Transport Scotland have put the A83 at Rest and be Thankful back on hazard alert, with an increased risk of landslides. It is asking drivers to exercise ‘extreme caution’ when travelling on this section.
The Met has issued a severe weather warning – very heavy rain – for the Strathclyde region, with Argyll and the Isles in the firing line on Thursday 5th and Friday 6th July.
Like I said expect extreme weather for at least the next five years because every time the bathtub boats cannot sail or the roads are likely to close the weather will be extreme.
Has our MSP got any further with his vision of tunnels under the Firth of Clyde and the Irish Sea. Is he going to throw one in under the Arrochar Alps?
Has he actually done anything to get a final solution for the A83?
Mike Russell mentioned a tunnel in Japan. The earthquake and tsunami in Japan caused horrendous damage to infrastructure and a major nuclear alert. Within weeks repairs had been effected on motorways etc. Here we are 5 years down the line and Mike Russell has not managed to get a temporary solution in place for the A83 and he has not even managed to get plans drawn up for a permanent solution. He has managed to get a “not fit for purpose” ferry service in Dunoon.
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Here is a video of a landslide taking place
http://www.youtube.com/watch?v=E5FF3vIEIqg
Here are the after effects
http://www.youtube.com/watch?v=vJtYTbQecNE
The hills in the above seem to be quite gentle and wooded.
I have no idea the extent of the problem at the “Rest” but if it is remotely like the above the road could be shut for years.
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Not remotely like the above – whereas the problem at the Rest is due to rainfall saturation of just the surface material overlaying the bedrock causing it to ‘lose its grip’ on the side of a glacially over-steepened valley, at Maierato in Calabria it was apparently the effect of water saturation, and decomposition, of a very deep zone of soft rocks and clays leading to a big chunk of hillside sliding and crumbling away.
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Our MSP said “The longer term route survey also needs to report quickly”.
You wrote “the problem at the Rest is due to rainfall saturation of just the surface material overlaying the bedrock causing it to ‘lose its grip’ on the side of a glacially over-steepened valley”.
Do you have a link to a report saying the Rest situation is “just surface material” and quantify the tonnage of the material that might slip and the stability of the bedrock? The Rest is very steep the “surface material” could be considerable.
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No, I don’t have a link – I have a letter from the British Geological Survey, in Edinburgh, about ten years ago in reply to a question to them on whether the A83 would be more secure if relocated to the route of the forestry road on the opposite side of the glen upstream of the ‘Wee Rest’.
They explained that Glen Croe was an example of a valley that had been gouged deeper by glacial action, leaving the sides steeper than their natural angle of repose. The sides would continue to erode until they reached a stable slope angle. As far as I’m aware the surface ‘drift’ material is generally a relatively shallow layer over the bedrock.
There’s also Scotland Transerv’s ‘Geotechnical desk study’ of July 2008, available via Google.
I’ll email a scan of the BGS letter to F.A., so hopefully it’ll be available to read.
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The British Geological Survey have a good page on the problem here;
http://www.bgs.ac.uk/landslides/RABT_2009.html
There is an informative poster on the 2007 slide here
http://www.bgs.ac.uk/downloads/start.cfm?id=1245
The bedrock does not seem to be playing much of a part in the problem, though the poster mentions a fault in the bedrock, the bedrock being highly fractured in places, and the scouring flow of the slip opening up jointing in the bedrock.
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The photo in the 2007 report clearly shows how landslips can also threaten the old road below the A83, so there’s the question of whether this route might not be a viable emergency alternative.
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Robert, for once I am going to agree with you.
The slips appear to travel a vertical distance of 100m and a horizontal distance of 150m to hit the A83.
After the A83 the gradient then actually increases before slacking off.
To get from the A83 to the old road seems to be a vertical distance of 75m and a horizontal distance of 100m.
It does look like the old road could also get hit at the same time as the A83.
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Somewhere in the recent government-commissioned reports there’s reference to historic records of the old road being affected by landslides and/or rockfalls, so it’s all the more surprising that Transport Scotland should now be considering this route as the emergency alternative.
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