Heavy rainfall in August 2004 caused flash flooding in the village of Boscastle in Cornwall, damaging homes and businesses. The physical causes were intense rainfall over a short period which the small rivers could not cope with, exacerbated by steep slopes and saturated ground. Human factors included development in a narrow floodplain and an increased summer population. The effects included economic losses, property damage, infrastructure disruption and mental trauma for residents from the devastation. While Boscastle has always been at flood risk, some experts believe climate change may be increasing the potential for extreme storms.

1. Case Study – Boscastle Floods
Flash floods in Cornwall devastated the tourist village of
Boscastle during August. The settlement was badly damaged
leading to an extensive clear-up and on-going repair work,
after heavy, intense rainfall caused local rivers to burst their
banks.
The Causes
A hazard is a negative interaction between physical and human
systems. The causes of a hazard therefore encompass
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(2)
The physical factors responsible (in this case, heavy
rainfall and catchments characteristics that promote rapid
surface run-off) and
The human factors that have brought people, knowingly
or not, into an environment where they are now at risk.
Physical Causes

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Three rivers – the Valency, Jordan and Paradise - converge
on the village of Boscastle. The majority of the damage was
attributable to the Valency.
Heavy rain was caused by extreme frontal activity. In total,
an input of 3 million tonnes of water was added to a tiny
drainage basin, whose size is just 40 square kilometres.
Attention must be paid not just to the total volume of rain but
also the intensity with which it fell. 185mm arrived in just
five hours, the majority falling in the first two hours. Under
such conditions, infiltration-excess overland flow is
inevitable, with the rate of input of rainwater greatly
exceeding the infiltration capacity of any soil type.
The soils were already saturated from previous rainfall earlier
in the week, encouraging overland flow to begin even sooner.
The three river valleys are very steep and narrow. A broader
floodplain would have helped to soak up excess water and to
dissipate energy more effectively (through an increased
hydraulic radius).
The steep valley sides mean that soils are thin, as a result of
mass movement, with limited storage capacity.
The parent material is old, hard sandstone with limited
permeability. The rivers here are naturally flashy.
Surrounding vegetation includes agricultural land with limited
interception storage, although there is some forestry along
the riverbanks. (So conditions would have been even worse,
without these patches of woodland!)
The rain coincided with high tide in the bay. This restricted
the rate of exit of floodwater into the harbour.
Human Causes
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The settlement of Boscastle has been allowed to develop on a
narrow flood plain on the west coast of England, where
rainfall is often high.
The rainfall hit at the worst time of year when the settlement
population doubles to 2,000 as tourists arrive, many of who
are following the South West Coast Path. Much higher levels
of motor vehicle damage were also experienced, as a result
of this influx. In addition, shops were carrying greater levels
of stock than at other times of the year.
• Although new flood defences were set to be built in October,
work had not yet started.
• Overall, excellent emergency services and Environment
Agency response meant no lives lost. However, due to the
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3. transient nature of the tourist population, it took a long time
to clearly establish that there had been no fatalities.
The Effects
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Economic losses Much of rural Cornwall is classified as a
deprived region. It is one of the UK’s poorest rural counties,
with EU Objective One status, meaning that incomes are
below 75% of the EU average (Financial Times, 18 August
2004). A victim of early de-industrialisation, the region’s
mining industries are now long-gone leaving it overdependent on tourism. Luckily, a strong association with
Arthurian legends and with the writer Thomas Hardy has
helped foster high visitor-numbers for Boscastle (Hardy met
his wife there and helped build St Juliot’s church). However,
most shops will now stay shut for the rest of the season and
the bad publicity is likely to reduce tourist numbers during
future years, resulting in a negative multiplier effect for the
entire local community.
Wider regional impact In addition, the effect may spread
beyond Boscastle if other river-line settlements are perceived
to be at risk by tourists. Boscastle businesses can claim
compensation from their insurance companies (claims for
‘disruption to trading’ in Boscastle could amount to £15m).
However, others businesses elsewhere-in Cornwall cannot,
even though they too may suffer reduced trade next year.
This is a cause for concern, with tourism accounting for 30%
of Cornwall’s GDP. The population doubles during July and
August each year, with tourists spending up to £1 billion
throughout the county.
House price falls People will find the value of their homes
permanently reduced, now that Boscastle is associated with a
serious flood risk. It has been suggested that values have
halved (The Guardian, 19 August 2004).
Mental trauma Many residents will suffer stress and anxiety
during the year ahead, with insurance loss adjusters advising
that it may be six months before properties are sufficiently
repaired for homeowners to permanently return (The
Guardian, 21 August 2004). Environment Agency post-event
surveys have repeatedly shown that this is one of the worst
problems that flood victims face: they cannot physically
return to their homes even when the floodwaters have
receded. North Cornwall District Council banned Boscastle
residents from returning to even look at their homes for the

4. first ten days, while structural engineers inspected properties.
Health and Safety legislation also required that 76 up-ended
cars, masses of uprooted trees and sewage-contaminated
silts needed to be moved from the village streets before they
could be re-opened to the public. Only now can actual interior
repairs such as re-plastering begin, and this will take many
more months. In some cases, the historic character of the
houses in Boscastle is likely to cause extra problems. Many
are Grade II Listed buildings, which means that repairs will
take even longer, as restoration will require specialist
attention.
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Heavy property damage Six properties were destroyed
outright. Most others will require between £15,000 and
£30,000 for repairs.
Shared amenities such as the village green are now covered
with silt and up-ended cars. These are serious costs for a
small community with a seasonal employment problem, due
to its over-reliance on summer tourism. Insurance companies
will reimburse most people.
Some home and car owners will not receive compensation if
(a) they lack insurance cover or (b) they find that they are
not entitled to payment because insurers regard this unusual
event as an ‘Act of God’.
Infrastructure disruption Both bridges in the village have
been destroyed and sections of road have been swept away.
Telephone, water, electricity and gas supplies were all
immediately interrupted.
Irreplaceable loss of historical artefacts The ‘Witch Museum’ –
which is fifty years old and receives 50,000 visitors a year –
has seen some of its unique contents damaged (BBC R4,
Today, 18 August 2004).
Is Global Warming To Blame?
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‘The Met Office said that heavy, thundery downpours
developed by midday across south-west England on 16
August 2004.
These showers formed bands which aligned themselves with
the wind helping to maintain the heavy rain across certain
areas of north Cornwall for several hours.
The trigger mechanisms for these storms appeared to be
convergence of winds along the coast and the high ground in
the local area which also helped to generate showers. It
would appear that the serious nature of these floods was
exacerbated by the local topography around Boscastle.

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The historical record shows that Boscastle has always been a
hazardous environment and prone to steep rises in discharge
after heavy rain.
However, recent events are more severe than any other
hydrograph event on record. Could global warming be a
culprit?
Increasingly, many meteorologists and hydrologists believe
so. Flash floods have, of course, always been a feature of the
UK’s climate, located as we are along a “battle zone” where
hot tropical air routinely makes aggressive contact with
colder polar air.
Whenever these two air masses converge, storms can occur
as the warmer, less dense tropical air rises above the colder
air and rapidly condenses. However, global warming makes
the potential for extreme storm damage greater. If tropical
air masses are warming, in response to climate change, then
their potential to hold moisture is increasing (water vapour
content is determined by the amount of heat energy
available). As they over-ride the cold air over the UK, the
volume and intensity of frontal rainfall that is released may
now be increasing.