At Sydney’s Green Square, a hidden water engineering project is helping to prevent flooding and reduce the precinct’s potable water use.
Built on land that was once a network of wetlands and creeks, the area 4 km south of the CBD is prone to flooding during heavy rain. The solution was to build a 2.4 km underground stormwater drain capable of carrying 30,000 L of water/second from Epsom Road, Zetland to an existing stormwater system at Alexandra Canal.
The project, developed by the City of Sydney and Sydney Water, was four years in the making and won the 2019 Infrastructure Project Innovation Award at the Australian Water Association’s NSW Water Awards earlier this year.
It involved a range of creative solutions to ensure life could go on as normal above ground while construction was carried out, including micro-tunnelling to allow tunnel boring machines to install 1.8 m diameter pipes up to 12 m underground.
Announcing the official opening of the drain earlier this month, City of Sydney Lord Mayor Clover Moore said the $140 million project was an example of how water resources could be used to reduce demand on drinking water, minimise flood risk, improve water quality and enable development.
“This is one of my favourite City projects, not because of its architectural beauty or immediately obvious utility, but because of its unseen significance,” Moore said.
“Many residents will not even now it’s here or, if they do, how important it is, but I can assure you that everyone would eventually notice its absence if we had not built this drain.”
The City of Sydney and Sydney Water formed the Drying Green Alliance with UGL Engineering, Seymour Whyte Constructions, Parsons Brinckerhoff and RPS Manidis Roberts to build the drain.
Sydney Water General Manager for Liveable City Solutions Paul Plowman said collaboration was key to the project’s success.
“By working together we have delivered innovative solutions that will greatly reduce the risk of flooding for residents and improve liveability for the local area,” he said.
“This is part of Sydney Water’s commitment to providing stormwater services to support growth and development in the Green Square area, to ensure Sydney remains a fantastic place to live and work in the future.”
Moore said the stormwater drain was a vital aspect of the council’s $540 million transformation plan for Green Square. This also includes a water recycling scheme, which will eventually treat up to 320 ML of stormwater each year.
The water is treated on-site at the Green Infrastructure Centre before being sent to storage tanks hidden under the nearby Matron Ruby Grant Park. It is then delivered to the Green Square town centre and surrounding apartment buildings via a series of purple pipes – making it easy to distinguish from potable water – and is used to flush toilets and water green spaces.
City of Sydney estimates the scheme will halve the amount of drinking water used in the town centre.