On Feb. 7, 2017, after several very large rainfalls, the Oroville Dam’s 179-foot-wide flood control outlet (FCO) spillway chute was releasing water to control the Lake Oroville reservoir level when it suffered a catastrophic failure.

Over the next nine months, the California Department of Water Resources worked towards meeting its Nov. 1, 2017 goal of replacing the spillway’s lower chute and sections of the upper chute and placing roller-compacted concrete (RCC) in the middle erosion area so the flood control spillway could handle flows up to 100,000 cubic feet per second (cfs). ALthough, as it turned out, the spillway wasn’t used during the 2017-2018 flood season. Part of the 2017 work was temporary, to be completed or redone in 2018. The 2018 phase of the project kicked off on May 8.

An important aspect of the work in 2017 was using RCC to fill the hole, as the temporary chute surface in the middle of the spillway, and to temporarily rebuild the sidewalls in the middle part of the chute. About 350,000 cubic yards of RCC was placed. Much of the aggregate was eroded material dredged from the Feather River.