The Annulus Billabong re-watering project

Annulus Billabong 1982

History of the area

A chain of billabongs has formed in the Lower Yarra River floodplain over a long time. This area was and still is of great cultural significance to the Wurundjeri people and features in their dreamtime stories. The settlement of Melbourne has caused major changes to river flows and the surrounding landscape, resulting in major changes to the billabongs. The Yarra Flats in this area were cleared and used for farming and dairying in the 1840-60s, and subsequently used for grazing cattle and horses up till today. Further human activity contributed to the disappearance of the billabongs, with many billabongs in the area being used as tip sites.

In the late 1950’s the Upper Yarra Dam was constructed which resulted in a significant reduction in flooding in the lower Yarra River floodplains.

Reduced rainfall with climate change has exacerbated the lack of flooding which is required to refill the important billabongs.

The Annulus Billabong

The Annulus Billabong was re-watered by the MMBW in the 1980’s by using windmills to pump water from the Yarra. At this time it was also converted from an ‘ox-bow’ billabong (ie horse-shoe shaped) into an annulus by evacuation across the southern isthmus. This created an island that was designed to be a wildlife haven. The re-watering was successful for several years but trees growing up around the windmills and funding cuts eventually ended this source of water for the billabong. Since then it has held water for a year or two after floods which have happened several times. The last flood was in 2011, and it has been dry since then up until 2020.

The Annulus Billabong is in a Wildlife Sanctuary and Conservation Area in the park. It is the most important wetland of the park and has been recently listed as one of the 20 key wetlands in the Melbourne Water Healthy Waterways Strategy for the Melbourne area. It is 1 of 11 key wetlands along the Yarra River.

The Annulus Billabong in February 2019

In October 2020 Melbourne Water pumped water from the Yarra River into the billabong to help restore the ecosystem which was suffering’s from the long period of dryness. This also gave valuable information on the amount of water required to restore the ecology of the billabong.

The Banksia Street Billabong

Banksia Street Billabong is just north of the Yarra Flats Park carpark and has an elongated U-shape.

During the 1960s, the billabong was mined for garden soil and then filled with waste materials, and the natural drainage runoff was redirected into the Yarra River in a large pipe.

Revegetation of the billabong and surroundings begun in the 1980s. The remnant Banksia Street Billabong is dry during dry periods but still fills during wet periods.

The Annulus re-watering proposal

The proposal is to more regularly introduce water into the Annulus (and  Banksia Street Billabong). Several options are being assessed to achieve this including: regular pumping of water from the Yarra River; lowering the entry point of water into the Annulus from the Yarra so that smaller floods swill fill the billabong; diverting stormwater which would require construction of a settling pond/wetland between Banksia Street and the Annulus Billabong.

The creation of a Banksia Street Wetlands is a project that has been “in the pipeline” as far back as 1983, when Yarra Valley Metropolitan Parks Drainage Division began discussing the transfer of stormwater from the Banksia St main drain to a wetlands just south of Banksia Street. The proposal has been raised and re-examined multiple times over the following years, and in 2009 a detailed design of the Banksia Street Wetlands was commissioned by Melbourne Water. As the main driver of the project at that time was nitrogen reduction in order to help meet the nitrogen reduction target in State Environment Protection Policy (SEPP), it was decided that the project cost-benefit ratio was not enough for the project to proceed. It has since been recognised that the Banksia Street Wetlands have the potential to deliver additional benefits beyond simply reducing nitrogen, and the project is currently being re-examined.

Project benefits

The Banksia Street Wetlands have the potential to deliver a number of significant benefits in line with key strategic drivers, including:

  • Stormwater quality improvement: the constructed wetlands will treat stormwater from the upstream urban catchment before this is discharged into receiving waters. Improved water quality of discharge will protect the Yarra River in line with key strategies including the Yarra Strategic Plan (in development), the Healthy Waterways Strategy (2018) and the recommendations in the Improving Stormwater Management Advisory Committee report (2018);
  • Watering source for Banksia Street Billabong and Annulus Billabong: potential to use constructed wetlands as a watering source to rejuvenate Banksia Street Billabong and Annulus Billabong. This was an outcome that was strongly supported by community during consultation for the Yarra Flats Park Concept Plan (2013) – many respondents were in support of rejuvenation of the billabong areas;
  • Liveability benefits: the Yarra Flats Park Concept Plan (2013) found that 79% of the community agreed that the wetland would be of community benefit and 64% said it would increase their use of the Yarra Flats Parklands.

Where are we at now?

Melbourne Water has commissioned and received a study for re-watering The Annulus which is a high priority for them.

Our friends group has had input into this.

The preferred option is the diversion of the Banksia Street stormwater drain which currently comes down the south side of Banksia Street to the river.

This option would require a settling pond and a wetland area either near Banksia Street or between The Boulevard and The Annulus area. Water would then be fed into The Annulus by gravity and also the Banksia Billabong which is north of the far end of the carpark. There is adequate water flowing down the drain for this. The level of water in The Annulus would need to be varied to mimic the once natural cycles of floods and dry times. The price tag for this would be in the realm of $2 million. (which is less than initial estimates).

In addition pumping river water into the billabongs would be advisable to add various organisms into the billabong ecology which only river water can provide.

We will have to wait and see what Melbourne Water decides to do but we believe they are keen to act.

The Annulus October 2020
Chestnut Teal family
The magic of water
The dawn of a new phase for the Annulus