Water for the environment for the Latrobe, Thomson and Macalister systems is held in Blue Rock Reservoir, Thomson Reservoir and Lake Glenmaggie respectively.
Environmental entitlements in these systems have unique characteristics that influence planning for environmental flows. The Thomson system receives a share of the daily inflows to the Thomson Reservoir and a secure annual allocation which is available on 1 July each year. In the Latrobe and Macalister systems, the availability of water for the environment depends on system inflows to Blue Rock Reservoir and Lake Glenmaggie respectively. Winter and spring are the peak inflow periods for all systems, so annual allocations are usually well-known before the start of summer. With several planned watering actions being met with natural flows in 2019–20 and the watering year ending with good inflows to storages, high carryover is likely in all systems and waterway managers will start 2020–21 with good water availability to deliver potential watering actions throughout the year.
During December 2019 and January 2020, severe bushfires burnt vast areas of east Gippsland. Heavy rainfall in these areas may wash ash and sediment into waterways including the Snowy River, which could have adverse effects on water quality and environmental values. Flushing flows planned for the Snowy River in winter and spring 2020 may help to mitigate some water quality impacts. West Gippsland was largely untouched by the recent bushfires, and waterways in that area may be essential for sustaining and restoring regional populations of aquatic animals. Environmental flows delivered to the Latrobe, Thomson and Macalister systems in 2020–21 aim to grow local populations of native fish, platypus and waterbirds, and some of these animals may disperse and contribute to the recovery of populations in nearby fire-affected areas in future years.
Most of the Gippsland region experienced below-average rainfall in 2017–18 and 2018–19, but climatic conditions varied considerably across the region in 2019–20. East Gippsland generally remained dry, although autumn rainfall was closer to the long-term average. West Gippsland had above-average rainfall in late winter 2019, near-average rainfall in spring 2019 and above-average rainfall in summer and autumn 2020. The higher rainfall and associated increase in natural streamflow in west Gippsland met many of the priority environmental watering actions for the Latrobe, Thomson and Macalister systems during 2019–20.
The Bureau of Meteorology climate outlook indicates wet conditions may continue into 2020–21, with winter rainfall predicted to be close to or slightly above the long-term average. Significant winter rain will deliver increased inflows to storages in west Gippsland that hold Victorian environmental water entitlements, and it may lead to high flow or overbank flows in some systems. Natural flows may meet many of the environmental flow requirements for the Latrobe, Thomson and Macalister systems early in 2020–21, and there may be opportunities to release environmental water — on top of natural freshes or as larger flows recede — to enhance environmental outcomes. For example, the duration of a fresh after a storage spill from Lake Glenmaggie could be extended to meet objectives for fringing vegetation
and reduce the risk of bank slumping and flush the Latrobe River estuary to export excess salt from the upper water column. If conditions are drier through spring and summer 2020 and into autumn 2021, environmental water will be used to protect high-value environmental assets (such as by providing critical flows for threatened migratory fish, particularly with bushfire potentially affecting waterway habitat in east Gippsland), and set aside sufficient reserves to deliver early-season watering priorities in 2021–22.
Allocations across the west Gippsland systems are largely influenced by storage inflows during winter and spring, and so by late spring waterway managers can determine which potential watering actions they will likely be able to deliver for the rest of the 2020–21 water year. Where critical demands cannot be met by existing allocations, the VEWH and its program partners may investigate alternative supply options (such as transfers or trades). The VEWH also works with storage managers to identify opportunities to adjust the pattern of consumptive water deliveries to support environmental watering outcomes while still meeting the needs of consumptive water users.
The NSW Department of Planning, Industry and Environment plans and manages environmental flows in the Snowy system in consultation with Victorian and Australian governments and relevant stakeholder groups. The water year for the Snowy system starts in May and finishes in April the following year, which differs from how water is managed in the other Gippsland systems. The total volume for release and daily release targets for the Snowy River from May 2020 to April 2021 were endorsed by the Snowy Advisory Committee in February 2020, and daily releases will not vary unless flows increase the risk of flooding downstream or operational constraints prevent delivery.