2.6.2.2.2 Gunnedah Basin Regional Model (GBRM)

The GBRM was built for Santos (CDM Smith, 2014). The purpose of the modelling was to assess the potential impacts to the groundwater resources and associated environmental values arising from proposed CSG extractions in the Gunnedah Basin (Figure 6). The GBRM was constructed using MODFLOW-SURFACT code (Panday and Huyakorn, 2008). The model has a rectilinear finite-difference grid, with cell dimensions from 1 to 5 km, and an active model area of approximately 53,200 km². The model was constructed with 24 numerical layers to represent Cenozoic, Cretaceous-Jurassic, Triassic and Permian units with a total thickness of greater than 1400 m. Upon investigation of the suitability of this model for use in BA, it was found that the model has limitations around the conceptualisation of the alluvium and Great Artesian Basin (GAB) layers that prevented it being used for BA purposes (see companion product 2.1-2.2 for the Namoi subregion (Aryal et al., 2018) for more details).