3.7.1 Key findings

A substantial body of transdisciplinary scientific research has greatly improved the understanding of geology, hydrology and ecology of the central-eastern Galilee Basin, where at least seven large coal mining developments are planned to commence operations in the coming decade. This BA has culminated in the impact and risk analysis presented here, which has illustrated that impacts to the groundwater and surface water systems of this area are very likely (greater than 95% chance) to accumulate at a regional scale, due to the spatial and temporal proximity of proposed mining operations. The high likelihood of cumulative hydrological changes means that the impacts previously predicted for individual mines in this region are likely to be larger in both extent and magnitude due to the expected interaction between nearby operations. However, the probabilistic modelling approach generates a broad range of predictions, reflecting inherent uncertainty in important physical parameters applied in the hydrological modelling (e.g. hydraulic conductivity and storage of aquifers). Additionally, the scale of impact affects the system components differently, exemplified by the variability of drawdown impacts for the different modelled aquifers (i.e. near-surface Quaternary alluvium and Cenozoic sediments, Clematis Group and upper Permian coal measures), and the differences in streamflow impacts across the low-flow, high-flow and annual flow components of the surface water regime. Collectively, these findings have important implications for future management of water resources in this region, particularly given the relatively low level of water extraction and use that has occurred in the past.

The modelled component of the CRDP for the Galilee subregion clearly indicates that the zone of potential hydrological change is largely confined to the Burdekin river basin, in particular, the upper catchment area of the Belyando River. Only relatively small areas at the western margin of the zone, where drawdown is less than 0.5 m, occur in the adjacent Cooper Creek – Bulloo river basin. The basis for defining most of the zone is the modelled cumulative groundwater drawdown in the near-surface aquifer, forming separate areas that define the northern part of the zone, and the southern part of the zone (refer to Figure 20 in Section 3.3). The northern sector encompasses the proposed Carmichael, China Stone and Hyde Park coal mines, with the southern part including the proposed Alpha, Kevin’s Corner, China First and South Galilee mines. Complementary surface water modelling, in places partially integrated with the groundwater modelling, indicates that potential cumulative surface water impacts may extend downstream along the main channel of the Belyando River, and the Suttor River below its junction with the Belyando, as far as Lake Dalrymple (i.e. the Burdekin Falls Dam), but not beyond. In particular, these changes in surface water hydrology of the Belyando and Suttor rivers, as well as in some headwater tributaries close to mining areas such as Sandy Creek, Native Companion Creek and North Creek, will most substantially affect the low-flow component of streamflow.

The median estimate (50th percentile) of changes to zero-flow days due to additional coal resource development is for increases of between 20 and 80 days along the Belyando and lower Suttor rivers. This will affect an approximately 250-km long section of the main Belyando River channel (and lowermost Suttor River) below its junction with Native Companion Creek. This change is either less than or comparable to variation that occurs naturally in the Belyando River. However, at the 95th percentile of modelling results these changes to the low-flow regime are substantially greater, with potentially (along similar stream reaches) over 200 days of increased zero flow. While impacts to the low-flow regime may propagate downstream in the Belyando river basin as far as Lake Dalrymple, potential ecological impacts along these stretches may be relatively limited. However, the level of impact experienced by different components of water-dependent ecosystems will vary. Although the water-dependent ecosystems of this region are well adapted to the high level of natural variability in surface water flow and availability, if thresholds of tolerance to variability in surface water are exceeded by sustained changes to the hydrological regime then important components of the ecosystem may be impacted. While many component species of these ecosystems are well adapted to wide variations in hydrological conditions, there are other species that may not be.

Annual flows are predicted to decrease by 5% to 20% in the near vicinity of the additional coal resource developments, and the magnitude and location of these modelled changes are very consistent across the range of probabilistic modelling results (i.e. 5th, 50th and 95th percentiles). Such reductions in modelled annual flow are mainly restricted to the tributary network that feeds into the Belyando River, concentrated along the stretches of Tallarenha Creek, Lagoon Creek and Sandy Creek that run close to the southern mining cluster, and on parts of North Creek and Bully Creek in the northern zone. However, reductions in annual flow above 5% are predicted to dissipate within 10 to 20 km downstream of the mines, to a point where surface water modelling suggests there will be no significant hydrological changes to annual flows in the downstream stretches of the Belyando and Suttor rivers.

It is very likely that cumulative drawdown exceeding 0.2 m in the near-surface aquifer will occur due to the interaction of dewatering the four mines in the southern mining cluster. At the 5th percentile of results the area affected covers about 1663 km² (including the area of the planned mines), although this area is modelled to be as large as 7898 km² at the 95th percentile, highlighting the relatively wide range in the extent and magnitude of drawdown predictions for the Galilee subregion. In the northern part of the zone, cumulative drawdown impacts in the near-surface aquifer due to all three proposed mines (Hyde Park, China Stone and Carmichael) are only evident at the 95th percentile of modelled results, although it is very likely that cumulative impacts due to interaction of the adjacent China Stone and Carmichael mines will occur. The patterns and extents of drawdown in the two deeper aquifers modelled for this BA (Clematis Group and upper Permian coal measures) differ from those of the uppermost aquifer. In particular, these deeper confined aquifers do not occur east of the mines, although drawdown impacts for these layers extend considerably further westwards into the central part of the Galilee Basin than they do for the near-surface aquifer, particularly for the Permian coal-bearing unit.

There are three clusters of springs within the zone of potential hydrological change, and these have a range of ecological, economic and sociocultural values. The proximity of some of these springs to the main mining clusters, particularly in the north, suggests that potential exists for mining-related impacts to occur and affect the ecological functioning of spring ecosystems. Potentially affected springs in the Galilee subregion are the Doongmabulla Springs complex, Permian springs cluster and Triassic springs cluster. A point of some scientific contention and debate in recent times has been the source aquifer(s) of the Doongmabulla Springs complex. The available scientific evidence, as outlined earlier in this product, has been evaluated as part of this assessment, and generally supports the Clematis Group as the main source aquifer for these springs, possibly with some contribution of groundwater from the underlying Dunda beds. However, evaluation of time-series Landsat data indicates that, regardless of the source aquifer, there is heterogeneity in the rate, timing and dynamics of supply for groundwater that supports the 187 individual spring vents of the Doongmabulla Springs complex.

Additional drawdown in excess of 0.2 m in the Clematis Group, as determined from the groundwater analytic element modelling (companion product 2.6.2 for the Galilee subregion (Peeters et al., 2018)), is very likely to affect 181 of the 187 springs in the Doongmabulla Springs complex. This result is consistent between the two different mine dewatering conceptualisations implemented in the analytic element model (AEM), as evaluated for this BA. However, under the alternative groundwater model conceptualisation (no drawdown propagation through the alluvium layer, which is considered to be a more appropriate conceptualisation for these springs), no springs in the Doongmabulla Springs complex are predicted to experience median additional drawdown in excess of 0.2 m. In the Permian springs cluster, five to seven of the springs are predicted to experience additional drawdown in excess of 5 m as their source aquifer is the upper Permian coal measures (Betts Creek beds and equivalents), the main target for coal mine dewatering. However, it is very unlikely (less than 5% chance) that aquifers in the Eromanga Basin (Great Artesian Basin (GAB)) or springs with source aquifers in the Eromanga Basin (e.g. Hutton Sandstone aquifer) will be impacted by drawdown due to additional coal resource development.

Almost half of the streams in the zone of potential hydrological change are groundwater dependent. Where receptor impact modelling results are available, up to 8% of groundwater-dependent streams are ‘at some risk of ecological and hydrological changes’, including additional groundwater drawdown in excess of 5 m, increased low-flow days, increased low-flow day spells and decreased overbank flows. This includes parts of Native Companion Creek, North and Sandy creeks, and the Belyando and Carmichael rivers. Most remaining streams are not groundwater dependent and so are unlikely to be affected by drawdown, including many temporary streams that are potentially impacted (e.g. as they occur in an area where open-cut mining or mine-site infrastructure is planned) but not represented in the surface water model. Up to 0.5% of the non-GDE streams in the zone (with receptor impact modelling) are ‘at some risk of ecological and hydrological changes’ from increased low-flow days and low-flow day spells, mainly on downstream parts of the Belyando and Suttor rivers upstream of Lake Dalrymple.

Most groundwater-dependent ecosystems in the zone of potential hydrological change occur on floodplains (64% of groundwater-dependent vegetation in the zone). Within large uncertainty bounds, up to 3% of groundwater-dependent ecosystems (where receptor impact modelling results are available) on floodplains are ‘at some risk of ecological and hydrological changes’ from additional drawdown and decreased overbank floods along parts of Alpha, North, Sandy and Tallarenha creeks and the Belyando and Carmichael rivers. Remaining groundwater-dependent vegetation in the zone (i.e. non-floodplain ecosystems) relies on groundwater associated with clay-rich plains, loamy and sandy plains, inland dunefields, and fine-grained and coarse-grained sedimentary rocks of the Galilee Basin. Up to 5% of groundwater-dependent vegetation outside of floodplains or wetlands is classed as being ‘at some risk of ecological and hydrological changes’ (again within large uncertainty bounds) near the proposed mines, where additional drawdown is greatest.

Of the 241 ecological assets in the zone, 148 meet criteria for potential hydrological impacts that place them ‘more at risk of hydrological changes’ due to additional coal resource development. A concentration of ecological assets occurs in the ‘Springs’ landscape group within the zone. Although the 200 springs in this landscape group occupy less than 1% of the area of the zone, 48 ecological assets (20% of all ecological assets in the zone) intersect with it, including 16 that are confined entirely to the zone. The Doongmabulla Springs complex is where most of these assets occur, which include the springs themselves as well as some nationally listed plants such as blue devil (Eryngium fontanum) and salt pipewort (Eriocaulon carsonii). Consideration of multiple lines of evidence – including signed digraphs, qualitative mathematical models, interpretation of various products derived from archived Landsat imagery and expert ecological knowledge of the threatened plant species – indicates that this level of drawdown will impact the ecological functioning of some ecological assets; however, there will be considerable variation in response across springs and spring complexes.

Additional drawdown in the deeper aquifer of the Clematis Group may occur in the vicinity of the Jericho town water supply. However, it is very unlikely that drawdown exceeds 2 m for any bore assigned to an economic water-dependent asset that sources water from the Clematis Group, including any of those near Jericho. Potential impacts on many of the bores near Alpha township cannot be ruled out, but it is not possible to quantify drawdown impacts for these bores due to limitations in the resolution of the BA groundwater modelling approach. Thus, this remains a key knowledge gap requiring further local-scale data and a more appropriate site-specific conceptualisation for groundwater modelling.