The proposed Tillegra Dam in the Hunter Region will release up to one million tonnes of greenhouse gases in its first twenty years of operation, according to a report released on the weekend by the UTS Institute for Sustainable Futures (ISF).
This would be the equivalent of putting an additional 27,000 cars on Newcastle's roads.
ISF researcher Dr Simon Fane said the dam would increase the climate change footprint of the Hunter Valley's water supply by 46 per cent.
"Such a massive impact is a nonsense given current international efforts to reduce atmospheric greenhouse gases. A sustainable water strategy would actually reduce emissions," Dr Fane said.
"Dams create greenhouse gases during construction but more importantly they continue to release greenhouse gas emissions as the vegetation in the inundation area rots over many years.
"Standing vegetation and soil store large amounts of carbon which are released into the atmosphere when the dam waters inundate the region. This process releases not only carbon dioxide, but also the much more potent greenhouse gas methane."
Wilderness Society campaigner Sam East said the dam would be an anachronism in every way.
"Large dams are inefficient, expensive and environmentally destructive," Ms East said. "The ISF report proves that Tillegra Dam is a climate change clanger. It will commit the Hunter to increased greenhouse gas emissions despite the fact that the water it is meant to deliver is completely unnecessary."
The report also found that Hunter Water's Environment Assessment Report for the project, released this month, significantly underestimates the greenhouse gas implications of the dam by ignoring methane emissions. It also puts forward shaky plans for off-setting these emissions including an unfunded hydro-electric plant and ill-conceived tree planting which in turn places large demands on water supply.
The Wilderness Society commissioned the report, An Assessment of Greenhouse Gas Emissions from the Proposed Tillegra Dam, to investigate the long term environmental impact of flooding the Williams River. It is available online at http://www.isf.uts.edu.au/publications/isf2009tillegraemissions.pdf