Glendoe: in the footsteps of the 'Hydro Boys'21 May 2007
Now half way through her task and burrowing deep into a Scottish hillside, Eliza Jane is almost a month ahead of schedule. Glendoe's £7M (US$14M) tunnel boring machine (TBM) is showing her mettle as progress in the Highlands follows in a rich seam of hydroelectric tradition. Chris Webb reports
Scottish & Southern Energy (SSE) chief executive Ian Marchant promised a scheme 'in keeping with the traditions of our predecessors'. Speaking at the launch of the company's application in 2003 to build the £140M (US$280M) Glendoe hydroelectric project, he was referring, of course, to the Highlands' worthy heritage of water power engineering that owes much to the visionary and pragmatist Thomas Johnston. The former secretary of state for Scotland in Churchill's wartime coalition government, it was Johnston who founded, in 1944, the North of Scotland Hydro Electric Board (NoSHEB).
Coincidentally, the first successful public supply of hydroelectricity occurred close to Glendoe, in nearby Fort Augustus, in 1890, while the first large-scale schemes came to fruition at Rannoch and Tummel Bridge in Perthshire, home of SSE's headquarters. It was Johnston, one of Churchill's wartime ministers, who kick-started 'power from the glens.'
The scenery of today may have changed relatively little since those most auspicious of times for the hydro industry in Britain, but construction methods have advanced almost beyond measure compared to those employed when NoSHEB performed its economic transformation in the Highlands, bringing renewable energy to post-War Scotland. Now some 16 months since construction began on the site, Glendoe is bringing to bear the latest in excavation techniques, including the help of the affectionately named Eliza Jane, a 21st century marvel of tunnelling capability. But more of this star of the show later.
Glendoe is the latest chapter in Scottish hydroelectricity development. The 100MW scheme is also a key component in the delivery of ambitious plans set by the Scottish parliament to secure 40% of the country's energy needs from renewable sources by 2020 – twice the target set by EU heads of state earlier this year. It follows an earlier Scottish climate change programme which set out the Executive's contribution to the UK climate change objectives, a key measure being the commitment that 18% of electricity generated in Scotland should come from renewables by 2010.
Scottish ministers approved plans to build the Glendoe project in July 2005. Situated at the western end of the Monadhliath mountains and to the east of Fort Augustus in Invernessshire, Glendoe will be Scotland's second biggest conventional hydroelectric power plant and the first to be built in half a century, after the Errochty scheme in Perthshire. Impounded by a 1km long dam at the head of Glen Tarff it is the longest dam in SSE's inventory, and the 11.5Mm3 capacity reservoir, fed by a network of aqueducts and pipes, will have a catchment of 75km2. The dam itself will rise to a maximum height of 35m.
From the dam the water will pass through a tunnel 8.5km in length to a power station located in a cavern deep below Borlum Hill at the eastern edge of Loch Ness, to where the water will be discharged after passing through the turbines. Connection to the public electricity distribution network will be by means of an underground 132kV power line from a new sub-station within the development site to the existing grid at Auchteraw.
The construction of Glendoe hydro scheme is quite simply the biggest civil engineering project currently underway in Scotland. Glendoe's network of tunnels is extensive - the system will be served by over 16km of passageways. An 8.6km aqueduct, 4.6m in diameter, will collect water and bring it to the reservoir while 8km of tunnels including the headrace, each some 5m in diameter, will convey water from the reservoir to the underground power station, and from there out into Loch Ness. In addition, a 1250m long access tunnel, 7m in diameter, will lead to the power station cavern.
Like most projects of this nature and scale, it is utilising an experienced international team. SSE and its main civil engineering contractor, Hochtief of Germany, say the project is on programme to commence generating electricity in the winter of 2008/9, when it will provide enough power for 250,000 homes. Glendoe will add this capacity to SSE's existing portfolio of 50 hydroelectric generation plants spread across the Highlands, along with its windfarms and conventional power plants in other parts of the UK. Created in 1998 from the merger of Scottish Hydro Electric and Southern Electric, SSE is the UK's biggest generator of power from renewables.
Civil engineering works
Work started in the mountainous Glendoe area at the beginning of last year. It will be the first hydroelectric scheme in the UK with a head of more than 600m which, along with other design considerations, will make it the most efficient scheme of its kind in the country. Not surprisingly, given the site's hard, faulted rock geology, the civil engineering works represent a considerable challenge, thanks also in part to the remoteness of the site. There is the requirement for some 20km of access roads just to provide right of way for the 400 or so workers and plant to reach the sites. The highest of these roads rises to around 750m.
Aside from the 200m long, 5m diameter TBM that is being used to drive the 8km of headrace tunnel, drill and blast techniques are being used elsewhere in the major excavations and to provide the launch pit for the tunnel-boring machine. Eventually, around 400,000 tonnes of rock – mainly schists – will have been hewn from the hillside. Britain's prime minister Tony Blair travelled to the Highlands to show his support for the scheme and to press the button for the first blasting, together with the Scottish forest minister Jack McConnell early last year.
With all the main components of the hydro scheme being underground, the dam and reservoir are the main structures that will be visible, yet little even of these will be seen from any nearby home or public road, according to SSE. That includes the massive power cavern in which will be housed the power station itself.
This vast cavern, some 250m below ground level and located roughly 2km from the banks of Loch Ness, will be 38m long, 18m wide and 32m high. Contained within it will be the Pelton turbine and the generator plant. A separate, smaller cavern will also be located adjacent to the power station cavern to house the main station transformer installation. One of the important benefits of hydro power is that it can be switched on very quickly to meet sudden increases in the demand for electricity. Under the right conditions, Glendoe will be able to reach full output in just 30 seconds.
When IWP&DC went to press, some 85% of the roof of the cavern had been exposed. Hochtief reported 'excellent progress' on carving out the cavern and over 60% of the volume of rock had then been excavated. The main access tunnel was completed earlier this year, and last month the massive reinforced concrete beams to support the plant's main crane had been cast, the crane itself having been commissioned three weeks ahead of schedule. This huge concrete beam was constructed in situ and anchored to the rock face at various points along its 35m length. The crane will be essential for future maintenance of the heavy equipment in the power station and will ultimately be rated to lift over 220 tonnes. In the meantime the crane is being used to complete the final construction of the cavern.
During the installation of the crane, blasting work was suspended in the cavern, but this has now resumed and is more than two thirds complete. Around 50,000 tonnes of rock will have been removed to build the cavern, when it is complete. This rock is being stockpiled at a site adjacent to the access tunnel portal where landscape reinstatement plans are currently being prepared to restore the area once the project is completed.
Work on the dam itself is making good progress after delays caused by the unsympathetic winter weather. With the coming of longer daylight hours and improved weather during April and May, progress improved considerably. It is being constructed from a combination of rock produced by the excavation of the aqueduct tunnel, and from a borrow quarry opened up adjacent to the dam, which will be flooded by the eventual impoundment of the reservoir. The upstream face of the dam will be clad with concrete, with the exposed downstream face being of natural rock.
Assembly of concrete batching equipment at the dam site is complete and this will permit structural concrete to be produced at up to 60m3 an hour. The dam is now excavated down to foundation level along 60% of its 1000m length, and work had begun last month placing the rockfill to form the embankment. Further along the dam site work is progressing with a view to diverting the river Tarff so that construction can begin on the embankment in the river bed.
Aqueduct construction, though behind programme, was also faring slightly better, and the building of the first of 15 intakes had begun last month. When complete, the intakes and aqueduct tunnels will form an extensive network to feed water in from several rivers and burns to supply the reservoir. Excavation works require activity to be taking place on several fronts, and a third portal was due to be opened by the middle of May for another drill and blast team to get started. Almost 900m of the 7.5km aqueduct tunnel had been completed and a second portal was being created half way along the 8km tunnel ready for the team to work from east to west.
Perhaps the most impressive piece of machinery used in constructing Glendoe is the enormous tunnel boring machine (TBM). The Eliza Jane had originally been built for a project in China. Subsequently refurbished by the tunnelling machine specialist Herrenknecht in Germany, it entered the hillside in summer 2006 and is set to emerge around two years later having created 8km of tunnels. Having got off to a fast start, the machine set off on its 16 month, 8km journey by delivering a blistering record week completing over 260m of tunnel, with a staggering 74m in a single, exceptional day. Average drive rate is about 25m a day. At present the TBM and her team are well ahead of schedule.
Hydroelectric schemes today are considerably more sensitive to the environment than their forebears in Johnston's day, of course. But SSE is justly outspoken of Glendoe's attention to such details. As part of the environmental awareness sewn into the fabric of the Glendoe project, the company says it is working closely with various organisations including the Scottish Environmental Protection Agency (SEPA), Scottish Natural Heritage (SNH) and the Royal Society for the Protection of Birds (RSPB).
In doing this it says it is helping to ensure that the local flora and fauna are protected both during the construction of the power station and in the future. As an example, it says, common scoters and Slavonian grebes live near to Glendoe for part of the year, and SSE has consulted with SNH and the RSPB to agree work schedules which will avoid disturbing the birds.
Moreover, it says, Glendoe is an ideal location for hydroelectric power as it allows water to be collected in a reservoir very high in the hills above the power station. The average annual rainfall in the hills around Glendoe is about 2000mm, compared to under 700mm in Edinburgh. Water from an area of 15km2 will drain naturally into the reservoir, and a system of underground pipes and tunnels will gather water from an additional area of 60km2 in the surrounding hills.
Glendoe's non-reliance on fossil fuels is SSE's greatest claim to the scheme's environmental credentials. In a world where most of its energy is derived from the burning of coal, oil and gas, essentially finite resources whose depletion is increasingly frowned upon, and where nuclear energy also has its critics, SSE believes hydro has a firm role in a low carbon economy. At a time when virtually every industrial activity is judged according to its impact on climate change, that is important, believes SSE.
Glendoe project chronology
October 2001: Planning begins.
July 2005: Scottish ministers give project the go-ahead.
January 2006: Start of site works.
September 2006: Start of headrace power tunnel construction using TBM.
January 2007: Completion of main access tunnel.
January 2008: Scheduled completion of power tunnel.
June 2008: Completion of tailrace outfall.
Early summer 2008: Construction of outfall from the 2km tailrace tunnel (which manoeuvred the TBM towards the creation of the main Power Tunnel, beyond the Power station) will be accomplished.
August 2008: Completion of dam.
November 2008: Completion of cavern and plant installation.
March 2009: Start generating.
November 2009: Completion of landscaping and reinstatement.
The scheme should be largely complete by Winter 2008.