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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

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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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4.0

5.0

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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

Dames & Moore

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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

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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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TABLE Al

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