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- Developing the conceptual model of causal pathways
- Appendix B Names and descriptions of causal pathway groups and causal pathways
For the purposes of bioregional assessments, causal pathways are the logical chain of events ‒ either planned or unplanned ‒ that link coal resource development and potential impacts on water resources and water-dependent assets.
The causal pathways are initiated by an activity associated with the coal resource development (as identified from the Impact Modes and Effects Analysis).
Causal pathways commonly overlap or link. For example, the depressurisation of coal seams to extract coal seam gas (CSG) will also produce water that needs to be managed or disposed of through surface water or groundwater systems.
A consistent set of names for causal pathways need to be used across all Assessments.
Causal pathways are classified into four groups, as follows. Each of these groups consists of between three to five causal pathways, as shown in Table 7 to Table 10.
The specified names for each group and causal pathway should be used consistently in reporting causal pathways for all subregions and bioregions.
B.1 ‘Subsurface depressurisation and dewatering’ causal pathway group
This group of causal pathways arises when coal mines and CSG operations intentionally dewater and depressurise subsurface hydrostratigraphic units (such as coal seams and aquifers) to permit coal resource extraction. Pumping groundwater to enable coal resource extraction modifies pre-existing groundwater gradients, for example, changes groundwater levels, pressures or compositions of aquifers. A number of activities may affect the pressure gradients that control the direction and rate of groundwater transmission within different hydrostratigraphic layers, for example: pumping of the watertable to lower the groundwater level to enable open-cut coal mining; pumping of the target coal resource layer to allow underground mining; or depressurising a water-saturated target coal seam to induce desorption and subsequent extraction of CSG. Groundwater level or pressure is most commonly altered, but other gradients can also be changed via this process, such as temperature, density or chemical composition (water quality). This causal pathway group also includes conventional groundwater extraction from aquifers, which may be undertaken to supply water resources to support development and production activities associated with coal mining or CSG operations. However, the scale of these effects is typically much less than those associated with mine dewatering or CSG extraction.
B.2 ‘Subsurface physical flow paths’ causal pathway group
This group of causal pathways involves physical modification of the rock mass or geological architecture by creating new physical paths that water may potentially infiltrate and flow along. Just because a new physical path is created does not necessarily mean that water will start flowing along it in preference to how it flowed before – it will still follow the path of least resistance, and be governed by pressure gradients. This causal pathway group can, however, potentially lead to direct hydraulic connection between the targeted coal resource layers and other hydrostratigraphic units (such as regional aquifers), by creating new zones of deformation in the rock mass. This may occur when the integrity of wells drilled for groundwater or gas extraction is compromised, or may occur due to hydraulic fracturing of coal seams. The cracking that occurs in the rock mass above underground longwall panels may also subsequently cause enhanced hydraulic connection, and potentially impact adjacent aquifers or aquitards in some circumstances. Propagation of these underground mining effects to the surface may also cause subsidence (as outlined in the surface water drainage causal pathway group below).
B.3 ‘Surface water drainage’ causal pathway group
This group of causal pathways involves the physical disruption and disturbance of surface topography and near-surface materials (vegetation, topsoil, weathered rock). Such landscape changes can alter parameters such as the direction, volume and quality of surface flow over the landscape within the mine lease, and may reduce runoff to the stream network. Land surface subsidence caused by underground coal mining is an important example of this group. Surface disturbance can also lead to enhanced soil erosion rates, which can then affect surface water quality, for example, through increased stream sediment loads. This group of causal pathways typically starts with activities associated with development of the mine site area, coal seam gas well network and related infrastructure. It can include activities such as diverting water around operations areas with drains or walls, realigning part of a stream network to permit mining to occur, or clearing vegetation and soil to construct a drilling pad.
B.4 ‘Operational water management’ causal pathway group
This group of causal pathways involves the modification of water management systems to facilitate sourcing, storing, using and disposing water at the coal resource development site. This is not a causal pathway of the natural hydrological system as such (as the other three are), but is associated with human-made water management rules, regulations and existing plans.
Table 7 Causal pathways in the ‘Subsurface depressurisation and dewatering’ causal pathway group
Causal pathway |
Relevancea (open-cut coal mine, underground coal mine, coal seam gas operation) |
Comments |
---|---|---|
Groundwater pumping enabling coal seam gas extraction |
Coal seam gas operation |
Intentional depressurisation of coal seams to reduce hydrostatic pressure and enable production of coal seam gas (and co-produced water) |
Groundwater pumping enabling underground coal mining |
Underground coal mine |
Intentional dewatering of coal resource layers to reduce groundwater pressures below level of base of mining |
Groundwater pumping enabling open-cut coal mining |
Open-cut coal mine |
Intentional dewatering to lower the watertable level so that open-cut mining operations may occur |
Unplanned groundwater changes in non-target aquifers |
Coal seam gas operation Underground coal mine Open-cut coal mine |
Groundwater extraction for resource development may unintentionally affect groundwater variables and parameters such as pressure, flow paths and water quality in non-target layers, in situations where direct hydraulic connections exist. Such hydraulic connections may occur preferentially via geological structures such as faults, or more diffusely where direct stratigraphic contact exists between layers. |
Groundwater pumping of target aquifer |
Open-cut coal mine Underground coal mine Coal seam gas operation |
Intentional extraction undertaken to supply water from a target aquifer, which is required for on-site development and production usage in the coal resource development operations (see also the ‘operational water management’ causal pathway group). |
aMine and coal seam gas operations are listed in relative order of importance.
Table 8 Causal pathways in the ‘Subsurface physical flow paths’ causal pathway group
Causal pathway |
Relevance (open-cut coal mine, underground coal mine, coal seam gas operation) |
Comments |
---|---|---|
Failure of well integrity |
Coal seam gas operation Underground coal mine Open-cut coal mine |
May create a direct fluid pathway between target formation and overlying aquifers, between the target formation and the surface, or between non-target formations. Additional to coal seam gas wells (main operation where this occurs), it can also include other types of boreholes, such as those drilled for coal exploration or groundwater extraction (though these generally have much smaller impacts compared to CSG extraction). |
Hydraulic fracturing |
Coal seam gas operation |
Intentional activity undertaken to change properties of target coal seams (such as permeability) to enhance gas production. Will create additional lateral flow paths within the coal seam. Depending on in situ rock properties and stress regime, poorly managed hydraulic fracturing can also potentially create fracture pathways linking target coal seams with adjacent hydrostratigraphic units which, in some cases, may be aquifers. There is potential for affecting groundwater flow gradients and changing various water quality parameters, for example, through injecting hydraulic fracturing fluids. |
Subsurface fracturing above underground longwall panels |
Underground coal mine |
Impacts most severe in fracture zone immediately above goaf, but may extend nearer to surface in the constrained deformation zone and laterally away from goaf into rib areas. Effects that propagate to the surface may result in subsidence (see Table 9). |
Extracting overburden to access coal |
Open-cut coal mine |
May permanently alter hydraulic properties of near-surface aquifers, in cases where overburden is used to backfill mining pits. Impacts unlikely until dewatering has ceased and groundwater levels recover. |
aMine and coal seam gas operations are listed in relative order of importance.
Table 9 Causal pathways in the ‘Surface water drainage’ causal pathway group
Causal pathway |
Relevance (open-cut coal mine, underground coal mine, coal seam gas operation) |
Comments |
---|---|---|
Intercepting surface water runoff |
Open-cut coal mine Underground coal mine Coal seam gas operation |
Includes building diversion walls and drains to manage surface water flows around mining pits, operational areas and surface infrastructure |
Altering surface water system |
Open-cut coal mine Coal seam gas operation Underground coal mine |
Diverting or realigning the pre-development surface water drainage, thereby changing the course and nature of the affected river and stream. Also includes other activities that can disrupt surface topography or structure, which may subsequently lead to enhanced erosion and impacts on surface water quality. |
Subsidence of land surface |
Underground coal mine Coal seam gas operation |
Creates artificial topographic lows where surface water may pool and thereby reduce overall volume of inflow to surface water systems. Subsidence may also alter surface slopes which can then affect flow paths and rates of flow to stream network. The magnitude of ground surface subsidence caused by coal seam gas operations is generally significantly less than that caused by underground mining. |
aMine and coal seam gas operations are listed in relative order of importance.
Table 10 Causal pathways in the ‘Operational water management’ causal pathway group
Causal pathway |
Relevance (open-cut coal mine, underground coal mine, coal seam gas operation) |
Comments |
---|---|---|
Sourcing water for on-site operations |
Open-cut coal mine Underground coal mine |
Mining operations may require supplementary water for on-site activities, which may need to be extracted from a nearby river or pumped from groundwater bores. These activities may contribute to reduction in surface water flows, or groundwater drawdown in target aquifers. |
Storing extracted water |
Coal seam gas operation Open-cut coal mine Underground coal mine |
Storing water in large holding dams and ponds may create a point source for leakage (unintentional outflow) which may reach surface water or groundwater systems. Some post-mining rehabilitation plans may involve creating a permanent artificial lake, which may act as groundwater sink. |
Discharging extracted water into surface water system |
Open-cut coal mine Underground coal mine Coal seam gas operation |
This may be a regulated activity governed by specific conditions and rules, or (less commonly) may be unregulated, for example, due to severe flood inundation or dam engineering failure. May increase surface water flow volumes, or affect water quality. |
Processing and using extracted water |
Coal seam gas operation Open-cut coal mine Underground coal mine |
Main impacts may relate to offsite use of co-produced coal seam gas water, for example, for irrigation of crops. Mine water may be reused on-site for various purposes, for example dust suppression, but will mostly be retained within area of operations. |
Reinjecting co-produced water into aquifer |
Coal seam gas operation |
Potential water management option for some coal seam gas operations. Not all sites are amenable to this option, but if managed correctly can have beneficial impacts to reinjection aquifers, for example, by increasing groundwater pressures. |
aMine and coal seam gas operations are listed in relative order of importance.

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
- References
- Datasets
- Citation
- Acknowledgements
- Contributors to the Technical Programme
- About this submethodology