When Failure Means Success: The Multi-Bay Fuse Plug Emergency Spillway at Piute Dam

Piute Dam, located in south-central Utah was constructed during the early 1900s by pioneer farmers and ranchers to provide an irrigation water supply. Evaluations in the 1990s indicated that the dam did not meet current dam safety standards. Franson Noble Engineering designed a four-bay fuse plug emergency spillway to meet current dam safety standards related to emergency spillways. A fuse plug spillway is designed to “fail” or erode when it is breached by flood waters protecting the entire dam from failure. The fuse plugs are designed to pass the Inflow Design Flood, which for Piute Dam is a rain-on-snow event with a peak inflow of 106,000 cfs. The existing service spillway could only pass 38% of this design flood. Because of high flows, severe erosion is expected to occur downstream from the fuse plug. Training walls and a downstream sheet pile cutoff that extend into bedrock will aid in controlling this erosion to reduce head cutting under the spillway and into the embankment. An upstream sheet pile cutoff was also constructed to reduce potential seepage beneath the emergency spillway. The new spillway consists of four 50-foot wide bays with fuse plugs ranging in height from 18 to over 23 feet. Based on modeling analyses, the fuse plug trigger elevations are set at incrementally higher elevations. This allows the “failed” fuse plugs to produce flood outflows similar to inflows, which would minimize the effects of downstream flooding, thus reducing potential liability to the owner from downstream flooding. The lowest fuse plug is designed to breach from the 500-year flood event to reduce the likelihood of premature fuse plug failure. The structure was constructed along the crest of Piute Dam in 2004 and 2005. 20 pp., various figures and photos.