Original subtitles

In this episode...

This is the largest water transfer project in the world!

...an engineering megaproject

that's sending water across China

to where it's desperately needed.

I think it's really amazing that all this water

slowly goes under this huge yellow river.

And the groundbreaking innovations from the past...

Wow. That is a long way up.

It's quite hard unless you know what you're doing,

and I'd imagine things can go wrong very easily.

...that make the impossible possible.

Captions by vitac... www.vitac.com

captions paid for by discovery communications

Beijing, China, is one of the world's largest cities,

home to over 21 million people.

But beneath the surface, there's a problem.

This giant city is seriously lacking in drinking water.

Beijing is actually

one of the most water-scarce cities on the planet.

The groundwater is so depleted,

it's actually causing subsidence.

In some areas of the city,

the earth is actually starting to collapse.

Rainfall in the city has been decreasing since the 1950s,

and the problem is only going to get worse.

The south of China has a much higher rainfall than the north,

so could it be possible to transport water

across the country from the south to the north?

Moving enormous quantities of water

across one of the world's biggest countries

seems impossible.

But engineers have come up with something truly spectacular.

The south-to-north water diversion project

is the largest and most ambitious in the world.

Once complete, the entire network will be

over 2,700 miles long,

more than the distance between New York and L.A.

Three routes... eastern, western, and central...

Will connect rivers from the south of China to the north

and transfer over 11 trillion gallons of water each year.

Of the three routes, the eastern has been completed,

and the western has yet to be started,

but the central is the most challenging.

On the central route,

the water must flow over 870 miles

entirely by gravity, with no pumps.

At the start, the Danjiangkou reservoir

will store over 7 trillion gallons of water.

The 5.5-mile-long Shahe aqueduct

will transport the water at 100,000 gallons per second.

It will then travel under the yellow river

and arrive 15 days later in Beijing.

China's water diversion project is so massive,

it takes days to drive from one end to another.

I'm following a central route from Danjiangkou to Beijing.

New York-based architect Wendy Fok

is traveling from the south to the north

to see how this seemingly impossible project

is being built.

It's such a huge challenge.

How do you move water

thousands of kilometers across a whole country?

How do you cross mountains, rivers, valleys,

and all these types of terrain and keep water flowing downhill?

How do you manage the flow of water over such large distances?

Wendy's journey along the central route

starts in the south

at one of the largest manmade lakes in China,

the Danjiangkou reservoir.

It's beautiful here.

The water here will travel over 850 miles north to Beijing.

Every drop of this water in this reservoir

is going to be heading north,

so in order to contain this much water,

you need a very big dam.

The original dam has been here since the 1950s,

but it's not big enough for this project.

When this dam became part

of the south-north water diversion project,

more water had to be contained.

So to do this, they had to raise the dam by 15 meters.

Raising a dam is not easy.

Old concrete and new concrete are not easy to join.

And the dam's location raises the stakes even higher.

There's approximately 700,000 people that live here,

so it's vital for the engineers

to make sure that a dam does not break.

To find a solution to raise the dam safely,

engineers had to look to the past.

I'm really excited to see this.

This place is part of engineering history.

Engineer Dan Dickrell is in

the Sierra Nevada mountains in California

to check out a construction

that could help inspire the engineers in China.

Wow!

This is the O'Shaughnessy dam.

It's 430 feet tall and 900 feet long.

When it was completed,

it was the second-biggest dam in the world.

Wow!

What an amazing view.

But the dam wasn't always this high.

The original dam, built in 1923,

created the Hetch Hetchy reservoir,

which provided water to the residents of San Francisco.

But within a year, the project hit a snag.

More water was required,

which needed the reservoir to become bigger.

The only way to do that was to raise the dam.

Wow. This is actually quite impressive.

I'm lucky to have access to this space.

Only people that maintain this dam are allowed in this place.

The problem with raising a dam is,

you have to put new concrete on top of old concrete.

Trying to get it to bind together,

there's a problem, because the new concrete

will shrink as it cures, as the water leaves that mixture.

That shrinkage can cause stress

in between the old concrete and the new concrete,

creating a poor bond.

A second issue... a larger dam allows more water to be stored,

but the pressure of that water behind this dam,

trying to force its way out, toppling the dam...

Those forces are tremendous.

At the time, no dam had ever been raised 85 feet,

but water engineer Michael O'Shaughnessy

was determined to build a revolutionary dam

that could achieve the impossible.

The original dam he built was 345 feet tall.

And that was big, but he was a smart guy

and he realized it might need to be bigger in the future.

His design needed to be adaptable.

So, O'Shaughnessy came up with a pioneering design adaptation

to his original dam that allowed it to be raised in the future.

O'Shaughnessy included a series of five-foot steps on the dam.

What this did is it increased the surface area,

and I'm able to bond

between the old concrete and the new concrete

to be as strong as possible.

Building a series of giant steps on the original dam

dramatically increased the surface area,

helping the new concrete to stick.

Engineers took O'Shaughnessy's trick of increasing adhesion

one step further

by scoring and notching the surface of the concrete,

allowing for a tighter bond

between the new and the old material.

The result is an incredible feat of engineering.

The overall reservoir capacity increased by 75 percent,

to an overall volume of over 530 billion liters of water.

More than 80 years after the raising of the dam,

it still provides water to the 2.5 million citizens

of the San Francisco area.

The Danjiangkou dam in south China

is 12 times longer than the O'Shaughnessy dam,

but engineers have still been able to raise it

by almost 50 feet.

This is one of the longest dams I've ever seen.

This dam is huge, and you could really see

the new and the old dam being joined together.

It is so big that the whole thing

actually feels like it's wrapping all around us.

It's amazing.

And with the sun setting, it's beautiful.

Joining the old and new concrete together

was the dam engineers' biggest challenge.

And like the O'Shaughnessy dam in California,

the secret was to increase the bonding area.

First, the existing concrete is blasted

to make thousands of grooves,

which, like the steps on the dam in California,

increase the size of the surface.

Then, thousands of steel rods are drilled into the dam

to help anchor the new concrete as it's poured on top.

It took four years for the dam

to reach its new height of over 577 feet.

But increasing the volume of water in the reservoir

by more than 3 trillion gallons creates a new challenge.

With too much water pressure,

the bottom of the dam would erode away

and the dam itself would tip over.

So to solve the high water pressure

and the base of the dam from eroding,

engineers had to install a huge grout curtain

on the base of the dam.

A grout curtain prevents the weight of water

from seeping underneath the dam's base.

Waterproof grout is injected beneath the dam,

forming a giant underground wall, or curtain, 213 feet deep

that holds the soil under the dam in place.

The engineers succeeded in raising the dam

and filling the reservoir.

But this is just the beginning.

The water now has an 870-mile-long journey north

through some of the country's most challenging terrain.

So digging a very long, very deep tunnel

in this very soft ground is a huge engineering challenge.

China's south-to-north water diversion project

will use three routes

to draw water from the country's southern rivers

and supply it to the drier cities in the north.

The project's central route

begins at the giant Danjiangkou dam.

From here, water will flow entirely by gravity

along aqueducts and open channels

870 miles north to Beijing.

And the water needs to keep flowing

no matter what lies in its path.

155 miles north of the dam

is one of the most challenging terrains on the route...

The Shahe river.

The region's heavy rainfall and swollen rivers

can cause havoc.

This is the Shahe river.

Usually in the rainy season, this is all filled with water.

The ground is really soft, so it's often flooded.

"Shahe" also means "sandy river."

Seasonal flooding will breach the channels

of the diversion project.

Open channels would not work in terrains like this,

so engineers had to devise a new way to move the water.

Could the solution be found thousands of years in the past?

Archeologist Jens Koehler is in Rome, Italy,

seeing how this ancient city met its need for water.

For the first 400 years of Rome's history,

the city relied on water supply from the Tiber river

and from groundwater Wells.

The city was growing,

and these people needed not only space, but water.

There was plenty of water in the Apennine mountains,

62 miles away.

The Romans just needed to find a way to move it.

Roman author Vitruvius

wrote about civil engineering and architecture.

His work on transporting water

was an essential influence for Roman engineers.

Incredibly, what they achieved 2,000 years ago

is still visible today.

This is the solution of Rome's water problems...

The Roman aqueducts.

Rome had 11 of these aqueducts.

These enormous structures

are up to 56 miles long and 108 feet high.

Water comes from the mountains

and flows in the water channel towards the city.

One of the oldest aqueducts is the aqua Marcia.

One can still look into the water channel.

The water level was about two feet high.

This may be one-third or half of this,

but the Roman water is very hard.

It's full of minerals.

And you see this here,

it accumulated up to something like 20 centimeters.

The Romans also devised a way to prevent leaks.

This is plaster

mixed with crushed tiles and crushed pottery.

So something what protects water from penetrating.

We know that they probably mixed olive oil in

to make it even more water-resistant.

Roman engineers started building

more and more ambitious aqueducts.

Aqua Claudia is 43 miles long and over 98 feet high.

Completed around 47 A.D., it took six years to build.

This is one of the best parts of the aqua Claudia.

More than 100 arches of massive stone

are preserved here.

Like the engineers in China,

the Romans had to transport water

across challenging terrain, using only gravity

to keep the water flowing at just the right speed.

Vitruvius recommends as a gradient 0.02 percent...

20 centimeters on a distance of one kilometer...

Because fast-running water causes turbulences

and could damage the aqueduct channel,

and fast water streams transport all impurities...

Pebbles, sand, everything.

Did you want to have this in your final fountains in Rome,

in your drinking water?

No.

To keep the gradient correct,

Vitruvius describes a leveling device called a chorobates.

You see the plumb lines,

and yes, they are both out of level.

Water can be used to check the slope.

I have more water on my right and less on the left.

Let me try to level this.

Once the chorobates is level,

it's possible to continue the straight line

to the next arch position,

using the sights and marking it on a vertical pole.

Down with the finger.

Down.

A little bit up.

And here we are.

Once they knew where level was,

the Roman engineers could build their aqueducts

with the correct gradient.

To decide the gradient, now we have to take off something.

For example, a centimeter or only a half,

depending on the distance.

The same process could be repeated, one arch at a time,

the entire length of the aqueduct.

Using simple tools, the Romans built vast aqueducts

at precise gradients

with an accuracy almost equal to modern devices.

It meant nearly 300 million gallons of water

reached Rome every day,

the same as New York City today.

We are at Fontana di Trevi,

beautiful fountain that is still fed by water

through an ancient aqueduct.

We can learn from Roman aqueducts.

Their simple but efficient construction may help us

to resolve several water transport problems today.

Back at the Shahe river in China,

engineers will need to use this same ancient ingenuity

as they attempt to build the largest aqueduct in the world.

Inspired by the ancient Romans, the Chinese are building

the largest aqueduct in the world at the Shahe river

as part of their south-north water diversion project.

At over 1,300 tons, each section is too big to transport.

Instead, they are constructed on-site using giant molds.

So, right now, we're in front

of the biggest mold that makes the aqueducts.

It is about 7 meters by 9 meters and 40 meters in length.

It's the fastest in-situ, concrete-poured mold in China.

The sections can be built quickly,

but they need to be strong enough

to withstand the forces of the water.

The shape of the mold is super important.

When water flows through it, if it were a square,

all the forces would be on the stress points on the corners.

However, in this case it is a "U"

so that forces are evenly distributed onto the sides.

With the giant u-shaped sections in place,

the enormous aqueduct can be filled.

The Shahe aqueduct carries over 80,000 gallons of water a second

across China's challenging terrain.

Like the Roman aqueducts,

it's constructed at a precise slope of .02 percent

so the water can run along its length.

Site operator Li Zhi manages the flow.

We set meters along the route

to monitor the change of the flow rates

and the volume of the water at any time.

We use a centralized control.

This remotely controlled system, located in Beijing,

can operate 64 curved gates to control the flow rate.

It took engineers 5 years to complete

the 6-mile-long Shahe aqueduct.

Water can now cross the flood-swept area.

But the next obstacle on the central route

is much harder to overcome.

143 miles north of the aqueduct

is one of China's biggest rivers.

This is the yellow river,

and it is the second-longest river in China.

At over 3,000 miles long,

laden with more than a billion tons of silt,

and with a highly erratic flow,

the yellow river is too unreliable

to supply enough good water to the north.

So the south-to-north diversion project has to cross it.

The yellow river is especially difficult to cross

because it wanders its course every year

and it really changes a lot.

And the central route is gravity-fed.

To keep the water flowing downhill,

building above is not an option.

So engineers had to dig underneath into a tunnel.

So digging a very long, very deep tunnel

in this very soft ground is a huge engineering challenge.

At the tunnel entrance,

the scale of the challenge comes into view.

I think it's really amazing that all this water

slowly goes under this huge yellow river.

There's an 8-meter drop that goes from the south side

to the north side.

This keeps the water flowing under gravity.

To ensure the water flows without pumps,

the tunnel's entrance is higher than its exit.

The pressure caused by gravity

will push the water under the river

and keep pushing it upwards...

An amazing 148 feet to the other side.

But with pressure inside the tunnel from the force of water

and pressure outside the tunnel from the weight of the river,

engineers needed a solution to prevent any failures.

Engineer Hu Jingyu is at the project's crossing point.

The yellow river tunnel

uses a double lining structure.

Let me show you.

The outer lining is designed to withstand

the outside water pressure, and the inner lining

is to withstand the inside water pressure.

Between the two linings, there is a drainage blanket

which is about 6 millimeters thick.

At the bottom, we set three drainage pipes.

These will collect all the leaking water

and drain it away as soon as possible.

This releases the pressure between the two linings.

With the plan for the water pressure in place,

construction of the tunnel could begin.

When the water started to flow to the north,

I was very excited and I really wanted to cry.

Once it crosses the yellow river,

the water can flow unobstructed to Beijing.

The south-to-north water diversion project

will carry trillions of gallons of water to Beijing.

But the central route has more than 621 miles

of open channels that are difficult to construct.

To build a channel as long as this is a huge challenge.

That's moving billions of tons of earth.

Could a solution lie

with a pioneering 19th century railroad engineer?

So what we're going to do now is test the accuracy

of the steam shovel using this apple.

China's south-to-north water diversion project

is the world's largest.

It connects the wet south with the dry north.

And New York-based architect Wendy Fok

is on an incredible journey

to see the scale of this groundbreaking engineering.

A dam was raised 49 feet to form a reservoir

for over 7 trillion gallons of water.

From here, the water flows through a 6-mile-long aqueduct

and a 2.5-mile-long tunnel on its way to Beijing.

After moving water across the mighty yellow river,

engineers are dealing with another challenge.

How do you move water across a country?

For most of the central route, it's aboveground

in huge, open channels, just like this one.

Along the central route,

there are more than 620 miles of open channels

that had to be dug quickly.

But to build a channel as long as this

is a huge challenge.

That's moving billions of tons of earth,

and digging slopes like this is not straightforward.

29 billion cubic feet of earth and rock needed to be moved.

To find a solution, the engineers need inspiration

from one of history's innovators.

Crane operator Katie Kelleher is moving soil near Birmingham

in England�s west Midlands.

The industrial revolution

in the mid-19th century in Britain and America

meant we needed a lot more transport links.

This led to planning of new railways and new canals.

At the time, these projects could only be dug by hand.

Digging by hand does get the job done, as you can see.

The problem is, it's really, really slow.

The engineers needed to come up with a new way

to move earth really fast.

In 1835, civil engineer William Otis

was working on a 41-mile-long railroad in Massachusetts.

To help with this backbreaking work,

the 22-year-old devised a groundbreaking invention...

...the steam shovel.

This monster machine uses around 1 ton of coal a day

to heat almost 3,000 gallons of water to make steam.

The pressure from the steam moves 6 pistons,

which drive cables to move the boom and dipper up and down

or turn and propel the machine.

William Otis wanted it to be based around

the guy working with the spades.

So you can see you've got the beam here

and you've got the dipper down here,

so it's a bit like an arm.

So it's a bit like my arm, up to my elbow,

and my hand's coming down into the bucket.

So if you think of it a bit like a gentleman digging

and working away like that...

So this machine actually replaces the work of 30 men.

With the help of owner Graham and furnaceman David,

Katie's getting a unique chance

to operate the steam shovel herself.

You have three levers... One to slew it 'round,

you have one to move the bucket up and down,

and you also have a button to release the bucket.

Unless you know what you're doing,

something like this is very, very difficult.

Okay.

Take the weight on the brake. Right, push it there.

Put on your brake. Yep.

That's it. Slew around.

The way this arm works is like nothing I've ever seen.

Pull the right?

Yeah.

Whoa!

So you can see, the steam shovel takes a lot of effort to drive.

It is not easy at all.

It doesn't have any electronics.

It's quite hard unless you know what you're doing,

and I'd imagine things can go wrong very easily.

So I think I'll let the expert, Graham,

show us how it's done properly.

With Graham at the controls,

it's time to show what this machine's capable of.

So what we're going to do now

is test the accuracy of this steam shovel using this apple.

The goal is to pick up just the apple

with as little soil as possible.

So, as you can see, we did pick up

quite a bit of soil as well.

But for 100 years ago, it was very, very impressive.

William Otis' steam shovel was able to quickly

and accurately shift more than 550 tons of earth.

In addition to America�s railroads,

steam shovels dug some of the world's longest canals,

including the 50-mile-long Panama canal.

And by the late 19th century, there were hundreds

of these amazing machines across America and Britain.

When we think of engineering now, we think of excavators.

They're almost everywhere.

We owe all of these excavators to the brilliant William Otis

and his magnificent steam shovel machines.

In China, 5,000 excavators

are digging 29 billion cubic feet of earth and rock

to create the channels that make up

the south-to-north water diversion project's

central route.

But the sides of the channel all need to be dug at the same angle

to ensure that the concrete facing on top won't crack.

So some of the excavators are equipped

with cutting-edge technology

far beyond anything William Otis could have imagined.

In China, 5,000 excavators are being used to create channels

that will make up the central route

of the south-to-north water diversion project.

To ensure the concrete facing on top of these channels

won't crack, they will need to be dug at the same angle.

The excavators are equipped with cutting-edge technology

to get the job done.

Site manager Jorg Schittenhelm oversees the new breed...

The laser-guided excavator.

The apple test is used to see if the laser-guided digger

can pick up the apple with more precision than the steam shovel.

The excavators are extremely accurate,

but in China, they must repeat the same maneuvers

again and again.

This time, the apple test is more challenging.

With the start position measured and memorized,

the test can begin.

This laser-guided technology is invaluable

for the 621-mile-long open channels.

Engineer Wang Shouming oversees the Jiaozuo open channels.

During the construction,

we used a lot of innovations and newly designed machines,

which improved the efficiency of our construction.

Because the excavator has a track,

that means it can pass through the muddy land

and the slope of our canal, so it's very powerful.

Secondly, it is flexible.

It can move forwards and backwards

and rotate 360 degrees quickly,

which also ensures that it has a high efficiency.

Thirdly, it has a powerful bucket

which can scoop up 1 to 2 cubic meters in one go.

Excavated with laser precision,

the 621-mile-long open channels can be dug 30 percent faster.

But some sections need extra treatment

before the water can start to flow.

Engineer Cheng Dehu has been looking at the problem.

The central route

of the south-to-north water diversion project

will pass through

more than 380 kilometers of expansive soil.

This clay-ridden section of soil expands as it gets wet

and shrinks as it dries.

This movement could cause the channel to crack.

The solution we used was to add 5 percent cement

to the weak, expansive soil,

which completely changes its features.

After stabilizing the expansive soil,

engineers could apply the finish to the open channel.

The operation in the past five years

shows the treatment works well.

But as the central route finally reaches Beijing,

engineers will have to design a solution that allows the water

to travel under one of the busiest cities in the world.

More than 850 miles away

from its starting point at the Danjiangkou dam,

the central route

of China's south-to-north water diversion project

is approaching Beijing.

Now the water will have to travel

under one of the busiest cities in the world.

Deputy chief engineer Wang lei oversees the route.

The underground construction is very complex.

There are railway bridges, highway bridges, and rivers.

The distance between the bridge paths and our tunnel

is as little as 1 meter in places.

In the past three years,

the citizens of Beijing weren't affected at all.

They didn't even notice that there was such a massive project

being constructed under the roads and subways

they use every day.

The water from the central route has finally arrived

at the Tianjin reservoir in Beijing.

After a 15-day journey, the water transferred

by the south-to-north water diversion project

is flowing to us from this opening.

Flowing entirely by gravity across China,

along the largest aqueduct on the planet,

through the colossal yellow river tunnel

and along 621-mile-long open channels...

...the water's journey is complete.

The water has made it to Beijing.

It traveled from the south to the north of China.

70 percent of Beijing's water

comes from the water diversion project.

It's an engineering marvel.

It's one of the largest water diversion projects

in the world.

It's amazing how the engineers were able

to design open channels, aqueducts and tunnels.

The south-north water diversion project

is truly one of the most amazing engineering projects

that I've ever seen.

The Danjiangkou dam and reservoir

hold over 7 trillion gallons of water.

The water flows by gravity for 870 miles

from the south to the north of China.

The 6-mile-long Shahe aqueduct

will transport almost 100,000 gallons of water per second.

At the yellow river,

the water travels along a 2.5-mile-long tunnel

before reaching Beijing.

This water diversion project is the latest

in China's long history of engineering achievements.

I feel this project is magnificent.

I'm very proud to be a part of it.

Seeing this clear river flowing to Beijing,

it means the city can enjoy fresh water.

I'm so pleased.

Wow!

By drawing on the innovators of the past,

many challenges have been overcome.

I think that this is

the most magnificent water diversion project on earth.

It took us many years to build,

but it will benefit our citizens for thousands of years.

I'm incredibly honored

to be part of the south-to-north water diversion project.

The engineers

at the south-to-north water diversion project

have succeeded in making the impossible possible.

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