Environmental Engineering Reference
In-Depth Information
drifting sand accumulated alongside breakwaters built in 1910 to stabilise the
entrance to a coastal lagoon known as Ringkøbing Fjord and ensure ship access
to the port of Ringkøbing on the shores of that lagoon. Sand extracted from the
widened beach north of the breakwaters was trucked southward to renourish the
downdrift beach, which had been cut back up to 45 m as the result of the drift
interception (Møller
1990
). This transfer of sand from an accreted beach updrift
to an eroded beach downdrift is an example of bypassing (Sect.
4.3.3
, p. 65),
while sediment moved from an accreted beach downdrift back to a depleted beach
updrift is termed recycling (Sect.
4.3.2
, p. 66).
4.2.3 Sediment from Harbours
A major source of sediment for beach renourishment has been sand and
gravel dredged from harbours and port approaches. The first such project was
in 1922, when 1.3 million m
3
of sand dredged from New York Harbour was
deposited on a 1 km stretch of beach on nearby Coney Island (Hall
1952
;
Dornhelm
1995
).
Following construction activity at Ennore Port on India's east coast,
3.5 million m
3
of dredged sediment was transported through a pipeline to a
beach immediately north (Ramana Murthy 2008). The sediment provided
defence against erosion, apparently as a result of the port construction, as well
as a cost-effective use of dredge material. Out of the total quantity of dredged
sediment, 700,000 m
3
was placed on the upper beach to raise the berm crest,
with the remainder spread across the nearshore zone to increase the beach
width by 500 m.
During the winter of 2005-2006, 1.1 million m
3
of sand dredged from the
entrance channel of Poole Harbour were used to renourish the nearby beaches of
Swanage, Poole and Bournemouth.
Sand dredged to maintain a navigable boat channel at Barnegat Inlet, New
Jersey was used in 1979 to renourish an eroded ocean beach on nearby Long
Beach Island (Psuty
1984
), and 2 million m
3
of sand obtained from a similar boat
channel was used to restore the beach on Sandy Hook, New Jersey, where a spit
had been breached by erosion in 1982.
Sand dredged from the harbour at Rio de Janeiro in the 1940s was used to ren-
ourish Copacabana Beach, which was meagre until it was thus enlarged to provide
a wide shore recreational area above normal high tide level (Vera Cruz
1972
). At
Robe, in South Australia, sand dredged to maintain the port approach was dumped
to restore an adjacent beach.
Several beach renourishment projects in New Zealand have used sediment
available as a by-product of port dredging or marina projects (Healy et al.
1990
).
Dredging at the ports of Napier, New Plymouth and Tauranga Harbour produced
large quantities of sand and gravel, which have been used to renourish beaches
downdrift.
