Environmental Engineering Reference
In-Depth Information
At New River, North Carolina a loss of 16 % of the original renourishment left
coarser and better-sorted sediment, which helped to improve the performance of
the restored beach (Hobson
1977
).
The short-term construction phase can render the beach unusable, which in turn
can have economic implications. Changes to the beach following renourishment
may have impacts on recreational use. Where beaches are renourished with coarser
sediment than the native sediment, usually in an attempt to improve durability, the
resulting beach profile can be steeper. This coupled with the coarser sediment size
make the beach less attractive to beach users.
Renourishment may also cause changes to nearshore bathymetry and wave
breaking patterns, with implications for surf-riding conditions. This has been
considered on a number of Australia's east coast beaches, for example Collaroy-
Narrabeen, north of Sydney, where decisions on the methods of coastal man-
agement were influenced by their potential impacts on surf conditions, despite
previous renourishments making use of sediment dredged from the adjacent
lagoon entrance. Pitt (
2012
) compared a number of case studies from around the
world where beach renourishment projects had resulted in both negative and posi-
tive impacts for surf riding conditions. At Scheveningen in the Netherlands, beach
renourishment steepened the neashore profile and covered sandbars, resulting in
poorer surfable conditions. In 2010 70,000 m
3
of sand was used to shape a point
extending 100 m offshore. The sand bar which created plunging waves provided
suitable surfing for up to 3 months. At Long Branch New Jersey, United States,
renourishment was designed to improve conditions for surfing, but failed. At
Aramoana Beach, New Zealand, offshore disposal of dredged sediment unexpect-
edly improved surfing opportunities. At Cronulla, Australia, beach nourishment
included the offshore placement of sediment with the aim of improving surf condi-
tions, and this was successful, resulting in more pronounced wave refraction, wave
amplification and wave focusing.
Artificial coastlines have become extensive in Singapore, where land rec-
lamation increased the area of the island by nearly 25 % between 1960 and
2010. On the northern (Strait of Johore) coast at Jurong and Changi some sec-
tors were reclaimed by dumping earth and weathered rock, leaving their seaward
edges unprotected, so that wave action could sort the sediment and form beaches.
Longshore drift carried some of the reworked sediment to downcoast sectors,
where beaches were improved if the sediment received was sandy, but spoiled
where they were blanketed with silt and clay (Wong
1985
).
6.2 Costs and Benefits of Beach Renourishment
Beach renourishment is costly, but may be economically justifiable on sectors of
the coastline, such as seaside resorts, where the emplaced beaches will be much
used, or where the beach will protect property or infrastructure that is at risk from
erosion or flooding.
