North Fork Siphon Condition Evaluation

The North Fork Siphon is an essential element of the Central Utah Project, a vast network of water facilities operated by the Central Utah Water Conservancy District (CUWCD) to deliver clean water to customers in northeastern and central Utah. The 72-inch diameter siphon was completed in 1987, and was constructed using primarily prestressed concrete cylinder pipe (PCCP). The siphon has a lay length of 4,750 feet, a vertical elevation difference of 716 feet, and an inclination in places up to 70%. CUWCD commissioned two visual/sounding and electromagnetic (EM) inspections of the siphon in 2009 and in 2014. Of 233 PCCP segments inspected in 2009, eight pipes were identified as having significant structural damage (wire breaks). In 2014, only one of these 8 pipes was reported as having significant structural damage. This discrepancy in EM results led CUWCD to commission an independent inspection of the siphon in November 2016. The number of defects detected during the new inspection was much greater than anticipated: 196 pipes exhibited serious defects, with 24 having structural defects indicative of incipient failure. This paper provides an overview of the inspection and its findings, the condition assessment and pipe rating system devised for the siphon, and the options presented for managing the siphon.