Cornwall - Damaging Sea of 6th Jan

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Cornwall - Damaging Sea of 6th Jan

Postby Graham Easterling » 2014 Jan 07, 11:33

No long account here as it's been well covered in the news. However the sea was more powerful than you would have normally expected for the swell height. In fact the swell height at Sevenstones had a return period of about 1 year and was virtually identical to that on 27th December. The damage was largely due to the fact the waves were fast moving long period (whilst the waves in March '08 were bigger on the tip of Cornwall, but more locally generated.) Also there was more focusing of the waves this time, some of the swells where there was focusing on a reef were enormous.

I received this information:- Numerical modelling shows that the peak energy period has been up to 16-18 seconds. In deep water this gives a crest-to-crest wavelength of 400-500 metres. In 100m water depth the crest-to-crest wavelength would be around 350-450m while in 20m waterdepth the crest-to-crest wavelength would be 200-250m. Such long waves with a significant height of 10m or so are immensely powerful. It’s a situation that occurs only very rarely in the south of England.

The following updated 10/1

Also, from 2 involved with the Sennen lifeboat & NCI Land's End (Gwennap Head)
"Certainly Terry and myself are of the opinion that 2008 was not just bigger, but in a different class. . .we discussed this morning as to why the N Coast has suffered more this time. Its my recollection that the swell of 2008 was generated off SW Ireland and came to us from WNW which you would think would impact the N Coast just the same as it did Sennen Cove.

I think an important additional factor was that this storm came after 2 weeks of large seas, with the wind always in much the same direction. As a result 'beach top' sand levels were exceptionally low on many of the beaches exposed to this direction (allowing the powerful waves to break nearer the shore than normal ) and sea defence structures had already weakened to some extent. Just 1 wave totally removed the blockhouse on the end of Porteath pier. A pic of a wave nearing the missing blockhouse is attached.

If anybody hasn't seen what the significantly bigger sea of March 10 2008 looked like, good pics @ (click photo for larger image).

A couple of my photos of Sennen around 10:00 on 6th Jan also asttached.
SennenStorm060114 (12).jpg
SennenStorm060114 (12).jpg (74.66 KiB) Viewed 451 times
SennenStorm060114 (3).jpg
SennenStorm060114 (3).jpg (78.8 KiB) Viewed 451 times
5683417-large.jpg (78.57 KiB) Viewed 451 times

Penzance Weather Station
Grid Ref:
SW464231 - Post Code: TR18 4TP
19m AMSL - Aspect SSE
In a SE - NW orientated valley

23 Years of Penzance Weather Records :
Graham Easterling
Posts: 316
Joined: 2011 Nov 30, 20:29
Location: Penzance, Cornwall

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