Download the full report below ▼

Evaluating the contribution of Commonwealth environmental water to observed environmental outcomes

Our approach:

To undertake the Basin-scale evaluation, the evaluation team use water delivery and outcomes data provided by the CEWH’s Science Program, along with monitoring data provided by the 7 Selected Areas. Other publicly available data may be used where the relevant data are not collected by the Selected Areas.   Evaluation of the contribution of Commonwealth environmental water to observed environmental outcomes for the 6 Basin Themes is dependent on the data available.  When delivered with other water, ecological outcomes cannot be apportioned with current methods and Commonwealth environmental water is reported as contributing to, or supporting, the environmental outcomes of the watering action.  For the 2022-2023 year:

• The multi-year Hydrology (instream), Fish and Vegetation themes have sufficient data to model and compare environmental outcomes both with and without Commonwealth environmental water (counterfactual modelling²). 
• The Ecosystem Diversity, Species Diversity and Vegetation themes identify environmental responses in locations that received Commonwealth environmental water (often in conjunction with other sources of environmental or non-environmental water) and, where feasible, compare with areas that did not receive Commonwealth environmental water.³ 
• The Hydrology (inundation) and Food Webs and Water Quality themes use flow and water quality metrics to infer likely outcomes.³
• The Fish (annual), Vegetation (annual), and Food Webs and Water Quality themes summarise findings across Selected Areas. 

NB: Monitoring of ecological outcomes was constrained in 2022–23 due to wet conditions. Outcomes reported for the 2022–23 water year are based on fewer monitoring locations and should be interpreted with caution.

Partnering on watering actions 

Commonwealth environmental water is often delivered in conjunction with other environmental water holdings and non-environmental water releases (such as for irrigation or during high-flow events). Commonwealth environmental watering actions for the 2022–23 evaluation year and cumulative over the 9 evaluation years (2014–15 to 2022–23) are provided in Table 1. 

Table 1 Summary statistics for most recent evaluation year and multi-year evaluation period 

Dash (–) statistic not available. CEW = Commonwealth environmental water 

Evaluation reporting 

Each Basin Theme prepares a technical evaluation report for each water year. Key outcomes and lessons for adaptive management from these evaluation reports are brought into this annual synthesis report together with relevant outcomes from research highlights. To provide consistency over the life of Flow-MER and its predecessors, some content from these annual reports may be reused from previous years. In these cases, all efforts have been made to cite the relevant Long Term Intervention Monitoring, Environmental Water Knowledge and Research or Flow-MER publication. All reports published by the CEWH are available from the Australian Department of Climate Change, Energy, the Environment and Water website. 

Flow-MER partnership 

Basin-scale Flow-MER is led by CSIRO in partnership with the University of Canberra. Collaborators on the 2022–23 evaluation include Alluvium, the Arthur Rylah Institute, Charles Sturt University, South Australian Research & Development Institute, NSW Department of Primary Industries, the Australian River Restoration Centre and Brooks Ecology & Technology

Royal spoonbill (left) and Australian white ibis (right) foraging in a temporary warrambool (wetland) that adjoins the Gwydir Warrambools. Photo credit, Tamara Kermode, 2rog.

Executive summary 

Strategic management of Commonwealth environmental water by the Commonwealth Environmental Water Holder (CEWH) is central to achieving (Murray–Darling) Basin Plan 2012 (the Basin Plan) objectives. Water for the environment is strategically used by the CEWH to protect and restore hydrological regimes and connectivity within and between water-dependent ecosystems (Basin Plan S8.06). This involves connecting river reaches during dry times and connecting the river to the floodplain during wetter periods, as well as connecting and maintaining in-channel habitat and providing cues for breeding and movement. 

Commonwealth environmental water delivery in 2022–23 

Annual rainfall in 2022–23 was above or equivalent to the long-term average in Basin valleys. Total runoff in the Basin in 2022–23 was 67,760 GL, much greater than the average of 33,271 GL per year since 2014, when monitoring of Commonwealth environmental water began. Following very wet conditions in 2021–22, high rainfall resulted in high inflows across the Basin. Basin storages started at 91% of total capacity (20,216 of 22,258 GL) in July 2022, increasing to 100% through the water year. High volumes of surface water runoff in 2022–23 generated high flows across Basin river systems, especially in the late winter and spring of 2022, resulting in overbank flooding and extensive floodplain inundation. 

Many planned watering actions were not delivered in 2022–23 due to high natural flows; however, wet conditions provided opportunities to extend the duration of inundation of floodplains, wetlands and marshes, providing habitat and resources for recruitment and growing cycles for a range of species. 

• In 2022–23, 102 watering actions delivered 1,385 GL of Commonwealth environmental water to rivers, wetlands and floodplains across all 19 Basin valleys where the CEWH holds entitlements. 

• Commonwealth environmental water supported 22,205 km of rivers, 202,071 ha of lakes and wetlands, 71,837 ha of floodplains and 23,768 ha of estuary in the Coorong and Murray Mouth. 

• Commonwealth environmental water was used to extend the duration of widespread natural flooding in the Condamine Balonne, Lachlan, Gwydir, Macquarie and Murrumbidgee valleys. 
• Despite above-average annual rainfall across the Basin, summer was relatively dry in southern valleys and 1,196 GL of Commonwealth environmental water was used to maintain flows in southern river systems. 

Basin-scale evaluation 

The Flow-MER Basin-scale evaluation assesses the contributions of Commonwealth environmental water to meeting environmental objectives stated in chapters 8 and 9 of the Basin Plan and in the Basin-wide environmental watering strategy (the Strategy). Six Flow-MER Themes are evaluated using data from Flow-MER monitoring locations in 7 Flow-MER Selected Areas plus data for the 19 Basin valleys where the CEWH holds water entitlements. This synthesis reports on outcomes from the use of Commonwealth environmental water since the beginning of Selected Area monitoring in 2014. The evaluation addresses how Commonwealth environmental water contributed to, supported or influenced environmental outcomes. Detailed findings and supporting evidence are presented in 6 thematic evaluation reports and 7 Selected Area reports (Basin-scale thematic evaluations and Area-scale evaluations are reported separately). 

Contribution to Basin Plan objectives since 2014 

Commonwealth environmental water has made substantial contributions to achieving the objectives and desired outcomes of the Basin Plan and the Strategy. Outcomes since 2014 are summarised below. For some outcomes, the evaluation can estimate the contribution of Commonwealth environmental water. In most cases, Commonwealth environmental water is shown to have supported outcomes (that is, in conjunction with other water delivery) or contribution is inferred from recorded observations at monitoring locations receiving environmental water. 

Biodiversity – to protect and restore water-dependent ecosystems 

What did Commonwealth environmental water contribute to ecosystem diversity? 

Since 2014, 15,443 GL of Commonwealth environmental water has supported 249,079 ha of lakes and wetlands, 187,486 ha of floodplains, 27,715 km of waterways and 23,768 ha of estuarine ecosystems, representing 85% of the diversity of aquatic ecosystems found in the Basin (as measured by Australian National Aquatic Ecosystems [ANAE] types). 

Using the ANAE classification system, 66 aquatic ecosystem types have been identified in the Basin, of which 64 ecosystem types (97%) are represented on the area of floodplain that is able to receive Commonwealth environmental water. The frequency of delivery of Commonwealth environmental water over the 9 years broadly aligns with the expected requirements of ecosystem types; that is, more frequent support of permanent rivers, lakes, meadows and permanent tall marsh, and less frequent inundation of temporary channels, swamps and floodplains. Between 2014 and 2023, Commonwealth environmental water supported 56 ecosystem types (85% of the types that occur in the Basin) on at least one occasion. 

What did Commonwealth environmental water contribute to species diversity? 

Commonwealth environmental water has supported submerged, amphibious and damp-loving plant species, native fish, waterbirds and a range of other fauna, including species of conservation significance. 

• The delivery of Commonwealth environmental water has played a substantial role in maintaining native plant species across the Basin. 790 plant taxa have been recorded at Flow-MER floodplain, wetland and riverine monitoring locations since 2014, including 520 native groundcover plant species, of which 101 species are listed as rare or threatened. 10% (79) of the recorded plant species have only occurred at locations that experienced a wetter hydrological regime because of environmental water. This includes submerged (2), amphibious (21) and damp-loving (14) species unlikely to persist without environmental water. 
• Since 2014, 15 native fish species have been recorded from sampling of adult fish communities from riverine monitoring locations and 20 species of frog were reported from wetland monitoring locations. Commonwealth environmental water has had a significant influence on the presence of southern bell frogs (listed as Vulnerable under the Australian Environment Protection and Biodiversity Conservation Act 1999 [EPBC Act]) and has supported nursery habitats for hatchling Macquarie turtles, long-necked turtles and broad-shelled turtles. 
• Widespread unregulated floodplain inundation triggered significant waterbird breeding events across the Basin in 2022 and 2023. There was large-scale breeding by aggregate-nesting waterbirds – Australian white ibis, Australian pelicans, royal spoonbill, yellow-billed spoonbill, straw-necked ibis, glossy ibis, little pied cormorant, little black cormorant, Australasian darter, great cormorant, nankeen night-heron, white-necked heron, white-faced heron, eastern great egret and plumed egret. Commonwealth and other environmental water was used in 2022 and 2023 to extend the duration of inundation in support of waterbird breeding. 
• Commonwealth environmental water has supported habitats of a wide range of waterbird species. Since 2014, 137 waterbird and raptor species, including 59 threatened or migratory species, were recorded from locations that received Commonwealth environmental water. One example is the Australasian bittern (listed as Endangered under the EPBC Act), which requires wetland and floodplain habitats with areas of tall emergent vegetation. Since 2014, 110 known locations of Australasian bittern received Commonwealth environmental water at least once. 

What did Commonwealth environmental water contribute to vegetation community diversity? 

Environmental water is preventing the loss of characteristic wetland and floodplain plants by maintaining wetter hydrological regimes. In the absence of Commonwealth environmental water, important assemblages of species would be markedly reduced in extent. There would be a reduction in vegetation community richness, with a high risk of permanent transitions to altered vegetation community assemblages and loss of resilience of water-dependent plant communities. 

• Delivery of Commonwealth environmental water since 2014–15 has resulted in distinct inundation regimes across the floodplains and wetlands of the Basin that display significant differences in functional and structural assemblages of vegetation. There is greater diversity and cover of submerged, amphibious and damp-loving species at locations that have wetter regimes because of environmental watering. In the absence of Commonwealth environmental water, many locations across the Basin would have experienced notably drier water regimes. It is very likely this would have resulted in the near-absence of submerged species and substantially less diversity and cover of amphibious and damp-loving species at these locations. 

What did Commonwealth environmental water contribute to sustaining native fish populations? 

Commonwealth environmental water has provided a range of benefits to native fish populations and supported critical life-history processes, such as recruitment, body condition and population growth. 

• Commonwealth environmental water is shown to have contributed to increased fish spawning, recruitment, frequency of occurrence, population growth rates, body condition and improved community composition in some monitoring locations for some species. Fish responses to Commonwealth environmental water delivery were primarily driven by reductions in the number of low-flow days and, to a lesser extent, increased average daily flows and changes in flow variability. 
• There was no loss of native species – 15 native fish species, including 6 key freshwater species as identified by the Strategy, have been detected over the monitoring program. The number of detected species fluctuated over the monitoring period, although changes were relatively minor and the majority of species were detected regularly. Murray cod spawning and recruitment to young-of-year occurred in most years. The 2016–17 Murray River hypoxic blackwater event and associated major fish death events, or possible fish emigration out of the area, resulted in marked reductions in recruits and adults in several monitoring locations. Murray cod populations have continued to steadily recover from these hypoxic blackwater events in recent years (though recruitment was minimal in most monitoring locations in 2022–23). 
• Flow-MER research showed that Commonwealth environmental water supported critical life-history processes of golden perch, including spawning, body condition and population growth. Between 2014 and 2023, spawning of golden perch increased with delivery of Commonwealth environmental water. Golden perch need hundreds of kilometres of connected flowing water for their spawning migrations and spawning often coincides with increased flow during spring and summer. Commonwealth environmental water helped maintain their habitat by providing connected flow events across regions and at critical times. 

———————————————————————————-

What did Commonwealth environmental water contribute to Ramsar wetlands in the Basin? 

11 of the 16 Ramsar wetlands in the Basin can receive Commonwealth environmental water. Since 2014, all 11 received Commonwealth environmental water at least once (in conjunction with other water delivery). 

• Commonwealth environmental water was delivered to 8 Ramsar sites in 2022–23, supporting approximately 165,000 ha of 51 different ecosystem types within the Ramsar estate. For example, in 2021–22, Commonwealth environmental water supported waterbird breeding in the Gwydir Wetlands, contributing to the first simultaneous breeding across Narran Lake Nature Reserve, the Macquarie Marshes and Gwydir Wetlands Ramsar sites in 24 years. In 2022–23, a wet spring stimulated waterbird breeding across these sites for a second consecutive year and Commonwealth and other environmental water extended the duration of natural flooding to maintain water at nesting and foraging sites. 

Ecosystem function – to protect and restore the ecosystem functions of water-dependent ecosystems 

What did Commonwealth environmental water contribute to the restoration of flow regime? 

Environmental flows are used to extend duration of flows, align the timing of flows more closely with the natural regime, or match the natural frequency of flow events. 

• Over the 9-year period, 27,715 km (52% of all the river length on the managed floodplain) was supported by Commonwealth environmental water, which plays a more significant role during drier periods. For example, Commonwealth environmental water contributed over 97% of total flow in the Darling River at Bourke in 2017–18. Commonwealth environmental water supported a 10% overall increase in flows in the Barwon Darling in 5 out of 9 years of monitoring. The exceptions were the wet periods of 2016–17 and 2020–23, where unregulated water inflows were significantly high. Commonwealth environmental water supported a 30% overall increase in flows in the Murray River in 2015–16, 2017–18 and 2019–20, all of which were significantly dry periods across the Basin. 
• The Strategy sets flow volume and depth targets for the Coorong, Lower Lakes and Murray Mouth. In drier years, Commonwealth environmental water contributes up to 100% of flows at the barrages. In most years, except in wetter years such as 2021–23, barrage flow requirements are not met, even with Commonwealth environmental water. 

What did Commonwealth environmental water contribute to patterns and rates of ecosystem respiration and primary productivity? 

• Over the 9-year period, riverine ecosystems of the Goulburn, Edward/Kolety–Wakool, Lachlan, Gwydir and Junction of Warrego and Darling river systems were predominantly heterotrophic, that is, consuming more carbon than they were producing.  
• The Lower Murray River was mostly a net producer of carbon (autotrophic) up to 2021–22, driven by phytoplankton and relatively low turbidity in the slow-flowing channels. However, high flows in 2022 shifted the Lower Murray River into heterotrophy, reflecting a return to a flowing system more closely resembling metabolic patterns at other Areas. The Murrumbidgee River System regularly alternated between heterotrophy and autotrophy over the 9 years, depending on conditions (such as season). 
• Independent of Commonwealth environmental watering actions, rates of gross primary production are most strongly influenced by seasonal changes (e.g. light and temperature) and site-specific drivers, such as bioavailable nutrient concentrations and reduced light availability due to turbidity. 

Water quality – to maintain water quality and meet targets for salt export, salinity and dissolved oxygen 

What did Commonwealth environmental water contribute to dissolved oxygen levels and salinity regimes? 

In low-flow years, Commonwealth environmental water has become increasingly important for managing dissolved oxygen levels, sustaining salt export from the Basin and for limiting salt import to the Coorong. 

• The Basin Plan target for dissolved oxygen is to maintain a value of at least 50% saturation, which equates to a dissolved oxygen concentration of approximately 4–5 mg/L. In drier years, delivery of Commonwealth environmental water has decreased the likelihood of low dissolved oxygen in the Lower Murray by increasing water mixing and oxygen exchange at the surface and elevating flow velocity above 0.18 m/s. 
• The Basin Plan salt-export objective (2 million tonnes per year) aims to ensure adequate removal of salt from the Murray River system into the Southern Ocean. Commonwealth environmental water has resulted in over 4 million additional tonnes of salt export through the barrages and has reduced salt import by more than 26 million tonnes since 2014. Commonwealth environmental water is important for maintaining salt export from the Basin and limiting net salt import to the Coorong during drier years. 
• Commonwealth environmental water contributed to maintenance of river salinity (electrical conductivity) below 800 µS/cm at Morgan over the 2014–23 period. Salinity was maintained within the range required for potable water in the Murray River in 2014–23, with water about 10% fresher due to environmental flows. 

Key findings 

Strategic management of Commonwealth environmental water by the CEWH is central to achieving the Commonwealth’s Basin Plan objectives. The Flow-MER Basin-scale Project evaluates the ecological responses to the delivery of Commonwealth environmental water to support legislative requirements under the Basin Plan, inform adaptive management, and support environmental water managers. This evaluation reports on outcomes from the use of Commonwealth environmental water for the most recent water year (2022–23) and cumulative outcomes since the beginning of the program in 2014. It assesses the contribution of Commonwealth environmental water to Basin Plan objectives and provides considerations for adaptive management. Monitoring was constrained in 2022–23 due to wet conditions. Outcomes reported for the 2022–23 water year are based on fewer monitoring locations and should be interpreted with caution. 

The most recent water year, 2022–23 

• In 2022–23, 102 watering actions delivered 1,385 GL of Commonwealth environmental water to rivers, wetlands and floodplains across all 19 Basin valleys where the CEWH holds entitlements. 

• Rainfall in 2022–23 was above the long-term average in most valleys in the Basin. Wetter conditions meant that Commonwealth environmental water was used to extend the duration of widespread natural flooding in the Condamine Balonne, Lachlan, Gwydir, Macquarie and Murrumbidgee valleys. 

• Despite wetter conditions across the Basin during most of the year, summer was drier in the south and 1,196 GL of Commonwealth environmental water was used in southern valleys to maintain flows. 

• Commonwealth environmental water supported 22,205 km of rivers, 202,071 ha of lakes and wetlands, 71,837 ha of floodplains and 23,768 ha of estuary in the Coorong and Murray Mouth. 

• Basin Plan target flow volumes were achieved for the Coorong, Lower Lakes and Murray Mouth in 2022–23 through a combination of natural and other flows and Commonwealth environmental water. Water-level thresholds in the Lower Lakes were maintained (Basin Plan objective 8.06). 

• 437 GL of Commonwealth environmental water were delivered to 8 Ramsar sites in 2022–23. 

• Of 66 ANAE types found in the Basin, the Commonwealth can deliver environmental water to 64 representative types. In 2022–23, Commonwealth environmental water was delivered to 53 types (or 83% of those able to receive it). 

• Due to high natural flows, Commonwealth environmental water made a relatively small contribution to salt export, exporting 151,000 tonnes of salt (5% of total salt export to the ocean) in 2022–23. 

• Commonwealth environmental water supported submerged, amphibious and water-dependent plant species: 291 plant species were recorded at wetland and riverine monitoring locations in 2022–23 – 73% were native and 10 species were observed at these locations for the first time. 

• 43 groundcover plants known to be used by Aboriginal people were recorded, including 12 only seen at locations that experienced a wetter inundation regime because of environmental water. 

• 13 native fish species were detected in 2022–23 at Flow-MER monitoring locations, including an adult river blackfish (Gadopsis marmoratus) detected in the Edward/Kolety–Wakool for the first time. 

• Spawning of golden perch (Macquaria ambigua), a key fish species as denoted by the Strategy, occurred in the Goulburn River. In the Lower Murray River, there was evidence of Murray cod (Maccullochella peelii) recruitment and golden or silver perch eggs were detected during unregulated high spring flows. 

• Australian smelt (Retropinna semoni) had higher abundances (representative of recruitment for this short-lived species) than in previous years in the Edward/Kolety–Wakool and Murrumbidgee river systems, likely because greater hydrological connectivity increased favourable breeding habitats. 

• Exotic common carp (Cyprinus carpio) and goldfish (Carassius auratus) displayed strong recruitment, likely due to unregulated high flows and overbank flooding providing favourable conditions. 

• 84 species of waterbirds, including 35 species of conservation significance, were reported from the Warrego, Darling, Murrumbidgee, Macquarie, Central Murray, Lachlan and Condamine valleys and aggregate-nesting species were recorded breeding across multiple valleys. 

• 11 frog species, including the southern bell frog (Litoria raniformis), a species of conservation significance, were reported from Flow-MER and NSW monitoring in the Murrumbidgee and Lachlan valleys. 

Multiple water years, 2014–23 

• Over the 9-year period, 15,443 GL of Commonwealth environmental water were delivered to 56 ecosystem types representing 249,079 ha of lakes and wetlands, 187,486 ha of floodplain, 27,715 km of waterways and 23,768 ha of estuarine ecosystems. 

• Between 2014 and 2023, all 11 of the 16 Ramsar sites able to receive Commonwealth environmental water were inundated. 

• Commonwealth environmental water has resulted in over 4 million additional tonnes of salt export through the barrages and has reduced salt import by more than 26 million tonnes since 2014. 

• Commonwealth environmental water has been used to decrease the likelihood of, and support recovery from, widespread hypoxic events across the Basin. 

• Commonwealth environmental water supported 45% of floodplain–wetland Flow-MER monitoring locations, contributing to diversity and cover of submerged, amphibious and damp-loving plant species. 

• 790 groundcover plant taxa were recorded at monitored floodplain, wetland and riverine locations since 2014, including 520 native and 216 exotic species; 75 taxa are known to be used by Aboriginal people, including 33 that require flooding to occur. 

• 101 groundcover plant species that are listed as threatened were recorded at monitoring locations. 

• 15 native fish species and 5 exotic fish species were detected during the 9-year monitoring program by in-channel river sampling of adult fish communities. 

• Commonwealth environmental water contributed to increased fish spawning, recruitment, frequency of occurrence, population growth rates, body condition and improved community composition in some monitoring locations and for several species. 

• Positive fish responses to the delivery of Commonwealth environmental water were primarily due to reduced number of low-flow days, increased average daily flows and changes in flow variability. 

• Since 2014, 117 waterbird and raptor species have been reported – 59 of these are of conservation significance. 

• Commonwealth environmental water had a significant influence on the presence of southern bell frogs (listed as Vulnerable under the EPBC Act). 

Basin-scale Flow-MER summary metrics 2022–23