Groundwater isn't being replenished as it once was, affecting local wildlife

Groundwater is a major source of water for Perth and makes up around 70% of the total amount of water used in the region.

Not only does it currently supply around 40% of Perth’s drinking water, thousands of household garden bores across the city also directly tap into this precious resource to keep lawns and gardens green. It’s used to maintain parks and sporting grounds, so we all have green spaces to enjoy. Farmers also rely on groundwater to supply us with locally grown produce.

Importantly, groundwater is also the lifeblood that sustains our local lakes, wetlands and connected bushland, which provide habitat for native wildlife.

Among the many effects of climate change, groundwater supplies aren’t being replenished as they once were even despite the recent rainfall in Perth, putting our groundwater-dependent ecosystems and the birds, turtles, and other animals that rely on these habitats at risk.

Less rain means less groundwater

Declining groundwater levels are closely linked to reduced winter rainfall recorded in Perth since the 1970s. Even though Perth’s winters can feel chilly and wet, the rain we receive today is nowhere near the amount of water needed to fully replenish groundwater supplies back to historical levels.

In fact, Perth has experienced a 20% decline in average annual rainfall since the 1970s. While this reduction may not seem dramatic, its impact on groundwater levels in some areas is significant when combined with the increase in groundwater use over the same time as our city has grown.

Perth’s groundwater is a complex system that can be thought of as a layered cake of aquifers. The superficial aquifer is a very important part of the Gnangara groundwater system, as it can be easily accessed by many users including gardeners, farmers, local councils, Water Corporation and the environment.

Water levels in the superficial aquifer have been declining over the past 40 years as a result of decreasing rainfall, increased groundwater use and pine plantations, which absorb a large portion of rainfall before it can make its way down into the aquifer. Since 1979, average superficial aquifer levels across the mound have decreased by about 3.5 metres (DWER, 2021).

The impact on our wetlands and bushland

Local wetlands and bushland that rely on groundwater are becoming more water stressed. Many wetlands, including the internationally significant Ramsar-listed Lake Forrestdale, are filling up less frequently or drying more quickly.

Wetlands are also much-loved recreation spots—such as Loch McNess and Perry Lakes. Part of what makes these spots so nice to visit is the wildlife within and surrounding the water. When a wetland or groundwater-dependent ecosystem becomes water stressed, it can impact on the delicate natural balance of the ecosystem and the habitat of iconic WA wildlife, such as the south-western snake-necked turtle, black swan and Carnaby’s cockatoo. In addition to being a home to our native wildlife, some of our wetlands are also visited by birds migrating from the Arctic Circle each summer.

Popular recreation spot Joondalup Picnic Cove

What can we do?

To help replenish our precious groundwater supplies, we further treat recycled wastewater at our Advanced Water Recycling Plant and inject that water directly into our underground aquifers.

But saving groundwater is up to all of us, not just big businesses or households with a garden bore, as around 40% of drinking water from our taps is supplied by groundwater.

At home, here are a few simple things we can all do to reduce our impact on our precious groundwater:

• Choose the right irrigation controller for your garden and program it to only water once on your rostered watering days. Finding the correct run times for your sprinklers will also help avoid overwatering.
• Switch off your sprinklers during winter, as part of the annual Winter Sprinkler Switch-off.
• Create a more waterwise garden.
• Every drop you save inside and outside your home counts. Find more waterwise advice.

Learn more about groundwater’s role in WA from the Department of Water and Environmental Regulation, who manage groundwater in our state.