- Bioregional Assessment Program
- Developing the conceptual model of causal pathways
This submethodology describes the process for developing the conceptual model of causal pathways in bioregional assessments (BAs). Causal pathways summarise and synthesise the potential linkages between coal resource development and the impacts on water and water-dependent assets. They are useful for describing the current state of knowledge, establishing common understanding between disciplines, communicating the characteristics of the system, generating hypotheses about potential impacts, and framing the results of a BA.
Conceptual models are abstractions or simplifications of reality. A number of conceptual models are developed for a BA, including the conceptual models for geology, surface water and groundwater, which underpin the numerical modelling. A conceptual model for a BA consists of:
- a clearly documented purpose
- a documentation of the process used to develop the conceptual model
- the elements of the overall conceptual model (e.g. narrative text, pictorial diagrams, influence diagrams)
- conceptual sub-model or sub-models for finer scale representations
- the evidence base underpinning the conceptual model.
A specific type of conceptual model used in BAs is a conceptual model of causal pathways, which characterises the causal pathways, the logical chain of events ‒ either planned or unplanned ‒ that link coal resource development and potential impacts on water and water-dependent assets. The conceptual model of causal pathways brings together a number of conceptual models developed in a BA.
The construction of the conceptual model of causal pathways requires the Assessment team to first synthesise and summarise the key system components, processes and interactions for the geology, hydrogeology and surface water of the subregion or bioregion. The spatial scale of the synthesis varies with specific requirements and the quality, coverage and availability of data. Finer resolution sub-models may be required in some places. Emphasising gaps and uncertainties is as important as summarising what is known about how various systems work.
Consideration must be given to how the causal pathways link to the assets. Given the potential for very large numbers of assets within a subregion or bioregion, and the many possible ways that they could interact with the potential impacts, a landscape classification is next applied to group together areas to synthesise understanding and reduce complexity. For BA purposes, a landscape class is an ecosystem with characteristics that are expected to respond similarly to changes in groundwater and/or surface water due to coal resource development. They are present on the landscape across the entire BA subregion or bioregion and their spatial coverage is exhaustive and non-overlapping. The rule set for defining the landscape classes is underpinned by an understanding of the ecology, hydrology (both surface water and groundwater), geology and hydrogeology of the subregion or bioregion. The nature and number of landscape classes needs to balance the heterogeneity across the subregion or bioregion, while not combining ecosystems that are hydrologically very different. The landscape classes are an important input to the development of conceptual models of causal pathways and the reporting of impacts and risks from coal resource development.
Conceptual models of causal pathways are developed for the two potential futures considered in BAs:
- 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 causal pathways are initiated by an activity associated with the coal resource development in the two futures (baseline and CRDP). These are identified from a hazard analysis (using the Impact Mode and Effects Analysis method), where development activities, impact causes, impact modes and water-related (hydrological) effects that might result from the specific coal resource development in the subregion or bioregion are considered.
Examples of potential hydrological effects or changes include:
- surface water: disruption of the natural surface drainage (e.g. interception of runoff by the pit or storage dams, as result of subsidence or by diversion of a stream network) or the extraction of water from – and disposal of water to – a local stream network
- groundwater: altered groundwater levels, flows, directions, quality, preferential pathways and inter-aquifer connectivity, as a result of dewatering, depressurisation and other development activities (e.g. wells)
- surface water ‒ groundwater interactions: changes due to altered recharge from the stream network or reduced baseflow from the deeper groundwater to the streams.
For BAs, a consistent set of causal pathways are used across all Assessments. These causal pathways are aggregated into four causal pathway groups:
- subsurface depressurisation and dewatering
- subsurface physical flow paths
- surface water drainage
- operational water management.
Causal pathways commonly overlap or link. For example, the depressurisation of coal seams to extract coal seam gas will also produce water that needs to be managed or disposed of through surface water or groundwater systems.
The relative importance of these causal pathways depends on the consolidated understanding of the key system components, processes and interactions across the geology, hydrogeology and surface water, and a consideration of the specific perturbations to that system that may arise from coal resource development in that subregion or bioregion. The hazard analysis prioritises individual hazards as a first step, but the Assessment teams need to place these priorities within the broader context of the current system understanding and the logic of the causal pathway groups.
The causal pathways are extended to consider potential impacts on landscape classes that result from the potential hydrological changes. While available spatial information, including preliminary modelling results, is used to assist in defining the causal pathways conceptually, more precise spatial representation of the model results and impacts can only be finalised towards the end of the BA. Interactions between the landscape classes and the surface water and groundwater are broadly characterised, which will support the development of receptor impact models in a later stage of the BA. Those receptor impact models will then be used to assess impacts on landscape classes and water-dependent assets. In some cases the characterisation of a landscape class may conceptually rule out potential impacts – for example, a landscape class related to dryland agriculture may not depend on surface water or groundwater.
The causal pathways, and the particular process for creating them, need to be documented as specified in this submethodology. The process includes consultation and testing of causal pathways with domain experts and those with local knowledge through a specific BA workshop on causal pathways and other engagement with individuals.
The causal pathways from coal resource development to hydrological changes are reported in product 2.3 (conceptual modelling). The causal pathways from hydrological changes to impacts on landscape classes and assets is reported in product 2.7 (receptor impact modelling) for only those landscape classes that are potentially impacted. Conceptual models for those landscape classes, and the selection of the most appropriate hydrological response variables and receptor impact variables, occur at that time. The causal pathways are subsequently informed and revised by results from the impact and risk analysis as reported in product 3-4 (impact and risk analysis).
METHODOLOGY FINALISATION DATE
- 1 Background and context
- 2 Introduction to conceptual modelling in bioregional assessments
- 3 Building conceptual models in bioregional assessments
- 4 Outputs from conceptual modelling
- Appendix A Diagrams of causal pathways
- Appendix B Names and descriptions of causal pathway groups and causal pathways
- Contributors to the Technical Programme
- About this submethodology