Performance during industry discharge events

Hunter River Salinity Trading Scheme Performance Report 2023–24.

Water discharged and total flow

A total of 449ML of saline water was discharged into the Hunter River by five Scheme participants across 13 river registers during July 2023 to June 2024. This represented 0.2% of the total flow of water past Singleton for the same period (189,029ML). This is small when compared to the previous financial year – where an unprecedent 230 river registers (discharge opportunities) occurred, resulting in a total of 49,596 ML of saline discharge, 2% of the total flow past Singleton (2,549,470ML).

A comparison of monthly industry discharge and Hunter River flow volumes is shown in Figure 3.

Figure 3: Monthly industry discharge of salt water compared with flow past Singleton 2023-24

Total salt load

A total of 1,291 tonnes of salt was discharged to the Hunter River by 5 Scheme participants during July 2023 to June 2024. Participants used 9.6% of the TAD (13,426 tonnes) compared to 37% used in the previous, far wetter year.

Figure 4: Comparison of annual industry discharge, TAD, Hunter River salt load and flow past Singleton, 2013-2024. * Flood flow TAD was removed from 2021 onwards. The higher figures represented in the 2020-21 data include flood flow TAD

Table 3 shows the relationship between the natural salt load of the Hunter River and the discharges made by industry, over a nine-year period.

Table 3: Proportion of industry salt discharges in Hunter River salt loads

Saline discharges

Average daily flow (ML/day) was approximately three times lower (516 M/day) than the average flow since 2000 (1426 ML/day). Salinity at Singleton was mostly above the allowable limit/target between July 2023 and April 2024. This meant few opportunities to discharge occurred, with only three separate events between April and June 2024. Industry discharges in 2023-24 represented only 1.5% of the total salt load that flowed past Singleton. Figure 5 below shows the breakdown of industry discharges with river flow and river salt loads for each quarter of 2023-24.

Figure 5: Comparison of quarterly industry discharge, TAD, Hunter River salt load and flow past Singleton for 2023-24

The average yearly EC for each sector is shown in Table 4. The EC in the upper sector of the river decreased from the 2022-23 year by 4.8% but was still the second highest of recent years. The middle and lower sectors however averaged out as much higher than in recent years - 27.6% and 29.8% increases, respectively.

Table 4: Comparison of average annual EC for each sector

Figure 6 shows average salinity in all three sectors, and includes target EC limits, over a ten-year period.

Figure 6: Salinity measurements in all three river sectors (Upper, Middle, Lower)