Neatly concealed beneath a lush green lawn, Bondi’s new stormwater initiative not only saves 50 million litres of drinking water a year, it also cuts pollution from entering the iconic waves that lap its shore.

By Brian McCormack

Excavating a massive pit beside Sydney’s famous Bondi Beach in order to build and bury a 300,000-litre concrete storage tank was a challenging task for Waverley Council two years ago.

Today, however, that tank is the mainstay of a sustainability initiative that each year harvests, treats and re-uses 50 million litres of stormwater that was previously discharged, untreated, into the ocean at the southern end of the beach.

That translates into saving 50 million litres of potable water, which in the past had been used for irrigation, cleaning and ablution purposes around Bondi. 

Moreover, the new project also reduces stormwater pollution at the beach itself, while remaining unobtrusively underground to maintain public space.

Completed early last year, the project is part of Waverley Council’s Environmental Action Plan for 2012-2020. 

An ambitious element of this eco-roadmap is to ensure that its consumption of mains-water clocks in at 2005-06 levels by the year 2020. 

Considering Bondi Park and Bondi Pavilion used 59 per cent of the Council’s mains-water in 2011-12, the new stormwater harvesting facility is a significant milestone on that roadmap. 

And, in line with its eco commitment, the council has also made the whole installation carbon neutral by powering the project’s treatment plant with a 10kW solar system mounted on the roof of Bondi Pavilion.

Tight schedule

Building such a large and complex structure on the grassy slopes beside one of the world’s busiest beaches was a tough task when construction began in September 2011. 

“We had to work to a tight four-month timeline,” says Council Project Manager, Corey Fox. “That’s because all major works had to be completed and the site reinstated by mid-December to allow full public access during the busy summer period.”

But time constraint wasn’t the only issue, recalls Fox. “The soil in the park behind the beach is very sandy, which made it difficult to keep stable when making deep excavations for the construction of underground infrastructure,” he says. 

“Plus, we had to work on a site which hosted a maze of underground services, including a network of international submarine fibre optic cables. Needless to say, you have to tread pretty carefully around obstacles like that – especially when you’re driving an augur bore right alongside them!”

Reliable supply source

The main off-take for the Bondi stormwater scheme is from a large Sydney Water Corporation (SWC) junction pit, situated at the southern end of the park, which receives water from the 115-hectare Bondi South catchment. Water flows at a rate of four litres per second into this junction pit and, after passing through SWC gross pollutant traps, is conveyed via a single-trunk drain for discharge at Bondi's southern shoreline.

The Bondi stormwater scheme draws water at the rate of two litres per second from this source. However, it also handles polluted stormwater run-off from Campbell Parade – the heavily trafficked, tourist strip that runs the length of Bondi Beach.

For this run-off, the stormwater system uses Hydrocon porous pipe filtration technology to remove heavy metals, hydrocarbons and phosphorous. 

A bio-retention garden was originally planned to isolate and treat the Campbell Parade run-off, but at the time of construction a master plan for Bondi Park was still under review, so the underground Hydrocon filtration system was designed as an alternative to better manage the water. Not only does this work to improve the water quality at Bondi Beach, it has also improved system operation by reducing oil content in the harvested stormwater, which was fouling the backwash screen. 

Disinfection fully automated

The Bondi stormwater system uses grinder pumps to harvest water, which is then subjected to 100-micron backwash filtration and UV treatment. The system is fully automated with 24/7 inline monitoring of UV transmission rates to ensure effective disinfection. 

According to Fox, the monitoring of UV transmission was chosen over turbidity measurement, because an earlier stormwater-harvesting project at nearby Bronte Beach had demonstrated there was little correlation between turbidity levels and UV kill-rates. 

The system incorporates state-of-the-art technology with telemetry control, which enables staff to remotely manage it using a smartphone application. 

Built with support from the NSW Government’s Climate Change Fund, the scheme is delivering significant cost savings for Waverley Council. It also had community support from the outset, with the council keeping residents and visitors constantly in the loop via explanatory signage, web updates, newsletters and bulletins.

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