Performance in each sector: Hunter River Salinity Trading Scheme performance report 2022-23

The sections below cover annual salinity and flow information in the upper, middle and lower sectors. Salinity levels are compared with the established salinity targets. While the yearly average EC increased, this is mainly due to low flows in the river from January to June 2023, where the average daily ambient EC increased well above each sector’s respective EC target.

Upper sector: Hunter River upstream of Denman

The salinity target for the upper sector is 600µS/cm during high flows (shown in Figure 6 below as a pink line) and 900µS/cm during flood flows (shown in Figure 6 below as a red line). Figure 6 shows the average salinity and average river flow in the upper sector for the whole of 2022-23. For easier reference, this has been split into six-monthly periods in Figure 7 for July to December 2022 and Figure 8 for January to June 2023.

Industry discharges largely occurred between July to December 2022 (Figure 7). With 134 discharge opportunities occurring almost daily during this period. There was only one discharge in the later 6 months, on 8-9 June 2023 (Figure 8).

Average annual salinity in the upper sector was 743µS/cm. This was largely due to the high ambient salinity in the river during low flow periods from January to June 2023¹. Historically the ambient salinity in the upper sector is typically above the 600µS/cm target. This target will be reviewed as part of the review of the Protection of the Environment Operations (Hunter River Salinity Trading Scheme) Regulation 2002, due to be completed by end 2026.

On 24 March 2023, the daily average salinity was recorded over 1500µS/cm (figure 8). This was a low flow day when no participants were permitted to discharge. The EPA and WaterNSW have investigated the event and were unable to determine a source. The EPA and WaterNSW are continuing to closely monitor EC levels for any further unusual activity.

On days when industry discharges were permitted, the upper sector daily average salinity was 484µS/cm, largely keeping within the high flow salinity target of 600µS/cm. The daily average salinity did exceed the 600µS/cm target on 7 occasions (5% of the total permitted discharges for 2022-23), with EC levels ranging between 607 to 668µS/cm.

The unprecedented rainfall in 2022 created significant water management issues for Scheme participants, particularly those in the upper sector and resulted in an emergency discharge event in July 2022 (Section 4). This event highlighted the challenges with extreme weather which may not have been considered in the original Scheme design. As such, the Scheme’s operation in extreme weather is under review and will be considered as part of the Regulation review. 

Despite these challenges, the Scheme performed relatively well to manage participant discharges to largely maintain the salinity within or very close to target levels during high and flood flow conditions.

Middle sector: From Denman to the junction of the Hunter River and Glennies Creek

The salinity target for the middle sector is 900µS/cm for both high flows and flood flows (shown in Figure 9 below as a red line). Figure 9 shows the average salinity and average river flow in the middle sector for the whole of 2022-23. For easier reference, this has been split into six-monthly periods in Figure 10 for July to December 2022 and Figure 11 for January to June 2023.

Industry discharges largely occurred between July to December 2022, with 167 discharge opportunities in the middle sector, again occurring almost daily during this period (Figure 10).  There was only one discharge in the later 6 months, on 9-10 June 2023 (Figure 11).

Average annual salinity in the middle sector was 864µS/cm. There were 176 days when salinity in the river was over the EC target, however this was largely due to the high ambient salinity in the river during low flow periods from January to June 2023.

On days when industry discharges were permitted, salinity in the middle sector remained mostly below the sector target of 900µS/cm. There were two occasions when the target was exceeded (representing 1% of the total permitted discharges for 2022-23) and EC levels were 913µS/cm and 974µS/cm.

The Scheme performed well during all discharge events with salinity in the middle sector remaining largely below the sector salinity target.

Lower sector: From the junction of the Hunter River and Glennies Creek to Singleton

The salinity target for the lower sector is 900µS/cm for both high flows and flood flows (shown in Figure 12 below as a red line). Figure 12 shows the average salinity and average river flow in the lower sector for the whole of 2022-23. For easier reference this has been split into six-monthly periods in Figure 13 for July to December 2022 and Figure for January to June 2023.

Industry discharges largely occurred between July to December 2022, with 172 discharge opportunities for industries in the lower sector (Figure 13).

Average annual salinity in the lower sector was 770µS/cm. There were 106 days when salinity in the river was over the EC target, however this was all due to the high ambient salinity in the river during low flow periods from January to June 2023 (Figure 14).

On days when industry discharges were permitted, salinity in the lower sector remained below the sector target of 900µS/cm. Overall, the Scheme performed well in managing industry discharges to keep salinity within the target.