Annual environmental water priorities in the Gwydir catchment 2022–23

The Gwydir catchment covers 25,596 square kilometres. The eastern upland creeks mainly flow into the Gwydir River upstream of Copeton Dam. Downstream, on the western floodplain, the main Gwydir River splits into its main distributaries – the Mehi River (south), Carole Creek (north), Lower Gwydir and Gingham Channels (west/central).The Big Leather (Lower Gwydir) watercourse supports the State’s largest stand of marsh club rush. The Gingham Watercourse contains important colonial waterbird breeding habitats. The Gwydir wetlands are home to four wetland parcels listed under the Gwydir Ramsar landholder agreement. The Gwydir catchment supports important Aboriginal cultural values for the Kamilaroi/ Gomeroi people.

Water for rivers and wetlands

In 2022–23 water managers will use an adaptive approach to support fish and colonial waterbird populations and downstream connectivity by using water for the environment to maintain a natural flow regime. Contingencies are also in place to provide environmental flows to water-dependent assets when required.

The Gwydir catchment experienced improved water availability in the later part of 2020, with wet conditions continuing through 2021 and 2022. Major flooding occurred across the Gwydir River floodplain during March and April 2022.

During the 2021–22 water year, water managers used water for the environment to return flows into the downstream Barwon River via the Mehi River. Whittaker’s Lagoon was refilled. They also used water for the environment to support a significant colonial waterbird breeding event that occurred in the Gwydir Wetlands after natural flooding.

Weather and water forecast

The El Niño–Southern Oscillation (ENSO¹) outlook remains at La Nina, with a return to neutral ENSO during winter, meaning average or wetter conditions are likely. Further, the Bureau of Meteorology has forecast average temperatures in Central NSW.

Water managers have prepared watering plans that consider a range of weather and water availability scenarios. This is known as resource availability scenario planning. Moderate to wet conditions are forecast for the Gwydir 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

Heavy catchment rainfall, resulting in large river flows and floodplain flooding, may trigger colonial waterbird breeding events in the wetland systems. In response, water managers may provide 15–25 gigalitres (GL) of held water for the environment to support these events.

Native fish

Water managers may use up to 25 GL to support native fish communities. Early season environmental flows may be triggered by inflows at Copeton Dam with a view to deliver supporting environmental flows later in the season.

Vegetation

Water managers may use up to 40 GL across the catchment. Rainfall may trigger delivery of held environmental water into the Mehi River, Carole Creek and/or the Gwydir wetlands system. Water managers are likely to release further environmental flows into the Mallowa Watercourse this season to continue vegetation improvements.

Connectivity

Water managers may provide up to 14 GL of water for the environment in the Carole Creek, Mehi and Gwydir rivers this season to provide connectivity support to native fish communities during extended dry periods. In addition to in-valley connectivity, water managers may consider addressing connection to the Barwon River if warranted during the year.