Keyfile Floods at Boscastle Geoprojects
Flooding is a regular occurrence
in the UK during recent years. No one knows exactly why but one possibility is
global warming. Flooding however is a natural process, it is a river’s way of
coping with excessive amounts of water in its drainage basin. Some causes of
flooding are –
- Snow
melting on higher ground releasing water held in store
- Increased
run off in tributary valleys increasing the flow of a river
- Impermeable
rock preventing water from soaking into the ground
- The
water table may be high because the ground is already saturated from
previous periods of heavy rain.
- Steep
slopes may cause increased surface flow on the sides of the valley
Very often it is a combination
of these causes, in particular the last two.
August, 2004 was a very wet
month throughout the United Kingdom with many areas receiving double the
average of August rainfall.
According to the Environment Agency –
The devastating flash flood in Boscastle was
among the most extreme ever recorded in Britain.
A flash flood is
a sudden flood event caused by a hydrologic response of the drainage basin.
Flash floods are normally strongly localized and associated with extreme
showers or thunderstorm activity, when high rates of precipitation occur in a
short period of time.
Flash floods usually arise when rain falls over a small catchment basin. The terrain may channel the extreme run-off to produce a flood peak that reaches its maximum in just a few minutes or hours. Flash floods are increasingly observed in urban areas where the surface is unable to absorb large amounts of water in a short period. Often the impetus and velocity of flood water are much more important than the associated water levels and duration in terms of potential impact.
The
Boscastle flood (16.8.04)
Boscastle is the only natural
harbour for 20 miles along the North Cornwall Coast. For a hundred years the village was a thriving port, but the
coming of the railways, whilst ending the isolation of North Cornwall, soon saw
its decline as a trading port. Since then however, Boscastle has developed as a
tourist destination with thousands of people visiting the village every Summer.
Boscastle village, clings to the
side of the Valency valley. The High
Streethave many properties with traditional stone and slate porches, and large
slate flagstones leading up the garden path. Amongst the tourist attractions
are Craft shops, a Witches Museum, a disused watermill, even a bakers and fruit
shop. Old inns such as the Cobweb, and the Napoleon.
The photograph below shows the power
of the water in that cars and rubble are piled on top of each other
Lynmouth Floods – 52 years to the day
The Boscastle
flash flood happened 52 years to the
day after the disaster that devastated Lynmouth in North Devon.
On that night
of August 15-16, 1952, 35 people were killed and hundreds lost their homes as a
torrent swept through the fishing village. In the previous 24 hours 9 inches of
rain had fallen on exmoor, already saturated by two wet weeks.
A 90 million ton
wall of brown water rolled down from the moors and broke the banks of the East
Lyn and West Lyn rivers.
The water burst
into the village at 200 mph, the 12 ft. waves carried trees, telegraph poles
and boulders that dislodges entire walls, cottages and parked cars. The debris
collected against bridges that burst to release surges of water 30 ft. high.
Cars
swept away
Cars were swept out to sea,
bridges were washed away and people clung to rooftops and trees for safety as
torrential rain hit the area.
Emergency workers mounted a huge
operation to rescue residents and holidaymakers along a 32-km (20-mile) stretch
of the north Cornwall coast around Boscastle.
Within an hour of arriving there as a tourist, I
watched 80 cars being picked up like dinky toys and doing their convoluted
dance out to sea. Within three hours half a bridge was washed away, many
buildings were destroyed, people's houses and possessions floated away, roads
were lifted up and crashed down onto cars like the jaws of a monster
masticating its prey.
A comment from a foreign tourist
Seven helicopters from the Coastguard, the Royal
Navy and the Royal Air Force hovered overhead, winching people trapped by the
churning brown waters to safety.
As the tide and the flood waters
receded on Tuesday morning, police divers searched the harbour as a police
"body recovery" team stood by.
Cars, boulders and uprooted
trees were strewn through the streets. Some shops had been torn in half by the
floodwaters, which struck at 1445 GMT.
At the flood's peak some roads
were submerged under 2.75 metres (9 feet) of water, and rescuers described the
village as "devastated".
Damage
to property – The Museum of Witchcraft
The Museum of Witchcraft has
been severely affected by the floods.
The Museum of Witchcraft, houses
the world’s largest collection of witchcraft related artefacts and regalia. The
museum has been located in Boscastle for over forty years and is amongst
Cornwall’s most popular museums.
Almost 50% of the artefacts in the storeroom of The Museum of Witches
were lost, and due to the fact access
was almost impossible for nearly three weeks the silt had time to destroy quite
a lot of the pieces.
There was a problem with ‘catastrophe tourists’
strolling in to buildings to check out what’s going on. A large group of people
walk in to the museum to say hello. This is despite large “No Entry” signs at
the entrance to the harbour.
Cause
The flash flood at Boscastle was
caused by a collision of winds. The day had been very warm, drawing in sea
breezes along the coast.
When they joined forces with a wet southerly air flow they
shot upwards with a dangerous mix of warm, moist, highly unstable air. Nearby
Bodmin Moor thrust up the air mass even higher.
A line of thunderclouds rocketed over 10km high, their
tops streaming into anvil shapes as high-level winds swept air away from the
storm, helping suck more air from below. The thunderclouds grew so tall that
they created intense downpours leading to more than 5 inches of rain falling
around Boscastle in just a few hours, and possibly more over higher ground.
With the ground already
saturated from recent rains, the storm waters were funnelled down steep river
valleys and burst
Huge
funnels!
Whilst torrential rain is key to the onset of flash
flooding, the drainage and topography of the surrounding area determines the
scale and impact of the event. When there is torrential rain that cannot be soaked up or
drained away, this leads to ‘run-off’ – water running over the soil rather than
sinking into it.
This run-off can cause localised but severe flooding. In places
such as Boscastle, steep-sided valleys can act as huge funnels for this water,
channelling it very quickly down to the sea, and sometimes with devastating
results for local communities. This is what happened in Lynmouth on exactly the
same day 52 years ago.
The timing of disasters such as
that in Boscastle is important. As this happened during the day people were
awake and could be rescued by the emergency services. If it had happened during
the night most people would have been asleep and there would have been a higher
likelyhood of injuries or even deaths.
In 1987 the timing of the storm
was also important. It happened during the night when people were not on the
road and in danger of getting crushed under falling trees.
Effect
on tourism
About 90% of Boscastle’s economy is dependent on
tourism. After the flood, more than 20 accommodation providers were forced to
shup, many of them individually owned bed and breakfasts. As about two thirds
of the business is done during the six week school holiday, the effects were
even more devastating with half the three weeks remaining.
Tasks:
|
1.
By using a good search engine such as
google a fact file for Boscastle to show it’s geographical location, population
and the extent that tourism is a major business for the village 2.
Do the tourists who visit Boscastle
come there to stay or do they stay elsewhere and briefly visit the village? 3.
What is the main attraction of
Boscastle? 4.
By using a map of the area explain the
main routes into the village and any problems that a large number of visitors
may cause? 5.
Give your view as to the future for
tourism businesses and employees in the village in the short term (three
months), in the medium term (a year) and in the longer term? 6.
Draw a flow diagram to illustrate the
weather happenings in the Boscastle area during the previous two days? 7.
The term disaster is frequently used
and misused. By using the internet searching under the words climate disasters,
make a list which in your opinion are the five worst disasters to happen in
Britain during recent years and secondly do the same exercise for the top five
disasters in the world. |
8.
Find out more about flooding on the
webside – www.environment-agency.gov.uk/floodwarning