How does the Gnangara groundwater system work?
The Gnangara groundwater system is a basin of water-holding sands and gravels interspersed with clays. It underlies Perth between the Hills and the coast and the area from the Swan River to Gingin Brook. It stretches over 2200 square kilometres under the coastal plain.
In the Gnangara system, deeper water is up to 35 000 years old and the geological structure is much older (up to 175 million years old). The system is made of many layers of sand, sediment and clay. Pores between the sand hold water, which mostly comes from winter rainfall making its way down through the soil to recharge the aquifers.
The system contains three main aquifers:
- The shallow, unconfined Superficial aquifer (the Gnangara Mound).
- The deep, mostly confined Leederville aquifer.
- The deepest, mostly confined Yarragadee aquifer.
The Gnangara Mound is the common name for the Superficial aquifer in a large mound of sandy soil located north of Perth. The watertable in the aquifer forms a groundwater mound, where rainwater recharges groundwater at a higher rate than water flows horizontally through the aquifer.
The Gnangara system provides almost half of all the water used in the Perth metropolitan area each year. It supplies water for agriculture, parks, ovals and gardens on the Gnangara system, and water for Perth’s scheme supply – distributed by the Water Corporation. Gnangara groundwater also supports environmental features such as lakes, wetlands and vegetation.
The deeper Leederville and Yarragadee aquifers are mostly used for scheme water supply.
How has Gnangara groundwater been managed to date?
Ministerial conditions and commitments were established in 1986 to manage how groundwater was abstracted for public water supply and manage the expected growth in private licensed use at the time. See more information on Ministerial conditions on the environment page.
In 2009 we released the Gnangara groundwater areas allocation plan. This provided the first steps to returning the over-allocated system to balance, after 40 years of declining rainfall and recharge to groundwater. It is a strong first step in adjusting our groundwater management in the context of drier climate and has resulted in the following:
- Significantly reduced abstraction for public water supply.
- Increased compliance and enforcement activities.
- Increased protection of groundwater-dependent ecosystems, by moving abstraction to lower risk areas, including the deeper confined aquifers.
Since then we have regularly evaluated our management against the plan’s objectives and released two evaluation statements:
The brochure Our groundwater future in Perth: Securing Gnangara groundwater and adapting to climate change summarises most of this website and why a new plan is a necessary response to climate change.
Find more information about the Gnangara groundwater system, including reports and studies, on our main website.