Reducing risk to downstream people and property

Norway and Oakdale Spillway Expansion

NIPSCO LLC owns and operates two hydroelectric projects—the Norway and Oakdale Hydroelectric Facilities—on the Tippecanoe River in Indiana. Each project, built in the early 1920s, consists of a powerhouse integrated with earth embankment dams, concrete gravity and buttress structures, and spillways.

After investigations identified insufficient spillway capacities to pass the probable maximum flood (PMF) without overtopping the earth embankments at each facility, we were brought in to deliver risk-informed decision making (RIDM) services. Our team worked with NIPSCO to identify an acceptable inflow design flood (IDF) for each facility and evaluate potential risk mitigation measures including structural and non-structural approaches.

Our multi-year study—one of the Federal Energy Regulatory Commission’s (FERC) pilot RIDM projects—included a baseline risk assessment, potential risk reduction measures, potential failure modes analyses (PFMA), and an estimation of annual failure probabilities, incremental life loss, and physical property damage. We also developed a complex, multi-variable risk analysis model to justify reductions in design flows in accordance with FERC guidelines and the established tolerable risk guidelines.