Basin states, the Commonwealth Environmental Water Holder and the MDBA worked together to deliver 2,250 GL of environmental water to the annual watering priorities during 2015–16. The water delivered includes return flows (parcels of water delivered at multiple downstream sites) and a small amount of planned environmental water.
The majority of the water was used for increasing flow variability and longitudinal connectivity, and maintaining waterbird habitat. Maintaining flow variability and longitudinal connectivity will assist in protecting and maintaining the condition of refuge areas (places where birds can survive during the drought). Figure 14 shows the different types of flow that make up the flow regime.
Outcomes for fish, birds and vegetation were improved by aligning watering with biological cues and topping up (or piggybacking) existing flows with environmental water. Water that drained back into the rivers following watering events was also re-used for other priorities downstream.
Collaboration between governments to combine their water holdings, coordinate watering events and reuse water is important for achieving better environmental outcomes. Collaboration is even more critical in dry times, when it can be difficult to meet watering priorities. During 2015–16, 86% of all the environmental water used in the Murray–Darling Basin was in combined watering events.
In the mid-Murrumbidgee, low water availability and community concerns about flooding of private property meant that some important flows were not able to be delivered to the Mid-Murrumbidgee Wetlands in 2015–16. The shift to wetter conditions later in 2016 meant the wetlands received water.
Environmental water was also used to help maintain the condition of Moira grass in the Barmah-Millewa Forest. However, only part of the Moira grass could be watered due to low water availability and operational delivery constraints limiting flows to 15,000 ML/day in the River Murray below Yarrawonga. These two examples highlight the importance of long-term water planning and addressing constraints to ensure environmental water can be delivered as efficiently and effectively as possible. See adapting the sustainable diversion limits for more information about addressing constraints.
At the end of the river system, positive benefits were achieved for the Lower Lakes. These included improving the condition of vegetation on the fringes of the lakes, and aiding native fish movement.
Hattah Lakes water management structure
The flow regime and its connection to river ecology
The flow regime of rivers and streams is often categorised into the following components, each of which is important to ecosystem health and maintaining ecological functions and processes.
Overbank flows connect the river to the floodplains and wetlands. These flows provide opportunities for fish and invertebrates to move out of the river channel to forage and reproduce. Overbank flows provide habitat and food for bird breeding.
Bankfull flows are the larger flow events that fill the river channel and may inundate channel benches, the riparian zone, anabranches and low parts of the floodplain. They are important for the water-dependent ecosystem surrounding the floodplain. These flows also provide opportunities for birds to breed and allow fish to move.
Freshes are small-to-medium flow events that inundate benches or small anabranches, but stay in the river channel. They are generally relatively short in duration (i.e. a few days to a month). These flows replenish soil water for riparian vegetation, maintain in-stream habitats and cycle nutrients between parts of the river channel.
Base flows are an important component of the flow regime — they maintain aquatic habitat for fish, plants and invertebrates. Base flows comprise long-term seasonal flows which provide drought refuge during dry periods and contribute to nutrient dilution during wet periods or after a flood event.
Longitudinal and lateral connectivity support ecological processes that are dependent on hydrologic connectivity: both longitudinally, along rivers; and laterally, between rivers and their floodplains and wetlands. The maintenance of natural patterns of longitudinal and lateral connectivity is essential to the viability of populations of many riverine species.
Figure 14: A river cross-section showing components of a flow regime
Outcomes for watering priorities
This section briefly describes outcomes for each of the 11 watering priorities for 2015–16, and the volume of water delivered to each priority. The volumes include ‘overlaps’ where environmental water contributed to meeting multiple priorities. For example, water that was primarily delivered to meet the flow variability and connectivity priority also provided benefits for the native fish habitat and movement priority.
1. Basin-wide flow variability and connectivity
Around 1,500 GL of environmental water was used to enhance the connectivity of rivers and increase flow variability throughout the Basin. This included return flows, (i.e. water that passed through a site or wetland, and was used for environmental benefits further downstream). The water provided many benefits, including protecting and maintaining the ecological condition of critical refuge areas.
In the northern Basin, this priority included providing environmental flows to enhance natural flows in the Macquarie Marshes, and to maintain resilience for fish and vegetation in the Gwydir, Condamine, Moonie and Border rivers. These flows also enhanced connectivity through the Darling to the Menindee Lakes. In the southern Basin, the water provided benefits at multiple locations, including the Barmah–Millewa Forest, and in the Coorong, Lower Lakes and Murray Mouth.
2. River Murray weir pool variation (Euston to Blanchetown)
Careful management of weir pools by raising and lowering water levels at particular times can help mimic the naturally variable flows that would have occurred in the past. In 2015–16, weir pool management activities were used to create spring flushes and localised inundation, and to maintain base flows, including for the Lindsay-Wallpolla Islands area. Weir raising combined with river flows and pumping also enable environmental water to be delivered to Lake Wallawalla. These activities provided benefits for fish and vegetation through enabled wetland inundation, reinstating faster and slow moving habitat for fish and supporting connectivity.
3. Coorong, Lower Lakes and Murray Mouth
Around 900 GL of environmental water flowed through to the end of the River Murray system during 2015–16. Much of the water that reached the Coorong, Lower Lakes and Murray Mouth was delivered to meet the Basin-wide flow variability and connectivity priority, and provided benefits throughout the River Murray system. The water helped improve water quality and contributed to meeting the Basin Plan salinity targets at Morgan and the Lower Lakes.
The water was also used to maintain freshwater flows into the Coorong, aid native fish movement and improve the condition of vegetation fringing the Lower Lakes. Fish monitoring showed the total number of species present in the region was similar to previous years, and there was a high number of juvenile fish, indicating strong recruitment and survival. However, total fish abundance was lower than previous years.
The delivery of environmental flows in winter also helped fish migrate hundreds of kilometres upstream to breed.
Fish movements through fishways
The southern Murray–Darling Basin provides important habitats for a number of fish species, and the Coorong and Lower Lakes support 43 different fish species. This represents more than 50% of the fish species found within the Basin.
Water regulation structures built along rivers, including weirs and dams block fish movement, preventing fish from migrating along the river, breeding and carrying out their natural life cycle. This has led to the need to build effective fish bypasses or fishways to restore fish passage along the River Murray. The MDBA began the Sea to Hume fish passage project in 2001. As part of the project, 15 fishways were installed and this is assisting the Coorong, Lower Lakes and Murray Mouth Recovery project to ensure that each barrage has at least one fishway by 2017.
Historically high catches of congolli, common galaxias and the eel-like pouched lamprey were recorded following an environmental water event in winter 2015 in the Coorong, Lower Lakes and Murray Mouth.
One microchipped pouched lamprey was monitored travelling almost 900 km upstream. Like salmon, pouched lamprey need to migrate upstream from sea water to spawn. This once locally common species has become locally rare due to its migratory paths being blocked. Improvements in their numbers and movement are encouraging.
The environmental watering was a coordinated effort, delivered by the Commonwealth Environmental Water Holder, the South Australian Government and the MDBA on behalf of The Living Murray initiative.
4. Basin-wide in-stream and riparian vegetation
In-stream and riparian or ‘river-edge’ vegetation of the rivers throughout the Murray–Darling Basin is vital to the functioning of riverine ecosystems. Around 560 GL of environmental water contributed to improving the condition of these areas and replenishing seedbanks.
Outcomes in the Macquarie Marshes illustrate that watering to improve vegetation condition can have positive effects for fish and waterbirds as well. In the Great Cumbung Swamp at the end of the Lachlan River, environmental watering replenished common reedbeds and river red gum woodlands. This led to thousands of waterbirds, including straw-necked ibis and yellow-billed spoonbills, gathering in the swamp to forage and breed.
5. Mid-Murrumbidgee Wetlands
A volume of 57 GL of water was delivered in the Mid-Murrumbidgee Wetlands. However, ongoing community concerns about the potential for watering to cause flooding of private property meant the volume delivered was much less than planned. Monitoring showed that the watering still provided benefits for vegetation, fish, frogs and waterbirds, including increased abundance of flathead gudgeons and Murray–Darling rainbow fish, high numbers of grey teals and black winged stilts.
The wetter conditions in winter 2016 provided much needed water to the wetlands and may alleviate the need to prioritise the site again in 2017–18.
6. Macquarie Marshes
Around 55 GL of environmental water was released in the Macquarie River to improve connectivity, reaching the marshes and maintaining some critical vegetation habitat. This year’s effort builds on the previous year, and has resulted in restoration of the reed beds and the congregation of colonial nesting birds.
Multiple year benefits of watering in the Macquarie Marshes
The Macquarie Marshes is an internationally-recognised Ramsar wetland and one of the largest freshwater wetlands in the Murray–Darling Basin. The Macquarie Marshes include large areas of reed beds, water couch, and river red gum forests and woodlands, which provide important breeding habitat for many species of colonial-nesting waterbirds.
During 2015–16, environmental water was used to assist the recovery of several reed bed areas that were burnt during the very dry years of 2014, 2015 and 2016.
Since the return to wetter conditions during the winter and spring of 2016, several waterbird colonies have been observed with birds nesting, including within the previously burnt areas. This has demonstrated the importance of delivering water to maintain the condition of wetlands during the dry times, ready for when wet conditions return. However, it is important to remember that this is a localised success. Successful breeding events will need to occur over many years and at multiple locations to redress the long-term decline in waterbird numbers.
Of course, environmental watering provides benefits to the whole wetland ecosystem, and the watering events through the dry years of 2014 and 2015 also benefited many other species. The New South Wales Office of Environment and Heritage and landholder monitoring undertaken throughout the system detected a range of frogs, waterbirds such as the Australasian bittern, bats, and vegetation communities benefitting from the flows.
7. Moira grass at the Barmah–Millewa Forest
Environmental water delivered downstream for the River Murray as a whole (343 GL) also supported watering of Moira grass (which received an additional 60 GL) and colonial nesting birds (which received an additional 27 GL) in the Barmah-Millewa Forest.
Moira grass watering priority in the Barmah–Millewa Forest
Watering to maintain the condition and range of Moira grass in the Barmah-Millewa Forest was a Basin-wide watering priority in 2015–16. In spring, governments were able to augment existing flows to increase the duration and extent of a watering event. This action was designed to build upon a successful watering of the forest two years earlier.
The delivery was restricted by the current regulated release limit of 15,000 ML/d from Yarrawonga Weir. This limit prevents delivery of larger volumes of water to the Barmah–Millewa Forest, which would be required to achieve optimum inundation of Moira grass. In 2015–16, only 20% of the forest was able to be inundated. The benefits of relaxing the delivery constraint, as well as other constraints across the Basin, are being assessed through a Constraints Management Strategy, and the constraint projects being developed by Basin states, as part of the sustainable diversion limit adjustment mechanism.
Despite the constraint, monitoring detected growth of the Moira grass, with some flowering and replenishment of the seedbank. The water was delivered as part of a multi-site watering action along the River Murray. About 80% of the water that reached the floodplain returned to the river enriched with food and carbon to provide further benefits downstream as an important food source for fish, yabbies and other river animals. The New South Wales Office of Environment and Heritage, the Victorian Environmental Water Holder, the Commonwealth Environmental Water Office and the MDBA, on behalf of The Living Murray initiative, coordinated the delivery of the environmental water. This included 343 GL from the Commonwealth Environmental Water Holder and 60 GL from joint governments.
Following observations of waterbirds breeding in the Barmah–Millewa Forest there was a small follow-up environmental watering in the 2015–16 summer. Basin governments delivered an additional 27 GL to extend the watering and support the breeding of more than 1000 waterbirds. The environmental water helped waterbirds complete breeding cycles, so that the chicks could survive and successfully fledge. The monitoring also found a significant proportion (around 14%) of the global population of the endangered Australasian bitterns inhabiting and breeding in the forest.
8. Basin-wide waterbird habitat and future population recovery
Around 167 GL of environmental water was used to protect significant waterbird sites across the Basin. The emphasis was on maintaining the condition of bird refuges.
Due to the dry conditions of 2015–16, there were limited opportunities to support bird breeding. In the Barmah–Millewa Forest, 27 GL of watering was used to maintain water levels for colonial nesting birds to complete their nesting cycle, including up to 14% of the world’s endangered Australasian bittern population. Wetter conditions during winter provided an opportunity to use water to enhance breeding opportunities for birds in the Macquarie Marshes.
While localised bird breeding events were a positive outcome of the annual watering program, the total number of waterbirds across the Basin declined further, and similar to the previous year, waterbird breeding was at an all-time low. It will take many years to see if continued successes at the local and regional scales will be able to reverse the long-term decline in bird numbers across the Basin.
9. Basin-wide native fish habitat and movement
Over 157 GL of environmental water delivered during 2015–16 contributed to improving fish habitat and movement, with 45 GL of the water directly targeting this priority.
In the Gunbower Forest, tens of thousands of native fish were recorded moving from the River Murray back into Gunbower Creek, while in the Hattah Lakes, environmental flows encouraged golden perch to move back into the River Murray. In the Barmah–Millewa Forest, large-bodied native fish, including Murray cod and golden and silver perch spawned. In the northern Basin, environmental watering in the Macquarie and Condamine rivers supported connectivity and enhanced native fish movement.
10. Northern Basin fish refuges
More than 60 GL of environmental water was delivered to support the long-term recovery of native fish populations by protecting drought refuges and supporting connectivity in the northern Basin. The water helped maintain important populations of silver perch in the Border, Warrego, Condamine and Gwydir catchments by supporting recruitment and aiding fish movement and dispersal.
In the Lower Balonne, water managers used environmental water to replenish waterholes and provide connectivity between waterholes. The flows were timed to coincide with the breeding season of many native fish species and provided opportunities for fish to spawn.
11. Silver perch
Over 900 GL of environmental water, including water that was re-used at multiple locations, was delivered in response to this silver perch priority. This water resulted in benefits for silver perch throughout the Murray–Darling Basin. In the southern Basin, silver perch benefitted from watering in the Edward–Wakool, mid-Murray, and Murrumbidgee rivers. Monitoring showed that silver perch passed through almost all locks of the River Murray. Monitoring in the Edward–Wakool system indicated a 10-fold increase in silver perch recruitment compared with the 2014–15 year. In the mid–Murray, silver perch were detected spawning in October and November 2015.
Learning about fish
Each year Basin governments and scientists learn more about the conditions required to trigger fish spawning, and are using this information to guide future watering. For example, silver perch and golden perch larvae were detected in the River Murray this year following environmental watering. However, spawning does not occur every time a similar flow cue is provided. This suggests that other environmental factors may be in play. Monitoring the outcomes of watering events and collecting data over many years will help improve knowledge about the conditions required for spawning so watering strategies can be adapted accordingly.
As with natural flooding, environmental water also contributes to carp breeding. While carp continue to make up the largest biomass of fish species in the Basin, governments are considering ways to reduce the carp population and ensure the benefits of environmental water for native fish are maximised.