Rainfall across the western region in 2020-21 varied seasonally and geographically. In the Glenelg system, rainfall was above the long-term average for much of winter and spring, with natural inflows delivering most of the planned watering actions from July to December 2020. Water for the environment was needed to help maintain continuous flows from Rocklands Reservoir to the estuary from December 2020 through to May 2021. Rainfall in the Wimmera system remained below average for the fourth consecutive year. A high-rainfall event in February 2021 delivered the largest flow in the Wimmera River since 2016, but other parts of the Wimmera system had few natural events, and inflows to the catchment’s storages were low. Water for the environment was used to maintain drought refuges in the MacKenzie River and Burnt Creek from mid-October 2020 and to maintain flow in the Wimmera River downstream of Dimboola from January 2020. Water for the environment was also used to freshen water quality and prevent a hypoxic blackwater event in the Wimmera River after the February flood. No flows were delivered in the Mount William Creek, due to natural top-ups in the upper section and accumulated passing flows that refilled pools in December 2020.
Water storages across the Wimmera-Mallee System Headworks were collectively at 31 percent capacity at the start of 2020-21. They rose to 40 percent in November 2020 and were below 30 percent of capacity at the end of April 2021, which is slightly less than at the same time in 2020. The VEWH received 57 percent allocation against its environmental entitlement for the Wimmera and Glenelg rivers in 2020-21. The wetlands environmental entitlement and CEWH did not receive any allocation in 2020-21.
Below-average rainfall and well-above-average temperatures are predicted for the western region in winter 2021. The Wimmera- Mallee storages will need significant inflows before any allocations are made to the environmental entitlement. The storage manager has indicated that entitlement holders will receive low allocations in 2021-22 under drought, very dry, dry and average climate scenarios, and they are unlikely to receive full allocations even under a wet scenario.
If environmental allocations do not significantly increase in winter/spring 2021, water for the environment for the rest of 2021- 22 will be managed in line with drought, very dry and/or dry climate scenarios in the Wimmera and Glenelg systems. This will be the fifth consecutive year that environmental watering actions in the Wimmera and Glenelg systems have been managed according to drier-than-average climate scenarios. The focus in 2021-22 will likely be on delivering minimum low-flow and small freshes as needed to maintain continuous river flow where possible, to maintain refuge pools where continuous flow cannot be achieved and to protect water quality.
Carryover from 2020-21 will be critical in supporting these watering actions. If inflows into the storages support higher environmental allocations, water for the environment may be used to deliver winter/spring freshes and low flow in the Glenelg River through to reach 3, deliver additional winter/spring freshes in the Wimmera River and extend the summer/autumn low flow and freshes through to reach 3 of the MacKenzie River. Winter/spring inflows to the Wimmera-Mallee storages will need to be well above average, to allow wet-scenario watering actions to be delivered in 2021-22.
The Wimmera-Mallee wetlands entitlement is not likely to receive any allocation in 2021-22 under drought, very dry or dry climate scenarios and only small volumes under average and wet climate scenarios, so managed environmental deliveries to those sites will rely on carryover from 2020-21. The continuing focus of environmental watering in the Wimmera-Mallee wetlands will be to provide refuge and maintain habitat in the dry landscape to support local plants and animals. Carryover will also be prioritised to allow critical wetland deliveries in future years until new allocations are made.
