Wales: Severn Bore Coast


Wales: Severn Bore

Nicholas Crane explores the coast of south Wales, where the second highest tidal range in the world has had a huge impact on lives for thousands of years.


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It's a part of the coastline where one natural phenomenon dominates pretty much everything,

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from defence to building regs.

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The Welsh coastline has one of the most extreme tidal ranges in the world.

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The extreme tides mean that twice a day, every day,

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there's a vertical rise in sea level of between 12 and 14 metres.

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That's an incredible 40 feet in old money, pretty much as high as that house over there.

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And from time to time,

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those tides create an awesome, almost unbelievable spectacle.

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I'm standing on the banks of the River Severn.

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It's the longest river in Britain,

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much of it marking a border between England and Wales.

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And although it's late at night,

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there are people like me dotted along the river banks, anxiously watching, anxiously waiting to see

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an incredible natural spectacle.

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It's the Severn Bore. I've waited much of my life to see the Severn Bore.

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It's one of nature's miracles, rather like the Northern Lights or a double rainbow.

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If you ask the locals, they'll tell you the Bore has a mind of her own.

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I'm sure there's something moving up there. The river's lost its shine.

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All I can hear my own heart pumping like mad.

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PEOPLE WHOOP

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Breaking waves! There's breaking waves on the far side. Here it is, this is fantastic!

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Must be about 200 metres away, and I can see the breaking wave already.

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CHILDREN CALL: Look! What's that?

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This placid river is suddenly being ripped up

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and all the laws of nature have been thrown into reverse, broken,

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because there's a great standing wave just MOVING...unstoppably

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the wrong way. It's coming upstream.

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-And it looks like something living!

-LOUD RUSH

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And it's breaking on this side, too,

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so we've got waves on both sides, this huge wall of surf that's

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breaking out right close to me here and going out 15 metres, fantastic!

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Absolutely incredible.

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There are more waves following it.

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My god, that huge wave!

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Fantastic!

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Run quick, because the river goes through some bends further upstream,

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if I'm quick I'll be able to cut the Bore off and meet it further up.

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The Bore first appears some five miles inland from the sea

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as the Severn suddenly bottlenecks.

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Then it takes the best part of an hour

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to follow the river's twists and turns to Minsterworth, where I am.

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And in another five minutes or so, it should reach Minsterworth church.

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CYCLE BRAKES SQUEAK

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Made it. What's the time?

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I reckon I've got about a minute at most

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until the Bore comes creaming round that corner down there.

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SOUND OF RUSHING WATER

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Now I've seen it once,

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I'm beginning to understand why thousands of years ago, the people who lived along this riverbank

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looked at this wave with awe and a lot of incomprehension.

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In fact, in ancient Welsh, this was just known as "the roaring wave".

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Absolutely awesome.

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From Minsterworth, the Bore continues relentlessly,

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ripping at the river banks all the way to Gloucester.

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But make no mistake about it,

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what we're looking at isn't caused by the tide - the Bore IS the tide.

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It's the raging sea 20 miles inland.

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The entire river has been forced backwards,

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and those waves taste of salt!

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But if I'm to find out exactly what causes the Severn Bore,

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at least part of the answer must lie 240,000 miles up there in the night sky,

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because what I do know is that it's not Britannia that rules the waves,

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it's the Moon.

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Just like two kids spinning in a playground,

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the Earth and Moon are in a constant pirouette around each other

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and also around the Sun.

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As it rotates around our planet, the Moon exerts a gravitational pull

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on the greatest single mobile mass on Earth, the sea,

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which is physically moved backwards and forwards to give us high and low tides.

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Although much further away from Earth, the Sun also exerts its own massive gravitational pull.

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So when, on occasions, the Sun, Moon and Earth align in a straight line,

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the pull of the Sun and Moon together almost doubles the effect.

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And it's no surprise that what we get on Earth is exceptionally high or "spring" tides -

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exactly when we get the biggest bores on the River Severn.

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So the Sun and Moon cause the tides,

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but the Severn Estuary has the second highest tides not just in the UK, but in the entire world.

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Second only to The Bay of Fundy in Canada. Why?

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Well, the morning after the night before, the tide has gone into full reverse.

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In search of answers, I've met up with oceanographer Chris Wooldridge.

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Tide's now pouring back out to the Atlantic

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and the buoy's being tilted over by the force of the water, isn't it?

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It's beginning to go like a train, you know.

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How does the shape of the Bristol Channel, the Severn Estuary, convert into this tidal wave further inland?

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Because down here it looks fairly placid.

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Well, the very shape itself - an ever-narrowing funnel -

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plus the length of the basin, the length of the estuary,

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and the gradient and shape of the seabed.

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These are the unique factors that combine to trigger the Severn Bore.

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This wall of water brought in from the Atlantic,

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it's got to go somewhere.

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It's been dragged across the ocean by the pull of the Moon, and the landmass wants to stop it.

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But that tidal wave is going to run on, forced into an ever-narrowing funnel and forced up at speed.

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So you've got the whole Atlantic Ocean squeezing up this funnel and then rushing upstream.

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Wow!

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Uh-oh! WATER ROARS

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Unlike the Northern Lights or a double rainbow, the Bore adheres to a strict timetable

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and it's no surprise that crowds flock to see it, nor that many feel the urge to ride it. To tame it.

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The beauty is that with two tides a day, there's a twice-daily rodeo.

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What is amazing is that for hundreds, if not thousands of years,

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people have apparently struggled to LIVE with these tides rather than running a mile.

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Professor Martin Bell has spent 20 years examining evidence of this struggle

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preserved deep in the thick tidal mud of the Gwent Levels, between the Severn Bridge and Cardiff.

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Martin has promised to show me something incredible preserved in this mud. My first impressions?

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Well, the mud-flats of the Gwent Levels don't have quite the instant appeal of the Valley of Kings

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or even Salisbury Plain!

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This grey, claylike material is laid down in layers, like layers of... cake icing, eh, except more skiddy?

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Yes, and these sediments, banded sediments, incredibly, preserve human footprints.

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-So you can see...

-Is that what these are?!

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-Yes, these are actually Mesolithic human footprints.

-That is astonishing!

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Made in the soft mud, but now semi-consolidated as the whole things become compressed.

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As you see, they're quite small.

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They are obviously mostly children of seven, eight, nine, probably.

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So roughly when do these footprints date from?

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7,000 years ago, at a time of very rapid sea-level rise, when the whole estuary was really inundated.

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Previous to that, there'd been a bay

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stretching between Pembrokeshire and Devon, but suddenly this funnel-shaped estuary opened up.

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It's at that time that the huge tidal range, 14.8 metres, would've developed.

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-That was the beginning of the Severn Bore?

-Exactly.

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-These children could've seen the first tides that caused the Severn Bore?

-Yes.

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SOUNDTRACK: CHILDREN LAUGH...

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..WATERFOWL CALL

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Subtitles by Red Bee Media Ltd - 2006

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Email [email protected]

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