Most of the rock strata within the model are fully saturated and Darcy’s equation governs the flow of . However, many of the identified in the for the (see companion product 1.3 for the Hunter subregion ()) lie close to the surface, and are either within the or are directly affected by it. Therefore, single-phase unsaturated Darcy-Richards physics is used in the model.
The groundwater model assumes water has a constant bulk modulus of 2 GPa, and that the Biot coefficient is 1, which is standard practice in poroelasticity (the study of fluid flows in elastic media, see Detournay and Cheng, 1993). Therefore, the specific storage does not include any effects from rock elasticity. If the Biot coefficient is less than 1 and the rock bulk modulus is not too large then the specific storage is increased because the rock grains can be squashed to accommodate more water. For example, if is 0.05 and rock bulk modulus is 10 GPa, then the maximum specific storage (at Biot coefficient 0.525) is almost twice that used by the groundwater model. This causes the response time of any effect to be increased (but not linearly with respect to storage increase since the main driver of the timescales involved is the mine pumping rates) and reduces the magnitude of the drawdown. Therefore, by assuming the Biot coefficient is unity or that the rock is incompressible, the Hunter groundwater model will slightly overestimate the magnitude of drawdown. Since porosity is varied by more than an order of magnitude in the analysis, it more than compensates for any changes in specific storage from varying the Biot coefficient. To assess the effect of altering the Biot coefficient or the rock bulk modulus, the emulators can be biased towards slightly higher porosity.
To represent the hydrological changes due to longwall mining on groundwater fluxes, hydraulic conductivities are enhanced in mesh elements above the longwall mines. Section 18.104.22.168 details the relevant parameters for defining magnitude and depth of enhancement.
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 and conclusions
- Currency of scientific results
- Contributors to the Technical Programme
- About this technical product