BEN SCHOEMAN DOCK BERTH DEEPENING Specialist ... - Transnet

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6.2.3 Dredge spoil disposal site 6.2.3.1 Alteration of seafloor sediment characteristics affecting biological communities The discharge of ~1.2 million m 3 of dredge spoil to the dredge spoil disposal site will inundate the resident benthos, possibly disrupting community structure and ecological processes at the site. The identified dump sites are approximately 3kmx2km which should result in an average inundation depth of 30cm-40cm. Maurer et al. (1980, 1981, 1982) and Hall (1994) have shown that most of the major faunal classes in the benthos would be able to withstand such burial depths, and, once the dumped sediment stabilised, it is likely that fauna will both migrate into the spoil dump area and recruit to it (Newell et al. 1998) with a relatively short recovery period (Ellis 1996). However, due to the spoil dumping practices followed by dredgers and/or barges carrying dredge spoil it is considered to be highly unlikely that an even distribution of dumped dredge spoil will be achieved. It is more probable that the dumping will result in multiple heaps of dredge spoil distributed across the chosen dredge spoil dump area. Under this scenario instantaneous burial depths may be 50cm–70cm which could cause higher mortality levels in the benthos. Recovery periods should be equally short though. The two candidate dredge spoil dump sites differ in sediment properties and in benthos community structure. The deeper site (#1) is characterised by a more or less uniform fine sand sediment and a high similarity in benthos community structure across the site. The 'worst case' average deposition pattern predicted by the simulation modelling for this site is shown in Figure 24. This particular deposition distribution will be that generated by spoil discharge during the cutter suction dredger phase. The bulk of the deposition will occur on the designated dump site but the surrounding area, including the northern edge of the Table Mountain MPA is also expected to receive sediment. Average depositional thickness is predicted to be low outside of the dump site, however, ranging from 1cm-5cm. Most of the affected area within the MPA will have deposition
Figure 24: The predicted worst case mean depositional thickness at dump site #1 over the duration of the simulation period for the cutter suction dredger. Copied from Figure B.1.9 in Van Ballegooyen et al., 2006) 74
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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
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
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: Diving birds such as cape cormorant
Page 85 and 86: Figure 25 depicts the simulation mo
Page 87 and 88: 6.2.3.2 Alteration of benthic biolo
Page 89 and 90: Impact Assessment Table No Mitigati
Page 91 and 92: Nature of impact - Turbid plumes of
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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BEN SCHOEMAN DOCK BERTH DEEPENING Specialist ... - Transnet

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