Page - 158 - in Book of Full Papers - Symposium Hydro Engineering

At about 10:10 am on February 7, 2017, on-site DWR personnel noticed a substantial disturbance in the service spillway’s flow pattern, while discharges were being ramped up from about 1,200 m3/s (42,500 ft3/s) to about 1,490 m3/s (52,500 ft3/s). On-site DWR personnel contacted DWR headquarters in Sacramento, and an order to close the service spillway gates was issued at about 11:15 am on February 7, 2017. After the gates were fully closed by about 12:25 pm, it was found that a significant section of the service spillway chute slab was missing, and a large erosion hole existed in the foundation in the area where the slab sections were missing, as shown in Fig. 9. This initial erosion hole in the service spillway chute was examined by a climb team on the morning of February 8, 2017. Fig. 9 Service spillway chute damage observed after gates were closed on February 7 DWR knew that it would need to operate the damaged service spillway because of expected inflow to Lake Oroville; hence, it was decided to begin opening the spillway gates to test the service spillway’s capabilities in the damaged condition. The gates were reopened at about 4:00 pm on February 8, 2017, and several different discharge levels were trialed through February 10, while the service spillway chute was observed for additional damage. Spillway discharge reached 1,840 m3/s (65,000 ft3/s) at 3:00 am on February 10, and was held there for about 17 hours. At about 8:00 pm on February 10, the service spillway discharge was reduced to about 1,560 m3/sec (55,000 ft3/s) and maintained at that level through 3:35 pm on February 12. Meanwhile, inflows to Lake Oroville continued to increase. Sometime between about 7:00 and 8:00 am on February 11, the reservoir level exceeded Elevation 274.6 m (901 ft), and water began flowing over the emergency spillway crest structure for the first time in the facility’s history. The reservoir level increased to a maximum level of about Elevation 275.1 m (902.6 ft), about 0.49 m (1.6 ft) above the emergency spillway’s crest, at about 3:00 pm on February 12, about 31 hours after the flow over the emergency spillway began. The flow over the 158