This rather sad-looking railway viaduct behind me
means a lot to me, you know, because right from being a very small boy,
I used to go climbing in the iron girders
when I was eight years old. When a train came,
with a load of coal wagons on, the whole lot used to shake about.
In foggy days... There's a little ledge up there
that just looked like a sentry box.
This guy sat there all night with a coke brazier and the fog signals.
You'd stick them on the track. Each time the engines come - bang! bang!
It were really exciting times in a way.
Before this road appeared,
the valley were about 50 or 60 foot deeper.
The River Croal which is still down there somewhere under the road
used to flow along the bottom.
From the earliest times, man's had the problem of going across rivers.
The first bridges were very simple affairs.
By the Middle Ages, they were more ambitious.
Even then, they were limited by the length of the arch they could build.
In 1741, Europe's first wrought-iron suspension bridge was built over the River Tees.
The basic principle of suspending a path or roadway from cables
rather than building one on arches meant wider spaces could be crossed.
The idea was taken up rapidly.
But it was not until the 1820s
that advances in the design and manufacture of wrought-iron chains
made it possible for Thomas Telford to build his two suspension bridges
in North Wales.
When it was opened in 1826,
the Menai Bridge was the longest suspension bridge in the world.
Telford's original wrought-iron chains
have now been replaced by steel.
So I went to have a look at the Conwy Bridge
where all the original wrought iron is still in place.
Telford surveyed quite a few places round Conwy
for his bridge.
But he selected this place near the castle,
because the rock for the anchors - the anchor chambers - was superior.
There were plenty of it.
It started in 1822, when the first stones were laid.
Then he got the chains across in an odd way. They built a rope bridge
and started from each end, advancing towards the centre.
He must have been nervy with that tonnage resting on ordinary ropes.
Then the middle pin went in
and, once they'd got the chains across, it were quite a simple job
putting the vertical bolts or bars down to the road surface
and building a road on it.
In all, it took a little more than four years to construct.
All the iron work was made in a workshop in Shrewsbury.
Basically, each chain consists of five bars,
about ten feet long by about four,
by an inch and a quarter thick,
with an eye forged on each end.
They're all held together by...
fishplates that are spaced in-between them
and then two bolts slammed through the lot, three inches in diameter.
It's certainly a good bit of drilling and fixing.
It's stood the test of time.
Thomas Telford was one of our greatest civil engineers.
He built roads, bridges and canals.
But one of his most dramatic engineering feats
is this aqueduct that carries the Shropshire Union Canal
across a valley high above the River Dee near Llangollen
in North Wales.
19 arches, each with a span of 45ft
carry the waterway over in a cast-iron trough.
We're now about to go over
Mr Telford's famous aqueduct.
I've read about it and seen it on postcards.
The sides are thin, made of cast iron.
Number one,
it would be better if I got it lined up right.
How much space is on each side? When the boat's on it, three inches.
We're going to bump into the side.
Here we go.
When exactly were it completed?
When were it built?
They started it in 1795.
It was completed in 1805.
And it must have been a wonderful feeling
when they first did it, when they first filled it up with water.
They left it, didn't they, for quite some time
to see if it leaked or anything terrible happened?
How far up is it?
It's 126ft
at the highest point over the Dee.
They're all sandstone pillars coming up.
The arches are cast iron as well.
Cast-iron arches. Yeah, the rails, the arches.
Under the towpath is all cast iron.
Do they ever empty it? Yes, to do maintenance.
In a hard winter, they have to break the ice, else it would push the sides out.
If it did freeze, it wouldn't do it any good. To empty the aqueduct,
it's about three hours,
just the aqueduct.
How big's the bung hole?
It's probably about a couple of feet, if that.
A foot and a half, two foot square.
It's fairly big, then. Big waterfall down into the River Dee.
I bet it's a rare sight when it's gushing out.
Does it ever go over the edge? No, because there's a weir at the far end.
So if there's any excess water, it runs over the weir into the river.
But it's never run over the top.
I wonder what these other holes were for.
I don't know. They've never had a rail on as far as we know.
They might be for a rail.
Unless it was part of the casting when they casted it.
Now, this aqueduct has got a strange name
that I can't pronounce. I'll let you do it.
It's called the Pontcysyllte Aqueduct.
The Ponty-suckley Aqueduct?
Yes. I knew I'd get it right. A bit of practice.
There's another boat coming. He's coming this way.
He's waiting for us to come off.
MUSIC OBSCURES CONVERSATION
The building of Britain's canal network
in the 18th and early 19th centuries
left a legacy of great engineering projects.
As well as aqueducts to get across valleys, they also had the problem
of getting over hills. If they came to a small hill,
they'd dig a cutting. If they came to a longer hill
with a plateau, they'd build locks up one side and down the other.
If they came to a big hill,
they'd build a tunnel through it.
This is the Dudley Tunnel which was opened
in 1792
to connect Dudley with the Birmingham canal.
Modern canal boats have got engines.
But, of course,
in the olden days, they had horses.
What did they do with the horse when they came to a tunnel? Simple.
They'd let the horse wander over the top of the hill itself.
Or one of the boat crew would lead it over, one of the kids, maybe.
And then they'd have to
use manpower to get the boats through.
70 ton of tackle.
There'd be about 30 ton of goods in the boat which weighed 15 tons.
The one method was to use a boat shaft and push on the roof.
But that used to wear the bricks away.
So the canal company preferred them to use legging.
Things have changed. People got paid to do the legging.
Now people pay us to let them do the legging. Want a go? Aye.
We've got a legging board here.
Put the board across the middle of the boat.
This is where we get friendly.
How's that?
I'm going to enjoy this.
OK? Get down flat.
Oh, like that! Right.
Which way are we going? Push towards the stern,
towards the cabin.
The wall's going further away!
We're doing a fair rate of knots.
I don't fancy it for two mile!
You don't want to do it for a living? No.
I'd sooner be a traction engine driver.
They used to cheat a bit.
They'd sometimes tie three boats together.
Once they got them going, they'd keep them going
and earn three times the money. My cap's falling off!
In lots of ways, it's a lot harder to build a canal than a motorway,
when you think of getting water across valleys and all of that.
The credit goes to those who built all this.
On the main canals, workers were named navvies - navigators - because they were building a waterway.
I suspect when it came to the tunnels,
they got more skilled labour in to do that.
Here we are, light at the end of the tunnel.
Keep running in the air, you keep it going!
The name stayed with the navvies. In the 1800s they had more work
building the railways.
It was an age of massive engineering projects.
Isambard Kingdom Brunel tunnelled under the Thames at Rotherhithe,
the first tunnel under a vast expanse of water.
When he was building his Great Western Railway in the 1830s,
he crossed the river at Maidenhead on the longest and flattest arches ever built,
a record that still stands today.
The coming of the railways pushed forward the development of bridges.
As the 19th century progressed,
bridge-building became daring and dramatic, but not without mishaps.
The Tay Bridge was opened in 1878.
But one year later, it collapsed in a storm
just as a train was crossing over.
The engine and all its carriages plunged into the river.
All 75 people on board lost their lives.
The bridge's designer, Thomas Bouch, had already made plans for a bridge
across the Firth of Forth.
After the disaster, they were dropped. A new design was sought.
The bridge that was constructed
was the greatest engineering wonder of the Victorian age.
The design of the Forth Bridge had two major innovations
the use of steel and the cantilever principle.
Three great piers were built.
On these, they erected steel towers.
From the towers,
the six cantilevered arms were built out on both sides.
By the time it was completed in 1890,
it was the wonder of its age.
I would have loved to have seen it
when steam trains came thundering across,
and to have been able to go up on the girders with the painting gangs.
Now the bridge carries
150 trains a day, but most are just little diesels.
It's now 110 years old and a major refurbishment is under way.
It gave me the chance to have a good look.
When you climb on the Forth Bridge,
it's amazing how the great cantilevers
are not mechanically connected at all.
To allow for contraction and expansion,
they are just linked up together like a chain.
And it's because of this, of course,
that when you stand on the very top of it,
350ft up in the sky,
and a locomotive comes onto the bridge
under the cantilevers,
you can feel the whole thing rock.
It was a great feeling up there and a credit to the men who built it -
and all that based on the cantilever principle.
So let's have a practical demonstration of how it works.
This is the principle of the cantilever bridge,
very similar to the Forth Bridge.
Whether Mr Fowler did anything like this or not, I don't know.
As you can see, it's supporting the whole weight of my wife here,
with not too much effort.
If I were replaced by a girder,
one up and one down with middle supporting struts,
it would be quite successful.
It's creaking a bit but it's holding her weight.
This bit here in my sort of...left hand
is the cantilever.
This other bit is the counterbalance
that stops the thing from falling over.
I've come to London to see another Victorian engineering feat -
Tower Bridge, built at the end of the 19th century.
Inside that great castle-like exterior,
there's a great big steel frame
that was constructed by the same men who built the Forth Bridge.
Before the Victorian age, there had never been a bridge downstream of London Bridge.
But a massive growth in the population made a new one essential.
The problem was, this stretch of the river
had some of London's busiest docks.
Any bridge would have to give up to a 140ft clearance for tall ships.
The solution came from Horace Jones, the city architect,
with his design for Tower Bridge.
It took eight years to build
and five major contracting companies,
and the relentless labour of 500 men.
There's about 11,000 tons
of steel in the towers and walkways and roadways.
On the completion of the steelwork,
it was clad in Cornish granite and Portland stone,
both to protect the iron work and give it that beautiful appearance.
When you come inside one of the towers,
you can see its great steel skeleton all riveted together.
The whole thing would stand up without the fancy stonework
or beautification on the outside.
It's a wonderful bit of iron work.
Let's do some riveting.
The bridge is hydraulically operated.
The original machinery is in the engine rooms,
including these beautiful steam engines that once powered
the hydraulic pumps.
The energy that was created was stored in six massive accumulators,
like this.
So as soon as the power was needed to lift the bridge, it was there.
Great engineering didn't end with the Victorians.
Just downstream from Tower Bridge,
there's an example of a modern engineering feat.
Over the last 20 years,
there's been some impressive engineering achievements,
two of which have been the Channel Tunnel and the Thames Barrier here.
This unique piece of engineering spans the Woolwich Reach
and it's 520 metres from this side to the other.
Basically, it consists of ten large gates
that are supported on great concrete piers and abutments
which the gates actually swivel round.
The piers also contain all the machinery
for activating the thing in case of emergencies.
Each of the four main gates
weighs 3,700 tons.
When open, they stand as high as a five-storey building
and as wide as Tower Bridge.
It took 4,000 men and women
from all over Britain, to construct it. It took eight years.
It cost nearly £500 million.
Most people won't know where we are, Martin.
You don't expect tunnels like this under lock gates. That's right.
This is the concrete sill.
The main reason for the tunnels is to give us access to the piers.
But the sill's there
like a door frame for the gate,
so the gate can open and close in and out of this concrete sill.
There's two of these, isn't there,
one on each side of the hollow bit the gate sits in when it's open.
That's right. The two tunnels give us duplicate services.
They both carry power and water.
So if one flooded, we could still close the barrier using the other.
This is the machinery room.
Here are the big hydraulic rams
which we use to close and open the gates.
When we pump the hydraulic oil in, they pull on the link to rotate the gate.
Blooming 'eck.
This is an interesting bit.
It's the great crank that makes it go round.
This is connected to the other end of the hydraulic cylinders.
As the hydraulic cylinders push and pull, it rotates this rocking beam
that's connected to a gate arm that rotates the gate out of the sill.
The 3,600 tons comes rising up to close out the tide.
If there's a spring tide, a strong easterly wind and a low pressure,
they combine to create a high tide
and that's when we need to go into closure mode.
We've actually closed 33 times to protect London from flooding.
We can actually close the barrier in 15 minutes.
But it creates a dangerous water hammer effect.
So we like to take two hours to close.
The notch level around the pier there,
that's the height of the walls
upriver towards London.
So you know, if it's getting near there,
things are getting dodgy? We need to be closed
if it's near the notch. The width of the piers
is the same as Tower Bridge.
That's this internationally-known design.
So that anyone who builds a boat
which is wider than this,
it won't fit through here or Tower Bridge.
It won't fit through the Panama Canal and so on. I didn't know that.
The Thames Barrier isn't really a bridge
or a tunnel.
But it's a great piece of engineering
that combines elements of each.
Building it has been a major challenge but within a year,
engineers had started to make plans for an equally ambitious project -
a tunnel under the Channel.
There have been many attempts to link England and France by tunnel.
But it wasn't till the 1980s
that the British and French governments agreed
to the Channel Tunnel link.
It opened in 1994.
It's made up of three tunnels.
Two are for the trains
and the third is a central service tunnel.
Work on the tunnel started in December 1987.
They cut their way under the Channel
with these huge tunnel-boring machines.
It took three years before the British and French tunnelling teams
achieved their breakthrough
and another four years before it opened.
The whole thing is a wonderful piece of civil engineering.
But, unlike bridges, there's not a great deal of it you can see.
To see the latest bridge-building design and construction,
I went back north to the River Humber.
In the 1960s and 1970s,
Britain led the world in the design and building of suspension bridges.
This bridge over the Humber, behind me,
at the time of its building was the biggest in the world.
Alas, I'm sad to say, the good old Japanese have built one bigger.
Work began in 1973.
It took eight years to complete.
Thousands of tons of wire and concrete were used
and over 1,000 people were engaged in its making over various periods.
The towers are 533ft high.
I was taken up to the top by Roger Evans, the bridge master.
Well, Roger,
here we are
500ft above the River Humber.
How the heck did this start with the first wire, sort of thing?
It starts with a couple of men in a boat
laying a wire rope on the bottom of the river,
taking it over the top of the other tower and pulling it tight.
When you can get several of them across,
you can put a mesh on top to make a walkway.
It must have been a hairy business... I wasn't here.
..with dog clips holding them onto the wires
as they advanced out across.
Would a gale like this
sort of stop work? I should imagine...
Yeah, it's getting near that level.
When they're actually working with the cable spinning,
the wheel's pulling the wires across that way at 30mph,
then a cross wind maybe 40mph blowing sideways on.
So, very hazardous. It took longer as a result.
How long is it from end to end?
It's about a mile and a half
between the two anchorages.
Think how much wire it is - 15,000 wires going a mile and a half.
There's enough to go
nearly twice round the world. It looks quite fragile, really.
I know there's many tons... How much weight is there in the bridge?
The cables weigh 11,000 tons. Their first job is to support their own weight!
And then you've got 17,000 tons of road there.
On a good day, we've got 6,000 tons of traffic.
So we're talking big figures.
So these pillars are really under some compression? Yeah.
That's why they can bend so much.
They have a compressing force in them, so when they bend, you don't get cracks.
Am I right or am I wrong?
I felt distinctly that the things were moving when we came out.
I can feel it here. I'm leaning on this and the tower moves slightly.
At 500ft, they've got to do, haven't they?
Where we are, it's designed to move two feet
either way.
Them cables that go from one side of the Humber Estuary to the other,
what most people don't realise is, there are 14,000 pieces of wire
forming a cable two feet in diameter.
It has unbelievable tensile strength.
Ten times what Mr Telford's wrought-iron bars have got.
It's not 14,000 separate pieces.
It's one bit that crosses the width of the river from this chamber
up, over, down, up and over
and back again 200 times,
making it 400 passes in all.
Each of these 400 bundles is about that big.
And they all fan out in this great chamber,
this great mass of wires like rays of sunlight
coming from a funnel near the top.
How many tons of concrete is it anchored to?
Well, we're in the middle of about...
300,000 tons of mass
and 20,000 tons of pull trying to drag a 30,000-ton lump to the river.
How many bits of wire is there
altogether?
You're looking at 15,000 bits.
22½ thousand miles.
And then, of course, these wonderful bolts
that hold it all down.
There are, like,
12 little 'uns.
They go through this great block.
Really, you'd think that when you look at that lot,
you'd think it were almost impossible to compress it
into a two foot diameter iron rope...well, steel rope.
I always think that.
It's from these slender-looking cables
that the whole weight of the road is suspended.
Subtitles by Michael Bartlett ITFC - 2000
E-mail us at subtitling@bbc.co.uk