The unique challenges of maintaining coastal sewer infrastructure

Aug 25, 2023

Loader tells Trenchless Australasia that it can be hard to identify minor issues, meaning that sometimes faults are only seen when there is a system failure. “There’s a range of things that will contribute to damaging the sewer network,” says Loader.

“Anything from ageing infrastructure, tree root intrusion, cross connections from private properties where they’ve connected their sewer in the storm water, either deliberately or unknowingly.” “Even just movement within the soil can sometimes dislodge pipe connections.” Unique to coastal regions, however, is the ingress of salt water – which speeds up corrosion of water assets.

“Flooding is also more frequent in coastal areas – storm surges and sea-levels rising can contribute to infiltration,” Loader says. The combination of a number of ecologically sensitive locations in the area and the dense urban population along the coast means that, when leaks do happen, the impact can be exaggerated compared to less complex urban environments, with public health being at the forefront.

Late in 2022, the combination of these various pressures on the system resulted in Terrigal Beach – in the southeast of the council’s jurisdiction – receiving a poor water quality rating, partially due to sewer infiltration. In response, the council commenced a massive relining program to mitigate the sewer outflow that was contributing to pollution in the area.

Since the pollution at Terrigal Beach was identified, Central Coast Council has relined over 125 kms of sewer mains. Contractors working on this effort are using spiral-wound liner on most of the system. Larger pipes, however, have required cured-in-place pipe (CIP)

“We have another 93 km to replace in the next five years – 25 km of which will be done in this financial year,” says Loader. “Plus, we’ve got about 1000 kms of vulnerable material – sewer gravity mains that will be assessed for relining.”

Asset management on this kind of scale required by the council’s network is an ongoing task. “It’s kind of like painting the Harbour Bridge. By the time you’ve inspected the whole network, it’s time to go back to the start,” Loader says.

To stay proactive in its asset management activities, the council combines the services of a dedicated, full time CCTV inspection crew with more reactive, issue-specific operators that respond to specific blocks or leaks as they occur in the network.

The whole operation is organised through a kind of triage system. The council has all the data regarding different parts of the sewer network – the age of the pipes, time since last inspection, condition, pipe material. This information is assessed so that the council knows where best to deploy its resources.

“We’re currently developing the Water and Sewer Master Plan,” says Loader. “We’re analysing the network assessing the brownfield areas that aren’t connected to it and determining if and how they should be.”

Loader says Central Coast Council has been identified as a growth council. “We have a lot of developer-led infrastructure being installed so Council’s role is to ensure that our trunk mains and treatment plants are suitably sized to accommodate the increased population,” he says.


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Clemence Carayol

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