Abstract

A minor peatslide event occurred near Llyn Ogwen, Snowdonia National Park, North Wales in November 2005, during a period of heavy rainfall. The mass movement consisted of some 250 m3 of peat debris that obstructed the A5 London to Holyhead trunk road and affected a nearby construction project. Four principal factors contributed to the peatslide: (1) prolonged wet weather; (2) saturated peat conditions; (3) a steeply dipping surface of smooth rockhead of Ordovician microgranite; (4) a natural drainage pipe at the point of initiation of the slide. Safety measures to protect road users included erection of concrete barriers along the highway verge to prevent secondary debris from reaching the carriageway, removal of displaced blocks of peat from the flow track of the peatslide and a programme of geological surveillance to monitor for any variations in site conditions. A remedial strategy was suggested to protect the slope from further degradation. However, conservation designations at the site gave rise to stringent conditions for environmental engineering works and so greater reliance on natural vegetation recovery will probably apply in this case.

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