3.2 Methods

Summary

The impact and risk analysis for the Hunter subregion follows the overarching methodology described in companion submethodology M10 (as listed in Table 1) for analysing impacts and risks (Henderson et al., 2018). The impact analysis quantifies the magnitude and extent of the potential hydrological or ecosystem changes due to additional coal resource development. The risk analysis considers not only the magnitude of the potential impact, but also the likelihood of the impact.

Impacts to water-dependent landscapes and assets can be caused by changes in streamflow regime and drawdown of the regional watertable. The impact and risk analysis uses the conceptual model of causal pathways and probabilistic estimates of hydrological changes to identify where impacts to landscapes and assets might occur. Receptor impact models are used to translate potential hydrological changes to potential ecosystem changes for the key landscape classes.

For bioregional assessment (BA) purposes, the regional watertable is the upper groundwater level within the unconfined aquifer, where pore water pressure is equal to atmospheric pressure. Within the Hunter subregion, the regional watertable exists in the alluvium of the Hunter river basin and Macquarie-Tuggerah lakes basin, and in the weathered and fractured rock units beyond the alluvium. Changes in drawdown of the regional watertable due to additional coal resource development were modelled using the finite element modelling package, MOOSE.

Surface water modelling was undertaken using the Australian Water Resources Assessment landscape model (AWRA-L) and river model (AWRA-R). Results for nine hydrological response variables were reported for 65 model nodes across the subregion and extrapolated to stream links to better represent changes in surface water across the assessment extent.

Results from the groundwater and surface water modelling are used to define the zone of potential hydrological change due to additional coal resource development. Potential impacts on landscape classes and assets are assessed by overlaying their locations on the zone of potential hydrological change. The potential for impacts upon landscape classes and assets outside this zone is deemed very unlikely (less than 5% chance) and they are ruled out of further analysis. Within this zone, the potential for impacts on landscape classes and assets is assessed using indicators of hydrological change (hydrological response variables) and ecosystem change (receptor impact variables).

The databases, tools and geoprocessing that support the impact and risk analysis are summarised in this section.