Science in action monitoring the Gwydir River system

It was a long hot summer in the state's north-west. The Gwydir and Mehi Rivers had ceased to flow. Native fish were stranded in isolated refuge pools. And local communities were worried.

Eastern long necked turtle (Chelodina longicollis) at Boolooro Bridge refuge pool in the Gwydir River

While there was water on the horizon - a planned 'stock and domestic replenishment flow' scheduled to occur in mid-May - it would be too far away. Local environmental water managers were concerned that an extended dry would see many large refuge pools dry down completely with the potential for large losses of native fish. It was also possible that both the timing and the size of the planned 'replenishment flow' could result in water quality issues that may inadvertently harm the remaining stressed fish population.

It had happened before, back in 2009. That event had prompted the NSW Office of Environment and Heritage (OEH) to instigate independent protocols for re-starting the river with a low environmental flow. Trigger periods were established to begin monitoring pools and prepare to deliver low flows to protect key refuge sites. The other key criteria was to restart the rivers with a low flow environmental release well ahead of any higher stock and domestic replenishment flow. This protocol was developed with advice from the Gwydir Environmental

Earlier this year, with refuge pools drying up, OEH set about implementing its low flow protocol for the first time.

Wetlands and Rivers Conservation Officer Jane Humphries was part of a small team of scientists and water managers led by Daryl Albertson, the OEH Gwydir Environmental Water Manager, at the forefront of the decision-making process.

'There were three options available to us,' Ms Humphries said.

'Our first option was to use environmental water held in reserve to restart the river in targeted reaches. We would gradually refill river pools and raise the river flows to low levels before the condition of the major refuge pools started to deteriorate and well before the delivery of the higher replenishment flow. In doing so we aimed to protect the remaining refuge pools and prevent issues from a sudden high flow restarting of the rivers.

'Alternately, we could choose to do nothing and hope that our experiences in 2009 would not be repeated.

'Or, we could hope for rain to return flows to the river.

'There were risks with all three options, but based on science and experience we chose to go ahead with the low flow option,' she said.

Water buybacks and inflows into Copeton Dam which had filled accounts since 2010 meant OEH had access to additional environmental water reserves. These reserves would provide for a low flow during the extended dry spell without compromising carryover for future seasons and other environmental purposes.

But it wasn't as simple as turning on a tap or opening up a weir.

'Before the low flow began David Preston and I conducted field assessments to determine the condition of key refuge pools in targeted sections of the rivers and creeks,' Ms Humphries said.

'We used a 'rapid assessment methodology' to gauge water levels, water quality and the habitat conditions of 12 different pools.

'Using kayaks, we navigated three cross-sections of each pool measuring dissolved oxygen, temperature, pH and salinity at the surface and then at 50 centimetre intervals to the maximum depth of the pool. As part of the process, we also recorded the colour, smell and presence of surface leaf and organic matter, habitat quality assessment and made note of any other animals in or around the pool.

'In between these key refuge sites, we also did a visual check of other large pools to see if there was any urgent need to check these or to commence flows sooner than planned. With the exception of one pool on the Mehi River, within the town, all of the larger pools were in relatively good condition. Some shallower pools had dried up and in a few, we observed some dead fish including native and introduced species,' Ms Humphries said.

Results of the field assessment were discussed at a meeting of OEH, DPI Fisheries, DPI Water and WaterNSW in early April 2016. From there, the decision was made to begin a low flow release that would refill pools before water levels and quality in the refuge pools deteriorated and to allow the river to rise gradually ahead of the replenishment flow some weeks later.

'We kept a close eye on the river and refuge pools as the low flow made its way through, reconnecting the pools and restoring the flow through the system,' Ms Humphries said.

'Above and below the front of the flows, we took some water quality measurements but no issues were detected.

'Two weeks after the low flow began, we revisited some of the original refuge pools and found them all in good condition - completely filled with low flows connecting them,' she said.

The low flow reconnected pools along the Gwydir from Tareelaroi to Tyreel then down towards Brageen on the Gwydir and on the Gingham below Tyreel, eventually extending beyond Tillaloo. In the Mehi, the low flow reached from Tareelaroi to Combadello and then eventually to Gundare; and in Carole Creek from the offtake to below Midkin and eventually to near Garah.

WaterNSW released the planned replenishment flow in May with water reaching all of the targeted rivers and creeks and extending to Moomin Creek.

Conditions across the Gwydir valley returned to dry in the months following the low flow and subsequent replenishment flow. As a result, the river below Tareelaroi once more ceased to flow for a period of five days. However, significant rain in early June and catchment inflows from a larger rainfall event to the east provided small freshes and low flows.

As the water has returned to the river, so too have the people.

'That was something we noticed during our monitoring,' Ms Humphries said.

'The social benefit of water flowing in the rivers and creeks meant people could fish, swim, camp and enjoy the river again.

'By and large, the community was supportive of the way we chose to manage environmental water during the dry spell. Once the local fishing community understood our plan and the processes involved in delivering the low flow, they were very supportive.

'Others saw the drying down as a natural process and felt our intervention was unnecessary.

'To me, the Gwydir River is a special place because it's where I grew up, it's where I live and now work. It shaped my family for many generations. I remember fishing and swimming in the Gwydir, grazing cattle on Big Leather and mustering on our family and neighbouring properties. Later I worked in irrigation where I was still splashing in Gwydir water.

'I will always remember parts of the Watercourse country before Copeton Dam, but it is a part of history now and I wouldn't wish it undone.

'I do feel privileged to be in a job where I can do my bit to look after the Gwydir, its rivers, creeks watercourse and wetlands. Science is an important part of that. It underpins our basic knowledge and understanding of systems, informs our decision making and helps us to determine what outcomes are possible through management of water for the environment.

'Combined with the knowledge of Aboriginal people and local landholders, we are able to achieve some fantastic outcomes with the water available to us,' she said.