The Methodology for bioregional assessments of the impacts of coal seam gas and coal mining development on water resources (the BA methodology) (Barrett et al., 2013) states:
The central purpose of BAs is to analyse the impacts and risks associated with changes to water-dependent assets that arise in response to current and future pathways of CSG and coal mining development.
The impact and risk analysis for the Gloucester subregion (Component 3 and Component 4) followed the logic described in companion submethodology M10 (as listed in Table 1) for analysing impacts and risks (Henderson et al., 2018), and is summarised diagrammatically in Figure 5. It built on, and was only possible because of, the contextual information (Component 1) and knowledge from the conceptual models of causal pathways, numerical groundwater and surface water modelling, and data analysis (Component 2). These components are described in detail in preceding products for the Gloucester subregion. The impact and risk analysis represents the culmination of efforts to improve the knowledge base around the coal resource development, and to understand how water resources and water-dependent assets may be affected by hydrological changes caused by additional coal resource development in the Gloucester subregion.
Figure 5 Overarching methodology for impact and risk analysis in bioregional assessments
CSG = coal seam gas, GW = groundwater, HRV = hydrological response variable, RIV = receptor impact variable, SW = surface water
The impact analysis quantified the magnitude and extent of the potential hydrological and ecosystem changes due to additional coal resource development. This included:
- direct impacts: a change in water resources and water-dependent assets resulting from coal seam gas (CSG) and coal mining developments without intervening agents or pathways
- indirect impacts: a change in water resources and water-dependent assets resulting from CSG and coal mining developments with one or more intervening agents or pathways
- cumulative impacts: the total change in water resources and water-dependent assets resulting from CSG and coal mining developments when all past, present and reasonably foreseeable actions that are likely to impact on water resources are considered.
The risk analysis is related, but considered not only the magnitude and extent of the potential impact but also the likelihood of that impact. This is often framed as ‘consequence multiplied by the likelihood’. The quantification of the likelihood was underpinned by an uncertainty analysis that allowed probabilistic statements about events or impacts occurring. Within BAs, the uncertainty analysis stochastically propagated uncertainties in underlying hydrological parameters through hydrological models to produce distributions of potential surface water and groundwater changes. These in turn were input to receptor impact models to produce distributions of receptor impact variables which were chosen as indicators of potential ecosystem impacts.
BAs identified risks through a hazard analysis and analysed those risks by estimating the magnitude and likelihood of specific impacts. The risk assessment, risk evaluation and risk treatment that occur as part of broader risk management (see, for example, ISO 31000:2009 Risk Management Standards) are beyond the scope of BAs because they require careful consideration of a number of non‐scientific matters and value judgments; these are roles of proponents and government regulators in the first instance.
This product first describes the hydrological changes, and then the potential impacts of those changes on landscape classes and water-dependent assets, which contain ecological, economic and sociocultural values. These regional-scale results do not replace the need for detailed site or project specific studies, nor should they be used to pre-empt the results of detailed studies that may be required under NSW legislation. Where potentially significant impacts are identified from the regional scale analysis, local scale information can be used to better define the risk.
BAs present the likelihood of certain impacts occurring, for example, the percent chance of exceeding 0.2 m of drawdown in a particular aquifer and location. The underpinning data and information is available at www.bioregionalassessments.gov.au for others to use in their own targeted risk assessments. Users can choose thresholds of impact that may threaten the specific values they are trying to protect and calculate the corresponding likelihood of occurrence. More details about hydrological changes and potential impacts in the Gloucester subregion are available at www.bioregionalassessments.gov.au/explorer/GLO.
Product Finalisation date
- 3.1 Overview
- 3.2 Methods
- 3.3 Potential hydrological changes
- 3.4 Impacts on and risks to landscape classes
- 3.5 Impacts on and risks to water-dependent assets
- 3.6 Commentary for coal resource developments that were not modelled
- 3.7 Conclusion
- Contributors to the Technical Programme
- About this technical product