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00:00:37,400 --> 00:00:40,960
This rather sad-looking
railway viaduct behind me

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00:00:40,960 --> 00:00:46,960
means a lot to me, you know,
because right from being
a very small boy,

3
00:00:46,960 --> 00:00:49,960
I used to go climbing
in the iron girders

4
00:00:49,960 --> 00:00:53,400
when I was eight years old.
When a train came,

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00:00:53,400 --> 00:00:57,920
with a load of coal wagons on,
the whole lot used to shake about.

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00:00:57,920 --> 00:01:02,400
In foggy days...
There's a little ledge up there

7
00:01:02,400 --> 00:01:06,120
that just looked like a sentry box.

8
00:01:06,120 --> 00:01:11,000
This guy sat there all night with
a coke brazier and the fog signals.

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00:01:11,000 --> 00:01:15,840
You'd stick them on the track. Each
time the engines come - bang! bang!

10
00:01:15,840 --> 00:01:19,040
It were really exciting times
in a way.

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Before this road appeared,

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the valley were about
50 or 60 foot deeper.

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The River Croal which is still down
there somewhere under the road

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00:01:28,840 --> 00:01:31,440
used to flow along the bottom.

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From the earliest times, man's had
the problem of going across rivers.

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The first bridges
were very simple affairs.

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By the Middle Ages,
they were more ambitious.

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Even then, they were limited by the
length of the arch they could build.

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In 1741, Europe's first
wrought-iron suspension bridge
was built over the River Tees.

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The basic principle of suspending
a path or roadway from cables

21
00:02:04,560 --> 00:02:10,040
rather than building one on arches
meant wider spaces could be crossed.

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The idea was taken up rapidly.

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But it was not until the 1820s

24
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that advances in the design and
manufacture of wrought-iron chains

25
00:02:21,600 --> 00:02:26,600
made it possible for Thomas Telford
to build his two suspension bridges

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in North Wales.

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When it was opened in 1826,

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the Menai Bridge was the longest
suspension bridge in the world.

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Telford's original
wrought-iron chains

30
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have now been replaced by steel.

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So I went to have a look
at the Conwy Bridge

32
00:02:44,160 --> 00:02:48,400
where all the original wrought iron
is still in place.

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00:02:48,400 --> 00:02:52,400
Telford surveyed
quite a few places round Conwy

34
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for his bridge.

35
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But he selected this place
near the castle,

36
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because the rock for the anchors -
the anchor chambers - was superior.

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There were plenty of it.

38
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It started in 1822,
when the first stones were laid.

39
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Then he got the chains across in an
odd way. They built a rope bridge

40
00:03:14,640 --> 00:03:19,080
and started from each end,
advancing towards the centre.

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He must have been nervy with that
tonnage resting on ordinary ropes.

42
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Then the middle pin went in

43
00:03:26,400 --> 00:03:31,080
and, once they'd got the chains
across, it were quite a simple job

44
00:03:31,080 --> 00:03:35,360
putting the vertical bolts or bars
down to the road surface

45
00:03:35,360 --> 00:03:37,400
and building a road on it.

46
00:03:37,400 --> 00:03:42,040
In all, it took a little more
than four years to construct.

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00:03:42,040 --> 00:03:46,120
All the iron work was made
in a workshop in Shrewsbury.

48
00:03:46,120 --> 00:03:49,360
Basically, each chain
consists of five bars,

49
00:03:49,360 --> 00:03:51,800
about ten feet long by about four,

50
00:03:51,800 --> 00:03:54,240
by an inch and a quarter thick,

51
00:03:54,240 --> 00:03:56,560
with an eye forged on each end.

52
00:03:56,560 --> 00:03:59,600
They're all held together by...

53
00:03:59,600 --> 00:04:02,760
fishplates that are spaced
in-between them

54
00:04:02,760 --> 00:04:07,560
and then two bolts slammed through
the lot, three inches in diameter.

55
00:04:07,560 --> 00:04:11,120
It's certainly
a good bit of drilling and fixing.

56
00:04:11,120 --> 00:04:14,040
It's stood the test of time.

57
00:04:15,480 --> 00:04:19,440
Thomas Telford was one
of our greatest civil engineers.

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00:04:19,440 --> 00:04:22,000
He built roads, bridges and canals.

59
00:04:23,360 --> 00:04:27,760
But one of his most dramatic
engineering feats

60
00:04:27,760 --> 00:04:31,800
is this aqueduct that carries
the Shropshire Union Canal

61
00:04:31,800 --> 00:04:35,920
across a valley high above
the River Dee near Llangollen

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00:04:35,920 --> 00:04:38,000
in North Wales.

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00:04:38,000 --> 00:04:41,560
19 arches, each with a span of 45ft

64
00:04:41,560 --> 00:04:45,440
carry the waterway over
in a cast-iron trough.

65
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We're now about to go over

66
00:04:48,880 --> 00:04:51,960
Mr Telford's famous aqueduct.

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I've read about it
and seen it on postcards.

68
00:04:56,800 --> 00:04:59,480
The sides are thin,
made of cast iron.

69
00:04:59,480 --> 00:05:01,680
Number one,

70
00:05:01,680 --> 00:05:04,960
it would be better
if I got it lined up right.

71
00:05:04,960 --> 00:05:10,520
How much space is on each side?
When the boat's on it, three inches.

72
00:05:10,520 --> 00:05:13,040
We're going to bump into the side.

73
00:05:13,040 --> 00:05:15,120
Here we go.

74
00:05:15,120 --> 00:05:17,920
When exactly were it completed?

75
00:05:17,920 --> 00:05:20,000
When were it built?

76
00:05:20,000 --> 00:05:22,000
They started it in 1795.

77
00:05:22,000 --> 00:05:24,320
It was completed in 1805.

78
00:05:25,400 --> 00:05:28,920
And it must have been
a wonderful feeling

79
00:05:28,920 --> 00:05:33,600
when they first did it, when
they first filled it up with water.

80
00:05:33,600 --> 00:05:36,800
They left it, didn't they,
for quite some time

81
00:05:36,800 --> 00:05:41,560
to see if it leaked
or anything terrible happened?

82
00:05:41,560 --> 00:05:43,720
How far up is it?

83
00:05:43,720 --> 00:05:45,760
It's 126ft

84
00:05:45,760 --> 00:05:48,280
at the highest point over the Dee.

85
00:05:48,280 --> 00:05:51,640
They're all sandstone pillars
coming up.

86
00:05:51,640 --> 00:05:54,680
The arches are cast iron as well.

87
00:05:54,680 --> 00:05:58,160
Cast-iron arches.
Yeah, the rails, the arches.

88
00:05:58,160 --> 00:06:01,600
Under the towpath is all cast iron.

89
00:06:01,600 --> 00:06:05,880
Do they ever empty it?
Yes, to do maintenance.

90
00:06:05,880 --> 00:06:12,000
In a hard winter,
they have to break the ice,
else it would push the sides out.

91
00:06:12,000 --> 00:06:16,960
If it did freeze, it wouldn't do it
any good. To empty the aqueduct,

92
00:06:16,960 --> 00:06:18,960
it's about three hours,

93
00:06:18,960 --> 00:06:21,040
just the aqueduct.

94
00:06:21,040 --> 00:06:23,120
How big's the bung hole?

95
00:06:23,120 --> 00:06:26,560
It's probably about
a couple of feet, if that.

96
00:06:26,560 --> 00:06:28,840
A foot and a half, two foot square.

97
00:06:28,840 --> 00:06:33,280
It's fairly big, then. Big
waterfall down into the River Dee.

98
00:06:33,280 --> 00:06:37,400
I bet it's a rare sight
when it's gushing out.

99
00:06:37,400 --> 00:06:43,240
Does it ever go over the edge?
No, because there's a weir
at the far end.

100
00:06:43,240 --> 00:06:48,080
So if there's any excess water, it
runs over the weir into the river.

101
00:06:48,080 --> 00:06:50,440
But it's never run over the top.

102
00:06:50,440 --> 00:06:53,600
I wonder
what these other holes were for.

103
00:06:53,600 --> 00:06:57,680
I don't know. They've never had
a rail on as far as we know.

104
00:06:57,680 --> 00:06:59,840
They might be for a rail.

105
00:06:59,840 --> 00:07:03,640
Unless it was part of the casting
when they casted it.

106
00:07:03,640 --> 00:07:07,120
Now, this aqueduct
has got a strange name

107
00:07:07,120 --> 00:07:10,240
that I can't pronounce.
I'll let you do it.

108
00:07:10,240 --> 00:07:13,080
It's called
the Pontcysyllte Aqueduct.

109
00:07:13,080 --> 00:07:15,320
The Ponty-suckley Aqueduct?

110
00:07:15,320 --> 00:07:19,000
Yes. I knew I'd get it right.
A bit of practice.

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00:07:20,600 --> 00:07:24,080
There's another boat coming.
He's coming this way.

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00:07:24,080 --> 00:07:26,520
He's waiting for us to come off.

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00:07:38,720 --> 00:07:40,920
MUSIC OBSCURES CONVERSATION

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The building
of Britain's canal network

115
00:07:51,680 --> 00:07:54,320
in the 18th
and early 19th centuries

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00:07:54,320 --> 00:07:57,600
left a legacy of great
engineering projects.

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00:07:57,600 --> 00:08:03,160
As well as aqueducts to get across
valleys, they also had the problem

118
00:08:03,160 --> 00:08:07,120
of getting over hills.
If they came to a small hill,

119
00:08:07,120 --> 00:08:10,600
they'd dig a cutting.
If they came to a longer hill

120
00:08:10,600 --> 00:08:15,480
with a plateau, they'd build locks
up one side and down the other.

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00:08:15,480 --> 00:08:17,480
If they came to a big hill,

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00:08:17,480 --> 00:08:20,000
they'd build a tunnel through it.

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00:08:20,000 --> 00:08:23,200
This is the Dudley Tunnel
which was opened

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00:08:23,200 --> 00:08:26,040
in 1792

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00:08:26,040 --> 00:08:29,280
to connect Dudley
with the Birmingham canal.

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00:08:29,280 --> 00:08:31,920
Modern canal boats have got engines.

127
00:08:31,920 --> 00:08:34,040
But, of course,

128
00:08:34,040 --> 00:08:36,600
in the olden days, they had horses.

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What did they do with the horse
when they came to a tunnel? Simple.

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They'd let the horse wander
over the top of the hill itself.

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Or one of the boat crew would lead
it over, one of the kids, maybe.

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00:08:50,520 --> 00:08:53,000
And then they'd have to

133
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use manpower
to get the boats through.

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00:08:55,760 --> 00:08:57,800
70 ton of tackle.

135
00:08:57,800 --> 00:09:03,200
There'd be about 30 ton of goods
in the boat which weighed 15 tons.

136
00:09:03,200 --> 00:09:07,680
The one method was to use
a boat shaft and push on the roof.

137
00:09:07,680 --> 00:09:10,720
But that used
to wear the bricks away.

138
00:09:10,720 --> 00:09:14,800
So the canal company preferred them
to use legging.

139
00:09:14,800 --> 00:09:18,720
Things have changed.
People got paid to do the legging.

140
00:09:18,720 --> 00:09:23,200
Now people pay us to let them
do the legging. Want a go? Aye.

141
00:09:23,200 --> 00:09:25,520
We've got a legging board here.

142
00:09:28,800 --> 00:09:31,840
Put the board
across the middle of the boat.

143
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This is where we get friendly.

144
00:09:37,320 --> 00:09:39,280
How's that?

145
00:09:41,400 --> 00:09:44,000
I'm going to enjoy this.

146
00:09:44,000 --> 00:09:46,040
OK? Get down flat.

147
00:09:46,040 --> 00:09:48,120
Oh, like that! Right.

148
00:09:48,120 --> 00:09:51,720
Which way are we going?
Push towards the stern,

149
00:09:51,720 --> 00:09:53,760
towards the cabin.

150
00:09:53,760 --> 00:09:56,000
The wall's going further away!

151
00:09:59,040 --> 00:10:01,400
We're doing a fair rate of knots.

152
00:10:01,400 --> 00:10:03,920
I don't fancy it for two mile!

153
00:10:03,920 --> 00:10:06,800
You don't want to do it
for a living? No.

154
00:10:06,800 --> 00:10:09,600
I'd sooner be
a traction engine driver.

155
00:10:09,600 --> 00:10:11,880
They used to cheat a bit.

156
00:10:11,880 --> 00:10:15,160
They'd sometimes tie
three boats together.

157
00:10:15,160 --> 00:10:18,960
Once they got them going,
they'd keep them going

158
00:10:18,960 --> 00:10:22,920
and earn three times the money.
My cap's falling off!

159
00:10:24,600 --> 00:10:29,320
In lots of ways, it's a lot harder
to build a canal than a motorway,

160
00:10:29,320 --> 00:10:34,200
when you think of getting water
across valleys and all of that.

161
00:10:34,200 --> 00:10:37,280
The credit goes to those
who built all this.

162
00:10:37,280 --> 00:10:44,760
On the main canals, workers were
named navvies - navigators - because
they were building a waterway.

163
00:10:44,760 --> 00:10:47,600
I suspect
when it came to the tunnels,

164
00:10:47,600 --> 00:10:50,760
they got more skilled labour in
to do that.

165
00:10:50,760 --> 00:10:54,720
Here we are,
light at the end of the tunnel.

166
00:10:57,120 --> 00:11:00,400
Keep running in the air,
you keep it going!

167
00:11:00,400 --> 00:11:05,880
The name stayed with the navvies.
In the 1800s they had more work

168
00:11:05,880 --> 00:11:08,720
building the railways.

169
00:11:08,720 --> 00:11:12,200
It was an age
of massive engineering projects.

170
00:11:12,200 --> 00:11:18,280
Isambard Kingdom Brunel tunnelled
under the Thames at Rotherhithe,

171
00:11:18,280 --> 00:11:22,320
the first tunnel
under a vast expanse of water.

172
00:11:25,400 --> 00:11:30,320
When he was building his
Great Western Railway in the 1830s,

173
00:11:30,320 --> 00:11:36,160
he crossed the river at Maidenhead
on the longest
and flattest arches ever built,

174
00:11:36,160 --> 00:11:38,600
a record that still stands today.

175
00:11:39,840 --> 00:11:45,040
The coming of the railways pushed
forward the development of bridges.

176
00:11:45,040 --> 00:11:47,520
As the 19th century progressed,

177
00:11:47,520 --> 00:11:53,000
bridge-building became daring and
dramatic, but not without mishaps.

178
00:11:53,000 --> 00:11:56,080
The Tay Bridge was opened in 1878.

179
00:11:56,080 --> 00:11:59,160
But one year later,
it collapsed in a storm

180
00:11:59,160 --> 00:12:02,320
just as a train was crossing over.

181
00:12:04,800 --> 00:12:09,480
The engine and all its carriages
plunged into the river.

182
00:12:09,480 --> 00:12:12,280
All 75 people on board
lost their lives.

183
00:12:15,560 --> 00:12:20,680
The bridge's designer, Thomas Bouch,
had already made plans for a bridge

184
00:12:20,680 --> 00:12:22,840
across the Firth of Forth.

185
00:12:22,840 --> 00:12:27,320
After the disaster, they were
dropped. A new design was sought.

186
00:12:27,320 --> 00:12:29,760
The bridge that was constructed

187
00:12:29,760 --> 00:12:34,040
was the greatest engineering wonder
of the Victorian age.

188
00:12:34,040 --> 00:12:38,920
The design of the Forth Bridge
had two major innovations

189
00:12:38,920 --> 00:12:42,160
the use of steel
and the cantilever principle.

190
00:12:42,160 --> 00:12:44,840
Three great piers were built.

191
00:12:44,840 --> 00:12:47,280
On these, they erected steel towers.

192
00:12:47,280 --> 00:12:50,120
From the towers,

193
00:12:50,120 --> 00:12:54,120
the six cantilevered arms
were built out on both sides.

194
00:12:55,520 --> 00:12:58,400
By the time
it was completed in 1890,

195
00:12:58,400 --> 00:13:00,280
it was the wonder of its age.

196
00:13:02,280 --> 00:13:04,920
I would have loved to have seen it

197
00:13:04,920 --> 00:13:08,040
when steam trains
came thundering across,

198
00:13:08,040 --> 00:13:13,040
and to have been able to go up on
the girders with the painting gangs.

199
00:13:14,560 --> 00:13:17,200
Now the bridge carries

200
00:13:17,200 --> 00:13:21,160
150 trains a day,
but most are just little diesels.

201
00:13:23,520 --> 00:13:27,960
It's now 110 years old and
a major refurbishment is under way.

202
00:13:27,960 --> 00:13:30,880
It gave me the chance
to have a good look.

203
00:13:33,760 --> 00:13:36,400
When you climb on the Forth Bridge,

204
00:13:36,400 --> 00:13:39,840
it's amazing
how the great cantilevers

205
00:13:39,840 --> 00:13:43,520
are not mechanically connected
at all.

206
00:13:43,520 --> 00:13:46,360
To allow for contraction
and expansion,

207
00:13:46,360 --> 00:13:49,800
they are just linked up together
like a chain.

208
00:13:49,800 --> 00:13:52,480
And it's because of this, of course,

209
00:13:52,480 --> 00:13:55,480
that when you stand
on the very top of it,

210
00:13:55,480 --> 00:13:58,120
350ft up in the sky,

211
00:13:58,120 --> 00:14:01,120
and a locomotive
comes onto the bridge

212
00:14:01,120 --> 00:14:03,120
under the cantilevers,

213
00:14:03,120 --> 00:14:05,480
you can feel the whole thing rock.

214
00:14:08,680 --> 00:14:13,360
It was a great feeling up there and
a credit to the men who built it -

215
00:14:13,360 --> 00:14:16,640
and all that
based on the cantilever principle.

216
00:14:16,640 --> 00:14:21,520
So let's have a practical
demonstration of how it works.

217
00:14:21,520 --> 00:14:25,360
This is the principle
of the cantilever bridge,

218
00:14:25,360 --> 00:14:27,800
very similar to the Forth Bridge.

219
00:14:27,800 --> 00:14:32,880
Whether Mr Fowler did anything
like this or not, I don't know.

220
00:14:32,880 --> 00:14:38,560
As you can see, it's supporting
the whole weight of my wife here,

221
00:14:38,560 --> 00:14:40,600
with not too much effort.

222
00:14:40,600 --> 00:14:43,440
If I were replaced by a girder,

223
00:14:43,440 --> 00:14:47,280
one up and one down
with middle supporting struts,

224
00:14:47,280 --> 00:14:49,520
it would be quite successful.

225
00:14:50,560 --> 00:14:54,600
It's creaking a bit
but it's holding her weight.

226
00:14:54,600 --> 00:14:58,320
This bit here
in my sort of...left hand

227
00:14:58,320 --> 00:15:00,920
is the cantilever.

228
00:15:00,920 --> 00:15:03,960
This other bit
is the counterbalance

229
00:15:03,960 --> 00:15:07,200
that stops the thing
from falling over.

230
00:15:11,960 --> 00:15:16,840
I've come to London to see another
Victorian engineering feat -

231
00:15:16,840 --> 00:15:20,600
Tower Bridge, built
at the end of the 19th century.

232
00:15:20,600 --> 00:15:23,880
Inside that great
castle-like exterior,

233
00:15:23,880 --> 00:15:26,320
there's a great big steel frame

234
00:15:26,320 --> 00:15:31,000
that was constructed by the same
men who built the Forth Bridge.

235
00:15:31,000 --> 00:15:37,880
Before the Victorian age,
there had never been a bridge
downstream of London Bridge.

236
00:15:37,880 --> 00:15:43,160
But a massive growth in the
population made a new one essential.

237
00:15:43,160 --> 00:15:46,000
The problem was,
this stretch of the river

238
00:15:46,000 --> 00:15:48,680
had some of London's busiest docks.

239
00:15:48,680 --> 00:15:53,840
Any bridge would have to give
up to a 140ft clearance
for tall ships.

240
00:15:55,960 --> 00:15:59,800
The solution came from Horace Jones,
the city architect,

241
00:15:59,800 --> 00:16:02,840
with his design for Tower Bridge.

242
00:16:02,840 --> 00:16:04,960
It took eight years to build

243
00:16:04,960 --> 00:16:09,560
and five major
contracting companies,

244
00:16:09,560 --> 00:16:12,200
and the relentless labour
of 500 men.

245
00:16:12,200 --> 00:16:14,240
There's about 11,000 tons

246
00:16:14,240 --> 00:16:17,880
of steel in the towers
and walkways and roadways.

247
00:16:17,880 --> 00:16:21,320
On the completion of the steelwork,

248
00:16:21,320 --> 00:16:25,080
it was clad in Cornish granite
and Portland stone,

249
00:16:25,080 --> 00:16:30,480
both to protect the iron work and
give it that beautiful appearance.

250
00:16:30,480 --> 00:16:33,400
When you come inside
one of the towers,

251
00:16:33,400 --> 00:16:37,600
you can see its great
steel skeleton all riveted together.

252
00:16:37,600 --> 00:16:41,880
The whole thing would stand up
without the fancy stonework

253
00:16:41,880 --> 00:16:44,880
or beautification on the outside.

254
00:16:44,880 --> 00:16:47,920
It's a wonderful bit of iron work.

255
00:16:47,920 --> 00:16:49,880
Let's do some riveting.

256
00:16:52,120 --> 00:16:56,280
The bridge
is hydraulically operated.

257
00:16:56,280 --> 00:16:59,120
The original machinery
is in the engine rooms,

258
00:16:59,120 --> 00:17:03,800
including these beautiful
steam engines that once powered

259
00:17:03,800 --> 00:17:06,840
the hydraulic pumps.

260
00:17:06,840 --> 00:17:11,520
The energy that was created was
stored in six massive accumulators,

261
00:17:11,520 --> 00:17:13,560
like this.

262
00:17:13,560 --> 00:17:18,200
So as soon as the power was needed
to lift the bridge, it was there.

263
00:17:19,520 --> 00:17:24,120
Great engineering
didn't end with the Victorians.

264
00:17:24,120 --> 00:17:26,840
Just downstream from Tower Bridge,

265
00:17:26,840 --> 00:17:30,600
there's an example
of a modern engineering feat.

266
00:17:30,600 --> 00:17:32,680
Over the last 20 years,

267
00:17:32,680 --> 00:17:36,920
there's been some impressive
engineering achievements,

268
00:17:36,920 --> 00:17:42,240
two of which have been the Channel
Tunnel and the Thames Barrier here.

269
00:17:42,240 --> 00:17:46,440
This unique piece of engineering
spans the Woolwich Reach

270
00:17:46,440 --> 00:17:49,840
and it's 520 metres
from this side to the other.

271
00:17:49,840 --> 00:17:52,920
Basically,
it consists of ten large gates

272
00:17:52,920 --> 00:17:57,640
that are supported on great
concrete piers and abutments

273
00:17:57,640 --> 00:18:00,760
which the gates
actually swivel round.

274
00:18:00,760 --> 00:18:03,720
The piers also contain
all the machinery

275
00:18:03,720 --> 00:18:08,200
for activating the thing
in case of emergencies.

276
00:18:08,200 --> 00:18:10,200
Each of the four main gates

277
00:18:10,200 --> 00:18:12,360
weighs 3,700 tons.

278
00:18:12,360 --> 00:18:16,600
When open, they stand
as high as a five-storey building

279
00:18:16,600 --> 00:18:19,360
and as wide as Tower Bridge.

280
00:18:21,360 --> 00:18:23,640
It took 4,000 men and women

281
00:18:23,640 --> 00:18:28,280
from all over Britain, to construct
it. It took eight years.

282
00:18:28,280 --> 00:18:30,720
It cost nearly £500 million.

283
00:18:37,640 --> 00:18:40,920
Most people won't know
where we are, Martin.

284
00:18:40,920 --> 00:18:46,400
You don't expect tunnels like this
under lock gates. That's right.

285
00:18:46,400 --> 00:18:48,440
This is the concrete sill.

286
00:18:48,440 --> 00:18:53,080
The main reason for the tunnels
is to give us access to the piers.

287
00:18:53,080 --> 00:18:55,120
But the sill's there

288
00:18:55,120 --> 00:18:57,360
like a door frame for the gate,

289
00:18:57,360 --> 00:19:01,800
so the gate can open and close
in and out of this concrete sill.

290
00:19:01,800 --> 00:19:04,320
There's two of these, isn't there,

291
00:19:04,320 --> 00:19:09,720
one on each side of the hollow bit
the gate sits in when it's open.

292
00:19:09,720 --> 00:19:14,000
That's right. The two tunnels
give us duplicate services.

293
00:19:14,000 --> 00:19:16,440
They both carry power and water.

294
00:19:16,440 --> 00:19:21,120
So if one flooded, we could still
close the barrier using the other.

295
00:19:21,120 --> 00:19:23,840
This is the machinery room.

296
00:19:23,840 --> 00:19:26,200
Here are the big hydraulic rams

297
00:19:26,200 --> 00:19:29,080
which we use
to close and open the gates.

298
00:19:29,080 --> 00:19:34,920
When we pump the hydraulic oil in,
they pull on the link
to rotate the gate.

299
00:19:36,640 --> 00:19:38,680
Blooming 'eck.

300
00:19:38,680 --> 00:19:40,760
This is an interesting bit.

301
00:19:40,760 --> 00:19:44,600
It's the great crank
that makes it go round.

302
00:19:44,600 --> 00:19:48,840
This is connected to the other end
of the hydraulic cylinders.

303
00:19:48,840 --> 00:19:53,840
As the hydraulic cylinders push and
pull, it rotates this rocking beam

304
00:19:53,840 --> 00:19:58,640
that's connected to a gate arm that
rotates the gate out of the sill.

305
00:19:58,640 --> 00:20:02,760
The 3,600 tons comes rising up
to close out the tide.

306
00:20:02,760 --> 00:20:07,600
If there's a spring tide, a strong
easterly wind and a low pressure,

307
00:20:07,600 --> 00:20:10,240
they combine to create a high tide

308
00:20:10,240 --> 00:20:14,320
and that's when we need
to go into closure mode.

309
00:20:14,320 --> 00:20:19,000
We've actually closed 33 times
to protect London from flooding.

310
00:20:24,280 --> 00:20:27,640
We can actually close the barrier
in 15 minutes.

311
00:20:27,640 --> 00:20:30,720
But it creates
a dangerous water hammer effect.

312
00:20:30,720 --> 00:20:33,640
So we like to take
two hours to close.

313
00:20:37,440 --> 00:20:40,720
The notch level
around the pier there,

314
00:20:40,720 --> 00:20:42,960
that's the height of the walls

315
00:20:42,960 --> 00:20:45,000
upriver towards London.

316
00:20:45,000 --> 00:20:47,840
So you know,
if it's getting near there,

317
00:20:47,840 --> 00:20:51,320
things are getting dodgy?
We need to be closed

318
00:20:51,320 --> 00:20:54,840
if it's near the notch.
The width of the piers

319
00:20:54,840 --> 00:20:57,400
is the same as Tower Bridge.

320
00:20:57,400 --> 00:21:01,440
That's this
internationally-known design.

321
00:21:01,440 --> 00:21:03,520
So that anyone who builds a boat

322
00:21:03,520 --> 00:21:05,600
which is wider than this,

323
00:21:05,600 --> 00:21:08,680
it won't fit through here
or Tower Bridge.

324
00:21:08,680 --> 00:21:13,880
It won't fit through the Panama
Canal and so on. I didn't know that.

325
00:21:13,880 --> 00:21:17,240
The Thames Barrier
isn't really a bridge

326
00:21:17,240 --> 00:21:19,320
or a tunnel.

327
00:21:19,320 --> 00:21:22,440
But it's a great piece
of engineering

328
00:21:22,440 --> 00:21:24,800
that combines elements of each.

329
00:21:24,800 --> 00:21:28,880
Building it has been a major
challenge but within a year,

330
00:21:28,880 --> 00:21:33,960
engineers had started to make plans
for an equally ambitious project -

331
00:21:33,960 --> 00:21:36,000
a tunnel under the Channel.

332
00:21:36,000 --> 00:21:40,840
There have been many attempts to
link England and France by tunnel.

333
00:21:40,840 --> 00:21:42,920
But it wasn't till the 1980s

334
00:21:42,920 --> 00:21:47,160
that the British
and French governments agreed

335
00:21:47,160 --> 00:21:49,120
to the Channel Tunnel link.

336
00:21:51,440 --> 00:21:54,880
It opened in 1994.

337
00:21:54,880 --> 00:21:57,640
It's made up of three tunnels.

338
00:21:57,640 --> 00:22:00,560
Two are for the trains

339
00:22:00,560 --> 00:22:03,600
and the third
is a central service tunnel.

340
00:22:08,920 --> 00:22:12,560
Work on the tunnel
started in December 1987.

341
00:22:12,560 --> 00:22:15,200
They cut their way
under the Channel

342
00:22:15,200 --> 00:22:18,480
with these
huge tunnel-boring machines.

343
00:22:18,480 --> 00:22:23,720
It took three years before the
British and French tunnelling teams

344
00:22:23,720 --> 00:22:25,760
achieved their breakthrough

345
00:22:25,760 --> 00:22:28,600
and another four years
before it opened.

346
00:22:32,280 --> 00:22:36,560
The whole thing is a wonderful
piece of civil engineering.

347
00:22:36,560 --> 00:22:41,200
But, unlike bridges, there's not
a great deal of it you can see.

348
00:22:41,200 --> 00:22:46,680
To see the latest bridge-building
design and construction,

349
00:22:46,680 --> 00:22:49,560
I went back north
to the River Humber.

350
00:22:53,160 --> 00:22:55,200
In the 1960s and 1970s,

351
00:22:55,200 --> 00:23:00,480
Britain led the world in the design
and building of suspension bridges.

352
00:23:00,480 --> 00:23:03,320
This bridge over the Humber,
behind me,

353
00:23:03,320 --> 00:23:07,360
at the time of its building
was the biggest in the world.

354
00:23:07,360 --> 00:23:12,280
Alas, I'm sad to say, the good old
Japanese have built one bigger.

355
00:23:12,280 --> 00:23:14,720
Work began in 1973.

356
00:23:15,720 --> 00:23:18,560
It took eight years to complete.

357
00:23:18,560 --> 00:23:23,040
Thousands of tons of wire
and concrete were used

358
00:23:23,040 --> 00:23:28,120
and over 1,000 people were engaged
in its making over various periods.

359
00:23:33,800 --> 00:23:36,440
The towers are 533ft high.

360
00:23:36,440 --> 00:23:41,520
I was taken up to the top
by Roger Evans, the bridge master.

361
00:23:46,720 --> 00:23:48,800
Well, Roger,

362
00:23:48,800 --> 00:23:50,840
here we are

363
00:23:50,840 --> 00:23:53,080
500ft above the River Humber.

364
00:23:53,080 --> 00:23:57,480
How the heck did this start
with the first wire, sort of thing?

365
00:23:57,480 --> 00:24:00,200
It starts
with a couple of men in a boat

366
00:24:00,200 --> 00:24:03,440
laying a wire rope
on the bottom of the river,

367
00:24:03,440 --> 00:24:07,760
taking it over the top of the
other tower and pulling it tight.

368
00:24:09,240 --> 00:24:12,160
When you can get
several of them across,

369
00:24:12,160 --> 00:24:15,840
you can put a mesh on top
to make a walkway.

370
00:24:15,840 --> 00:24:19,080
It must have been
a hairy business... I wasn't here.

371
00:24:19,080 --> 00:24:23,000
..with dog clips
holding them onto the wires

372
00:24:23,000 --> 00:24:25,080
as they advanced out across.

373
00:24:25,080 --> 00:24:27,440
Would a gale like this

374
00:24:27,440 --> 00:24:30,240
sort of stop work?
I should imagine...

375
00:24:30,240 --> 00:24:32,920
Yeah, it's getting near that level.

376
00:24:32,920 --> 00:24:36,960
When they're actually working
with the cable spinning,

377
00:24:36,960 --> 00:24:41,040
the wheel's pulling the wires
across that way at 30mph,

378
00:24:41,040 --> 00:24:44,720
then a cross wind maybe 40mph
blowing sideways on.

379
00:24:44,720 --> 00:24:48,120
So, very hazardous.
It took longer as a result.

380
00:24:48,120 --> 00:24:50,200
How long is it from end to end?

381
00:24:50,200 --> 00:24:52,200
It's about a mile and a half

382
00:24:52,200 --> 00:24:54,440
between the two anchorages.

383
00:24:54,440 --> 00:25:00,440
Think how much wire it is - 15,000
wires going a mile and a half.

384
00:25:00,440 --> 00:25:02,560
There's enough to go

385
00:25:02,560 --> 00:25:07,000
nearly twice round the world.
It looks quite fragile, really.

386
00:25:07,000 --> 00:25:11,760
I know there's many tons... How
much weight is there in the bridge?

387
00:25:11,760 --> 00:25:17,400
The cables weigh 11,000 tons.
Their first job is to support
their own weight!

388
00:25:17,400 --> 00:25:20,640
And then you've got
17,000 tons of road there.

389
00:25:22,440 --> 00:25:26,160
On a good day,
we've got 6,000 tons of traffic.

390
00:25:26,160 --> 00:25:28,440
So we're talking big figures.

391
00:25:28,440 --> 00:25:33,240
So these pillars are
really under some compression? Yeah.

392
00:25:33,240 --> 00:25:36,160
That's why they can bend so much.

393
00:25:36,160 --> 00:25:42,360
They have a compressing force
in them, so when they bend,
you don't get cracks.

394
00:25:42,360 --> 00:25:44,400
Am I right or am I wrong?

395
00:25:44,400 --> 00:25:49,040
I felt distinctly that the things
were moving when we came out.

396
00:25:49,040 --> 00:25:53,920
I can feel it here. I'm leaning on
this and the tower moves slightly.

397
00:25:53,920 --> 00:25:57,000
At 500ft,
they've got to do, haven't they?

398
00:25:57,000 --> 00:26:00,880
Where we are,
it's designed to move two feet

399
00:26:00,880 --> 00:26:02,880
either way.

400
00:26:05,120 --> 00:26:09,800
Them cables that go from one side
of the Humber Estuary to the other,

401
00:26:09,800 --> 00:26:14,680
what most people don't realise is,
there are 14,000 pieces of wire

402
00:26:14,680 --> 00:26:17,320
forming a cable
two feet in diameter.

403
00:26:17,320 --> 00:26:20,240
It has
unbelievable tensile strength.

404
00:26:20,240 --> 00:26:25,240
Ten times what Mr Telford's
wrought-iron bars have got.

405
00:26:27,800 --> 00:26:30,320
It's not 14,000 separate pieces.

406
00:26:30,320 --> 00:26:35,160
It's one bit that crosses the width
of the river from this chamber

407
00:26:35,160 --> 00:26:38,040
up, over, down, up and over

408
00:26:38,040 --> 00:26:40,040
and back again 200 times,

409
00:26:40,040 --> 00:26:42,480
making it 400 passes in all.

410
00:26:42,480 --> 00:26:45,960
Each of these 400 bundles
is about that big.

411
00:26:45,960 --> 00:26:50,440
And they all fan out
in this great chamber,

412
00:26:50,440 --> 00:26:53,680
this great mass of wires
like rays of sunlight

413
00:26:53,680 --> 00:26:56,080
coming from a funnel near the top.

414
00:26:58,760 --> 00:27:01,800
How many tons of concrete
is it anchored to?

415
00:27:01,800 --> 00:27:04,440
Well,
we're in the middle of about...

416
00:27:04,440 --> 00:27:06,480
300,000 tons of mass

417
00:27:07,960 --> 00:27:12,760
and 20,000 tons of pull trying to
drag a 30,000-ton lump to the river.

418
00:27:12,760 --> 00:27:14,840
How many bits of wire is there

419
00:27:14,840 --> 00:27:16,880
altogether?

420
00:27:16,880 --> 00:27:19,680
You're looking at 15,000 bits.

421
00:27:20,760 --> 00:27:22,920
22½ thousand miles.

422
00:27:22,920 --> 00:27:25,960
And then, of course,
these wonderful bolts

423
00:27:25,960 --> 00:27:28,000
that hold it all down.

424
00:27:28,000 --> 00:27:30,560
There are, like,

425
00:27:30,560 --> 00:27:32,920
12 little 'uns.

426
00:27:32,920 --> 00:27:35,320
They go through this great block.

427
00:27:35,320 --> 00:27:39,160
Really, you'd think
that when you look at that lot,

428
00:27:39,160 --> 00:27:43,200
you'd think it were almost
impossible to compress it

429
00:27:43,200 --> 00:27:47,120
into a two foot diameter
iron rope...well, steel rope.

430
00:27:47,120 --> 00:27:49,280
I always think that.

431
00:27:49,280 --> 00:27:52,200
It's from
these slender-looking cables

432
00:27:52,200 --> 00:27:56,440
that the whole weight of the road
is suspended.

433
00:28:17,360 --> 00:28:22,240
Subtitles by Michael Bartlett
ITFC - 2000

434
00:28:22,240 --> 00:28:27,320
E-mail us at subtitling@bbc.co.uk