2.6.2.3 Model development

Summary

The regional analytic element groundwater model (GW AEM) is developed to simulate the drawdown under the coal resource development pathway (CRDP) and under the baseline coal resource development (baseline), at the groundwater receptors in the weathered zone. The difference in drawdown between CRDP and baseline is due to the additional coal resource development. The GW AEM also provides the change in groundwater level in the weathered zone underneath the Avon River and Karuah River alluvium. This will provide the boundary condition for the alluvial groundwater models of the Avon River and Karuah River.

The conceptualisation of the regional model allows the hydraulic properties of the interburden and coal seams to decrease exponentially with depth and to stochastically vary the number and position of coal seams, the presence of seismic faults and the position of subseismic faults.

To assess the impact of coal resource development on groundwater receptors situated in the alluvium of the Avon and Karuah systems and on the surface water – groundwater flux for these river systems, two MODFLOW groundwater models are developed.

They are both two-layer models in which the upper layer represents the alluvial aquifer and the lower layer serves to interact with the regional groundwater model that predicts the change in groundwater level in the underlying weathered zone due to coal resource development.