Charles Sturt University adjunct professor and local ecologist David Goldney says Bathurst Regional Council's management of the Winburndale Rivulet between 2017 and 2019 caused the extinction of the water body's platypus population.
At a forum convened by the NSW Central Tablelands council last week to discuss an environmental assessment [EA] looking to amend the licence to operate Winburndale Dam, Dr Goldney revealed findings from his independent report stating council's neglect of environmental flow releases brought about the extinction.
"The extinction is almost entirely due to the low flows, which are completely unacceptable to maintain the conservation status of platypi," he said.
"To maintain a platypus population in that rivulet, you need two to four megalitres a day, which clearly wasn't delivered at the height of the drought."
In early 2020, Winburndale landowner Michael Inwood said council affirmed across 2019 that "there'd been no visible flow into the dam, and that they'd released 0.6 to 0.8 of a megalitre daily."
The EA proposal prepared for the Natural Resources Access Regulator [NRAR] would permit council to release flows from the dam's release valve at a rate of 0.78 megalitres per day when the water's below crest level, with seasonal adjustments.
Dr Goldney labelled the proposal, prepared by Orange engineering consultants Premise, inaccurate.
"The rainfall they used to do their modelling is based on Bathurst Airport data from the Bureau of Meteorology [BOM], but rainfall figures at Yetholme are 30 per cent higher," he said.
However, Premise consultant David Walker dismissed this claim as "incorrect."
"The rainfall is based on solo data generated from multiple rainfall stations within the Winburndale catchment area," Mr Walker said.
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Dr Goldney said the proposal is too reliant on historical data, and suggests the modelling should be based on a "back to basics" approach.
"The modelling effectively compares proposed releases with historical releases under the assumption the foundations have ecological integrity; perhaps they do, perhaps they don't," he said.
"There's no flow gauge at the dam's gulf, which probably adds another five to 10 per cent to the water yield, and there's probably significant amounts coming from nearby springs."