The Hunter subregion is part of the Northern Sydney Basin bioregion (Figure 3). The Northern Sydney Basin bioregion is located north-west of Sydney in eastern Australia. The bioregion adjoins the Northern Inland Catchments bioregion in the north-east and the Sydney Basin bioregion in the south. The Northern Sydney Basin bioregion covers an area of about 17,390 km2.
Figure 3 Hunter and Gloucester subregions in the Northern Sydney Basin bioregion
The adjacent Sydney Basin bioregion and subregions within the Northern Inland Catchments bioregion are also shown.
The Hunter subregion covers about 17,045 km2. The Hunter subregion is defined from four data sources, being: (i) the geological Sydney Basin (Tadros, 1995), (ii) the geological Werrie Basin (Carey, 1934; DMR, 2002), (iii) the Hunter Central-Coast surface water catchments (Geoscience Australia, 2006) and (iv) the Australian coastline derived from the 1:250,000 topographic dataset (Geoscience Australia, 2006). These are shown in Figure 4 .
Figure 4 Boundary definitions of the Hunter subregion
Data: (i) Sydney Basin, Tadros (2005), (ii) Werrie Basin, Geoscience Australia (Dataset 1), (iii) the coastline and the Hunter-Central Coast surface water catchment boundaries, Geoscience Australia (Dataset 2)
The Werrie Basin is a transitional basin between the Sydney and Gunnedah geological basins and, due to its relatively small size, the Werrie Basin is not currently included in the Australian Geological Provinces Database (Geoscience Australia, 2013). As this feature is so small and ill defined, in some geological circles it is termed the Werrie Syncline. Definition of the Hunter subregion used a spatially disconnected part of the Gunnedah Basin (Geoscience Australia, 2009) with a boundary that closely resembles other more detailed definitions of the Werrie Basin (Carey, 1934; DMR, 2002).
The Hunter Central-Coast surface water catchments conform to the boundary of the area formerly managed by the Hunter-Central Rivers Catchment Management Authority (CMA; DIPNR, 2003). It was this CMA boundary that was used when the Hunter subregion was defined in 2012. From 1 January 2014, all CMAs in NSW transitioned into local land services (LLS) regions (NSW Government, 2014) and part of the Central-Coast portion of the Hunter subregion is now part of the Greater Sydney LLS region (Figure 5). However, as it was included in the Hunter-Central Rivers CMA boundary when the Hunter subregion was defined in 2012, it is maintained as part of the Hunter subregion.
