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.