Executive summary

The Hunter subregion is part of the Northern Sydney Basin bioregion and includes the major coastal cities of Newcastle and Gosford-Wyong (Figure 2). It is known for its coal mining, power generation, equine and viticulture industries. It includes two Ramsar-listed wetlands and contains part of the Greater Blue Mountains World Heritage Area. The total area investigated for this assessment (the assessment extent) is the same as the subregion extent, which covers 17,045 km².

Regional-scale hydrological modelling identified changes in groundwater and streamflow due to coal resource development for two futures (Box 1). The baseline future comprises 42 mines (22 open-cut and 20 underground) that were operating in December 2012. The coal resource development pathway (Box 1) was the most likely future for the subregion (as of September 2015) and includes the baseline developments plus 22 additional coal resource developments: 4 new open-cut mines, 2 new underground mines and 16 expansions to existing operations. Surface water and/or groundwater modelling were not undertaken for a small number of these developments. No coal seam gas (CSG) developments exist or are proposed in the subregion.

Additional coal resource development could lead to 19% of the assessment extent experiencing hydrological changes that exceed defined thresholds (Box 4). Outside this zone of potential hydrological change, hydrological changes are not significant, and hence impacts are very unlikely (less than 5% chance).

Modelling indicates potentially large changes in flow regime in Wyong River, Loders Creek, Saddlers Creek, Wollar Creek and a number of ephemeral creeks (Figure 12). Fourteen percent, or 2441 km², of the assessment extent has at least a 5% chance of greater than 0.2 m drawdown in the regional watertable due to additional coal resource development. Modelling of the Wyong River using local-scale data indicates that large changes in the flow regime are unlikely in that river.

The two Ramsar-listed wetlands are outside the zone of potential hydrological change and so are very unlikely to be impacted.

Potentially impacted ecosystems in the zone include 102 km² of groundwater-dependent ecosystems (GDEs) (predominantly rainforests, forested wetlands, and wet and dry sclerophyll forests), and 634 km of perennial and 518 km of intermittent streams.

Modelled changes in ecologically important flows indicate a higher risk to the condition of riverine forested wetlands along the Goulburn River compared to other riverine forested wetlands in the subregion.

Changes in water availability in the Hunter Regulated River at Greta are very likely (greater than 95% chance) to exceed 5 GL per year, but very unlikely to exceed 12 GL per year, over the period 2013 to 2042.

Drawdowns exceeding 2 m due to additional coal resource development are very likely for 13 bores. The number of water supply bores where drawdown exceeds 2 m is very unlikely to be more than 170. Under the NSW Aquifer Interference Policy, ‘make good’ provisions could apply to licensed water holders affected by drawdowns of greater than 2 m. More detailed site-specific studies are needed to review the predicted changes in areas where regional-scale modelling indicates a high probability of large drawdowns.

Almost 140 km² of the Greater Blue Mountains World Heritage Area is within the zone but most is not predicted to be impacted because it supports vegetation that does not depend on groundwater. About 1.5 km² of forested wetland in this World Heritage Area could be affected by drawdown due to additional coal resource development.