Gnangara groundwater system
The Gnangara groundwater system is Perth's largest source of good quality, fresh water. It provides a crucial part of Perth’s public water supply as well as water for public open spaces, an extensive area of local agriculture and our gardens. It also supports nationally significant groundwater-dependent ecosystems, such as wetlands and Banksia woodlands. These groundwater-dependent ecosystems support biodiversity, help create our ‘sense of place’ and make our city an attractive place to live.
Stretching about 2200 square kilometres along the coastal plain north of the Swan River to Gingin and east to the Darling Scarp, the Gnangara groundwater system comprises four main aquifers:
- The shallow, unconfined Superficial aquifer (the Gnangara Mound).
- The shallow, semi-confined Mirrabooka aquifer.
- The deep, mostly confined Leederville aquifer.
- The deepest, mostly confined Yarragadee aquifer
The Gnangara groundwater system
What is the Gnangara Mound?
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.
Water use from the Gnangara groundwater system
Gnangara groundwater provides over 40 per cent of Perth’s drinking water each year, as well as local water for agriculture, public open space and domestic gardens.
Gnangara groundwater also supports ecosystems such as lakes and wetlands that provide important environmental functions and contribute to the social and recreational value of our communities.
Groundwater for public water supply comes from all of the aquifers in the system, with less taken from the Superficial aquifer to reduce impacts on groundwater-dependent ecosystems. More water is taken from areas of the Leederville and Yarragadee aquifers that are not connected to the Superficial. Private licensed use mostly comes from the Superficial aquifer.
Water use from the Gnangara groundwater system is managed through the Gnangara groundwater areas allocation plan, which defines how much water is available for use and guides water licensing from the system within the set allocation limits.
See how we are tracking against the plan objectives in the Gnangara groundwater areas allocation plan: Evaluation statement 2011–2014.
Gnangara Mound water levels
Groundwater levels across the Gnangara Mound have generally been in decline for the last 40 years because of decreasing rainfall, continued use of groundwater for a range of important uses, and pine plantations limiting recharge.
In some areas, the rate of groundwater level decline has slowed and stabilised since 2011. This is a positive response to the department’s actions to reduce and redistribute groundwater abstraction and reflects more consistent rainfall since the very low rainfall in the latter half of the last decade (2006 and 2010 were record dry years).
Average groundwater levels of the Gnangara Mound
The graph below is based on monthly water level measurements at 43 monitoring bores across the Gnangara Mound.
For each bore we compare these monthly measurements to the highest recorded groundwater water level. We then average the results to show relative changes in groundwater levels over time.
Bores for the graph were selected from our existing monitoring network on the Gnangara Mound, with a minimum of ten years of data.
Average groundwater levels of the Gnangara Mound (Superficial aquifer).