Great Lowbidgee Landscape
The Murrumbidgee

The Murrumbidgee

Protecting and restoring the rivers and wetlands of the Murrumbidgee Valley

OPINION: Local Engagement Officer for the Commonwealth Environmental Water Holder (CEWH) Michele Groat shares her thoughts on the response by CEWH to maximise the opportunities and minimise the risks of the recent floods affecting the Murrumbidgee. The Commonwealth Environmental Water Holder (CEWH) manages the water that has been recovered under Basin Plan initiatives including water efficiency projects and water purchases. In the Murrumbidgee, the CEWH manages a portfolio of High Security, General Security and Supplementary entitlements. Entitlements managed by the CEWH retain the same characteristics and rules (i.e. allocation, carry over and fees) as other licence holders.  

 

As a Local Engagement Officer for the CEWH I have been asked with all the flooding is there still a need for environmental water this year? Hasn’t nature done it all for us? Interestingly, while nature has done most of the heavy lifting there are still plenty of reasons environmental water is needed in wet years. So what do we use it for in a wet year?

 

Supporting Waterbird Breeding

 

As the old saying goes, “if you build it, they will come”. Over the past couple of years, Commonwealth and NSW environmental water managers have been working together with landholders, including the Nari Nari Tribal Council, to deliver water onto the floodplain to grow wetland plants, frogs and bugs in the lower part of the Murrumbidgee River (Lowbidgee). When the big rains and floods came last year, the wetlands were in good condition to support a large influx of waterbirds, with thousands of birds making the most of the very good habitat and food available in the Lowbidgee. Over 52 different waterbird species have been observed, including the nationally threatened Australasian Bittern, as well as grebes, ducks, black swans, herons and white-bellied sea-eagles…. the list goes on. Many of these waterbirds rely on floods and full wetlands to breed.

Many of these species have also bred, with some in the tens of thousands, like Pelicans and the straw-necked ibis, also known as the ‘Farmer’s friends’ (and not be confused with its cousin, the white ibis or “Bin Chicken”). Importantly, if the water levels in their breeding grounds (rookeries) rise too high, nests can flood. If they drop too much, adult birds may abandon their nests and feral animals, such as foxes and pigs, can gain access to the colonies. And if the water quality deteriorates in the rookeries, the birds are at risk of diseases. So environmental water managers monitor these large breeding colonies and use water for the environment to support these breeding sites when necessary. The skies in the Lowbidgee are full of juvenile birds taking full advantage of healthy wetlands, good habitat and plentiful food.

Pelican breeding colony, Gayini. Photo: Madeline Clark

 

Waterbird surveys over the last 40 years have shown a long-term decline in bird numbers so the prolonged flooding and wetter conditions we have been experiencing over the last 2 years has been a real reprieve for Australian waterbird populations, as in dry times, these large breeding events simply do not occur.

Find out more here: Waterbird breeding bonanza in the Basin – DCCEEW

 

Mitigating low oxygen water

 

In wet years like this, low oxygen (or hypoxic) blackwater events become a real risk.

Blackwater can occur when floods wash organic matter (such as leaves, grass and bark) into the rivers. Carbon is released from organic matter and the water becomes very dark – like a really-strong pot of tea. This provides food for water bugs, crayfish and native fish and plays an important role in maintaining a healthy river.

However, too much organic matter from big floods can see naturally occurring bacteria multiply quickly to feed on the massive amounts of carbon, but in doing so deplete the water of oxygen. When oxygen levels become too low, it can kill fish and other aquatic animals. During floods the river is at greater risk of low oxygen blackwater – especially during the hot summer months.

Blackwater in Cowabbie Cr entering Bundidgerry Creek. Photo DPI Fisheries

Over summer, river operators, irrigation corporations and environmental water managers worked together to mitigate low oxygen blackwater across a number of valleys, including in the lower Murrumbidgee River. As floodwaters receded, we delivered water for the environment to improve water quality. No major fish deaths have been reported in the lower Murrumbidgee valley this year, which has been a great result for our native fish. As always, we’ve been careful to avoid exacerbating flooding conditions and negatively impacting any landholders.

Find out more here: Low-Oxygen Blackwater and Water for the Environment – DCCEEW

 

Extending natural flows

 

The Murrumbidgee River is a ‘working river’, which means water storages are managed to conserve water and only drawn upon to meet minimum flow targets for river health and water orders for irrigation, town water supply, other industry demands and environmental water orders. The ‘tail-end’ of natural flows are typically captured in the dams. This can reduce the duration of flows reaching wetlands. It can also cause a sudden drop in river height, which may lead to riverbank slumping and erosion and can sometimes have detrimental effects on native fish habitat.

Water for the environment can be delivered on the back of these flows to extend the volume and duration of water reaching important wetlands, such as the Mid Murrumbidgee Wetlands. It can also allow for a slower, more gradual recession, reducing the risk of bank slumping and erosion.

The graph below shows how water for the environment (in green) was used to extend the duration and manage the recession of flows at Wagga Wagga in March 2022.

Flows at Wagga Wagga in March 2022. Water for the environment (in green) was delivered to extend the duration and provide a more gradual recession after an unregulated flow (in blue). Credit: WaterNSW

 

Working together to build resilience into the future

 

After a couple of good years, we are looking to build the resilience of our rivers and wetlands before the next drought. We are starting our planning for next year, however, providing ‘top-up’ flows to wetlands is likely to be needed to lock in the gains that have been achieved to date. This will include using our carry over allowance, so we can provide environmental flows early in the new water year, mimicking how rivers would have behaved naturally.

Environmental water management is a collaborative exercise involving numerous partners, including NSW Department of Planning and Environment, WaterNSW, Murray-Darling Basin Authority, First Nations peoples, local landholders, and scientists. We are grateful for their support and look forward to continuing to work together to benefit the rivers and wetlands of the Murrumbidgee valley.

 

Michele Groat is the CEWH Local Engagement Officer in Griffith, NSW supporting the management of the water that has been recovered under Basin Plan initiatives. She has extensive knowledge and experience in areas of water management and environmental stewardship having held roles at NSW Environment Protection Authority (EPA), RiverReach, Murrumbidgee Valley Stakeholder Group and Ricegrowers’ Association prior to her current position. 

 

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