Snowy River increased flows

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 knowledge and evidence from past releases. For flows of 2,500 ML/d 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.

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 8am and 4pm.

The volumes and timing of high-flow releases (in excess 2,500ML/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.

Each day the planned daily flow commences at 00:00am local time on the listed date and continue for 24 hours. Where a 8-hour peak flow is planned within the day, these will be released between 08:00am and 4:00pm.

For the high-flow releases, the days leading up to and following the release will have intermediate flows to create a more natural flow release pattern (hydrograph) that maximises ecological benefits.

The water will be released into the Snowy River from Lake Jindabyne and travel down the river to the estuary at Marlo, Victoria.

The Snowy Water Licence defines flushing flows as those exceeding 5,000 ML/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 up to 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.

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.  They also scour sediments which helps to improve the riverine habitat and increase the food available for fish, frogs and platypus.

In addition to the high-flow releases, smaller releases are made throughout the year. The daily volumes are listed on 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.

As an outcome of the Snowy Water Licence Review, flexible delivery of smaller flows was introduced in 2024/25 on a trial basis, whereby the dates of some releases were changed to respond to natural cues such as rainfall events. This trial will continue throughout 2025/26 to help support river health and water dependant plants and animals including native fish.

An adaptive management approach is commonly applied in other rivers’ environmental watering programs.

This means that for releases under 2,500 ML/d, the volume and timing of planned releases may change without notice. Flexible delivery will not apply to high-flow events (i.e. greater than 2,500 ML/day) for the 2025/26 water year.

Delivering flows in response to natural cues aims to give dam releases a better chance to combine with rainfall-driven tributary inflows across the lower Snowy Catchment. This assists healthy river functions including helping to maintain a Snowy River estuary connection to the sea. This supports critical habitat for native fish migration and breeding, including for the Australian grayling which is nationally listed as vulnerable.

Flexible delivery will not apply to high-flow events (i.e. greater than 2,500 ML/d) for the 2025/26 water year, although we may move towards greater flexibility of high-flow events in the future. Appropriate safety management planning would be developed to support this.

Planned flows may be modified or cancelled subject to climatic, environmental or operational conditions near to the time of release. The department will endeavour to inform the public of changes to high-flow releases, where possible.

Whilst the volumes of smaller releases are also planned at the start of the year, these may be changed at any time without notice. This allows greater flexibility in the delivery of environmental releases, which provides improves environmental outcomes.

Natural inflows from tributaries will generally have a greater impact on river flow rates, water levels and ecosystem processes than the environmental flows, particularly further downstream. The impact will be more significant in wetter years with more natural runoff.

Rising water 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 will vary from year to year.

The flow peak will naturally reduce as it progresses downstream but could still be detected near 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.

High-flow water releases are designed to better mimic the natural flow characteristics that are seen in Snowy montane rivers. This includes 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.

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.

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.

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.

The NSW, Victorian and Commonwealth governments agreed to purchase water entitlements and undertake water efficiency projects in the regulated Murray and Murrumbidgee rivers to create an annual entitlement for environmental water in the Snowy montane rivers. The amount of water allocated to the entitlement each year is subject to the amount of rainfall, snowmelt, and inflows into the southern Murray-Darling Basin storage dams.

Wetter conditions and stronger inflows across the southern Murray-Darling Basin may generate larger volumes of water for environmental flows. Drier years result in lower allocations and therefore less water for the environment.