18.104.22.168.2.1 Drawdown due to additional coal resource development
As discussed in Section 22.214.171.124, the primary objective of the modelling is to provide probabilistic estimates of at the due to . The regional watertable is where the majority of the ecological, economic and sociocultural are dependent upon water. Drawdown in the confined part of the Pilliga Sandstone is also predicted as there are economic assets dependent upon this water source.
At each Figure 3, Section 126.96.36.199), time series of groundwater level in the regional watertable are simulated for the and the . The maximum difference in drawdown (dmax) between the modelled CRDP and baseline, due to additional coal resource development, and the year of maximum change (tmax), are calculated using the difference between the two time series. This is illustrated in Figure 21 for one model node.(shown in
Groundwater level is relative to height above the Australian Height Datum (AHD).
CRDP = coal resource development pathway. Additional drawdown is the maximum difference in drawdown (dmax) between the coal resource development pathway (CRDP) and baseline, due to additional coal resource development.
188.8.131.52.2.2 Change in surface water – groundwater flux due to additional coal resource development
The difference in the Figure 14 in Section 184.108.40.206. The changes in surface water – groundwater flux upstream of each surface water in Figure 14 in Section 220.127.116.11 are aggregated at the node. The resulting change in flux time series are inputs to the surface water modelling, as documented in Section 18.104.22.168 and in greater detail in companion product 2.6.1 for the Namoi subregion ( ).– flux due to is simulated for points along the groundwater model stream network shown in
Generally, theof water by coal mines causes to decrease. However, the modelling indicates that longwall mining can also increase baseflow. This is due to hydraulic conductivity enhancement above underground mines and is explained in more detail in a numerical experiment reported in the groundwater modelling product for the ( ). The results concluded that there are three ways that baseflow can increase due to mining:
- in the short term (weeks), water stored in the interburden can be released as the groundwater finds a new equilibrium after the enhancement of hydraulic conductivity due to the collapse of the (this is modelled in the groundwater model)
- when the groundwater’s new phreatic surface is deeper than prior to mining, resulting in less evapotranspiration from groundwater (this is modelled in the Namoi subregion groundwater model)
- in the longer term (years), when a new equilibrium is established, the enhanced conductivity means that: (i) groundwater moves faster due to an increase in that more than compensates for a reduction in hydraulic gradient (this is modelled); and (ii) rainfall is potentially higher (this is not modelled).
The maximum and minimum change in the surface water – groundwater flux for each time series and for each stream reach in the river model have been summarised in Figure 22. This shows that decreases in the surface water - groundwater flux occur in the vicinity of all coal resource developments but increases in surface water – groundwater flux only occur in the vicinity of longwall mines.
Figure 22 The 5th, 50th and 95th percentiles of the change in surface water - groundwater (SW-GW) flux predicted for each reach in the river model domain for the minimum and maximum change in a time step over the period 2013-2102
Product Finalisation date
- 22.214.171.124 Methods
- 126.96.36.199 Review of existing models
- 188.8.131.52 Model development
- 184.108.40.206 Boundary and initial conditions
- 220.127.116.11 Implementation of the coal resource development pathway
- 18.104.22.168 Parameterisation
- 22.214.171.124 Observations and predictions
- 126.96.36.199 Uncertainty analysis
- 188.8.131.52 Limitations
- Currency of scientific results
- Contributors to the Technical Programme
- About this technical product