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Flow in the Coliban River below Malmsbury Reservoir is regulated by the operation of the Malmsbury, Lauriston and Upper Coliban reservoirs. An important distinction between the Coliban River and other regulated Victorian systems is the lack of irrigation demand that may be met by managed releases downstream of system storages. Flow in the river is influenced by the passing-flow entitlement, which depends on catchment inflows and major flood events in the catchment.

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 flow including low oxygen levels in the river between Malmsbury Reservoir and Lake Eppalock. 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 2021-22.

Traditional Owners
Environmental water holder

Environmental watering objectives in the Coliban River

Increase the abundance and diversity of small- bodied native fish
Platypus icon
Increase the platypus population
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

Maintain streamside woody vegetation and facilitate recruitment
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.

Traditional Owner cultural values and uses

In planning for environmental flows in the Coliban River, Dja Dja Wurrung Clans Aboriginal Corporation and North Central CMA have considered how environmental water management assists with the preservation of historical and contemporary cultural values including promoting a sense of place and spiritual connection.

The Dja Dja Wurrung Country Plan 2014-2034 describes their aspirations around the management of rivers and waterways and articulates Dja Dja Wurrung peoples’ support for the reinstatement of environmental flows as an overall objective for the management of water on Country.

The Kapa Gatjin and North Central CMA have been working together to identify opportunities and sites where water for the environment can support the Dja Dja Wurrung’s aspirations for the Coliban River.

Activities to further this work have been suspended due to COVID-19 restrictions, but it is anticipated that activities on Country will be undertaken as restrictions ease in 2021-22.

Social, recreational and economic values and uses

In planning the potential watering actions in Table 5.6.3, North Central CMA considered how environmental flows could support values and uses including:

  • water-based recreation (such as canoeing, fishing and water sports)
  • riverside recreation and amenity (such as birdwatching, bushwalking, camping and cycling)
  • socio-economic benefits (such as diversions for domestic and stock uses, benefits to the local and regional economies from recreational activities, ecosystem services [such as carbon storage, groundwater recharge and water-quality regulation], lower salinity costs and blackwater and blue-green algae risks for landholders, and contributions to community enjoyment, health and recuperation).

Recent conditions

Total annual rainfall in the Coliban River catchment in 2020-21 was slightly above the long-term average, and the temperature was slightly cooler than average. August, October and January were significantly wetter- than-average months. November was hotter and dryer than average. Accumulated passing flows that make up the holdings of water for the environment were lost when Malmsbury Reservoir spilled in October 2020, but high rainfall in January 2021 allowed additional passing flows to be accumulated to replenish the supply for planned environmental flows.

Passing flows, natural inflows and the managed release of accumulated passing flows maintained a continuous flow from Malmsbury Reservoir to Lake Eppalock throughout most of the year, and the summer cease-to-flow period at the downstream end of the reach was shorter than in previous years. High-rainfall events delivered moderate- sized freshes, and more variable flow in the lower reach in August, September and November 2020 and the October spill of Malmsbury Reservoir delivered a high flow through the whole system.

Releases of water for the environment in the Coliban River were delivered in line with an average climate scenario in 2020-21. One of the planned watering actions for the average scenario — the summer and autumn low flow — was partly achieved, while the summer and autumn fresh was not delivered. In particular, the wetter-than- average conditions provided additional flow in the system and helped maintain water quality, which meant summer/ autumn low flows could be delivered continuously rather than as pulses.

Scope of environmental watering

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

Potential environmental watering action

Expected watering effects

Environmental objectives

Winter/spring low flow (2.5 to 25 ML/day during June to November)

  • Maintain a connected river that allows small-bodied native fish and platypus to disperse throughout the river
  • Increase wet areas for native aquatic and streamside plants, while limiting terrestrial species encroaching the river channel
  • Increase flow to mix water in pools, to prevent stagnation and a decline in water quality
  • Increase the wetted area for habitat for waterbugs
Fish iconPlatypus iconPlant iconInsect iconWater drop icon

Winter/spring fresh (one fresh of up to160 ML/day for three to five days during June to November)

  • Maintain up to 65 cm water depth between pools, so native fish can disperse throughout the river and colonise sites
  • Encourage female platypus to select a nesting burrow higher up the bank, to reduce the risk of a higher flow later in the year flooding the burrow when juveniles are present
  • Increased the wetted river perimeter for fringing and edge vegetation
  • Increase the wetted river perimeter to increase habitat for waterbugs
  • Flush organic matter to reduce the risk of declining water quality in summer
Fish iconPlatypus iconPlant iconInsect iconWater drop icon

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

  • Maintain 3-6 cm water depth between pools for native fish movement, and maintain river pool depth
  • Wet the channel to maintain in-stream aquatic and fringing vegetation
  • Maintain aquatic habitat that supports waterbugs, native fish and platypus
  • Maintain water quality including oxygen levels
Fish iconPlatypus iconPlant iconInsect iconWater drop icon

Summer/autumn freshes (two freshes of 25 to 160 ML/day for three to five days during December to May)

Maintain the water depth through riffle-run habitats of 8-20 cm for 25- 50 ML/day event to maintain water quality and habitat for waterbugs

Maintain water depth through riffle-run habitats of 45-61 cm for a 160 ML/day event to:

  • increase the water depth to facilitate the movement of fish and platypus
  • clean sediment and biofilms from river substrates
  • wet the benches and low banks to promote the growth and recruitment of fringing vegetation
Fish iconPlatypus iconPlant iconInsect iconWater drop icon

Pulsed summer/autumn low flow (five to 15 ML/ day for 14 days during December to May, trigger- based)

Triggers:

  • oxygen level is below 5 mg/L
  • water temperature is above 28o
  • there are low or cease- to-flow river conditions
  • Improve water quality including oxygen levels
  • Maintain refuge habitat for aquatic animals, including fish and platypus
Fish iconPlatypus iconWater drop icon

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
  • Malmsbury and District Landcare Group
  • Coliban Water
  • Commonwealth Environmental Water Office
  • Department of Environment, Land, Water and Planning
  • Game Management Authority
  • Individual Landholders and community members
  • VRFish
  • Dja Dja Wurrung Clans Aboriginal Corporation

Page last updated: 22/01/21