This article provides a description of the site visit to Sloy dam at Loch Sloy, and the Sloy hydroelectric power (HEP) station at Loch Lomond carried out as part of the 16th biennial conference of the British Dams Society in Glasgow 2010. The visit took place on 28 June 2010 and included tours of the turbine hall, the control room, the high-pressure pipelines and the concrete buttress dam. The visit included a presentation on Scottish and Southern Energy's dams and reservoir assets as well as the construction of the dam and power station and future site improvement plans.
One of the two site visits at this year's conference was to Scottish and Southern Energy's (SSE's) dam on Loch Sloy and the hydroelectric power (HEP) station it feeds on the shores of Loch Lomond, 3 km away. At the HEP station, we were welcomed enthusiastically by a swarm of bloodthirsty midges and SSE's Jim Sandeman and Bill Jack, our tour guides for the day. As we were led into the power station a plaque listing the names of the 21 construction workers killed during the construction reminded us of the improvements in construction safety in the last half century.
SSE has over 20 000 employees and produces 11·3 GW of electricity each year to supply its 9·35 million customers. Of this, 1·15 GW is from conventional hydropower and 0·3 GW from pumped storage schemes. SSE operates 96 (mainly concrete) dams on 79 large raised reservoirs with an average retained volume of 40 Mm3 per reservoir. Sloy dam is one of eight buttress dams that SSE own.
The Sloy HEP station, situated on the shore of Loch Lomond, was built in 1950 and is the largest conventional hydropower station in the UK with an installed capacity of 152·5 MW generated by 4 vertical axis Francis turbines operating at a gross head of 280 m (Figure 1). It generates some 130 million units per annum and is primarily used as a peaking station with a response time of 3 min and a load factor of 10%.
SSE is currently planning an ambitious project to build a pumping station alongside the HEP station in order to convert it to a pumped storage scheme. The planned twin 30 MW pumps running for 6hrs/day (during the night) will double the load factor of the system to 20% and provide additional peaking power to the grid.
The draw off from the dam is connected to a 3 km long low-pressure horseshoe tunnel through the hillside. This bifurcates in two stages and then connects to the four high-pressure pipelines that run for 470 m down the steep hillside to the power station (Figure 2).
Our lunch break was accompanied by a fascinating slide show of photographs of the construction of the dam (see Figure 3), and before we left the power station we were shown the turbine house and the enormous control desk where some of us got a bit sidetracked (Figure 4).
The coach then drove us up to Sloy dam where our guide Stuart King described the geology and construction of the dam. We walked up the access road that runs downstream of the dam then up through an unlined tunnel through the hillside to the right abutment.
Sloy dam is a concrete gravity buttress dam, 55 m high in the centre and 358 m long at crest level. This category A reservoir has a catchment area of 17 km2 with a standard annual average rainfall of around 3200 mm. The dam impounds a reservoir of some 35 800 000 m3. During construction, sand for the concrete was sourced from the shores of Loch Lomond, and the aggregate was quarried from the nearby mountains.
The dam and the dramatic Scottish countryside provided plenty of photo opportunities (Figure 5) and, at the end of this excellent site visit, the BDS group returned to the coaches for our final stop of the day – a whisky distillery. There were no stragglers.
Many thanks to Scottish & Southern Energy, Jim Sandeman, Bill Jack and Stuart King for their kind hospitality.
