3.7 Conclusion


The future development of seven large coal mines in the central-eastern Galilee Basin is very likely (greater than 95% chance) to lead to cumulative hydrological changes in regional groundwater and surface water systems. These changes will affect a larger area (i.e. of groundwater drawdown) and total length of stream network than previously predicted from any individual mine-scale impact assessments. The combined extent of changes to surface water and groundwater above specified thresholds define the zone of potential hydrological change for the Galilee subregion, outside of which impacts to water resources and water-dependent assets are very unlikely (less than 5% chance) to occur.

Changes to surface water systems are mostly confined to the Belyando river basin (and the lowermost parts of the Suttor river basin downstream of its junction with the Belyando), and are likely to have the greatest level of impact on the low-flow component of streamflow, such as zero-flow days. Increases in the number of zero-flow days accumulate along the length of the affected stream network, as the various local tributaries affected by mining impacts join the main channel of the Belyando River. Cumulative streamflow changes are greatest along an approximately 250-km long stretch of the main channel of the Belyando River from downstream of its junction with Native Companion Creek, as far as Lake Dalrymple (Burdekin Falls Dam). Changes in hydrological response variables for the high-flow and annual flow components of streamflow will also occur, although these impacts are relatively less than those associated with low flow. Many of the species that inhabit water-dependent ecosystems in the region are adapted to the high levels of natural variability in these surface water systems. However, if thresholds of tolerance to variability are exceeded by sustained changes to the hydrological regime then it is possible that important components of the water-dependent ecosystems may be impacted.

Cumulative groundwater impacts due to dewatering the seven coal mines in the Belyando river basin will variably affect three main groundwater systems, including near-surface Quaternary alluvium and Cenozoic sediments, and the deeper confined aquifers of the Clematis Group and upper Permian coal measures (e.g. Betts Creek beds and stratigraphic equivalents). The total area of the groundwater component of the zone of potential hydrological change, which affects the near-surface aquifer, is well over 13,000 km2, forming two geographically separate areas. In the south, cumulative groundwater impacts are very likely to occur around the four proposed mines at South Galilee, China First, Alpha and Kevin’s Corner. However, in the north, cumulative drawdown in the upper aquifer due to interaction caused by dewatering of Carmichael, China Stone and Hyde Park is only evident at the 95th percentile of modelling results. The pattern and spatial extent of drawdown zones for the two deeper confined aquifers (Clematis Group and upper Permian coal measures) differs substantially from that of the alluvial aquifer, occurring only to the west of the mines and extending much further beyond the extent of the zone, towards central parts of the Galilee Basin. Drawdown in the coal-bearing unit is particularly large, and very likely (>95% chance) to exceed 5 m in most places in the modelling domain.

The impact and risk analysis of the Galilee subregion is primarily a cumulative, regional-scale analysis focused on the effects of the seven coal mines modelled in the coal resource development pathway (CRDP). This focus does limit the degree to which results can be used to assess local-scale effects. Furthermore, there are important knowledge and data gaps that may add to the uncertainty around future predictions of local impacts. These gaps include: lack of ecohydrological understanding of vegetation water requirements and how these relate to hydrological response variables, long term effectiveness of rehabilitation and post mine-closure legacy issues, and the absence of long-term, high-quality monitoring data relating to ecological components, groundwater levels, and water quality.

There is considerable opportunity to build upon the work undertaken for this bioregional assessment (BA) and further enhance the understanding of impacts and risks to the subregion’s water resources and many water-dependent assets.

Areas outside of the zone of potential hydrological change are very unlikely to be impacted by the seven coal mines modelled in the coal resource development pathway (CRDP). Given the high degree of confidence in ruling out areas based on the BA modelling approach, more refined modelling and impact analysis using higher-resolution local-scale information could be applied to the central-eastern Galilee Basin to enhance the understanding of cumulative impacts at a far more detailed scale than originally assessed. A purpose-built numerical groundwater flow model (the Galilee Basin hydrogeological (GBH) model), developed as a complementary tool for this BA, could be adopted as a robust starting point for any future finer-scale analysis of cumulative impacts, especially for the series of stacked aquifers that occur in the eastern Galilee Basin (although considerable investment would be required to enable this). There are also other opportunities to improve and update the findings from this BA, including integrating the wealth of geological and geophysical data acquired during the past decade to enhance the current understanding of the structural and stratigraphic architecture around the area of the proposed coal mining developments. This work could form the foundation for enhanced hydrogeological conceptualisations and more sophisticated modelling in areas of known uncertainty or complexity, such as the Doongmabulla Springs complex. There is also considerable scope for applying time-series remote sensing data to enable a better understanding of variability in ecosystem responses to natural climate cycles, thereby providing an important level of baseline knowledge against which any future impacts could be compared. Further research opportunities to improve knowledge of the complex interactions between riverine and terrestrial ecosystems, and groundwater systems, would also help address important knowledge gaps recognised from this BA.

The findings from this BA can be used to help the Australian and Queensland governments, the coal mining industry and members of the community to make better-informed decisions about the management of water resources in the Galilee subregion. Further, these results can be used to focus future monitoring networks, critical for testing and validating (or invalidating) the Assessment’s predictions of impacts and risks. The modular nature of the Methodology for bioregional assessments of the impacts of coal seam gas and coal mining development on water resources (BA methodology) (Barrett et al., 2013) means that various components of the investigation can also be updated in future as the need arises, such as any future changes in the CRDP or the availability of specific coal mine project data to include in any revised future modelling and analysis. Other data and information, such as the water-dependent asset register and lists of hazards and causal pathways, will remain relevant for future assessments. The full suite of data, information and knowledge generated during the course of the BA for the Galilee subregion is available at www.bioregionalassessments.gov.au/assessments/galilee-subregion.

Last updated:
6 December 2018
Thumbnail of the Galilee subregion

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