Desk study and walk-over survey of Rhiw Landslip, Lleyn Peninsula

This report describes the findings of a walkover survey and desk study commissioned by Gwynedd Council. BGS were asked to investigate the geology and geomorphology in the area around Plas yn Rhiw, Gwynedd where landslide activity has led to the closure of an important road. BGS were also asked to comment upon the findings of an existing ground investigation by the consultants Ove Arup & Partners and upon a proposed re-routing of the road. This survey is in general agreement with the findings of the Ove Arup report that the landslide activity at Plas yn Rhiw occurs within heterogeneous glacial outwash deposits overlying relatively stiff units of glacial till. Although the prediction of future landslide activity is difficult due to the nature of the geology and the effect of previous remediation work on the landslide it is thought likely that, providing care is taken with the disposal of ground and surface water from the site, Route E1A is a viable long-term route for the road.