On Thursday, Independent MP Justin Field successfully moved in the upper house for a committee to examine the controversial plan.

It comes almost two weeks after advisers to the United Nations noted "with concern" that raising the wall by 14 metres is expected increase the frequency of inundation of the heritage-listed Blue Mountains.

"There are very legitimate concerns about the impact this proposal will have on the World Heritage areas, Aboriginal cultural heritage, the Warragamba community and on plans for significant future property development on the flood plain," Mr Field said in a statement on Thursday.

"This proposal has never been fully tested within the communities who will be impacted and the alternative options have never been subject to a public debate."

The project came under scrutiny earlier this year after AAP revealed the Berejiklian government was actually planning 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.

Critics say the plan puts at risk threatened flora and fauna that could be inundated by dammed water in the Blue Mountains, while the state government insists it will help prevent flooding of the Hawkesbury-Nepean Valley.

The inquiry will examine, among other details, conflicting reports on the planned height for a raised wall, the adequacy of the environment impact assessment process and the flood risk assessment for the Hawkesbury-Nepean Valley area, according to the terms of reference.

Mr Field, who will be part of the committee, said he was looking forward to engaging with affected communities and stakeholders.

Earlier this month, the World Heritage Centre, which advises the UN committee in charge of world heritage properties, published its position on the project.

It recommended the World Heritage Committee - which will likely adopt the decision at its annual meeting from June 30 - urge the NSW and federal governments to submit to it any environmental impact statements for assessment before making a final decision on the project.

The plan will be subject to federal government approval after the environmental impact statement is released later in 2019.

Australian Associated Press