2.1.2 Geology

Summary

An existing three-dimensional geological model was adapted to define regional-scale geology for modelling impacts of coal resource development on water-dependent assets in the Namoi subregion. The model was adapted from CDM Smith’s geological model that was developed for Santos’ Gunnedah Coal Seam Gas Project. The CDM Smith model was modified in areas where more updated geological knowledge was available, namely in the Surat Basin and the alluvium. The geological model also forms the basis of the conceptual modelling of causal pathways and for the hydrogeological modelling.

The geological model is an interpretation of the subsurface geology and structure of the Gunnedah and Surat basins. The tops and bottoms of each stratigraphic layer in the Gunnedah Basin were extracted from the CDM Smith model, and in the Surat Basin from the Water Resource Assessment of the Great Artesian Basin (GABWRA) and the Hydrogeological Atlas of the Great Artesian Basin (GAB Atlas). The thicknesses for each modelled layer were calculated from these surfaces.

The geological model is just one of many possible representations of the system based on information available. However, the geological model is considered to provide a fit-for-purpose tool at a regional scale to aid in understanding how coal resource development may affect water resources and water-dependent assets, and for the conceptual modelling of causal pathways. The model can be updated and refined in the future with the input of additional or new datasets.