Conservationists have condemned government plans to raise Warragamba Dam wall 17 metres, three more than originally planned, concerned about further inundation of national park.
Documents on the federal Department of Agriculture, Water and the Environment website reveal WaterNSW sought a variation to the existing 14m plans. The variation was approved by the environment department on July 29.
WaterNSW said the increase was in keeping with the NSW Secretary's Environmental Assessment Requirements that the project withstands the impact of future climate change.
"The full supply level, spillway levels and flood impact levels remain unchanged from the original referral and proposed action. All upstream and downstream temporary inundation levels, durations and associated impacts remain unchanged from the original proposal," the document says.
The document confirms the increased height would not increase capacity of the dam (as was the case with the originally planned 14 metres).
The Colong Foundation for Wilderness has opposed the raising of the dam wall from the start, citing numerous issues including loss of important Indigenous sites and threats to native species.
Campaign manager Harry Burkitt criticised the plan to increase the wall, saying further national park was under threat of inundation under the 17m proposal.
"Estimates by the Colong Foundation for Wilderness place an additional 15 kilometres of watercourses and 1000 hectares of world heritage national parks under threat from a 17-metre dam wall raising scenario," Mr Burkitt said.
"This is on top of the 65 kilometres of watercourses and over 5000 hectares of national parks and world heritage landscapes that would be flooded by the 14-metre proposal."
Mr Burkitt said existing environmental and cultural assessments must be redone if WaterNSW was to proceed with a 17-metre raising plan.
"The assessments undertaken to date for the project have been for a 14-metre dam wall raising," he said. "However, this must be redone given the dramatic expansion to the size of the dam proposal to a 17-metre raising."
The assessment found that "existing flood risk is set to increase and that the existing dam crest would need to be raised to achieve the same benefits in 2090 as raising the dam crest by 14 metres under historical conditions".
WaterNSW does not propose to raise the spillway crest levels a further three metres. However, the document states the spillway crests could be raised in the future.
"This approach enables for only the spillway crest heights can be raised in the future to accommodate climate change impacts without having to raise the dam structural abutments," it reads.
"Any future proposal for an increase in the spillway crest heights would be subject to a separate environmental assessment and approval from the relevant regulatory authorities."
But Stuart Ayres, the Minister for western Sydney, said the 17m wall height related to abutments and the road deck and did not have a role to play in storing water.
"As the wall is for flood mitigation only and not storage, this project ensures temporary inundation occurs behind the dam wall rather than people's living rooms, streets and businesses," he said.
A spokesman for federal Environment Minister Sussan Ley said the variation does not include any change to the proposed spillway height.
