Building one of Australia’s most densely populated new urban developments on a former swamp turned high-hazard flash flooding zone might seem like folly.

However, successful collaboration and innovative thinking has found a stormwater drain solution, the implementation of which has been so successful that it could transform the way we tackle such projects in the future.

In his paper Innovative Stormwater Infrastructure – The Green Square Stormwater Drain, to be presented at the IPWEA International Public Works Conference in August, Technical Services Manager Peter Shields from the City of Sydney explains there were a series of unique factors that made the project such a success.

“It's always tricky when you're trying to overcome flooding and pipes aren't usually used for this, so to use pipes to address high hazard flooding in large flood events is, in itself, quite unusual," he says. 

However, Shields explains, the main innovation with the project was the employment of micro-tunnelling to install the drain. While micro-tunnelling has been around for about a decade, its use has mainly been restricted to sewage pipes.

“The pipes are laid at incredibly deep depths of 9-12 metres below the surface, which is very unusual in local government,” he explains. “That was a huge innovation for this project because it basically meant the community wasn't interrupted because we weren't digging up everywhere, we were just tunnelling underneath it all. We had to take the pipe through areas where there are a lot of existing high volume roads and it would have had drastic impacts on traffic and the community in general. There would have been a lot of noise, plus a lot of spoil and excavated material that would have had to be dumped, so [avoiding all that] has resulted in wonderful outcomes for the community.”

Shields says the micro-tunnelling method also saved them considerable time and money and carried less risk.

“You don't need any of the construction plant equipment you normally have, and you don't have the safety issues you normally have, because you're not digging deep holes all the way along.”

An additional benefit of micro-tunnelling is its high accuracy.

“The tunnelling machine is guided by a laser and the computer of the tunnelling machine is continuously monitoring its alignment with that and it corrects itself to make sure it stays on the right path. Normally engineers have to design pipes to slope one percent, because it’s impossible for blokes out there laying trenches to do it any more accurately than that. But with micro-tunnelling, you don't have those standard issues, you can lay it at much flatter grades.”

Even the way the Green Square Stormwater Drain contract ran was innovative, Shields explains, as it was an alliance project between City of Sydney, Sydney Water – a state government entity – and four other companies. Shields says this set-up, while not without challenges, enabled much of the innovation of the project.

“Because we had the alliance contract, it allowed all six enterprises involved to look at better ways of doing things, and visit the costing and the scope and do that in a flexible way.”

To learn more about this groundbreaking project, be sure to attend Shield’s presentation at the IPWEA International Public Works Conference, held at the Perth Conference and Exhibition Centre, WA from August 20-23.