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2.5 Water balance assessment for the Hunter subregion

Executive summary

Google Earth image of the Hunter River west of Muswellbrook

This product uses results from surface water and groundwater numerical modelling to assess how water balances might be different as a result of coal resource development in the Hunter subregion for three time periods: 2013 to 2042, 2043 to 2072, and 2073 to 2102.

Water balances are reported for the two futures considered in a bioregional assessment:

  • baseline coal resource development (baseline): a future that includes all coal mines and coal seam gas fields that were commercially producing as at December 2012.
  • coal resource development pathway (CRDP): a future that includes all coal mines and coal seam gas fields that are in the baseline as well as those that were expected to begin commercial production after December 2012.

The difference in results between these potential futures is due to the additional coal resource development – all coal mines and coal seam gas fields, including expansions of baseline operations that were expected to begin commercial production after December 2012.

Water balances for the Hunter subregion

Most of the coal resource developments in the Hunter subregion occur around the Hunter River from Muswellbrook and Singleton, south of Maitland, in the headwaters of the Goulburn River and inland and around Lake Macquarie and Tuggerah Lakes.

A groundwater balance can be generated for the entire Hunter subregion (over 34,000 square kilometres). The overall change in groundwater balance due to additional coal resource developments is predicated to be a small volume. For example, in 2013 to 2042, additional coal resource developments result in modelled reductions of the median groundwater contribution to streamflow of 0.2%. This rises to 2.4% for the period 2073 to 2102, reflecting the lag in response of the surface water – groundwater flux to mine pumping.

The surface water balances comprise rainfall, surface water outflow, and losses (including evapotranspiration and water extractions). In the Hunter subregion, there are two surface water basins that are largely closed from each other, so the analysis was conducted separately on two areas:

  1. In the western part of the subregion, the catchment area of the Goulburn River upstream of stream gauge 210006 is 3400 square kilometres.  Changes modelled at this gauge include most of the cumulative changes associated with the additional coal resource developments at Bylong, Moolarben, Ulan West and Wilpinjong coal mines. The median reductions in mean annual streamflow at this gauge due to the additional coal resource development were between 0.4–1.0 percent of the baseline streamflow.
  2. In the western and central parts of the subregion, the catchment area of the Hunter River and its tributaries upstream of gauge 210001 is 16,485 square kilometres. Changes modelled at this gauge include most of the cumulative changes from the Goulburn River coal mines listed above, as well as  the additional resource developments at Ashton, Bengalla, Bulga, Drayton South, Liddell, Mount Arthur, Mount Owen, Mount Pleasant and Mount Thorley-Warkworth and Wambo coal mines. The median reductions in mean annual streamflow at this gauge due to the additional coal resource development in this area vary from 1.1 to 2.4 percent of baseline streamflow.

This analysis is part of a series of products, which describe how surface water and groundwater is potentially impacted by coal resource development into the future. The product informs impact and risk analysis (Component 3 and 4) products, which examine the risk to, and potential impacts on, water resources and water-dependent assets due to coal resource developments.

Last updated:
15 June 2018