Aerial photo of slip failure at
OverstrandThe village of Overstrand is located
immediately above the coastal cliffs of North Norfolk, which
historically have been susceptible to cliff recession, landsliding
and cliff failure. The cliff at High Street has been progressively
failing for years, with the current landslide forming a discrete
mudslide at the eastern end of High Street and extending from the
northern boundary of Ivy Farm down onto the beach access road
below.
Mott MacDonald was appointed to undertake a feasibility study for
the High Street coastal cliff failure, to assess the mechanisms
involved in the landsliding and to provide initial design options
for possible slope remediation.
The assessment, combining a desk study, geomorphological walk-over
survey and coastal cliff recession assessment, concluded that the
cliffs at Overstrand have been retreating naturally. This is
typical of rapid cliff failure events where no chalk raft thrust
deposits are observed in the coastal cliff sequence. The main cause
of instability of the High Street Landslide is understood to be due
to previous landsliding events, over-steepening of the slope during
the construction of the beach access road and seepage/groundwater
related effects in the slope.
Several preliminary design options were postulated for remedial
works for the slope. However, as the risk of loss of infrastructure
and human life is currently considered limited and as the cost of
appropriated medium to long term remediation options generally
exceeds £300,000 for all design options, North Norfolk District
Council considered that suitable works were not cost-effective. The
head of the High Street Landslide will continue to propagate slowly
inland and westwards the most appropriate management response of
‘do nothing/monitor’ has been implemented at the High Street
Landslide.
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