The Snowy River originates on the slopes of Mount Kosciuszko. It drains the eastern slopes of the Snowy Mountains in New South Wales before flowing through the Snowy River National Park in Victoria and into Bass Strait.
There are four major dams and multiple diversion weirs in the upper Snowy River catchment that divert water to the Murrumbidgee and River Murray valleys. The hydrological effects of the Snowy Mountains Scheme are substantial, but they are partly alleviated by the contribution of flows from tributaries (such as the Delegate River in New South Wales and the Buchan and Brodribb rivers in Victoria).
Construction and operation of the Snowy Mountains Hydroelectric Scheme previously diverted 99 percent of the Snowy River’s mean annual natural flow at Jindabyne. The loss of flow changed the structure and function of the river, reduced the opening of the Snowy River entrance to Bass Strait and resulted in a decline in environmental values.
The Victorian, New South Wales and Commonwealth governments have recovered water to help restore damage done by decades of limited flow. Victorian water for the environment available for use in the Snowy system is held in the Murray, Goulburn and Loddon systems. This water is made available for environmental flows in the Snowy River via a substitution method, whereby Victorian water for the environment replaces water that was earmarked for transfer from the Snowy to Victoria to support irrigation demands.
The remaining environmental values in the upper reaches and tributaries of the Snowy River include freshwater fish (such as river blackfish and Australian grayling). The lower reaches support estuary perch and Australian bass that move between saltwater and freshwater systems. The estuary contains estuarine and saltwater species such as flathead, mulloway and black bream. The floodplain wetlands of the Snowy River near Marlo provide feeding and breeding areas for wetland and migratory birds.
The water year in the Snowy system runs from May to April. In 2018–19, about 137,087 ML3 of water for the environment was used to deliver five winter/spring highflow events in the Snowy River. A major flushing flow was planned for October 2018, but prolonged, dry conditions and low inflows into Jindabyne Dam resulted in the flow rate being reduced, from 8,620 ML per day to 5,000 ML per day.
Scope of environmental watering
The New South Wales Department of Planning, Industry and Environment plans environmental flow releases in the Snowy River, in consultation with the Victorian Government.
Environmental watering from May 2019 to April 2020 will aim to mimic the typical flow pattern of a mixed snowmelt/ rainfall river system characteristic of the Snowy Mountains. The releases will aim to support ecological processes in the Snowy River below Jindabyne Dam and maintain a healthy river that is much smaller than the natural channel that existed before the river was regulated.
East Gippsland CMA has monitored the lower reaches and estuary over the past seven years. The results show that the managed environmental flows help improve physical and ecological processes, increase ecosystem productivity and improve aquatic habitat.
Five high-flow releases are scheduled between June and November 2019. A large, flushing flow is scheduled for late October 2019 and includes an eight-hour peak at a rate equivalent to 5,000 ML per day. Other peak flows will mimic winter rainfall events. These peak flows aim to improve the physical attributes of the river by scouring and depositing sediment and increasing available aquatic habitat. High flows will be sustained from July to December, to help mix water in the estuary to benefit plants and fish (such as Australian bass). Low flows will then be released until the end of the water year in April 2020.
The total volume planned for release in 2019–20 (including contributions from water savings in Victoria and New South Wales) is 118,671 ML.
The NSW Government is responsible for planning environmental flow releases in the Snowy River and consults the Victorian Government about the planned releases.
In 2018, the Snowy Advisory Committee will be formed. Its members will represent Aboriginal, local community and environmental interests, alongside relevant NSW and Victorian government agencies. The role of the Snowy Advisory Committee will be to provide community and expert input about the pattern of environmental flow releases to the Snowy River and Snowy montane rivers, to ensure their ongoing health.