Recharging Perth’s water supply
Associate Professor Sally Thompson, UWA
Water is a precious commodity in Western Australia. Whilst traditionally, Perth has relied on rainfall and streamflow to fill our dams, a decline in rainfall since the mid 1970’s has led to groundwater and desalination playing a larger role, particularly during hotter periods of high demand.
Whilst desalination has partly replaced the role that surface water supplies played for Perth residents, groundwater has also been a critical source of water for drinking, and for irrigation of private gardens, horticulture and public open space. However as Perth’s climate continues to dry, there has been a renewed focus on measuring and evaluating how much water is replenishing the essential groundwater aquifers.
The replenishment of groundwater aquifers is called recharge. Whilst research into the response of recharge to climate change has been limited, it is essential for future water planning that Government can predict this response – particularly because it is suspected that the drops in recharge that take place may exceed drops in rainfall.
Hydrologist and Associate Professor Sally Thompson School of Engineering, Civil, Environmental and Mining Engineering, UWA School of Agriculture and Environment, and the Centre for Water and Spatial Science, leads a multidisciplinary team from The University of Western Australia who are using their expertise to understand how much water is replenishing Perth’s groundwater aquifers over time. They are working in collaboration with experts from the Department of Water and Environmental Regulation (DWER), advisors from the Water Corporation and CSIRO.
“There is a direct connection between the vegetation and trees that need that water, and the water we need to give us a beautiful and comfortable environment to live in.”
Groundwater aquifers are growing in importance for the environmental health of Perth.
Perth as a hot spot
For a long time, the Southwest of Western Australia has been one of the only places in the world where all the climate change are in agreement that the future will be drier and hotter than the conditions seen in the 20th Century. Scientists globally recognise this as unique and valuable to their own climate change issues and are looking to Western Australia for how we are managing and adapting to changing conditions.
There has also been keen interest from the hydrology community and local government on the connection between groundwater and how water resources are currently being used.
“Perth is not just the place where we are based and live and love, it is also very much at the global forefront of climate change impacts.”
Between 40-60% of Perth’s drinking water comes from groundwater.
The anatomy of a drought
In 2019, Associate Professor Thompson became interested in understanding the reliance of groundwater for drinking water and liveability, the lack of measurement of how much is returned to aquifers, and how amounts vary as the Perth climate changes.
In May 2020, Associate Professor Thompson, as part of the Cooperative Research Centre for Water Sensitive Cities published the: Guiding urban water management in areas that experience high seasonal groundwater: Expert Panel report. The report offered technical guidance for urban development planning in high groundwater areas and suggested the need for additional research into an improved understanding of recharge dynamics.
In 2020 the team also began collaborating with the State Government Department of Water and Environmental Regulation (DWER) to develop new systems to accurately measure how much water is entering the aquifer, in addition to monitoring water level fluctuations.
In 2020, the team commenced the Recharge Estimation Collaboration Project, in collaboration with DWER and the CSIRO. It has been funded by DWER until 2025 as part of the State Groundwater Investigation Program.
The project aims to:
- Establish monitor stations to assist in the estimation of recharge on the Swan Coastal Plain
- Test, develop and apply recharge estimation methods
The team have established seven observatory stations across the 12,000km Western Australian Swan Coastal Plain’s Gnangara Aquifer system, from Dandaragan to Myalup. These monitor rainfall and water as it enters the surface and moves to the groundwater aquifers. Due to large variations in environment in the aquifer system, they have been strategically located to catch different kinds of soils, land uses and climates.
The team works closely with farmers in Dandaragan, who are using the data to improve pasture management and are hoping to conduct additional irrigation research in the Myalup region.
“We’re engaged with some fantastic farmers who have volunteered their land and who ask questions about the best ways to manage their irrigation water.”
Aquifers are an essential water source for a healthy environment.
In support of the project, the Government of Western Australia has published a webpage to outline the project details and how the findings are being used to monitor resources and inform future modelling.
- Whilst the previously used water table fluctuation method can be used to estimate recharge rates, it is subject to uncertainties. The new method is generally more robust for deeper groundwater systems with monthly or greater sampling frequency.
- A suite of modelling methods ranging from simple to complex can be used to estimate recharge.
- Monitoring data collected by UWA will assist in constraining recharge estimates for all modelling methods.
- Long-term monitoring using consistent methodologies and assessing different components of the climate variables will be implemented.
- The monitoring and modelling efforts will be used to develop future versions of the Perth Region Aquifer Modelling System (PRAMS) and other coastal plain groundwater models, making recharge estimates more reliable, enhancing the Government’s ability to make better predictions, and more informed decisions.
Funded by DWER, the Recharge in a Changing Climate Project which runs from 2023 – 2026 looks at the climate change impacts as a result of changes in aquifers. At the same time, UWA has funded the team’s project to introduce a novel geospatial approach to assessing climate change impacts on grasslands.
Using multiple data sets including historical data over 60 years, in 2024 the team looked at how recharge has changed over time. Their review shows that the significant declines in recharge as the climate has dried, has occurred faster than the replenishment of aquifers.
Data collected and infrastructure is also supported by the use of Terrestrial Ecosystem Research Network (TERN) infrastructure, which is enabled by the Australian Government’s National Collaborative Research Infrastructure Strategy (NCRIS).
Having more accurate observations around groundwater recharge estimation is informing DWER on how best to rebalance the aquifers and adjust future water forecasting and sustainable management of groundwater systems.
“We are showing the profound impacts that changes in rainfall volume have on how much water makes it to the groundwater, and that small changes in rainfall can have a big impact on recharge.”
Some of the Recharge Estimation Collaboration team.
A multi-measured approach
The conventional approach of digging a deep hole and inserting sensors to take measurements only provides information about the environment around the hole, rather than the broader landscape.
In 2023, the team worked with soil geomorphologist Associate Professor Matthias Leopold, UWA School of Agriculture and Environment to develop a variety of techniques to better measure water resources and predict drought vulnerable areas. Similarly, the team used geophysics to develop techniques that provide a much larger footprint of what happens when rain from tree canopies infiltrates the soil. These technologies have been embedded into the seven observatories managed by the team.
The observatories include drilled holes with water sensors that feed down into an ERT (Electrical resistivity tomography). The ERT is a long line that injects electricity into the ground and measures how it is transmitted, giving two-dimensional slice observations of the water content in the subsurface. Access tubes at each end also emit neutrons to monitor how they get absorbed by water in the sub surface. Paired with these technologies are weather stations that observe the climate, as well as soil sampling to help understand the soil composition, and satellite feeds to help the observations scale up. Whilst some of the data is provided in real-time, some data requires analysis to ensure it is reliable. All data is delivered to the State Government and stakeholders.
Their Banksia Woodland site in Gin Gin is co-located with a TERN, and Australian and New Zealand Flux Research and Monitoring Network (OzFlux). It includes a comprehensively suite of technologies:
- Eddy Covariance towers, which use 3D high speed measurements of wind speed, temperature and humidity to allow the measurement of evaporation
- Electrical Resistivity Tomography
- Groundwater wells
- Soil moisture measurements from the land surface to the groundwater
- Neutron moisture meter access tubes
Research such as this provides government policy makers with aquifer recovery as a viable option for water resource management in Western Australia that has additional flow-on benefits to the environment. Restoring our underground aquifers could be the solution to a greener, cooler, and more liveable city, particularly as our climate warms.
“By returning some of the water we don’t currently use back underground, we keep the wetlands wet, the rivers flowing, and our trees drinking and staying alive through the hot summers.”
Repairing the body with nature in mind