The New South Wales government agency charged with delivering the controversial raising of the Warragamba dam wall insists the project will have an overall economic benefit, despite not knowing how much it will have to pay in environmental offsets.
Dismissing criticisms of the project, WaterNSW on Monday released a series of long-awaited reports responding to almost 2,500 submissions objecting to the plan to raise the wall by 14m in a controversial bid to reduce flood risk in the Hawkesbury-Nepean Valley.
The proposal has been the subject of significant pushback, including from a series of government departments, local councils and environment groups, who have raised concerns about its impact on the World Heritage-listed Blue Mountains area, as well as Aboriginal cultural heritage and threatened species.
But the agency has dismissed the vast majority of those concerns, insisting that the project would mean 5,180 homes would be spared from a worst-case scenario flood event – a 68% reduction.
It found that a one-in-100-year flood in the Hawkesbury Nepean Valley would affect about 7,600 residential properties, require the evacuation of about 55,000 people and cause about $3bn in damage.
It has also sought to play down the project’s impact on the environment.
Despite Guardian Australia revealing in 2020 that the federal government had raised concerns the project could wipe out half of the population of the critically endangered regent honeyeater – and WaterNSW’s own review finding it could have a “potential significant impact” on the species – the reports released on Monday played down the risk.
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Instead, it found its previous findings were based on a “very conservative position” and that temporary inundation of its habitat caused by the project “may not have a significant impact”.
The reports released also included changes to the way the dam would operate, which could affect future regulatory decisions, experts who reviewed the data said.
Harry Burkitt, the general manager of Wilderness Australia and an opponent of the project, said the changes were “trying to blur the lines” of how the dam would operate.
“WaterNSW have not only dismissed out of hand the public’s submissions, but also the detailed advice of NSW government agencies,” Burkitt said.
Guardian Australia also previously revealed that the agency’s own updated modelling had found the project would cause “irreversible harm” to Aboriginal cultural heritage if it went ahead.
Opponents of the project have insisted it would not alleviate flood risk in the valley, and some have instead called for funding for property buybacks.
But the reports by WaterNSW dismiss those calls, saying a land buyback would be prohibitively expensive. Based on June 2021 housing price figures, it found that a wide-scale property buyback would cost about $5.2bn.
While the agency said the project had returned a cost-benefit ratio of 1.05 – anything greater than 1 is expected to deliver a net benefit when compared with the cost of the project – WaterNSW said it did not know how much it needed to pay in environmental offsets for the project.
“As suitable, publicly or privately owned [land] has not yet been identified, and the offset requirements are not confirmed, it is difficult to cost the offset program,” it stated.
“The Warragamba Offset Program will consider and respond to non-biodiversity values as well as the biodiversity values of the World Heritage and national park areas.”
The release of both the preferred infrastructure and response to submissions reports mean the project will now be again opened for submissions, before further review by the state’s planning authority.
However, any approval is likely to be months away – and would require signoff by the federal government.