CS44C - Concurrent Session 44C: Best Practices for Fuse Plug Spillway Design and Construction and Sanford Dam Fuse Plug Performance Evaluation

Fuse plug embankments offer a means for economically increasing spillway capacity while maximizing reservoir storage. They have been constructed at many dams and are often incorporated into facility modifications to address hydrologic overtopping concerns. A properly designed fuse plug embankment will prevent operation of a spillway until a specified reservoir level is exceeded. At this point, the one-time-use “erodible gate” will breach rapidly to develop additional spillway capacity. Bureau of Reclamation Research Report REC-ERC-85-07, Hydraulic Model Studies of Fuse Plug Embankments, is frequently cited by designers. Although this is an excellent reference, it focuses on model test results rather than design guidance, and some technical details in the report may be misunderstood by practitioners without expertise in hydraulic modeling and an understanding of hydraulic and structural similitude. Site-specific conditions, flood loading variabilities, and locally available construction materials can also contribute to making fuse plug spillway design challenging. These factors may produce designs that do not perform as intended during a major flood (i.e., fail to fully erode at the intended rate or develop full design capacity of the spillway).

The failure of Edenville Dam in May 2020 activated the Sanford Dam fuse plug spillway at the next reservoir downstream. Although the fuse plug did eventually fully erode, the spillway had insufficient capacity to pass the incoming dam-failure flood from Edenville, so Sanford Dam still overtopped and failed. A forensic evaluation of the fuse plug operation was performed after the incident using a variety of evidence including excellent aerial drone and cell phone videos that allowed for a uniquely detailed examination of the fuse plug operation. This investigation and a review of other known fuse plug operations and incidents provide insight into important design, construction, and maintenance considerations that impact fuse plug embankment performance. Key topics covered in this paper include best practices for design and construction of fuse plug spillways, performance of Sanford Dam’s fuse plug, key issues from case histories that have led to poor or suboptimal performance, and recommendations for review and evaluation of existing and proposed fuse plug designs.