Reviving Urban Wetlands: Adjunct Prof Unpacks Perry Lakes Renaissance

Published on 09 January 2024

An environmental expert delivered a captivating and enlightening talk to more than 50 people at the Friends of Lake Claremont ‘Night Chats’ on 15 August 2023, an event that provided insight into the Town of Cambridge's Perry Lakes water diversion project.

Dr Don McFarlane, an Adjunct Professor at the School of Agriculture and Environment at The University of Western Australia (UWA) and Education Officer for the Friends of Perry Lakes, unravelled how Perry Lakes, like many urban wetlands, faced an uncertain future, grappling with the devastating effects of climate change and increased groundwater extraction.

Startling climate data reveals that recent rainfall levels are the lowest for more than 800 years, as evidenced by limestone cave deposits and Antarctic ice cores. Additionally, precipitation has shifted from prolonged periods of rain to sporadic showers, reducing recharge to aquifers.

Rising average annual maximum temperatures and evaporation rates in Perth since 1980 have reduced recharge further, necessitating urgent action to combat Perry Lakes' desiccation.

Dr McFarlane's talk unveiled a history of strategies examined by the Town to reverse Perry Lakes' drying, with an initial focus on managed aquifer recharge using treated wastewater from the Subiaco Wastewater Treatment Plant in 2008 to 2010. This would replenish groundwater and allow more secure irrigation of Alderbury and Perry Lakes reserves while ensuring that nutrients and pathogens were removed before water entered the lakes.

“The amount of treated wastewater increases each year so it could be a fallback if the current initiative were to be affected by a lack of water,” Dr McFarlane said.

“Ultimately, the council decided to redirect water from the Herdsman to Floreat main drain. This achievement was realised by transferring pumped drain water into the existing stormwater system near McLean Oval on Ulster Road.”

A key aspect of this project is the integration of stormwater entry into West Lake, accommodating pumped Herdsman Main Drain water when the main drain holds sufficient water and faces no conflicts with street runoff. There is a pipe connecting West and East Lake which flows when West Lake is about half full.

Dr McFarlane emphasised that the system needed to be monitored because there is uncertainty about the amount and quality of water in the main drain, how much added water will be lost to evaporation and seepage through the lake beds, and whether there is sufficient pump capacity if the lakes did not fill sufficiently, especially if the climate continues to dry.

“Monitoring is also required of water quality and biological responses to the additions,” he said.

Adding water directly into the lake rather than via the aquifer as proposed in the earlier proposal using treated wastewater adds some risk to water quality. Therefore, Baumia and other wetland species have been installed to attenuate suspended solids, nitrogen, and phosphorus from incoming water, helping to safeguarding the overall ecosystem's health.

The benefits of these initiatives extend beyond environmental considerations. The community and nearby residents are poised to reap substantial rewards from Perry Lakes' revival. In 2009, the additional value added to existing nearby properties by having open water in the lakes was estimated to be $54 million, with an additional $25 million for properties in a new residential development near the lakes. These properties will, therefore, contribute a higher proportion of rates, so it is a “beneficiary pays” system.

Dr McFarlane concluded that the diversion of main drain water into Perry Lakes heralds a new era for nature conservation, aesthetic enhancement, and economic prosperity.

“It promises to reduce lakebed exposure, mitigating the release of nutrients and heavy metals, while concurrently fortifying groundwater levels and irrigation water security,” he said.

“Furthermore, it holds the potential to mitigate pollution at Floreat Beach, safeguarding both the environment and the community's wellbeing.”

The Friends of Perry Lakes, working closely with the Town of Cambridge and the broader community, remain steadfast in their commitment to seize this unique opportunity. Together, they aim to help this transformative project and maximise its benefits for all stakeholders involved.

View Dr McFarlane's Presentation Slides(PDF, 7MB)

Watch Dr McFarlane's Presentation Video