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crest structure and the absence of erosion protection downstream of the crest structures may have also contributed to the development of the erosion. 5. WHY THE INCIDENT HAPPENED The February 2017 Oroville Dam spillway incident was the result of interactions of numerous physical and human factors, beginning with the design of the project and continuing during the nearly half-century until the incident. The incident was generally the result of a long-term systemic failure of DWR, regulatory, and general industry practices to recognize and properly address the deficiencies and warning signs which preceded the incident. There was no one root cause, nor can the incident reasonably be “blamed” mainly on any one individual, group, or organization. 5.1. SERVICE SPILLWAY The conditions that led to the service spillway chute failure have their roots in the original design and construction of the chute, which, combined with the locally poor geologic conditions at the site, resulted in vulnerabilities in the as-built structure. These vulnerabilities were not recognized in various inspections and evaluations that were completed throughout the history of the structure. In fact, warning signs of the vulnerabilities came to be accepted as “normal,” and then generally were not questioned further. Because the seriousness of the vulnerabilities was never recognized, chute slab repair efforts were neither well- conceived nor effective, and likely contributed to the deterioration of chute conditions over time. As detailed in the forensic investigation report [1], the spillway chute design was generally at the middle of the range of practice for the 1960s for spillway chutes founded on rock. For a structure of the significance of Oroville Dam, the IFT would expect the design to have reflected the best practices of the time, which it did not. The one aspect in which the design was at the very low end of practice of the time was the significant protrusion of the chute underdrains into the slab section. This feature was uncommon and led to the development of extensive cracking over the drains and resulting leakage through the slab at the cracks. Communication among geologists, designers, and construction managers during the service spillway’s design and construction apparently was poor. This ultimately resulted in a design which was probably more appropriate for a spillway chute on rock foundations rather than one constructed on more variable foundation conditions, including strongly weathered rock, most notably an extensive area of such material at the location of the initial chute slab failure. These conditions 164