A rural lobby group wants to know why has there been no supplementary water event announced for the NSW Murray River system.

The Ricegrowers Association of Australia (RGA) says large portions of daily inflows are “unaccounted for”.

It estimates that an average of 25 gigalitres per day has flowed into the Murray River system below Hume Dam since October 12, while irrigation demand through the Murray’s two largest irrigation districts averaged just 4.5 gigalitres per day.

“This leaves another 20 gigalitres per day of flow unaccounted for,” the RGA said in a written statement.

“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 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.

Since October 1, the RGA says 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.

The water released from Lake Victoria is generally used to meet downstream water demand, predominantly South Australian demand.

“However, since the start of August, the flow across the South Australian border has averaged more than nine gigalitres a day (747 gigalitres in total),” the RGA says.

“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 gigalitres for August, 77 gigalitres for September and 112.5 gigalitres for October plus 58 gigalitres per month for dilution and losses).

“It is hard to understand why this flow to South Australia is now being propped up by releases from Lake Victoria,” the lobby says.

The ricegrowers’ advocates say South Australia appears to be benefiting from substantial flows across the border at the expense of a supplementary event in “our neck of the woods”.

The RGA has written to state and federal water ministers and the government agencies involved in making a supplementary water announcement to outline its concerns and seek an announcement as soon as possible.