Coastal protection at Jarlshof
Context for coastal hazards and climate change on Shetland
Dr James Hansom, University of Glasgow
Shetland benefits from a hard rock coastline which slows the impact of coastal processes and thus on any changes that are forced. However, in terms of the drivers of coastal change, Shetland suffers the disadvantage of a slowly rising sea level, a severe wave energy environment whose maximum wave heights have been increasing over the last few decades and, as a function of its rocky and indented nature, an extremely limited supply of coastal sediment available to come onshore to produce beaches. Thus the soft coastal features of Shetland, are regionally rare and are a valuable resource both in terms of recreation and as the site of a significant number of key elements of infrastructure.
The net result of interaction of these conditions render the coast of Shetland subject to change over a range of timescales. Rock coasts are changing on a timescale that does not interact in a significant way with infrastructure or agriculture, but beaches are changing on a much faster and more immediate timescale. This is a problem because many beaches in Shetland carry roads, protect scarce agricultural land, and support or protect major infrastructure (eg Sumburgh airport, various ferry terminals and installations). The recent trend of coastal flooding and erosion of many of these beaches is of concern not only at present, but also in the future, when enhanced sea levels and wave impacts are predicted and sediment supplies will have dwindled further. Since sediment supply is of equal significance to storminess and sea level rise as a driver of erosion and flooding, any actions that impact negatively on the sediment supply to beaches and reduce the sediment residence time on beaches are to be avoided. For example, armouring of the rear of gravel and sand beaches as a method of erosion control acts to further increase sediment losses via wave reflection and drawdown and may be but a temporary solution that does not fully address the underlying problem.
In many locations beach nourishment may be a more sustainable and more cost-effective solution to beach erosion than armouring and, in the Shetland context, a solution that is appropriate to the bay-head beaches common in the islands. Strategies that conserve sediment, minimise structural intervention, release coastal land to allow flexibility in the position of the coast and that then integrate into a coastal zone management plan are logical ways forward for planning for coastal change in Shetland. This route requires the assembly of a range of data specific to the Shetland coast in order to assess the coastal threat and to assess the risk to beaches, land and infrastructure. Some of this data is available but requires to be assembled in a coherent and targeted fashion. Other data remains to be gathered and this requires a phase of research to progress in parallel with the task of data assembly from existing sources.