An assessment of greenhouse gas emissions from the proposed Tillegra Dam

Institute for Sustainable Futures, UTS
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The proposed Tillegra Dam would be a significant source of greenhouse gas (GHG). The claims that the dam would be carbon neutral cannot be sustained and the environmental assessment report (EAR) for the Tillegra project needs to be amended. Even if the GHG emissions from the dam’s construction are ignored, it is estimated that a total of at least 327,400 t CO2-eq (tonnes of carbon dioxide equivalent) of GHG emissions would result from the Tillegra Dam in its first 20 years. However there are large uncertainties associated with surface emissions from water storage dams and these alone could easily contribute 1.0 million t CO2-eq. Excluding its construction, the Tillegra Dam will increase the operational GHG intensity of water supply in the Lower Hunter by at least 46%. The potential surface emissions alone from the proposed Tillegra Dam could be equivalent to adding an extra 27,000 cars to the Hunter’s roads. The bulk of the GHG emissions from the Tillegra Dam will be surface emissions generated as flooded organic material decomposes. Decomposition produces carbon dioxide and methane. Methane gas surface emissions will be of particular concern because methane has a global warming potential 72 times that of carbon dioxide over a 20-year timeframe, and 25 times that of carbon dioxide over a 100-year timeframe (IPCC 2007). Once the dam was constructed, the increased emissions would be unavoidable because unlike the GHG emissions associated with new supplies such as recycled or desalinated water, the emissions from large dams occur regardless of whether their water is used. The GHG assessment in the Tillegra EAR ignores methane generation and release from the storage. This would be the largest source of GHG, and this major flaw means that the EAR needs to be amended. The carbon offset claims in the EAR are also unsound. The EAR claims that there would be a significant offset for renewable energy generated by a mini hydroelectric plant but no such plant is included in the project. Also of concern is the simplistic inclusion of tree planting as an offset with no consideration of important factors such as the loss of soil carbon in the establishment of plantations on agricultural land. In stark contrast to the GHG emissions from the Tillegra Dam proposal, a sustainable water strategy for the Lower Hunter, based on improved water efficiency and water conservation measures, could reduce GHG emissions by an estimated 1.5 million tonnes of t CO2-eq over a 20-year period.
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