The Yarragadee Aquifer is a significant freshwater

aquifer An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials ( gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characteris ...

located in the south west of

Western Australia Western Australia (commonly abbreviated as WA) is a state of Australia occupying the western percent of the land area of Australia excluding external territories. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to th ...

and predominantly beneath the Swan Coastal Plain west of the

Darling Scarp The Darling Scarp, also referred to as the Darling Range or Darling Ranges, is a low escarpment running north–south to the east of the Swan Coastal Plain and Perth, Western Australia. The escarpment extends generally north of Bindoon, to t ...

. It has a north–south range from about

Geraldton Geraldton ( Wajarri: ''Jambinu'', Wilunyu: ''Jambinbirri'') is a coastal city in the Mid West region of the Australian state of Western Australia, north of the state capital, Perth. At June 2018, Geraldton had an urban population of 37,648. ...

to the south coast, but with a split in the formation south of

Perth Perth is the capital and largest city of the Australian state of Western Australia. It is the fourth most populous city in Australia and Oceania, with a population of 2.1 million (80% of the state) living in Greater Perth in 2020. Perth i ...

, Western Australia. The southern part is known as the South West Yarragadee Aquifer. The aquifer is quite deep, situated hundreds of metres below ground level and with a thickness ranging up to about two kilometres. In the Perth area, the Yarragadee Aquifer is located beneath the Leederville Aquifer, which itself is located beneath two superficial aquifers known as the

Gnangara Mound The Gnangara Mound is an area north of Perth, Western Australia where a large mound of sandy soil reaches an elevation of about . It stores about of fresh water, about one hundred times Perth's current annual water usage. It is currently the si ...

and Jandakot Mound. These aquifers are separated by impervious layers with no groundwater, called

aquitard An aquifer is an underground layer of water-bearing, permeability (Earth sciences), permeable rock, rock fractures, or unconsolidated materials (gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary ...

s. The Yarragadee Aquifer stores about 1000 cubic kilometres of water, compared to about 20 cubic kilometres in the Gnangara Mound. As such it is seen as a potential source of water, and the Water Corporation of Western Australia currently extracts about 45 gigalitres per year from the aquifer. One cubic kilometre is equivalent to 1000 GL. Ultimately the Yaragadee Aquifer is replenished by rainfall. This recharging is usually where there are outcroppings near other aquifers like the Leederville Aquifer. There are also outcrops near the surface in the vicinity of the

Blackwood River The Blackwood River is a major river and catchment in the South West of Western Australia. Course The river begins at the junction of Arthur River and Balgarup River near Quelarup and travels in a south westerly direction through the tow ...

. Current models estimate this recharge at about 280 to 340 GL per year. This groundwater can remain in the aquifer for many years; in some areas the age of the groundwater is over 30,000 years. Geologically, the aquifer is part of what is known as the Yarragadee Formation, which is a relatively thick geological unit in the

Perth Basin The Perth Basin is a thick, elongated sedimentary basin in Western Australia. It lies beneath the Swan Coastal Plain west of the Darling Scarp, representing the western limit of the much older Yilgarn Craton, and extends further west offshore. C ...

. Formed during the

Jurassic The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...

Period, the Yarragadee Formation is composed primarily of non-marine fluviatile feldspathic, poorly sorted sandstones which are porous and poorly cemented, hence allowing for considerable groundwater reserves. It grades from a shale-siltstone dominated base to a cleaner sandstone in the upper portions of the formation, probably representing increased subsidence or filling of the basin during the late Jurassic. The Dalkeith Hot Pool was formed by water from the Yarragadee Aquifer.

References

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