Boscastle

• The worst floods in the UK tend to occur in August. Ground becomes saturated in particularly wet summers, and if a severe storm then follows, the result is large volumes of hortonian overland flow.
• 16 August 1952 - Lynmouth flood (34 deaths)

  16 August 2004 - Boscastle flood (no deaths)

  'eerie echo of the Lynmouth horror' - Daily Telegraph
• Media exaggeration: 'the village of Boscastle will never be the same again' - yet, Lynmouth was rebuilt, with the river diverted and flood defences put in place.
• Boscastle is a small village on the north Cornish coast. Lying at the mouth of the River Valency, it is surrounded by fairly steep, often wooded slopes. Just upstream from the village two steep-sided valleys meet, those of the Valency and the Jordan. A third stream, the Paradise, also flows. All three burst their banks, almost simultaneously
• Boscastle has a mixture of residential and local service functions, alongside and important tourist industry, earning income for the local community
• Prior to 16 August, the village had not been flooded in living memory. Therefore, few flood prevention measures had been taken
• Key physical factors promoting flash flooding are:

  • impermeable rock
  • small and round basin
  • steep relief
  • lack of vegetation
  • antecedent moisture
  • storm downpours
• Impermeable rock does not let water drain through it, with permeable rock (Millstone Grit sandstone) lying underneath. However, saturation from the bedrock from previous high rainfall resulted in the sandstone behaving as if it was impermeable. This encourages surface run off and shortens the lag time on the hydrograph.
• In a small drainage basin rainwater is likely to reach a channel in a relatively short time. If the basin is quite round in shape, flow distances to channels are minimised. Both circumstances contribute to the shortening of lag time.
• Individual slopes, especially the wooded valley sides close to Boscastle village, have a considerable gradient. Large, denser vegetation does reduce flood risk.
• The storm which resulted in the flash flood took place in the early afternoon. 50mm of rainfall fell in the space of two hours, and within another hour, the flood waters were in full spate. This represents an incredibly short lag time.
• The surge of water through the village was reported as being 10 feet high
• The village car park lies at the top end of the main street. Cars parked here were among the first objects to get washed down, 50 in total. One became trapped under the bridge carrying the road across the river. In its turn, it then caught even more material, branches especially. Water piled up behind this barrier, and when it gave way, the surge was huge
• 120 people had to be winched to safety by helicopters from Cornwall and Portland, taking 3 hours. The 7 helicopters used made this the largest RAF and Royal Navy joint rescue since 1979. This saved people including: several children, a woman with a severed thumb, and a man having a heart attack, despite the harsh weather conditions
• At 3:46 pm on 16 August 2004, a member of Boscastle's rescue team reported that river levels had risen by 7 feet in one hour
• During these events, coastguard teams watched the harbour in hope of spotting anyone being washed in.
• 1000 residents affected, with no deaths. Accounting for everyone was extremely difficult however, as many tourists were involved
• Local MP, Paul Tyler, was trapped in his cars five miles away up the A39. The roads were heavy with traffic. At Camelford, several miles south, the river was flowing at bankfull, so residents sandbagged houses near to the river
• The basic clean-up operation was completed within a few days because a large number of men and machinery were committed to the task, despite the continued poor weather
• The county council estimated the damage to the bridges, ditches and other small scale infrastructure would cost £250,000 to rectify. Damage to buildings (6 destroyed) and businesses was estimated a several millions of pounds
• Differences between 1952 and 2004:

  • more emergency services available
  • speed of communications quicker
  • time of day - Lynmouth occurred at night, Boscastle in the afternoon
  • more homeowners and businesses with insurance