1.1.4 Hydrogeology and groundwater quality


The hydrogeological systems in the Hunter subregion are associated with Permian-Triassic fractured rock aquifers, alluvial aquifers along major rivers and creeks, and a coastal sand aquifer in the coastal zone of the region. The Hunter Valley represents a regional groundwater discharge zone and a dividing streamline for groundwater flow. Similar to surface water, the main regional groundwater fluxes south from Hunter-Mooki thrust fault, which forms the northern boundary of the Sydney Basin, largely following the subregion’s topography from upland towards the river channels with overall discharge to the ocean.

The Hunter Valley Alluvium aquifer is an important groundwater management unit (GMU). It is fully allocated with total licensed abstraction of 80.4 GL/year. The Kingdon Ponds and Dart Brook alluvial aquifers, located in the north-west of the subregion, are the major components of this groundwater management unit. The Tomago sands are an important water resource for the Newcastle area, being one of three main water sources. The Tomago sands groundwater resource is an important drought contingency but surface water catchments dominate potable water supplies during normal times.

The Hunter subregion is spatially dominated by fractured rock aquifers, including those in the Liverpool Range Volcanics, Jurassic, Narrabeen and Permian sedimentary (mainly sandstone) group. However groundwater yields from these aquifers are generally low.

The Permian units are associated with a series of coal measures and intervening marine sequences. The saline water associated with this geological unit is thought to have a controlling influence on the overall water quality of the Hunter River (Kellett et al., 1989). The weathered profile, or regolith that is up to 100 m thick, can act as an unconfined aquifer which feeds into local springs after high rainfall, though most are depleted during extended dry and drought periods. Enhanced permeability of these formations is associated with faults and fractures, particularly in the hinge areas and limbs of anticlines.

The coal seams exhibit many joints and cleats and are the main aquifers within the Permian units. Groundwater in the regolith and deeper coal measures can be isolated due to the presence of less permeable interburden formations, unless vertical faulting provides a connecting pathway to deeper strata.

Groundwater diffuse recharge from Permian material is estimated at less than 2% of annual rainfall, with high values associated with areas of the enhanced regolith permeability. Alluvial aquifers also receive recharge from the natural river flow and particularly during flooding; this is supplemented by leakage or environmental water releases from water supply dams. Groundwater discharge forms river baseflow throughout the subregion, which is more persistent in the main Hunter alluvial systems than in the elevated areas. There is potential for groundwater within the Hunter subregion to interact with groundwater systems to the south (Sydney Basin) or to the west (Gunnedah Basin), mainly within deeper strata, but the volumetric fluxes between these basins are likely to be minimal.

Last updated:
18 January 2019
Thumbnail of the Hunter subregion

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