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 the passing flow can be managed – for example, it can be accumulated and released when most needed – to help mitigate some risks associated with a 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 has a high delivery cost. There is no plan to use the water in 2023-24.

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

Maintain 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

The Coliban River system is on Dja Dja Wurrung Country.

The Djaara (Dja Dja Wurrung people) Nation Statement in the Victorian Government’s Water is Life: Traditional Owner Access to Water Roadmap 2022 and the Dhelkunya Dja (Healing Country) Country Plan 2014-2034 both describe Djaara’s aspirations around the management of water on their Country.

Djaara’s Kapa Gatjin (water advisory) Group and the North Central CMA have been working together to identify sites where water for the environment can support Djaara’s aspirations for the Coliban River. They have also been identifying opportunities for Djaara to be more involved in managing and administering environmental water, with the aim of Djaara ownership and management of environmental water.

In recent years, Djaara has completed several Aboriginal Waterways Assessments in the upper and lower catchments of the Coliban River.

Social, recreational and economic values and uses

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

water-based recreation (such as swimming, canoeing and fishing)
riverside recreation and amenity (such as socialising, relaxing, birdwatching, bushwalking, camping and cycling)
socioeconomic benefits, including 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.

Scope of environmental watering

The term ‘environmental watering’ refers to the active delivery of held environmental water to support particular environmental objectives by altering the flow in a river or the water level in a wetland. While other terms are sometimes used to describe the delivery of environmental water, ‘environmental watering’ is deliberately used here and in seasonal watering statements to ensure consistency in the legal instruments that authorise the use of water for the environment in Victoria.

Table 5.6.3 describes the potential environmental watering actions in 2023-24, 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 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 up to 6 cm water depth between pools for native fish movement and maintain river pool depth Maintain wet areas for native aquatic and streamside plants Prevent stagnation and a decline in water quality Maintain aquatic habitat that supports waterbugs, native fish and platypus
Winter/spring fresh (one fresh of up to 160 ML/ days for three to five days during June to September)	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 fresh(es) (one to 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 low or cease-to-flow river conditions high water temperatures	Improve water quality, including oxygen levels Maintain refuge habitat for aquatic animals, including fish and platypus

Page last updated: 01/12/22