Environmental Engineering Reference
In-Depth Information
beach that had been stable, in contrast with other nearby beaches that did need
renourishment and about the colour of the dumped sand (yellow with an iron
oxide stain: sand from the same quarry dumped on another Port Phillip Bay beach
at Rye had quickly lost this stain by wave wash and rainfall) and its coarser tex-
ture (which is actually good management practice, see below). The suggestion
that beach nourishment in Half Moon Bay could reduce erosion on Red Bluff was
based on incorrect assumptions about the processes at work on the cliff.
In November 2011 the sand heaps were retrieved by lorries and taken round to
another beach at Altona, on the far side of Port Phillip Bay, where renourishment
was necessary.
4.2 Sources of Sediment for Beach Renourishment
Almost any kind of durable sediment of suitable grain size can be used for beach
renourishment, providing it does not contain pollutants or hazardous items such
as broken glass fragments or jagged metal. Sediment is obtained from sites
known to engineers as 'borrow areas', a curious term which is only really appro-
priate in situations where the sand and gravel are expected to drift back where
they came from. It would be better to refer to them as 'source areas'. Ideally the
sediment should have similar grain size characteristics to the natural beach sedi-
ment (James
1974
; USACE
2002
); if not, allowance must be made for the rapid
removal of the finer constituents and adjustments in profile as waves sort the
emplaced beach.
Sources of sediment for beach renourishment should be sought as close as pos-
sible to the sector to be replenished, in order to minimise transportation costs. A
beach is more likely to be renourished if a source of suitable material exists within
an economic distance: for Bournemouth (Sect.
4.2.7
, p. 49) the ideal beach fill was
available in the form of china clay residue (quartz and feldspar sand and gravel)
from Hensbarrow Downs in Cornwall, but this was over 200 km away, too far to
be economically worthwhile, and it was necessary to use sand and gravel dredged
from the nearby sea floor (Willmington
1983
) and later from within adjacent Poole
Harbour (Cooper
1998
).
The various sources of sediment for beach renourishment are as follows:
4.2.1. Sediment from land quarries
4.2.2. Sediment from other beaches
4.2.3. Sediment from harbours
4.2.4. Sediment from coastal lagoons
4.2.5. Sediment from river channels and alluvial plains
4.2.6. Sediment from tidal inlets
4.2.7. Sediment from the sea floor
4.2.8. Sediment from distant sources
4.2.9. Sediment from mining waste
4.2.10. Sediment from recycled materials
