3.2 Methods

Summary

The core objective of the bioregional assessment (BA) for the Galilee subregion was to analyse the potential impacts on and risks to water-dependent assets caused by hydrological changes that arise due to additional coal resource development. The approach closely followed the high-level reasoning set out in companion submethodology M10 for analysing impacts and risks, and the key findings of this multi-disciplinary scientific investigation in the Galilee subregion represent the main outcome of this BA process. The particular emphasis of the impact analysis was geared towards quantifying the regional extent and magnitude of the potential hydrological and ecosystem changes due to additional coal resource development. The risk analysis, while closely related to impacts, importantly also evaluated the likelihood of such changes.

The water-dependent ecosystems and assets that are potentially impacted due to the proposed coal resource developments in the Galilee subregion may experience changes in either groundwater or surface water systems (or both). These changes may arise, for example, due to variations in certain functions of the streamflow regime, such as reductions in annual flow or increases in number of low-flow days, or due to reductions in aquifer levels caused by groundwater drawdown. Consequently, the Galilee subregion impact and risk analysis relied on the conceptual understanding of causal pathways, and used these as the basis for numerical modelling to generate probabilistic estimates of hydrological changes. The causal pathways provided the logical basis for clearly linking coal mining operations and associated activities to the surrounding hydrology, and the modelling approach then explored the potential distribution of changes to water quantity and availability both above and below ground. Subsequently, qualitative mathematical models and receptor impact models were used to translate the potential hydrological changes to ecosystem-level changes for the subregion's main water-dependent landscape groups, such as streams and terrestrial groundwater-dependent ecosystems on floodplains.

The BA for the Galilee subregion adopted a precautionary 'rule-out' approach for impact and risk analysis, and the probabilistic modelling results were used to develop the zone of potential hydrological change. This zone, which is less than 3% of the land area of the Galilee assessment extent (the initial focal point for this BA), integrates both groundwater and surface water modelling results attributed to the impacts of the subregion's additional coal resource development. Potential impacts to ecosystems (landscape classes) and water-dependent assets were initially evaluated by geographic overlay analysis. Any landscape classes or assets that were completely outside of this zone were considered very unlikely (less than 5% chance) to be impacted by the additional coal resource development, and were hence ruled out from further analysis.

The scale and complexity of the impact and risk analysis for the BA for the Galilee subregion, with a large number of multi-dimensional input datasets from a variety of scientific disciplines, required an innovative approach to information management and processing. A custom-built impact and risk analysis database facilitated effective BA data handling, and allowed three main types of system-level analyses for the BA, including the analysis of hydrological changes (Section 3.3), the analysis of ecosystem (landscape groups) changes (Section 3.4), and the analysis of changes to water-dependent assets (Section 3.5). In all three cases, the focus was on the quantifiable impacts and risks that may occur within the Galilee subregion’s zone of potential hydrological change.