BEN SCHOEMAN DOCK BERTH DEEPENING Specialist ... - Transnet

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BEN SCHOEMAN DOCK DREDGING Specialist Study on Sediment Toxicology And Marine Ecology 1 INTRODUCTION Ben Schoeman Dock in the Port of Cape Town is scheduled to be deepened from its current depth range of 10.4 – 14m below chart datum (CD) to -15.5m CD to accommodate the new generation of larger container ships. The deepening will entail the removal by dredging of ~ 1 230 000m 3 of material. A small fraction of this (~10%) will be rock that may have to be fractured by multiple small parcel blasting prior to excavation. Dredging in coastal environments is a listed activity under South African environmental law (National Environmental Management Act (NEMA) 107 of 1998 Chapter 5) and as such requires detailed assessment before regulatory approval can be given. Therefore the proposed dredging programme required evaluation in terms of its likely effects on the natural environment. This specialist report was commissioned for this purpose. The specific brief for the assessment was: o Provide an assessment of the target dredge sediment properties in terms of particle size distributions, contaminant concentrations and toxicity to marine organisms o Identify the areas that may be at risk from the proposed activities o Identify the biological communities that may be at risk in these areas o Qualify the risks that the proposed operations may pose in terms of accepted water and sediment quality guidelines o If water and/or sediment quality guidelines are exceeded, quantify the risks in terms of the proportions of biological populations under threat and qualify these in terms of ecological consequences, and o Devise a practical monitoring programme that will, firstly, allow real time control of project activities to reduce environmental risks and, secondly, facilitate a quantitative determination of actual versus predicted project impacts. 1
2 METHODOLOGY For the assessment two major sources of information were accessed. The first of these comprises the peer reviewed scientific literature and various contract research and survey reports available for the Port of Cape Town and Table Bay. The second is data and information from site specific surveys in the Ben Schoeman Dock Basin and at two candidate dredge spoil dump sites in outer Table Bay conducted as part of this study. Information from these sources was synthesized in a desk top evaluation of the potential impacts of the proposed project. 2
Page 1 and 2: BEN SCHOEMAN DOCK BERTH DEEPENING S
Page 3 and 4: the test organisms. The EC 5 is usu
Page 5 and 6: Turbidity Upwelling Vulnerable Wrac
Page 7 and 8: Another important issue is the poss
Page 9: 6.2.1.3 Settlement of material susp
Page 13 and 14: The proposed deepening of the Ben S
Page 15 and 16: 4.3 Cumulative effects Table Bay re
Page 17 and 18: undetectable in 80% of the measurem
Page 19 and 20: 5.1.3 Biological communities The ma
Page 21 and 22: Supralittoral fringe (Littorina zon
Page 23 and 24: Niambia sp. Coleoptera Diptera Tylo
Page 25 and 26: Midlittoral zone - The intertidal o
Page 27 and 28: Fish - Nearshore and in the sandy b
Page 29 and 30: 2000 at Robben Island revealed furt
Page 31 and 32: Table 2: Common whales and dolphins
Page 33 and 34: Table 3: Site, time, mean count (co
Page 35 and 36: 150000 125000 100000 Kg 75000 50000
Page 37 and 38: sensitive because of its conservati
Page 39 and 40: Schoeman Dock occurred in 1971 (Pro
Page 41 and 42: Table 7: Hydrocarbon distributions
Page 43 and 44: care concentration ranges for cadmi
Page 45 and 46: SS mg/l Boxplot for TSS 80 60 40 20
Page 47 and 48: The mean values calculated above ar
Page 49 and 50: o o possibility of the dredge spoil
Page 51 and 52: The gravel sized component of the s
Page 53 and 54: Table 12a: London Convention Annex
Page 55 and 56: Benthos distributions in Block #1 -
Page 57 and 58: 40 40 30 Site 1A 30 Site 1B % Speci
Page 59 and 60: 2 Cluster Dendrogram and MDS ordina
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the well developed ripples in the c
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6 IMPACT IDENTIFICATION AND ASSESSM
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Accordingly the potential environme
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Impact Assessment Table No Mitigati
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are summarised in the table and it
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Figure 21b: Predicted number of day
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considered to be low. Further, the
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A A B B B Figure 23a and b: Predict
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dependent on these include the harm
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structures. The apparent lack of su
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Diving birds such as cape cormorant
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Figure 24: The predicted worst case
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Figure 25 depicts the simulation mo
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6.2.3.2 Alteration of benthic biolo
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Impact Assessment Table No Mitigati
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Nature of impact - Turbid plumes of
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Figure 26b: Predicted worst case ex
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Figure 27b: Predicted worst case ex
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suspended sediment concentrations i
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Figure 28a: Dredge spoil dump site
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6.2.3.6 Elevated water column turbi
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The evaluation with mitigation is:
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Figure 29a: Predicted exceedance in
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6.3 Cumulative Impacts The proposed
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Impact summary Table (cont.) Impact
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Impact summary Table (cont.) Impact
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mitigated by ensuring that the Cutt
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operations at Coega Port. Prepared
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Glassom D., K. Prochazka and G.M. B
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Protekon 2006. Port of Cape Town co
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