A trickle, not a flood: environmental watering in the Murray–Darling Basin, Australia
FULL REPORT
Summary of "A trickle, not a flood: environmental watering in the Murray-Darling Basin, Australia" (2021)
Overview
Published in 2021 in Marine and Freshwater Research, this study by Yiwen Chen, Matthew J. Colloff, Anna Lukasiewicz, and Jamie Pittock from The Australian National University evaluates environmental watering in the Murray-Darling Basin from 2012-13 to 2018-19. The research assesses the Commonwealth Environmental Water Office (CEWO) flows from 2014-15 to 2018-19, compares outcomes with the Basin-wide Environmental Watering Strategy (EWS), and incorporates insights from water manager interviews. It highlights deficiencies in achieving wetland conservation goals under the Murray-Darling Basin Plan.
Background
The Murray-Darling Basin spans 1.06 million square kilometers in southeast Australia, hosting 30,000 wetlands covering 25,000 square kilometers, including 16 Ramsar sites. Historically altered by grazing, timber harvesting, and river regulation, the Basin’s ecosystems have been further stressed by irrigation diversions, drought, climate change, and floodplain harvesting. The Basin Plan, enacted under the Water Act 2007, aims to reallocate 2,750 gigaliters per year from irrigators to the environment, managed by the CEWO and state agencies, to restore flow-dependent ecosystems.
Key Findings
The study found that only 21% of CEWO water was delivered as flood events, reaching 9 of 19 river valleys and inundating 7% of wetland areas in those valleys annually, equating to just 0.8% of major Basin wetlands. Small wetlands along the South Australian Murray received frequent small volumes (median 43 hectares, 125 megaliters), while only 12% of river red gum areas targeted by the EWS were flooded, with half of these events likely insufficient for ecological benefits. Total environmental water averaged 1,905 gigaliters per year, below the 2,750-gigaliter target, with CEWO contributing 59% (7,893 gigaliters net total from 2012-13 to 2018-19).
Ecological Outcomes
Wetlands and flood-dependent vegetation, such as river red gum, black box, coolibah, and lignum, have not received adequate flooding to maintain their extent and condition. Only 8% of the managed floodplain area saw flooding, with events often too brief or poorly timed to meet ecological needs (e.g., river red gum requires 4-7 months of flooding every 1-3 years). This shortfall threatens biodiversity, including waterbirds and native fish, and the ecological character of Ramsar sites.
Constraints and Challenges
Interviews with 13 water managers revealed operational limits, including rules restricting flooding on private land (65% of the managed floodplain), insufficient water volumes, and delivery constraints due to downstream wetland locations. Reporting is fragmented and lacks detail on flood extent, depth, and duration, complicating adaptive management. Climate change, unaccounted for in the Plan’s sustainable diversion limits, exacerbates these issues amid a hotter, drier future.
Implications
The study concludes that current environmental watering is a “trickle, not a flood,” failing to deliver the magnitude, duration, and extent needed for wetland conservation. Institutional rigidity and political compromises, such as delays in addressing climate change until the 2026 review, hinder progress. A “triage by default” scenario has emerged, prioritizing smaller, accessible wetlands over larger, ecologically significant ones, risking the transition of many wetlands to dryland ecosystems.
Recommendations
The authors advocate relaxing rules on flooding private land to enhance water delivery efficiency and effectiveness. They call for improved monitoring with detailed inundation data and conceptual ecosystem models to support adaptive management. Reframing water policy to prioritize key wetlands under climate change pressures is deemed essential to meet the Basin Plan’s statutory goals by 2024.
Conclusion
This research underscores significant gaps between environmental watering intentions and outcomes in the Murray-Darling Basin. Without substantial policy and management reforms, the Plan’s ecological objectives—resilient wetlands, healthy vegetation, and thriving biodiversity—remain unachievable, necessitating urgent action to align water delivery with ecological needs and future climate realities.