Letters / More peatslides once Viking is built
Wednesday’s localised heavy rain events, although exceptional, was not unprecedented. A rainfall event in September 2003, for example, was even more severe. Both events were due to slack areas of low pressure sitting over Shetland in such a way that associated shower clouds developed into exceptionally heavy downpours. One of the main factors in triggering both these events was the shape of the hills of Central Mainland inducing convergence of the airflow and rapid uplift of very moist air and the exceptional build up of deep shower clouds.
Highly visible consequences of both these events were of course the peat-slides and bog bursts that destroyed property and blocked roads. Such slides during a sudden ‘uplowsin’ are to be expected in a few places after long dry periods such as we had this summer and in 2003.
Over thousands of years Shetland peat covered hills have developed a natural drainage system to shed the water from these events. The growing layer of blanket bog above the peat sheds excess water as sheet floods into an intricate network of peat pipes and gullies that in turn feed the burns that flow into the voes. Flooding of public roads on the other hand is due to inadequate capacity of road-side drainage and culverts; this is particularly evident where the roads cut across the natural drainage network coming off the hills.
Increased occurrences of peat slides, bog-bursts and washed out roads are something that we better get used to; particularly those who live, work and travel through the windfarm clusters Viking Energy intend to build across the hills of Central Mainland. The network of roads and quarries they intend to build for these windfarms cut across, and severely disrupt, the natural drainage pattern of the hills. When the windfarm infrastructure and turbine bases are in place the natural drainage will no longer be able to safely drain away extremely heavy rainfall, resulting in road wash outs and many more bog-bursts and peat slides.
In their environmental impact statement I note that Viking Energy have grossly underestimated the expected rainfall amounts for the wind farm area. I notice also that they have not taken into account the risk or calculated the return period of extreme rainfall events. We may think that Wednesday’s rainfall events, that may be expected to occur every 5 or 10 years, are extreme, but there is evidence in Shetland hills of much more dramatic rainfall events that have occurred in the past, perhaps with a return period of hundreds of years.
By all accounts a family had a lucky escape on Wednesday, I hope that those who live in the windfarm clusters are equally as lucky when the Viking Energy induced inevitable happens.
Allen Fraser
Meal
Hamnavoe
Burra
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