Tuggeranong Creek drain to be naturalised under proposed Healthy Waterways program

The first phase of the project, currently being designed, includes converting a concrete drain in Tuggeranong Creek, reconnecting a branch of Tuggeranong Creek to its inflow and naturalising a small Tuggeranong drain.

Elements of natural channels will be reintroduced to the drains in the hope of improving water quality and the amenity of the area, as well as increasing biodiversity.

Ralph Ogden, ACT Healthy Waterways Manager, said Tuggeranong Creek had meandered naturally through the Tuggeranong valley prior to the concrete drain being installed as part of a flood mitigation effort.

He said by replacing a sinuous channel with a straight drain, a c-shaped section of the creek was cut off.

The largest of the three proposed projects aims to pump some of the flow into the isolated channel, then pipe it back into the drain.

He said the aim was to slow the flows and increase the interaction between the water, vegetation and soils.

"When water infiltrates into the soils, it gets naturally cleansed, that's what happens in a natural catchment," Mr Ogden said.

"By slowing it down and by allowing it to interact with the vegetation, the sediments are cleaned or filtered out."

The ACT government has engaged Sydney consultancy, Alluvium, to design the naturalised waterways.

The company has also been engaged to conduct a feasibility study of potential water savings through revision of the ACT's water sensitive urban design general code.

Tuggeranong has been chosen as the first location to trial naturalisation of Canberra's concrete drains, due to ongoing concerns over water quality flowing into the lake.

The project will likely be expanded across the ACT should the project, already being trialled in Sydney, Brisbane and Melbourne, be deemed a success and a government priority.

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Mr Ogden said the benefit was not just to water quality but also to "dampening the flow".

"One of the things you get with urbanisation, due to all the concrete we put in urban areas, is the water not going into the soil and getting a chance to be absorbed by plants and evaporate - so you actually get bigger flood peaks in urban areas," he said.

Mr Ogden said when the water went directly into the Tuggeranong channel via the drain, there was around three times the amount of discharge.

"One of the big benefits of running it through this old channel, is it gets a chance to absorb into the sides of the channel and the bottoms of the channel and go into the shallow aquifers," he said.

Many of the city's concrete stormwater drains were once natural creeks, and have been identified as potentially susceptible to flooding.

Mr Ogden said one of the considerations of the project will be to ensure slowing the water down won't increase the flood risk in the short term.

"The concrete drains solve one of our problems, they're very good at getting rid of floodwaters," he said.

"What we have to do is come up with a solution that ticks all other boxes, it gets rid of the floodwater, but also cleans the water, improves biodiversity and improves the amenity."

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