VEWH - Coliban River

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 2022-23.

Environmental watering objectives in the Coliban River

Increase the abundance and diversity of small-bodied native fish

Facilitate recolonisation by native fish species (including river blackfish) that have been presumed lost

Increase the platypus population

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

Maintain an adequate diversity and biomass of waterbugs to break down dead organic matter and supply the river’s food chain

Maintain water quality to support aquatic life and ecological processes

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 (trading as DJAARA) Kapa Gatjin (water advisory) Group 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 Dhelkunya Dja (Healing Country) Country Plan 2014-2034 describes their aspirations around the management of rivers and waterways and articulates Djaara’s (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 Djaara’s aspirations for the Coliban River and play a greater role in the management and administering of environmental water, with an aim of future ownership and management of environmental water.

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 swimming, canoeing, fishing and water sports)
riverside recreation and amenity (such as socialising, relaxing, birdwatching, bushwalking, camping and cycling)
socio-economic benefits (such as tourism to Malmsbury, 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

Rainfall in the Coliban River catchment during 2021-22 was close to the long-term average. Accumulated passing flows that made up the holdings of water for the environment were lost when Malmsbury Reservoir spilled in late July 2021. However, unregulated and natural flows following this spill provided the required winter/spring low flow and six freshes between July and January. The largest event peaked at 1,493 ML per day at Lyal in September 2021, and it was the largest flow in the river since the 2016 floods.

Deliveries of water for the environment for the Coliban system were managed in line with an average climate scenario throughout 2021-22. All planned watering actions for the Coliban River were fully or partially achieved with passing flow, natural inflow and/or the managed release of accumulated passing flow. Passing flow provided continuous flow between Malmsbury Reservoir and Lake Eppalock, and 2021-22 was the first year since 2011-12 that the Coliban River had not had a cease-to-flow event. Some accumulated passing flow was used to deliver a fresh in April 2022 to support the dispersal of juvenile platypus.

Scope of environmental watering

Table 5.6.3 describes the potential environmental watering actions in 2022-23, their expected watering effects (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 5.6.3 Potential environmental watering actions, expected watering effects and associated environmental objectives for the Coliban River

Potential environmental watering action	Expected watering effects	Environmental objectives
Coliban River (targeting reach 1)
Winter/spring low flow (2- 10 ML/day during June to November)	Maintain a connected river that allows small-bodied native fish and platypus to disperse throughout it Increase wet areas for native aquatic and streamside plants while limiting terrestrial species encroaching into the river channel Mix water in pools to prevent stagnation and a decline in water quality Increase the wetted area for habitat for waterbugs
Winter/spring fresh (one fresh of up to 160 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 greater flow later in the year flooding the burrow when juveniles are present Increase 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
Summer/autumn low flow (2-10 ML/day during December to May)	Maintain up to 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
Summer/autumn freshes (two freshes of 25- 160 ML/day for three to five days during December to May)	Increase the water depth through riffle-run habitats to 8-20 cm for a 25-50 ML/day event to maintain water quality and habitat for waterbugs Increase the water depth through riffle-run habitats to 45-60 cm for a 160 ML/day event 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
Pulsed summer/autumn low flow (5-15 ML/day for up to 14 days during December to May, trigger-based) Triggers: the oxygen level is below 5 mg/L the air temperature is above 28° there are low or cease-to-flow	Improve water quality, including oxygen levels Maintain refuge habitat for aquatic animals, including fish and platypus

Scenario planning

Table 5.6.4 outlines potential environmental watering and expected water use under a range of planning scenarios.

The potential environmental flows required for the Coliban River include low flow and freshes under all climate scenarios, but the magnitude of particular flows and the numbers and durations of freshes that can be delivered will vary between scenarios, based on available supply and other flows in the system. Where supply is limited, low flow will be delivered at the lower end of the recommended magnitude to maintain some connecting flow for a longer period. Freshes will be delivered where possible to facilitate the dispersal of platypus and fish and clean biofilms from in-stream surfaces.

The highest-priority watering action in the Coliban River under all climate scenarios is the summer/autumn low flow to maintain sufficient habitat for native fish, platypus and waterbugs. Natural baseflow and tributary inputs help to maintain some flow through the Coliban River during winter and spring each year, but long sections of the river contract to a series of pools or completely dry during late summer and autumn, especially in dry years. Releases of water for the environment in summer and autumn help to maintain water quality (especially when oxygen levels are low) and maintain the depth of pools in the upper reaches to help sustain populations of native fish and platypus. Providing Malmsbury Reservoir does not spill over winter/ spring, passing flows that were banked but not used in 2021-22 will be carried over and used to help maintain a continuous low flow under all climate scenarios in 2022-23. If a continuous flow cannot be maintained, shorter, pulsed flows may be delivered to maintain refuge habitats as required. These trigger-based pulses will most likely be needed under a dry scenario but may also be needed under wetter scenarios if there is insufficient supply to deliver continuous low flow in late summer or early autumn. Where possible, summer and autumn freshes will be delivered to facilitate fish and platypus movement and support fringing vegetation. These freshes will aim to be delivered in March or April to support juvenile platypus dispersal and reduce predation.

Accumulated passing flows can be carried over for use in the next year, but it will be forfeited if Malmsbury Reservoir spills. A carryover target of 720 ML has been set for all climate scenarios to ensure enough supply for high-priority summer and autumn low flows in 2023-24. This target will be revised throughout the year based on climatic forecasts, the risk of spill and the extent to which priority actions for 2022-23 have been met. For example, delivering at least one summer/autumn fresh in 2022-23 will be a higher priority than achieving the full 720 ML carryover target.

Planning scenario table

Table 5.6.4 Potential environmental watering for the Coliban River under a range of planning scenarios

Planning scenario	Drought	Dry	Average/Wet
Expected river conditions	Little to no natural flow	Some natural flow	Extended periods of natural flow, including some high-flow events and reservoir spills
Expected availability of water for the environment¹	1,600 ML	2,000 ML	2,800 ML
Coliban River (targeting reach 1)
Potential environmental watering – tier 1 (high priorities)	Tier 1a (can be achieved with predicted supply)
	Winter/spring low flow (lower magnitude in the range) Summer/autumn low flow (lower magnitude in the range) Pulsed summer/autumn low flow (trigger-based)	Winter/spring low flow Summer/autumn low flow Summer/autumn fresh (one fresh, lower magnitude) Pulsed summer/autumn low flow (trigger-based)	Winter/spring low flow Summer/autumn low flow Summer/autumn fresh(es) (one to two freshes, lower magnitude) Pulsed summer/autumn low flow (trigger-based)
	Tier 1b (supply deficit)
	Summer/autumn low flow (higher magnitude) Summer/autumn fresh (one to two freshes)	Winter/spring fresh (one fresh) Summer/autumn fresh (one additional fresh, increased magnitude)	Winter/spring fresh (one fresh) Summer/autumn fresh (one to two freshes at higher in magnitude)
Potential environmental watering – tier 2 (additional priorities)	N/A
Possible volume of water for the environment required to achieve objectives	1,460 ML (tier 1a) 920 ML (tier 1b)	1,870 ML (tier 1a) 1,900 ML (tier 1b)	2,280 ML (tier 1a) 2,500 ML (tier 1b)
Priority carryover requirements for 2023-24	720 ML

¹ As there is no formal environmental entitlement in the Coliban River, these are estimated volumes of passing flows that may be accumulated for a managed environmental flow.

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: 01/12/22