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 > 0:00:50One benefit of a temperate climate
0:00:50 > 0:00:52is our wonderful labyrinth of rivers.
0:00:53 > 0:00:57Giant waterways powered by rain,
0:00:57 > 0:01:00that 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 > 0:01:33the Firth of Forth, the 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 > 0:01:47I'm starting my estuary odyssey
0:01:47 > 0:01:51a pebble's throw from 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.
0:02:37 > 0:02:40- This is it.- This is it, Nick. Here we are on top of the Forth Bridge.
0:02:52 > 0:02:55Up here, right in the middle of the Firth of Forth
0:02:55 > 0:02:57you can get a real sense
0:02:57 > 0:03:00of 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.
0:03:17 > 0:03:22This estuary is so huge that even from this incredible vantage point,
0:03:22 > 0:03:25inland it just fades into invisibility.
0:03:25 > 0:03:28The only way of actually getting a true sense of its size
0:03:28 > 0:03:31is by looking at a map.
0:03:34 > 0:03:36This is the mouth of the estuary
0:03:36 > 0:03:39marked by this little island, the Isle of May, here.
0:03:39 > 0:03:44In the other direction, 60 miles inland,
0:03:44 > 0:03:47the water gets less and less salty, gets fresher and fresher,
0:03:47 > 0:03:50until you reach Stirling here,
0:03:50 > 0:03:52where this estuary is born.
0:03:56 > 0:03:58Starting at its birthplace,
0:03:58 > 0:04:00I'm flying the length of the waterway.
0:04:01 > 0:04:04Will the change in wildlife
0:04:04 > 0:04:08help pinpoint the elusive spot where river becomes sea?
0:04:08 > 0:04:12My guide is marine ecologist Stuart Clough.
0:04:14 > 0:04:16And as we pass over Stirling,
0:04:16 > 0:04:18the river's very beautiful seen from above,
0:04:18 > 0:04:20it's like a huge coiled rope.
0:04:20 > 0:04:23You're in classic lower river territory here, erm,
0:04:23 > 0:04:24lower freshwater river.
0:04:24 > 0:04:28The place where the tide just starts to have its effect.
0:04:28 > 0:04:32And even now the mud banks are starting to appear on the side.
0:04:32 > 0:04:35And in those, you've got all kinds of worms and shellfish
0:04:35 > 0:04:38that live within those sediments, and they become food for birds.
0:04:38 > 0:04:40It's a fantastic environment.
0:04:40 > 0:04:44Is it possible to identify the point at which this river, the Forth,
0:04:44 > 0:04:46ceases to be a river
0:04:46 > 0:04:49and begins to be sea?
0:04:49 > 0:04:51From a biologist's perspective, it's a continuum -
0:04:51 > 0:04:54it changes all the time.
0:04:54 > 0:04:56As we move into saltwater,
0:04:56 > 0:05:00the big hitters start to surface -
0:05:00 > 0:05:02dolphins, seals,
0:05:02 > 0:05:05and even whales have all been spotted here.
0:05:08 > 0:05:11We're now over the sunlit seaside, aren't we, Stuart?
0:05:11 > 0:05:13It's completely changed.
0:05:13 > 0:05:17Absolutely, yeah. We're right out in the outer estuary now.
0:05:17 > 0:05:19The freshwater influence is a long way behind us,
0:05:19 > 0:05:20the beaches are sandy.
0:05:24 > 0:05:28At the edge of the estuary,
0:05:28 > 0:05:30we get a box-office view of the gannets of Bass Rock.
0:05:32 > 0:05:36This swirling mass makes the most of food from the sea
0:05:36 > 0:05:38and shelter from the land.
0:05:39 > 0:05:41Where are we now?
0:05:41 > 0:05:43We're just adjacent to the Isle of May -
0:05:43 > 0:05:46very much the outer limit of the estuary.
0:05:46 > 0:05:51We've flown the whole way from the freshwater of a river
0:05:51 > 0:05:54to the saltwater of the open sea.
0:05:54 > 0:05:57Over an extraordinary diversity of habitats
0:05:57 > 0:06:02both human and natural - estuaries are worlds of their own.
0:06:10 > 0:06:1120 million of us,
0:06:11 > 0:06:16one third of the UK's population, live on an estuary.
0:06:19 > 0:06:23Their flat shorelines are perfect for building,
0:06:23 > 0:06:28so each of these coastal highways comes with its own gatekeeper.
0:06:32 > 0:06:34Great cities surge up
0:06:34 > 0:06:38where mighty rivers plunge into the sea.
0:06:38 > 0:06:42It's fitting that the country's capital
0:06:42 > 0:06:44crowns the most hard-working waterway of all -
0:06:44 > 0:06:46the titanic Thames.
0:06:49 > 0:06:53For centuries, Londoners have swallowed up the benefits
0:06:53 > 0:06:54the estuary brings in.
0:06:56 > 0:06:58The sea brought riches from abroad,
0:06:58 > 0:07:03and the river supplies two thirds of the city's drinking water.
0:07:04 > 0:07:10But the Victorians found a new job for old Father Thames -
0:07:10 > 0:07:13doing their dirty work.
0:07:16 > 0:07:22Tessa's getting to grips with a grubby tale of triumph and tragedy.
0:07:23 > 0:07:27The power of the tide gave an eminent Victorian engineer
0:07:27 > 0:07:29an extraordinary idea -
0:07:29 > 0:07:35turn the Thames into a giant self-flushing loo.
0:07:36 > 0:07:41The tidal range of the river is huge - around eight metres.
0:07:41 > 0:07:48This powerful ebb and flow gave rise to an ingenious sewer plan -
0:07:48 > 0:07:50release excrement as the tide turns,
0:07:50 > 0:07:52and let the outgoing flow
0:07:52 > 0:07:55flush London's waste way out to sea.
0:07:57 > 0:07:59The city's relationship with the sea
0:07:59 > 0:08:03spawned a sewer system that was the envy of the world.
0:08:03 > 0:08:05Opened in 1865 by the Prince of Wales
0:08:05 > 0:08:08this subterranean labyrinth
0:08:08 > 0:08:11elevated its mastermind, Joseph Bazalgette,
0:08:11 > 0:08:15to become a hero of the Victorian age.
0:08:18 > 0:08:22Bazalgette's master plan demanded a warren of waste pipes,
0:08:22 > 0:08:25a network over 1,000 miles long
0:08:25 > 0:08:30to carry the capital's raw sewage out to the Thames.
0:08:30 > 0:08:32It took six years to build,
0:08:32 > 0:08:36constructed so well it still forms the backbone
0:08:36 > 0:08:39of London's sewer complex.
0:08:39 > 0:08:43Over 300 million bricks placed so precisely
0:08:43 > 0:08:46they form watertight tunnels.
0:08:48 > 0:08:51You know how to treat a girl, don't you, Rob?
0:08:51 > 0:08:54I do, I take them only to the best spots.
0:08:54 > 0:08:56Impressive as this labyrinth is,
0:08:56 > 0:08:59it's only the means to a watery end.
0:08:59 > 0:09:03The city's sewage still needed sweeping out to sea,
0:09:03 > 0:09:04so it was piped towards the coast
0:09:04 > 0:09:07to pass the problem onto the tide.
0:09:07 > 0:09:09The muck flowed downstream
0:09:09 > 0:09:13to arrive at the final triumph of the entire system,
0:09:13 > 0:09:17the pumping station at Crossness.
0:09:25 > 0:09:29This is staggering!
0:09:29 > 0:09:31It's like some sort of ballroom.
0:09:37 > 0:09:40It's a real indication of the level of pride
0:09:40 > 0:09:44they took in their work, the beauty is just breathtaking.
0:09:44 > 0:09:46And these huge pumps
0:09:46 > 0:09:50are even named after members of the royal family.
0:09:53 > 0:09:58The pumping stations were the final stage of Bazalgette's grand plan -
0:09:58 > 0:10:01they pushed the sewage up into huge reservoirs,
0:10:01 > 0:10:05to be stored until the tide began to turn.
0:10:10 > 0:10:12When the tide started to ebb,
0:10:12 > 0:10:15they released the sewage into the Thames just there.
0:10:15 > 0:10:18They relied on the surge of seawater
0:10:18 > 0:10:22to whisk Londoners' muck out of sight and out of mind.
0:10:22 > 0:10:25This was Joseph Bazalgette's big tidal flush -
0:10:25 > 0:10:30his plan to turn the Thames into one gigantic toilet bowl was complete.
0:10:32 > 0:10:36Bazalgette was heralded as the city's saviour.
0:10:36 > 0:10:40But is there a skeleton lurking in London's water closet?
0:10:42 > 0:10:45Life may have been rosy for those in central London,
0:10:45 > 0:10:49but it didn't smell so sweet for those living downstream.
0:10:53 > 0:10:58Like a real-life toilet, the Thames is full of U-bends.
0:10:58 > 0:11:02The waste wasn't clearing as fast as Bazalgette had imagined,
0:11:02 > 0:11:06and the consequences turned out to be devastating.
0:11:08 > 0:11:10It's the 3rd of September 1878,
0:11:10 > 0:11:14the pleasure steamer The Princess Alice
0:11:14 > 0:11:18is on its way back to London crammed with passengers.
0:11:18 > 0:11:20The day-trippers had been enjoying fresh air
0:11:20 > 0:11:22at the mouth of the estuary
0:11:22 > 0:11:25but, returning to the city, near the sewage outlet,
0:11:25 > 0:11:29the pleasure steamer was struck by disaster.
0:11:32 > 0:11:34It collides with another boat.
0:11:34 > 0:11:39Hundreds are flung into the river, many will be drowned.
0:11:39 > 0:11:41But it's even worse than that.
0:11:44 > 0:11:47Revealing the gruesome fate of those floundering in the estuary
0:11:47 > 0:11:50is local historian Joz Joslin.
0:11:51 > 0:11:55So the vessel's upended, and hundreds of people are in the water.
0:11:55 > 0:11:59Yes. And lots of them are women and children,
0:11:59 > 0:12:00and they're screaming,
0:12:00 > 0:12:03and unfortunately it's not water that they're in,
0:12:03 > 0:12:07they're actually in sewage, so there was no oxygen.
0:12:07 > 0:12:10A lot of them died because there was no air to breathe.
0:12:10 > 0:12:13So they're either being suffocated or drowning.
0:12:13 > 0:12:15Or poisoned.
0:12:15 > 0:12:17How revolting. And the majority died?
0:12:17 > 0:12:19Yes, the majority died.
0:12:19 > 0:12:21They said that every street in the east end of London
0:12:21 > 0:12:22had lost somebody,
0:12:22 > 0:12:25because it was their Sunday school outings
0:12:25 > 0:12:27that were on board the vessel.
0:12:28 > 0:12:31The pleasure boat sank close to the sewage works,
0:12:31 > 0:12:34and the timing could not have been worse.
0:12:35 > 0:12:39The Beckton sewage outlet pipe carrying all of North London's waste
0:12:39 > 0:12:43had just discharged its stinking load into the river.
0:12:46 > 0:12:51Over 600 people choked to death in a toxic soup of human filth.
0:12:57 > 0:12:59After the tragedy,
0:12:59 > 0:13:02Bazalgette's sewage system came under the spotlight.
0:13:04 > 0:13:07A commission of inquiry delivered a damning indictment,
0:13:07 > 0:13:11concluding "it is neither necessary or justifiable
0:13:11 > 0:13:18"to discharge sewage in its crude state into any parts of the Thames".
0:13:18 > 0:13:22The Pall Mall Gazette took Bazalgette to task, stating
0:13:22 > 0:13:27"the natural man in him, puts off the evil day of having to admit failure".
0:13:28 > 0:13:32Luckily for Bazalgette, the muck didn't stick,
0:13:32 > 0:13:37but London did pull the plug on his big tidal flush.
0:13:37 > 0:13:41In 1887, a new system started.
0:13:41 > 0:13:45Now the solid human waste was pumped into vessels like this.
0:13:45 > 0:13:50The excrement was shipped out to the open sea and dumped.
0:13:52 > 0:13:58Balzalgette's tunnels still bring raw sewage here to the Crossness Works,
0:13:58 > 0:14:02but now the solid matter's burnt off to make electricity.
0:14:04 > 0:14:06The liquid sewage is treated -
0:14:06 > 0:14:09it goes from this...
0:14:09 > 0:14:10to this.
0:14:10 > 0:14:12And the cleaned-up fluid?
0:14:12 > 0:14:15It still gets the big tidal heave-ho,
0:14:15 > 0:14:19and is discharged into the Thames, where the river and the sea collide.
0:14:28 > 0:14:32The Severn estuary used to pose a fearsome challenge
0:14:32 > 0:14:35on any journey between England and Wales.
0:14:36 > 0:14:41The two countries were divided by this massive tear in our coastline.
0:14:42 > 0:14:46Avoiding it meant a diversion deep inland.
0:14:47 > 0:14:52Even so, only hardy travellers would brave the deadly waters.
0:14:59 > 0:15:03Today, a concrete solution spans this vast channel.
0:15:05 > 0:15:10But conquering the Severn was a bold venture fraught with peril,
0:15:10 > 0:15:12as Mark is about to discover.
0:15:15 > 0:15:19Dashing over the estuary from Wales to England commuters take
0:15:19 > 0:15:23the elegant crossings their lives depend on for granted.
0:15:25 > 0:15:28But imagine a world before this bridge was possible.
0:15:28 > 0:15:31A world without steel cables,
0:15:31 > 0:15:34without reinforced concrete,
0:15:34 > 0:15:37when the sea reigned supreme.
0:15:37 > 0:15:43That was a challenge faced by the Victorians to cross the River Severn.
0:15:48 > 0:15:52The formidable collision of river and sea facing the early engineers
0:15:52 > 0:15:54can still be experienced.
0:15:56 > 0:15:59It's one of the most dangerous seaways in the world,
0:15:59 > 0:16:01and I'm just a little bit excited.
0:16:04 > 0:16:08The Severn Area Rescue Association is going to pit me against the ebb tide.
0:16:11 > 0:16:14Cast off!
0:16:14 > 0:16:17The power of the tide here is just extraordinary!
0:16:23 > 0:16:27As the tide goes out it's like a maelstrom.
0:16:27 > 0:16:31The waters were an immense challenge,
0:16:31 > 0:16:35but by the 1840s crossing the river by boat was old hat.
0:16:39 > 0:16:42An irresistible new force was spreading across Britain -
0:16:42 > 0:16:44the railways.
0:16:44 > 0:16:47Come hell or high water,
0:16:47 > 0:16:50estuaries weren't going to stand in the way of progress.
0:16:54 > 0:16:58The great Victorian engineer Isambard Kingdom Brunel
0:16:58 > 0:17:02is a hero of mine - he'd already managed to cross the Avon gorge
0:17:02 > 0:17:05with a mighty suspension bridge.
0:17:05 > 0:17:09When his railway came to Bristol, he wanted to cross into South Wales,
0:17:09 > 0:17:11and planned an even bigger suspension bridge.
0:17:11 > 0:17:13Here are the preliminary sketches.
0:17:15 > 0:17:19The biggest problem was the sheer scale of the span
0:17:19 > 0:17:22that Brunel required - over 1,000 feet.
0:17:25 > 0:17:28He left a little note in his notebook
0:17:28 > 0:17:31which says "Is 1,100ft practicable?"
0:17:35 > 0:17:37Brunel's bridge was never built,
0:17:37 > 0:17:43but if taking trains over the water defeated the best brain of the age,
0:17:43 > 0:17:45how about going underneath?
0:17:47 > 0:17:50A tunnel - was that the answer?
0:17:50 > 0:17:55Digging deep to create a railway under the water -
0:17:55 > 0:17:58this was very bold, big thinking.
0:17:59 > 0:18:04This is one of the original drawings of the tunnel from around 1887,
0:18:04 > 0:18:09and you can see how the track comes down underneath the deepest part
0:18:09 > 0:18:11of the Bristol channel here in The Shoots,
0:18:11 > 0:18:15and gradually up to the Welsh side.
0:18:15 > 0:18:18So what we've got here is around seven miles of railway track.
0:18:21 > 0:18:24That passage under the estuary is now a vital link
0:18:24 > 0:18:27between England and Wales.
0:18:27 > 0:18:31Carrying over 250 trains a day.
0:18:34 > 0:18:37The railways had proved irresistible,
0:18:37 > 0:18:41with rival Victorian companies vying for routes,
0:18:41 > 0:18:46by the time it was finished the tunnel already had a competitor.
0:18:51 > 0:18:56In 1879, trains had started to roll over the estuary,
0:18:56 > 0:18:59but the bridge's sturdy uprights -
0:18:59 > 0:19:04always an obstacle to shipping - would ultimately prove its downfall.
0:19:07 > 0:19:13Do you see, that's a tower where the railway bridge once crossed
0:19:13 > 0:19:15the Severn estuary.
0:19:15 > 0:19:18I've got a photograph that shows the stanchions
0:19:18 > 0:19:22marching across the river - now totally destroyed.
0:19:26 > 0:19:30The raging waters where river and sea smash together
0:19:30 > 0:19:32would deliver a fatal blow to the rail bridge.
0:19:37 > 0:19:42In October, 1960, the Arkendale carrying oil,
0:19:42 > 0:19:45and the Wastdale laden with petrol
0:19:45 > 0:19:50were heading for combustible collision.
0:19:50 > 0:19:55The Arkendale was carried in by the surging tide.
0:19:55 > 0:19:59That powerful current would drive it into the Wastdale
0:19:59 > 0:20:04on a foggy night at Sharpness Docks.
0:20:04 > 0:20:06As Alan Hayward knows.
0:20:07 > 0:20:10They were coming up river intending to come into the docks here,
0:20:10 > 0:20:14but they were accidentally swept past.
0:20:14 > 0:20:18And then they collided and became in effect stuck together.
0:20:19 > 0:20:22Disabled ships in thick fog,
0:20:22 > 0:20:25carrying 600 tonnes of inflammable cargo
0:20:25 > 0:20:31at the mercy of a swirling sea, propelled them to disaster.
0:20:33 > 0:20:36They were desperate to separate from each other,
0:20:36 > 0:20:38fighting by steering in different directions
0:20:38 > 0:20:40but it just didn't work,
0:20:40 > 0:20:42and they only had about four minutes before
0:20:42 > 0:20:44they would reach the railway bridge.
0:20:46 > 0:20:50The rail bridge across the Severn loomed out of the fog,
0:20:50 > 0:20:55a collision with the ships carrying oil and petrol was now inevitable.
0:21:01 > 0:21:03A lot of sparks would have been created
0:21:03 > 0:21:05which ignited the petrol in one of the vessels.
0:21:08 > 0:21:11The fuel of course spilt out over the river,
0:21:11 > 0:21:13so the whole river became a mass of flame.
0:21:17 > 0:21:20First mate Percy Simmonds was aboard one of the tankers.
0:21:20 > 0:21:24His son Chris was 13 at the time.
0:21:24 > 0:21:26I try to imagine that night and what he was going through,
0:21:26 > 0:21:30and it must have been just terrible with the flames and everything.
0:21:30 > 0:21:34I'm just sure he was determined to make it across this river somehow
0:21:34 > 0:21:37and make it back to us.
0:21:38 > 0:21:42Daylight and a low tide revealed wrecks of the fuel tankers,
0:21:42 > 0:21:45smouldering on a sandbank.
0:21:45 > 0:21:49Soon the first body was found.
0:21:49 > 0:21:51They identified the body there,
0:21:51 > 0:21:56and they you know let Mum know that, yeah, it was definitely Perce.
0:21:57 > 0:22:01Chris's father Percy died along with four others
0:22:01 > 0:22:03on that terrible evening.
0:22:03 > 0:22:09The damaged bridge was too expensive to repair, it was demolished.
0:22:09 > 0:22:15But each day, when the tide recedes, scars of tragedy are revealed.
0:22:15 > 0:22:18Out there of course are two hulks buried now in the sands,
0:22:18 > 0:22:20that have been washed over by countless tides.
0:22:20 > 0:22:24But they're still there. They're there as monuments.
0:22:24 > 0:22:26They're here as a reminder to all of us.
0:22:30 > 0:22:32It's immensely humbling
0:22:32 > 0:22:35to be next to such a vast body
0:22:35 > 0:22:37of brooding water,
0:22:37 > 0:22:40even on a calm day like this.
0:22:40 > 0:22:46One can feel the power where rivers and sea collide.
0:22:56 > 0:23:00Surging waters urge us on to fresh endeavours.
0:23:02 > 0:23:05And we're not alone in finding creature comforts
0:23:05 > 0:23:09around the fringes of our great seaways.
0:23:10 > 0:23:16The tide brings in the bounty that makes our estuaries brim with vitality.
0:23:24 > 0:23:29Safe havens that offer boundless prospects.
0:23:29 > 0:23:34Where rivers collide with the sea our coast comes alive,
0:23:34 > 0:23:37and opportunity awaits.