Hume Dam likely to fill this year

The dam is currently 80 per cent full, and there are positive signs from the Bureau of Meteorology that more rain will come in August and into spring.

MDBA river operations head Andrew Reynolds said modest pre-releases from the Hume Dam were likely to occur soon.

"They will be well within the channel capacity, so they won't have any real impact on people downstream," Mr Reynolds said.

"Given the outlook, we have a fair degree of confidence the Hume Dam will fill this year, and there will be a spill.

"We still have significant air space available to us, in the vicinity of 600 gigalitres, to use to manage floods."

Bureau of Meteorology water and agriculture general manager Matt Coulton said authorities were confident there would be wetter than average conditions in the coming months in the region.

"Upstream of the Hume Dam catchments adjacent to the upper Murray River are wetter than they have been for several years, and it won't take very much rain to produce quite a rapid response in river levels," Mr Coulton said.

Mr Reynolds said the MDBA would look at historical records, as part of its basis for managing the dam and what volumes might need to be stored.

"It will continue to be a juggling act of managing some airspace and inflows coming into the storage," he said.

Since the 2016 flood, the MDBA had improved its ability to understand weather conditions.

"We will continually reevaluate where the storage is at," he said.

He said the predicted wetter conditions could mean steady inflows, similar to those happening now.

"The issue comes to us if we get a full storage and a really heavy wet period, over several days, or a rainfall event followed by another one," he said.

"That generates a much higher peak inflow.

"The outlook we have does not tell us if we are going to have an event like that, it just tells us it's going to be wetter than average over the longer run."

He said 150 millimetres of rain had fallen in a few days in 2016, followed up by a similar event only a few days later.

"What we are seeing are 20-30mm rainfall events and a few days later the same, so it's a quite different pattern of rainfall," he said.

Mr Coulton said the catchments were not "quite as wet" as they had been in 2016, but they were close.

"In terms of the outlook, the negative Indian Ocean Dipole we had in 2016 was one of the strongest on record but the current event we are having isn't quite that strong," he said.

Moulamein, NSW ricegrower Jeremy Morton called for irrigators in the state to be allowed to take advantage of the unregulated or supplementary flows, likely to occur below the Hume.

They have been capped at 25pc of historical use.

"We could exhaust supplementary limits, have a relatively low allocation and a flood at the same time," Mr Morton said.

"Given we have systemic underuse, there needs to be higher account limits for supplementary access.

"In a highly variable climate it makes perfect sense to allow for higher water use in wet years when the environment is enjoying a water bonanza."

He said rules put in place to stop too much water being taken had seen underuse of up to 375GL a year, while in four of the past 13 years general security was zero.

"On average, that's 400,000 tonnes of rice," he said.

He said water had not been available because of dry conditions, but this year "there's going to be water everywhere".

"The environment will have the best watering it's had since 2016, but we won't be able to touch a drop of it," he said.

"Let's go hard, have a crack, because we know another drought is going to come along and production of those annual crops will come under enormous pressure.

"We need these good years to be really good, so we can mongrel through the dry years."