- Bioregional Assessment Program
- Hunter subregion
- 2.6.2 Groundwater numerical modelling for the Hunter subregion
- 22.214.171.124 Review of existing models
A review of groundwater models that have been developed for use in the Hunter subregion was undertaken. Existing models were found to be local-scale models intended to assess groundwater hydrological changes of mining at the individual mine scale. Their spatial extents and resolutions mean they are not suitable for modelling cumulative hydrological changes of multiple mining operations at the scale of the Hunter subregion. Furthermore, they are deterministic models, not suited to quantification of modelling uncertainties using a probabilistic approach.
Groundwater modelling undertaken as part of a mine’s environmental assessment provides local-scale information on hydraulic properties for informing the regional-scale modelling undertaken in this product.
Results from a limited number of local-scale mine groundwater models have been used to suggest a groundwater impact zone can be approximated around existing open-cut mines in the Hunter Coalfield using a generalised buffer of 4 km (EMM, 2015). The groundwater modelling reported here goes further: it includes current and proposed, open-cut and underground mines within the Hunter, Western and Newcastle coalfields; considers the timing of the developments; performs a cumulative impact assessment; and includes an estimation of the changes in surface water – groundwater flux that inform the Hunter surface water model. These are all framed within a comprehensive uncertainty analysis.
Many local-scale groundwater flow models have been developed in the Hunter subregion to support mine environmental assessments. These are generally local-scale models developed to assess the hydrological changes due to a single development. Table 4 summarises the spatial extent and resolution of 43 models reviewed for the Hunter subregion. Model domains vary from as little as 26 km2 (Awaba; GHD, 2010) to 2750 km2 (Moolarben; Aquaterra, 2008b). Not one comes close to providing the level of coverage needed for regional-scale groundwater assessments. Pixel sizes range from a very fine 5 m in the COSFLOW model for Bulga Coal (Guo et al., 2014) to 340 m in the MODFLOW-SURFACT model for Spur Hill (HydroSimulations, 2013a), with average pixel size of around 65 m. This granularity is intended to capture a level of detail about the hydrogeological domain appropriate to a site-scale assessment, but is too fine for practical regional-scale modelling. The groundwater model developed for the Hunter subregion covers an area of approximately 34,000 km2, with a best spatial resolution of 500 m.
Quantification of the uncertainties arising from model conceptualisation, parameterisation and available data is a major objective of the bioregional assessments. These mine-scale models were not intended to evaluate the direct, indirect and cumulative hydrological changes of mining operations in a probabilistic manner. Rather, the intent of these models is to use the best local-scale information available (often collected by the mining company and the consultant preparing the assessment) to determine as accurately as the information allows, the specifics of mine water pumping, drawdowns and local disruptions to surface drainage for the purposes of obtaining licences to dewater mines and to discharge to streams, and to develop environmental management plans that minimise impacts to the environment. The environmental assessments contain a wealth of information concerning local hydraulic properties (conductivities and porosities), which have been used to inform the development of the Hunter groundwater model (see Section 2.1.3 of companion product 2.1-2.2 for the Hunter subregion (Herron et al., 2018)).
For reasons of scale, extent and purpose of modelling, none of the models listed in Table 4 is appropriate for use in a bioregional assessment.
Table 4 Summary of existing groundwater models in the Hunter subregion
In a study of Mid Hunter groundwater (EMM, 2015), commissioned by DPI Water to inform the development of the now commenced (from 1 July 2016) Water Sharing Plan for the North Coast Fractured and Porous Rock Groundwater Sources, results from some local-scale mine groundwater models were used to determine the extent of significant drawdown from coal resource developments in the Hunter Coalfield. Results suggested that the union of a generalised buffer of 4 km around each existing mine could be used to define the potential impact area from all the mines in the Hunter Coalfield based on drawdowns less than or equal to 2 m. In contrast to this study, the groundwater model described here also: includes the Western and Newcastle coalfields, underground mines, and proposed and approved developments that had not commenced at the time of study; considers the timing of the developments; performs a cumulative impact assessment; and includes an estimation of the changes in surface water – groundwater flux that inform the Hunter surface water model. These are all framed within a comprehensive uncertainty analysis.
Product Finalisation date
- 126.96.36.199 Methods
- 188.8.131.52 Review of existing models
- 184.108.40.206 Model development
- 220.127.116.11 Boundary and initial conditions
- 18.104.22.168 Implementation of the coal resource development pathway
- 22.214.171.124 Parameterisation
- 126.96.36.199 Observations and predictions
- 188.8.131.52 Uncertainty analysis
- 184.108.40.206 Limitations and conclusions
- Currency of scientific results
- Contributors to the Technical Programme
- About this technical product