BEN SCHOEMAN DOCK BERTH DEEPENING Specialist ... - Transnet

o
o
possibility of the dredge spoil discharge and/or the dredge spoil discharge
activities exerting deleterious environmental affects at these sites, and
Water depths in the candidate sites should be sufficient to allow a large degree of
containment of discharged dredge spoil within the site boundaries, and
There should be minimal constraint to environmental monitoring.
Matching the above criteria against seafloor types that could be inferred from detailed
1m interval bathymetric maps (Woodborne 1983) led to the selection of the two
candidate sites (Block #1 and #2) shown in Figure 9. Side scan sonar and single beam
bathymetric surveys were conducted on these sites on 31 August 2006. The results are
reported in MGU (2006). The analogue side scan record from these surveys was used to
select suitable grab sampling sites to determine sediment properties and benthic
macrofaunal community structure. Sample sites were selected according to gross
sediment types, i.e. visible on the side scan record and, in the shallower site at least, the
absence of rock. The geographic positions of the sample sites are shown on Figure 9
and Figure 10 shows the approximate site locations on the side scan record. Data from
this survey was to be used to identify the respective suitability of the candidate sites for
harbour dredge spoil disposal and to provide a pre-impact quantitative baseline against
which future changes associated with dredge spoil disposal could be compared.
#2
#1
Figure 9: Candidate dredge spoil dump sites in 60-70m (Block #1) and ~40m (Block #2)
depths off Mouille Point and the sediment properties and benthos sampling sites
(denoted by green and red circles respectively).
40