A year in the Border Rivers catchment: 2023–24

Natural rainfall and dam spills achieved a range of ecological outcomes in the Border Rivers system in 2023–24.

Key outcomes

Under wet to very wet conditions, significant flows in the catchment met environmental demands, resulting in:

• continuous connection to the Barwon River for the whole year
• multiple flow events in the Boomi River across a range of flow categories, including small and large freshes, bankfull and overbank events
• inundation of large areas of the floodplain
• summer flows in Morella Watercourse.

Catchment conditions

During 2023–24, weather patterns in the Border Rivers region were driven by various climate conditions including a strong La Niña event. This resulted in high rainfall and moderate temperatures, with significant flows throughout the system as major dams reached and exceeded storage capacity.

Higher than average flows and significant floodplain inundation occurred through the catchment. This met instream and floodplain environmental demands and negated the need to deliver water for the environment throughout the water year. 

Partnering with Aboriginal peoples

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 the 2023–24 water year, environmental water managers did not deliver water for the environment in the Border Rivers catchment due to rainfall, flows and releases from Pindari Dam to meet irrigation needs.

Water managers are building relationships with the Gamilaraay (Kamilaroi) people in the Border Rivers region to understand the cultural significance of the Border Rivers region and Macintyre River floodplain. There are many important sites in the region, one such site is Boobera Lagoon, south-west of Goondiwindi on the Macintyre River floodplain along Morella Watercourse. The Gamilaraay (Kamilaroi) people believe Boobera Lagoon is the resting place of Garriya (rainbow serpent). The site is estimated to contain millions of stone artefacts as well as scar and canoe trees.

Watering aims

The Annual environmental water priorities in the Border Rivers catchment 2023–24 were developed under predicted dry weather and water availability. There was a 50% chance of El Niño occurring, which is higher than average for that time of year. Short-term lower than median rainfall was also forecast. Aims for the use of water for the environment were to respond to or enhance natural events for the benefit of:

• native fish populations in the Severn, Dumaresq, Macintyre and upper Barwon rivers
• deliver flows for fish breeding, recruitment, and connectivity.

Water managers planned to deliver a small fresh to support native fish, but did not need to complete the delivery because of natural flows and Pindari Dam releases. Rainfall and the resulting natural flows:

• improved and maintained ecological health and resilience
• restored and maintained key floodplain and wetland linkages
• provided opportunities for plants and animals to breed, move and thrive throughout the catchment. 

Water delivery

No environmental water was released from Pindari or Glenlyon dams this year. Significant flows were observed throughout the catchment in regulated and unregulated watercourses.

The Pindari stimulus flow was triggered for use but was not delivered because natural flows and dam releases provided ample water across the catchment. This means 8,000 megalitres are available for use in 2024–25. Daily releases provided flows throughout the year, with translucency rules enabling the release of additional water to support flow in the downstream system for about 75% of the year.

The Commonwealth Environmental Water Holder participated in supplementary events in the NSW Border Rivers in December 2023, February 2024 and April 2024. A total of 1,437 megalitres was activated 3 times, which used 100% of the Commonwealth Environmental Water Holder’s NSW supplementary licence volume.

The Commonwealth Environmental Water Holder participated in several unsupplemented events in the Queensland Border Rivers. These events increased connectivity through the Border Rivers catchment and into the downstream Barwon River system.

This table and chart provide a summary of the 1,437 megalitres of water for the environment delivered in the Border Rivers catchment during the 2023–24 watering year.

Figures were accurate at the date of publishing but may be adjusted. The watering event number in the table and chart relate to the location number marked on the map.

Notes: CEW = Commonwealth licensed environmental water.

Outcomes

Environmental watering targets have been developed for the catchment through the NSW Border Rivers Long-Term Water Plan. Analysis of these targets for 2023–24 indicates that all flow events where held environmental water can influence were met.

The use of Commonwealth Environmental Water Holder NSW Border Rivers supplementary water was protected from the Border Rivers and into the Barwon River. This protection was maintained by active management rules as the water moved down the system. The flow events:

• enhanced inter- and intra-valley connectivity
• contributed to greater access to a range of habitats for water-dependant species
• improved breeding, dispersal and recruitment opportunities for native fish.

Some highlights from this year include widescale floodplain inundation, flows in Morella Watercourse and Boomi River, and many opportunities for aquatic and floodplain species to complete all or part of their life cycles.

The Department of Climate Change, Energy, the Environment and Water and the Commonwealth Environmental Water Holder participated in the WaterNSW Customer Advisory Group for the Border Rivers. Environmental water managers are important participants in this group, which represents members from across the catchment including many water-user groups. It provides a forum for members to receive and share information on water issues in the catchment.

Case study: connectivity and why it is important

Connectivity in rivers and wetlands means water moving between one location and another. When we talk about connectivity in broad terms, we use words like longitudinal, lateral, intra- and inter-valley.

Longitudinal connectivity describes water movement from upstream to downstream in the river channel. Lateral connectivity often refers to water flows from the river onto the floodplain and in some instances floodplain anabranches. Intra-valley connectivity is where the connection occurs within the catchment, for example from the Severn River into Macintyre River. Inter-valley connectivity is where flows connect 2 catchments, for example flows from Macintyre River into Barwon River connect the Border Rivers and Barwon–Darling catchments.

Connectivity in catchments is important for hydrological, chemical/geochemical and ecological cycles.

Connectivity is critical for the ecological functioning of the Border Rivers. Without sufficient connectivity, many species would diminish and potentially become extinct. Many aquatic species have adapted to this connectivity, which improves individual and population health through nutrient cycling and allowing genetic dispersal. Connectivity during wetter times also builds resilience, with benefits gained, to sustain the ecosystem during drier times.

In the Border Rivers, connectivity is critical to fish such as the golden perch (Macquaria ambigua). These fish require flow to reproduce as they swim upstream to spawn. Their eggs then larvae drift downstream to enter the slow flowing, highly productive floodplain and wetland habitats to grow. The larvae grow rapidly before returning to the main river channels as juvenile fish. In 2023–24 longitudinal, lateral, intra- and inter-valley connectivity was observed. The most significant connectivity event occurred in April 2024 when connections were made between many watercourses, including the Macintyre, Boomi and Barwon rivers; Whalan Creek and Morella Watercourse; and much of the floodplain between them. The initial flow across the floodplain from near Goondiwindi to near Mungindi lasted more than 2 weeks.

The lateral connectivity onto the floodplain has continued, with some ephemeral floodplain lagoons still inundated at the start of August 2024. This means they have been inundated for over 4 months, an ideal duration for many aquatic species to complete their life cycles.