0:00:02 > 0:00:04SHIP'S HORN BLARES
0:00:09 > 0:00:11This is Coast.
0:00:39 > 0:00:42In the British Isles, we're familiar with wet weather
0:00:42 > 0:00:45blown in from the wild seas.
0:00:48 > 0:00:51One benefit of a temperate climate is our wonderful
0:00:51 > 0:00:52labyrinth of rivers.
0:00:53 > 0:01:00Giant waterways powered by rain, that all run to the coast.
0:01:01 > 0:01:04As rivers and seas collide, great estuaries emerge.
0:01:12 > 0:01:15Making our mark on these colossal watery spaces
0:01:15 > 0:01:18has taken centuries of struggle.
0:01:18 > 0:01:21That's left a wealth of extraordinary stories
0:01:21 > 0:01:24waiting to be discovered along our estuaries.
0:01:26 > 0:01:28We're braving three of our greatest -
0:01:28 > 0:01:30the Firth of Forth,
0:01:30 > 0:01:33the Thames and the mighty Severn.
0:01:33 > 0:01:37We're here to explore what becomes of the coast
0:01:37 > 0:01:40when rivers and seas collide.
0:01:45 > 0:01:48I'm starting MY estuary odyssey a pebble's throw
0:01:48 > 0:01:51from Edinburgh, on the Firth of Forth.
0:01:53 > 0:01:56The scale of this seaway is staggering,
0:01:56 > 0:01:59it's impossible to take the whole thing in.
0:02:01 > 0:02:05What I could really do with is something tall to climb up.
0:02:05 > 0:02:07So I can get a bird's-eye view.
0:02:13 > 0:02:17Only the engineering marvel of the Forth Rail Bridge
0:02:17 > 0:02:21does justice to the sheer spectacle of the estuary.
0:02:22 > 0:02:23As we're coming up here,
0:02:23 > 0:02:26you can see the rivets on this bridge that hold it together.
0:02:26 > 0:02:306.5 million rivets, and every one of them has been painted by hand.
0:02:36 > 0:02:39- Is this it?- This is it, Nick. Here we are on top of the Forth Bridge.
0:02:46 > 0:02:49SHIP'S HORN BLARES
0:02:52 > 0:02:55Up here, right in the middle of the Firth of Forth,
0:02:55 > 0:03:00you can get a real sense of the huge scale of this estuary.
0:03:00 > 0:03:03I can see the Pentland Hills right over there,
0:03:03 > 0:03:06there's the dark volcanic bump of Arthur's Seat
0:03:06 > 0:03:10rising above the white buildings of Edinburgh.
0:03:10 > 0:03:14Looking west, I can see all the way out to the open sea - the North Sea.
0:03:16 > 0:03:20And looking inland, in this direction, there's even more.
0:03:22 > 0:03:24Here's the Forth Road Bridge,
0:03:24 > 0:03:26arching over the water in front of me,
0:03:26 > 0:03:28behind it Rosyth Naval Base...
0:03:30 > 0:03:33In the far distance I can just make out
0:03:33 > 0:03:36Grangemouth Power Station oozing smoke into the sky.
0:03:39 > 0:03:45This estuary is so huge that even from this incredible vantage point,
0:03:45 > 0:03:48inland it just fades into invisibility.
0:03:48 > 0:03:51The only way of actually getting a true sense of its size
0:03:51 > 0:03:54is by looking at a map.
0:03:57 > 0:03:59This is the mouth of the estuary
0:03:59 > 0:04:02marked by this little island, the Isle of May, here.
0:04:02 > 0:04:06In the other direction, 60 miles inland,
0:04:06 > 0:04:10the water gets less and less salty, gets fresher and fresher,
0:04:10 > 0:04:15until you reach Stirling here, where this estuary is born.
0:04:16 > 0:04:18IGNITION RATTLES, ENGINE PURRS
0:04:18 > 0:04:23Starting at its birthplace, I'm flying the length of the waterway.
0:04:24 > 0:04:31Will the change in wildlife help pinpoint the elusive spot where river becomes sea?
0:04:31 > 0:04:36My guide's marine ecologist Stuart Clough.
0:04:36 > 0:04:38And as we pass over Stirling,
0:04:38 > 0:04:41the river's very beautiful seen from above,
0:04:41 > 0:04:43it's like a huge coiled rope.
0:04:43 > 0:04:46You're in classic lower river territory here, erm,
0:04:46 > 0:04:47lower freshwater river.
0:04:47 > 0:04:50The place where the tide just starts to have its effect.
0:04:50 > 0:04:54And even now the mud banks are starting to appear on the side.
0:04:54 > 0:04:58And in those you've got all kinds of worms and shellfish
0:04:58 > 0:05:01that live within those sediments, and they become food for birds.
0:05:01 > 0:05:03It's a fantastic environment.
0:05:03 > 0:05:08Is it possible to identify the point at which this river, the Forth,
0:05:08 > 0:05:11ceases to be a river and begins to be sea?
0:05:11 > 0:05:14From a biologist's perspective, it's a continuum -
0:05:14 > 0:05:15it changes all the time.
0:05:15 > 0:05:17On the one hand, it's a no-man's land
0:05:17 > 0:05:18and on the other hand,
0:05:18 > 0:05:21it's a diverse and rich place with masses of life.
0:05:25 > 0:05:29Life is rich where rivers and seas meet.
0:05:33 > 0:05:36And where WE flock, so does the wildlife.
0:05:38 > 0:05:43As we move into saltwater, the big hitters start to surface -
0:05:43 > 0:05:46dolphins, seals,
0:05:46 > 0:05:49and even whales have all been spotted here.
0:05:52 > 0:05:55We're now over the sunlit seaside, aren't we, Stuart?
0:05:55 > 0:05:57It's completely changed.
0:05:57 > 0:06:01Absolutely, yeah. We're right out in the outer estuary now.
0:06:01 > 0:06:03The freshwater influence is a long way behind us,
0:06:03 > 0:06:05the beaches are sandy.
0:06:05 > 0:06:06If we were down at sea level now,
0:06:06 > 0:06:09what kind of birds and so on would we be looking at?
0:06:09 > 0:06:12Auks - like razorbills and guillemots and puffins.
0:06:12 > 0:06:14You've got fulmar, you'll have kittiwakes, you'll have gannets -
0:06:14 > 0:06:19real marine species, that you'd never find in the freshwater parts of the estuary.
0:06:24 > 0:06:26At the edge of the estuary,
0:06:26 > 0:06:30we get a box-office view of the gannets of Bass Rock.
0:06:30 > 0:06:35This swirling mass makes the most of food from the sea
0:06:35 > 0:06:38and shelter from the land.
0:06:38 > 0:06:40Where are we now?
0:06:40 > 0:06:42We're just adjacent to the Isle of May -
0:06:42 > 0:06:45very much the outer limit of the estuary.
0:06:45 > 0:06:51We've flown the whole way from the freshwater of a river
0:06:51 > 0:06:54to the saltwater of the open sea.
0:06:54 > 0:06:58Over an extraordinary diversity of habitats,
0:06:58 > 0:07:02both human and natural - estuaries are worlds of their own.
0:07:09 > 0:07:1020 million of us,
0:07:10 > 0:07:15one third of the UK's population, live on an estuary.
0:07:18 > 0:07:22Their flat shorelines are perfect for building,
0:07:22 > 0:07:27so each of these coastal highways comes with its own gatekeeper.
0:07:32 > 0:07:34Great cities surge up
0:07:34 > 0:07:38where mighty rivers plunge into the sea.
0:07:38 > 0:07:41It's fitting that the country's capital crowns the most
0:07:41 > 0:07:46hard-working waterway of all - the titanic Thames.
0:07:49 > 0:07:53For centuries, Londoners have swallowed up the benefits
0:07:53 > 0:07:55the estuary brings in.
0:07:55 > 0:07:58The sea brought riches from abroad,
0:07:58 > 0:08:02and the river supplies two-thirds of the city's drinking water.
0:08:04 > 0:08:10But the Victorians found a new job for old Father Thames -
0:08:10 > 0:08:12doing their dirty work.
0:08:15 > 0:08:21Tessa's getting to grips with a grubby tale of triumph and tragedy.
0:08:23 > 0:08:27The power of the tide gave an eminent Victorian engineer
0:08:27 > 0:08:29an extraordinary idea -
0:08:29 > 0:08:34turn the Thames into a giant self-flushing loo.
0:08:36 > 0:08:41The tidal range of the river is huge - around eight metres.
0:08:41 > 0:08:48This powerful ebb and flow, gave rise to an ingenious sewer plan.
0:08:48 > 0:08:50Release excrement as the tide turns,
0:08:50 > 0:08:55and let the outgoing flow flush London's waste way out to sea.
0:08:58 > 0:09:00The city's relationship with the sea
0:09:00 > 0:09:03spawned a sewer system that was the envy of the world.
0:09:03 > 0:09:08Opened in 1865 by the Prince of Wales, this subterranean labyrinth
0:09:08 > 0:09:11elevated its mastermind Joseph Bazalgette
0:09:11 > 0:09:16to become a hero of the Victorian age.
0:09:18 > 0:09:23Bazalgette's master plan demanded a warren of waste pipes,
0:09:23 > 0:09:26a network over 1,000 miles long
0:09:26 > 0:09:30to carry the capital's raw sewage out to the Thames.
0:09:30 > 0:09:32It took six years to build.
0:09:32 > 0:09:34Constructed so well,
0:09:34 > 0:09:39it still forms the backbone of London's sewer complex.
0:09:39 > 0:09:44Over 300 million bricks, placed so precisely,
0:09:44 > 0:09:46they form water-tight tunnels.
0:09:49 > 0:09:51You know how to treat a girl, don't you, Rob?
0:09:51 > 0:09:54I do, I take them only to the best spots.
0:09:54 > 0:09:59Impressive as this labyrinth is, it's only the means to a watery end.
0:09:59 > 0:10:02The city's sewage still needed sweeping out to sea,
0:10:02 > 0:10:07so it was piped towards the coast to pass the problem onto the tide.
0:10:07 > 0:10:11The muck flowed downstream to arrive at the final
0:10:11 > 0:10:17triumph of the entire system, the pumping station at Crossness.
0:10:25 > 0:10:31This is staggering! It's like some sort of ballroom.
0:10:37 > 0:10:40It's a real indication of the level of pride
0:10:40 > 0:10:44they took in their work, the beauty is just breathtaking.
0:10:44 > 0:10:50And these huge pumps are even named after members of the royal family.
0:10:53 > 0:10:58The pumping stations were the final stage of Bazalgette's grand plan -
0:10:58 > 0:11:02they pushed the sewage up into huge reservoirs,
0:11:02 > 0:11:05to be stored until the tide began to turn.
0:11:10 > 0:11:15When the tide started to ebb, they released the sewage into the Thames just there.
0:11:15 > 0:11:22They relied on the surge of seawater to whisk Londoners' muck out of sight and out of mind.
0:11:22 > 0:11:26This was Joseph Bazalgette's big tidal flush -
0:11:26 > 0:11:31his plan to turn the Thames into one gigantic toilet bowl was complete.
0:11:33 > 0:11:36Bazalgette was heralded as the city's saviour.
0:11:36 > 0:11:40But is there a skeleton lurking in London's water closet?
0:11:42 > 0:11:45Life may have been rosy for those in central London,
0:11:45 > 0:11:49but it didn't smell so sweet for those living downstream.
0:11:53 > 0:11:57Like a real-life toilet, the Thames is full of U-bends.
0:11:57 > 0:12:02The waste wasn't clearing as fast as Bazalgette had imagined,
0:12:02 > 0:12:06and the consequences turned out to be devastating.
0:12:08 > 0:12:11It's the 3rd of September, 1878.
0:12:12 > 0:12:15The pleasure steamer, The Princess Alice,
0:12:15 > 0:12:18is on its way back to London crammed with passengers.
0:12:18 > 0:12:23The day-trippers had been enjoying fresh air at the mouth of the estuary,
0:12:23 > 0:12:26but returning to the city, near the sewage outlet,
0:12:26 > 0:12:29the pleasure steamer was struck by disaster.
0:12:32 > 0:12:34It collides with another boat.
0:12:34 > 0:12:39Hundreds are flung into the river, many will be drowned.
0:12:39 > 0:12:41But it's even worse than that.
0:12:43 > 0:12:47Revealing the gruesome fate of those floundering in the estuary
0:12:47 > 0:12:50is local historian Joz Joslin.
0:12:51 > 0:12:55So the vessel's upended, and hundreds of people are in the water.
0:12:55 > 0:12:59Yes. And lots of them are women and children,
0:12:59 > 0:13:00and they're screaming,
0:13:00 > 0:13:03and unfortunately, it's not water that they're in,
0:13:03 > 0:13:07they're actually in sewage, so there was no oxygen.
0:13:07 > 0:13:10A lot of them died because there was no air to breathe.
0:13:10 > 0:13:13Uh! So they're either being suffocated or drowning.
0:13:13 > 0:13:15Or poisoned.
0:13:15 > 0:13:17How revolting. And the majority died?
0:13:17 > 0:13:19Yes, the majority died.
0:13:19 > 0:13:23They said that every street in the East End of London had lost somebody,
0:13:23 > 0:13:27because it was their Sunday school outings that were onboard the vessel.
0:13:28 > 0:13:31The pleasure boat sank close to the sewage works,
0:13:31 > 0:13:34and the timing could not have been worse.
0:13:35 > 0:13:37The Beckton sewage outlet pipe,
0:13:37 > 0:13:39carrying all of North London's waste,
0:13:39 > 0:13:43had just discharged its stinking load into the river.
0:13:46 > 0:13:51Over 600 people choked to death in a toxic soup of human filth.
0:13:57 > 0:13:58After the tragedy,
0:13:58 > 0:14:02Bazalgette's sewage system came under the spotlight.
0:14:04 > 0:14:10Members of the local historical society read the words of their forefathers.
0:14:10 > 0:14:14"There had been an accumulation of black, greasy, filth along the shore.
0:14:14 > 0:14:18"The filth settles on the steps as the tide goes down."
0:14:18 > 0:14:20"The river in hot weather is very bad.
0:14:20 > 0:14:24"In some places it smells so bad you cannot stand it."
0:14:24 > 0:14:27A commission of inquiry delivered a damning indictment,
0:14:27 > 0:14:32concluding, "It is neither necessary or justifiable
0:14:32 > 0:14:38"to discharge sewage in its crude state into any parts of the Thames".
0:14:38 > 0:14:43The Pall Mall Gazette took Bazalgette to task, stating,
0:14:43 > 0:14:48"The natural man in him puts off the evil day of having to admit failure".
0:14:49 > 0:14:53Luckily for Bazalgette, the muck didn't stick,
0:14:53 > 0:14:58but London did pull the plug on his big tidal flush.
0:14:58 > 0:15:01In 1887, a new system started.
0:15:01 > 0:15:06Now the solid human waste was pumped into vessels like this.
0:15:06 > 0:15:10The excrement was shipped out to the open sea and dumped.
0:15:10 > 0:15:15They were known locally as Bovril boats, amongst other things.
0:15:15 > 0:15:19We used to call them... Well, never mind what we used to call them!
0:15:19 > 0:15:21- What did you call them? - No, I'm not saying.
0:15:21 > 0:15:24They used to come and moor - they had moorings for them -
0:15:24 > 0:15:27and they would take the residue of it.
0:15:27 > 0:15:28Cos all the fluids were taken off,
0:15:28 > 0:15:30so it was almost solid the stuff
0:15:30 > 0:15:33that they took out - human detritus -
0:15:33 > 0:15:35so that it wasn't into the river.
0:15:37 > 0:15:41Sewage-carrying ships didn't just do the dirty work of London,
0:15:41 > 0:15:44they were once a common sight on our estuaries,
0:15:44 > 0:15:48cleaning up Glasgow, Belfast and other coastal cities.
0:15:52 > 0:15:57London's Bovril boats were finally pensioned off in 1998.
0:16:00 > 0:16:05Bazalgette's tunnels still bring raw sewage here to the Crossness Works,
0:16:05 > 0:16:09but now the solid matter's burnt off to make electricity.
0:16:11 > 0:16:13The liquid sewage is treated -
0:16:13 > 0:16:15it goes from this...
0:16:15 > 0:16:17to this.
0:16:17 > 0:16:19And the cleaned-up fluid?
0:16:19 > 0:16:21It still gets the big tidal heave-ho
0:16:21 > 0:16:26and is discharged into the Thames, where the river and the sea collide.
0:16:38 > 0:16:42We're on a journey to discover what becomes of the coast
0:16:42 > 0:16:45when rivers and seas collide.
0:16:47 > 0:16:53I'm exploring the Firth of Forth on Scotland's east coast,
0:16:53 > 0:16:57where canny folk profited from their prime location -
0:16:57 > 0:17:00ideal for seaborne business.
0:17:00 > 0:17:06And with rich seams of coal for power, the population boomed.
0:17:06 > 0:17:10With more mouths to feed, getting enough fresh food was tricky,
0:17:10 > 0:17:13so they looked to the sea to preserve their provisions.
0:17:16 > 0:17:19You'll find the evidence at St Monans.
0:17:23 > 0:17:29Here, food processing created a curious landscape.
0:17:31 > 0:17:35The shore is lined with lots and lots
0:17:35 > 0:17:38of very strange grass-covered humps,
0:17:38 > 0:17:41and what seems to be a ruined building over there
0:17:41 > 0:17:44and up there, a stone windmill.
0:17:46 > 0:17:50The ruins of industrial activity reveal themselves the more you look.
0:17:55 > 0:17:57This land was remodelled by people
0:17:57 > 0:18:00making the most of one bounty from the sea
0:18:00 > 0:18:04that isn't in short supply - salt.
0:18:04 > 0:18:09Before refrigeration, salt was a valuable commodity -
0:18:09 > 0:18:12preserving herring, landed along the east coast.
0:18:14 > 0:18:17Scottish salt was also exported to England,
0:18:17 > 0:18:20turning a tasty profit for the saltworks.
0:18:23 > 0:18:27Those strange hummocks come in sets - each set of hummocks
0:18:27 > 0:18:30is the ruins of a pan house.
0:18:30 > 0:18:32Inside each of those pan houses,
0:18:32 > 0:18:36there was an iron pan about 6 metres by 3 metres,
0:18:36 > 0:18:38with coal fires beneath it.
0:18:38 > 0:18:42Sea water was pumped - probably using this windmill - from the sea
0:18:42 > 0:18:44in pipes up to each pan house.
0:18:44 > 0:18:48Once it had been boiled off in the pans, you had salt.
0:18:51 > 0:18:55A rare film brings the enterprise back to life.
0:18:57 > 0:19:02Saltworks once flourished along Scotland's east coast.
0:19:02 > 0:19:08The last operation at Prestonpans didn't close its doors until 1974.
0:19:11 > 0:19:15It was the abundance of coal along this estuary
0:19:15 > 0:19:20that made it a good site for boiling up sea water.
0:19:21 > 0:19:24A sample of sea water stirs up a mystery,
0:19:24 > 0:19:27right at the heart of this forgotten industry.
0:19:29 > 0:19:32Out there is the sea full of salt.
0:19:34 > 0:19:36And I can certainly taste it.
0:19:36 > 0:19:39This little brook running into the sea...
0:19:41 > 0:19:43..doesn't taste salty at all.
0:19:43 > 0:19:46So, why is freshwater fresh
0:19:46 > 0:19:51and why is sea water salty?
0:19:54 > 0:19:59It's one of those brilliantly simple infuriating questions
0:19:59 > 0:20:04that kids ask - why is the sea salty?
0:20:04 > 0:20:06I'm enlisting the help of a grown-up.
0:20:06 > 0:20:10Simon Boxall's from the National Oceanography Centre -
0:20:10 > 0:20:13he should be able to work it out.
0:20:13 > 0:20:16We've all swum in the sea, we know it doesn't taste like freshwater,
0:20:16 > 0:20:18Simon, but why is it salty?
0:20:18 > 0:20:21You have to go right back to the beginning-stage of the earth,
0:20:21 > 0:20:23back several billion years.
0:20:23 > 0:20:24And if you go back that far,
0:20:24 > 0:20:26the earth was a completely different place -
0:20:26 > 0:20:30it was full of volcanic eruptions, there was lots of steam around,
0:20:30 > 0:20:33but, also, there was a lot of sodium in the rocks,
0:20:33 > 0:20:36and that sodium was being hit by the hydrochloric acid
0:20:36 > 0:20:38that was given off by these volcanic vents.
0:20:38 > 0:20:41And then we take these two very harmful chemicals...
0:20:41 > 0:20:43On the one hand, you've got the element of sodium - very reactive -
0:20:43 > 0:20:47and on the other hand, you've got chlorine - very dangerous and very reactive.
0:20:47 > 0:20:50You put the two together and you create...sodium chloride.
0:20:50 > 0:20:53Which is the sort of thing you sprinkle on your chips.
0:20:53 > 0:20:55Certainly isn't harmful, at all.
0:20:55 > 0:20:59So you've got this hydrochloric acid pouring out of the volcanic vents,
0:20:59 > 0:21:03meeting the sodium hydroxide which is lying around in the rocks on the sea bed,
0:21:03 > 0:21:07creating this stuff called sodium chloride, which is salt.
0:21:07 > 0:21:13These ancient chemical reactions gave birth to our salty seas.
0:21:15 > 0:21:18We can create those sort of primordial days.
0:21:18 > 0:21:20We can actually take some hydrochloric acid -
0:21:20 > 0:21:23the sort of stuff that came out of the vents of the volcanoes.
0:21:23 > 0:21:25We've got some dilute sodium hydroxide -
0:21:25 > 0:21:27which represents the stuff that was in the rocks.
0:21:27 > 0:21:29And between us, if you want to, we can make salt.
0:21:29 > 0:21:32We can take these two quite nasty chemicals
0:21:32 > 0:21:35and produce something that's really more vital to life in many ways.
0:21:35 > 0:21:38This is hydrochloric acid - it's very dilute.
0:21:38 > 0:21:41And we're going to pop it into this vessel here.
0:21:42 > 0:21:46OK, we're then going to add our sodium hydroxide.
0:21:46 > 0:21:50At the moment, basically, the sodium and the chlorine are combining
0:21:50 > 0:21:52and giving off heat - can you feel that?
0:21:52 > 0:21:54It's warm! Really warm, wow!
0:21:54 > 0:21:58We've effectively neutralised that acid, that sodium hydroxide,
0:21:58 > 0:22:03and what we have in there now is basically water...and salt.
0:22:04 > 0:22:08We've compressed billions of years of the earth's evolution
0:22:08 > 0:22:11to make a miniature ocean.
0:22:11 > 0:22:16Boiling off our DIY sea water leaves the prize ingredient.
0:22:19 > 0:22:23So, here it is, our very own home-made salt.
0:22:24 > 0:22:28White crystals that washed wealth in from the sea
0:22:28 > 0:22:30to help feed an estuary.
0:22:40 > 0:22:45On a journey around our estuaries, we've arrived at the mighty Severn.
0:22:46 > 0:22:50Here, the Atlantic Ocean surges in to collide
0:22:50 > 0:22:53with Britain's longest river.
0:22:53 > 0:22:57The Severn Estuary has a staggering rise of tidal water,
0:22:57 > 0:23:00some 15 metres in all.
0:23:04 > 0:23:07The sea swirls in strange patterns here.
0:23:09 > 0:23:13And its currents would wash the bodies of wrecked sailors
0:23:13 > 0:23:17to the same spot again and again -
0:23:17 > 0:23:20the village of Brean.
0:23:27 > 0:23:34Those unknown souls delivered to the doorstep of Brean needed burial -
0:23:34 > 0:23:37a sorrowful ritual remembered in song.
0:23:37 > 0:23:42Folk singer and storyteller June Tabor recalls the Brean Lament.
0:23:44 > 0:23:48The first thing that strikes you about being here,
0:23:48 > 0:23:49it's timeless.
0:23:49 > 0:23:54It could be any time between now and 200 years ago.
0:23:54 > 0:23:57And the old timbers of this ship
0:23:57 > 0:24:00going nowhere ever again.
0:24:00 > 0:24:03The men who were on this ship -
0:24:03 > 0:24:05did they survive?
0:24:09 > 0:24:15# The waters they washed them ashore
0:24:15 > 0:24:18# Ashore
0:24:18 > 0:24:25# And they never will sail the seas no more
0:24:25 > 0:24:31# We led them along by the churchyard wall
0:24:31 > 0:24:38# And all in a row we buried them all. #
0:24:40 > 0:24:44The song The Brean Lament describes
0:24:44 > 0:24:48what happened quite commonly along this coast
0:24:48 > 0:24:51when bodies were washed up.
0:24:51 > 0:24:57You have to give them a burial, but not in the main churchyard -
0:24:57 > 0:25:00in a separate sailors' graveyard.
0:25:03 > 0:25:07It was quite strongly believed along this stretch of coast
0:25:07 > 0:25:12that the sea might decide to reclaim their bodies as its own.
0:25:12 > 0:25:16They didn't want the dead of the village
0:25:16 > 0:25:19being taken at the same time.
0:25:19 > 0:25:25And, possibly, as a way of appeasing the sea,
0:25:25 > 0:25:30the sailors' boots were buried below the tide line,
0:25:30 > 0:25:33so the sea would have something to take.
0:25:35 > 0:25:42# We led them along by the churchyard wall
0:25:42 > 0:25:50# Where all in a row we buried them all
0:25:52 > 0:26:03# But their boots we buried below the tide
0:26:03 > 0:26:10# On Severnside. #
0:26:21 > 0:26:24The Severn Estuary used to pose a fearsome challenge
0:26:24 > 0:26:27on any journey between England and Wales.
0:26:29 > 0:26:34The two countries were divided by this massive tear in our coastline.
0:26:35 > 0:26:39Avoiding it meant a diversion deep inland.
0:26:39 > 0:26:45Even so, only hardy travellers would brave the deadly waters.
0:26:52 > 0:26:56Today, a concrete solution spans this vast channel.
0:26:58 > 0:27:02But conquering the Severn was a bold venture fraught with peril,
0:27:02 > 0:27:05as Mark is about to discover.
0:27:07 > 0:27:11Dashing over the estuary from Wales to England, commuters take
0:27:11 > 0:27:16the elegant crossings their lives depend on for granted.
0:27:18 > 0:27:21But imagine a world before this bridge was possible.
0:27:21 > 0:27:24A world without steel cables,
0:27:24 > 0:27:26without reinforced concrete,
0:27:26 > 0:27:30when the sea reigned supreme.
0:27:30 > 0:27:34That was a challenge faced by the Victorians
0:27:34 > 0:27:36to cross the River Severn.
0:27:40 > 0:27:45The formidable collision of river and sea facing the early engineers
0:27:45 > 0:27:47can still be experienced.
0:27:49 > 0:27:52It's one of the most dangerous seaways in the world,
0:27:52 > 0:27:54but I'm just a little bit excited.
0:27:56 > 0:28:02The Severn Area Rescue Association is going to pit me against the ebb tide.
0:28:04 > 0:28:07Cast off!
0:28:07 > 0:28:09The power of the tide here is just extraordinary!
0:28:16 > 0:28:20As the tide goes out, it's like a maelstrom.
0:28:20 > 0:28:24The waters were an immense challenge,
0:28:24 > 0:28:29but by the 1840s, crossing the river by boat was old hat.
0:28:31 > 0:28:35An irresistible new force was spreading across Britain -
0:28:35 > 0:28:37the railways.
0:28:37 > 0:28:39Come hell or high water,
0:28:39 > 0:28:43estuaries weren't going to stand in the way of progress.
0:28:47 > 0:28:50The great Victorian engineer Isambard Kingdom Brunel
0:28:50 > 0:28:55is a hero of mine - he'd already managed to cross the Avon gorge
0:28:55 > 0:28:57with a mighty suspension bridge.
0:28:57 > 0:29:01When his railway came to Bristol, he wanted to cross into South Wales,
0:29:01 > 0:29:04and planned an even bigger suspension bridge.
0:29:04 > 0:29:06Here are the preliminary sketches.
0:29:07 > 0:29:11The biggest problem was the sheer scale of the span
0:29:11 > 0:29:15that Brunel required - over 1,000 feet.
0:29:17 > 0:29:20He left a little note in his notebook,
0:29:20 > 0:29:24which says, "Is 1,100ft practicable?"
0:29:27 > 0:29:30Brunel's bridge was never built,
0:29:30 > 0:29:36but if taking trains over the water defeated the best brain of the age,
0:29:36 > 0:29:38how about going underneath?
0:29:39 > 0:29:43A tunnel - was that the answer?
0:29:43 > 0:29:47Digging deep to create a railway under the water -
0:29:47 > 0:29:52this was very bold, big thinking.
0:29:52 > 0:29:57This is one of the original drawings of the tunnel from around 1887,
0:29:57 > 0:30:02and you can see how the track comes down underneath the deepest part
0:30:02 > 0:30:04of the Bristol Channel here in The Shoots,
0:30:04 > 0:30:07and gradually up to the Welsh side.
0:30:07 > 0:30:11So what we've got here is around seven miles of railway track.
0:30:13 > 0:30:17That passage under the estuary is now a vital link
0:30:17 > 0:30:20between England and Wales,
0:30:20 > 0:30:24carrying over 250 trains a day.
0:30:25 > 0:30:30Passengers are oblivious to a catastrophe that nearly sank
0:30:30 > 0:30:34the tunnel before the first train ran,
0:30:34 > 0:30:37and it's a problem that still lurks below.
0:30:41 > 0:30:43So here we go.
0:30:44 > 0:30:48I've been granted access to a shadowy water world,
0:30:48 > 0:30:49few get to see.
0:30:51 > 0:30:53It's great - we're just coming into the cutting,
0:30:53 > 0:30:58the portal's ahead, and we're about to go under the sea.
0:31:01 > 0:31:04Ah! Whay!
0:31:04 > 0:31:06Isn't that fantastic?!
0:31:08 > 0:31:11We're heading for the deepest point in the tunnel.
0:31:15 > 0:31:18Just 50ft above us, millions of gallons of water
0:31:18 > 0:31:24are swirling around - the River Severn and the sea are in full flow.
0:31:24 > 0:31:28Keeping the water out here is hard enough,
0:31:28 > 0:31:31but can you imagine if there was a flood down here?
0:31:33 > 0:31:36With an estuary hanging over their heads,
0:31:36 > 0:31:40engineers knew there'd be seepage of seawater,
0:31:40 > 0:31:45but it was freshwater that nearly drowned the project.
0:31:46 > 0:31:53Nobody expected this - a raging torrent!
0:31:53 > 0:31:56They'd broken through to an underground spring.
0:31:57 > 0:32:02In October, 1879, water began to pour into the tunnel.
0:32:04 > 0:32:06The workers fled for their lives.
0:32:09 > 0:32:13The disaster struck when a shaft dug on the Welsh coast
0:32:13 > 0:32:17cut into an underground river deep below the surface.
0:32:20 > 0:32:24For four years the engineers made desperate attempts
0:32:24 > 0:32:30to block the freshwater spring, but every effort proved futile.
0:32:32 > 0:32:36And it's been flooding in at this alarming rate ever since.
0:32:38 > 0:32:42If they couldn't stop the spring water, they'd have to live with it.
0:32:45 > 0:32:48The only solution were pumps, massive ones like this
0:32:48 > 0:32:52that pump the water out as fast as it comes in,
0:32:52 > 0:32:53right up to the surface.
0:32:56 > 0:33:00Leighton Jenkins helps keep the tracks dry today.
0:33:00 > 0:33:03So what would happen if the pumps actually failed?
0:33:03 > 0:33:05Every second counts,
0:33:05 > 0:33:08as soon as the pumps stop, we'd have to inform the control
0:33:08 > 0:33:11within 10 minutes just to shut the tunnel itself,
0:33:11 > 0:33:14and within 20 minutes we've got water coming up through the tracks,
0:33:14 > 0:33:16so every second absolutely counts.
0:33:16 > 0:33:18But have they yet failed?
0:33:18 > 0:33:21No, not as far as I know, no. Not while I'm on the shift anyway.
0:33:21 > 0:33:24LAUGHTER
0:33:24 > 0:33:27The railways had proved irresistible,
0:33:27 > 0:33:31with rival Victorian companies vying for routes.
0:33:31 > 0:33:36By the time it was finished, the tunnel already had a competitor.
0:33:41 > 0:33:46In 1879, trains had started to roll over the estuary,
0:33:46 > 0:33:48but the bridge's sturdy uprights -
0:33:48 > 0:33:54always an obstacle to shipping - would ultimately prove its downfall.
0:33:57 > 0:34:02Do you see? That's a tower where the railway bridge once crossed
0:34:02 > 0:34:04the Severn Estuary.
0:34:04 > 0:34:07I've got a photograph that shows the stanchions
0:34:07 > 0:34:12marching across the river - now totally destroyed.
0:34:15 > 0:34:20The raging waters where river and sea smash together
0:34:20 > 0:34:23would deliver a fatal blow to the rail bridge.
0:34:27 > 0:34:32In October, 1960, the Arkendale - carrying oil -
0:34:32 > 0:34:35and the Wastdale - laden with petrol -
0:34:35 > 0:34:40were heading for combustible collision.
0:34:40 > 0:34:45The Arkendale was carried in by the surging tide.
0:34:45 > 0:34:49That powerful current would drive it into the Wastdale
0:34:49 > 0:34:53on a foggy night at Sharpness Docks,
0:34:53 > 0:34:56as Alan Hayward knows.
0:34:56 > 0:35:00They were coming up river intending to come into the docks here,
0:35:00 > 0:35:03but they were accidentally swept past.
0:35:03 > 0:35:07And then they collided and became, in effect, stuck together.
0:35:08 > 0:35:11Disabled ships in thick fog,
0:35:11 > 0:35:15carrying 600 tonnes of inflammable cargo
0:35:15 > 0:35:20at the mercy of a swirling sea, propelled them to disaster.
0:35:22 > 0:35:25They were desperate to separate from each other,
0:35:25 > 0:35:27fighting by steering in different directions
0:35:27 > 0:35:29but it just didn't work,
0:35:29 > 0:35:31and they only had about four minutes before
0:35:31 > 0:35:34they would reach the railway bridge.
0:35:35 > 0:35:39The rail bridge across the Severn loomed out of the fog,
0:35:39 > 0:35:44a collision with the ships carrying oil and petrol was now inevitable.
0:35:50 > 0:35:52A lot of sparks would have been created,
0:35:52 > 0:35:55which ignited the petrol in one of the vessels.
0:35:58 > 0:36:00The fuel, of course, spilt out over the river,
0:36:00 > 0:36:03so the whole river became a mass of flame.
0:36:06 > 0:36:10First mate Percy Simmonds was aboard one of the tankers.
0:36:10 > 0:36:13His son Chris was 13 at the time.
0:36:13 > 0:36:16I try to imagine that night and what he was going through,
0:36:16 > 0:36:19and it must have been just terrible with the flames and everything.
0:36:19 > 0:36:23I'm just sure he was determined to make it across this river somehow
0:36:23 > 0:36:26and make it back to us.
0:36:27 > 0:36:32Daylight and a low tide revealed wrecks of the fuel tankers,
0:36:32 > 0:36:35smouldering on a sandbank.
0:36:35 > 0:36:38Soon the first body was found.
0:36:38 > 0:36:40They identified the body there,
0:36:40 > 0:36:46and they, you know, let Mum know that, yeah, it was definitely Perce.
0:36:46 > 0:36:51Chris's father Percy died along with four others
0:36:51 > 0:36:53on that terrible evening.
0:36:53 > 0:36:58The damaged bridge was too expensive to repair, it was demolished.
0:36:58 > 0:37:04But each day, when the tide recedes, scars of tragedy are revealed.
0:37:04 > 0:37:08Out there, of course, are two hulks buried now in the sands,
0:37:08 > 0:37:11that have been washed over by countless tides.
0:37:11 > 0:37:13But they're still there. They're there as monuments.
0:37:13 > 0:37:16They're here as a reminder to all of us.
0:37:19 > 0:37:21It's immensely humbling
0:37:21 > 0:37:24to be next to such a vast body
0:37:24 > 0:37:27of brooding water.
0:37:27 > 0:37:31Even on a calm day like this,
0:37:31 > 0:37:36one can feel the power where rivers and sea collide.
0:37:46 > 0:37:49Surging waters urge us on to fresh endeavours.
0:37:51 > 0:37:55And we're not alone in finding creature comforts
0:37:55 > 0:37:58around the fringes of our great seaways.
0:38:00 > 0:38:02The tide brings in the bounty
0:38:02 > 0:38:05that makes our estuaries brim with vitality.
0:38:13 > 0:38:19Safe havens that offer boundless prospects.
0:38:19 > 0:38:23Where rivers collide with the sea, our coast comes alive,
0:38:23 > 0:38:26and opportunity awaits.