Abstract Description: Cedar Cliff dam is located near Cullowhee, North Carolina. Constructed in 1952, the dam is owned by Duke Energy and is operated in concert with two upstream hydroelectric development. The primary spillway is a rock cut channel through the right abutment, controlled by a tainter gate; the auxiliary spillway is a rock cut channel through the left abutment, originally controlled by two erodible fuse plugs.
In order to meet the updated PMF criteria and to make auxiliary spillway releases more incremental, the auxiliary spillway capacity was increased, and the Fusegate® System was selected to replace the fuse plugs as spillway control. The project consisted of enlarging the existing rock cut channel to an entrance width of 250 feet and installing six 25-ft high semi-labyrinth Fusegates®.
Design of Fusegates®, particularly calculation of ballast requirements, requires accurate tailwater levels between the nappe and the Fusegate®. Downstream channel conditions and air pressure under the nappe affect tailwater. Design calculations, and results of the physical model testing performed at Alden Research Laboratory, showed that the proposed spillway system was adequate to satisfy the design criteria. Phase I of the construction works by Sequoia Services, which included erosion and sediment control measures; clearing and grubbing; and other infrastructure improvements on the boat ramp, access road and laydown areas, were completed in January 2021. Phase II construction undertaken by Barnard Construction Company, Inc. started towards the completion of Phase I with the removal of the two fuse plugs and the concrete splitter wall at the auxiliary spillway, followed by the rock excavation of the channel and construction of a broad crested weir to accommodate the Fusegates®. Phase II also included the removal of the existing parapet wall and concrete dam crest, and replace with a PMF wall, concrete keyway (cutoff), graded filter on either side of the keyway, and new concrete pavement.
The construction of Fusegates® undertaken by Hydroplus started at the beginning of December 2023 when the new broad crested weir was ready and took approximately five months based on a compressed schedule. The Cedar Cliff Fusegates® are the first completed Fusegate® project regulated by FERC, and the second tallest in the US.
Learning Objectives:
Demonstrate a unique Fusegate System application.
Learn about physical testing for aeration of nappe.
Describe the construction of a large auxiliary spillway with Fusegates.
