Water resources - Availability - Queensland
Groundwater Management Unit: Great Artesian Basin - Surat - Queensland
Introduction
The groundwater resource characteristics for the Great Artesian Basin - Surat - Queensland groundwater managment unit are presented below. This includes technical detail on aquifer properties and water level change for key monitoring bores.
What is the character of Great Artesian Basin - Surat - Queensland's groundwater resource?
Vital Statistics:
| Area | 88,050km2 |
|---|---|
| Total Water Allocated | 96,720 ML/yr |
| Total Water Used | 890 ML/yr |
| Average Salinity | 983 mg/L |
| Sustainable Yield | 71,960 ML/yr |
| Depth to top of aquifer | 0 m |
Aquifer Description:
The GAB is generally described in terms of hydrogeological basins. These are major formations of deposited sediments called strata that dip towards their centre and have the ability to store and carry water.
The known geology of earth is over 4500 million years old, and over this time, several hydrogeological basins have formed separately from each other in terms of depth and location.
The most recently occurring basins are shallowest from natural surface and hence, are most commonly accessed for ease and economic reasons. The GAB is comprised of three such basins: the Carpentaria Basin, the Eromanga Basin, and the Surat Basin. Note that several other basins of greater geological age lay below these three more recent basins.
The Eastern Downs (QLD) zone lies completely within the Surat Basin.
The Surat Basin is about 280000 sq km and is located in the bottom southeast corner of the GAB and spreads south from Queensland to NSW to the Coonamble Embayment. It also adjoins the Eromanga Basin. The Nebine Ridge (a ridge of basement rocks in southern Queensland) structurally separates these two basins. Its geological age varies from the Cretaceous Period (66-144 million years) to the Triassic Period (213-248 million years). The Bowen and Gunnedah basins underlie the Surat Basin. The Eastern Downs (QLD) zone contains a portion of the underlying Bowen Basin.
The Eastern Downs (QLD) zone varies in a saturated thickness from 0 m (at the zone boundaries) to 3000 m (towards the centre). The average saturated thickness is 1350 m and average depth to top of aquifer is 550 m.
The Eastern Downs (QLD) zone consists of up to twelve confined sedimentary formed aquifer systems. Generally increasing in depth, they are the Griman Creek Formation, the Nullawurt Sandstone Member, the Mooga Sandstone, the Kumbarilla beds, the Gubberamunda Sandstone, the Pillaga Sandstone, the Springbok Sandstone, the Hutton Sandstone, the Eurombah Formation, the Boxvale Sandstone Member, the Precipice Sandstone and the Clematis Sandstone. They comprise of continental quartzose sandstones of the Mesozoic Era. The intervening confining beds consist of mudstone, siltstone, and / or sequences of marine sediments.
Anticipated rainfall recharge of the Eastern Downs (QLD) zone occurs along the eastern zone boundary. Groundwater flow paths are initially from the neighbouring Eastern Recharge B hydrologic zone, and then in a generally southern direction. There is one spring group located in the southwestern corner of the Eastern Downs (QLD) zone.
Method used for determining sustainable yield:
The GABCC have suggested that the sustainable yield for the entire GAB is about 450000 ML/yr. This figure was produced without the use of a time-stepped water balancing groundwater computer model. It was based on water balancing deductions incorporating some broad-based assumptions on natural recharge, springs replenishment, vertical leakage, sub-surface marine discharge, bore discharge (570000 ML/yr), and the knowledge that entire GAB has been experiencing declining water levels since 1880.
The sustainable yield for the this GMU was estimated by proportioning the sustainable yield for the entire GAB down by the ratio of active artesian bores within the GMU to the total number of active artesian bores in the whole GAB.
Hence, the sustainable yield for the Eastern Downs (QLD) zone was estimated at 71960 ML/yr.
Note that this sustainable yield is not an estimate based on the physical hydrogeological characteristics of the GMU but rather in accord with present flow extraction proportions.
Assumptions used for allocating development categories:
The Eastern Downs (QLD) zones present average annual abstraction rate was estimated at 96720 ML/yr, which was assumed also to equal the annual allocation. This rate is greater than its estimated sustainable yield by 24760 ML/yr or 34.4 %, and therefore categorised as over- abstracted and over-allocated.
Are groundwater levels changing?
Technical information on the key groundwater bores and monitoring stations is presented below, including hydrographs where available. Link to a discussion on groundwater levels and trends at a State level as it relates to dryland salinity.
There are no bore monitoring stations recorded in this area for this assessment
Further information
- Queensland Water Resources Assessment 2000 Report
- Queensland Water Resources Assessment 2000 Technical Report
- For more information about water and other natural resource issues link to www.nrm.qld.gov.au
Key
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