Rain sparks 'refilling process' for MurrayDavid Mark for AM, Tuesday December 29, 2009 - 10:42 EDT
The rain that has been bucketing down in the north of New South Wales is falling in the Darling River catchment, but it is hard to say if the water will make it all the way down the Murray River.
Even so, there is optimism that the rain will soak the system, making it easier for future falls to flow south.
The director of the Environment Institute at the University of Adelaide, Mike Young, says water makes its way down the Murray-Darling system "very slowly".
"People have to understand that the Darling River is not like the River Murray - once it starts to flow, then it spreads out over kilometres wide, it's a big, very flat system," he said.
"The soils are black cracking clay soils with massive cracks and each one of those cracks has to be filled up.
"Once it's been filled up, then the clay has to expand, and once that happens, then it starts to flow.
"So it really creeps down, it needs massive amounts of water ... once the soil is wet, then we can have massive floods coming down the Darling."
Mr Young says once the flooding down the Darling occurs, water has to make its way through the Menindee Lakes before reaching the River Murray.
"Water flows in and it fills up all of those lakes and that water remains as New South Wales water until the lakes get to a height, and then it becomes part of the River Murray system," he said.
"Once that happens then water can come on through down through the Lower Darling, which is one of the driest systems of all at the moment.
"I was up there only in the last few days where the Darling meets the Murray and it's one of the driest parts of the entire Australian outback at the moment."
Mr Young says the water that is currently falling in the north of New South Wales is unlikely to make a "significant difference" to the River Murray now.
"But what it does do is it fills up the top of the system, refills all of the dams at the top and as it starts to come down through the system, then that prepares the way for the next bit to come through and make a very very big difference," he said.
"This is the start of hopefully a refilling process. We can be optimistic I suppose at this stage that if there's any more rain that comes in, that rain would make a very very big difference.
"And there's a reasonable chance we could get some more."
© ABC 2009
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