Upper Peninsula Power Company (UPPCo) incorporated risk-informed decision making to develop unique, cost-effective solutions that address significant spillway deficiencies at Victoria Dam. Victoria Dam, situated on the West Branch of the Ontonagon River in Upper Peninsula, Michigan, is capable of safely passing only about 25 percent of the Probable Maximum Flood (PMF). The project is required to safely pass the full PMF, which was established as the Inflow Design Flood (IDF) due to potential downstream hazard to the City of Ontonagon, Michigan. Flood frequency analysis indicated that earth embankment sections of the dam could be overtopped for flood events exceeding approximately 200 years, with potential downstream impacts associated with embankment failure. Conventional measures for increasing spillway capacity by more than four times, which is required to pass the IDF, are not feasible. Evaluating the probability of flood loading and associated consequences of embankment failure enabled UPPCo to establish a design flood criterion for the modified embankment sections that is approximately 50 percent of the PMF. A key to the success of this project is UPPCo’s decision to perform additional, detailed dam failure and hazard assessments to fully understand the downstream consequences of various spillway adequacy solutions. Integration of these risk assessments into alternative analyses for various structural and non-structural concepts was essential to determine cost-effective project modifications that meet spillway adequacy requirements. The final combination of structural modifications and non-structural measures will meet dam safety objectives to reduce the probability of embankment overtopping to approximately one in 10,000 years and safely pass extreme floods up to the PMF. This manuscript will discuss the evaluations that were conducted, which facilitated the development of cost-effective solutions for spillway adequacy.
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