Variations and trends in the sensitivity of machair soils and coastal landforms to erosion, South Uist, Outer Hebrides

  • Elizabeth Young

    Student thesis: Doctoral ThesisDoctor of Philosophy


    The machair is a coastal grassland system found only in parts of northern and western Scotland and Ireland. Despite its limited geographic distribution, machair landscapes have high ecological, geomorphological, and cultural significance, as recognised by numerous conservation designations and legislation. In January 2005 a severe storm caused extensive damage in the Outer Hebrides, drawing attention to the sensitivity of the machair coast to erosion. The aim of this research was to investigate variations and trends in the sensitivity of three field sites within the South Uist machair to soil and coastal erosion, and to interpret measured change alongside analysis of historic climate data. Two of the sites selected, Cille Pheadair and Staoinebrig, experienced some of the most dramatic geomorphological changes associated with the 2005 storm, while the third site, Milton, appeared to be more resistant to change. A combination of fieldwork, laboratory tests, and archive work was used to obtain and analyse information about sediment budgets, shoreline indicator change, and sediment erodibility, along with contextual climatic information. A key result of this work is the provision of a detailed framework of short-medium term cyclical changes and fluctuations in the coastal change, which provides a context for interpreting and responding to longer term trends in erosion and/or accretion. Results indicated high spatial and temporal variability in the erodibility of machair soils and landforms, with no clear relationship between climatic factors and rates of erosion. Considerable short-term variations in beach volume and the position of dynamic shoreline indicators caution against the relaibility of using ‘snap-shot’ historic datasets to infer long-term rates of change. It is proposed that the machair landscape currently functions in a state of highly dynamic equilibrium, which has been maintained over the last ~130 years. While storm events such as the January 2005 storm have locally dramatic consequences, they do not appear to have disrupted the overally physical and ecological functions of the system. This contribution is particularly timely given current concerns for the future of the machair landscape under predicted sea-level and climate change scenarios, and the potential for inappropriate hard-engineering responses to the perceived risk.
    Date of Award2015
    Original languageEnglish
    SponsorsThe James Hutton Institute
    SupervisorSue Dawson (Supervisor) & Blair McKenzie (Supervisor)


    • Machair
    • Soil erosion
    • Coastal geomorphology
    • Outer Hebrides
    • Erosion
    • Historic climatology
    • RTK dGPS

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