The Gnangara groundwater system covers an area of approximately 2200 sq km, bounded by the Swan River to the south, Gingin Brook to the north and between the coast and the Darling fault.
It is the major source of potable water for public water supply in the south-west of Western Australia.It also supports an extensive horticultural industry, urban parks and recreational areas, industrial activities and a range of unique ecological systems.
In the last 30 years, particularly the last decade, there has been less rain to recharge groundwater, which has had a direct impact on the groundwater stored in the system.
Groundwater-dependent ecosystems in Gnangara have adapted to a water regime of winter recharge that supports these ecosystems through typically hot, dry summers. However, declining groundwater levels across the system, combined with the drying climate trend have resulted in a corresponding decline in the health of groundwater-dependent ecosystems.
The Department of Water completed an investigation program in this area that was part funded by the Australian Government’s Water for the Future initiative.
What were the outcomes of the projects?
The final report – Water for the future – Support for a Statutory plan for the Gnangara Mound summarises the implementation and findings of the project. The most significant findings and management implications for the project areas were:
- We have improved the calibration of the groundwater model using results from intensive drilling program.
- The model now provides the opportunity to explore increasing abstraction from the confined aquifer to supply Perth future drinking water demand without affecting groundwater dependant ecosystems.
Through these projects we have also:
- improved our understanding of shallow groundwater systems
- improved our understanding of the confined aquifer system
- researched water allocation alternatives
- investigated unlicensed water use
- developed pathways for the management of over-allocated systems
- developed environmental water provisions in the context of a drying climate
What were the products generated through the project?
The following are reports completed and published:
- Acquisition and Processing Report: Seismic Reflection and Ground penetrating Radar Transects across the Northern Gnangara Mound; Perth Basin; WA
- Calibration of the coupled Perth Regional Aquifer Model, PRAMS 3.2, July 2009
- Development of Local Area Groundwater Models – Gnangara Mound, Lexia wetland report, Sept 2009
- Development of Local Area Groundwater Models – Gnangara Mound, Lake Nowergup report
- Evaluation of Mechanisms for releasing unallocated water in Western Australia, Part A – Selection of market instrument, June 2010
- Review into the management of over-allocated water resources in the Gnangara groundwater management area, Feb 2009
- Perth Shallow Groundwater systems Investigation: Lake Mariginiup, HG36
- Hydrogeochemical Assessment of Superficial Aquifers, HG37
- Perth regional aquifer modelling system (PRAMS), HG 39
We also produced the following unpublished reports. They include highly technical reports, chemical analysis results; bore drilling data and internal DoW policies.
- Bore completion report for Perth SGS systems Investigation Stage1, HR266
- Variable statistics for a site set: SGS Stage 1 sites
- Bore completion report for the SGS investigation stage 2, HR276
- Variable Statistics for a site set:SGS Stage 2
- All Site Details Report – Lake Goollelal
- All site details Report – lake Gwellup
- Bore completion report – Perth SGS investigation – Stage 3, HR281
- All site details Report – Pipidinny wetland
- All site details Report – Quinn Wetland
- All site details Report – Timuru lake
- All site details Report – Yeal Lakes
- Conceptual geology of the North Gnangara Mound, HR288
- North Gnangara bore – completion report, HR277
- WSA Asset register 2008/2009
- Perth Shallow Groundwater systems Investigation – Forestdale Lake
- Perth Shallow Groundwater systems Investigation – Lexia Wetlands
- Perth Shallow Groundwater systems investigation – North Lake
- Perth Shallow Groundwater systems investigation – lake Nowergup
- North Gnangara Core Drilling and Core Analysis
- Perth Shallow Groundwater systems Investigation – Loch McNess, HG43
- Evaluation of Mechanisms for releasing unallocated water in Western Australia, Part B: Pricing of unallocated water resources, June 2010
- (Operational Policy 2.01 – Confirming over-allocation Gnangara Mound
- Ecohydrological Study, May 2010
Members of the public who are interested to access information within the reports are invited to contact the Department of Water Library on 63646425. Where reports contain confidential information, the department will provide a summary report upon request by the public.
How will the information be used?
The information will directly support improvements to future management of the resource. We will use this information to review and update the current water allocation plan and develop a new plan for Gnangara by 2012. The next allocation plan will also be informed by the land and water use recommendations of the Gnangara Sustainability Strategy (GSS), and will align with the department’s Perth Peel Regional Water Plan. It will also be consistent with the requirements of the National Water Initiative.