The NSW government has been told to rework its plans to raise the Warragamba dam wall. 

Officials from the state’s department of planning, industry and environment, Heritage NSW and the department’s environment, energy and science division (EES) have offered significant criticisms of the government plans. 

They say that the government’s $1.6 billion plan to raise the wall by up to 17 metres failed to properly assess or justify impacts to the Greater Blue Mountains world heritage area. 

They found that the evaluation of the project’s impact on world heritage values was based on “incorrect assumptions”.

Additionally, officials said the assessment of the WaterNSW project incorrectly excluded Aboriginal heritage from the world heritage values of the area, potentially ignoring sites of high cultural value. 

“EES does not consider the impacts of the project on the natural and cultural values of the national parks estate and Greater Blue Mountains World Heritage Area have been adequately assessed or justified,” said Dean Knudson, the deputy secretary of biodiversity, conservation and science.

The assessment concluded that the project would have minimal impact on threatened species, but the official review found this was “not supported by the data or evidence”.

The EIS also failed to address requests from the World Heritage Committee that the government fully consider all potential impacts to the outstanding universal values of the area. There were inadequate surveys of threatened species habitat and the assessment of aquatic ecology did not identify that raising the dam wall would result in inundation of about 284km of rivers and streams during floods.

While WaterNSW was found to have correctly identified the process for sourcing environmental offsets for the project, it did not identify the actual location of proposed offsets or whether it was possible to meet the offsets requirements.

The state’s new infrastructure minister, Rob Stokes, shares the final say on the dam project with Stuart Ayres, the minister for western Sydney.

However, Mr Stokes says a final decision on the project will sit with the government as a whole.