The first major flood after eight years of drought is flowing down the Balonne River in southern Queensland this week in what could be the first real test of the northern projects of the Murray-Darling Basin Plan, struck in 2012.

Key points: Up to 200,000 megalitres a day of water was being released from EJ Beardmore Dam to move through Queensland and NSW

Up to 200,000 megalitres a day of water was being released from EJ Beardmore Dam to move through Queensland and NSW St George irrigators celebrated the first significant flow in eight years, and a chance to test the Murray-Darling Basin Plan

St George irrigators celebrated the first significant flow in eight years, and a chance to test the Murray-Darling Basin Plan Water flowing downstream will meet with the driest soil profile in well over 100 years

As the Balonne River peaked at 12.22 metres in St George on Thursday, huge volumes of water — up to 200,000 megalitres per day — were released from EJ Beardmore Dam to move through southern Queensland and into northern New South Wales.

But how far will the water travel, and who will be able to divert it as it makes its way south?

Queensland and South Australia are the only states to have all their Murray-Darling Basin plans accredited by the Commonwealth, with the Department of Natural Resources setting the rules for diversion of this flood.

Irrigating communities back in business

Irrigators in St George were celebrating the first significant flow in eight years and the opportunity to test their water plans under the Murray-Darling Basin Plan.

Cotton Australia chairman and local irrigator Hamish McIntyre said the water resource plans finalised late last year had been largely untested.

"They haven't had many opportunities to work, and for us then to reflect on how they are working," he said.

"[It will test] if they are meeting the critical human needs up front for our regional towns through to the environment and on to entitlement holders — whether it be irrigators or the great work floods do on the flood plains for grazing."

Cotton grower Hamish McIntyre says is the best flow in the Balonne in eight years. ( ABC News: Lydia Burton )

He said water harvesting for the region was announced by the Queensland Government on February 16.

"The water that came in [prior] to that was heading down for environmental needs on the front of the flow, and it pushed on down into New South Wales," he said.

"Since then we've had more rain so the size of the flow has really escalated.

"But still at the front of that [major flood], our water resource plan [worked] and the front of the flow pushed well down into NSW and joined up with water from heavy rain down there around the border."

Mr McIntyre said it was great to see the plans working in their initial stages.

"Look, with all the water running throughout the Basin we believe that the flows, the connectivity, should be right through to Wentworth eventually. So it's wonderful," he said.

"In our operation we hope to half fill our storages [and] if we end up with half our volumetric limit we'll be very happy."

The first significant water flows through the Balonne river system will allow irrigators to refill empty storages and grow cotton this spring. ( ABC Rural: Cassie Hough )

Situated between St George and Dirranbandi, the owners of Whyenbah Station were also optimistic about the potential for winter and spring cropping.

"The wonderful thing is the river flooding and being able to pump some water into our storages that have been empty for quite some time," said farmer Amelia Sevil.

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"About 18 months ago we went through the Healthy Headwaters program and raised the height of the wall and divided it into two storages.

"I think we'll definitely fill one side, and maybe go into the other side, so it certainly gives us a much more positive outlook for either some winter cropping or potentially growing cotton, depending on how much [water] ends up coming down," Ms Sevil said.

What about Cubbie Station?

Australia's largest irrigated cotton farm, Cubbie Station, made a commitment last year that following a prolonged drought period, and in the event the state agency announced the 'low flow' rule for extraction, it would voluntarily contribute 50 per cent of its entitlement up to 10GL.

Cubbie Agriculture CEO Paul Brimblecombe said that commitment had now been achieved over a five-day period, by limiting diversions.

Cubbie Station is the largest cotton farm in Australia, with nearly 20,000 hectares of irrigated cropping country. ( ABC Southern Queensland: Nathan Morris )

"The low flow rule... flagged the commencement of the Cubbie contribution as we outlined back in July last year," he said.

That 'low flow' rule was associated with the commencement of a flood and required all irrigators to contribute water towards the environment, stock and domestic needs downstream.

"We're fortunate to see a major flood now working its way through the Lower Balonne, but it did start out as a low flow event," Mr Brimblecombe said.

Cubbie Station has a series of large dams near the Culgoa river, and water licences for over 460 gigalitres. ( ABC Southern Queensland: Nathan Morris )

Water storages on Cubbie were now being filled in accordance with the station's authorised diversions, Mr Brimblecombe said.

Cubbie Station can store up to 469 gigalitres, but Mr Brimblecombe said it was too early to tell how much of its storages would be filled in this flood event.

"It's a major flow, a major flood, and like all irrigators we're able to extract reasonable volumes," he said.

There would be no cotton harvest this year, but Mr Brimblecombe was optimistic the station would be able to plant 15,000 hectares of irrigated cotton in spring.

Everybody gets a drink

Just across the border in New South Wales, Rory Treweeke is a floodplain grazier on the Narran river at Angeldool.

He said the flow of water experienced this month was of sufficient volume to wash over any commitments made under the Murray-Darling Basin Plan.

"The plan is, by and large, to do with some of the smaller to medium flows that come through the system, and try to rearrange the extraction of water out of them," he said.

Angledool station in north-west NSW during a previous flood event. ( Supplied: Rory Treweeke )

"[This] is turning into a big flood, basically. Everybody gets a drink — irrigators and floodplain graziers alike — and all the people down below the system," Mr Treweeke said.

"Once the river at St George gets over 120 gigalitres a day, there are caps on extractions at that level so that nobody can increase their daily take above the maximum that's set," he said.

"The arguments have always been over the small and medium sized flows that are obviously more frequent than big floods and therefore there is a greater contest between end users for that water," he said.

Driest soil profile in a century

Rory Treweeke said the water flowing downstream would meet with the driest soil profile in well over 100 years, which could affect its reach.

"That is obviously going to soak up a lot of water and so, how far it runs out, I think there's a big question mark over that at the moment," he said.

But he said the water would come as a welcome relief.

"As a floodplain grazier and farmer, it's exactly what we needed to replenish our soil profile.

"It's coming at an ideal time of the year because it's still warm and as the floodwater dries back we should get very good growth and obviously, an excellent full profile to plant our winter crops into," Mr Treweeke said.

Basin Plan 'now in action'

Meantime, the Murray-Darling Basin Authority said that for many people in Queensland and northern New South Wales, the rain of recent weeks signalled the first major break in the drought since the Basin Plan was signed into law in 2012.

"The MDBA is watching this water closely via satellite as it heads into the heart of the Basin, through land still parched in some areas," said Murray-Darling Basin Authority chief executive Philip Glyde

"This takes collaboration and trust," he said.

Mr Glyde said it was a testament to the Basin Plan that irrigators in Queensland started taking water from the flow only once they were permitted, in accordance with clear and transparent rules in the State Government's water resource plans.

"Credit is also due to the New South Wales Government for imposing wide-ranging embargoes on water extraction in order to protect these first flows, as they had agreed to do. However, downstream water users were confused and raised some criticisms in relation to the partial lifting of the embargoes and these decisions were not transparent for all to see.

"We look forward to the New South Wales Government putting forward water resource plans that build these protections into their rules, providing confidence and transparency for all," he said.

Mr Glyde said a good deal of water was expected to reach Menindee Lakes next month and ultimately to join with the Murray.