Planning Considerations - Beach Renourishment - page 110

which affects the incubation temperature. The renourished beach can include
higher berms which can make it difficult for turtles to move up the beach to
favourable nesting sites.
Increased accretion downdrift from renourished beaches may have adverse
effects on ecosystems, as at Saintes Maries de la Mer, on the southern coast of
France, where sand is drifting on to the Camargue salt marshes. At Rapid Bay
in South Australia sand and gravel eroded from a beach formed by quarry waste
dumping has drifted northward across the sea floor, blanketing formerly rich eco-
systems on reefs and impoverishing the local fishery (Bourman 1990 ). Sediment
can also be eroded and moved offshore, impacting on nearshore habitat such as
seagrass. Reference has been made to the proliferation of nearshore seagrass as a
consequence of bulldozing sand up on to the beach at Rosebud, Victoria, Australia
(Sect. 4.3.6 , p. 71).
Beach renourishment can increase the suspended sediment concentrations of
adjacent waters, both at the time of sand placement and subsequently as sediments
are redistributed. During the renourishment of Swanage, Poole and Bournemouth
beaches in 2006, of a total volume of sediment pumped ashore 30 % was lost from
the beach (CIRIA 2010 ). Several factors can contribute to the amount of sediment
suspension during and after placement on the beach, including the mode of place-
ment, meterological conditions and the proportion of finer sediment contained
in the renourished beach. Higher concentrations of suspended sediment cause
increased turbidity, but this a temporary effect and is often dispersed quickly by
wave action (Van Dolah et al. 1992 ). Furthermore, nearshore biological communi-
ties have a natural resilience to shifts in turbidity, which is a natural phenomenon
(Van Dolah et al. 1994 ). Wilber et al. ( 2006 ) recorded higher suspended sediment
concentrations in the swash zone adjacent to the renourishment site compared with
other areas, but little difference in the surf zone or nearshore. The study also found
higher suspended sediment extensive following storms than after beach renourish-
ment. Studies conducted by Rakocinski et al. ( 1996 ) during and after extensive
beach restoration at Perdido Key, Florida, demonstrated important changes in ben-
thic structure in response to silt/clay loading in the nearshore and offshore areas,
more than 2 years after the end of the project. Responses of the fauna included
decreased species richness and total abundance.
Substantial amounts of sediment dredged from the sea floor for use in beach
renourishment can be lost during delivery to the shore. The Rockaway Beach pro-
ject in 1975-1977 lost 10 % of the volume of sediment originally excavated from
the sea floor before it reached the beach. Some was lost during dredging, some as
the barges were filled, and some as they were emptied on to the shore. Such losses,
mainly of fine-grained sediment, modify the grain size distribution of the material
that reached the beach. At Rockaway Beach the losses of fine-grained sediment
were not a problem, as relatively coarse sediment was required for beach renour-
ishment there.
On the island of Sylt (Sect. 4.3.2 , p. 62) a million m 3 of sand was extracted
from the sea floor, but more than 20 % of it (also mainly the fine fraction) had been
lost before the balance of 770,000 m 3 actually reached the shore (Dette 1977 ).