The representations of surface water – groundwater interactions, mine pit dewatering, coal seam gas (CSG) activities and horizontal and vertical discretisation in the regional model are identified as having the greatest potential effect on model predictions in the qualitative uncertainty analysis. The revised Office of Groundwater Impact Assessment (OGIA) model released for public comment in early 2016 has addressed many of the model data and resource availability and technical issues. The consistency between OGIA 2012 and revised OGIA 2016 model predictions of hydrological change lends confidence to the bioregional assessment (BA) model predictions. The main opportunities to reduce predictive uncertainty in the regional model for this BA are related to the representation of hydrological changes in surficial aquifers that affect surface water – groundwater interactions and groundwater-dependent ecosystems.

The regional groundwater model was developed with the single purpose ‘to provide a suitable tool for assessing the impacts of CSG development on water levels in the aquifers present within the Surat cumulative management area’. It is ‘therefore on its own not necessarily suitable for predicting responses to arbitrary changes in hydrological conditions, developing sustainable water resource management policies, assessing impacts on groundwater-dependent ecosystems or quantifying surface water – groundwater interactions’ (GHD, 2012, p. 50). However, it has the best available representation of CSG development in the Surat cumulative management area and is considered fit for purpose for BA groundwater modelling, with the exception of criteria related to the representation of water fluxes in surficial aquifers.

Hydrological changes arising from coal resource development for two possible futures – the baseline and the coal resource development pathway (CRDP) – are assessed using a probabilistic approach to inform the assessment of direct impacts on groundwater-dependent assets, such as groundwater-dependent ecosystems and economic bores. The focus on the deep regional aquifers targeted by CSG development, means that the conceptual model of causal pathways that describes the logical chain of events ‒ either planned or unplanned ‒ that link coal resource development and potential impacts on water and water-dependent assets will inform the assessment of indirect impacts.

Maximum baseline groundwater drawdown associated with CSG production (in excess of 700 m) is predicted near the towns of Chinchilla and Roma. Baseline groundwater drawdown associated with CSG production in the vicinity of the coal mines is generally less than 10 m. Hydrological changes in the vicinity of the five baseline coal mines are generally within 5 to 10 km (maximum 15 to 20 km) of the modelled pits. Additional groundwater drawdown in the vicinity of proposed coal mines is generally within 20 to 40 km (maximum 50 to 60 km) of the proposed pits. Overall, 86 of the 19,000 economic bores are predicted to experience more than 5 m additional groundwater drawdown in the Maranoa-Balonne-Condamine subregion.

Last updated:
17 October 2018
Thumbnail of the Maranoa-Baloone-Condamine subregion

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