| Date: | 16 August 2004 |
| Affected: | Boscastle; Crackington Haven |
| Damages: | Extensive |
The 2004 Boscastle flood (Cornish: An Lanwes Kastel Boterel 2004) occurred on Monday 16 August 2004 in the two villages of Boscastle and Crackington Haven[1] in Cornwall, England, United Kingdom. The villages suffered extensive damage after flash floods caused by an exceptional amount of rain that fell over eight hours that afternoon. The flood in Boscastle was filmed and extensively reported, but the floods in Crackington Haven and Rocky Valley were not mentioned beyond the local news. The floods were the worst in local memory. A study commissioned by the Environment Agency from hydraulics consulting firm HR Wallingford concluded that it was among the most extreme ever experienced in Britain. The peak flow was about 140 m3/s, between 5:00 pm and 6:00 pm BST. The annual chance of this (or a greater) flood in any one year is about 1 in 400.[2] The probability each year of the heaviest three-hour rainfall is about 1 in 1300 (although rainfall probability is not the same as flood probability). At midday on 16 August 2004, heavy thundery showers had developed across the South West due to a weak disturbance to the northeast of the United Kingdom.[3]
The last time Boscastle had suffered notable flooding was in 1996 as a result of Hurricane Lili, but floods are recorded in 1847, 1957, on 3 June 1958 (one man drowned) and on 6 February during the Winter of 1962–63 in the United Kingdom. On 16 August 1952, 52 years to the day before Boscastle's 2004 flood, the small town of Lynmouth, 50miles north-east along the north coast in Devon near Exmoor, suffered extensive damage in a catastrophic flood, in which 34 people lost their lives.
On 16 August, warm air picking up moisture – due to residual heat from the Atlantic Ocean – travelled toward the Cornish coast as prevailing winds. Upon contact with the topographically vertical coast, these winds experienced a strong up-drafting force, thus causing internal moisture to rise and consequently cool as a string of storm clouds. With convergence[4] and coalescence, enhanced moisture levels resulted in heavy rainfall on the afternoon of 16 August 2004. 185 mm (7 inches) of rain fell over the high ground just inland of Boscastle. At the peak of the downpour, at about 15:40 GMT, 24.1mm of rain (almost one inch) was recorded as falling in just 15 minutes at Lesnewth, 2.5miles up the valley from Boscastle. In Boscastle, 89mm of rain was recorded in 60 minutes. The rain was very localised: Otterham and Lesnewth, both a few miles inland from Boscastle, recorded 24-hour totals of 200 mm and 185 mm respectively on the day,[5] whereas four of the nearest 10 rain gauges showed less than 3 mm of rain in the same period. The cause of the very heavy localised rain is thought to be an extreme example of what has become known as the Brown Willy effect.
The torrential rain led to a 2m (07feet) rise in river levels in one hour. A 3adj=on0adj=on wave, believed to have been triggered by water pooling behind debris caught under a bridge and then being suddenly released as the bridge collapsed, surged down the main road. Water speed was over 4-1NaN-1, more than enough to cause structural damage. It is estimated that 20000000m2 of water flowed through Boscastle that day alone. The steep valley sides and the saturated surface ensured a high amount of surface run-off.
Changes in farming practice in the area also possibly contributed, sewage could have been a cause as well, with a reduction of trees and hedges higher up the valley causing water to flow through more quickly than would have been the case in the past. No one died in the flood.
75 cars, 5 caravans, 6 buildings and several boats were washed into the sea ; approximately 100 homes and businesses were destroyed, and some had to be demolished; trees were uprooted and debris were scattered over a large area. In an operation lasting from mid-afternoon until 2:30 am, a fleet of 7 Westland Sea King helicopters rescued about 150 people clinging to trees and the roofs of buildings and cars. No major injuries or loss of life were reported. It was widely reported by newspapers at the time that the only injury was a broken thumb. The estimated cost of damage was £15 million.[6]
Most work took place in the winter season (October–May), during the off-season. The carpark was reduced to half-capacity (120 spaces) in winter, in order for works to take place, and then back to 240 spaces in summer.
During the flood of 2004, 14 cars became lodged beneath the old stone bridge; this caused a huge backlog of flood water and debris, adding to the damage caused in the surrounding area.
The main structure of the lower bridge survived the flood; however, the stone walls did not, and were washed away. On 1 May 2005, the official reopening of the village, wooden fences were used on the bridge to temporarily replace the stone walls. The bridge used to have a concrete plaque on it saying "This bridge is the private property of the lord of the manor, August 1887". This was lost during the flood, but then recovered from the harbour in good condition. This bridge has now been replaced with a new one.
The new bridge, which is a few metres further down the river than the old bridge, was installed on 18 December 2007, and was made by Cornish Concrete, a company based near Truro. The main arch is made from reinforced concrete, with metal railings.
The old bridge, which was over 100 years old, was demolished in early April 2008.
Boscastle flooded again, although not nearly as badly as the 2004 floods. After an afternoon of intense localised rainfall, and a week of steady rain everyday, a small flood happened on 21 June 2007. 30 mm fell on the area in one hour. Roads had become flooded in the area and in the village, most water came from the saturated fields around the village. Many drains had become blocked. Roads around the Tintagel, Camelford and Davidstow area were closed off to stop people visiting the village. River levels were alarmingly high, but the banks contained the water. However the many culverts of the River Jordan had overflowed onto the villages roads, adding to the amount of water on the roads. The new storm culvert joining the River Jordan to the River Valency was at full capacity, but did not flood. Services and organisations called in included:
The Environment Agency's flood defences installed after the 2004 flood worked and kept the water in the river channel. A few properties in the village were flooded by 30NaN0 from water flowing down the streets, rather than from the river flooding, although the damage was not nearly as bad as the 2004 flood. The two main roads (B3266, B3263) were blocked with flood waste and debris, although this was cleared and the roads reopened the following morning. The Environment Agency looked at the culverts around the village and will change them all to modern drainage
