CIfA 2021 A Guide for Clients

28 THE ISLE OF LEWIS AND HARRIS Another island community that has experienced major change, most recently during the Covid-19 pandemic, and over the centuries, is the Isle of Lewis in the Outer Hebrides. It is the most northern of all of the Western Isles with a population of around 18,500. A mainland electricity link was first established in 1991 and it is vital that this infrastructure is maintained and updated. Stornoway’s substation operated for 30 years but needed to be replaced in 2018 as part of the project to improve the power connection between Stornoway and the other islands. Simon Hall, consents and environment manager at SSEN, explains: ‘Replacement isn’t as simple as removing the old substation and installing the new one. This would leave the island without power, so SSEN had to be creative with its plans for replacement. In simple terms it had to build a new one next door to the existing substation and, only when it was completely finished, switch all of the cable connections over to the new unit.’ Protecting and preserving peatland Creating the new substation involved another challenge for the team. A challenge that had been gathering for hundreds, if not thousands of years – the presence of peat deposits. Peatlands are the largest natural terrestrial carbon store and the restoration and protection of peatland is a priority for the Scottish government as it seeks to reduce its carbon footprint. It follows that SSEN with support from WSP needed to minimise disturbance to Harris and Lewis’s rich and ancient peatlands, and also consider peat restoration projects. Although the site of the existing substation was already fixed, the team was able to position the new substation in a way that minimised the amount of peat that was disturbed from about 10,000 cubic metres to 4,000 cubic metres. Furthermore, the team made sure that the deepest layers were not affected. This was achieved primarily by looking at the size and orientation of the compound. Given the island’s long history and rich cultural heritage assets, WSP was also asked to carry out an archaeological assessment of the site, which encountered evidence of prehistoric funerary activity in the area. WSP’s Kevin Mooney explains: ‘This took the form of a stone circle, which was identified and scheduled in 1992. It was completely obscured by around two metres of peat so the potential existed for further archaeological remains where peat deposits were present. So we introduced a phased approach of archaeological monitoring during the construction of the substation.’ It also became apparent that very little radiocarbon dating had been done of peat deposits across Lewis so SSEN agreed to carry out a paleo-environmental survey, which involved drilling out a core sample of the peat to ascertain its age at various depths. ‘We found peat dating to the Mesolithic, Bronze Age and medieval times,’ says Kevin. ‘So from these early dates, right to the current period, we had a fully preserved stratigraphic sequence, or what we call an environmental baseline on Lewis. Ultimately, the results of this work will be put on record allowing for further research at the University of the Highlands and Islands.’ Kevin Mooney MCIfA, WSP Episode 2 podcast ©WSP