Hunter River Salinity Trading Scheme 2022-23 Performance

2022–23 continued to present challenging weather conditions for EPA, WaterNSW and scheme participants. During the first half of the financial year, July to December 2022, the Hunter River experienced significant rainfall, resulting in an unprecedented 230 river registers (discharge opportunities). This, along with similar high rainfall at the end of 2021–22, lead to continued water management issues for Scheme participants. Noting, even though there was an increased number of discharge opportunities, there was also a higher volume of site water to manage.

Many Scheme participants were able to manage their site water by using the discharge opportunities, however one participant, Mangoola Coal Operations Pty Ltd (Environment Protection License No. 12894), requested an emergency discharge with the EPA in July 2022. Mangoola were permitted to discharge outside of Scheme discharge opportunities for a 10-day period on emergency grounds.

In the second half of the financial year, January to June 2023, rainfall drastically reduced with only 2 river registers. These river registers were triggered by controlled environmental flow releases from Glenbawn Dam to support local fish migration.

Due to the low flow conditions in the Hunter River in the January to June 2023, the salinity in the river naturally spiked well-above the salinity targets across all three sectors, only falling below them during the environmental release in June 2023.

Overall, the Scheme performed effectively to minimise salinity in the Hunter River. Despite the challenges in July to December 2022, the average salinity was largely maintained below the electrical conductivity targets in each of the upper, middle and lower sectors of the Hunter River. The average salinity did spike above these targets in the upper and middle sectors during participant discharge opportunities, 26 and 2 times respectively, but these were only marginally above the targets and participants discharging during these times kept within their allocated total allowable discharge.

The extreme wet weather presented water storage and management challenges for industry. There was a 101% increase in discharge opportunity events in 2022–23, demonstrating the increased need for participants to discharge whenever opportunities were available. However, most participants managed their onsite water within the regulatory framework, only discharging during available opportunities and only one participant discharged outside of the opportunities available, being permitted to do so under emergency provisions. In doing so, participants have supported the overall scheme objective, by balancing their need to discharge with the needs of agricultural water users and the environment.

Scheme performance during 2022–23

There were 15 Scheme participants during the 2022–23 financial year. During this time:

• 10 participants discharged
• 3 did not discharge
• 2 did not hold discharge licences (cannot discharge).

Table 1 below shows a breakdown of the participants and their discharge status.

During July 2022 to June 2023, the Hunter River catchment received higher rainfall compared to past years. Observed rainfall in the year ranged between 600–1800mm of which 400–1,200mm was observed during the first half (July to December 2022) while the second half (January to June 2023) was relatively dry. Frequent rainfall from July 2022 through to November 2022, generated intermittent peak flows along the river system. This resulted in high river flows, and increased discharge opportunities. Flows started to recede in December 2022 and the last river register was published on 20 December 2022. No significant rainfall was observed in the second half of the period.

In 2022–23, there were a total of 230 river registers published, of which 58 were revised and reissued due to changes in river flow and salinity levels. From 4 July to 20 December 2022, there were almost daily river registers. Table 2 below shows the monthly breakdown of river registers published and revised throughout the period.

Table 2 Monthly breakdown of river registers published and revised in 2022–23.

The only discharge opportunities in the second half period were two river registers published in June 2023, as a result of controlled environmental river flow releases from Glenbawn Dam.

Glenbawn Dam is located to the northeast of Dartbrook in the Hunter Region and supplies water for irrigation, power generation, stock, industry and households, as well as providing flood mitigation and environmental flows in the region. Releases from the dam are managed by WaterNSW and typically are not significant enough to trigger river registers¹. In the case of the two river registers published in June 2023, significant high rainfall meant Glenbawn Dam had reached capacity, requiring a dam release into the Hunter River which was already experiencing high flow.

From the 230 river registers published, there were 473 discharge opportunities across all sectors. 11 discharges occurred outside of these periods (see Section 4. Emergency Discharge Event for more details). Participants used 397 of these opportunities, generating 836 individual discharge events. Table 3 below represents the breakdown of discharge opportunities and events per sector.

1 To trigger a river register, a dam release must result in river flows through Singleton exceeding the high flow threshold of 2,000ML. Glenbawn Dam releases are either to maintain environmental flows in the Hunter River, from water purchased by shareholders under water sharing plans or to manage the Dam when it has reached capacity (spill).

Table 3 Breakdown of discharge opportunities and events, including total number of sector credit factor of less than 0.7 was applied per sector in 2022-23.

Sector credit factor

The credits held by each sector of the Hunter River entitle the sector to a percentage of the TAD. This percentage may exceed sector electrical conductivity (EC) targets if a higher number of credits are held in one sector. The sector credit factor is applied to reduce the discharge opportunity (% of TAD per credit) and keep the sector’s salt load below sector EC targets. In 2022–23, the upper sector experienced a sector credit factor of less than 0.7 in 62 of their discharge opportunities, compared to five in the middle sector and nil in the lower sector.