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Barwon Water releases passing flows in the order of 1-5 ML per day in both the upper east and west branch from the West Barwon Reservoir. These releases may increase to 15 ML per day in September in a wet year. When the reservoir is above 40,000 ML, all natural flows are passed down the east branch between January and March. Flood spills from the reservoir, and natural inflows from unregulated and regulated tributaries add to the passing flows in the west branch. Regulated and unregulated tributaries add to passing flows in the east branch.

The Upper Barwon River Environmental Entitlement 2018 enables water to be made available for the environment from the West Barwon Reservoir. The entitlement provides an average of 1,000 ML per year and up to 2,000 ML of the total storage capacity at full supply. Water for the environment was first delivered to the upper Barwon in 2018-19. The current entitlement provides only enough water to meet the highest ecological objectives in the upper Barwon east branch (reach 4) and the upper Barwon west branch (reach 3) under particular climatic conditions.

Proportion of water entitlements in the Upper Barwon River held by private users, water corporations and environmental water holders on 30 June 2020

Traditional Owners

System map

Environmental watering objectives in the Upper Barwon River

Platypus icon
Maintain the abundance and improve the condition and extent of platypus populations
Insect icon
Increase the abundance and improve the breeding and recruitment 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
Maintain the abundance, and improve the breeding and recruitment of migratory fish species, including short- finned eels, Australian grayling, tupong, broad-finned galaxias and common galaxias

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, southern pygmy perch and river blackfish
Plant icon
Improve the condition and extent of in-stream vegetation to provide structural habitat for waterbugs and various fish species

Improve the condition, extent and diversity of emergent macrophyte vegetation and streamside vegetation to provide structural habitat and stabilise the channel and lower banks

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, which provide important habitat for fish and other aquatic animals.

Recent conditions

Rainfall in the upper Barwon catchment in 2021-22 was slightly above the long-term average. The West Barwon Reservoir spilled for more than three months from July 2021, and the reservoir remained above 90 percent capacity throughout the year.

Water for the environment in the upper Barwon River system was managed according to an average climate scenario throughout 2021-22. All planned watering actions in the east branch were fully met through a combination of passing flows and natural flow events. Passing flows and natural flows also met most of the planned watering actions in the west branch. Water

for the environment was used to maintain target summer/autumn low flows in the west branch when needed. Water for the environment was not delivered in the east branch during 2021-22.

Traditional Owner cultural values and uses

The reaches of the Barwon River that can be most influenced by water delivered from the West Barwon Reservoir sit in Eastern Maar Country. In February 2020, the Eastern Maar Aboriginal Corporation (EMAC) received Registered Aboriginal Party status under the Aboriginal Heritage Act 2006 over a large portion of land in south-west Victoria, including the Barwon River upstream of Winchelsea. The EMAC was invited to be involved in the development of Corangamite CMA’s seasonal watering proposal, as good opportunities exist within these reaches to support Eastern Maar values and aspirations associated with the waterway.

Corangamite CMA is working with Wadawurrung Traditional Owners Aboriginal Corporation (WTOAC) to understand opportunities to provide for cultural values and uses and other aspirations for the management of water for the environment in the Barwon River downstream of Winchelsea.

Both the EMAC and WTOAC have formal plans for how to heal Country in the region, and Corangamite CMA continues to work with them to identify cultural values aligned with the seasonal watering plan process.

Social, recreational and economic values and uses

In planning the potential watering actions in Table 3.7.1, Corangamite CMA considered how environmental flows could support values and uses, including:

  • water-based recreation (such as canoeing, kayaking, swimming and fishing, particularly for river blackfish)
  • riverside recreation and amenity (such as birdwatching, camping and walking)
  • socioeconomic benefits (such as for diverters for stock needs and domestic use: water levels and water quality can rely on the delivery of water for the environment, particularly in summer).

Scope of environmental watering

Table 3.7.1 describes the potential environmental watering actions in 2022-23, their expected watering effect (that is, the intended physical or biological effects of the watering action) and the longer-term environmental objectives they support. Each environmental objective relies on one or more potential environmental watering actions and their associated physical or biological effects.

Table 3.7.1 Potential environmental watering actions, expected watering effects and associated environmental objectives for the upper Barwon River

Potential environmental watering action

Expected watering effects

Environmental objectives
Upper Barwon River (targeting reach 3 – west branch)

Winter/spring low flow (20-30 ML/day during June to November)

  • Maintain connectivity and an adequate water depth in the channel/pools to support fish and platypus foraging and breeding habitat
  • Maintain an adequate depth of permanent water in the channel to promote the recruitment of aquatic and streamside plants and to limit the encroachment of terrestrial species
  • Provide sufficient flow velocity to mix pools
Fish iconPlatypus iconPlant iconWater drop icon

Summer/autumn low flow (3-30 ML/day during December to May)

  • Maintain an adequate depth of permanent water in the channel/pools to provide habitat to support resident and migratory fish, platypus and waterbugs
  • Reduce encroachment by terrestrial plants into the aquatic zone
  • Provide minimum velocity to mix and flush pools

Fish iconPlatypus iconPlant iconInsect iconWater drop icon

Upper Barwon River (targeting reach 4 – east branch)

Winter/spring low flow (1-9 ML/day during June to November)

  • Maintain connectivity and an adequate water depth in the channel and pools to support fish and platypus foraging and breeding habitat
  • Maintain an adequate depth of permanent water in the channel to promote the recruitment of aquatic and streamside plants and to limit the encroachment of terrestrial species
  • Provide sufficient flow velocity to mix pools

Fish iconPlatypus iconPlant iconWater drop icon

Summer/autumn low flow (0.5-5 ML/day during December to May)

  • Maintain an adequate depth of permanent water in the channel/pools to provide habitat to support resident and migratory fish, platypus and waterbugs
  • Reduce encroachment by terrestrial plants into the aquatic zone
  • Provide minimum velocity to mix and flush pools

Fish iconPlatypus iconPlant iconInsect iconWater drop icon

Summer/autumn freshes (two to three freshes, of 9 ML/day for two days during December to May)

  • Provide longitudinal connectivity with water over riffles to allow fish to migrate upstream and fish and platypus to move between pools to breed, feed and find new habitats
  • Submerge woody debris and clean hard surfaces to provide breeding substrate for resident freshwater fish
  • Mobilise sediment and scour algae to maintain waterbug communities in the dry period by flushing organic matter into the channel to provide food after inundating benches for platypus
  • Provide a mosaic of wetted areas to improve emergent and streamside vegetation on terraces, the channel edge and the lower bank
  • Provide minimum velocity to mix and flush pools

Fish iconPlatypus iconPlant iconInsect iconWater drop icon

Scenario planning

Table 3.7.2 outlines potential environmental watering and expected water use under a range of planning scenarios.

The upper Barwon environmental entitlement can only support a small proportion of the environmental flow recommendations for the upper Barwon River. However, high carryover volumes from 2021-22 and the forecast of high allocations mean that the volume of water available to support environmental flows in the upper Barwon system in 2022-23 will be greater than in previous years under all climate scenarios.

Planned watering actions for the upper Barwon River are derived from recommendations in the upper Barwon River Environmental Flows Study. The Corangamite CMA is aware that many of the flow magnitudes recommended in the environmental flows study cannot be delivered without inundating private land, so the planned watering actions presented in Table 3.7.1 are deliberately less than the known channel capacity constraints. Also, water levels will be monitored during any planned delivery of water for the environment in 2022-23, especially if significant rain is forecast, so that release rates can be promptly adjusted to avoid affecting streamside landholders. The flow rates presented in Table 3.7.1 are expected to provide a lower environmental benefit than the full environmental flow recommendations. The Corangamite CMA will continue to work

with relevant agencies and landholders to investigate options that will allow some of the recommended environmental flows to be delivered closer to their target magnitude in future without affecting private land.

Under all climate scenarios, water for the environment will be used to maintain a continuous flow in the east and west branches during summer and autumn. Delivery of water for the environment in the east branch is prioritised over the west branch when supply is limited because the east branch has greater environmental values and relatively small flows in the east branch have the potential to deliver significant environmental outcomes. In the east branch, the priority will be to deliver summer/autumn low flows under all climate scenarios and summer/autumn freshes under dry, average and wet scenarios. The summer/autumn freshes will help to improve water quality and provide opportunities for fish and platypus to disperse throughout the system, breed and take advantage of increased food and habitat under wet and average climatic conditions.

The increased volume of water for the environment available under average and wet climate scenarios will be shared between the east and west branches and will be used to supplement natural events. The summer and autumn low flows in the west branch can be of greater magnitudes, as presented in Table 3.7.1, under average and wet climate scenarios to achieve better outcomes for fish, platypus and vegetation. Any remaining water for the environment under an average or wet climate scenario will be used to supplement winter and spring low flows in the east and west branches and flows further downstream. Winter and spring freshes in reaches 3 and 4 are essential for the system, but due to channel choke points from willow and glyceria and channel capacity and delivery constraints, these are not planned to be delivered by water for the environment and are not included in this seasonal watering plan.

The tier 1a and 1b watering actions presented should help to maintain current environmental values and conditions in the upper Barwon River. However, a larger environmental entitlement and complementary works that address non-flow-related impacts in the catchment (such as constrictions) will be needed to significantly improve environmental conditions.

The carryover reserve for the upper Barwon River is 500 ML for 2023-24.

Planning scenario table

Table 3.7.2 Potential environmental watering for the upper Barwon River under a range of planning scenarios

Planning scenario

Drought

Dry

Average

Wet

Expected river conditions

  • Disconnected pools
  • Cease-to-flow events
  • Deteriorating water quality
  • Disconnected pools during summer and autumn
  • Cease-to-flow events
  • Low flow in summer and autumn
  • Peak flow in winter and spring
  • Continuous flow throughout the year
  • Reservoir spills are likely, especially during winter and spring

Expected availability of water for the environment

  • 1,500 ML
  • 2,000 ML
  • 2,500 ML
  • 3,000 ML

Upper Barwon River (targeting reach 3 – west branch)

Potential environmental watering – tier 1 (high priorities)

Tier 1a (can be achieved with predicted supply)

  • Summer/autumn low flow (partial)
  • Summer/autumn low flow (partial)
  • Summer/autumn low flow (partial)
  • Summer/autumn low flow

Tier 1b (supply deficit)

  • Winter/spring low flow
  • Summer/ autumn low flow

(delivered at upper magnitude)

  • Winter/spring low flow
  • Summer/ autumn low flow

(delivered at upper magnitude)

  • Winter/spring low flow
  • Summer/ autumn low flow

(delivered at upper magnitude)

  • Winter/spring low flow

Potential environmental watering – tier 2 (additional priorities)

  • N/A

Upper Barwon River (targeting reach 4 – east branch)

Potential environmental watering – tier 1 (high priorities)

Tier 1a (can be achieved with predicted supply)

  • Summer/autumn low flow
  • Summer/autumn low flow
  • Summer/autumn freshes (two freshes)
  • Summer/autumn low flow
  • Summer/autumn freshes (two freshes)
  • Summer/autumn low flow
  • Summer/autumn freshes (three freshes)

Tier 1b (supply deficit)

  • Winter/spring low flow
  • Winter/spring low flow
  • Winter/spring low flow
  • Winter/spring low flow

Potential environmental watering – tier 2 (additional priorities)

  • N/A

Possible volume of water for the environment required to achieve objectives

  • 1,464 (tier 1a)
  • 7,602 ML (tier 1b)
  • 1,947 (tier 1a)
  • 6,697 ML (tier 1b)
  • 2,513 (tier 1a)
  • 4,305 ML (tier 1b)
  • 2,986 (tier 1a)
  • 2,896 ML (tier 1b)

Priority carryover requirements for 2023-24

  • 500 ML

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
  • Upper Barwon Surface Water Advisory Group
  • Land and Water Resources Otway Catchment
  • Barwon Water
  • Department of Environment, Land, Water and Planning Water and Catchments
  • Southern Rural Water
  • Colac Otway Shire Council
  • Landholders on the Upper Barwon Surface Water Advisory Group
  • Recreational users on the Upper Barwon Surface Water Advisory Group
  • Eastern Maar Aboriginal Corporation
  • Wathaurung Aboriginal Corporation
  • Wathaurung Aboriginal Corporation

Page last updated: 01/07/22