Deep trouble in hydro mountain

Published Date: 18 August 2009
By Craig Brown
A HIGHLAND hydro-electric scheme capable of powering a quarter of a million homes has been switched off barely a month after it came online, when a rock collapse partially blocked a vital water-carrying tunnel.
Scottish and Southern Energy (SSE) said that the blockage at the £140 million Glendoe hydro-electric plant, to the east of Fort Augustus in Inverness-shire, was noticed last week. It was caused by "internal rock falls" which occurred a third of a way along a 7km tunnel which carries water from the reservoir through the mountainside, to the "power cavity" where the turbine rooms are located. The blockage was only detected when a drop in the station's water pressure was noticed. A spokesman for the company said Glendoe power station was then shut down and the tunnel drained so engineers could examine the rock fall. "We went through the process of de-watering the tunnel, which takes about a week, mainly because you want to let the water out at a speed where you won't dislodge anything that might be in the tunnel into the turbine area and do any damage," he said. "The next stage is to do a proper investigation to find out what caused it and if there are any other locations where this may be a problem."A team of engineers has already entered the tunnel to carry out an initial survey. The spokesman was unable to give any indication as to when the station would come back online "Until this is done, it is impossible to say how long it will take," he said. "However, what we have said is that we will give an update at our interim results in November, so it's several months away before we will be able to say anything more. Clearly, if we are able to do anything before then, we will." The power station can produce around 180 million units of green electricity, with a maximum capacity of 100MW, enough electricity to power almost 250,000 homes. It does not provide base power to the SSE's supply but comes online when the company's other power stations are working at peak capacity.Glendoe is Scotland's second-largest conventional hydro-electric station and the first large-scale station to be built since 1957, when the Errochty station in Perthshire, which has a capacity of 75MW, was opened.The station began extensive testing in December, but only went online last month. The spokesman said that it had been a "relatively big decision" to shut down the power station but said that in the absence of concrete knowledge on the extent of the problem, it had been the safest option. As yet, there are no indications as to what caused the fall; whether it was vibration that dislodged the rocks or a geological weakness in the area. However, the spokesman said that there had been extensive geological surveys carried out before, during and after the construction of the tunnel to ensure its integrity.