Following relatively dry years in 2018-19 and 2019-20, average rainfall and temperature conditions were observed throughout west Gippsland during most of 2020-21. Below-average rainfall was recorded for the region in July, but a large-scale La Niña event brought average-to-above-average rainfall in the second half of 2020 and January 2021. The Durt-Yowan (Latrobe), Carran Carran (Thomson) and Wirn wirndook Yeerung (Macalister) rivers had relatively high flow throughout winter and spring, and minor flooding occurred in the lower reaches of Durt-Yowan (Latrobe River). All of the lower Latrobe wetlands included in the environmental watering program — Sale Common, Dowd Morass and Heart Morass — filled during 2020-21, and Lake Wellington was the freshest it has been — that is, it has the lowest salinity levels — since 2012.
East Gippsland had below-average rainfall in early winter, and much of the catchment was still suffering from dry conditions in 2019-20 and the bushfires that burnt vast areas of the catchment in December 2019 and January 2020. Rainfall increased significantly in July, and the second half of winter 2020 and autumn 2021 were wetter than average. A large rain event across eastern Australia in March 2021 caused minor flooding in some east Gippsland rivers.
The Bureau of Meteorology climate outlook suggests that warmer-than-average temperatures and average to slightly above-average rainfall may occur in the Gippsland region in early 2021-22. Such climatic conditions would likely result in increased inflows to storages in west Gippsland that hold Victorian entitlements to water for the environment, and it may lead to high flow or overbank flows in some systems. The El Niño–Southern Oscillation outlook has been downgraded to inactive, and it is not anticipated to be a significant influencer of the climate in early 2021-22.
Water for the environment for the Latrobe, Thomson and Macalister systems is held in Blue Rock Reservoir, Thomson Reservoir and Lake Glenmaggie respectively. High carryover into 2021-22 is expected in all three west Gippsland river systems because natural events helped meet many of the planned environmental watering actions in 2020-21. The supply of water for the environment going into 2021-22 is likely to be higher than in recent years, which should enable high-priority watering actions to be delivered in winter and spring, without compromising the ability to meet critical demands later in the year.
Allocations across the west Gippsland systems are largely influenced by storage inflows during winter and spring, and so by late spring 2021 waterway managers will be able to determine which potential watering actions they can deliver in summer and autumn. If climatic conditions remain close to the long-term average or become wetter, available water will likely be used to deliver larger-magnitude, longer-duration watering actions to consolidate and build on the environmental outcomes observed in 2020-21. Specific watering actions under these scenarios will aim to have another successful recruitment event for native migratory fish in the Latrobe, Thomson and Macalister systems, enhance recovery of aquatic animal and vegetation communities that were affected by previous dry periods and promote longer- term resilience in the systems. Achieving these flow outcomes may involve timing releases of water for the environment to extend the duration of natural freshes or managed spill releases (where they do not cause impacts to third parties) to optimise outcomes from these events.
If 2021-22 sees a return to drier conditions, the planned flows will likely be delivered at the lower end of their recommended magnitude and duration. There is expected to be sufficient supply to still meet most of the high-priority watering actions planned for dry and drought climate scenarios in 2021-22. Under a drought scenario, environmental watering will focus on protecting high-value assets (such as critical flows for threatened migratory fish, especially species that would normally rely on habitats that were burnt in east Gippsland) and setting aside sufficient reserves to deliver early-season watering priorities in 2022-23.
Environmental watering in the lower Latrobe wetlands in 2021-22 will aim to fill all three wetlands at least partially, given the wetlands experienced several years of dry conditions before 2020-21. It will be preferable to fill the wetlands under average and wet conditions.
The environmental Water Holdings in west Gippsland are not sufficient to meet all the priority flows identified in environmental flow studies, which are ultimately needed to significantly improve the condition of Durt-Yowan (Latrobe River), Carran Carran (Thomson River) and Wirn wirndook Yeerung (Macalister River). Policy actions to increase the supply of water for the environment are being considered through the Central and Gippsland Region Sustainable Water Strategy process, which is due to be completed in 2022-23. In the interim, the VEWH and its program partners may consider alternative supply options (such as transfers or trades) to help boost supply for specific watering actions. 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 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 2021 to April 2022 were endorsed by the Snowy Advisory Committee in February 2021, and daily releases will not vary unless flows increase the risk of flooding downstream or operational constraints prevent delivery.
