Environmental Engineering Reference
In-Depth Information
softer Red Bluff Sand, dissected into gullies by runoff and seepage. It was suggested
that the erosion of Red Bluff could be controlled by renourishing the sandy beach
in Half Moon Bay in order to widen it about 10 m and allow it to extend round the
base of the cliff as a protection against storm wave erosion (Fig.
4.1
). Erosion on the
cliff was largely due to gulleying and seepage, which was also delivering sand to
the beach. The idea that renourished beach sand in Half Moon Bay would drift on
to the coastline salient beneath Red Bluff and remain there was doubtful because of
the problem of maintaining a beach on a coastline salient, where the normal condi-
tion is drift divergence in response to incident waves arriving parallel to the coastline
(Fig.
4.2
a). Elsewhere, a beach may persist on a coastal salient (promontory or head-
land) if obliquely-arriving waves maintain longshore drift past it (Fig.
4.2
b).
In October 2011 contractors began dumping lorry-loads of sand brought from
an inland quarry on the beach at Half Moon Bay. There were protests by local
people and the beach nourishment project was halted with about 60 heaps of sand
dumped on the beach (Fig.
4.1
). The protests were about the renourishment of a
Fig. 4.2 a
Where waves
arrive parallel to the coastline
they produce a divergence of
drift (
arrowed
) on a coastal
salient (headland), so that
a beach is not maintained
there.
b
Where waves arrive
at an angle to the coastline
they produce longshore drift,
so that a beach may persist
round a coastal salient,
maintained by sediment in
transit
