Annual environmental water priorities in the Lachlan catchment 2023–24

Water that is allocated and managed specifically to improve the health of rivers, wetlands and floodplains is known as water for the environment.

NSW environmental water management teams work with local community advisory groups including landholders, Aboriginal stakeholders, partner agencies and other interested community members to develop detailed annual plans for the use of water for the environment in each catchment, including how its use is prioritised.

The catchment

The Lachlan catchment covers an area of 90,000 km². Nearly 1,300 km of the 1,400-km 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 Swamp, all of which are listed in the Directory of Important Wetlands in Australia.

The Lachlan catchment has important Aboriginal cultural values. Environmental watering actions consider Aboriginal values and uses in consultation with communities.

The Lachlan is Country to the Wiradjuri, Nari Nari, Mutthi Mutthi, Ngiyampaa and Yita Yita Aboriginal people.

Water for rivers and wetlands

In 2023–24, water managers will focus on completing a cycle of wetland water regimes including a natural drying phase. They will consider the seasonal inundation of priority wetlands and floodplains to maintain improvements in condition of long-lived woody shrublands (lignum, nitre goosefoot), black box and river red gum wetlands, as well as macrophyte, rushes and reed beds. Work will continue on development of a strategy to support the full life cycle requirements of threatened species of waterbirds, native fish and frogs. This may include flows to enable breeding, recruitment and dispersal at a catchment scale, as well as to support permanent areas of habitat under dry conditions.

The full 350 GL of translucent flows was delivered each year for the last 3 years and more of the lower Lachlan floodplain remains inundated since summer 2023. Over 100,000 ibis nests were counted in the Booligal Wetlands and southern bell frogs bred in the Great Cumbung Swamp.

During 2022–23, the Department of Climate Change, Energy, the Environment and Water (the department) worked with partner agencies and stakeholders to deliver more than 30 GL of held environmental water and planned environmental water. Water for the environment was pumped into lower Merrimajeel Creek for the first time supporting Dry Lake vegetation and Wiradjuri cultural connections. Two Lachlan River freshes were delivered after flooding receded to reduce the risk of widespread fish kills from poor water quality, particularly blue green algal blooms.

Aboriginal water management priorities

Water for Country is environmental water use planned by the department and Aboriginal people to achieve shared benefits for the environment and cultural places, values and/ or interests.

In 2023–24 we will partner with Aboriginal groups in the Lachlan to support priority outcomes for the catchment. We will continue to be guided by Ngiyampaa people in delivering flows to Booberoi Creek and expand into Willandra Creek. As part of the water management plan project, we are seeking to build relationships and support On Country connections with Wiradjuri people in the mid Lachlan, and with Nari Nari, Mutthi Mutthi, Wiradjuri and Yita Yita people in the Great Cumbung Swamp region and lower Lachlan floodplain.

Management will also be guided by the Mawambul co-management group for Kalyarr National Park, and Wiradjuri aspirations for Dry Lake (Keiross Lake) and Lower Mirrool Creek Floodplain. In addition, we aim to learn from Mutthi Mutthi people on the values for Box Creek below Lake Tarwong, recognising the important role of Aboriginal knowledge and perspectives in water management responsibilities.

Weather and water forecast

The prolonged wet conditions and significant flooding from 2020 to 2023 means conditions for early 2023–24 are wet to very wet. The maximum volume of all environmental water provisions is likely to be available during 2023–24 given most storages remain near full capacity.

However, as at early June an El Niño¹ watch was issued and the April to June 2023 forecast is for below median rainfall and above median temperatures. Streamflow forecast for March to May 2023 is near median flow. With Wyangala Dam near full capacity, the traditional winter storage inflow and downstream tributary inflow period will influence how wet the system is and our need for environmental water.

In summary, the 2023–24 water year will start with high available water resources and a residual wet landscape. A return to moderate to dry rainfall–inflow conditions is anticipated with a 50% chance of El Niño developing in late 2023 into 2024.

Water managers have prepared watering plans that consider a range of weather and water availability scenarios. This is known as resource availability scenario planning. Wet to very wet conditions are forecast for the Lachlan catchment in 2023–24.

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

Key planned actions for 2023–24

Waterbirds

If needed, 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 the pelicans at Lake Brewster.

Native fish

Water managers will deliver up to 30 GL in a series of whole of system seasonal freshes from Wyangala (including mid Lachlan anabranches) to provide food and cues to move and breed for native fish populations (multi-site and multi-objective flow). These freshes will also improve water quality and reconnect isolated reaches and pools after low flow periods.

Vegetation

Water managers will focus on successive waterings of floodplain vegetation:

• lignum shrublands in Merrowie Creek, Box Creek and Willandra Creek
• phragmites, reed beds and river red gum woodland in the Great Cumbung Swamp (up to 25 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.

Connectivity

Water managers will consider a system-scale watering event (up to 90 GL) in winter 2024, targeting overbank and small wetland flows for follow-up floodplain watering for long-term resilience and refuge habitat.

Map of proposed annual priority targets in the water resource plan area 2023–24