Frequently asked questions
The NSW Government is implementing environmental water releases to improve the health of the Snowy River below Jindabyne Dam.
What is a high-flow event?
High-flow events are releases of 2,500 ML/d or greater. This is the flow threshold at which the department and Safety Technical Advisory Group consider that potential safety risks may begin to occur, based on local risk knowledge and evidence from past releases. For flows of 2,500 MLid or greater, the department instigates the processes set out in the Safety Management Plan including extensive public communications.
The threshold has been increased from 2,000 ML/d to 2,500 ML/d as evidence from past releases has been collected and will continue to be reviewed.
What are peak flows within a high-flow event?
High-flow releases from Jindabyne Dam generally have a constant flow rate for 24 hours. However, in some cases an additional peak flow is included in the release. This is a higher rate of release that occurs between 08:00am and 4:00pm.
How much environmental water will be delivered?
The volumes and timing of high-flow releases (in excess 2,500 ML/d from Jindabyne Dam) for the upcoming water year are listed on the department's website. The daily release volumes for all flows are listed on Snowy Hydro's website.
What time are releases made from Jindabyne Dam?
Each high-flow release will commence at 00:00am local time on the listed date and continue for 24 hours. Where a larger peak flow is planned within the day, these will be released between 08:00am and 4:00pm.
Why are there high flows either side of a large release?
For the high-flow releases, the days leading up to and following the release will have immediate flows to create a more natural flow pattern (hydrograph) that maximises ecological benefits.
Where will the water flow?
The water will be released into the Snowy River from Lake Jindabyne and travel down the river to the estuary at Marlo, Victoria.
What is a flushing flow?
The Snowy Water Licence defines flushing flows as those exceeding 5,000ML/d. These can be included in the plan when the water year allocations exceed 100,000 ML. Flushing flows need to be delivered from the spillway gates of Jindabyne Dam, as the cone valves can only deliver a flow rate of 5,000 ML/d. This is why flushing flows can only be delivered when dam levels are high enough to release water through the spillway gates.
Why are flushing flows important?
Flushing flows are important to help develop a more defined river channel within the former riverbed to assist in achieving the long-term goal of returning the Snowy River to a smaller, but healthy Montane River.
Are smaller releases made throughout the year?
In addition to the high-flow release, frequent smaller releases are made throughout the year. The aily volumes are listed on the Snowy Hydro's website. The public is notified about high-flow releases only, given that flows less than 2,500 ML/d pose less downstream safety risks.
How is flexibility being introduce in the delivery of smaller releases?
As an outcome of the Snowy Water Licence Review, flexible delivery of smaller flows may be introduced on a trial basis in 2024/25, whereby releases will made in response to natural cues such as rainfall events. This will help support river health and water dependent plants and animals including native fish.
The trials may include:
- Varying releases based on Thredbo trigger flows - responding to natural flow cues based on real-time Thredbo River flow triggers resulting from rainfall events. If triggered, the highest planned release for the month (<1,500 ML) will occur in the Snowy River around one day after the Thredbo flow trigger. This will be done on up to four occasions throughout the water year. The default date for the highest flow is the 25th day of the month if not triggered.
- Varying release to achieve flows to the estuary - trial and monitor a series of low flow variations to support estuary health and help keep the estuary entrance open during summer and autumn 2025. Planned daily lows will be increased in February if conditions are dry. The water would be moved from a higher flow period in autumn to achieve this if required.
How high will the water rise in the Snowy River?
Rising ater levels may result from a combination of the environmental releases and natural tributary inflows. The combination of varying release volumes and natural conditions means that the peak flows in the river ill vary from year to year.
The flow peak will naturally reduce as it progresses downstream, but could still be detected ear the mouth of the Snowy River at Jarrahmond in Victoria.
The rise in water levels will vary depending on your location and inflows from tributaries, but flows are intended to remain within the river channel. In confined gorge reaches, the water level increase could be slightly greater than elsewhere.
What is the purpose of environmental releases?
High-flow water releases are designed to better mimic the natural flow characteristics that are seen in Snowy montane rivers, including snowmelt and 'freshes' that occurred before the construction of the Snowy scheme, with the aim of improving the long-term health of these river systems.
The designed flow patterns include a higher degree of daily and seasonal flow variability.
The high-flow events allow the river to re-establish stream function and improve the in-stream habitat.
Frequent smaller flow releases have been demonstrated to improve river health by establishing a new smaller channel, wetting the riparian zone and promoting the establishment of aquatic and riparian vegetation.
The long-term aim of Snowy environmental flows is to restore the river below Jindabyne Dam by scouring a smaller channel with a rocky or gravel base, better supplying pools and riffles (water running quickly over gravel beds) with fresh oxygenated water and reconnecting the river
Why have multiple high-flow events?
Results from previous studies from the Snowy Flow Response Monitoring and Modelling Program show that most of the physical work (sediment movement and channel maintenance) in the river channel occurred within hours of the peak flow rate. This means multiple high-flow events of shorter duration work better than one longer event.
The continuation of the pattern of multiple high flows with short duration draws on the results of previous releases, which demonstrated that regular flow disturbances flushing the sediment from the stream bed establishes a new, smaller channel within the former channel of the Snowy River.
Additionally, the high-flow events wet the riparian zone, promoting the establishment of aquatic and riparian vegetation and providing important habitat for water dependant animals including native fish, waterbugs, frogs and platypus.
Why are the high-flow events generally in winter and spring?
The environmental water release strategy attempts to mimic the natural hydrological characteristics of the Snowy River. Before the Snowy Scheme was constructed, high-flow events during winter and spring were commonplace.
Historically, the flow regime of the Snowy River at Jindabyne showed a greater frequency of flood peaks during winter and spring. The smaller winter flow peaks were typically associated with the passage of cold fronts delivering rain to lower elevation catchments and snow to higher elevations. The typically larger spring flow peaks resulted from rain-bearing weather systems in association with rapid melting of snow.
Why is there more water available in some years?
The partner governments agreed to recover from western irrigation areas a volume of environmental water for the Snowy River. The amount of water available each year is subject to the amount of rainfall, snowmelt and inflows into the southern Murray-Darling Basin storage dams.
In recent years there have been wetter conditions and stronger inflows across the southern Murray Darling Basin
Why are flow releases above 5,000 ML/d dependant on Jindabyne Dam levels?
The cone valves on Jindabyne Dam can only deliver flow rates up to 5,000 ML/d. To deliver higher flow rates, Jindabyne Dam levels must be at or above 64% of active storage level to enable releases over the lower spillway gates. If a flushing flow is planned (flows with peaks above 5,000 ML/d), and dam levels are not sufficiently high to deliver water over the spillway gates, then the planned flushing flows will be restricted to a maximum of 5,000 ML/d.
Can I view the flows?
Members of the public are reminded that they should exercise their own judgment about the safety of any viewing site based on the conditions on the day. The township of Dalgety and the Snowy River at Jacks Lookout have suitable viewing locations.
Can I swim and use my water sports equipment anywhere along the river?Â
Recreational use of the river during the period in which the high flows are taking place is not recommended. These high-flow events are considered unsafe for recreational water activities as the flows could dislodge debris in the river.
What safety action should I take?
Individual landholders should take all necessary precautions with stock and property, both before and during the additional flows. This may involve moving any assets away from the bank of the river.
The NSW Government recommends that equipment should be secured or elevated three metres higher than the existing base water level in the Snowy River.
What is the NSW Government doing to ensure the flows are delivered safely?
The NSW Department of Climate Change, Energy, the Environment and Water works with Snowy Hydro, local councils, the State Emergency Service, the Bureau of Meteorology and other key stakeholders to review risks prior to high flow releases. Flows may be modified or cancelled with short notice if risks are deemed unacceptable. We encourage the public to check our website for any changes closer to the scheduled events.