EVIDENCE is mounting that floods gushing through northern Australia are among the biggest on record, and downstream states such as Victoria are rapidly raising expectations about the amount of water they will receive from them.
Victoria and South Australia are confident they will each get 500 billion litres in the carve-up of water flow down the Darling River.
Less than a week ago, water officials in Victorian and South Australia were expecting about 300 billion litres each, but expectations have soared as more data comes to hand.
Five hundred billion litres is enough to fill Sydney Harbour or enough to supply Melbourne's needs for about 17 months - although the water will not go directly to Melbourne.
Massive flows are coming to central Australia's other ephemeral catchments, including the Lake Eyre system and the big Bulloo River catchment near the north-eastern corner of South Australia.
Satellite images from Geoscience Australia show the enormous volume of water flowing through the inland rivers.
University of NSW professor Richard Kingsford said it would have profound environmental benefits. "This is definitely now the one-in-20 year floods," he said.
The floods, sparked by downpours in Queensland, are flowing along the Darling River in NSW towards the Murray River near Mildura.
Analysis by the Bureau of Meteorology has highlighted the size of the floods - 16 of the 30 river gauges in the Queensland section of the Murray-Darling have been showing their highest water levels.
Other gauges were showing their highest water levels since the 1950s.
While the floods will only pass through a small corner of Victoria's north-west, the rest of the state will benefit because under water-sharing rules it will be able send less of its own water down the Murray to supply South Australia.
This means a strong start to the next Victorian irrigation season in August is almost assured.
Victorian Water Minister Tim Holding said it was too early to speculate on the amount of water that would flow to Victoria from the floods.
But he said: "The estimates we are hearing point to an extremely promising boost for farmers and the Murray River”.
Professor Kingsford said having simultaneous floods in neighbouring catchments was creating the best bird-breeding conditions since 1990.
"It will hatch out millions of micro-crustaceans and plants . . . the biggest compound effect is in the species that can move between the catchments like waterbirds," he said.
He said the catchments had already had heavy rains in January, meaning the flows would go much further than usual.
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