ESTUARINE BIODIVERSITY SPECIALIST STUDY FOR · PDF fileestuarine biodiversity specialist study for an eia for deepening, lengthening and widening of ... caisson quay wall

ESTUARINE BIODIVERSITY SPECIALIST STUDY FOR AN EIA

FOR DEEPENING, LENGTHENING AND WIDENING OF

BERTH 203 TO 205, PIER 2, CONTAINER TERMINAL, IN THE

PORT OF DURBAN

Report prepared for Nemai Consulting

October 2012

Prepared for

Nemai Consulting

PO Box 1673

Sunninghill 2157

Johannesburg, South Africa

Tel: (011) 781 1730

Fax: (011) 781 1731

Prepared by

Sean Porter, Barry Clark & Ken Hutchings

8 Steenberg House

Silverwood Close

Tokai 7945

Tel: (021) 7013420

Fax: (086) 542 8711

www.anchorenvironmental.co.za

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Executive Summary

This study assesses the marine-estuarine ecological impacts of a proposal by Transnet

National Ports Authority (TNPA) to deepen, widen and lengthen Berths 203 to 205 of Pier No 2 in the

Port of Durban, South Africa. These berths are to be expanded 170 m west, 100 m east and 50 m

seaward. Three construction options for the quay walls exist, namely Deck on Pile option, a Sheet

Pile option; and a Caisson option. Each of the three options destroys a similar amount of intertidal

and subtidal habitat. Amounts of open water habitat lost varies between options but this is not

considered significant.

The habitat area potentially affected by the proposed project is located in the central parts

of the harbour, and consists of open water area, subtidal soft sediments and intertidal-sand-flat

habitat at Centre Bank that is zoned for conservation according to the draft Bay of Natal Estuary

Management Plan. The subtidal habitat ranges in depth from 0 to 16 m CDP, and comprises 30 to

70% mud. Intertidal and shallow subtidal habitat at Centre Bank is very different and composed of

less than 5% mud and predominantly fine to medium sands (0.125 - 0.500 mm).

Over 563 marine species have been recorded within the Port of Durban and it is recognised

as being an extremely important nursery area for juvenile fishes, many of which are critically

dependent on estuaries. The intertidal and shallow subtidal sand flats provide particularly important

habitat for fishes, Callianasid prawns and other invertebrates which in turn support large numbers of

waders and other waterbirds. Deeper subtidal areas are dominated by many different species of

Polychaete worm and different fish communities. There are a number of Ramsar Site criteria that

the Bay meets.

The expected impacts include destruction and disturbance of intertidal and subtidal soft

bottom habitat and associated invertebrate and fish communities resulting from the expansion of

the Berths, dredging and the placement of stabilising mattresses on the western, eastern and

southern slopes of Centre Bank and rocky scour protection adjacent to berths. These effects may be

reduced only by strict adherence to a suite of proposed mitigation measures that include

refilling/backfilling and enlarging of the Centre Bank sand flat (via Option 3G) in addition to strict

operating rules pertaining to dredging such that the extent of any turbidity plumes are minimised

and do not exceed specified threshold levels. It is believed that all residual impacts of the proposed

development will be offset with the adoption of Option 3G provided that the artificial extension of

Centre Bank can be done successfully from an ecological perspective. There is however both

uncertainty and risk associated with the artificial creation of sand bank habitat in estuaries as there

is little literature on the subject. Offshore dredge spoils do however recover successfully and are

colonised by organisms relatively quickly. It is therefore expected that this mitigation measure will

be successful with a medium level of certainty. Overall impact significance can therefore be reduced

to low levels A monitoring program to determine the actual impacts of the widening of the Berths on

the biodiversity of Durban Harbour is recommended and described, from pre-construction and into

the operational phase of the Berths. In addition, monitoring of the backfilled part of the Centre Bank

sand bank and the artificially enlarged portion of this sand bank is recommended. Monitoring of

turbidity levels during dredging is also prescribed to ensure that threshold limits are not exceeded.

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Table of Contents

1 Introduction ................................................................................................................................ 1

2 Development proposal ............................................................................................................... 1

3 Scope ......................................................................................................................................... 11

4 Concerns raised by I&APs pertinent to this study .................................................................... 12

5 Methods .................................................................................................................................... 16

6 Description of the affected environment ................................................................................. 16

6.1 Habitat types within the Durban Harbour and relevant environmental characteristics. ..... 16

6.2 Overview of the biodiversity in the Port of Durban .............................................................. 21

6.2.1 Overview of the macrofaunal community composition and relative abundance within

the Port of Durban ........................................................................................................................ 23

6.2.2 Overview of the fish fauna in the Port of Durban ......................................................... 27

6.3 Centre Bank habitat and biodiversity .................................................................................... 29

6.4 Dredge channel habitat and biodiversity .............................................................................. 30

6.5 Little Lagoon habitat and biodiversity ................................................................................... 33

7 Potential for RAMSAR Site designation .................................................................................... 39

8 Potential habitat transformation as a result of the proposed development ........................... 41

9 Impact on microalgae, macrofaunal and ichthyofaunal communities ..................................... 46

9.1 Site-specific considerations in the assessment of potential impacts on the biodiversity of

the Port of Durban ................................................................................................................. 46

9.2 Impact description and assessment ...................................................................................... 48

10 Mitigation .................................................................................................................................. 67

11 Monitoring Programme ............................................................................................................ 68

12 References ................................................................................................................................ 69

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1 Introduction

Transnet National Ports Authority (TNPA) is planning to deepen, widen and lengthen Berths 203 to

205 of Pier No 2 in the Port of Durban, South Africa. The rational is to improve the safety of the

berths as they do not conform to minimum Eurocode 7 Safety Standards. In addition, the efficiency

of the Port will be concomitantly increased.

Nemai Consulting was appointed to conduct the Scoping and Environmental Impact Assessment

(EIA) study, and subsequently subcontracted Anchor Environmental Consultants to conduct a

specialist study on potential impacts of the development on the local estuarine marine ecology of

the Port of Durban.

2 Development proposal

The proposed upgrade of the existing Berths 203 to 205 of Pier No 2 is located in the eThekwini

Municipality in the Port of Durban. The proposed upgrade will include the following:

Westward lengthening of Berth 205 by 170 m;

Eastward lengthening of Berth 203 by 100 m;

Seaward widening of Berths 203, 204 & 205 by 50 m;

Deepening by dredging of the berth channel, approach channel and vessel turning basin;

from the current depth of -12.8 m to -16.5 m Chart Datum Port (CDP);

Offshore disposal of dredge material;

Offshore sand winning for infill material;

Installation of new Ship to Shore cranes and associated infrastructure;

Precasting of beams, storage of sheet piles or construction of caissons at Bayhead Lot 10;

and

Stabilisation of the Centre Bank with subtidal mattress’s

Artificial extension of Centre Bank to mitigate against habitat loss (Development Options 3C

to 3G)

Three technical options will be considered for the berth, namely, a Deck on Pile option, a Sheet Pile

option; and a Caisson option (Figure 1, Figure 2 & Figure 3). The Caisson option may involve further

excavation of the seabed after dredging if clay occurs and not sand in certain parts of the

foundation. Indications are that there are very unfavourable soft clays (Hippo Mud) for the entire

area beneath the footprint of where Berth 205 may be extended (ZAA 2012b). Construction of

crushed stone, sand, rockfill or soil-cement replacement foundation to a minimum total depth of

2.35 m below seabed level is required in order that a minimum Factor of Safety of 2.0 for bearing

capacity is achieved (ZAA 2012b). This could create a localised and temporary enhancement of

turbidity.

The Sheet-pile option will involve driving to bedrock HZM-1180 MD King piles at 2.258 m intervals as

well as AZ-26 section infill panels between these, to an average depth of -35 m CDP and as deep as -

55 CDP at the eastern end of Berth 203 (ZAA 2012b). A barge will be used for this operation before

dredging is conducted. Once the sheet-pile wall is stable then the area in front of it can be dredged

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deeper. The driving in of the piles and panels is likely to create a localised and temporary

enhancement of turbidity at the construction site.

The Deck-on-pile option will require outer piles spaced at 6.67 m intervals along with inner piles, all

to be driven down to an average depth of -35 CDP. Piles are likely to be driven from a barge or

travelling platform. (ZAA 2012b).

In addition, various incremental development options are proposed to mitigate the loss of sand flat

on Centre Bank during and after construction of the quay walls (Figure 4, Figure 5 & Figure 6) and to

reduce the footprint of the dredge area (Figure 7, Figure 8 & Figure 9). Option 3B (Figure 4) shows

the dredging layout prior to mitigation. Option 3C (Figure 5) then shows how the dredged area of

the Centre Bank sand flat at the western end of Berth 205 could be backfilled up to the quay wall.

Option 3D (Figure 6) includes backfilling of the Centre Bank sand flat up to the western end of the

quay wall as well as infilling along the southern edge of the Centre Bank with dredged material as

compensation for sandbank area lost as a result of the expansion of the existing quay wall. Later

options (i.e. Options 3E to 3G) all progressively reduce the size of the dredge footprint and increase

the artificial southwards extension of the Centre Bank sand flat in an attempt to mitigate against the

loss of sand bank due to the proposed westward extension of Berth 205 into the Centre Bank.

Due to the proposed dredging and deepening of the shipping lanes adjacent to the berths, the

stability of the Centre Bank is now a concern and therefore support mattresses on the western,

southern and eastern sides where the slope is at a gradient of 1:3 have been proposed to mitigate

against slumping and erosion (Figure 10). Mattresses on the western and eastern slopes will be

overlaid onto the surfaces of the slopes of the sand bank and extend from -16.5 m to 0 m CDP

(Figure 10). Mattresses on the southern slopes will only overlie areas of the bank at depths of -16.5

to -12.8 m CDP (Figure 10).

Figure 1. Proposed upgrade of the existing Berths 203 to 205 of Pier No 2 in the Port of Durban - Deck on Pile Quay

Wall option.

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Figure 2. Proposed upgrade of the existing Berths 203 to 205 of Pier No 2 in the Port of Durban - Sheet Pile Quay Wall

option.

Figure 3. Proposed upgrade of the existing Berths 203 to 205 of Pier No 2 in the Port of Durban - Caisson Quay Wall

option.

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Figure 4. Option 3B showing the dredge layout relative to the Centre Bank sand flat and Piers 2 and 1.

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Figure 5. Option 3C showing how the sand flat at the western end of Berth 205 can be in-filled up to the quay wall.

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Figure 6. Option 3D showing the area in-filled at the western end of Berth 205 and the proposed expansion of the southern edge of the Centre Bank sand flat shown in brown.

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Figure 7. Option 3E shows the reshaping of the dredged area to reduce its overall extent and increase the size of the proposed expansion of the sand bank (brown area).

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Figure 8. Option 3F. The shape of the dredged area at Little Lagoon end (i.e west end) is now modified to reduce the risk of affecting Little Lagoon, and also to further increase the size of the proposed extension of the sandbank relative to its size in previous options (i.e. Options 3D-3E).

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Figure 9. Option 3G. Volume of dredged area further reduced from previous options and the proposed southwards extension of the sandbank increased even more.

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Figure 10. Option 3G showing areas of the sand bank that will be stabilised with mattresses. Red shading indicates where mattresses will cover the slopes of the sand bank from -16.5 to 0 m CDP and orange shading where mattresses will cover the slopes of the sand back from depths of -16.5 to -12.8 m CDP.

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3 Scope

The scope of the specialist estuarine ecology study was agreed as follows:

i) A description of the affected environment, identified as the whole of the Durban Bay but

focussing specifically on the dredge channels adjacent to Berth 203-205, the central sand

bank and the area referred to as Little Lagoon, and its importance to all biota aside from

avifauna1, based on available data;

ii) An assessment (using suitable evaluation criteria) of all potential impacts (direct, indirect

and cumulative) on the biodiversity of Durban Bay associated with all project alternatives;

iii) Recommendations for suitable mitigation measures as required;

iv) A statement of the significance of impacts associated with each issue, which will specify

whether or not a pre-determined threshold of significance (i.e. changes in effects to the

environment which would change a significance rating) has been exceeded, and whether

or not the impact presents a potential fatal flaw or not, both before and after application

of impact management actions; and

v) A statement of which of the project alternatives will have the least impact on biodiversity.

1 Note that impacts on birds are addressed in a separate study

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4 Concerns raised by I&APs pertinent to this study

A number of issues were raised and captured in the Comments and Response Report

prepared as part of the Scoping phase for this study that are relevant to this specialist study. These

are captured in Table 1 below and have been addressed in this report.

Table 1. Issues raised and during the Scoping phase of this project relevant to this study

COMMENT/QUERY/ISSUE RAISED BY

One of the main impacts that need to be considered is the impact on the Central Sandbank and the Little Lagoon. There is a need to quantify the loss of the Central Sandbank so that this impact can be mitigated.

WESSA

One of the main impacts that need to be considered is the impact on the Central Sandbank and the Bayhead Mangroves.

Bruce Soutar

How will the sandbanks be impacted by the berthing of larger ships. WESSA

The sand beds are “soft habitats” and are the driving force behind the productivity of the Durban Bay Estuary as a marine nursery.

WESSA

Asked for a schematic illustration of the actual boundaries of the dig-out of the central sandbank (i.e. the exact footprint of the impact on the Central Sandbank).

Rory O’Connor

Expressed disagreement with the proposed project due to the impact on the Central Sandbank. Noted that fish spawn on the sandbanks and thus the proposed project will impact on future marine life and the subsistence fisherman who rely on the Central Sandbank.

Michael Padayachee, KZN Subsistence

Fisherman Forum

Asked how fish breeding on the Central Sandbank will be impacted on. Michael Padayachee,

KZN Subsistence Fisherman Forum

Asked if there will be any impact on the current sand stockpile adjacent to the Little Lagoon and Sandbank?

Max Magnussen

Expressed concern that the extension of the Berth into the Central Sandbank will cause the banks of the sandbank to collapse.

Michael Padayachee, KZN Subsistence

Fisherman Forum

What is the extent of the impact on the Central Sandbank and whether the scour protection at Berth 205 will be visible at spring low tide.

Max Magnussen

What is the extent of the impact on the Central Sandbank? Hoosen Bobat

Expressed concern that extending Berth 205 into the Central Sandbank will have impacts on juvenile fish and other marine life and pointed out that it would be better to start 50m inland.

Per Bjorvig

This project is necessary however negative impacts on the Central Sandbank should be mitigated through offsets.

Lindy Delport, Process Pipe

Asked what is the exact extent of the impact on the Central Sandbank? Kamcilla Pillay, Daily

News

Asked what is the exact extent of the impact on the Central Sandbank and how will this impact the ecology of the sandbank?

Patrick Eugene, KZN Subsistence Fisherman

Forum

Expressed concern that the sandbanks are a very sensitive ecological area and should not be tampered with.

Vivienne Venter

The following issues were likely to have a negative impact and would require further assessment: 1. Slope stability of the sandbanks; 2. Increased tug/ship action resulting in additional wave action on the bed and

Coastal Policy and Coastal, Stormwater

and Catchment Management

13


slopes of the sand banks; 3. Removal and loss of habitat; and 4. Changes in the tidal prism and erosional impacts on the sandbanks.

Department, eThekwini Metropolitan Municipality

One of the main impacts that need to be considered is the impact on the Little Lagoon.

Carolyn Schwegman: WESSA

Has rehabilitation of the Little Lagoon taken place by Transnet. Bianca Mckelvey:

WESSA

Enquired as whether any offset measures against impacts on the Little Lagoon were being considered.

Sabelo Nkosi: Development Planning,

Environment and Management:

eThekwini Metropolitan Municipality

There does not appear to be enough baseline data related to biophysical monitoring throughout the entire Durban bay system.

WESSA

How will the Durban Bay Estuary Management Plan will be incorporated into the planning process.

WESSA

Expressed concern that Durban Bay has been at a tipping point for a long time and its sustainability is hanging by a thread and that it cannot be viewed as just a harbour. Durban Bay needs to be treated as an ecosystem that provides free goods and services.

Judy Bell

Expressed concern about the potential impacts of the project on the ecological health of the Bay and hence its ability to continue to deliver high value goods and services that are irreplaceable to the region.

Bianca Mckelvey WESSA

Expressed concern that although the footprint of the development may appear to have a proportionally small direct impact on the important habitat of the Bay, the direct impacts on important habitats and the whole ecology of the Bay are far larger than the footprint of the proposed extension, given the various activities than would need to take place beneath the surface water (eg. extensive dredging) and the knock-on impacts these would have. Expressed concern that there may be significant anticipated impacts on the most significant and productive habitats of the Bay, exacerbated by unexpected changes that will have an uncertain impact on the health and resilience of the ecosystem.


It is critical that the potential impacts on the Bay not be viewed in isolation, but rather with the current condition and resilience of the Bay in mind. Some of the potential impacts of the proposed development may not seem highly significant, until the cumulative impacts are taken into consideration.


The following comments were raised: 1. Durban Bay is one of the only three South African estuaries that falls in the Estuarine Bay categories and as a result of the strong marine influence, the system supports more species than almost any other estuary in South Africa. 2. Due to the strong degree of conductivity that occurs in aquatic environments, changes to one of these areas has far reaching regional consequences. 3. There are studies to suggest that Durban Bay is at a threshold where further development could result in ecological collapse. 4. At a local scale, the loss of biodiversity within Durban Bay would severely compromise the long term functioning of the system. 5. Approximately 57% of the Bay has been infilled. In addition, only 4% of the natural shoreline, 14% of the tidal flat area, and 3% of the mangrove areas remain. 6. The impact of the proposed development includes: a. Direct loss of intertidal sandbank; b. Further loss of the intertidal sandbank as a result of erosion due to larger vessels moving through the area; c. Infilling and subsequent loss of water areas; and

Environmental Planning and Climate Protection

Department, eThekwini Metropolitan

Municipality

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d. Loss of subtidal areas as a consequence of dredging. 7. The loss of a portion of the remaining intertidal sandbanks represents a major issue and would compromise the ecological functioning of the system. 8. The relative importance of the Central Sandbank has been highlighted in the previous Transnet eThekwini Municipality Port Initiative (TEMPI) process. 9. At present, the Sandbanks support the largest population of the Sandprawn Callianassa kraussi in the province. 10. The system also supports diverse assemblages of benthic invertebrates. 11. The shallow inundated areas associated with these sandbanks provide refuge for a number of juvenile fish species that would otherwise be under significant predation threat in the deeper main channels. 12. These intertidal areas also provide habitat for Water bird assemblages including Palaearctic waders. 62 waterbird species listed in the Bonn Convention have been recorded in Durban Bay. 13. South Africa is a signatory to The Bonn Convention, which requires that measures to conserve migratory waterbirds are taken. 14. The proposed infilling will result in further pelagic and subtidal benthic habitat loss leading to a further reduction to the carrying capacity of the system. 15. Dredging is likely to result in a complete change in the ecological functioning of the system due to the increase in depth and redistribution of sediment. 16. Therefore the Environmental Planning and Climate Protection Department (EPCPD) does not support the proposed development. The EPCPD will only reconsider this position if the requirements of the 1999 RoD be adequately addressed.

Expressed concern regarding the incremental infill of the Durban Bay and the impact on Central Sandbank and Bayhead Mangroves.

Bruce Soutar

How would the expansion impact the heritage site (mangroves)? Noted that in regards to the Mangroves, there may be indirect impacts even if there is no direct construction footprint as the health of the mangroves is linked to the health of Durban Bay Estuary.

WESSA

Will the proposed project have an impact on the Mangroves.

Desmond D’Sa, South Durban Community

Environmental Alliance

Expressed concern that the proposed project will cause destruction to the sea-life especially the mangroves.

KZN Subsistence Fisherman’s Forum

Noted that the Draft EMP for the Bay (recently been published for comment) clearly outlines the longstanding concerns of all stakeholders about the continuing degradation of the Durban Bay, driven by escalating levels of pollution and cumulative habitat loss. The proposed development appears to be in complete contradiction of many of the findings of the EMP, which emphasises the need to halt habitat loss, enhance existing habitats, and stabilize the environments within the Bay over the next five year period.

Bianca Mckelvey, WESSA

The team should consider offsetting the ecological impact on the sandbank. Lindy Delport, Process

Pipe

The use of compensation for un-mitigatable impacts, otherwise known as a biodiversity offset, is not theoretically possible in an estuarine environment. Examples of attempted offsets in estuarine environments internationally have shown that the end results are likely to be entirely unexpected and that success of such measures is entirely outside of human control, but is dependent on unpredictable, external environmental factors. The risk of failure is therefore extremely high, and failure would leave the impacts of the development essentially unmitigated, handing the environmental cost of the development to South African society.


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WESSA are not in favour of the use of offsets in any circumstance, and feel that this should only be considered in truly exceptional circumstances (as described in provincial policy)


Possible impacts as well as mitigation measures are identified in the EIA Phase. KZN Department of

Water Affairs

Who is the Estuarine Specialist? WESSA

The Specialist studies must consider national conservation goals and targets that have not yet been integrated into provincial systematic conservation planning (for example, the national target of 100% for mangrove communities


Requested that the results of various specialist studies need to be holistically considered, so that all studies start from the same baseline of information, and results can be properly integrated and thus we were pleased to hear at the Open Day that all specialists will be given the opportunity to meet and discuss preliminary results throughout the assessment process


Reiterated that the inclusion of impacts upon subsistence use of the Bay into studies on ecological impacts is illogical. Given the significance of impacts to this sector, the impact of the proposed development on subsistence fishing (both on-site and as a result of potential loss of productivity in local fisheries) must be considered in appropriate detail by a suitably qualified specialist


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5 Methods

A number of studies have been completed in recent years covering the estuarine biota of the Port of

Durban, including the intertidal and shallow subtidal sand banks (see for example Pillay, 2002; Angel

& Clark, 2008; Newman et al. 2008; Weerts, 2010). These data were used to assess the significance

of potential impacts that the proposed development may have on the biota of the Port of Durban in

the future. Furthermore, spatial data on habitat types relevant to the macrofauna of the Port and

spatial data on the development footprint were analysed using GIS software to determine the scale

of the impacts. Data were projected according to the Latitude Orientated (Transverse Mercator)

coordinate system with 31 degrees latitude set as the central meridian and Hartebeesthoek 94 as

the datum.

6 Description of the affected environment

6.1 Habitat types within the Durban Harbour and relevant

environmental characteristics.

There are a number of habitat types within the Port of Durban that could potentially be affected by

the proposed development (Figure 11). These include:

1. intertidal sand flat habitat (the wetted area between the lowest and highest astronomical

tides),

2. shallow subtidal sand flat habitat (extends from the lowest astronomical tide down to a

depth of -1 m ) including areas such as at Little Lagoon, medium subtidal habitat at the

upper margins of the dredged shipping channels (-1m to -3 m)

3. deep subtidal such as the lower edges of shipping channels and deeper portions channels

from a depth of -3 m to -12.8 m).

In all cases, the habitat area includes the substratum and the overlying water column and are

important for a range of organisms, the most important of which include microalgae (benthic

microalgae and phytoplankton), invertebrates (benthic invertebrates and zooplankton), fish and

birds. Few macroalgae and no rooted plants such as mangroves occur in the area potentially

affected directly or indirectly by the development and are thus not considered in detail here.

Intertidal sand flats in the Port of Durban vary in their elevations, but most of the surface area lies at

heights of between 0 – 1m CDP (CSIR 2012b) (Figure 12). They consist of varying proportions of sand

and mud, with the mud content ranging from 5 to 50% (Figure 13) (Wright, 1996). The intertidal flats

of the Centre Bank, the Fish Wharf and Yacht Basin are largely dominated by sand (80-90%), with

medium and fine grain sands the dominant size class by weight (Wright, 1996; Newman et al. 2008).

The intertidal areas at Bayhead, adjacent to the mangroves, are, by contrast, comprised of

proportionally more mud with a sand fraction of 50-70%. Comparatively little shallow and medium

shallow subtidal areas of the bay remain and most of it has been dredged to -12.8 m (Figure 12). The

majority of these deep subtidal areas of the harbour consist of varying proportions of sand and mud

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too; however mud content is generally higher, ranging from 10 to 90%. Mud content is highest near

the head of the bay and lowest near the harbour mouth (Figure 13) (Wright, 1996).

Durban Harbour is considered to be highly transformed, with most of the natural habitat destroyed

as a result of dredging operations during the construction of the harbour (Allan et al. 1999). Very

little of the natural habitat remains, and it is estimated that only 14% of the original tidal flats

remain (Allan et al. 1999). These tidal flats have been dredged to depths of approximately 13 m

below sea-level, which is the operational depth of the Port (Weerts, 2010). The mangrove swamp

area has also been severely reduced. Durban Harbour had an extensive mangrove forest of

approximately 200 ha in extent, but 78% of this was physically removed in 1979 when construction

of the harbour began (Ward & Steinke, 1982). These habitats have been replaced with open water

areas and concrete Berths to allow for the safe passage and mooring of large vessels (Figure 14).

Figure 11. Aerial view of the Port of Durban during spring-low tide showing the intertidal sand flats and deeper (mostly)

dredged shipping channels covered by open water.

Currently, intertidal flats in the harbour constitute an area of 144.5 hectares, while the substratum

lying beneath the open waters is the dominant habitat covering an area of 714.6 ha (McInnes et al.

2005). This dominat habitat has been artificalliy created by dredging, and dredge scars are very

evident (Figure 15). The Centre Bank, an intertidal sand bank adjacent to the proposed development

is 83 ha in size and the largest of four sand flats in the port (eThekweni Municipallity 2008). The

Centre Bank is also the most isolated of the sand flats as most of it is situated within the middle of

the harbour and surrounded by water (Figure 11).

Recent physico-chemical data have been collected for the Port of Durban by Newman et al. (2008).

Bottom salinity levels of the harbour waters are homogenous at 35 ppt, despite the input of

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freshwater at the Bayhead. Bottom water temperatures show little spatial variation and typically

range from 19 to 22°C seasonally. Bottom dissolved oxygen levels are low and approximate 6 mg.L-1

for most of the central area of the harbour but are lower near the Bayhead.

Figure 12. Tidal bank elevations in the Port of Durban (from CSIR 2012b).

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Figure 13. Proportion of mud comprising the sediments of Durban Harbour (adapted from Wright 1996).

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Mangroves Tidal flats Open water Dry land/infilled areas

Figure 14. Durban Harbour showing how extensive areas of tidal flat and mangrove swamp that were present in the

1800s have been destroyed and dredged with very little remaining (Modified from Allan et al. 1999).

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Figure 15. Dredge-scour marks are obvious throughout the main shipping channels and the area adjacent to Pier 2

where Berths 203 to 205 are to be expanded (courtesy ZAA Engineering Projects & Naval Architects).

6.2 Overview of the biodiversity in the Port of Durban

Historical records show that the Port of Durban supported a high diversity of flora and fauna with a

mixture of both tropical and subtropical species. Day and Morgan (1956) were the first to conduct a

comprehensive inventory of the fauna present. They recorded a total of 563 species from various

habitats within the Port area. Forty years later, a similar survey was conducted by Hay et al. (1995),

although it did not consider fauna closely associated with the mangroves. This study found far fewer

species than Day and Morgan (1956), but highlighted the importance of the bay as a nursery area,

and the disappearance of juvenile penaeid prawns, habitat requirements for which were no longer

being met. Differences in the number of species from different taxonomic groups recorded in these

two surveys is presented in Table 2.

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Table 2. Total number of species, from 19 invertebrate and 1 vertebrate taxonomic group, found within Durban

Harbour. Column A includes species collected during the 1950 and 1952 biological survey (Day & Morgan

1956) and Column B. species collected during the 1991-1992 biological survey (Hay et al 1995).

Taxonomic group A. No. species collected in the 1950-

1952 surveys

B. No. species collected in the 1991-

1992 surveys

Hydrozoa 21

Zoantharia 1

Pennatulacea 1

Nemertea 1

Echiuroidea 1

Sipunculoidea 7

Oligochaeta 1

Polychaeta 75 21

Lamellibranchiata 5

Gatropoda 61 8

Scaphopoda 1

Bivalvia 36

Pycnogonida 1

Cirripedia 9

Copepoda 1

Cumacea 1

Amphipoda 15 4

Tanaidacea 1

Isopoda 12 1

Panaeidacea 2

Anomura 16 2

Macrura 20

Brachyura 66 4

Stomatopoda 2

Tectibranchs 8

Asteroidea 2

Ophiuroidea 3

Echinoidea 5

Holothuroidea 3

Tunicata 15

Pisces 186 39

Total No. species 563 95

Since this time, concern has been growing regarding the poor biological status and loss of estuarine

habitat in the KwaZulu-Natal region, brought on by sedimentation and increasing frequency of

mouth closure. The development of harbours at Richards Bay and Durban have in some way

mitigated this, and now support the largest areas of sheltered intertidal habitat in the province

(Cyrus & Forbes 1996).

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6.2.1 Overview of the macrofaunal community composition and relative abundance

within the Port of Durban

A total of at least 60 taxa (species) have been recorded in the soft-sediment habitats of the Port of

Durban in recent surveys undertaken by Pillay (2002), Angel & Clark (2008), Newman et al. (2008),

and Weerts (2010) (Table 3). Overall, diversity is highest among the Polychaetes with 27 taxa

recorded, followed by the Malacostraca with 18 taxa. Other important classes well represented

include the Gastropods and Bivalves.

In recent times, relatively more sampling has been conducted in sand-flat habitats than in the

deeper subtidal areas of the Bay, partly because the ecological role the sand banks play is recognised

as being disproportionately important. The benthic fauna in the deeply dredged channels is

reportedly depauparate, consisting of a few species of coelenterates, amphipods, isopods,

polychaetes, annelids and crabs (Hay 1993). Results show very low abundance (<50 individuals.m-2)

and low levels of diversity (<6 taxa.m-2) of invertebrates in these areas (Angel & Clark, unpublished

data). This is likely due to the periodic dredging operations required to maintain the ports operating

depth, disturbance caused by ship propellers and the anoxic conditions of the sediments that is a

characteristic of much of the deeper sediments in the harbour (Newman et al. 2008) (Figure 15).

Highest diversity and biomass of invertebrates is undoubtedly attained at the remaining intertidal

and shallow subtidal sand-flat habitats which are not dredged and are comparatively well

oxygenated. Newman et al. (2008) recorded an average of 10 to 12 taxa per square meter,

depending on which sand flat was investigated, while Pillay (2002) recorded 38 taxa at Little Lagoon

alone. Highest diversities appear to be found at this shallow subtidal flat adjacent to the intertidal

areas. Densities of organism at Little Lagoon were high, with a mean density of 2 888 ind.m-2

recorded by Newman et al. (2008), while Pillay (2002) recorded 3 226 individuals of Apseudes

digitalis per square metre and 578 inds.m-2 of Prionospio sexoculata. Average densities are also high

for the intertidal flats, with Centre Bank reportedly having an average density of 902 ind.m-2

(Newman et al. 2008). Furthermore, the intertidal sand flats are well recognised for their abundance

of Callianassid prawns (Callianasa kraussi) (Newman, 2008; Weerts, 2010). Macrofauna residing in

these sand flats ultimately support important assemblages of fishes and birds (Allan et al. 1999;

McInnes et al. 2005; Newman et al. 2008).

24

Table 3. Invertebrate taxa recorded in five different habitats in the Port of Durban (Pillay 2002; Angel & Clark 2008; Newman et al. 2008; Weerts, 2010).

Phylum Class Family Genus Species

Centre

Bank

sand

flats

Other

sand

flats

Little

Lagoon

Subtidal

area to be

dredged

Other

Annelida Polychaeta Capitellidae Notomastus latericeus

x

x x

Glyceridae Glycera alba

x

Nephtyidae Nephtys dibranchis

x x

Nereididae Dendronereis arborifera x x

Onuphidae Diopatra neapolitana capensis x x

Orbiniidae Orbinia bioreti x

Phyllodocidae Phyllodoce castanea

x

Nereididae Nereis caudata x

Nephtyidae Nephtys sphaerocirrata x

Spionidae Prionospio cirrifera x

Spionidae Prionospio sexoculata x x x

Spionidae Polydora sp.

x x

Sabellidae Oriopsis sp.

x

Sabellidae Desdemona ornata x x

Poecilochaetidae Poecilochaetus serpens x x

Capitellidae Capitella capitata x

Glyceridae Glycera convoluta

Cossuridae Cossura coasta

x x

Glyceridae Glycera natalensis x x

Cirratulidae Tharyx dorsobranchialis

x

Orbiniidae x

Orbiniidae Scoloplos johnstonei x x

Cirratulid x

Spionidae Scololepsis squamata

x

http://www.marinespecies.org/aphia.php?p=taxdetails&id=22496




25


Centre

Bank

sand

flats

Other

sand

flats

Little

Lagoon

Subtidal

area to be

dredged

Other

Annelida Polychaeta Nereididae Ceratonereis erythroensis

x

Sabellidae Megaloma Sp.

x

Eunicidae Marphysa depressa x

Annelida Clitellata Hirudinea sp. x

Mollusca Gastropoda Nassariidae Nassarius kraussianus x x x

Nassariidae Nassarius spp. x x

Terebridae Duplicaria capensis x x

Naticidae Natica qualteriana

x x

Naticidae Polinices tumidus

x x

Solenidae Solen cylindraceus x x x x

Acteocina fusiformis

x

Tellina prismatica x

Mollusca Bivalvia Veneridae Dosinia hepatica x x

Veneridae Eumarcia paupercula x x x

Mytilidae Brachidontes virgiliae x x

Cardiidae Fulvia papyracea

x

Arthropoda Malacostraca Alpheidae Betaeus jucundus x x x

Callianassidae Callianassa kraussi x x x

Goneplacidae Thaumastoplax spiralis

x x

Upogebiidae Upogebia capensis x

x x

Cirolanidae Cirolana c.f. fluviatilis x

x x

Anthuridae Haliophasma sp. x

Leptanthuridae Leptanthura laevigata x

Bodotriidae Iphinoe truncata x

Aoridae Grandiddierella sp. x






26


Centre

Bank

sand

flats

Other

sand

flats

Little

Lagoon

Subtidal

area to be

dredged

Other

Arthropoda Malacostraca Parapseudidae Apseudes digitalis

x x

Upogebiidae Upogebia africana x

Anthuridae Cyathura estuaria x

Cirolanidae Cirolana luciae x

Melitidae Melita zeylanica

x

Corophium triaenonyx

x

Aoridae Grandiddierella bonnieroides

x

Camptandriidae Paratylodiplax blephariskios x

Hymenosomatidae Hymenosoma orbiculare x

Arthropoda Branchiopoda Cladocera x x

Sipunculida x

All phyla All classes All families All genera All species 161 24 32 12 12

1. Note that while species richness (number of taxa) at the Centre bank appears lower than other intertidal sand flats in the port this is simply an artefact of the fact that Centre

Bank is considered in isolation here while all the other sand flat areas are lumped together as “Other sand flats”. Centre bank on its own has richer fauna than any other sand

flat site when these are considered in isolation.










27

6.2.2 Overview of the fish fauna in the Port of Durban

The fish fauna in the Port of Durban was considered very diverse in the 1950s when a total of 186

species were recorded by Day & Morgan (1956). The most-common fish species’ recorded during

this time were Terapon jarbua, Mugil cephalus, Lisa dumerilii, Ambassis gymnocephalus and

Leiognathus equula. Several of these species are estuarine dependent and the Bay was found to be a

valuable nursery ground for these fishes. The two most recent surveys have recorded 29 (Angel &

Clark 2008) and 34 species (Newman et al. 2008). They confirmed the findings of previous studies, in

that the majority of fishes in the Bay are estuary dependent (Day & Morgan, 1956; Cyrus & Forbes

1996, Forbes et al. 1996). Similar methods were used between surveys although the effort, timing

and specific localities differed somewhat.

Detailed information on catches was available for surveys undertaken by Angel & Clark (2008) who

collected a total of 696 fish in 19 gill and seine net samples. The most prolific species in terms of

abundance were the Ambassids (29.9%), mainly because of a high catch of bald Glassy Ambassis

gymnocephalus at one of the sites, Leiognathids (10.5%) comprising a sole representative the Slimy

Leiognathus equula, and Mugilids (5 species, 8.2%) consisting mainly of groovy mullet Liza dumerilii.

These three families comprised nearly half the community (48%). The majority of species caught

were similar to those recorded by Hay et al. (1995) and Day & Morgan (1956).

Table 4. Species of fish recorded by Agel & Clark (2008) with an indication of which were also recorded by Hay et al.

(1995) and Day & Morgan (1956).

Genus Species Hay et al. (1995) Day & Morgan (1956)

Ambassis gymnocephalus Y Y

Ambassis natalensis Y Y

Caranx sexfaciatus N Y

Chanos chanos N Y

Crenidens crenidens N Y

Diplodus sargus capensis N Y

Elops machnata Y Y

Favonigobius reichei N N

Gerres rappi Y N

Gerres acinaces Y Y

Gerres filamentosus Y Y

Lactoria cornuta Y Y

Leiognathus equula Y Y

Liza richardsonii N Y

Liza dumerilii Y Y

Liza macrolepsis Y Y

Phtheirichthys lineatus N N

Platycephalus indicus Y Y

Pomadasys commersonnii Y Y

Pomadasys maculatus N N

Pseudorhombus arsius Y Y

28

Genus Species Hay et al. (1995) Day & Morgan (1956)

Rhabdosargus sarba Y Y

Scomberoides lysan N Y

Sillago sihama Y Y

Sphyraena putnamiae N Y

Torquigener balteus N N

Tylosurus crocodilus Y Y

Valamugil buchanani Y Y

Valamugil robustus N Y

A study by Newman et al. (2008) a few months later focusing on the fish communities of the shallow

sand flats found similar results. Three species of Ambassidae (glassies) made up most of the

community (83%), followed by Mugilidae (mullets, six species, 7%) and Gerreidae (pursemouths,

three species, 5%). These three families comprised 95% of the fishes.

Species not necessarily recorded by these two studies but which have been recorded just outside of

Durban Harbour in similar habitat, and are likely to inhabit areas affected by the proposed

development are included in Table 5.

Table 5. Soft bottom demersal fish species recorded in beach seine net catches off Durban Bay (adapted from Beckley

and Fennessey, 1996)

Teleosts Common name

Argyrosomus japonicus Dusky kob

Argyrosomus thorpeii Squaretail kob

Cociella sp. Spotfin flathead

Cynoglossus lida Roughscale tongue sole

Johnius dussumieri Mini-kob

Lithognathus mormyrus Sand steenbras

Otolithes ruber Snapper kob

Paralichthodes algoensis Measels flounder

Paraplagusia bilineata Fringelip tonguefish

Parupeneus macronema Band-dot goatfish

Parupeneus rubescens Blacksaddle goat fish

Platycephalus indicus Bartail flathead

Plotosus lineatus Striped eel catfish

Pomadasys commersonnii Spotted grunter

Pomadasys kaakan Javelin grunter

Pomadasys maculatum Saddle grunter

Pomadasys olivaceum Olive grunter

Pseudorhombus elevatus Ringed flounder

Saurida undosquamis Largescale lizzardfish

Sillago sihama Silver sillago

Umbrina robinsoni Slender bardman

29

Elasmobranchs

Aetobatus narinari Spotted eagleray

Dasyatis chrysonota Blue stingray

Dasyatis kuhlii Blue spotted sting ray

Gymnura natalensis Butterfly ray

Himantura gerrardi Sharpnose stingray

Rhinobatos annulatus Lesser guitarfish

Rhinobatos leucospilus Greyspot guitarfish

Rhyncobatos djiddensis Giant guitarfish

Torpedo sinuspersici Marbled electric ray

6.3 Centre Bank habitat and biodiversity

The Centre Bank is a large intertidal and subtidal sand flat, with an intertidal area of approximately

83 hectares. The subtidal section forms the slopes of the sand flat which are steep and fall away

quickly to the Port operational depth of -12.8 m (Weerts 2010) (Figure 16). The intertidal area is

comprised of material with a median grain size of approximately 0.25 mm (Newman et al. 2008). The

majority (≈ 90%) of this material is therefore fine to medium sands, with only 3% comprising of mud

(Newman et al. 2008). Sorting coefficients average 0.4 and range from 0.21 to 0.65 depending on the

area of the bank (Newman et al. 2008). Total organic content is relatively low compared to other

sand banks in the harbour and ranges from 0 to 0.5% (Newman et al. 2008). Salinity levels

correspond with that of seawater (35 ppt) and turbidity levels are very low, generally between 2 and

5 NTU (Newman et al. 2008). Dissolved oxygen levels are close to saturation at 5-6 mg.l-1.

The Centre Bank is one of the least polluted areas in the Port, and presents the most favourable

conditions for growth of benthic microalgae (diatoms) (MER/ERM 2011). Sediment-core samples

have shown that there is a greater diversity of species here compared to the other banks in the Port,

probably because of the more favourable water quality here (MER/ERM, 2011). The abundance of

diatoms supports a suite of microorganisms that in turn, support many species of macrofauna and

juveniles fishes (MER/ERM 2011). Shallow areas and in particular sand banks are known to be

extremely important nursery areas for juvenile fishes (Blaber 1974; Cyrus & Forbes 1996; Weerts &

Cyrus 2002). The Centre Bank therefore plays an extremely important role in providing suitable

habitat for young fish.

The most diverse group of macrofauna at the Centre Bank appears to be the Polychaetes, followed

by Malacostracans (Table 3). The sand bank is particularly prevalent with high densities of sand

prawn Callianasa kraussi, higher than for most of the other sand banks in the Port (Newman et al.

2008). These crustaceans play a crucial role as bioturbators by increasing the sediment-water

interface, thereby facilitating particle exchange between the sediment and water column. They are

also a very important food source for fish.

Most abundant fish species in the waters surrounding the Centre Bank are Ambassis gymnocephalus,

A. natalensis, Diplodus sargus capensis, Sillago sihama and Liza dumerilii (Angel & Clark, 2007;

Newman et al. 2008). Other species recorded on Centre Bank include Amblyrhynchotes honckenii,

Crenidens crenidens, Favonigobius reichei, Gerres acinaces, G. acinaces, G. filamentosus, G.methueni,

G. Rappi, Platycephalus indicus, Pomadasys commersonnii, Sphyraena barracuda, Favonigobius

30

reichei, L. richardsonii, Valamugil buchanani, Crenidens crenidens, Platycephalus indicus, Lactoria

cornuta and a yet to be described species of Torquigener.

Figure 16. Tidal bank elevation categories relative to the footprint of Option 3F (from CSIR 2012b).

6.4 Dredge channel habitat and biodiversity

Most of the shipping channels in the Port of Durban have been dredged to a depth of approximately

– 12.8 m. For the purposes of this report characteristics of only the dredge channels in the area

proposed for dredging will be described. Most of the area to be dredged for this project is comprised

of sandy sediment, while mud typically dominates those areas adjacent to the southern side of

Centre Bank and across the channel to the eastern side of Pier No 2 (CSIR, 2012a) (Figure 17). There

is considerable evidence, however, that suggests that these habitats were historically more muddy

than they are today (MER/ERM, 2011). Total organic content of these sediments is strongly

correlated with the proportion of mud, and ranges from 0.4 to 2.6 % (CSIR, 2012a) (Figure 18). It is

31

generally higher than on the Centre Bank. Salinity levels approximate those of seawater (35 ppt) and

bottom turbidity levels are low, generally between 6 and 14 NTU (Newman et al. 2008). Dissolved

oxygen levels are close to saturation at 5-6 mg.l-1 (Newman et al. 2008).

Benthic primary productivity is likely to be relatively low compared with the Centre Bank due to the

attenuation of light by the overlying water column. As a consequence, benthic diatom biomass is

low. The most abundant macrofauna found in the dredge channels are Polychaetes especially

Notomastus latericeus, Orbinia bioreti and Nephtys dibranchis followed by Gastropods particularly

the tick shells Nassarius kraussianus, Duplicaria capensis and Natica qualteriana (Angel & Clark,

2007). A number of species of Decapod are also present including the mud prawn Upogebia

capensis, Thaumastoplax spiralis and Cirolana fluviatilis (Angel & Clark 2007).

The ichthyofaunal community in the dredge channels comprises various species of Mugillids

(Mullets), especially Valamugil buchanani, Liza macrolepsis and L. richardsonii. Other common

species include pursemouths Gerres rappi and G. Acinaces, saddle grunter Pomadasys maculatum,

bartail flathead Platycephalus indicus and two Sparids including Crenidens crenidens and Diplodus

sargus capensis (Angel & Clark, 2007). Species that are more prevalent in the upper reaches of the

water column include the Carangids like needlescaled queenfish Scomberoides lysan and Caranx

sexfasciatus, and other piscivores such as the sawtooth barracuda Sphyraena putnamiae (Angel &

Clark 2007).

32

Figure 17. Spatial distribution of sands and mud in the proposed dredge area (Source: CSIR 2012a).

33

Figure 18. Distribution of the total organic material contained within surface sediments (Source: CSIR 2012a).

6.5 Little Lagoon habitat and biodiversity

The Little Lagoon area comprises predominantly intertidal habitat, but incorporates an important

shallow subtidal area of 19 200 m2 that reaches depths of -1.6 m during spring low tide (Forbes &

Demetriades 2003) (see Figure 16). It is located on the southern end of the Centre Bank sand flat.

The deeper areas of Little Lagoon comprise relatively fine sediments with median particle sizes of 0.1

mm (very fine grained sand according to the Wentworth Scale), while shallower areas that more

exposed to wave action have slightly coarser median grain sizes of 0.2 - 0.3 mm (medium grained

sand) (Forbes & Demetriades 2003). The sediments in this area were found to have relatively high

proportions of organic matter ranging from 2.0 to 6.9 % organic content with an overall mean of

3.4% (Forbes & Demetriades 2003). This is significantly higher than that at intertidal areas of Centre

Bank and the subtidal dredge channels. Water temperatures are typical of shallow parts of

subtropical estuaries and ranged between 18 and 29°C depending on the season (Forbes &

Demetriades 2003). Salinity levels generally correspond to that of sea water (35 ppt) although during

34

high periods of rainfall values as low as 21 ppt have been recorded (Forbes & Demetriades, 2003).

Water clarity is generally considered to be clear with average values of 28 and 14 NTU for summer

and winter respectively. However, values as high as 100 NTU have been recorded for short periods

during windy and turbulent conditions (Forbes & Demetriades 2003). Dissolved oxygen levels are

high (6.9 – 7.7 mg.l-1) (Forbes & Demetriades 2003).

Phytoplankton densities are considered to be low as chlorophyll a values of only 0.06 – 1.3 µg.L-1

were recorded by Forbes & Demetriades (2003) over the course of a two year period. Zooplankton

present in Little Lagoon have been also studied by Forbes & Demetriades (2003), and are numerically

dominated by Copepods, especially Paracalanus crassirostris (Table 6). Other important components

of the zooplankton were larvae of caridean crustaceans.

Table 6. Zooplankton community composition of Little Lagoon recorded by Forbes & Demetriades (2003). Numbers are

average densities per m3 based on 23 replicate samples.

Taxon 2001 2002

Mar June Sept Dec Mar Aug Oct Dec

CNIDARIA

Hydrozoa medusae <1 <1

Calycophora 2 2

CTENOPHORA 1 <1 2

CHAETOGNATHA 5 1

CRUSTACEA

Copepoda 1003 721 595 1185 121 863 425 3300

Ostracoda 2

Cumacea <1 <1

Mysidacea

Mesopodopsis sp. <1 7 1 1 0 1 1 2

Stomatopoda (larvae)

Penaeoidea

Lucifer sp. 1 1

Caridae (larvae) 18 33 33 28 1 7 1

Brachyura

Zoea-type larvae 2 14 20 2 1 3 31 5

Megalopa larvae 1

CHELICERATA

Pycnogonida <1

MOLLUSCA

Bivalvia

Bivalve spat 86 8

CHORDATA

Larvacea 1 6 3 4 4

In terms of benthic macrofauna, intertidal areas are dominated by the sand prawn Callianassa

kraussi and the soldier crab Dotilla fenestrate . In addition to these, shallow subtidal areas are

generally more diverse and a total of 37 taxa have been found in these parts by Forbes &

Demetriades (2003). The community here is dominated numerically by polychaete worms especially

Glycera longipinnis and Prionospio sexoculata, followed by isopods particularly Leptanthura

35

laevigata, Cumaceans and the Molluscs Nassarius kraussianus, Dosinia hepatica and Eumercia

paupercula (see Pillay 2002) (Table 7). Densities of organisms were found to lie between 500 and 2

000 animals per m2, although densities of greater than 10 000 animals per m2 were recorded at some

areas during certain times of the year (Forbes & Demetriades 2003).

At least 36 species of fishes occur in Little Lagoon. The most abundant component (>80%) being the

Glassy Ambassis dussumieri (Table 8) (Forbes & Demetriades 2003). Other species that are notable

here yet occur at considerably lower numbers (<5%), are Glassnose Thryssa vitrirostris, the pouters

Gerres filamentous and G. Acinaces, slimy Leiognathus equulus, groovy mullet Liza dumerilii and the

smelt Sillago sihama. The majority of these species were found to be estuary-dependent and it is

well recognised that Little Lagoon provides extremely valuable nursery habitat for many juvenile

fishes (Cyrus & Forbes 1996; Forbes & Demetriades 2003).

36

Table 7. Average densities (individuals/m2) of macrofauna sampled at various sites (A1-C4) at Little Lagoon. Values are

based on means of three site and six seasonal replicates (after Pillay, 2002).

A1 A2 A3 A4 B1 B2 B3 B4 C1 C2 C3 C4

Polychaeta

Cirratulidae

Unidentified Cirratulid polychaetes 1 1280 173 53 17 85 145 199 0 112 474 28

Phyllodicidae

Phyllodoce castanea 0 7 1 2 1 0 0 4 0 5 1 0

Cossuridae

Cossura coasta 0 228 2 0 2 73 5 0 0 406 39 0

Orbiniidae

Scoloplos johnstonei 2 0 2 2 0 2 0 0 12 3 4 2

Spionidae

Prionospio sexoculata 343 578 356 374 272 304 487 613 229 409 411 330

Polydora sp. 0 0 0 0 0 2 1 0 1 0 0 0

Scololepis squamata 2 7 0 0 0 4 0 0 0 0 0 0

Nereidae

Ceratonereis erythroensis 0 0 0 3 0 5 0 3 0 0 0 0

Dendronereis arborifera 6 5 7 42 3 0 22 64 0 1 0 10

Glyceridae

Glycera sp. 66 44 63 41 70 41 56 82 53 42 61 104

Capitellidae

Unidentified capitellid polychaetes 73 17 2 1 5 3 0 2 16 28 10 0

Sabellidae

Megalomma sp. 0 2 0 0 0 0 0 0 0 0 0 0

Desdemona ornate 44 10 169 505 4 6 137 52 2 25 24 22

Maldanidae

Unidentified Maldanid polychaetes 0 0 1 2 0 0 0 0 0 0 0 0

Eunicidae

Marphysa depressa 0 1 0 0 0 0 0 0 0 0 0 0

Crustacea

Anomura

Upogebia africana 1 0 0 0 0 0 0 0 0 0 1

Callianassa kraussi 36 0 0 5 31 46 0 8 16 5 61 22

Macrura

Betaeus jucundus 0 0 0 0 0 0 0 0 0 0 1 0

Isopoda

Cyathura estuaria 2 1 0 0 0 0 0 0 0 0 0 0

Cirolana luciae 10 0 0 0 6 5 0 0 0 36 2 1

Leptanthura laevigata 74 92 81 375 96 137 140 304 118 60 114 150

Amphipoda

Melita zeylanica 2 0 0 2 0 0 0 1 0 0 0 0

Corophium triaenonyx 0 19 10 0 0 0 1 0 0 0 1 1

Grandidierella bonnieroides 5 2 20 13 3 2 0 7 5 0 5 20

Cumacea

Cumacea 152 28 100 264 126 35 87 170 155 9 106 151

Brachyura

Thaumastoplax spiralis 2 1 0 0 1 3 0 0 2 2 0 2

Paratylodiplax blephariskios 0 24 0 0 0 38 0 0 0 14 0 1

Hymenosoma orbiculare 1 0 0 0 0 0 0 0 0 0 0 0

Tanaidacea

Apseudes digitalis 0 3226 510 301 1 40 1037 13 0 5 124 3

Mollusca

Gastropoda

Nassarius kraussianus 2 58 103 25 2 49 84 57 2 53 24 32

Acteocina fusiformis 0 10 6 5 0 38 10 25 0 3 0 9

37

A1 A2 A3 A4 B1 B2 B3 B4 C1 C2 C3 C4 Bivalvia

Eumarcia paupercula 12 20 55 13 10 14 54 53 6 10 9 24

Solen cylindraceus 0 4 1 2 1 2 5 2 0 1 0 0

Dosinia hepatica 13 26 77 33 22 46 67 37 10 15 22 23

Brachidontes virgiliae 0 35 24 0 0 0 22 11 1 0 0 2

Fulvia papyracea 0 0 2 0 0 1 0 0 0 0 2 0

Tellina prismatica 0 22 9 1 1 14 3 2 0 25 4 0

Sipunculida 2 0 0 0 0 0 0 0 0 0 0 0

Number of species 22 26 23 22 20 25 18 21 15 22 21 21

38

Table 8. Numbers of fish caught in seine and gill nets in the Little Lagoon based on 18 replicates from March 2001 to December

2002. EDC = Estuarine Dependence Category (after Whitfield 1998).

Family

Species

2001 2002

EDC Mar Jun Sep Dec Mar Jul Sep Dec

Ambassidae Ambassis dussumieri Ib 2844 1467 1213 61 7279 425 645 3

Ambassis natalensis Ib 2 5 2 17 2 0 2

Belonidae Strongylura sleiurus III 1

Bothidae Pseudorhombus arsius III 1 3 3

Carangidae Caranx sexfasciatus IIb 7 1 3 1

Caranx juvenile IIb 1 4

Lichia amia IIa 1

Scomberoides tol III 8 7 1 4 15 1 4

Clupeidae Hilsa kelee IIc 4

Engraulidae Thryssa vitrirostris IIa 1 28 2 256 7

Gerreidae Gerres acinaces IIb 4 1 14 30 12 125 2 6

Gerres filamentosus IIb 57 130 54 52 15 2 8 17

Gerres juvenile IIb 1 7 23 1 12

Gerres roppi IIb 1 1

Gobiidae Glossogobius callidus 1

Glossogobius giuris Ib 2 4 1 18 3

Oxyurichtyhs ophthalmonema ? 10 4 3

Haemulidae Pomadasys comersonnii IIa 1 2 7 1 5 5 7

Pomadasys olivaceum 1

Leiognathidae Leiognathus equulus IIc 9 72 8 70 41 13 23 0

Mugilidae Liza alata ? 24

Liza dumerilii IIb 19 19 25 6 11 75 3 14

Liza macrolepsis IIa 2 26 6

Mugil cephalus 2

Myxus capensis IIa 1

Valamugil buchanani IIa 2 2 3 1 1

Valamugil cunnesius IIa 8

Mullet juveniles <40mm 4 3 1 3 1 1

Lutjanidae Lutjanus russelli IIc? 1

Lactoria cornuta III 1 1

Platycephalidae Platycephalus indicus IIc 7 6 3 2 1 2 2 2

Sillaginidae Sillago sihama IIc 82 17 43 23 409 3 8 5

Sparidae Crenidens crenidens III 1 3 1

Rhabdosargus sarba IIa 2 4 1

Rhabdosargus holubi IIa 17 11 6 1 1 2

Sphyraenidae Sphyraena jello IIc? 1 2 5

Tetraopdontidae Amblyrhynchotes honckenii III 4 4 9 4 2 2 2 0

Total species 19 25 17 23 18 17 17 13

Total individuals 3070 1827 1399 348 7820 919 720 73

39

7 Potential for RAMSAR Site designation

The draft Bay of Natal Estuarine Management Plan alludes to the possibility of establishing a Ramsar site in the Bay.

The original criteria for Ramsar site designation have been revised by the 7th (1999) and 9th (2005) Meetings of the

Conference of the Contracting Parties, superseding earlier criteria adopted by the 4th and 6th Meetings of the COP

(1990 and 1996), to guide implementation of Article 2.1 on designation of Ramsar sites. The following table details

each of these criteria and provides a basic assessment on whether Durban Bay meets any of these criteria (Table 9).

Table 9. Criteria for Ramsar site designation and an assessment of whether Durban Bay meets any of these criteria

Group Criteria Does it meet the criterion?

Comment

A: Sites containing representative, rare or unique wetland types

Criterion 1. A wetland should be considered internationally important if it contains a representative, rare or unique example of a natural or near natural wetland type found within the appropriate biogeographic region

Yes Durban Bay contains mangrove swamp habitat. Only 4 300 ha of mangroves remain in South Africa (van Niekerk & Turpie 2012). In addition. Durban Bay contains sand and mud banks, of which only 4 000 ha remain in South Africa (van Niekerk & Turpie 2012).

B: Site of international importance for conserving biological diversity –Criteria based on species and ecological communities

Criterion 2. A wetland should be considered internationally important if it supports vulnerable, endangered, or critically endangered species or threatened ecological communities

Likely A number of estuary-associated fish species in South Africa have been evaluated for inclusion on the IUCN Red List. Once given attention, it is likely that these and others will find their way on to the IUCN Red List (van Niekerk & Turpie 2012). In addition, it is likely that Durban Bay is used as nursery area for IUCN Critically Endangered sawfish Pristis microdon, P. pectinata and P. zijsron (van der Elst 1993).

Criterion 3. A wetland should be considered internationally important if it supports populations of plant and/or animal species important for maintaining the biological diversity of a particular biogeographic region.

Yes Durban Bay supports an important population of rare mangroves. The Bay is recognised as an important nursery area for many estuary dependent fishes and supports at least 71 estuary associated fishes caught in South African fisheries (van Niekerk & Turpie 2012). It is also listed as a national priority estuary for biodiversity conservation according to the National Biodiversity Assessments Estuary Component (van Niekerk & Turpie 2012).

Criterion 4. A wetland should be considered internationally important if it supports plant and/or animal species at a critical stage in their life cycles, or provides refuge during adverse conditions.

Yes 28 species of fish occur in the bioregion that have critical life stages totally dependent on estuaries (Whitfield estuarine dependence categories Ia & IIa) and are known to occur or are likely to occur in Durban Bay (Whitefield 1998).

B: Site of international importance for conserving biological diversity – Specific criteria based on waterbirds

Criterion 5. A wetland should be considered internationally important if it regularly supports 20,000 or more waterbirds

No

Criterion 6. A wetland should be considered internationally important if it regularly supports 1% of the

Unlikely, but possibly for Kelp and Grey-

Allan D. pers. comm. Also see Allan et al. 1999 & 2002; McInnes et al. 2005.

40

Group Criteria Does it meet the criterion?

Comment

individuals in a population of one species or subspecies of waterbird.

headed gulls and possibly Swift Tern.

B: Site of international importance for conserving biological diversity – Specific criteria based on fish

Criterion 7. A wetland should be considered internationally important if it supports a significant proportion of indigenous fish subspecies, species or families, life-history stages, species interactions and/or populations that are representative of wetland benefits and/or values and thereby contributes to global biological diversity.

Yes Durban Bay is recognised as an important nursery area for many estuary dependent fishes and supports at least 71 estuary associated fishes caught in South African fisheries (van Niekerk & Turpie 2012).

Criterion 8. A wetland should be considered internationally important if it is an important source of food for fishes, spawning ground, nursery and/or migration path on which fish stocks, either within the wetland or elsewhere, depend.

Yes The National Biodiversity Assessment 2011: Estuarine Component (Van Niekerk & Turpie 2011) lists Durban Bay as a very important nursery estuary for general biodiversity and for sub-adult kob species and possible for pupping of the Zambezi Shark currently listed as Near Threatened by the IUCN Red List (also see Cyrus & Forbes 1996; Forbes et al 1996). It may also be used as nursery areas for IUCN Critically Endangered sawfish Pristis microdon, P. pectinata and P. zijsron (van der Elst 1993).

B: Site of international importance for conserving biological diversity – Specific criteria based on other taxa

Criterion 9. A wetland should be considered internationally important if it regularly supports 1% of the individuals in a population of one species or subspecies of wetland-dependent non-avian animal species.

No

This analysis shows that there are a number of Ramsar site criteria which Durban Bay is likely to meet. These are

specific to the Bays invertebrate and fish biodiversity, particularly the diversity of estuary-dependent fishes it

supports, the significant nursery function it provides, rare habitat types that support these species and that Durban

Bay is likely to contribute rare habitat for IUCN Red Listed fishes, such as sawfishes and suitable sanctuaries for

pupping of Zambezi Shark.

8 Potential habitat transformation as a result of the proposed development

Sections of all broad macrofaunal and ichthyofaunal habitats recognised in the harbour will be negatively affected by

the proposed development. Portions of the existing intertidal sand flats and shallow, medium and deep subtidal

areas will be completely destroyed by the dredging required for the expansion of the Berths for all options (3A to

3G). Spatial analyses by the CSIR (CSIR 2012b) show the loss and gains associated with each development option for

estuarine habitat in various depth categories relative to CDP (high intertidal = >1m; low intertidal = 0 to 1m; shallow

subtidal = -1 to 0m; medium subtidal = -3 to -1m & deep subtidal = -12 to -3m) for the Central Bay tidal banks and

those at Little Lagoon adjacent to the Centre Bank. Development Option 3C results in the loss of a significant amount

of high value intertidal, shallow subtidal, medium subtidal and deep subtidal habitat at the Centre Bank; and the loss

of intertidal habitat but a gain in shallow subtidal habitat at Little Lagoon tidal banks (Table 10). In an effort to

41

mitigate these losses, a series of iterative development proposal was explored. Option 3D, the next in the sequence

entails infilling of a certain amount of the existing shipping channel to create artificial sand bank habitat, but this too

results in the loss of a significant amount of intertidal and medium subtidal habitat (Table 11). Option 3E entails

reshaping and reducing the extent of the proposed dredge footprint, such that there is no nett loss of habitat at

Little Lagoon tidal banks, but does, however, result in the loss of significant amounts of medium subtidal and

intertidal habitat at Centre Bank. Option 3F, was then designed to mitigate the loss of medium subtidal habitat and

intertidal habitat by significantly increasing the nett gain of shallow subtidal and intertidal habitat at Centre Bank.

The final option, Option 3G, further enhances Option 3F by increasing the nett gain in intertidal (by 2.12%) and

shallow subtidal habitat (by 30.4% or 4 ha) such that the overall foot print of the development will incorporate a net

gain of 0.04%.

Table 10. Projected changes in tidal habitats for development Option 3C.

Central Bay Tidal Banks

Pre-development

area (m2)

Development footprint area

(m2)

Long-term stable state

area (m2)

Development footprint

change (%)

Long-term stable state change (%)

High Intertidal 48710 31143 30582 -36.1 -37.2

Low Intertidal 1063327 1023682 1008390 -3.7 -5.2

Shallow Subtidal 80752 75484 91332 -6.5 13.1

Medium Subtidal 78222 71931 71941 -8.0 -8.0

Deep Subtidal 394657 357247 357247 -9.5 -9.5

Total 1665669 1559485 1559492 -6.4 -6.4

Little Lagoon Tidal Banks

Pre-development

area (m2)


(m2)


area (m2)


change (%)


High Intertidal 12895 11065 11063 -14.2 -14.2

Low Intertidal 139436 141240 138010 1.3 -1.0

Shallow Subtidal 51360 51376 54611 0.0 6.3

Medium Subtidal 6406 6413 6413 0.1 0.1

Deep Subtidal 17865 17865 17865 0.0 0.0

Total 227962 227960 227963 0.0 0.0

Table 11. Projected changes in tidal habitats for development Option 3D.


Pre-development

area (m2)


(m2)


area (m2)


change (%)


High Intertidal 48710 31054 30568 -36.2 -37.2

Low Intertidal 1063327 1056349 1040938 -0.7 -2.1


Medium Subtidal 78222 69178 69240 -11.6 -11.5

Deep Subtidal 394657 343460 343598 -13.0 -12.9

Total 1665669 1588611 1588753 -4.6 -4.6


Pre-development

area (m2)


(m2)


area (m2)


change (%)


42

High Intertidal 12895 11154 11063 -13.5 -14.2

Low Intertidal 139436 141174 138010 1.2 -1.0


Medium Subtidal 6406 6406 6413 0.0 0.1

Deep Subtidal 17865 17865 17865 0.0 0.0

Total 227962 227959 227963 0.0 0.0

Table 12. Projected changes in tidal habitats for development Option 3E. Nd means no data.


Pre-development

area (m2)


(m2)


area (m2)


change (%)


High Intertidal 12895 11154 Nd -33.9 Nd

Low Intertidal 1063327 1068521 Nd 0.5 Nd

Shallow Subtidal 80752 88696 Nd 9.8 Nd

Medium Subtidal 78222 69199 Nd -11.5 Nd

Deep Subtidal 394657 343523 Nd -13 Nd

Total 1665669 1602153 Nd -3.8 Nd


Pre-development

area (m2)


(m2)


area (m2)


change (%)


High Intertidal 12895 11154 Nd 13.5 Nd



Medium Subtidal 6406 6413 Nd 0.1 Nd

Deep Subtidal 17865 17865 Nd 0.0 Nd

Total 227962 227959 Nd 0.0 Nd

Table 13. Projected changes in tidal habitats for development Option 3F. Nd means no data.


Pre-development

area (m2)


(m2)


area (m2)


change (%)






Deep Subtidal 394657 336274 Nd -14.8 Nd

Total 1665669 1663621 Nd -0.1 Nd


Pre-development

area (m2)


(m2)


area (m2)


change (%)


High Intertidal 12895 11154 Nd 13.5 Nd





43

Total 227962 227985 Nd 0.0 Nd

Table 14. Projected changes in tidal habitats for development Option 3G. Nd means no data.


Pre-development

area (m2)


(m2)


area (m2)


change (%)






Deep Subtidal 394657 336274 Nd -14.8 Nd

Total 1665669 1666292 Nd 0.04 Nd


Pre-development

area (m2)


(m2)


area (m2)


change (%)







Total 227962 227985 Nd 0.0 Nd

A relatively large area of deep subtidal habitat will also be transformed. Deep subtidal habitat at a depth of mainly -

12.8 m and covering an area of approximately 130 hectares will be dredged to a depth of -16.5 m (Nemai Consulting

2012). A relatively small portion (2%) of this dredged area, between 2 to 3 ha (depending on which Quay Wall option

is selected), will be further transformed by the deposition of rock for scour protection (Nemai Consulting 2012). This

rock will form a layer approximately 0.5 m deep on the dredged harbour bottom. The area of subtidal habitat so

affected makes up approximately 19% of this habitat type in the harbour. More serious is the loss of intertidal and

shallow subtidal sand-flat habitat due to the dredging that is proposed as a result of enlarging the Berths (see Table

10 to Table 14). This assumes that the outputs from the stable state models of Weerts et al. (2012b) will prevail and

that no more of the sand flat will be lost via erosion after construction. We have reviewed the modelling work

conducted for this study and are indeed confident that this is the case

Also of concern is the loss of shallow subtidal habitat situated on the western, eastern and southern sides of Centre

Bank as a result of the placing of concrete-filled stabilising mattresses on these slopes to act as scour protection. This

habitat is different from the deeper subtidal areas that will be dredged and more important to invertebrates and

fishes, especially juvenile fishes. The placement of mattresses is a measure to ensure that the Centre Bank is not lost

as dredging operations will take place adjacent to the toe of the Centre Bank and there is concern that this may

cause the banks to slump and erode.

Furthermore, concern has been raised that the Bayhead mangroves may be impacted negatively by the proposed

development and operation of the Berths. No impact on the estuarine biodiversity of the mangroves, either direct or

indirect, is expected to occur with a high degree of confidence. A similar conclusion was reached by the CSIR

emanating from their study on long term impacts of the proposed development (CSIR 2012b). The mangroves are

44

sufficiently far away (≈1 km) from the development footprint that they will not be disturbed during the construction

and operational phases.

Figure 19. The Port of Durban showing where dredging is proposed relative to subtidal and intertidal habitats.

45

9 Impact on microalgae, macrofaunal and ichthyofaunal communities

Several perceived impacts have been identified as a result of the expansion of Berth 203-205, associated dredging

activities, scour protection (rocky) and stabilising mattresses. These include:

Loss and disturbance of intertidal habitat and associated benthic microalgae, macrofauna and ichthyofaunal

communities at the Centre Bank caused by dredging activities;

Loss and disturbance of subtidal habitat and associated benthic microalgae, macrofauna and ichthyofaunal

communities as a result of dredging activities, construction of the quay walls, and the installation and

permanent placement of stabilising mattresses on the western, southern and eastern slopes of Centre Bank;

Transformation of subtidal soft sediment habitat adjacent to quay walls to rocky scour protection (i.e large

rocks 50cm in height packed close together)

Loss and disturbance of water column habitat and associated phytoplankton, zooplankton and ichthyofaunal

communities as a result of dredging operations, quay wall construction and the quay walls themselves.

Suspension of fine sediment and increased turbidity at and adjacent to the dredge sites impacting on

primary production, and filter-feeding organisms on the substrate and in the water column in and adjacent

to the dredge area;

Sediment deposition around the dredging site (largely fine sediment rejected from screening and from

hopper overfill);

Resuspension of potentially toxic trace metals and hydrocarbons in dredge sediments from the harbour and

their effects on macrofauna and fish communities in the vicinity of the dredge foot print.

Each of the impacts mentioned above is likely to affect biota associated with the Port of Durban in different ways

and at varying intensities depending on the nature of the affected habitat and the sensitivity of the associated biota.

9.1 Site-specific considerations in the assessment of potential impacts on the

biodiversity of the Port of Durban

Intertidal-sand-flat habitat in the Port of Durban has been reduced to 14% of its original extent (Allan et al. 1999)

and much of it transformed into deeper subtidal areas for shipping. The intertidal sand flats in the Port of Durban

have been recognised as extremely important to the ecological functioning of the Port of Durban (Newman et al.

2008; Weerts 2010). These areas are considered the most important habitats in the Port in need of conservation

(Allan et al. 2005), and have accordingly been zoned for conservation by the Bay of Natal Estuary Management Plan

(ERM/MER 2012). Furthermore, Durban Bay has been included in a subset of estuaries identified in the estuary

component of the South African National Biodiversity Assessment as requiring partial protection in order to provide

for the conservation of estuarine biodiversity in South Africa (Van Niekerk & Turpie 2012). Large populations of sand

prawns are found on these banks, and such large population are not found anywhere else in KwaZulu-Natal, except

possibly in the Kosi estuarine system (Weerts 2010). In addition, the banks represent very important habitat for

juvenile fishes (Day & Morgan 1956; Cyrus & Forbes 1996; Forbes et al. 1996).

McInnes et al. (2005) have stated that based on a four-year study of the avifauna of the Port of Durban, their results

“suggest that potentially half the waterbird population of Durban Harbour could be negatively impacted as a result

of any modification of this area.” This is because the intertidal sand banks play a critical role in providing food in the

form of invertebrates (macrofauna) to many of the bird species. Furthermore, there is a high abundance of juvenile

fish within the Bay, a large proportion of which feed specifically on intertidal invertebrates (Cyrus & Forbes 1996;

Forbes et al. 1996). If the invertebrate-prey is reduced by the reduction of intertidal habitat then this will result in a

decrease in the abundance of juvenile fish which will have a negative effect on piscivorous birds, as densities of this

trophic guild of waterbirds have been correlated with densities of fish (Siegfried 1981; Hockey & Turpie 1999). Many

46

of the other species of birds, particularly Palaearctic waders are dependent on the Centre Banks for food and are

protected by the Bonn Convention on the Conservation of Migratory Species which South Africa is signatory too

(Bonn 2012).

Although the proposed development (Option 3C) will reduce the existing tidal banks by only 10 ha before mitigation

(with Option 3G) (CSIR, 2012b), the cumulative impact becomes an issue because so much of the original habitat has

already been lost. Intertidal sand flats, the dominant component of the Centre Bank, are considered to be scarce on

the east coast of South Africa and Durban Bay makes an important contribution to this habitat type in the region

(CSIR 2012b). Conservation targets for many habitat types have been set at 20%, this includes estuarine habitats (van

Niekerk & Turpie 2012) and many marine habitat types (see review by Porter et al. 2011). The further dredging and

destruction of this habitat to allow for the westerly expansion of Berth 205 is likely to result in less than 20% of this

habitat type remaining in central KwaZulu-Natal and possibly KwaZulu-Natal as a whole, and will decrease the

amount in Durban Bay to a mere ≈10% of its original extent.

This is of major concern because Durban Bay could well be at a tipping point where extinction probabilities

significantly and sharply increase when less than 20-25% of a particular habitat remains (Lamberson et al. 1993,

Fahrig 1997, Travis 2003). In essence, a disproportionately high number of species are lost when habitats are

reduced by this extent (Radford et al. 2005). If this habitat is already compromised (e.g. pollution, fragmentation,

climate change), then the risk of extinctions are even higher (Fahrig 1997, Fahrig 2002, Travis 2003). Extinctions in

Durban Bay have already occurred (Obeng 2010).

An important objective of the draft Bay of Natal Estuarine Management Plan (ERM/MER 2012) is to protect and

enhance estuarine habitats that are characteristic of the original Bay; and to explore opportunities for

rehabilitating/improving and expanding existing soft habitat. All sand flats, including the Centre Bank and Little

Lagoon are earmarked for protection (ERM/MER 2012). Any destruction or degradation of these sand banks would

therefore be in direct contravention of the daft management plan for the Bay (ERM/MER 2012).

In terms of assessing potential impacts on the macrofauna of subtidal areas to be dredged (with the exception of

Little Lagoon), consideration is given to the fact that these areas are already highly disturbed by previous dredging

operations and propeller wash, sediments are near anoxic and diversity and biomass of these areas has been shown

to be relatively low especially for deeper areas (>3 m) that do not form the slopes of intertidal banks. Forbes et al

(1996) have shown that species abundance is two to seven times greater in undredged habitats than in shipping

channels which are periodically dredged and disturbed.

9.2 Impact description and assessment

The impacts of dredging activities largely relate to the physical removal of substratum and the associated fauna

residing on or in it, along the path of the dredge head, and to a degree the impact of resultant deposition of rejected

material by screening and overfill of the hopper (Newell et al. 1998). In general, macrofaunal communities residing

in the fine sediments of estuaries, such as those in the deeper subtidal areas of the harbour, are low in diversity and

comprise species well adapted to rapid recolonization on substratum that is frequently disturbed (Newell et al.

1998). Rates of recovery reportedly are in the range of 6-8 months for estuaries with fine muds, such as the subtidal

areas in much of the Port of Durban, where disturbance is frequent and precludes the establishment of relatively

long lived organisms (Newell et al. 1998). Contrastingly, rates of recovery become far longer for communities

occurring in stable sandy and gravelly substrata such as those found at the intertidal sand banks and Little Lagoon

(Newell et al. 1998).

Fishes are also affected by dredging, particularly those that are bottom dwelling like gobies and sole as they are

sucked up by the dredger and are often killed in the process. Other larger species may simply be disturbed

temporarily. Apart from this, turbidity increases with dredging as can the concentration of potentially toxic trace

47

metals and hydrocarbons as they are resuspended by such activities. Most estuarine-associated fishes in KwaZulu-

Natal are well adapted to high levels of turbidity (Blaber, 1981). Few estuaries fall into the clear water categories (<

10 NTU) of Cyrus (1988), with most either semi-turbid (10-50 NTU) or turbid (> 50 NTU). While Durban Harbour is,

for the most part, relatively low in turbidity (≈ 10-15 NTU), values of at least 25 NTU near the bottom are not

uncommon (Newman et al. 2008). Piscivorous fishes in estuaries often rely on visual detection methods for

capturing their prey, and increasing turbidity levels can impact negatively on this. However, piscivorous species are

generally of marine origin and can exit the estuary if turbidity levels become too high or too widespread. Turbidity

generated by the dredging is anticipated to be localised, and fish are able to move to more favourable areas of the

harbour.

Sessile organisms however, particularly those that filter-feed are most likely to be impacted as material suspended

by dredging is likely to be largely inorganic resulting in feeding difficulties. For autotrophic organisms such as

microphytobenthos and phytoplankton, suspended material blocks light, the higher the suspended solids the more

light is attenuated.

Various site specific plume-model simulations have been produced for dredging operations to be conducted as part

of this project by ZAA Engineering Projects & Naval Architecture (ZAA, 2012a). These model simulations cover what

is assumed to be worst case scenario conditions where wind speed, wave height, wave period and direction are

constant at 20 m.s-1, 3 m, 10 s and 146.25° respectively, but natural tidal variations apply. Prevailing wind is

incorporated into the model in the two most-common directions (202.5° and 22.5°) spanning both neap and spring

tide cycles. Four scenarios have therefore been modelled.

Results show that plumes are most widespread during conditions of spring tides and south-westerly winds (202.5°),

and during conditions of neap tides with north-easterly winds (22.5°) (ZAA, 2012a) Figure 22, Figure 23, Figure 24 &

Figure 25). Generally, surface and bottom plumes did not differ much. Maximum suspended sediment

concentrations are modelled to occur at the site of the hopper and remain fairly localised. Peak sediment

concentrations reaching the Centre Bank are predicted to occur during conditions of spring tide and north-easterly

wind (22.5°) at levels of less than 28 mg.L-1 (ZAA 2012a). Levels of suspended sediments were found to closely

correspond at both high and low tides.

Maximum predicted turbidity levels coming into contact with the Centre Bank are therefore slightly higher than the

maximum levels recorded by Newman et al. (2008) near the floor of Durban harbour (≈25 NTU = 21 mg.L-1). Dredging

is therefore likely to cause a maximum of a two-fold increase in suspended sediment levels at Centre Bank.

The affect of these turbidity levels on fish are likely to be low and localised to a relatively small area. Maximum

turbidity levels at Centre Bank are predicted to be 58 NTU (backgroundmax + dredgemax = Total turbidity in NTU). Most

fishes in estuaries of KwaZulu-Natal are semi-turbid water species (Cyrus 1988) and are likely to be unperturbed by

the predicted levels of turbidity. Those that may be negatively affected, such as Pursemouths, can move to other

areas of the harbour as the plume is likely to be localised.

Benthic invertebrates are often more susceptible to the effects of turbidity, particularly those that filter-feed, as

many lack the mobility inherent to fishes and therefore can ingest high levels of inorganic material filtered from the

water resulting in lower growth rates or starvation and mortality. Steffani et al. (2003) have provided guidelines for

concentrations of suspended solids in relation to the risk it poses to marine invertebrates:

Low risk: < 20 mg.L-1

Medium risk: 20-80 mg.L-1

High risk, requiring mitigation: > 80 mg.L-1

Maximum levels of suspended solids in mg.L-1 modelled to reach Centre Bank equal 49 mg.L-1. This puts the dredging

operation within the centre of the medium-risk category, according to Steffani et al. (2003), but still within

acceptable levels for macrofauna and shallow water benthic microalgae. However, levels of suspended solids are

48

higher closer to the hopper and may well approach 80 mg.L-1 putting the significance of the dredging operation in

the high risk category. Models show that this may only occur in a localised area and not all the time.

Based on the above considerations a threshold limit of 50 mg.L-1 suspended solids adjacent to the Centre Sand bank is

affirmed.

The risk of toxicity resulting from the suspension of heavy metals, hydrocarbons and polychlorinated biphenyls

associated with the suspended dredge material is considered to be low with no significant impact on the

biodiversity. Newman (CSIR, 2012a) concluded that “Based on the low concentrations of metals and organic

chemicals in sediment within and near the dredging footprint there is a very low probability that chemicals released

from the sediment during the dredging and spoil disposal processes will be present in the water column at toxic

concentrations.” No impact in terms of toxicity is therefore predicted on any of the living organisms within the Port

based on this investigation.

Impacts during the construction of the deck on pile, sheet pile or caisson quay wall (whichever is ultimately chosen)

are likely to result in disturbances to subtidal organisms in the near vicinity of the construction site and are likely to

vary depending on which quay wall option is chosen. A brief summary of the construction methods for each quay

wall option was given in Section 2 Development proposal. Impacts are anticipated to be most severe for the

construction process of the Caisson Quay wall option as this is likely to involve further excavation after dredging that

may lead to a further enhancement of turbidity levels. Thereafter, piles have to be driven into the seabed for all

three of the quay wall options, and the impacts of this phase of the construction are likely to be similar for all three

options. Impacts are predicted to be of a low magnitude, as the area has already been recently disturbed by

dredging operations, and localised and short term turbidity plumes are likely to result. Some level of noise

disturbance will also be created during the construction phase. However, the species inhabiting the Port of Durban

are not likely to be impacted by this as they have a high tolerance for noise and are most likely already accustomed

to it.

In terms of the specific technical option regarding which type of quay wall design once constructed results in the

least impact on biodiversity, it can be said that all three options have similar footprints on the substratum as rock

scour is needed at the foot of the expanded Berths in all cases. The Deck on Pile option would probably have the

least impact as it allows for free movement of water among the piles. However, it is the least favourable option from

an engineering perspective and also needs to be serviced more regularly than the Caisson quay wall. The relative

importance of the pelagic habitat that would be saved as a result of selecting this option is extremely low, and thus

would not strongly mitigate against either of the other two options. In addition, disturbance due to maintenance is

unlikely to be any more severe than the disturbance anticipated from the normal operation of the berths. Therefore

no particular quay wall option is likely to be significantly better over the others from an estuarine biodiversity

perspective.

The impact of scour protection adjacent to the quay walls is likely to have a negative impact as it will result in a

permanent loss of habitat for soft sediment organisms. However, it will create new habitat in the form of hard rock

substrata which is likely to be colonised by different assemblages of marine invertebrates and fishes. The area that

will be transformed with scour protection will be relatively small (approximately 2% of the dredged area or 2-3 ha

depending on which quay wall option is selected), is already artificial and is an area that is already regarded as being

highly disturbed due to various activities associated with the Port.

Stabilising concrete filled mats (HydrotexTM) on the southern side of Centre Bank subtidal sand flat are also proposed

to ensure that the Centre Bank does not erode and slump due to dredging adjacent to the toe of the Centre Bank.

This involves the laying down and filling with concrete of custom made articulated block mats, that are cable

reinforced. These block mats are woven double layer synthetic material pockets that are pumped in situ with

structural grout. The affect of this will be the loss of shallow, medium and deep shallow subtidal sandbank habitats

49

(0 to 12.8 m below CDP) (ZAA Engineering Projects & Naval Architects, 2012) and the mortality of all invertebrates

living in this part of the sand bank (Figure 10). As the mattresses are permanent, this would lead to a permanent loss

of shallow subtidal sandy habitat and the creation of new artificial habitat different from the natural habitat.

However, with the adoption of Option 3G a net gain of 0.04 % will result despite the stabilising mattresses.

Each envisaged impact resulting from the proposed development during construction (Table 15 to Table 27),

operation (Table 34) and periodic maintenance phases (Table 35) of the new quay were assessed separately, results

of which are presented in the tables below. In addition, impacts expected from the various proposed mitigation

measures are also assessed (Table 28 to Table 33). All of these assessments are summarised in Table 36. A detailed

description of how impacts are assessed is given in Appendix 1.

50

.

Figure 20. Surface-plume model results for conditions of neap tide with a wind direction of 202.5° showing suspended sediment (kg.m-3

).

Figure 21. Bottom-plume model results for conditions of neap tide and with a wind from 202.5° showing suspended sediment (kg.m-3

).

51

Figure 22. Surface-plume model results for conditions of neap tide with wind from a direction of 22.5° showing suspended sediment (kg.m-

3).

Figure 23. Bottom-plume model results for conditions of neap tide and wind from a direction of 22.5° showing suspended sediment (kg.m-

3).

52

Figure 24. Surface-plume model results for conditions of spring tide and wind from 202.5° showing suspended sediment (kg.m-3

).

Figure 25. Bottom-plume model results for conditions of spring tide and wind from 202.5° showing suspended sediment (kg.m-3

).

53

Figure 26. Surface-plume model results for conditions of spring tide and wind from 22.5° ° showing suspended sediment (kg.m-3

).

Figure 27. Bottom-plume model results for conditions of spring tide and wind from 22.5° ° showing suspended sediment (kg.m-3

).

54

Table 15. Impact 1: Ecological effects due to the permanent loss of intertidal and shallow subtidal habitats at Centre Bank.

Extent Intensity Duration Consequence Probability Significance Status Confidence

Without mitigation

Local 1

High 3 Long-

term 3 High 7

Definite High -ve High

Essential mitigation measures: Option 3G Optional mitigation measures: Conversion of DCT stockpile into intertidal and shallow habitat

With mitigation

Local 1

Medium 2

Long-term 3

Medium 6 Probable Medium -ve Medium

Table 16. Impact 2: Ecological effects due to the permanent loss of deep subtidal and open water habitats


Without mitigation

Local 1

Medium 2

Long-term 3

Medium 6 Definite Medium -ve High

Essential mitigation measures: Increase the amount of shallow and medium subtidal habitat via Option 3G Optional mitigation measures: Conversion of DCT stockpile into intertidal and shallow habitat

With mitigation

Local 1

Low 1 Long-

term 3 Low 5 Probable Low +ve Medium

Table 17. Impact 3: Ecological effects due to the temporary loss of sediment habitat and associated infauna in dredging footprint


Without mitigation

Local 1

Medium 2

Medium-term 2

Low 5 Definite Low -ve High

Essential mitigation measures: Reduce dredge footprint (Option 3G) Optional mitigation measures:

With mitigation

Local 1

Medium 2

Medium-term 2

Low 5 Definite Low -ve Medium

Table 18. Impact 4: Ecological effects due to the release of contaminants in sediment into the water column caused by dredging to the extent that toxic effects manifest


Without mitigation

Local 1

High 3 Short-term 1

Low 5 Improbable Very low -ve High

Essential mitigation measures: Not applicable Optional mitigation measures:

With mitigation

Not applicable

55

Table 19. Impact 5: Ecological effects due to the release of nutrients in sediment porewater to the extent that microalgae are stimulated to bloom status


Without mitigation

Local 1

Medium 2

Short-term 1

Very low 4 Improbable Insignificant -ve Medium


With mitigation

Not applicable

Table 20. Impact 6: Ecological effects due to the reduction in dissolved oxygen concentrations


Without mitigation

Local 1

Medium 2

Short-term 1

Very low 4 Possible Low -ve Medium

Essential mitigation measures: Conduct dredging operations as efficiently as possible and reduce turbidity levels Optional mitigation measures:

With mitigation

Local 1

Low 1 Short-term 1

Very low 3 Possible Low -ve Medium

Table 21. Impact 7: Ecological effects caused by the smothering of subtidal bottom-dwelling organisms due to the settlement of suspended sediment outside the dredging footprint


Without mitigation

Local 1

Medium 2

Short-term 1

Very low 4 Probable Very low -ve Medium

Essential mitigation measures: i) Continuous monitoring should be undertaken of turbidity levels during the dredge operations. Data from the

turbidity monitoring instruments should be available in real time to the person coordinating dredging activities. Dredging operations should be halted immediately if turbidity levels exceed a threshold level of 50 mg.L

-1 (see Porter et al. 2012) at any of the monitoring stations and should not recommence until levels have

declined below this level.

ii) If turbidity frequently exceeds threshold levels at the monitoring stations adjacent to the central sand bank and/or in Little Lagoon during dredging operations, use of ‘Silt Curtains’ at the burrow pit may be necessary. The lower end of the ‘skirt’ must be allowed to rest upon the seafloor, and the top of the ‘skirt’ must be above the water surface.

iii) Another option to reduce turbidity is to choke the dredge hopper overflow with a fully automated system. In this scenario, a computerized process controller ensures dynamic adjustment of the valve in the overflow funnel which chokes the flow in such a way that a constant fluid level in the hopper is maintained and, as a result, no air is taken down with the suspension leaving the hopper. This generally results in a significant decrease in turbidity.

iv) The time period over which the dredging operation is to take place should be minimised, to avoid the daily re-suspension of sediments.

Optional mitigation measures:

56

With mitigation

Local 1

Low 1 Short-term 1

Very low 3 Possible Insignificant -ve Medium

Table 22. Impact 8: Ecological effects of increased suspended solids concentrations on filter feeding organisms


Without mitigation

Local 1

Medium 2

Short-term 1




-1 (see Porter et al. 2012) at any of the monitoring stations and should not recommence until levels

have declined below this level.





With mitigation

Local 1

Low 1 Short-term 1


Table 23. Impact 9: Ecological effects of increased suspended solids concentrations and turbidity on benthic microalgae


Without mitigation

Local 1

Medium 2

Short-term 1






ii) If turbidity frequently exceeds threshold levels at the monitoring stations adjacent to the central sand bank

57

and/or in Little Lagoon during dredging operations, use of ‘Silt Curtains’ at the burrow pit may be necessary. The lower end of the ‘skirt’ must be allowed to rest upon the seafloor, and the top of the ‘skirt’ must be above the water surface.




With mitigation

Local 1

Low 1 Short-term 1


Table 24. Impact 10: Ecological effects of increased suspended solids concentrations and turbidity on water column primary production


Without mitigation

Local 1

Medium 2

Short-term 1










With mitigation

Local 1

Low 1 Short-term 1


Table 25. Impact 11: Ecological effects of increased suspended solids concentrations and turbidity on pelagic organisms

58


Without mitigation

Local 1

Low 1 Short-term 1










With mitigation

Local 1

Low 1 Short-term 1


Table 26. Impact 12: Ecological effects of smothering of deep subtidal sediment due to rocky scour protection adjacent to quay walls


Without mitigation

Local 1

Low 1 Long-

term 3 Low 5

Definite Low -ve High

Essential mitigation measures: Increase shallow and medium subtidal habitats (i.e. Option 3G) Optional mitigation measures:

With mitigation

Local 1

Low 1 Long-

term 3 Low 5

Possible Very low -ve High

Table 27. Impact 13: Ecological effects of habitat transformation due to rocky scour protection adjacent to quay walls


Without mitigation

Local 1

Low 1 Long-

term 3 Low 5

Definite Low -ve High


With Local Low 1 Long- Low 5 Possible Very low -ve High

59

mitigation 1 term 3

Table 28. Impact 14: Ecological effects of smothering of habitat due to scour protection mattresses on Centre Bank shallow subtidal sand banks.


Without mitigation

Local 1

Medium 2

Long-term 3

Medium 6 Definite Medium -ve Medium


With mitigation

Local 1

Low 1 Long-

term 3 Low 5

Possible Very low -ve Medium

Table 29. Impact 15: Ecological effects of smothering of habitat due to scour protection mattresses on Centre Bank deep subtidal sand banks.


Without mitigation

Local 1

Low 1 Long-

term 3 Low 5

Definite Low -ve Medium


With mitigation

Local 1

Low 1 Long-

term 3 Low 5

Possible Very low -ve Medium

Table 30. Impact 16: Ecological effects of habitat transformation due to scour protection mattresses on Centre Bank shallow subtidal sand banks


Without mitigation

Local 1

Medium 2

Long-term 3

Medium 6 Definite Medium -ve Medium


With mitigation

Not applicable

Table 31. Impact 17: Ecological effects of habitat transformation due to scour protection mattresses on Centre Bank deep subtidal sand banks


Without mitigation

Local 1

Low 1 Long-

term 3 Low 5

Definite Low -ve Medium


With mitigation

Not applicable

60

Table 32. Impact 18: Ecological effects of southwards extension of Centre Bank habitat (by Adoption of Option 3G) for estuarine organisms


Without mitigation

Local 1

Low 1 Long-

term 3 Low 5 Definite Low +ve Medium

Essential mitigation measures: Sediment used to construct the artificial bank should be of similar physical properties to the existing Centre bank.

With mitigation

Not applicable

Table 33. Impact19: Ecological effects of smothering of organisms on the southern slopes of Centre Bank due to artificial sand bank extension (by adoption of Option 3G).


Without mitigation

Local 1

Medium 2

Long-term 3

Medium 6 Definite Medium -ve High


With mitigation

Not applicable

Table 34. Impact 20: Ecological effects of operation of the quay


Without mitigation

Local 1

Low 1 Long-

term 3 Low 5 Possible Low -ve Medium

Essential mitigation measures: Not applicable

With mitigation

Not applicable

Table 35. Impact 21: Ecological effects of maintenance of the quay


Without mitigation

Local 1

Low 1 Short-term 1

Very low 3 Definite Low -ve Medium

Essential mitigation measures: Not applicable

With mitigation

Not applicable

61

Table 36. Summary of potential impacts as a result of the proposed development.

Source

of

impact

Impact identified Consequence Probability Significance Status Confidence

Imp

acts

ass

oci

ated

wit

h d

red

gin

g an

d q

uay

co

nst

ruct

ion

& e

xpan

sio

n in

Du

rban

Har

bo

ur

Impact 1: Ecological effects due to the permanent loss

of intertidal and shallow subtidal habitats at Centre

Bank.

High Definite High -ve High

With Mitigation Medium Probable Medium -ve Medium

Impact 2: Ecological effects due to the permanent loss

of deep subtidal and open water habitats

Medium Definite Medium -ve High

With Mitigation Low Probable Low +ve Medium

Impact 3: Ecological effects due to the temporary loss

of sediment habitat and associated infauna in

dredging footprint

Low Definite Low -ve High

With Mitigation Low Definite Low -ve Medium

Impact 4: Ecological effects due to the release of

contaminants in sediment into the water column

caused by dredging to the extent that toxic effects

manifest

Low Improbable Very low -ve High

With Mitigation Not applicable

Impact 5: Ecological effects due to the release of

nutrients in sediment porewater to the extent that

microalgae are stimulated to bloom status

Very low Improbable

Insignificant -ve Medium

62

Source

of

impact



Impact 6: Ecological effects due to the reduction in

dissolved oxygen concentrations

Very low Possible Low -ve Medium

With Mitigation Very low Possible Low -ve Medium

Impact 7: Ecological effects caused by the smothering

of subtidal bottom-dwelling organisms due to the

settlement of suspended sediment outside the

dredging footprint

Very low Probable Very low -ve Medium

With Mitigation Very low Possible Insignificant -ve Medium

Impact 8: Ecological effects of increased suspended

solids concentrations on filter feeding organisms




solids concentrations and turbidity on benthic

microalgae




solids concentrations and turbidity on water column

primary production



Impact 11: Ecological effects of increased suspended solids concentrations and turbidity on pelagic


63

Source

of

impact


organisms

With Mitigation Very low Probable Very low -ve Medium

Impact 12: Ecological effects of smothering of deep subtidal sediment due to rocky scour protection adjacent to quay walls


With Mitigation Low Possible Very low -ve High

Impact 13: Ecological effects of habitat transformation due to rocky scour protection adjacent to quay walls


With Mitigation Low Possible Very low -ve High

Impact 14: Ecological effects of smothering of habitat

due to scour protection mattresses on Centre Bank

shallow subtidal sand banks.

Medium Definite Medium -ve Medium

With Mitigation Low Possible Very low -ve Medium

Impact 15: Ecological effects of smothering of habitat


deep subtidal sand banks.

Low Definite Low -ve Medium

With Mitigation Low Possible Very low -ve Medium

Impact 16: Ecological effects of habitat transformation


shallow subtidal sand banks

Medium Definite Medium -ve Medium

64

Source

of

impact



Mit

igat

ion

Impact 17: Ecological effects of habitat transformation


deep subtidal sand banks

Low Definite Low -ve Medium


Impact 18: Ecological effects of southwards extension

of Centre Bank habitat (by adoption of Option 3G) by

0.04 % for estuarine organisms

Low Definite Low +ve Medium


Impact 19: Ecological effects of smothering of

organisms on the southern slopes of Centre Bank due

to artificial sand bank creation (by adoption of Option

3G)

Medium Definite Medium -ve High


Op

erat

ion

&

mai

nte

nan

ce o

f q

uay

Impact 20: Ecological effects of operation of the quay Low Possible Low -ve Medium


Impact 21: Ecological effects of maintenance of the quay

Very low Definite Low -ve Medium


65

10 Mitigation

Measures required to mitigate impacts on estuarine organisms of Durban Bay have largely been built

into the project design in the form of additional development options (Options 3C-G). These

mitigation measures were identified during the project design phase as a result of interactions

between specialists on the EIA team, the project engineers (ZAA) and the developer (Transnet). The

various development options represent incremental changes in the project design developed in an

effort to mitigate loss of intertidal habitat from the Centre Bank. The target for these mitigation

measures was zero nett loss of intertidal and shallow subtidal habitat and was considered to have

been achieved under development option 3G. The decision to artificially extend Centre Bank,

however, should not be taken lightly. There is uncertainty and risk that the new sand flat will not be

fully colonised or function as successfully as the original sand flat. The worst case scenario is that it

could do more harm than good because, assuming that the artificial bank does not function

ecologically, by extending it the southern slopes of the current productive Centre Bank are

effectively smothered at the same time. The likelihood of success to a large extent will depend on

the characteristics of the sediment used for construction and its stability and erosion resistance. The

artificial portion of Centre Bank should be of the same (or similar) grain size composition as the

existing Centre Bank area.

Literature on the colonisation of artificial sand banks in estuaries is limited. There is however

information on the impacts and colonisation of offshore dredge spoil. Studies in the OSPAR maritime

area (North-East Atlantic) indicate recovery rates for species richness, abundance and diversity to

range from 3 months to 2 years (Bolam et al. 2006; Stronkhorst et al. 2003; Bolam & Whomersley

2005; Van Dalfsen & Lewis 2006). It is assumed that a similar time period for full colonisation of the

artificial habitat will be required in this case as well.

It is also important to recognise that the extension of Centre Bank provides an opportunity for proof

of concept provided colonisation of the newly created habitat is properly monitored after it is

established. If the development is successful then this could be used in other areas of the Bay for

purposes of restoration.

Additional mitigation measures not incorporated in the project design options to be implemented

during the construction and operational phase of the project considered essential for effectively

mitigating impacts identified in this study include the following:

1. Continuous monitoring should be undertaken of turbidity levels during the dredge

operations, and data from such monitoring work should be available in real time to the

person coordinating dredging activities. Dredging operations should be halted immediately

if turbidity levels exceed a threshold level of 50 mg.L-1 at any of the designated monitoring

stations and should not recommence until levels have declined below this point.

2. If turbidity frequently exceeds threshold levels at the monitoring stations adjacent to the

central sand bank and/or in Little Lagoon during dredging operations, ‘Silt Curtains’ at the

burrow pit should be used to mitigate this. The lower end of the ‘skirt’ must be allowed to

rest upon the seafloor, and the top of the ‘skirt’ must be above the water surface.

3. Turbidity should be minimised by choking the dredge hopper overflow with a fully

automated system. In this scenario, a computerized process controller ensures dynamic

adjustment of the valve in the overflow funnel which chokes the flow in such a way that a

66

constant fluid level in the hopper is maintained and, as a result, no air is taken down with

the suspension leaving the hopper.

4. The time period over which the dredging operation is to take place should be kept as short

as possible, to avoid the daily re-suspension of sediments.

5. Sediment used to construct the artificial bank should be of similar physical properties to the

existing Centre Bank.

6. As far as possible construct the artificial extension of Centre Bank during winter when

migrant waders are absent.

Additional, optional mitigation measures are proposed as follows:

1. Keep the dredge hopper stationary during dredge operations.

2. Undertake construction work as quickly as possible to minimise the time period of

disturbance.

3. Conversion of DCT stockpile into intertidal and shallow habitat

11 Monitoring Programme

The aim of the biodiversity monitoring programme is to assess the impact and effectiveness of the

proposed mitigation measures, and the rate or recovery and recolonisation of the affected areas

once dredged. These data will be invaluable for assessing the effectiveness of the offsets proposed

in this study and their potential use in future where habitat replacement (offsets) may be required

again in the future.

Key activities to be undertaken as part of this monitoring programme include the following:

(i) Monitor real-time turbidity levels adjacent to Centre Bank during dredging operations

such that if threshold levels are reached then dredging can be momentarily halted and/or

mitigation measures activated if threshold levels are exceeded on an ongoing basis.

(ii) Undertake baseline surveys of the composition, abundance and biomass of macrofauna

and fish communities in the intertidal area of the central sand bank immediately prior to

the commencement of the dredging operations and use these data along with

corresponding data from the post construction period to assess potential impacts and

rates of recovery of biotic communities in areas potentially affected by the dredging

activities and rates of colonisation in the newly in-filled areas at the western end of Pier 2

and along the southern edge of the central bank. Sampling should be conducted on at

least two occasions prior to the initiation of the dredging activities, immediately after

completion of the dredging, and at six monthly intervals for a period of three years

following this date.

67

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70

Appendix 1: Impact Rating Methodology

The significance of all potential impacts that would result from the proposed project is determined

in order to assist decision-makers. The significance rating of impacts is considered by decision-

makers, as shown below.

· INSIGNIFICANT: the potential impact is negligible and will not have an influence on the decision

regarding the proposed activity.

· VERY LOW: the potential impact is very small and should not have any meaningful influence on

the decision regarding the proposed activity.

· LOW: the potential impact may not have any meaningful influence on the decision regarding

the proposed activity.

· MEDIUM: the potential impact should influence the decision regarding the proposed activity.

· HIGH: the potential impact will affect a decision regarding the proposed activity.

· VERY HIGH: The proposed activity should only be approved under special circumstances.

The significance of an impact is defined as a combination of the consequence of the impact

occurring and the probability that the impact will occur. The significance of each identified impact2

was thus rated according to the methodology set out below:

Step 1 – Determine the consequence rating for the impact by determining the score for each of the

three criteria (A-C) listed below and then adding them. The rationale for assigning a specific rating,

and comments on the degree to which the impact may cause irreplaceable loss of resources and be

irreversible, must be included in the narrative accompanying the impact rating:

Rating Definition of Rating Score

A. Extent – the area over which the impact will be experienced

Local Confined to project or study area or part thereof (e.g. limits of

the concession area)

1

Regional The region (e.g. the whole of Namaqualand coast) 2

(Inter) national Significantly beyond Saldanha Bay and adjacent land areas 3

B. Intensity – the magnitude of the impact in relation to the sensitivity of the receiving environment, taking into

account the degree to which the impact may cause irreplaceable loss of resources

Low Site-specific and wider natural and/or social functions and processes are negligibly

altered

1

Medium Site-specific and wider natural and/or social functions and processes continue albeit in

a modified way

2

High Site-specific and wider natural and/or social functions or processes are severely altered 3

C. Duration – the time frame for which the impact will be experienced and its reversibility

Short-term Up to 2 years 1

Medium-term 2 to 15 years 2

Long-term More than 15 years (state whether impact is irreversible) 3

The combined score of these three criteria corresponds to a Consequence Rating, as follows:

Combined Score (A+B+C) 3 – 4 5 6 7 8 – 9

Consequence Rating Very low Low Medium High Very high

2 This does not apply to minor impacts which can be logically grouped into a single assessment.

71

Example 1:

Extent Intensity Duration Consequence

Regional 2

Medium 2

Long-term 3

High

7

Step 2 – Assess the probability of the impact occurring according to the following definitions:

Probability– the likelihood of the impact occurring

Improbable < 40% chance of occurring

Possible 40% - 70% chance of occurring

Probable > 70% - 90% chance of occurring

Definite > 90% chance of occurring

Example 2:

Extent Intensity Duration Consequence Probability

Regional 2

Medium 2

Long-term 3

High

7

Probable

Step 3 – Determine the overall significance of the impact as a combination of the consequence and

probability ratings, as set out below:

Probability

Improbable Possible Probable Definite

Co

nse

qu

en

ce Very Low INSIGNIFICANT INSIGNIFICANT VERY LOW VERY LOW

Low VERY LOW VERY LOW LOW LOW

Medium LOW LOW MEDIUM MEDIUM

High MEDIUM MEDIUM HIGH HIGH

Very High HIGH HIGH VERY HIGH VERY HIGH

Example 3:

Extent Intensity Duration Consequence Probability Significance

Regional 2

Medium 2

Long-term 3

High

7

Probable

HIGH

Step 4 – Note the status of the impact (i.e. will the effect of the impact be negative or positive?)

Example 4:

Extent Intensity Duration Consequence Probability Significance Status

Regional 2

Medium 2

Long-term 3

High

7

Probable

HIGH

– ve

72

Step 5 – State the level of confidence in the assessment of the impact (high, medium or low).

Depending on the data available, a higher level of confidence may be attached to the assessment of

some impacts than others. For example, if the assessment is based on extrapolated data, this may

reduce the confidence level to low, noting that further groundtruthing is required to improve this.

Example 5:


Regional 2

Medium 2

Long-term 3

High

7

Probable

HIGH

– ve

High

Step 6 – Identify and describe practical mitigation and optimisation measures that can be

implemented effectively to reduce or enhance the significance of the impact. Mitigation and

optimisation measures must be described as either:

Essential: must be implemented and are non negotiable; and

Optional: must be shown to have been considered and sound reasons provided by the

proponent if not implemented.

Essential mitigation and optimisation measures must be inserted into the completed impact

assessment table. The impact should be re-assessed with mitigation, by following Steps 1-5 again to

demonstrate how the extent, intensity, duration and/or probability change after implementation of

the proposed mitigation measures.

Example 6: A completed impact assessment table


Without mitigation

Regional 2

Medium 2

Long-term

3

High

7

Probable

HIGH

– ve

High

Essential mitigation measures:

xxxxx

xxxxx

With mitigation

Local 1

Low 1

Long-term

3

Low

5 Improbable VERY LOW – ve High

Step 7 – Prepare a summary table of all impact significance ratings as follows:

Impact Consequence Probability Significance Status Confidence

Impact 1: XXXX Medium Improbable LOW –ve High

With Mitigation Low Improbable VERY LOW High

Impact 2: XXXX Very Low Definite VERY LOW –ve Medium

With Mitigation:

Not applicable

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Indicate whether the proposed development alternatives are environmentally suitable or unsuitable

in terms of the respective impacts assessed by the relevant specialist and the environmentally

preferred alternative.

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