Photo Source ABC Goulburn Murray News - Anne Trebilcock

Supplementary Event in the NSW Murray?


The Ricegrowers’ Association of Australia (RGA) questions why a supplementary event has not yet been announced for the NSW Murray River system.

Since Monday October 12, on average more than 25 gigalitres per day has flowed into the Murray River system below Hume Dam. A majority of this flow has come from the three Victorian tributaries: the Ovens, the Kiewa and the Goulburn.

While we understand that some of this flow is being used to meet irrigation demand. We also understand that demand from the Murray’s two largest irrigation districts, being Murray Irrigation and Goulburn Murray Water, during this time has only averaged 4.5 gigalitres per day.

This leaves another 20 gigalitres per day of flow unaccounted for. The RGA understands that some of this 20 gigalitres represents environmental water orders, and that some of this water will be used for river operations and by irrigators outside of the Murray’s main irrigation schemes.

However, even when taking this into account, we still estimate that the current surplus flow in the system would be at least 10 gigalitres per day.

The Murray Darling Basin Authority (MDBA) has advised that the key reason a Supplementary Event has not been called to date is because there is capacity within Lake Victoria to re-regulate these flows. This is despite the fact that Lake Victoria was all but full at the start of October 2020.

Since 1 October, 50 gigalitres of water has been drained from Lake Victoria, and the MDBA is planning for a further 50 gigalitres to be drained prior to this current river flush reaching Lake Victoria. This essentially creates 100 gigalitres of airspace in Lake Victoria to capture this current event.

The water released from Lake Victoria is used to meet downstream water demand, being predominantly South Australian demand. However, since the start of August, the flow across the South Australian border has averaged more than 9 gigalitres a day (747 gigalitres in total). This is more than double the volume that South Australia is entitled to for this time of the year as set out in the Murray-Darling Basin Agreement (66 giglalitres for August, 77 gigalitres for September and 112.5 gigalitres for October plus 58 gigalitres per month for dilution and losses).

While much of this flow has been the remnants of the last supplementary event, it is hard to understand why this flow to South Australia is now being propped up by releases from Lake Victoria. All in all, it appears that South Australia is benefitting from substantial flows across the Border at the expense of a supplementary event in our neck of the woods.

Nevertheless, if the total airspace in Lake Victoria will likely reach 100 GL, and the total surplus flow in the system is estimated to be 10 gigalitres a day, then based on our calculations only 10 days of this current flow should be required to fill Lake Victoria.

Hence considering this current event commenced on October 12, being 11 days ago, we would expect a NSW Murray supplementary event to be called any day now. This position is further supported by the fact that there is strong predictions for more rain in the catchment over the next few days.

Taking this all into account, it is hard to understand today’s statement from the MDBA in their ‘River Murray Weekly Report’ that “if upcoming rain reduces system demands and losses, whilst further boosting tributary inflows, the potential for a renewed period of unregulated (surplus) flow in the Murray will increase”. The apparent lack of urgency seems to be totally oblivious to what’s actually happening in the system, or at the very least, extremely conservative. 

If a supplementary event was to be called in the near future, the current NSW Murray general security allocation position (27%) means growers could access supplementary water against both their supplementary entitlements, and their general security entitlements (as an Uncontrolled Flow event). Hence this would provide a significant opportunity for growers to increase their overall access to water.

For our region, this means a significant opportunity for an economic, water and productivity boost. Considering the recent impacts of drought, COVid-19 and the resulting recession, overly conservative behavior by the relevant government agencies at this point in time, is hard to comprehend.

The RGA has written to both our State and Federal Water Ministers, as well as the government agencies involved in making a supplementary water announcement to outline our concerns and seek an announcement as soon as possible.

*Information used for the purpose of this release are taken from the MBDA ‘The River Murray System – Live River Data’ webpage: on 23 October 2020.