BEN SCHOEMAN DOCK BERTH DEEPENING Specialist ... - Transnet

Intensity:
This predicts whether the impact is destructive or innocuous and
is described as low (where environmental functions and/or processes are negligibly
altered), medium (where the environment continues to function but in a modified
manner), or high (where environmental functions and/or processes are severely altered).
Probability: Here the likelihood of the impact occurring is assessed as
improbable (90% chance that the impact will
occur).
The status of the identified impacts and the degree of confidence in the predictions are
also given as follows:
Status of impact: Classification of the impact as positive (a benefit), negative (a
cost), or neutral.
Confidence: The degree of confidence that can be invested in the predictions
based on the available information and specialist knowledge.
When impacts are identified as negative with a significance rating of medium or higher,
or precaution should be applied, mitigation objectives are set (i.e. ways of reducing
negative impacts), and attainable mitigation actions recommended. In the case where
mitigation is not feasible or necessary, this will be stated as such.
Monitoring procedures and review programmes to assess the effectiveness of mitigation
are recommended.
6.2 Assessment of potential environmental Impacts
In this assessment the risk factors and associated effects listed in section 4 are matched
against the environmental attributes and features described in section 5. This allows
identification of potential impacts and their evaluation according to the criteria set out in
section 6.1. The potential impacts are partitioned by location where the effects
(stressors) originate, i.e. the dredge area within Ben Schoeman Dock, the candidate
dredge spoil disposal sites, and adjacent environments. The impacts are further divided
by activity; i.e. dredging and blasting in the dredge area and spoil dumping at the
disposal sites.
6.2.1 Harbour dredge area: dredging
6.2.1.1 Removal of biological communities in the dredge target areas
During the proposed dredging approximately 1.2 million cubic metres of sediment will be
dredged from the port. These sediments will have marine biota associated with them
which will be removed along with the dredge spoil. There is a marked gradient within the
port in biofouling organisms on harbour structures, biomass declining rapidly with
distance from the harbour entrance. There are no reported surveys on spatial
distributions of benthos in the sediments but spot sampling in Duncan Dock, Victoria
Basin and Alfred Dock showed a complete absence of fauna (CMS 1995a). This was
attributed to anoxic sediments and hydrocarbon pollution. Such a severe situation is not
expected for Ben Schoeman Dock Basin sediments, as indicated by AVS and
hydrocarbon concentrations, but it is likely that the soft sediment benthos is
impoverished.
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