Annual environmental water priorities in the Lachlan catchment 2022–23

The Lachlan catchment covers an area of 90,000 square kilometres. Nearly 1,300 kilometres of the 1,400-kilometre river is regulated by water storages, of which Wyangala Dam is the largest at 1,220 gigalitres (GL).

The river originates near Gunning in the tablelands and ends at the Great Cumbung Swamp. Important sites include the Booligal Wetlands, Lake Brewster, Lake Cowal, Great Cumbung Swamp and Lachlan Swamps, all of which are listed in the Directory of Important Wetlands in Australia.

The Lachlan catchment has important Aboriginal cultural values with environmental watering actions considering Aboriginal values and uses in consultation with communities. The Traditional Owners of the Lachlan are the Wiradjuri, Nari Nari, Ngiyampaa and Yita Yita.

Water for rivers and wetlands

In 2022–23, the focus will be to enhance natural conditions and opportunities for plants and animals to breed, move and thrive in line with ecological cues. This includes developing an adaptive watering strategy to maintain refuges and key breeding habitat to support the growth in the lower Lachlan southern bell frog population.

High flows resulting from rainfall and airspace releases have kept the Lachlan storages filling and spilling during the past 12 months. The full 350 GL of translucent flows was delivered, and the lower Lachlan floodplain system was inundated for more than 12 months.

During 2021–22, the Department of Climate Change, Energy, the Environment and Water (the department) worked with the Commonwealth Environmental Water Holder (CEWH) and stakeholders to deliver 20GL of licensed water and more than 15 GL of Environmental Water Allowance (EWA) to the lower Lachlan system.

The timing and cooperative management of environmental flows in Merrowie Creek led to Lake Tarwong filling for the first time since 2016. The active management of Lake Brewster in partnership with WaterNSW supported the largest Australian pelican breeding event for more than 30 years at the site.

Weather and water forecast

The El Niño–Southern Oscillation (ENSO) outlook remains at La Nina, with a return to neutral ENSO during winter, indicating that rainfall is likely to be above average across the catchment. All storages in the Lachlan are effectively full and are likely to continue to spill in line with rainfall–inflow events throughout winter.

Water managers have prepared watering plans that consider a range of weather and water availability scenarios in case it rains more or less than expected. This is known as resource availability scenario planning. ‘Very wet to moderate’ conditions are forecast for the Lachlan catchment in 2022–23.

_{1. ENSO: The interaction between the sea surface and atmosphere over the Pacific Ocean which results in dryer or wetter conditions (El Nino or La Nina).}

Resource availability scenario

Key planned actions for 2022–23

Waterbirds

If required, core breeding, foraging and migratory wader habitats will be topped up in early spring and autumn to provide food and shelter for waterbirds (up to 10 GL). Water managers will make additional water (up to 10 GL) available to support bird breeding events, such as Lake Brewster pelicans.

Native fish

Water managers will deliver flows to support fish breeding and dispersal, targeting, but not limited to, continued golden perch recruitment. Flows for fish will maintain water quality in refuge systems, such as Booberoi Creek, while supporting habitat and food sources.

Vegetation

Water managers will focus on successive waterings of floodplain vegetation, lignum shrublands in Merrowie Creek and phragmites reed beds and river red gum woodland in the Great Cumbung Swamp (up to 20 GL). These watering actions will promote recovery in vegetation condition and recruitment. These sites will also contribute to waterbird and connectivity outcomes.

Additional volumes (up to 8 GL) will promote seed setting and establish inflow and outflow wetlands at Lake Brewster.

Water managers will deliver flows in the greater Cumbung region to maintain quality in-channel and wetland aquatic vegetation for southern bell frogs and to promote breeding.

Connectivity

Water managers will consider supplementing translucent flow events to extend floodplain inundation and connectivity to the river system across the lower Lachlan system (up to 40 GL), including Willandra Creek (up to 5 GL).