Rising above 100-year flood levels for Johnson Property Group and Lake Macquarie City Council

Some community bridges are trickier to deliver than others. Our recent project for Johnson Property Group at Cooranbong, 120km north of Sydney, is certainly evidence of that.

In addition to being a significant cable-stay structure in an ecologically sensitive, flood-prone location, there was considerable extra pressure due to a Voluntary Planning Agreement (VPA) between Johnson Property Group and Lake Macquarie City Council.

“Johnson Property Group is developing a major residential release at Cooranbong called Watagan Park,” explains Fleetwood Project Lead, Adrian Trimmer. “It’s a fantastic community, well underway, but in order to progress to the next stage of development, Lake Macquarie City Council requested a major new pedestrian and cycling bridge first be delivered across nearby Dora Creek. It was one of those situations where time really is money – the stakes were high!”

Engaging Early

Having successfully completed another pedestrian bridge at Cooranbong, Johnson Property Group chose Fleetwood to design and construct the new structure. “We were engaged early in the process as the sole contractor,” says Adrian Trimmer. “That provided some big efficiencies for the project and allowed us to offer significant input to reduce the inherent project risks at every stage.” Fleetwood’s role on the project spanned everything from influencing the initial design of the bridge, confirming feasibility and informing the budget, to creating a methodology that worked for both the client and the sensitive site.

Beautiful and durable

Our vision was for the new bridge to complement the historic Cooranbong Swing Bridge built at the nearby Weet-Bix factory site back in 1934. To achieve this, a custom twin tower cable-stay design was developed. However, in order to deliver on Council’s brief to withstand a 1 in 100-year flooding event, a significant clear span of 50 metres was required.

“50 metres is a major structure, especially for a cable-stay pedestrian bridge,” reflects Fleetwood Head of Delivery, John Dahdah. “It called for several design innovations including carefully angling the support towers, as well as using specialised tension cables from Italy. While we explored the option of using AS 2156, we ultimately designed the bridge to AS 5100 together with the Ausroads cycle code. It will be standing long after we’re all gone!”

Large scale, high sensitivity

Given the sensitive habitat of the Dora Creek catchment, which flows into pristine Lake Macquarie, there were considerable environmental risks to be carefully managed. “As just one example, the sheer scale and height of the structure meant crane selection was especially important to avoid damage to the surrounding creek banks,” says John Dahdah. “Persistent wet weather, including flooding at the start of the construction window, also made site conditions quite treacherous at times.”

The bridge superstructure and towers were manufactured at Fleetwood’s state-of-the-art facility in Sydney, with pre-assembly in mid-August. Final installation was completed in September 2022 with the bridge set to open to the public in mid-November. A fantastic result for the project stakeholders – and the local Cooranbong community!

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