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 from coal resource developments in some of Australia’s major coal-bearing basins. The assessments distinguish 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. Given the regional-scale focus, the modelling does not account for local-scale details (e.g. the presence of local aquitards; stream condition). Areas identified in a bioregional assessment (BA) as at risk of potentially significant impacts serve as ‘red flags’ for directing further local investigation. Governments, industry and the community can then focus on areas that are potentially impacted when making regulatory, water management and planning decisions. In some cases, the risk of adverse impacts may be substantially diminished or negligible when local-scale factors are considered.

The impact and risk analysis considers 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) is not conducted as part of BAs.

The purpose of the following sections 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 the Bioregional Assessment Programme, use of the term ‘coal resource development’ specifically includes coal mining (both open-cut and underground) as well as CSG extraction. However, other forms of coal-related development activity, such as underground coal gasification and microbial enhancement of gas resources, are not within the scope of the assessment.

The two futures considered in a BA are:


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. Figure 3 shows the location of the coal resource developments and companion product 2.3 (Herr et al., 2018) provides details of the timelines for these developments.

Thus, the primary focus of a BA is on the potential impacts on water resources and water-dependent assets that are attributable to additional coal resource development. In the Namoi subregion, these include nine coal mine developments (including Caroona, which as of 2017 is not going ahead) and one CSG development. In this Assessment, the baseline includes six existing coal mines (see companion product 2.3 (Herr et al., 2018)).

Although the difference in potential impacts between these two futures is the focus of the assessment, the potential impacts under the baseline are important for regional context. For instance, the potential implications to groundwater-dependent assets of an additional 2 m of drawdown may depend on whether the drawdown under the baseline is 0.05, 0.5 or even 50 m. Potentially important impacts due to coal resource development under the baseline may also occur in parts of the subregion where additional coal resource developments have no further effect. The assessment gives less attention to these. The year in which maximum drawdown occurs under each future is unlikely to coincide and simply adding the drawdown results in a worst-case scenario that is unlikely to eventuate. Maximum drawdown occurs when the drawdown difference is at its maximum between the baseline and a ‘no-development’ scenario, and between the CRDP and the baseline scenario. These maximum drawdowns could (and in fact are likely to) occur at different times.

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 Commonwealth Government. Based on information available at the time, the CRDP for the Namoi subregion was finalised in 2015 (see companion product 2.3 (Herr et al., 2018) for the Namoi subregion) to allow the hydrological numerical modelling to commence. Developments in the CRDP may ultimately be implemented in different ways (e.g. changes to timing) or circumstances of coal resource developments may even change (e.g. a proponent may withdraw for some reason). For example, the Caroona development is now not going ahead, even though it is included in the CRDP. This reflects the dynamic nature of resource investment decision making, which may ultimately respond to diverse economic, political or social factors. Consequently, the CRDP is a representation of an indicative future. It highlights potential changes for water resources and water-dependent assets where assessment of local conditions will improve future understanding. Equally as important, the CRDP plays a role in identifying where changes will not occur and thus flagging where potential impacts to water resources and water-dependent assets are very unlikely.

The modelling held factors such as climate change or land use (e.g. agriculture) 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 to be small because the focus of BAs is on reporting the impacts of additional coal resource development, i.e. the difference in results between the CRDP and baseline. Where potential hydrological or ecological changes due to the additional coal resource development are identified it will be important to consider those changes in conjunction with local information and in the context of other water related changes that may occur in the Namoi subregion (e.g. irrigation or water extraction for human consumption) as that could also influence the ecological trajectory. This could be part of a more complete regional assessment of cumulative impacts beyond BA. Focus on water quantity and availability

BAs focus solely on water-mediated impacts, and specifically those related to water quantity, groundwater level or water resource availability. The scope of the BAs determined that potential water quality impacts are limited to salinity. Some broader water quality hazards are identified through the dedicated hazard analysis but the scientific analysis is restricted to salinity and is only addressed qualitatively. BAs are also concerned with 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 occur over long periods of time, sometimes decadal, and which may create the potential for flow-on effects through the wider 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 in BAs because regulatory site-based risk management and mitigation procedures address these issues, and because they are unlikely to create potential cumulative impacts. The assessment identifies impacts and risks associated with water quality attributes other than salinity that potentially happen as a result of coal resource development, but does not analyse these further. Assessment of regional-scale cumulative developments

BAs analyse the cumulative impacts of coal resource developments at a regional scale, and do not focus specifically on individual mines or CSG operations. The baseline and CRDP for the Namoi subregion each comprise a suite of developments, which are distributed across the assessment extent at variable distances from each other and have variable, but often overlapping, periods of operation. Thus there is potential for the impacts to accumulate to varying degrees in both space and time.

Regional-scale models 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 more extensive and extends greater distances downstream of developments than what occurs 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 existing state and Commonwealth legislation require. The hydrological and ecological systems modelling in a BA is appropriate for assessing the potential impacts on and risks to water resources and water-dependent assets at the regional scale, whereas the modelling undertaken for a mining proponent’s development, as part of an environmental assessment, occurs at a much finer scale and makes use of local information to more accurately represent the local situation. Therefore, results from these detailed mine-specific studies may differ from BA results. Employing a BA to invalidate existing site-specific modelling or impact assessments would be a fallacy; instead, BA results are useful in identifying broad areas where risk to assets and ecosystems from future coal resource developments are likely. Focus on predictive uncertainty

BAs consider parameter uncertainty 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 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.

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 are likely to lie within the distribution of modelled changes. This assumption is likely to be tested 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 regional 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 local management response. For example, the presence of a local aquitard that is not a feature of regional groundwater model may reduce potential near-surface hydrological and ecological impacts inferred using the regional model. This should be taken into account in any conditions or 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 cannot be quantified were considered qualitatively. Integrating ecological complexity with a landscape classification

Subregions are complex landscapes with a wide range of ecological systems that interact with human activities. 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 currently possible. Abstraction and a systems-level classification can manage the challenges of the dimensionality of the task.

The BA defines a set of landscape classes as ecosystems with characteristics that are expected to respond similarly to changes in groundwater and/or surface water due to coal resource development. The spatial coverage of landscape classes across the subregion is exhaustive and non-overlapping, and there is expected to be less heterogeneity in the response within a landscape class than between landscape classes. This reduces the complexity for each subregion and is appropriate for a regional-scale assessment. The landscape classification characterises the landscape and focuses on the key processes, functions and interactions for the individual landscape classes. The landscape classification for the Namoi subregion builds on existing well-accepted classifications and is described in detail in companion product 2.3 for the Namoi subregion (Herr et al., 2018). The landscape classification allows effort to be focused on those landscape classes that are water dependent.

The assessment of impacts on and risks to water-dependent ecological assets relies heavily on the landscape classification. Potential impacts to individual assets are assessed via the landscape classes where they are located. For each of those landscape classes, the assessment is based on the qualitative mathematical models for those landscape classes and the indicators of hydrological change or ecosystem change that experts have identified as important for that landscape class. Ruling out potential impacts

An important outcome of the multiple components of the BA is to identify areas of the subregion that additional coal resource development is unlikely to impact. The Assessment team rules out potential impacts where possible, both spatially and in terms of specific groundwater or surface water effects, so as to concentrate on where potential impacts have a higher probability of occurring. This process starts with the identification of a preliminary assessment extent (PAE) for a subregion or bioregion that is a conservative spatial boundary, encompassing areas of potential impact based on the most likely coal resource developments within the subregion or bioregion. The PAE is where assessment effort is focused, including in the collation of water-dependent assets, the creation of landscape classes to summarise key surface ecosystems, and the construction of numerical surface water and groundwater models.

Results of the hydrological modelling provide the details to finalise the ‘assessment extent’ used in the impact and risk analysis. No changes to the Namoi PAE were necessary, and the assessment extent for the Namoi subregion is the same as the PAE identified in companion product 1.3 for the Namoi subregion (O’Grady et al., 2015).

Results of the hydrological modelling also define the zone of potential hydrological change (Section 3.3.1). Potential impacts on water-dependent landscape classes and assets are ruled out if they are wholly outside the zone of potential hydrological change. Thus, the zone identifies 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 important, this logical and consistently applied process rules 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:
6 December 2018
Thumbnail of the Namoi subregion

Product Finalisation date