2.5.2 Water balances

Summary

The hydrological changes from proposed coal resource developments in the Galilee subregion are presented in the following ways: surface water – in terms of net changes in surface water flow over three time periods (2013 to 2042, 2043 to 2072 and 2073 to 2102); groundwater – a conceptual groundwater balance at 2012 (pre-development) and then at 30 years in the future (when proposed mines are in production).

The Galilee subregion coal resource development pathway (CRDP) consists of 17 proposed coal and coal seam gas (CSG) resource development projects (see companion product 2.3 for the Galilee subregion (Evans et al., 2018a)) of which only 7 were considered to have enough available information for inclusion in the additional coal resource development (i.e coal mining projects included in the modelling).

The model area for both water balances is that portion of the Galilee subregion that lies within the Burdekin river basin, specifically the Belyando river basin. The Belyando River is a tributary to the Burdekin River. All seven coal mining projects included in the modelled CRDP are situated within in the headwaters of the Belyando river basin.

The surface water balance is presented at a specific location on the Belyando River (node 53) that captures resultant changes in streamflow of the seven modelled coal mining projects in the Galilee subregion, while the groundwater results are presented for the portion of the Belyando River basin included in the modelling area.

For the surface water balance, the major difference noted between the baseline and modelled CRDP is the decrease in surface water outflow. This is due to interception of surface runoff on the mine sites rather than a decrease in baseflow discharge due to groundwater extraction. This change in flow magnitude between the baseline and modelled CRDP futures is less than 1% at model node 53 on the Belyando River, and is within the uncertainty of the predicted surface water flow.

The conceptual groundwater balance primarily focuses on the major components of the groundwater system: recharge, discharge, storage, and changes to storage through groundwater usage. While this represents a relatively simple approach with non-stochastic outputs it does demonstrate that 30 years into the future, the seven coal mining operations in the Galilee subregion will substantially increase the volume of groundwater extracted (primarily due to mine dewatering). This increase in groundwater usage may be the equivalent of up to 66% of estimated groundwater recharge. This represents a substantial change in the groundwater balance in comparison to the pre-mining situation. Future work should focus on improving the understanding of recharge processes in the Galilee Basin, as well as improved volumetric estimates of the components of the water balance.

Most of the pumped groundwater will be used within the coal projects as part of the mine water management system. However, from mine environmental impact statement (EIS) documentation it is apparent that additional water will also need to be sourced external to the mine areas for operational purposes. As of April 2016, the amount and sources of external water are yet to be finalised. This represents a largely unknown but additional factor for the groundwater and surface water balances.