Wyangala Dam operations update

A meeting of the Lachlan Valley airspace reference panel on 1 August heard that with a wet catchment and inflows continuing to arrive, releases from Wyangala Dam will continue in order to create airspace.

Storage levels may dip to 93% in mid-August before returning to 95% by end of the month in preparation for the irrigation season. Wyangala Dam storage capacity is currently 94.8% full, leaving 5.2% “airspace” potentially available for flood mitigation.

The Lachlan Valley airspace reference panel includes representatives of local government, irrigation groups, environmental water holders and other key government agencies.

Background:

Damage to Lake Brewster and the infrastructure around the lake occurred during the extensive Lachlan Valley flood event in late 2022. Significant damage was sustained to the weir pool levees, inlet channel, and lake embankments.

Emergency repairs by WaterNSW in 2023 and 2024 restored much of the infrastructure’s operational function.  Constraints remain on flow capacity of the Brewster Weir pool (5,000 ML/d), Lake Brewster inlet channel flow (960 ML/d) and Lake Brewster storage capacity (79.5%) and require further works to resolve.

Restrictions on flow rates and storage levels at both Lakes Brewster and Cargelligo have been implemented frequently since the 2022 floods, to mitigate potential impacts on landholders in the vicinity.

Works to repair the Brewster Weir levee are being accelerated, which will contribute to overall precautionary flood mitigation measures, and include the establishment of a dedicated support team to co-ordinate operations, planning, logistics, and communication functions. Lake Brewster will not exceed 79.5% of capacity during this next phase of repairs.

It is anticipated that the works to permanently return Lake Brewster to full capacity could take up to 12 months to complete. WaterNSW will continue to review operational requirements throughout the repair project and communicate with stakeholders and local communities.

Lakes Brewster and Cargelligo serve as important secondary storages for water users and the environment in the Lachlan Valley, many kilometres downstream of Wyangala Dam.

Wyangala Dam holds approximately 1200 gigalitres at 100% of capacity (full supply). In November 2022 during the height of the flooding the dam received inflow of 800 gigalitres. In the three months from October to December 2022 the total inflow figure was approximately 1700 gigalitres.