Water NSW managing water releases after huge inflows into Split Rock, Keepit and Copeton Dams

The spillways of dams including Copeton, Keepit and Split Rock have been in full flight after last week's rainfall and inflows into the water storages.

On Monday, Copeton was sitting at 98.3 per cent, with thousands of megalitres of water still continuing to flow into the dam from upstream.

Split Rock Dam near Manilla was at 104.5 per cent on Monday afternoon with high volumes of water still flowing in after last week's deluge.

At Lake Keepit, the dam was hovering at 99.6 per cent on Monday, after slow and timed releases over the weekend.

Water NSW said the deluge on Thursday and Friday had exacerbated the already wet and soaked catchments, but releases had been calculated in conjunction with the Bureau of Meteorology and State Emergency Service (SES).

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"Both Keepit and Copeton dams exceeded capacity overnight Friday after receiving very large volumes of water from upstream, generated by widespread storm activity," a Water NSW spokesperson said.

"At no point during the most critical hours of the inflow peak did the dams' releases exceed the rate of flow into the storage, thereby reducing the potential flood impact from their catchments.

"Water was held back in both dams until exceptionally high downstream tributary rivers began receding, further mitigating flood heights."

The spillway at Keepit was in overdrive after record inflows into Split Rock Dam sent water flowing down the Namoi, while Manilla River was also turbocharged in the rain.

"Keepit Dam storage was also receiving water from Split Rock Dam upstream on the Manilla River, which continues to exceed capacity after receiving record inflows," the Water NSW spokesperson said.

"The large and rapid inflows into Copeton Dam were nevertheless only half the record flow in the Horton River downstream."

The Bureau of Meteorology said in its latest flood warning on Monday afternoon that releases from Keepit Dam peaked overnight on Sunday, and "this flow combined with inflows from the Peel, and Mooki Rivers have caused major flooding at Gunnedah".

"Flood operations are being conducted by WaterNSW at Copeton Dam," the Bureau said.

"The dam releases will vary subject to inflow and downstream tributary flow rates. WaterNSW are working closely with the Bureau, NSW SES and landholders to plan release strategies."

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