3.4 Impacts on and risks to landscape classes

Summary

The diverse natural and human-modified ecosystems in the Galilee assessment extent were classified into 31 landscape classes, which were aggregated into 11 landscape groups based on their biophysical characteristics and dependence on groundwater and/or surface water. Landscape classes that occur outside of the zone of potential hydrological change are very unlikely (less than 5% chance) to be impacted by additional coal resource development and include more than 100,000 km² of groundwater-dependent vegetation, 387,000 km of streams, 8,900 km² of wetlands and 1,359 springs in the assessment extent. Receptor impact modelling was undertaken for five of the 11 landscape groups in the assessment extent.

Estimates of overall ecosystem risk integrate understanding from the conceptual model of causal pathways, hydrological and ecological modelling, and expert opinion. The strength of this approach lies in its ability to provide a measure of relative ecosystem risk, emphasising where further attention should focus using local-scale modelling. Importantly, this integrated analysis approach also provides clarity around the ecosystems that can be ruled out from further assessment on the basis of impacts being very unlikely.

‘Springs’ landscape group

Groundwater flow from springs supports endemic flora and fauna, the building of peat mounds and associated groundwater-dependent ecosystems. The Doongmabulla Springs complex includes 187 individual spring vents near the Carmichael River and its tributaries. The available hydrogeological evidence indicates that the Clematis Group aquifers, rather than the deeper Permian aquifers, are the primary source aquifers for these springs. Springs are not represented directly in the groundwater analytic element model (AEM), with drawdown estimated by comparing model layer drawdown (for the appropriate source aquifer) at the known location of the springs. Alternative AEM conceptualisations were used to evaluate the likely scale of overestimated drawdown predictions at some springs, including the Doongmabulla Springs complex. The original AEM conceptualisation predicts that drawdown due to additional coal resource development is very likely to exceed 0.2 m in the source aquifer of 181 of the 187 springs in this complex. However, estimates using the alternative AEM conceptualisation indicate that no springs are predicted to experience median additional drawdown in excess of 0.2 m.

In the Permian springs cluster, it is very likely that at least 5 springs and very unlikely that more than 7 springs will experience drawdown in excess of 5 m in the upper Permian coal measures due to additional coal resource development. Potentially affected springs include the Albro, Lignum, Storys and Mellaluka springs. Drawdown for the 12 springs in the Triassic springs cluster cannot be reliably estimated by the AEM, but is likely to fall within the range predicted for the Clematis Group model layer. None of the other 1353 Great Artesian Basin (GAB) springs of the Eromanga Basin are in the zone of potential hydrological change.

‘Streams, GDE’ landscape group

Almost half of the streams in the zone of potential hydrological change are interpreted to be groundwater dependent (2801 km). Potential hydrological impacts include additional groundwater drawdown in excess of 5 m, increased low-flow days, increased low-flow spells and decreased overbank flows. Expert opinion, modelled hydrological changes and changes to ecological indicators, such as woody riparian vegetation and mayfly nymph density, indicate that up to 8% of groundwater-dependent streams (where quantifiable) in the zone of potential hydrological change are ‘at some risk of ecological and hydrological changes’. This includes parts of Native Companion, North and Sandy creeks and the Belyando and Carmichael rivers.

Streams, non-GDE’ landscape group

Remaining streams in the zone of potential hydrological change are not groundwater dependent (3484 km) and so are unlikely to be affected by groundwater drawdown. This includes most of the temporary streams (1028 km) in the zone of potential hydrological change that are potentially impacted but not represented in the surface water model, including parts of Bully, Lagoon, North, Sandy and Tomahawk creeks and Carmichael River. Potential hydrological changes include increased low-flow days and low-flow spells along up to 177 km of temporary streams in the zone. The analysis indicates that up to 0.5% of non-GDE streams with receptor impact modelling are ‘at some risk of ecological and hydrological changes’, mainly in downstream parts of the Belyando and Suttor rivers.

‘Floodplain, terrestrial GDE’ landscape group

Most groundwater-dependent vegetation in the zone of potential hydrological change occurs on floodplains (2433 km² or 64% of groundwater-dependent vegetation in the zone). It is very unlikely that more than 296 km² of groundwater-dependent vegetation on floodplains experiences more than 5 m of drawdown due to additional coal resource development. Over half of the groundwater-dependent ecosystems (716 km²) in the zone are located on floodplains intersected by temporary streams that are potentially impacted but not represented in the surface water model. Potential hydrological changes include decreased overbank flows that may affect up to 355 km² of floodplain vegetation. Expert-derived estimates indicate that up to 3% of groundwater-dependent vegetation on floodplains are ‘at some risk of ecological and hydrological changes’ (where changes can be quantified), and these occur mainly along parts of Alpha, North, Sandy and Tallarenha creeks and the Belyando and Carmichael rivers.

‘Non-floodplain, terrestrial GDE’ landscape group

Approximately one-third of groundwater-dependent ecosystems in the zone (1189 km²) rely on groundwater associated with clay plains, loamy and sandy plains, inland dunefields, or fine-grained and coarse-grained sedimentary rocks. It is very unlikely that more than 68 km² (or 2% of groundwater-dependent ecosystems in the zone) experiences more than 5 m of drawdown due to additional coal resource development. This landscape group is located outside of alluvial river and creek flats and is therefore unaffected by changes to surface water flow regimes. There is some level of risk of a small change in percent foliage cover to up to 5% of non-floodplain, groundwater-dependent ecosystems located outside of floodplains or wetlands, particularly near the proposed coal mines where additional drawdown is greatest.