Cedar Cliff Dam Spillway Upgrade with Giant Fusegates

When the Inflow Design Flood (IDF) was raised to full Probable Maximum Flood (PMF) by the Federal Energy Regulatory Commission (FERC), Duke Energy evaluated a wide range of alternatives to increase spillway capacity at their Cedar Cliff dam in North Carolina. This paper presents the details of the design and construction of the selected Fusegate System on the modified auxiliary spillway to replace the existing fuse plugs. It also covers the physical hydraulic modeling of Fusegates, which was performed to verify the ventilation of the nappe and its potential impact on the tailwater levels. Model test results showed that semi-labyrinth type Fusegates selected for the project were sufficiently self-ventilating and did not require ventilation lines or nappe breakers. Cedar Cliff is the first completed Fusegate project regulated by FERC with the second tallest units in the world.