The Snowy Advisory Committee met via video conference on 9 February to finalise environmental water planning for 2022–23, review environmental water delivery so far for 2021–22 and receive a presentation from Australian National University on the Snowy Water Inquiry Outcomes Implementation Deed (SWIOID).
The 2021–22 Snowy and montane rivers environmental watering program
It was a wet end to 2021, with the wettest November since 1992 and the wettest December on record. The committee, NSW Government and Snowy Hydro agreed to bring forward the delivery of 10,000 ML of environmental water to December 2021 in an attempt to mitigate the risk of a dam spill, while also achieving environmental outcomes for the Snowy River. However, with significant rainfall of 120 to 140 millimetres across the Jindabyne Dam catchment on 18–19 December, the dam spilt on 20 December. Several pre-releases (controlled spills) were made for the remainder of December to mid-January 2022 to reduce the risk of further spills and manage public safety. The accounting of the spill and pre-releases has resulted in an environmental water 'borrow' of 18,700 ML. This volume will have to be paid back from future water allocations for the Snowy River.
With the exception of the dam spill and pre-releases from Jindabyne Dam, environmental water releases have been on track.
Upper Murrumbidgee River
There is insufficient environmental water available for the upper Murrumbidgee to maintain daily releases for the entire 2021–22 water year, with releases ceasing on 20 January. A small flush is planned for April to promote productivity (food) for native water-dependent animals such as the Macquarie perch.
Daily environmental releases to the targeted montane streams are also tracking as planned, providing essential water to aquatic plants and the animals they support, including frogs and water bugs.
Planning environmental water releases for 2022–23
The committee discussed how to use environmental water in 2022–23. As allocations reflect the current wet conditions, the committee's advice is for a wet scenario.
The committee uses available science and knowledge to inform its advice on the use of environmental water for the Snowy River. A 'natural flow scaling' approach is applied as the basis for designing daily flow patterns. As Thredbo River flow volumes are similar to the modified Snowy River, historic flow data from the Thredbo is used as a reference for daily and seasonal flows in the Snowy River below Jindabyne.
The 2022–23 water allocations will provide an opportunity to deliver a flushing flow to the Snowy River for the second year in a row. The flushing flow combined with several other higher flow releases during spring is expected to mobilise and flush sediments along and to the sides of the river channel, improving the health and condition of the riverbed. The higher flows will also flush sediment from gravel and cobbles (riffles), benefiting macroinvertebrates by providing them with suitable habitat.
Several planned releases of greater than 1500 ML/day in spring and early summer will fill some of the connected ponds (wetlands), encouraging water plants to grow, providing important habitats for frogs and other aquatic animal to breed and feed.
There will be adequate environmental water in 2022–23 to maintain flows in all the montane streams where an environmental flow has been allocated. This includes the upper Murrumbidgee, upper Snowy River, Goodradigbee River, Middle Creek, Diggers Creek and the Geehi River. Flows to these streams will provide essential habitat for water-dependent animals, including water bugs, frogs, native fish and platypus. Maintaining flows also provides essential habitat for the stony creek frog that attach their eggs to in-stream substrates.
Upper Murrumbidgee River
The committee's advice for the upper Murrumbidgee for 2022–23 is to apply a modified natural scaling approach and to 'keep it (the river) clean'. This includes 3 high flows above 1000 ML/day timed to flush gravels and cobbles before the Macquarie perch breeding season to provide a better substrate for the eggs. Fourteen flows above 500 ML/day to help flush the river and clean cobbles, and 19 short cease-to-flow periods, which will result in 136 days of no flows.
The Department of Planning and Environment has several projects that will help to improve our understanding of the Snowy and montane rivers and ensure the committee provides informed advice.
A geomorphology study will be undertaken to assess the Snowy River channel and the changes that have occurred to the river since environmental water deliver began in 2002. This work will be completed by the end of this financial year. The findings will be provided as a report and a presentation at the next Snowy Advisory Committee meeting.
Upper Murrumbidgee and Mowamba Instream Barriers and Habitat Assessment has commenced. The project will identify potential barriers for native fish.
eDNA DPE will contribute funding to this NSW-wide project to identify freshwater vertebrates. Survey locations will include the Snowy River.
Snowy Water Inquiry Outcomes Implementation Deed research paper
The Australian National University presented its findings on an independent review of the Snowy Water Inquiry Outcomes Implementation Deed. The findings included recommendations for a formal review and clarity of water allocations. You can read the report: Snowy River environmental flows post-2002: lessons to be learnt.
Go to report
The committee next plans to meet in May 2022.