BEN SCHOEMAN DOCK BERTH DEEPENING Specialist ... - Transnet

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The risks of compromising beneficial uses in the harbour area are assessed as: Nature of impact – Dredging induced turbid plumes and/or remobilised contaminants compromises beneficial uses of the harbour water body Extent – Local, any effects should be limited to the harbour Duration – Short-term, only during dredging; water exchanges should constrain the persistence of any elevated concentrations of suspended sediments or trace metals Intensity – Low Probability – Improbable, simulation modelling predicts that critical threshold levels will not be compromised at the beneficial use sites Status of impact - Negative Degree of confidence – High Significance – Insignificant, due to low probability and short duration Mitigation – Not considered to be necessary due to the low significance Impact Assessment Table No Mitigation Extent Intensity Duration Consequence Probability Significance Status Confidence Local Low Shortterm Very Low Improbable INSIGNIFICANT -ve High 1 1 3 1 Mitigation n/a n/a n/a n/a n/a n/a n/a n/a Note: The Two Oceans Aquarium has established emergency procedures to cope with unsuitable quality intake water. These include running the aquarium system in recirculation mode and/or obtaining seawater from an alternative location such as Granger Bay and using road tankers to transport the water to the aquarium. Discussions with aquarium staff indicated that the system can be run in recirculation mode for periods of days at most. During this time all feeding would cease and there would be a decrease in water quality but not to an extent as to cause mortalities in aquarium inventory. Renewing seawater by road tanker would allow almost indefinite isolation from the harbour but would, of course, entail sharply higher costs compared to normal operations. Therefore, although not predicted to be necessary in this assessment of risks generated by the proposed dredging operations, the Two Oceans Aquarium does have procedures in place that would protect it from compromised water quality in the region of its seawater intakes. 6.2.1.8 Importation of alien species by dredgers and associated ecological effects Dredgers may transport alien biota in ballast water, in residual sediment in their hoppers or even attached as biofouling organisms on their hulls. The release of alien species into the Port of Cape Town by dredgers carries the risks of allowing the establishment of populations and potential competitive exclusion (food, space, nutrients) of indigenous species. In the worst case such imports may lead to the development of invasive populations with the capacity to severely disrupt and modify communities and ecological processes (IUCN 2000). Despite a long history of international shipping passing through South African ports there are only 16 confirmed cases of alien species becoming established in the country's coastal waters and/or ports (Awad et al. 2004, Robinson et al. 2005). The best known of these is the Mediterranean mussel Mytilus galloprovincialis, currently the mainstay of the local mussel farming industry, the ascidian Ciona intestinalis, a biofouling organism common in harbours, and the European shore-crab Carcinus maenas. Oher alien species that have or may exert deleterious effects on ecological processes or industries 67
dependent on these include the harmful algal bloom dinoflaggelate species Alexandrium tamarense and Gymnodinium cf. mikimotoi and the brown microalgae Aureococcus anophagefferens (Awad et al. 2004). In addition to the above 22 species are classified as 'cryptogenic', i.e. organisms with wide distributions suspected of being alien. The Port of Cape Town is known to support established communities of Ciona intestinalis, Diplosoma listerianum, Metridium senile, Carcinus maenas, and Schimmelmannia elegans (Robinson et al. 2005). It is also known to be inhabited by a range of cryptogenic species that have become established but do not posses large populations. These observations indicate that the probability for the import and establishment of alien organisms may be appreciable. The potential impact is assessed as: Nature of impact – Import and release of alien species by dredgers and their establishment in habitats within the harbour area Extent – Local to regional with possible extension to national Duration – Long term to permanent; once established it is unlikely that alien species would be obliterated by natural processes of competition, predation etc Intensity – Medium Probability – Probable Status of impact – Negative Degree of confidence – Medium; Alien and invasive alien species have established populations in South African coastal waters even if these are not generally widespread Significance – High Mitigation – Essential: Apply the ballast water management protocols stipulated in the IMO International Convention for the Control and Management of Ship's Ballast Water and Sediments and NPA’s requirement for dredgers to physically wash all hoppers immediately prior to first entering South Africa’s territorial waters when travelling from foreign ports (e.g. CES 2001), with verification of application. The implementation of the above measures should reduce the probability of the impact occurring to improbable as measurements for ballast water at least have shown that the treatment reduces viable organisms by 95%. However the degree of confidence would remain 'medium' as residual sediments may not be totally removed by these processes, especially those caught up in pipelines and corners in dredger hoppers. The evaluation with mitigation is: Nature of impact – Import and release of alien species by dredgers and their establishment in habitats within the harbour area Extent – Local to regional with possible extension to national Duration – Long-term to permanent; once established it is unlikely that alien species would be obliterated by natural processes of competition, predation etc Intensity – Medium Probability – Improbable Status of impact – Negative Degree of confidence – Medium; Alien and invasive alien species have established populations in South African coastal waters and one of the routes may have been sediment; that may not be completely removed by the washing process. Significance – Low, because of low probability of the impact occurring. Note this differs from the rating in the table below which is an artefact of the prescribed generic scoring 68
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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
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
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: A A B B B Figure 23a and b: Predict
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 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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