Rainfall across northern Victoria in 2020-21 was close to the long-term average in most areas, although slightly below the long- term average in the north-west and parts of the eastern ranges. Mean maximum temperatures were close to or slightly above average across the region. Winter rainfall resulted in some relatively small, unregulated flow events in the Goulburn, Ovens and Kiewa rivers. Further rain in spring gradually increased storage levels and provided occasional unregulated pulses that remained within the channel in the regulated rivers. Environmental flows were delivered to rivers and wetlands across the region in 2020-21 to provide what would have occurred naturally without river regulation and to support native plants and animals.
Inter-valley transfers (IVTs) from the Goulburn system to the Murray system over summer and autumn were reduced from 50,000 ML per month in 2019-20 to 40,000 ML per month in 2020-21, to help protect native vegetation and reduce bank erosion in the lower Goulburn River. Anecdotal evidence suggests the rate of bank erosion has slowed and there has been some recovery of native vegetation, but the river is far from fully recovered. Monitoring will continue to assess the condition of the banks and bank vegetation over the next few years.
The climate outlook from June to August 2021 indicates average to above-average rainfall and average to above-average temperatures are likely. However, it appears autumn 2021 will be relatively dry, so moderate to high rainfall will be needed to wet the catchments before there will be significant natural inflows to waterways and storages. Above-average rainfall throughout winter and spring 2021 should increase water in storage and deliver some natural flow pulses in the rivers. Environmental flows may piggyback onto or extend the duration of natural events, where doing so helps achieve particular environmental flow objectives. If 2021-22 is considerably drier than average, environmental flows will mainly be used to maintain rather than improve the health of native plants and animals in the region’s rivers and wetlands.
Many of the Murray River floodplains have not been inundated since 2016-17, and they are prioritised for environmental watering in 2021-22 under all climate scenarios to prevent native plant communities from exceeding their tolerable dry period. Watering floodplain wetlands at Hattah Lakes, and across Lindsay, Mulcra and Wallpolla Islands will be especially important in 2021-22 because proposed construction activities for the Victorian Murray Floodplain Restoration Project will prevent planned environmental flows to these sites in 2022-23 and 2023-24. A watering event that commenced at Hattah Lakes in autumn 2021 is likely to continue into winter and spring 2021, while planned watering actions at Gunbower Forest are likely to commence in winter or spring 2021 even under a dry climate scenario. Without these environmental flow events, the health of the plant and animal communities that live on the floodplain will significantly decline.
Operational inter-valley transfers of water (IVTs) from the Goulburn system via lower Broken Creek and the Goulburn and Campaspe rivers to the Murray River are again expected to feature prominently in summer and autumn 2021-22. Specific IVT limits will be determined through the review of the Goulburn to Murray trade rule, which is due to conclude in June 2021.
Proposed rates of IVT delivery remain above recommended environmental flow rates, but importantly they remain significantly lower than in past years. It will be essential to enable environmental flows to be adaptively managed year-round, to support the health of the lower Goulburn River and other waterways, including downstream sites.
The allocation outlook for 2021-22 provided by the Northern Victoria Resource Manager on 17 May 2021 indicated low opening allocations across all systems, particularly for the smaller Broken and Bullarook systems that are likely to have zero opening allocation. The larger Murray, Goulburn, Campaspe and Loddon systems are expected to open below 25 percent allocation to high-reliability water shares. Carried-over water can be delivered in all systems, and it will likely be important for meeting early- season demands from July 2021.
Under an extreme dry1 scenario, very little increase in water allocation is expected during 2021-22. Under a dry climate scenario, the Broken and Campaspe systems may reach 30 percent allocation, while the Murray, Goulburn and Loddon systems may reach 60 percent allocation. All systems should get close to or reach 100 percent allocation under average or wet scenarios in 2021-22. The Northern Victoria Resource Manager has not provided an outlook for low-reliability entitlements, but for planning purposes the VEWH has assumed no allocation against low-reliability entitlements during 2021-22 unless there are significantly above-average inflows to storages.
Under drought and dry climate scenarios, environmental flows are expected to focus on protecting and maintaining habitat for native plants and animals, to avoid decline or loss. Examples include watering selected wetlands in the Kerang Lakes to maintain vegetation and provide refuge for waterbirds and maintaining low flow in rivers to protect native fish and platypus. In some systems (such as the Goulburn River), relatively high volumes of carryover will enable the delivery of some larger watering actions — actions that can usually be delivered only under average climate scenarios — to be delivered in a dry climate scenario, to improve or enhance environmental outcomes.
If conditions and allocations improve, water for the environment may be used to deliver larger events to improve the health of the environment. Under average and wet climate scenarios, larger floodplain watering events are planned at icon sites along the Murray River, and additional wetlands will likely be watered across the region. These larger-scale watering events will increase the quality and quantity of wetland habitat for waterbirds, frogs and turtles, support waterbird breeding events and transfer carbon from floodplains to rivers to increase the productivity of food webs and provide food for native fish and other aquatic animals. Increased flows in creeks and rivers will aim to increase the abundance of waterbugs, enhance the breeding and recruitment of native fish and improve fringing bank vegetation.