Original subtitles

SAMANTHA BOND: Extreme weather events

can be shockingly destructive.

From the Great Storm of 1987, and the Big Freeze of 1963,

to the devastating London floods of 1928.

But perhaps the biggest and most shocking

weather disaster to hit Britain came in January 1607,

in the form of huge tidal waves.

WOMAN: The water that came in was tremendous.

There's no two ways about it.

They travelled the length of the Bristol Channel and Severn Estuary,

killing hundreds of people,

taking out buildings and devastating villages.

We should acknowledge as the single greatest

destructive event in Barnstable's history.

In this programme,

we tell the story of the great tidal waves

hour by hour and, using historical documents,

recount just how destructive they were.

This is the worst flood in the last thousand years in the Severn.

But one important question remains:

Just what caused this terrible disaster?

The early 1600s were a time of great change for England and Wales.

In 1603, the Scottish James VI

had become James I of England and Wales,

the beginning of the Stuart era.

1607 will see the first permanent English settlement

established in the New World -

Jamestown, named after the king.

But despite all this change and expansion,

for many people, existence continues as it has for centuries.

CHILD LAUGHS

But life is fragile.

The whole of the early-modern pre-modern world,

people live in a world in which the chance of dying is very, very high.

So if you lived in an early-modern city,

plague outbreaks might come along every 10, 20 years

and kill vast numbers of people.

Communities, societies, economies

have to be able to roll with the punches

cos the punches are coming constantly.

Most people outside the cities work in agriculture

and will be born, work, grow old, and die in the same village or town.

Also in 1607, an extreme weather event

will hit England and Wales

so powerful that it will devastate whole communities.

By the end of January 1607,

there has been a six-week-long warm and wet spell

creating perfect conditions for storms.

Powerful south-westerly winds

have been battering the vulnerable Cornish coast for days.

And today, the 30th of January,

the locals are expecting one of the highest tides of the year...

..but they have no idea of the extent of what's heading for them.

During the night,

the people at the prosperous port town of Barnstaple

have noticed a violent storm out at sea.

The parish clerk wrote in the parish register

that the storm started at 3:00 in the morning.

They were certainly aware of a storm that was remarkable,

remarkable enough to get a...

People must have woken up.

Six miles away, right on the coast, is Appledore.

In 1607, it was a tiny fishing port with a small population,

where the rivers Taw and Torridge poured into the Bristol Channel.

It's a dark, cold winter morning,

so I would've expected at three to four in the morning

people were still in bed.

They would have been aware of it

by their shutters rattling outside their windows.

They would have heard the wind whistling down their chimneys.

They would have been quite worried.

Then, as dawn is approaching...

..huge waves start hitting the village of Appledore.

With the simple-structured buildings giving no resistance

to the force of water and with no sea defence walls,

huge waves raced through the narrow streets and engulfed the town.

But the waves are carrying something even more dangerous.

As the tide comes in,

a 60-ton laden ship

was pushed inland quite some distance

by the weight of the water, by the force of the water.

After flooding Appledore,

the waves head up the River Taw at incredible speed.

They travel six miles, past farmland and homes,

straight towards the flourishing market town of Barnstaple.

In 1607,

Barnstaple is considered a wealthy little town.

Fashionable,

the houses are full of spectacular plaster ceilings,

wonderful carved rooms.

This was a content and agreeable place to be.

Barnstable is a popular, thriving market town,

home to hundreds of people.

A busy economic hub in 1607, people's livelihoods are at risk.

With the rise in international trade to the Americas,

Barnstable's position on the North Devon coast

meant it was becoming an important port.

They were building all along The Strand

as part of this general expansion of the quay area.

It's around 7:30am,

and some residents are still sleeping.

The waves sweep in and wreak havoc

on the building works along the quay.

We have a tidal river.

Tide comes in, goes out twice a day.

They're used to that,

but they're not used to a great surge.

They're not used to waves coming in.

And they know, particularly if they're down by the quays,

that, you know, they're incredibly vulnerable.

The home of the Frost family is right at the water's edge.

People try and escape as best they can,

but as it's early morning, some are caught unawares.

WOMAN SCREAMS

People died at Barnstable.

GIRL SOBS

The walls being destroyed, so the roof fell down.

A man and his two daughters.

A contemporary account gives us the names of those killed.

The death of one James Frost and two of his children,

in which his house fell down upon them and killed them.

The parish register names his daughters as Sabine and Catherine.

For Barnstable...

the thing which gave them their prosperity,

the sea, suddenly turns against them.

These huge waves have already flooded nearby Appledore.

With Barnstable's waterfront in ruins,

the waves are now heading straight into the town.

SAMANTHA BOND: It's the early morning

of the 30th of January, 1607.

Huge waves have hit the ports of Appledore and Barnstable

on the North Devon coast.

The surge of water has swept six miles inland

and has destroyed buildings along the riverside,

killing three people instantly.

WOMAN SCREAMS

Now the waves are pushing water up,

into the narrow streets of Barnstaple.

The storm not only hits the whole riverside and goes into the town,

but it overwhelms what little defences they had.

Robert Langdon, the parish clerk, recorded the event.

LANGDON: "There was such a mighty storm and tempest

"from the river of Barnstable, with the coming of the tide,

"that it caused much loss of goods and houses."

It goes up the lower part

of what's now High Street at South Gate.

It goes up Crock Street and Maiden Lane or Maiden Street.

It goes up a lot further than they had expected a flood would go.

Barnstable's a low-level place,

you know, the town doesn't have a hill,

and the water sweeps in and stretches up into the streets.

It's five to six feet higher, the water level,

than it is normally.

There's a lot of damage to the buildings, to the quay area.

We can see in the maps that they have defensive structures

built around that side of the town,

but they're not good enough for what is the highest flood

that anybody has ever seen at that time.

The waters reach all the way into the town,

but stop short of St Peter's Church and St Anne's Chapel

right in the centre,

which means the waves have forced water

around a hundred yards from the river's edge.

And those buildings are saved.

It's all the buildings around the quay area,

around the river in the lower part of town

which are particularly... affected.

The prosperity was all about access to the sea,

and this flood strikes at that,

because the very thing which gives them their wealth takes it away.

It's from the town clerk that we get much of our information

about the effects of the flood.

Thanks to a remarkable discovery Todd Gray made a few years ago,

The Lost Chronicle of Barnstable, written by clerk Adam Wyatt.

In Barnstable, we have the town clerk...

..responsible for the day-to-day care of Barnstable.

He realises he needs a record of what happened.

And the flood is an event

which is unlike anything that they've experienced before,

so it gets a lot of attention.

His account paints a vivid picture of the flood.

"There was such a flood or tide

"as the like was never seen in this town.

"It came into all the houses and cellars near the quay

"with such a power that it burst open doors

"that were locked and bolted,

"and threw down many houses and walls.

"Thus the town hath lost in salt, sugar, woad to the value of £1,000."

That's the equivalent of around a quarter of a million pounds today,

a huge sum for such a small town.

An account written a few years later says...

"It subverted houses, drowned beasts,

"and destroyed people, of whom some, to save their lives,

"were constrained from their upper rooms

"to take boat and be gone."

The flood, you know, we should...

acknowledge as the single greatest destructive event

in Barnstable's history.

Before the horrors of this morning,

Barnstable was a prosperous town with a bright future.

But all of this new development is now in ruins.

Just before sunrise, in the space of a few minutes,

a community has been devastated.

But the waves are only just getting started.

They are now heading for one of the world's

most remarkable stretches of water,

and the people that live alongside it.

The Severn Estuary is one of the wonders of the British Isles.

It's a powerful body of water

exposed to the full might of the Atlantic Ocean.

Its special geography is what will make this flood so devastating.

The Severn Estuary is quite a unique place.

We have the third highest tidal range in the world.

The tidal range is something like 33 foot in places. That's huge.

So it's quite a hostile environment.

The Bristol Channel is this perfect funnel shape.

So what happens is as the water is coming in and pushing in,

the shallow depth and the funnel shape of the land

will compress the water

and push it up towards the River Severn.

That constriction will then make the wave more powerful.

If you kind of imagine like a bellows.

You push it,

then there's a huge kind of shaft of air which comes out.

Whenever the tide comes in, it's like this sort of bellows.

But if you then combine that

with a powerful Atlantic weather system coming in

with a storm coming in and interrupting it

just the right moment so that when the bellows goes like that,

it goes...

And suddenly, it's much more extreme than you expected.

Now around 8am,

the huge waves move up the Bristol Channel,

reaching the lowlands of Somerset at incredible speed.

When you come into the Severn Estuary,

the coastline opens out into coastal lowlands,

and it's in those low-lying areas

where the full force of the flood was felt.

Sea walls line the mouth of the River Parrett at the coast

and should stop the waves crashing through,

but they were never designed

to protect against something as big as these waves.

Once the level of water has risen to the top of those sea walls,

whether it's broken them or not,

it's going to come over the sea walls

and onto the land behind.

The River Brue that helps drain the Somerset levels

into the sea also overflows,

flooding a nearby village.

So, in Huntspill, 28 people drowned,

and some of the people in Huntspill

might have tried to make it to the church.

The church is on a little bit of higher ground, as you often find.

On the opposite bank of the River Brue

are Burnham-on-sea and Brent Marsh.

The waves destroy a mile length of seawall.

People beginning their days

witness a terrifying sight as the waters flood in.

A news pamphlet of the time is thought to describe the scene.

MAN: "Many of the spectators that they imagined it had been some fog

"or mist coming with great swiftness towards them,

"and with such smoke as if mountains were all on fire.

"And to the view of some,

"it seemed as if myriads of arrows had been shot forth

"all at one time."

And the water that came in was tremendous.

There's no two ways about it.

And so the isolated farmsteads

on Brent Marsh would have been underwater.

It would have surprised the people.

Clearly, back in 1607,

there was no means of communicating between the villages and towns,

and people would have been surprised by it.

It must have been a terrifying sight.

People wouldn't have known the sea wall had gone

until they looked out and found the water was there.

There's a huge difference between the water coming up sort of so high

and water coming up that high.

You know, it's the difference between...

having to wade through water and drown.

Many would have reacted in panic,

desperately trying to avoid the waves

flowing rapidly over their land.

As they were aware of water coming in,

they would have looked to obviously save themselves.

People who died because they were caught out in a field

and they climbed a tree.

And then, you know, possibly they died of exposure.

We're obviously in an agricultural farming community,

so we're dealing with a large number of beasts and animals

that need some sort of protection from this water coming in.

It's difficult.

It's difficult for people to witness and to deal with.

I think it's fair to say that there would have been

a lot of animals lost.

The waves sweep on.

Within minutes, they reach the village of Brean,

six miles further up the coast.

The impact is tremendous.

Brean itself is particularly exposed.

Nine out of the 11 houses were damaged.

26 people drowned there as well.

News pamphlets published soon after the disaster described the scene.

MAN: "The forced waters, having gotten over their wanted limits,

"are affirmed to have run at their first entrance

"with a swiftness so incredible

"as that no greyhound could have escaped by running before them."

Farmer John Goode of Brean loses his wife and nine servants

when the waves strike

but saves himself by clinging on to a chunk of thatched roof.

It carries him for more than a mile before washing him up on dry land.

MAN: "Mighty hills of tumbling water over one another

"in such sort as if the greatest mountains in the world

"had overwhelmed the low villages or marshy grounds."

These spectacular waves that struck at dawn

have battered the English coastline and flooded huge areas of Somerset.

Whole villages have been devastated.

Farms, homes and livestock have all been destroyed,

and at least 80 people drowned.

Now at Brean,

only the local church, the 13th-century Saint Bridget's,

survives of the original village,

keeping its lonely vigil over the sea.

Almost everything else was destroyed by the force of the water.

It's now around 8:30am.

The unprecedented waves

have been relentlessly pushing their way inland,

flooding towns and villages for more than two hours.

Now they have the vulnerable, low-lying Gwent levels

on the Welsh coast in their sights.

Like the Somerset levels,

this part of Wales is a large, isolated area

dotted with small farms and tiny villages.

Many of the homes on the low-lying land

are especially vulnerable.

Most of those people who died,

I mean, some died because their houses were actually washed away.

Houses in this area may well have been of cob.

Cob is basically mud mixed with straw,

erm, to stiffen it.

Once a cob building got very wet, as it would have done with a flood,

it would just crumble away, really, and be washed away.

People lost their homes as well as property,

and in many cases, sadly, their lives.

Many small communities live right on the coastline.

The communities living on the Wentlooge level,

at places such as Peterstone and St Brides Wentlooge,

were right down in the firing line.

There was nowhere else for them to go to.

The areas which really suffer,

it's not just the countryside, it's for people on the levels.

The only reason why they're not flooded constantly

is because they've got these flood barrier defences.

So that's fine.

But what it means is that when the water overtops those,

those barriers, then it just... the water floods in,

and, you know, it's like water going over the edge of your bath.

It's fine until it goes over the edge,

and then it causes a terrible mess.

The huge surge of water shows no signs of relenting

and pushes on along the Gwent coastline.

After Peterstone, it washes over St Brides.

We know a little bit more,

perhaps, about St Brides and what happened there,

because there's a wonderful stone plaque

in the porch of the church.

And it tells you at the bottom the height of the flood.

Part of the stone is sort of crumbling away.

It's a little bit difficult,

but the memory is the most important thing.

Everybody knows about the flood

because of that particular inscription.

At Goldcliff, a mile back from the sea,

there is another plaque.

It states that the water came up to its level,

that £5,000 worth of damage was caused and 22 people drowned.

The pamphlet Lamentable Newes out of Monmouthshire

describes the subversion of 26 parishes,

which gives a good indication of how much chaos the waves caused.

In the space of just a few hours,

these massive waves have devastated whole communities

and changed the landscape forever

and are now heading for the major port and city of Bristol.

SAMANTHA BOND: It's around 9am on the 30th of January, 1607.

Mountainous waves are surging

along the Bristol Channel and Severn Estuary.

After flooding the towns of Appledore

and Barnstaple in North Devon, killing three people...

..the tide has pushed these huge waves

up the low-lying Somerset and Gwent levels,

killing hundreds of residents and destroying villages,

farms and isolated homes.

In terms of the Bristol Channel,

we have this sloshing bathtub effect.

Because of the shape of it,

what will happen is as the water goes up the channel,

it will bounce from one coastline to the other.

And that will amplify your wave.

On the English side of the estuary,

the waves are approaching the city of Bristol,

which lies around eight miles from the coast,

but the waves don't seem to be losing momentum.

Bristol, by modern standards, it was really small,

it was about 12,000 people.

So we kind of think today, that's really small,

but that still makes it probably the second

or third largest city in England.

The Avon Gorge connects the Bristol Channel to the city.

The waves head up this narrow channel straight for the port.

There was damage to the ports.

We know that warehouses on the quays would have been also compromised.

The overflowing rivers Avon and Frome

force water quickly up the streets.

Around five years ago,

Dr Evan Jones, an expert on the city's history,

discovered something in the Bristol archives that proved invaluable

in understanding what happens next.

I found this one chronicle which hadn't been published before,

chronicler, it's a kind of long, detailed description

of the various things, the astonishing things.

You know, it's flooding the whole of central Bristol.

So he talks about how the water rose

as far as the bottom steps of St Nicholas' crowd door.

He illustrates it by saying that a bargeman pushed his boat

off the steps on St Nicholas' Church

and describes the water rising halfway up the seats

in various churches in the town.

The chronicle says...

MAN: "And in the city of Bristol,

"all the lower part were drowned about four or five foot.

"The waters were up in St Stephen's, St Thomas'

"and temple churches halfway up the seats.

"The merchants received great losses

"in their storehouses and cellars by it."

Once again, the very thing that people relied on

for their livelihoods, their very lives,

has shown how easily it can turn against them.

But despite the terror, the suffering and the destruction,

human bravery prevails.

Around 30 miles from Bristol,

the village of Arlingham sits on a peninsula

surrounded on three sides by the Severn.

And when the waves reach up to here,

Arlingham is right in the firing line.

The water in Arlingham itself,

I think it came up almost to the cross in Arlingham.

The cross is at the centre of the village, no longer visible.

The parish records, written by the vicar,

tell us how this community came together in the face of catastrophe.

The poor vicar and his wife and his new baby

lived in practically

the lowest-lying house in the village.

They were in great peril.

The village keeps a communal boat, which is used to rescue people

and animals from the rapidly rising waters.

He wrote in his parish register that they were among

those 20 or so people that were rescued by boat...

..and taken up to the church, up to higher ground.

And he also wrote of those people that had that not happened,

they might have stived, ie suffocated or starved to death.

They were cut off, basically.

By around 11am that day,

after five hours of raging across the landscape,

the waves finally stop.

In Wales, the floods have reached Chepstow,

where two people are reported to have drowned.

On the English side, the waters have reached

over 35 miles north of Bristol.

When it eventually gets up to Gloucester,

the tide actually starts to lose its impetus.

So it's still going to be up high for quite a while,

but it's dropping.

The pamphlet God's Warning to His People of England says...

MAN: "So violent and swift were the outrageous waves

"that pursued one another with such vehemence,

"and the waters multiplying so much in so short a time,

"that in less than five hours space, most of the country,

"and especially the places that laid low, were overflowing."

The news of the sheer size of the flood

and the devastation it has caused

soon reaches the capital city, London.

In an age before newspapers,

pamphlets, small documents reporting news from all over the country,

leap onto the story.

One of our best sources about the 1607 flood

comes from a series of four pamphlets

that were published in London,

the first of which probably was printed around about 17 days

after the event itself.

That news would have had to have travelled to London,

and the pamphleteers would have decided what pieces of information,

what intelligence to include.

It's a period you don't get sort of daily newspapers,

but you are beginning to get a culture of printers

presenting news pamphlets,

especially relating to a particular event or happening.

And it's the birth of kind of cheap popular print.

Along with that, it's the birth of something

we should maybe recognise today

as almost a kind of tabloid newspapers

where, you know, sensational stuff sells,

sort of terrible events sell.

What was particularly remarkable about this one,

it was one of the first events where the journalist,

if you want to call them that, had this really bright idea.

So, this is a pamphlet which gets produced in London

a few days after the flood.

A true report of certain wonderful overflowings of water.

Now lately in Somersetshire

and destroying many thousand men and children

and overflowing and being whole towns and cities.

What's really astonishing about this one,

the news editor who's doing this,

they think, "I know a way of selling this

"is, actually, we'll illustrate it on the front cover."

So right on his front cover,

he has this woodblock print commissioned,

which is actually showing depictions

of all the terrible events which are described in the flood.

And that's kind of one of the things

which makes it almost kind of revolutionary for its time.

And a lot of people still couldn't read.

So the imagery on the front of the pamphlet

is very, very powerful indeed.

Got people up trees escaping the flood.

A baby in a crib. Animals drowning.

You know, the story of this flood gets reproduced all around Europe.

That image and the prevalence of it, it kind of...

even in the 17th century, it basically goes viral.

The relentless surge of water may have finally stopped,

but people's difficulties are only just beginning.

Huge stretches of coastline have flooded,

rivers have burst their banks,

and many miles of land have been covered by water.

With much of the coastal lands on the English and Welsh sides

already inundated from heavy rainfall before the flood,

the extra body of water has been catastrophic.

The church at the village of Kingston Seymour in North Somerset

has a plaque placed there not long after the flood

that tells us how high the waters reached.

And this plaque records that the height of the water

was five foot in the church.

The plaque states that many persons were drowned

and much cattle and goods were lost

and how long the waters took to subside.

The water in the church was five-feet high,

and the greatest part lay on the ground about ten days.

The parish register for Almondsbury in Gloucestershire

offers more clues.

The register tells us that there was this great flood,

and then you also see the burials of people.

And it took quite some time,

almost a month for the last of those burials to happen.

So clearly, it also took quite some time

for people's bodies to be found,

for that area to be accessed.

Records barely exist for the devastation caused

along the Welsh coast.

Names or numbers of the dead weren't recorded.

We don't know the extent of the loss of life in Peterstone.

But the church has always had a problem

when the water table is really high or there's been a lot of flooding

because they can't bury their dead in the churchyard.

And so we think that probably any casualties from Peterstone

would have been taken to be buried at nearby Rumney Church.

A huge coordinated effort would be required

to organise the clean-up operation.

The biggest problem they had was the fact that

because the water is now inside these flood barriers,

it takes days or weeks for water to be able to then

kind of drain that land.

These are rich agricultural lands

that these people's ancestors have farmed for thousands of years.

If they are to have any future here, they must do as their ancestors did.

And also, in lots of places,

it's actually breached the flood barriers.

So the defences have been kind of washed away,

and they have to be rebuilt.

There is a huge undertaking to find and bury the dead.

The clean-up and rebuilding operations are colossal,

all in extremely tough conditions.

Landowners are expected to contribute to a central fund

to repair or replace the vital sea defences.

500 men alone are employed in Somerset

to rebuild the sea wall at Burnham.

It is laborious, painstaking work.

It was a collective effort,

so people owned or tenanted land,

and they were responsible for whichever drains

or sea walls were on their land.

In the aftermath of the 1607 flood,

they were very, very busy, as you might imagine.

It will take many months for life to get back to anything like normal,

but people are determined to carry on and not be defeated.

But the story of the flood refuses to go quietly into history.

Scientists and historians are continuing to investigate

the unique factors that could have caused these huge waves.

The early 17th century

sits in a period known as the Little Ice Age.

It's a period from the 16th and 17th centuries,

goes on to the 19th century.

Within that period, there's different periods within it.

And this one period between 1560 and 1630

is usually called the Grindelwald Fluctuation.

The Grindelwald Fluctuation

is a period within the Little Ice Age

which saw huge expansion of glaciers

in the Grindelwald area of Switzerland.

We know that it was a very cold period.

And we know that there were some extreme weather

or extreme climate change in this period.

It's not just that things are getting cooler in this period,

but it seems like the whole climatic system is disturbed

and mixed up.

But it wasn't just the global climate

during that period that caused these huge waves.

As we're coming up to the flood, we have a new moon.

The biggest tides, the spring tides,

occur after the new or the full moon.

Spring tide is just the big tides we get every two weeks

as a result of the lunar cycle.

They happen at new moon and full moon,

and it's when the water level in the tide cycle is at its highest.

And then you'll get an extra special type of spring tide, as in 1607.

That happens once every four and a half years.

It's to do with a special planetary alignment,

and this will obviously increase the sea height, tide height

a lot more than you would normally have on a normal spring tide.

It was a combination of all these factors that proved so deadly.

If it had just been the tide, it wouldn't have caused a flood.

The only real reason why you get these flood events

is usually when you get a storm surge.

Storm surge is the other component of high water levels at the coast.

And that's when a very big depression,

a big storm system, pushes water ahead of it.

So the high wind speeds push water ahead of the storm,

and that raises the water levels at the coast.

And it really does depend on timing.

With the 1607 flood, there was a storm.

If that storm had come an hour or two earlier

or an hour or two later, we wouldn't have had a huge flood.

So those two factors together, the tide and the storm surge,

are what creates the high water levels at the coast.

And in the case of the 1607 event,

we combine a tide that's almost at the highest level

that we ever see in the astronomical cycle,

with a big storm surge of one or maybe 1.2m.

But this is only the beginning

of a historical and scientific detective story.

A team of geologists

have proposed that this event was Britain's own tsunami.

Have they solved the mystery of the great waves?

SAMANTHA BOND: It is the 30th of January, 1607.

Huge waves have swept up the Bristol Channel and Severn Estuary,

flooding lands and destroying lives.

In 2002, a team of geologists led by Professor Simon Haslett

suggested a new possible cause - a huge tsunami.

Tsunami are usually associated with Asia and the Pacific,

so a tsunami hitting British shores would have been extraordinary.

A tsunami is a wave that is created

by a displacement of the water column,

and that displacement can be caused by undersea earthquakes,

which can actually shift the seabed up and down.

It can be caused by landslides under the sea.

Tsunami tend to be very powerful because they contain within them

the energy that's transferred to them by whatever caused them.

Simon and his team embarked on a mission to gather evidence.

Previous authors talked about sand layers occurring

in the Severn Estuary margins.

And if you know the Severn Estuary,

perhaps driven across the Severn Bridge and things like that,

you'll know by looking down that it's a very muddy estuary.

To see layers of sand is quite unusual

and requires an explanation for how they got there.

And also, a general stripping away

of the salt marshes of the Severn Estuary,

because we think, from the previous work that's been undertaken,

that none of the salt marshes that currently exist

in the Severn Estuary date back

before the middle of the 17th century.

But it's at Dunraven Bay on the South Wales coast

that Simon found the most convincing evidence yet.

We looked at boulder accumulation.

Boulders elsewhere have been seen to be a good indicator,

whether they've been moved by either storms or by tsunami,

and so by measuring them, we can work out the forces,

the wave height that is required to move these boulders.

The results of our boulder analysis

has shown that only a relatively small tsunami would be capable

of moving the boulders into the accumulations that we've identified.

So from our studies, the results indicate that these boulders

are much more likely to be moved by a tsunami than by a storm.

But historians have struggled to find accounts of seismic activity

from the period big enough to have caused such a tsunami.

But there is a third possibility - a different type of tsunami.

A meteotsunami is an ocean wave

caused by a rapid change in air pressure.

What happens is we get a storm out at sea,

and the dramatic change in air pressure

from the low pressure centre of the storm

will alter the sea level.

On average, in the UK,

we get five to seven meteotsunami a year.

Simon's research was a call

for experts of all disciplines to try and solve this mystery.

When the tsunami theory was first mooted in 2002,

it sort of sparked a bit of a imagination with me.

And so about 15 years ago,

I sort of rose to their challenge

which they had put out in their paper saying,

"Look, in order to test our hypothesis,

"we need somebody to look in depth

"at the historical and the archaeological records."

From my own research,

which has been very detailed in a lot of different records

that people wouldn't normally have thought about using,

I have managed to pick up information about the storm itself.

One of the major clues is that we know from a true report,

the first of the pamphlets, that there was a storm,

a storm surge over in Norfolk on the same day,

but in the evening.

Rose Hewlett is writing a PhD at the University of Bristol

on the evidence for the 1607 flood being a storm.

So for now, the debate continues.

The jury's out on whether the 1607 flood was caused by a tsunami

or by a storm or by some other mechanism.

So we really do need to push ahead

and look at these other avenues of research

so we get a better evaluation of the competing theories.

But what worries most people,

especially those living along this treacherous coastline,

is could something like the 1607 flood happen again?

Events such as the 1607 flood

have happened before and could happen again.

We've certainly had very large storm surges.

There's so many variables,

and you've just got to have everything lined up

to get something that's enormous.

Paul Bates is a professor of hydrology

at the University of Bristol.

He uses all kinds of data to develop simulations to try and predict

future extreme weather events.

What could really change the size of floods

into the future is sea-level rise.

If we pump a lot of carbon into the atmosphere,

we may, by the end of the century,

get 70 or 80cm of sea-level rise along the Bristol Channel coast.

For those areas, we would have to raise the flood defences

to achieve the same level of protection

that we've got at the moment.

We currently protect ourselves against events which happen

on average once every two or three centuries.

They could theoretically always happen,

but they have a very low probability.

Sea level rise means that probability gets bigger.

So that would mean that we have to build our flood defences

at two to four metres higher than we currently have them,

or we abandon large areas of the coast

and decide that they are too risky to live in.

Extreme events like the 1607 flood

show us just how lethal weather and water can be.

And it is extreme.

This is the worst flood in the last thousand years in the Severn.

From the pamphlets and from the parish registers,

we get an idea of the number of deaths.

Total immediate death toll was between 300 and 500 people.

So still a considerable number.

And every one was a tragedy.

From the plaques in the churches

scattered across the Welsh and English coasts...

..to the parish registers and the chronicles

all the way to London and the pamphlets and onward,

this huge weather event has left its mark

on the landscape and its people in more ways than one.

But tough landscapes and tough weather make tough people.

Generation after generation of farming families

stay on the land.

People were looking to reclaim land

and make the best of what they had,

er, build up their sea defences, get on with it.

It's the trade they know.

The scale of that disaster in 1607 appears to have been

the worst natural disaster to hit British soil.