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Last Updated: Tuesday, 17 August, 2004, 12:17 GMT 13:17 UK
Flash flooding a 'freak event'

Flash floods such as those seen in north Cornwall are caused by a unique set of circumstances, weather experts say.

While sustained rainfall is obviously key, it is the drainage and topography of the surrounding area which ultimately causes large scale flooding.

Unfortunately, Boscastle, where 6cm (2ins) of rain fell in two hours on Monday causing a three-metre high wall of water to rush through the village, met the criteria.

Phil Avery, of the BBC Weather Centre, said while the rainfall in this case was heavy it was certainly not exceptional.

Drainage and the topography of area are key to flash floods

Slaughter Bridge near Camelford in Cornwall had the same rainfall in a two-hour period as Boscastle on Monday - as have other areas of the country in recent months.

Mr Avery said: "If this had happened say in East Anglia where the land if flat you not have seen the flash floods.

"What happened here is that the torrential rain was in an area where the conditions were such that the water was channelled through the village.

"The topography of the area, the high ground, valleys and the fact there are only two rivers for the water to run into meant that we saw such devastation.

"But the recent wet weather also played a role. The ground in the area was water logged, which meant the rain just sat on the surface."

Met Office meteorologist Wayne Elliott agreed. "The crucial things in this case were the high ground and the area only having two rivers. Coupled with the already high water table, the conditions were just right," he said.

It really was a freak event. There is not much people can do to protect themselves
Meteorologist Wayne Elliott

The high ground acted as a trigger for the weather - forcing the air to rise and cool, creating rain, Mr Elliott added.

And coastal winds converging on the area gave it extra "oomph".

But despite a spate of flooding across the country in recent years, Mr Elliott said flooding was not becoming more common.

"You cannot put it down to global warming. It really was a freak event. There is not much people can do to protect themselves.

"We were forecasting heavy rain in our 4am bulletins but the key is when and where this is going to happen. If it had been 20 miles up the road, the situation would have been different."

The BBC's Fergus Walsh
"The village of Boscastle was hit by a freak, highly localised weather event"

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