The Berejiklian government says its proposal to raise the wall at least 14 metres will help mitigate flood risks on the Hawkesbury-Nepean floodplain while temporarily inundating parts of the heritage-listed area.

But the state coalition's own leaked charts reveal the project would provide a "small benefit", according to flood management expert Professor Jamie Pittock.

"It's a surprising result," the Australian National University academic said in a statement on Monday.

"It really undercuts the argument for raising the dam wall."

Prof Pittock argues that "no matter how high you build that dam wall, floods will still happen in the Hawkesbury-Nepean Valley".

Blue Mountains Mayor Mark Greenhill says raising the wall would flood heritage-listed land, wipe out cultural heritage sites and local animal species and "trash key tourist markets that support local jobs".

He's now calling on Canberra to kill off the project given the Commonwealth has the final say.

"This is a threat to the very fabric of the Blue Mountains environment and the pressure must now be on the national government of Australia to step in and put a stop to this mad policy," Mr Greenhill said in a statement.

The project came under closer scrutiny earlier this year after AAP revealed the state government was planning to raise the dam abutments at each end of the wall by 17 metres to allow for a further raising.

The World Heritage Committee will review the environmental impact statement before any final decision because of the extent of temporary inundation to the area.

Traditional owners last week slammed a draft Aboriginal cultural heritage assessment for the wall raising claiming it disregards local culture.

The bushland has a rich indigenous history and Gundungurra woman Kazan Brown claimed there were hundreds of sites that haven't been included in the assessment, labelling it "insulting" and "culturally insensitive".

Australian Associated Press