The US' California Coastal Conservancy has released a report saying that the removal of PacifiCorp's Klamath river dams would be feasible, safe and affordable - following Monday's Federal Energy Regulatory Commission (FERC) recommendation to leave the structures erected.

The study reports that the toxicity of the sediment is very low, and will not affect the method or cost of dam decommissioning. In addition, it says the sediment transport below Iron Gate would be unlikely to cause any flooding. ‘The results of this study and FERC’s economic analysis show that dam removal is not only feasible and safe, it is cheaper. This should remove any doubt that dam removal is the best strategy for the Klamath River and [the dams’ owner] PacifiCorp,’ said Steve Rothert of American Rivers.

Volume and physical and chemical characteristics of the sediment was also investigated by the study, by collecting 45 sediment samples at 26 locations in Iron Gate, Copco 1 and JC Boyle reservoirs. Of the 27 sediment samples analysed, only one sample contained concentrations exceeding test screening criteria. The study found that no sediment samples contained metals, pesticides, herbicides, PCBs, DDT or dioxins at concentrations above screening levels. The only contaminants detected above screening levels were ethylbenzene and xylenes. The report describes these as common volatile organic compounds (or VOCs) found in oils and gasoline, which likely came from spills from ecreational boats.

The study also found that the volume of sediment stored behind the three reservoirs was greater than previously expected. However, even under the worst-case scenario, the report concludes that natural erosion of the sediments would not pose a flood risk downstream. Previous studies estimated a total of 11.06Mm3 stored in the reservoirs. The study released today estimates 15.5Mm3 is trapped by the dams. The study estimates that only 2.9Mm3 of sediment would be eroded downstream of Iron Gate because much of it would sit beyond the reach of the restored river channel.

The report concluded that the sediment would not have to be mechanically excavated and could erode naturally downstream without causing a risk of contamination or flooding.

Conservation groups and tribes consider dam removal vital to recovering Klamath salmon and insist it would help communities throughout the basin, especially the commercial fishing and tribal communities, and were displeased with the FERC opinion.

The studies can be downloaded from the American Rivers website via the link below.

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