Surface water numerical modelling for the Gloucester subregion. Product 2.6.1 for the Gloucester subregion from the Northern Sydney Basin

Zhang, Y. and Viney, Neil and Peeters, L and Wang, B and Yang, Ang and McVicar, TR and Marvanek, SP and Shi, Xiaogang and Pagendam, DE and Singh, RM (2016) Surface water numerical modelling for the Gloucester subregion. Product 2.6.1 for the Gloucester subregion from the Northern Sydney Basin. CSIRO PUBLISHING. ISBN 9781925315202

Abstract

Coal and coal seam gas (CSG) development can potentially affect water-dependent assets (either negatively or positively) through a direct impact on surface water hydrology. This product provides modelled estimates of the potential surface water impacts of likely coal resource developments in the Gloucester subregion. First, the methods are summarised and existing models are reviewed, followed by details regarding the development of the model. The product concludes with predictions of the hydrological characteristics of the system that may change due to coal resource development (referred to as hydrological response variables) also taking into account uncertainty. Surface water modelling in the Gloucester subregion follows the companion submethodology M06 (as listed in Table 1) (Viney, 2016). No river modelling was carried out because the rivers in the subregion are unregulated and their catchments are relatively small. Instead, predicted streamflow is obtained by accumulating output from a spatially-explicit streamflow model (the Australia Water Resource Assessment Landscape model, AWRA-L). The modelling domain comprises the Gloucester and Karuah river basins and includes 34 modelling nodes at which daily streamflow predictions are produced. The model simulation period is from 2013 to 2102. The conceptual model for the Gloucester subregion (in companion product 2.3 for the Gloucester subregion), indicates that CSG and large coal mining development have the potential to directly affect the regional groundwater system and that this direct effect can propagate through to the alluvia of the Gloucester and Karuah river systems. Any impact on the groundwater in the alluvium of those rivers in turn has the potential to affect streamflow and therefore surface water resources in the stream networks of the Gloucester and Karuah rivers. CSG development may impact streamflow if aquifer depressurisation reduces baseflow, while open-cut coal mines, in addition to reducing baseflow through groundwater drawdown, will intercept and retain surface runoff which has the potential to affect streamflow directly. Surface water modelling results estimate hydrological changes arising from coal resource development by comparing the difference in predicted water levels between two possible futures – the baseline and the coal resource development pathway (CRDP) – to provide an estimate of changes that are attributable to the additional coal resource development (ACRD). Results are reported at 30 receptors, which are points in the landscape where water-related impacts on assets are estimated. There are three open-cut coal mining operations in the Gloucester CRDP, as well as one coal seam gas (CSG) field. The Stratford Mining Complex and the Duralie Coal Mine are both baseline mines (i.e. in commercial production as of December 2012) that also have future expansion projects.