Conceptual models of causal pathways are a specific type of conceptual model that characterises the causal pathways, the logical chain of events ‒ either planned or unplanned ‒ that link coal resource development and potential impacts on water resources and water-dependent assets.
These conceptual models bring together the existing understanding and conceptual models of the key system components, processes and interactions for the geology, hydrogeology, surface water, and surface ecosystems, and consider the most plausible and important impacts and their spatial and temporal context. The conceptual modelling draws heavily on companion products from Component 1: Contextual information, which is summarised in Section 2.3.2, Section 2.3.3 and Section 2.3.4.
The causal pathways underpin the construction of groundwater and surface water models, and frame the assessment of the impacts on and risks to water and water-dependent assets. The approach taken in the Gloucester subregion has leveraged existing state-based resources and knowledge of geological, surface water and groundwater conceptual models. The Assessment team summarised the key system components, processes and interactions for the geology, hydrogeology and surface water of the subregion and these were refined through individual consultation with external stakeholders. The focus of the workshop was to improve the landscape classification (described in Section 2.3.3) and description of the conceptual model of causal pathways. Discussion with representatives at the workshop focused on knowledge gaps and uncertainties identified by the Assessment team.
In a BA, the identification and definition of causal pathways are supported by a formal hazard analysis, known as Impact Modes and Effects Analysis (IMEA) as outlined in companion submethodology M11 (as listed in Table 1) for hazard analysis (Ford et al., 2016) and illustrated in Figure 5 (Section 2.3.1). IMEA is a variant of the established hazard analysis tool, Failure Modes and Effects Analysis (FMEA). The causal pathways are based on the outcomes of this hazard analysis and current understanding of the way ecosystems and landscape classes in the subregion work and interact. The IMEA rigorously and systematically identifies the potential hazards, defined as events, or chains of events, that might result in an effect (change in the quality and/or quantity of surface water or groundwater). Only hazards identified through the IMEA process are considered further in the BA. Additionally, the IMEA considers all the possible ways in which activities may lead to changes or impacts, before assessing the severity, likelihood and detectability of such impacts under current controls through structured scoring.
Key to an IMEA is identifying activities, planned events associated with a CSG operation or coal mine. Activities are grouped into components, which are grouped into life-cycle stages. It is important to assign activities to their appropriate life-cycle stage because the scale and duration of similar activities can be different for each life-cycle stage, which is reflected in the scores for severity and/or likelihood of the impacts resulting from these activities.
Activities for CSG operations are separated into five life-cycle stages and four components:
- life-cycle stages: (i) exploration and appraisal, (ii) construction, (iii) production, (iv) decommissioning, and (v) work-over
- components: (i) wells, (ii) processing facilities, (iii) pipelines, and (iv) roads and infrastructure.
Activities for open-cut mines are separated into five life-cycle stages and three components:
- life-cycle stages: (i) exploration and appraisal, (ii) development, (iii) production, (iv) closure, and (v) rehabilitation
- components: (i) open pit, (ii) surface facilities, and (iii) infrastructure.
An impact cause is an activity (or aspect of an activity) that initiates a hazardous chain of events. An activity can have undesirable effects (such as water and gas extraction that unintentionally reduces groundwater pressure to unacceptable levels) or desirable effects (such as reinjection of co-produced water to restore groundwater pressure in a heavily utilised aquifer).
An impact mode is the manner in which a hazardous chain of events could result in an effect. There might be multiple impact modes for each activity or chain of events. The impact modes may arise through various mechanisms, including anthropogenic activities that are planned and expected to occur as part of operations; unplanned events due to human error or infrastructure failure; or through combination with external factors (e.g. heavy rainfall or flood events).
Examples are illustrated in Figure 5 (Section 2.3.1):
- An example for open-cut coal mines (Figure 5(a)) is initiated with the activity ‘dewatering down to coal seam for an open-cut mine’, which is the impact cause. The impact mode (‘intentional dewatering down to coal seam’) leads to the effect (‘change in groundwater quantity (drawdown)’), which in turn may result in an ecological impact, ‘reduced groundwater availability for a groundwater-dependent ecosystem’.
- An example for CSG operations (Figure 5(b)) is initiated with the activity ‘corridor or site vegetation removal for CSG operations or coal mine’, which is the impact cause. Subsequent events (‘rainfall event’ and ‘soil erosion’) then combine to form the impact mode (‘soil erosion following heavy rainfall’) that leads to multiple effects (‘change in surface water quantity and surface water quality’) and associated stressors (‘surface water flow’ and ‘total suspended solids (TSS)’). In turn, this may cause an ecological impact, ‘change of condition of habitat for a given species’.
Participants in IMEA workshops were invited to identify all plausible hazards and impact modes on an activity-by-activity basis, together with the potential hydrological effects on groundwater and/or surface water. Each hazard is scored with respect to the severity, likelihood and time to detection. The IMEA elicits an interval (upper and lower score) for each hazard that all workshop participants agree upon:
- The severity score describes the magnitude of the impact resulting from a hazard, which is scored so that an increase (or decrease) in score indicates an increase (or decrease) in the magnitude of the impact.
- The likelihood score describes the annual probability of a hazard occurring, which is scored so that a one-unit increase (or decrease) in score indicates a ten-fold increase (or decrease) in the probability of occurrence.
- The detection score describes the expected time to discover a hazard, scored in such a way that a one-unit increase (or decrease) in score indicates a ten-fold increase (or decrease) in the expected time (measured in days) to discover it.
Two overarching hazard ranking scores are calculated:
- hazard score, the sum of the severity score and likelihood score
- hazard priority number, the sum of severity score, likelihood score and detection score.
It is important to emphasise that despite the use of severity scores and likelihood scores, the hazard ranking scores do not provide an absolute or even relative measure of risk. IMEA provides a relative rank of hazards. The value of this analysis lies in the systematic and thorough identification of hazards and in their ranking relative to each other. Hazards with higher scores do not imply that the risks associated with those potential hazards are in some way significant or apply equally across the subregion at all times, only that it is important that these hazards (along with many others) are considered for inclusion in the BA.
There is considerable structure and hierarchy within these lists of IMEA hazards (Bioregional Assessment Programme, Dataset 1) with the finer-level hazards aggregating to successively coarser resolutions. For example, there are a range of activities as part of CSG operations that may require the removal of site vegetation (the impact cause), including the creation of pipeline networks, storage ponds, site processing plants, water treatment plants, ground-based geophysics and the construction of access roads; these may all potentially result in changes to surface water quality from soil erosion following heavy rainfall (impact mode).
The hazards identified by the IMEA represent a conceptual model of the chain of events that begins with an activity and ends with a potential impact on groundwater or surface water; causal pathways include these chains of events and also extend to resulting ecological impacts (see Figure 5 in Section 2.3.1). Causal pathways are considered for CSG operations and open-cut coal mines separately, for both the baseline coal resource development (baseline) and the coal resource development pathway (CRDP). A full suite of generic causal pathways for hazards due to coal mines and CSG operations is presented in figures in an appendix in companion submethodology M05 (as listed in Table 1) for developing a conceptual model of causal pathways (Henderson et al., 2016). These figures identify activities, impact causes and impact modes as well as those aspects of surface water and groundwater that might be affected. The causal pathways in the submethodology are generally applicable to all subregions or bioregions; this section presents specific results for the Gloucester subregion.
Hazards are grouped for the Gloucester subregion if they have the same causal pathways, even if those hazards occur because of different activities, at different life-cycle stages, or at different intensities. This smaller set of causal pathway groups provides a useful starting point for summarising and representing the causal pathways associated with coal resource development (e.g. through influence diagrams) and focusing on those causal pathways that are in scope for BA.
The spatial footprint for the identified hazards and causal pathways identified is a core focus of the conceptual modelling, and is arrived at on the basis of existing knowledge, scientific logic and preliminary hydrological modelling results. An important aspect of this is using those same sources to identify which landscape classes (and receptors) may be affected by a potential hydrological change that arises from those causal pathways, and (equally importantly), which classes of receptors will not be affected. Throughout the BA, areas of the PAE that will not be affected are progressively ruled out in order to focus efforts of the Assessment team and ultimately the impact and risk analysis.
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- 2.3.1 Methods
- 2.3.2 Summary of key system components, processes and interactions
- 2.3.3 Ecosystems
- 2.3.4 Baseline and coal resource development pathway
- 2.3.5 Conceptual modelling of causal pathways
- Currency of scientific results
- Contributors to the Technical Programme
- About this technical product