Environmental Engineering Reference
In-Depth Information
• Grain size (modal, range) and shape (rounded, angular): proportions of sand,
granules, pebbles, cobbles, shells, rock fragments, alien particles (brick, glass,
earthenware).
• Dominant minerals (quartz, feldspar, carbonates, olivine).
• Evidence of source(s) of beach sediment (continuing or relict).
• Wave regime, storm effects, seepage, runoff.
• Tide ranges (neap, spring).
• Evidence of longshore drift (dominant direction or seasonally alternating).
• Evidence of offshore-onshore movements of beach sediment.
• Presence of microcliffs, berms and washovers.
• Evidence of history (maps, remote sensing, previous surveys).
• Evidence of rates or erosion or accretion over a speciied time
• Indications of cause(s) of beach erosion.
An example of an unsatisfactory beach renourishment project, apparently
because of inadequate preliminary investigation, can be quoted from Half Moon
Bay, on the NE coast of Port Phillip Bay, Australia. This bay extends between head-
lands at Red Bluff, to the north, and Black Rock Point, to the south, and contains
an arcuate sandy beach about 450 m long and up to 25 m wide at mean high tide. It
is fronted by shallow water with sand bars that diminish incident wave action, and
is still receiving sand eroded from gullies in soft Red Bluff Sand in the cliff at Red
Bluff. For this reason it had been the most stable of Melbourne's bayside beaches,
apart from a limited response to alternating seasonal longshore drift: during sum-
mer southerly wave action drifts sand northward, widening the beach at the north-
ern end and narrowing it to the south, while in winter westerly wave action reverses
this drift (Sect.
4.3.2
, p. 64). The alternations have been balanced, so that there have
not been net gains or losses from this beach compartment in recent decades.
The cliff at Red Bluff has a basal outcrop of hard Black Rock Sandstone, which
is exposed to occasional storm waves from Port Phillip Bay, but has changed very
little in the past half-century. This Black Rock Sandstone is overlain by 25 m of
Fig. 4.1
Heaps of sand
dumped on the beach at
Half Moon Bay, Melbourne,
Australia, prior to being
spread on the renourished
beach © Geostudies
