3.2.2 Causal pathways

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.

Figure 7

Figure 7 Conceptual diagram of the causal pathway groups associated with open-cut and underground coal mining

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

Causal pathway group

Hazards from Impact Modes and Effects Analysis (IMEA)

Surface water drainage

  • water management structures (dams, levee bunds and diversions)
  • rainwater and runoff diversion
  • waste rock blasting, excavation and storage administration, workshop, service facilities (construction phase)
  • topsoil excavation and storage
  • mine access construction
  • longwall coal extraction
  • bord-and-pillar coal extraction
  • construct own quarry for road base, etc.
  • off-lease and on-lease roadways
  • rail easement construction
  • recontoured landforms (slopes, gradients, etc.)
  • topsoil and waste rock dump site preparation
  • ventilation shaft construction.

Operational water management

  • discharge of treated mine water into the river (regulated)
  • discharge of treated mine water into the river (unregulated).

Subsurface depressurisation and dewatering

  • longwall coal extraction
  • bord-and-pillar coal extraction
  • pit wall (stabilisation) dewatering, treatment, reuse and disposal
  • development of mine panels (construction of roadways)
  • mine access (shaft / incline) construction
  • mine access (adit / incline) construction
  • gas post-drainage, surface to goaf: drilling
  • ventilation shaft construction
  • drilling and coring
  • gas post-drainage, surface to goaf: drilling
  • gas pre-drainage, surface to inseam: drilling
  • gas pre-drainage, underground: drilling
  • inseam gas pre-drainage, underground: drilling
  • mine dewatering drilling: drilling.

Subsurface physical flow paths

  • longwall coal extraction
  • bord-and-pillar coal extraction
  • post-closure water filling the pit
  • groundwater supply bore
  • mine access (adit / incline) construction
  • mine access (shaft / incline) construction
  • ventilation shaft construction
  • mine expansion too close to river/lake.

Data: Bioregional Assessment Programme (Dataset 1)

Last updated:
15 March 2019
Thumbnail of the Hunter subregion

Product Finalisation date