A landslip near the site of a proposed road serving the Viking windfarm north of Sandwater has prompted concern from the project’s opponent.
Those behind the project were not worried by the landslip but one critic, Ian Tinkler, walked the top of Mid Kame ridge and examined the source of the landslip.
He says it stemmed from a peaty pond on top of the ridge, or watershed. After recent heavy rainfall – which Mr Tinkler said was nothing remarkable for the time of year – it apparently burst its banks.
Mr Tinkler said this was exactly where Viking Energy planned a road going the entire length of the ridge from end to end, and called the area “mighty unstable”.
He estimated the size of the landslip was about 60 metres across at the top and the peat about 1.5 to 2.5 metres deep.
He said: “Chunks [of peat] about the size of a Transit van were displaced downhill, each one would easily destroy a house. There was no evidence of disturbance of the ground by vehicles, just a natural slip.
“The watershed of hills is very unstable, there may well be slips to come on both sides of hill. This would have certainly taken a Viking Energy access track with it.”
He maintained that the slip would have taken any track, or turbine base, down to bedrock. And he questioned if the peat slide happened naturally, what would happen if 20-tonne vehicles drove on it.
Sustainable Shetland vice-chairman James Mackenzie said the Mid Kame was supposed to have 11 wind turbines on it, but peatland ecologist Dr Olivia Bragg had pointed out to Viking Energy, while advising them on road routes, that in her opinion the area was particularly at risk from landslips.
However, Mr Mackenzie said that other assessments had rated landslips as an insignificant hazard.
He said: “The methods used for assessing stability are limited, and measure ‘shear strength’ within the body of the peat, but most peat slides have been lifting off from what’s underneath, so assessments are not the whole story.”
The situation could be exacerbated by engineering works, particularly in the construction phase, he said, and the landslip was “right where the road would need to be”. The possibility of landslips was “very worrying”, as some of the roads would be up to 10 metres wide.
In response, Viking Energy project manager Aaron Priest said the peat slip “would not affect Viking’s plans”, but the company did not wish to expand on this.
One specialist Richard Birnie of LandForm Research, who had once done work for Viking Energy, said that such a “bog burst” could happen again – it had happened recently at Channerwick and Uradale.
The former research scientist with the Macaulay Instititute, specialising in peatland management, said that Viking Energy’s peatland management plan would have to include “general improvement of the peatland condition” in order to prevent peat slides, as blanket bog was known to be “mechanically weak”.
The peat could be stabilised by reducing grazing and blocking erosion gullies, and peat could be prevented from dislodging by draining water away from critical sites.
Mr Mackenzie added: “If there were no risk posed by the windfarm and its infrastructure, why then was a peat stability assessment a requirement of the environmental impact assessment?
“Anybody that thinks that the scale of engineering works won’t have an impact on the hydrology and structure of peat in the vicinity is turning a blind eye to the inevitable.
“You only have to look at what happened at Derrybrien in Ireland for an example of a very bad case scenario.
“Although careful design, good site management and environmental control can help prevent disasters, what worries me is that the assessments done for Viking Energy conclude that overall there is little to be worried about regarding peat stability, while the frequency of peat slides recently, within the windfarm area, indicate otherwise.
“Also it is now acknowledged by peatland experts that there is much yet to be learned about such phenomena as peat pipes and how they affect stability, and also the method of assessment may not be appropriate as it was developed for mineral soils.”