2.3.5.4 Gaps

This section draws together all the elements up to specifying causal pathways for baseline and CRDP, and includes the gaps in each of the individual components.

The level of specification in the potential causal pathways represented reflects the current state of knowledge. In general, data limitations in the Gloucester subregion contribute importantly to gaps in the Assessment team’s conceptualisation of the potential causal pathways. For instance, limited geological datasets, sparse data on surface water – groundwater interactions and the lack of current specification on some of the operational water management all affect the conceptualisation of potential causal pathways. The specific nature of these data limitations are typically explored in more detail through the development of surface water and groundwater models (refer to the companion products 2.6.1 and 2.6.2 for the Gloucester subregion (Zhang et al. (2018) and Peeters et al. (2018)) respectively).

For the flow pathways due to coal mines and CSG operations the greatest gap is knowledge of the faults and fractures of the geological layers. For example, there is not a clear idea of the location of all the largest faults in the geological Gloucester Basin, and both the nature, location, regional versus local extent, hydraulic properties and extent of smaller potential pathways between adjacent layers is only known theoretically. This makes any absolute statement on the spatial extent of a groundwater level decline due to CSG operations difficult. Uncertainty analysis does allow a probabilistic estimate of maximum groundwater level decline at the regional scale and the drawdown propagation is minimal (refer to Section 2.6.2.8 in companion product 2.6.2 for the Gloucester subregion (Peeters et al., 2018)). Because these realisations were random and modelled at the regional scale, no general comment can be made about potential local impacts of any single future well.

When placing each project in baseline and CRDP in its spatial context with landscape classes and GDEs, the underlying data is of such a large scale that it only coarsely covers the small Gloucester PAE. To this end the final classification was greatly generalised to five landscape classes in the ‘Groundwater-dependent ecosystem (GDE)’ landscape group and seven landscape classes in the ‘Riverine’ landscape group; at the regional scale of analysis, reach lengths of 1 to 3 km were considered too detailed (Section 2.3.3).