Tree roots turn Modbury sewers upside down

Resembling creatures in Stranger Things, a giant half-tonne tree root mass has been removed from the sewers in Adelaide’s north-east – preventing potential community interruption and sewage overflows.

The five-kilometre-long, 675-millimetre-diameter sewerage pipe travels beneath suburban streets and reserves between Bridge Road in Walkley Heights and Kelly Road in Para Vista, with a large number of trees in the area.

During a 30-minute period, SA Water’s crews carefully attached several lifting slings to the cluster’s main roots, before fixing them to an excavator’s arm, which expertly guided the mass out of the concrete sewer chamber.

SA Water’s Senior Manager of Field Operations Colin Bell said other sections along the pipe also had extreme root intrusion, while some yielded around 200 kilograms of wet wipes.

“Our crews were convinced they entered an episode of Stranger Things after making the discovery!” Colin said.

“We were first alerted to the potential invasion after a substantial blockage occurred in another section of pipe within Walkley Heights, when we discovered what appeared to be a tree literally growing inside the sewers.

“Typically, areas in the foothills or surrounded by natural spaces experience a higher number of blockages, due to tree roots breaking into pipes in search of water and blocking the flow of sewage to our treatment plants.

“In fact, thirsty tree roots are the leading cause of sewer blockages within our network across South Australia.

“Due to the sheer weight of the root mass in Modbury, we needed the help of our excavator to safely pull the cluster out of the chamber – with our crews achieving this in one clean attempt, which was a great feat!

“Weighing in at around half a tonne and measuring five metres in length, we needed to break it down into smaller pieces of roots to transport and dispose of it at our Bolivar plant.

“A significant amount of behind-the-scenes work went into preparing for this job, with our investigations along the pipe finding that several other sections were impacted by tree roots and at risk of further blockages.

“To reduce the risk of blockages downstream when removing the mass, our crews proactively cleaned around 500 metres of this part of pipe every night over a number of weeks, working in the early hours of the morning to reduce any potential disruption to the community and take advantage of lower flows in the network.

“Our cleaning also yielded a few more surprises, such as 200 kilograms of wet wipes and several metres of rope, serving as a timely reminder to the community to consider what they’re flushing down the toilet.

“There’s a range of preventative measures we have invested in to reduce the risk of blockages from tree roots, with the community able to access our Healthy Pipes online tool to help people plant the right tree in the right place on their property, along with our ongoing sewer cleaning program and innovative tree root barrier trial.”

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