The Boscastle Flood

16th Aug 2004

Where is Boscastle?

Where is Boscastle?

• Two rivers (Valency & Jordan) converge on the village of Boscastle. The majority of the damage was attributable to the Valency.

• The River Valency’s valley has a high relief and steep sides - surface runoff was increased.

• No broad floodplain - the River’s floodplain had been urbanised reducing infiltration and increasing surface runoff.

• Heavy rain was caused by extreme frontal activity. (Hurricane Alex)– In total, an input of 3 million tonnes of water was added to a tiny drainage basin of just

40 sq/km– 185mm of rain fell in 5hrs, most of it fell in the first 2hrs

• Infiltration-excess & overland flow is inevitable, (the rate of input of rainwater massively exceeding the infiltration capacity of the surrounding soil type.

• The soils were already saturated from previous rainfall – more overland flow• More than 440 million gallons of flood water poured down the main high street

in Boscastle• The rain coincided with high tide in the bay. This restricted the discharge rate of

floodwater into the harbour.

What were the causes of the flood - Physical factors

What were the causes of the flood - Human factors

• 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.

• Early settlers would have been attracted by ‘site’ factors such as the fresh water supply and access to a natural harbour.

• There are now around 1,000 permanent residents, most of who rely upon the situation of the settlement to provide tourist revenues (it is close to the South West Coast Path).

• 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.

What were the consequences? – Immediate/short term factors

• At 3.46pm river levels had risen by 7 feet (2.15 m) in one hour • Heavy property damage

– Six properties were completely destroyed. 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.– 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 were destroyed and sections of road have been swept away.– Telephone, water, electricity and gas supplies were all cut-off

• Irreplaceable loss of historical artefacts – The ‘Witch Museum’ – 50 years old and receives 50,000 visitors a year – Some of its unique contents were damaged

• No deaths - But at least one resident suffered a heart attack• Due to the nature of the tourist population, and the time of year the flood struck, it

took a long time to clearly establish that there had been no fatalities

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What were the consequences? – Long-term factors

• Economic losses – Much of rural Cornwall is classified as a deprived region. It is one of the UK’s poorest rural

counties. A victim of early deindustrialisation, the region’s mining industries are now long-gone leaving it over-dependent on tourism.

– Most shops stayed shut for the rest of the season and the reduction in tourist numbers during future years, may result in a negative multiplier effect for the entire local community. “We've actually lost 79% of our turnover this winter”• In addition, shops were carrying greater levels of stock than at other times of the year.

– House prices fell – People found 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

• 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.

What were the consequences? – Long-term factors

Continued...• 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.

– 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 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.

What were the consequences? – Physical changes

• Sediment accretion– Much of the village’s open land, including gardens and the

village green, were covered with fresh beds of alluvial silt.– As the floodwaters receded and the three rivers lost energy,

they deposited a large amount of sediment (most houses contained a two-foot deep deposit of mud).

• River channel changes – The bed of the River Jordan is 10ft higher than before the

flood, as a result of sediment transport and deposition.– It has also changed its course.

Is global warming to blame?

Heavy, thundery downpours developed by midday across south-west England on 16th August .

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.

It would appear that the serious nature of these floods was exacerbated by the local topography around Boscastle.

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.

Responses – Short term• A flood warning was issued for parts of Cornwall at 3:30pm

– Boscastle wasn’t specifically warned. • A search and rescue operation was setup

– Lasted until 2:30am the next day– RAF helicopters worked between 6 and 9pm to rescue over 150

stranded citizens & tourists– Overall, excellent emergency services and Environment Agency

response meant no lives lost• 11 Days after the flood people were allowed to return to their

homes to salvage their belongings.• Prince Charles visited the town 2 days after the flood and

donated a large sum of money to the town.• A few days after the flood, geologists flew over the area to assess

the risk of landslides triggered by the heavy rain.

Responses – Long term• Flood defence system (New flood defences were set to be built in October, work had

not yet started then)– Deepened the River Valency by 2 metres – increase capacity & reduce risk of flooding– The remains of the “lower bridge” that triggered a 3m wave was demolished and replaced

with a larger bridge that would be more difficult to block with debris.– In 2007, these defences were put to the test and a much smaller, more controlled flood

occurred. • Businesses were offered compensation for lost revenue & to cover costs to repair

shops etc.• Main car park raised by 1 metre

– Left as an area that can flood in order to cope with excess water• Afforestation on the upper catchment slopes • The effects of the flood caused people in Boscastle to take their environmental

footprint far more seriously – They were led to believe that climate change exacerbated by human activity was responsible

for the “freak weather” that caused the river to flood. – When buildings were reconstructed, they were done so in an environmentally friendly manner

with insulation, double glazing etc.– The town won 5 awards for its eco-friendliness.

Before After

No arch allows for more water to pass underneath the bridge

• Levels of property damage in Lynmouth (1952) and Boscastle (2004) are very similar, notably the number of properties damaged.

• Loss of life is very different. No lives were lost in 2004, partly reflecting improvements in flood warning techniques, levels of public education and emergency service preparation for such extreme hazard events.

• Seven Navy and coastguard helicopters as well as 17 fire engines were quickly scrambled to help stranded residents escape from the roofs of their houses.

• The Environment Agency web site now provides 24hr flood warning information, which may have alerted people of the impending danger.

• The same physical factor - extreme frontal rainfall - was the primary cause of the hazard in both cases. 185mm in 5hrs in Boscastle, compared with 230mm over 14hrs in Lynmouth.

• Both events also occurred in the same part of the world under near-identical conditions of geology and relief.

• However, the hazard impact was greater at Lynmouth, claiming 34 lives, due to one key additional factor: the blocking of theriver Lyn’s narrow-arched road-bridge.

What are the comparisons with Lynmouth?