A draft environmental impact statement for the Warragamba Dam project confirms the sides of the wall will be raised 17 metres to allow for future expansion, putting at risk heritage listed forest in the Blue Mountains.
The coalition government has repeatedly said the wall will be raised 14 metres to help prevent flooding of the Hawkesbury-Nepean Valley below the world-famous Blue Mountains.
But AAP revealed in March the Berejiklian government was actually going to raise each end of the wall - the dam abutments - by 17m so it could easily be modified in the future to hold back additional water.
The secret documents revealed the wall would be "structurally" raised 17m but "operational" at 14m.
Now the draft EIS, seen by AAP, confirms the plan involves "raising the wall by 14m with abutments for 17m".
The statement - which is due to be made public later this year - isn't assessing the impact of raising the wall 17m despite the fact this would inundate a much larger upstream area of the heritage-listed Blue Mountains.
Critics say the plan would put at risk threatened flora and fauna that could be inundated by dammed water.
Premier Gladys Berejiklian was quizzed about the proposed height of the dam wall in mid-March.
"I ask you to rely on what's in the public domain - that's what we've announced (and) that's what's happening," she told reporters at the time.
The federal government in September 2017 told the UNESCO World Heritage Committee the wall would be raised 14m.
Members of the Give a Dam community group are this week travelling to UNESCO headquarters in Paris to brief the committee of the project's potential negative impacts.
"If the Australian government allows the NSW government to continue down their destructive path of raising the dam wall, UNESCO will rightfully come down on Australia like a tonne of bricks," campaign director Harry Burkitt told AAP in a statement.
Infrastructure NSW on Tuesday was asked if the government was planning to raise the wall 17m in the future.
The agency replied that "the NSW secretary of the Department of Planning and Environment has required the project to be designed, constructed and operated to be resilient to the future impacts of climate change".
Australian Associated Press
