THE ailing Murray-Darling basin could get a bigger-than-expected injection of water after fresh modelling found the river system would be much better off if irrigation volumes were cut by more than the government proposes.
Flood plains and wetlands in the lower basin would be significantly improved if the system was flushed with an extra 3200 billion litres a year and if more water was released from dams and lakes, the new analysis found.
At present the draft basin rescue plan recommends returning 2750 billion litres a year, mostly by buying back irrigators' water rights.
Federal Water Minister Tony Burke keenly welcomed the new modelling by the independent Murray-Darling Basin Authority. But it has entrenched the dour battle between the states, with South Australia backing the higher figure but Victoria branding it ''totally unacceptable'', a sentiment that New South Wales supports.
The modelling found the environment would be better served by relaxing so-called ''constraints'' in the system - including releasing more water from the Hume Dam on the Victoria-NSW border and from the Menindee Lakes in western NSW.
But this would also likely involve finding ways to stop flooding of infrastructure such as roads and bridges, and buying easements to allow flooding of private property.
Mr Burke stopped short of committing to the higher figure but said he was enthusiastic about the outcomes of the research, saying the benefits exceeded his expectations and it could ''make a massive environmental difference''.
''I had always hoped that it would show some sort of environmental improvement. It has gone way beyond what I hoped it would.
''The environmental outcomes that are in this really go a long way further than I thought they were going to at 3200 (billion). So there's a level of optimism that comes [out] of that for me.''
But he said he was ''holding back on any final call and any final decision while I work through it with other ministers''.
Mr Burke will need to speak with his state counterparts, who are crucial in any final plan.
Constraints are the points along the river system where, if too much water is flushed through it, flooding of infrastructure or property occurs.
The authority did not assess whether it was possible to relax the constraints. But it did say that getting around these constraints would ''require a commitment and significant investment from both state and federal governments''.
This ''could be of critical importance to the long-term sustainability of vegetation communities'', it found.