Defining the PAE allows the asset register to be compiled in parallel with the assessment of the coal and coal seam gas resources (Lewis et al., 2014) and the development of the coal resource development pathway (see pending companion product 2.3) for the subregion.
Because development of the Galilee PAE occurred prior to any modelling or significant data analysis taking place as part of the Galilee BA, the following principles guided the development of the PAE:
- The PAE had to encompass all conceivable, conceptualised scenarios, and be conservative and precautionary.
- The PAE had to encompass all potential coal resource developments within the Galilee subregion (see Lewis et al., 2014).
- There needed to be a buffer zone around the PAE area to avoid potential boundary effects during modelling and impact assessment (e.g. not having enough data outside the modelled area of interest to show the true edge of potential response and impact areas).
The Galilee PAE was constructed from two parts: a surface water PAE and groundwater PAE.
The surface water PAE was constructed according to the following steps:
- Identify major catchments in the Galilee subregion and identify where the major drainage channels ended.
- Identify major infrastructure in the catchments where surface water flow could be significantly impeded (e.g. dams).
- If infrastructure such as a major dam exists, then the PAE was stopped at that point, as it was assumed any impacts would be captured rather than propagated further downstream. The exception was the surface water PAE in the Burdekin river basin. For the Burdekin River, the surface water PAE was extended beyond the Burdekin Falls dam to the coast. This was done to ensure that assets in the vicinity of the Burdekin River directly downstream of the dam were included in the asset register as all of the coal developments at an advanced approval stage in the Galilee subregion are located in the headwaters of the Burdekin river basin.
- If there was no significant infrastructure, then the surface water PAE was extended along the main drainage to the outlet of the catchment. This was either at the sea or Kati Thanda – Lake Eyre.
- A buffer of 5 km was placed around all drainage channels, to capture any near-stream assets and counter potential data errors in GIS datasets.
The groundwater PAE was constructed according to the following steps:
- The whole of the Galilee subregion was included according to the precautionary principle. This approach was taken because, at the time of development of the PAE, there was limited information available about potential coal resource developments and potential hydrogeological connectivity.
- A buffer of 20 km was applied to the eastern margin of the subregion. Here, the reasoning was that the eastern margin of the Galilee subregion forms a major geological boundary and it is envisaged that drawdown of the watertable from developments would not extend far into adjoining geological regions. In addition, a 20 km buffer would include much of the Belyando River catchment, which is an area in which impacts could potentially occur as a result of its proximity to proposed coal resource developments.
- At the time of development of the Galilee PAE, it was still uncertain how far any potential hydrological responses might extend into overlying aquifers associated with the Eromanga Basin. Thus a 200 km buffer was applied to the western and southern margins of the subregion. The reasoning here was that the overlying Eromanga Basin rock units extend to the west and south of the Galilee subregion.
- The section of PAE boundary extending north-east from Cloncurry corresponds with the edge of the Eromanga Basin. This basin margin edge approximates a major groundwater divide in the Great Artesian Basin.
The Galilee PAE is a composite of this groundwater PAE and surface water PAE (Figure 3).
Data: Geoscience Australia (Dataset 22), Bioregional Assessment Programme (Dataset 24)
