Upper Murrumbidgee River increased flows
In determining how to use the environmental water recovered for the Snowy River through the Snowy Water Initiative, the New South Wales, Victorian and Commonwealth governments jointly agreed that ecological objectives would be achieved by storing and then releasing sufficient volumes to provide annual flushing flows.
Similar to the Snowy River, when there is sufficient environmental water available, a modified ‘flow scaling’ approach has been applied to the Murrumbidgee River to assist in providing natural seasonality and daily variability.
These higher flows facilitate the improvement in the physical condition of the in-stream habitat by scouring and transporting fine sediment (i.e. primarily, sand, silt and clay). Meeting ecological objectives was identified as a high priority during the Snowy Water Inquiry.
Higher flows are important to improve river health. It is expected that as the river physically responds over time to the higher flows, the focus of the recovery process will transition to meet other ecological objectives.
2022–2023 water year
A total of 35,773 megalitres (ML) of environmental water will be released to the Upper Murrumbidgee River below Tantangara Dam during the 2022–23 water year.
The Snowy and Montane River Increased Flows (SMRIF) release pattern has been designed to include three high-flow events from Tantangara Dam into the Upper Murrumbidgee River. These high-flow releases are designed to more closely mimic the natural characteristics of the Murrumbidgee River, including snowmelt and ‘freshes’ that occurred before the construction of the Snowy Mountains Scheme.
There will be no environmental flow released from Tantangara for 20 periods totalling 140 days, as there is insufficient water available to maintain the flow regime for every day of the year that includes multiple high peaks. During this time, Snowy Hydro Limited is required to make releases to maintain flows at or above 32 ML/day at Mittagang Crossing, if tributary flows do not provide this level of flow.
Upcoming environmental releases
The table below shows the upcoming environmental releases from Tantangara Dam for the remainder of the 2022-23 water year. The resulting flows from each release will be protected using temporary water restrictions that apply to unregulated licence holders in the Murrumbidgee I and II water sources.
| Release date | Release peak | Total volume (ML) |
|---|---|---|
| Tuesday 7 February until Friday 10 February 2023 | 125 ML/day on 9 February 2023 | 285 ML |
| Sunday 26 February until Tuesday 28 February 2023 | 125 ML/day on 27 February 2023 | 205 ML |
| Saturday 22 April until Friday 28 April 2023 | 125 ML/day on 26 April 2023 | 309 ML |
Note: The peak flow releases will occur over 24 hour period, commencing at 12:00pm (midday) Eastern Standard Time. The release date for these flow peaks could change as they are weather-dependent.
The release dates in the table are earlier than the dates that the temporary water restriction applies. The time difference is due to the time it takes for the environmental flows to reach the water sources where they will be protected by the temporary restriction.
How to comply with the temporary water restriction
A temporary water restriction will be used to protect the upcoming environmental releases. To comply with the restriction, unregulated licence holders in the Murrumbidgee I and II must not pump if flows at the relevant gauge are below the temporarily raised access thresholds published in the order for that day.
Details on the raised access thresholds and the days they apply can be found on page 4 and 5 in the Temporary Water Restriction (Murrumbidgee I Water Source and Murrumbidgee II Water Source) Order 2023