Port Hedland Port Authority
South West Creek Dredging Approvals – Benthic Habitats
Survey Report
South West Creek Dredging Approvals
Benthic Habitats Survey Report
301012-01318-EN-REP-0001
6 October 2010
Port Hedland Port Authority
South West Creek Dredging Approvals – Benthic Habitats
Survey Report
Disclaimer
This report has been prepared on behalf of and for the exclusive use of Port Hedland Port
Authority, and is subject to and issued in accordance with the agreement between Port Hedland
Port Authority and WorleyParsons Services Pty Ltd. WorleyParsons Services Pty Ltd accepts no
liability or responsibility whatsoever for it in respect of any use of or reliance upon this report by
any third party.
Copying this report without the permission of Port Hedland Port Authority and WorleyParsons
Services Pty Ltd is not permitted.
It is expected that this document and its contents, including work scope, methodology and
commercial terms will be treated in strict confidence by Port Hedland Port Authority and that
the contents will be used by Port Hedland Port Authority only for the purpose of selecting a
consultant for the project.
PROJECT 301012-01318-EN-REP-0001 - SOUTH WEST CREEK DREDGING APPROVALS
REV
DESCRIPTION
ORIG
REVIEW
A
Issued for internal review
SS
TA
B
Issued for client review
T Al-Hashimi
P Mellor
WORLEYPARSONS
APPROVAL
N/A
DATE
1-Oct-10
6-Oct-10
Page ii
D Collins
CLIENT
APPROVAL
N/A
DATE
Port Hedland Port Authority
South West Creek Dredging Approvals – Benthic Habitats
Survey Report
Contents
Terms and abbreviations ................................................................................................................................. v
Executive summary .........................................................................................................................................1
1.
2.
Introduction.............................................................................................................................................2
1.1
Project Overview....................................................................................................................................2
1.2
Background ............................................................................................................................................3
1.3
Scope of Work........................................................................................................................................5
Legal Requirements and Relevant Guidelines ..........................................................................................5
2.1
3.
Environmental Assessment Guidelines ................................................................................................5
Methods ..................................................................................................................................................7
3.1
Literature Review...................................................................................................................................7
3.2
Survey Design.........................................................................................................................................7
3.2.1
Intertidal survey ..............................................................................................................................9
3.2.2
Subtidal survey................................................................................................................................9
4.
3.3
Data Analysis and Habitat Classification .............................................................................................9
3.4
Habitat Map Production .....................................................................................................................10
Results ...................................................................................................................................................11
4.1
Consolidated map of BPPH .................................................................................................................11
4.2
Mapped BPP.........................................................................................................................................13
4.2.1
Coral Communities........................................................................................................................13
4.2.2
Seagrass ........................................................................................................................................13
4.2.3
Algae .............................................................................................................................................14
4.2.4
Bare Sediment & Microphytobenthos ..........................................................................................15
4.2.5
Soft-bottom Communities ............................................................................................................16
4.2.6
Mangroves ....................................................................................................................................16
4.3
Spatial Distribution of Benthic Habitats.............................................................................................18
4.3.1
Proposed dredge footprint ...........................................................................................................18
4.3.2
Proposed disposal area.................................................................................................................21
4.3.3
Mangrove habitat influenced by dredge activities .......................................................................22
5.
Discussion..............................................................................................................................................24
5.1
Benthic Habitats in the Proposed Dredge Footprint .........................................................................24
5.2
Benthic Habitats in Spoil Ground 1.....................................................................................................24
5.3
Benthic Habitat Impacts in the Broader Zone of Influence...............................................................24
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Port Hedland Port Authority
South West Creek Dredging Approvals – Benthic Habitats
Survey Report
6.
References.............................................................................................................................................26
Appendices
Appendix 1 – Survey Site Locations
Figures
Figure 1-1 Proposed dredging footprint..........................................................................................................4
Figure 3-1 Location of benthic habitat survey sites ........................................................................................8
Figure 4-1 Consolidated BPPH map for Port Hedland harbour .....................................................................12
Figure 4-3: Acanthastrea exposed at low tide in South West Creek .............................................................13
Figure 4-3: Turfing algae community identified at the junction of South West Creek and West Creek........14
Figure 4-4: Habitat dominated by mud or sand with sparse shell fragments...............................................15
Figure 4-5: Decayed cyanobacterial mats observed during the field investigation ......................................16
Figure 4-6: Tidal inundation in relation to mangrove density.......................................................................17
Figure 4-7 Map of BPPH types within the proposed dredge footprint .........................................................20
Figure 4-8 Benthic Habitats of Spoil Ground I (BHPBIO 2009) ......................................................................22
Figure 4-9 Distribution of mangroves surrounding South West Creek..........................................................23
Tables
Table 1-1 Benthic Habitat Survey Task Descriptions.......................................................................................5
Table 4-1 Coverage of benthic habitats within the proposed dredge footprint............................................19
Page iv
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South West Creek Dredging Approvals – Benthic Habitats
Survey Report
TERMS AND ABBREVIATIONS
BHPBIO
BHP Billiton Iron Ore
BPP
Benthic Primary Producer
BPPH
Benthic Primary Producer Habitat
EPA
Environmental Protection Authority
GIS
Geographic Information System
MPB
Micro Phytobenthos
PHPA
Port Hedland Port Authority
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Survey Report
EXECUTIVE SUMMARY
Port Hedland Port Authority (PHPA) proposes to expand the current facilities within Port Hedland
Port to create a Tug and Small Vessel Cyclone Protection Facility within South West Creek. Capital
dredging will be undertaken to remove 2.5 Mm3 of sediments from the seabed, thus providing safe
depth for tug boats and small vessels to manoeuvre and berth at all stages of the tide.
The proposed dredging operations will create an associated plume that will affect the turbidity of
surrounding waters and sedimentation processes resulting in the potential disturbance or loss of
subtidal Benthic Primary Producers (BPPs) in the affected area. In accordance with the
Environmental Protection Act 1986 (EP Act), all proposals that may result in potential disturbance or
loss of marine benthic primary producer communities or habitats, should apply the principles
outlined in EPA Guidance Statement No. 3.
In the areas surveyed has very low benthic habitat diversity, and is generally similar to the bare
sediment area. As the area is naturally turbid, very little light penetrates to the seabed. Benthic
primary producers (such as seagrass and corals) are either non existent or live in isolated
communities.
The risk of increased turbidity having long-term significant impacts on benthic ecosystems in the
harbour will be buffered by the natural resilience of the biota to turbidity. If the physical processes
which favoured the colonising of the communities are maintained, these communities are likely to
recover and colonise suitable substrates.
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1.
INTRODUCTION
1.1
Project Overview
Port Hedland Port Authority (PHPA) proposes to expand the current facilities within South West
Creek, Port Hedland to provide mooring for tug and small vessels during periods of cyclone activity
(Figure 1-1). The proposal is known as the South West Tug & Small Vessel Mooring Cyclone
Protection Facility and will comprise the following proposed works:
•
A low intensity dredging program using one backactor dredge;
•
Dredging of fine surface sediments within an area totalling 426 442 m2 to a depth of -6.0 m CD
within South West Creek;
•
A total dredge volume of 2.5 Mm3 has been calculated to be removed from the dredge area;
•
The expected duration of the proposed dredging is 38 weeks, with commencement at the end of
October 2010 and completion at the end of July 2011. This is based on a dredge rate of ~68,000
m3 per week; and
Dredge material will be placed offshore at a previously used spoil ground (Spoil Ground I) (Figure
1-1). Dredge material will be transported to the spoil ground for disposal via hopper barges.
The dredging operations will directly impact benthic substrate within the proposed dredge footprint
and will result in the production of a sediment plume that may have indirect effects on habitats
within the vicinity of the dredging and disposal operations. In accordance with the Environment
Protection Act 1986 (EP Act), all proposals that may result in disturbance to or loss of marine benthic
primary producer habitat (BPPH) should adhere to the principals and guidelines recommended
within the Environmental Protection Authority (EPA) Environmental Assessment Guidelines No. 3,
(formally Guidance Statement No. 29), Protection of Benthic Primary Producer Habitats In Western
Australia’s Marine Environment (EPA 2009).
This report presents the findings of the benthic habitat survey conducted for the proposed PHPA
dredging project and previously collected data from Port Hedland harbour used to create a
consolidated high resolution benthic habitat for the project footprint and inner harbour.
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1.2
Background
Port Hedland is located approximately 1,660 km north of Perth within the Pilbara region of Western
Australia. The Port of Port Hedland is defined as “water within a radius of 10 nautical miles (nm) of
Hunt Point Beacon (Beacon 47)” (PHPA 2001) and is managed by PHPA under the Port Authorities
Act 1999 (WA). The port consists of a 20 nm dredged channel leading (inshore) to a dredged basin
between Nelson Point and Finucane Island, where several intertidal creeks converge. The harbour
has been highly modified by dredging activities and development and operation of port related
industry.
The proposed project is located adjacent to the existing inner harbour area of Port Hedland, at the
mouth of South West Creek (Figure 1-1). The site is a tidal creek, with current seabed levels ranging
from 0.0 m CD to -4.0 m CD. The site is sheltered but experiences fast tidal currents as a result of
the high tidal range experienced in the region. The marine habitats found in Port Hedland are
characteristic of those found along the arid coastlines of the Pilbara. Recent benthic habitat surveys
have been undertaken in the inner harbour for BHP Billiton Iron Ore’s (BHPBIO) RGP5 and RGP6
developments.
These have identified five distinct mixed benthic primary producer (BPP)
communities throughout Port Hedland habour, during which coral colonies were recorded in South
East Creek, South West Creek and Stingray Creek (SKM 2009b).
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Figure 1-1 Proposed dredging footprint
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Survey Report
1.3
Scope of Work
PHPA have commissioned WorleyParsons Pty Ltd (WorleyParsons) to conduct a benthic habitat
survey to acquire baseline data on the distribution of benthic habitats within the proposed dredge
footprint and to compile existing information in order to create a benthic habitat map for the marine
environment adjacent to the development area.
The survey data will be used to guide the
management decisions required to satisfy the requirements of EPA Environmental Assessment
Guideline No. 3 (EPA 2009) and to aid in identifying the direct and indirect impacts on BPPH caused
by the proposed dredging works.
The benthic habitat survey was undertaken from 31 July to 4 August 2010 and the tasks undertaken
described in Table 1-1.
Table 1-1
Benthic Habitat Survey Task Descriptions
Task
Task Description
Benthic Habitat
Mapping (Intertidal)
Undertake intertidal survey along predetermined transects spaced 50 m apart with a
photo taken using a 0.5 m² quadrat at each survey location.
Benthic Habitat
Mapping (Subtidal)
A subtidal snorkel survey at high tides along predetermined transects spaced 50 m
apart with a photo taken using a 0.5 m² quadrat at each survey location.
2.
LEGAL REQUIREMENTS AND RELEVANT GUIDELINES
2.1
Environmental Assessment Guidelines
The EPA Environmental Assessment Guideline No. 3 defines BPPH as seabed communities within
which algae (e.g. macroalgae, turf and benthic microalgae), seagrass, mangroves, corals or mixtures
of these groups are prominent components (EPA 2009). The EPA recognises the fundamental
ecological importance of BPPHs and the potential consequences of their loss. It is also acknowledged
that almost all marine development proposals will result in the loss of some of these important
habitats (EPA 2009).
For the purposes of this study, the following definitions were adopted:
•
Benthic Primary Producers (BPP) are primarily marine plants such as seaweeds, seagrasses,
mangroves, turf algae, and benthic microalgae, but also includes the scleractinian corals (which
gain a large proportion of their energy from internal symbiotic microalgae).
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•
BPPHs are a combination of the BPPs and the substrata that can support them. BPPHs include
not only areas of existing BPPs, but also areas which previously supported them or which may be
colonised by BBPs in the future. Examples of BPPHs include coral reefs, seagrass meadows,
mangrove forests, intertidal mud flats and seabed where macroalgal, coral or seagrass
communities have grown and could grow.
•
Other benthic habitats such as those dominated by sessile animals that have light requiring
organisms associated with them (e.g. soft corals, sponges and ascidians) are recognised as being
important but the loss of or damage to these habitats would be treated separately in the
environmental impact assessment process.
This report groups distinct benthic communities into broad biotic groups based on the primary biota
types.
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3.
METHODS
3.1
Literature Review
All available literature and previous studies relevant to the Port Hedland area were reviewed and
used to present the description of benthic habitats within Port Hedland harbour and provide data to
allow an integrated benthic habitat map to be produced for the inner harbour. Compilation of
existing data included acquisition, reprocessing and presentation of existing habitat maps.
3.2
Survey Design
In order to map benthic habitats within the proposed dredge footprint a total of 171 survey points
were surveyed along eight transects (A to H), with each survey point set at 50 m intervals (Figure
3-1). The GPS coordinates for each survey point are provided in Appendix 1.
The survey was designed to take place during the spring tidal phase to maximise on the deeper less
turbid water during the peak of the high tide to obtain good quality images as well as to target the
exposed intertidal areas during low tides.
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Figure 3-1
Location of benthic habitat survey sites
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3.2.1
Intertidal survey
During the spring low tides, intertidal surveys of benthic habitats within the survey area were
conducted on foot at predetermined 50 m interval sites. Each site was identified using GPS
coordinates and still photographs of the benthic habitat taken within a 0.5 m² scaled quadrat frame.
The quadrat was labelled with the site name and a handwritten field log was kept for each site
deployment, including any observations made at each site.
3.2.2
Subtidal survey
Subtidal surveys were carried out at predetermined locations set at 50 m intervals using an
underwater photography of the benthic habitat within a scaled 0.5 m² quadrat frame. Each site was
located using a GPS and pre-determined coordinates. Once the vessel was on site, a marker buoy
was thrown in the water to mark the site. At each survey location the snorkeler placed the quadrat
on the seabed and took a photo using a water proof camera.
The quadrat was labelled with the site name and a handwritten field log was kept for each site
deployment, including any observations made during photo capture.
Visibility was insufficient for the drop camera video survey method to be employed therefore the
subtidal survey was undertaken using in-water still photography by snorkelers.
3.3
Data Analysis and Habitat Classification
All photographs for each survey site were classified in the office by a marine scientist to determine
key habitat types. In order to maintain a consistent approach with other benthic habitat mapping
exercises conducted in the Port Hedland harbour area, BHPBIO’s habitat classification scheme used
for the RGP6 project was applied to benthic habitat data collected for this study (BHPBIO 2009).
These categories can be broken down as follows:
•
Avicennia marina - open heath
•
Canopy algae
•
Small algae
•
Avicennia marina - scrub
•
Canopy and small algae
•
•
Avicennia marina/Rhizophora
stylosa
•
Canopy and turf algae
Small algae and turf
algae
•
Hard coral
•
Soft coral
•
Hard coral, soft coral and
small algae
•
Soft coral and small
algae
•
Turf algae
•
Rhizophora stylosa - low forest
•
Rhizophora stylosa - scrub
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3.4
Habitat Map Production
A benthic habitat map was compiled from a variety of geophysical datasets including bathymetry
and aerial photography, in order to quantify the spatial distribution of the main intertidal and
subtidal environments within the footprint. Habitat boundaries were manually digitised in a GIS
environment.
Studies relevant to this composite map production include:
•
WorleyParsons (2010). South West Creek Dredging Approvals - Benthic Primary Producer Habitat
Mapping.
•
WorleyParsons (2010). South West Creek Tug Harbour and Small Vessel Cyclone Mooring Facility
Baseline Mangrove Community Investigation.
•
SKM (2009). "RGP6 Port Facilities Definition Phase Study - BPPH: Subtidal Habitat Mapping."
•
SKM (2009). Benthic Primary Producer Assessment Intertidal. RGP6 Port Facilities.
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4.
RESULTS
4.1
Consolidated map of BPPH
Mapping of BPPH, including mangroves, has been undertaken both within the proposed dredge
footprint and disposal ground, where direct habitat losses may occur, and in adjacent areas
potentially influenced by indirect impacts. Figure 4-1 provides a consolidated benthic habitat map
for within Port Hedland inner harbour which has been developed from all available data as discussed
in Section 1.
A GIS intersect analysis of the communities presented on the map give the following areas:
Canopy Algae – 29.1 Ha
Canopy and Small Algae – 1.2 Ha
Canopy and Turf Algae – 0.5 Ha
Hard Coral – 0.2 Ha
Hard Coral, Soft Coral and Small Algae
– 0.02 Ha
• Small Algae – 64.644 Ha
• Small Algae and Turf Algae – 8.53Ha
• Soft Coral – 0.07 Ha
•
•
•
•
•
•
•
•
•
•
•
•
Soft coral and Small Algae – 0.4 Ha
Turf Algae – 72.9 Ha
Avicennia marina Open Heath – 79.8 Ha
Avicennia marina Scrub – 520.6 Ha
Avicennia marina/Rhizophora stylosa – 19.6
Ha
Rhizophora stylosa Low Forest – 187.7 Ha
Rhizophora stylosa Scrub – 52.5 Ha
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Figure 4-1
Consolidated BPPH map for Port Hedland harbour
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4.2
Mapped BPP
4.2.1
Coral Communities
The distribution of habitat supporting coral communities within Port Hedland harbour has been
identified as sparse (<0.1%), and appeared to be limited to three isolated communities; South East
Creek, South West Creek and Stingray Creek. Coral communities are similar between creeks, and are
dominated by small sized corals less than 15 cm in diameter (BHPBIO 2009).
The diversity of hard coral species was relatively low within the creeks, primarily consisting of the
hard coral families Mussidae, Faviidae and Dendrophyllidae. Coral genera identified within the listed
families as sparsely occurring within the harbour include Plesiastrea, Goniopora, Favia, Favites and
Trachyphyllia
(BHPBIO 2008).
These corals are known to be resilient to the effects of
sedimentation and ability to withstand the low light regime common in a highly turbid environment
(Huisman 2004; Gilmour et al. 2006).
Figure 4-2: Acanthastrea exposed at low tide in South West Creek
4.2.2
Seagrass
Investigations undertaken on areas which may be impacted directly from dredging activities,
including nearshore areas and within the Port Hedland harbour identified no seagrass communities .
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4.2.3
Algae
The macroalgae of northwest Western Australia are not well known (Huisman 2004). One of the
most prolific groups of macroalgae present in the Pilbara region is the genus Sargassum (Huisman
2004). These plants exhibit a pattern of annual growth followed by senescence with individual plants
attaining lengths of 3 m by late summer before breaking off above the holdfast in early winter. The
detached Sargassum form large floating rafts, some of which drift ashore while others are carried
offshore by tidal and wind induced surface currents. These algae are known to occur on the shoals
offshore from Port Hedland (LeProvost et al. 1984). During this field investigation it was noted that a
small amounts of macroalgae were also present within dredging footprint. In addition some turfing
algae were present on the rocky substrate at the junction of West and South West Creek (Figure
4-3).
Figure 4-3: Turfing algae community identified at the junction of South West Creek and
West Creek
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4.2.4
Bare Sediment & Microphytobenthos
The largest area of habitat consists of bare sediment, which is dominated by mud or sand with
sparse shell fragments (Figure 4-4). The region is highly turbid due to a combination of natural and
anthropogenic impacts. The area is relatively devoid of features, supporting only very sparse
filamentous green algae and polychaete burrows in some areas.
Given the extent of subtidal sandy habitat within the project area, and the relatively shallow
bathymetry of the inner harbor, it is likely that MPB occurs throughout the project area, although its
abundance and distribution has not been previously described.
MPB generally consist of diatoms, dinoflagellates, cyanobacteria, and other microscopic primary
producers that live on the soft seabed.
WorleyParsons (2010b) surveyed cyanobacterial mats that there were relatively small patches at
among samphires in within Stanley Point (Figure 4-5).
Figure 4-4: Habitat dominated by mud or sand with sparse shell fragments
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Figure 4-5: Decayed cyanobacterial mats observed during the field investigation
4.2.5
Soft-bottom Communities
Hard pavement areas within the Port Hedland Inner Harbour support the settlement of low
abundance of soft corals comprising colonies of gorgonians and sea whips (BHPBIO 2008). Filter
feeder communities were very sparse, with the dominant filter feeder being sponge, and less than
1% coverage was identified in small areas within the inner harbour (BHPBIO 2009).
4.2.6
Mangroves
The mangroves in the Port Hedland area are part of the suite of species that occur in the arid Pilbara
coastal region. In this regional coastal tract, there is a gradient in species richness from north to
south (Semeniuk et al. 1978; Semeniuk 1993), with the northern end of the coastal tract, in the
DeGrey River delta area, supporting eight species of mangrove and the most southern part of the
Pilbara Coast, in the southern to middle Exmouth Gulf area, supporting six species. Port Hedland
occurs towards the northern end of this species richness gradient, with seven species of mangroves
(Avicennia marina, Aegialitis annulata, Aegiceras corniculatum, Bruguiera exaristata, Ceriops tagal,
Osbornia octodonta, and Rhizophora stylosa), with Osbornia octodonta occurring in specific localised
habitats in the Port Hedland region.
The mapping presented in this document has split the communities into:
•
Avicennia marina - open heath
•
Avicennia marina - scrub
•
Avicennia marina/Rhizophora stylosa
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•
Rhizophora stylosa - low forest
•
Rhizophora stylosa - scrub
Typically, dense stands of mangroves occupy areas within the intertidal zone, where tidal inundation
is sufficiently frequent to maintain adequate sediment water content and salinity levels for
colonisation by mangroves. As distance from the waterline increases, the height and cover of
mangrove vegetation decreases, giving way to salt marsh (samphire) and bare tidal flats as
sediments become dryer and more saline (Figure 4-6).
The distribution of various mangrove forest-types and dominant species was determined using a
series of high resolution aerial photographs taken during July 2004 and July 2008. Identification of
dominant mangrove species was based on the results of ground-truthing of transects
(WorleyParsons 2010b).
Figure 4-6: Tidal inundation in relation to mangrove density
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4.3
4.3.1
Spatial Distribution of Benthic Habitats
Proposed dredge footprint
Due to high natural turbidity within the Port Hedland Harbour, it was thought that no significant
subtidal BPPHs existed, with the benthos characterised as fine mud and shell grit (FMG 2004).
Previous reports have described sparse benthic flora present as filamentous green algae with little
epifauna, and Sargassum spp. communities in Stingray Creek (PHPA 2003).
The majority of the harbour area consisted of abiotic substrate (~80%), with sparse patches of turf
algae, small algae and filter feeder communities distributed throughout the harbour. Hard substrate
supporting hard coral and soft coral communities was sparsely distributed, with only very low cover
of benthic primary producers (BPP) and filter feeders recorded. Sargassum spp. and macroalgae was
found in dense patches in the eastern creeks of Stingray Creek. No seagrass communities were
found in the study area.
The most widespread BPPHs in the inner harbour were supporting mixed assemblages of small
algae, turf algae and filter feeder biota classes growing in shallow waters on sand, pebble and
boulder substrates. These communities are not diverse and are dominated by species which are fast
growing and tolerant to the dynamic physical processes of the harbour. Such species are likely to
rapidly recolonise any area of the suitable habitat within the harbour in the event of disturbance.
The dredge footprint was generally unvegetated. Macroalgae and turf algae habitat was recorded
from a small number of the sites surveyed (10 and 4 sites, respectively). Polygons representing the
likely distribution of each BPPH type were produced, based on the point data. The habitats within
dredge footprint are considered typical of those found within the creek systems surrounding the
inner port area with bare sediments and macro algae being the most dominant habitat types (Figure
4-7).The coverage of benthic habitats within the proposed dredge footprint is presented within
Table 4-1.
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1
Table 4-1
Coverage of benthic habitats within the proposed dredge footprint
Benthic Habitat type
Coverage (ha)
Percentage Cover (%)
Small algae
4.70 ha
11%
Soft coral and small algae
0.19 ha
0.01%
Turf algae
2.30 ha
0.05%
Bare silt/sand
331.12 ha
78%
1
10.94% not surveyed
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Figure 4-7
Map of BPPH types within the proposed dredge footprint
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An assessment of non-BPPH was also undertaken, with a significant cover (≥ 10%) of filter feeders
(sponge and soft coral) recorded at one site (E20, Figure 3-1).
4.3.2
Proposed disposal area
As Spoil Ground I is an existing and active disposal area, a survey for BPPH was not undertaken.
Approximately 1.85 Mm3 of dredge material has been dumped over three maintenance dredging
events in 2001, 2004 and 2007, averaging between 500,000 m3 and 850,000 m3. In 2009, 880,000 m3
of capital material was disposed at Spoil Ground I from dredging undertaken at Harriet Point. Any
BPPH originally occurring within this area was considered ‘lost’ following the initial use of this area
as a disposal area.
Water depths within Spoil Ground I range in depth from -8 to -13 m CD (chart datum). The disposal
ground area does not support any benthic primary producers of significance due to the lack of
available hard substrate for colonisation by corals and macroalgae, and the shifting nature of the
sediments which pose a significant challenge for colonisation by seagrass (GHD 2007). The majority
of biota present within Spoil Ground I is invertebrate infauna (GHD 2007).
Surveys of the benthic habitats of offshore and nearshore reefs and adjacent islands within the Port
Hedland region and a representative area (‘Spoil Ground One’) immediately adjacent to Spoil
Ground I was undertaken between January and February 2008 for BHPBIO Outer Harbour
Development. This representative area was found to be barren with limited benthic biota observed
(Figure 4-8). In addition, no notable BPPH or feeding grounds for higher trophic level organisms were
recorded during the survey (BHPBIO 2009).
Descriptions of benthic habitats from the BHPBIO (2009) baseline surveys in the broader area of
Spoil Ground I indicated that the benthic habitat offshore from Port Hedland is characterised by
extensive plains of sand/silt substratum (within and in close proximity to Spoil Ground I) and ridge
lines of hard pavement. A number of offshore ridge lines were identified which were found to
support occasional patches of sparse biota, including macroalgal habitat, hard corals, sponges and
soft corals (e.g. gorgonians, sea whips) (BHPBIO 2009) (Figure 4-8). Of the hard coral habitat
surveyed, the dominant genus was Turbinaria. Other species recorded included Porites and
Acropora at some survey locations. At two sites closer to the coastline (i.e. near Weerdee and
Downes Islands), there were a few small colonies of Turbinaria observed in highly turbid water
(BHPBIO 2009).A map of BPPH in the area surrounding Spoil Ground I has previously been prepared
for BHPBilliton’s RGP6 project and is reproduced Figure 4-8.
21
Port Hedland Port Authority
South West Creek Dredging Approvals – Benthic Habitats
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Figure 4-8
4.3.3
Benthic Habitats of Spoil Ground I (BHPBIO 2009)
Mangrove habitat influenced by dredge activities
The dominant species types in the area, Avicennia marina and Rhizophora stylosa, are readily
distinguishable from one another and were mapped with a reasonably high reliability. Ceriops
australis and other minor species could not be reliably identified using aerial photographs and were
therefore not mapped. However the ground-truthing survey found that these species are present in
the area in low abundances.
Mangrove communities were identified based on mangrove
assemblage classification descriptions provided by Semeniuk (2007) A total of five community types
were identified:
•
Avicennia marina & Ceriops australis open heath - an open formation (<60% vegetated),
dominated by Avicennia.
•
Avicennia marina & Ceriops australis scrub - closed vegetation with trees 2-4 m high.
•
Avicennia marina low forest - closed vegetation with trees 4-6 m high.
22
Port Hedland Port Authority
South West Creek Dredging Approvals – Benthic Habitats
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•
Rhizophora stylosa scrub - closed vegetation with trees 2-4 m high.
•
Rhizophora stylosa low forest - closed vegetation with trees 4-6 m high.
The developed mangrove community classification map has been provided in Figure 4-9
(WorleyParsons 2010b). Figure 4-9 was morphed to data collected by SKM in 2009 (2009a) to
produce the composite shown in Figure 4-1.
Figure 4-9
Distribution of mangroves surrounding South West Creek
23
Port Hedland Port Authority
South West Creek Dredging Approvals – Benthic Habitats
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5.
DISCUSSION
5.1
Benthic Habitats in the Proposed Dredge Footprint
The following subtidal BPP Habitats will be directly lost due to dredging:
•
Small Algae – 4.7 ha.
•
Soft Coral and Small Algae (grouped) – 0.19 ha; and
•
Turf Algae – 2.2 ha.
5.2
Benthic Habitats in Spoil Ground 1
Descriptions of benthic habitats from the BHPBIO (2008) baseline surveys in the broader area of
Spoil Ground I indicated that the benthic habitat offshore from Port Hedland is characterised by
extensive plains of sand/silt substratum (within and in close proximity to Spoil Ground I) and ridge
lines of hard pavement. A number of offshore ridge lines were identified which were found to
support occasional patches of sparse biota, including macroalgal habitat, hard corals, sponges and
soft corals (e.g. gorgonians, sea whips) (BHPBIO 2008). Of the hard coral habitat surveyed, the
dominant genus was Turbinaria. Other species recorded included Porites spp. and Acropora spp. at
some survey locations. At two sites closer to the coastline (i.e. near Weerdee and Downes Islands),
there were a few small colonies of Turbinaria observed in highly turbid water (BHPBIO 2008).
Due to the Spoil Ground I’s historical and continued use as an area for disposal of dredged material
the area does not support any flora or fauna of significance due to the lack of available hard
substrate for colonisation by corals and macroalgae, and the shifting nature of the sediments which
pose a significant challenge for colonisation by seagrasses (GHD 2007).
5.3
Benthic Habitat Impacts in the Broader Zone of Influence
The combined benthic habitat map (Figure 4-1) developed from data from this baseline habitat
survey and benthic habitat mapping for previous projects (i.e. BHPBIO 2008; BHPBIO 2009) has
identified the following benthic habitats (excluding mangroves) occurring within the inner harbor:
•
Canopy algae
•
Small algae
•
Small algae and turf
•
Avicennia marina - open heath
24
Port Hedland Port Authority
South West Creek Dredging Approvals – Benthic Habitats
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algae
•
Avicennia marina - scrub
•
Soft coral
•
•
Soft coral and small
algae
•
Turf algae
•
Avicennia marina/Rhizophora
stylosa
•
Canopy and small algae
•
Canopy and turf algae
•
Hard coral
•
Hard coral, soft coral and small
•
algae
Rhizophora stylosa - low forest
Rhizophora stylosa - scrub
These can be broken down into coral and algae communities, which are dependent on light reaching
the bottom. It difficult to understand cumulative impacts or impacts previously survived by these
species. These communities are known to be resilient and tolerant to high sediment loads.
WorleyParsons (2010a) undertook predictive light modelling from major dredging projects in a
separate study to understand previously tolerated light regimes of these BPP.
25
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South West Creek Dredging Approvals – Benthic Habitats
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6.
REFERENCES
BHPBIO (2008). Environmental Referral Document: Port Hedland Finucane Island Dredging, October
2008.
BHPBIO (2009). Environmental Referral Document - Nelson Point Dredging, RGP6 Port Development,
Port Hedland. Assessment on Referred Information.
EPA (2009). Environmental Assessment Guideline 3: Protection of Benthic Primary Producer Haitats
in Western Australia's Marine Environment. Perth, WA, Environmental Protection
Authority.
FMG (2004). "Pilbara Iron Ore and Infrastructure Project. Marine Environmental Impacts and their
Management. Prepared for Fortescue Metals Group by DAL Science & Engineering Pty Ltd."
GHD (2007). Long Term Dredge Material Management Plan. Brisbane.
Gilmour, J. P., T. F. Cooper, et al. (2006). Early warning indicators of change in the condition of corals
and coral communities in response to key anthropogenic stressors in the Pilbara, Western
Australia, Australian Institute of Marine Science.
Huisman, J. M. (2004). "Marine benthic flora of the Dampier Archipelago, Western Australia."
Records of the Western Australian Museum Supplement 66: 61-68.
LeProvost, Semeniuk, et al. (1984). Port Hedland Port Development Notice of Intent. Vol. 1 & 2.
PHPA.
(2001).
"
Facilities
and
Port
Services:
Description."
from
http://www.phpa.wa.gov.au/. Port Hedland Port Authority
PHPA (2003). "Port Hedland Port Authority Environmental Management Plan. January 2003.".
Semeniuk, V. (1993). "The mangrove systems of Western Australia 1993 : Presidential Address."
Journal of the Royal Society of Western Australia. 76: 99-122
Semeniuk, V. (2007). The mangroves of Utah Point, Port Hedland - regional setting, description,
processes, significance, prediction of port construction impacts, and mitigation. Port
Hedland Port Authority. Port Hedland.
26
Port Hedland Port Authority
South West Creek Dredging Approvals – Benthic Habitats
Survey Report
Semeniuk, V., K. Kenneally, et al. (1978). Mangroves of Western Australia. . Perth, Western
Australian Naturalists' Club. .
SKM (2009a). Benthic Primary Producer Assessment Intertidal. RGP6 Port Facilities.
SKM (2009b). "RGP6 Port Facilities Definition Phase Study - BPPH: Subtidal Habitat Mapping."
WorleyParsons (2010a). Benthic Habitat Dredging Tolerances and Implications for this Project. Tug
Harbour and Cyclone Mooring Facility.
WorleyParsons (2010b). South West Creek Tug Harbour and Small Vessel Cyclone Mooring Facility
Baseline Mangrove Community Investigation.
27
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Appendix 1 – Survey Site Locations
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Port Hedland Port Authority
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Survey Report
Benthic Habitat Survey Site Locations (GDA 94)
Transect Number
Site Number
Easting
Northing
A
1
663217.76
7751043.50
A
2
663249.28
7751082.31
A
3
663280.81
7751121.11
A
4
663312.34
7751159.92
A
5
663343.86
7751198.73
A
6
663375.39
7751237.54
A
7
663406.92
7751276.35
A
8
663438.44
7751315.16
A
9
663469.97
7751353.96
A
10
663501.49
7751392.77
A
11
663533.02
7751431.58
A
12
663564.55
7751470.39
A
13
663596.07
7751509.20
A
14
663627.60
7751548.01
A
15
663659.13
7751586.82
A
16
663690.65
7751625.62
A
17
663722.18
7751664.43
A
18
663753.70
7751703.24
A
19
663785.23
7751742.05
B
1
663256.57
7751011.97
B
2
663288.09
7751050.78
B
3
663319.62
7751089.59
B
4
663351.15
7751128.40
B
5
663382.67
7751167.20
B
6
663414.20
7751206.01
B
7
663445.72
7751244.82
B
8
663477.25
7751283.63
B
9
663508.78
7751322.44
B
10
663540.30
7751361.25
B
11
663571.83
7751400.06
B
12
663603.36
7751438.86
B
13
663634.88
7751477.67
B
14
663666.41
7751516.48
B
15
663697.93
7751555.29
B
16
663729.46
7751594.10
B
17
663760.99
7751632.91
B
18
663792.51
7751671.72
B
19
663824.04
7751710.52
B
20
663855.56
7751749.33
29
Port Hedland Port Authority
South West Creek Dredging Approvals – Benthic Habitats
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Transect Number
Site Number
Easting
Northing
C
1
663295.38
7750980.44
C
2
663326.90
7751019.25
C
3
663358.43
7751058.06
C
4
663389.95
7751096.87
C
5
663421.48
7751135.68
C
6
663453.01
7751174.49
C
7
663484.53
7751213.30
C
8
663516.06
7751252.10
C
9
663547.59
7751290.91
C
10
663579.11
7751329.72
C
11
663610.64
7751368.53
C
12
663642.16
7751407.34
C
13
663673.69
7751446.15
C
14
663705.22
7751484.96
C
15
663736.74
7751523.76
C
16
663768.27
7751562.57
C
17
663799.79
7751601.38
C
18
663831.32
7751640.19
C
19
663862.85
7751679.00
C
20
663894.37
7751717.81
D
1
663334.18
7750948.92
D
2
663365.71
7750987.73
D
3
663397.24
7751026.54
D
4
663428.76
7751065.34
D
5
663460.29
7751104.15
D
6
663491.82
7751142.96
D
7
663523.34
7751181.77
D
8
663554.87
7751220.58
D
9
663586.39
7751259.39
D
10
663617.92
7751298.19
D
11
663649.45
7751337.00
D
12
663680.97
7751375.81
D
13
663712.50
7751414.62
D
14
663744.02
7751453.43
D
15
663775.55
7751492.24
D
16
663807.08
7751531.05
D
17
663838.60
7751569.85
D
18
663870.13
7751608.66
D
19
663901.66
7751647.47
D
20
663933.18
7751686.28
D
21
663964.71
7751725.09
30
Port Hedland Port Authority
South West Creek Dredging Approvals – Benthic Habitats
Survey Report
Transect Number
Site Number
Easting
Northing
E
1
663372.99
7750917.39
E
2
663404.52
7750956.20
E
3
663436.05
7750995.01
E
4
663467.57
7751033.82
E
5
663499.10
7751072.63
E
6
663530.62
7751111.43
E
7
663562.15
7751150.24
E
8
663593.68
7751189.05
E
9
663625.20
7751227.86
E
10
663656.73
7751266.67
E
11
663688.25
7751305.48
E
12
663719.78
7751344.29
E
13
663751.31
7751383.09
E
14
663782.83
7751421.90
E
15
663814.36
7751460.71
E
16
663845.89
7751499.52
E
17
663877.41
7751538.33
E
18
663908.94
7751577.14
E
19
663940.46
7751615.95
E
20
663971.99
7751654.75
E
21
664003.52
7751693.56
E
22
664035.04
7751732.37
F
1
663411.80
7750885.87
F
2
663443.33
7750924.67
F
3
663474.85
7750963.48
F
4
663506.38
7751002.29
F
5
663537.91
7751041.10
F
6
663569.43
7751079.91
F
7
663600.96
7751118.72
F
8
663632.48
7751157.53
F
9
663664.01
7751196.33
F
10
663695.54
7751235.14
F
11
663727.06
7751273.95
F
12
663758.59
7751312.76
F
13
663790.12
7751351.57
F
14
663821.64
7751390.38
F
15
663853.17
7751429.19
F
16
663884.69
7751467.99
F
17
663916.22
7751506.80
F
18
663947.75
7751545.61
F
19
663979.27
7751584.42
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South West Creek Dredging Approvals – Benthic Habitats
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Transect Number
Site Number
Easting
Northing
F
20
664010.80
7751623.23
F
21
664042.32
7751662.04
F
22
664073.85
7751700.84
F
23
664105.38
7751739.65
G
1
663450.61
7750854.34
G
2
663482.14
7750893.15
G
3
663513.66
7750931.96
G
4
663545.19
7750970.77
G
5
663576.71
7751009.57
G
6
663608.24
7751048.38
G
7
663639.77
7751087.19
G
8
663671.29
7751126.00
G
9
663702.82
7751164.81
G
10
663734.35
7751203.62
G
11
663765.87
7751242.42
G
12
663797.40
7751281.23
G
13
663828.92
7751320.04
G
14
663860.45
7751358.85
G
15
663891.98
7751397.66
G
16
663923.50
7751436.47
G
17
663955.03
7751475.28
G
18
663986.55
7751514.08
G
19
664018.08
7751552.89
G
20
664049.61
7751591.70
G
21
664081.13
7751630.51
G
22
664112.66
7751669.32
G
23
664144.19
7751708.13
H
1
663489.42
7750822.81
H
2
663520.94
7750861.62
H
3
663552.47
7750900.43
H
4
663584.00
7750939.24
H
5
663615.52
7750978.05
H
6
663647.05
7751016.86
H
7
663678.58
7751055.66
H
8
663710.10
7751094.47
H
9
663741.63
7751133.28
H
10
663773.15
7751172.09
H
11
663804.68
7751210.90
H
12
663836.21
7751249.71
H
13
663867.73
7751288.52
H
14
663899.26
7751327.32
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Transect Number
Site Number
Easting
Northing
H
15
663930.78
7751366.13
H
16
663962.31
7751404.94
H
17
663993.84
7751443.75
H
18
664025.36
7751482.56
H
19
664056.89
7751521.37
H
20
664088.42
7751560.18
H
21
664119.94
7751598.98
H
22
664151.47
7751637.79
H
23
664182.99
7751676.60
33