Murray River: Yarrawonga Weir to Wakool Junction

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Scenario: selected_flow at Yarrawonga Weir - Current flow limit

Legend

Upper limit of inundation extent for flow option¹

More typical inundation extent for flow option²

Embankment/levee

Reference gauges³

A legend for the topographic basemap used on this map can be accessed via this link

Details

Please select a scenario from the above for specific details

This option is for a flow limit of selected_flow at Yarrawonga Weir, which is the current flow limit (base case).

The mapping shows the following extents:

upper limit of inundation for this flow limit option (light blue)¹
an inundation extent more typically experienced when these higher environmental flow deliveries are made (dark blue)²

These extents show the inundation outcomes for the flow options being investigated vary depending on catchment conditions and would be less than the modelled upper flow limit in most cases.

¹The upper limit inundation extent assumes catchment conditions are wet (with low infiltration and evaporation losses) and flows are held at this level for an extended duration, substantially greater than the normal duration environmental flow releases would occur. Environmental flow releases causing this inundation extent across the full length of the river system would be infrequent or rare.

²The more typical inundation extent shows an inundation extent more frequently experienced under this flow limit option, under more typical catchment conditions and environmental flow release durations.

Flow rates and gauge heights

Estimated flow rates and gauge heights for the upper limit inundation extent across this project area are shown in Table 1, below.

Table 1: Flow rates and gauge heights

Frequency, timing and duration

The proposed frequency of managed environmental flows under the Reconnecting River Country Program (i.e., flows greater than 15,000 ML/d and up to the upper flow limit) would vary over time depending on water availability, climate and ecological conditions.

Over the long-term, it is anticipated these higher environmental flow deliveries would occur on average about four to five years per decade, comprising some smaller events and some larger events up to the flow limit.

Flows would include some new events and some events extending the duration of existing unregulated events using water for the environment. They would not occur during extreme wet conditions when there is elevated flood risk.

Most of these higher environmental flow deliveries would occur from August to October, with river rises occurring slightly later in downstream areas as these flows move through the system. Occasionally, and when conditions are appropriate, deliveries might occur slightly earlier in June to July, or slightly later in November (December in downstream areas).

Deliveries in November would be infrequent and would mostly involve adding to an existing unregulated flow event to improve environmental outcomes or manage hypoxic blackwater risk.

The duration of these higher environmental flow deliveries would be up to seven to 21 days at the peak flow rate (in some years this would be the upper flow limit; in some years smaller flows would be delivered). This would be followed by a gradual reduction in flows back to background flow levels.

Occasionally lower flows (e.g., 15,000 to 30,000 ML/d) may be delivered for up to 30 days to support the health of low-lying wetlands and waterbird breeding events.

Assumptions regarding Goulburn River flows

Flows from the Goulburn River have a significant effect on flows in the Murray River system downstream of the Goulburn junction, through the Koondrook-Perricoota Forest and parts of the Wakool River system (including Barbers, Thule and Merran Creeks).

The program’s modelling allows for concurrent high flows in both the Murray and Goulburn Rivers associated with either managed flows up to the flow limits being investigated in both valleys or managed high flows in the Murray concurrent with unregulated flows in the Goulburn (noting higher flow deliveries would avoid conditions where there is an elevated risk of exceeding the agreed flow limits).

Accordingly, the modelling allows for high flows at Torrumbarry and through watercourses downstream of the Goulburn junction. The modelling is conservative and most managed environmental flows under the program would be lower than those modelled and mapped here.

For all scenarios, the modelling has assumed the Torrumbarry cutting channel into the Koondrook-Perricoota Forest would remain closed and Swan Lagoon regulators would be open.