NSW has failed to properly assess impact on wildlife of Warragamba dam changes, federal government says

Raising the wall of the Warragamba dam could affect half the remaining population of the critically endangered regent honeyeater and would put forest and woodland communities at risk of extinction, according to a summary of the environmental impact statement for the proposal, contained in a leaked federal environment department document.

The department found the New South Wales government had failed to properly assess how its proposal to raise the wall of the dam by 17 metres to mitigate flood risk in western Sydney would affect endangered wildlife.

The document obtained by Guardian Australia is the federal environment department’s assessment of the analysis carried out for the developer, the state government-owned WaterNSW, of the project’s likely effects on flora and fauna listed as nationally significant under federal environmental law.

WaterNSW is required to produce such an analysis as part of its environmental impact statement, which the federal government will use to determine if it should approve the raising of the dam wall.

The federal department found:

• WaterNSW made only a “low” effort to survey the area for koalas before concluding they would not be significantly affected by the project.

• It conducted no targeted surveys for the swift parrot before concluding they would not be significantly affected, a view the federal department rejected.

• WaterNSW’s EIS concluded the project would mean the minimum loss of 5%-7% of the total remaining regent honeyeater population, which numbers only a few hundred.

• The EIS found several threatened ecological communities would be put at risk of extinction, and it was unclear whether WaterNSW could mitigate that risk.

‘Significant negative impact’

The environment department found several flaws in the water agency’s wildlife analysis.

Those include failing to conduct sufficient surveys to check for the presence of species such as the koala, which WaterNSW’s assessment concluded would not be significantly affected by the project.

“The survey effort in the EIS appears low,” the document states.

The department notes the project area contains important foraging habitat for koalas and that the loss of 20 hectares or more of habitat critical to the animal’s survival would constitute a significant impact on the species.

Related: 'So much that will be lost': concerns grow over plan to raise Warragamba dam wall

The officials stress WaterNSW needed to reassess the project’s effects on the koala in light of the summer bushfires, which destroyed koala habitat across the state.

WaterNSW told a state parliamentary hearing at the end of June it was not planning any further field work.

In the case of the critically endangered swift parrot, the department said WaterNSW had conducted no targeted surveys, yet had concluded raising the dam wall would not significantly affect the species.

“The EIS states no significant impact to swift parrot, however the department considers the project could have a significant impact on this species,” officials wrote.

In the upstream area where flood waters would be held, the department noted the project would likely “modify, destroy, remove or decrease” foraging habitat used by swift parrots by up to 3,035 hectares – a reduction of 49% – and downstream there could be a loss of 962 hectares.

“Loss of foraging habitat on the mainland is threatening the breeding cycle of the species due to loss of foraging resources necessary to result in a successful migration to Tasmania,” the department wrote.

“The project could have a significant negative impact on the recovery of this critically endangered species.”

The department also said WaterNSW’s EIS concluded the project would have serious ramifications for the critically endangered regent honeyeater in the upstream area of the Burragorang Valley.

It said this included the loss of a minimum 21 to 25 birds (an estimated 5%-7% of the total remaining population, according to the document) but up to 200 birds could be affected (an estimated 50%).

The department said WaterNSW had failed to conduct any surveys for the bird downstream and it did not agree with the water agency’s conclusion that changes to vegetation would not make the area more vulnerable to invasion by noisy miners, which are a known threat to the regent honeyeater.

Samantha Vine, the head of conservation at Birdlife Australia, said the organisation estimated just 250-300 regent honeyeaters remained in the wild and the Burragorang Valley was one of only five known contemporary core breeding sites for the species.

“Regent Honeyeaters are nomadic and breed only where and when conditions are good, so in some years it might be the only place they breed, meaning the entire population can be impacted by the loss of a core breeding site,” she said.

She said Australia’s weak environmental laws meant decision makers could still approve development in one of the last remaining havens for the bird.

Threatened ecological communities

The environment department’s document says WaterNSW’s environmental assessment did not make clear whether significant effects on woodland and forest communities caused by changes to inundation and the flow of streams and rivers could be mitigated or offset.

The woodland and forest areas are known as threatened ecological communities (TEC), meaning they contain multiple plants, animals and organisms in a single, unique habitat.

“The EIS itself finds that several TECs are at risk of significant impact or even extinction,” officials wrote.

The department’s document states WaterNSW identified three communities downstream of the dam – the Cumberland Plain shale woodlands and shale-gravel transition forest; the shale standstone transition forest of the Sydney Basin bioregion; and the western Sydney dry rainforest and moist woodland on shale – that would be significantly affected or driven to extinction due to hydrological changes.

It says WaterNSW also needed to clarify the remaining total extent of another forest area – the Cooks River/Castlereagh ironbark forest – as its analysis appeared to suggest the whole of this community was within the project area, meaning the legal requirement to deliver an offset that benefited conservation “may not be possible”.

Further flaws identified by the department included WaterNSW’s conclusion that raising the wall would not have a significant effect on the vulnerable greater glider, despite the agency finding the project would lead to the loss of about 238 individuals.

The department also disagreed with the agency’s finding that its project would not have a significant impact on the vulnerable giant burrowing frog.

A spokeswoman for the environment department said WaterNSW was still working on the EIS and it “must meet the statutory assessment requirements under both state and national environmental law”.

“This includes a comprehensive assessment of the likely impacts to EPBC-listed threatened species and communities and world heritage values and any proposed mitigation or offset measures,” she said.

She said the federal government had advised the World Heritage Committee of the proposal and that it was under environmental assessment.

“The draft EIS will be placed on public exhibition to provide the opportunity for the interested stakeholders to point to critical gaps and raise concerns in the assessment,” she said.

Related: UN concerns about Warragamba dam plan labelled ‘extreme embarrassment’ for NSW

But Harry Burkitt, a campaign manager at the Colong Foundation for Wilderness, said the federal government should be doing more.

“It’s now clear the WaterNSW environmental assessment is critically flawed,” he said.

“The federal government must ensure the environmental assessment complies with Australian law and our Unesco obligations before it goes anywhere near public exhibition.”

WaterNSW did not provide responses to specific questions about the problems identified in the leaked document.

A NSW government spokeswoman said the draft EIS was being prepared for public consultation.

“Feedback from the state and commonwealth departments on the draft EIS is an important component in developing the final document for public exhibition,” she said.

“The NSW government looks forward to public exhibition of the EIS, which will allow for the proposal to be assessed on its merits and for all interested stakeholders to provide comment.”