Geoscience Reference
In-Depth Information
10.4.5.2 Aggregate dredging sites
can be used to inform risk assessments of planned,
active and ceased dredging activities. For one
bank off southern England, EMS data showed
that dredging intensities in some areas reached up
to 5 -15 hours per year per 100 m
2
box (Boyd
et al. 2004). Note that fishing trawlers over a
certain size on the European UK continental
shelf are also subject to EMS.
A range of remediation activities related to
aggregate dredging are undertaken in UK waters,
including minimizing the total area licensed/
permitted for dredging, and carefully locating any
new dredging areas with regard to the findings
of an Environmental Impact Assessment. Further,
dredging practices are adopted that minimize
impact and operators are required to monitor the
environmental impacts of their activities. Finally,
dredging operations are controlled through the
use of conditions attached to the dredging licence.
As a result, basic strategies for remediation for
aggregate dredging are developing rapidly (e.g.
EMU 2004). Guiding principles include drawing
upon the best scientific advice possible to estab-
lish (i) the need for remediation, (ii) the general
goals and specific objectives of remediation and,
Risk assessment and management are based
broadly on maximizing the potential for post-
cessation change back to pre-existing conditions.
The basic techniques include:
1
minimizing the area of impact and dredging
intensities, which determines the starting point
for 'recovery';
2
maximizing time-gaps between successive
dredging events (
c
. 6 years can produce near re-
establishment, but it depends upon the sediment-
ary dynamics), gaps between individual dredging
furrows and the depth of individual furrows;
3
using a site-specific assessment of impact
and recovery, based on 'types' of gravel biotic
assemblages;
4
leaving a thickness of at least 0.5 m of com-
parable coarse substrates (Boyd et al. 2004).
For UK waters, a valuable management tool
is the Electronic Monitoring System (EMS),
which automatically records the geographical
location and duration of dredging and dis-
posal activity on board each dredging vessel
(Fig. 10.14). Such data form a valuable set that
Dredging intensity in hours in
each 100 m x 100 m block
<1.00
1.00 -1.99
2.00 -2.99
3.00 -3.99
4.00 -4.99
South-east
England
>5.00
Area 22
200 m
0 (km) 100
Fig. 10.14
Dredging intensity in hours per 10,000 m
2
block for a site off Felixstowe (Area 422), south-east England for the year 1995.
Dotted line indicates boundaries of disposal ground. (Adapted from Boyd et al. 2003.)
