A journey around the great estuaries of Britain - the Firth of Forth, Thames and Severn.
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This is Coast.
In the British Isles, we're familiar with wet weather
blown in from the wild seas.
One benefit of a temperate climate
is our wonderful labyrinth of rivers.
Giant waterways powered by rain,
that all run to the coast.
As rivers and seas collide great estuaries emerge.
Making our mark on these colossal watery spaces
has taken centuries of struggle.
That's left a wealth of extraordinary stories
waiting to be discovered along our estuaries.
We're braving three of our greatest,
the Firth of Forth, the Thames and the mighty Severn.
We're here to explore what becomes of the coast
when rivers and seas collide.
I'm starting my estuary odyssey
a pebble's throw from Edinburgh, on the Firth of Forth.
The scale of this seaway is staggering,
it's impossible to take the whole thing in.
What I could really do with is something tall to climb up
so I can get a bird's-eye view.
Only the engineering marvel of the Forth rail bridge
does justice to the sheer spectacle of the estuary.
As we're coming up here
you can see the rivets on this bridge that hold it together.
6.5 million rivets, and every one of them has been painted by hand.
This is it. This is it, Nick. Here we are on top of the Forth Bridge.
Up here, right in the middle of the Firth of Forth
you can get a real sense
of the huge scale of this estuary.
I can see the Pentland Hills right over there,
there's the dark volcanic bump of Arthur's Seat
rising above the white buildings of Edinburgh.
Looking west, I can see all the way out to the open sea - the North Sea.
And looking inland, in this direction, there's even more.
Here's the Forth Road Bridge
arcing over the water in front of me,
behind it Rosyth naval base.
In the far distance
I can just make out Grangemouth power station
oozing smoke into the sky.
This estuary is so huge that even from this incredible vantage point,
inland it just fades into invisibility.
The only way of actually getting a true sense of its size
is by looking at a map.
This is the mouth of the estuary
marked by this little island, the Isle of May, here.
In the other direction, 60 miles inland,
the water gets less and less salty, gets fresher and fresher,
until you reach Stirling here,
where this estuary is born.
Starting at its birthplace,
I'm flying the length of the waterway.
Will the change in wildlife
help pinpoint the elusive spot where river becomes sea?
My guide is marine ecologist Stuart Clough.
And as we pass over Stirling,
the river's very beautiful seen from above,
it's like a huge coiled rope.
You're in classic lower river territory here, erm,
lower freshwater river.
The place where the tide just starts to have its effect.
And even now the mud banks are starting to appear on the side.
And in those, you've got all kinds of worms and shellfish
that live within those sediments, and they become food for birds.
It's a fantastic environment.
Is it possible to identify the point at which this river, the Forth,
ceases to be a river and begins to be sea?
From a biologist's perspective, it's a continuum -
it changes all the time.
On the one hand it's a no-man's-land
and, on the other hand, it's a diverse and rich place
with masses of life.
Life is rich where rivers and seas meet.
And where we flock, so does the wildlife.
As we move into saltwater,
the big hitters start to surface -
and even whales have all been spotted here.
We're now over the sunlit seaside, aren't we, Stuart?
It's completely changed.
Absolutely, yeah. We're right out in the outer estuary now.
The freshwater influence is a long way behind us,
the beaches are sandy.
If we were down at sea level now
what kind of birds and so on would we be looking at?
Auks - like razorbills and guillemots and puffins.
You've got fulmar, you'll have kittiwakes, you'll have gannets -
real marine species that you'd never find
in the freshwater parts of the estuary.
At the edge of the estuary,
we get a box-office view of the gannets of Bass Rock.
This swirling mass makes the most of food from the sea
and shelter from the land.
Where are we now?
We're just adjacent to the Isle of May -
very much the outer limit of the estuary.
We've flown the whole way from the freshwater of a river
to the saltwater of the open sea.
Over an extraordinary diversity of habitats
both human and natural - estuaries are worlds of their own.
20 million of us,
one third of the UK's population, live on an estuary.
Their flat shorelines are perfect for building,
so each of these coastal highways comes with its own gatekeeper.
Great cities surge up
where mighty rivers plunge into the sea.
It's fitting that the country's capital
crowns the most hard-working waterway of all -
the titanic Thames.
For centuries, Londoners have swallowed up the benefits
the estuary brings in.
The sea brought riches from abroad,
and the river supplies two thirds of the city's drinking water.
But the Victorians found a new job for old Father Thames -
doing their dirty work.
Tessa's getting to grips with a grubby tale of triumph and tragedy.
The power of the tide gave an eminent Victorian engineer
an extraordinary idea -
turn the Thames into a giant self-flushing loo.
The tidal range of the river is huge - around eight metres.
This powerful ebb and flow gave rise to an ingenious sewer plan -
release excrement as the tide turns,
and let the outgoing flow
flush London's waste way out to sea.
The city's relationship with the sea
spawned a sewer system that was the envy of the world.
Opened in 1865 by the Prince of Wales
this subterranean labyrinth
elevated its mastermind, Joseph Bazalgette,
to become a hero of the Victorian age.
Bazalgette's master plan demanded a warren of waste pipes,
a network over 1,000 miles long
to carry the capital's raw sewage out to the Thames.
It took six years to build,
constructed so well it still forms the backbone
of London's sewer complex.
Over 300 million bricks placed so precisely
they form watertight tunnels.
You know how to treat a girl, don't you, Rob?
I do, I take them only to the best spots.
Impressive as this labyrinth is,
it's only the means to a watery end.
The city's sewage still needed sweeping out to sea,
so it was piped towards the coast
to pass the problem onto the tide.
The muck flowed downstream
to arrive at the final triumph of the entire system,
the pumping station at Crossness.
This is staggering!
It's like some sort of ballroom.
It's a real indication of the level of pride
they took in their work, the beauty is just breathtaking.
And these huge pumps
are even named after members of the royal family.
The pumping stations were the final stage of Bazalgette's grand plan -
they pushed the sewage up into huge reservoirs,
to be stored until the tide began to turn.
When the tide started to ebb,
they released the sewage into the Thames just there.
They relied on the surge of seawater
to whisk Londoners' muck out of sight and out of mind.
This was Joseph Bazalgette's big tidal flush -
his plan to turn the Thames into one gigantic toilet bowl was complete.
Bazalgette was heralded as the city's saviour.
But is there a skeleton lurking in London's water closet?
Life may have been rosy for those in central London,
but it didn't smell so sweet for those living downstream.
Like a real-life toilet, the Thames is full of U-bends.
The waste wasn't clearing as fast as Bazalgette had imagined,
and the consequences turned out to be devastating.
It's the 3rd of September 1878,
the pleasure steamer The Princess Alice
is on its way back to London crammed with passengers.
The day-trippers had been enjoying fresh air
at the mouth of the estuary
but, returning to the city, near the sewage outlet,
the pleasure steamer was struck by disaster.
It collides with another boat.
Hundreds are flung into the river, many will be drowned.
But it's even worse than that.
Revealing the gruesome fate of those floundering in the estuary
is local historian Joz Joslin.
So the vessel's upended, and hundreds of people are in the water.
Yes. And lots of them are women and children,
and they're screaming,
and unfortunately it's not water that they're in,
they're actually in sewage, so there was no oxygen.
A lot of them died because there was no air to breathe.
So they're either being suffocated or drowning.
How revolting. And the majority died?
Yes, the majority died.
They said that every street in the east end of London
had lost somebody,
because it was their Sunday school outings
that were on board the vessel.
The pleasure boat sank close to the sewage works,
and the timing could not have been worse.
The Beckton sewage outlet pipe carrying all of North London's waste
had just discharged its stinking load into the river.
Over 600 people choked to death in a toxic soup of human filth.
After the tragedy,
Bazalgette's sewage system came under the spotlight.
Members of the local historical society
read the words of their forefathers.
"There had been an accumulation of black, greasy,
"filth along the shore.
"The filth settles on the steps as the tide goes down."
"The river in hot weather is very bad.
"In some places it smells so bad you cannot stand it."
A commission of inquiry delivered a damning indictment,
concluding "it is neither necessary or justifiable
"to discharge sewage in its crude state
"into any parts of the Thames".
The Pall Mall Gazette took Bazalgette to task,
stating "the natural man in him,
"puts off the evil day of having to admit failure."
Luckily for Bazalgette, the muck didn't stick,
but London did pull the plug on his big tidal flush.
In 1887, a new system started.
Now the solid human waste was pumped into vessels like this.
The excrement was shipped out to the open sea and dumped.
They were known locally as Bovril boats, amongst other things.
We used to call them... Well, never mind what we used to call them!
What did you call them? No, I'm not saying.
They used to come and moor - they had moorings for them -
and they would take the residue of it.
Cos all the fluids were taken off,
so it was almost solid the stuff
that they took out - human detritus -
so that it wasn't into the river.
Sewage carrying ships didn't just do the dirty work of London -
they were once a common sight on our estuaries,
cleaning up Glasgow, Belfast and other coastal cities.
London's Bovril boats were finally pensioned off in 1998.
Bazalgette's tunnels still bring raw sewage here
to the Crossness Works,
but now the solid matter's burnt off to make electricity.
The liquid sewage is treated -
it goes from this...
And the cleaned-up fluid?
It still gets the big tidal heave-ho,
and is discharged into the Thames, where the river and the sea collide.
The Severn estuary used to pose a fearsome challenge
on any journey between England and Wales.
The two countries were divided by this massive tear in our coastline.
Avoiding it meant a diversion deep inland.
Even so, only hardy travellers would brave the deadly waters.
Today, a concrete solution spans this vast channel.
But conquering the Severn was a bold venture fraught with peril,
as Mark is about to discover.
Dashing over the estuary from Wales to England,
commuters take the elegant crossings their lives depend on for granted.
But imagine a world before this bridge was possible.
A world without steel cables,
without reinforced concrete,
when the sea reigned supreme.
That was a challenge faced by the Victorians
to cross the River Severn.
The formidable collision of river and sea facing the early engineers
can still be experienced.
It's one of the most dangerous seaways in the world,
and I'm just a little bit excited.
The Severn Area Rescue Association
is going to pit me against the ebb tide.
The power of the tide here is just extraordinary!
As the tide goes out it's like a maelstrom.
The waters were an immense challenge
but, by the 1840s, crossing the river by boat was old hat.
An irresistible new force was spreading across Britain -
Come hell or high water,
estuaries weren't going to stand in the way of progress.
The great Victorian engineer Isambard Kingdom Brunel
is a hero of mine -
he'd already managed to cross the Avon gorge
with a mighty suspension bridge.
When his railway came to Bristol, he wanted to cross into South Wales,
and planned an even bigger suspension bridge.
Here are the preliminary sketches.
The biggest problem
was the sheer scale of the span that Brunel required -
over 1,000 feet.
He left a little note in his notebook,
which says "is 1,100ft practicable?"
Brunel's bridge was never built,
but if taking trains over the water defeated the best brain of the age,
how about going underneath?
A tunnel - was that the answer?
Digging deep to create a railway under the water -
this was very bold, big thinking.
This is one of the original drawings of the tunnel from around 1887,
and you can see how the track comes down
underneath the deepest part of the Bristol channel here, in The Shoots,
and gradually up to the Welsh side.
So what we've got here is around seven miles of railway track.
That passage under the estuary is now a vital link
between England and Wales.
Carrying over 250 trains a day.
Passengers are oblivious to a catastrophe
that nearly sank the tunnel before the first train ran,
and is a problem that still lurks below.
So, here we go.
I've been granted access to a shadowy water world
few get to see.
It's great - we're just coming into the cutting,
the portal's ahead, and we're about to go under the sea.
Isn't that fantastic?!
We're heading for the deepest point in the tunnel.
Just 50ft above us
millions of gallons of water are swirling around -
the River Severn and the sea are in full flow.
Keeping the water out here is hard enough,
but can you imagine if there was a flood down here?
With an estuary hanging over their heads,
engineers knew there'd be seepage of seawater,
but it was freshwater that nearly drowned the project.
Nobody expected this -
a raging torrent!
They'd broken through to an underground spring.
In October 1879, water began to pour into the tunnel.
The workers fled for their lives.
The disaster struck when a shaft dug on the Welsh coast
cut into an underground river deep below the surface.
For four years, the engineers made desperate attempts
to block the freshwater spring,
but every effort proved futile.
And it's been flooding in at this alarming rate ever since.
If they couldn't stop the spring water, they'd have to live with it.
The only solution were pumps,
massive ones like this that pump the water out as fast as it comes in,
right up to the surface.
Leighton Jenkins helps keep the tracks dry today.
So what would happen if the pumps actually failed?
Every second counts,
as soon as the pumps stop we'd have to inform the control
within 10 minutes to shut the tunnel itself,
and within 20 minutes we've got water coming up through the tracks,
so every second absolutely counts.
But have they ever failed?
No, not as far as I know, no. Not while I'm on a shift anyway.
The railways had proved irresistible.
With rival Victorian companies vying for routes,
by the time it was finished the tunnel already had a competitor.
In 1879, trains had started to roll over the estuary,
but the bridge's sturdy uprights -
always an obstacle to shipping -
would ultimately prove its downfall.
Do you see, that's a tower
where the railway bridge once crossed the Severn Estuary.
I've got a photograph
that shows the stanchions marching across the river -
now totally destroyed.
The raging waters where river and sea smash together
would deliver a fatal blow to the rail bridge.
In October 1960, the Arkendale, carrying oil,
and the Wastdale, laden with petrol,
were heading for combustible collision.
The Arkendale was carried in by the surging tide.
That powerful current would drive it into the Wastdale
on a foggy night at Sharpness Docks.
As Alan Hayward knows.
They were coming upriver intending to come into the docks here,
but they were accidentally swept past.
And then they collided and became, in effect, stuck together.
Disabled ships in thick fog,
carrying 600 tonnes of inflammable cargo
at the mercy of a swirling sea,
propelled them to disaster.
They were desperate to separate from each other,
fighting by steering in different directions,
but it just didn't work.
And they only had about four minutes
before they would reach the railway bridge.
The rail bridge across the Severn loomed out of the fog,
a collision with the ships carrying oil and petrol was now inevitable.
A lot of sparks would have been created
which ignited the petrol in one of the vessels.
The fuel, of course, spilt out over the river,
so the whole river became a mass of flame.
First mate Percy Simmonds was aboard one of the tankers.
His son Chris was 13 at the time.
I try to imagine that night and what he was going through,
and it must have been just terrible with the flames and everything.
I'm just sure he was determined to make it across this river somehow
and make it back to us.
Daylight and a low tide revealed wrecks of the fuel tankers
smouldering on a sandbank.
Soon the first body was found.
They identified the body there,
and they, you know, let Mum know that, yeah, it was definitely Perce.
Chris's father Percy died along with four others
on that terrible evening.
The damaged bridge was too expensive to repair, it was demolished.
But each day, when the tide recedes,
scars of tragedy are revealed.
Out there, of course, are two hulks,
buried now in the sands that have been washed over by countless tides.
But they're still there. They're there as monuments.
They're here as a reminder to all of us.
It's immensely humbling
to be next to such a vast body of brooding water.
Even on a calm day like this
one can feel the power
where rivers and sea collide.
Surging waters urge us on to fresh endeavours.
And we're not alone in finding creature comforts
around the fringes of our great seaways.
The tide brings in the bounty
that makes our estuaries brim with vitality.
Safe havens that offer boundless prospects.
Where rivers collide with the sea our coast comes alive
and opportunity awaits.
If it ever came to pass that Mr Corbyn were the Prime Minister,
this country would be a basket case.
Well, I think we're a basket case now. Have you seen Southern Rail?
Have you seen the National Health Service?
And we'll be more of a basket case once she triggers Article 50.