way
50:05to save Venice.
50:06But are these mobile gates
50:10the best way
50:11to save Venice?
50:13Ammerman can't help
50:13wishing there were
50:14more choices.
50:16What you're going at
50:16with the gates
50:17is one big final thing.
50:19It's like trying to throw
50:20a long touchdown pass
50:22or hit a home run.
50:24And what's going to happen
50:25if you miss?
50:25And that doesn't work.
50:26You have nothing in place
50:28as a building block
50:29for the next generation
50:29to take you out
50:31to 2,100
50:32or 2,200.
50:36He supports more studies
50:37and openness
50:38to new ideas.
50:40The engineers say
50:41with or without
50:42more research
50:43it's time to build.
50:46As a general rule
50:48I suspect
50:48that wait and see
50:50when you deal
50:51with phenomena
50:52that change
50:53on global change scales
50:56would be a rather
50:57unsuitable procedure.
50:59Especially if you have
51:00to protect treasures
51:01of humankind
51:03like the city of Venice.
51:04It's art,
51:05it's heritage,
51:06it's architecture.
51:08I think you first
51:10have to act
51:11and learn simultaneously.
51:13If you only want
51:13to study
51:14and the sea level
51:15rises quickly
51:16you lose Venice
51:18and you lose the lagoon.
51:19You lose both.
51:21So we think
51:22this solution
51:23is very good
51:25for the short term
51:26and if you postpone
51:29and study
51:29and study
51:29and study
51:30and study
51:31we may study
51:31until the sea
51:32has risen 50 centimeters
51:34then you're not safe.
51:38Today the Italian government
51:40seems intent
51:41on building the gates
51:42which could take
51:44eight to ten years.
51:46If the gates
51:47are constructed
51:47there's little doubt
51:48that they will stop
51:49the worst floods
51:50at least for a while.
51:51But at some point
51:54the mobile gates
51:55may not be enough
51:57to hold back
51:58the rising sea.
52:00Having invested
52:01so much
52:02will the government
52:03be able to launch
52:04an even bigger project
52:06if the gates
52:07become obsolete?
52:09In the long term
52:11that temporary solution
52:12costing perhaps
52:14three billion US dollars
52:16will have to be repeated
52:17by something
52:18more permanent.
52:21Venice
52:22and its lagoon
52:23will have to be
52:24sealed off
52:24from the sea.
52:28What would it take
52:30to create
52:30a permanent solution
52:31for Venice?
52:33There seem to be
52:34two main possibilities.
52:37Wall off the city
52:38from the lagoon
52:39or wall off the lagoon
52:41from the Adriatic
52:42with permanent dikes
52:43transforming it
52:45into a freshwater lake.
52:47For a city
52:49so intimately linked
52:50to the sea
52:51both proposals
52:53seem unthinkable.
52:56But the water
52:57is rising.
52:59Eventually
52:59something will have
53:01to give.
53:04The Venice
53:05you know today
53:06cannot be preserved
53:07as it is today.
53:12Because all the data
53:13we have
53:13on global sea level
53:15and local sea level
53:16is to our disadvantage
53:17when it comes
53:18to the city of Venice.
53:21It was built
53:22on a salt marsh
53:23at sea level
53:23in a sinking area
53:25and unfortunately
53:27sea level
53:27is rising.
53:34For now
53:35those who love Venice
53:37hold their breath
53:38hoping that the city
53:41that has defied time
53:43for so many centuries
53:44will somehow manage
53:47to hold on.
53:56Rising sea levels
53:58shipping channels
53:59the weight
54:00of the city itself.
54:02On Nova's website
54:03use a clickable map
54:05to see all the ways
54:06that Venice
54:06is under siege
54:08at pbs.org
54:10or America Online
54:11keyword
54:11PBS.
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