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How the scheme works

Hunter River flow categories

The central idea of the scheme is to only discharge salty water when there is lots of low salt, fresh water in the river.

This is when the river can best handle salt discharges because:

  • large amounts of fresh water dilute the saltier discharge so the impact on the river is not as great
  • through careful control, the mixture of river and discharge water can be kept fresh to meet water quality standards.

Going with the flow

Monitoring points along the river are used to measure whether the river is in low flow, high flow or flood flow.

When the river is in low flow, no discharges are allowed.

When the river is in high flow, limited discharge is allowed, controlled by a system of salt credits. The amount of discharge allowed depends on the ambient salinity in the river, so it can change daily. The total allowable discharge is calculated so that the salt concentration does not go above 900 µS/cm in the middle and lower sectors of the river or above 600 µS/cm in the upper sector.

When the river is in flood, unlimited discharges are allowed as long as the salt concentration does not go above 900 µS/cm. Members of the scheme coordinate their discharges so that this goal is achieved.

River divided into 'blocks'

The water in the river is nominally divided into numbered blocks. A block is a section of water that flows past Singleton in a day. So, block '2010-198' is the block of water that will flow past Singleton on the 198th day of 2010 (17 July). This block of water will flow past other points on the river on different days.

For each block, the scheme operators continually monitor the flow level and the ambient salinity and then calculate how much salt (if any) can be added to the block ('Total Allowable Discharge') so that salinity stays under the target.

  Example of discharge block 1  Example of discharge block 2  Example of discharge block 3  Example of discharge block 4

The river is divided into numbered blocks. For example, block '2010-198' will pass Singleton on the 198th day of 2010 (17 July). In this example, suppose block 198 could hold 112 tonnes of salt.

On 15 July, block 198 passes Site A. With 20 credits, Site A could discharge 2.24 tonnes (112 x 20 x 0.1%).

On 16 July, block 198 passes Site B. With 45 credits, Site B could discharge 5.04 tonnes (112 x 45 x 0.1%). If Site A did not discharge, it could trade 20 credits to Site B which could then discharge 65 credits of salt or 7.28 tonnes (112 x 65 x 0.1%).

On 17 July, block 198 passes Singleton with salt concentration less than 900 µS/cm.

Credits determine who can discharge salt

There are a total of 1000 salt discharge credits in the scheme and different licence holders have different numbers of credits (see Scheme participants and management for a list of credit holders and the initial credit allocation). Licence holders can only discharge salt into a river block in proportion to the credits they hold: 1 credit allows a discharge of 0.1% of the total allowed.

So, suppose block 2010-198 could handle 112 tonnes of salt (the Total Allowable Discharge for this block). Then a licence holder with 20 credits could discharge 2.24 tonnes (112 x 20 x 0.1%) into that block and a licence holder with 45 credits 5.04 tonnes (112 x 45 x 0.1%).

The licence holder performs a second calculation to determine what volume of their discharge water contains the permitted tonnage of salt.

Note: the River Register indicates when discharges can occur.

Credits can be traded

The need for licence holders to discharge depends on highly variable operational conditions at each site. Credit trading gives each licence holder the flexibility to increase or decrease their allowable discharge from time to time while limiting the combined amount of salt discharged across the valley. 

An online trading system allows licence holders to trade quickly and simply. The trades can be for one or many blocks (for example, a single day or longer periods) and the terms of the trade are negotiated by the parties involved.

This credit register ensures the information on credit holdings is publicly available at all times. Other information on the trading scheme is also available.

Access by any person to this online trading system is solely on the basis of their acceptance of the Terms of Use Disclaimer. Please read this.

Note that, among other things, while the Office of Environment and Heritage and the State provide information on this site in good faith, they accept no responsibility for the accuracy, completeness or timeliness of the information whether provided by them or any external site linked to this site.

Online Credit Exchange Facility Members must also comply with the Online Credit Exchange Facility Terms and Conditions outlined on the site.

Page last updated: 18 June 2013