Fractured Rock, Palaeovalleys and Alluvial Aquifers

Groundwater resources from local to intermediate-scale aquifers across regional parts of Western Australia (WA) provide a crucial source of water for industry, livestock, domestic use, and community water supplies, particularly in areas where traditional sedimentary aquifers are limited or absent. This includes aquifers found in fractured and weathered rocks, ancient drainage features like palaeovalleys, and alluvial aquifers associated with the channels and floodplains of streams and their tributaries. Fractured rock aquifers are prevalent across the Arunta, Musgrave, Pilbara, and Yilgarn blocks, while palaeovalley aquifers are widespread throughout the state, from the Canning Basin in the north to the Officer Basin and Yilgarn Block, extending to the southern coastline. Alluvial aquifers are present in association with some of the state’s major streams, notably in the Canning and Carnarvon basins and the Pilbara Block. The groundwater resources from these local to intermediate-scale aquifers are managed within several groundwater management areas (GMAs).

Groundwater resources are overseen within 24 Groundwater Management Areas (GMAs) and several Groundwater Management Sub-Areas (GMSAs). Regions with larger allocation limits and entitlements are often associated with significant economic activities. For example, the Pilbara and Goldfields GMAs—key mining regions—have substantial groundwater allocations to meet the high water demands of mining operations. Similarly, agricultural regions within the Canning–Kimberley GMA also exhibit larger allocation limits to support extensive farming practices.

Brackish groundwater in the fractured rock, palaeovalley, and alluvial aquifers across WA

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.

Groundwater quality varies significantly, ranging from fresh to saline, influenced by factors such as rock composition, depth, and recharge rates. In areas with low recharge, like parts of the Yilgarn Craton, groundwater can be brackish to saline due to prolonged interactions between water and rock, which increase the dissolved mineral content. Analysis of available information has led to the identification of predominant groundwater salinity statuses for management areas and subareas. This demonstrates that groundwater salinity transitions from mainly fresh to marginal in the north (Canning–Kimberley GMA), to brackish in the Goldfields GMA, and even saline in the southern regions of the state.

In Western Australia’s Groundwater Management Areas (GMAs), the brackish groundwater resources, excluding the main sedimentary basins, exceed 2,000 GL, considering allocation limits and entitlements, which are primarily tied to the mining regions of the Pilbara and Goldfields. However, an accurate assessment of available allocation is challenging due to a limited understanding of the relationship between allocation limits and entitlements within the large GMAs. While the groundwater resources are generally suitable for desalination based on water quality alone, their actual availability still needs further evaluation.

Palaeovalley aquifers are among the most significant sources of brackish groundwater, with potential resources exceeding 1,000 GL. In northern Western Australia, these aquifers typically exhibit lower salinity, attributed to a higher proportion of renewable groundwater. However, salinity tends to increase towards the south, particularly in the Goldfields region, where palaeovalley aquifers are often saline. Despite water quality concerns, over 300 GL of brackish groundwater in this area has been allocated, with 250 GL in entitlements.

In alluvial aquifers, the total brackish groundwater resources amount to 54 GL, alongside an additional 30 GL in entitlements. Approximately 34 GL remains potentially available for allocation, predominantly in coastal alluvial aquifers located within the Pilbara and Gascoyne regions, as well as in the southern GMAs.

Although irrigated agriculture exists in certain areas, such as the Gascoyne alluvial aquifers, the arid climate and remoteness of the region present significant challenges to the expansion of large-scale agricultural projects. Nevertheless, remote communities often depend on these water resources.

Explore these aquifers here:

• Fractured Rock and Weathered Rock Aquifers
• Palaeovalley Aquifers

Desalination and brine management

The analysis centred on a specific palaeovalley region known as the “Murchison palaeovalleys,” located to the north-east of Geraldton in the Midwest region of Western Australia.

Most of the palaeovalleys show elevated concentrations of alkalinity (HCO3-) and sulfate (SO42-), with some levels being significantly high, necessitating substantial pre-treatment prior to desalination.

A major challenge in desalinating water from these palaeovalleys is the presence of silicon (Si). All palaeovalleys containing brackish water have at least some samples with silicon concentrations exceeding 10 mg/L, and many palaeovalleys—representing 90% of the data—exhibit levels greater than 30 mg/L. This necessitates extensive pre-treatment, which could affect the economic viability of the projects.

Palaeovalley aquifers can serve both as a storage solution for treated water and a disposal option for brine. While these aquifers may be suitable for managed aquifer recharge (MAR), implementing this would require comprehensive hydrogeological studies and regulatory approval.

Renewable energy

The analysis was also conducted for the “Murchison palaeovalleys.” Geographically, this region has a lower wind resource compared to the coastal areas of Western Australia, making hybrid renewable generation primarily dependent on solar PV output. Consequently, the Levelised Cost of Energy (LCOE) tends to be higher in the southern part of the region and lower in the middle and northern areas, where solar resources are more abundant.

The mean costs of hybrid renewable energy for brackish groundwater desalination in these regions are slightly lower than the average values across Western Australia. This indicates that, on average, it is less expensive to power desalination using renewable energy in these areas compared to other parts of the state.