Geoscience Reference
In-Depth Information
10.4.4 'Beneficial use' of dredged material
during placement and/or subsequent isolation
of the material from benthic organisms. Such
options include operational modifications, use of
subaqueous discharge points, diffusers, subaque-
ous lateral confinement of material, or capping
of contaminated material (Francingues et al.
1985; USACE/EPA 1992). Currently, the broad
research programme Dredging Operations and
Environmental Research (DOER 2005) is under-
way, conducting research designed to provide
dredging project managers with technology to
improve cost-effective operation, evaluation of
risks associated with management alternatives
and environmental compliance.
Canada has a range of measures in place to pro-
tect its marine environment, under the Canadian
Environmental Protection Act, 1999 (CEPA), and
to meet international commitments. Environment
Canada conducts representative monitoring at
sites of disposal at sea, and in 2003, monitor-
ing activities were conducted at 17 disposal
sites (London Convention 2005; www.ec.gc.ca/
seadisposal/) involving assessments of the phys-
ical, chemical and biological characteristics. Per-
mits for disposal include the generation of 'impact
hypotheses', which form the basis of subsequent
monitoring. Physical monitoring involves the
collection of relevant geological information for
determining the area of deposition, delineating
the disposal-site boundaries, studying the accu-
mulation of dredged material within the area of
deposition and documenting evidence of sedi-
ment transport from the disposal site. Associated
biological and chemical assessments are under-
taken, the monitoring design for which takes into
account the site's size and dispersal characteris-
tics. Major sites of disposal (
Dredged material can be a valuable resource,
but at present, in the UK, only
c
. 1% of material
dredged for disposal at sea is currently reused in
the marine environment. This may be higher in
other countries but data are not easily available.
In many countries, research is being undertaken
to identify ways of increasing the percentage of
dredged material used in beneficial use schemes.
Use of such material on the shelf is minimal,
and includes shoreline protection by depositing
material on the inner shelf (Small et al. 1997).
Most other beneficial use schemes are associated
with the coastline, including habitat restoration,
the maintenance of coastal sediment cells and the
(re-)creation of beach or saltmarsh habitats (e.g.
the DECODE project, http://www.cefas.co.uk/
decode/use.htm). The joint website of the U.S.
EPA and U.S. Army Corps of Engineers lists
details of a number of valuable case studies
(http://el.erdc.usace.army.mil/dots/budm/).
10.4.5 Managing impacts
Around the world there are generally four main
impacts to manage. Regarding material inputs
to continental shelves, the disposal of dredge
spoil is the main issue, and regarding sea-bed
disturbance, the main issues relate to trawling,
aggregate dredging and marine mining. Dredge
spoil and aggregate dredging are considered
below.
10.4.5.1 Dredge spoil disposal
In the USA, the U.S. Army Corps of Engineers
(USACE) and the U.S. Environmental Protec-
tion Agency (EPA) have statutory responsibilities
for the management of dredged material place-
ment in ocean, inland and nearshore waters.
When considering open-water placement of
dredged material, the potential for water col-
umn and benthic effects related to sediment
contamination is to be evaluated, and manage-
ment options considered that aim to reduce the
release of contaminants to the water column
100,000 m
3
yr
−1
of dredged material) are monitored at least every
5 years, and monitoring of other sites is based on
volume, proximity to sensitive areas, or level of
public concern. In common with many monitor-
ing programmes, Canada's programme depends
on funds gained from the collection of fees from
permittees. In the UK, annual Aquatic Envir-
onment Monitoring Reports (AEMR) include
sections on marine monitoring activities (available
from www.cefas.co.uk).
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