Water supply change crucial

COPPERLODE Falls Dam and Behana Creek water sources service 98 per cent of the Cairns local government area’s population.

In March 2018, both sources of supply were cut by a storm event, and Cairns ran itself down to just one and a half days of treated water availability before supply could be restored.

Now a hydrology expert wants to see major changes to the way Cairns Regional Council manages water supply and demand to avoid similar incidents in the future.

“We shouldn’t have a system where if you turn off one source it cuts supply to the whole city – that’s not good,” Dr HanShe Lim, a JCU lecturer in hydrology, said.

“Part of increasing resilience of infrastructure is to have backup and multiple sources of supply. We need to have modern infrastructure that’s able to cope with all kinds of conditions, especially storm condition.

“But water resilience is more complex than just infrastructure. Resilience also relies on effective demand management.”

The three pillars upholding Cairns’ water supply are: supply from Copperlode via the Freshwater Creek water treatment facility, supply from Behana, and Cairns Regional Council’s network of treated water reservoirs. Each showed their vulnerability during the 2018 calamity.

The intake from Copperlode was blocked by storm debris and took four days to remove.

Elevated turbidity levels shut down Behana’s water treatment facility, an outcome that “typically” occurs during significant rainfall events.

And the reservoirs held 257 megalitres (ML), about four and half days of supply in March 2018, when the city’s average daily water consumption for that month was 55ML.

Annually, it’s now 64.85ML, up from the 2018 average of 63.66ML.

The council maintains the event did not result in a critical water supply shortage, according to its 2022 water security report.

Mark Wuth, the council’s infrastructure and assets director, said the council had addressed, or plans to address, all three areas of vulnerability.

“The $2.16m Freshwater Water Treatment Plant upgrade has significantly improved screening to both prevent blockages and also enhance accessibility to allow debris to be more easily removed,” Mr Wuth said.

“There is a plan to upgrade the functionality of the Behana water treatment plant by installing equipment upstream … to scour dirty water during high turbidity.

“There is a new $18m water reservoir to be constructed in Mount Peter and the council has undertaken a number of reticulation network improvements that assist in balancing the water stored in reservoirs across the city.”

Mr Wuth said the council also intends to construct new pump stations at Trinity Beach and Edmonton that can redistribute water between reservoirs and maximise storage capacity.

“The water supply network is constantly evolving and improving,” he said.