The recent peat slides and bog bursts in the Viking Energy wind farm area, at Dury Voe and Runn Hill, highlight the unacceptable risk that this development poses to people and property by the industrialisation of most of the central mainland.
I pointed out that this high risk was well known and being ignored by Viking Energy in my letter (‘Wake up Mr Wishart’; SN 30/7/10).
Peat slides and bog burst happen because blanket bog (peat) is by its very nature in a state of unstable equilibrium, that is to say that a relatively small change in its environment can lead to catastrophic failure of the integrity of the bog.
In the case of the recent bog bursts and peat slides in the central mainland the change that caused these was phenomenally heavy, but much localised, rainfall. Such rainfall events are extremely rare and are due to several meteorological elements coming together and combining with the local topography to form a zone of convergence of warm, moist air. This zone became almost stationary over the hills and the rising moist air created an extremely heavy rainstorm that persisted for a number of hours.
The effect of the heavy rain was a local and very quick build up of a great weight of water on the surface growing layer and the fibrous mat (the acrotelm) beneath. This weight acting on the slope eventually overcame the strength of the acrotelm and set it moving by tearing the fibrous mat that held it in place on the compacted peat beneath.
The shearing stress and release of pressure on the compacted peat then liquefied it, causing it to flow out from beneath the acrotelm. This flow caused catastrophic failure of the peat covered slope and rushed down-slope carrying large ‘floes’ of vegetation with it.
This is not the only way in which bog bursts and peat slides can occur but it underlines the fragility of the hills of the central mainland. The risk of bog bursts and peat slides on such fragile ecosystems is greatly increased by invasive activity such as that proposed by Viking Energy in constructing and operating their four large wind farm areas.
Unlike other large wind farms, such as Whitelee (built on a granite plateau), the central mainland project is to be built on steep hill ridges across vast areas of active blanket bog.
Much of Viking Energy’s 100km of access roads that they intend to carve across hillsides of the central mainland will be so called ‘floating roads’. These cut through the growing layer and the acrotelm and ‘float’ (actually they sink into) on the compacted peat beneath.
Because the growing layer and the acrotelm are the part of the bog where all rainfall and natural drainage occur, these roads act as water dams blocking the natural drainage of the bog. This means that down-slope from the access road, the intricate root systems, which under normal conditions act as an anchor for the bog, start to shrink and die back.
Whereas extremely rare weather conditions have caused bog bursts and peat slides up to now, weakening the vegetation mat in this way makes them much more likely during periods of ‘normal’ heavy rainfall. Eventually peat and the peat-slides will dry out and erode leaving horribly scarred hillsides down to the bedrock all across central mainland.
Upslope from the road, dammed up water will infiltrate the road building material increasing pore water pressure. Such an increase of pore pressure within the road material will make the roads vulnerable to being washed away by the build up of water up-slope during periods of heavy rain.
No doubt Viking Energy will try to address some of these problems by constructing road-side drains, cross drains and culverts. Of course these cannot even begin to mimic the complex natural hydrology and drainage of the hillsides and valleys so artificial drains will become sources of erosion and scarring of the hillsides.
In winter time drains and culverts will become blocked by snow and ice and become largely ineffective. In order to keep the wind farm sites operational in winter snowploughs will often need to be in constant operation for long periods. Ploughed and compacted snow will cause major drainage problems, particularly during rapid thaw, which is often accompanied by heavy rain. This also will affect the loading on the acrotelm, increasing the risk of peat-slides and road wash-out in the windfarm areas.
The ‘floating roads’ need to be capable of carrying loads well in excess of 100 tons and withstand thousands of journeys by massive and heavily laden construction traffic. The roads ‘float’ in a peat layer which is naturally thixotropic, that is to say is effectively solid but will become liquid when subjected to shearing stress as we saw at Nesting. The building of these roads and the operation of heavy traffic is in effect a shearing stress making the roads liable to become the locus for bog burst and peat slides.
Nowhere else in Britain has there been a proposal to construct and maintain a huge wind farm across such a steep and fragile terrain as that of the central mainland. As we’ve seen in the south mainland in 2003, bog bursts and peat slides can happen quickly, violently and without warning and luckily that time without fatal consequences.
So apart from all the other negative environmental consequences of this project I have no doubt that the construction and operation of this wind farm will put property and lives at risk through increased risk of catastrophic bog bursts and peat slides.
The Viking Energy project, if it gets planning permission, will be very much in uncharted and untried territory and the consequences of getting it wrong could be both disastrous and tragic.
The Viking Energy project already looks to be a toxic financial investment for Shetland Charitable Trust, however this would pale into insignificance should there be a bog burst leading to fatalities in a known high risk area.
I hope the directors of Viking Energy and the trustees have sought ‘best legal advice’ on the laws of corporate responsibility in case the worst should happen.
I believe that the choice of the central mainland as a site for such a large industrial project is a wrong and dangerous one. The charitable trust should pull the plug on this project now while it still has the power to do so.
Allen Fraser BSc (Hons). Dip Pol Con (Open)