A 2km-long underground stormwater drain that can carry the equivalent of 1,200 bathtubs of water per minute is now running under Sydney.

The award-winning engineering project will play a critical role in reducing the risk of flooding in the inner Sydney suburb of Green Square, while also improving water quality and saving drinking water.

“This is one of my favourite City projects, not because of its architectural beauty or immediately obvious utility, but because of its unseen significance,” says lord mayor Clover Moore.

“Many residents will not even know it’s here or if they do, how important it is, but I can assure you everyone would eventually notice its absence if we had not built this drain.”

Green Square’s town centre sits on a floodplain that used to be a network of wetlands and creeks between the city centre and Sydney Airport, where heavy rain can cause hazardous flooding.

In 2015, severe storms caused dangerous flooding on Joynton Avenue, one of the area’s major thoroughfares. In 2018, Green Square was hit by a ‘once in a hundred years’ storm, but due to stormwater drain infrastructure already in place, the area did not flood.

The drain can carry up to 30,000 litres of stormwater per second from Epsom Road to Alexandra Canal, significantly reducing potential flooding across the area, especially on Joynton Avenue and Botany Road in Zetland.

Most of the route runs through or under property owned by the City. The drain route was chosen to minimise impact on residents, businesses and the environment.

The project’s technical and logistical challenges were met with engineering innovations, including:

Micro-tunnelling that enabled tunnel boring machines to install huge 1.8m diameter pipes up to 12 metres underground while minimising traffic, environmental and community disruption
The largest gross pollutant traps available in Australia were installed to treat stormwater runoff and to improve water quality in the Cooks River
A new harvesting system now diverts stormwater from the drainage system to a water recycling plant in Green Square, designed to deliver up to 320 million litres of stormwater annually to new buildings and open spaces.

Green Square Stormwater drain environment

As part of the project, the Huntley Street bridge in Alexandria was raised and lengthened and the area around the Shea’s Creek open channel was renewed to make it a more attractive and usable public space. A shared path will provide a safe space for people walking and riding bikes along the creek’s eastern side, from Maddox Street to the mouth of Alexandra Canal.

A new separated cycleway on Epsom Road will further support people riding in the area and mean Green Square will have more cycling routes than any other part of Sydney, with bike links from four directions into the town centre.

Architecture News & Editorial Desk

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