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Barwon Water releases passing flows in the order of 1–5 ML per day (and up to 15 ML per day in September during a wet year) from the West Barwon Reservoir into the West Barwon River. Flood spills from the reservoir and natural inflows from unregulated and partly regulated tributaries add to the passing flows.

A new entitlement was established in April 2018, enabling water for the environment to be used in the upper Barwon River for the first time in 2018–19. The entitlement provides 1,000 ML per year on average from the West Barwon Reservoir.

In light of this new entitlement, the Corangamite CMA updated the Upper Barwon, Yarowee and Leigh rivers environmental flows study in 2018–19, to ensure management decisions are underpinned by the best available science and information. The Environmental Flows Technical Panel included a representative of the Wadawurrung Traditional Owner group, to specifically consider the Aboriginal values of the waterways in their region.

System map

Grey river reaches have been included for context. The coloured extent of the upper Barwon River (including the East and West branches) is provided as a preliminary indication of where water may be able to be delivered if the entitlement is granted.

Environmental watering objectives in the Upper Barwon River

Maintain the abundance, and improve the breeding and recruitment of migratory fish species including short-finned eels, Australian grayling and tupong, broad-finned galaxias and common jollytail

Maintain the abundance, and improve the breeding and recruitment of resident freshwater fish including several species of galaxias, Australian smelt, big-headed gudgeon, Yarra pygmy perch and river blackfish
Platypus icon
Maintain the abundance, improve the condition and extend the distribution of platypus populations
Plant icon
Improve the condition and extent of native instream vegetation, to provide structural habitat for macroinvertebrates and various fish species

Increase the extent and diversity of emergent macrophyte vegetation, to provide structural habitat and stabilise banks

Increase the extent and diversity of native riparian vegetation

Improve the condition and extent of native floodplain vegetation
Insect icon
Increase the abundance of waterbugs as a food source for fish, frog and platypus populations
Water icon
Maintain water quality for native fish, waterbugs, aquatic vegetation and other water-dependent animals

Environmental values

The upper Barwon River is home to native fish species including the Australian grayling, river blackfish, short-finned eel, southern pygmy perch, Australian smelt and various galaxias. The system retains some submerged aquatic vegetation, undercut banks, overhanging vegetation and riffle-pool sequences: these provide important habitat for fish and other aquatic animals.

Recent conditions

The Barwon River catchment was drier and warmer than average in 2018–19. The very first release of water for the environment started in January 2019, with a summer fresh delivered down the west branch of the Barwon River to mitigate observed cease-to-flow conditions at Ricketts Marsh.

Despite adopting a conservative flow rate for this first release, some flow spilt out of the channel at constriction points created by historic infrastructure and exotic vegetation. These constrictions will need to be managed in future, to realise the full benefit of the environmental watering program.

The release shed light on the capacity of water for the environment to affect downstream reaches. It took two weeks for the released water to travel from West Barwon Reservoir to Winchelsea. The peak flow at Winchelsea was only 20 percent of the maximum flow release at the reservoir outlet. These statistics highlight the importance of wetting-up a river to reduce losses, and they confirm that the influence of water for the environment is limited to the upper reaches under the current system operations.

Scope of environmental watering

Table 1 Potential environmental watering actions and objectives for the upper Barwon River

Potential environmental watering action1

Functional watering objective

Environmental objective

Summer/autumn low flows (0.5–30 ML/day during December to May)

  • Provide water in pools for habitat and food sources
  • Maintain an adequate depth of permanent water in the channel to support resident fish, platypus and macroinvertebrates, promote recruitment of native aquatic vegetation and limit encroachment by terrestrial plants
  • Provide minimum velocity to maintain mixing in pools
Fish iconPlatypus iconPlant icon Water drop icon 

Summer/autumn fresh (15–50 ML/day for two days during December to May)

  • Provide water over riffles to allow fish to move between pools to
    breed, feed and find new habitats
    Submerge woody debris and clean hard surfaces to provide breeding substrate
  • Sustain macroinvertebrate communities in the dry period by
    inundating benches
  • Provide longitudinal connectivity between reaches
  • Provide a mosaic of habitats within the stream channel, on benches and on lower banks that have different inundation patterns
    Support plant growth on terraces, the channel edge and lower bank
  • Provide minimum velocity to mix and flush pools

Fish iconPlatypus iconPlant icon Insect iconWater drop icon

Winter/spring low flow (10–50 ML/day during April to November)

  • Provide water in pools for habitat and food sources
    Maintain an adequate depth of permanent water in the channel to promote the recruitment of aquatic and riparian plants and to limit the encroachment of terrestrial species
  • Provide minimum velocity, to mix pools
  • Mobilise sediment from the base of pools for a sustained duration

Fish iconPlatypus iconPlant icon Water drop icon

1 Potential watering actions apply to both the east and west branch of the upper Barwon River.

Engagement

Table 2 shows the partners and stakeholder organisations with which Corangamite CMA engaged when preparing the Upper Barwon River seasonal watering proposal.

Seasonal watering proposals are informed by longer-term regional catchment strategies, regional waterway strategies, environmental flow studies, water management plans and other studies. These incorporate a range of environmental, cultural, social and economic perspectives and longerterm integrated catchment and waterway management objectives. For further details, refer to the Corangamite Regional Catchment Strategy and the Corangamite Waterway Strategy.

Table 2 Partners and stakeholders engaged in developing the Upper Barwon River system seasonal watering proposal

Partner and stakeholder engagement
  • Land and Water Resources - Otway Catchment
  • Upper Barwon Surface Water Advisory Group
  • Individual landholders who are on the Upper Barwon Surface Water Advisory Group
  • Colac Otway Shire Council
  • Barwon Water
  • Department of Environment, Land, Water and Planning
  • Southern Rural Water
  • Victorian Environmental Water Holder
  • Individual recreational users who are on the Upper Barwon Surface Water Advisory Group
  • Eastern Maar Aboriginal Corporation
  • Wathaurung Aboriginal Corporation