Perth, Western Australia
by Mikaela Hearne
Groundwater is an extremely important resource in WA, and it currently supplies approximately two-thirds of the state’s water. In recent years, Western Australia and in particular the South West and Perth Regions have become hotter and drier due to climate change, (as discussed in our blog “Bore Water”) and this in turn has resulted in less incursion into our drinking water dams and lower groundwater recharge through rainfall infiltration. The impacts of climate change are being felt in various ways across the nation and the world, specifically relating to water though, the impacts from climate change will likely be determined by three primary drivers: local climate, land characteristics and local land / water management strategies (PIRD, 2019).
Australia’s use of groundwater has increased significantly over recent decades. For example, in the 13 years from 1983 to 1996 our national reliance on groundwater increased by nearly 90 per cent (Geoscience Australia, 2020). The future of groundwater in Australia is projected to rise, due to surface water resources being less available with the local droughts and climate changes (Geoscience, 2020). Consequently, with reduced rainfall and significant increasing use, the local groundwater system has shifted out of balance and the previously healthy system is now under pressure (DWER, 2018).
Gnangara groundwater system stretches over 2,200 square km and is an underground basin of water-holding sands and gravels scattered with clays. It underlies the Swan Coastal Plain from Perth between the hills and the coast and the area from the Swan River to Gingin Brook (DWER, 2020).
The system comprises three main aquifers, the shallow superficial aquifer known as the Gnangara mound, and the deeper Leederville and Yarragadee aquifers.
Gnangara groundwater is abstracted for use to irrigate parks, ovals, gardens, agricultural land and for Perth’s drinking water. It currently provides almost half of all the water used in Perth Metro area each year. This groundwater system also supports our natural environment and numerous groundwater dependent ecosystems (DWER, 2018). Overall, the health of the Gnangara Groundwater system is integral in supporting the regional water quality of lakes and wetlands as well as providing support to native flora and fauna species and fostering a sense of place for our communities.
Since the 1970’s rainfall, streamflow and recharge to groundwater have declined. Most of our rainfall occurs during winter and consequently when the groundwater is recharged. In 2009 the average annual rainfall was 729mm, in 2010 483mm; 578mm in 2015 and 524mm in 2019 (BOM, 2020). It is expected that between now and 2030 the average annual rainfall will range between 650mm and 700mm with there being more dry years in between (DWER, 2018).
Higher groundwater use and less rainfall has also resulted in the drying out of wetlands and related vegetation. In 2017, 16 out of the 30 representative wetland and vegetation sites were lower than the criteria levels set by the Minister of Environment (DWER, 2018). As another result of the groundwater system being out of balance, water quality in many areas is in decline due to not enough groundwater flowing out of the system into the rivers and coast to prevent saltwater intrusion to the aquifers. Essentially, climate change is expected to exacerbate saltwater intrusion due to sea level rise coupled with higher temperatures (increasing localised water demand) and reduced precipitation which would reduce the surface water available for aquifer recharge (Kumar, Carsten, & Keith, 2007). In W.A Saline water has already moved inland in the Superficial aquifer in some places and has caused dryland salinity (DWER, 2018).
(2006 compared to 2015)
If we can rebalance the system, we can continue to have sufficient groundwater for communities, industry and the environment. In essence, groundwater levels need to be stabilised enabling key areas to recover.
The community, local government, Department of Water and Water Corporation are implementing several strategies that will help in achieving better balance. These strategies can be grouped into 3 broad categories; sustainable groundwater; water efficiency and innovation and alternative sources (DWER, 2018).
Efficiency and innovation will be key to making Gnangara system last longer and be more sustainable (DWER, 2018).
Eventually, establishing alternative water sources will take pressure of Gnangara groundwater and build climate resilience for businesses and the community (DWER, 2019).
Moving forward, all water users need to evolve and adjust groundwater use in this drier climate. Everyone needs to contribute through a collective change in how we use water and how we manage and interact with water.
New projects, residential housing and other urban developments are perfect opportunities to promote alternative local water supply options and solutions, that are fit for purpose and more efficient systems compatible with less rainfall. Local councils within W.A have already begun to demonstrate innovative initiative by implementing smarter solutions, including the City of Kalamunda who have adopted a system where winter drainage water is recycled through managed aquifer recharge to irrigate parks in summer (DWER, 2019).
An updated Water Allocation plan, which will guide the rebalancing and set new limits and licensing requirements on groundwater availability for the Gnangara system is being developed by DWER in consultation with the Water Corporation and water users. DWER will phase in new solutions and work with local communities and water users to minimise the impacts of the transition. Additionally, the modelling and work being done on the Perth and Peel Water @ 3.5 million assesses the future water demand and water supply strategies for when the regions populous reaches 3.5 million by 2050.
Our Groundwater Future in Perth, Department of Water and Environmental Regulation, May 2018
Kumar, A. N., Carsten, S., & Keith, L. B. (2007). Modelling seawater intrusion in the Burdekin delta irrigation area, north Queensland, Australia. Agricultural Water Management, 89, 217–228. [Crossref], [Web of Science ], [Google Scholar].