New research led by UNSW Sydney's Centre for Ecosystem Science has revealed the alarming extent of decline of streamflow in one of the continent's longest rivers, the Murrumbidgee River in Australia's Murray-Darling Basin.
Over the past three decades, the river has lost 55% of its water at the town of Hay, due to the building of dams and upstream water diversions for human activities. The most severe impacts are being felt in the river's largest wetland, the Lowbidgee Floodplain (3250 km2), a critical ecosystem with significant environmental and cultural values that depends on regular flooding to thrive.
With the effects of climate change, major overbank flows – the vital flooding that sustains these wetlands – could drop by up to 85% under river regulation and projected climate scenarios until 2075, threatening the plants, animals, and people who rely on this water. A team of researchers from UNSW's Centre for Ecosystem Science and Water Research Laboratory, in partnership with the Nari Nari Tribal Council and CSIRO Environment, has conducted a comprehensive analysis of the changes in river flow patterns in the lower Murrumbidgee River since 1890. Their findings, published in the international Journal of Environmental Management, underscore the urgent need for action to protect riverine ecosystems.
Floods: essential for wetlands
Over the last century, 26 major dams and reservoirs have been built along the 1700 km Murrumbidgee River, diverting much of the natural flow for irrigation. What may seem like progress – longer periods between major floods – can be devastating for the environment.
"Flooding isn't something to fear in these wetlands – it's essential for life to thrive," says Jan Kreibich, the PhD candidate at UNSW who led the study.
"The Lowbidgee Floodplain depends on regular inundation. Without it, entire ecosystems are collapsing."
This floodplain is home to one of Australia's largest lignum shrublands, expansive river red gum and black box forests, freshwater turtles, the endangered Southern bell frog, and critical fish refugia. It's also a vital breeding ground for large colonies of waterbirds.
But the importance of the Lowbidgee Floodplain goes beyond its ecological significance. For the Nari Nari people, who have lived on this land for tens of thousands of years, these wetlands hold deep cultural and spiritual value. Their long history with the land is evidenced by earth mounds, burial sites, scar trees and middens. In 2019, 880 square kilometres of the Gayini Wetlands – a major part of the Lowbidgee Floodplain – were returned to the Nari Nari Tribal Council after 180 years of dispossession. However, the drying up of these wetlands threatens not just the environment but also their cultural heritage.
Jamie Woods, one of the authors and Nari Nari Tribal man as well as General Manager of Gayini wetlands making up much of the area, says: "This is a wake-up call about how much damage has been done to our Country and cultural and environmental values from upstream development, with climate change further reducing flows."
River regulation and climate change
While climate change poses a serious threat, the study highlights that river regulation has had an even greater impact so far. Human-made interventions have caused flood return periods to more than double, disrupting the natural cycle that keeps these wetlands healthy.
"Climate change could reduce river flows by another 7-10% by 2075, adding to the impacts of water management which were 5-8 times greater," explains author Professor Richard Kingsford, Director of UNSW's Centre for Ecosystem Science.
"The main driver of change right now is river regulation. That's something we can change if we choose to."
The UNSW researchers created models to simulate natural river flows, showing how the Murrumbidgee would behave without the interference of dams and irrigation diversions. They compared these models to observed river flow data and ran future climate change scenarios using global climate models.
Their research offers a clear message: addressing the impacts of river regulation is the most immediate and effective way to protect the Murrumbidgee River's freshwater ecosystems. By restoring more natural water flows, it's possible to build resilience against future climate challenges.
"This research highlights how the ecosystem is suffering a death by a thousand cuts. Each upstream diversion is another cut on the downstream wetlands," says author Professor William Glamore from UNSW's Water Research Laboratory.
A call to action
"There's hope for the Murrumbidgee River system, but we need to act now," says Mr Kreibich. "If we increase water-use efficiency, especially in irrigation, and the delivery of targeted environmental flows, we can help restore these ecologically and culturally significant floodplain wetlands."
The researchers are calling for better management of Australia's freshwater ecosystems to protect biodiversity, reduce the impacts of climate change, and honour the cultural heritage of First Nations Peoples. "This is about more than just the environment – it's about our shared future," Mr Kreibich adds.
