Carnarvon Basin

Image of rockpool with rocky cliffs behind

The Carnarvon Basin, located in Western Australia’s Gascoyne region, is a geologically rich and complex area, stretching across both onshore and offshore zones. It covers an expansive 115,000 km² on land and extends offshore over an area of 535,000 km². The basin has significant hydrocarbon resources, particularly in its northern offshore regions, while the southern portion is largely onshore and hosts a variety of important aquifers. Within the Carnarvon Basin, the aquifers supply over 96 GL (gigalitres) of groundwater for beneficial use. Some of the most significant aquifers in the region are associated with sedimentary bedrock formations, particularly the Birdrong Sandstone, which is regarded as the most prospective regional aquifer due to its depth, water quality, and hydrogeological properties. Another notable aquifer is the Tumblagooda Sandstone, which provides a local water resource near Kalbarri, although its use is limited in other areas due to its deep depth, often more than 500 meters below ground level. Other formations, such as the Keogh Formation, Ballythanna Sandstone, and Kopke Sandstone, are also tapped for water resources within the Carnarvon Basin. The Kopke Sandstone, although deep, is favoured in the northern regions of the basin, particularly between the Wooramel and Gascoyne rivers, due to its higher pressure and lower salinity compared to the Birdrong Sandstone. Among the more superficial aquifers, the Gascoyne River alluvium stands out as the most significant alluvial system in the region. It has a groundwater allocation limit of 21.7 GL per year, with the primary uses being irrigated agriculture and public water supply. Overall, the Carnarvon Basin’s diverse aquifer systems and rich hydrogeological features are central to the region’s water supply, particularly for agriculture and public consumption. However, managing groundwater resources in this vast area requires balancing the competing needs for water, particularly as water use in aquifers like the Gascoyne River alluvium grows with agricultural demand.

Brackish groundwater

Brackish groundwater is a promising source of water for consumptive use and was defined in the project by salinity levels ranging from 1,000 to 15,000 mg/L of total dissolved solids (TDS). The project classified Western Australia’s brackish groundwater resources into different categories based on their salinity levels:

  • Brackish: aquifers or their section within a Groundwater Management Area (GMA) where 100% of bores produce brackish groundwater.
  • Mainly brackish: aquifers or their section within a Groundwater Management Area (GMA) where over 50% of bores produce brackish groundwater.
  • Some brackish: aquifers or their section within GMA where 25% to 50% of the bores produce brackish groundwater.

The Carnarvon Basin contains significant brackish groundwater resources across aquifers such as the Birdrong, Tumblagooda and Kopke sandstones, and the Keogh Formation and Ballythanna Sandstone member. Across the basin, there is about 156 GL of groundwater resources that have been previously characterised. The most promising opportunity for brackish groundwater development is from aquifers hosted in the the Keogh Formation and Ballythanna Sandstone in the south-east of the basin, representing about 24% of the basin’s currently characterised groundwater resources. Other parts of the basin may offer other opportunities, but some areas are data sparse.

Explore these aquifers here:

Desalination and brine management

Information on groundwater quality in the Carnarvon Basin is scarce, with only a few datasets available for the Birdrong aquifer. Elevated concentrations of bicarbonate (HCO3), sulfate (SO42), and calcium may need to be taken into account prior to desalination. Additionally, data on iron (Fe) and manganese (Mn) concentrations are limited, and there is no information available for silicon.

Use of evaporation ponds and encapsulation infrastructure are likely to be suitable for any potential development subject to approval, particuarly those inland. Other brine management options such as aquaculture, algal horticulture, energy storage and production will depend upon the nature of any development by a potential proponent, the amount and composition of the brine and the approval of certain practices.

A significant portion of the coastal marine environment along the coast of the Carnarvon Basin is designated as marine parks, such as Ningaloo Reef, which limits opportunities for brine marine disposal.

Renewable energy

The Carnarvon Basin has the least-cost hybrid renewable energy site in WA suitable for brackish groundwater desalination and the estimated mean and maximum energy costs of water desalination across the Basin are lower than those across WA. This indicates that the Carnarvon Basin is one of the regions with the potential for lower cost brackish groundwater desalination. Within the basin the cost of electricity generation is lower along the coastline where there are greater wind resources and relatively higher at the southern and northern ends of the region.