Environmental Engineering Reference
In-Depth Information
the unusual floods of 2014. Further protective works, including more beach ren-
ourishment, are now being considered.
On the north-east coast of Port Phillip Bay, Australia, a sector of natural vege-
tated bluffs south from Quiet Corner had been stable until the beach fronting them
was depleted following the completion of a masonry sea wall at Black Rock, to the
north, in 1939. Reduction of the beach allowed waves from the west to generate
stronger longshore drift, so that the beach fronting the bluffs gradually dwindled.
By the 1960s storm waves were undercutting these bluffs, and erosion was threat-
ening to undermine this part of the coastal highway (Fig.
5.1
).
A proposal to extend the sea wall to halt this cliffing was opposed by local resi-
dents, who argued that the beach should be renourished to prevent storm waves
reaching the base of the bluff, which would also restore scenic and recreational
values. In response, a beach terrace 100 m long, 25 m wide, and a metre above
high spring tide level, was formed by pumping coarse shelly sand in from the sea
floor during the winter of 1984 (Fig.
5.2
). This coast shows a seasonal alterna-
tion in longshore drift, and because of the SSW aspect of the shore the longshore
drift is stronger to the SE in the summer half-year than to the NW in the win-
ter half-year. The outcome was that sand lost from the renourished beach south of
Quiet Corner was carried south-eastward each winter by longshore drift by waves
arriving from the west, so that as this beach became narrower, while the beach SE
to Banksia Point and beyond widened (Fig.
5.2
a, b). There was little north-west-
ward drift in the summer, so the emplaced beach did not grow in that direction
(X on Fig.
5.2
c). Successive profile surveys showed that the emplaced beach was
also cut back by storm waves, some of the finer sand withdrawn from the beach
being deposited as a sand bar that persisted in the nearshore zone, the crest of
which moved shoreward in calmer weather and seaward during storms (Fig.
5.3
).
Although somewhat depleted, this renourished beach has remained in position for
30 years, and has served its purpose of protecting the bluff base from storm wave
erosion as well as maintaining a recreational resource.
The sandy beach between Picnic Point and Red Bluff at Sandringham, on the
NE coast of Port Phillip Bay, stands in front of vegetated bluffs. As on the other
Fig. 5.1
The shore south of
Black Rock in 1968, when
storm waves at high tide
were eroding the base of the
backing bluff. © Geostudies
