3.2.2 Causal pathways


The conceptual model of causal pathways describe the logical chain of events ‒ either planned or unplanned ‒ that link coal resource development to potential impacts on water resources and water-dependent assets. These causal pathways provided the logical and transparent foundation for the impact and risk analysis and are described in companion product 2.3 for the Maranoa-Balonne-Condamine subregion (Holland et al., 2016).

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 Maranoa-Balonne-Condamine subregion. The hazard analysis identified 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). It is important to ensure that all hazards are addressed by the impact and risk analysis, but this does not mean that all causal pathways need to be assessed in the same way, only that they are all addressed in some way.

The many individual ‘hazards’ themselves were not represented directly in the hydrological models, but instead were grouped into four causal pathway groups, which reflect the main hydrological pathways by which the effects of a hazard can propagate from its origin. These simplified pathways are broadly represented in the BA hydrological models. These causal pathway groups are:

  • ‘Subsurface depressurisation and dewatering’
  • ‘Subsurface physical flow paths’
  • ‘Surface water drainage’
  • ‘Operational water management’.

Figure 5, Figure 6 and Table 3 describe the system components and associated hydrological effects of the causal pathways considered to be in scope for open-cut coal mines and CSG operations in the Maranoa-Balonne-Condamine subregion (refer Section 2.3.5 in companion product 2.3 (Holland et al., 2016)). Hydrological effects associated with coal resource development occur in four system components:

  • ‘watercourses within and downstream of tenements’ system component
  • ‘alluvium and watercourses in aquifer outcrop areas within and downstream of tenements’ system component
  • ‘aquifers within tenements’ system component
  • ‘aquifers’ system component.

The hydrological models represent causal pathways through their conceptualisations and parameterisations. The outputs from the hydrological models do not identify individual causal pathways but rather integrate the various possible causal pathways into the predicted hydrological response at particular points in space and time.

Not all hydrological effects can be modelled. Some cannot be modelled due to scale or complexity and were addressed qualitatively using the current conceptual understanding and knowledge base. Changes in water quality due to coal resource development activities were considered qualitatively through potential effects on stream salinity (Section 3.3.4). Some identified hazards were deemed to be local in scale and addressed by existing site-based management, whereas some were considered knowledge gaps (e.g. because the location and volume of reinjection of co‑produced water to restore groundwater pressure in a depleted aquifer is unknown). Others were considered of such low likelihood and/or consequence for broader cumulative impacts at the regional scale 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 Maranoa-Balonne-Condamine subregion is described in companion product 2.3 (Holland et al., 2016). The cumulative effects of aquifer depressurisation associated with coal resource development in the Maranoa-Balonne-Condamine subregion predicted by the groundwater numerical modelling is described in companion product 2.6.2 (Janardhanan et al., 2016). Hydrological effects that can and cannot, or have not been modelled are indicated in Figure 6.

Figure 5

Figure 5 Conceptual diagram of the causal pathway groups associated with coal seam gas operations and open-cut coal mines for the Maranoa-Balonne-Condamine subregion

This conceptual diagram is not drawn to scale. The inset schematic shows hydraulic fracturing of a coal seam, where a mixture predominantly composed of water (blue) and sand (yellow), with minor amounts of chemical additives, is injected at high pressure into the well to produce small cracks in the coal (lighter grey zone). This process enhances the permeability of the coal seam, enabling larger volumes of gas and water to be subsequently pumped from the well.

This figure has been optimised for printing on A3 paper (420 mm x 297 mm).

Figure 6

Figure 6 System components and associated hydrological effects of the causal pathways considered to be in scope in the Maranoa-Balonne-Condamine subregion, for both the baseline and coal resource development pathway

Hydrological effects denoted by symbols with black font are not predicted by numerical modelling in the Maranoa-Balonne-Condamine subregion, but are instead assessed qualitatively.

This figure has been optimised for printing on A3 paper (420 mm x 297 mm).

Table 3 Causal pathways in the Maranoa-Balonne-Condamine subregion and their associated hazards, hydrological effects, system components and temporal context

Each causal pathway is listed in a chain of logic from the hazard and associated hydrological effects to system components (as defined in Figure 5) that may contain potentially impacted assets or ecosystems.


Causal pathway group – Causal pathway

Hazards (impact mode)

Hydrological effects

System components

Temporal contexta

Subsurface depressurisation and dewatering – Groundwater pumping enabling coal seam gas extraction, Groundwater pumping enabling open-cut coal mining, Groundwater pumping of target aquifer

Aquifer depressurisation, Aquifer depressurisation (coal seam), Groundwater extraction (groundwater supply bore), Localised watertable reduction, Reduction in pressure head (pump testing), Very localised watertable reduction

Groundwater flow (reduction), Groundwater level, Groundwater pressure

Target aquifer

Short term,

Long term

Subsurface depressurisation and dewatering – Unplanned groundwater changes in non-target aquifers

Aquifer depressurisation (fault-mediated), Aquifer depressurisation (non-target, non-reservoir), Deliberate dewatering (pit wall stabilization), Miss perforation of target aquiferb

Surface water flow, Groundwater direction, Groundwater flow (reduction), Groundwater pressure, Groundwater quality, Groundwater quantity/volume

Non-target aquifer,

Alluvium and watercourses in aquifer outcrop areas within and downstream of tenements

Medium to long term,

Long term

Subsurface physical flow paths – Failure of well integrity

Bore leakage between aquifers, Bore leakage to surface, Fluid loss to aquifer, Incomplete seal, Incomplete/ compromised cementing/casing (gas leakage), Incomplete/ compromised cementing/ casing (linking aquifers), Intersection of artesian aquifer, Miss perforation of target aquiferb (connecting aquifers), Mud pressure imbalance, Seal integrity loss

Surface water quality, Groundwater quality, Groundwater composition, Groundwater pressure

Aquifers within tenements,

Watercourses within and downstream of tenements

Short term,

Long term

Subsurface physical flow paths – Hydraulic fracturing

Accidental intersection of fault, Changing non-target aquifer properties (physical or chemical), Changing target aquifer properties (physical or chemical), Connecting aquifers (too much pressure), Contaminate non-target aquifer (chemical), Contaminate target aquifer (chemical), Intersection of aquifer

Aquifer properties, Groundwater composition, Groundwater pressure, Groundwater quality

Target aquifers within tenements,

Non-target aquifers within tenements

Long term

Subsurface physical flow paths – Extracting overburden to access coal

Artificial point of recharge, Enhanced aquifer interconnectivity, Groundwater sink, Linking aquifers, preferential drainage

Surface water flow, Change to zero-flow days, Groundwater direction, Groundwater pressure, Groundwater quality, Groundwater quantity/volume

Alluvium and watercourses in aquifer outcrop areas within and downstream of tenements,

Aquifers within tenements

Medium to long term,

Long term

Surface water drainage – Altering surface water system

Change to natural surface drainage, Disruption of natural surface drainage

Surface water direction, Surface water quality, Surface water volume, Groundwater quantity/volume

Alluvium and watercourses in aquifer outcrop areas within and downstream of tenements

Medium to long term

Surface water drainage – Subsidence of land surface

Subsidence

Surface water direction

Watercourses within and downstream of tenements

Long term

Operational water management – Discharging extracted water into surface water system

Discharge to river, Discharge to river following heavy rainfall, Discharge to river: rising watertable, Discharge to river (via first or third party)

Surface water flow, Surface water quality, Groundwater level, Groundwater quality

Alluvium and watercourses in aquifer outcrop areas within and downstream of tenements

Short term

Operational water management – Processing and using extracted water

Increase discharge to rivers following irrigation, Raise watertable following irrigation, Soil salt mobilization following irrigation

Surface water flow, Surface water quality, Groundwater level, Groundwater quality

Alluvium and watercourses in aquifer outcrop areas within and downstream of tenements,

Watercourses within and downstream of tenements

Short term

Operational water management – Reinjecting co-produced water into aquifer

Injection of water into aquifer

Groundwater composition, Groundwater pressure

Aquifers targeted for reinjection

Long term

Operational water management – Storing extracted water

Change to natural surface drainage, Disruption of natural surface drainage (freshwater storage), Disruption of natural surface drainage (mine water storage), Disruption of natural surface drainage (tailings water storage), Excessive runoff during closure (water management structures)

Surface water direction, Surface water flow, Surface water quality, Surface water volume, Groundwater quality, Groundwater quantity/volume

Alluvium and watercourses in aquifer outcrop areas within and downstream of tenements,

Watercourses within and downstream of tenements

Medium to long term

Full descriptions of the causal pathways and causal pathway groups are available in companion submethodology M05 (as listed in Table 1) for developing a conceptual model of causal pathways (Henderson et al., 2016).

ashort term = less than 5 years, medium term = 5 to 10 years, long term = 10 to 100 year

bMisspelled in the hazard workshop. Correct terminology is ‘mis-perforation of coal seam’.

Typology and punctuation are consistent with the hazard analysis (Bioregional Assessment Programme, Dataset 1).

Data: Bioregional Assessment Programme (Dataset 1)

Last updated:
30 October 2018
Thumbnail of the Maranoa-Baloone-Condamine subregion

Product Finalisation date

2017
PRODUCT CONTENTS