The Surat geological basin dips in the south-west direction, which means that the main geological units are absent in the north of the model extent. Similarly, the main geological units of the Bowen Basin are absent to the east and west of the mapped boundaries of this basin. There is no evidence of groundwater connectivity across the Surat and Bowen geological basin boundaries (GHD, 2012). For this reason, no-flow boundary conditions are assigned to all model cells in the north-west and north-east of the modelled areas (GHD, 2012) (Figure 7). No-flow boundary conditions are also assigned to the western boundary of the model area as ‘little or no interaction is thought to occur across the Nebine Ridge’ (GHD, 2012, p. 56).
Potentially significant groundwater flows are thought to occur across the mapped boundary between the Surat and Clarence-Moreton geological basins in the east across the Kumbarilla Ridge (GHD, 2012; Ransley and Smerdon, 2012). MODFLOW General Head Boundary (GHB) cells are assigned to the model layers corresponding to the Walloon Coal Measures, Hutton Sandstone and Precipice Sandstone along this boundary (GHD, 2012).
Groundwater in the Surat Basin along the southern boundary of the model along the Queensland state border continues to flow in a southerly direction. For this reason, groundwater flow in this area is simulated by assigning GHB cells at the modelled ground surface in each of the productive coal or aquifer units present at this location (GHD, 2012).
No flow and GHB cell locations over the entire OGIA model extent are shown in Figure 7. The groundwater model domain encompasses current and future key stresses related to coal resource development. Modelled drawdown does not extend to the lateral boundaries within the prediction period, indicating that coal resource development is sufficiently remote to reduce the impact of the boundary conditions on the model predictions.
Source: adapted from Figure 15 Grid and Boundary Conditions. Steady State Regional Model (GHD, 2012)
