Boscastle flood summary
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Boscastle flood summary Boscastle flood summary Document Transcript

  • 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 (1) (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
  • • • • • • • • • • 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 • 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 •
  • transient nature of the tourist population, it took a long time to clearly establish that there had been no fatalities. The Effects • • • • 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
  • 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. • • • • • 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? • • • ‘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.
  • • • • • 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.