BEN SCHOEMAN DOCK BERTH DEEPENING Specialist ... - Transnet

Figure 22: Predicted worst case exceedance (days) of 10mg/l suspended sediment
within the surface layer of the harbour. (Cutter Suction Dredger; copied from Figure
B.1.2, Van Ballegooyen et al., 2006)
None of the predicted distributions of suspended sediments generated by the dredging
show that either the Two Oceans Aquarium or the waters in Table Bay immediately
outside of the harbour entrance should be compromised by dredging in the Ben
Schoeman Dock area in any of the dredging scenarios. Examples are Figures 20 and
21a and b. The latter figure also shows that the RSA (and ANZECC 2000) water quality
guidelines for trace metals should not be exceeded for any period longer than 0.25 days
outside of the Ben Schoeman Dock dredge area. However, this does not provide any
indication of whether short term spikes in trace metal concentrations may occur. Figure
23a and b plot simulated time series of dissolved copper concentrations adjacent to the
Two Oceans Aquarium intake and at the harbour entrance. It is clear that the predicted
concentrations are well within the RSA water quality guidelines for the maintenance of
ecosystems and, therefore, easily satisfy both RSA (DWAF 1995) and ANZECC (2000)
guidelines for aquaculture.
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