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MIDDLE ARM PENINSULA INDUSTRIAL SUBDIVISION
PRELIMINARY ENVIRONMENTAL REPORT
for
Department of Lands & Housing
Dames & Moore Job No.12087-010-073
January 1990
TECHNICAL
. LIBRARY DARWIN
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MIDDLE ARM PENINSULA INDUSfRIAL SUBDMSION
PRELIMINARY ENVIRONMENTAL REPORT
TABLE OF CONTENTS
1 . 0 . INTRODUCTION
1.1 THE PROPONENT
1.2 BACKGROUND
1 .3 OBJECTIVES
1.4 PRESENT STATUS OF THE PROPOSAL
1.5 LOCATION
1.6· SUMMARY OF KEY ISSUES
2.0 DESCRIPTION OF THE PROPOSAL
2.1 SUBDIVISION PLAN
2.1.1 General
2.2
2.1 .2 Physical Constraints on Development
SERVICES
2.2.1 Roads and Rail
2.2.2
2.2.3
0 2.2.4
2.2.5
Drainage
Gas, Water and Power
Sewage and Garbage Disposal
Telecommunications
2.2.6 Fire Protection
2.3 SAFETY PROVISIONS
2.3.1 Transportation of Hazardous Materials
2.3.2 Buffer Zones
2.4 PROJECT CONSTRUCTION
2.4.1 Timing
2.4.2 Construction Stages
3.0 PROJECT ALTERNATIVES
3.1 LAND USE ALTERNATIVES
3.2 . SUBDIVISION LAYOUT
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5.0
6.0
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PLANNING AND DEVELOPMENT CONSIDERATIONS
4.1 IMPLICATIONS OF RELEVANT LEGISLATION AND POLICIES
4.2 LOCATION OF INDUSTRY
DESCRIPTION OF THE EXISTING ENVIRONMENT
5.1 PHYSICAL ENVIRONMENT
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5.3
5.1.1 Climate
5.1.2 Land Systems
BIOLOGICAL ENVIRONMENT
5.2.1 Terrestrial Flora
5.2.2 Terrestrial Fauna
5.2.3 Marine Environment
SOCIAL AND ECONOMIC ENVIRONMENT
5.3.1 Current and Proposed Land Use
5.3.2 Current and Proposed Services
5.3.3 Significant Sites
ENVIRONMENTAL LIMITATIONS
6.1 WATER IMPACTS AND MANAGEMENT
6.1.1 Surface Waterways
6.1.2 Surface Runoff
6.2
6.3
6.4
6.1.3 Accidents
6.1.4 Groundwater
IMPACTS ON GEOLOGY, SOILS AND LANDFORMS
AIR QUALITY IMPACTS
BIOLOGICAL IMPACTS AND MANAGEMENT
6.5 STORM SURGE AND GREENHOUSE EFFECTS
6.6 VISUAL IMPACTS
6.7 FUTURE DEVELOPMENTS
6.8 SUMMARY OF PREDICTED IMPACTS, LIMITATIONS AND
SAFEGUARDS
SOURCES OF INFORMATION
7 . 1 REFERENCES
7.2
7.3
AUTHORITIES CONSULTED
STUDY TEAM
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APPENDIX A AIR QUALITY AND BIOLOGICAL IMPACTS AND MANAGEMENT
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LIST OF FIGURES
Location of Middle Arm Peninsula
Industrial Subdivision
Conceptual Layout of Proposed
Industrial Subdivision
LIST OF TABLES
Monthly Climatic Data for Darwin
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MIDDLE ARM PENINSULA INDUSfRIAL SUBDMSION
PRELIMINARY ENVIRONMENTAL REPORT
1.0 INTRODUCTION
1.1 THE PROPONENT
The proponent of the proposed Middle Arm Peninsula industrial subdivision
development is the Northern Territory Department of Lands and Housing. The
contact officer for this proposal is Mr Herman Mouthaan, Director, Land
Development Strategies Branch, Department of Lands and Housing, Land
Development Strategies, P 0 Box 40246, Casuarina, NT, 0811.
1.2 BACKGROUND
Middle Arm Peninsula was identified in the Darwin Regional Structure Plan 1984
as an area suitable for "major offensive and hazardous industrial developments
where environmental considerations would preclude such development closer to
Darwin suburbs or Palmerston". Other large scale general industries would
also be suitably located in this area.
At the time the Regional Structure Plan was prepared, there were plans to
develop a major port in association with the Channel Island Power Station.
,_ ~ Although a port is no longer necessary to service the power station, roads and
services constructed for the power station will also be able to service the
proposed industrial subdivision.
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At present, feasibility studies are being carried out for a propos~d Liquefied
Natural Gas facility which may be located on the seaward end of Middle Arm
Peninsula. This facility would require construction of a deep-water port on
Middle Arm Peninsula.
Although the Middle Arm Peninsula was recognised by the Darwin Regional
Structure Plan 1984 as appropriate for industrial development, the land is
currently zoned for Rural Living purposes in accordance with the Darwin Rural
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Area Plan 1983. Rezoning of the land for industrial uses will therefore be
necessary.
1.3 OBJECTIVES
The objective of the Middle Arm Peninsula industrial subdivision is to make
use of a sui table area near Darwin for the establishment of general and
hazardous or offensive industry. The need for suitable land for this form of
land use was identified in the Darwin Regional Structure Plan 1984. The
industries which may establish in the subdivision may· include chemical
r ' manufaCtUring 1 prOCeSSing Of animal prOdUCtS 1 petrOChemical and gaS prOCeSSing
and storage. Maritime and maritime related industries may also be located in
the subdivision. Inoffensive or non-hazardous industries will be r ,
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preferentially located on land nearest to the proposed residential area of
Weddell.
1.4 PRESENT STATUS OF THE PROPOSAL
The proposed subdivision is in the planning phase. As stated earlier in
Section 1.2, the land is zoned rural residential and thus the land will need
to be re-zoned before any headworks for the subdivision are undertaken. Also,
the land is presently under the jurisdiction of the Litchfield Shire Council.
Some of the land also is subject to the Darwin Port Authority Act 1973 and
would need to be excised from the port, similarly to Channel Island.
This Preliminary Environmental Report examines the environmental and planning
issues related to the establishment of the necessary serv:ices for an
industrial subdivision on Middle Arm Peninsula. It should be noted that the
assessment of environmental impacts for specific industrial developments
within the industrial subdivision will be a matter for the proponents of those
developments as development proposals arise.
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1.5 LOCATION
The proposed industrial subdivision on Middle Arm Peninsula is surrounded by
Darwin Harbour with East Arm to the north and Middle Arm to the south. To the
south east of Middle Arm Peninsula lies the proposed location for the new town
of Weddell. Figure shows the location of the proposed industrial
subdivision in relation to Darwin Harbour and existing and future urban areas.
1.6 SUMMARY OF KEY ISSUES
The main environmental issues arising from the proposed industrial subdivision
on Middle Arm Peninsula will ultimately be concern for the hazardous nature
of indust~ies which may operate within the subdivision and the potential for
impact . on the surrounding mangroves and Darwin Harbour.
summarised below:
Key issues are
o Any accidental or deliberate release of ecotoxic chemicals through
an industrial accident, during transport, or due to fire or
extreme climatic events has the potential to harm workers within
the subdivision and to affect the surrounding mangroves and Darwin
Harbour environment. The location of the subdivision necessitates
strict controls on industry, to ensure that off-site impacts are
minimized. Preparation and promotion of an accident response
plan, which not only minimises the hazard to human life but also
to the local environment, should be a priority of the development.
These issues will need to be considered and assessed by each
industry establishing in the subdivision.
0 Middle Arm Peninsula supports a mature and diverse mangrove
community which contributes to the productivity of Darwin Harbour.
A mangrove management plan has been prepared for the Coastal
Management Committee (CMC, unpubl. doc.), which is expected to
recommend the conservation and protective management of
significant areas of mangroves on Middle Arm Peninsula for educa-
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tion research, and to ensure that the quality of Darwin Harbour
environment is maintained.
The mangrove management plan is yet to be endorsed by the NT
Government, however the design concept of the subdivision
acknowledges the goals of the mangrove management plan.
Establishment of an industrial subdivision on Middle Arm Peninsula
will also provide protection of the mangrove areas by restricting
uncontrolled access to the area and reducing other development
pressures.
o Although not considered a health problem, the numbers of biting
insects in the vicinity of the proposed industrial subdivision may
create unpleasant outdoor or un-screened working conditions (see
Section 6.4). The biting insect problem may increase as numbers
of workers within the subdivision increases and public pressure
may force a remedy to the problem at a later stage.
2.0 DESCRIPTION OF THE PROPOSAL
2.1 SUBDIVISION PLAN
Figure 2 shows a plan of the proposed subdivision ..
2.1.1 General
The proposed subdivision is accessed from Palmerston via the Channel Island
access road. General industry will be located to the west of the access
road, closest to the proposed town of Weddell, and offensive and hazardous
industries will be located closer to Channel Island. The area south of the
Channel Island access road is proposed as the new site for the Work Health
Authority's explosives and hazardous materials storage site.
Barge and small boat access to Darwin Harbour at either East Arm (Elizabeth
River) or Middle Arm (Haycock Reach) is proposed for some of the subdivision
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blocks, with a possible dredged canal in the general industrial area (Figure
2) . The dredged canal has the dual purpose of providing harbour access to the
general industrial area and reducing mosquito breeding areas near the proposed
Weddell residential area. Provision for future direct road access to East Arm
Peninsula via a bridge has also been made.
2.1.2 Physical Constraints on Development
The general layout of the proposed industrial subdivision is constrained by
the topography.of the site including extensive mangroves in littoral areas and
dissection of the higher ground by four major creeks with associated
mangroves. Within the study area, there are approximately 2200ha of high
ground (above 4rn AHD) and 2000ha of mangroves.
, , It is proposed that the industrial area will accommodate potential hazardous
or offensive industries, which will be separated from proposed residential
areas such as Weddell by an area of light and general industrial development.
This concept will optimise the use of industrial land and ensure that heavy
industry is separated from residential areas.
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2.2 SERVICES
2.2.1 Roads and Rail
The subdivision layout of access roads and potential railway line spurs is
shown on Figure 2. The alignment of access roads is restricted by the local
terrain and access roads will generally be spur roads from the main Channel
Island access road, with many roads ending in cul-de-sacs.
All access roads will be constructed to NAASRA road design guidelines and
Department of Transport and Works specifications as arterial or local roads.
Local roads will include an 8m wide sealed, single carriageway with 4% cross
fall.
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Railway spur easements are provided which will service most parts of the
industrial subdivision. A railway marshalling yard is planned near the centre
of the site.
The railway spurs will be linked with the proposed Alice Springs to Darwin
standard gauge railway and constructed to a standard consistent with the main
Australian standard gauge rail network. On the relatively flat topography of
the industrial subdivision area, this will involve construction of a 1435mm
nominal gauge track on a 1m high formation with a crest width of 9m (Dames &
Moore 1984a).
2.2.2 Drainage
Preliminary design of the drainage system for the proposed subdivision area
has been initiated by the Department of Transport and Works.
The drainage system will be designed to take into account topographical and
hydrological constraints. It may be necessary to alter the proposed easements
for drainage structures if recommended by the Department of Transport and
Works and its consultant.
The design of the drainage structures will also take into account the need to
contain and collect hazardous materials in the event of accidental spills.
2.2.3 Gas. Power and Water
Industries located in the subdivision which have specific requirements for gas
will be able to take advantage of the close proximity of the gas pipeline to
Channel Island.
Provision of power to the subdivision will require a transformer to reduc~ the
voltage and a distribution network to each allotment. It is expected that
power distribution will be via overhead lines. Easements for power lines
will generally be included adjacent to road reserves.
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Industries will require water of drinking quality for staff use. High quality
water may also be. necessary for industrial and manufacturing purposes. This
water is expected to be supplied from Darwin River Dam which already supplies
water to Channel Island Power Station. The volume of water of this quality
required by a fully operational industrial subdivision is not known at this
stage and will depend on the nature of industries establishing in the
subdivision. The potential requirement of certain industries for seawater to
use for co·oling. purposes is also unknown at this stage. This issue will need
to be considered during the planning and development of individual industries.
Adequate water supplies will also be required for fire-fighting purposes. The
rate of water supply required would depend on the nature of ·individual
industries and requirements in excess of supply could be sourced from storage
tanks.
2.2.4 Sewage and Garbage Disposal
A site for sewage treatment ponds is proposed in a mangrove area in the north
eastern part of the subdivision (Figure 2). These ponds will allow primary
and secondary treatment of sewage with discharge of the treated effluent to
East Arm. Sewers will be installed to collect and transfer sewage from each
allotment to the treatment works. Pumping stations may also be required at
strategic locations.
Larger sewage treatment works are also proposed to be located in the southern
portion of the subdivision to serve the residential areas of Weddell.
In the initial stages of the development, there will be no sewerage system
provided. Sewage disposal will then be the responsibility of each industry.
These industries would probably utilise individual septic systems constructed
and operated to the guidelines of the Department of Health and Community
Services.
demand.
Sewage ponds and sewers would be constructed when required by
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The Power and Water Authority can enter into an agreement with an industry to
accept trade waste into the sewage system from that .establishment. Acceptance
of trade waste is assessed on an individual basis, taking into account the
nature of the waste and the system for treatment of the waste.
Hazardous wastes could be stored or treated in the proposed hazardous
materials site in the southern section of the subdivision. Non-hazardous
wastes would either be collected by a contractor or delivered directly to the
waste disposal site at Palmerston or, later, at Weddell.
2.2.5 Telecommunications
Provision-of telecommunications will be the responsibility of the developer
and the individual allotment owners. Easements for telecommunication services
will be provided within road reserves.
2.2.6 Fire Protection
At present, the NT Bush Fires Council accepts responsibility for fire
protection within the Middle Arm Peninsula area. However, as industries move
into the proposed subdivision, the responsibility for fire protection would
transfer to the NT Fire Services, with the nearest Fire Station being at
Palmers ton.
Bush fire protection at the site could be improved by construqtion of a fire
break between the mangroves to the south of the subdivision and.the turn-off
to the subdivision.
Fire protection at the Work Health Authority's proposed explosives and
hazardous materials site will be achieved by perimeter fire breaks, by minimum
distances between explosives storage areas and by clearing of trees and shrubs
and mowing of grass in the upland areas. Mangroves will not need to be
disturbed for fire protection.
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Fire protection at each of the hazardous industrial sites will need to comply
with the Australian Standards Association conditions for fire safety. These
conditions will depend on the nature of the industries establishing in the
subdivision, however, as a general rule it is anticipated that disturbance
to mangroves will be kept to a minimum.
The Fire Services Unit of the Department of Tr~nsport and Works recommends
that a subdivision layout incorporating cul-de-sacs be avoided for industrial
fire safety reasons. An industrial fire at the entrance to the cul-de-sac may
cut off the only escape route for firemen and workers trapped by a fire. The
environmental problems associated with this option are discussed in Section
3.2.
2.3 SAFETY PROVISIONS
2.3.1 Transportation of Hazardous Materials
Transportation and storage of hazardous materials is strictly controlled by
the Work Health Authority work~ng to the conditions of the Australian
Standards Association (ASA). The ASA classifies dangerous goods into eight
major categories and ensures that incompatible categories [for example
flammable liquids (Class 3) and poison gas (Class 2.3)] are not stored or
~J transported together.
All transportation of hazardous materials will be according to the ASA
regulations. These regulations ensure that the driver has the appropri~te
authorization and licence to convey. Placards showing the nature of goods are
required to be displayed on vehicles transporting dangerous goods and bulk
carriers also display emergency information panels. This enables fast and
correct response by authorities in the event of an accident.
l.~ The possibility for road transport accidents involving dangerous goods will
also be reduced by subdivision road design and layout which will minimise
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intersections between roads and between roads and rail. Cautionary signage,
lighting and traffic lights will be provided as necessary.
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2.3.2 Buffer Zones
The subdivision layout shown on Figure 2 shows two sites with an approximate
BOOm buffer between the centre of the site and neighbouring industrial blocks.
These blocks could be used for, say, manufacture of explosives which require
a large buffer zone.
The storage areas within the proposed hazardous materials site would also have
at least an BOOm buffer between the location of the hazardous materials and
the closest public access areas.
The mangroves surrounding the industrial subdi_vision are also a buffer between
the public and the hazardous industries. The mangroves would restrict access
by water to the subdivision (except in· those areas with barge landings and
canals) and the presence of the subdivision would also restrict public access
by land to the mangroves.
2.4 PROJECT CONSTRUCTION
2.4.1 Timing
At present, timing for construction of the forward works associated with the
subdivision is unknown. Construction will not commence until .the
environmental assessment process is complete and the subdivision approved and
the area is appropriately zoned for hazardous and offensive industries.
2.4.2 Construction Stages
It is anticipated that the subdivision will be developed in stages. The
first stage anticipated for construction is shown on Figure 2 and this will
include lots for both hazardous and general industry. As the first stage of
the subdivision is occupied, additional stages will be developed at locations
to be determined to cater for demand.
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Relocation of the hazardous materials site from its current location at Hidden
Valley to the new location in the southern part of the subdivision would
depend on constraints at their current location. Construction of the sewage
ponds adjacent to this site will depend on the development of the Weddell
residential areas.
Timing for construction of the proposed. d.irect bridge connection between the
industrial subdivision and the Trade Development zone will depend on a number
of factors, including demand.
3.0 PROJECT ALTERNATIVES
3.1 LANQ USE ALTERNATIVES
Alternative land uses for Middle Arm Peninsula could include rural residential
living, outdoor recreation or conservation. Alternative locations for
hazardous and offensive industries and alternative land uses for the Middle
Arm Peninsula area were considered during preparation of the Darwin Regional
Structure Plan 1984. Middle Arm Peninsula was favoured for the location of
hazardous and offensive industries because of the area's potential access to
the harbour and isolation from residential areas .yet relatively close
proximity to commercial centres. Establishment of an alternative land use on
Middle Arm Peninsula would mean that hazardous and offensive industries would
need to establish in less favourable areas.
3.2 SUBDIVISION LAYOUT
The subdivision layout is constrained by four large creeks within the area.
One alternative subdivision layout is to provide road access around the
perimeter of the subdivision area. This layout would create additional
drainage problems at the site but would improve the fire safety provisions of
the subdivision. This layout would also provide additional access for
monitoring of, for example, runoff from industrial sites and biting insects,
but would also provide greater access for the public to the industrial areas,
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possibly with associated security problems, and greater access to mangrove
areas.
Another alternative would be to link the two main areas with limited access
by a bridge across Creek H. This alternative would lead to significant
disturbance of Creek H and involve high cost of construction in mangrove
areas, and is therefore not recommended.
4.0 PLANNING AND DEVELOPMENT CONSIDERATIONS
4.1 IMPLICATIONS OF RELEVANT LEGISLATION AND POLICIES
At presen~, several Government policies exist, or are being developed, which
are relevant to the Middle Arm proposal, and in particular, may affect later
stages of the development. These are the N.T. Coastal Management Policy,
Darwin Harbour Mangrove Management Plan and the National Water Quality
Guidelines.
Amongst other objectives, the Coastal Management Policy requires that planning
priority is given to uses dependant on a coastal location, and that major
developments affecting the coastal zone are subj~ct to environmental
assessment. A major initiative under the Coastal Management Policy has been
the preparation of the Darwin Harbour Mangrove Management Plan, a draf~ of
which has been completed and will be considered for adoption by Government in
the near future.
National Water Quality Guidelines are being prepared by the collaboration of
the environmental agencies of the states and territories. The finalisation
of these guidelines is expected within one or two years, after which the N.T.
may legislate on the implementation of these guidelines via a new act or by
amending existing legislation i.e., Control of Waters Act.
These pieces of legislation and policies will most probably be in effect and
be requireq to be considered during later stage of the development.
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The following acts and policies have possible implications for the
development:
Darwin Port Authority Act
The act gives the Darwin Port Authority control of the area around the Darwin
Harbour including parts of Middle Arm Peninsula. Prior to the development,
probably at the time of rezoning the area, it will be necessary t.o excise the
area of the subdivision from the jurisdiction of the Port Authority. A
similar procedure was carried out during development of the Channel Island
Power Station.
Control of Waters Act- National Water Ouafity Guidelines
This NT Act and the National Guidelines currently being developed will enable
effective control of developments, discharges and other land based inputs into
waterways, including structures likely to obstruct waterways. Compliance
with these procedures will be important for the development of all
infrastruct~re which might alter the current surface hydraulics of the area,
thereby causing changes to the existing runoff characteristics.
Industries likely to be established on Middle Arm Peninsula will involve the
handling of hazardous, flammable and petrochemical products. The design of
the drainage system will need to provide adequate measures to prevent the
discharge of these materials onto public land and into the waterways. This
requirement will have to be extended to the design of the individual
allotments at a later stage. In this regard the relevant legislation includes
the Prevention of Pollution of Waters by Oil Act, and the Water Supply and
Sewerage Act.
When the industries to be established on the individual allotments are being
decided upon, further legislation will have to be complied with, such as the
Fire Service Act, the Marine Act, and the Soil Conservation and Land
Utilisation Act.
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4.2 LOCATION OF INDUSTRY
~he proposed first stage of the subdivision occupies an area in the
southeastern end of the Middle Arm Peninsula. West of the peninsula is
Channel Island with a gas fired power-station. The northwestern part of the
peninsula is being investigated for the establishment of an LNG plant. The
area east of the peninsula is the envisaged location of a new town, Weddell.
The planning of the subdivision takes into account constraints presented by
the proximity of the power-station, the proposed LNG plant and the residential
development of Weddell. The selection of industries to be established and
location of industries will also need to take these factors into
consideration.
5.0 DESCRIPTION OF THE EXISTING ENVIRONMENT
5.1 PHYSICAL ENVIRONMENT
5.1.1 Climate
Middle Arm Peninsula is located within the monsoonal tropics. The closest
meteorological station with comprehensive climatic data is located at Darwin
Airport. Monthly climatic data for Darwin Airport are shown in Table 1.
The monsoonal climate of Darwin and the Top End has two distinct seasons - the
hot, wet season from November to March and the hot, dry season from May to
September. April and October are transition months (Parkinson 1986).
Darwin has an average annual rainfall of 1661mm, most of which falls between
November and March. Humidity over this period averages 70-80%. In the dry
season, humidity is often below 40% and there is virtually no rainfall.
Maximum temperatures are hot year-round with November being the hottest month
with an average of 33°C. Dry season monthly maximum temperatures vary between
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30°C and 32°C. The monthly minimum temperature is lowest in July with an
average of 19°C and the daily minimum rarely falls below 16°c.
Darwin has a yearly average of 8. 4 sunshine hours per day.
monthly average is 10.2 hours in August.
The highest
Prevailing winds during the wet season are light west to north-westerly,
freshening in the afternoon due to sea breezes. In the dry season, the
prevailing winds are the south-easterly trade winds (Parkinson 1986).
5.1.2 Land Systems
There are three land systems present in the study area (Wood et al. 1985).
These are:
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Keefer's Hut land system
Baker land system
o Littoral land system
The Keefer's Hut land system is part of the Koolpinyah surface and is
developed on tertiary Cainozoic sediments.
gravelly slopes with relief up to 20m.
outcrops and drainage is usually rapid.
The landform consists of gentle
There may be scattered laterite
Soils of this land system may be
shallow gravelly yellow massive earths, gravelly red massive earths or
moderately deep lithosols. Yellow earthy and siliceous sands may be present
in drainage lines.
Keefer's Hut land system is considered to have a moderate capability for urban
development with shallow and gravelly soils being the main limitation (Wood
et al. 1985).
Baker land system is located south of the access road to Channel Island. The
land system is developed on lower Proterozoic sediments and is characterised
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with outcrops of siltstone, ·quartz greywacke, quartzite and conglomerates.
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Deeper lithosols and yellow duplex soils may be found on the lower slopes of
ridges and alluvial flats.
Baker land system is considered to have low capability for urban development
due to the extent of steep terrain and shallow stony soils (Wood et al. 1985).
The Littoral land system which borders the subdivision includes the mangrove
fringe of ·the coast and rivers and is developed on quaternary Cainozoic
sediments. The mangrove fringe is up to 600m wide with slopes up to 0.9%.
The area is flooded daily by high tides. The soils of the Littoral land
system are saline muds which can be interspersed by laterite outcrop.
r ' The Littoral land system is considered to have a low capability for
development due to tidal inundation (Wood et al. 1985).
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5.2 BIOLOGICAL ENVIRONMENT
5.2.1 Terrestrial Flora
Keefer's Hut land system on Middle Arm Peninsula includes outcrops of low
relief (<20m) with mid-high woodland (Erythrophleum chlorostachys, Eucalyptus
confertiflora) with a second story tree layer (Xanthostemon sp., Buchanania
sp., Petalostigma sp.), numerous shrubs (Cycas sp., Xanthostemon sp., Pandanus
sp., Melaleuca spp.) and annual (Sorghum sp.) and perennial (Heteropogon
tri ticeus, Chrysopogon latifolius) grasses. Narrow drainage line_s support
open forest (Melaleuca spp., Erythrophleum chlorostachys, Eucalyptus papuana)
with Pandanus sp. understorey, merging to open woodland (~. polycarpa, ~.
papuana, Planchonia sp., Lophostemon sp.) with perennial grasses (Coelorachis
sp., Heteropogon sp., Imperata sp. and Themeda sp.) away from creek lines.
Areas of higher relief (up to 20m) support woodland and open forest (~.
bleeseri, ~. confertiflora, ~. tetrodonta) with scattered low trees
(Planchonia sp., Buchanania sp.) and shrubs (Cycas sp., Grevillea decurrens)
grading to low woodland (Melaleuca viridiflora) with scattered shrubs
(Lophostemon lactifluus, Pandanus sp.).
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A small area of land south of the existing main road is classified as Baker
land system, having low hills and ridges 10-20m high supporting woodland
(Eucalyptus dichromophloia, ~- bleeseri, ~- miniata, ~- tetrodonta, ~
tectifica, ~- foelscheana) with a low tree understorey (Terminalia
ferdinandiana, Xanthostemon sp., Owenia vernicosa) and shrub layer (Grevillea
decurrens, Livistona humilis, Cochlospermum fraseri, Cycas armstrongii). In
this area south of the road are small hills (20-46m high) which support
islands of monsoon vine thicket, within the woodland and mangrove forests.
These. knolls are of special interest as monsoon thicket communi ties are
relatively rare compared with other vegetation types in the Top End (Clyde
Dunlop, CCNT, pers. comm.).
The Littoral land system supports an estuarine fringe of mangrove forest
subject to tidal flooding and is discussed further in Section 5.2.3.
There are no rare or threatened plant species registered in the area (Briggs
and ·Leigh 1984) .
5.2.2 Terrestrial Fauna
Although there has been no detailed terrestrial fauna survey of the area, it
is expected that the wildlife is representative of the Top End, and it is
unlikely that rare or endangered species inhabit the area.
Examination of the CCNT Coastal Resources Atlas, and the Recreation and
Conservation Priori ties Register indicated that no terrestrial sites of
special faunal significance are known to occur in the proposed industrial
areas.
5.2.3 Marine Environment
The mangrove forests that dominate all areas of Middle Arm Peninsula between
mean sea level and the hinterland fringe at 4m AHD are an important habitat
LJ and serves as a vital biological resource and a critical buffer zone between
land and sea. This importance has been documented by Dames & Moore (1984b).
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The essential functions of mangroves as a land-sea interface, faunal habitat
and as primary producers in coastal food chains supporting valuable
recreational and commercial fisheries are also reviewed in some detail in
Dames & Moore (1988).
The mangroves surrounding the proposed general industry and hazardous industry
subdivisions on Middle Arm Peninsula have been designated as conservation or
research/educational, and management zones respectively in the draft Mangrove
Management Plan (Dames & Moore 1988). They are generally extensive mature
mangroves of h~gh density with well-developed zonation and requiring varying
degrees of protection. The Conservation subzones within the proposed
subdivision incorporate mangroves in Creeks F, G and J of East Arm and east
of Creek G in Haycock Reach, Middle Arm. ~he areas have been recommended for
reservation as Aquatic Parks under the ·Fish and Fisheries Act, or subject to
environmental assessment prior to minor development such as boat ramps and
board walks. The Management subzones in the proposed subdivision included all
mangroves west of Creek G of Middle Arm and along East Arm west of Creek F and
east of Creek J. The areas were targeted for some development subject to
assessment through the Environmental Assessment Act and the Planning Act. The
Research and Educational subzone includes Creek H off East Arm. This is an
area where significant scientific research has taken place since 1984, and is
intended to provide an area for future scientific research and education to
, J advance knowledge and information exchange on the natural components and
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processes of a pristine mangrove community.
The mangrove communities of the whole of East and Middle Arms are extensive
and significant systems registered in the CCNT Coastal Resources Atlas as
having a ground coverage of over 6400 and 7300 ha respectively. Over 19
mangrove tree species occur in these areas. Creek H, which enters ·the middle
of the proposal area from East Arm, has been a major area for mangrove
research in the Northern Territory. Scientists from NARU (North Australian
Research Unit of the Australian National University) have carried out research
on a variety of projects such as mangrove productivity, ecophysical studies,
tidal modelling and water chemistry and, in conjunction with the NT Museum
and DIT (now NTU) invertebrate and bird fauna. A number of papers (both
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published and in press) are based on this research, including Larson et al.
(1987), Woodroffe et al. (1988) and Hanley (in press).
The mangroves within the proposal area are part of a reasonably extensive area
of 'excellent' bird habitat (CCNT Coastal Resources Atlas) which adjoins
'good' bird habitat around Middle Point from Creek A to Jones Creek (McKean
and Martin 1986) . The mangrove communi ties of the proposal site were
considered diverse and above average, supporting most common bird species as
well as supposed 'rarities' . One of the rocky islands near Oyster Rocks (just
to the south west of the proposal site) in Middle Arm has a small breeding
colony of Pied Cormorants (Phalacrocorax varius) one of only four known
breeding colonies in the Northern Terri tory. The sparsely distributed Great
billed Heron (Ardea sumatrana) breeds i:n mangroves along Middle Arm (J.
McKean, pers. comm.). Middle Arm is one of the few accessible places in the
Top End where the White-breasted Whistler (Pachycephala lanioides) is known
to occur. The Great-billed Heron, White-breasted Whistler and Mangrove Golden
Whistler (Pachycephala melanura) are all mangrove specialists confined to the
northern Australian coastline, but occurring in disjunct populations of
apparently low densities.
According to CCNT, the mangroves in the proposed subdivision are considered
an important dry season refuge for Burdekin Ducks (Tadorna rajah) of high
' J conservation significance at an international level ( CCNT Recreation and
Conservation Priorities Register). However the species is not included in ·the
CONCOM list of Endangered Vertebrates of Australia and its Island Territories,
nor is it considered threatened by RAOU (Joost Brouwer, pers. comm.) or Collar
and Andrew (1988).
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The Darwin Harbour area is a known_habitat for dugongs which feed on seagrass
and frequent shallow bays and channels that are protected from strong winds
and heavy seas (Bayliss 1986). An aerial survey in 1"983 detected dugong in
low to moderately high concentrations of 0. 01 - 0. 1 animals per square
kilometre in all waters of East and Middle Arms, excluding minor creeks (CCNT
Coastal Resources Atlas). Dugongs are listed as endangered in the IUCN Red
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Data Book but they are not included on the CONCOM List of Endangered
Vertebrates of Australia and its Island Territories.
Saltwater crocodiles inhabit Darwin Harbour and its estuaries (Messel et al.
1981) but there are no known breeding sites in the vicinity of the proposed
subdivisions.
Channel Island coral reef is possibly within the area of im.pact of the
proposed subdivision. This unique reef, along the north east of the Island
is a specialised coral community supporting a wide spectrum of fish and
invertebrate life. It is considered of high conservation priority due to its
vulnerability, proximity to Darwin and projected future use for recreation
(CCNT Recreation and Conservation Priorities Register).
Biting insects are an important consideration in developments for human
occupation in the Top End as, in addition to creating a nuisance, they can
present a public health problem through transmission of diseases. Biting
insects of the Northern Territory include mosquitoes and midges, with march
flies occurring to a lesser extent. Ninety-five species of mosquito have been
identified in the Northern Territory with 65 species collected in the Darwin
area and 61 species from Palmerston (Liehne 1985). Of these, 15 are
considered as serious pests or vectors of disease. They breed in the
intertidal mangrove zone and low-lying zone between mangroves and terrestrial
open forest from 3. 3 AHD to 1 .. Om above maximum high tide at various times of
the year (Whelan 1988).
Thirty-three species of biting midge (Culicoides) have been recorded in the
Darwin area (Liehne 1985). These species are not known to carry diseases of
man, but are vectors of a number of serious virus and parasitic diseases of
domestic stock. The major pest species to man is ~ ornatus, which breeds in
the mangrove zone. Other biting insects recorded· in this area include the
march flies (Tabanidae). They do not transmit any human diseases but are
vectors of some parasitic diseases of stock. Two main species have been
identified as pests to man in the Palmerston area, Tabanus rubriventris and
Tabanus cinerescens.
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The proposed subdivision area has a relatively high density of biting midges.
Trap sites on the eastern edges of the subdivision and on Creek J of East Arm
had very high numbers of ~- ornatus compared with other trap sites throughout
the proposed Weddell town development area and along the Elizabeth River
(Whelan et al. 1988). Mosquito species capable of transmitting diseases as
well as pest species were present in relatively low numbers. No large or
uncontrollable mosquito breeding areas are evident on the proposed subdivision
area (Peter Whelan, Dept. Health and Community Services, pers. cornrn.).
5.3 SOCIAL AND ECONOMIC ENVIRONMENT
5.3.1 Current and Proposed Land Use
The area is currently zoned ·for rural living purposes in accordance with the
Darwin Rural Area Plan 1983. There are no permanent campsites in the area and
use by bush walkers and field naturalists appears to be low.
The CCNT Recreation and Conservation Priori ties Register identifies an
airstrip fqr radio-controlled model aeroplane flying to the north of the
Channel Island access road and south of Creeks G, Hand J. However, the NT
Model Aeronautical Association Inc. currently uses fields at East Point and
Leanyer.
There are abandoned nursery, grow-out ponds and associated aquaculture
developments at Middle Arm Prawn Farm constructed by Taiwan Australia Prawns
Pty Ltd., near the terrestrial-mangrove margin south west of the proposed
subdivision. A pearl culture farm is located in Creek B off East Arm.
The waterways adjacent to the proposed subdivisions are a major recreation
resource for fishing and boating. Direct access to East and Middle Arms is
afforded by the public concrete boat ramps at Elizabeth River, Quarantine
Station and Channel Island, and to Middle Arm from the informal boat launching
areas at Oyster Point, Haycock Reach and Blackmore River. The Channel Island
coral reef is a specialised community.with a low level of current usage by
scientists, naturalists and scuba divers. Fish and shell collectors have
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caused some damage to the reef since access via the Channel Island access road
improved (CCNT Coastal Resources Atlas). The waters off Channel Island, in
particular Town Hall Hole, are good fishing areas with medium usage at present
(CCNT Coastal Resources Atlas).
There has been no major environmental disturbance such as clearing or
extractive industries to the proposed subdivision area. Clearing has occurred
for the Amadeus Basin to Channel Island natural gas pipeline an~ power lines
from Channel Island to Darwin and Palmerston. NT Gas's City Gate Gas Station
is located on the pipeline south of the access road and regulates gas pressure
to the Channel Island power station. Some areas were also cleared for borrow
areas for the construction of the Channel Island access road and transmission
r ' tower pads. Fires have been common throughout the area in the dry season.
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The proposed subdivision is not subject to current mining/exploration activity
or gazetted as reserve from occupation.
5.3.2 Current and Proposed Services
At present road access is restricted to a few dirt tracks to the north and
south of the main bitumen Channel Island access road. The natural gas
pipeline and electricity power lines to Channel Island run generally parallel
to the main access road.
These current services will be extended to service the proposed subdivision
(see Section 2. 2) . Other services such as water, sewage and
telecommunications will be incorporated into the proposed subdivision (see
Section 2. 2) as will a rail link with. the proposed Darwin-Alice Springs
railway (Figure 2).
5.3.3 SignificantSites
The Aboriginal Areas Protection Authority advises that it has no registered
,L- _) sacred sites within the proposed subdivision area. Howeve_r, this does not
mean that there are no sacred sites located in the area, but rather reflects
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the situation that Aboriginal custodians for this area have not sought
protection for Sacred Sites under Northern Territory law (D. Ritchie, AAPA,
pers. comm.).
The Aboriginal Areas Protection Authority can issue an "Authority Certificate"
to the proponent after a request is made by the proponent under Section 20(3)
of the Aboriginal Sacred Sites Act 1989 and proper consul tat ion by the
Authority with custodians. This "Authority Certificate" sets out the
conditions (if any) on which the proposed work may be carried out or use made
of the land.-
One site of historical, sociological or cultural significance has been
recorded within the proposal area ·(CCNT Coastal Resources Atlas and
Recreational and Conservation Priorities Register) and consultation with Kim
Ackerman of Northern Territory Museum of Arts and Sciences (Register- of
Archaeological Sites) . The site, of cultural and historic interest, comprises
a shell midden covering 200 x 50m (minimum) in the woodland at GM 128082 on
the Bynoe 1:100,000 map R621- 5072. However, lack of official archaeological
investigation in the proposed subdivision area may be a reason for this
paucity of recorded significant sites. There are middens on some vine-thicket
knolls (Keith Presnell, PAWA, pers. comm.) and possibly other middens on the
higher ground in the area (Kim Ackerman, NT Museum, pers. comm.). In the
mangroves, there are an undetermined number of midden heaps mainly of mollusc
shells with some artefacts, pome of which may be already disturbed (William
Brothers- CMPS Engineers 1985).
If middens, stone tools or other evidence of past use are located during
development of the proposed subdivision, works will be suspended pending
investigations, in accordance with the Native and Historical Objects and Areas
Preservation Act. The appropriate authorities (the Northern Territory Museum
of Arts and Sciences, the Aboriginal Areas Protection Authority, and the
Conservation Commission of the Northern Territory) will then be notified to
allow assessment of the cultural significance of the site. There is no
legislation specifying a maximum time period allowed for assessment of the
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site however, if justified, archaeological consultants may be employed by the
developer to avoid unnecessary delays (Kim Ackerman, NT Museum, pers.comm.).
6.0 ENVIRONMENTAL LIMITATIONS
6.1 WATER IMPACTS AND MANAGEMENT
Some water quality data which is relevant to the proposed subdivision has been
presented. in Caldwell Connell Engineers (1974, 1976, 1984), Hydrographic
Surveys Pty Ltd (1981) and Presnell (1985), and collected by the then water
Division of the NT Department of Transport and Works. The North Australian
Research Unit (NARU) has carried out a wate~ chemistry program at Creek H
which is an important study for understanding the little known estuarine water
quality relationships in Darwin Harbour.
Any development involving hazardous industries has the potential to affect
water quality in the surrounding area unless appropriate safeguards are
included in the design. The main water-related impacts with potential to
arise from this development are:
o Pollution of the creeks, estuaries and harbour by nutrients, heavy
metals, BOD, hydrocarbons and other contaminants.
o Contamination of'groundwater.
o Spillage of toxic chemicals resulting from transport accidents,
fires and accidental releases of effluent.
o Increased volume and channelling of runoff resulting from
clearing, road construction and drainage, leading to erosion and
increased sediment loads.
Environmental safeguards will be incorporated in the development of the
L.J subdivision to minimise or avoid these potential impacts (see Section 6.4).
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6.1.1 Surface Waterways
The Middle Arm Peninsula is situated in the south-eastern corner of Darwin
Harbour, a natural harbour with a calculated volume of 2. 46x1 o9 m3 at mean sea
level (Caldwell Connell 1976) and an opening to the sea of 5.5 km at its
narrowest point. The Peninsula is bounded to the north by the Elizabeth
River, and to the south by Haycock Reach. Both of these watercourses are
estuarine in the vicinity of Middle Arm Peninsula, with most water movement
taking place by means of tidal action. The proposed development should have
no impact on the riverine section of either watercourse.
The creeks and rivers in the area appear generally well-flushed by a tidal run
of up to eight metres and so moderate inputs of nutrients, heated cooling
water, biological oxygen demand (BOD) and other non-toxic contaminants may be
assimilated with no significant adverse effects. This includes moderate
quantities of secondary treated sewage effluent from the two planned treatment
plants. In view of the configuration of the harbour, it is very likely that
exchange with the open ocean, and hence flushing of Darwin Harbour, is
limited, as was found to be the case in·Cockburn Sound, Western Australia,
which was also the site of an industrial subdivision (Steedman and Craig,
1979). Future large-scale industrial development in Darwin Harbour will
require an examination of the circulation within the Harbour and estuarine
, ~ areas to determine the efficiency with which contami~ants will be lost to the
open sea. This will have an important bearing on what quantities of effluent
may be safely discharged into the harbour or its tributaries.
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The waters of Darwin Harbour currently contain relatively high concentrations
of nutrients and suspended solids (Currey, 1988). These concentrations show
large variations, due to variations in tides and seasons.
Careful control of toxic effluents such as heavy metals, pesticides and
hydrocarbons will be necessary due to the importance and vulnerability of the
mangrove communities in the area.
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6.1.2 Surface Runoff
Runoff is expected to increase following clearing of vegetation and
construction of roads, carparks and buildings. This runoff is likely to be
more concentrated in area and have a higher velocity than natural runoff. It
will carry increased loads of sediment as a result of this higher velocity and
ground disturbance, leading to increased concentrations of suspended solids
in the creeks. This increase will be kept within acceptable levels by the
following basic procedures:
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Clearing of vegetation will be kept to the minimum necessary.
Construction works will be carried out during the. dry season
where possible, and disturbed areas rehabilitated or stabilised
prior to the start of the wet season.
Drainage lines will be constructed to minimise water velocities
and incorporate detention basins and barriers to encourage
deposition of suspended sediments. The design of these structures
will take account of the high runoff rates likely during wei;:
season storms.
In addition to increased sediment loads, runoff water will carry nutrients,
hydrocarbons-and heavy metals from roads and other paved areas, however the
amounts of these are unlikely to be sufficient to cause concern.
Individual industries will add a variety of contaminants to runoff from their
premises. As a general rule, each industry will be required to incorporate
measures to minimise the potential for contamination.
include:
These measures may
0 Surface drainage should be contained within the premises by means
of bunds and drains. Runoff should be routed through interceptor
pits, detention basins or settling ponds, depending upon the
nature of the industry. For industries dealing with hazardous
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materials, these detention facilities should be large enough to
contain the maximum size of spill resulting from a "worst case"
scenario.
o Hazardous materials including hydrocarbons should be stored in
sealed, bunded pits designed to be cyclone proof.
o The drainage system should be capable of intercepting debris and
litter.
o Underground storage tanks should be discouraged or, if necessary,
a regular testing programme should be required to ensure no leaks
occur.
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Potential exists for deterioration of water quality as a result of chemical
spillages arising from transport accidents, major fires or accidental
releases.
However, the overall design of the subdivision will provide the means to
contain and recover spillages before they reach the mangrove areas of
watercourses. This may be achieved by directing stormwater drainage into
retention basins before release into the environment. These basins would
serve a secondary purpose of removing excess suspended solids from the runoff.
During the wet season, special precautions will need to be taken to allow
adequate drainage of stormwater yet still provide for retention of any
spillages.
6.1.4 Groundwater
The main aquifer in the Middle Arm area is the Burrell Creek Formation, a
fractured rock aquifer comprising sandstone, siltstone, shale and greywacke
with low yield potential except. perhaps along some isolated_ fracture zones.
These zones are unlikely to yield more than 170 m3 d-1. This formation is
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overlain by a thin cover of sand and alluvium which is unlikely to contain
groundwater. Groundwater levels are likely to be between 1m and Sm above mean
sea level.
Two main impacts on groundwater are possible as a result of the development,
assuming groundwater is not used as a water source. They are:
o Contamination of groundwater through seepage of ~ontaminated
water, particularly from the proposed hazardous wast~ storage site
or from underground storage tanks.
0 Raising of the water table due to clearing and increased
infiltration.
In the absence of specific data concerning groundwater depth, flow
characteristics and hydraulic conductivity of the area it is only possible to
make general observations as to the relative likelihood or severity of these
potential impacts.
Groundwater Contamination
Some contamination of the shallow aquifer is likely as a result of
infiltration. This contamination will be carried in the general groundwater
'~ flow and eventually reach the creeks and bays. The extent of contamination
will depend upon the depth o~ the groundwater, the capacity of the soils to
bind contaminants and the measures adopted to minimise contamination. These
measures may include the sealing of the ground surface in areas where spills
(major or minor) may potentially occur, proper design of drainage systems and
siting of hazardous industries away from areas of shallow groundwater or
highly leaching soils. Given the slow rate of contaminant transport through
groundwater, contamination by non-toxic materials should not pose a major
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Of more concern is the planned siting of a hazardous materials storage site
in the·southern portion of the subdivision. Materials to be stored at this
site are unknown but are likely to include oils, solvents, heavy metals and
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toxic organic compounds. Great care will be taken in planning this facility
to avoid leaching of toxic materials into groundwater and hence to the marine
environment. Assessment of the site will be undertaken and reported on by the
Work Health Authority before any works are commenced.
Rise in Groundwater Levels
Groundwater levels may rise in areas wher~ the natural vegetation is cleared.
Rises in average groundwater levels of two or three metres are not uncommon.
Consequences of this phenomenon can include the seasonal flooding of low
lying areas, salinisation of soils and the death of vegetation due to
waterlogging.
This problem will be minimised by the rete11-tion of natural vegetation wherever
, l possible. In the area of this planned development, its effect is expected to
be minor or negligible.
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6.2 IMPACTS ON GEOLOGY, SOILS AND LANDFORMS
The potential impacts of the proposed subdivision on the geology, soils and
landforms of the area will be minimised by sound planning and implementation
of soil conservation practices. As development will be constrained to the
well drained landforms which are gently sloping there will be no need for
major changes to the landform such as large cut and fill areas.
Construction of the access roads and the railway line will require borrow pits
for extraction of road base and railway formation material .. The possible
location of these borrow pits is not known, but extraction of materials from
and rehabilitation of borrow pits will follow Conservation Commission
guidelines (Applegate 1983) to minimise adverse impacts.
Vegetation clearance within the proposed subdivision area for construction of
roads, railways, fire breaks, car parks and industrial buildings and for
·'- _j installation of services will leave the soil susceptible to erosion. To
minimise this risk, as far as possible construction activities will be
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Areas of land cleared will be limited to that necessary to complete work
timely and efficiently and to provide safe working conditions. Topsoil will
be removed from cleared areas where appropriate and respread after work is
completed to aid rehabilitation or, if not required to be respread over its
source site, topsoil will be respread over other areas to be rehabilitated.
Topsoil will not be stockpiled over the wet season and all disturbed sites
will be rehabilitated before the wet season.
6.3 AIRQUALITY IMPACTS
Air quality is unlikely to be affected by this proposal for development of the
necessary services for the Middle Arm Pen~risula industrial subdivision.
However, air quality may be affected by emissions from industries which may
establish in the zone. These possible air quality impacts are discussed in
, ' Appendix A.
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6.4 BIOLOGICAL IMPACTS AND MANAGEMENT
Areas of the terrestrial environment, woodland and forest habitat, will be
disturbed by clearing for access roads, industrial buildings and associated
infrastructure. Unnecessary habitat disturbance will be avoided. Remnant
terrestrial vegetation will remain as corridors to undisturbed habitat as
well as shade and screen areas.
The terrestrial habitat that characterises the subdivision is small in area
and well-represented throughout the Top End. However, disturbance to the
small knolls that are found in the area proposed for the hazardous materials
storage site, may mean the loss of an uncommon vegetation community that is
close to and accessible to Darwin scientists and naturalists (Clyde Dunlop,
CCNT, pers. comm.). There is a need for further investigation and possible
protection of these unusual communities.
Due to the lack of local information on the marine ecosystem, environmental
controls and constraints with conservative design and management practices
will be necessary to significantly limit adverse impacts of development on the
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marine environment. Direct disturbance to mangrove communi ties will be
limited to relatively small areas for the possible construction of barge
landings and a dredged canal. However, any industrial development adjacent
to mangroves with possibilities of direct water access through mangroves has
the potential to affect the marine environment. The impact of pollution,
alteration or removal of mangroves on the productivity of biological marine
resources with particular reference to commercial and recreational fisheries,
will need to be addressed in relation to specific development proposals within
the subdivision. There is a need for longer term studies and baseline
monitoring, as well as an assessment of the value and productivity of the ·
mangrove resource. The Australian Marine Sciences Association ( 1977)
recommend a buffer zone for protection of a mangrove community. Where
practical, this will be used as a guide in the siting of future developments.
The following are areas of potential concern, some of which may be alleviated
by sound engineering design and environmental management,· such as:
o Earthworks and vegetation clearance related to building railways,
roads and fire breaks, and establishment of industrial sites and
services may be a source of silt which could cause local
sedimentation in East Arm, Middle Arm and associated smaller
creeks. Erosion control techniques (see Section 6. 2) should
minimize these affects.
o The input of sediment, leachate or pollutants may affect not only
the local environment but also sensitive areas-up and downstream
of the subdivisions. The subdivision lies in an area of
relatively pristine mangrove habitat which is highly biologically
productive and makes a vital contribution to commercial fish,
prawn and mud crab industries, and the health of the Darwin
Harbour environment. The area is also a permanent and seasonal
refuge habitat for breeding and migratory birds. Near the
entrance to Middle Arm lies the unique coral community of Channel
Island reef. The slightest change (particularly aseasonal) in sea
water turbidity and freshwater input, let alone pollutants may
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adversely affect this sensitive and significant habitat (Russel
Hanley, NT Museum, pers. comm.).
o Dredging of channels for commercial shipping access and barge
landings needs careful consideration. The impact of increased
sedimentation and water turbidity has been mentioned previously.
Land disposal of reduced marine ~uds from dredge spoil or
excavations has been clearly identified as creating acidic and
saline spoil which is costly and difficult to rehabilitate, and
provides another source of acid leachate pollution.
0 The r~lationship between mangroves and biting insects is a strong
public perception as well as an important environmental planning
constraint and management problem in the proposed subdivision.
All areas of the subdivision are within the buffer zones of 1km
and 1 . Skm recommended between urban development, and biting midge
and mosquito breeding grounds, respectively.
o There will be a severe biting midge Culicoides ornatus problem at
any proposed subdi vis.ion close to their mangrove breeding areas
(Peter Whelan pers. comm.). The area has large densities of
Culicoides spp. (Whelan et al. 1988). Outdoor activities and
major centres of human activity could be concentrated in areas of
the subdivision most distant from mangroves. Storage and ·less
labour-oriented activities could be located around the perimeters
to act as a buffer between mangroves and the major centres of
human activity. Air conditioned workplaces, fine meshed wire
screens, the use of personal insect repellants outside and a
restriction on activities in the early morning and late
afternoon/evenings could assist in avoidance of the problem, but
may be impractical on industrial subdivisions. The only permanent
way to control the biting midge problem is to fill all mangrove
breeding grounds to neap tide level (Peter Whelan pers. comm.),
however this has significant environmental and economic costs and
is not recommended.
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o Although there is currently no mosquito problem, construction of
stormwater drainage, roads, embankments, and mangrove disturbance
will disrupt the natural drainage system with the potential for
the creation of mosquito breeding habitats. The existing drainage
channels and general hydrology of the project area are being
examined by the Department of Transport and Works and its
consultant. This study will enable design and re-routing to
ensure that all low-lying areas will drain freely and not pond
water. Stormwater drains should extend into tidal areas to avoid
pending.
0 Construction activities may create mosquito breeding habitat. The
contractors responsible for construction must be made aware of
these problems so that excavation and fill operations are carried
out in such a way that they do not pond water. Construction
practice guidelines developed for the NT Coastal Management
Committee should be followed (Whelan 1989) . Fill operations
should be inspected prlor to the onset of the wet season and any
depressions created through settlement refilled.
o The Medical Entomology Branch of the Department of Health and
Community Services, will be requested to inspect and monitor the
·area for biting insect populations and identify problem areas to
be rectified.
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An access easement within the subdivision lots, between the
subdivision and mangroves, will enable monitoring by the
appropriate authorities of mosquitoes and biting midges, as well
as policing of industrial lots for possible leaching, dumping or
spills of effluent or ecotoxins and alternative access to the
blocks in the event of an emergency.
Weed species such as Leucaena leucocephala, Carica papaya, Sida
sp. and Chloris gayana, may invade disturbed areas of terrestrial
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and mangrove habitat along roads, drains, landfill and areas of
sewage sludge and effluent discharge.
o Proper drainage is needed to avoid large scale mangrove tree death
caused by tidal inundation or changes in soil salinity.
o Access roads, transmission towers or railways passing through the
mangroves should utilise areas of lowest primary productivity and
greatest difficulty in regeneration or rehabilitation; the most
suitable areas are salt flats, previously disturbed or cyclone
damaged areas and the landward Ceriops zone.
Other potential environmental impacts and · safeguards relating to the
establishment of hazardous industries in the subdivision are discussed in
Appendix A.
6.5 STORM SURGE AND GREENHOUSE- EFFECTS
Storm surge must be considered in any coastal development in the susceptible
zone, especially in the case of residential developments and those involving
the use or storage of toxic chemicals. The primary surge zone is the one in
one hundred year storm surge which is 5.4 metres above Australian Height
Datum (AHD) .. Road embankments and landfill final surface levels must account
for a minimum freeboard above. high tide level with allowance for cyclone storm
surge. Arterial road embankments are designed with a minimum shoulder level
at RL S.Om to provide a minimum freeboard of 1m above high tide level. The
fill level of coastal land-filled developments would normally be in the range
RL S.Om to RL 5.5m depending on the development proposal and storm surge
analysis.
Scientists predict that the 'Greenhouse effect' which is the global warming
of the earth as a result of increasing levels of carbon dioxide in the earth's
atmosphere, will cause sea level rises of 20 to 140 centimetres within the
next fifty years (Bell 1987). However recent thinking tends towards 20-30cm
(Werner 1989). This will cause coastal flooding of low-lying areas, extensive
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erosion and saltwater intrusion into groundwater. Other predicted effects of
the climatic changes are an increasing frequency and intensity of extreme
weather patterns such as tropical cyclones, a higher average rainfall,
increase in rainfall intensity and a rise in the water table (Bell 1987,
Pearman 1988).
The storm surge risk which is related to sea le~el height, and the intensity
and frequency of tropical cyclones will increase in the Darwin area. Despite
the uncertainty of these climatic changes, future engineering design criteria
for coastal developments may be planned to withstand a storm event with an
annual exceedance probability (AEP) of 1:1,000 rather than a 1:100 AEP storm
event, with a possible rise of 2 metres in the present design storm level in
Darwin (Arthur 1989).
Storm surge and Greenhouse effects may affect the proposed subdivision in the
following ways:
o Low-lying areas will become tidal and storm surge zones will
expand further inland
o Drainage patterns will alter and water table will rise
0 Mangrove zonation will alter according to changes in water depth,
salinity and physical action of waves and currents
o With increased incidence of cyclones, the coast will be more
subject to erosion, wave batter and flooding.
To safeguard the subdivision area against these potential effects:
o Embankment and land levels need construction above 6m AHD. Peak
100 year storm event levels at Elizabeth Point, East Arm and
Colvin Point, Middle Arm are 4.95 and 5.0 AHD respectively (Blain
Bremner & Williams Pty Ltd. 1983). The peak levels from 1:1,000
AEP events recommended to be adopted in planning for future
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developments are 6. 2 and 6 ~ 3 AHD respectively {Werner 1989). This
limits the area of land in the subdivision suitable for
development.
o Any seaward embankments need to be protected by strong
construction.
o The mangrove fringe will remain as an undisturbed buffer zone
protecting the subdivision from coastal influences.
o More stringent erosion control measures than presently acceptable,
may be necessary.
0 Stormwater drainage will need to accommodate the increased
rainfall and runoff.
CSIRO's Tropical Ecosystems Research Centre in Darwin have a grant for a
regional study programme starting in 1990 to study predictions and impacts of
the Greenhouse effects. The relatively long term research data on Creek H off
East Arm could be valuable for using the area as a benchmark for monitoring
Greenhouse effects.
6.6 VISUAL IMPACTS
Clearing for access roads, fire breaks and subdivision will have a visual
impact on the natural bush setting. Remnant natural woodland should be left
when possible to maintain the attractiveness of the bush setting, provide
shade, a screen from main roads and help control erosion.
Harbour views of the general industries and offensive and hazardous industries
subdivision from the waterways should be relatively unchanged due to the
mangrove buffer zone, except for the small areas of mangroves cleared for
barge access. However, excessive clearing or high structures may be visible
from the waterways, exposed above the mangrove buffer zone and from roads
within the subdivision.
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6. 7 FUTURE DEVELOPMENTS
Possible developments within the Middle Arm Peninsula area include the
proposed LNG facility and ancillary works and the residential town of Weddell.
The future of the LNG facility is unlikely to be affected by the construction
and occupation of the industrial subdivision. Although connected by road, the
two areas on Middle Arm Peninsula are well separated by Creeks A and B and
associated mangroves.
Weddell will also be well separated from the industrial subdivision by the
Channel Island access road and Creek K. An additional buffer distance is
provided by the siting of general industries within the subdivision in the
areas closest to the future town of Weddell.
6.8 SUMMARY OF PREDICTED IMPACTS, LIMITATIONS AND SAFEGUARDS
A summary of the potential impacts of the proposed industrial subdivision
means of limiting on safe gua~ding against these impacts and resulting
predicted impacts is tabulated below.
POTENTIAL IMPACT
Mosquito
breeding
LIMITATIONS AND SAFEGUARDS
Avoid pending water
Ensure all sites are well
drained
Construct borrow pits to
CCNT guidelines
Follow 'Guidelines to
Prevent Mosquito Breeding'
(Whelan 1988)
PREDICTED IMPACT
Minimal increase in
mosquito breeding
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POTENTIAL IMPACT
Soil erosion
Biting midges
Loss of
mangroves
Habitat loss
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LIMITATIONS AND SAFEGUARDS
Minimise area cleared
Construction during the dry
season
Rehabilitate before the wet
season
Stockpile topsoil and
respread
Use of repellants
Avoid working outdoors
during early morning and
evening
Air-condition buildings or
screen with a fine mesh
Wear long-sleeved shirts
and trousers
Areas of mangroves will
only be cleared where
necessary for access to the
·harbour
Areas f9r disturbance
should be preferentially
located in less diverse
areas
Vine thicket knolls in the
hazardous waste storage
area should be investigated
before development
PREDICTED IMPACT
Some increase in soil
erosion, however
significant problems
will be avoided
Exposed workers may
experience discomfort
from high numbers of
biting midges in the
area
Some loss of
mangroves will be
necessary but the
overall impact should
be minimal
Disturbance of vine
thicket knolls will
only occur after
clearance by the CCNT
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POTENTIAL IMPACT
Fauna - birds
Fauna - dugong
Loss of Creek H
for research
and education
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LIMITATIONS AND SAFEGUARDS
Mangrove habitat should be
protected from pollution
Large scale disturbance of
mangroves will be avoided
Oyster-rock and Pied
Cormorant breeding grounds
will be protected
Minimise sedimentation,
dredging, leachates and
pollutants which may affect
seagrass beds
Do not disturb mangroves
surrounding Creek H
PREDICTED IMPACT
There is unlikely to
be significant impact
on the avifauna of
the Middle Arm
Peninsula
Impact is likely to
be minimal
Creek H will lose
some of its value as
a pristine research
area but would become
a valuable area for
assessment of the
environmental impacts
of the proposed
subdivision.
Potential for
accidental spills of
toxic chemicals may
affect the value of
research in the area·
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POTENTIAL IMPACT
Marine
environment and
water quality
Storm surge and
Greenhouse
effects
Bush fires
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LIMITATIONS AND SAFEGUARDS
Prepare an accident
response plan which will
protect the marine
environment
Ensure that hazardous
chemicals are adequately
disposed of
Conservative design should
take account of these
potential impacts
Construct a fire break at
the south-eastern end of
the subdivision
Protect. individual lots as
necessary by construction
of perimeter fire breaks
and selectively slashing
vegetation to reduce fuel
loads
PREDICTED IMPACT
Minor changes in
water quality and the
marine environment
may be expected from
sewage pond outflow
and industrial storm
water outflow
There should be no
significant effect of
storm surge or the
Greenhouse effect on
the subdivision or
the local environment
(via the subdivision)
if structures are
designed adequately
Bush fires are
unlikely to be a
problem in the
subdivision
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POTENTIAL IMPACT
Industrial
fires
Weed invasion
Visual impacts
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LIMITATIONS AND SAFEGUARDS
Follow Australian Standards
to reduce the possibility
of industrial fires
Prepare a fire safety
action plan which aims to
protect human life and the
local environment
Revegetate areas as soon as
possible after disturbance
washdown any construction
vehicles which have been
working in weed infested
areas
Avoid disturbance of
mangrove areas
Maintain as much native
vegetation as possible
PREDICTED IMPACT
Predicted impact will
depend on the nature
of industries
establishing in the
subdivision and the
levels of fire safety
and protection
adopted by each
industry
Unlikely to be an
increase in weed
numbers
Visual impact of the
subdivision from the
waterways is likely
to be minimal
Views of the
subdivision from the
air and land will be
altered considerably
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POTENTIAL IMPACT
Accidental
spills of
hazardous
materials
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LIMITATIONS AND SAFEGUARDS
Spill traps should be
provided for all indust~ies
using hazardous materials
to protect the surrounding
environment
An emergency response plan
to limit the effect uf any
accidental spillage should
be prepared
PREDICTED IMPACT
Potential impact will
depend on the level
·of safeguards adopted
by individual
industries and
planning for the
subdivision as a
whole
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7.0 SOURCES OF INFORMATION
7.1 REFERENCES
Applegate R.J. 1983. Guidelines for Effective Rehabilitation of Borrow Pits
in the Top End. CCNT Technical Report No.13.
Arthur J.T. 1989. Greenhouse effect induced climatic change as it relates
to the Northern Terri tory. In. P. A. Werner ( ed. ) Greenhouse 88:
Planning for climatic change. CCNT, Darwin.
Australian Marine Sciences Association 1977 .. Guidelines for the Protection
and_ Management of .Estuaries and Estuarine Wetlands. Guidelines for
the Protection and Management of AMSA, East Melbourne.
Bayliss P. 1986. Factors affecting aerial surveys of marine fauna, and their
relationship to a census of dugongs in the coastal waters of the
Northern Territory. Aust. Wildl. Res. 13: 27-37.
Bell A. 1987. Prepare now for climatic change, scientists warn. Ecos 53:
18-21 .
Blain Bremner & Williams Pty Ltd. 1983. Greater Darwin Storm Surge Study
Part 3: Extreme Water Level Frequencies. Prepared for Dept. of Lands,
NT.
Briggs J.D. and Leigh J.H. 1984. Delineation of important habitats of rare
and threatened plant species in the Northern Territory.
Canberra.·
CSIRO:
Caldwell Connell Engineers 1974. Darwin East New Town. Sewage. Oceanogra
phic Investigations (Nov 1974).
Construction, NT Branch.
Prepared for Dept. of Housing and
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-44-
caldwell Connell Engineers 1976. Darwin East New Town. Sewage Study 1974 -
1976. Final Report prepared for Dept. of Housing and Construction, NT
Branch.
caldwell Connell Engineers 1984. Disposal of Marine Muds Environmental
Implications. Prepared for Northern Territory Electricity Commission
Channel Island Power Station Project.
Collar N.J. and Andrew P. 1988. Birds to Watch. ICBP World Checklist of
Threatened Birds. ICBP, Cambridge England.
Currey N.A. 1988. Darwin Harbour ambient w~ter quality. In: Larson H.K.,
Michie M.G. and Hanley J.R. (eds)~ Darwin Harbour. Australian National
University North Australia Research Unit Mangrove Monograph No.4.
Dames & Moore 1984a. Alice Springs - Darwin Standard Gauge Railway. Final
Environmental Impact Statement. Report for Department of Transport and
Construction. May 1984.
Dames & Moore 1984b. Mangrove Resource Delineation. Northern Territory
Coastline. Stage 1. Prepared for CCNT.
Dames & Moore 1985a. Darwin Harbour Study - Definition of Long Term studies
and Monitoring Requirements. Report for Water Resources Division, Dept.
of Mines & Energy.
Dames & Moore 1985b. Mangrove Resource Delineation Stage 2. Mangrove
Resource Management Summary Report. Report for Environment Unit CCNT.
Dames & Moore 1988. Mangrove Delineation Study Stage 3. Mangrove Zone
Management Plan Darwin Harbour N. T. Report for CCNT on behalf of
Coastal Management Committee.
Lei Department of Housing & Construction, 1981. Storm Surge at Darwin. Maritime
Works Branch. September 1981.
l. J
Dames & Moore
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Hanley J.R. in press. Notes on the invertebrate fauna of a mangrove forest
in Darwin Harbour, N.T., Australia.
Hydrographic Surveys Pty Ltd ( 1981 ) • Darwin East Arm Trawler Facility.
Report on Survey for Northern Territory Department of Transport and
Works, Appendix C. Darwin East Arm Proposed Fisheries Development.
Report on Engineering Investigations for Trawler Berths (1981).
·Larson H.K. 1 Michie M.G. and Hanley J.R. 1988 (eds.). Proceedings of the
Workshop· on Research and Management held in Darwin Harbour. ANU, NARU.
Liehne P. 1985. ~osquito and biting midge investigations, Palmerston. 1982-
1985. Prepared for Palmerston Development Authority.
r 1 Messel 1 H. 1 Vorlicek G. C. 1 Elliott M. 1 Wells A. G. and Green W.J. 198.1.
Surveys of Tidal Systems in the Northern Territory of Australia and
their Crocodile Populations. Monograph 17. Darwin and Bynoe Harbours
and their Tidal Waterways.
OECD 1985. Environmental Effects of Electricity Generation. Organisation
for Economic Co-operation and Development.
Parkinson G. 1986 (Ed.). Atlas of Australian Resources. Third Series .
Volume 4. Climate. Division of National Mapping~ Canberra.
Pearman G.I. 1988 (Ed.). Greenhouse planning for climate change. CSIRO.
Presnell K. 1985. A Composite Report on the Current Situation with Respect
to Mud Disposal at Channel Island. Northern Territory Electricity
Commission.
~ .J Steedman R.K. and P.D. Craig (1979). Numerical Modelling Study of Circulation
L. J
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and Other Oceanographic Aspects of Cockburn Sound. Report to the
Department of Conservation and Environment, Western Australia, by R.K.
Steedman & Associates. DCE Report No.64.
Dames & Moore
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Werner P.A. 1989. Greenhouse 88: planning for climatic change. CCNT, Darwin.
Whelan P. 1988. Construction practice near tidal areas in the Northern
Territory. Guidelines to Prevent Mosquito Breeding. Report for the
N.T. Coastal Management Committee.
Whelan P., Booth D. and Kelton W. 1988. Biting insect investigations and
comment on the proposed Newtown (Weddell) Development, Darwin N.T.,
N.T. Dept. of Health and Community Services.
William Brothers - CMPS Engineers 1985. Amadeus Basin to Darwin National Gas
Pipeline. Listing of sites of environmental concern.
J J Wood B.G.~ Fogarty P.J. and Day K.J. 1985. The Land Systems of the Darwin
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Region. Conservation Commission of the Northern Territory Technical
Report No.24.
Woodroffe C.D., K.N. Bardsley, P.J. Ward and J.R. Hanley 1988. Production of
mangrove
Australia.
litter in a macrotidal embayment, Darwin Harbour,
Estuarine, Coastal and Shelf Science 26: 581-598.
7.2 AUTHORITIES CONSULTED
NT Museum of Arts and Sciences - Russell Hanley, Kim Ackerman
Conservation Commission of the NT
Department of Health and Community Services - Peter Whelan
Work Health Authority - Terry McKay
Department of Transport and Works Fire Services Unit - Allen Tarriffe
NT Bush Fires Council - Bill Goodwin
Aboriginal Areas Protection Authority - David Ritchie
Power and water Authority - Mike Burgess
N. T. I
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7.3 STUDY TEAM
Peter Wright
David Blatchford
Dr Kris Fabian
Kerry Greenwood
Sue Noske
Phil Bayley
Cathy Paxton
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Senior Environmental Scientist
Senior Environmental Scientist
Senior Engineer
Earth Scientist
Environmental Scientist.
Environmental Scientist
Environmental Scientist
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PORT DARWIN 0
0
~proposed subdivision
:.::-,.: :.,:..= .. ::. m a.n groves :.·:· ... ·.·.;
A -J creeks
0 I
LOCATION OF MIDDLE ARM PENINSULA
INDUSTRIAL· SUBDIVISION
2 I
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6 KM I
FIGURE 1 DAMES a MOORE
0 l..
• sewage treatment works
mangroves
0 knolls over 20m
1111111111 buffer· zones :
CONCEPTUAL LAYOUT OF PROPOSED I
INDUSTRIAL SUBDIVlSION I.
WEDDELL
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STATION: Darwin Airport RECORDS COMMENCED: 1941
JAN FEB
Mean Monthly 409 355
MAR
316
TABLE 1 MONTHLY CLIMATIC DATA FOR DARWIN
RAINFALL (mm)
APR MAY JUN JUL AUG SEP
99 17 2 6 18
OCT NOV DEC ANN
72 142 224 1661
===========================================================·===================================
Mean Day Max Mean Day Min
31.7 24.7
31.4 31.8 24.6 24.4
32.6 23.9
31.9 21.9
TEMPERATURE (Deg. c)
30.4 19.8
30.3 19.2
31.2 20.6
32.4 23.0
33.0 24.9
33. 1 25.2
32.5 25.2
31.9 23. 1
==============================================================================================
Mean 9.00am Mean 3.00pm
82 70
84 72
83 67
75 52
RELATIVE HUMIDITY (%}
67 43
63 39
64 38
68 41
71 48
71 53
74 59
77 65
73 54
==============================================================================================
SUNSHINE HOURS
Mean 5.6 5.9 6.6 8.7 9.5 9.9 1 0. 1 10.2 9.8 9.4 8.4 7.2 8.4
==============================================================================================
SOURCE: Bureau of Meteorology
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APPENDIX A
Appendix A outlines potential environmental impacts and management of
hazardous industries which may establish in the subdivision zone.
A.1 AIR.QUALITY IMPACTS
Air pollutants have the potential to affect vegetation, fauna, human health,
soils, water, climate and visibility. Emission controls will be imposed on
any new industry with the potential for emitting air pollutants. This is to
ensure that air emissions from the industry have no adverse environmental
impact on the surrounding land-use.
Of concern are pollutants such as sulphur dioxide (S02), nitrous oxides (NOx),
carbon oxides (COx), hydrocarbons, odours and particulates. Other air
emissions, such as fluorine and chlorine, may also be emitted depending on the
type of industry. Some chemical odours can also be emitted which are
detectable at very small concentrations and cause human discomfort.
The industrial mix of the proposed subdivision can not be determined and
therefore it is not possible to estimate the likely level of impact that may
result from.industrial air emissions. Table A1 has been compiled to provide
an indication of relevant air quality criterion that could form a basis for
planning the industrial development of the site. The data presented in this
table should be used as a guide as each industry seeking to locate within the
industrial subdivision will need to be assessed in detail.
If the emission levels are maintained to ensure protection of human health,
then the impacts of air emission on the biological environment should be
minimal.
Gas processing and storage facilities are likely to emit so2, COx, hydrocarbons
and may have strong odours from mercaptans and H2S escaping from the plant.
L _j Depending upon the animal product processing, there may be some so2 and
odorous emissions. Odours such as H2S have been associated with tanneries.
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Sulphur Dioxide: so2 can affect vegetation although the concentrations which
can cause damage and the tolerance of each species to so2 varies widely.
Little is known of the impact of so2 on mangroves. so2 injury to vegetation
results in chlorosis (chlorophyll loss) and death of leaf tissue between veins
and tips. For this to occur, S02 must enter the plant to cause the damage,
usually via the stomata. The effect of so2 on human health is an extremely
complex issue as it is thought that the effects of long-term exposure to so2
are strongly influenced by its combination with other pollutants (such as
particulates). so2 can irritate the bronchial tract. The World Health
Organisation (WHO) recommended level for the pro~ection of health for a one
hour average is 350ug/m3.
Nitrous Oxides: NOx can cause leaf damage to plants similar to so2, but it
is less toxic than so2. It is also thought that NOx and S02 have a synergistic
effect in reducing plant growth. Little is known of the effects on human
health of NOx, particularly exposure to low levels of NOx. The National Health
and Medical Research Council (NH&MRC) recommend a 1~hour maximum exposure of
320ug/m3 .
Particulates and Trace Metals: Particulate matter refers to the dust which
may be emitted from unsealed roads, stockpiles and raw materials handling.
This dust may cause an impact in terms of its physical properties such as
visibility etc., or from the trace metals which may adsorb on the dust and be
dispersed in the environment. Some trace metals may constitute health
problems from either direct toxicity or risk of cancer. Some act as catalysts
in the conversion of so2 to acid sulphates, and consequently, may indirectly
contribute to respiratory irritant effects. Others may form biologically
reactive and harmful compounds in the atmosphere by being combined with
sulphate ions (OECD, 1985).
Carbon Dioxide: C02plays a role in maintaining the earth's heat balance by
absorbing heat radiation from the earth's surface, trapping it, and preventing
it from dispersing into space. This phenomenon is known as the."Greenhouse
Effect". It is currently thought that an increase of C02 concentration in the
atmosphere may increase the average global surface temperature by 3°C .±. 1. 5°C.
This could result in a rise of sea level, changes to rainfall and weather
L" patterns and an increase in number and intensity of extreme events such as
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cyclonic storms. Control methods for preventing the release of C02 are
extremely costly and the most appropriate control is fuel efficiency.
Each industry must conform with meeting the criteria set out in Table A1.
These levels are primarily for protection of human health and are directly
relevant for the proposed Weddell residential development. Higher levels may
be acceptable within the industrial boundary and surrounding buffer zone, as
long as the levels in residential areas do not exceed the criteria.
Another concern is the impact of air emiss.ions on the biological environment,
such a~ mangroves, surrounding vegetation and terrestrial and aquatic fauna.
A.2 POTENTIAL BIOLOGICAL IMPACTS AND MANAGEMENT
Industrial runoff, stormwater outfall, outfall from sewage ponds and seepage
from garbage systems can be a source of organic pollution, with high nutrient
input causing dense algal growth and turbidity. The adjacent tidal creeks may
be affected, although the tidal estuaries of East and Middle Arms are well
flushed,-.diluting leachates and sediments.
The accidental spillage of hazardous materials on site and in transit to
industries such as chemical manufacturing and petrochemicals processing and
storage could have serious environmental impacts. This could adversely affect
the flora and fauna (both terrestrial and marine) in the local area or along
the main estuaries, depending on the type, extent and source of the spill.
Land spills could be contained by drainage design. Contingency plans for
such events will be a requirement of development. In principle, industries
with pollution potential should not be situated near highly productive
ecosystems such as Creek H and the adjacent conservation sub ~ones.
Any extensive clearance or disturbance of mangroves can produce physical
and/or ecological changes to the coastal environment such as exposing shores
to the erosive effects of wind and wave action or affecting drainage patterns
which may encourage mosquito breeding or create odours and stagnant
backwaters. The intimate relationship between mangroves, their producti vi ties
and near-shore marine fauna can also be affected by any significant clearance
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clearance or reclamation, and the subdivision is sensitively sited to skirt
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mangrove areas. The location of the subdivision away from the coastline
should also prevent employee$ disturbing mangrove communities. The area and
extent of any possible disturbance to mangroves should be kept to a minimum
initially during development, rather than relying on costly clean up,
restoration and rehabilitation. Where possible, disturbance should be limited
to areas of tree death and salt flats, and to areas where off-site impacts
will be minimized.
There is sufficient scientific data mainly from overseas work, to plan for
rehabilitation of disturbed areas of mangroves .after development. However,
it is likely to be very costly and labour intensive owing to the difficulty
of establishing propagules in the intertidal zone.
Although there is no information from East and Middle Arms on the occurrence
of seagrass, it. is known that seagrass beds are adversely affected by
siltation, industrial effluents, petroleum products and dredging. Seagrass
is important as food for dugongs and as nurseries for commercial prawn
fisheries .. Seagr~ss also stabilizes marine substrate. Development at the
proposed subdivision sites has some potential to affect this habitat in East
and Middle Arm estuaries.
Sewage ponds are potential mosquito breeding habitats, particularly if they
are poorly designed, managed or maintained. Problems with mosquito breeding
in sewage ponds elsewhere in the Northern Territory have resulted from the
growth of bankside vegetation and build-up of solids in the corners of ponds,
thus creating sheltered habitats in which the larvae can escape natural
predation. Increased mosquito numbers in association with birds which are
often attracted to sewage ponds, become vectors for diseases such as
Australian Encephalitis.
Whelan ( 1988) has made a number of recommendations for the control of mosquito
breeding in sewage ponds. Sewage ponds should be sited on bare mud flat areas
in preference to existing mangrove areas to minimise ecological disturbances.
Increased use of estuaries such as East and Middle Arm through boating,
fishing, tourism and commercial shipping/barging can place pressures on
fisheries and important fauna and their habitats. However, levels of use
anticipated from the subdivision development alone do not warrant concern.
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Wake and wave action, particularly from barges, could disturb the normally
protected mangroves and tidal flats.
Increased freshwater input into the creeks and estuaries from the use of water
for landscaping and for industrial and manufacturing purposes, has the
potential to affect mangrove zonation and marine fauna.
The possible use of sea water for cooling purposes by certain industries
presents the potential problem of the discharge of warm sea water into
adjacent creeks. Large increases in sea water temperature are known to affect
marine life.
Mangrove areas targeted for disturbance by drains, landfill or water access
should be subject to assessment using the rapid assessment of resource value
techniques outlined in Dames & Moore (1988).
Hazardous· industries should be situated on adjacent terrestrial hinterland
above predicted storm surge heights rather than in landfilled mangrove areas.
Access to harbour waterways can be serviced by wharves or embankments which
pass directly through the mangroves. The mangroves continue to provide
erosion protection and stability for the shoreline sediments, an assimilation
mechanism for wa~tewater or stormwater runoff and a wind and wave -debris
buffer for the development.
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SUMMARY OF RELEVANT AIRQUALITYCRITERIA
SUBSTANCE
Sulphur dioxide
Nitrogen dioxide
Carbon monoxide
Particulate matter
Note: VEPA NH~MRC
~lHO
US EPA ( 1 ) (2) ( 3)
( 4)
AUTHORITY CRITERIA GROUND LEVEL
CONCENTRATION ug/m3
NH&MRC Occupational pealth 5,000 (8-hour day)
NH&MRC General population Annual average 60 1-hour average 700 10-minute average 1,400
USEPA Annual average 80 24-hour, primary ( 1 ) 365 3-hour, secondary (2) 1,300
VEPA 24-hour, acceptable ( 3) 171 1-hour, acceptable 486 24-hour, detrimental ( 4) 314 1-hour, detrimental 972
WHO Annual average 40-60 24-hour 100-150 1-hour 350
NH&MRC 1-hour maximum 320 US EPA Annual average 100 VEPA 24-hour, acceptable 123
1-hour, acceptable 308 24-hour, detrimental 308 1-hour, detrimental 513
WHO 1-hour average 30,000 WHO 8-hour average 10,000.
USEPA Annual arithmetic mean - primary 50 24-hour - primary 150
WHO Annual average 40 24-hour 100-150
Victoria Environment Protection Authority National Health and Medical Research Council World Health Organisation - Protection of Health United States Environmental Protection Authority primary - to protect public health secondary - to protect public welfare acceptable levels should not be exceeded more than three times per year detrimental levels should never be exceeded.
Dames & Moore
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