3.7.4 Gaps, limitations and opportunities

This impact and risk analysis allows governments, industry and the community to focus on areas that are potentially impacted by future coal mining in the Galilee Basin when making regulatory, water management and planning decisions. Due to the conservative nature of the BA modelling and the application of the precautionary principle, the greatest confidence in results is for those areas that are very unlikely to be impacted (that is, areas outside the zone of potential hydrological change, or the equivalent zones that can be defined for the two deeper aquifers of the Clematis Group and upper Permian coal measures).

Where the potential for impacts to occur has been identified, further work may be required to improve the predictions of the potential magnitude of impacts to ecosystems and individual assets. This important consideration needs to be explicitly emphasised here; given the regional-scale nature of the assessment and the application of a relatively low resolution modelling approach to assess cumulative impacts across a very broad area, the Assessment team cautions against adopting any specific point-scale results as the basis for future management or regulatory decisions. Although the probabilistic approach to modelling provides a high level of confidence that the reported range that spans the 5th to 95th percentile for a particular hydrological response variable is robust, it would be inappropriate to simply adopt a single probabilistic result (even the median) as basis for future decision making. For such cases, further work incorporating an appropriate level of local data and information may be required to refine and improve confidence in finer-scale modelling results.

Below is a summary of the key knowledge gaps identified during the course of this BA, where understanding the potential impacts of coal resource development could be improved through further targeted research. This is particularly important for the Galilee subregion given it is a greenfield basin for coal production, and so does not have the same history of data and information surrounding baseline coal resource developments as many of the other regions evaluated as part of the Bioregional Assessment Programme. Overall

The CRDP for the BA of the Galilee subregion was originally defined in December 2014 and, once decided, was ‘locked in’ for the duration of this assessment (companion product 2.3 for the Galilee subregion (Evans et al., 2018)). This approach, consistent with companion submethodology M04 (as listed in Table 1) for developing a coal resource development pathway (Lewis, 2014), was needed to provide certainty for the subsequent stages of data analysis and modelling that underpinned the impact and risk analysis. However, by locking in the CRDP at this time, it was not possible to later review or revise the focus for the quantitative analysis, even if mine development changes were made that invalidated aspects of the CRDP.

Future iterations of surface water and groundwater modeling to support management or planning decisions in the Galilee Basin should revisit the choice of individual mining projects (and their development characteristics) in the CRDP and assess if any updates or changes are required. This may be as simple as revising (as needed) the development schedules for the seven coal mines that were modelled in this Assessment. Alternatively, a different selection of proposed mining operations of characteristics may need to be considered in a future iteration of the CRDP, potentially leading to a revised zone of potential hydrological change.

Some consideration could also be given to the merits (or otherwise) of evaluating multiple potential development scenarios for the Galilee Basin to assess a range of future development options. This could, for example, look at varying the number of mining operations both in the central-eastern part of the basin, as well as in the other areas where future mining could proceed (i.e. the northern part of the basin near Hughenden and Pentland, as discussed in Section 3.6). Additionally, future modelling iterations could also evaluate the potential for hydrological interaction between coal mining operations and CSG development in the basin’s most prospective central CSG fairway.

As explained in companion product 2.6.1 (Karim et al., 2018b) and companion product 2.6.2 (Peeters et al., 2018) for the Galilee subregion, the BA modelling approach focussed on the maximum predicted change in hydrological response variables (such as maximum drawdown or annual flow) during the 90-year simulation period of 2013 to 2102. This timeframe covers the proposed operational period of the seven mines in the modelled CRDP, but extends only 30 to 40 years beyond the expected mining period. Consequently, the modelling did not examine potential hydrological changes post-2102, or factor in the long-term effectiveness of rehabilitation or any post mine closure legacy issues such as impact of open pits on groundwater systems. Consequently, there is an opportunity for any future modelling efforts to cover a longer simulation period post-mining, as well as to capture the potential effects of rehabilitation and other post-closure issues. Geology

Significant effort was devoted in this BA to building a regional-scale geological model of the Galilee Basin, integrating it (where applicable) with the existing model of the overlying Eromanga Basin from the GAB Atlas (Ransley et al., 2015). This geological model was used to enhance the Assessment team’s conceptual understanding of the geology and hydrogeology of the Galilee subregion, aid in the development of the groundwater modelling, and provide a suitable framework for visualising the regional-scale stratigraphic and structural architecture. However, despite these important advances in better understanding the geology of the Galilee Basin, there are limitations in the resolution of the regional geological model for supporting more localised applications, for example, mapping the finer-scale structure and stratigraphy of the Galilee Basin and overlying Cenozoic alluvium and regolith/sediment cover within the zone of potential hydrological change.

The Assessment team considers that a significant opportunity exists to improve the surface geological and structural mapping along the central-eastern margin of the Galilee Basin, which would aim to address some notable discrepancies in the current mapping (across different scales). New mapping efforts should ideally incorporate as much information as possible from recent geophysical surveys (as discussed below) and exploration/resource drilling, as well as any available finer-scale mapping or geological modelling that may have been completed to aid in coal exploration or evaluation activities. In particular, compiling and integrating the extensive amount of drill-hole and other company data collected since the mid-2000s would provide new information that would undoubtedly help fill existing knowledge gaps and uncertainties. For example, new or revised structural and stratigraphic data would help to refine the known extents of Galilee Basin stratigraphic units in key areas within the zone of potential hydrological change (Section 3.3). It would also likely improve understanding of the thickness of Cenozoic sediment cover across the eastern part of the Galilee Basin. Information such as this could then be used to refine knowledge of the three-dimensional geological architecture within this main area of interest, potentially leading to more robust and reliable hydrogeological conceptualisations to underpin subsequent modelling.

As previously mentioned, the application of targeted geophysical surveys, such as airborne electromagnetic surveys, would help improve understanding of the geological structure and stratigraphic architecture of the Galilee and Eromanga basins, as well as the overlying Cenozoic sediment/regolith. Airborne electromagnetic data would provide especially valuable data for the upper 200 to 300 m of the subsurface (depending upon the relative conductivity of the various regolith and rock types), thereby improving the definition of near-surface faults that could potentially act as pathways for groundwater flow and interaction between different source aquifers. Such data could also provide useful information on the potential for connectivity between shallow aquifers in Cenozoic sediments and the deeper aquifer systems of the Galilee Basin. Fortunately, the aforementioned Galilee – Eromanga airborne electromagnetics surveys recently completed by Geoscience Australia as part of the Exploring for the Future program (Geoscience Australia, 2017) will be gradually released in the next few years, thereby providing an important source of new data to help address such questions in the future. Groundwater and surface water

The probabilistic approach to modelling undertaken in the Assessment is ideally suited to deal with data and knowledge gaps. The Assessment team focused on integrating data and information that were quality assured and relevant for this regional-scale analysis. However, this meant that some data and information about the Galilee subregion were not used to inform the modelling – for instance, because it was localised and ad hoc in its coverage, lacked reliable metadata to quality assure the data, was not available to the Assessment team at the time of analysis, or because operational constraints prevented collating and scrutinising the data to the standards set out in the BA.

An important aspect of the groundwater modelling approach for this BA was the choice of a wide array of model parameterisations (i.e. within bounds of several orders of magnitude around known point-scale data for parameters such as hydraulic conductivity). These parameter ranges were used to represent the possibility of a variably connected hydrogeological system ranging from highly conductive and highly connected aquifers through to low-conductivity, poorly connected aquitards. This approach provided results that effectively put an upper limit on the area of potentially significant hydrological change (i.e. the definition of the zone of potential hydrological change). In flagging gaps and identifying opportunities for improvement in the modelling, it is important to be aware that more and better data will not necessarily improve the predictions from the regional-scale modelling, but could contribute to better constraining model results for local-scale application.

As previously described, the groundwater modelling approach that underpinned the impact and risk analysis for this BA used a relatively low-resolution AEM with simplified hydrogeological conceptualisation. Although this was considered appropriate to address the overarching objective of the BA for the Galilee subregion (Section 3.3), future groundwater modelling efforts focused on the seven coal mines within the zone of potential hydrological change would be enhanced by adopting a more sophisticated modelling approach. Fortunately, a complementary regional-scale numerical groundwater flow model was developed as a supporting product for this BA (although it was not sufficiently advanced during the course of the BA to allow it to be used as the basis for the BA probabilistic modelling assessment). Thus, the Assessment team recommends that any further groundwater modelling and analysis focused on the proposed mining operations in the zone would benefit by adopting and further developing the existing GBH model (Turvey et al., 2015; companion product 2.6.2 for the Galilee subregion (Peeters et al., 2018)). However, it should be noted that considerable further investment in time and resources would be required to advance the model, and enable it to be used for future cumulative impact assessment. Enhancing the GBH model would help to better understand the overall water balance and hydraulic fluxes between different aquifers and the surface water system, allow for the evaluation of different coal resource development scenarios (i.e. update the CRDP future used as basis for the modelling in this BA), and provide a suitable platform for future planning and management of water resources in the Galilee subregion. The existing strengths and limitations of the GBH model, as well as suggested areas for further work and improvement, are well described in Turvey et al. (2015) and companion product 2.6.2 for the Galilee subregion (Peeters et al., 2018).

The impact assessment would benefit from better characterisation of surface water – groundwater interactions along the Belyando River (and its tributaries) with adjacent Cenozoic aquifers, and an improved understanding of potential for connectivity between aquifers in Cenozoic sediments and deeper aquifers in the Galilee Basin. As mentioned above, the acquisition of new regional-scale airborne electromagnetics data in selected parts of the Galilee Basin in mid-2017 by Geoscience Australia as part of Exploring for the Future (Geoscience Australia, 2017) affords considerable potential to address these issues.

Hydrogeological interpretation of spring source aquifers within the zone (a noted point of current scientific debate) would benefit from additional field-based measurements and data collection, for example, using suitable environmental tracers, geophysical data and application of local-scale groundwater modelling. Additionally, an improved understanding of the geological structure and stratigraphy within the zone (as previously flagged) would help underpin development of a more suitable local-scale hydrogeological conceptualisation to use as basis for further groundwater modelling of potential cumulative impacts to springs and their source aquifers.

An enhanced understanding of water balance components, including recharge, evapotranspiration, inter-aquifer leakage, and groundwater fluxes between the Galilee and Eromanga basins would improve future updates to this Assessment. This work would build upon the higher-level water balance reporting presented for this BA (companion product 2.5 for the Galilee subregion (Karim et al., 2018a)), and include revised/updated estimates of mine water extraction, on-site use and any potential stream releases (if appropriate).

The distribution of surface water model nodes in this BA did not enable a comprehensive extrapolation to network reaches, and resulted in definition of some ‘potentially impacted’ reaches, where hydrological changes could not be quantified. A higher density of surface water modelling nodes and gauging information, located immediately upstream of major stream confluences as well as upstream and downstream of mining operations, would allow the point-scale information to be interpolated to a larger proportion of the stream network. More extensive quantification of hydrological changes along the stream network would also enable better spatial coverage of the results of the receptor impact modelling. Assessing ecological impacts

An improved understanding of the water dependency of the various threatened species, threatened ecological communities and endangered regional ecosystems that occur within the zone of potential hydrological change would assist in their future management, and in understanding their potential to be impacted by coal resource development. For example, the response of various water-dependent species and ecosystems to predicted decreases in the low-flow component of the surface water system would provide valuable insights to better understand how the predicted hydrological changes could lead to potential ecological impacts.

More refined vegetation mapping and ongoing research to enhance the identification of groundwater-dependent ecosystems in the subregion would improve assessment of impacts on ecological water-dependent assets. In particular, groundwater dependency for the purposes of this BA was largely determined by spatial intersection of the ecological assets identified as GDEs (most of which were derived from the National atlas of groundwater dependent ecosystems (GDE Atlas) (Bureau of Meteorology, 2012). with the various landscape groups. This approach estimates groundwater-dependent vegetation, which are but one component of a potentially dependent ecosystem, but not the complexity inherent across the broader ecosystem. Further, it does not assess interaction between groundwater and surface water. In the case of the approach taken in the BA, groundwater dependency is based on one ecological attribute, although there may be more complex hydrological dependencies within the landscape group (i.e. multiple ecosystems may exist within such a group).

The actual dependency on groundwater of the GDEs in the water-dependent asset register is mainly based on a spatial association with accessible groundwater (e.g. in areas where the water table occurs at relatively shallow depths below surface), rather than any actual demonstrated level of dependency. To demonstrate a level of dependency requires more detailed information on the system in question than is currently available. Thus, further research to track key biophysical processes of the groundwater-dependent ecosystems, such as rate of actual evapotranspiration and vegetation growth rates, and interpreting these processes in an ecohydrological framework will improve understanding of the interactions between changes in groundwater availability and the health of terrestrial vegetation that relies on groundwater. This type of analysis can be performed by field measurement and/or use of time-series remote sensing methods (e.g. building on the preliminary use of such remotely sensed data described in Section 3.5.2).

In general, in the Galilee subregion, there is limited understanding of interactions between riverine and terrestrial ecosystems and groundwater. For instance at finer scales, it would be useful to have a clearer understanding of the level of reliance on groundwater in gaining-stream systems such as Dyllingo Creek and Carmichael River, their role in ecological and hydrological connectivity in the landscape, and whether small changes in groundwater pressure might alter refugial pool persistence during dry times. Interactions among groundwater dependent ecosystems are important, as is the representativeness of the indicators selected as receptors of the various landscape class ecosystems. The receptor impact modelling approach was strongly influenced by the availability of expertise; therefore, the suitability of the selected indicators could be re-assessed because the hydrological thresholds were extrapolated based on the assumed responses of quite a small subset of ecosystem components.

As actual water requirements of different plant communities are only approximately known, future assessments and expert elicitation would be assisted by more work to identify suitable bio-indicators of ecosystem condition, or alternative methods of assessing the condition of water-dependent ecosystems. Again, this is likely best performed using field measurement and/or time-series remote sensing data.

The remote sensing techniques applied for this BA (see Section 3.2 and Section 3.5) demonstrates the potential for multi-decadal earth observation data to provide insight into the spatial and temporal dynamics of vegetation and wetlands and can be used to assess potential groundwater dependency of surface features (e.g. such as streams). Although the Hovmöller plots are useful for visualising these data and help to highlight both spatial and temporal features of interest, further quantitative analysis can be done to separate the features that are likely to be:

  • rainfall dependent (i.e. greenness/wetness features that show a strong correlation with rainfall)
  • streamflow dependent (i.e. features distributed along the stream channel network, or that are highly correlated with proximal gauging stations)
  • groundwater dependent (i.e. features that are show high levels of persistence (greenness or wetness) with weak – no correlation with antecedent rainfall conditions).

Placing these types of data into the temporal context of the rainfall record and the spatial context of known groundwater assets further enhances its utility. This information can be placed into additional context through the use of suitable terrain analysis, and with reference to the history of any known disturbance events.

Remote sensing imagery suggests that different spring groups within the Doongmabulla Springs complex have markedly different responses in the persistence of water at surface. This could be due to variations in spring flow to different spring groups, as well as localised variations in vegetation cover and geomorphology (among other factors). This suggests that the response near-surface from changes in groundwater pressure (due to additional coal resource development) could vary between spring groups, which in turn may have a bearing on spring water balance and resilience of ecological communities inhabiting different spring groups. Better understanding of how hydrological changes may propagate through ecological communities at springs would assist with management of the threatened ecological communities and species associated with individual spring groups.

Four water-dependent landscape groups within the zone of potential hydrological change were not considered for receptor impact modelling in this BA due to their relatively small areas of overlap with the zone, and as part of prioritising resources within the operational constraints of the BA. Given that these landscape groups are potentially impacted though, potential impacts to each group could be evaluated more explicitly in future through the application of receptor impact modelling. More generally, there is also an opportunity to address some of the limitations of the overall receptor impact modelling approach identified for specific cases (see companion product 2.7 for the Galilee subregion (Ickowicz et al., 2018)). For example, this could focus on:

  • considering the interconnections between adjacent landscape groups (or classes) in more detail, particularly in cases where impacts on different trophic structures outside of the affected class are plausible
  • expanding the receptor impact modelling focus to also consider short-term pulse perturbations (relative to the long-term press perturbations that arise from more sustained changes)
  • investigating how the boundaries of specific landscape classes and their responses to hydrological change may change over time. Assessing impacts to economic assets

The assessment of impacts to groundwater economic assets for this BA was done using the management framework of the Water Plan (Great Artesian Basin) 2006 and its associated resource operations plan. However, this plan was superseded in September 2017 by the Water Plan (Great Artesian Basin and Other Regional Aquifers) 2017, implemented through a new water management protocol. Consequently, there is now an opportunity to update the account of impacts to economic groundwater assets in light of these recent management changes. Importantly, the new planning regime now specifically includes groundwater sourced from the upper Permian coal measures (e.g. Betts Creek beds) within the Galilee Basin which, as shown from the modelling undertaken for this BA, is expected to be the hydrostratigraphic unit in which drawdown will be of greatest extent and magnitude. Consequently, the register of water-dependent assets compiled for the Galilee subregion should be updated to reflect the new planning arrangements. These changes will likely mean that the number of groundwater economic assets potentially affected by drawdown will be greater than the five assets reported in Section 3.5.2 for this BA.

The town water supply bores at Alpha are part of an economic asset that occurs within the zone of potential hydrological change. However, as explained in Section 3.5.3, the outputs of the groundwater modelling for this BA were not able to accurately predict water level changes for bores that source water from the Cenozoic sediment aquifer near Alpha. Consequently, it is not possible on the basis of the BA modelling to evaluate the potential for groundwater impacts to adversely affect the Alpha town water supply borefield. Clearly, these bores are part of an important water-dependent asset in the zone, and there is a need for further local-scale hydrogeological assessment, in order to develop an appropriate management response to any potential impacts due to additional coal resource development.

Additional information around the depth of bore screens and stratigraphic information for those bores for which the source aquifer is currently unknown would improve the ability to assess the potential for impact from the groundwater modelling results. Further, knowledge of which aquifer a bore taps into will improve estimates of water take from different aquifers, which has potential implications for the regional aquifer water balance. Water quality

Due to large yearly variation in annual streamflow volumes in the Belyando River, changes in hydrology due to additional coal resource development may not necessarily lead to substantial changes at a regional scale in many water quality parameters, such as salinity, at least beyond the naturally occurring annual variability already experienced. However, available baseline water quality data are patchy. Sampling programs to determine water quality in wet and dry seasons in different parts of the river basin would provide an improved regional baseline and could be beneficial for future studies, such as assessment of potential changes in water quality parameters that could occur, with a shift in the relative contributions of surface runoff and groundwater to streamflow.

Available groundwater quality data are relatively sparse in many parts of the Galilee subregion, including within the zone of potential hydrological change. Existing groundwater analytical data for this area cover broad timeframes and a range of different sampling and analysis methods, meaning that there is considerable variability in the coverage (both areally and with depth) and quality of data. Sufficient baseline hydrochemistry data measured at a number of key sites (guided with reference to the groundwater modelling predictions from the BA) would be important to provide a useful reference standard for the key aquifer systems, against which potential future changes to groundwater quality due to additional coal resource development could be assessed. Particular emphasis could be placed on collecting a suite of stable isotopes and trace element data that may assist in determining important hydrogeological characteristics, and which would help to better define groundwater flow paths both within and between different aquifers, improve the characterisation of the source aquifers for various springs (especially the Doongmabulla Springs complex), evaluate the likelihood of aquifer compartmentalisation, and improve the definition of aquifer recharge processes and groundwater residence times within the main aquifers. Climate change and land use

In comparing results under two different futures in this assessment, factors such as climate change and land use are held constant. Future assessment iterations could look to include a broader range of potential climate scenarios, along with a more accurate representation of competing land and water uses (particularly in and around the zone of potential hydrological change). Incorporating a broader range of development types (such as water used for agricultural purposes) and other potential hydrological stressors to the system would generate a more comprehensive understanding of cumulative impacts on the landscapes and water resources of the region. Identifying potential interactions among certain types of land use and the hydrological and chemical effects of coal resource development would test some of this BAs underlying assumptions. If such interactions are found to be minimal, this would help support the assumption that land-use differences over time can be 'factored out' by the differential approach currently used in the assessment. Of course, adding further complexities and a much broader scope to the modelling scenarios would likely require increased resourcing and novel assessment approaches, in order to generate robust impact predictions.

There is a relatively low density of meteorological stations in the Galilee subregion which has implications for the development of some types of hydrological models. Therefore, to increase the level of predictability of rainfall estimates for rainfall-runoff modelling, it would be beneficial if additional rainfall and temperature gauges were installed at key areas in the subregion (such as along the eastern margin, particularly near the zone of potential hydrological change where multiple coal resource developments are planned). While other meteorological variables would also benefit from being measured with enhanced spatial density, the overall gain would be minimal when compared to measuring rainfall with greater accuracy. Improved resolution in meteorological parameters, such as temperature and rainfall, would improve the resolution of site and semi-regional scale water balances in areas such as the Doongmabulla Springs complex, or the northern Belyando river basin in the vicinity of the proposed Carmichael, China Stone and Hyde Park coal mines.

Last updated:
6 December 2018
Thumbnail of the Galilee subregion

Product Finalisation date