Assessing the Ecological Risks of Dam Removal. P. J. Sheehan, R. J. Wenning, B. D. Wright, N. M. King, D. J. Paustenbach, and D. M. Becklin, McLaren/Hart, Inc., 1320 Harbor Bay, Parkway, Suite 100, Alameda, CA 94502; and Sportfish Heritage, Grants Pass, OR 97528
The Savage Rapids Dam, located on the Rogue River in southern Oregon, is the primary diversion facility for the Grants Pass Irrigation District. This dam has been in place for over 70 years. The Bureau of Reclamation recently conducted a study to identify a permanent solution to the fish passage problems at the Savage Rapids Dam and has recommended removal of the Dam. Approximately one million cubic yards of sediment have accumulated behind the dam and no rigorous evaluation of the risks that may be posed by the release of those sediments was conducted as part of the Bureau of Reclamation study. We are currently conducting a prospective assessment of short- and long-term effects that sediment release might have on the Rogue river ecosystem. The assessment will include a chemical and physical characterization of impounded sediment, a modeling simulation of the redistribution of sediment in the river with time following removal of the dam, and finally, a characterization of risks to aquatic organism populations associated with potential exposures to chemicals and habitat modifications. Data analysis and modeling will be performed using geographic information system (GIS) tools. Risks will be described in terms of the probability of percentage reductions in fish and macroinvertebrate populations. This risk assessment should provide new insights into the types, probability, and magnitude of undesirable effects likely to occur as the result of a dam removal project to address this impediment to fish migration.
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