BEN SCHOEMAN DOCK BERTH DEEPENING Specialist ... - Transnet

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Due to the apparent differences in areal scales of potential impacts of suspended sediments the two dredge spoil dump sites are assessed separately. SITE #1 Nature of impact – Turbid plumes of suspended sediment negatively affect biota in and adjacent to the dredge spoil dump site #1 Extent – Local; largely restricted to within an approximately 5km radius of the centre of the spoil dump site but with an isolated patch of longer exceedances immediately north of the harbour entrance. Durations of exceedances of concentrations above the 20mg/l threshold outside of these areas are probably 100mg/l are predicted to be restricted to the dump site and immediately adjacent areas Duration – Short; recovery should commence on completion of the dredging programme and be largely attained within 1-3 years. Intensity – Low Probability – Possible Status of impact – Negative Degree of confidence – High Significance – Insignificant; the spatial extent should be small relative to the amount of similar habitat in Table Bay and recolonisation should be rapid as any effects are likely to be chronic as opposed to acute (Hall 1994). Mitigation – None Impact Assessment Table No Mitigation Extent Intensity Duration Consequence Probability Significance Status Confidence Local Low Shortterm Very Low Possible INSIGNIFICANT -ve High 1 1 3 1 Mitigation n/a n/a n/a n/a n/a n/a n/a n/a SITE #2 Nature of impact – Turbid plumes of suspended sediment negatively affect biota in and adjacent to the dredge spoil dump site #2 Extent – Regional; a large proportion of the Table Bay sea floor will be exposed to suspended sediment concentrations above 20mg/l for periods exceeding the set three days of continuous exposure limit and concentrations >100mg/l are predicted to affect the seabed north of the dump site itself Duration – Short; recovery should commence on completion of the dredging programme and be largely attained within 1-3 years. Intensity – Medium; effects should be chronic in nature but may lead to temporary shifts in community structure. This may have implications for biodiversity because of the diversity of habitats that may be affected Probability – Probable Status of impact – Negative Degree of confidence – Medium Significance – Medium; the potential spatial extent of impact is large relative to the known distributions of habitat types and Table Bay itself. However, recolonisation should be rapid as any effects are likely to be chronic as opposed to acute (Hall 1994). Note this differs from the rating in the table below which is an artefact of the prescribed generic scoring system Mitigation - Optional: do not use this site for dredge spoil dumping. The evaluation with mitigation is: 81
Nature of impact – Turbid plumes of suspended sediment negatively affect biota in and adjacent to the dredge spoil dump site #2 Extent – None Duration – None Intensity – None Probability – Improbable Status of impact – Neutral Degree of confidence – High Significance –Insignificant Impact Assessment Table No Mitigation Mitigation Extent Intensity Duration Consequence Probability Significance Status Confidence Regional Medium Short- Low Probable LOW -ve Medium 2 2 term 5 1 None 0 None 0 None 0 Not significant 0 Improbable INSIGNIFICANT Neutral High 82
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BEN SCHOEMAN DOCK BERTH DEEPENING S
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the test organisms. The EC 5 is usu
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Turbidity Upwelling Vulnerable Wrac
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Another important issue is the poss
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6.2.1.3 Settlement of material susp
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2 METHODOLOGY For the assessment tw
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The proposed deepening of the Ben S
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4.3 Cumulative effects Table Bay re
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undetectable in 80% of the measurem
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5.1.3 Biological communities The ma
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Supralittoral fringe (Littorina zon
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Niambia sp. Coleoptera Diptera Tylo
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Midlittoral zone - The intertidal o
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Fish - Nearshore and in the sandy b
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2000 at Robben Island revealed furt
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Table 2: Common whales and dolphins
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Table 3: Site, time, mean count (co
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150000 125000 100000 Kg 75000 50000
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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
Page 61 and 62: the well developed ripples in the c
Page 63 and 64: 6 IMPACT IDENTIFICATION AND ASSESSM
Page 65 and 66: Accordingly the potential environme
Page 67 and 68: Impact Assessment Table No Mitigati
Page 69 and 70: are summarised in the table and it
Page 71 and 72: Figure 21b: Predicted number of day
Page 73 and 74: considered to be low. Further, the
Page 75 and 76: A A B B B Figure 23a and b: Predict
Page 77 and 78: dependent on these include the harm
Page 79 and 80: structures. The apparent lack of su
Page 81 and 82: Diving birds such as cape cormorant
Page 83 and 84: Figure 24: The predicted worst case
Page 85 and 86: Figure 25 depicts the simulation mo
Page 87 and 88: 6.2.3.2 Alteration of benthic biolo
Page 89: Impact Assessment Table No Mitigati
Page 93 and 94: Figure 26b: Predicted worst case ex
Page 95 and 96: Figure 27b: Predicted worst case ex
Page 97 and 98: suspended sediment concentrations i
Page 99 and 100: Figure 28a: Dredge spoil dump site
Page 101 and 102: 6.2.3.6 Elevated water column turbi
Page 103 and 104: The evaluation with mitigation is:
Page 105 and 106: Figure 29a: Predicted exceedance in
Page 107 and 108: 6.3 Cumulative Impacts The proposed
Page 109 and 110: Impact summary Table (cont.) Impact
Page 111 and 112: Impact summary Table (cont.) Impact
Page 113 and 114: mitigated by ensuring that the Cutt
Page 115 and 116: operations at Coega Port. Prepared
Page 117 and 118: Glassom D., K. Prochazka and G.M. B
Page 119 and 120: Protekon 2006. Port of Cape Town co
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