The Australian Government’s Bioregional Assessment Programme provides transparent scientific information to better understand the potential impacts of coal seam gas and coal mining developments on water resources and water-dependent assets. This presentation is an overview of the groundwater modelling that was conducted in six subregions: Gloucester, Hunter, Namoi, Galilee, Clarence-Morton and Maranoa-Balonne-Condamine.
Although each model was developed using different code, they addressed the same research question in a similar way. Each model provides a probabilistic prediction of the changes in drawdown and surface water – groundwater interactions for two alternate futures, a baseline and additional coal resource development. All of these models have been designed to be numerically robust to enable a comprehensive sensitivity analysis to be conducted resulting in a comprehensive uncertainty analysis of the model predictions.
The sensitivity analysis revealed that the model parameters that the predictions are sensitive to are not always the same model parameters that the observations are sensitive to. This has major implications for our confidence in model predictions – a well calibrated model may not be constraining the predictive uncertainty. This has resulted in drawdown predictions where the 95th percentile can be several orders of magnitude greater than the 5th percentile.
Overall, the drawdown at the water table was greatest for open cut coal mines but they had the smallest extent, conversely coal seam gas developments had the least drawdown at the water table but over a greater area. The potential for cumulative impacts on drawdown of the water table exist where developments are close together.
This suite of models is developed independent of the proponents and regulators of coal resource developments and so can provide unbiased information to all stakeholders. To demonstrate transparency of the modelling, all inputs, outputs and executables will be available from http://www.bioregionalassessments.gov.au.