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On 15th and 16th August 1952, a storm of tropical intensity broke over south-west England, depositing 229 millimetres (9.0 in) of rain within 24 hours on an already waterlogged Exmoor. It is thought that a cold front scooped up a thunderstorm, and the orographic effect worsened the storm. Debris-laden floodwaters cascaded down the northern escarpment of the moor, converging upon the village of Lynmouth; in particular, in the upper West Lyn valley, a dam was formed by fallen trees, etc., which in due course gave way, sending a huge wave of water and debris down that river. A guest at the Lyndale Hotel described the night:
"From seven o'clock last night the waters rose rapidly and at nine o'clock it was just like an avalanche coming through our hotel, bringing down boulders from the hills and breaking down walls, doors and windows. Within half an hour the guests had evacuated the ground floor. In another ten minutes the second floor was covered, and then we made for the top floor where we spent the night." The river Lyn through the town had been culverted to gain land for business premises; this culvert soon choked with flood debris, and the river flowed through the town. Much of the debris was boulders and trees.Overnight, over 100 buildings were destroyed or seriously damaged along with 28 of the 31 bridges, and 38 cars were washed out to sea. In total, 34 people died, with a further 420 made homeless.
At the same time, the River Bray at Filleigh also flooded, costing the lives of three Scouts from Manchester who had been camping alongside the river.
Similar events had been recorded at Lynmouth in 1607 and 1796. After the 1952 disaster, the village was rebuilt, including diverting the river around the village. In 2001, a BBC Radio 4 documentary suggested that the events of 1952 were connected to government operation Project Cumulus involving cloud seeding experiments being conducted in southern England at the time. There does not presently seem to be any direct evidence to support such allegations, but conspiracy theories have been fuelled by rumours of missing or destroyed government documents relating to the experiments.
On 16 August 2004 - exactly 52 years later, a similar event happened in Cornwall, when flash floods caused extensive damage to Boscastle, but without loss of life. The hydrological setting of these two villages is very much the same.
"From seven o'clock last night the waters rose rapidly and at nine o'clock it was just like an avalanche coming through our hotel, bringing down boulders from the hills and breaking down walls, doors and windows. Within half an hour the guests had evacuated the ground floor. In another ten minutes the second floor was covered, and then we made for the top floor where we spent the night." The river Lyn through the town had been culverted to gain land for business premises; this culvert soon choked with flood debris, and the river flowed through the town. Much of the debris was boulders and trees.Overnight, over 100 buildings were destroyed or seriously damaged along with 28 of the 31 bridges, and 38 cars were washed out to sea. In total, 34 people died, with a further 420 made homeless.
At the same time, the River Bray at Filleigh also flooded, costing the lives of three Scouts from Manchester who had been camping alongside the river.
Similar events had been recorded at Lynmouth in 1607 and 1796. After the 1952 disaster, the village was rebuilt, including diverting the river around the village. In 2001, a BBC Radio 4 documentary suggested that the events of 1952 were connected to government operation Project Cumulus involving cloud seeding experiments being conducted in southern England at the time. There does not presently seem to be any direct evidence to support such allegations, but conspiracy theories have been fuelled by rumours of missing or destroyed government documents relating to the experiments.
On 16 August 2004 - exactly 52 years later, a similar event happened in Cornwall, when flash floods caused extensive damage to Boscastle, but without loss of life. The hydrological setting of these two villages is very much the same.
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The Boscastle flood of 2004 occurred on Monday, 16 August 2004 in the two villages of Boscastle and Crackington Haven in Cornwall, England, United Kingdom. The villages suffered extensive damage after flash floods caused by an exceptional amount of rain that fell over the course of eight hours that afternoon. The flood in Boscastle was filmed and extensively reported but that in Crackington Haven was not mentioned beyond the local news. The Boscastle flooding was caused by rainfall which the river could not hold. 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 140m³/s (tonnes), between 5:00pm and 6:00pm BST. The annual chance of this (or a greater) flood in any one year is about 1 in 400. 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).
The rainfall on the afternoon of 16 August 2004 was very heavy. 185 mm (7 inches) of rain fell over the high ground just inland of Boscastle, England. At the peak of the downpour, at about 15:40 GMT, 24 mm of rain (almost one inch) was recorded as falling in just 15 minutes at Lesnewth, 2.5 miles (4 km) up the valley from Boscastle. In Boscastle itself, 89 mm (3.5 inches) of rain was recorded in 60 minutes. The rain was very localised: four of the nearest 10 rain gauges, all within a few miles of Boscastle, showed less than 3 mm of rain that day. 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 river banks were overflowing causing the bank to burst next to a car park and it washed away cars out to sea.
The torrential rain led to a 2 m (7 ft) rise in river levels in one hour. A 3 m (10 ft) 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 in excess of 4 m/s (10 mph), more than sufficient to cause structural damage. It is estimated that 20 million tonnes (440 million gallons) of water flowed through Boscastle alone that day. The steep valley sides, and the saturated surface ensured a high amount of surface run-off.
However in an episode of Discovery Channel's Perfect Disaster, it states that the floods might have been caused by a phenomenon called a "blocking high". A blocking high is a large area of static high pressure. It can happen anywhere in the world, and the effect is deadly because the high pressure can stall other weather systems around it.
The rainfall on the afternoon of 16 August 2004 was very heavy. 185 mm (7 inches) of rain fell over the high ground just inland of Boscastle, England. At the peak of the downpour, at about 15:40 GMT, 24 mm of rain (almost one inch) was recorded as falling in just 15 minutes at Lesnewth, 2.5 miles (4 km) up the valley from Boscastle. In Boscastle itself, 89 mm (3.5 inches) of rain was recorded in 60 minutes. The rain was very localised: four of the nearest 10 rain gauges, all within a few miles of Boscastle, showed less than 3 mm of rain that day. 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 river banks were overflowing causing the bank to burst next to a car park and it washed away cars out to sea.
The torrential rain led to a 2 m (7 ft) rise in river levels in one hour. A 3 m (10 ft) 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 in excess of 4 m/s (10 mph), more than sufficient to cause structural damage. It is estimated that 20 million tonnes (440 million gallons) of water flowed through Boscastle alone that day. The steep valley sides, and the saturated surface ensured a high amount of surface run-off.
However in an episode of Discovery Channel's Perfect Disaster, it states that the floods might have been caused by a phenomenon called a "blocking high". A blocking high is a large area of static high pressure. It can happen anywhere in the world, and the effect is deadly because the high pressure can stall other weather systems around it.
