Glendoe Hydro Scheme
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The Glendoe Hydro Scheme for the
generation A generation is all of the people born and living at about the same time, regarded collectively. It also is "the average period, generally considered to be about 20–⁠30 years, during which children are born and grow up, become adults, and b ...
of hydro-electric power is located in the Monadhliath Mountains near
Fort Augustus Fort Augustus is a settlement in the parish of Boleskine and Abertarff, at the south-west end of Loch Ness, Scottish Highlands. The village has a population of around 646 (2001). Its economy is heavily reliant on tourism. History Early histo ...
, above
Loch Ness Loch Ness (; ) is a large freshwater loch in the Scottish Highlands. It takes its name from the River Ness, which flows from the northern end. Loch Ness is best known for claimed sightings of the cryptozoology, cryptozoological Loch Ness Mons ...
in the Highlands of
Scotland Scotland is a Countries of the United Kingdom, country that is part of the United Kingdom. It contains nearly one-third of the United Kingdom's land area, consisting of the northern part of the island of Great Britain and more than 790 adjac ...
. The change in financial incentives following the publication of the Renewables Obligation in 2001 caused Scottish and Southern Energy (SSE) to reconsider a number of schemes that had been mothballed in the 1960s by the
North of Scotland Hydro-Electric Board The North of Scotland Hydro-Electric Board (1943–1990) was founded to design, construct and manage hydroelectricity projects in the Highlands of Scotland. It is regarded as one of the major achievements of Scottish politician Thomas Johnston, ...
, and plans for the Glendoe scheme were resurrected. Construction started in 2006, and
Hochtief Hochtief AG is a global provider of infrastructure technology and construction services, with locations in North America, Australia, and Europe. The Essen based company is primarily active in the fields of high tech, energy transition, and sustai ...
completed the scheme in 2009. It is operated by SSE and was opened on 29 June 2009 by Queen Elizabeth, accompanied by the Duke of Edinburgh. Part of the main headrace tunnel collapsed in August 2009, and remedial work was not completed until 2012, with generation restarting in April. SSE and Hochtief failed to agree on who was responsible for the cost of the failure, but SSE were awarded damages in 2018 in the court of appeal, despite an adjudication and the first court case finding that the cost was an operational risk to be borne by SSE.


History

The completion of several schemes by the
North of Scotland Hydro-Electric Board The North of Scotland Hydro-Electric Board (1943–1990) was founded to design, construct and manage hydroelectricity projects in the Highlands of Scotland. It is regarded as one of the major achievements of Scottish politician Thomas Johnston, ...
in the early 1960s brought to an end over two decades of expansion of conventional hydro-electricity in the Highlands of Scotland. Subsequently, Cruachan was commissioned in 1968, and Foyers in 1974, but both of these were pumped storage schemes. In 2001, the
Scottish Parliament The Scottish Parliament ( ; ) is the Devolution in the United Kingdom, devolved, unicameral legislature of Scotland. It is located in the Holyrood, Edinburgh, Holyrood area of Edinburgh, and is frequently referred to by the metonym 'Holyrood'. ...
set an objective of increasing the proportion of electricity generated from renewable sources to 18 per cent by 2010, as part of their Scottish Climate Change Programme. The publication of the Renewables Obligation in 2001 made any new hydro-electric scheme eligible under the incentive, whereas previously only those under 10 
Megawatts The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named in honor o ...
 (MW) had qualified. This changed the financial incentives for building new hydro-electric plants, and SSE plc, who inherited most of the Hydro-Electric Board's assets when the electricity industry was privatised, reviewed all of the large schemes that the Board had considered, but which had not been built. Nearly all had been abandoned because of their environmental impact in areas which had a high amenity value, but the exception was Glendoe. Various configurations were then considered, from a small
run-of-the-river Run-of-river hydroelectricity (ROR) or run-of-the-river hydroelectricity is a type of hydroelectric generation plant whereby little or no water storage is provided. Run-of-the-river power plants may have no water storage at all or a limited amou ...
scheme generating under 10 MW, to a huge pumped storage scheme. The smaller schemes were discarded because of the cost of transferring the water from the Glendoe plateau down to Loch Ness, while the pumped storage option was discarded because it would not qualify under the Renewable Obligation scheme, and because the difference in levels between the top reservoir and Loch Ness was sufficient that it would be extremely costly to overcome the issues this would introduce. Once the choice of Glendoe was made in October 2001, an environmental statement was produced and the design was refined by May 2003. SSE then applied for planning consent under section 36 of the Electricity Act 1989, and this was eventually granted in June 2005. Although there were few objections to the scheme, and the local community was supportive, SSE did not know how long the planning consent process would take, and so began a design and build tendering process which ran concurrently. Because they could not undertake investigative work until deals with the landowners had been agreed, the design was kept flexible throughout the process. The turbine house might be above or below ground, the output of the scheme could be between 50 MW and 100 MW, while the dam could be constructed of rockfill or roller compacted concrete. A contract for the scheme was awarded to
Hochtief Hochtief AG is a global provider of infrastructure technology and construction services, with locations in North America, Australia, and Europe. The Essen based company is primarily active in the fields of high tech, energy transition, and sustai ...
in December 2005, and they began producing the detailed designs and starting construction from January 2006. Before work could start on the main scheme, various enabling works had to be done. The bridge that carries the B862 road over the River Tarff near Fort Augustus had to be strengthened to cope with the weight of construction vehicles, and this work was done in five weeks starting on 21 November 2005. A refurbished
tunnel boring machine A tunnel boring machine (TBM), also known as a "mole" or a "worm", is a machine used to excavate tunnels. TBMs are an alternative to drilling and blasting methods and "hand mining", allowing more rapid excavation through hard rock, wet or dry so ...
was ordered from Herrenknecht, a start was made on the of roads needed to access the various sites where work was to be carried out, and a planning application was made to allow work camps to be constructed. These were built high up on the Glendoe plateau, and accommodated most of the 750 workers who were employed on the project.


Construction

A ceremony attended by
Tony Blair Sir Anthony Charles Lynton Blair (born 6 May 1953) is a British politician who served as Prime Minister of the United Kingdom from 1997 to 2007 and Leader of the Labour Party (UK), Leader of the Labour Party from 1994 to 2007. He was Leader ...
, the
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, and
Jack McConnell Jack Wilson McConnell, Baron McConnell of Glenscorrodale, (born 30 June 1960) is a Scottish politician who served as first minister of Scotland and leader of the Labour Party in Scotland from 2001 to 2007. McConnell served as the Minister f ...
, the
First Minister of Scotland The first minister of Scotland () is the head of government of Scotland. The first minister leads the Scottish Government, the Executive (government), executive branch of the devolved government and is th ...
, marked the formal start of construction. They detonated an explosive charge, to begin the reshaping of the valley. A reservoir for the scheme was created by building a dam across the River Tarff. The dam is long, and some high where it crosses the original course of the river, but much lower at the sides. It is a rock fill dam, with most of the rock coming from a quarry which was flooded as the reservoir filled with water. The upstream side is faced with concrete, while the downstream side is exposed rock. The dam cannot be seen from any of the houses and public roads in the area. The catchment for the reservoir is around as it is fed by the upper reaches of the River Tarff, the Caochan Uilleim, and runoff from the A' Chraidhleag bog.Ordnance Survey, 1:25000 map Water is collected from another by intakes constructed on numerous streams, and transporting the water to the reservoir by a network of underground pipes and tunnels. The main tunnel is long, of which were constructed by the drill-and-blast method and lined with
shotcrete Shotcrete, gunite (), or sprayed concrete is concrete or mortar conveyed through a hose and pneumatically projected at high velocity onto a surface. This construction technique was invented by Carl Akeley and first used in 1907. The concr ...
. The rest was built using the
cut-and-cover A tunnel is an underground or undersea passageway. It is dug through surrounding soil, earth or rock, or laid under water, and is usually completely enclosed except for the two Portal (architecture), portals common at each end, though ther ...
technique. There are a further of diameter pipe to complete the network. Water is collected from at least 14 intakes which feed into the network. When full, the reservoir covers around and its surface is at above
Ordnance datum An ordnance datum (OD) is a vertical datum used by an ordnance survey as the basis for deriving altitudes on maps. A spot height may be expressed as above ordnance datum (AOD). Usually mean sea level (MSL) at a particular place is used for the d ...
. (AOD). Water is drawn down to a maximum of below this level when the power station is operating, on environmental grounds. The power station was constructed underground, in a cavern and high, excaved from solid rock by drill-and-blast. The cavern is below the surface, at a level where the tailrace to Loch Ness is almost horizontal. A tunnel connects the reservoir to Loch Ness, with the turbines about from the loch. Some of it was cut by drill-and-blast, but the majority was created by a diameter tunnel boring machine, long and named "''Eliza Jane''" after a competition by local schoolchildren. There is a drop of from the reservoir to the turbine house, and most of the headrace tunnel slopes uphill at a gradient of 12 per cent. The hard rock tunnel boring machine started at the bottom end in September 2006 and worked continuously for 16 months to reach the top on 7 January 2008, having cut through of rock. There is a second smaller cavern which houses the transformers next to the turbine house cavern, and the complex is accessed by a tunnel long, running from near the B862 road from Fort Augustus. For schemes between 50 MW and 100 MW, the tunnels would need to be a similar size, as making them smaller also makes building them more difficult. The cost of building either scheme is therefore similar, and SSE took the decision to go with the larger size, as it also has significant operational benefits. Consideration was given to using a fully-pressurised
Francis turbine The Francis turbine is a type of water turbine. It is an inward-flow reaction turbine that combines radial and axial flow concepts. Francis turbines are the most common water turbine in use today, and can achieve over 95% efficiency. The pro ...
or a multi-jet
Pelton turbine The Pelton wheel or Pelton Turbine is an impulse-type water turbine invented by American inventor Lester Allan Pelton in the 1870s. The Pelton wheel extracts energy from the impulse of moving water, as opposed to water's dead weight like the t ...
. While a Francis turbine can be brought online and offline more quickly, the slope of the ground between the reservoir and the turbine house meant that there were no suitable sites to build a surge shaft, and so the engineering needed to cope with pressure changes would have been complex. A Pelton turbine takes longer to bring online or offline, but deflectors can be used so that the turbine stops before the water flow does, which significantly reduces pressure surges. SSE decided that they could cope with the slower response time, as the benefits of the Pelton system's simplicity outweighed the complexity of the Francis system. They therefore chose to install an Andritz six-jet vertical-axis Pelton turbine which can generate up to 100 MW, from a peak flow of .
Alex Salmond Alexander Elliot Anderson Salmond ( ; 31 December 1954 – 12 October 2024) was a Scottish politician who served as First Minister of Scotland from 2007 to 2014. A prominent figure in the Scottish nationalist movement, he was Leader of the Sc ...
in his role as First Minister of Scotland initiated the filling of the reservoir on 1 September 2008. Hochtief completed the contract two months early, and the station had been generating power since January 2009 when a formal opening of the scheme took place on 29 June 2009, at which Queen Elizabeth accompanied by
Prince Philip, Duke of Edinburgh Prince Philip, Duke of Edinburgh (born Prince Philip of Greece and Denmark, later Philip Mountbatten; 10 June 19219 April 2021), was the husband of Queen Elizabeth II. As such, he was the consort of the British monarch from h ...
officiated. The power station is operated remotely from SSE's control centre in
Perth Perth () is the list of Australian capital cities, capital city of Western Australia. It is the list of cities in Australia by population, fourth-most-populous city in Australia, with a population of over 2.3 million within Greater Perth . The ...
.


Station shutdown

In August 2009 the station was shut down and the headrace tunnel drained because of internal rock falls near the upper end of it. Although the equipment in the power station was not affected, Glendoe was unable to generate power until repairs were made. SSE reported that electricity generation was unlikely to proceed until at least April 2011. SSE employed Jacobs Gibb and Jacobs UK as their engineers, and the original designs were for a fully-lined tunnel constructed by drill-and-blast. However, during the tendering process, Pöyry Energy JV who were the design engineers for Hochtief recommended that a tunnel boring machine should be used to excavate the tunnel. This would give a much smoother finish to the walls of the tunnel, and only around 40 per cent would need to be lined. Decisions as to how much lining to apply were taken once the rock could be seen, and less than one percent was actually lined. The completed tunnel was carefully inspected by Hochtief, Pöyry, Jacobs and SSE before being signed off. After about 8 months of use, some of the tunnel collapsed and was blocked by the rock fall. Robert Galbraith QC was appointed by Hochtief and SSE to adjudicate in 2011, and decided that Hochtief were not to blame for the collapse. Rather than take the dispute to arbitration, where the issues would be judged by technically qualified, professional engineers, SSE chose to pursue the matter in court, where it would be decided on legal issues by judges who were not technically qualified. The collapse occurred in the Conagleann Fault Zone, around from the top end of the tunnel. The fault was known from its appearance at surface level, but during tunnelling, the tunnel boring machine had passed through it, and SSE recorded that its existence was imperceptible. A contract for repair work was awarded to BAM Nuttall, who built a diversion tunnel around the rockfall by drill-and-blast. This was full-lined with of waterproof concrete, and they also applied a concrete lining to almost half of the rest of the tunnel. A downstream access tunnel was also built as part of the repair contract. Energy generation at the scheme restarted in August 2012. SSE issued proceedings seeking to recover £130 million in repair and reinstatement costs and £65 million in alleged loss of profit from Hochtief, but in December 2016 Hochtief was held by the Scottish Court of Session not to have been liable for the collapse, and that it was an operational risk to be borne by SSE. In an appeal decided in 2018, SSE were awarded more than £107 million in compensation. The judges hearing the appeal split 2-to-1 in SSE's favour. Hochtief subsequently appealed, and the case will be heard by the
Supreme Court In most legal jurisdictions, a supreme court, also known as a court of last resort, apex court, high (or final) court of appeal, and court of final appeal, is the highest court within the hierarchy of courts. Broadly speaking, the decisions of ...
.


Scheme details

Glendoe has a
hydraulic head Hydraulic head or piezometric head is a measurement related to liquid pressure (normalized by specific weight) and the liquid elevation above a vertical datum., 410 pages. See pp. 43–44., 650 pages. See p. 22, eq.3.2a. It is usually meas ...
of , the highest of any hydro-electric scheme in the United Kingdom, and is thus ideally suited to generating large amounts of energy from the stored water in the reservoir, especially when combined with the relatively high annual rainfall in the area of around . At the time of its construction, it was the largest of Scotland's recent civil engineering projects, with Hochtief as the design and build contractor. The scheme is predicted to produce about 180  GWh of electricity per year, and to operate at a load factor of approximately 20 percent. This is based on the amount of water falling on the catchment in an average year, and is enough to provide approximately 5% of the electricity consumption of the city of
Glasgow Glasgow is the Cities of Scotland, most populous city in Scotland, located on the banks of the River Clyde in Strathclyde, west central Scotland. It is the List of cities in the United Kingdom, third-most-populous city in the United Kingdom ...
.


References


Bibliography

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External links


SSE Glendoe website
{{Scottish energy Hydroelectric power stations in Scotland Buildings and structures in Highland (council area)