Page - 156 - in Book of Full Papers - Symposium Hydro Engineering

The photograph in Fig. 8 shows a section of the concrete chute slab that was removed during post-incident forensic excavations. Protrusion of the underdrain into the slab section, cracking above the underdrain, repair of the concrete above the reinforcing layer, and recurrence of the cracking are all illustrated in this photograph. Fig. 8 Section of service spillway chute slab removed during post-incident forensic investigation 2.7. SERVICE SPILLWAY CHUTE UNDERDRAIN FLOWS In its first report, DWR’s Independent Board of Consultants (BOC), which was convened after the February 2017 incident to provide review and advice for the spillway recovery and repair program, commented that: “The amount of drain water flowing from the pipe discharge openings along the spillway training walls seems extraordinarily large.” [3] The IFT concurred. The amount of water that discharged from the chute drains when there was flow in the service spillway was unprecedented in the IFT’s experience. Significant flows from the service spillway chute drain outfalls were observed at the time of the first discharge through the spillway, in 1969, as described in a DWR report and DSOD notes [4, 5, and 6]. The report states that the high flows from the outfalls were related to spillway discharge and that the “high flows from 156