2.3.5.4 Gaps

Coal mine operations in the Hunter subregion are mature, and have been ongoing for more than 100 years. Many of the hazards from mining have been observed in the subregion (e.g. subsidence, changes to aquifer connectivity, depressurisation of aquifers and disruption of natural drainage) and their potential effects on water resources and water-dependent assets are recognised. The local experience of coal mining hazards and their effects is supported by international experience, and the risks from many hazards are managed through existing regulatory controls on mine planning and operations management.

One hazard that has occurred, but is not well documented, is subsidence in and around the subregion’s coastal lakes due to underground mining. Depth of longwall mining and properties of the interburden influence the extent of subsidence at the surface and magnitude of changes in hydraulic properties due to fracturing. The latter is hard to predict, but is explored through the wide range of hydraulic properties in the groundwater modelling. The extent to which flora and fauna within coastal lakes (e.g. seagrass beds) have been impacted by subsidence historically is not well known. To manage the risks from subsidence, NSW regulations require additional conditions and approvals from proponents for mines that will operate close to, or beneath, lakes and estuaries.

The causal pathway groups link hazards to subregion assets but do not predict the impact. Numerical modelling is needed to determine whether the magnitude of change from mining activities and strength of connection to each subregion asset, as mediated by existing regulatory controls, are sufficient to impact each asset. This is a gap being addressed through the quantitative modelling within the BAs. However, while there is a good conceptual understanding of the potential for subsidence to impact coastal lake habitats, the groundwater modelling does not represent base-level changes in lake beds from subsidence.