3.1.2 Scope and context

The objective of the Bioregional Assessment Programme is to understand and predict regional-scale cumulative impacts on water resources and water-dependent assets caused by coal resource developments in Australia's major coal-bearing sedimentary basins. The assessments identify areas where water resources and water-dependent assets are very unlikely to be impacted (with a less than 5% chance) from those where water resources and water-dependent assets are potentially impacted. Governments, industry and the community can then focus on areas that are potentially impacted when making regulatory, water management and planning decisions.

The impact and risk analysis considered only biophysical consequences, such as changes in hydrology or ecology; fully evaluating consequences requires value judgments and non-scientific information that is beyond the scope of BAs. A full risk assessment (with risk evaluation and risk treatment) was not conducted as part of BAs.

The purpose of this section is to highlight design choices that have steered the direction of this BA and culminated in the impact and risk analysis. Further details about the design choices are provided in companion submethodology M10 (as listed in Table 1) for analysing impacts and risks (Henderson et al., 2018). Choice of modelled futures

A BA is a regional analysis that compares two futures of coal resource development. In BAs, the term ‘coal resource development’ specifically includes coal mining (both open-cut and underground) as well as CSG extraction. Other forms of coal-related development activity, such as underground coal gasification and microbial enhancement of gas resources, were not within the scope of the assessment.

The two futures considered in the BA for the Gloucester subregion are:

  • baseline coal resource development (baseline): a future that includes all coal mines and CSG fields that are commercially producing as of December 2012
  • coal resource development pathway (CRDP): a future that includes all coal mines and CSG fields that are in the baseline as well as those that are expected to begin commercial production after December 2012.

The difference in results between CRDP and baseline is the change that is primarily reported in a BA. This change is due to the additional coal resource development – all coal mines and CSG fields, including expansions of baseline operations, that are expected to begin commercial production after December 2012.

In the Gloucester subregion, the additional coal resource development (shown in Figure 4) includes: (i) expansion of the Duralie open-cut mine, (ii) expansion of the Stratford open-cut mine, (iii) establishment of the Rocky Hill Mine, and (iv) establishment of Stage 1 of the Gloucester Gas Project.

The Duralie expansion was approved in November 2011, with mining operations due to commence in 2013 and cease in 2024. The Stratford expansion was approved in May 2015, with mining operations due to commence in 2015 and cease in 2026. As of February 2017, Rocky Hill is awaiting approval. In February 2016, AGL Energy Ltd formally announced that they were not pursuing the Gloucester Gas Project. However, despite uncertainties around Rocky Hill, and the Gloucester Gas Project not being developed, both are included in the CRDP for the Gloucester subregion, consistent with the BA approach presented in companion submethodology M04 (as listed in Table 1) for developing a coal resource development pathway (Lewis, 2014).

The CRDP is the most likely future, based on the analysis and expert judgment of the Assessment team in consultation with coal and gas industry representatives, state agencies and the Australian Government. The CRDP was finalised for the Gloucester subregion based on information available in October 2015 (Dawes et al., 2018, Section to allow the hydrological numerical modelling to commence. In reality, developments in the CRDP may ultimately be implemented in different ways (e.g. changes to timing), or circumstances of coal resource developments may change (e.g. a proponent may withdraw for some reason, as is the case for the Gloucester Gas Project). This reflects the dynamic nature of resource investment decision making, related to diverse economic, political or social factors. Consequently, the CRDP needs to be viewed as an indicative future that highlights potential changes for water resources and water-dependent assets that may need to be considered further in local analyses or via approval conditions required by regulators. Equally as important, the CRDP plays a role in identifying where changes will not occur, flagging where potential impacts to water resources and water-dependent assets are very unlikely.

BAs primarily focus on the potential impacts to water resources and water-dependent assets that are attributable to the additional coal resource development. Potentially important impacts under the baseline may occur in parts of the Gloucester subregion that are not further affected by additional coal resource development, and so are given less attention in the assessment. However, the potential impacts under the baseline may be important in interpreting impacts due to additional coal resource development. For instance, the potential implications to groundwater-dependent ecosystems of an additional 2 m of drawdown in the regional watertable may depend on whether the drawdown under the baseline is 0.10, 1.0 or even 10 m.

Factors such as climate change and land use (such as agriculture) were held constant between the two futures. Although the future climate and/or land use may differ from those assumed in BAs, the effect of this choice is likely small because the focus of BAs is on reporting the difference in results between the baseline and CRDP. Focus on water quantity and availability

BAs focus solely on water-related impacts, and specifically those related to water quantity and availability. Potential water quality hazards were identified through the comprehensive hazard analysis undertaken as part of conceptual modelling for the Gloucester subregion (Dawes et al., 2018), but the analysis, as determined by the BA scope, was limited to salinity and was only addressed qualitatively.

BAs focus on those surface water and groundwater effects that may accumulate, either over extended time frames or as a result of multiple coal resource developments. These typically correspond to changes in surface water and groundwater that are sustained over long periods of time, sometimes decades, and which may create the potential for flow-on effects through the hydrological system.

Many activities related to coal resource development may cause local or on-site changes to surface water or groundwater. These are not considered explicitly in BAs because they are assumed to be adequately managed by site-based risk management and mitigation procedures, and are unlikely to create potential cumulative impacts. Impacts and risks associated with water quality attributes other than salinity that are potentially affected by coal resource development are identified, but not analysed further, in this BA. Assessment of regional-scale cumulative developments

BAs are designed to analyse the cumulative impacts of coal resource developments at a regional-scale, and not focus specifically on individual mines or CSG operations. The baseline and CRDP futures for the Gloucester subregion include a suite of developments, the potential impacts of which may overlap to varying degrees in both time and space.

Regional-scale models are used to predict the cumulative hydrological changes and potential impacts of those developments on landscape classes and water-dependent assets from multiple developments over time. The area of potential impact is expected to be more extensive and extend greater distances downstream of developments than what is predicted from site-scale, single-mine models. In some cases, the spatial or temporal alignment of certain coal resource developments can allow for attribution of potential effects to individual developments, but that occurs because of that alignment rather than by design.

Results of the impact and risk analysis reported in this product do not replace the need for the detailed site- or project-specific investigations that are currently required under existing state and Commonwealth legislation. The hydrological and ecological systems modelling undertaken for a BA are appropriate for assessing the potential impacts and risks to water resources and water-dependent assets at the ‘whole-of-basin’ scale, whereas the modelling undertaken by a mining proponent for an individual development as part of an environmental assessment, occurs at a much finer scale and makes use of local information. Therefore, results from these detailed mine-specific studies are expected to differ from those from a BA. However, as a range of potential parameter values are considered in a BA, it is expected that the range of possible outcomes predicted by a BA will encompass the results from individual site-specific studies. Focus on predictive uncertainty

In BAs, parameter uncertainty was considered as fully as possible when predicting hydrological outcomes (i.e. changes to surface water or groundwater) and ecological outcomes (i.e. changes to ecologically relevant receptor impact variables). For example, groundwater models were run many thousands of times using a wide range of plausible input parameters for many of the critical hydraulic properties, such as the hydraulic conductivity and storage coefficients of all modelled hydrogeological layers. This differs from the traditional deterministic approach used more routinely for groundwater and surface water modelling and is driven by the risk analysis focus of BAs.

While models are constrained to data, the density of reliable observation data is sparse, so results may not represent local conditions well. However, they do consistently represent the risk and uncertainty at all sites through probability distributions of possible hydrological changes, where the area, depth, timing and assumed pumping rates of each development largely determine the spatial variation, and lack of detail about the physical environment at any given point in the assessment extent define the uncertainty.

Given the wide range of plausible input parameters used in the regional modelling, the hydrological changes due to additional coal resource development at any given location within the assessment extent can be assumed to lie within the distribution of modelled changes. This assumption may not be true near open-cut mines where potentially steep hydraulic gradients at the mine pit interface are poorly resolved in the regional groundwater models. These areas are excluded from the ecological analysis for this reason. Where the BA regional-scale analysis identifies an area as ‘at risk’ of large hydrological changes and potentially significant impacts on ecological, economic and/or sociocultural values, local-scale information may be necessary to constrain the predictive uncertainty to something more representative of local conditions, and more appropriate for informing the management response.

The quantitative representation of the predictive uncertainty through probability distributions allows BAs to consider the likelihood of impacts with a specified magnitude and underpins the impact and risk analysis. Sources of uncertainty that could not be quantified through numerical modelling were considered qualitatively. A landscape classification

Subregions are complex landscapes with a wide range of human and ecological systems. The systems can be discrete, overlapping or integrated. Because of this complexity, a direct analysis of each and every point, or water-dependent asset, in the landscape across the subregion is not possible. Abstraction and a system-level classification were used to manage the challenges of the dimensionality of the task.

A set of landscape classes was defined that are similar in their physical, biological and hydrological characteristics. This reduced the complexity for each subregion and is appropriate for a regional-scale assessment. The landscape classification focuses on the key processes, functions and interactions for the individual landscape classes and assumes that ecosystems within each landscape class respond similarly to predicted hydrological changes. The landscape classification for the Gloucester subregion built on existing well-accepted classifications and is described in detail in companion product 2.3 for the Gloucester subregion (Dawes et al., 2018). The landscape classification allowed effort to be focused on those landscape classes that are water dependent.

The assessment of impacts on and risks to water-dependent ecological assets relied heavily on the landscape classification. Potential impacts to individual assets were assessed via their constituent landscape classes. For each of those landscape classes, the assessment was based on the qualitative mathematical models for those landscape classes and the indicators of hydrological change or ecosystem change identified as important for that landscape class. Ruling out potential impacts

An important outcome of this BA was to identify areas of the Gloucester subregion that are not likely to be impacted by additional coal resource development. Potential impacts were ruled out where possible, both spatially and in terms of specific groundwater or surface water effects, in order to concentrate the analysis where potential impacts have a higher probability of occurring. This process started with identifying a preliminary assessment extent (PAE) for the subregion that is a conservative spatial boundary, encompassing areas of potential impact based on the most likely coal resource developments within the subregion. The PAE is where assessment effort was preferentially focused, when collating water-dependent assets, creating landscape classes to summarise key surface ecosystems, and constructing numerical surface water and groundwater models.

The results of the hydrological modelling were used to refine the PAE to the ‘assessment extent’ for this product. The assessment extent (~481.2 km2) used in this product is only slightly larger than the PAE (~468.2 km2) identified in companion product 1.3 for the Gloucester subregion (McVicar et al., 2015). This 13.0 km2 increase was needed to account for small sections of the Karuah River, Mill Creek and Avondale Creek that weave in and out of the PAE boundary (which was defined by the geological Gloucester Basin at that part of the PAE).

Potential impacts were ruled out using a zone of potential hydrological change. This zone was defined using probabilities of exceeding thresholds in multiple hydrological response variables. A key role of the zone of potential hydrological change was to identify landscape classes that should be investigated further through qualitative mathematical modelling and receptor impact modelling, and, as required, through use of local information to better define the risk and appropriate management response. Equally as important, this logical and consistently applied process ruled out landscape classes or water-dependent assets where potential impacts due to additional coal resource development are very unlikely (less than 5% chance) to occur.

Last updated:
18 December 2018
Thumbnail of the Gloucester subregion

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