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The rivers of the south-eastern Murray-Darling Basin (MDB) and the associated irrigation areas of the southern riverine plain (SRP) in south-eastern Australia have undergone major hydrological changes over the last 30 years. These include a period of lower rainfall; a rebalance of surface water diversions between consumptive and environmental water uses under the MDB Basin Plan, improvements in water infrastructure; water trade out of the region; and falling groundwater levels. All these changes increase losses from streams to groundwater systems; potentially leading to the need for greater releases from dams to maintain baseflow in the major rivers. Baseflow is important for conveyance of water, water quality and baseflow-dependent ecosystems during dry periods. Hydrological changes in the SRP will reduce the streamflow by 2029–30 by an estimated 80 to 320 GL/yr. Further hydrological changes by 2029–30 will reduce the streamflow by another 50 GL/yr in the following decade. This is the first assessment of the cumulative stream impacts of the SRP and is relatively lower than previous assessments for single drivers. The current approach of mitigating unexpected losses is to increase conveyance loss budgets as required. This could be extended to mitigate the lower end of potential impacts; but further steps to reduce losses may be required towards the upper end. Further actions include a review of extraction limits for surface water and groundwater, trigger levels, and a greater shift towards conjunctive water management. Groundwater extraction, which has dominated impacts, is increasing from a relatively low proportion of the extraction limit in Goulburn-Murray Sedimentary Plain and shallow aquifers of the SRP. Over time, climate change will become more dominant as a driver. Most monitoring required to support mitigation already exists, but data is not collated or reported in a form relevant for stream impacts. Modelling also needs to be updated with reporting of more relevant outputs. [ABSTRACT FROM AUTHOR]

For over two decades, Australia has sought to address the effects of the over allocation of water resources in the Murray-Darling Basin through implementation of the Murray Darling Basin Plan (2012). It is increasingly apparent that the impacts of climate change on surface runoff and water demand will profoundly impact rivers, potentially negating the Basin Plan's achievements. It will be critical that we use the lessons from the last two decades to inform adaptation to climate change. Environmental water allocations over the last decade have focussed on providing base flows, freshes, and overbank flows, within a Natural Flow Regime paradigm. In a climate-changed world managers have three broad options. The first would be to continue to pursue single loop adaptive management making improvements within the existing framework. The second option would be to adapt the system approach to focus on a subset of sites, akin to maintaining aquatic reserves. The third option would be to move flow management away from the natural flow paradigm to a more functional regime. This approach would invoke the second adaptive management loop by evaluating options for adaptation and developing processes for navigating trade-offs among social, economic, cultural, and environmental values and between protection, restoration, and adaptation. Changes in water availability because of climate change will require more than incremental adaptation (first loop adaptive management) and will necessitate consideration of either protecting a smaller suite of spatial areas or a smaller set of functional outcomes. This requires profound change to some of the Basin Plan's approaches to environmental flow management. The review of the Basin Plan in 2026 provides a rare opportunity to adapt the Basin Plan from a foundation of protect and restore to one that includes adaptation, and this will require substantive changes to the Basin Plan (second loop adaptive management). [ABSTRACT FROM AUTHOR]

Australia's water management futures are again under discussion as drought impacts and bushfires hit communities. Water and ecological system limits are being reached resulting in fish kills and dwindling water levels in storages. Awareness is also rising around the inequities in current water governance regimes for First Peoples across the Australian continent and beyond. Here we provide a brief overview and research on: the ingenuity of Indigenous waterscape and landscape knowledge and practices to care for country and community, including the development of agricultural systems and sophisticated fish and eel trapping systems that are thousands of years old; the devastating impacts of colonisation on First Peoples, their country and ability to maintain some cultural practices; and the ongoing contestation over water governance, right from Federation, including the eight waves of water reforms in the Murray-Darling Basin. Current challenges and needs for reform are also presented including: hydrological scientific uncertainties, such as around return flows and their adjustment due to irrigation infrastructure efficiency increases, and new design methodologies, such as for flood estimation inputs to hydraulic models; adjusting current governance regimes of sustainable diversion limits and water markets to provide alternative value to Australia, beyond economic value drivers, that better respond to the benefit of all basin communities in the face of ongoing extreme climate variability and climate change; and determining positive ways forward for truly valuing and allowing First Peoples' knowledge, practices, culture and law to provide a basis for developing the next waves of Australia's water management reform journey. [ABSTRACT FROM AUTHOR]