[Ground Engineering is a publication of the geotechnical sector ]
By Claire Smith
An application by Viking Energy to use larger turbines at its planned
Viking Wind Farm project in Shetland has led to calls for further
investigation of the ground condition risks to the project.
The onshore wind farm could become the UK’s third biggest if it gains
planning approval, however, campaign group Sustainable Shetland believes
that ground risk issues have been overlooked.
In an open letter to the Shetland Islands Council’s planning committee,
Sustainable Shetland vice chair James Mackenzie has called for greater
scrutiny of the risk of peat slides within the scheme site.
Mackenzie said that the details of the risk were revealed in a report by
Andy Mills of AM Geomorpholgy which was appended to the planning officer’s
report on the Viking Wind Farm variation application.
Mackenzie said, in his open letter: “Mills’ report concerns the issue of
peat slides, which are known to occur in Shetland with increasing frequency
and with potentially devastating, even life-threatening, consequences. It
is of great significance that new Scottish government guidelines on peat
stability assessment (PSA) issued in 2017 recognize the special
characteristics of peat. Please note the following extract, the final
paragraph (bolded and italicised) of which implies that the original PSA
supplied by Viking Energy in its 2009 environmental impact assessment, and
submitted, without amendment, for its Variation Application, is
inappropriate and/or unreliable.”
Mills’ report states: “Peat landslides are a characteristic landscape
response of peat uplands to intense rainfall events, and the importance of
understanding their impacts and the potential for their occurrence is now
well understood. It is estimated that Scotland’s peatlands hold
approximately 50% of the UK’s total soil carbon store (Cummins et al.,
2011), and as infrastructure pressure on peat uplands increases, the
potential impacts of wind farm developments must be considered alongside
their potential benefits.
“In recent years, costs and benefits have been considered not just in terms
of the stability of the peatland (this guidance), but the volumes of peat
excavated, reused and potentially lost during construction (Scottish
Renewables and SEPA, 2012) and the carbon balance of the wind farm
(Scottish Government, 2011). In recognition of the importance of peat as a
carbon store, a number of policy documents and national plans make clear
the Scottish Government’s intention to protect, manage and restore degraded
peatlands to their natural functions, biodiversity and benefits, and in so
doing create a source of carbon sequestration (Scottish Government, 2017;
Scottish Natural Heritage, 2015a).
“Just as wind farms and their associated infrastructure may be affected by
or cause peat landslides, other infrastructure such as road networks, flood
defences, drainage, power lines, residential areas and farmland may also be
affected. Terrestrial habitats in the path of a peat landslide may be
damaged by ground displacement and by burial by debris, and aquatic
habitats damaged by incorporation of landslide debris in watercourses
(McCahon et al., 1987). In addition, the displacement and break-up of peaty
debris after a landslide event will ultimately result in small scale
depletion of the terrestrial carbon store (Nayak et al., 2008).
”Typically, slope instability and landslide hazard assessments have
followed a standard approach, detailed in a number of statutory and
guidance documents (e.g. BS5930, 1999; Department of Environment, 1990;
1996). However, previous investigations have illustrated that the
geotechnical controls of peat landslides differ from landslides in mineral
soils (dry peat is typically 90% – 95% organic matter) and that
pre-conditions for failure are not well accounted for by site investigation
methods detailed in existing documentation. For example, peat has special
hydrological properties (90% water content), it has a very low density and
is often very fibrous in nature (Hobbs, 1986, 1987). Therefore, this
guidance has been developed to ensure that appropriate and reliable peat
landslide hazard and risk assessments can be undertaken during the planning
of upland electricity generation developments such as wind farms…”
Mackenzie has called on the planning committee to reject the planning
variation “or at the very least I would hope that a condition requiring
resubmission of the PSA is attached to any approval”.
Mackenzie added: “That the draft conditions do not include any
consideration of peat stability is a major omission.”
GE understands that the application to increase the tip height of the
turbines will raise the permitted maximum height from 145m to 155m to allow
the project to benefit from the latest turbine innovation, which has moved
on since outline permission was granted in 2012.
It is believed that councillors have delayed their decision on the application.
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