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Flows in the Coliban River downstream of Malmsbury Reservoir are regulated by the operation of the Malmsbury, Lauriston and Upper Coliban storages. An important distinction between the Coliban River and other regulated Victorian systems is the lack of irrigation demand. Therefore, flows in the river are influenced by the passing- flow entitlement, which depends on catchment inflows, transfers of water to Lake Eppalock and major flood events in the catchment.

Reach 1 of the Coliban River below Malmsbury Reservoir to Lake Eppalock can benefit from environmental watering. The VEWH does not have any environmental entitlements in the Coliban system, but passing flows can be managed — for example, they can be accumulated and released when most needed — to help mitigate some risks associated with critically low summer/autumn flows including low-dissolved- oxygen levels. A small volume of Commonwealth water for the environment is held in the system, but the high cost of delivery means there is no plan to use it in 2019–20.

Environmental watering objectives in the Coliban River

Increase the abundance and diversity of small- bodied native fish
Clean fine sediment from substrates to support biofilms
Platypus icon
Increase platypus communities by providing opportunities for successful breeding and dispersal
Plant icon
Increase the cover and diversity of aquatic plants

Increase the cover and diversity of fringing vegetation, while limiting encroachment into the middle of the channel
Insect icon
Maintain adequate diversity and biomass of waterbugs, to break down dead organic matter and support the river’s food chain
Water icon
Improve water quality and maintain healthy levels of dissolved oxygen in pools

Environmental values

The Coliban River provides important habitat for platypus, rakali (water rats) and small-bodied native fish (such as flat-headed gudgeon and mountain galaxias). The Coliban River also contains a diverse range of waterbugs supported by stands of emergent and submergent aquatic vegetation. It is bordered by remnant patches of stream bank shrubland vegetation and woodland containing river red gum, callistemon, woolly tea-tree and inland wirilda, which provide habitat for terrestrial animals.

Recent conditions

Rainfall in the Coliban River catchment during 2018–19 has been variable although generally below average. Rainfall between August and November is essential for filling the Coliban storages, and it was about 75 percent of the long- term average in 2018. For most of the year, there were little to no unregulated flows from catchment run off, so flows

in the Coliban River were generally well-below minimum environmental flow recommendations.

Passing flows from Malmsbury Reservoir were reduced from up to 8 ML per day to 4 ML per day during winter/ spring, to build a reserve that could maintain continuous flows through parts of the Coliban River over summer. Without this action, most of the Coliban River would have likely stopped flowing in summer. Even with the release of these accumulated passing flows, the lowest reaches of the Coliban River contracted to a series of isolated pools in March 2019.

Accumulated passing flows were used to deliver a summer/ autumn fresh of 50 ML per day for three days from Malmsbury Reservoir in early March 2019, to support fish and platypus movement, maintain aquatic and fringing vegetation, improve water quality and waterbug habitat

and flush organic material and sediment from in-stream substrates. The timing of this fresh was amended to align with a Dja Dja Wurrung field trip for a series of Aboriginal waterways assessments. Dja Dja Wurrung representatives were able to witness the progress of the fresh through the system and observe the transition from a series of disconnected pools into a flowing river.

Scope of environmental watering

Table 1 Potential environmental watering actions and objectives for the Coliban system

Potential environmental watering action

Functional watering objective

Environmental objectives

Pulsed summer/autumn low flow (5–15 ML/day for up to two weeks during December to May as required)

  • Maintain water quality including dissolved oxygen levels
  • Maintain refuge habitat for aquatic animals including fish and platypus
Fish iconPlatypus icon Water drop icon

Summer/autumn low flow (1–10 ML/day during December to May)

  • Maintain aquatic habitat that can support waterbugs, native fish, platypus and aquatic and fringing vegetation
  • Maintain water quality including dissolved oxygen levels
Fish iconPlatypus iconPlant iconInsect iconWater drop icon

Summer/autumn freshes (two freshes of up to
160 ML/day for up to three days during December to May)1

  • Maintain the water depth through riffle-run habitats of 5–20 cm for a 25–50 ML/day event to maintain water quality and habitat for waterbugs
  • Maintain the water depth through riffle-run habitats of 45–55 cm for a 160 ML/day event to:
  • increase the water depth to facilitate fish and platypus movement
  • clean river substrates
  • inundate the low benches to support the fringing vegetation
  • clear sediment and biofilms from hard substrates in the bottom of the channel
Fish iconMountain icons Platypus iconPlant iconInsect iconWater drop icon

1The actual volume and duration of freshes will depend on available water resources, climatic conditions and conditions within the river.

Engagement

Table 2 shows the partners and stakeholder organisations the North Central CMA engaged in preparing the Campaspe system seasonal watering proposals.

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 North Central Regional Catchment Strategy and the North Central Waterway Strategy.

Table 2 Partners and stakeholders engaged in developing the Campaspe system seasonal watering proposals

Partner and stakeholder engagement
  • Individual Landholders
  • Coliban Water
  • Commonwealth Environmental Water Office
  • Victorian Environmental Water Holder
  • Department of Environment, Land, Water and Planning
  • Local canoe clubs
  • Victorian Game Authority
  • Dja Dja Wurrung Clans Aboriginal Corporation