Rainfall across the northern region in 2019–20 was below the long-term average for the third consecutive year, and total annual rainfall in parts of the Mallee was among the lowest on record. Despite the overall dry conditions, there were some wetter months. Rain in July and August 2019 produced small natural flow events in the Ovens River, which flowed into the Murray above Barmah Forest, and in the Loddon River. Rainfall in April and May 2020 caused minor flooding in the Ovens, Kiewa and Broken catchments. Spring and early summer were dry and water for the environment was used to deliver the required water regime in the region’s regulated rivers during these months, particularly spring freshes in the Campaspe, Goulburn, Loddon and Murray rivers.
Operational demands in the lower Murray through summer resulted in inter-valley transfers (IVTs) being delivered from the Goulburn River, Campaspe River and lower Broken Creek. High IVTs during summer continued to compromise some of the environmental outcomes, particularly in the lower Goulburn River, as they reduce bank vegetation and increase the risk of erosion and bank failure. An interim operating limit on IVTs of up to 50 GL per month was applied by the Minister for Water to minimise the environmental risk to the lower Goulburn River in 2019–20. The intention of the limit was to reduce the effect on bank vegetation and minimise erosion, while still meeting downstream demands. Initial monitoring data indicated that vegetation was again impacted, with the effect on erosion still being assessed. Small, disconnected waterways (such as upper Broken Creek) had little to no flow over summer, except for environmental flows which were used to avoid loss of critical habitat.
The climate outlook from June to August 2020 indicates average to above-average temperatures and higher-than- median rainfall is likely for northern Victoria. The wetting-up of catchments and inflows into major storages during this time will be important to support early season allocations and water availability in 2020–21. Wetter conditions and higher streamflows may result in unregulated flows throughout winter. Longer-term outlooks have a lower level of confidence, but as at May 2020 climate models were predicting a negative Indian ocean dipole event in winter/spring 2020, which increases the likelihood of above-average rainfall during this time.
The allocation outlook for 2020–21 provided by the Northern Victorian Resource Manager (NVRM) on 15 May 2020 indicated low opening allocations are likely across all systems. Carryover of water into 2020–21 will be important to meet early season environmental demands, and possibly most 2020–21 demand if winter/spring is dry to extremely dry. Smaller systems (such as the Campaspe and Broken) are forecast to receive small (if any) increases in allocation during 2020–21 under the extreme dry1 and dry scenarios, whereas the Goulburn, Loddon and Murray systems are more likely to get closer to a moderate allocation of around 50 percent high-reliability water shares in all but an extreme dry scenario. Under average to wet scenarios, allocations may increase more quickly in the smaller systems in response to increased inflows — a boom-or-bust type of response — when compared to the Goulburn/Loddon and Murray systems, which tend to have more gradual increases as they are larger systems. It may be difficult to commit significant volumes of environmental water to enhance unregulated events in the Goulburn and Murray rivers if these events occur before environmental allocations increase. The NVRM has not provided an outlook for low-reliability entitlements, but for planning purposes the VEWH has assumed allocation against low-reliability entitlements during 2020–21, unless significant rain provides inflows that are more than expected under an average scenario or in line with a wet scenario.
Under a dry scenario, environmental flows are expected to focus on protecting and maintaining habitat for native plants and animals to avoid decline or loss. Examples include watering wetlands (such as Horseshoe Lagoon on the Goulburn River) to maintain vegetation and provide refuge for waterbirds and to maintain low flow in the Campaspe River and other rivers to protect water-dependent species including native fish and platypus. If conditions and allocations improve, water for the environment may be used to deliver larger events to improve the health of environmental values that have experienced hot, dry conditions over the last two years. Under average to wet scenarios, larger floodplain watering events at icon sites along the Murray are planned, as is the watering of additional wetlands 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 the floodplain to the rivers to increase the productivity of food webs and provide food for 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.
1Goulburn-Murray Water’s resource outlooks refer to the driest outlook as ‘extreme dry’. In the seasonal watering plan, the driest planning scenario is usually called ‘drought’.