Upper Molonglo Catchment

  • Two priority projects, comprising a wetland and two rain gardens, have been chosen for the Upper Molonglo catchment.
  • An estimated $3.4 million will be invested in the catchment over three years.
  • Research indicates the combined projects will remove 3% of suspended solids, 3% of phosphorus and 2% of nitrogen from the Molonglo and Queanbeyan rivers.

Proposed priority projects

Wetland - Reserve adjacent to Morrisett Street, Queanbeyan

The proposed wetland will utilise open space next to Queanbeyan River between Morisset Street and Ford Street, Queanbeyan and improve water quality by trapping sediments and nutrients flow through the Queanbeyan River. It will also enhance the area and increase its appeal as a recreational space for the local community by providing opportunities for seating, bird watching and nature appreciation. The design allows for some open space to be retained for existing activities such as dog walking.

Rain gardens – Alanbar Street and Kenneth Place, Karabar

The proposed project will involve the establishment of two rain gardens; one on the open grassed area north of Margaret Donoghoe Park and one in Alanbar Street, in the suburb of Karabar. The area will be landscaped to incorporate vegetation and filtering media such as geo-sand to remove nutrients and sediment. The rain garden has been designed to avoid the existing mature tree on the north side of the site. The existing walking and cycle path will be realigned to go around the garden. The second rain garden system is proposed within the Kenneth Place roundabout.

Catchment facts

  • Incorporates two main rivers - the Molonglo River and the Queanbeyan River, downstream of the Googong Dam.
  • Includes all the land that drains into the Molonglo River, down to where it meets the Queanbeyan River.
  • Only priority catchment for the project that is multi-jurisdictional, with management involving the Australian Government, ACT and NSW governments.
  • The Molonglo River is about 115 km long, flowing from the Great Dividing Range above Captains Flat through the ACT to the Murrumbidgee River.
  • The Molonglo River has a small dam at Captains Flat in the upper reaches of that catchment.
  • The Queanbeyan sewage treatment plant discharges into the Molonglo River upstream of Lake Burley Griffin.
Total Area – 171.3 km2

Land Use Zone

Area (km2)

Area (ha)

Area (%)

Pervious Area

151.78

15177.71

88.87%

Low Density Residential

3.89

388.50

2.27%

Medium Density Residential

6.30

630.22

3.69%

High Density Residential

0.44

44.07

0.26%

Commercial and Industrial

2.24

223.71

1.31%

Transport

6.14

613.83

3.59%

Upper Molonglo - Totals

170.78

17078.05

100%

Water Quality Issues

  • The catchment is a major contributor to water quality in the Murrumbidgee River, especially during floods.
  • Land use practices along the Molonglo and Queanbeyan rivers are key threats to their water quality.
  • Specifically, increased nutrient concentrations in the Molonglo River are linked to clearing of native vegetation in the upper reaches for farming, which causes erosion and sedimentation.
  • During periods of low flow, water quality and flow duration in the Molonglo River is heavily influenced by discharge from the Queanbeyan sewage treatment plant. This has also resulted in increased levels of phosphorus and other contaminants that cause algal blooms.
  • Water quality research indicates that the highest levels of pollution in the catchment occur in Queanbeyan's urban areas.
  • The highest concentrations of contaminants in the Queanbeyan and Molonglo rivers have been recorded just before the point where they meet.
  • The Queanbeyan River upstream from where it meets the Molonglo River is the single most affected point in the catchment.

Catchment options

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