Aquaculture Groundwater Resource Atlas - Nullabor (Eucla Basin)
Overview
The Eucla Basin contains an unconfined limestone aquifer, and a confined sandstone aquifer at the base. The groundwater is deep and is of generally high salinity. Potable groundwater only exists around the inland margin of the limestone aquifer. There are relatively few bores, used for pastoral purposes, and for supply along the Trans Australian Railway and Eyre Highway. Water for potable use has to be desalinated.
The section below drawn from west to east across the basin illustrates the geological structure. At the base is the Cretaceous Loongana Sandstone, which is the artesian aquifer on Roe Plains. This is overlain by shales of the Toondi and Madura Formation. The unconfined aquifer consists mainly of the Wilson Bluff Limestone and the Abrakurrie Limestone, with greensands of the Cretaceous Nurina Formation, and the Eocene Hampton Sandstone at the base.
West-east geological section across the Eucla Basin
| Aquifer potential of geological units in the Eucla Basin | ||
|---|---|---|
| Age | Formation | Aquifer potential |
| Quaternary - Pliocene | Roe Calcarenite | Unconfined aquifer |
| Early- Middle Miocene | Colville Sandstone | Unsaturated |
| Nullarbor Limestone | Unsaturated | |
| Abrakurrie Limestone | Unconfined aquifer | |
| Eocene | Wilson Bluff Limestone (Toolinna Limestone) |
Unconfined aquifer |
| Hampton Sandstone | Unconfined aquifer | |
| Cretaceous | Nurina Formation | Unconfined aquifer |
| Toondi Formation | Aquiclude | |
| Madura Formation | Aquiclude | |
| Loongana Sandstone | Confined aquifer | |
Unconfined Aquifer
The limestone aquifer is the major groundwater resource in the Eucla Basin. It consists mainly of the Wilson Bluff Limestone and the Abrakurrie Limestone. These overlie relatively impermeable Cretaceous Madura formation. The Wilson Bluff and Abrakurrie Limestones are overlain by the Nullarbor Limestone, which is largely unsaturated. The aquifer is several hundred metres thick, and the water table is relatively deep, ranging up to a hundred metres below surface along the Trans Australian Railway. Low salinity potable groundwater is available only around the north western margin of the basin where recharge occurs in depressions known as dongas. The groundwater salinity rises to the south towards the coast. It is mainly brackish along the railway and increases to become saline along the Eyre Highway. The aquifer is used for potable supplies along the north west margin and for stock water supply in the centre. Groundwater in the caves near the Eyre Highway is generally saline.
Groundwater salinity in the limestone aquifer
Loongana Sandstone
The Loongana Sandstone is the basal artesian aquifer in the Eucla basin, overlying the granitic bedrock. It is overlain by the impermeable Madura Formation, except around the inland margin of the basin where recharge is likely to occur. It is generally less than 33m thick, and is several hundred metres below the surface at Madura and Eucla. Bores on the Roe Plains such as at Madura are artesian.
The groundwater salinity is lowest in the centre of the basin north of Eucla, and increases to the south and west. The high salinity in the west probably results from recharge from hypersaline groundwater in Tertiary Palaeochannels draining the Goldfields. High groundwater salinity along the coast on Roe Plains, reported to be 51 to 74 ppt in oil exploration wells Eyre 1 and Eucla 1, is probably the result of flow from the unconfined limestone aquifer where the confining beds are absent (see Section above).
Groundwater of around 4 ppt from the Loongana Sandstone aquifer is desalinated for potable supply at Eucla.
Further information is contained in Commander (1991) and Lowry (1970).
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