How could coal resource development result in hydrological changes?

The assessment identified potential hazards (Dataset 11) associated with coal resource development that could result in hydrological changes, such as aquifer depressurisation due to groundwater extraction. The hazard analysis, including a description of the top 30 ranked hazards identified for coal mining and CSG developments, is presented in Section 2.3.5 of Evans et al. (2018b). Hazards in scope were further assessed by first estimating relevant hydrological changes through hydrological modelling and then identifying potential impacts on, and risks to, water-dependent ecosystems and assets (as described in the following sections).

In the bioregional assessment context, four causal pathway groups summarise the chains of events that commonly arise from coal resource development activities (letters A to D in the list below correspond to those shown in Figure 7):

  1. ‘Subsurface depressurisation and dewatering’ is triggered by extraction of groundwater to enable CSG extraction, and mine dewatering of open-cut pits and underground operations. This directly affects the local and regional groundwater systems, and indirectly affects surface water – groundwater interactions. Potential effects are likely to be in the short term (less than 5 years) for groundwater pressure changes, to long term (10 to 100s of years) for changes in groundwater movement or quality.
  2. ‘Subsurface physical flow paths’ are initiated by activities that cause physical changes to the rock mass or geological layers (such as underground coal mining), resulting in new physical paths that water may potentially gain access to and flow along. Potential effects are in the medium (5 to 10 years) to long term and are likely to be restricted to aquifer or aquifer outcrop areas, but can also affect connected watercourses within and downstream of mines.
  3. ‘Surface water drainage’ is triggered by activities that physically disrupt the surface and near-surface materials (vegetation, topsoil, weathered rock). Medium- to long-term cumulative effects are possible for watercourses within and downstream of development. Activities may include construction of diversion walls and drains, interception of surface runoff, realignment of streams, and groundwater extraction for CSG production or underground coal mining leading to subsidence of the land surface.
  4. ‘Operational water management’ is triggered by modification of surface water systems to allow storage, disposal, processing and use of extracted water. Potential effects are likely to be in the medium to long term and include impacts on watercourses within and downstream of operations.

Many activities related to coal resource development may also cause more localised or on-site changes to surface water or groundwater. These are not considered explicitly in bioregional assessments because they are considered to be adequately managed by site-based risk management and mitigation procedures (for example, licence conditions accompanying environmental approvals), and are unlikely to result in regional-scale cumulative impacts.

Figure 7

Figure 7 Conceptual diagram of the causal pathway groups that are associated with generic underground and open-cut coal mines

This schematic diagram is not drawn to scale. This generic diagram does not specifically relate to any proposed coal mines in the Galilee subregion, nor does it represent any specific geographic features, geological units or land uses in the subregion. Rather, the mining operation shown here illustrates examples of the four causal pathway groups defined in bioregional assessments (see Section 2.3.5 of Evans et al. (2018b)). The underground arrows refer to groundwater extraction, whereas above-ground arrows illustrate various aspects of mine water management, which may include transferring extracted groundwater around the mine site.

ROM = run of mine


Conceptual modelling, product 2.3 (Evans et al., 2018b)

Surface water numerical modelling, product 2.6.1 (Karim et al., 2018a)

Groundwater numerical modelling, product 2.6.2 (Peeters et al., 2018)

Developing the conceptual model for causal pathways, submethodology M05 (Henderson et al., 2016)

Systematic analysis of water-related hazards associated with coal resource development, submethodology M11 (Ford et al., 2016)

Impact Modes and Effects Analysis for the Galilee subregion (Dataset 11)

Last updated:
6 December 2018