2.6.2.1 Methods

Summary

The groundwater numerical modelling is designed to provide probabilistic estimates of groundwater drawdown and changes in the surface water – groundwater exchange flux due to additional coal resource development in the Hunter subregion. Results can be expressed in terms of contour maps of the probability of exceeding a specified depth of drawdown and/or percentiles of drawdown depths. The approach in the Hunter subregion is consistent with the Bioregional Assessment Programme’s companion submethodology M07 (as listed in Table 1) for groundwater modelling (Crosbie et al., 2016), and companion submethodology M09 (as listed in Table 1) for propagating uncertainty through models (Peeters et al., 2016).

The model chain comprises a subregion-wide groundwater model, built specifically for the Hunter subregion and model emulators, trained on a large number of groundwater model simulations, to characterise the prediction uncertainty for two hydrological response variables: dmax, maximum difference in drawdown for one realisation within an ensemble of groundwater modelling runs results, obtained by choosing the maximum of the time series of differences between two futures, and tmax, the year of maximum change.

The modelled changes in surface water – groundwater exchange flux inform the potential hydrological changes on total streamflow, modelled using the Hunter subregion surface water model (see companion product 2.6.1 for the Hunter subregion (Zhang et al., 2018)).

This section summarises the groundwater modelling approach with reference to the Hunter subregion conceptual model and the objectives of the bioregional assessment.