COCKBURN SOUND MANAGEMENT COUNCIL
THE STATE OF COCKBURN SOUND:
A PRESSURE-STATE-RESPONSE REPORT
Prepared for:
COCKBURN SOUND MANAGEMENT COUNCIL
Prepared by:
D.A. LORD & ASSOCIATES PTY LTD
In association with:
PPK ENVIRONMENT AND INFRASTRUCTURE PTY LTD
JUNE 2001
REPORT NO. 01/187/1
CONTENTS
EXECUTIVE SUMMARY __________________________________________________ v
1. INTRODUCTION ________________________________________________________ 1
1.1
1.2
1.3
1.4
BACKGROUND ___________________________________________________________________
ENVIRONMENTAL HISTORY OF COCKBURN SOUND _________________________________
ENVIRONMENTAL MANAGEMENT APPROACH FOR COCKBURN SOUND _______________
THIS DOCUMENT _________________________________________________________________
1
2
5
7
2. MARINE COMPONENT __________________________________________________ 9
2.1 REGIONAL CONTEXT _____________________________________________________________ 9
2.2 ECOSYSTEM OVERVIEW __________________________________________________________ 9
2.3 STATE OF THE MARINE ENVIRONMENT ___________________________________________ 10
2.3.1 Water movement in the Sound ____________________________________________________ 10
2.3.2 Coastal processes _____________________________________________________________ 18
2.3.3 Water quality _________________________________________________________________ 22
2.3.4 Marine sediments______________________________________________________________ 29
2.3.5 Marine flora__________________________________________________________________ 32
2.3.6 Marine fauna _________________________________________________________________ 40
2.4 PRESSURES ON THE MARINE ENVIRONMENT ______________________________________ 43
2.4.1 Ecosystem overview ____________________________________________________________ 43
2.4.2 Physical alterations to the environment ____________________________________________ 44
2.4.3 Nutrient enrichment ____________________________________________________________ 44
2.4.4 Contaminants_________________________________________________________________ 47
2.4.5 Cooling waters________________________________________________________________ 48
2.4.6 Foreign marine organisms_______________________________________________________ 48
2.4.7 Commercial and recreational fishing ______________________________________________ 49
2.5 MANAGEMENT RESPONSES ______________________________________________________ 51
2.5.1 Current management responses___________________________________________________ 51
2.5.2 Gaps in the management responses________________________________________________ 52
2.5.3 Gaps in information needed for management ________________________________________ 53
3. LAND COMPONENT ___________________________________________________ 61
3.1 OVERVIEW______________________________________________________________________ 61
3.2 THE LAND AND ITS USES_________________________________________________________ 61
3.2.1 Coastal fringe landform_________________________________________________________ 61
3.2.2 Groundwater aquifers __________________________________________________________ 61
3.2.3 Coastal flora and fauna _________________________________________________________ 62
3.2.4 Land uses ____________________________________________________________________ 64
3.3 PRESSURES ON COCKBURN SOUND DUE TO LAND USE _____________________________ 68
3.3.1 Contaminants from different land uses _____________________________________________ 68
3.3.2 Contamination of groundwater ___________________________________________________ 69
3.3.3 Contaminant inputs due to surface waters and atmospheric fallout _______________________ 70
3.4 ENVIRONMENTAL MANAGEMENT OF LAND USE ___________________________________ 71
3.4.1 Current management responses___________________________________________________ 71
3.4.2 Gaps in the management responses________________________________________________ 72
3.4.3 Gaps in information needed for management ________________________________________ 72
4. SOCIAL AND CULTURAL COMPONENT _________________________________ 73
4.1 OVERVIEW______________________________________________________________________ 73
4.2 SOCIAL AND CULTURAL USES OF COCKBURN SOUND AND ITS FORESHORE__________ 73
4.2.1 Existing and potential social uses _________________________________________________ 73
4.2.2 Aesthetics/seascapes ___________________________________________________________ 79
4.2.3 Heritage _____________________________________________________________________ 79
4.3 PRESSURES ON COCKBURN SOUND DUE TO SOCIAL AND CULTURAL USES __________ 80
4.3.1 Existing and potential uses ______________________________________________________ 80
4.3.2 Aesthetics/seascapes ___________________________________________________________ 81
4.3.3 Heritage _____________________________________________________________________ 81
4.4 ENVIRONMENTAL MANAGEMENT OF SOCIAL AND CULTURAL USES ________________ 81
4.4.1 Current management responses___________________________________________________ 81
4.4.2 Gaps in the management responses________________________________________________ 82
4.4.3 Gaps in information needed for management ________________________________________ 83
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
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5. ECONOMIC COMPONENT ______________________________________________ 85
5.1 OVERVIEW______________________________________________________________________ 85
5.2 ECONOMIC USES OF COCKBURN SOUND __________________________________________ 85
5.2.1 Industry _____________________________________________________________________ 85
5.2.2 Shipping (Commercial and Defence)_______________________________________________ 85
5.2.3 Commercial fishing ____________________________________________________________ 89
5.2.4 Aquaculture __________________________________________________________________ 90
5.2.5 Tourism _____________________________________________________________________ 90
5.3 PRESSURES ON COCKBURN SOUND DUE TO ECONOMIC USES _______________________ 91
5.3.1 Industry _____________________________________________________________________ 91
5.3.2 Shipping _____________________________________________________________________ 91
5.3.3 Commercial fishing ____________________________________________________________ 92
5.3.4 Aquaculture __________________________________________________________________ 93
5.3.5 Tourism _____________________________________________________________________ 93
5.4 ENVIRONMENTAL MANAGEMENT OF ECONOMIC USES_____________________________ 93
5.4.1 Current management responses___________________________________________________ 93
5.4.2 Gaps in the management responses________________________________________________ 96
5.4.3 Gaps in information needed for management ________________________________________ 97
6. RECOMMENDED RESEARCH AND INVESTIGATION PROGRAMME _______ 99
6.1 MARINE ________________________________________________________________________ 99
6.2 LAND___________________________________________________________________________ 99
6.3 SOCIAL AND CULTURAL ________________________________________________________ 100
7. REFERENCES AND FURTHER RECOMMENDED READING ______________ 101
8. ACKNOWLEDGMENTS________________________________________________ 113
9. GLOSSARY ___________________________________________________________ 115
10.
ii
ABBREVIATIONS__________________________________________________ 117
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
TABLES
Table 1.1
Relationship between Environmental Values and Environmental Quality
Objectives _____________________________________________________ 6
Table 2.1
Flushing times for Cockburn Sound ________________________________ 18
Table 2.2
Average chlorophyll levels at various sites in Cockburn Sound, summer
2000/2001 ____________________________________________________ 25
Table 2.3
Changes in nitrogen concentrations in Cockburn Sound sediments ________ 30
Table 2.4
Sediment contaminant levels in 1994 sediment survey (DEP, 1996) and
1999 sediment survey (DAL, 2000)_________________________________ 31
Table 2.5
Estimated changes in plant production in Cockburn Sound since the
1950s ________________________________________________________ 37
Table 2.6
Estimated changes in nitrogen used by plants in Cockburn Sound since
the 1950s _____________________________________________________ 38
Table 2.7
Summary of emergency overflows from the Woodman Point Wastewater
Treatment Plant to Cockburn Sound since 1990 _______________________ 45
Table 2.8
Estimated contaminant inputs from licensed industrial discharges to
Cockburn Sound________________________________________________ 47
Table 2.9
Potential framework for cumulative impact assessment strategy __________ 59
Table 3.1
Estimated loads of nitrogen in groundwater discharged to Cockburn
Sound ________________________________________________________ 70
Table 4.1
Recreational fishing effort in the Cockburn Sound/Owen Anchorage
region, 1996/97 ________________________________________________ 73
Table 4.2
Estimated boat use at public boat ramps _____________________________ 79
Table 5.1
Ship arrivals to Cockburn Sound (FPA outer harbour) in 2000 ___________ 85
Table 5.2
Operators and cargo handled at commercial jetties in Cockburn Sound _____ 88
Table 5.3
Details of commercial fisheries operating in Cockburn Sound Fisheries
Block 9600 ____________________________________________________ 89
Table 5.4
Licensed industrial discharges to Cockburn Sound _____________________ 91
FIGURES
Figure 1.1
Cockburn Sound_________________________________________________ 3
Figure 1.2
The Pressure-State-Response model _________________________________ 7
Figure 2.1
Wave height in Cockburn Sound during a severe storm with westerly
winds ________________________________________________________ 11
Figure 2.2
Surface circulation patterns during summer (left) and winter (right) _______ 13
Figure 2.3
Depth-averaged currents during summer in Cockburn Sound and
surrounds _____________________________________________________ 13
Figure 2.4
Transect from Fremantle through Cockburn Sound and out through the
Causeway, showing water density conditions representative of summer ____ 16
Figure 2.5
Transect from Fremantle through Cockburn Sound and out through the
Causeway, showing water density conditions representative of autumn_____ 16
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
iii
Figure 2.6
Transect from Fremantle through Cockburn Sound and out through the
Causeway, showing water density conditions representative winter-spring __ 17
Figure 2.7
Shoreline movement in Mangles Bay from DMH (1992) ________________ 21
Figure 2.8
Summer water quality monitoring sites in Cockburn Sound ______________ 22
Figure 2.9
Summer chlorophyll levels in Cockburn Sound versus summer nitrogen
inputs from human activities (outfall discharges; groundwater; surface
water; atmospheric deposition; and spills from ship loading/unloading) ____ 23
Figure 2.10
Summer chlorophyll levels in Cockburn Sound versus summer nitrogen
inputs from human activities (outfall discharges excluding the Woodman
Point WWTP outfall; groundwater; surface water; atmospheric
deposition; and spills from ship loading/unloading) ____________________ 24
Figure 2.11
Summer water quality at Cockburn Sound sites 6, 8, 9 and 10, versus
summer nitrogen inputs from human activities (outfall discharges;
groundwater; surface water; atmospheric deposition; and spills from ship
loading/unloading) ______________________________________________ 26
Figure 2.12
Estimated nitrogen inputs from sediments and human activities in 1978,
and amount of nitrogen required by phytoplankton and MPB ____________ 28
Figure 2.13
Estimated nitrogen inputs from sediments and human activities in 2000,
and amount of nitrogen required by phytoplankton and MPB ____________ 28
Figure 2.14
Benthic habitats in Cockburn Sound ________________________________ 33
Figure 2.15
Historical sequence of seagrass dieback in Cockburn Sound _____________ 35
Figure 2.16
Conceptual diagram of nutrient cycling processes in Cockburn Sound in
1950 _________________________________________________________ 39
Figure 2.17
Conceptual diagram of nutrient cycling processes in Cockburn Sound in
1978 _________________________________________________________ 39
Figure 2.18
Conceptual diagram of nutrient cycling processes in Cockburn Sound in
2000 _________________________________________________________ 40
Figure 2.19
Estimated nutrient inputs to Cockburn Sound from outfall discharges;
groundwater; surface water; atmospheric deposition; and spills from ship
loading/unloading in 1978, 1990 and 2000 ___________________________ 46
Figure 2.20
Annual commercial fish catches in Cockburn Sound Fisheries Block
9600 since 1977 (excludes mussels from aquaculture) __________________ 50
Figure 3.1
Land uses in Cockburn Sound’s catchment ___________________________ 65
Figure 4.1
Social and cultural uses of Cockburn Sound __________________________ 74
Figure 4.2
Peak recreational use in Owen Anchorage during snap-shot survey________ 78
Figure 5.1
Economic uses of Cockburn Sound _________________________________ 86
Figure 5.2
Types of commodities handled by the FPA___________________________ 88
APPENDICES
Appendix A Estimation of nutrient pools and nutrient turnover in Cockburn Sound ____ 121
Appendix B
iv
Estimation of nutrient and contaminant inputs into Cockburn Sound______ 125
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
EXECUTIVE SUMMARY
Cockburn Sound is the most intensively used marine embayment in Western Australia. Its deep,
sheltered waters are extremely popular for fishing and recreation, and it is also the site of a busy port,
an industrial area that depends on port facilities, and a strategic naval base. These multiple uses
demand careful environmental management and planning, especially as all types of use are expected to
intensify.
The Cockburn Sound Management Council (CSMC) is currently preparing an Environmental
Management Plan (EMP) to coordinate environmental management and planning for the Sound and its
catchment. The EMP needs to be based on up-to-date information on the environmental state of the
Sound, the pressures on it, and the management responses in place to manage those pressures. This
document is a Pressure-State Response (P-S-R) report prepared to provide that information. The
report follows the proposed EMP structure of four components: marine, land, social/cultural and
economic. Key gaps in management responses and information that are making management more
difficult have also been identified, and a research programme recommended to address information
gaps.
MARINE COMPONENT
Studies in the late 1970s found that industrial discharge into Cockburn Sound had caused widespread
contamination of sediments and biota, poor water quality and widespread loss of seagrass on the
eastern margin of the Sound. The loss of seagrass was attributed to light starvation due, in turn, to
shading caused by nutrient-stimulated growth of epiphytes (algae that grow on seagrass leaves) and
phytoplankton (microscopic algae in the water). The two main sources of nutrients were pipeline
discharges: the KNC/CSBP outfall, and the Water Authority’s Woodman Point wastewater treatment
plant outfall.
In the early 1990s, the Southern Metropolitan Coastal Water Study (SMCWS) found that seagrass
dieback had slowed considerably, but nutrient-related water quality was only slightly better than in the
late 1970s. Contaminated groundwater had replaced industrial discharge as the main nitrogen input to
the Sound, and came mainly from two short areas of coastline: the southern part of the Kwinana
Industrial Area; and in the Jervoise Bay Northern Harbour. Industrial discharge of metals and organic
contaminants (e.g. pesticides and petroleum products) had decreased substantially, as had
contamination of sediments and biota. There was, however, widespread contamination of sediments
and mussels with tributyltin (TBT, a highly toxic ingredient in antifoulant paints commonly applied to
boats), with particularly high levels near harbours, marinas and commercial and naval wharves. The
introduction of foreign marine organisms via shipping activities (ballast discharge, hull fouling) was
also raised as a concern.
Work undertaken since the early 1990s has found no further deterioration of the health of surviving
seagrass meadows, and no significant losses related to water quality. Overall water quality has
improved slightly since the early 1990s, apart from in the Jervoise Bay Northern Harbour. Nutrient
inputs from human activities have declined from a estimated 2000 tonnes/year in 1978 to about 300
tonnes/year in 2000, about 70% of which is from groundwater. The three main areas from which
nutrient-rich groundwater is coming are: the southern part of the Kwinana Industrial Area
(74 tonnes/year); the Jervoise Bay Northern Harbour (66 tonnes/year); and rural areas (46
tonnes/year).
Estimated amounts of metals and oil discharged by industry have continued to decrease due to
improved waste treatment practices, and are presently about one sixth to one thousandth of those
discharged in 1978, depending on the contaminant in question. A 1999 sediment survey found that
contaminant levels (including arsenic and mercury) were well below environmental guidelines, apart
from TBT in some areas. TBT levels in sediments were generally lower than in 1994, but still high in
the Jervoise Bay Northern Harbour and adjacent to naval facilities in Careening Bay. A survey in
1999 also confirmed the presence of two acknowledged foreign marine pests in the Sound: the
European fan worm Sabella cf. Spallanzanii, and the Asian date mussel Musculista senhousia. These
two pests are prolific growers and can out compete native species, affecting biodiversity, but this does
not seem to be occurring in Cockburn Sound.
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
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Nutrient-related water quality remains one of the two main environmental concerns in Cockburn
Sound, and there have been concerted efforts by industry to reduce nitrogen inputs from groundwater.
WMC’s Kwinana Nickel Refinery has reduced nitrogen discharges from about 500 tonnes/year in
1990 to 8 tonnes/year; there has been a 14% improvement at the Wesfarmers CSBP site in the four
years to 2000, and inputs to the Jervoise Bay Northern Harbour are expected to decrease from
66 tonnes/year to 26 tonnes/year within a year.
Nutrient-related water quality has been monitored by means of summer surveys of chlorophyll levels
(an accepted measure of phytoplankton growth) since 1977. There have been large decreases in
nitrogen inputs to the Sound during summer, but this has not been matched by a similar decrease in
chlorophyll levels. Up to 1990, the largest nutrient input to Sound was a ‘point’ source (the
KNC/CSBP outfall) that was clearly related to overall chlorophyll levels in the Sound. Now
chlorophyll levels are mainly determined by sediment nutrient cycling and diffuse nutrient inputs
(groundwater), and the relationship between nutrient inputs from human activities and chlorophyll
levels is less direct. With the present level of understanding, it is not possible to predict to what extent
further reductions in diffuse nutrient inputs from human activities will reduce overall chlorophyll
levels in the Sound, and available data indicate any response is likely to be slow. Further reductions in
diffuse nutrient inputs should, however, result in localised improvements in water quality.
The other main environmental concern in Cockburn Sound is TBT contamination, and a number of
management measures address this. The WA State Government has banned the use of TBT on vessels
less than 25 m long, and restricted its use to low-leaching paints on boats over 25 m. The Royal
Australian Navy has banned TBT use on ships less than 40 m in length, and is replacing TBT on larger
warships with a copper-based paint. The Fremantle Port Authority has banned ‘in-water’ hull cleaning
when ships are at berth (believed to be a major contributor of TBT to sediments). Insofar as
international shipping is concerned, the International Maritime Organization has recently announced
that it will ban application of TBT to ship’s hulls from January 2003. These measures are expected to
produce significant decreases in TBT contamination due to shipping movements. The high levels of
TBT in Cockburn Sound sediments at present appear to be more related to shipping maintenance areas
than shipping movements, and forthcoming bans on the use of TBT should reduce inputs from these
areas too.
LAND COMPONENT
Land uses within the Cockburn Sound catchment includes urban areas, defence, industry, agriculture
and conservation. Expansions in urban areas, defence and industrial land use are either planned or
expected, while rural areas are being encroached by urban and industrial use. Coastal areas reserved
for conservation include Woodman Point Regional Park, Beeliar Regional Park and Rockingham
Lakes Regional Park, and their boundaries are unlikely to change.
A population increase of 30% is expected in mainland urban areas in next 10 years, and a 25%
increase in personnel and ships on Garden Island by 2004 (as part of the ‘Two Oceans’ defence
policy). For industrial use, there is the proposed development of 800 hectares of general light
industrial land over the existing townsite of Wattleup, and the extension of heavy industry into 100
hectares of land in the Hope Valley area. The marine construction and maintenance industry is also
expanding in the Henderson shipbuilding area, and there is the proposed East Rockingham Industrial
Park (IP14) between Mandurah and Patterson Roads.
The main way that land uses affect the environment of Cockburn Sound is by contamination of
groundwater and surface water that flows into the Sound. At present, nutrient inputs to the Sound are
largely from groundwater contaminated by industry, but as noted earlier, these are decreasing and the
relative role of rural areas is starting to become significant. There is less information on other
groundwater contaminants such as metals and organic compounds, but indications are that this kind of
contamination does not migrate as far from its source as nutrient contamination, and so is less likely to
be discharged into the Sound.
SOCIAL AND CULTURAL COMPONENT
Cockburn Sound is extremely popular for recreational fishing, water sports (swimming, boating,
yachting, diving, windsurfing, skiing) and beach use. It is also important for the social values of
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COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
aesthetics, maritime heritage (its association with early settlement in WA and the presence of four
historic wreck sites) and indigenous heritage (notably Aboriginal mythology about the creation of
Garden and Rottnest Islands).
Cockburn Sound is particularly popular for family/small boat use, due to its sheltered nature. For
boat-based recreational fishing within coastal waters from Augusta to Kalbarri, the Sound is second in
importance only to the Hillarys area. A 1999 survey of public boat ramps estimated that 44,270 boats
were launched in Cockburn Sound, and this is predicted to increase by 75% in the next 20 years.
Coastal access between the CBH jetty and Woodman Point is becoming increasingly restricted due to
industrial development. Coastal access has emerged as a key issue during preparation of this report.
Community concerns have been expressed that, with population increases, more people will want
beach access, while less and less beach is becoming available. There is the potential for intense
recreational pressure at the Woodman Point and the Rockingham foreshore.
Management of coastal recreational activities focuses on zoning to separate incompatible uses,
ensuring suitable facilities (rubbish bins, toilets) are available and providing suitable paths and/or
barriers to control erosion. The City of Cockburn, Town of Kwinana and City of Rockingham all have
coastal, foreshore and/or recreation management plans in place, all of which are currently being
reviewed and that will undergo further review to ensure consistency with the CSMC’s EMP.
Recreational fishing is managed by means of licences, bag limits, minimum sizes (e.g. fish length,
crab carapace width) and fishing gear controls set by Fisheries WA and enforced by Fisheries Officers.
A review of recreational fisheries management arrangements for the west coast is also currently under
way.
ECONOMIC COMPONENT
Economic uses of Cockburn Sound include industry, shipping (commercial and defence), commercial
fishing, aquaculture and tourism.
Cockburn Sound is the outer harbour of the Port of Fremantle, and there were 967 ship arrivals (232
naval vessels) in 2000. In the 1999/2000 year, the Fremantle Port Authority (inner and outer harbour)
handled 23.4 million tonnes of commodities (mainly petroleum products, grain and alumina), the large
majority in Cockburn Sound. Shipping is closely linked to industry in Cockburn Sound, with industry
in the Kwinana Industrial Area alone estimated to produce goods worth at least $6 billion/year.
Commercial fisheries that operate within Cockburn Sound target crabs (estimated value about
$1 million/year) table fish (estimated value about $240,000/year) and baitfish (estimated value about
$900,000/year, but includes waters outside Cockburn Sound). The mussel aquaculture industry within
Cockburn Sound has a dollar value of the same order as the commercial crab catch. Tourism operators
ferry about 18,000 people through or into Cockburn Sound each year, grossing about $1.4 million.
The main effects—and management—of industry and shipping on Cockburn Sound were discussed
earlier. Commercial fishing and aquaculture in Cockburn Sound are carefully managed activities: the
former by controls on access, boat size, catch size, and fishing gear that can be used; and the latter by
access, and spacing of aquaculture lines. The charter fishing industry also came under management
for fish catches in July 2000, following a major review of charter fishing and associated ecotourism.
KEY GAPS IN MANAGEMENT AND INFORMATION
Management gaps
Previous efforts to manage Cockburn Sound have been hampered by lack of a consistent and
coordinated management approach across different levels of government, industry and community
groups. Two main areas where a coordinated approach is needed are catchment management and
resolution of recreational access, as follows:
•
Industrial discharge to the Sound has decreased substantially, and groundwater quality below
the larger industries is improving. Therefore, the relative contaminant contribution of the more
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
vii
•
diffuse sources throughout the catchment (e.g. rural areas) will increase. In most cases direct
intervention of these sources will not be justified, but long-term improvement in groundwater
quality throughout the catchment could be addressed (and future groundwater problems
avoided) by developing a catchment management plan that involves local councils and major
industrial and rural land users/owners; and
The social and cultural use of Cockburn Sound is arguably one of the most sensitive
management issues in Cockburn Sound. At present, there is no coordinated management
approach examining ways in which the existing coastline—and associated recreational
facilities—can be developed/upgraded/re-zoned to best meet present and future recreational
needs.
The CSMC provides a mechanism for coordinating environmental management and planning, and has
already commenced coordination of the above two activities. There has, however, been some
comment on the exclusion of Garden Island from the defined area under the jurisdiction of the CSMC,
as it needs to be considered as much as the eastern coastal boundary in any environmental planning
and management.
Information gaps
Water quality in the Sound is controlled by factors such as water circulation and exchange, water
depth and the size, proximity and type (eg. outfall discharge or groundwater) of nitrogen input(s):
these factors differ between the shallow regions (i.e. water depths less than 10 m) on the east and west
of the Sound, the deep central basin, and the poorly flushed waters of the southern basin, and are
pivotal in determining the water quality that can be attained. Environmental decision-making is
currently being made more difficult by incomplete understanding of the factors controlling water
quality within the Sound, notably the responses to diffuse nutrient inputs and the role of sediment
nutrient cycling. This information is also needed to predict the effects of any development proposals
that alter circulation and exchange characteristics within and between development area(s). As
accurate prediction of circulation and flushing characteristics is needed before water quality can be
predicted, there are also increasing demands being made of hydrodynamic models.
There are four main areas where information is needed to improve understanding of nutrient-related
water quality:
•
•
•
•
Additional data to improve hydrodynamic modelling of Cockburn Sound (this would also
improve understanding of coastal processes in the Sound);
An agreed conceptual model of nutrient cycling in Cockburn Sound and the effects of nutrient
inputs;
Data on sediment nutrient cycling characteristics; and
An agreed method for evaluating cumulative impacts.
Finally, it is noted that despite the sensitivity surrounding social and cultural uses of Cockburn Sound,
it has not been studied as much as environmental issues. The coordinated management and planning
of social and cultural uses in the Cockburn Sound is in urgent need of data on the type, location and
intensity of recreational uses.
-o0o-
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COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
1.
INTRODUCTION
1.1
BACKGROUND
Coastal areas are favoured sites for concentrated human settlement, especially near
rivers. Settlement in Western Australia is typical of this pattern: the metropolitan
region of Perth, the capital city, is centred on the Swan/Canning estuary, and about
1.3 million people (over 70% of the State’s population) live in a narrow strip of coast
90 km long and 10–40 km wide. People use this environment to supply and
manufacture the goods required for living, to absorb their wastes, and for recreation.
This concentrated level of human activity creates pressures on the coastal
environment that can cause environmental degradation.
Cockburn Sound, some 20 km south of the Perth-Fremantle area, has two features
that are unique along Perth’s metropolitan coast: its degree of shelter from ocean
swell, and its depth (Figure 1.1). As a result of these features, it is also the most
intensively used marine embayment in Western Australia.
The Sound is 16 km long and 9 km wide, with a 17−22 m deep central basin. Garden
Island extends along almost the entire western side of the Sound, providing shelter
from ocean swells and making the Sound an ideal place for recreation and fishing.
The sheltered, deep waters of the Sound make it equally ideal as an outer harbour for
the Perth/Fremantle area, a site for industries requiring port facilities, and a strategic
naval base. As a result, Cockburn Sound experiences the combined pressures of
fishing, recreation, waste disposal, industry, shipping and naval activities.
The multiple uses of Cockburn Sound demand careful, coordinated environmental
planning and management. Lack of such management in the 1960s and 70s resulted
in the environmental degradation of the Sound. Management measures in the 1980s
and 1990s have improved many aspects of the Sound’s environmental health, but
further improvement is needed in some localised areas (e.g. the decline in water
quality in the Jervoise Bay Northern Harbour since 1997). Pressure on the Sound is
also increasing due to population growth and increasing industrial development,
shipping and naval activities.
The Cockburn Sound Management Council (CSMC) is a State Government response
to ongoing concerns about existing and future pressures on Cockburn Sound. The
CSMC is a Committee of the Board of the Water and Rivers Commission (WRC),
and consists of 26 members drawn from a cross-section of state and local
government departments, community groups, industry, and commonwealth defence.
The first CSMC meeting took place in August 2000.
The CSMC’s main role is to develop an Environmental Management Plan (EMP)
that coordinates environmental management and planning for the Sound and its
catchment. In an interrelated exercise, the Environmental Protection Authority
(EPA) and Department of Environmental Protection (DEP) are developing an
Environmental Protection Policy (EPP) for Cockburn Sound, that addresses pollution
issues. This EPP will define environmental quality objectives (EQOs) and
environmental quality criteria (EQC)—particular aspects of water, sediments and
marine organisms (e.g. contaminant levels in water, sediments and fish)—to protect
the recognised environmental values of the Sound. A key focus of the CSMC’s EMP
will be the development of management strategies to ensure the EQOs and EQC of
the EPP are met.
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
1
To develop the EMP, information is needed on the present environmental state of the
Sound, the pressures on it, and the environmental management responses already in
place. The purpose of this report on ‘The State of Cockburn Sound’ is to provide
that information, specifically to:
•
•
•
1.2
Provide an up-to-date description of the state of Cockburn Sound and its
catchment, the pressures on the resources base, and the current management
responses;
Identify the gaps in the current management responses and indicate
management strategies to address these gaps; and
Outline a research and investigation program to improve the information and
knowledge base for future decision-making.
ENVIRONMENTAL HISTORY OF COCKBURN SOUND
Until 1954 Cockburn Sound was used mainly for recreational purposes, commercial
fishing, and—during both World Wars—for Commonwealth defence activities
(particularly on Garden Island). There are many anecdotes of the clear waters,
plentiful fish and extensive, healthy seagrass meadows along the eastern shores of
the Sound during these years (Norm Halse1, pers. com.).
In 1954 industrial development in the Sound commenced with the building of an oil
refinery at James Point. The next 25 years saw the addition of iron, steel, alumina
and nickel refining/processing plants, chemical and fertiliser production plants and a
bulk grain terminal. Wharves and groynes were built and channels dredged for
shipping access: the Sound became the ‘outer harbour’ for the Fremantle Port
Authority. At the northern end of the Sound, a wastewater treatment plant was
commissioned at Woodman Point in 1966 to treat sewage from Perth’s southern
suburbs. At the southern end of the Sound, a rockfill causeway connecting Garden
Island with the mainland was built between 1971−1973. The causeway is broken by
two trestle bridges (one 305 m long, and one 610 m long)2, through which limited
ocean exchange occurs. The causeway was built to service a naval base on Garden
Island, which was constructed between 1973 and 1978.
The developments that took place from 1954 onwards resulted in deterioration of the
environment, and in the 1970s conflict with recreational users became an additional
issue. The first environmental studies were carried out in the early 1970s (funded by
the Fremantle Port Authority) and identified two major environmental problems:
•
•
Deteriorating water quality, due to ‘blooms’ of phytoplankton (microscopic
algae floating in the water); and
Widespread loss of seagrass as a result of light starvation, due in turn to the
shading caused by increased growth of epiphytes (algae that grow on seagrass
leaves) and phytoplankton.
1
Norm Halse, RecFishWest
The present Causeway design is the result of a joint agreement between the Australian Navy (that
wanted an open trestle structure) and the FPA (that wanted a solid connecting groyne to provide
maximum protection against westerly waves for a future merchant shipping harbour).
2
2
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
Figure 1.1 Cockburn Sound
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
3
Due to public pressure, the Western Australian Government funded a three year
(1976−1979) Cockburn Sound Environmental Study (DCE, 1979). The study
identified a large variety of contaminants in industrial discharges to the Sound, and
in groundwater underlying industries. The decline in seagrass meadows and increase
in phytoplankton levels were, however, linked to a massive increase in nutrient
loading to the Sound. It was estimated that over 90% of this increased nutrient
loading came from two sources: the outfall shared by the Kwinana Nitrogen
Company (KNC) and the CSBP fertiliser works, and the outfall of Woodman Point
Wastewater Treatment Plant (WWTP). These two outfalls discharged the nutrients
phosphorus and nitrogen, but nitrogen was identified as the main nutrient responsible
for the increased algal growth. The KNC subsequently installed a steam scrubber to
remove a large proportion of nitrogen from its effluent (December 1982), and the
Water Authority of Western Australia diverted discharge from the Woodman Point
wastewater treatment plant out of Cockburn Sound and into waters 4 km off Cape
Peron (July 1984).
To assess the influence of changes in nitrogen loading to the Sound, weekly
measurements of water quality over summer (variously funded by government and
industry) were carried out. These studies found that although water quality in the
early 1980s was much improved compared to the late 1970s, it declined again during
the late 1980s. This decline in water quality was one of the main triggers for the
DEP’s 1991–94 Southern Metropolitan Coastal Waters Study (DEP, 1996). The
EPA recognised that a better information base was needed to manage the cumulative
impacts of waste discharges into local coastal waters. The SMCWS was undertaken
to meet that need, and studied coastal waters from Fremantle to Mandurah, with
particular attention to Cockburn Sound.
Key findings of the SMCWS for Cockburn Sound were as follows:
•
•
•
•
•
•
4
Nutrient-related water quality in the early 1990s was only slightly better than in
the late 1970s;
Seagrass dieback had slowed considerably, but some losses were still occurring
(mainly at the southern end of the Sound) and there was no evidence of
seagrass re-establishment anywhere;
Unlike the 1970s, industrial outfalls were no longer the main source of nitrogen
entering the Sound. Instead, an estimated 70% of nitrogen inputs was from
contaminated groundwater under two industrial sites: the coastline next to
Western Mining Corporation and CSBP, and north of the shipbuilding area in
Jervoise Bay;
Contaminant inputs from industry were far less than in the late 1970s. Levels
of metals and organic contaminants (e.g. pesticides and petroleum products) in
sediments and mussels were generally well below environmental guidelines
and food standards, except for arsenic and mercury levels in sediments at a few
sites.
There was widespread contamination of sediments and mussels with tributyltin
(TBT, a highly toxic ingredient in antifoulant paints commonly applied to
boats), with particularly high levels near harbours, marinas and commercial
and naval wharves;
All beaches monitored met human health guidelines for swimming and
shellfish harvesting, except Palm Beach, which exceeded the shellfish
harvesting guideline for faecal bacteria; and
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
•
At least 18 species of foreign marine organisms were present, brought in by
discharge of ship ballast water and/or shedding of organisms attached to ships’
hulls.
Economic development of the Cockburn Sound region also accelerated in the 1990s,
with a series of large-scale developments along the eastern margin of Cockburn
Sound being proposed, including:
•
•
•
•
•
A residential marina in Mangles Bay (Department of Transport);
Long-term plans for a harbour at Naval Base/Kwinana (Fremantle Port
Authority);
An additional berth at the FPA bulk cargo jetty (Fremantle Port Authority);
A private port at James Point (James Point Pty Ltd); and
Industrial infrastructure and harbour development in southern Jervoise Bay
Southern Harbour (Department of Commerce and Trade).
Due to concerns about the cumulative environmental impact of these developments,
the EPA prepared Bulletin 907; strategic environmental advice for the marine
environment of Cockburn Sound (EPA, 1998). A key recommendation of Bulletin
907—based in turn on a recommendation of the SMCWS (DEP, 1996)—ultimately
led to the formation of the CSMC.
1.3
ENVIRONMENTAL MANAGEMENT APPROACH FOR COCKBURN
SOUND
One of the main objectives of the SMCWS was to design a coordinated management
approach for the protection of Perth’s coastal waters from pollution, which could
then be extended in principle to other coastal areas of Western Australia (DEP,
1996). This approach involved the following steps:
•
•
•
•
Identification of Environmental Values (EVs) for coastal waters;
Identification of Environmental Quality Objectives (EQOs) to support the EVs;
Deciding the areas where various EQOs will apply; and
Development of Environmental Quality Criteria (EQC) to ensure the EQOs
will be met.
A discussion paper addressing the above issues was released on 19th October 1998
(EPA, 1998), followed by public workshops and an invitation for written public
comment between 19th October and 18th December 1998 (Jacoby et al., 1999). At
these workshops it was recognised that Perth’s metropolitan coast is no longer as it
was before European settlement, and population pressure alone prevents a return to
‘natural’ conditions even with the most stringent management measures. What can
be achieved is ecologically sustainable development, in which environmental, social
and economic goals are integrated.
In February 2000 the EPA released a working document describing Environmental
Values (EVs) and Environmental Quality Objectives (EQOs) for Perth’s coastal
waters (EPA, 2000). The EVs recognise the importance of the marine environment
in terms of:
•
•
Ecosystem health;
Fishing and aquaculture;
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
5
•
•
Recreation and aesthetics; and
Industrial water supply.
Six EQOs, or specific management goals, were developed to protect these EVs. The
EQOs, and their relationship to the EVs are shown in Table 1.1.
Table 1.1 Relationship between Environmental Values and Environmental Quality Objectives
ENVIRONMENTAL VALUE
Ecosystem health
Fishing and aquaculture
Recreation and aesthetics
Industrial water supply
ENVIRONMENTAL QUALITY OBJECTIVE
EQO 1. Maintenance of ecosystem integrity
EQO 2. Maintenance of aquatic life for human
consumption
EQO 3. Maintenance of primary contact recreation
values
EQO 4. Maintenance of secondary contact recreation
values
EQO 5. Maintenance of aesthetic values
EQO 6. Maintenance of industrial water supply
values
The above management approach taken by the EPA/DEP is broadly consistent with
that recommended by the National Water Quality Management Strategy (NWQMS),
as outlined in the Australian and New Zealand Guidelines for Fresh and Marine
Water Quality (ANZECC/ARMCANZ, 2001, due for imminent release). Western
Australia is a signatory to the NWQMS.
The national approach to setting environmental guidelines (similar to EQC) has
moved away from single values that divide what is environmentally acceptable from
what is not (ANZECC/ARMCANZ, 2001). Instead, conservative guidelines are
proposed that are well below any real cause for environmental concern, but which
are sufficient to ‘trigger’ further investigations to determine whether a problem might
exist.
This approach also allows local environmental conditions and the
environmental sensitivity of local species to be taken into account.
The EPA/DEP held a series of workshops in February 2001 to start deriving EQC.
The types of measurements for which EQC are being developed include:
•
•
•
•
•
•
Nutrient-related effects;
Contaminant levels in water and sediments;
Biological indicators of excessive levels of contaminants or nutrients (e.g.
imposex3 in marine snails;
Safety of seafood for human consumption;
Recreational safety (e.g. faecal bacteria in water, harmful algal blooms); and
Aesthetics (e.g. water clarity and colour, dust films, faunal deaths, rubbish,
maintenance of aesthetic features and natural character of the area).
The Cockburn Sound EPP builds on the national strategy by setting three levels of
EQC that demarcate increasing levels of management intervention linked, in turn, to
increasing levels of environmental risk. The first level of EQC—which, if met,
means no management intervention is needed—will be based largely on the national
guidelines (ANZECC/ARMCANZ, 2001), in accordance with their intended
purpose. The types of EQC and their derivation are explained in full by McAlpine
and Masini (2001).
3
6
Development of male reproductive organs in females due to the antifoulant ingredient TBT
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
1.4
THIS DOCUMENT
This report on the State of Cockburn Sound, follows the Pressure-State-Response
(P-S-R), model of the Organisation for Economic Co-operation and Development
(OECD), that has been adopted by National and State governments in Australia for
State of the Environment (SoE) reporting (Figure 1.2).
Figure 1.2 The Pressure-State-Response model
The report is intended to:
•
•
•
Summarise and update the findings of the SMCWS for Cockburn Sound;
Focus on the main factors affecting environmental management; and
Be written in style suitable for the interested public.
The report is not intended to be as detailed or as comprehensive as the SMCWS.
Also, as a broad cross-section of people were consulted during preparation of the
report, opinions sometimes differed on how environmental data should be interpreted
and/or what the most the important factors influencing the environment were. In
addition, comments or explanations were sometimes offered in the absence of
sufficient data to back them, usually to stimulate further discussion and/or direct
further work. Where the report cites differing opinions or speculative statements,
these are clearly identified as such.
The structure of the report follows that of the EMP being prepared by the CSMC,
and so addresses four main ‘components’: marine, land, social/cultural and
economic. These four components are addressed in Sections 2, 3, 4 and 5,
respectively.
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
7
The marine component (Section 2) follows P-S-R format, describing the
environmental state of Cockburn Sound, the main pressures on it, and the responses
currently in place to manage those pressures. Key gaps in management responses
and information are also identified.
The land, social/cultural and economic components (Sections 3, 4 and 5) provide
more detail on these human uses of Cockburn Sound and its catchment that are
causing pressure on Cockburn Sound. The management responses to those pressures
are also described, and the key gaps in management and information identified.
Land uses, social/cultural uses and economic uses are considered only as far as their
potential for pressure on Cockburn Sound.
The final section (Section 6) recommends a research and investigation programme to
provide key information that will improve environmental decision-making.
8
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
2.
MARINE COMPONENT
2.1
REGIONAL CONTEXT
The present Perth metropolitan coastal region was formed by a sea level rise that
took place about 10,000 years ago. At that time, the sea-level was approximately
27 m below present, but rose rapidly over a period of about 3,600 years to reach 3 m
above its present level. Sea level then dropped slightly to reach the present level,
about 1,500 years ago, and has stayed relatively constant since then.
The sharp rise in sea level between 10,000 and 6,400 years ago drowned the previous
shoreline. The present shoreline was formed when the sea spilled over the Garden
Island Ridge into lower land known as the Warnbro-Cockburn Depression. This
depression is bounded on its eastern side by the Spearwood Ridge that forms the
basis of the mainland shore today. Only the high points of the Garden Island Ridge
remain, and form the offshore chain of islands (Penguin Island, Garden Island,
Carnac Island) and reefs seen today (Figure 1.1). Further west another ridge, the
Five Fathom Bank Ridge, is completely submerged (Figure 1.1). These two lines of
islands and reefs protect Perth’s southern coastal waters from ocean swell to varying
degrees.
The Five Fathom Bank Ridge, Garden Island Ridge and Spearwood Ridge are made
up of limestone (Tamala Limestone). Wave action has eroded much of the two
submerged ridges, and transported the eroded sands shorewards. Today’s shoreline
therefore consists of sandy beaches and limestone rocky shores and headlands, while
the seabed consists of extensive sandy areas and limestone reefs. In some areas, the
pattern of wave action has deposited sand at right angles to the shore, forming
shallow sandy banks that separate deeper areas. Cockburn Sound is separated from
Warnbro Sound by Rockingham Bank, and from Owen Anchorage by Parmelia Bank
(Figure 1.1).
The coastal waters of the region are strongly influenced by the Leeuwin current,
which flows from the equator southwards along WA’s coast. The waters of the
Leeuwin current are clear, warm and low in nutrients. Nutrient input to coastal
waters from rivers is also low (by world standards). In addition, due to the
pronounced Mediterranean climate of the region (long, hot, dry summers and cool
wet winters), most river flow occurs in winter and early spring, with little or no river
flow to the sea from late spring to early autumn. Nor are there any nutrient-rich
upwellings of colder, deeper water, such as occur off the south coast of Africa and
South America.
Due to the above combination of factors, the nearshore coastal waters of the southwest of WA are—by world standards—shallow, nutrient-poor, clear, and of low to
moderate wave energy. The strength of the Leeuwin Current and amount of outflow
from rivers also varies considerably from year to year, which can affect regional
water quality.
2.2
ECOSYSTEM OVERVIEW
The nutrient-poor waters of the south-west of WA support little growth of plankton
(microscopic plants and animals), and so lack the rich plankton-based fisheries of
south-west Africa and South America. Instead, marine plant production is dominated
by seagrass ‘meadows’ on the shallow sandy areas (which contribute both seagrass
and epiphyte production), and seaweed ‘gardens’ on the reefs. The fisheries depend
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
9
on the production of these reefs and seagrass meadows, and so are described as
‘benthic’ (seabed)-based, rather than plankton-based.
The diversity and abundance of marine species is highest in and around the reefs,
followed by seagrass meadows. The deep basins (e.g. Cockburn Sound) also support
a rich seabed community dominated by species that feed on detritus (dead and
decaying organic material).
Perth’s coastal waters are essentially a temperate environment, but tropical species
are also found due to the influence of the Leeuwin Current. Perth is within a region
of ‘biogeographical overlap’ that extends from Cape Leeuwin to North West Cape, in
between the main temperate biogeographic region (Cape Leeuwin to South
Australia) and tropical biogeographic region (north-east of North West Cape). This
overlap region has fewer species than the two main biogeographic regions. Perth’s
waters are at the southern end of the overlap region, and so temperate species
predominate. Endemic species (i.e. species only found in Western Australia) make
up 10–25% of the species in Perth’s metropolitan waters, depending on the type of
organism (e.g. crustaceans, shellfish, worms) in question.
Although the region is relatively poor in marine species in general, it has the highest
number of species of seagrass in Australia. There are only about 50 species of
seagrass worldwide, 13 of which are found in Perth’s coastal waters. There are six
main ‘meadow-forming’ species: Amphibolis griffithii, A. antarctica, Posidonia
australis, P. sinuosa, P. angustifolia and P. coriacea.
The most dense stands of seagrass occur in shallow sheltered areas and consist of
meadows of P. sinuosa or P. australis. Cockburn Sound had extensive areas of these
species before the massive seagrass loss that occurred in the late 1960s/early 1970s.
Less sheltered areas (e.g. Owen Anchorage, and much of Marmion Marine Park)
tend to have patchy meadows of A. griffithii and P. coriacea; species that can tolerate
greater wave and current action than P. sinuosa and P. australis.
As noted in Section 1.1, Cockburn Sound is unique along Perth’s metropolitan coast
due to its degree of shelter from ocean shell, and its depth. These physical features
are responsible in turn for its regional significance in ecological terms: extensive
areas of species of seagrass that prefer sheltered conditions, and organic-rich silts on
the seabed of the deep basin that support species of plants and animals not found
elsewhere on the central west coast of Western Australia, other than Warnbro Sound.
2.3
STATE OF THE MARINE ENVIRONMENT
2.3.1
Water movement in the Sound
Modelling of water movement in Cockburn Sound—and of substances transported
by water—has been the subject of a number of studies from about 1977 until present.
The hydrodynamics of the Cockburn Sound region have been reviewed in some
detail by Hearn (1991), D’Adamo (1992) and the DEP (1996). There are also
numerous detailed supporting documents of field work and modelling studies carried
out as part of the SMCWS that are summarised and referenced in DEP (1996).
Studies since 1996 have been more ‘site-specific’ than ‘ecosystem-wide’, and have
focussed on the effects of proposed developments within and adjacent to Cockburn
Sound: these studies have not altered the fundamental understanding of water
movement in the Sound (as established in earlier work), but have refined
understanding of some aspects. The following summary is drawn largely from work
done up to 1996, while areas of improved understanding due to more recent work are
also discussed.
10
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
The hydrodynamics of Perth’s coastal waters is a complex combination of windforced waves, tides, large-scale currents (the Leeuwin and Capes Currents) and
localised currents due to density differences in the water column, and long period
waves (Pattiaratchi et al., 1995). The complexity is due to variations in the relative
strength of each of these factors with the weather and season.
Very little offshore wave energy reaches Cockburn Sound due to the shelter provided
by Garden Island along the western shore, the Causeway at the southern end of the
Sound, and Parmelia Bank at the northern end of the Sound (2–5 m deep, apart from
the 150 m-wide FPA channel, which is 14.7 m deep). The sheltering effect of these
physical barriers during a severe winter storm is shown in Figure 2.1.
Figure 2.1 Wave height in Cockburn Sound during a severe storm with westerly winds
Note : From MRA (2000). Reproduced with permission from Cockburn Cement Limited. Colour grading from large waves in
red through to small waves in blue.
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
11
As little as 5% of the swell wave energy penetrates to southern Cockburn Sound
(DEP, 1996). However, the degree of shelter depends on wave direction and the
location within Cockburn Sound being considered. For example, the gap between
Carnac Island and Garden Island allows some west and north-west swell to reach
James Point, while Southern Flats and the Causeway prevent most south-west swell
from reaching James Point.
As a result of the protected nature of the Sound, the three main processes that control
its hydrodynamics are (Hearn, 1991):
•
•
•
Wind;
Horizontal pressure gradients due to wind, tides, waves, atmospheric pressure
and continental shelf waves (which create differences in water pressure due to
differences in water level); and
Horizontal pressure gradients due to buoyancy effects (differences in water
density).
The three main processes are briefly described below.
Wind
Waves and currents in Cockburn Sound are primarily a result of wind forcing.
During summer the dominant wind direction is south to south-west, and winds are
typically quite persistent: 50% of winds have speeds of 5–9 m/s. The daily sea
breeze cycle is also very important. In winter the main wind direction is westerly,
though northerly winds often occur: winds are more variable with occasional periods
of calm and strong storm winds, and 50% of winds have speeds of 2–7 m/s.
The wave climate in Cockburn Sound is dominated by wind-generated waves. Data
from 1996-1997 indicate that typical waves in summer have a significant wave
height (i.e. the height of the highest one third of waves) of <0.7 m. During winter
storm events, significant wave height approaches 1.25 m (JPPL, 2001).
Wind is also the main driving mechanism of circulation within the Sound when the
wind speed is above 5 m/s. During calm periods (wind speed <5 m/s), circulation
within Cockburn Sound becomes complex and is driven by a combination of wind
and horizontal pressure gradients.
Along the coastal margins of Cockburn Sound and in the surface waters (to a depth
of at least 10 m) the net current is northward during summer, due to the prevailing
south to south-westerly winds. Current velocities are up to 0.2 m/s during average
conditions and are strongest offshore from James Point. During winter, and periods
of calm, the current velocities drop to below 0.1 m/s. The shallow inshore region has
strong, depth-averaged wind-driven flows, but bottom friction results in relatively
rapid (12–24 hours) reduction in flows after the onset of calm conditions (Hearn,
1991). This feature is important when assessing circulation responses with the onset
of calm conditions. Surface currents under typical summer conditions, and under
northerly winds in winter, are shown in Figure 2.2.
Depth-averaged currents provide an indication of the net transport within Cockburn
Sound in summer. The circulation pattern is dominated by two gyres: one
circulating anti-clockwise in the region north of James Point, and one clockwise in
the region south of James Point. These two gyres are shown in Figure 2.3. The
gyres are due to wind-driven flow in the shallow nearshore regions and return flow
against the wind at depth (approximately below 10 m). The return flow at depth
12
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
against the wind arises from alongshore pressure gradients generated by the wind
driven flow.
Figure 2.2 Surface circulation patterns during summer (left) and winter (right)
Note: Adapted from PHC (2000) Oceanographic Review - Project C4: Effects on Circulation and Exchange from the
Construction of a Seaway through Success and Parmelia Banks, reproduced with permission from Cockburn Cement Limited.
Figure 2.3 Depth-averaged currents during summer in Cockburn Sound and surrounds
Note: Obtained from modelling work done as part of PHC (2000) Oceanographic Review - Project C4: Effects on Circulation
and Exchange from the Construction of a Seaway through Success and Parmelia Banks. Reproduced with permission from
Cockburn Cement Limited.
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
13
Horizontal Pressure Gradients
Horizontal pressure gradients are the result of differences in water pressure between
two areas. Differences in water pressure may be grouped into those driven by wind,
tides, waves, seiches and atmospheric pressure (i.e. differences in water pressure due
to differences in water level); and those driven by horizontal differences in water
density (often called ‘buoyancy effects’). Each is discussed below.
a) Gradients due to wind, tides, seiches, waves and atmospheric pressure
Changes in water levels due to different forcings occur at different time scales, and
may be periodic (e.g. tides) or irregular (e.g. continental shelf waves). Changes due
to winds can happen over daily time scales, while tides and seiching produce effects
over weekly time scales. Sea level is also influenced by the passage of high pressure
systems, storm surges and other long period forcings, including continental shelf
waves (DEP, 1996), and these occur over time scales greater than a week.
Changes in water level due to wind are the result of the interaction of wind and the
complex topography of the coastline. During periods of strong wind such as a northwest or westerly storm, water is pushed up against the coast by wind and wave
forcing. The more enclosed a basin, such as Cockburn Sound, the greater the ‘setup’
of water against the coast. More open coastal regions surrounding Cockburn Sound
may not have as much setup, and the difference in water level between Cockburn
Sound and adjacent areas drives the circulation.
Changes in water level due to tides and seiching result in current speeds that are
generally between 1–2 cm/s. The tidal range is between 0.1 and 0.9 m in Cockburn
Sound but is typically around 0.5 m. The tidal cycle is usually daily (one high and
one low water per day), but sometimes twice-daily. Changes in water level during
daily tides are 2–3 times higher than during twice-daily tides. Seiching is the result
of the water level in the Sound oscillating in response to a disturbance such as a
change in wind forcing. Although seiching contributes variations to the sea level of
0.1 m in Cockburn Sound, effects on current speeds are generally small to negligible.
Changes in water level due to high pressure systems, including storm surges and
continental shelf waves depend on both local and remote weather conditions. Low
frequency oscillations, such as continental shelf waves, are able to penetrate
Cockburn Sound (Hearn, 1991) and can contribute approximately 10 cm/s to ambient
current speeds.
b) Buoyancy effects
The saltier and/or colder that water is, the more dense it is. Buoyancy effects arise
when waters of differing densities are adjacent to one another, with the less dense
water flowing over the denser water. A well-known example of buoyancy effects is
the flow of seawater up the Swan River close to the river bed, while surface fresh
water flows the opposite direction toward the sea.
In Cockburn Sound, horizontal density differences can be caused by groundwater
discharge; differences in evaporation and cooling between Cockburn Sound and
adjacent waters; flow from the Swan River; cooling water discharges; and
differences in cooling between nearshore waters and deeper basin waters. These
density differences can influence circulation in localised areas such as the nearshore
region (due to differential heating and cooling, groundwater discharge, cooling water
discharge), or over the entire Sound (due to differential evaporation and cooling
between Cockburn Sound and adjacent waters, Swan River discharge).
14
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
In autumn the waters of Cockburn Sound are typically more dense than adjoining
areas, and horizontal density gradients lead to the movement of buoyant (i.e. less
dense) water into the Sound. These less dense, surface waters result in distinct
vertical layers of water (termed ‘stratification’) within Cockburn Sound. Under
stratified conditions, diffusion of oxygen from surface waters to deeper waters is
slowed, and the rate of oxygen demand by organisms in the deeper waters and on the
seabed may exceed the rate of supply. Wind of sufficient strength and duration (see
below) can break down this stratification and mix the waters column vertically, but
during extended periods of calm (e.g. greater than a week), deeper waters within
Cockburn Sound can become oxygen depleted. Severe oxygen depletion can have
profound ecological effects, including the death of organisms, and increased
sediment nutrient release which, in turn, can worsen water quality.
In winter and spring the waters of the Sound are typically less dense than adjoining
areas, and denser water moves into the lower depths of Cockburn Sound during calm
periods. This dense water is mixed into the lighter surface layer during periods of
storm activity (D'Adamo and Mills, 1995). In the absence of storms, the denser
waters at the bottom of the Sound also result in stratification, increasing the
likelihood of oxygen depletion.
The horizontal pressure gradients due to density differences between Cockburn
Sound and adjacent waters determine the flushing of Cockburn Sound during the
autumn and winter-spring seasons. Density gradients act to transport water into and
out of Cockburn Sound during calms, thereby flushing the surface waters in autumn
and the bottom waters in winter. Flushing of the bottom waters of Cockburn Sound
during autumn, and of surface waters during winter, depends on wind events that mix
the whole water column (generally requiring wind speeds >5 m/s for 2-3 days or
more), followed by re-establishment of density gradients. Such wind events are rare
in autumn, and so the deep basin waters of the Sound are particularly poorly flushed
in autumn.
Seasonal patterns in water movement
Three distinct hydrodynamic regimes have been identified in Cockburn Sound based
on the relative importance of wind and pressure gradients in determining circulation
patterns and flushing: ‘summer’, ‘autumn’ and ‘winter-spring’ (DEP, 1996). The
key characteristics of the three seasons are as follows:
•
•
Summer. During summer, winds are the most important factor controlling the
hydrodynamics. Circulation is wind-driven (see Figure 2.2 and Figure 2.3) and
the waters within both the Sound and adjacent waters are vertically well mixed
(Figure 2.4)—and therefore well oxygenated—due to a combination of wind
mixing during the day (due to sea breezes) and surface cooling of the water
column at night (cooler surface waters sink towards the seabed, enhancing
vertical mixing); and
Autumn. During autumn the wind subsides and pressure gradients determine
the circulation. The waters in the Sound are of a greater density (cooler and
more salty) compared to adjacent waters due to evaporation that has occurred
during the summer and rapid cooling during autumn (Figure 2.5). The
gradient between the denser waters of Cockburn Sound and the lighter adjacent
water controls the flushing of Cockburn Sound to the greatest extent.
Stratification within the Sound becomes apparent due to movement of lighter
water into the Sound, and as noted previously, extended periods of calm may
result in oxygen depletion of bottom waters.
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
15
Figure 2.4 Transect from Fremantle through Cockburn Sound and out through the Causeway,
showing water density conditions representative of summer
Note: From D'Adamo and Mills (1995). Density contours are density value minus 1000 kg/m3. Transect location on the right.
Figure 2.5 Transect from Fremantle through Cockburn Sound and out through the Causeway,
showing water density conditions representative of autumn
Note: From D'Adamo and Mills (1995). Density contours are density value minus 1000 kg/m3. Transect location on the right.
16
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
•
Winter-spring. In this ‘season’ the circulation is primarily driven by pressure
gradients, punctuated by periods of wind-driven circulation due to storm
activity (see Figure 2.2). The waters within the Cockburn Sound become
progressively lighter than waters further offshore (Figure 2.6) due to the
relative lowering of salinity. Salinity is lowered within Cockburn Sound due to
freshwater inflow, particularly from rivers. The relatively rapid response of the
shallow waters of Cockburn Sound to heating (compared to offshore waters) as
spring progresses also contributes to the relative decrease in density. Denser
water moves into the lower depths of Cockburn Sound during calm periods
(wind speeds typically less than 5 m/s), and stratification persists until broken
down by the passage of winter low pressure systems about every 7-10 days
(D'Adamo and Mills, 1995).
Figure 2.6 Transect from Fremantle through Cockburn Sound and out through the Causeway,
showing water density conditions representative winter-spring
Note: From D'Adamo and Mills (1995). Density contours are density value minus 1000 kg/m3. Transect location on the right.
Recent modelling of water movement in Cockburn Sound
Since the SMCWS (DEP, 1996) modelling of Cockburn Sound has been confined
mainly to developments along the eastern margin of Cockburn Sound. Recently,
models have been developed to examine the impact of: the ‘Seaway’ (widening of
the present FPA channel from 150 m to 1.5 km) proposed as part of Cockburn
Cement’s Environmental Review and Management Programme (Cockburn, 2000);
the James Point Pty Ltd Stage One Development, (JPPL, 2001); and cooling water
discharges north of James Point. These models can examine effects at smaller scales
(50–100 m) and incorporate a greater range of physical processes than models
previously applied to Cockburn Sound. The models are able to simulate physical
processes at a 50–100 m scale along the eastern margin of Cockburn Sound and a
250–300 m scale in the remainder of the Sound, over weekly time-scales.
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
17
The recent studies of Cockburn Sound have furthered understanding in two areas:
the flushing of Cockburn Sound; and the hydrodynamics of the eastern margin,
including the characteristics of the cooling water discharges north of James Point.
Flushing is a measure of the exchange and replenishment of the water in an area with
surrounding water. A long flushing time reflects low exchange with adjacent waters
and a short flushing time reflects higher exchange. The water quality of Cockburn
Sound is due in part to its enclosed nature, which reduces exchange with the water of
Owen Anchorage to the north and the open ocean to the west. Flushing times affect
the dilution of nutrient and contaminant inputs as well as a variety of ecological
processes, and can be used to assess the ecological implications of changes in the
circulation of Cockburn Sound.
There are many ways to measure the time over which Cockburn Sound is flushed.
To be consistent with previous modelling of Cockburn Sound (DEP, 1996) the
‘e-folding’ time has been used, which estimates the time taken for 63% of Cockburn
Sound to be flushed. A summary of the most recent estimates of flushing times is
given in Table 2.1, and are consistent with previous estimates by the DEP (1996).
Table 2.1 Flushing times for Cockburn Sound
AUTUMN
37 days
WINTER
22 days
WINTER STORM
28 days
SUMMER
44 days
Note: Reproduced with permission from Cockburn Cement Limited (Cockburn,, 2000).
The above estimates refer to flushing of the Sound as a whole. Flushing is least in
summer because the prevailing winds set up circulation gyres that tend to confine
water within the Sound (Figure 2.3). As noted previously, flushing in winter is
primarily due to the horizontal pressure gradients (buoyancy) that occur: flushing
during winter storms is actually less because wind mixing lessens the pressure
gradients that drive water movement. Flushing in autumn is also primarily due to
pressure gradients, but takes longer than flushing in winter: this is mainly because
the movement of denser bottom waters out of the Sound (over the barrier of Parmelia
Bank and through the Causeway) in autumn requires more energy than the
movement of denser waters into the Sound during winter. There is also little vertical
mixing (due to wind) in autumn to aid flushing of bottom waters.
Flushing times in more ‘localised’ areas along the eastern margin of the Sound have
been also estimated to examine the impact of proposed harbour developments, and
include the influence of cooling water discharges from Western Power and the BP
Refinery (JPPL, 2001). The shallow waters of the eastern shelf are well mixed and
flushing times are approximately 1 day or less. Flushing times are far greater in the
partially enclosed waters of the Jervoise Bay Northern Harbour, generally 5–14 days.
The most poorly flushed area of the Sound is considered to be the bottom waters of
the southern basin, but no estimates of flushing times have been made.
There have been no investigations of changes in flushing times from year to year due
to changes in wind patterns and pressure gradients (e.g. due to differences in Swan
River flow, groundwater discharge).
2.3.2
Coastal processes
Coastal areas are seldom stable. There is nearly always some degree of erosion or
accretion (accumulation) occurring at the shoreline, although this may balance out
over a year or more. This erosion/accretion of the shoreline occurs because sand is
suspended into the water by waves breaking on the shore: if the waves are
18
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
approaching the beach at an angle, this creates a longshore current that can move the
suspended sand. This transport of suspended sand is accompanied by ‘bedload’
transport, where sand is rolled over the seabed by the force of the breaking waves.
Waves, nearshore currents, the weather (winds, barometric pressure) and changes in
water level are important factors determining erosion/accretion patterns at the
shoreline. Artificial structures such as groynes, harbours and offshore breakwaters
alter natural patterns of longshore sediment movement.
Two forces have generated the present coastal morphology of Cockburn Sound:
southerly wind systems that set-up longshore sediment transport through local wind
waves and longshore currents during the spring and summer months; and north-west
storm systems consisting of swell waves, local wind waves and wind-driven currents.
The relative contributions of these forces are in a close balance, with a small net
southerly trend leading to the accretion that has formed James Point.
The sheltered nature of Cockburn Sound results in less wave energy to move
sediment compared to other metropolitan beaches, and changes in the Sound’s
coastline evolve relatively slowly. Changes to the coastline due to development are
occurring more quickly than adjustment of sand movement patterns to those
developments.
Environmental Resources of Australia (ERA, 1973) examined aerial photographs
taken between 1954 and 1972, and found that the beaches within Cockburn Sound
were accreting. The most notable area of accretion was where the Garden Island
Causeway joined the mainland, and this accretion was occurring before the
Causeway was constructed. A significant exception to the pattern of accretion was at
James Point, where the shoreline retreated approximately 30 m, and this was verified
by measurement of beach profiles (ERA 1972, 1973).
The loss of extensive seagrass meadows from the eastern margin of Cockburn Sound
between 1967 and 1973 was believed to have accelerated erosion at James Point
during 1971 (ERA, 1972). However, the Causeway was also constructed around the
same time (1971–1973), which reduced the wave energy arriving at James Point
from the south-west by up to 75% (Hsu, 1992), resulting in proportionally more
energy arriving from the north-west, and reinforcing southerly movement of
sediment. Due to the loss of seagrass and the construction of the Causeway at about
the same time, plus the relatively slow response of the shoreline to those changes, it
is not possible to say which of these two events was responsible for alterations to the
coastline after the late 1960's/early 1970's. Recent modelling of wave conditions in
Cockburn Sound (during a moderate swell, a typical sea breeze pattern, a moderate
storm and a severe storm) has also predicted a net annual direction of sediment
movement from north to the south within Cockburn Sound, except at the
Rockingham Jetty (MRA, 2000). Modelling results suggest this net movement is at
least partly due to the Causeway reducing the amount of swell energy entering the
Sound from the south.
Coastal processes and shoreline stability have been investigated at some specific
areas around Cockburn Sound, generally due to proposed developments (James
Point, Mangles Bay) or as a result of existing developments (Jervoise Bay,
Woodman Point and Mangles Bay). The coastline in the vicinity of James Point has
been investigated to the greatest technical extent due to the protection of this
headland by the establishment of offshore breakwaters (Hsu, 1992) and proposed
developments to the north (JPPL, 2001). The following sections summarise what is
known about these areas.
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
19
James Point
Examination of the vegetation line between Naval Base and James Point since the
construction of the Causeway has shown the shoreline to be stable with episodes of
local change (Andrews, 1979). Localised changes have been pronounced at James
Point due to the higher wave energy and currents relative to the majority of the
Cockburn Sound coastline (see Figure 2.1 and Figure 2.2).
Severe erosion of the small sand cliffs at James Point has occurred since 1953 and
has been attributed to the passage of north-west storms (Hsu, 1992). The low
pressure associated with these storms raises the water level, allowing wave attack to
occur higher up the beach line, resulting in the erosion of the sand cliffs behind the
primary dunes. When sand is eroded from these cliffs it is moved onto the beach and
then subsequently offshore or along-shore. After a storm, sand cannot be returned to
the cliff face and the erosion is permanent. To prevent further erosion of the beach at
James Point, offshore breakwaters were constructed to increase the beach width and
therefore reduce the effect of the storm surge.
Aerial photographs indicate that the shoreline immediately north and south of James
Point has remained relatively stable. The BHP jetties to the north of James Point
have had minimal impact on the shoreline position. Aerial photographs from 1973 to
1999 also show that there is relatively large seasonal sedimentation around the
Western Power intake and outfall infrastructure. When northward transport is
dominant (summer months) the sedimentation is to the north of this area, and during
the winter months it is to the south.
Overall, aerial photographs indicate that net sediment transport is to the south: the
sand moves along the beach north of James Point and becomes trapped at James
Point.
Mangles Bay
Erosion has been occurring in Mangles Bay since the Causeway was constructed.
The Causeway prevents the natural pattern of sediment movement from Cape Peron
into Cockburn Sound (DMH, 1992), and so there is accumulation of sand on the
western side of the Causeway and erosion on the eastern side to as far as the Bell
Street Boat ramp (Figure 2.7). This erosion is still continuing, and is mitigated by
transport (by truck) of sediment from the western side of the Causeway to the eastern
side (pers. com. Gary Middle, Shire of Rockingham).
Woodman Point and Jervoise Bay
Woodman Point and Jervoise Bay have undergone changes due to developments
since 1913. Of greatest significance in this region are the Woodman Point and
WAPET Groynes, built off the tip of Woodman Point. Between 1913 and 1918
Woodman Point was built out approximately 400 m and extended south-westward a
similar distance by means of a rubble structure, as part of a plan to develop the
peninsula into a naval facility (Powell and Emberson, 1981).
Jervoise Bay has also undergone development, particularly in the past 30 years.
Modifications to the coastline in this region include dredging, infilling, and the
establishment of breakwaters (1991 to 1997) to encompass the Northern Harbour.
Due to the protected nature of this part of Cockburn Sound, changes to the coastline
in response to these modifications have been gradual. The most recent studies in this
area have been undertaken by MRA (2000) for the Department of Commerce and
Trade, and Andrews (1979).
20
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
Figure 2.7 Shoreline movement in Mangles Bay from DMH (1992)
The present erosion of the beach to the west of the Northern Harbour is of
considerable concern to local beach users. Due to the many alterations that have
already occurred in this area plus the slow response times of the coastline, it is
proving difficult to decide the main factor(s) responsible for the erosion and develop
a mitigation plan.
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
21
2.3.3
Water quality
The water quality of Cockburn Sound during ‘summer’ (December to March) has
been monitored at the same eight sites (Sites 4–11 in Figure 2.8) every one to three
years since 1977.
10m
Carnac Island
WP
Woodman Point
NC
6a
6b
5
4
7
10m
10m
d
n Islan
Garde
8
9
Careening Bay
10m
10
Kwinana
Beach
SC
11
Cape Peron
Mangles Bay
0 1
km
N
Figure 2.8 Summer water quality monitoring sites in Cockburn Sound
Note: The original site 6 was lost when the northern breakwater of the Jervoise Bay Northern Harbour was built.
Average water temperature in the Sound varies from about 16°C in winter to 24°C in
summer (the shallows are 2–3°C cooler in winter and 2–3°C warmer in summer).
Water salinity varies slightly from that of the open ocean (which is about 35 parts per
22
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
thousand), typically declining to about 34 ppt in winter (due to outflow from the
Swan River) and reaching 36 ppt in autumn (due to evaporation during the summer
months).
The waters of the Sound are generally well oxygenated, although if calm weather
persists for more than a week the deep waters at the southern end of the Sound may
become low in oxygen. This is because bacteria in the organic-rich sediments use up
oxygen faster than the water can supply it. Oxygen levels in the bottom waters
sometimes become so low that the bacterial decay of sediment organic matter is
affected, and the release of nutrients from sediments to the water column increases.
Water quality monitoring in Cockburn Sound focuses on nutrient-related effects,
especially the growth of phytoplankton (measured as ‘chlorophyll a’ levels) as this
provides a good indication of the available nutrient supply. Water clarity (measured
as ‘light attenuation’) is also a useful measure, as it is affected by phytoplankton
levels. Monitoring of contaminants (e.g. metals, pesticides) in water is not done
routinely, as levels are generally too low to detect. Sediments and marine organism
accumulate contaminants, and so are a better means of detecting long-term, low-level
contaminant inputs (see Section 2.3.4).
Summer water quality data for Cockburn Sound (based on all eight sites) from 1977
onwards are shown in Figure 2.9, along with the summer nutrient inputs from human
activities as estimated using the methods of Muriale and Cary (1995). Estimated
nutrient inputs from 1990 onwards differ slightly from those of Muriale and Cary
(1995), as better estimates of the groundwater inputs from the Kwinana Nickel
Refinery area are now available.
Summer N inputs versus chlorophyll
4
Summer N input
Summer chl.
3
600
2
300
1
0
1977
Chl. levels (ug/L)
N input (tonnes)
900
0
1981
1985
1989
1993
1997
2001
Year
Figure 2.9 Summer chlorophyll levels in Cockburn Sound versus summer nitrogen inputs from
human activities (outfall discharges; groundwater; surface water; atmospheric deposition; and
spills from ship loading/unloading)
Note: The green symbol for chlorophyll gives the mid-point of the data range, and the vertical bars show the middle 50% of the
data. This gives an indication of how much the values fluctuate over summer. The blue vertical bars show ±30% of nutrient
inputs, which is the typical error associated with estimating both outfall discharges (Martinick and Mackie Martin, 1993) and
groundwater discharge (Appleyard, 1994).
The same information is repeated in Figure 2.10, but with nutrient input from the
Woodman Point wastewater treatment plant (WWTP) excluded from summer
nutrient inputs: this was done because there is some uncertainty about the degree of
influence of nutrient inputs from the WWTP on overall water quality in the Sound up
to 1984. The results of Chiffings (1979) indicate that the sewage plume did enhance
phytoplankton growth in summer at least part of the time. More recent reviews
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
23
(Muriale and Cary, 1995) suggest that nutrient inputs from the WWTP were not as
significant as first thought in influencing overall water quality, on the basis that
typical surface currents during summer would have moved the largely buoyant
sewage plume northwards out of the Sound most of the time (Mills and D’Adamo,
1995). This is supported by Figure 2.10, which shows a stronger relationship
between nutrient inputs and chlorophyll level up to 1984 than evident in Figure 2.9.
Summer N inputs (minus WWTP discharge) versus chlorophyll
4
N input (tonnes)
Summer N input
Summer chl.
3
600
2
300
1
0
1977
Chl. levels (ug/L)
900
0
1981
1985
1989
1993
1997
2001
Year
Figure 2.10 Summer chlorophyll levels in Cockburn Sound versus summer nitrogen inputs
from human activities (outfall discharges excluding the Woodman Point WWTP outfall;
groundwater; surface water; atmospheric deposition; and spills from ship loading/unloading)
Note: Symbols as for Figure 2.9.
Regardless of whether Figure 2.9 or Figure 2.10 is referred to, it is clear that there
has been a large decline in nutrient inputs to the Sound, but no similar scale of
decline in chlorophyll levels. It is known that discharge from the KNC/CSBP
pipeline had a major influence on overall water quality in the Sound up to at least
1990 (via large increases chlorophyll levels over the south-eastern part of the Sound),
but chlorophyll levels from 1977 to the present cannot be predicted by means of a
single, simple relationship to nitrogen inputs from human activities.
There have been a number of suggestions offered to explain the lack of a single,
predictive relationship between estimated nitrogen inputs from human activities and
overall chlorophyll levels in the Sound, as follows:
1.
24
Up until 1991 the major source of nitrogen from human activities was
discharge from the KNC/CSBP pipeline, and there was a clear relationship
between estimated nitrogen inputs from human activities and overall
chlorophyll levels in the Sound. Since then, nitrogen inputs from human
activities have declined substantially and furthermore the major source is now
groundwater diffusing in from about 1 km of shoreline south of James Point
and in the vicinity in the Jervoise Bay Northern Harbour (see Section 2.4.3).
The spatial pattern of increased chlorophyll levels produced by these two types
of discharge appears to be quite different, and it is possible that groundwater
nutrient inputs may result in more elevation of chlorophyll levels at sites along
the eastern shore, whereas elevation of chlorophyll levels due to pipeline
discharges was dispersed over a larger area. The relationship between nitrogen
input and overall chlorophyll levels in the Sound (as detected by the eight sites
monitored) has therefore changed.
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
2.
3.
4.
5.
6.
Summer water quality was only measured once every 4–6 weeks up until the
1982/83 survey, when weekly measurements commenced. However, data for
one site (site 10) were collected every week from in the summer of 1977/78
(Figure 2.11), unlike the other seven sites which were only monitored three
times in the same period. If weekly data from December 1977 to March 1978
for this site are used, the median summer chlorophyll value is 4.3 µg/L, yet if
only data are used from the three dates the other sites were sampled, the value
is 2.7 µg/L. Thus, sampling up to the 1982/83 survey may not have been
frequent enough to accurately document the chlorophyll levels present at the
time, and the true extent of the improvement in water quality since the 1977–81
may not be reflected in Figure 2.9 or Figure 2.10.
Chlorophyll measurements in the early 1980s are underestimates due a change
in measurement techniques at that time. The technique used in the early 1980s
was found to produce artificially low results4.
Water quality data are based on eight sites. Improvements in water quality due
a decrease in the area where high chlorophyll levels occur around any site(s)
could be missed by the present sampling programme.
High chlorophyll levels in the summer of 1991/92 may be partly due to
regional effects, notably the unusually long ENSO (El Nino/Southern
Oscillation) event from 1990–1994 (atypically high chlorophyll levels also
occurred in Warnbro Sound (see also Section 2.3.5).
The estimates of nutrient inputs are subject to large errors, particularly
groundwater discharges. In addition, groundwater discharge is extremely
variable both seasonally (maximum flow occurs in late spring/early summer),
and with changes in sea level (e.g. due to tides, weather conditions).
Chlorophyll levels also vary widely between different parts of the Sound. In relative
terms, the lowest levels occur in the central and western parts of the Sound (sites 4, 5
and 8), the highest values in the south-east (sites 9, 10 and 11) and within the
Jervoise Bay Northern Harbour (site 6b), and intermediate values in the north-east
(sites 6a and 7) (Table 2.2).
Table 2.2 Average chlorophyll levels at various sites in Cockburn Sound, summer 2000/2001
Site 4
0.8
(0.5–1.4)
AVERAGE µg/L OF CHLOROPHYLL FOR SUMMER 2000/2001
(range shown in brackets)
Site 5
Site 6a
Site 6b
Site 7
Site 8
Site 9
Site 10
1.0
1.4
8.6
1.4
1.2
2.1
2.5
(0.7–1.7) (0.7–3.1)
(1.1–
(0.7–3.0) (0.5–1.9) (1.2–3.7) (1.3–3.7)
43.3)
Site 11
1.9
(0.9–3.1)
Note: Data reproduced courtesy of the Kwinana Industries Council.
Differences in chlorophyll levels between individual sites occur due to differences in
site-specific conditions such as flushing time, water circulation, water depth, and the
size, proximity and type (eg. outfall discharge or groundwater) of nitrogen input(s).
The influence of site-specific conditions is illustrated in data for sites 6, 8, 9 and 10
in Figure 2.11. The clearest and most dramatic example of the influence of sitespecific conditions is evident at site 6, which receives significant nitrogen inputs
from contaminated groundwater and has undergone significant changes in circulation
and flushing rates through construction of the Jervoise Bay Northern Harbour.
4
Dr Rod Lukatelich, researcher at the Botany Department (University of WA) laboratory where the
early 1980s work was undertaken. Currently Environmental Manager of BP Refinery.
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
25
N inputs versus Site 6 chlorophyll
8
N inputs
Site 6a chl.
Site 6b chl.
6
600
4
300
2
0
1977
Chl. levels (ug/L)
N input (tonnes)
900
0
1981
1985
1989
1993
1997
2001
Year
N inputs versus Site 8 chlorophyll
8
N input
Site 8 chl.
600
6
4
300
2
0
1977
Chl. levels (ug/L)
N input (tonnes)
900
0
1981
1985
1989
1993
1997
2001
Year
N inputs versus Site 9 chlorophyll
8
N inputs
Site 9 chl.
6
600
4
300
2
0
1977
Chl. levels (ug/L)
N input (tonnes)
900
0
1981
1985
1989
1993
1997
2001
Year
N inputs versus Site 10 chlorophyll
8
N inputs
Site 10 chl.
6
600
4
300
2
0
1977
Chl. levels (ug/L)
N input (tonnes)
900
0
1981
1985
1989
1993
1997
2001
Year
Figure 2.11 Summer water quality at Cockburn Sound sites 6, 8, 9 and 10, versus summer
nitrogen inputs from human activities (outfall discharges; groundwater; surface water;
atmospheric deposition; and spills from ship loading/unloading)
Note: The original site 6 was built over by the Jervoise Bay northern breakwater in 1997. Site 6a is located 50 m west of site 6,
and site 6b is located within the Jervoise Bay northern harbour.
26
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
At site 6 (Jervoise Bay) there was a steady decline in water quality in the 1990s.
With the completion of the northern breakwater of the Northern Harbour in late
1997, water quality deteriorated inside the Harbour and generally improved outside
the Harbour (based on comparisons with earlier data for site 6), although poor quality
water from inside the harbour sometimes moves out of the harbour on outgoing tides
and affects a larger area. These effects are evident in data from intensive summer
monitoring (three sites in the Harbour and six sites outside), funded by the
Department of Commerce and Trade (DAL, 2001), and are due to confinement
within the Harbour of nitrogen-rich groundwater that had previously dispersed over a
larger area of the Sound.
Site 9 is the site most affected by large inputs of nitrogen from industry in the past.
The nitrogen inputs from industry in this area have decreased dramatically in the last
10 years, and there are signs of improvement in water quality. As noted earlier, the
chlorophyll data for the late 1970s and 1980 may not accurately reflect the poor
water quality at that time, and so the true extent of improvements at site 9 since the
late 1970s may not be apparent in the data. Site 10 was also affected by the same
industrial inputs as site 9 (although probably to a lesser extent given the summer
pattern of water movement), and clearly shows the poor state of the Sound in the late
1970s. However, the water quality at site 10 has also shown some signs of
worsening in the last few years (whereas site 9 appears to be improving), possibly
indicating some other influence at this site.
Site 8 is in the middle of the Sound, and clearly has better water quality than Sites 6,
9 and 10 on the eastern margin of the Sound. Water quality at site 8 has changed
little in the past 10 years, apart from the summer of 1991/1992, when there was a
‘Sound-wide’ increase in chlorophyll levels (also in Warnbro Sound; DEP, 1996).
The reason for this regional increase remains unclear.
The data for sites 6, 8, 9 and 10 clearly show that total nitrogen inputs to the Sound
due to human activities are less important in determining a site’s water quality than
characteristics specific to that site. This is important to bear in mind when both
predicting and managing water quality.
The above discussion focuses on the influence of nutrient inputs to Cockburn Sound
due to human activities, but there is one additional final factor that plays an
important role in determining water quality (and chlorophyll levels): sediment
nutrient cycling. Simple diagrams showing estimated annual nitrogen inputs from
human activities and annual rates of sediment nitrogen cycling in 1978 and 2000 are
shown in Figure 2.12 and Figure 2.13, along with the amount of nitrogen needed by
phytoplankton (microscopic algae in the water) and MPB (microscopic algae on and
in the sediments). Sediment data for 2000 are based on Bastyan and Paling (1995,
cited DEP, 1996). Sediment nutrient cycling in 1978 was estimated to be only
slightly higher than in 2000. Although sediment nutrient levels in the southern basin
of the Sound were markedly higher in 1978 (see Section 2.3.4) and so sediment
nutrient cycling was assumed to be greater, this area only represents a small
proportion of the Sound. There is little information on sediment nutrient cycling and
historical changes in sediment nutrient levels for the shallow margins of the sand.
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
27
Figure 2.12 Estimated nitrogen inputs from sediments and human activities in 1978, and
amount of nitrogen required by phytoplankton and MPB
Figure 2.13 Estimated nitrogen inputs from sediments and human activities in 2000, and
amount of nitrogen required by phytoplankton and MPB
28
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
The estimates in Figure 2.12 and Figure 2.13 are crude but, coupled with information
presented earlier serve to illustrate that:
•
•
In 1978, large nitrogen inputs from pipeline discharge were a major influence
on chlorophyll levels; and
At present, sediment nutrient cycling and diffuse inputs from human activities
(i.e. groundwater) appear to be the main factors controlling chlorophyll levels.
With the present level of understanding of nutrient cycling, it is not possible to
predict to what extent further reductions in diffuse nutrient inputs to the Sound will
affect overall chlorophyll levels. Available data suggest any response could be slow:
Figure 2.9 and Figure 2.10 indicate that there has been little change in overall
chlorophyll a levels in the Sound since inputs of nitrogen from human activities
during summer dropped below about 100 tonnes (about 400 tonnes/year, in 1998).
Further reductions in nitrogen inputs from human activities will, however, be
important in reducing localised effects on water quality (Figure 2.11). Future
changes in localised water quality may also occur within and between man-made
structures (eg. harbours) due to changes in water circulation and reduced flushing
times: these in turn could confine any existing nutrient inputs within a smaller area
(as has happened in the Jervoise Bay Northern Harbour) and/or cause increased
accumulation of organic matter in the sediments and increased sediment nutrient
flux.
2.3.4
Marine sediments
Water movement plays a major role in determining sediment type within Cockburn
Sound. In deeper areas the sediments tend to be fine and silty, while shallower areas
experience more wave and current action and so have sandy sediments (the finer
particles are easily suspended and swept away). Deeper areas accumulate fine
organic particles (e.g. dead plankton, faecal material), and so are naturally more
organically enriched than shallower areas. The proportion of fine particles (the silt
and clay fraction), in turn, influences the amount of naturally present metals: the
more silt and clay, the higher the metal levels. The original source of a sediment
(e.g. calcium carbonate from marine organisms versus material eroded from the land)
also has a strong influence on natural levels of metals (calcium carbonate generally
has far lower levels of metals than sediments eroded from the mainland.
Contaminants discharged to marine environments—and any increased production of
organic matter due to nutrient enrichment—typically accumulate in the sediments,
especially in sheltered, relatively deep areas such as Cockburn Sound. However, it is
often difficult to determine how contaminated sediments are, and whether they pose
a threat to marine life. Not only do different sediments have different ‘background’
levels of metals, but the silt+clay, organic matter and sulphur in sediments can bind
contaminants in forms that can’t be taken up by marine life (i.e. the contaminants are
not biologically available, or ‘bioavailable’). Thus, the same level of contamination
may cause no effect in one type of sediment but severe effects in another.
In the 1976–79 Cockburn Sound Environmental Study, widespread contamination of
sediments was found. A sediment study carried out as part of the SMCWS in 1994
found that contaminant levels had decreased significantly since the late 1970s, due to
large reductions in wastewater discharges from industry. Metal levels found in 1994
were generally below DEP draft guidelines, apart from arsenic and mercury in some
localised areas near industries or harbours. Very high levels of tributyltin (a highly
toxic ingredient in antifoulant paints commonly used on large commercial vessels)
were also found throughout the Sound, particularly near shipping facilities (see also
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
29
Section 2.4.5). Organic contaminants (e.g. pesticides, petroleum hydrocarbons,
PCBs) were at very low levels in 1994, and were not considered cause for concern.
Available data (Table 2.3) also indicate that levels of organic matter and nitrogen in
the sediments of the deep basin at the southern end of the Sound were higher in 1978
than in 1994, presumably due to the greater phytoplankton production. The
remainder of the Sound appears to have been affected to a lesser extent, and
presently differs little from Warnbro Sound, but there are few data for the shallow
margins of the Sound.
Table 2.3 Changes in nitrogen concentrations in Cockburn Sound sediments
AREA
Cockburn Sound
Southern basin
Central basin (20 m)
Northern basin (20 m)
Eastern flats (<10 m)
Warnbro Sound
Central basin (20 m)
Central basin (16 m)
NITROGEN IN SEDIMENTS (µ
µg N/g dry weight of sediment)
1978*
1994**
3,099 (2770–3,304) (6,600?)***
1,792 (1036–2,436)
1,344 (812–2,044)
896
2,448
1,708 (1,180–2,004)
1,624
673
-
1,624 (1497–1,751)
800
* From Chiffings, 1987
** From Bastyan and Paling, 1995
*** One site of the four sites measured had an exceptionally high value of 6,600 µg N/g dry weight of sediment
In 1999 there was a survey of contaminant levels in sediments at a number of
SMCWS sites, using the same sampling techniques and analytical methods (DAL,
2000). The results of the 1999 survey for metal levels in Cockburn Sound
sediments—and Warnbro Sound sediments as an example of an non-degraded
environment—are shown in Table 2.4 along with the DEP’s 1994 data for the same
sites. Organic contaminants were also measured, but were below detection limits
(similar to the DEP’s 1994 results) and so are not shown.
Differences between the 1994 and 1999 surveys have to be interpreted with some
care, as natural sediment variability is. Also, when metal level are near analytical
detection limits (as is the case for cadmium, mercury, copper, and nickel at many
sites), values within 5–10 times of the detection limit can be unreliable.
The two most striking differences between 1994 and 1999 are the apparent declines
in arsenic and TBT levels. These apparent improvements may be real, but values in
1994 may have been elevated due to analytical errors as these two substances,
particularly TBT, are notoriously difficult to analyse. What can be concluded is that
levels of arsenic (and all other metals) in Cockburn Sound sites are well below the
national ‘Interim Sediment Quality Guidelines’ (ISQGs) for the protection of marine
ecosystems (also shown in Table 2.4), and TBT contamination is less than indicated
by 1994 results. In relative terms, Jervoise Bay and Careening Bay were the most
contaminated sites, particularly with TBT and, in the case of Careening Bay, with
copper.
The 1999 survey also involved preliminary attempts to determine what natural levels
of metals in Cockburn Sound sediments should be, based on data for a range of
uncontaminated sites in adjacent waters. This was done for chromium, copper, lead,
nickel and zinc. Results indicated that there was lead contamination near areas of
shipping activity, and widespread zinc contamination throughout the Sound.
30
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
Table 2.4 Sediment contaminant levels in 1994 sediment survey (DEP, 1996) and 1999 sediment survey (DAL, 2000)
SITE AREA
Owen Anchorage
Owen Anchorage
Jervoise Bay marina
Cockburn Sound, north basin
Alcoa jetty
Cockburn Sound, central basin
James Point
CBH jetty
Cockburn Sound, southern basin
Mangles Bay
Careening Bay***
Warnbro Sound shallows
Warnbro Sound basin
DEP SITE
CODE
ISQG-Low
0401
1310
1530
3000
3210
4000
4010
4500
4800
5020
C430
WS12
WS27
Arsenic
20
Cadmium
1.5
Chromium
80
Copper
65
CONTAMINANT*
Mercury
0.15
Nickel
21
Lead
50
1994
1999
1994
1999
1994
1999
1994
1999
1994
1999
1994
1999
1994
1999
Zinc
200
1994 1999
4.0
<0.5
9.5
51.0
74.0
64.0
9.5
68.0
75.0
<0.5
4.0
7.5
3.5
2.5
1.1
2.7
2.6
3.0
2.5
1.5
3.8
4.9
2.0
6.3
0.8
8.2
0.6
<0.2
0.8
0.6
0.3
0.7
<0.2
0.6
0.4
<0.2
0.6
0.8
<0.2
<0.1
<0.1
<0.1
<0.1
0.09
0.11
0.17
0.32
0.29
0.13
0.16
<0.1
<0.1
11.0
0.6
6.2
14.0
11.0
19.0
2.4
21.0
19.0
<0.2
5.2
5.7
<0.2
18
11
11
19
13
25
8.4
27
29
10
23
13.7
14.3
0.8
0.4
13
3.7
7.1
4.7
2.1
7.6
8.2
0.2
0.8
1.0
0.5
4.0
3.0
15
6.0
8.4
7.8
1.7
12
11
4.1
60.0
3.9
2.3
1.9
<.05
0.20
0.05
0.05
<.05
<.05
0.16
0.06
<.05
0.05
<.05
<.05
<0.1
<0.1
<0.1
<0.1
0.07
<0.1
<0.1
0.12
<0.1
<0.1
<0.1
<0.1
<0.1
4.3
1.6
5.6
8.1
5.6
9.6
3.1
11.0
12.0
1.1
4.2
4.9
1.2
1.3
1.4
4.0
5.8
4.9
8.2
1.1
12.0
12.0
2.4
7.2
1.9
2.6
5.0
1.4
9.5
15.0
11.0
17.0
5.3
23.0
24.0
2.4
6.4
5.4
1.7
<1.0
1.5
8.7
7.6
9.4
7.9
<1.0
11.0
11.0
2.4
30
0.8
3.9
1.8
1.0
16.0
19.0
16.0
17.0
5.5
25.0
30.0
0.8
1.7
1.5
1.5
1.1
2.6
28.0
24.0
25.0
25.0
2.6
35.0
36.0
8.6
67.0
1.7
6.0
TBT**
5
1994 1999
4.9
3.7
342
12.9
1171
10.7
19.5
22.7
29.3
5.9
65.9
13.7
2.7
<1
<1
29
<1
<1
15
<1
<1
<1
<1
190
<1
<1
* 1999 values of greater than ten-fold difference to 1994 values are shaded light grey, values greater than the ISQG-Low values are shaded dark grey. All data in µg/g dry weight of sediment, unless otherwise stated.
** data in µg/g
*** comparisons not valid as a slightly different site in deeper water was used in the 1999 survey
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
31
It is important to distinguish between the terms ‘contamination’ and ‘pollution’,
which have carefully defined meanings. Contamination is the presence of a
substance in the environment due to human activities, and pollution is when the
substance is at levels sufficient to cause adverse environmental effects. The results
of the 1994 and 1999 sediment surveys indicate some lead and zinc contamination in
Cockburn Sound, but values were still well below national guidelines. The only
substance at pollution levels was TBT, notably in Jervoise Bay and Careening Bay.
2.3.5
Marine flora
The marine flora of Cockburn Sound include seagrasses, seagrass epiphytes,
phytoplankton and the microphytobenthos (MPB, microscopic algae similar to
phytoplankton, but which live on and in the seabed). There are also macroalgae
(seaweed) on small patches of reef in the Sound, while an unknown amount of drift
algae from reefs outside the Sound enters via tidal currents through the Causeway,
and via north-west storms at the north end of the Sound, and accumulates in the deep
basin. These aquatic plants provide the basis for food webs in the Sound.
The distribution of aquatic plants can be simply described in terms of the type of
benthic (i.e. seabed) habitat. The distributions of seagrass, sand, reef and silt habitats
were accurately mapped in 1999 (DAL et al., 2000), and are shown in Figure 2.14:
phytoplankton and MPB occur throughout the Sound.
Seagrasses
The historical loss of seagrass in Cockburn Sound documented in the 1976–79
Cockburn Sound Environmental Study has recently been re-analysed using the latest
mapping techniques (DAL, 2000). The pattern of loss found in the earlier study has
been confirmed: in 1967 seagrass was widespread in waters less than 10 m deep
(Figure 2.15), and much of the seagrass on the eastern flats of the Sound was lost
between 1967 and 1972. Between 1972 and 1982 further losses occurred on
Southern Flats, and on the eastern shore of Garden Island in Careening Bay and
around the Armaments Jetty. Seagrass losses on Southern Flats occurred after 1972,
and appear to be more linked to sediment movement caused by the construction of
the Causeway. The losses in Careening Bay and around the Armaments Jetty were
due to naval development (dredging). Additional small-scale losses (1.8 ha) have
occurred in Mangles Bay due to boat moorings (mooring chains ‘scythe’ seagrass as
the boats swing round). There has been little loss since 1982 except for small areas
on the eastern shore of Garden Island. There have also been several reports5 of
healthy clumps of seagrass on the eastern flats of the Sound, in areas where the
historical dieback took place, although these are not apparent in the mapping (aerial
photograph resolution does not detect clumps of seagrass less than 2 m in diameter,
and patches less than 30 m2 are not presented in maps).
The total area of seagrass within the CSMC boundary has declined from 2,821 ha in
1965/676 to 632.3 ha in 1999 (Figure 2.15). These figures differ from those reported
in earlier exercises (Cambridge, 1979; DEP, 1996; DAL et al., 2000) as each refers
to a different study boundary (note that the CSMC boundary excludes much of
Parmelia Bank).
5
Dr Eric Paling, Environmental Sciences, Murdoch University. Dr Helen Astill, Aquatic Ecologist,
D.A. Lord & Associates Pty Ltd.
6
Aerial photos from slightly different years sometimes had to be used to compile images for the area
within the CSMC boundary (see also Figure 2.15)
32
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
HOLDING PAGES (X2) FOR A3 FIGURE
Figure 2.14 Benthic habitats in Cockburn Sound
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
33
Second holding page for figure 2.14 (back of A3 figure)
34
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
HOLDING PAGE
Figure 2.15 Historical sequence of seagrass dieback in Cockburn Sound
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
35
The massive loss of seagrass on the eastern flats from 1967 to 1972 has been
attributed to nutrient enrichment effects, as explained earlier in Section 1.2. During
work done for the 1999 mapping, information was found to suggest that while
nutrient enrichment was undoubtedly a major cause of seagrass loss, there were other
stresses on seagrasses at that time. The following dates and activities are noted:
•
•
•
•
•
1966:
Nutrient-rich discharge commenced from the Woodman Point
wastewater treatment plant;
1969: Nutrient-rich discharge commenced from the KNC;
1967: Discharge of large amounts of gypsum from CSBP;
1968–70: Dredging of the Stirling and Callista Channels and turning basins,
and dumping of dredge spoil over a large area about 1 km north-west of the
Alcoa jetty (note: dumping of dredge spoil would have smothered seagrass,
and dredge spoil dumping creates far more turbidity than dredging itself); and
1968–70: Intensive scallop dredging of the Sound.
The DEP have an ongoing seagrass monitoring program that includes annual surveys
of seagrass health, carried out by Edith Cowan University. The results of the 1998,
1999, 2000 and 2001 surveys, coupled with the 1999 mapping described above,
indicate no further deterioration of the health of surviving seagrass meadows, and no
significant losses related to water quality. There are, however, some ongoing
concerns about the health of seagrass in Mangles Bay as the annual surveys show
low shoot densities, high epiphyte loads and turbid water (due to suspended organic
material) compared to other sites in Cockburn Sound. The greater stress on seagrass
in this area appears to be due to increased retention of organic matter (which may be
due to the Causeway) (Lavery7, pers. com.).
Reefs
There are patches of reef along the eastern shore of the Sound between Challenger
Beach and the Jervoise Bay northern harbour, and isolated hummocks on the eastern
flats, mainly along the eastern fringe (Figure 2.14). The shoreline reefs are carry
mainly brown algae (kelps and Sargassum),while on the reefs further offshore red
algae are more common. Green algae (Ulva, Cladophora) are also common, and
some of the reefs have patches of coral, including the reef-building species Flavites
(Halpern Glick Maunsell, 1997).
Phytoplankton and MPB
Phytoplankton levels, as measured by chlorophyll a levels, were described in Section
2.3.4. There has been no study of MPB in Cockburn Sound.
The species of phytoplankton present in Cockburn Sound were studied in 1978 by
Chaney (1978), and between 1992 and 1994 as part of the SMCWS (Helleren and
John, 1995). There are over 300 species present in the Sound, the four main groups
being diatoms (Bacillariophyta), dinoflagellates (Dinophyta), silicoflagellates
(Chrysophyta) and blue-green algae (Cyanophyta).
Diatoms typically predominate in local coastal waters, yet Helleren and John (1995)
found that in both Cockburn and Warnbro Sounds there was a marked dominance by
silicoflagellates (up to 95% of cells present) in autumn/winter, particularly the
species Dictyota octonaria. This differed to earlier findings by Chaney (1978), when
7
Dr Paul Lavery, Senior Lecturer, Department of Environmental Management, Edith Cowan
University
36
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
unidentified ‘Chlorophytes’ dominated the autumn/winter period. The dominance of
silicoflagellates in the early 1990s caused concern because a similar species in
northern European waters is associated with broad-scale nutrient enrichment.
However, a follow-up study in 1999 found that silicoflagellates were present, but at
far lower levels than in 1992 to 1994. A tentative explanation for the presence of the
silicoflagellates between 1992 and 1994 may be that an unusually long ENSO event
(El Nino/Southern Oscillation) occurred from 1990 to 1994, and so coastal water
levels were low and the southwards flowing Leeuwin Current was weak. This may
have allowed southern waters to move up the coast more than usual, along with the
silicoflagellates (which are a cool water species), which subsequently flourished in
the slightly nutrient-enriched conditions (Stuart Helleren8 pers. com.).
A number of species of dinoflagellates have been found in Cockburn Sound that
are—if present in shellfish or fish—potentially harmful to human health, but all the
species identified are widespread in local coastal waters, including Warnbro Sound.
Occasionally, the blue-green algae Oscillatoria erythraea (Trichodesmium)—which
can cause skin irritations to swimmers—appears as surface slicks in Cockburn Sound
(as in autumn 2001). This species often blooms in offshore waters up and down the
south-west coast of WA in late summer/early autumn (when conditions are calm),
and sometimes drifts into nearshore areas.
At present, the only ongoing studies of phytoplankton species are for the Jervoise
Bay Northern Harbour (as part of the Department of Commerce and Trade’s
monitoring commitments), and by the mussel aquaculture industry around their lease
site at Southern Flats and the Kwinana Grain Jetty. Potentially toxic species have
been detected by both monitoring programmes but, to date, subsequent testing has
established that the all species involved were non-toxic varieties.
Implications of seagrass losses and increased phytoplankton levels to food webs
and nutrient cycling in Cockburn Sound
The loss of seagrass and increase in phytoplankton levels in the Sound has
dramatically altered plant production patterns.
Estimated changes in plant
production since the 1970s are shown in Table 2.5, and the amount of nitrogen used
in that plant production in Table 2.6. The estimates in these two tables involve an
number of assumptions (documented in Appendix A), are necessarily crude, and
exclude the (unknown) role of reef algae entering the Sound. What Table 2.5 does
show is a switch from co-domination by seagrass meadows and phytoplankton/MPB
to domination by phytoplankton/MPB. The amount of nitrogen used by plants also
increased greatly in the 1970s, as phytoplankton/MPB—which need lots of
nitrogen—were able to grow due to the large nitrogen inputs at that time (Table 2.6).
The tables also suggest that total plant production today is less than in the 1950s, but
phytoplankton/MPB production and nitrogen use is still higher than in the 1950s.
Table 2.5 Estimated changes in plant production in Cockburn Sound since the 1950s
PERIOD
SEAGRASS
1950'S
1978
PRESENT DAY
11,700
2,250
2,250
PRODUCTION (tonnes carbon/year)
SEAGRASS
PHYTOPLANKEPIPHYTES
TON AND MPB*
3,100
13,800
600
25,300
600
16,000
TOTAL
28,600
28,150
18,850
Microphytobenthos, i.e. microscopic algae growing on and in sediments, as opposed to phytoplankton which float in the water.
8
Stuart Helleren, Dalcon Environmental
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
37
Table 2.6 Estimated changes in nitrogen used by plants in Cockburn Sound since the 1950s
PERIOD
SEAGRASS
1950'S
1978
PRESENT DAY
470
90
90
NITROGEN USE (tonnes nitrogen/year)
SEAGRASS
PHYTOPLANKEPIPHYTES
TON AND MPB*
120
2,120
20
3,840
20
2,790
TOTAL
2,710
3,950
2,900
Microphytobenthos, i.e. microscopic algae growing on and in sediments, as opposed to phytoplankton which float in the water.
The implications of these changes to the food web have yet to be investigated.
Within local coastal waters, studies have established that food transfer is via an
algae invertebrate fish pathway, whether the algae is seagrass epiphytes, reef
algae, phytoplankton or MPB. Little seagrass production appears to enter the food
web. This is because seagrass leaves are very seldom grazed, being low in protein
and—unlike algae—containing unpalatable phenols and a lot of structural material
including fibre (cellulose and lignin) (Klumpp et al., 1989). The majority of seagrass
material becomes detritus and undergoes bacterial decomposition: during this
process a high proportion (90—99%) of seagrass carbon is lost as respired carbon
dioxide. In contrast, seagrass epiphytes, MPB and phytoplankton are grazed and so
enter the food web directly. On this basis, the estimated plant production presently
available to support the food web in the Sound (epiphytes+phytoplankton+MPB)
differs little to that in the 1950s (and in fact was higher around 1978). However,
species of fauna that prefer seagrasses as a physical habitat have obviously been
disadvantaged.
If further significant declines in plant production occur in Cockburn Sound (due to
ongoing reductions in nutrient inputs from human activities, and declines in sediment
nutrient reservoirs; see below), declines in the populations of fish, crustaceans and
shellfish may also result, notably those species that use the Sound for part or all of
their life cycle. Effects on species of fish and crustaceans that pass through the
Sound on their way to other areas would obviously be far less, and would be difficult
to predict.
The loss of seagrass has also changed the nutrient-cycling processes in Cockburn
Sound, and these, in turn, may affect what can be achieved with management of
nutrient inputs from human activities. An attempt to explain the nutrient cycling
changes from the 1950s to the present using a conceptual model is presented in
Figure 2.16, Figure 2.17 and Figure 2.18. These diagrams are not meant to be taken
as definitive, but rather as a starting point for further discussions to decide on an
agreed conceptual model of nutrient cycling in Cockburn Sound.
When extensive seagrasses were present on the eastern margin in the 1950s, benthic
nutrient cycling was dominated by the meadows themselves, and phytoplankton
levels would have been low. There would have been little nutrient release from the
sediments to the water column (due to the presence of seagrass roots), and much of
what was released would have been taken up by seagrass leaves and/or epiphytes
(Figure 2.16).
With the loss of seagrass meadows and greatly increased phytoplankton levels in
1978, not only were sediments enriched on the eastern margin and in the southern
part of the deep basin (which would have led to more frequent periods of low oxygen
in basin waters), but nutrient inputs (from both human activities and sediment
release) would have rapidly fueled new phytoplankton growth (Figure 2.17).
38
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
Figure 2.16 Conceptual diagram of nutrient cycling processes in Cockburn Sound in 1950
Figure 2.17 Conceptual diagram of nutrient cycling processes in Cockburn Sound in 1978
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
39
Figure 2.18 Conceptual diagram of nutrient cycling processes in Cockburn Sound in 2000
In 2000/2001, nutrient inputs from human activities are far less than in the 1970s, but
nitrogen inputs—whether from human inputs or sediment release—are potentially
more directly available for phytoplankton growth than when seagrasses were present.
Even if nutrient inputs from human activities today were as low as in the 1950s, the
absence of Posidonia meadows means it is uncertain whether phytoplankton levels
on the eastern margin would be as low as in the 1950s, due to both the legacy of
enriched sediments and the potentially more direct availability of nutrients to
phytoplankton. The role of MPB in nutrient cycling (both on the eastern margin and
in the deep basin) is an unknown factor here: providing they receive sufficient light,
MPB may replace part of the role of seagrasses in reducing sediment nutrient flux to
the water column. Obviously there are a variety of factors to be considered when
predicting future scenarios, including reductions in nutrient inputs from human
activities, the persistence of enriched sediments, seagrass re-growth (and what
species re-grow), the role of MPB, water clarity, and changes in water circulation
due to further developments.
2.3.6
Marine fauna
The fauna of Cockburn Sound have been studied less regularly and extensively than
the flora. This is partly because faunal studies are time consuming and expensive,
and partly because results are often very difficult to interpret due to the considerable
natural variations that occur in fauna populations.
Zooplankton
Zooplankton in Cockburn and Warnbro Sounds were studied from 1992 to 1994 as
part of the SMCWS, and were found to be typical of temperate coastal regions, apart
from large blooms of radiolarians during late winter and early spring (DEP, 1996).
As for silicoflagellates, there was some indication that the radiolarians were
associated with cooler waters (DEP, 1996), and so their presence may also be linked
to the ENSO event from 1990 to 1994 (see Section 2.3.5).
40
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
Zooplankton in Cockburn Sound 1992 to 1994 were about twice as abundant as
zooplankton in Warnbro Sound, presumably in response to the greater food supply
(phytoplankton).
Invertebrate fauna
The benthic invertebrate fauna of the deep basin have been studied in 1978 (as part
of the 1976–79 Cockburn Sound Environmental Study) and 1993 (as part of the
SMCWS). The deep basins of Cockburn Sound, Warnbro Sound and Owen
Anchorage contain fine organic-rich silts due to accumulation of detritus from
surrounding areas, and have species of flora and fauna that, to date, have been found
nowhere else on the central west coast of Western Australia (Wilson et al., 1978).
The 1993 survey of benthic invertebrates found that more species were present, and
in greater numbers, in the northern half of the Sound compared to the southern half.
More species were found in the northern half of the Sound in 1993 compared to
1978, yet the reverse was found for the southern half of the Sound. In 1993, the
bivalve Solemya—which prefers low oxygen conditions—was also found in the
southern half of the Sound.
It is difficult to interpret the spatial patterns in 1993. The southern end of the Sound
has sediments with a higher proportion of fine particles, more nutrients and more
frequent periods of low oxygen than the northern half. These are all factors that
influence benthic invertebrate populations, and is the explanation favoured by
Chalmers (1993) for the differences found. Elevated metal levels in the sediments of
the southern half of the Sound have also been suggested as a possible explanation
(DEP, 1996), although metal levels are well below those typically associated with
adverse effects. Differing recruitment of fauna (i.e. settling out of juvenile or larval
stages in plankton) can also cause large differences between years. For example, the
bivalve Solemya found in the 1993 survey was not present in a later survey by Glover
and Taylor (1999).
Two acknowledged marine pests have also been found in the benthic fauna of
Cockburn Sound: the European fan worm Sabella cf. Spallanzanii, and the Asian
date mussel Musculista senhousia (see Section 2.4.6).
The SMCWS included survey of contaminant levels in mussels in 1991 and 1994.
Mussels are particularly useful for detecting very low levels of contaminants in
seawater because they feed by filtering the water column, and retain all the
contaminants present. The two surveys found that with one exception (TBT), levels
of organic contaminants were either below detection limit or (in the case of the
pesticide DDT) very low. In contrast, TBT contamination was widespread (see also
Section 2.4.4).
Levels of cadmium, chromium, lead, mercury and nickel in mussels were below
detection limits at all sites. Concentrations of aluminium, arsenic, copper, iron,
manganese and zinc were detectable, but below Australian and New Zealand Food
Authority (ANZFA) guidelines. All metals were present at lower levels than found
in an earlier study by Chegwidden (1978), and this was attributed to the large
decreases in contaminants that had occurred. In relative terms, zinc was more
elevated than other metals (although still below ANZFA guidelines), which supports
the results in Section 2.3.4 suggesting that zinc levels are elevated in Cockburn
Sound sediments.
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
41
Fish
Dybdahl (1979) estimated that there were about 130 species of fish and 14 large
crustacean and mollusc species in Cockburn Sound. Fisheries WA9 have provided
the following list that indicates (but is not limited to) the commercially/recreationally
important species known to frequent various habitats in the Sound:
•
•
•
•
Open (deep) water. Snapper, pilchards, bonito (also dolphins, seals and
penguins).
Shallow water with sandy seabed. Whiting, juvenile King prawns, anchovies,
blue sprat, whitebait.
Seagrass meadows. Leatherjackets, wrasse, crabs, herring.
Jetties and groynes. Herring, yellow tail, scad, trevally, samson fish, mussels.
Earlier work by Penn (1977) also suggests that the deep basin is an important habitat
for whiting, squid, cuttlefish, butterfish, sampson fish, sand skipjack, crabs and
snapper.
There is a lack of detailed studies on fish nursery areas within the Sound. Larval fish
communities in seagrass meadows were studied as part of the SMCWS (Jonker,
1993), but there is little information on other habitats. It was found that meadows in
Mangles Bay had similar species but significantly greater numbers of larvae than
meadows off eastern Garden Island. This was attributed to greater food supply (i.e.
higher phytoplankton levels), increased shelter due to the higher epiphyte loads, and
greater retention of larvae due to the calmer waters of Mangles Bay compared to the
Garden island site.
Although there is little information on fish nursery areas within the Sound, the
breeding success of the species listed above would be affected by adverse impacts on
their feeding grounds. The opinion of Fisheries WA is that both feeding areas and
nursery areas are important in affecting fish populations, and that the whole of
Cockburn Sound is significant as a fish nursery/habitat.
Other recent fish studies include work by Curtin University of Technology on fish
health using biochemical markers (biomarkers) that indicate exposure to
contaminants. To date, biomarkers of hydrocarbon exposure have been found at all
sites examined (the highest levels were not in Cockburn Sound, but adjacent to
Fremantle Fishing Boat Harbour). This work is ongoing, and there is also a
forthcoming study in Cockburn Sound examining DNA damage and stress proteins
as fish biomarkers in response to contamination (Monique Gagnon10, pers. com.).
Marine mammals, reptiles and seabirds
A resident population of bottlenose dolphins (Tursiops sp.) lives in Cockburn Sound,
and has become a popular tourist attraction. About 180 animals have been identified
as using Cockburn Sound, and approximately a quarter of these are adult females
with calves, which is unusually high for dolphin populations (Donaldson11,
unpublished data).
Loggerhead, Leatherback and Green turtles sometimes stray as far south as Cockburn
Sound, but this is rare.
9
Provided by Eve Bunbury, Fisheries WA, after discussions with Fisheries WA personnel.
Dr Monique Gagnon, Research Fellow, Department of Environmental Biology, Curtin University.
11
Rebecca Donaldson, Ph. D. researcher at the School of Biological Sciences, Murdoch University
10
42
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
At least 12 species of seabirds are found in the Cockburn Sound/Warnbro Sound
area, but as the eastern shores of Cockburn Sound are heavily developed, they are of
far lesser importance as a nesting, feeding and roosting area than the Shoalwater
Islands Marine Park and Garden Island.
A small colony of Little Penguins Eudyptula minor (maximum 50 adults) has been
established in limestone walling at Careening Bay since at least 1986. Regular
migratory birds utilising Cockburn Sound include the Fairy Tern Sterna nereis and
Bar-tailed Godwit Limosa lapponica. Migratory birds that may utilise the Cockburn
Sound on a transitory basis include the Great Egret Egretta alba, the Eastern Reef
Egret Egretta sacra, White-bellied Sea Eagle Haliaeetus leucogaster, the Ruddy
Turnstone Arenaria interpres, the Caspian Tern Sterna caspia and the Crested Tern
Sterna bergii. Young Australasian gannets also tend to feed in the Sound until
mature and then return to New Zealand (Bob Goodall pers. com.).
2.4
PRESSURES ON THE MARINE ENVIRONMENT
2.4.1
Ecosystem overview
The main types of pressures on the marine environment of Cockburn Sound due to
human activities are as follows:
•
•
•
•
•
•
Physical alterations to the environment which cause direct or indirect habitat
loss, effects on water quality or alterations to coastal processes;
Nutrient enrichment (which can also cause habitat loss);
Contaminant inputs;
Discharge of cooling waters;
Introduction of foreign marine species; and
Over-fishing.
In relative terms, it is the first two of the above pressures that have had the greatest
impact on Cockburn Sound, especially when acting in concert. It was the cumulative
impact of human uses of the Sound that caused the large-scale loss of seagrass
meadows and deterioration in water quality in the late 1960s and early 1970s,
notably the combination of nutrient-rich industrial discharge, nutrient-rich municipal
wastewater discharge, construction of the Causeway, FPA dredging and RAN
dredging.
A more recent example of cumulative impact is the alteration of circulation patterns
due to harbour construction, combined with contaminated groundwater inputs, that
have led to water quality problems in the Jervoise Bay Northern Harbour. Ongoing
problems in predicting and managing sediment transport along the Sound’s beaches
are also due to the cumulative impacts of shoreline and offshore structures and beach
re-nourishment programs.
Nutrient inputs to the Sound have been reduced dramatically, but there remains the
potential for reduced water quality on the eastern margin of the Sound due to altered
circulation patterns and flushing characteristics associated with several large-scale
developments that are either under construction (the Jervoise Bay Southern Harbour)
or proposed (FPA Harbour and the James Point Private Port). There is little doubt
that reduced flushing will result in lesser water quality within these large-scale
harbour developments, but their potential for effects further afield (between-harbour,
and in the broader Sound) remains unclear. Careful interpretation of effects will be
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
43
needed, as water quality within the Sound may be affected by regional events (e.g.
ENSO events, unusually strong or unseasonal outflow from the Swan River), and
local events such as enhanced nutrient release from deep basin sediments at the
southern end of the Sound during extended periods of calm.
2.4.2
Physical alterations to the environment
Physical alterations that have (or that will soon) cause direct or indirect habitat loss
(seagrass meadow and shallow sand), effects on water quality and alterations to
coastal processes in Cockburn Sound, are as follows:
•
•
•
•
•
•
•
•
•
•
2.4.3
Building of the at Woodman Point and WAPET groynes off the tip of
Woodman Point;
Spoil disposal at Woodman Point;
FPA dredging of shipping channels and turning basins, and disposal of dredge
spoil;
RAN dredging for harbour development on Garden Island;
Construction of the Causeway;
Construction of BP’s offshore breakwaters at James Point;
Construction of the breakwaters and reclamation of waterfront for the Jervoise
Bay Northern Harbour;
Reclamation of waterfront, and dredging associated with the Jervoise Bay
Southern Harbour;
Boat mooring damage in Mangles Bay and eastern Garden Island; and
Shoreline/road stabilisation works at Challenger Beach.
Nutrient enrichment
Nutrients entering Cockburn Sound due to human activities fall into two broad
categories, ‘point’ sources and ‘diffuse’ sources, as follows:
•
•
‘Point’ sources - nutrient discharge from a focussed source, e.g. industry
outfalls, sewage outfalls, spillage from jetties during loading/unloading, spills
from shipping accidents; and
‘Diffuse’ sources - nutrients from no clearly defined point of discharge, e.g.
groundwater discharge, surface run-off from urban and rural areas (usually
channelled into water body via stormwater drains or agricultural drainage
channels), Swan River outflow, atmospheric fallout (nitrogen oxides from
industry discharge and car exhaust fumes).
There are five industrial outfalls presently discharging into Cockburn Sound:
Western Power (largely cooling water but some contaminants present), BP Refinery
(largely cooling water, but small amounts of treated wastewater), Tiwest Joint
Venture, Wesfarmers CSBP, and Millenium Chemicals. The amounts of nutrients
entering the Sound from the five industrial outfalls are documented as part of DEP
licence conditions for discharge. These are discussed in some detail in Section 5.3.1.
In addition, the Water Corporation has two emergency outfalls off Woodman Point:
the old domestic wastewater outfall (situated 1.8 km offshore from Woodman Point),
and the Jervoise Bay outfall (situated inside the Jervoise Bay Northern Harbour,
180 m from the shore). Discharge from these outfalls is small-scale and infrequent,
and has contributed less than seven tonnes since 1990, as shown in Table 2.7.
44
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
Table 2.7 Summary of emergency overflows from the Woodman Point Wastewater Treatment
Plant to Cockburn Sound since 1990
DATE
DURATION OF
OVERFLOW
(Hours/Minutes)
Cockburn Sound outlet
1990
16/03/90
0.30
23/03/90
0.10
12/05/90
0.24
1991
08/03/91
2.00
20/04/91
1.00
23/05/91
0.52
23/11/91
0.58
1993
06/03/93
3.23
19/06/93
1.00
1994
16/04/94
0.10
1995
08/08/95
1.26
20/10/95
6.00
1996
11/05/96
5.06
1997
29/01/97
7.30
1998
10-11/07/98
16.10
3–4/08/98
15.25
SUBTOTAL
Jervoise Bay outlet
1995
20/10/95
0.20
SUBTOTAL
TOTAL
OVERFLOW
VOLUME
(ML)
LOADS TO COCKBURN SOUND
(TONNES)
Suspended
Total
Total
Solids
Nitrogen
Phosphorus
0.0005
0.002
2.145
<0.001
<0.001
0.257
<0.001
<0.001
0.116
<0.001
<0.001
0.021
0.504
0.180
0.314
2.106
0.069
0.022
0.038
0.253
0.027
0.010
0.017
0.114
0.005
0.002
0.003
0.021
5.700
0.200
0.684
0.024
0.308
0.011
0.057
0.002
560
0.067
0.030
0.006
8.160
3.875
0.979
0.465
0.441
0.209
0.082
0.039
13.690
1.643
0.739
0.137
18.025
2.163
0.973
0.180
36.160
35.510
127.1315
5.243
4.616
16.524
1.989
1.811
6.796
0.372
0.284
1.212
1.140
1.140
128.2715
0.137
0.137
16.661
0.062
0.062
6.858
0.011
0.011
1.223
Diffuse sources are much harder to estimate accurately, but the main contributors at
present are industrial groundwater, and groundwater under agricultural land at
Spearwood. Diffuse sources are largely due to catchment uses, and are discussed in
detail in Section 3.3.
The role of past nutrient inputs in causing seagrass loss and poor water quality was
discussed in some detail in Sections 2.3.3 and 2.3.5. Nitrogen inputs to Cockburn
Sound from human activities have declined from an about 2,000 tonnes/year in 1978,
to 1,080 tonnes/year in 1990, to ~300 tonnes/year in 2000. A breakdown of the
major contributors in these three years is shown in Figure 2.19. Estimated inputs in
2000 were: groundwater 212.4 tonnes, industrial discharges 54.7 tonnes, ship
loading spills 5.6 tonnes, surface drainage 4.3 tonne and atmospheric fallout
20.4 tonnes.
Groundwater discharges remain the main input of nitrogen to the Sound, and
industrial sources (discharges plus groundwater) contribute about 75% of the total.
The Kwinana Nickel Refinery is no longer the main contributor, and because
industrial loads have decreased so much the relative contribution of rural
groundwater is starting to become significant.
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
45
N inputs in 1978 (Total ~2,000 tonnes/year)
Atmosphere
1%
Groundwater
9%
Others
9%
KNC/CSBP
discharge
51%
Woodman Point
WWTP discharge
30%
N inputs in 1990 (Total ~1,080 tonnes/year)
Atmosphere
2%
Jervoise Bay
groundwater
6%
CSBP discharge
40%
KNR
groundwater
36%
BP refinery
discharge 9%
Others
7%
N inputs in 2000 (Total ~ 300 tonnes/year)
CSBP discharge
10%
Atmosphere
Other discharges
7%
9%
Other GW
Ship spillage
9%
2%
Rural
groundwater
Surface waters
15%
1%
CSBP
groundwater
25%
Jervoise Bay
groundwater
24%
Figure 2.19
Estimated nutrient inputs to Cockburn Sound from outfall discharges;
groundwater; surface water; atmospheric deposition; and spills from ship loading/unloading in
1978, 1990 and 2000
Note:
46
The areas of the pie-graphs are proportional to their relative inputs.
Excludes inputs from sediment nutrient release.
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
The potential importance of Swan River outflow as a nutrient source to Cockburn
Sound is uncertain. Winter outflow from the Swan River typically carries between
250 and 900 tonnes of nitrogen (DEP, 1996), but it is difficult to know what
proportion enters—and is retained in—Cockburn Sound. Chiffings (1979) notes that
river outflow is generally considered to move out to sea and then north or south
along the coast, but seldom into Owen Anchorage and even less so into Cockburn
Sound. Regional water quality data supports this (DEP, 1996). Chaney (1978) also
found that phytoplankton growth rates in winter were less than a third of rates at the
end of summer (suggesting little increase in phytoplankton production due to Swan
River nutrients), but this was at a time when nutrient inputs from human activities
were much higher than at present. Now that nutrient inputs from human activities
are much lower, the relative importance of Swan River outflow as a nutrient source
to Cockburn Sound will be greater. Although Swan River outflow may still be minor
source of nutrients in most years, it may provide a major input to the Sound in years
of unusually large flow.
As noted previously, areas such as Cockburn Sound with a history of nutrient
enrichment from point and/or diffuse sources can also have increased ‘stores’ of
nutrients in their sediments. Release of these nutrients contributes to the symptoms
of nutrient enrichment and can maintain those symptoms even after the original
cause of the problem has gone. The nutrient stores in Cockburn Sound sediments
have declined considerably since 1978 (see Section 2.3.4), but the extent to which
sediment nutrient release has changed is unknown.
2.4.4
Contaminants
Metals and organic contaminants
As for nutrients, contaminants entering Cockburn Sound due to human activities fall
into two broad categories: point sources and diffuse sources. Contaminant loads
from industrial point sources are documented as part of DEP licence conditions, but
there are few data for diffuse sources (see Section 3.3).
The large decreases in contaminant discharges from industrial point sources since
1978 are shown in Table 2.8, and present discharges are discussed in more detail in
Section 5.3.1.
Table 2.8
Sound
Estimated contaminant inputs from licensed industrial discharges to Cockburn
YEAR
1978
2000
Arsenic
unknown
34
Chromium
2,065
1
CONTAMINANT INPUT (kg/year)
Copper Mercury
Lead
Nickel
3,809
105
3,259
571*
600
2
16
79
Zinc
8,557
1,077
Oil
363,540
4,547
* Probably an underestimate.
The data in Table 2.8 indicate that sediment contamination in the Sound is a legacy
of past rather than current inputs.
Tributyltin
Tributyltin (TBT) is the active ingredient in antifoulant paints that the majority of the
world’s shipping fleet uses. TBT based paints are extremely reliable, offering up to
five year’s protection against both the growth of organisms such as barnacles on
ships’ hulls (that would otherwise slow a ship down due to increased drag, resulting
in increased fuel consumption), and the spread of foreign marine organisms. TBT
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
47
based paints were also commonly used in WA on small (less than 25 m long)
commercial and recreational boats up until about 1992.
TBT is highly toxic to a wide range of marine organisms, and can cause serious
effects at extremely low concentrations. The classic symptom of TBT contamination
is ‘imposex’ (development of male reproductive organs) in female snails, which can
block egg release and make them sterile. TBT breaks down rapidly in marine waters
but accumulates in marine sediments, and is the sediment contaminant of greatest
concern to the DEP.
Many countries have partial or complete bans on the use of TBT based paints. In
1991 the WA State Government imposed a ban on the use of TBT on vessels less
than 25 m long, and restricted its use to low-leaching paints on boats over 25 m.
The SMCWS included a 1993 survey of imposex in marine snails, and a 1994 survey
of sediment TBT levels. The sediment survey found widespread contamination of
Cockburn Sound sediments with TBT. Very high TBT levels were found next to
ship berthing and ship maintenance facilities (DEP, 1996), along with 100%
incidence of imposex in marine snails (Field, 1993). Many interstate and overseas
studies have also found that slipways, drydocks and washdown yards (where boats
are scraped down and repainted with antifoulant) are a major point source of TBT to
the marine environment.
A further study on imposex in marine snails was carried out in 1999, and found a
significant improvement in areas visited by recreational vessels less than 25 m long
(e.g. Cottesloe to Ocean Reef, Rottnest Island), but not at sites adjacent to ports and
other commercial shipping activities where vessels greater than 25 m long are
berthed or serviced. In Cockburn Sound, 100% incidence of imposex was found at
the four sites surveyed: three sites in the Jervoise Bay/Challenger Beach area, and
one site at Colpoys Point near the naval berthing facility (Reitsema12, pers. com.).
Therefore, although the 1999 sediment survey indicated greatly decreased levels of
TBT at Jervoise Bay, they are still sufficient to cause imposex.
2.4.5
Cooling waters
There are two cooling water discharges into Cockburn Sound: Western Power
(about 1,600 ML/day) and BP Refinery (about 440 ML/day). These shoreline
discharges cause some increase in temperature close to the outfalls (about 2°C) but
this dissipates rapidly and effects are hard to detect after a couple of hundred metres.
The discharges appear to have very little effect on marine biota.
2.4.6
Foreign marine organisms
Cockburn Sound has been visited by international shipping since the 1830s, and has
been a regular port of call for national and international vessels since 1954. Foreign
marine organisms can enter WA waters via discharge of ships’ ballast water prior to
loading cargo. Contaminated ballast water may be from international shipping, or
ships from other Australian ports where foreign marine organisms are present (e.g.
Port Phillip Bay, Hobart). Organisms attached to ships’ hulls may also fall off, or be
scrubbed off during ‘in-water’ cleaning of hulls and propellers. In-water cleaning
was allowed in Cockburn Sound until several years ago, but has since been banned
by the FPA.
12
48
Tarren Reitsema, post graduate researcher at School of Public Health, Curtin University
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
A survey of introduced marine pests in FPA waters (including Cockburn Sound) was
carried out in 1999 (CRIMP, 2000 unpublished) as part of a Australian port survey
programme that was a joint initiative of the Australian Association of Port and
Marine Authorities (AAPMA) and the CSIRO Centre for Research on Introduced
Marine Pests (CRIMP), and supported by the Australian Ballast Water Management
Advisory Council (ABWMAC). This programme was designed to provide
information for a ballast water management decision system for Australian waters
(see also Section 5.4.1).
Sites sampled in Cockburn Sound included all commercial and naval jetties. At least
18 exotic marine organisms have become established in local coastal waters (DEP,
1996; CRIMP, 2000 unpublished). Two ABWMAC targeted pest species have been
recorded in Cockburn Sound: the European fan worm Sabella cf. Spallanzanii
(throughout the Sound), and the Asian date mussel Musculista senhousia (Southern
Flats). The European fan worm and Asian date mussel are prolific growers, and can
out compete native species, affecting biodiversity. The CRIMP study indicated that
these two pest species do not seem to be having this effect in FPA waters.
Other species recorded in Cockburn Sound that are either introduced or of unknown
origin, but which are not significant environmental or economic threats include: the
fish Tridentiger trigonocephalus, the bryozoans Bugula neritina, B. flabellata,
Tricellaria occidentalis, Cryptosula pallasiana and Watersiproa subtorquata(?), the
hydroid Tubularia raphi, and the ascidians Asidiella aspersa and Ciona intestinalis.
2.4.7
Commercial and recreational fishing
Commercial and recreational fishing result in direct removal of target species of fish.
Depending on the fishing method used, there can also be losses due to by-catch (nontarget species). Other pressures include fuel spills; rubbish; loss of gear (nets, lines,
hooks, sinkers etc); and habitat damage from propeller and hull scour, nets and
anchors.
The fishing gear allowed in Cockburn Sound and the present level of fishing effort is
not believed to be a major pressure on Cockburn Sound. The main management
issue is likely to be the sustainability of the combined catches of commercial and
recreational fishing as recreational fishing pressure increases. Pressures due to
recreational fishing are discussed in more detail in Section 4.3, and commercial
fishing in Sections 5.3.3 and 5.3.4.
Commercial fishing
The level of fish harvesting from Cockburn Sound from 1977 onwards was estimated
from WA Fisheries annual commercial fish catch data for Cockburn Sound Fisheries
Block 9600. This area includes all waters within a line that extends from South Mole
at Fremantle west to Stragglers Rocks, then through West Success Bank to Carnac
Island to Garden Island, along the eastern shore of Garden Island and to John Point
on the mainland (Penn, 1999). Although this area includes Owen Anchorage, most
commercial fishing occurs within Cockburn Sound.
Annual commercial catches of finfish and molluscs (includes squid and octopus but
excludes mussels), crabs, mussels and baitfish are shown in Figure 2.20. The mussel
data are for wild harvest only: there are no data for before 1982 or after 1992 as
fewer than 5 boats collected the catch, and Fisheries policy is to not release data
under these circumstances. However, wild mussel catches before 1982 and after
1992 were extremely low.
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
49
Baitfish
Finfish/molluscs
Crabs
Mussels
Total
1800
1500
1200
900
600
300
2000
1998
1999
1996
1997
1994
1995
1993
1991
1992
1989
1990
1987
1988
1985
1986
1984
1982
1983
1980
1981
1978
1979
0
1977
Catch (tonnes live weight)
Annual commercial fish catches
Year
Figure 2.20 Annual commercial fish catches in Cockburn Sound Fisheries Block 9600 since
1977 (excludes mussels from aquaculture)
The greater part of commercial catch until about the last three years has been baitfish
(which feed on plankton). However, changes in the fisheries cannot be linked to
changes in plant production in the Sound, as the former are due to many factors
including market pressure, change in gear type and fishing effort, and recruitment
effects.
Finfish catches (especially garfish catches) have been increasing since the 1970s,
causing some concern to Fisheries WA. Conversely, catches of King George
whiting, western sand whiting, squid and octopus have all declined in recent years.
Reasons for the declines are not fully understood, but are thought to include
environmental factors, fishing pressure and/or market considerations.
Mussel aquaculture in Western Australia began in Cockburn Sound in 1988 to
overcome the declining catches of the wild capture fishery and to provide a more
consistent source of product. The large majority of mussels now harvested from
Cockburn Sound are from aquaculture. Mussel aquaculture is undertaken in
Cockburn Sound, Warnbro Sound and Albany, and total harvests in the last two years
have been 663 tonnes and 683 tonnes, respectively. Harvest data for Cockburn
Sound area cannot be released due to commercial confidentiality, but a significant
proportion of the harvest comes from Cockburn Sound.
Recreational fishing
Cockburn Sound is very popular for recreational fishing. The main species caught
are crabs, whiting (especially King George whiting), Australian herring, squid,
garfish, trevally, dhufish, tailor and pink snapper (Sumner and Williamson, 1999).
These are many of the species targeted by commercial fishers.
Data on recreational fishing pressure on Cockburn Sound were collected during a
12 month survey in 1996/97, and have been provided by courtesy of the Fisheries
WA Research Division. During this survey, there were an estimated 12,083 boat
trips in Cockburn Sound. The recreational catch for crabs was estimated as
18.8 tonnes (about 5.2% of the commercial catch of 360 tonnes). For finfish, catch
weights were estimated for Australian herring (13 tonnes) King George whiting
50
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
(9 tonnes), whiting other than King George (7 tonnes), skipjack trevally (5 tonnes),
tailor (3 tonnes) and garfish (2 tonnes), giving a combined catch of 39 tonnes13—
about 65% of the commercial finfish catch of 60 tonnes (excluding baitfish) for the
same period. In addition, 58,000 squid were caught by recreational boat fishers. As
these data do not include shoreline recreational fishing, it is clear that the recreational
finfish catch is of a similar magnitude to the commercial catch.
2.5
MANAGEMENT RESPONSES
2.5.1
Current management responses
There are a number of national strategies that encompass protection for the marine
environment. These include the National Strategy for the Conservation of
Australia’s Biological Diversity (for the protection of biological diversity and
maintain ecological processes and systems), and the National Water Quality
Management Strategy.
The National Water Quality Management Strategy has set out a framework for the
management of natural waters. As noted in Section 1.3, the NWQMS approach has
been followed in the coordinated management framework currently being developed
by the EPA and DEP for the protection of Perth’s coastal waters. The EPP being
developed for Cockburn Sound is a part of that exercise, and the Australian and New
Zealand Guidelines for Fresh and Marine Water Quality (ANZECC/ARMCANZ,
2001 due for imminent release) will play an important role in the development of
some EQC.
The formation of the CSMC itself is a direct management response to the lack of
coordination recognised in EPA Bulletin 907, which in turn is based on a
recommendation of the SMCWS (DEP, 1996).
Management responses specific to land use (impacts on groundwater, surface water),
social/cultural uses (recreational uses including fishing) and economic uses
(industrial discharges, shipping, commercial fishing and tourism) are dealt with in
Sections 3, 4 and 5 respectively.
Local government
The boundary of the CSMC’s jurisdiction includes three local governments: the City
of Cockburn, the Town of Kwinana and the City of Rockingham. Local
governments play a key role in the management of coastal areas by zoning to
separate incompatible uses, providing and maintaining suitable and safe recreational
facilities and paths, and undertaking erosion control measures. The following
information is noted:
•
•
13
City of Cockburn: has a Coastal Management Strategy and a Coastal Works
Plan that addresses coastline works, foreshore rehabilitation and reserve
management. It has recently released its State of the Environment report, and
is currently undertaking the development of its Local Agenda 21 Plan which is
part of the City of Cockburn's overall Sustainable Development Strategy. It is
also currently preparing an Environmental Management System to address all
aspects of its business;
Town of Kwinana: has an Environmental Policy and a Coastal Management
Plan. The latter is currently being updated in Kwinana’s Environmental
Data generated by Neil Sumner, Fisheries WA
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
51
•
Management Plan. Protocols for undertaking beach erosion controls have
recently been modified to include greater stakeholder involvement and advice
from relevant State Government department; and
City of Rockingham: has a Strategic Coastal Management Plan for all of its
beaches (and forming the framework for all the individual management plans),
which is currently being reviewed. It also has a List of Environmental
Priorities, and has released its first (2000–2001) State of the Environment
Report incorporating an Environmental Action Plan.
At present, environmental management and planning by each of the Councils
proceeds—for the most part—on a case-by-case basis, and management approaches
differ slightly. The three Councils do not, at present, follow any common or
coordinated approaches or protocols for the various aspects of coastal management
and planning, because none is available. However, the Western Australia Municipal
Association has established a Coastal Management Advisory Group (for the whole
State ) which aims to better co-ordinate coastal planning, and Cockburn, Kwinana
and Rockingham are represented on that group. The three Councils also have a good
communication network for environmental issues, and the Environmental Officers
liase on issues which impact on the three Councils and/or Cockburn Sound. Thus,
while each Council may formulated separate responses, they liase closely for
proposals which may effect the broader region. All three Councils are also
represented on the Cockburn Sound Conservation Committee, which offers a forum
to address concerns from each of the Councils regarding proposals and impacts to
Cockburn Sound. The councils are presently awaiting guidance from the CSMC’s
EMP (all three councils are represented on the CSMC) before refining their own
planning and management initiatives to be consistent with the EMP.
The boundary of the CSMC’s jurisdiction abutts Garden Island. The RAN has an
EMP for Garden Island and HMAS STIRLING, and this is currently being revised to
reflect and complement initiatives at the regional level. Defence is also currently
investigating whether there are any localised impacts on seagrass on the east coast of
the island due to groundwater contaminated by nutrients from its sewage farm
(Wykes, pers. com).
Community groups
Community groups such as Com-Net, CORKE, Cockburn Power Boat Association,
RecFishWest, Kwinana Watchdog Group and the Conservation Council play a vital
role as ‘environmental watchdogs’ and in raising community awareness about
environmental matters. The long history of strong community interest in the
environmental problems of Cockburn Sound also helped encourage the formation of
the CSMC.
2.5.2
Gaps in the management responses
The CSMC will overcome the main problem in previous management efforts, by
attempting to implement a consistent and coordinated management approach across
different levels of government, industry and community groups.
There has been some comment on the exclusion of Garden Island from the defined
area under the jurisdiction of the CSMC, as it needs to be considered as much as the
eastern coastal boundary in any environmental planning and management.
52
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
2.5.3
Gaps in information needed for management
The EPA’s Bulletin 907 on strategic environmental advice for Cockburn Sound
(EPA, 1998) noted that environmental decision-making was being made more
difficult by key information gaps in four main areas:
•
•
•
•
Hydrodynamics;
TBT inputs from shipping activities;
Nutrient cycling and algal blooms; and
Ecology (i.e. biological assemblages).
During compilation of this P-S-R report it was clear that the main information gaps
to do with understanding and/or representing ecological processes within the
Cockburn Sound remain unchanged. In particular, there is a need for:
•
•
•
Additional data to improve modelling of a) water movement in Cockburn
Sound and b) coastal processes in Cockburn Sound;
An agreed conceptual model of nutrient cycling in Cockburn Sound and the
effects of nutrient inputs; and
An agreed method for evaluating cumulative impacts.
Each are discussed below.
Modelling of water movement in Cockburn Sound
Bulletin 907 (EPA, 1998) was prepared largely in response to the potential impact of
several large-scale harbour developments on water movement within the Sound, and
the subsequent effects on water quality and ecology. Accurate predictions on water
movement are thus essential as they underpin all subsequent predictions on water
quality and ecology.
The fundamental hydrodynamic processes within Cockburn Sound are well
understood, and are backed up by an extensive set of field data (e.g. water salinity,
temperature, density; DEP, 1996, and references cited therein). However, this
information is not sufficient to allow examination of effects on water quality and
ecology within the Sound over time frames of up to several years (EPA, 1998) or to
investigate site-specific processes at the small scale (<100 m). Bulletin 907 (EPA,
1998) identified the following information requirements:
•
•
•
•
•
Effects of density stratification on circulation and mixing of contaminant and
other materials;
Simulations for a far wider range of meteorological and seasonal conditions,
assessed against appropriate field measurements;
Hydrodynamic simulations over ecologically meaningful time frames (up to
several years);
Further data required to characterise the autumn period when long residence
times of the bottom waters of the deep basin are of ecological significance; and
Estimation of turbidity in the Sound through use of a sediment mobilisation
and transport model, appropriately coupled to a hydrodynamic model (note that
this would also cover contaminants adhering to sediments).
Recent hydrodynamic modelling of Cockburn Sound has included the use of
stratification to investigate development proposals (Cockburn, 2000; JPPL, 2001).
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
53
These simulations were undertaken over a wide range of meteorological conditions
and assessed against field data collected during the autumn period. The following
discussion addresses the remaining three requirements identified by the EPA (1998).
Seasonal circulation patterns due to wind and tides are relatively well understood and
therefore well represented in models, but circulation due to forces that acts over
yearly time-scales is less well understood (mainly horizontal pressure gradients and
buoyancy effects). Effectively, this means that circulation during calm periods
(generally autumn) is not well represented in models, nor are differences between
years.
The current limitations of modelling are largely due to a lack of relevant field
measurements, plus the inability of current computer resources to undertake longterm simulations. There is also a lack of field data to assess the influence of
localised effects upon circulation. For example, it is widely recognised that the
southern region of Cockburn Sound is sheltered from the predominantly southerly
winds while the northern region is open to the full impact of these winds.
As noted previously, prediction of effects on water quality and ecology depend on
predicted effects on water movement, and increasing demands are being placed upon
models to aid environmental management. The ability of models to produce
defensible results over the long term (seasonal, annual and inter-annual) is hampered
by the lack of long-term field measurements. Field data collected over longer
periods will also improve the present understanding of seasonal processes (e.g. what
happens during calm periods).
Key data requirements are considered to be as follows:
•
•
•
•
Long-term wave data. Minimum requirements are considered to be two wave
measurement sites within Cockburn Sound (one in southern region, one in
northern region) and one offshore (already in operation). This will be
particularly useful in interpreting changes in sediment transport in the Sound
and addressing the potential issue of sediment mobilisation;
Long term current meter deployments, also collecting temperature and salinity
data, at the northern and southern entrances to Cockburn Sound, to use for
model simulations of periods of up to several years;
Further salinity and temperature surveys, which should also be coupled with
continuous profiling of vertical current structure, and which will also aid in the
development and application of hydrodynamic models over time periods of
several years; and
Sampling should be coordinated whenever possible with biological and
ecological sampling programs.
With the ability to model at smaller scales (e.g. less than 100 m) localised effects
such as groundwater discharges can also be resolved. Improved computer
technology will also allow the refinement of wind patterns, bathymetry and friction.
Models will need to incorporate information such as:
•
•
•
54
Variations in winds in different parts of the Sound, and with time;
The effects on currents and waves of changes in ‘bottom friction’ as they pass
over different types of seabed (e.g. seagrass, bare sand, rubble); and
Linkages between hydrological models (surface and groundwater) to determine
the influence of freshwater inflows.
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
Coastal processes
Information from previous coastal studies of Cockburn Sound is spread over a wide
variety of agencies with different time-frames for developments, different needs and
agendas, and commercial arrangements. A general recommendation is for a study
that collates all the existing information to establish a conceptual model of coastal
processes within Cockburn Sound.
In particular, it is noted than an extensive data set of offshore beach profiles has been
collected around Cockburn Sound by the Royal Australian Navy (RAN) between
1976 and 1990. These RAN data are the only set of continuous beach profile
measurements collected within Cockburn Sound: analysis of these data and further
surveying of these profiles would provide extremely valuable information. There are
also a number of aerial photographic surveys that have been undertaken in the region
and that could be used to examine shoreline movement. Many agencies have already
undertaken localised analyses (e.g. Department of Transport, Maritime Division;
DMH, 1992), and should be contacted to collate as much historical information as
possible.
Further investigation of coastal landforms and processes needs to be centred on field
measurement and wave modelling.
The field measurements will improve
understanding of coastal processes and lead, in turn, to improve modelling of those
processes. Some of the key data required for coastal processes are the same as for
water movement in the Sound. Key data requirements are considered to be as
follows:
•
•
•
•
Wave climate. Directional wave data inside Cockburn Sound needs to be
collected at the same time as wave data outside Cockburn Sound. A
relationship between wave data collected inside Cockburn Sound and outside
(currently in operation) can be established for the purposes of calibrating and
validating a numerical wave model (see also recommendations for water
movement in Cockburn Sound). The FPA has a non-directional wave recorder
at the entrance to the Stirling Channel, and although the data are generally
unavailable for commercial reasons the FPA have indicated they would be
happy to assist in this respect, given certain precautions;
Nearshore currents (see recommendations for water movement in Cockburn
Sound);
Weather. The weather of the Perth coast is relatively well measured, but there
are few specific data for the Cockburn Sound region. Nor has the variation of
winds within Cockburn Sound been examined (see also recommendations on
water movement in Cockburn Sound). It is noted that the RAN is presently
establishing a full weather station at Careening Bay with several automatic
reception sites around Garden Island, and as this is a joint exercise with the
Bureau of Meteorology, data will be available to the public;
Variations in water level. Water level variations are an important contributor
to the coastal processes within Cockburn Sound. Due to the low energy wave
environment the beach widths are relatively narrow, and storm surges (rises in
water level due to a combination of wave setup, wind setup and low
atmospheric pressure) can cause significant erosion of higher areas of beaches.
The effect of storm surges can be predicted using extreme water levels (e.g. 1
in 10, 1 in 50 and 1 in 100 year water level) from long term sea level records.
Presently, a wave staff is in operation near the entrance to the Stirling Channel,
and a similar instrument is located on Parmelia Bank. The staffs and data are
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
55
•
•
owned by the Fremantle Port Authority and the data record is approximately
4 years long;
Beach Profile Data. The extensive data set of offshore beach profiles collected
by the RAN should be monitored and used in conjunction with wave modelling
and shoreline movement plans to establish sediment transport over a variety of
time scales (weeks to decades); and
Aerial Photography. Annual aerial photography is useful for examining the
stability of the shoreline over long periods (5 to 10 years). Regular aerial
photography is best undertaken at the end of summer when the beaches are
most prograded and storm activity is unlikely to occur. The possibility of using
the annual photography undertaken by the Department of Land Administration
(DOLA) for preparation of the metropolitan street directory also needs
investigating.
Nutrient cycling in Cockburn Sound and the effect of nutrient inputs
Bulletin 907 (EPA, 1998) recognised the following information requirements for
nutrient cycling and the ecology of Cockburn Sound:
•
•
Nutrient cycling and algal blooms:
More accurate estimates of nitrogen inputs from groundwater and how
they vary seasonally;
Estimates of sediment oxygen and nutrient fluxes throughout the Sound,
and the role of vertical mixing in determining oxygen levels in the water;
Water quality models to predict algal biomass, oxygen depletion and
light attenuation;
Improved knowledge (and incorporation into models) of feedbacks
between ecological processes and nutrient cycling (e.g. the role of
zooplankton and benthic filter feeders in controlling phytoplankton
density and distribution); and
Improved knowledge of dinoflagellate cyst distributions and conditions
leading to germination.
Ecological:
Data on the existing biological assemblages on the eastern margin, both
within and beyond existing harbour areas;
Improved understanding of implications of changes in water and
sediment quality for distribution and function of biological communities;
and
Relationships between assemblages and local populations of fish and
crabs, and the connections between these local populations and the
fisheries.
The need for more accurate estimates of nitrogen inputs from groundwater and how
they vary seasonally is discussed in Section 3.4.3, and the ability to model the
movement of such inputs was discussed earlier. Research on conditions leading to
dinoflagellate cyst germination is a highly specialised field, and is currently being
undertaken by Dr Gustaaf Hallegraeff at the University of Tasmania.
The remaining information requirements distil into—or depend on—the need for an
agreed conceptual model of nutrient cycling (particularly nitrogen): that is, the key
processes affecting water and sediment quality, and the relative importance of those
key processes. These processes will need to be determined before implications to the
56
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
distribution and function of biological communities and consequent effects on
fisheries can be considered.
It is suggested that one useful starting point for further discussion is the simple
conceptual model of nutrient enrichment presented in this document, which focuses
on sediment nutrient cycling, water quality and phytoplankton/MPB growth. Other
useful models are also available from the Port Phillip Bay Study (CSIRO, 1996) and
the Moreton Bay Study (Dennison and Abal, 1999).
A key information gap is up-to-date data on sediment characteristics in Cockburn
Sound, particularly the levels of nutrients, organic matter and chlorophyll a (the latter
being an indication of MPB growth). This information, used in combination with
generic relationships for recognised key processes available in the scientific literature
(and data ranges that are likely to be applicable to Cockburn Sound) could be used to
refine a conceptual model.
The outcome of the above process will be recognition of the key features controlling
water quality in different parts of the Sound, and how to tailor management
approaches accordingly. For example, characteristics of water depth, circulation,
flushing, sediment nutrient cycling and proximity to nutrient inputs from human
activities differ between the shallow regions (i.e. water depths less than 10 m) on the
east and west of the Sound, the deep central basin, and the poorly flushed southern
basin: these factors are pivotal in determining the water quality that can be attained
in these four main areas, and how to get the best environmental return for
management effort.
Cumulative impact assessment
Cumulative impact occurs when the impact associated with an activity overlaps and
adds to the impact from other activities. When multiple activities occur in a region,
any one activity may result in an acceptable modification of environmental
conditions, but the changes associated with all activities may be unacceptable. As
noted in Section 2.4.1, the major environmental problems in Cockburn Sound (past
and present) are due to cumulative impacts.
Cumulative impacts need to be assessed over a variety of spatial scales (immediate
area of proposal, adjacent areas, and the whole of Cockburn Sound), and short-term,
medium-term and long-term effects considered. It will also be important to
recognise the increasing levels of uncertainty inherent when predicting effects on
water quality and ecology due to changes in circulation and flushing times: effects
on fauna depend upon effects on water quality and sediment quality, which in turn
depend on changes in circulation and flushing times. Predictions at each level have
their own inherent uncertainty as well as incorporating the uncertainty of the
preceding step, and these will have to be acknowledged in any interpretations of
potential effects (e.g. by quoting ranges as well as ‘most likely’ values). Assessment
of cumulative impacts in Cockburn Sound is also complicated by the legacy of
impacts due to past discontinued practices: the Sound is not in a pristine state.
An agreed and consistent basis for cumulative impact assessment is needed to assess
the potential impacts of future developments on the marine environment of Cockburn
Sound. It is suggested that investigation of the cumulative impact of development
within Cockburn Sound uses a modelling approach (with a hydrodynamic model as
the basis), to allow a wide range of processes and scenarios to be investigated and
compared relatively quickly. A potential framework for cumulative impact
assessment is given in Table 2.9, and is offered as a basis for further discussion.
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
57
Monitoring programmes
There are a number of monitoring programmes currently in place that it is anticipated
the CSMC will become responsible for. These monitoring programmes are listed
below, with suggestions for additional work:
•
•
•
58
The DEP’s monitoring of seagrass health every year and seagrass distribution
every three years. It is suggested that monitoring of seagrass health be
expanded to include sites along eastern Garden Island, as protecting remaining
healthy meadows of seagrass in the Sound is a high priority. A survey of the
eastern flats (the main area where the historical dieback of seagrasses occurred)
is warranted, to investigate several reports on the existence of patches of
healthy seagrass. The possibility of natural recolonisation of seagrass in this
part of Cockburn Sound needs to be checked;
The KIC’s water quality surveys of eight sites once a week from December to
March inclusive. It is suggested that the existing sites be reviewed and added
to, and that fluorometry runs be undertaken to better characterise the spatial
patterns of chlorophyll in the Sound. It is also recommended that light sensors
and artificial seagrasses (a means of measuring epiphyte growth) be deployed
in the Sound at several key locations to check on the conditions for seagrass
growth. It is anticipated that results of this monitoring will be compared
against the EQC set in the EPP for Cockburn Sound; and
A survey of contaminant levels in sediments at a selection of previously
monitored sites should be carried out every five years, to confirm that there is
no long-term accumulation of contaminants.
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
Table 2.9 Potential framework for cumulative impact assessment strategy
ISSUE
SPATIAL SCALE
TIME SCALE
ASSESSMENT TOOL(S)
(days, months,
years)
Circulation and
residence time
Marine water
quality
Sediment quality
Benthic habitat
Coastal processes
and littoral drift
(including impacts
on the seabed)
Dunes
Terrestrial
vegetation
Groundwater
quality
Surface water
quality
Within proposal area
Areas adjacent to proposal
Within Cockburn Sound
Within proposal area
Areas adjacent to proposal
Within Cockburn Sound
Within proposal area
Areas adjacent to proposal
Within Cockburn Sound
D-M-Y
D-M-Y
M-Y+
D-M
D-M
M-Y+
Y+
Y+
Y+
Within proposal area
Areas adjacent to proposal
Within Cockburn Sound
Within proposal area
Areas adjacent to proposal
Within Cockburn Sound
Y
Y
Y
M-Y+
M-Y+
M-Y+
Within proposal area
Areas adjacent to proposal
Within Cockburn Sound
Within proposal area
Areas adjacent to proposal
Within Cockburn Sound
Within proposal area
Areas adjacent to proposal
Within Cockburn Sound
Within proposal area
Areas adjacent to proposal
Within Cockburn Sound
Y+
Y+
Y+
Y
Y
Y
M-Y+
M-Y+
M-Y+
M-Y+
M-Y+
M-Y+
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
LEVEL OF INVESTIGATION
AND FOLLOW UP
LIKELY SIGNIFICANCE OF
IMPACTS
(low, medium or high priority)
(low, medium or high)
Dependent on proposal
Dependent on proposal
- Calibrated hydrodynamic model
- Calibrated hydrodynamic model
- Water quality information collected to date
- Conceptual model of nutrient cycling
- Organic build up: zones of maximum residence time
and lowest current velocities in hydrodynamic model
- Conceptual model of nutrient cycling
- Sediment quality information collected to date
- Analysis of historical information
- Detailed habitat map
- Analysis of historical data
- Calibrated hydrodynamic model
- Coastal process model
- Analysis of historical information
- Site survey and assessment
- Analysis of historical information
- Site survey and assessment
- Collation of historical data and desktop assessment
- Proponent’s commitment on groundwater impacts
- Collation of historical data, desktop assessment
- Proponent’s commitment on drainage design
59
3.
LAND COMPONENT
3.1
OVERVIEW
Land uses within the Cockburn Sound catchment includes urban areas, defence,
industry, agriculture and conservation. The main way that these land uses affect the
environment of Cockburn Sound is by contamination of groundwater and surface
water that flows into the Sound. It has been estimated that there are potentially more
than 70 groundwater contaminant plumes within the Kwinana area alone. Emissions
from motor vehicles and industry also contribute to contaminant inputs to the Sound
via atmospheric fallout.
The varying degrees to which the main land uses contribute contaminants to the
Sound are discussed in this section. A brief description of the landform, flora and
fauna of the coastal fringe is also provided.
3.2
THE LAND AND ITS USES
3.2.1
Coastal fringe landform
Earlier in this report (Section 2.1) the Tamala Limestone (TL) of the Spearwood
Ridge was identified as the underlying formation of the present coastline of
Cockburn Sound. The Tamala Limestone comprises an upper layer of pale yellow
medium to coarse grained sand that has decomposed from the deeper limestone,
which in turn is a pale yellow/brown variably cemented fine to coarse grained lime
sand with shell debris (calcarenite). It is overlain by varying thicknesses of Safety
Bay Sand (SBS), which is a calcareous medium grained quartz sand with shell debris
of shallow marine, coastal plain and aeolian (wind-transported) origin.
Woodman Point at the northern end of the Sound is comprised of Safety Bay Sand.
This thins southward to a narrow strip along the current shoreline of the Jervoise Bay
Northern Harbour. Tamala Limestone outcrops at the coast from Russell Road to
Naval Base, then Safety Bay Sand reappears, and extends from the industrial strip to
Cape Peron. The coastal fringe of the Safety Bay Sand is also known as the Becher
Sand due to its marine rather than aeolian origins (Davidson, 1995). However for the
purposes of this report, it will be referred to as the Safety Bay Sand.
3.2.2
Groundwater aquifers
The Safety Bay Sand and Tamala Limestone extend down to approximately 25 m
below AHD (Australian Height Datum, which is approximately equivalent to mean
sea level). The Safety Bay Sand extends down to approximately 10 m below AHD,
lying above and on the coastal side of the outcropping limestone. The Safety Bay
Sand and the Tamala Limestone are often separated by a thin (0.5 to 1 m) silty or
clayey shell bed (Appleyard, 1994).
Groundwater in the SBS and TL aquifers flows from the Jandakot Mound, located
about 10 km to the east, and discharges into the nearshore marine environment.
Groundwater flow through the TL aquifer is highly variable ranging from about 200
to 2000 m/year (Davidson, 1995), and is about an order of magnitude lower through
the SBS aquifer (i.e. about 20 m/year). Near the coast, fresh groundwater overlies
saline marine water that has moved into the lower section of the aquifer due to its
greater density. As groundwater approaches the coast it is forced over this more
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
61
dense saline ‘wedge’, and follows the path of ‘least resistance’ to discharge into the
shallow, nearshore zone.
The volume and distribution of groundwater flow is influenced by the hydraulic
conductivity of the aquifer through which it is flowing, the presence of preferred
pathways (‘karst’ formations or holes in the limestone) and fluctuations in sea level
and groundwater elevation. The difference between groundwater elevation and sea
level is particularly important in determining the rate of groundwater discharge.
Passmore (1970) and Spencer (1993) found that the rate of groundwater discharge is
inversely related to the sea level at the time.
It is anticipated that most groundwater discharge will occur in the nearshore zone.
Investigations carried out by Thomas & Evans (1995) found that groundwater from
the Tamala Limestone and the Safety Bay Sand discharged up to 40 m from shore in
the vicinity of the Alcoa Refinery. Davidson (1995) mentions anecdotal reports of
offshore groundwater discharge from springs connected to solution channels in the
Tamala Limestone. Appleyard (1994) suggests that discharge from the Safety Bay
Sand takes place at or near the shoreline, while discharge from the Tamala
Limestone may take place several hundred metres offshore when it is overlain by the
clayey confining bed. Where the limestone is not confined, groundwater discharge
commonly takes place from springs and seeps at the base of limestone cliffs.
Groundwater also flows into the Sound from Garden Island. CSIRO research shows
that there is no true unconfined aquifer at Garden Island: the local sand and
limestone are so porous that rainwater rapidly filters down to sit on saltwater that is
an extension of the two bounding water bodies, the Indian Ocean and Cockburn
Sound. There are pressure differences between the two water bodies, with daily and
seasonal variation in height and lateral movement. On the whole, the pressure
differences result in eastward movement of groundwater, with diffusion from one
side of the island to the other in a matter of months (Wykes et al., 1999).
3.2.3
Coastal flora and fauna
Eastern shore of Cockburn Sound
There are two main vegetation complexes along the eastern coastal fringe of
Cockburn Sound, as follows:
•
•
Quindalup vegetation complex, which occurs on Safety Bay Sand. The two
main areas are at Woodman Point Regional Park, and Mangles Bay/Cape Peron
area (part of the Rockingham Lakes Regional Park). There are also isolated
patches from James Point to Cape Peron, also at Woodman Point (Quindalup
Dunes); and
Cottesloe Complex-Central-South (Spearwood Dunes), which occur on the
coastal strip from Alcoa to the Jervoise Bay Southern Harbour, much of which
is in the Beeliar Regional Park. The vegetated limestone cliffs in this area are
unique in the Perth metropolitan region.
Vegetation associations within the Quindalup complex include herblands, sedgeland
and Acacia shrubland. Vegetation associations within the Cottesloe Complex
include low, closed heath dominated by Melaleuca leterita/Acacia saligna or
Melaleuca huegelii; and dense low closed heath/thicket dominated by Dryandra
sessilis.
62
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
Searches of databases maintained by the Department of Conservation and Land
Management (CALM) found the following threatened flora records for the coastal
strip of the Sound:
•
•
•
Grevillea olivacea (Priority 4 species), a low spreading to open shrub that
occurs in coastal Quindalup dune and limestone areas. It is typically associated
with Acacia shrublands on pale leached sands, and is considered likely to occur
in suitable habitat from Woodman Point to Rockingham;
Dodonaea hackettiana (Priority 4 species) which occurs at Woodman Point
(Halpern Glick Maunsell, 1997) and is also known from within Beeliar
Regional Park (Keighery, 1996); and
Verticordia plumosa (Declared Rare Flora). Whilst there is a record for this
species on CALM’s database for the Cockburn area, it is considered unlikely to
still persist. The original collection for this record was in 1900 and there are no
other populations of the species known from the locality.
Several other flora species of interest occur in the Cockburn Sound area (Keighery
and Keighery, 1993; Halpern Glick Maunsell, 1997). These species are largely
restricted to limestone and Quindalup substrates and include Rhagodia baccata
subsp. dioica, Nemcia reticulata, Petrophile serruriae subsp. nov., Hibbertia spicata
subsp. leptotheca and Pimealea calcicola. Survey work in the Quindalup dunes west
of Coastal Reserve 24309 has also recorded a new variant of Stylidium bulbiferum
which may represent a new species (A. Lowrie14, pers. com.; Halpern Glick
Maunsell, 1998).
CALM databases were also searched for records of terrestrial fauna species of
special conservation significance likely to occur in the area. Three species were
found:
•
•
•
Southern Brown Bandicoot Isoodon obesulus fusciventer. This species is
locally common in dense swamps and other areas with intact understorey in the
south-west of the state and has recently been downgraded from Schedule 1 to a
Priority species. It is known from several populations in nearby areas
including Woodman Point (How et al., 1996). CALM currently regards this
species as ‘Conservation Dependent’. It is considered likely to occur
throughout most of the area where the understorey remains intact;
Peregrine Falcon Falco peregrinus (a Schedule 4 species). The Peregrine
Falcon is widespread across all of Australia, but only occurs at very low
densities and with a patchy distribution. It is known to favour coastal areas and
open woodlands amongst other habitats (Johnstone and Storr, 1998) and may
be an occasional visitor to the area; and
Carpet Python Morethia spilota imbricata (a Schedule 4 species). This subspecies is broadly distributed across much of the south-west, but has been
given its protected status due to the fact that it is not common anywhere in its
range. Carpet Pythons are known to occur in Quindalup and Spearwood
systems, particularly on the northern margins of the Perth Metropolitan area
(Biota Environmental Sciences, 2000). The species is considered possible for
the study area, but only likely to be at low abundance if present.
The Quindalup system generally supports a diverse reptile assemblage that is largely
restricted to coastal dune systems. Several Quindalup species which were previously
14
Dr Alan Lowrie, Specialist consultant to the WA Herbarium.
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
63
listed on the priority fauna listings, such as the Lined Burrowing Skink Lerista
lineata and the Black-striped Snake Simoselaps calonotus, have recently been downgraded from this status.
Garden Island
Although Garden Island is outside the CSMC boundary, the following information is
included for completeness. The flora and fauna of Garden Island are of both regional
and national significance.
The Quindalup vegetation complex on Garden Island includes sedgeland, heathland,
shrubland, and extensive tracts of ‘low, closed coastal forest’ of Callitris preissii
(Rottnest Island Cypress) and Melaleuca lanceolata. The latter is classified by
CALM as a restricted and threatened community in Western Australia, with the
Melaleuca lanceolata population being the only one in the Perth Metropolitan
Region (disjunct from Margaret River). Several other disjunct populations of plant
species that occur in this community are considered of regional significance,
including Amyema melaleucae, Lasiopetaum angustifolium, Lepidium puberulum,
Boronia alata, Myostis australis (may be a misidentification of Cynoglossum
australe, another rarely collected species recently confirmed by an herbarium
specimen – B. Wykes pers. com.), Leucopogon insularis and Pittosporum
phylliraeoides (Keighery et al., 1997)
Fauna surveys have identified 94 species of birds, 14 species of reptile and one
native mammal (the tammar wallaby) (Brooker et al., 1995, Robinson et al., 1987).
The tammar wallaby Macropus eugenii (a Schedule 4 species ) and carpet python
Morelia spilota occur abundantly on Garden Island, and bush birds of the island
include disjunct populations of the Brush Bronzewing Phaps elegans (a Schedule 4
species) and Golden Whistler Pachycephala pectorali (Wykes et al., 1999). The
island is a regionally important nesting site for many bird species. Garden Island is
visited by 14 migratory species recognised under the Japan Australia Migratory Bird
Agreement (JAMBA) and/or China Australia Migratory Bird Agreement (CAMBA),
and is listed in the Register of the National Estate for a variety of natural and cultural
heritage values.
3.2.4
Land uses
Existing and planned land uses are shown in Figure 3.1, along with known or
potential contaminated sites.
Urban areas
The three local government authorities located within the Cockburn Sound
catchment area are the City of Cockburn, the Town of Kwinana and the City of
Rockingham. The two main urban areas are centred around Rockingham,
Shoalwater, Safety Bay and Cooloongup; and Medina, Orelia, Calista, Kwinana and
Parmelia. These are also the areas where urban expansion is planned, along with
some areas of Wattleup and Beeliar around Thomson’s Lake. A population increase
of 30% in the next 10 years is anticipated, and the new urban areas will require
sewage and rubbish collection. This in turn will demand more capacity at rubbish
tips and wastewater treatment plants to process urban wastes.
64
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
HOLDING PAGES (X2) FOR A3 FIGURE
Figure 3.1 Land uses in Cockburn Sound’s catchment
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
65
Second holding page for figure 3.1 (A3)
66
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
Increased presence of Navy personnel at Garden Island is also expected. As part of
the ‘Two Oceans’ defence policy, a 25% increase in personnel and ships (homeporting, maintenance, re-fitting) is planned by 2004. This will increase housing
demand in mainland urban areas as well as expanding the naval presence on Garden
Island.
Industry
Heavy industry is centred on the suburbs of East Rockingham, Kwinana Beach and
Naval Base, and includes an oil refinery, chemical production, an alumina refinery,
power generation, a titanium dioxide plant, cement production and a nickel refinery.
Heavy industry is of considerable importance to the State economy, with the
Kwinana Industrial Area (KIA) alone estimated to produce goods worth at least
$6 billion/year (Baker, pers. com.15). An international ship building precinct
(construction, repair and maintenance of steel and aluminium-hulled vessels) is also
based at Henderson, at the Jervoise Bay Northern Harbour. The attraction of these
area for industry lies in the shipping facilities, road and rail transport, energy, cooling
water, and proximity of synergistic industries.
The Fremantle-Rockingham Industrial Area Regional Strategy (FRIARS) report is
intended to resolve potential conflict between industrial and other land uses in the
region (WAPC, 2000a). FRIARS also recognises the KIA as the premier industrial
area in the State, and seeks to protect the KIA and preserve opportunities for heavy
industries and port facilities. The recommendations include the development of 800
hectares of general light industrial land over the existing townsite of Wattleup, and
the extension of heavy industry into 100 hectares of land in the Hope Valley area.
The proposed developments will ultimately see the loss of the towns of Wattleup and
Hope Valley.
Other areas of industrial expansion include the marine construction and maintenance
industry for the oil, gas and resource industry currently being built at the Jervoise
Bay Southern Harbour, and the proposed East Rockingham Industrial Park (IP14)
between Mandurah and Patterson Roads. The Jervoise Bay industries undertake a
considerable amount of work maintaining and re-fitting Defence vessels, and are
poised to undertake more with the current proposal to ‘home port’ 50% of all naval
vessels at Garden Island.
Future proposals include the Global Olivine Water-to-Energy Plant, the Western
Power upgrade, the James Point Private Port (which could include the live sheep
trade) and the proposed FPA harbour.
Agriculture
The main rural areas are in Mandogalup, Hope Valley Wattleup and Munster. Rural
activities include:
•
•
•
•
Market gardens (346 hectares);
Cut flower production (60 hectares);
Turf farms (38 hectares); and
Orchards (11 hectares).
15
Mike Baker, Executive Officer of the Kwinana Industries Council. Estimate currently being
refined by the Kwinana Industries Council and the Chamber of Commerce and Industry
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
67
There is a general pattern of encroachment on these areas by urban and industrial
use.
Conservation
Coastal areas reserved for conservation include Woodman Point Regional Park,
Beeliar Regional Park and Rockingham Lakes Regional Park. Regional Parks are
managed under cooperative arrangements between State Government, Local
government and the community, coordinated by CALM. The extent of these existing
regional parks is unlikely to change. The ‘Bush Forever’ 10 year strategic plan
(which combines the System 6 Update Program, Perth Environment Project, surveys
by CALM and wetland mapping by the WRC) essentially adopts the existing
Regional Park boundaries with little alteration (WAPC, 2000b). ‘Bush Forever’ is a
‘whole of government’ initiative, and implementation plan, designed to identify,
protect and manage regionally significant bushland on the Swan Coastal Plain.
‘Bush Forever’ listings for coastal areas of Cockburn Sound are:
•
•
•
Site No. 341, Woodman Point Regional Park (includes CALM managed land—
Reserve 42469—reserved for the Conservation of Flora and Fauna);
Site No. 346, Henderson/Naval Base, Brownman Swamp, Mt Brown Lake and
Adjacent Bushland (includes Metropolitan Region Scheme ‘A’ Class Reserve
A24309, reserved for ‘Parks and Recreation’, and is part of Beeliar Regional
Park; and
Site No. 355, Cape Peron and Adjacent Bushland, Peron,/Shoalwater Bay
(includes a ‘C’ Class Crown Reserve, and is part of Rockingham Lakes
Regional Park).
Garden Island is also listed as Bush Forever Site No. 63. It is also subject to
additional protection under the Commonwealth Environment Protection and
Biodiversity Act, is listed on the Register of the National Estate, and is a location for
JAMBA/CAMBA species of migratory birds.
3.3
PRESSURES ON COCKBURN SOUND DUE TO LAND USE
3.3.1
Contaminants from different land uses
Urban areas
In urban areas, gardening practices can contribute nutrients, metals and pesticides to
groundwater, while a range of contaminants is present in urban stormwater runoff.
Surface runoff from a large proportion of the Rockingham, Shoalwater, Safety Bay
area is collected by the Lake Richmond drain, which discharges into Mangles Bay.
This is the largest stormwater drain discharging into the Sound.
Urban areas also require sewage collection (or septic tanks) and rubbish collection,
which in turn means increased capacity at rubbish tips and wastewater treatment
plants is needed to process these wastes. Inappropriate storage and/or disposal of
waste has the potential to contaminate land, groundwater and surface waters. For
example, the old sludge drying beds of the Woodman Point wastewater treatment
plant were one of the two main contributors to nutrient rich groundwater entering the
Jervoise Bay Northern Harbour.
At the naval facility on Garden Island, there is wastewater treatment at a sewage
farm close to the west coast of Garden Island, and effluent is disposed to surface
68
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
water/groundwater. The eastward movement of groundwater from one side of the
island to the other in a matter of months (Wykes et al., 1999) has implications for
sewage effluent currently discharged, and for any future contaminant plumes. Some
stormwater runoff also goes directly into Careening Bay. There is also fuel storage
on the island.
Industry
Groundwater under industrial sites and tailing ponds can become contaminated with
a range of nutrients and chemicals, depending on the industry in question.
Contamination usually happens due to inappropriate storage of chemicals or
inadequate maintenance of drainage/storage areas. Sometimes there are accidental
spills on-site or in transit (road and rail).
Discharge of contaminated surface water from industries to the Sound is less
common. Surface water at many of the industrial facilities is managed internally via
sumps and soak wells. However, the old BHP concrete conduit has been observed to
collect surface water from unused BHP land and drain into the Sound. There is also
a stormwater drainage channel from the BHP sites that exits to Cockburn Sound
immediately north of the BHP No. 1 jetty.
Agriculture
Agricultural land use can contaminate groundwater with nutrients and metals (mainly
cadmium) from fertilisers and wash down areas, pesticides and herbicides, and fuel
from fuel storage areas. Losses of nutrients can be considerable due to the porous
nature of local soils, and the amounts of nutrients and water needed to grow
commercially viable crops.
Conservation
Conservation uses are not considered to result in any contamination of surface or
groundwater that might impact on Cockburn Sound.
3.3.2
Contamination of groundwater
Contaminant loads to Cockburn Sound that occur via groundwater from the eastern
shore have been estimated based on data provided by industry located within the
catchment. This work updates that of Hine (1998, unpublished) and utilises the same
methodology as Appleyard (1994) in estimating groundwater fluxes to the Sound.
This study focussed on the industrial strip that fringes Cockburn Sound and has not
attempted to identify every source of groundwater impact throughout the catchment.
Generic data for regional impacts on groundwater quality by various land uses was
incorporated where appropriate. Groundwater monitoring data from 16 sites around
the Sound (given in Appendix B) were reviewed to update contaminant discharges to
the Sound. Most of the monitoring is for DEP or Water and Rivers Commission
(WRC) license conditions, although the scope of groundwater monitoring and
management programs at several facilities is well beyond licence requirements. In
addition to these major industrial sites there are a large number of smaller industrial
and commercial facilities that present potential impacts to the superficial aquifer and,
in theory, the Sound. No attempt was made to quantify these impacts as the data are
scarce and the magnitude of the potential impacts is very small compared to those of
the larger facilities.
The available data were quite variable in quality, and data for all analytes of interest
were not available for all sites. Nitrogen data were available for all the facilities
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
69
included in the survey and thus provide the most reliable indicator of contaminant
loading trends. Estimates of total nitrogen inputs to Cockburn Sound from
groundwater discharge are summarised in Table 3.1.
Table 3.1 Estimated loads of nitrogen in groundwater discharged to Cockburn Sound
SOURCE
Wesfarmers CSBP
Alcoa of Australia Refinery
BP Oil Refinery
WMC Resources
Water Corp (Woodman Point
Western Power Corp
Nufarm Ltd
Nufarm Coogee
Tiwest Joint Venture
Coogee Chemicals
Western Bioproducts
CBH
Millenium Chemicals
Spearwood Agricultural Area
Subtotals
Total Groundwater
AQUIFER
Tamala Limestone
(tonnes/year)
53.83
0.00
1.48
4.00
38.78
0.00
0.00
0.00
13.66
0.00
27.01
**
**
45.63
184.39
Safety Bay Sand
(tonnes/year)
20.24
0.00
3.42
4.00
*
0.15
0.00
0.06
0.09
0.00
*
**
**
*
27.96
212.35
* Aquifer absent.
** No data available.
Nitrogen contributions to the Sound from groundwater are declining. Groundwater
recovery at WMC’s Kwinana Nickel Refinery has reduced nitrogen discharges from
approximately 500 tonnes/year to the current estimate of eight tonnes. There has
also been a 14% improvement in ammonium discharges from the Wesfarmers CSBP
site in the four years to 2000. Groundwater recovery adjacent to the Jervoise Bay
Northern Harbour is also currently underway, and is expected to reduce nitrogen
fluxes from the Woodman Point WWTP and the Western Bioproducts facility from
the present 65.8 tonnes/year to 26.3 tonnes/year, a reduction of approximately 60%.
With these reductions by industry, the relative role of rural areas is starting to
become significant.
There is considerable groundwater contamination under industrial sites due to metals
and organic compounds, the most well-publiced site being the area under the old CIK
(Chemical Industries Kwinana) site (now Nufarm), which is contaminated by
phenolic compounds. Risk assessments of this type of contamination have been
carried out by Alcoa and Wesfarmers CSBP, and indications are that the mobility of
such contaminants is limited. Other sites have not been subject to risk assessment.
No quantitative data are available for contaminant loads due to groundwater
discharge from Garden Island, but groundwater investigations and monitoring bores
show no contaminant sources from Defence facilities on the island other than
nutrients from the wastewater treatment plant (Wykes et al., 1999), and this is
currently being investigated (Wykes16, pers. com.).
3.3.3
Contaminant inputs due to surface waters and atmospheric fallout
No information has been tabled on runoff from road reserves and urban catchments,
or from atmospheric deposition. Hine (1998) estimated that nitrogen input to the
Sound from surface runoff was 4.3 tonnes/year, and 20.4 tonnes/year from
atmospheric deposition. There are some data for the Lake Richmond drain that
16
70
Dr Boyd Wykes, Environmental Officer, Defence Estate Organisation WA.
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
indicate stormwater runoff may be underestimated. Discharge from this drain to
Mangles Bay was very variable from year to year between 1978 and 1986, but
averaged 2,270 ML/year (DMH, 1992). Based on average concentrations of
contaminants, the nitrogen loads discharged were 0.25 to 8.3 tonnes/year, and
chromium, copper, lead and zinc loads were 50, 32, 98 and 104 kg/year respectively,
which are of similar magnitude to some to industrial discharges (see Section 5.3.1).
South Jandakot Main Drain also discharges to the Sound, however monitoring data
were not available at the time of this report. The location and extent of the urban
drainage systems is not well documented and the location of discharge points is not
readily available. As industrial discharges to the Sound reduce due to cleaner
production practices and water reuse initiatives, the relative contribution from
sources such as urban catchment runoff will attract more attention.
3.4
ENVIRONMENTAL MANAGEMENT OF LAND USE
3.4.1
Current management responses
For the management of existing contaminated sites, new State legislation is proposed
(as an amendment of Part V of the Environmental Protection Act) that will improve
the identification, assessment and management of contaminated sites. The National
Environmental Protection Council’s (NEPC) National Environmental Protection
(Assessment of Site Contamination) Measure is also available to help industry adopt
sound environmental practice as part of a normal business.
Many of the major contributors to groundwater contamination have already
voluntarily undertaken groundwater remediation programmes (Kwinana Nickel
Refinery, Wesfarmers CSBP). The Water Corporation has decommissioned its old
sludge drying beds at Woodman Point. The Department of Commerce and Trade—
as part of its commitments to gain approval for the Southern Harbour development
—is undertaking remediation of groundwater contamination affecting the Jervoise
Bay Northern Harbour. Alcoa has developed a Groundwater Management Plan to
ensure that contaminants from its tailing ponds do not adversely affect Cockburn
Sound. Rural groups are also looking at developing best management practice
guideline for water and fertiliser use.
To prevent accidental spills, the Australian Dangerous Goods Code (Department of
Transport and Communications, 1992) provides detailed, stringent guidelines for the
transport of dangerous good, most of which are potential pollutants.
For new industries, license conditions developed during the EPA’s environmental
assessment process will help minimise environmental impacts. The Water and
Rivers Commission has also released draft guidelines for the location, specification
and operation of underground storage tanks.
As noted in Section 2.5.1, the RAN has an EMP for Garden Island and HMAS
STIRLING. The EMP is currently being revised, and will reflect and complement
initiatives at the regional level. The Department of Defence is also currently
investigating whether there are any localised impacts on seagrass on the east coast of
the island due to groundwater contaminated by nutrients from its sewage farm
(Wykes, pers. com). Garden Island is also protected under the Commonwealth
Environment Protection and Biodiversity Act, and Defence, as a Commonwealth
Department, is bound to manage the Island in accordance with the Act.
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
71
At the local government level, kerbside recycling programs and composting and
biodigestion to reduce organic waste to landfill are being adopted, along with the
general philosophy of ‘waste management hierarchy’ (avoid, reduce, recycle, treat,
dispose). Urban sensitive designs standards for new residential areas (to reduce
stormwater pollution) continue to be implemented.
At the community group level, the Clean up Australia Day removes large amounts of
rubbish.
3.4.2
Gaps in the management responses
Groundwater quality below the larger industrial facilities that fringe Cockburn Sound
is improving. There has been a dramatic decrease in licensed discharges since the
1970s, and further decreases are planned (see Section 5.3.1). Therefore, the relative
contaminant contribution of the more diffuse sources throughout the catchment (e.g.
rural areas) will increase. In most cases direct intervention of these sources will not
be justified, but long-term improvement in groundwater quality throughout the
catchment could be addressed by developing a catchment management plan. Such a
plan would address the various land uses throughout the catchment, identify those
activities that presently have the greatest impacts on groundwater quality, and
develop approaches (e.g. best management practices) to minimise future impacts.
The CSMC is the obvious organisation to prepare a catchment management plan and
coordinate priority-based implementation of catchment management measures with
local councils and major industrial and rural land users/owners. This process is
already underway.
3.4.3
Gaps in information needed for management
An inventory of contaminated sites in the catchment is needed. In addition, the
following studies are recommended to improve understanding of contaminant inputs
to the Sound from groundwater and surface water:
•
•
72
Mapping of storm water catchments around the urbanised areas of Rockingham
and Kwinana and the identification of discharges to the Sound. This should
include the estimation of contributions to groundwater by the urban areas,
location of major infiltration basins and the identification of storm water pipes
that discharge directly to the Sound; and
A systematic approach to quantifying the quality of groundwater discharging to
Cockburn Sound needs to be developed in cooperation with industries fringing
the Sound. Good quality data are currently being collected at many sites, but
the circulation of data is limited and there are likely to be inconsistencies in
data interpretation. Key monitoring sites should be identified at each of the
facilities where groundwater impacts are known to be occurring, with data
being provided to a central data base on a quarterly or six monthly basis. Both
the Safety Bay Sand and the Tamala Limestone aquifers should be monitored.
In most cases, the data requirements would fall within the sites’ current
monitoring programs, but a standard suite of analytes needs to be determined,
including nutrients, metals and hydrocarbons.
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
4.
SOCIAL AND CULTURAL COMPONENT
4.1
OVERVIEW
Cockburn Sound is an extremely popular area for social uses, which include:
•
•
•
Recreational fishing;
Water sports (swimming, boating, yachting, diving, windsurfing, skiing); and
Coastal use (beach activities, use of boat ramps).
Areas of social use are shown in Figure 4.1.
In addition, Cockburn Sound is important for aesthetics and heritage, which are not
so much social uses as values that are held. Each is discussed in turn below.
4.2
SOCIAL AND CULTURAL USES OF COCKBURN SOUND AND ITS
FORESHORE
4.2.1
Existing and potential social uses
Recreational fishing
Data on boat-based recreational catch and fishing effort for Cockburn Sound were
recently collected by a 12-month survey of coastal waters from Augusta to Kalbarri
during 1996/97 (Sumner and Williamson, 1999). The study area was divided into 5
x 5 nautical mile blocks which were used to record catch and fishing effort. Block
58BQ is centred on Cockburn Sound, Block 57BQ includes the southern fringe of
Cockburn Sound plus Shoalwater Bay and part of Warnbro Sound, and Block 59BQ
includes the northern fringe of Cockburn Sound and most of Owen Anchorage.
During the survey, fishers returning from their fishing trip were interviewed at boat
ramps and shown a map of the area and asked to identify the block where they
fished. Block 58BQ was recorded for most fishing within Cockburn Sound. Data
for Cockburn Sound are summarised in Table 4.1, along with data for Owen
Anchorage (Block 59BQ) for comparative purposes.
Table 4.1 Recreational fishing effort in the Cockburn Sound/Owen Anchorage region, 1996/97
FISHERY BLOCK AND
LOCATION
Block 58BQ: centred on Cockburn
Sound
Block 59BQ: centred on Owen
Anchorage
NO. BOAT TRIPS
ANGLING
9,372
NO. BOAT TRIPS
CRABBING*
2,711
TOTAL NO. OF
BOAT TRIPS
12,083
3,305
826
4,131
* mainly crabbing, but some of these boat crews were also angling.
Cockburn Sound is a very popular area for recreational fishers. Within coastal
waters from Augusta to Kalbarri it is second in importance only to the Hillarys area
(Block 62BQ where the number of boats fishing in a 12-month period exceeded
15,000).
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
73
HOLDING PAGES (X2) FOR A3 FIGURE
Figure 4.1 Social and cultural uses of Cockburn Sound
74
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
Second holding page for figure 4.1 (A3)
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
75
The main fish species caught in Cockburn Sound and Owen Anchorage by boatbased recreational fishers are:
Australian herring (13 tonnes), squid
(58,000 animals, weight not known), King George whiting (9 tonnes), whiting other
than King George (7 tonnes), skipjack trevally(5 tonnes), tailor (3 tonnes) and garfish
(2 tonnes) (Sumner pers. com.). By comparison the commercial finfish catch
(excluding baitfish) reported for 1998 (commercial fisheries block 9600) comprised
mainly garfish (22 tonnes), Australian herring (21 tonnes), tailor, skipjack trevally,
King George whiting, yellowtail scad and pink snapper (Penn, 1998). The total
commercial catch of fish (excluding baitfish) was 60 tonnes, compared to the
recreational catch of 39 tonnes for the fish listed above (excluding squid). Thus,
there is considerable overlap between the fish species caught by commercial and
recreational fishers. Furthermore, the fish catch by boat-based recreational fishers is
of similar size to that of commercial fishers. An earlier study (DCE, 1979) estimated
the boat-based recreational fish catch in 1978 as 210 tonnes. However, the two
studies are not directly comparable due to the different methods used. Among other
differences, the 1978 study included fish and crabs caught outside the Sound and
landed at a boat ramp inside the Sound. The 1996/97 survey only included fish
caught within Cockburn Sound.
Cockburn Sound is also particularly popular with recreational crabbers, who caught
18.8 tonnes in 1996/97. The boat-based recreational catch was 5.4% of the
commercial catch for the same period (347 tonnes; Penn, 1999). The boat-based
recreational catch in 1978 was estimated as 120 tonnes compared to a commercial
catch 26.7 tonnes for the same period (DCE, 1979). The comparative sizes of the
recreational and commercial catches appear to have changed since the 1978.
However, the results are not directly comparable for the reasons given above,
although the trend of a declining recreational catch and expanding commercial catch
is probably realistic.
Recreational boat-based fishing effort is fairly widespread throughout the Sound,
although fishing for pink snapper tends to occur near the channel markers south of
Parmelia Bank, including Woodman Channel, Three Fathom Bank and the main FPA
entrance channel. Recreational crabbers tend to fish in shallower waters than their
commercial counterparts. Net fishing is permitted in the Sound, but there is a
Department of Defence ban on recreational netting all year round within naval waters
around Garden Island (see Figure 4.1).
Based on predicted population increases (DOT, 1999), recreational fishing pressure
will increase by about 30% in the next 10 years, and by more than 50% in the next 20
years.
Water sports
Swimming appears to be the most popular water sport in Cockburn Sound, based on
a 1978 survey of beach use carried out during the 1976–79 Cockburn Sound
Environmental Study (Feilman & Associates, 1978), and again in a 1994 survey
(Dielesen, 1994). Kwinana, Wells Park, Rockingham and Palm Beaches and
Woodman Point are popular for swimming, and Challenger Beach, Kwinana Beach
and Woodman Point are popular for shore-based fishing. Sailing (yachting and
windsurfing) is popular in Mangles Bay. The area immediately offshore from
Churchill Park, Rockingham, contains a number of small wrecks (boats and an
aeroplane), and is an regionally important SCUBA diving site as well as being used
extensively for diver training by dive clubs in the Perth metropolitan region (mainly
the southern suburbs).
76
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
About two-thirds of Garden Island is open to the public in daylight hours, and is also
popular for picnics, swimming, diving (snorkel and SCUBA), fishing, sailing
(yachting and windsurfing) and surfing. There is a Department of Defence ban on
carrying and use of spear-guns and gidgees on Garden Island and within Naval
Waters around Garden Island. The Department of Defence also bans the landing of
pets on the island from boats, and no open fires are permitted at any time of the year
(free gas barbecues are provided at two public picnic areas maintained jointly by
CALM and Defence). For safety and security reasons, access to the south-eastern
and northern sectors is restricted, and private boats are advised to avoid waters
adjacent to naval facilities. Access to Garden Island is only by private boat, and
visitors must leave before nightfall.
There is also an Industrial Exclusion Zone between Kwinana and Challenger
Beaches (Figure 4.1). Many of the industries in this area operate under State
Agreement Acts that extend to the water mark, and so the land is effectively private
property. Strictly speaking, use of the beaches in this area requires the permission of
the industries occupying the adjacent land, but there is regular informal17 use of the
Barter Road Beach (north of the BHP No.1 Jetty) mainly for horse swimming.
Water skiing and ‘free style’ driving of personal water craft (i.e. jet ski) are restricted
to areas in Mangles Bay/Palm Beach. There is also a Department of Defence ban on
personal water craft all year round within naval waters around Garden Island.
Outside these areas, personal water craft are permitted but for the purposes of
boating regulations are considered as power boats, and must be driven accordingly.
There are no recent surveys of beach use in Cockburn Sound, but a snapshot survey
of Owen Anchorage in 1998 by Annandale (1999) included Woodman Point, and
found a similar pattern of use to the 1978 and 1994 surveys mentioned above
(Figure 4.2).
Annandale (1999) also investigated the issue of potential conflict between users, and
found that in most cases potential conflict was in the summer months when there
were more people using the study area. Swimmers were affected by the greatest
range of other users, with people using boats and/or jet skis cited most by other users
as affecting, or interfering with their recreational use of the area. Fishers were the
next most likely to affect other users of the area. Users in conflict with other users
were often engaged in the same activity, e.g. pleasure boats versus other pleasure
boats, and fishers versus other fishers.
Coastal Use
Coastal use includes activities such as boat launching, picnics, visits associated with
swimming, exercising, relaxation and exercising dogs. Horse exercising between the
Kwinana Grain Jetty and the Kwinana Wreck, and between the BHP No. 1 Jetty and
Western Power’s cooling water outlets (Barter Road Beach). At the Kwinana site
horse exercising is restricted to the hours of 4:00 am to 8:00 am, to avoid conflict
with swimmers and beach users. There are no time restrictions for horse exercising
at Barter Road Beach.
17
There has been no formalisation of ‘no go’ areas along the beach between BHP No.1 Jetty and
Western Power’s cooling water outfall by the Kwinana Town Council.
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
77
Bathers
200
Boats
Cars in Car Park
Fishers
Number of users
150
Picnickers
SCUBA Divers
100
50
0
Woodman
Point
Coogee Beach Northern End
of Coogee
Beach
Robbs Jetty
South Beach
(Success
Harbour to
Catherine
Point)
Fremantle
Marinas
Figure 4.2 Peak recreational use in Owen Anchorage during snap-shot survey
Note: From Annandale (1999), reproduced courtesy of Cockburn.
Cockburn Sound is particularly popular for family/small boat use due to its sheltered
nature. An indication of the intensity of recreational boat use can be obtained from a
1999 Department of Transport survey of public boat ramp. Estimated boat use at all
the public ramps in from Owen Anchorage to Warnbro Sound is shown in Table 4.2,
along with the estimated level of use in 2011 and 2021 based on predicted population
growth and assuming a similar level of boat ownership. The estimated 44,270 boats
launched in Cockburn Sound in Table 4.2 is considerably larger than the estimated of
angling/crabbing boat trips in Table 4.1 (12,083 boat trips), presumably as the former
includes all craft (power boats, yachts, windsurfers, personal water craft) and—
unlike Table 4.1—incorporates statistics for boats that go outside Cockburn Sound
(especially prevalent at the Cape Peron launching ramp).
The busiest times are September to April, especially January/February. The numbers
in Table 4.2 may also underestimate peak use. For example, at peak times at the
Cockburn Power Boat Association, about 1500 boats/day use the public ramp and
500 boat s/day at CPBA use the private RAMP (John Smedley18, pers. com.).
Coastal access to the coast between the CBH jetty and Woodman Point is becoming
increasingly restricted due to industrial development. Over this approximately
14 km stretch of coastline the only recreational access point that is formally
recognised is several hundred metres along Challenger Beach, part of which has
recently been covered by rock fill used in road/shoreline stabilisation works
undertaken by the Kwinana Town Council. As noted earlier, there is regular,
informal use of the Barter Road Beach, although this will diminish if current
development proposals are approved (the James Point Pty Ltd private port and James
Point Pty Ltd livestock holding facility). Community concerns have been expressed
that more and more people are wanting beach access, while less and less beach is
becoming available. Judging by the data in Table 4.2, the lack of access to this area
of coastline will also lead to increased congestion in other areas: there is the
18
78
John Smedley, Cockburn Power Boat Association
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
potential for intense recreational pressure at the Woodman Point and the
Rockingham foreshore. Existing facilities, particularly the boat ramps, also need
upgrading. Recreational plans that have been suggested to alleviate this pressure
include the Mangles Bay marina, and the Wanliss Street jetty development.
Table 4.2 Estimated boat use at public boat ramps
BOAT RAMP
Owen Anchorage
No ramps
SUBTOTAL
Cockburn Sound
Woodman Point
Challenger Beach, Naval Base
Kwinana Beach (Wells Park),
Kwinana
Palm Beach, Rockingham
Cape Peron, Rockingham
SUBTOTAL
Warnbro Sound
Carlisle St, Safety Bay
Bent St, Safety Bay
Donald Drive, Safety Bay
SUBTOTAL
TOTAL of 8 ramps
ESTIMATED NUMBER OF BOATS USED PER YEAR
(POWER BOATS AND YACHTS)
1999
2011
2021
0
0
0
0
0
0
16,520
1,980
3,300
21,375
2,601
6,406
24,673
3,030
8,622
9,250
13,220
44,270
12,600
20,298
63,280
15,162
25,964
77,451
1,980
6,610
2,640
11,230
55,500
3,004
9,872
3,981
16,857
80,137
3,899
12,895
5,176
21,970
99,421
Note: does not include the private boat ramps of Success Harbour or the Cockburn Sound Powerboat Association.
4.2.2
Aesthetics/seascapes
The Café strip and public walkways at Palm Beach are very popular with locals and
tourists, especially in January/February. Enjoyment of passive recreation in these
areas (e.g. sitting in a Café and admiring the view) depends greatly on the scenic
value of the coastal features, the clarity of the water and ambience of the area.
Aesthetic enjoyment of the rest of Cockburn Sound, whether boat or shore based,
depends on a variety of values, including the scenic value of the seascape, good
water quality, ‘closeness to nature’, ease of access, the diversity of marine life in
protected/sheltered waters and availability of clean seafood to catch/collect.
4.2.3
Heritage
Maritime heritage
Cockburn Sound has a long association with early settlement in Western Australia.
Captain James Stirling established the first free settlement in Australia at Cliff Head
on Garden Island in 1829, although the settlement moved to the mainland some
months later.
The exposed conditions in Gage Roads led increasing use of sheltered anchorage in
Cockburn Sound. Careening Bay was a popular ship repair and cargo unloading area
in the 1800s. However, Cockburn Sound was eventually marginalised after 1900 by
the construction of Fremantle port.
There are four historic wreck sites in Cockburn Sound: the Day Dawn (1890) and
Dato (1893) in Careening Bay, and the Contest (1874), and Amur (1887) in Mangles
Bay (Kenderdine, 1995). The Day Dawn and Dato also have national heritage listing
in the Register of the National Estate.
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
79
Indigenous heritage
According to the National Native Title Tribunal, Cockburn Sound is located within a
region covered by two registered Native Title claims: WC99/6—Combined
Metropolitan Working Group, and WC98/58—Gnaarla Karla Booja. The area is,
however, subject to another claim, WC95/86—Ballaruk, which has failed the
registration test and has been referred to the Federal Court. The current status of
these claims is uncertain and this may have implications under recent amendments to
the Native Title Act (effective from 30 September 1998) which are difficult to define
at this stage. Despite this, the Combined Metropolitan Working Group and Gnaarla
Karla Booja claims are still valid under the old Native Title Act.
There are many archaeological and ethnographic sites close to water sources in the
Perth metropolitan area, but very little archaeological evidence for use of the coastal
fringe. It is known that large groups of Aboriginal people congregated on the coast
and estuaries during summer and autumn, when fish and other aquatic resources were
abundant. The lack of archaeological evidence for occupation and use of the
Cockburn Sound coast may be partly due to the intensive development that has taken
place. Also, much of the Cockburn Sound catchment area has never been
systematically surveyed for Aboriginal sites. As Aboriginal burial sites are
commonly found in coastal dunes all along the West Australian coast, it is possible
that the coastal dues of Cockburn Sound may contain buried skeletal material, or
subsurface archaeological material.
The State Register of Aboriginal Sites records Site S02169, designated as the ‘Indian
Ocean’, which corresponds to the area of water between the mainland and Rottnest,
Carnac and Garden Islands and Cockburn Sound. The site concerns Aboriginal
mythology about the creation of the islands, especially Rottnest, during the sea level
rise that took place about 10,000 years ago (see Section 2.1). There are two versions
of the myth on the site file, but access to this information requires the permission of
the relevant Aboriginal groups.
4.3
PRESSURES ON COCKBURN SOUND DUE TO SOCIAL AND CULTURAL
USES
4.3.1
Existing and potential uses
Recreational fishing can cause environmental pressure due to overfishing; damage to
the seabed from fishing gear, moorings, anchors and landings; discharge of sullage;
oil spills; and litter (lost fishing gear and rubbish).
The types of fishing gear that recreational fishers are allowed to use is restricted, and
damage to the seabed is minimal: most recreational fishing is static.
There is little information on changes in recreational pressure in the Sound.
Recreational use has certainly increased, but fishers are more environmentally aware.
The recreational fishing survey by Sumner and Williamson (1999) found that most
fishers were aware of the fish size limits and bag limits set by Fisheries WA., and
kept to them.
Over-exploitation of some species (integrated with commercial take) may be a
concern with increasing recreational use due to population growth.
80
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
Water sports
As for fishers, non-fishing boat use can cause damage to the seabed from moorings,
anchors and landings; discharge of sullage; oil spills; and litter. Powerboats and
personal water craft can also scour the seabed (including seagrass meadows) with
their propellers. Some noisier forms of boat use (jet skis) may also disturb wildlife.
It was estimated that 1.8 hectares of seagrass was lost due to some 250 boat
moorings in Mangles Bay in 1987 (Lukatelich et al., 1987). A typical mooring can
remove between 3 to 300 square metres of seagrass, depending on the type of
mooring and length of mooring chain. It is noted that non-invasive types of
moorings are now available.
Coastal use
The main environmental pressure due to coastal uses is erosion and loss of foreshore,
and degradation of coastal vegetation. Dog and horse faeces and rubbish can also
affect water quality.
The increased pressure likely on coastal areas—due to both increased population
pressure and decreasing availability of coast—has already been noted.
4.3.2
Aesthetics/seascapes
No pressure is expected on the Sound due to passive recreation.
4.3.3
Heritage
No pressure is expected on the Sound due to either maritime or aboriginal heritage
values.
4.4
ENVIRONMENTAL MANAGEMENT OF SOCIAL AND CULTURAL USES
4.4.1
Current management responses
Marine conservation
The Marine Parks and Reserves Selection Working Group has recommended that the
representativeness of the existing Shoalwater Islands Marine Park would be
enhanced by extending its boundaries to include the area west of Garden and Carnac
Islands out to Five Fathom Bank (CALM, 1994). Bulletin 907 (EPA, 1998) notes
that the Minister for the Environment has requested the Marine Parks and Reserves
Authority to consider including seagrass meadows on eastern Garden Island,
Southern Flats and Mangles Bay in the State-wide System of Marine Conservation
Reserves. No further action has been undertaken on this proposal.
Maritime heritage
Under the Maritime Archaeology Act of 1973, all wrecks or objects dating prior to
1900 are deemed to be `historic shipwrecks or relics’ within the meaning, and subject
to the provisions, of the Act. The requirements of the Act are that the finding of any
object subject to the provisions of the Act be notified to the Western Australian
Maritime Museum and that in the case of any discovery being made of a number of
objects, or a wreck site, all activity be halted until an investigation to assess the
importance of the site has been carried out.
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
81
Indigenous Heritage
Under the Federal Act, Aboriginal Groups who have passed the registration test
retain the right to negotiate over certain developments that impinge on their claimed
native title rights and interests.
Under the State Aboriginal Heritage Act 1972, all Aboriginal people who wish to be
consulted about a proposed development should be included in the surveys and have
their concerns reported. It is also an offence under the Act to disturb any Aboriginal
site (e.g. burial grounds, symbols, objects, paintings, stone structures, carved trees).
Recreational fishing
Recreational fishing is currently managed by means of licences, bag limits, minimum
sizes (e.g. fish length, crab carapace width) and gear controls set by Fisheries WA
and enforced by Fisheries Officers. Recreational crabbers may use hand, nonpiercing wire hook, wire scoop net and drop net. Recently, there have also been
seasonal closures for pink snapper.
A review of recreational fisheries management arrangements for the west coast is
currently under way (Fisheries Management Paper No. 139). Amongst a variety of
management measures, the Paper revisits minimum sizes for various fish species
according to their size when sexually mature, and sets bag limits for most species
according to how ‘prized’ or vulnerable they are. Implementation of this
Management Plan will help ensure sustainable recreational fishing in the waters of
Cockburn Sound.
Fisheries WA also make a variety of educational brochures aimed at promoting
environmentally responsible fishing.
Community groups such as the CPBA and Recfishwest play an active role in
encouraging environmentally responsible fishing. For instances, the CPBA promotes
single species fishing competitions, where only one fish can be weighed in for each
species.
Water sports and coastal uses
Local governments play a key role in the management of water sports and coastal
areas by zoning to separate incompatible uses, ensuring suitable facilities (rubbish
bins, toilets) are available and providing suitable paths and/or barriers to control
erosion. There are a number of coastal, foreshore and/or recreation management
plans in place: City of Cockburn has a Coastal Management Strategy, the Town of
Kwinana has a Coastal Management Plan (currently being updated), and the City of
Rockingham has a Strategic Coastal Management Plan (currently under review). It is
anticipated that these will be revised (if necessary) to ensure consistency with the
CSMC’s EMP (refer also to Section 2.5.1).
Mooring owners in a small mooring area at the north of Garden Island have been
required by the Department of Defence to install non-invasive moorings where
damage was occurring to seagrass. The Department of Defence has also placed a ban
on further placement of moorings.
4.4.2
Gaps in the management responses
A key gap in management responses is a coordinated mechanism for dealing with
pressures on recreational access to Cockburn Sound. The eastern foreshore of
Cockburn Sound from Cape Peron to Woodman Point is 25.4 km long, but only
82
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
about 14.3 km is freely accessible to the public due to the presence of the Jervoise
Bay industrial area (3.8 km) and the main Kwinana Industrial Area from Alcoa to
Wesfarmers CSBP (7.3 km). There are additional small areas of beach within the
Kwinana Industrial area that are accessible to the community and presently used
informally. As noted previously, recreational access to the eastern shoreline of
Cockburn Sound is decreasing due to ongoing industrial development, yet
recreational pressure in the region is increasing.
At present, there is no coordinated management approach examining ways in which
the existing coastline—and associated recreational facilities—can be
developed/upgraded/re-zoned to best meet present and future recreational needs.
Any management and planning undertaken will need to encompass a broader area
than Cockburn Sound, as boat launching facilities in the Sound are also used to
access adjacent waters. Improved recreational access and facilities in areas adjacent
to Cockburn Sound could help reduce recreational pressure on the Sound.
A management matter related to coastal access is the potential effect of coastal
structures on adjacent beaches. The Coastal and Facilities Management Branch of
the Maritime Division of the Department of Transport have a system for providing
preliminary coastal engineering advice on coastal structures. There is, however, no
standard approach presently available for detailed assessment of coastal erosion
measures and adapting them for local conditions in Cockburn Sound. This is in large
part due to the lack of understanding of coastal processes in Cockburn Sound (see
also Section 2.5).
4.4.3
Gaps in information needed for management
Consideration of the social and cultural uses of Cockburn Sound is arguably one of
the most sensitive management issues in Cockburn Sound, yet the social and cultural
pressures on Cockburn Sound have been studied far less than commercial and
industrial pressures and environmental impacts. Clearly, this area needs further
study.
In particular, data is needed on the recreational uses of the Cockburn Sound area. A
comprehensive survey that establishes types of use, areas of use and intensity of use
is urgently needed for environmental management and planning. Ideally, this survey
could also examine the ways in which Cockburn Sound is valued, the key attributes
that underpin how it is valued, and what needs to be improved.
Fishing is one of the most important recreational uses of Cockburn Sound, and more
data is needed on recreational fishing effort, both boat-based and shore-based. It is
noted that a Fisheries WA survey of recreational fishing in Cockburn Sound—boatbased and shore-based (funded by the Fisheries Research Development Council)—
will commence on 1st September 2001 (Neil Sumner, pers. com.). Better estimates of
recreational catches will be needed for integrated catch management of fisheries, and
to plan for increased recreational fishing pressure as the population increases. There
is an encouraging precedent here, with the voluntary resource sharing agreement
recently agreed to by the fishing industry and recreational fishers for crabs in
Cockburn Sound.
To ensure sustainable fishing, more information is needed on the biology of
commercially and recreationally important fish species. Management measures will
be different depending on whether species are resident in the Sound, or have
important links with adjacent waters such as the Swan River. For instance, it is
known that the Sound is an important nursery for snapper, that the Swan River an
important nursery for Sound’s whiting population, and that crabs can complete their
entire life cycle in the Sound (Penn, 1977).
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
83
5.
ECONOMIC COMPONENT
5.1
OVERVIEW
Economic uses of Cockburn Sound include:
•
•
•
•
•
Industry;
Shipping (Commercial and Defence);
Commercial fishing;
Aquaculture; and
Tourism.
Industrial areas, shipping routes, and aquaculture lease areas are shown in Figure 5.1.
Industrial uses that affect the catchment of the Sound were addressed in Section 3, so
only direct impacts on the Sound are considered in this section.
5.2
ECONOMIC USES OF COCKBURN SOUND
5.2.1
Industry
Existing and proposed industrial uses in Cockburn Sound were discussed previously
in Section 3.2.4. As noted in Section 3.2.4, the Kwinana Industrial Area alone
produces goods worth at least $6 billion/year.
5.2.2
Shipping (Commercial and Defence)
Cockburn Sound is the outer harbour of the Port of Fremantle, and the navigation
channel dredged through Parmelia and Success Banks is the only means of access to
Cockburn Sound for larger cargo and naval vessels. Monthly and annual ship
arrivals recorded by the FPA for Cockburn Sound in 2000 are shown in Table 5.1.
Table 5.1 Ship arrivals to Cockburn Sound (FPA outer harbour) in 2000
PERIOD
January 2000
February 2000
March 2000
April 2000
May 2000
June 2000
July 2000
August 2000
September 2000
October 2000
November 2000
December 2000
TOTAL
COMMERCIAL
VESSELS
FISHING
VESSELS
57
71
66
64
57
57
54
53
55
58
49
69
710
0
0
0
0
0
0
0
1
0
0
1
0
2
NONCOMMERCIAL
VESSELS
1
2
1
3
3
0
5
5
0
2
0
1
23
NAVAL
VESSELS*
TOTAL
SHIPPING
6
15
19
21
26
14
18
17
9
21
32
34
232
64
88
86
88
86
71
77
76
64
81
82
104
967
Disclaimer: Whilst every effort has been made to ensure that the above information is accurate, the Fremantle Port Authority
gives no warranty regarding this information and accepts no liability for any inconvenience, or any direct or consequential
loss, arising from reliance upon this information. Readers should undertake their own inquiries to any of the facts referred to
before acting upon them.
* Information from Lieutenant Commander Robert Walker, Port Manager of HMAS Stirling
The total number of vessels visiting the outer harbour in 2000 was about 50% of the
total for the inner and outer harbour (1,945 arrivals).
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
85
HOLDING PAGES (X2) FOR A3 FIGURE
Figure 5.1 Economic uses of Cockburn Sound
86
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
Second holding page for figure 5.1 (A3)
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
87
There are six commercial jetties in Cockburn Sound (one of which is out of service).
Information on the jetty operators and types of cargo handled is given in Table 5.2.
Table 5.2 Operators and cargo handled at commercial jetties in Cockburn Sound
JETTY
Alumina Refinery Jetty
OPERATOR
Alcoa of Australia Ltd
Steelworks Jetty No. 1
Steelworks Jetty No. 2
BHP Transport
BHP Transport
Oil Refinery Jetty
BP Refinery *Kwinana)
Pty Ltd
Fremantle Port
Authority
Bulk Cargo Jetty Berths 1 & 2
Kwinana Grain Jetty
Cooperative Bulk
Handling Ltd
CARGO HANDLED
Loading of alumina loaded (north side of jetty)
Unloading of bulk caustic soda unloaded (south
side of jetty)
Out of service
Loading and unloading of cement clinker,
mineral sands, silica sands, iron ore, copper
concentrates, gypsum slag, sugar, fertiliser,
petroleum coke, LPG, coal, limestone, dolomite,
manganese
Loading and unloading of bulk petroleum
products
Berth 1: Unloading of phosphate, phosphoric
acid, sulphur, ammonium sulphate, potash,
ammonia, urea
Berth 2: Unloading of refined petroleum,
fertilisers, caustic soda, phosphates, ammonium
sulphate, sulphuric acid, LPG
Loading of grain
In the 1999/2000 year, the FPA (Inner Harbour and Outer Harbour) handled
23.4 million tonnes of commodities. Actual tonnages handled by individual jetties in
Cockburn Sound is commercially confident information, but a breakdown of the
commodities handled in the Inner Harbour and Outer Harbour is shown in Figure 5.2.
FPA Imports/Exports 1999/2000
Live sheep 1%
Other 18%
Chemicals 1%
Cement clinker 1%
Petroleum products
35%
Mineral sands 1%
Silica sands 1%
Animal feeds 2%
Caustic soda 2%
Fertilisers 3%
Alumina 11%
Grain 24%
Figure 5.2 Types of commodities handled by the FPA
Based on available data, it will be 20 years before overflow in the Inner Harbour is
breached, and a facility is needed in Cockburn Sound. A variety of alternative
designs (offshore ports, private ports, floating breakwaters) are presently being
considered by the FPA.
In addition to the ship movements recorded by the FPA, Jervoise Bay supports six
major shipbuilding enterprises which use the study area to sea trial their vessels. Sea
trialing is undertaken to ensure that the boats are seaworthy, predominantly in
Cockburn Sound but sometimes further north along the FPA channel and into Owen
Anchorage.
88
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
5.2.3
Commercial fishing
Cockburn Sound has been a site for commercial fishing for many years, but was not
registered as such until 1977. The ‘Cockburn Sound Fisheries Block 9600’ defined
at that time is all waters within a line that extends from South Mole at Fremantle
west to Stragglers Rocks, then through West Success Bank to Carnac Island to
Garden Island, along the eastern shore of Garden Island and to John Point on the
mainland. Although this region includes Owen Anchorage and Cockburn Sound,
most commercial fishing occurs within Cockburn Sound.
There are four commercial fisheries that operate within Fisheries Block 9600, and a
further two commercial fisheries that operate partly within Cockburn Sound. Details
of these six fisheries are summarised in Table 5.3, and are largely based on data from
the 1999/2000 State of the Fisheries Report (Penn, 2000).
Table 5.3 Details of commercial fisheries operating in Cockburn Sound Fisheries Block 9600
FISHERY AND BOUNDARIES
TARGET SPECIES
Cockburn Sound (Crab) Managed
Fishery:
Cockburn Sound Fisheries Block
9600#1
Cockburn Sound (Fish Net)
Managed Fishery:
Cockburn Sound Fisheries Block
9600#2
Cockburn Sound (Line and Pot)
Managed Fishery:
Cockburn Sound Fisheries Block
9600
Cockburn Sound (Mussel) Managed
Fishery:
Cockburn Sound Fisheries Block
9600
The West Coast Beach Bait (Fish
Net) Managed Fishery:
Moore River to Tims Thicket#3
(south of Mandurah)
West Coast (Purse Seine) Managed
Fisheries:
Lancelin to Cape Bouvard,
excluding Marmion Marine Park
blue manna (blue
swimmer) crab
garfish and Australian
herring (lesser amounts
of shark, whiting and
mullet)
whiting, pink snapper,
Australian herring
shark, garfish, squid,
octopus,
Mussels. Wild fishery
now very small, and
licences transferred to
aquaculture licences
Whitebait.
Pilchards, some scaly
mackerel.
NO. OF
LICENCES
16
1999/2000
CATCH
323 tonnes
1999/2000
VALUE*
~$1,000,000
96.5 tonnes
~$240,000
683 tonnes
(state-wide)
~$1,800,000
(state-wide)
107 tonnes
(total
fishery)
~$200,00
1,103
tonnes
(total
fishery)
~$700,000
4
32
(not all
currently
utilised)
14 statewide, 3 in
Cockburn
Sound
13
14
* To fishers.
#1 Excluding naval waters between Colpoy Point and Collie Head (at south end of Garden Island.
#2 Excluding an 800 m wide strip along 800 m length of Kwinana Beach, and an 800 m wide strip from Flinders Lane to John
Point(the tip of Cape Peron), and navy waters between Colpoy Point and Collie Head.
#3 Excluding an 800 m wide strip along 800 m length of Kwinana Beach, and an 800 m wide strip from Flinders Lane to John
Point.
The blue manna crab fishery is the most valuable in dollar terms, and Cockburn
Sound has long been a productive area for this species. Due to increasing levels of
competition between commercial and recreational fishers, a voluntary resource
sharing agreement was recently agreed to by the fishing industry, Recfishwest, and
Fisheries WA (Fisheries WA, 2000). The agreement will reduce the number of pots
used by professional fishers from 1,600 to 800 over three years, or will achieve a
share of the catch of five-eighths commercial and three-eighths recreational.
Finfish catches obtained by the Cockburn Sound (Fish Net) Managed Fishery have
been increasing since the 1970s, causing some concern. Conversely, the Cockburn
Sound (Line and Pot) Managed Fishery’s catches of King George whiting, squid and
octopus have all declined in recent years. Reasons for the declines are not fully
understood, but are thought to include environmental factors, fishing pressure and/or
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
89
market considerations. Finfish catches from these two fisheries have a relatively
small dollar value, but proximity makes the catch an important contribution to the
Perth metropolitan market for fresh table fish.
Harvesting of wild mussels (Mytilus edulis) began in Cockburn Sound in the early
1980s, but catches have since declined and have been very low or nonexistent in
recent years.
5.2.4
Aquaculture
Mussel aquaculture in Western Australia began in Cockburn Sound in 1988 to
overcome the declining catches of the wild capture fishery and to provide a more
consistent source of product. Mussel aquaculture is undertaken in Cockburn Sound,
Warnbro Sound and Albany, and for reasons of commercial confidentiality the
harvests for the Cockburn Sound area cannot be released. However, a significant
proportion of the 680 tonne/year harvest comes from Cockburn Sound (Western
Fisheries, 2001), and so the dollar value this industry is of the same order as the crab
fishery.
There are three lease areas in Cockburn Sound: north Garden Island, Kwinana Grain
jetty, and recently (1999) Southern Flats. The Kwinana Grain jetty used to be the
main site, but the long-term tenure of this area was uncertain, which led to the move
to Southern Flats. The first harvest from the Southern Flats area has returned better
growth rates than expected (Western Fisheries, 2001). The north Garden Island has
only a small area (approx. 20 ha) in use (Glen Dibben19, pers. com).
The industry requires relatively deep water (>10 m), good circulation, excellent
water quality (i.e. it requires low levels of faecal bacteria, contaminants, and toxic
species of phytoplankton), and slightly nutrient-enriched conditions (so that there is
sufficient phytoplankton for the mussels to feed on). To achieve reasonable growth
rates for mussels, chlorophyll levels need to be consistently above 1 µg/L, although
for best results the mean annual concentration should exceed 2 µg/L (Saxby, cited
Pearce et al., 2000).
Navigation is a major issue constraining further aquaculture development in
Cockburn Sound, although small recreational boats are able to move in among the
aquaculture lines and fish if they want to.
5.2.5
Tourism
Most boat tourist operators pass through Cockburn Sound to the more scenic islands
and reefs of the Shoalwater Islands Marine Park.
A survey of 17 tourism operators (about 60–80% of tour operators using the
Cockburn Sound/Owen Anchorage area) indicated that tourist activities included
marine charters (involved in diving, deep-sea fishing, sailing, seal and dolphin
watching and sight seeing), divers, dolphin tours, and a caravan park and recreation
camp at Woodman Point (Annandale, 1999). Most tourist activities were run
predominantly in the summer months from September/October to March/April.
The operators ferry a combined total of almost 18,000 people into, or through, the
area each year, grossing approximately $1.4 million. The predominant activities of
tourists are diving, snorkelling, swimming, fishing, squidding, and seal and dolphin
watching comprising most of the tourist activities in the region.
19
90
Glen Dibben, WA Fishing Industry Council (Inc.)
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
5.3
PRESSURES ON COCKBURN SOUND DUE TO ECONOMIC USES
5.3.1
Industry
The main direct effects of heavy industry in the Kwinana Industrial Area on
Cockburn Sound are due to discharge of industrial wastewater and—to a far lesser
extent—spills during ship loading/unloading. The link between nutrient-rich
wastewater discharge, seagrass loss and declining water quality in the late
1960s/early 1970s was described earlier in Sections 1.2 and 2.3.
The environmental pressures due to the shipbuilding and maintenance industries in
Jervoise Bay include reclamation of foreshore, dredging, altered flushing times,
physical loss of habitat (shore, seagrass, shallows), and TBT inputs.
Details on amounts of contaminants in licensed industrial discharges to the Sound
from heavy industry are given in Table 5.4.
Table 5.4 Licensed industrial discharges to Cockburn Sound
CONTAMINANT
AMOUNT DISCHARGED (kg/year)
Wesfarmers
Western
Tiwest Joint Millenium
CSBP
Power
Venture
Chemicals
Kwinana
Power
Station*
440 ML/day 17.76 ML/day Up to 1,600 4.95 ML/day 14 ML/day
ML/day
1,659
3,000
1,200
BP
Refinery
Flow volume
Ammoniumnitrogen
Nitrate-nitrogen
Total nitrogen
Total phosphorus
Total suspended
solids
Total dissolved
solids
Fluoride
Sulphide
Aluminium
Arsenic
Cadmium
Chromium
Copper
Lead
Mercury
Nickel
Vanadium
Titanium
Zinc
Oil
Phenol
7,414
12,039
2,734
53,660
28,571
3,837
6,000
9,000
200
500
2,747
270
52,000
94
13,414
54,710
6,771
105,754
101,469
101,469
191
7
16
12
2,400
20
16
360
0.3
200
397
100
1,800
5,859
1,200
6,180
69
13
-
3,900
50
27
20
1
20
0
2
10
0
TOTAL
300
300
80
6,180
50
2,603
34
36
1
600
16.3
2
79
313
300
1,077
4,547
270
* Western Power discharge values are derived from net inputs of a variety of chemicals and products used at the facility, and
not actual monitoring of the cooling water discharge.
New developments in the FRIARS area will also be expected to comply with best
environmental practice standards.
5.3.2
Shipping
The main pressures on Cockburn Sound due to commercial and RAN shipping are:
•
Construction of the Causeway;
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
91
•
•
•
Dredging and dredge spoil disposal;
TBT contamination; and
Introduction of foreign marine species from ballast water and ships hulls.
It is noted that the high levels of TBT presently in Cockburn Sound sediment appear
to be more related to shipping maintenance areas than to commercial and naval
shipping movements (see Sections 2.3.4 and 2.4.4). The CRIMP study of introduced
marine pests discussed in Section 2.4.6 also indicated that the foreign marine species
already introduced to FPA waters do not appear to be out-competing local biota at
present, but the introduction of new foreign marine species remains a concern.
A lesser pressure from shipping is spilling of cargo during loading/unloading. There
is also the potential for oil spills during bunkering, although this is minimal as
bunkering is carefully managed by both the FPA20 and the RAN. Improved loading
practices have also greatly reduced inputs from spillages at the FPA’s Bulk Cargo
Jetty during loading/unloading. The FPA has adopted a ‘no spillage’ policy at the
Bulk Cargo Jetty in the past few years, involving new drainage and bunding systems,
deflector plates and unloading equipment. The DEP’s present estimate of nitrogen
inputs from spills during loading/unloading is 5.6 tonnes/year, compared to an
estimated 27.9 tonnes/year in the early 1990s.
5.3.3
Commercial fishing
There is little environmental pressure due to commercial crabbing. The main method
used for crabs has switched in recent years from gillnets to pots, the latter causing
limited environmental damage due to bycatch and disturbance of the seabed. The
commercial catch is a relatively small proportion of the total crab population, which
is effectively renewed each year (as juveniles mature).
There is also little bycatch in the Cockburn Sound (Line and Pot) Managed Fishery
and Cockburn Sound (Net) Managed Fishery, as nearly all species caught are
marketed in the metropolitan area. The types of fishing gear that these two fisheries
are allowed to use (see Section 5.4) involve little damage to the environment (note:
trawling has been banned in Cockburn Sound since 1970). However, as noted
previously (Section 4.3), there is the potential for overexploitation of some species
due to combined commercial and recreational catches when recreational pressure
increases. Overfishing of some species may also lead to changes in populations of
non-target species due to imbalance in the food web (e.g. loss of top predator
species).
The West Coast Beach Bait Managed Fishery is based on the use of specifically
designed beach seine nets that are set by small dinghy and hauled by hand. There is
typically very little bycatch, and as all fishing occurs over sandy substrate and
fishing gear is relatively light, the impact on the seabed is minimal. Catches undergo
large fluctuations (due to the variability of natural populations), but have declined in
recent years, suggesting that breeding stocks may be low.
The West Coast Purse Seine Managed Fishery does not impact on the seabed, but
may affect the shoreline due to access by four-wheel drives and dragging boats over
the dunes. In 1995 and 1999 there were serious effects on stock due to Herpes virus,
and as a result a quota of 260 tonnes (5% of the total estimated stock) has been set
for the 2000/01 licensing period.
20
92
Details of bunkering controls and statistics on oil transfer management are available from the FPA
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
5.3.4
Aquaculture
Mussels feed off natural phytoplankton (i.e. no feed is added to the water). Faecal
wastes from the mussels can result in high organic loadings to the seabed, but the
risk is assumed to be low in Cockburn Sound as the mussels are more widely spaced
than elsewhere in the world (due to low phytoplankton levels). Nonetheless, the
potential for organic enrichment is currently being investigated in a joint research
program by the Fisheries Research Development Corp and the Aquaculture
Development Fund (Penn, 2000).
The potential for adverse effects on sensitive benthic habitats due to shading effects
(of the mussel lines) or organic loadings is also considered low as the lease areas are
not on top of seagrass, except at the north Garden Island site (which is little used).
As a positive impact, the mussel lines provide fish habitat. On the negative side,
they are also viewed as an eyesore that lessens the aesthetic value of the Sound.
5.3.5
Tourism
Negative effects of tourism can include disturbance to wildlife. There has also been
an undesirable tendency for people to feed wild dolphins.
5.4
ENVIRONMENTAL MANAGEMENT OF ECONOMIC USES
5.4.1
Current management responses
Industry
Licences for prescribed premises with the potential to cause pollution are issued by
the DEP under the Environmental Protection Act, 1986. Industry are legally obliged
to comply with DEP licence conditions, most of which include stringent monitoring
requirements. Many industries have also developed their own Environmental
Management Systems (EMS) to closely monitor all aspects of their business, and/or
are voluntarily undertaking environmental best practice.
The Woodman Point WWTP is now largely self-sufficient for power (due to methane
gas generated by it’s egg-shaped digesters) and is presently upgrading both storage
and treatment of wastewater. After the upgrade is complete, the risk of emergency
overflow into Cockburn Sound will be even less, and any wastewater discharged
would be of better quality.
In a combined industry and Water Corporation exercise, it is also planned to build a
Kwinana Water Recycling Plant that would process secondary treated wastewater to
a standard suitable for industrial use. This water will be used by industry, and in
return the Water Corporation will accept industrial wastewater into the Sepia
Depression pipeline, and discharge it into less environmentally sensitive waters 4 km
off Cape Peron. There will be less contaminant discharge into Cockburn Sound, and
pressure will be taken off the heavily utilised groundwater resources of the region.
Commercial shipping activities
Shipping activities are controlled by a number of international and commonwealth
regulations.
Mandatory international regulations for the prevention of pollution from ships, are
collectively known as MARPOL 73/78. MARPOL 73/78 contains detailed
regulations covering the various sources of ship generated sources of marine
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
93
pollution, including oil, noxious liquid substances in bulk, by harmful substances in
packaged form, sewage from ships, and garbage from ships. Australia is a full
member of the International Maritime Organisation (IMO) and a signatory to
MARPOL 73/78, although it is noted that Annex IV—which relates to sewage from
ships—is not in force yet (adherence to the principles of Annex IV is informal at
present). The Commonwealth Government’s Australian Maritime Safety Authority
(AMSA) audits compliance and currency of a vessel’s certificates as issued by the
IMO.
The IMO has also recently announced that it will ban application of TBT to ship’s
hulls from January 2003.
At the Commonwealth Government level, from the 1st July 2001 the Australian
Quarantine and Inspection Service (AQIS) will be implementing new mandatory
ballast water requirements for international vessels visiting Australian waters, and for
vessel movements between Australian ports. AQIS will use a risk-based decision
support system that takes into account a vessel’s previous ports of call, to determine
if ballast water discharge can take place and under what conditions (e.g. if ballast
water treatment is needed). The decision support system is based on the findings of
the CRIMP study referred to in Section 2.4.6.
Other relevant Commonwealth guidelines include:
•
•
•
Australian and New Zealand Environment and Conservation Council
(ANZECC) best practice guidelines for the provision of waste reception
facilities at ports, marinas and boat harbours in Australia and New Zealand
(ANZECC, 1996);
ANZECC code of practice for antifoulants (Hyder Consulting, 2000) for the
use of all products designed to keep marine vessels and structures free of
marine organisms; and
The Australian Maritime Safety Authority (AMSA) is the responsible authority
for shipping of dangerous goods. Any cargoes including fuel, stores or other
commodities whether packaged or in bulk, intended for carriage by sea having
properties come within the classes listed in the International Maritime
Dangerous Goods Code (IMDG code). Dangerous goods passing through ports
must be handled in compliance with the Australian Standard AS 3846-1998
(concerning the handling and transport of dangerous cargoes in port areas).
Also, many countries (including Australia) are actively investigating alternative,
more environmentally sensitive antifoulants, particularly silicone-based products that
act via a non-stick surface that inhibits attachment of biota. The combination of
these two activities is expected to result in a considerable reduction in TBT
contamination of Australian coastal areas within the next few years.
The current Commonwealth Government position is to ban TBT use on all vessels
from 1 January 2006. However, the Commonwealth Government has also specified
in its Australia’s Oceans Policy that it will comply with any ban put in place by the
IMO, and so the Commonwealth Government is preparing to meet the IMO’s 2003
deadline.
The Fremantle Port Authority maintains a comprehensive register that outline the
relevant international, national and state legislation affecting all aspects of its
operations. For example, within the National Plan to Combat Pollution of the Sea by
Oil and other Noxious and Hazardous Substances, the FPA have responsibility for
94
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
implementation of the plan within its area of jurisdiction (i.e. Cockburn Sound). In
particular, it is noted that the ANZECC code of practice for antifoulants has been
incorporated into FPA Regulations, and in-water hull cleaning is no longer allowed
to take place at berths. The FPA consider that this will have a significant effect on
TBT levels in sediments at commercial jetties, and that TBT is unlikely to
accumulate much in sediments due to hull leaching alone, and not at rates faster than
TBT breakdown rates in sediments.
Defence shipping
The Naval Waters Act applies to 500 m within Garden Island’s surrounding water.
Defence, as a Commonwealth Authority, is bound by the obligations of international
treaties and Commonwealth legislation, except where expressly exempt from
complying. Naval ships have been granted an immunity from MARPOL, and from
the Commonwealth Protection of the Sea (Prevention of Pollution from Ships) Act
1983 which implements the provisions of MARPOL convention, but the Royal
Australian Navy (RAN) seeks to comply with all relevant provisions except where
emergency conditions or operational imperatives dictate otherwise.
The Commonwealth Explosives Act 1961 and Explosive Regulations 1991 specify
the requirements of Defence in the transport, storage and handling of explosives by
land, sea or air. There are a number of Defence policies and procedures that are
specifically addressed at ensuring the RAN’s compliance with the Explosives Act,
1961 (note: The Australian Dangerous Goods Code provides guidance on transport,
storage and handling of dangerous goods, but not explosives).
The RAN is committed to environmental management, and has a comprehensive
environmental policy manual which sets out the RAN’s environmental obligations
and commitments in all areas of environmental management and impact assessment.
The Department of Defence also has an EMP in place for HMAS Stirling and Garden
Island, and all activities undertaken there. As noted in Section 3.5.1, the EMP is
currently being revised, and will reflect and complement initiatives at the regional
level.
Defence does not have to comply with State legislation, but attempts to do so when it
does not conflict with their operational imperatives (i.e. national security and
national emergencies). Navy commitment to environmental management is for
coexistence with State controlled areas and State legislation.
The Navy has already banned TBT use on ships less than 40 m in length, and is
replacing TBT on larger warships with a copper-based paint, with a self-polishing
capacity.
Commercial Fishing
A restricted entry regime was introduced for Cockburn Sound in 1985, and remained
in place until long-term management plans were adopted in 1995. Cockburn Sound
has been a totally managed fishery since 1995.
Management of major fishing activities is achieved through formal management
plans declared under the Fish Resources Management Act 1994, while other fishing
activities are managed through a combination of controls from: the Fish Resources
Management Regulations 1995; orders under the Act; and conditions attached to
fishing boat and commercial fishing licences. Management is achieved via controls
on access, boat size, catch size, and fishing gear that can be used.
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
95
Commercial access to crabs in Cockburn Sound is managed under the Cockburn
Sound (Crab) Management Plan, which restricts the season from December 1 to 30
September the following year, sets minimum legal crab size (well above the sexual
mature size) and catch size. Due to increasing levels of competition between
commercial and recreational fishers, a voluntary resource sharing agreement was
recently agreed to by the fishing industry, RecFishWest, and Fisheries WA (Fisheries
WA, 2000). The agreement will reduce the number of pots used by professional
fishers from 1,600 to 800 over three years, or will achieve a share of the catch of
five-eighths commercial and three-eighths recreational.
For finfish, octopus and squid, the methods allowed under the Cockburn Sound (Line
and Pot) Managed Fishery and Cockburn Sound (Net) Managed Fishery include
handline, longline, unbaited octopus pots, squid jigging, gill net, beach seine and
haul net (trawling has been banned since 1970). There was a temporary closure for
line fishing between 15th September and 31st October 2000 during snapper spawning
season.
The Cockburn Sound (Mussel) Managed Fishery is managed in accordance with an
agreement between the Minister for Fisheries and the Fremantle Port Authority (to
ensure navigational marking requirements are met).
Management of the West Coast Beach Bait Managed Fishery operates in waters from
Lancelin to Tims Thicket (near Mandurah) is by limited entry licence, and the use of
specifically designed beach seine nets that are set by small dinghy and hauled by
hand. There is typically very little bycatch, and as all fishing occurs over sandy
substrate and fishing gear is relatively light, the impact on the seabed is minimal.
Catches undergo large fluctuations (due the variability of natural populations), but
have declined in recent years, suggesting that breeding stocks may be low.
The West Coast Purse Seine Managed Fishery is managed under the provisions of
the West Coast Purse Seine Management Plan 1989. Management is currently based
on limited entry and controls on gear and boat size, but serious impacts on stock in
1995 and 1999 due to Herpes virus led to the Minister setting a quota of 260 tonnes
(5% of the total estimated stock) for the 2000/01 licencing period. Arrangements are
underway to change management to a quota basis, but this has yet to be legislated.
The extent of impacts on coastal areas due to vehicle and boat access is not known.
Aquaculture
All aspects of aquaculture are carefully controlled under a Shellfish Quality
Assurance Program. Freedom from contamination and meticulous hygiene are
essential for successful marketing of the product.
Tourism
The charter fishing industry came under management by Fisheries WA for fish
catches in July 2000, following a major review of charter fishing and associated
ecotourism.
5.4.2
Gaps in the management responses
No gaps apparent.
96
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
5.4.3
Gaps in information needed for management
As noted in Section 4.4 on recreational fishing, information is needed on the
combined commercial and recreational catches, and on links with adjacent areas such
as the Swan river, to improve management.
There may be a need to offset increased recreational fishing with reduced
commercial fishing. This could be achieved for some fisheries by re-adjustments to
number of licences through voluntary buy-back. This is a response often used in the
management of areas of high recreational pressure, such as estuaries.
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
97
6.
RECOMMENDED RESEARCH AND INVESTIGATION
PROGRAMME
The following suggestions for research and investigation are based on the
information gaps identified in previous sections. Within each section, suggestions
are listed in approximate order of management priority.
6.1
MARINE
•
•
•
•
•
•
•
•
An agreed conceptual model of the effects of nutrient inputs to Cockburn
Sound;
Up-to-date data on sediment characteristics in Cockburn Sound, particularly
the levels of nutrients, organic matter and chlorophyll a (the latter being an
indication of MPB growth);
An agreed method for evaluating cumulative impacts;
Additional data to improve modelling of water movement and coastal
processes in Cockburn Sound. In particular:
Long-term wave data.
Minimum requirements of two wave
measurement sites within Cockburn Sound (one in southern region, one
in northern region) and one offshore (already in operation). This will be
particularly useful in interpreting changes in sediment transport in the
Sound; and
Long-term current meter deployments, also collecting temperature and
salinity data, at the northern and southern entrances to Cockburn Sound.
A standard approach for assessing coastal erosion measures and adapting them
for local conditions;
Maintain and expand current monitoring of nutrient-related water quality in
summer (currently undertaken by the Kwinana Industries Council), seagrass
health every year and seagrass distribution every three years (currently
undertaken by the DEP);
Studies on the local populations of fish, crabs and the connections between
those local populations, the fisheries, and adjacent areas such as the Swan
River; and
The influence of the Causeway on the environmental quality of the Sound, and
the potential environmental benefits of modifying its design.
The first four items are of the highest priority, and it is strongly recommended that
they are discussed in a workshop attended by relevant government and scientific
personnel, to refine and agree on the key data requirements.
6.2
LAND
•
•
•
•
A catchment management programme for Cockburn Sound;
An inventory of contaminated sites;
Mapping of storm water catchments around the urbanised areas of Rockingham
and Kwinana and the identification of discharges to the Sound; and
A systematic approach to quantifying the quality of groundwater discharging to
Cockburn Sound (to be developed in cooperation with industries fringing the
Sound), using a standard suite of analytes.
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
99
6.3
SOCIAL AND CULTURAL
•
•
100
A comprehensive survey that establishes types, areas and intensity of
recreational use; and
Better estimates of recreational catches, both boat-based and shore-based, for
integrated catch management of fisheries, particularly when recreational
fishing pressure rises with population increases.
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
7.
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COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
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8.
ACKNOWLEDGMENTS
This report was prepared by Karen Hillman, Guy Gersbach, Mark Bailey, Helen
Astill (D.A. Lord & Associates Pty Ltd) and John Throssell (PPK Environment &
Infrastructure Pty Ltd). Report preparation and cover design was by Emma Newark
(D.A. Lord & Associates Pty Ltd). The following people also gave freely their time
and expertise, and are acknowledged with much pleasure:
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Professor George Kailis (Chairman, Cockburn Sound Management Council);
Anthony Sutton and Heidi Bucktin (Cockburn Sound Management Council);
Bryan Jenkins, Ray Masini, Philip Hine and Steve Watson (Department of
Environmental Protection);
Steve Wade, Gino Vallenti, Rod Townsend and Lee Woolhouse (Fremantle
Port Authority);
Ross Marshall and David Ryan (Department of Commerce and Trade);
Don Martin (Department of Resources Development);
Petrina Raitt (Department of Transport);
Tony Cappelluti, Eve Bunbury, Rod Lenanton, Neil Sumner, Suzy
Ayvazian, Gabrielle Nowara, Dan Gaughan, Ron Mitchell, Tim Leary, ,
Eva Lai and Mervi Kanga (Fisheries WA);
Amanda Stanithorpe (Ministry for Planning);
Steve Appleyard and Michelle Crean (Water and Rivers Commission);
Mike Pokucinski (Water Corporation);
Mike McCarthy (Maritime Museum);
Fred Wells (WA Museum);
Lieutenant Commander Robert Walker (Port Manager, HMAS Stirling);
Boyd Wykes (Defence Estate Organisation WA);
Kirsty Stratford (City of Cockburn);
Rosalind Murray (Town of Kwinana);
Garry Middle (City of Rockingham);
John Smedley (Cockburn Power Boat Association);
Norm Halse (RecFishWest);
Tarren Reitzema (School of Public Health, Curtin University);
Monique Gagnon (Department of Environmental Biology, Curtin University);
Eric Paling, Jenny Hale and Hugh Finn (Biological and Environmental
Sciences, Murdoch University);
Paul Lavery and Glenn Hyndes (Department of Environmental Management
Edith Cowan University);
Garth Humphreys (Biota Environmental Sciences Pty Ltd);
Stuart Helleren (Dalcon Environmental);
David Hearn (Division of Land and Water CSIRO);
Gavin Jackson (Gavin Jackson Pty Ltd);
Murray Burling (Port and Harbour Consultants);
John Polglaze (URS Australia Pty Ltd);
Martin Taylor (Chamber of Commerce and Industry);
Mike Baker (Kwinana Industries Council);
Rod Lukatelich and Andrew King (BP Refinery (Kwinana) Pty Ltd);
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
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Cameron Schuster and Mark Germain (Wesfarmers CSBP);
Steve Genoni (Alcoa World Alumina);
Grant Robinson (Coogee Chemicals);
Peter Tichelaar (Millennium Performance Chemicals);
Bruce Cadee (Nufarm Coogee);
Chris Lee (Nufarm Ltd);
Cheryl Willets (Tiwest Joint Venture);
Bruce Talbot (WMC Resources); and
Peter Christian (Western Power).
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
9.
GLOSSARY
Aeolian
Algae
Anaerobic
Anthropogenic
Aquatic
Aquifer
Assemblage
Bathymetry
Beneficial uses
Benthic
Bioaccumulation
Biodiversity
Biota
Biomass
CD
Chlorophyll a
Colonisation
Compliance
Contamination
Diffusion
Diurnal
Ecological function
Ecology
Ecosystem
Ecosystem integrity
e-folding time
Environmental
quality criteria
Environmental
quality objectives
Environmental
values
Epiphyte
Eutrophic
Eutrophication
Fauna
Flora
Gyre
Habitat
Heavy metals
Transported by wind.
Non-flowering aquatic plants. The larger plants of this group that occur in marine
environments, are called seaweed and the microscopic plants that float in the water are
called phytoplankton.
Without oxygen.
Resulting from human activity
Growing or living in or near water.
A layer of rock or soil capable of holding or transmitting water.
Recognisable grouping or collection of individuals or organisms.
Measurement of the changing ocean depth to determine the sea floor topography.
The ways a society uses or values an area (synonymous with environmental values).
Associated with the seabed (usually refers to fauna)
The accumulation of contaminants in organisms at levels above that of the ambient
environment.
The variety of all life forms: the different plants, animals and microorganisms, the
genes they contain and the ecosystems they form.
Defined as all plants, animals and microorganisms of a region.
The living weight of a plant or animal population, usually expressed on a unit area
basis.
Chart Datum. The plane or level to which surroundings (or elevations) or tide heights
are referenced. Used to provide a safety factor for navigation and usually a level lower
than mean sea level.
A complex molecule that along with other similar molecules, is able to capture sunlight
and convert it into a form that can be used for photosynthesis. All plants contain
chlorophyll a and the concentration of this molecule in water is commonly used as a
measure of phytoplankton biomass.
Movement of an organism into an area in which it was not previously present.
The degree to which stated project goals or requirements are attained.
Introduction of physical, chemical or biological substance or properties into the
environment by human activities (c.f. pollution).
The transfer of substances from regions of high concentrations to regions of lower
concentrations.
Daily.
Combined characteristics and processes occurring within an area.
Studies of the relations of animals and plants, particularly of animal and plant
communities, to their surroundings.
A community of organisms, interacting with each other plus the environment in which
they live and with which they also interact.
The ability to support and maintain a balanced, integrative, adaptive community of
organisms having a species composition, diversity and functional organisation
comparable to that of natural habitat of the region.
A means of measuring the flushing of a water body with water sourced from outside
the water body. The e-folding time is calculated by measuring the time taken for a
conservative tracer (see above), initially located solely in the water body of interest to
be diluted to 1/e (=0.368) of its original concentration.
The scientific benchmarks upon which a decision may be made concerning the ability
of an environment to maintain certain designated environmental quality objectives.
The long-term goals of an environmental management programme in relation to the
maintenance of the environmental (ecological and cultural) values of natural systems.
The ways a society uses or values an area (synonymous with beneficial uses).
Plant that grows attached to the outside of another plant.
Nutrient enriched (usually associated with deterioration of natural water bodies where
nutrient enrichment occurs through man’s activities).
An increase in the rate of supply of organic matter to an ecosystem caused by
unnaturally high loads of nutrients to that system.
Animals.
Plants.
Rotation, spinning motion. Used to describe large circular movement of water.
The place or environment occupied by individuals of a particular species, population or
community; has physical, chemical and biological attributes conducive to the
maintenance and propagation of those biota.
Such as zinc, copper, chromium which accumulate in sediments and tissues of biota,
and may be passed-up in the food chain. Heavy metals can be toxic at high levels.
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
115
Hydrodynamic
Infauna
Invertebrate
Light attenuation
Macroalgae
Mean Sea Level
Median
Microphytobenthos
Molluscs
Neap tides
Nutrients
Nutrient load
Percentile
Periphyton
Phytoplankton
Pollution
Species composition
Species richness
Spring tides
Stratification
Suspended solids
Terrestrial
Topography
Trophic
Turbidity
116
The movement or mixing of water as a result of forces such as wind stress at the water
surface.
Animals that live within the sediments of the sea floor.
Collective term for all animals which do not have a backbone or spinal column.
Light reduction (usually refers to a decrease in available light, which occurs with
increasing depth of water).
Large algae; seaweed.
The average height of the higher waters over a 19-year period. For shorter observation
periods, corrections are applied to eliminate known variations and reduce the results to
the equivalent of a 19-year value.
A statistical measure equivalent to the middle measurement in an ordered set of data
(there are as many observations larger than the median as there are smaller).
(MPB) Microscopic algae that live on or in sediments.
Soft-bodied animals usually partly or wholly enclosed within a calcium carbonate shell
(eg. shellfish).
Sets of moderate tides, which recur every two weeks and alternate with spring tides.
Elements or compounds essential for organic growth and development such as nitrogen
and phosphorus.
The quantity in tonnes per annum of nutrients released into the marine environment.
A measure that divides a group of ordered data into hundredths by quantities.
Mucous-like layer of microalgae, algal propagules, bacteria, microfauna and
particulate matter commonly found coating seagrass leaves.
Microscopic algae that float in the water column.
Introduction of physical, chemical or biological substance or properties into the
environment to the extent that causes adverse environmental effects.
Number and abundance of different types of species in a habitat.
Number of different types of species in a habitat.
Extreme high and low tides which alternate with neap tides and recur every two weeks.
Layering (vertical or horizontal) in a water property such as salinity or temperature.
Any solid substance present in water in an undissolved state.
Of the land.
Detailed description of a land or sea surface represented for example on a map.
Energy level in a food chain.
Measure of the clarity of a water body.
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
10.
ABBREVIATIONS
AMSA
ANZECC
ARMCANZ
CCI
CD
CSMC
DEP
DCT
DOT
DRD
EMP
EMS
EPA
EPP
EQO
EQC
FPA
IMDGC
IMO
KIC
MARPOL 73/78
MfP
MPB
NH & MRC
NH4
NOx
NWQMS
pH
PCWS
RAN
SMCWS
TBT
TN
TP
TSS
WRC
Australian Maritime Safety Authority
Australian and New Zealand Environment and Conservation Council
Agriculture and Resource Management Council of Australian and New Zealand
Chamber of Commerce and Industry
Chart Datum (datum for hydrographic surveys: approximately 0.76 m below AHD in
Perth coastal waters)
Cockburn Sound Management Council
Department of Environmental Protection
Department of Commerce and Trade
Department of Transport
Department of Resources Development
Environmental Management Programme
Environmental Management System
Environmental Protection Authority
Environmental Protection Policy
Environmental quality objective
Environmental quality criteria
Fremantle Port Authority
International Marine Dangerous Goods Code
International Maritime Organization
Kwinana Industries Council
The International Convention for the Prevention of Pollution from Ships, 1973, as
modified by the Protocol of 1978, or relating thereto.
Ministry for Planning
Microphytobenthos
National Health and Medical Research Council
ammonium nitrogen
nitrate + nitrite-nitrogen
National Water Quality Management Strategy
measure of acidity
Perth Coastal Waters Study
Royal Australian Navy
Southern Metropolitan Coastal Waters Study
tributyltin, active ingredient of many anti-fouling paints
total nitrogen
total phosphorus
total suspended solids
Water and Rivers Commission
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
117
APPENDIX A
ESTIMATION OF NUTRIENT POOLS AND NUTRIENT
TURNOVER IN COCKBURN SOUND
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
119
Appendix A Estimation of nutrient pools and nutrient turnover in Cockburn Sound
In general, the nitrogen in organic matter in sediments is the main ‘pool’ of nitrogen
in an aquatic ecosystem, followed by large plants such as seagrasses and algae, and
finally, the water column. Since the 1950s, Cockburn Sound and Parmelia Bank has
undergone an increase in sediment nitrogen levels in some areas, and a large
decrease in seagrass meadows (from 3,900 hectares in the 1950s to 750 hectares
today) that have affected the size of nitrogen pools. An approximation of these
changes is shown in Table 1.
Table 1 Changes in nitrogen pools in Cockburn Sound
PERIOD
1950'S
1978
PRESENT DAY
NITROGEN POOL (tonnes)
SEDIMENTS
*
8,800
11,000
11,000
SEAGRASS
100
20
20
SEAGRASS
EPIPHYTES
20
20
4
WATER
TOTAL
275
550
275
9195
11590
11299
present in the top 10 cm.
The above calculations are based on the following assumptions:
•
•
•
•
•
Cockburn Sound area of 92,210,000 m2 and volume of 1,610,000,000 m3;
A water content of 40% and bulk density of 1.245 used for dry sediments;
Average sediment nitrogen content in Cockburn Sound today is 1,560 mg/kg
dry weight, and is assumed to be the same in the 1970s;
Average total nitrogen in water in Cockburn Sound today is 170 µg/L (mg/m3);
and
Warnbro Sound values were used to approximate Cockburn Sound in the 1950s
- 1,250 mg/kg sediment nitrogen, and 170 µg/L (mg/m3) nitrogen in water (i.e.
similar to Cockburn Sound today).
Similar approximations can be made for the production of aquatic plants in Cockburn
Sound, and the amount of nitrogen used by those plants (Table 2 and 3).
Table 2 Historical changes in estimated plant carbon production in Cockburn Sound
PERIOD
PRODUCTION (tonnes carbon/year)
SEAGRASS
1950'S
1978
PRESENT DAY
11,700
2,250
2,250
SEAGRASS
EPIPHYTES
3,100
600
600
PHYTOPLANKTON
AND MPB*
13,800
25,300
16,000
TOTAL
28,600
28,150
18,850
Microphytobenthos, i.e. microscopic algae growing on and in sediments.
Table 3 Historical changes in estimated plant nitrogen turnover in Cockburn Sound
PERIOD
NITROGEN TURNOVER (tonnes nitrogen/year)
SEAGRASS
1950'S
1978
PRESENT DAY
470
90
90
SEAGRASS
EPIPHYTES
120
20
20
PHYTOPLANKTON
AND MPB*
2,120
3,840
2,790
TOTAL
2,710
3,950
2,900
Microphytobenthos, i.e. microscopic algae growing on and in sediments.
Note that phyto/MPBs require more N than seagrasses and epiphytes.
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
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The calculations in Tables 2 and 3 involve the following assumptions:
•
•
•
•
In healthy seagrass meadows, seagrass production is ~300 g carbon/m2/year
and epiphyte production ~80 g carbon/m2/year. Corresponding figures for
nitrogen turnover are 12 g N/m2/year and 3 g N/m2/year;
The combined production of phytoplankton and MPBs in the Sound in the
1950s was ~150 g carbon/m2/year, and nitrogen turnover ~23 g N/m2/year;
In 1978, phytoplankton production was enhanced over about half of the Sound
– about treble over a third of the Sound and about double over 17% of the
Sound; and
Presently, phytoplankton production over about one third of the Sound is about
double that of 1950s levels.
The calculations in Tables 2 and 3 are necessarily crude, but do illustrate that the
system switched from one co-dominated by seagrass meadows and
phytoplankton/MPB to one dominated by phytoplankton/MPB. The amount of
nitrogen used by plants also increased greatly, as plants that need more nitrogen
(phytoplankton/MPB) were favoured by nitrogen inputs in the 1970s. Tables 2 and 3
also indicate that total plant production in present day conditions is actually less than
in the 1950s, but phytoplankton/MPB production and nitrogen use is still higher than
in the 1950s.
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COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
APPENDIX B
ESTIMATION OF NUTRIENT AND CONTAMINANT
INPUTS INTO COCKBURN SOUND
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
123
Appendix B Estimation of nutrient and contaminant inputs into Cockburn Sound
Contaminant loads to Cockburn Sound that occur via groundwater and licensed
discharges have been estimated based on data provided by industry located within
the catchment. This work updates that of Hine (1998, unpublished), and uses the
same methodology as Appleyard (1994) to estimate groundwater fluxes to the Sound.
Information on licensed discharges, groundwater discharges, and the methods used to
calculate loads discharged in groundwater are presented below.
Licensed discharges
Licensed discharges into Cockburn Sound
CONTAMINANT
AMOUNT DISCHARGED (kg/year)
Wesfarmers
Kwinana
Tiwest Joint Millenium
CSBP
Power
Venture
Chemicals
Station*
440 ML/day 17.76 ML/day Up to 1,600 4.95 ML/day 14 ML/day
ML/day
1,659
3,000
1,200
BP
Refinery
Flow volume
Ammoniumnitrogen
Nitrate-nitrogen
Total nitrogen
Total phosphorus
Total suspended
solids
Total dissolved
solids
Fluoride
Sulphide
Aluminium
Arsenic
Cadmium
Chromium
Copper
Lead
Mercury
Nickel
Vanadium
Titanium
Zinc
Oil
Phenol
7,414
12,039
2,734
53,660
28,571
3,837
6,000
9,000
200
500
2,747
270
52,000
94
13,414
54,710
6,771
105,754
101,469
101,469
191
7
16
12
2,400
20
16
360
0.3
200
397
100
1,800
5,859
1,200
6,180
69
13
-
3,900
50
27
20
1
20
0
2
10
0
TOTAL
300
300
80
6,180
50
2,603
34
36
1
600
16.3
2
79
313
300
1,077
4,547
270
* Western Power discharge values are derived from net inputs of a variety of chemicals and products used at the facility, and
not actual monitoring of the cooling water discharge.
Groundwater discharges
The Cockburn Sound catchment includes a variety of landuses that may impact upon
groundwater quality. This study has focussed on the industrial strip that fringes
Cockburn Sound and has not attempted to identify every source of groundwater
impact throughout the catchment. Generic data are available for regional impacts on
groundwater by various land uses and this has been incorporated where appropriate.
Groundwater data from 16 sites around the Sound have been reviewed to update
groundwater contaminant discharges to the Sound. Most of the monitoring is
undertaken under DEP or WRC license conditions, although the scope of
groundwater monitoring and management programs at several facilities is well
beyond the licence requirements. Monitoring focuses on the superficial aquifers,
including the Safety Bay Sand and the Tamala Limestone. Groundwater Monitoring
programs at the sites are summarised in the following table below.
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
125
Groundwater Monitoring Summary
Operator
BP
Refinery
(Kwinana)L
Wesfarmers
CSBP Limited
Alcoa
World
Alumina
WMC
Resources
Water
Corporation
Western Power
Corporation
Nufarm Limited
Nufarm Coogee
Facility
Oil Refinery
Agrochemical
Manufacturing
Bauxite
Refining
and
Tailings Storage
Kwinana Nickel
Refinery
Woodman Point
WWTP
Cape
Peron
Discharge
Kwinana Power
Station
Agrochemical
Manufacturing
Chlor-alkali
Manufacture
Pigment
Manufacturing
Groundwater Monitoring Program
Number of Monitoring Bores
Tamala Limestone Safety Bay Sand
Compounds of Concern
Nutrients
Metals
Hydrocarbons
Inorganics
pH/EC
14
38
✔
✔
✔
✔
✔
✔
17
50
✔
✔
✔
✔
✔
✔
✔
✔
29
73
✔
9
na
✔
✔
✔
0
0
✔
✔
✔
0
15
✔
✔
✔
✔
✔
✔
✔
0
4
✔
✔
✔
37
✔
✔
✔
✔
10
✔
✔
✔
✔
4
✔
✔
✔
na
✔
✔
✔
Tiwest
Joint
4
Venture
Wesfarmers
LPG
0
LPG
Coogee
0
Chemicals
Millenium
0
Chemicals
Western
Starch
15
Bioproducts
Manufacturing
✔ Monitoring undertaken, but full details not listed.
126
Licensed
Discharge
✔
✔
Nickel
✔
✔
✔
✔
✔
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
In addition to these major industrial sites in the immediate vicinity of the Sound,
there are a large number of smaller industrial and commercial facilities that present
potential impacts to the superficial aquifer and, in theory, the Sound. In these cases
no attempt has been made to quantify these impacts as the data are scarce and the
magnitude of the potential impacts is very small in comparison to those presented by
the larger facilities.
Methods used to calculate mass of contaminants travelling in groundwater
The dominant groundwater flow direction below the study area is towards the coast
line, thus in the northern section of the study area near Woodman Point, groundwater
flow is westwards. In the southern section of the study area groundwater flow is
north to north-westerly. It is acknowledged that the interaction between groundwater
and the marine environment is complex and significant variations in groundwater
flow direction have been documented in the near coastal zone. However for the
purposes of this study is reasonable to assume that the observed regional water table
conditions are relevant and that groundwater leaving the sites of interest ultimately
discharges into the Sound. Groundwater velocity and through flow were estimated
as follows:
Groundwater velocity was estimated from the Darcian equation:
v=ki/n
Where:
v= groundwater velocity
k = hydraulic conductivity
i= hydraulic gradient
n= effective porosity
Groundwater throughflow in sectors of the coast was estimated from the Darcian
equation:
Q = Tiw
Where:
Q = groundwater throughflow occurring beneath the site (m3/d);
T = transmissivity of the aquifer formation (the product of the permeability (k) and
the saturated thickness (b), in m2/d;
i = hydraulic gradient (dimensionless); and
w = width of aquifer perpendicular to the direction of groundwater flow in metres.
To estimate the mass of contaminants leaving the sites of interest, the coastline was
divided by groundwater flow lines to form zones that could be represented by
monitoring programs from the respective facilities (i.e. industries). The width of
each zone is the same as the width of each facility perpendicular to the direction of
groundwater flow. Groundwater conditions for each zone is therefore characterised
by the monitor bores on each facility. The reliability of the groundwater quality data
for each zone is dependent on the number of monitor bores at each site. At some
facilities such as Wesfarmers CSBP and the BP Refinery, an extensive network of
monitor bores is present and these are monitored on a regular basis. Groundwater
below other smaller facilities may only be characterised by a few bores, and even at
the larger sites, information from the Tamala Limestone is generally limited in
comparison to the overlying Safety Bay Sand.
COCKBURN SOUND MANAGEMENT COUNCIL PRESSURE-STATE-RESPONSE
127