Maribyrnong

The Maribyrnong catchment is located to the northwest of Melbourne. The main waterways in the catchment are Jacksons Creek, which flows southeast from Mount Macedon, and Deep Creek, which flows south from Lancefield (Figure 3.4.1). These two tributaries join at Keilor North to form Mirrangbamurn (Maribyrnong River), which flows south to join Birrarung (Yarra River) at Yarraville before flowing into Port Phillip Bay.

Rosslynne Reservoir is in the upper reaches of Jacksons Creek near Gisborne and is the only major storage in the Maribyrnong catchment. The reservoir has a maximum release capacity of 20 ML per day under ideal conditions, which significantly constrains the environmental outcomes that can be achieved in the Maribyrnong system. Water for the environment is primarily used to support environmental outcomes in Jacksons Creek between Rosslynne Reservoir and the confluence with Riddles Creek (that is, delivery of water for the environment to reach 6, as shown in Figure 3.4.1). Jacksons Creek is a known groundwater-dependent ecosystem on the national Groundwater Dependent Ecosystems Atlas. This means ecological components in the system rely on groundwater for at least some period of time.

The VEWH does not hold an environmental entitlement in the Maribyrnong system, and it relies on opportunistic, temporary trade to meet demands. Melbourne Water (as diversion manager) and the VEWH work with local diversion licence holders to purchase unused water when it is available to support environmental outcomes. This arrangement is negotiated each year, is subject to water availability in the bulk entitlement and storage capacity, and only occurs with all parties’ agreement.

Maribyrnong pie chart

Proportion of water entitlements in the Maribyrnong system held by private users, water corporations and environmental water holders on 30 June 2020

System map

Environmental watering objectives in the Maribyrnong River

Protect and increase populations of native smallbodied fish

Protect platypus populations

Maintain the condition, abundance, diversity and structure of in-stream and streamside vegetation

Support a wide range and high biomass of waterbugs to break down dead organic matter and support the river’s food chain

Maintain water quality, particularly oxygen concentrations

Environmental values

The upper Maribyrnong catchment contains areas of intact streamside vegetation, which provide important habitat for native fish, including migratory short-finned eels, common and ornate galaxias, flathead gudgeon, tupong and Australian smelt.

A large population of waterbugs provides abundant food for a significant platypus population in several reaches of the Maribyrnong system.

Traditional Owner cultural values and uses

Melbourne Water is working with the Registered Aboriginal Parties within the Maribyrnong system — the Wurundjeri Woi Wurrung Cultural Heritage Aboriginal Corporation and the Bunurong Land Council Aboriginal Corporation — to strengthen relationships and increase Traditional Owner involvement in the planning and delivery of water for the environment.

There are more opportunities for Melbourne Water and the VEWH to work with Traditional Owner groups to identify and better integrate cultural values and their flow requirements into the environmental watering program on an ongoing basis.

Social, recreational and economic values and uses

In planning the potential environmental watering actions in Table 3.4.1, Melbourne Water considered how environmental flows could support social values such as community connection and amenity by planning flows that will maintain healthy habitat and improve water quality.

Scope of environmental planning

The term ‘environmental watering’ refers to the active delivery of water for the environment to support particular environmental objectives by altering the flow in a river or the water level in a wetland. While other terms are also used to describe the delivery of water for the environment, ‘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 3.4.1 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 1 Potential environmental watering actions, expected watering effects and associated environmental objectives for the Maribyrnong system

Potential environmental watering action	Expected watering effects	Environmental objectives
Winter/spring low flow (15 ML/day during June to November)	Maintain depth in pools and riffles to provide habitat for small-bodied native fish, platypus and waterbugs Prevent terrestrial vegetation encroachment
Summer/autumn low flow (4-6 ML/day during December to May)	Maintain pool habitat availability for small-bodied fish and platypus during low-flow periods Maintain a > 0.1 m median depth over riffles to provide macroinvertebrate habitat and inundate in-stream vegetation. Maintain continuous flow to limit pool stratification and maintain water quality
Summer/autumn freshes (five freshes of 15 ML/ day for four days every four to six weeks during December to May)	Increase depth over riffle to provide local movement of small-bodied native fish and platypus during the low flow period Maintain habitat and food resources for waterbugs Flush pools to maintain water quality

Page last updated: 01/07/22