Geoscience Reference
In-Depth Information
A Regional Environmental Assessment (REA)
of the eastern English Channel has focused
upon those sea areas that may be impacted by
dredging. The REA includes predictions of
dredging-related physical and biotic changes,
especially related to recolonization of the bed,
but the evidence base for such predictions requires
development. The findings of field-based studies
differ, ranging from minimal effects of distur-
bance following cessation of dredging (Robinson
et al. 2005) to significant changes in community
structure which persist over many years (Desprez
2000). Although some of these differences prob-
ably reflect the different sediment types and their
associated different physical dynamics, compo-
sition and biogeochemical cycling, links between
post-dredging ecological change and physical
processes need to be strengthened in order to
allow better transfer of conclusions to other areas.
local habitats (Rees, in Judd et al. 2003), yet
may also be viewed as having positive effects if
their presence reduces or halts trawling in the
area (Elliott & Cutts 2004).
Extraction of wave energy is also a rapidly
expanding field, and the UK is one of the richest
nations in terms of potential for wave energy
(Pelc & Fujita 2002). Extraction of wave energy
reduces the energy reaching the coast, and
whether this effect is perceived as beneficial or
detrimental depends on the specific coastline.
There are no significant impacts likely on shelf
sediments, however, unless there is an import-
ant active link between the coastal and shelf
sediments. Tidal flows are also a huge potential
energy source. World-wide, tidal power plants
could theoretically generate 500 -1000 terraWatt
hours per year (TWh yr
−1
, terra
10
12
) and
western Europe 100 TWh yr
−1
. Theoretically the
UK could generate 50 TWh yr
−1
, 125 times the
current UK use (0.4 TWh yr
−1
, www.dti.gov.uk)
although economic constraints mean that only a
fraction of this energy is likely to be exploitable
(Pelc & Fujita 2002). Tidal turbines are arrays
of impellors located above the bed, generally
in locations where tidal current speeds exceed
c
.2ms
−1
, and appear to have few anticipated
sedimentary impacts.
=
10.5.2.3 Offshore renewable energy developments
(OREDs)
For countries with continental shelves, the renew-
able energy resource can include tides, currents,
waves and offshore wind. The development of
offshore windfarms is now well underway in
some countries (section 10.3.2.5.). In December
2003, the UK Government announced a com-
mitment to generating 10% of the UK electricity
needs from renewable sources by 2010 and
20% by 2020. Most of this is likely to be met
by a major increase in the number and size of
offshore windfarms. By late 2005, there were
15 projects awarded and in the early stages of
planning, which will amount to a generation
capacity of 7.2 GW, potentially contributing
electricity to more than 4 million households.
Other types of development are increasingly
under consideration, including underwater
tidal turbines and floating offshore windfarms
(Pelc & Fujita 2002; Gill 2005). With offshore
structures, the likely impacts upon the shelf
sedimentary system are generally local in nature.
Some offshore structures, especially those cover-
ing extensive areas such as windfarms, cause
local disturbance, especially from scour around
foundations and the associated impacts upon
10.5.3 Sedimentary impacts of climate change
For continental shelves, it is probably true that
basic knowledge of natural sedimentary changes
on time-scales of decades is mostly insufficient
to allow anthropogenic changes to be confid-
ently identified and their significance assessed.
Studies of marine sediments and fossils can help
address whether recently measured shelf sedi-
mentary changes have occurred before. Although
the details of cause and effect may often be
imperfectly understood, better links are possible
between the understanding of the natural driv-
ing forces and the tools used for management
(Hardman-Mountford et al. 2005; Larcombe
et al. 2005; Rogers & Greenaway 2005). With
regard to shelf sediments, the main impacts of
climate change include results of changes in
sea-level and ocean circulation.
