The conceptual model of causal pathways describes the logical chain of events ‒ either planned or unplanned ‒ that link coal resource development to potential impacts on water and water-dependent assets. The causal pathways provide the logical and transparent foundation for the impact and risk analysis.
A systematic hazard analysis, using the Impact Modes and Effects Analysis method (described in companion submethodology M11 (as listed in Table 1) for hazard analysis (Ford et al., 2016)), was undertaken for the Hunter subregion to identify the activities that occur as part of coal resource development that might result in a change in the quality or quantity of surface water or groundwater. Hazards were prioritised according to the likelihood, severity and detectability of potential impacts (Bioregional Assessment Programme, Dataset 1). All hazards need to be addressed in some way for the impact and risk analysis, but this does not mean they all need to be assessed in the same way.
Individual ‘hazards’ are not represented in the hydrological models. Instead they were grouped into four causal pathway groups, which reflect the main hydrological pathways via which the effects of a hazard can propagate from its origin. These simplified pathways are broadly represented in the BA hydrological models. The causal pathway groups are:
- ‘Subsurface depressurisation and dewatering’
- ‘Subsurface physical flow paths’
- ‘Surface water drainage’
- ‘Operational water management’.
Figure 7 illustrates these causal pathway groups.
This schematic diagram is not drawn to scale.
ROM = run-of-mine
The effects of some hazards were not modelled. Changes in water quality due to coal resource development activities were generally deemed out of scope of the BA, except the potential effects on stream salinity. Changes in stream salinity were not modelled, but are considered qualitatively in Section 3.3.4. The physical process of subsidence is not simulated by the hydrological models, although some of the effects on hydrology from longwall panel collapse (i.e. hydraulic conductivity enhancement within the goaf) and subsidence at the land surface (i.e. interception of catchment runoff) are represented. Some identified hazards were deemed to be local in scale and addressed by existing site-based management; others were considered of such low likelihood and/or consequence (such as litter left by site contractors) that they were not included.
While the causal pathway groups are generic, the physical characteristics of a subregion, such as its geological, geophysical and topographic architecture, and related surface water and groundwater networks, will influence the hydrological connectivity across the subregion. The Assessment team’s conceptual understanding of the dominant geological and topographic influences on surface water and groundwater connectivity in the Hunter subregion is described in companion product 2.3 (Dawes et al., 2018).
Table 4 lists potential hazards arising from coal resource development in the Hunter subregion for each causal pathway group. Further details about hazards, their identified effects and their link to causal pathway groups are in companion product 2.3 for the Hunter subregion (Dawes et al., 2018).
The hydrological models represent causal pathways through their conceptualisation and parameterisation of changes in surface water drainage, dewatering of the mines, changes in hydraulic properties above longwall mines and discharges of mine water off site. The models integrate the hydrological changes from the different causal pathways into the predicted hydrological response across the model domain over time.
Table 4 Causal pathway groups and the associated hazards for the Hunter subregion
Data: Bioregional Assessment Programme (Dataset 1)
