The Lachlan valley has an area of 90,000 square kilometers, extending from the Great Dividing Range to the Great Cumbung Swamp on the Riverine plains. Nearly 1300 kilometres of the
1400-kilometre-long river is regulated by water storages, of which Wyangala Dam is the largest at 1220 gigalitres.
The Lachlan catchment remained very dry in 2019–20. Consequently, water for the environment was managed primarily to provide critical refuge and to avoid irreversible impacts on priority native fauna species and wetland vegetation communities.
The focus of water managers in 2019–20, with an expected very dry to dry resource availability scenario, as identified in the Lachlan Catchment Annual Environmental Watering Priorities 2019–20, was on supporting a variety of refuge sites for native plants and animals impacted by drought conditions.
The catchment followed the same low inflow trend from the 2018–19 season with no significant inflows recorded. Wyangala storage started the water year at 26%, dropped to as low as 8.5% in February 2020 and recovered slightly to 16% by June 2020. As a result of low inflows, the catchment stayed in Drought Stage 3 restrictions, with access to carryover allocation suspended and the delivery of water to most creeks off the Lachlan River reduced as a drought management measure by WaterNSW.
Support for refuge sites
The delivery of New South Wales and Commonwealth water for the environment in the Lachlan catchment during 2019–20 provided a variety of refuge types across summer and into autumn for native animals under stress from drought. Many sites remained inundated for at least 4 to 8 months, while deeper wetlands, such as the Cumbung, will retain water to provide an ongoing drought refuge into 2020–21.
Significant outcomes included:
- provision of critical foraging and roosting habitat for a diversity of waterbirds including endangered and migratory species
- provision of habitat to support the Lachlan’s last known population of olive perchlet, a small-bodied native fish
- support for a range of native wildlife and vegetation communities in anabranch systems and creeks
- mitigating against the risk of native fish kills through avoiding poor water quality conditions.
Partnerships with local field ornithologists and private landowners, as well as collaborations with other NSW water agencies, contributed to successful flows across the Lachlan catchment.