Environmental Engineering Reference
In-Depth Information
along the coast in the predominant direction of longshore drift, and at any par-
ticular point there is accretion as each lobe arrives, and erosion as it moves on. At
Somers, on the coast of Western Port Bay, Australia, a yacht clubhouse was built
on one such lobe in the 1970s, and was threatened by beach erosion that developed
as that lobe moved on (Fig.
2.9
).
Portsea, on the southern shore of Port Phillip Bay, Australia, has had recur-
rent beach erosion because of eastward longshore drift (Fig.
2.10
). Sand mov-
ing along the coast accumulates alongside headlands, and then is swept at
intervals round them as a series of migrating lobes. As each lobe arrives at
Portsea the beach widens, but as it moves on this beach diminishes. Segments
of sea wall have been constructed successively on sectors where beach erosion
was severe.
Attempts to blame the erosion of Portsea Beach in 2010 on the dredging of a
deeper and straighter entrance to Port Phillip Bay in 2008 failed because of evi-
dence that episodes of beach erosion occurred at several times prior to entrance
deepening, and because wave refraction diagrams drawn for configurations before
and after dredging showed no change in the pattern of waves or wave energy at
Portsea (Cardno
2011
). The beach was renourished, but the deposited sand quickly
drifted away to the east, and the coast at Portsea was then armoured with sandbags
to halt recession (Fig.
2.11
).
Fig. 2.9
The yacht club at Somers, Western Port Bay, Australia, was built on a sand lobe (out-
line:
dotted line
) that had migrated to this position, and then moved on along the coast. A boulder
rampart has been inserted to halt erosion here. © Geostudies
