Annual environmental water priorities in the Macquarie–Castlereagh 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 Macquarie–Castlereagh catchment covers more than 75,000 square kilometres in the state’s central west. It extends from the Blue Mountains to the Barwon River plains, with major tributaries including the Cudgegong, Talbragar and Bell rivers.

The catchment is home to the iconic Macquarie Marshes – one of the largest semi-permanent wetland systems and colonial waterbird breeding sites in inland Australia.

The catchment supports important cultural values for the Wiradjuri, Ngiyampaa, Wailwan and Kamilaroi Aboriginal people.

Water for rivers and wetlands

Following wet years in 2021 and 2022, the weather outlook for 2023 is dry and warm, signalling a possible return to dry conditions.

Based on projected dam conditions and current balances, environmental water accounts can expect an allocation of approximately 45% on 1 July 2023. This will mean projected balances:

• of approximately 278 gigalitres (GL) of carryover in the regulated Macquarie River and a further 150 GL of general security allocations, plus supplementary and unregulated licence balances
• of approximately 24GL of planned environmental water allowance in the regulated Cudgegong River, including residual water and new allocations.

The Environmental Water Advisory Group (EWAG) for the regulated catchment has prepared a multi-year rolling strategy to inform annual planning. For the 2023–24 water year, water managers plan to target outcomes for:

• native fish, wetland vegetation, waterbirds in the Macquarie regulated reach, and the targeted unregulated reaches downstream, and flow connection to the Barwon River
• native fish and river processes, including targeting flow variability in the Cudgegong regulated reach.

We plan to support river and wetland resilience over the next 2 to 3 years by holding a portion of water aside in general security carryover accounts for future use.

Aboriginal water management priorities

Water for Country is environmental water use planned by the Department of Climate Change, Energy, the Environment and Water and Aboriginal people to achieve shared benefits for the environment and cultural places, values and/or interests.

In 2023, we supported Tubba-Gah Maing Wiradjuri to complete an Aboriginal Waterways Assessment (AWA). AWA’s assist Aboriginal peoples to collate traditional knowledge about their significant waterways, and environmental and cultural values. The AWA process involves Aboriginal people going out on Country for several days and assessing chosen sites based on cultural significance and environmental health.

The Wayilwaan people in the regulated part of the catchment currently has a representative on the Macquarie Cudgegong Environmental Water Advisory Group (EWAG).

In 2023-24, we hope to:

• add further representatives to the EWAG from the Wiradjuri and Wayilwaan people with an interest in the regulated Macquarie and Cudgegong rivers
• continue to build local and regional relationships with Aboriginal people
• support Aboriginal representatives to include their priorities in EWAG discussions
• partner with Aboriginal people to examine watering viability for selected assets, including areas near Trangie and Warren.

Weather and water forecast

As at early June the El Niño–Southern Oscillation (ENSO¹) outlook is neutral, with a potential return to El Nino neutral during winter, meaning dry and relatively warm conditions are likely over autumn and winter 2023. It is possible this weather is an indication of a return to dry conditions.

Water managers have prepared watering plans that consider a range of weather and water availability scenarios. This is known as resource availability scenario planning. As of May 2023, conditions in the Macquarie– Castlereagh catchment are ‘wet’.

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

Resource availability scenario

Key planned actions for 2023–24

Native fish

Water managers will target native fish populations in the mid-Macquarie Wambuul River and regulated Cudgegong River.

The fish species targeted will depend upon weather conditions over spring. If river flows can be kept relatively stable, water managers will target flow generalists, like Murray cod and eel-tailed catfish, which benefit from steady flows. If more variable flows arise, water managers will consider actions for flow specialists, including golden perch.

Vegetation

At a minimum, water managers will deliver an environmental flow pulse in Spring 2023 to target the semi-permanent wetland and river red gum woodlands of the Macquarie Marshes, up to an area of approximately 40,000 hectares. This will support wetland vegetation to grow, flower and set seed.

As a further benefit, riparian vegetation along the mid and lower Macquarie Wambuul River and the regulated Cudgegong River is supported by regulated river operation. These flows help to recharge shallow groundwater systems and support dependent vegetation.

Connectivity

Connectivity of the Macquarie-Cudgegong catchment to the Barwon River has been consistent through 2021, 2022 and early 2023. With a relatively wet Macquarie Marshes, it is expected spring flows in 2023 will provide an ecologically valuable flow connection along the lower Macquarie River to the Barwon River. This will allow native fish to move between catchments and will also support some low or base flow in the unregulated Barwon River to Brewarrina.

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