1.1.4 Hydrogeology and groundwater quality


The Central West subregion includes groundwater systems in alluvial aquifers associated with major streams (including their precursors), volcanic rocks of the Warrumbungle and Liverpool ranges (Cenozoic Basalts), aquifers of the Great Artesian Basin (GAB), aquifers in the Gunnedah-Oxley Basin, and fractured rock aquifers of the Lachlan Fold Belt. These aquifers are incorporated into NSW water sharing plans, as well as the Murray–Darling Basin Plan.

Groundwater monitoring is undertaken by the NSW Government, and is generally limited to high-use alluvial aquifer systems and parts of the GAB. Additional monitoring may be undertaken by proposed resource developments and other actions with environmental conditions placed on their approval.

Groundwater is mainly sourced from the upper alluvial aquifers, and is most heavily used in the Lower Macquarie River system. Groundwater in the alluvial systems is generally of good quality, and reasonably fresh. There is some salinity variation and zonation in the alluvial systems, such as the highly saline zones adjacent to the Bogan River and salinity stratification in the (Pleistocene) Trangie Formation aquifer (Macaulay and Kellett, 2009). Water from the alluvial systems is used for town supply, irrigation, stock and domestic use.

Groundwater in the Cenozoic Basalts occurs in local flow systems and is generally fresh.

Groundwater in the Surat Basin system is found in the Drildool and Keelindi beds, as well as the Pilliga Sandstone. Between Narromine and Warren, these three aquifers are combined and referred to as the ‘Sandstone Aquifer’. Waters are generally fresh, and suitable for town water, stock and domestic use. Downstream of Warren, the high sodium adsorption ratio renders GAB waters generally unsuitable for irrigation use.

Water from the Gunnedah Basin groundwater system is of variable quality and generally low salinity. It is not used widely in the subregion as it underlies the alluvial and GAB systems in the eastern part of the subregion.

Watertable elevation in the Central West subregion decrease from the south to the north and north-west, and the groundwater flows in this direction. Recharge to the alluvial systems is dominated by flood recharge, with some component of rainfall contributing. Recharge to the basalt aquifers occurs by diffuse recharge from rainfall. Recharge to the GAB aquifers occurs in areas of outcrop to the south and south-east, with potential recharge via leakage from the lowermost alluvial system where it is in direct contact with unweathered GAB units. Studies by Radke et al. (2000) and Macaulay and Kellett (2009) identified leakage from the Macquarie and Castlereagh rivers as important local recharge sources for the GAB. Little is known about the recharge dynamics of the Gunnedah Basin system. It is likely to be recharged in outcropping areas and may be supplied by vertical leakage from the overlying GAB where the hydraulic gradient is downward.

Discharge from the alluvial systems is via seepage and baseflow, with some potential leakage to the GAB aquifers. Discharge from the basalt systems is as seepage, and local contributions to stream baseflow. Discharge from the GAB occurs as throughflow, as well as some component of vertical leakage to the Gunnedah Basin and possibly upwards into the alluvial systems. No information is available about discharge from the Gunnedah Basin.

Last updated:
5 January 2018