Mount Victoria to Lithgow Great Western Highway Upgrade ...

Mount Victoria to Lithgow Great Western Highway Upgrade

Strategic review of a Newnes Plateau corridor

CE001081_GWH NPC_ Draft Report_rev6 P a g e | 33

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34 | P a g e 12 November 2008

Technical Report

7 INTRODUCTION

The Newnes Plateau, and the wider region between Mount Victoria and Marrangaroo, has a

number of key ecological, historical and geological features. These features play a significant

role in the process of determining whether a road corridor can be identified within the region.

For the purposes of the corridor identification method these features have been termed

‘constraints’. The corridor options identified were determined by:

� The location of environmental features.

� Perceived cost/benefit of the environmental features on road construction/maintenance

costs.

� The need to minimise impacts from the proposed road on the environment.

� Outcomes of community consultation.

The potential corridors identified were ‘constrained’ by their potential impact upon the

environment and the impact of the environment on the cost of constructing and maintaining a

road within the corridor.

To determine whether a feasible corridor is available, it was necessary to identify and collate

environmental constraints (Section 8) and then map these constraints within a geographic

information system (Section 9). Once mapped, the constraints were subjectively assessed

(Section 10) and weighted (Section 11) to combine all the constraints into a unified geographic

data set. Cardno’s specialised in-house corridor selection program (Cardno EnCEP:

Environmental Constraint Evaluation Program) was then used to identify the least constrained

path across the Newnes Plateau, from the junction at Soldiers Pinch to the junction of the

Great Western Highway and Castlereagh Highway at Marrangaroo (Section 12). The same

process was used to identify a ‘base case’ corridor from Soldiers Pinch to Lithgow via the

Hartley Valley. The base case has been used as a point of comparison to assist in the evaluation

of potential corridor impacts.

The identified corridors are likely represent the net lowest environmental cost option for a

corridor between the nominated start and finish points, taking into account an extensive range

of environmental factors recognised within the study area. This is significantly different

approach from alternative corridor selection methods which often do not incorporate a broad

range of environmental constraints throughout the design process, or use them only for route

fine tuning or preliminary concepts.

Under the approach used here it is the environment itself, and the values assigned to the

environment, which essentially identifies a potential corridor.




8 CONSTRAINTS IDENTIFICATION AND

ANALYSIS PROCESS

Cardno adopted a general categorisation of common environmental factors to be considered

within any environmental study area and then specified known constraints based upon a

detailed literature review (including previous and concurrent studies), database searches, and

incorporation of community and stakeholder comments.

The general categorisation of environmental factors and the site specific environmental

constraints identified are detailed in Table 8.1.

Table 8.1 Environmental categories and constraints

Category Environmental Constraint

Physical environment Topography

Watercourses and dams

Geology, soils, and minerals

Mine subsidence

Ecological and related environment Parks and reserves

Threatened species and communities

Ecological communities

Water quality and catchments

Riparian corridors

Air quality, noise and pollution

Heritage environment Aboriginal heritage

Non-Aboriginal heritage

Native title status

Social environment Commercial value

Residence location

Education facilities

Social services

Land use and planning environment Land tenure

Major projects (approved and proposed)

Mining leases

Plantations

Australian Defence Force land

Existing infrastructure environment Roads

Railways

Electricity transmission lines

Following the preliminary identification of the need for these 25 constraints to be incorporated

into the corridor identification model, Cardno proceeded to acquire detailed geographic spatial

information and mapping of each of these constraints within the study area.




Technical Report

9 CONSTRAINTS MAPPING

A brief description of the study area in terms of each of the identified environmental

constraints and the source and format of the constraint information are detailed in the

following sections. Aerial photography shown in this section of the report is orthorectified data sourced from the

Department of Lands from photographs taken in 2000. Higher resolution orthorectified data for

the entire study area is not currently available.

9.1 PHYSICAL ENVIRONMENT

9.1.1 Topography

The topographic constraints in the study area are considerable due to the cliff and ridge

formations bounding Hartley Valley and Lithgow to the north-west. In particular, in terms of

engineering design, the need to minimise the road gradient (preferably below eight per cent) is

paramount. This restricts the number of points at which a road could descend from the

elevated areas. The road design curvature requirements (ie horizontal radii) also severely

reduce potential points of descent from the Newnes Plateau.

Elevations within the study area range from 305 m Australian height datum (AHD) to 1290 m

AHD. This is a significant elevation differential. The majority of Hartley Valley ranges between

770 m and 810 m AHD and elevations around Lithgow are around 900 m AHD. In contrast, the

elevation along the Newnes Plateau and the existing Darling Causeway generally vary between

1000 m – 1100 m AHD (the observed maximum height of 1290 m AHD is located in the south-

western corner of the study area, and is not part of the Newnes Plateau). Thus, both the Mount

Victoria to Lithgow base case corridor and Newnes Plateau corridor must descend at least 100

m at some point.

Digital terrain models were formed through a combination of 10 metre, two metre and one

metre contours provided from three sources; RTA, SKM, and data held by Cardno (Figure 9.1).

No aerial laser survey was available at the time of assessment. Data was analysed within the

geographic information system (GIS) software MapInfo and a three-dimensional model of

study area gradient was generated to identify key areas of steep slope. As expected, the

ridgelines and valleys of the Newnes Plateau are of greatest gradient, with gradients exceeding

60 per cent in some locations.




Figure 9.1 Study area topography




Technical Report

9.1.2 Watercourses and dams

The study area falls within the hydrological catchment covered by drinking water catchments

Regional Environmental Plan No. 1. It contains at least 95 separate water bodies including

rivers, creeks, lakes, swamps, and major dams. The most significant river within the study area

is the Coxs River in the western portion of the site which is fed by Lake Lyell from the north

and the Lett River from the east. The Lett River runs east to west through Hartley Valley, with

its headwaters in the vicinity of the Newnes Plateau, almost extending to the town of Bell.

Further to the north, Farmers Creek, also with its headwaters on the Newnes Plateau, flows in

a westerly direction through Lithgow, joining up with Lake Lyell to the west. Farmers Creek has

been dammed in its upper reaches and is a supply of drinking water for the city of Lithgow. The

only other major watercourses with the potential to affect/be affected by a corridor include

the upper tributaries of the Grose River (eg Crayfish Creek) to the east of the Darling Causeway

and the Wollangambe River, north of Bell on the plateau. Both of these systems flow to the

east.

The Newnes Plateau area is characterised by a number of swamp areas that become

disconnected and isolated systems in periods of extended dry weather.

The number of naturally formed ponds and swamps on the Plateau is unusual. These features

are associated with unique geological and biological assemblages and were recognised as

priority items for conservation in the corridor identification process. In addition to

environmental issues, there are considerable economic costs associated with road construction

across watercourses.

Existing watercourse mapping held by Cardno was supplemented with data obtained from the

New South Wales Department of Primary Industries – Fisheries (DPI Fisheries). DPI Fisheries

conducted a Key Fish Habitat survey in 2007 to identify areas of aquatic and riparian habitat in

NSW that are important to the maintenance of ‘fish’ (including aquatic invertebrate)

populations and communities and the commercial and recreational fishing industries and which

have the highest priority for being conserved and protected from potential adverse impacts

associated with development. As a by-product, this mapping also provides a detailed extent of

river and lake locations within the state. Watercourses present within the study area are shown

in Figure 9.2.




Figure 9.2 Watercourses and dam/reservoirs

(All watercourses shown with a 75m buffer)




Technical Report

9.1.3 Geology and minerals

The study area has a range of geological regions (Figure 9.3). The majority of the study area,

particularly the Newnes Plateau, is founded upon sandstone, with some deposits of dolerite,

ignimbrite and basalt within these areas. In the south-eastern portion of the study area the

predominant geological formation is volcanic granite, while alluvial sediments are present

along the riparian areas. Due to the sandstone base, common rock and soil formation groups

include the Lambie Group (quartzite, sandstone, siltstone and claystone) and Narrabeen Group

(sandstone, interbedded sandstone and siltstone, claystone and conglomerate). The sandstone

is underlain by Permian Coal measures at variable depths across the region (NSW Department

of Mineral Resources, 1998).

Shallow soils underlain by Hawkesbury sandstone are susceptible to wind and water erosion,

commonly resulting in exposed geological formations reflecting towers. Otherwise known as

Pagoda’s, several of these sandstone formations are known to occur within the study area.

The large sandstone base is a valuable resource due to its potential for extractive industry

operations (eg sand mining). Seams of other mineral deposits (eg coal, shale, clay, torbanite)

are widely present within the valley and are currently being utilised or are planned to be

utilised (Section 9.5).

9.1.4 Mine subsidence

Mining practices have occurred within Lithgow and around the Newnes Plateau since the

1870’s, primarily extracting coal and iron ore (Section 9.1.3). This mining extent has expanded

considerably in recent years with nearly a third of the study area being subject to active

mining licences (Section 9.5). Subsidence due to previous mining has been mapped by the New

South Wales Mines Subsidence Board around the Lithgow region under the Mine Subsidence

Compensation Act, 1961. This mapping is explicitly for areas covered for compensation under

the Act. Other areas where subsidence occurs are addressed and compensated (where

required) through alternative regulatory mechanisms. Indicative mapping of other likely

subsidence areas was not sourced for this assessment but would be available within subsidence

management plans from specific mines. The most likely areas of currently unidentified mine

subsidence areas are believed to be on the northern sides of the Marrangaroo Valley.

Available mine subsidence mapping for compensation areas is shown in

Figure 9.4. The incidence of mine subsidence can add additional cost to potential road

construction and maintenance projects. It also poses hazards associated with altered

hydrological flow regimes. Further investigation into mine subsidence for the area will be

required in the event that a corridor is selected through the Newnes Plateau for further

investigation.




Figure 9.3 Major geological regions




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Figure 9.4 Lithgow mine subsidence district

(Proclaimed 1962, Source: NSW Mine Subsidence Board)

Please note this figures does not include any current mining operations or likely subsidence.

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