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Oroville Dam Spillway Recovery Engineering and Construction Management

In early February 2017, heavy and sustained rainfall¡ªnearly 13 inches (33 centimetres) in less than a week¡ªpushed the Oroville Dam¡¯s spillways past their limit. An initial failure of the main spillway chute forced diversion to the emergency spillway, which experienced notable headward erosion (head-cutting) at the lower end of the spillway due to greater than anticipated flows. Operators were able to reopen the main spillway to divert spillway flows back to the main chute. However, this further eroded the failed chute downstream, which delivered significant amounts of rock and sediment into the downstream river, elevating the riverbed and causing backwater flow toward the dam toe and forcing closure of the hydroelectric plant.

The California Department of Water Resources (DWR), with financial assistance from the U.S. Federal Emergency Management Agency (FEMA), undertook the Oroville Spillway Repair project. DWR reached out to us under our multiple-service contract to inspect the spillway, create a monitoring plan, and provide roller-compacted concrete (RCC) spillway concrete design, dam safety services, hydraulic analysis, modeling, civil design, and cost estimating.

We conducted field surveys and monitoring while coordinating closely with FEMA, the Federal Energy Regulatory Commission (FERC), and DWR personnel. We incorporated climate analysis as part of both California Environmental Quality Act (CEQA) and National Environmental Policy Act (NEPA) compliance, as well as other departmental and Tribal coordination and approvals for direct impacts to biological, aquatic, and cultural resources. With the threat of erosion impacting nearby transmission lines, our team also provided environmental compliance and permitting consultations for the routing and siting of the new lines.

Throughout construction, we continued to support DWR with five full-time employees and three on-call RCC inspectors assigned onsite for engineering support and construction quality assurance and control. We also supplied a deputy project manager supporting DWR¡¯s project manager for the overall recovery effort.

In addition to bringing the spillway and dam facilities back into service, the recovery project shored up local resilience and prepared the damn and supporting structures to better handle heavy weather events in the future.