An unsustainable level of take: on-farm storages and floodplain water harvesting in the northern Murray–Darling Basin, Australia

ABSTRACT

Water resources for irrigation in the Murray–Darling Basin have been heavily over-allocated, with major detrimental effects on wetlands and rivers. The Murray–Darling Basin Plan is intended to return water from irrigated agriculture to the environment but requires comprehensive, accurate water accounting to achieve this objective. Floodplain harvesting – the diversion and storage of overland flows into on-farm dams – is widely practised by irrigators in the northern Basin. By reducing volumes of river flows, floodplain harvesting has negative effects on downstream water users and the environment. The volume of diversions is not known, creating a major source of uncertainty over water availability and use. We focussed on floodplain harvesting in northern New South Wales (NSW) catchments (Border Rivers, Gwydir, Namoi, Macquarie and Barwon-Darling) because the NSW government is attempting to licence and regulate the practice. We found in 2019–20 there were 1,833 storages in these catchments with a total surface area of 42,650 ha. Storage capacity has risen from 557 GL in 1993–94 to 1,067 in 1999–2000, 1,225 in 2008–09 to 1,393 GL in 2019–20, a 2.5-fold increase in 26 years. We estimated mean annual floodplain harvesting take (2004–2020) in northern NSW was 778 GL (range 632–926 GL). For context, this volume represents half of the mean volume of held environmental water released annually for the entire Basin between 2009–10 and 2018–19 (1,576 GL) and six times that for the northern NSW Basin (125 GL). The volume of take from floodplain harvesting is not sustainable and in breach of legislation on water use and management. We discuss the negative impacts of floodplain harvesting on downstream communities and flow-dependent ecosystems and their social justice implications.

KEYWORDS:

• Water resource development
• water reform policy
• water accounting
• upstream-downstream effects
• remote sensing
• Landsat detection of water

Acknowledgments

We thank Albert van Dijk for advice on techniques and access to remote sensing imagery and Abbas Mohammadi for technical assistance in the verification of dams from that imagery. PB, MS and WJ acknowledge support from Southern Riverina Irrigators, Southern Connected Basin Communities, Dharriwaa Elders Group, Berrigan Shire, North Victorian Irrigation Communities, Tolarno Station, Wentworth Shire Council, Brewarrina Shire Council, Sunraysia Citrus Growers, Inland Rivers Network, Australian Floodplain Association, Darling River Action Group, Wilcannia Tourism Association, West Darling Outdoor Recreation and Hunting Club, West Darling Fishing Club, First Nation’s Women’s Water Alliance and Murray Lower Darling Rivers Indigenous Nations. MJC is an affiliate of the Water Group within the Wentworth Group of Concerned Scientists. He did not receive funding for this work.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary material

Supplemental data for this article can be accessed here.

Notes

1 The DPIE legal advice of 2 October 2020(document 544) is available here: https://drive.google.com/drive/folders/1k13W2LMEQ-kMGreH1Ov7gYD33kfRMPM1

Additional information

Notes on contributors

Patrick Brown

Patrick Brown is a civil engineer, currently undertaking a PhD at the Fenner School of Environment and Society, The Australian National University. His research interests include public policy and management of water resources.

Matthew J. Colloff

Matthew Colloff is an Honorary Senior Lecturer at the Fenner School of Environment and Society, The Australian National University, His research interests include adaptation to climate change, water reform, ecosystem ecology and natural resources policy and management. He is a founder member of the Transformative Adaptation Research Alliance.

Maryanne Slattery

Maryanne Slattery is a Director of Slattery & Johnson. Her research interests include water policy and management in Australia.

William Johnson

Bill Johnson is a Director of water policy management consultants Slattery & Johnson. His research interests include the Murray-Darling Basin, whether it is possible to develop new governance institutions able to respond to increasing conflict over water, and how to include the needs and interests of marginalised groups.

Fiorenzo Guarino

Enzo Guarino is an adjunct at the Centre for Applied Water Science at the University of Canberra. His research interests include ecohydrology, ecology and natural resources management. He has a broad interest in fostering research that underpins decisions on the management of our natural environment.