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3-4 Impact and risk analysis for the Maranoa-Balonne-Condamine subregion

Executive summary

Condamine river weir on Darling Downs in Queensland, 2005 Credit: Arthur Mostead © Commonwealth of Australia (Murray–Darling Basin Authority)

This product describes the analysis of potential impacts of coal seam gas (CSG) and coal mining developments on water resources and water-dependent assets in the Maranoa-Balonne-Condamine subregion. This impact and risk analysis identified where water resources and water-dependent assets are very unlikely to be impacted (with a less than 5% chance), or are potentially impacted. Governments, industry and the community can then focus on the areas that are potentially impacted and apply local-scale modelling when making regulatory, water management and planning decisions.

The Maranoa-Balonne-Condamine subregion covers 144,890 km2 and is mainly within the Queensland part of the Murray–Darling Basin, with a small area in NSW. It includes the headwaters of the Condamine River and the Maranoa River as well as the floodplains of the Upper Darling Plains. The main cities and towns are Toowoomba, Warwick, Dalby, Chinchilla, Roma, St George and Goondiwindi.

The geographic area where impacts were assessed, known as the assessment extent, covers 129,956 km2.

The impact and risk analysis considered two potential coal resource development futures:

  • baseline coal resource development (baseline): a future that includes all coal mines and coal seam gas (CSG) fields that were commercially producing as at December 2012 and five CSG fields reported in the Annual report 2014 for the Surat underground water impact report
    • In the Maranoa-Balonne-Condamine subregion, there are five baseline coal mines (Cameby Downs Mine, Commodore Mine, Kogan Creek Mine, New Acland Coal Mine Stage 2 and Wilkie Creek Mine) and five baseline CSG fields (Australia Pacific Liquefied Natural Gas (LNG) Project, Santos Gladstone LNG Project, Queensland Curtis LNG Project, Surat Gas Project and Ironbark Project).
  • coal resource development pathway (CRDP): a future that includes all coal mines and CSG fields that are in the baseline as well as the additional coal resource development (those that were expected to begin commercial production after December 2012, including expansions of baseline operations)
    • In the Maranoa-Balonne-Condamine subregion, there are two additional open-cut coal mines (New Acland Coal Mine Stage 3, an extension to the existing New Acland Coal Mine, and The Range, a proposed open-cut mine).

The difference in results between CRDP and baseline is the change that is primarily reported in a bioregional assessment (BA). This change is due to additional coal resource development.

Potential hydrological changes

Impacts to water-dependent landscapes and assets are mostly caused by changes to groundwater in the regional watertable. The regional watertable represents the upper groundwater level within the near-surface aquifer, and may exist in different geological layers. Near the two additional coal resource developments it occurs in the alluvium, as well as the Main Range Volcanics and the Walloon Coal Measures. Springs and groundwater bores may be affected by hydrological changes in deeper geological layers, which may have ecological repercussions for surface ecosystems surrounding springs.

Predicted groundwater drawdown was used to define a zone to ‘rule out’ potential impacts. The zone of potential hydrological change is the area with at least a 5% chance of greater than 0.2 m drawdown due to additional coal resource development. This threshold is consistent with the most conservative minimal impact thresholds in NSW and Queensland state regulations, and is close to the practical resolution limits of modelled and measured drawdown. Because surface water modelling was not undertaken for this subregion, groundwater hydrological changes alone were used to define the zone.

Outside the zone of potential hydrological change, potential hydrological changes (and hence impacts) are very unlikely. Inside the zone, further work is required to determine whether the hydrological changes in the zone translate into impacts for water‐dependent assets and landscapes.

Drawdown in the regional watertable under the baseline has at least a 5% chance of exceeding 0.2 m in an area of 17,132 km2. Baseline drawdown in the regional watertable is typically less than 20 m and occurs in the east and north of the subregion, where deeper geological layers, including the Walloon Coal Measures, outcrop at the surface.

Drawdown in the regional watertable due to additional coal resource development is very unlikely to exceed 0.2 m, except within 15 km of New Acland Coal Mine Stage 3 and within 25 km of The Range coal mine. The area in the zone of potential hydrological change is 1544 km2 (11 times less than under the baseline), and includes 1095 km of streams.

Near New Acland Coal Mine Stage 3, additional drawdown in the regional watertable in excess of 0.2 m is very likely (greater than 95% chance) over an area of 7 km2 (containing 4 km of streams) and very unlikely to extend beyond an area of 134 km2 (containing 55 km of streams). Median baseline drawdown is less than 3.6 m in all model layers. Median additional drawdown is up to 65 m in the regional watertable next to the modelled pits, and up to 25 m in the Walloon Coal Measures, the target of CSG production, which is up to 120 m thick in this area.

Near The Range coal mine, additional drawdown in the regional watertable in excess of 0.2 m is very likely over an area of 377 km2 (containing 231 km of streams) and very unlikely to extend beyond an area of 1409 km2 (containing 1040 km of streams). Median baseline drawdown, associated with CSG fields to the south-west, is up to 8.3 m in the regional watertable and up to 82 m in the Walloon Coal Measures, which is up to 170 m thick in this area. Median additional drawdown is up to 10.2 m in all model layers in the vicinity of The Range coal mine.

Impacts on and risks to landscape classes

The heterogeneous natural and human-modified ecosystems in the Maranoa-Balonne-Condamine subregion were classified into 34 landscape classes, which were aggregated into five landscape groups based on their likely response to hydrological changes. Overall, more than 35,000 km2 of remnant vegetation, 59,000 km of streams, 1600 km2 of wetlands, 177 springs and 93,000 km2 of productive land within the assessment extent are very unlikely to be impacted, because they are outside the zone of potential hydrological change.

Within the zone of potential hydrological change, most of the area falls into two landscape groups with limited or no potential impact due to changes in the water regime arising from coal resource development:

  • ‘Dryland remnant vegetation’ (49% of the zone)
  • natural environments and dryland agriculture in ‘Human-modified’ (44% of the zone).

These areas are ruled out of potential impacts because they rely on incident rainfall and local surface water runoff and therefore are not considered water dependent for this assessment.

Outside the modelled mine pits, landscapes that are potentially impacted include:

  • Floodplain or lowland riverine (including non-GAB GDEs)’: 20 km2 of remnant vegetation and 299 km of streams, which are predominantly not groundwater dependent. Median drawdown due to additional coal resource development for floodplain or lowland riverine GDEs associated with alluvial or basalt aquifers is in addition to the range of natural watertable fluctuation (<2 m) and of a comparable magnitude
  • GAB GDEs (riverine, springs, floodplain or non-floodplain)’: 76 km2 of remnant vegetation and 319 km of temporary streams connected to GAB aquifers. None of the 153 GAB springs in the assessment extent are within 50 km of where there is at least a 5% chance of exceeding 0.2 m drawdown due to additional coal resource development in the source aquifer identified for each spring. Median additional drawdown is in addition to and of a comparable magnitude to the range of natural watertable fluctuation (<2 m)
  • ‘Non-floodplain or upland riverine (including non-GAB GDEs)’: 12 km2 of remnant vegetation and 477 km of temporary upland streams and wetlands that are not associated with floodplains or GAB GDEs. None of the 24 springs in the assessment extent that are connected to aquifers overlying the GAB (non-GAB springs) are potentially impacted. Local impact assessment and modelling is required to supplement regional groundwater model predictions of localised cumulative drawdown (<5 m) that may affect ecosystems dependent on permeable rock or basalt aquifers
  • ‘Human-modified’: 2 km2 of water-dependent human-modified land. Median additional drawdown in excess of 2 m may affect 0.2 km2

Impacts on and risks to water-dependent assets

Of the 2660 water-dependent assets nominated by the community for the subregion, most (2495) are very unlikely to be impacted because they experience less than 0.2 m drawdown due to additional coal resource development. This includes protected reserves, parks, bird habitats or key environmental assets, and surface water features classified as a spring, floodplain, lake, reservoir, estuary, marsh, sedgeland, bog, spring, soak, waterhole, pool, rock pool or billabong.

However, 130 water-dependent assets are subject to potential hydrological change due to additional coal resource development. This does not mean that these assets are definitely impacted – finer resolution models are required for that local-scale assessment of impact. On the basis of this assessment, however, there is not compelling evidence to rule out impacts for the following water-dependent assets:

  • 115 of the 2215 ecological assets, including 41 ecosystems. This includes potential habitats of 4 threatened ecological communities and 18 species listed under the Commonwealth’s Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act); an additional 6 endangered regional ecosystems and potential habitats of 11 species listed under Queensland’s Nature Conservation Act 1992; and 2 riparian vegetation assets.
  • 14 of the 310 economic assets, including one licensed surface water access right and 13 groundwater economic assets comprising 163 bores (7 water access rights and 6 basic water rights (stock and domestic)). Of these 163 bores, 17 to 30 are predicted to experience additional drawdown in excess of 5 m.
  • 1 of the 135 sociocultural assets, the Barakula State Forest, near Miles in Queensland, is located where drawdown in the regional watertable due to additional coal resource development exceeds 0.2 m with greater than 5% chance. It is very likely that 21 km2 (0.7% of the 3092 km2 forest) experiences more than 0.2 m of drawdown due to additional coal resource development.

Consultation with Traditional Owners in the Maranoa-Balonne-Condamine subregion identified an additional 56 Indigenous assets. Of these, 35 are cultural values associated with animals and plants that do not have geographic location information, which means they cannot be specifically assessed for impacts due to additional coal resource development.

Conclusion

Assessment results flag where future efforts of regulators and proponents can be directed, and where further attention is not necessary. Extending this Assessment should focus on incorporating surface water modelling and representing surface water – groundwater interactions.

Key knowledge gaps identified below detail where confidence in this Assessment can be improved through further work. For example, if new coal resource developments emerge in the future, the data, information, analytical results and models from this Assessment would provide a comprehensive basis for a subregion-scale re-assessment of potential impacts under an updated CRDP. The full suite of information is provided at www.bioregionalassessments.gov.au. Users can explore detailed results (including information for individual landscape classes and assets in the subregion) using a map-based interface in the BA Explorer, available at www.bioregionalassessments.gov.au/explorer/MBC.

Key knowledge gaps identified for this Assessment are:

  • hydrological modelling: the greatest opportunities to improve model predictions in this Assessment involve the incorporation of surface water modelling and surface water – groundwater interactions to quantify changes in streams and the regional watertable that may occur as a result of coal resource development. Using the revised OGIA 2016 model, with improved representation of regional geology, hydrostratigraphy and faults, as well as model discretisation, parameterisation and calibration, would increase confidence in this Assessment, as would water quality models and data
  • assessing impacts in the landscape: assessment of potential impacts to the landscape was limited to an overlay analysis. While this is valuable, receptor impact models would provide better indicators of potential changes in ecosystems. Improved knowledge about the nature of a species’ or community’s water dependency and identification of the geographic location of Indigenous cultural assets would also increase confidence in this Assessment
  • model resolution: there is a high level of confidence in the ability of the OGIA model to reflect broad-scale hydrological changes related to the cumulative impacts of coal resource development. However, while the resolution of the OGIA model is considered fit for purpose, a finer resolution model would be more suitable for local-scale analysis
  • climate change and land use: factors such as climate change or land use were held constant for the two coal resource development futures. Future assessments could include these and other stressors to more fully predict cumulative impacts of coal resource development.
Last updated:
12 July 2017