Hydro Scheme, Derryguaig, Mull
Client: Kilfinichen Estate
We were commissioned to install a 700kw run-of-river hydro scheme at Derryguaig — a wild open hill close to Ben More, the only Munro in the Inner Hebrides. This included associated access, construction of primary 2200 metres of penstock pipe and powerhouse, and secondary intakes. A Canyon Hydro turbo has been installed within the powerhouse.
Before any work commenced, a feasibility study was carried out. This revealed the presence of a species of rare wild orchids which could not be disturbed. In addition the site is located in an area adjacent to a Site of Special Scientific Interest and is frequented by considerable numbers of recreational hillwalkers. A planning condition stipulated that an ecological Clerk of Works was appointed to work closely with TSL and provide regular reports to Scottish Natural Heritage.
The first task was to prepare site access along the entire length of the penstock, due to the onerous reinstatement conditions this required the careful stripping and storing of turves for re-use, it was important that these retained moisture and would require watering in periods of dry weather. This was followed by construction of the steel framed powerhouse, then once access was gained, excavating for and installing the penstock pipe consisting of 1,600m ductile iron and 680 PE.
During all excavation operations silt traps had to be installed and carefully maintained to prevent any silty water reaching the adjacent watercourse.
Once all works on the hillside were complete, low ground pressure excavators with special adjustable buckets were used to reinstate the turf and all parties are extremely satisfied with the finished results. Pressure testing and commissioning was carried out in November 2014 and the scheme is now generating at full capacity.